WO2021023976A1

WO2021023976A1 - Laser apparatus comprising a plurality of semiconductor waveguides

Info

Publication number: WO2021023976A1
Application number: PCT/GB2020/051841
Authority: WO
Inventors: Alistair James Poustie; James Ashley HARRISON
Original assignee: Rushmere Technology Limited
Priority date: 2019-08-02
Filing date: 2020-07-31
Publication date: 2021-02-11
Also published as: GB201911099D0; GB2586080A

Abstract

An optical apparatus comprising one or more first optical reflectors and one or more second optical reflectors. A first semiconductor waveguide is located between the one or more first optical reflectors and the one or more second optical reflectors. A second semiconductor waveguide is located between the one or more first optical reflectors and the one or more second optical reflectors. An optical filter located between the one or more first optical reflectors and the one or more second optical reflectors. A first laser cavity extends between the one or more first optical reflectors and the one or more second optical reflectors; and, extends through at least the first semiconductor waveguide and the optical filter. A second laser cavity extends between the one or more first optical reflectors and the one or more second optical reflectors; and, extends through at least the second semiconductor waveguide and optical filter.

Description

LASER APPARATUS COMPRISING A PLURALITY OF SEMICONDUCTOR

WAVEGUIDES

The present invention is in the field of optical apparatus and optical systems. In particular, the optical apparatus is in the field of optical sources having a plurality of lasing cavities and optical systems for illuminating one or more external objects.

Optical light sources (IR or visible) are used for illumination in imaging and projection applications. Increasingly, laser light sources are being used for illumination due to their efficiency, brightness and the ability to illuminate with specific wavelengths of light. Laser sources are known that utilise an optical filter within the cavity. When multiple such laser sources are required for a particular application the cost increases and the footprint of the whole set-up increases due to each individual laser requiring a full set of its constituent components.

Laser sources are highly coherent, and therefore liable to spatial coherence effects, such as speckle. Speckle is an interference pattern that occurs when coherent light is scattered off an optically rough surface. It is observed as visible 'noise' on a uniform area of the scene and decreases the perceived contrast of the pictures. Camera based vision systems can become confused by a laser illuminated image. Lasers are increasingly being used for illumination in consumer mobile phone devices and CCTV monitoring systems.

Reducing speckle in laser illumination is important for any camera sensor-based detection and image recognition application.

US2019/0013640 (CHEUNG) describes a tunable laser comprising a waveguide including gain section. The waveguide overlies and is optically coupled to another waveguide. The another waveguide has a reflector at one end. A laser cavity is formed in the waveguides. US2017201070 (EVANS) describes a compact laser with extended tunability (CLET) that includes multiple segments or sections, at least one of which is curved, bent or non-collinear with other segments, so that the CLET has a compact form factor either as a singular laser or when integrated with other devices.

US2017098920 (DOERR) describes a tunable laser that includes an array of parallel optical amplifiers. The laser may also include an intracavity NxM coupler that couples power between a cavity mirror and the array of parallel optical amplifiers. Phase adjusters in optical paths between the NxM coupler and the optical amplifiers can be used to adjust an amount of power output from M-l ports of the NxM coupler. A tunable wavelength filter is incorporated in the laser cavity to select a lasing wavelength.

Summary

In a first aspect of the invention there is presented an optical apparatus comprising: one or more first optical reflectors; one or more second optical reflectors; a first semiconductor waveguide located between the one or more first optical reflectors and the one or more second optical reflectors; a second semiconductor waveguide located between the one or more first optical reflectors and the one or more second optical reflectors; an optical filter located between the one or more first optical reflectors and the one or more second optical reflectors; a first laser cavity: extending between the one or more first optical reflectors and the one or more second optical reflectors; extending through at least the first semiconductor waveguide and the optical filter; a second laser cavity: extending between the one or more first optical reflectors and the one or more second optical reflectors; extending through at least the second semiconductor waveguide and the optical filter.

The first aspect may be modified according to any suitable way disclosed herein, including but not limited to any one or more of the following.

The optical apparatus may be configured such that the light propagating within the first cavity is subject to a different optical frequency response of the optical filter than the light propagating within the second laser cavity.

The optical apparatus may be configured such that: the optical filter comprises a first face for receiving light propagating within the first and second laser cavities; light propagating within the first laser cavity is incident upon the optical filter at a first angle relative to the normal of the first face; light propagating within the second laser cavity is incident upon the optical filter at a second angle relative to the normal of the first face; the first angle being different from the second angle. The optical apparatus may comprise a device comprising: a first waveguide path comprising the first semiconductor waveguide; and, a second waveguide path comprising the second semiconductor waveguide; the device comprising a facet from which light propagating within the first and second waveguide paths is output towards the optical filter; the angle that the first waveguide path subtends to the facet is different to the angle that the second waveguide path subtends to the facet.

The optical apparatus may be configured such that the optical filter is disposed non-parallel to the facet.

The optical apparatus may be configured such that the first and second waveguide paths each comprise: a beginning length portion; starting at a further device facet; running in a first direction along the device; an end length portion: adjoining the beginning length portion; terminating at the facet; running in a direction different to the direction of the beginning portion.

The optical apparatus may be configured such that: the device comprises opposing first and second edges, each running between the facet and further facet; the first waveguide end portion converges towards the first edge as it extends towards the facet; the second waveguide end portion converges towards the second edge as it extends towards the facet.

The optical apparatus may be configured such that the device comprises opposing edges, each edge running between the facet and further facet; the first and second waveguide end portions converge towards a common edge as they extend towards the facet.

The optical apparatus may be configured such that: the device comprises further waveguide paths; a first one or more of the further waveguide paths each having a waveguide end portion converging towards the first edge; a second one or more of the further waveguide paths each having a waveguide end portion converging towards the second edge.

The optical apparatus may be configured such that the device comprises further waveguide paths each having waveguide end portions converging towards the common edge. The optical apparatus may be configured such that each of the first, second and further waveguide paths comprises waveguide end portions that each subtend a different absolute angle to the facet normal.

The optical apparatus may be configured such that: the first optical reflector is a partial optical reflector; the optical apparatus further comprises an optical combiner configured to: receive light output from the first laser cavity and the second laser cavity via the first optical reflector; combine the received light into a spatially combined optical output.

The optical apparatus may further comprise an illumination assembly configured to output the combined light to illuminate an external object

The optical apparatus may be configured such that the optical filter comprises an athermalised optical thin film filter.

The optical apparatus may be configured such that optical filter comprises a substrate material having a wavelength shift with temperature below 2pm/K.

The optical apparatus may be configured such that: each of the first and second laser cavities comprises a gain section and a phase control section; the length of at least one of: the gain section; and, phase control section, of the first laser cavity, being different to the length of the corresponding gain section and phase control section of the second laser cavity.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 shows a block diagram of an optical apparatus presented herein;

Figure 2a shows a diagram of an example of an optical apparatus;

Figure 2b shows a graph showing peak wavelength shift of an optical filter with incident angle;

Figure 3a shows an example of different optical passbands filtering different longitudinal lasing modes;

Figure 3b shows an example of different optical passbands filtering multiple different longitudinal lasing modes;

Figure 3c shows the example of figure 3b wherein longitudinal lasing modes have shifted in wavelength;

Figure 4 shows another example of an apparatus as described herein;

Figure 5 shows a further example of an apparatus as described herein;

Figure 6a shows an expanded view of a portion of the semiconductor chip as shown in figure 5;

Figure 6b shows an example of the different mode spectra from a three-laser cavity device similar to that shown in Figure 6a;

Figure 6c shows the combined mode spectra of Figure 6b together with different filter passbands;

Figure 7 shows a mobile computing device comprising an optical apparatus as presented herein.

Detailed description

There is presented an optical apparatus. Figure 1 shows a block diagram representing the optical apparatus 2 wherein the optical apparatus 2 comprises one or more first optical reflectors 4 and one or more second optical reflectors 6. The optical apparatus 2 also comprises a first semiconductor waveguide 8a located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. The optical apparatus 2 also comprises a second semiconductor waveguide 8b located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. The optical apparatus 2 also comprises an optical filter 10 located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. The optical apparatus 2 also comprises a first laser cavity 12a: extending between the one or more first optical reflectors and the one or more second optical reflectors; and, extending through at least the first semiconductor waveguide 8a and the optical filter 10. The optical apparatus 2 also comprises a second laser cavity 12b: extending between the one or more first optical reflectors 4 and the one or more second optical reflectors 6; and, extending through at least the second semiconductor waveguide 8b and the optical filter 10.

The apparatus 2 therefore provides multiple laser cavities 12a/12b that include a common optical filter 10 within the cavities. Using a common optical filter 10 has a number of advantages. One advantage is cost saving by only using a shared filter component. Another advantage is both time and cost saving by having to assemble fewer filter components for multiple laser cavities. Another advantage is a decrease in the over size (or 'footprint') of the overall apparatus 2 because less optical filters are required for a given number of laser cavities 12a/12b.

Other advantages and uses of the optical apparatus 2 are presented herein. The optical apparatus 2 may be used in a variety of end products, systems or methods, including but not limited to: object illumination systems; facial recognition systems; spectrometers and communication systems.

The semiconductor waveguides 8a/8b can each be electrically driven by constant current or by pulsed currents. In the pulsed current application, each semiconductor waveguide stripe can be driven at the same time or at different times with temporal current pulses. An example of pulsed driven operation is described underneath.

The optical apparatus 2 may be configured such that the light propagating within the first cavity 12a is subject to a different optical frequency response of the optical filter 10 than the light propagating within the second laser cavity 12b. Examples of this are described underneath. The optical apparatus may also be configured such that each of the first and second laser cavities 12a/12b also comprise waveguide paths with respective gain section and phase control sections. The length of at least one of: the gain section; and, phase control section, of the first waveguide path may be different to the length of the corresponding gain section and phase control section of the second waveguide path.

The optical apparatus 2 may have the different length gain and phase control sections without having the feature of the different optical frequency response; and vice versa. An example of an optical apparatus 2 having the feature of different optical filter frequency responses is shown in figures 2a and 4. An example of an optical apparatus 2 where such gain and phase control sections may be used without necessarily needing to have different optical filter frequency responses is shown in Figures 5 and 6 and described below. The optional features and configurations presented below for figure 2a may also apply to the example of figures 5 and 6.

In the alternative, the optical apparatus 2 may have both the features of the different optical frequency response and the different length phase and control sections.

The optical apparatus 2 may also be termed 'apparatus' throughout. The optical filter 10 may also be termed 'filter' throughout. A laser cavity may also be termed 'cavity' throughout. The semiconductor waveguides 8a/8b may be termed 'optical waveguides' or 'waveguides' throughout. The frequency response of a filter 10 in the context of this application also relates to the corresponding wavelength response, for example the full width half maximum of the passband filter response may be referred to by a wavelength range.

It is understood that the examples described herein may be modified according to any suitable feature described herein, including but not limited to any features described regarding the optical filter 10; the semiconductor waveguides 8a/8b; the optical reflectors; any other waveguide or imaging optics; any thermal control systems; any drive electronics and any information or data processing, assembly or methods of operation.

Example of operation An example operation of the optical apparatus 2 is shown in figure 2a. In this figure the light propagating within at least a first lasing cavity is subject to a different optical frequency response of the optical filter 10 than the light propagating within a second of the lasing cavities.

The elements shown in Figure 2a are not intended to be to scale nor necessarily have exactly correct orientations and angles, instead they are intended to show the type of element in the apparatus 102 in this example and its position relative to the other elements.

In this example a chip 122 forms part of an apparatus 102 having multiple laser cavities. The apparatus 102 includes a passband optical filter 110 that accepts light output from one of the chip facets 116. Light within the passband is passed through the filter 110 to a mirror 106 that reflect 5 the light back through the filter 110 and back into the chip 112. Multiple laser stripes 108a-e are included on the chip wherein each laser strip exits the chip at a different angle, which in turn means each laser beam exiting the chip 122 is incident upon the common optical filter 110 at a different angle. Because of this, each beam experiences a different filter optical frequency response, hence each stripe lases at a different wavelength. This example is further detailed below.

The advantages of an optical apparatus 102 of Figure 2a are now discussed. The at least two laser cavities of the optical apparatus 2 include the same optical filter 10 but are subject to a different filter frequency response. This frequency response directly affects the wavelength of light allowed to lase within the cavity 12a/12b. The first cavity 12a may therefore lase with a different wavelength than the second cavity 12b. The optical apparatus 2 may therefore be used in a number of different applications including but not limited to a multi wavelength optical source that uses a common filter element 10. For example, the outputs from the different laser cavities 12a/12b may be combined into a single output that may, with the aid of one or more other optical components, be used to illuminate an object, such as a user's face. One example use of the optical apparatus 2 is an illumination source for facial recognition. Laser speckle is a problem for such illumination systems. The effects of laser speckle can be reduced by dephasing the light output from the source by having a plurality of laser cavities each emitting a different wavelength. The optical apparatus 2, when configured as an optical source that combines the light output from both cavities provides an improved source for such illumination systems. The source has sufficient output illumination power because it combines at least two laser outputs but de-phases the total light because each laser cavity 12a/12blases within a different filter passband.

Similar advantages of dephasing the different lasing cavities 12a/12balso apply to other examples where laser cavities have different length gain/control sections.

The term 'de-phase' is used to refer to the result of bringing two optical light beams out of coherence with each other.

Turning back to discuss the details of figure 2a, the apparatus 102, in figure 2a, is configured as an optical source for use in an illumination system for facial recognition. This system may be part of an electronic device such as a mobile computing device, for example a tablet or mobile phone. The system may be part of other electronic devices.

The optical source comprises a semiconductor device 122 having five separate optical waveguides 108a-e. The term semiconductor 'device' 122 may also be termed 'chip' in this example. Each optical waveguide 108a-e comprises a length of core material running from a first chip end facet 114 to a second chip facet 116 opposite the first chip facet 114. The first and second chip facets 114, 116 are parallel to each other in this example, but do not need to be in principle. The first facet 114 has a partial reflectivity coating 104 that reflects a portion of the light incident from the waveguides 108a-e back into each respective waveguide and transmits a portion of the said light out from the chip 122, for example the coating 104 reflects between 80-99% of the light back into the waveguides. The partial reflectivity coating 104 in this example acts as the first optical reflector 4 as described above for all of the waveguides 108a-e. The second facet 116 has a low reflectivity coating 118 (for example an Anti-Reflection (AR) coating) that substantially transmits all of the light incident from the waveguides 108a-eout of the chip 122.

Light output from each of the waveguides 108a-e, through the end facet 116 and low reflectivity coating 118, is then incident upon a lens 120 which collimates the output light from each of the waveguides 108a-e. The light incident upon the lens 120 therefore passes through the lens 120 and exits the opposite side of the lens 120 propagating away from the second chip facet 116 and towards an optical thin film filter 110. The optical thin film filter 110 in this example is equivalent to the optical filter 10 as described above.

In this example the optical filter 110 is a thin film filter comprising multiple layers of materials designed to provide a bandpass frequency response within the wavelength range of operation of the apparatus 102. The filter 110 in this example is angled with respect to the chip end facet 116. The end facet 116 and the side of the filter 110 that accepts light from the lens 120 are therefore not parallel. This helps reduce unwanted reflected light from the filter 110 entering back into one of the waveguides 108a-e.

Light passes through the filter 110 and exits the filter 110 to be incident upon a curved optical mirror 106. The mirror 106 in this example is equivalent to the second optical reflector 6 described above. The mirror 106 is designed with a respective curvature and positioned, with respect to the other optical components in the apparatus 102, to reflect light back into the filter 110. In this manner the light is reflected back into the filter 110, passes through the filter 110 to be incident upon the lens 120. The backwards reflected light then passes through the lens 120 to be incident upon the low reflectivity coating 118 of the chip 122 at a position on the second chip facet 116 that allows the light to couple back into the waveguides 108a-e from which it originally exited the chip. The optical path that the light takes outwardly from the second chip facet 116 to the mirror 106 is preferably the same optical path as the light takes from the mirror 106 back to the second chip facet 116, however slight deviations in this optical path are acceptable as long as the light exiting the waveguides 108a-e is still coupled back into the same waveguides 108a-e after being reflected by the mirror 106. In this case the light travels back from the mirror 106 along a substantially similar optical path. The light entering the waveguides 108a-e, from being incident upon the low reflectivity coating 118, then travels along the entire length of the waveguide 108a-e until it reaches the first chip facet 114. The first chip facet 114 is coated, at least partially with a partial reflectivity coating 104. In this example the partial reflectivity coating 104 is equivalent to the first optical reflector 4 as described above. The partial reflectivity coating 104 covers the end facet 114 to an extent that the modes in each of the waveguides 108a-e incident from the waveguides 108a-e onto the first chip facet 114 are also incident upon the partial reflectivity coating 104.

There are five separate lasing optical cavities in this example. Each running between mirror 106 and partial reflectivity coating 104 and passing through the optical filter 110, the lens 120 the low reflectivity coating 118 and a different, separate, one of the waveguides 108a-e. For example, one optical cavity consists of the following optical pathway:

1. Light reflecting from the partial reflectivity coating 104 back into waveguide 108a and travelling along this waveguide to the second chip facet 116.

2. Light passing through the low reflectivity coating 118 and outwardly away from the second chip facet towards the optical lens 120.

3. Light passing through the optical lens 120 and outwardly towards the optical filter 110.

4. Light entering the optical filter 110, passing through the filter 110 and out from the filter (from an opposing side of the filter 110 from where the light was previously incident) towards the mirror 106.

5. Light reflecting from the mirror 106 back into the side of the filter 110 from where the light previously left.

6. Light passing back through the filter 110 and outward towards the lens 120, through the lens 120 and outward to be incident upon the low reflectivity coating 118.

7. Light passes through the low reflectivity coating 118 and back into waveguide 108a, then travelling back along this waveguide 108a to be incident upon the first chip facet 114 again. Along at least part of each waveguide 108a-e is an optical gain section that acts to amplify the light through stimulated emission and create lasing cavities between the mirror 106 and partial reflectivity coating 104, wherein each lasing cavity passes through a different one of the waveguides 108a-e.

The apparatus 102 therefore comprises a plurality of lasing cavities, each having its own set of supported longitudinal modes but each sharing a common optical filter 110 within its cavity. The longitudinal modes supported by each cavity are also governed by the wavelength gain profile of the lasing cavities. In this example each of the cavities comprises an active waveguide having a gain spectrum dictated by the materials forming the waveguide and the electrical drive current used to create the population inversion within the gain section of the waveguide 108a-e. Typically this gain profile is substantially similar for each of the waveguides 108a-e, but can be different.

The longitudinal modes within each cavity may be the same or may be different to the other lasing cavities in the same apparatus 102. The apparatus 102 may be designed to match the optical path lengths of the separate cavities by any suitable means including, but not limited to: positioning components such the lens 120, mirror 106, with respect to the chip 122. By doing this, the apparatus designer can alter the free space propagation distances between component for different cavities and/or the thickness of material the light has to take propagating through components. Additionally, or alternatively the laser chip 122 itself may be configured, for example in its manufacture or assembly, to provide differing optical path lengths along the different waveguides 108a-e. This may be different physical lengths of the waveguides 108a-e and/or the ability to actively tune the optical path length in the waveguides 108a-e by increasing or decreasing its refractive index. This may be done, for example, by increasing or decreasing the optical gain in a particular waveguide. In other examples given herein with separate phase control sections and gain sections may be used to control the gain of the waveguide and optical path length.

The chip 122 in this example is rectangular with opposing chip sides running from the two opposing end facets 116, 114. Each of the waveguides 108a-e has a first length portion with a first end starting at the first chip facet 114 and continuing parallel to the chip sides, away from the chip first facet 114 towards, but terminating at a second end before the second chip facet 116. Each straight first portion of the waveguides 108a-e adjoins to a respective second portion 108ai-ei of the same respective waveguides 108a-e. The second length portions 108ai-ei of the waveguides 108a-e extend continuously from the respective second ends of the first length portions of the waveguides 108a-e to the second chip facet 116. The first length portions in this example run parallel with each other towards the second facet of the chip, although in principle they do not have to. This chip design may be varied, for example, the first length portions do not have to be parallel to the chip sides; the chip may take a different in-plan shape.

In this example, each waveguide second portion 108ai-ei takes a path away extending towards the second chip facet 116 but away from at one of the chip sides. Each second portion 108ai-ei of the waveguides 108a-e extends away from the same one side. The angle at which the end of the each of the waveguides 108a-e meets the second chip facet 116 is different to any of the other waveguides. The 'angle' referred to here in the angle about the plane of the chip about which the waveguides 108a-e are spatially separated. The term 'angle' here is also referring to the 'absolute angle' in that angular orientation of the length of waveguide proximal to the second chip facet 116 is measured consistently in the same direction with respect to a single, fixed line of reference. In other words, if the second chip facet 116 has a normal extending inwardly into the chip 122, then each waveguide end portion 108ai-ei extends along a path proximal to the end of the second chip facet 116 that subtends a different absolute angle to that normal.

In principle, this configuration may apply to any optical apparatus 2 described herein, for example, the optical apparatus 2 of figure 1 wherein there are two or more laser cavities.

The angular relationship between the filter 10 and the second chip facet 116 is now described below with respect to Figure 2 and two of the laser cavities, although the same principles may apply to apparatus 102 with more than two laser cavities. The optical filter 110 typically comprises a thin film filter. The thin film filter 110 may comprise a first face at least partially facing the device and for receiving light output from the device 122. The first face of the filter 110 is disposed non-parallel to the second facet 110, although the apparatus 2 may operate by having the first face of the filter 110 be parallel to the chip second facet 116. The light propagating within the first laser cavity is incident upon the optical filter 10 at a first angle relative to the normal of the first face. The light propagating within the second laser cavity is incident upon the optical filter 10 at a second angle relative to the normal of the first face. The first angle is different from the second angle. Therefore, the incident angle of the light entering the filter in the first laser cavity is a different to the incident angle of the light entering the filter in the second laser cavity.

The angular relationship between the waveguides 108ai-ei and the second chip facet 116 is now described below with respect to two of the laser cavities similar to the sample shown in Figure 1 although the same principles may apply to apparatus 102 with more than two laser cavities as exemplified in Figure 2a. The optical apparatus 102, when embodied as a chip 122, may comprise a first waveguide path comprising the first semiconductor waveguide 8a and a second waveguide path comprising the second semiconductor waveguide 8b. The angle that the first waveguide path subtends to the chip second facet is different to the angle that the second waveguide path subtends to the facet.

Returning to figure 2a, the apparatus 102 may in principle have two or more laser cavities, preferably between 4-10 laser cavities, more preferably between 5-7 laser cavities. Having a plurality of cavities can be used by the apparatus 102 to provide separate wavelengths sources or increase the overall integrated optical power emitted from the optical apparatus 102 by combining the light output from two or more of the laser cavities. Increasing the number of waveguides 108a-e also increases cavity redundancy which helps if laser stripes comprising the waveguides become faulty during use. When the apparatus 102 combines the light from all of the laser cavities, 5-7 cavities present an optimum trade-off between high enough power and laser cavity redundancy vs chip size, electrical power requirements and difficulty in assembly.

In the example shown in figure 2a, each of the second length portions 108ai-ei of the waveguides 108a-e takes a curved path away from one of the chip sides. The second length portions 108ai-ei may take any suitable path that results in each waveguide subtending a different angle to second chip facet 116 the other waveguides 108a-e. In fact, the waveguides 108a-e may have any suitable length profile that allows them to subtend a different angle at the second chip facet 116.

The light exiting the second chip facet 116 from each of the waveguides 108a-e therefore takes a different absolute output angle from the low reflectivity coating 118 and hence a different angular path through the lens 120 and therefore a different incident angle to the optical filter 110.

The relationship of the waveguide paths with the thin film filter 110 may be that the first and second waveguide paths each comprise a beginning length portion and an end length portion. The beginning length portion starts at a first device facet 114 and runs in a first direction along the device 122. The end length portion adjoins the beginning length portion and terminates at the second facet 116 wherein the end length portion runs in a direction different to the direction of the beginning portion. In figure 2a, the device 122 comprises opposing edges, each edge running between the first facet 114 and the second facet 116. The first and second waveguide end portions converge towards a common edge as they extend towards the facet 116. In other examples the path directions of the end length portions may be different. For example, in figure 4, some of the waveguide end portions converge towards opposite edges of the device 122. The above description refers to two waveguides, however the principle may extend to two or more waveguides.

The ranges of angles incident upon the filter normal (i.e. the normal extending away from the filter input face) may be any of, but not limited to:

A) 0 degrees upto, but not including, 90 degrees;

B) >= 0.1 degrees upto, but not including, 90 degrees;

C) >= 0.1 degrees but < 15degrees.

The advantages of using smaller angles of incidence, such as 0.1 degrees to the filter 110 include less optical loss and lower polarization splitting.

Figure 2b shows a theoretical graph depicting an example of the change in peak transmission wavelength of a passband thin film optical filter 110 with respect to the incident angle of the light to the filter 110 normal. When light is normally incident to the filter then the peak transmission wavelength is around 1560nm whereas when light is incident at 10 degrees from the same normal the peak transmission wavelength is around 1554nm. The graph therefore shows that light incident upon the filter 110 at different angles experiences different passband frequency responses. The graphs shows points 150 along a curved angle/frequency relationship, however the theoretical relationship is expected to be a smooth curve going through each of the points 150.

In the example shown in figure 2a, each of the light beams, from the different waveguides 108a-e exiting the chip from the second chip facet 116 enter the optical filter 110 at different incident angles after being collimated by the lens 120. Because of the wavelength- angle relationship of the optical filter 110, each of the beams experiences a different frequency response from the filter. The result of this is that each optical cavity in the apparatus 102 supports a different one or more longitudinal modes. Even if each of the optical cavities have the same optical path length, hence support an identical longitudinal mode spectrum, the different filter frequency response that each cavity experiences means that each cavity lases with a different set of one or more longitudinal modes.

Figure 3a shows an example of a wavelength - intensity spectrum of the apparatus 102 of figure 2a. In figure 3a the different five cavities of the apparatus 102, corresponding to the different waveguides 108a-e, support an identical longitudinal mode spectrum. Each cavity is subject to a different frequency response from the optical filter 110 in the cavity. The dashed lines in figure 3a depict the bandpass filter frequency responses of the different cavities wherein 300a is the frequency response of the filter 110 for the cavity having waveguide 108a and the other frequency responses 300b-e are the filter frequency responses for the cavities having the respective waveguides 108b-e. In figure 3a, the longitudinal mode spacing and bandwidth of the frequency response are such that only a single longitudinal mode 302a-e is selected to lase within each cavity for each cavity. In other words, only longitudinal mode 302a is selected by the filter 110, with frequency response 302a, to propagate within the respective cavity. Furthermore, only longitudinal mode 302b is selected by the filter 110, with frequency response 302b, to propagate within another of the cavities, etc. Figure 3b shows another example of a wavelength - intensity spectrum of the apparatus 102 of figure 2a. In figure 3b the different five cavities of the apparatus 102, corresponding to the different waveguides 108a-e, support an identical longitudinal mode spectrum. Similarly to figure 3a, each cavity is subject to a different frequency response from the optical filter 110 in the cavity. The dashed lines in figure 3b depict the bandpass filter frequency responses of the different cavities wherein 304a is the frequency response of the filter 110 for the cavity having waveguide 108a and the other frequency responses 304b-e are the frequency responses for the cavities having the respective waveguides 108b-e. In figure 3b, the longitudinal mode spacing and bandwidth of the frequency response are such that two longitudinal modes are selected to lase within each cavity. For example, longitudinal modes 306a and 306ai are selected by filter response 304a to propagate within the cavity having waveguide 108a. An advantage of having two or more (multiple) longitudinal modes 306a- 306e, 306ai-306ei selected by each frequency response is that any wavelength shift in the longitudinal modes and/or the frequency responses does not result in no modes being supported the cavities.

A wavelength shift of the longitudinal mode spectrum and/or the filter frequency responses may result from reasons such as, but not limited to, different changes in operating characteristics such as component temperature which changes refractive indices and hence shifts the wavelength characteristics. In figure 3a, if the longitudinal modes 300a-e shift relative to the frequency responses 302a-e then certain shifts may result in no lasing from any of the cavities. This may happen if the longitudinal modes 300a-e move from coinciding with the peak transmission of the filter frequency responses 302a-e, as shown in figure 3a, to coinciding with low transmission portions of each frequency response 302a-e.

Figure 3c shows the frequency responses 304b-e and longitudinal modes of figure 3b wherein the chip 122 has undergone a temperature change resulting in a shift in the longitudinal modes of all the laser cavities. As highlighted in figure 3c, longitudinal modes 306e and 306ei originally selected by frequency response 304e for the cavity with waveguide 108e have shifted to new wavelengths denoted by 306eii and 306eiii. Similar shifts happen for the other laser cavities in the apparatus 102. Focusing on the cavity with waveguide 108e, after the wavelength shift, one of the modes 306eiii is now coincident with a low transmission portion of the frequency response 304e and will not lase. However, the adjacent mode 306eii is now coincident with the peak transmission of frequency response 304e and will lase. Having an apparatus 102 wherein the passband frequency response of the filter encompasses two or more longitudinal modes of at least one, preferably all, cavities, allows the apparatus 102 to always output light despite a wavelength shift between the longitudinal mode spectrum of the said cavity and the filter passband. This introduces reliability to the apparatus 102.

Further example of producing different optical frequency responses

With respect to the apparatus 2 of figure 1, there are other ways of providing light propagating within the first cavity 12a to be subject to a different optical frequency response of the optical filter 10 than the light propagating within the second laser cavity 12b. These include providing a chirped filter 10 that varies its passband peak wavelength along the width of the filter input face such that adjacent waveguide output beams incident upon the filter pass through different passband filter responses. This may be accomplished by changing the thickness, along the direction of the successive chip waveguides 8a/8b, of one or more of the layers making up the filter 10.

Optical filter

In some uses of the optical apparatus 102, for example speckle reduction, the optical apparatus 2 may require multiple longitudinal modes to be captured within the FWHM of the filter passbands, i.e. the FWHM is wider than one mode spacing preferably capturing several mode spacings.

The filter 110 may therefore have a frequency response with a full width half maximum (FWHM) wavelength range that is substantially the same as or greater than the wavelength separation between longitudinal modes of at least one of, preferably all of, the cavities supported by the apparatus 102. For other uses of the optical apparatus 102, for example a multiple cavity single longitudinal mode laser source, the desire may be to have a filter passband FWHM < longitudinal mode spacing.

For multiple longitudinal mode operation (within a single passband) the mode spacing may be >20GHz but <100GHz. For object detection/recognition applications, for example where speckle is trying to be reduced, longitudinal mode spacings may be <50GHz.

The filter may be comprised of one or more materials that are relatively insensitive to temperature variation. The optical filter 110 may therefore comprise an athermalised optical thin film filter. The optical filter comprises a substrate material achieving a filter wavelength shift with temperature below 2pm/K. This insensitivity may be temperature insensitivity with respect to refractive index and/or temperature sensitivity with respect to volume.

The filter 110 may comprise a glass substrate that is coated with one or more successive layers of material to form the thin film interference filter. The glass substrate compensates for the temperature dependence of the filter to provide an overall filter centre wavelength shift with temperature below 2pm/K.

A typical operating temperature range of the apparatus 102 may be between -40 degrees C to 85 degrees. C. The filter 110 may be designed to be substantially athermal compared to other components (such as the semiconductor waveguides) within this range.

The optical filter passband may be any suitable passband at normal incidence. The passband at normal incidence may have a peak wavelength between any of, but not limited to: 930- 950nm; 1500-1600nm: 1250 - 1750nm. For applications of the optical apparatus 102 aimed at reducing laser speckle in an illumination system the peak wavelengths may be 930- 950nm and/or 1500-1600nm. For uses of the optical apparatus 102 as a multi wavelength optical source for communications, the passbands may have peak wavelengths between 1250 - 1750nm. Other operational wavelength bands may also be used, for example any of the O-Band (1270nm to 1370nm); E-Band: (1371nm to 1470nm); S-Band: (1471nm to 1530nm); C-Band: (1531nm to 1570nm); L-Band: (1571nm to 1611nm).

The filter 110 may be a separate thin film bulk filter as shown in figure 2a or it may form part of another component such as the lens 120 or the mirror 106. The filter 110 may be angle tuneable such that it may take different angles with respect to the second facet of the device 122.

An optical apparatus 102 outputting light with a wavelength around the range of 940nm typically has more power and uses GaAs as a base semiconductor material system. Other wavelengths may be used including ranges around 1550nm as described herein. Such ranges are deemed 'eye-safe' because the human cornea absorbs such light. Such wavelength considerations are important when the use involves illuminating an animal or human face.

Regardless of the example, the face of the optical filter 110 facing the second chip facet 116 may be angled (not parallel) to reduce unwanted reflections going back into chip 122. Such an angle may be 1 degree or more between the two faces.

Illumination subassembly

The light output from the waveguides 108a-e through the first facet 114 and through the partial reflectivity coating 104 may be output into an illumination subassembly 124 as shown in figure 2a. The illumination subassembly 124 comprises one or more optical elements (not shown) configured to receive input light that has been output from the partial reflectivity coating 104, combine the light into one or more output beams, for example a single output beam, and output the combined beam. The illumination subassembly therefore collects the different light beams from the different laser cavities in the apparatus 102 and outputs them in a spatially combined beam that can be used to illuminate an object or scene. When the illumination subassembly 124 is a separate optical component to the chip 122, the chip and illumination sub assembly 124 may be separated by a space or may be physically contacting each other. The optical elements of the illumination subassembly 124 may be any one or more of, but not limited to, optical fibres, lenses, mirrors, optical modulators, shutters, beam splitters, beam combiners. The illumination subassembly 124 may have one or more of its elements coated with an antireflection coating to reduce the reflection of light from its elements going back into the waveguides 108a-e.

Some of the optical elements required to combine the light from the laser cavities and project the combined light may be formed upon one or more integrated optical elements upon the chip 122. For example, the partial reflectivity coating 104 may, instead of being on an end facet 114, be another thin film optical filter inserted into or onto a recess in the chip 122 that optically interfaced with the waveguides 108a-e. In this example arrangement, another portion of the same chip 122 residing the other side of partial filter contains further waveguides that combine, on chip, the light into a single output spatial mode.

The output of light of the waveguide modes to the illumination subsystem 124 may be facilitated by one or more optical fibres and/or chip waveguide tapers. In one example, an optical fibre may be used to couple out light from a single spatially combined mode from the chip 122 and output the light from the other end of the fibre with a lens (for example a lens ended fibre).

The illumination sub assembly 124 may be used for any suitable application, including but not limited to: an object illumination source for object recognition. This may be, for example facial recognition.

Other optical outputs

Instead of or in addition to the illumination subassembly 124 there may be a set of one or more optical elements configured to receive input light that has been output from the partial reflectivity coating 104, combine the light into a single output beam and output the combined beam. The combined beam may be output into free space, input into a waveguide or optical fibre.

Instead of or in addition to the illumination subassembly 124 there may be a set of one or more optical elements configured to receive input light that has been output from the partial reflectivity coating 104, and output the spatially separate light beams of the optical apparatus. The beams may be output into free space, input into a waveguide or optical fibre.

Coatings

The partial reflectivity coating 104 may comprise any one or more layers of material that provide a modified end chip facet reflectivity of any of: 50% - 99.9%, 60% - 99%, 70% - 99%, 80%-99%, 90% - 99%, 95%-99%. The apparatus 102 may be modified such that the partial reflectivity coating is made into a low reflectivity coating similar to the low reflectivity coating on the second chip facet 116. If this is done then a further partial reflector is required outside of the chip 122 (for example as part of the illumination assembly) to create the laser cavities.

The low reflectivity coating may comprise any one or more layers of material that provide a modified end chip facet reflectivity of any of but not limited to: 0% - 5%, 0% - 4%, 0% - 3%, 0%-2%, 0% - 1%, 0.1%%-1%.

Chip

The waveguides 108a-e may be any of a rib waveguide, ridge waveguide, buried waveguide or any other suitable waveguide structure comprising suitable semiconductor and/or dielectric materials that provide the functionality required by each of the said sections.

As discussed elsewhere herein, the light travelling through a chip 122 portion of a laser cavity may propagate through one or more waveguides 108a-e. This may be a single waveguide or a plurality of optically coupled waveguides. In some examples each waveguide 108a-e has multiple different longitudinal sections following successively on from one another along the length of the waveguide. These sections may be termed a gain section and a phase control section. These sections may have the same or different characteristics but are independently electronically controlled. For a phase control section using current injection to control its optical characteristics, the semiconductor medium in the phase control section preferably comprises a larger band gap than the semiconductor medium in the gain section. In principle the bandgap of the phase control section may be any bandgap, for example the bandgap in the phase control section may be the same as the gain section.

Preferably the phase control section and gain section are separately electronically controllable such that the current or voltage applied to the gain control medium is not applied to the phase control medium and vice versa. The gain medium is preferably electronically coupled to two electrical contacts. The phase control medium is preferably electronically coupled to two electrical contacts. One of the contacts may be a common ground or anode shared with the gain section. In principle the laser cavity section may comprise a plurality of gain sections and/or a plurality of phase control sections.

The chip 122 may have an in-plane shape of a rectangle as shown in figure 2a. Other shapes of chip 122 are also possible. The angle that the waveguides 108a-e make to the chip facet normal may be greater or less than 0 (i.e. not along the normal itself). This helps to minimize back reflections should the optical design of the apparatus 102 require it.

The chip 122 may take any size and shape but may typically have a length between the first and second facet between 0.5mm - 5mm. The wavelength of operation of the waveguides may be any of the wavelength 5 discussed herein. Typically the wavelength of operation is directly related to the material system of the chip 122. The waveguides and the chip may be formed of any suitable semiconductor material including but not limited to GaAs, InGaAs and doped variants thereof.

Light propagation between components Unless otherwise stated, light may propagate from different components within and/or to or from external components of the apparatus 102 using any suitable means. This may for example include any one or more of: free space propagation using bulk optic components to direct the light, using optical fibres and/or integrated optic waveguides to guide the light. Examples include buried channel waveguides, laser-inscribed waveguides and/or strip waveguides. Alternatively, or additionally, the light may be directly transmitted from adjoining components and/or via a direct laser beam.

System

A system is also provided that comprises the apparatus 102 and any one or more of the: A) illumination sub assembly 124; B) one or more electronic controllers for controlling any of the electronically driven elements described herein; C) any other optical, mechanical or electrical element. For example, the system may be a mobile device 702 having the optical apparatus and the illumination sub assembly wherein a processor within the mobile device acts as or drives an electronic controller in the device. The mobile device 702 may be, for example a tablet computer or mobile phone. The device 702 may comprise a housing, such as a case, wherein at least part of the illumination assembly is integral with and/or protrudes at least partially through the case. An example of such a system is shown in figure 7 which shows a mobile phone 702 with a screen 706 and interface button 704 and a portion off the illumination subassembly 124, 708 integral to the outer housing.

One or more temperature control elements, which may take the form of thermo-electrical cooler (TEC) comprising a Peltier element controlled by a TEC controller, may be coupled to the chip 122 and/or any other of the optical elements described for the apparatus 102. The temperature control element is configured to control the temperature of at least part of the optical apparatus 102. The Peltier element may be attached to, and in thermal contact with, the optical elements, whilst the TEC controller may be physically remote from the optical elements. The TEC controller may be connected to the Peltier element via wires or even a wireless connection wherein the Peltier element is provided with on board electronic control apparatus to receive electronic signals from the TEC controller and correspondingly provide a thermal output to the optical elements. Further examples

Figure 4 shows a further example of an optical apparatus 402, similar to the apparatus 102 wherein like numerals represent like components. In this figure, the ends of the two outermost waveguides 408ai, 408ei on each long edge of the chip deviate inwardly towards the central in-plane longitudinal chip axis running from the first facet 114 to the second facet 116. In figure 4 there is a middle waveguide 408c that runs straight along the whole chip, however such a straight waveguide is optional. Figure 4 also shows five waveguides, 408a-e however in principle there may be two or more waveguides. The device of figure 4 is also rectangular, however other shapes are also possible including a parallelogram. The middle waveguide 408c is shown to terminate at the second facet at normal incidence, however the incidence angle of any one or more of the waveguides 408a-e may be a non normal incidence to help reduce back reflections from the second facet 116 propagating back down the waveguides.

In other words, the device (chip), in this example, has at least first and second waveguide paths, for example 408d and 408b in figure 4. Each waveguide path comprises a beginning length portion, 408b, 408d starting at the first device facet 114 and running in a first direction along the device 402. Each waveguide path also comprises an end length portion 408bi, 408di adjoining the beginning length portion. The end length portions 408bi, 408di terminate at the second facet 116 and run in a different direction to the direction of the beginning portions 408b, 408d.

The device also comprises opposing first and second edges, each running between the first facet 114 and second facet 116. The first waveguide end portion 408bi converges towards the first edge as it extends towards the second facet 116. The second waveguide end portion 408di converges towards the second edge as it extends towards the second facet 116.

The device may comprise sets of waveguide paths, wherein figure 4 shows the example of five paths in total. The device may have a first set of one or more waveguide paths 408a, 408b each having a waveguide end portion 408ai, 408bi converging towards the first edge.

A second set of one or more of the further waveguide paths 408d, 408e each having a waveguide end portion 408di, 408ei converging towards the second edge.

Specifically, for figure 4, the device has a straight waveguide 408c and a first set of two waveguides having end length portions diverging away from one of the device edges and being incident upon the second facet at a negative angle with respect to the inwardly extending second facet normal. The device also has a second set of two waveguides having end length portions diverging away from the other of the device edges and being incident upon the second facet at a positive angle with respect to the inwardly extending second facet normal. Each set may have one or more waveguides wherein each waveguide in the set has an end length portion that is incident at a different angle to the second facet normal to the other end length portions in the same set. The arrangement of waveguides on the device may be symmetrical about the length of the device between the first and second facets.

Where the device has first and/or second sets of two or more waveguides, each waveguide in the respective set that is positioned further away from the other set has an end length portion diverging at a steeper angle towards the second facet, thus being incident at a larger absolute angle to the second facet normal.

The effect of the arrangement of waveguide paths in this example is that the waveguides 408a-e funnel into the second facet like a truncated converging taper. Light is output from each of the end length portions of the waveguides towards the lens. The pitch between the waveguides 408ai-ei at the second facet 116 is smaller than the pitch between the waveguides 408a-e at the first facet. Smaller angles of incidence going through the second facet 116 and other components means smaller polarization effects, lower waveguide propagation losses at the bends. It may also be simpler to create waveguides with a gentler gradient. In this example and others waveguide paths are split into first and second portions such as 408a and 408ai, however these may be different lengthwise portions of the same waveguide. In the example of figure 4, the angle made by any one of the waveguides 408ai-ei at the second chip facet 116 is shallower than that of the steepest equivalent angle made in the example shown in figure 2a. This allows for ease of manufacture and less bend loss along the waveguide as the mode goes around the curve. Even-though the angles made by the waveguides to the second chip facet normal are more gentle, the angles the light beams make with the filter 110 are still large enough to produce a large range wherein each light beam subtends a different angle to any other light beam from any other cavity. The reason for this is that the waveguide mode input face of the optical filter 110 is positioned non parallel to the second facet 116 of the chip. A curved reflector 106 is used to direct light back to the respective waveguide from whence the light originated.

Figure 5 shows another example of an optical apparatus 502. This optical apparatus 2, 502 comprises at its minimum, the following features referencing components from Figure 1. One or more first optical reflectors 4. One or more second optical reflectors 6. A first semiconductor waveguide 8a located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. A second semiconductor waveguide 8b located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. An optical filter 10 located between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. A first laser cavity 12a that extends between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. This laser cavity also extending through at least the first semiconductor waveguide 8a and the optical filter 10. A second laser cavity 12b extending between the one or more first optical reflectors 4 and the one or more second optical reflectors 6. This cavity also extending through at least the second semiconductor waveguide 8b and the optical filter 10. Each of the first and second laser cavities 12a/12b comprises a gain section and a phase control section. The length of at least one of: the gain section; and, phase control section, of the first waveguide path, being different to the length of the corresponding gain section and phase control section of the second waveguide path.

It is to be understood that all of the optional features and configurations provided in the examples with different optical frequency responses, may equally be applicable to an optical apparatus described for figure 5. Equally the waveguides shown in and described for figures 5 and 6 may form part of the apparatus 2, 102 in the examples shown previously. For example the gain and phase control sections may form the beginning length waveguides extending from the first chip facet 114, shown in figure 2a.

Figure 5 shows another example of an optical apparatus 502 similar to that of the optical apparatus 102 of figure 2a wherein like numerals represent like components. In Figure 5, all of the waveguides 508a-e are straight and do not have a curved end portion. In this example each waveguide 508a-e is comprised of different length gain and phase control sections as described above. Figure 6a shows an exploded view of the chip 522 of figure 5. The phase508aii-eii and gain 508ai-508ei sections of each laser are used to control the relative optical amplitude and phases of the light in each laser cavity, again, acting to de-phase the cavities with respect to each other. Each of the gain 508ai-508ei and phase sections 508ai- 508ei are separately electronically controllable by having a split contact.

The phase and gain section may be used to tune the laser cavity. For example, if it is desired to have each laser cavity on the chip 522 to have the same or substantially the same set of longitudinal modes then the phase / gain sections can be used to tune this. Variations may arise from the different optical path lengths along the cavities arising from any one or more of, but not limited to: different length semiconductor waveguides (for example if the waveguides in Figure 5 had the end sections of figure 2a); different path lengths through the lens 120 or optical filter 110; and or different path lengths between components.

Figure 6b shows three graphs Cl, C2 and C3 representing the longitudinal mode spectrums of three of the cavities on the device 522 shown in figures 5 and 6a. In this example shown in figure 6b, each of the longitudinal modes in each of the cavities, Cl, C2, C3, has substantially the same optical intensity, however the modes in different waveguides may have different intensities. In this example each cavity is shown to have five longitudinal modes however it is appreciated that the spectrum is broader than just five modes. The longitudinal modes spectrums of the cavities are slightly shifted in wavelength with respect to each other. This is done by electrically controlling the phase and optionally the gain sections of the cavities. Because each cavity is de-phased from each other, the combined light has a high optical output power from the multiple laser cavities, within a filter passband, but the combined light is de-phased compared to laser cavities with all the same phase.

Figure 6c shows the combined output of the waveguides after passing through the filter 110 at different angles. In this example the filter is angle-tuneable with respect to the device second facet 116 such that the output light beams output from the second facet 116 can be incident upon the filter at different angles, hence experience a different filter passband. The control of the angle of the filter 110 may be by an actuator controlled by electrical signals from the electronic controller described elsewhere herein. The passband of the filter in the example shown in figure 6c is only wide enough to capture a single longitudinal mode from each cavity. Each mode allowed to pass through the filter 110 from the different cavities is therefore of a different wavelength to the other modes. The device of this example may be controlled such that any of: A) all of the cavities have different longitudinal spectra, hence no longitudinal modes overlap; B) the longitudinal modes of two or more cavities may substantially overlap. In the case where the longitudinal modes of two or more cavities may substantially overlap, this may be chosen for applications where less de-phasing is required or where a narrow filter passband is used. For example, for an eight laser cavity device and a narrow optical filter passband, there may four sets of two cavities, each set having overlapping longitudinal mode spectra.

Another alternative example of the optical apparatus 2 is where the apparatus does not necessarily require either: A) different lengths of phase control and gain section as per figure 6a; B) each cavity experiencing a different optical frequency response as per figure 2a. The alternative configuration may resemble an apparatus similar to that shown in figure 5, but where each of the waveguides 580a-e may be identical.

In this alternative example the semiconductor waveguides can each be electrically driven by pulsed currents. In the pulsed current application, each semiconductor stripe can be driven at the same time or at different times with temporal current pulses. In the case of different times, the applied current pulses can be temporally synchronised to form a temporal strobe illumination. With current pulses applied to this optical source, the illumination detector can have its received photocurrent integrated over time so that the measured light comprises light pulses from different waveguides in the semiconductor chip. Alternatively, the detector can have the received photocurrent temporally gated so that the measured light from each waveguide can be separately analysed.

This alternative example may be adapted to use other components and configurations described in other examples herein, for example, using different length phase control and gain sections.

Uses of the optical apparatus

The optical apparatus 2 described herein may be used in a number of applications including but not limited to: object recognition such as facial recognition; a single wavelength optical source for optical communications, a multi-wavelength source for optical communications; optical sensors; spectroscopy. Different uses may require continuous wave or pulsed operation of the output light and the optical system may be directly controlled electronically to provide such signals or may include, or be optically coupled to an optical modulator to provide the desired modulated optical output. Modulators may include differential phase shift based modulators such as a Mach Zehnder modulator and/or an absorption based modulator such as an electro-absorption modulator.

When applied as an object illumination source, the wavelength of operation of the optical apparatus may be, for example, any of the atmospheric windows so that sufficient output light can illuminate the target. These windows may be centred around 940nm or 1550nm. The output illumination optical of the subassembly may comprise optical elements for dispersing the combined output light into a plurality of spots, for example in a grid. The optical apparatus in this example may form part of an electronic mobile device such as a mobile phone.

General considerations

The optical apparatus or system may be controlled by one or more electronic controllers. The electrical controller may take the form of a computer, use one or more printed circuit boards (PCB's), or comprise a processor and optionally memory elements having any software that performs this function. There may be a singular electronic controller or a plurality of electronic controllers.

The electronic controller may have an electronic processing means that is configured to control the operation of the controller and determine any of, but not limited to: the angle of the filters; the phase section and gain section electronic inputs; any temperature controller used to cool the apparatus; any of the other electrical components in a system comprising the optical apparatus.

Examples of electronic processing means are described as follows.

The processing means may comprise one or more processing devices. Any of the processing devices described herein may comprise one or more electronic devices. An electronic device can be, e.g., a computer, e.g., desktop computer, laptop computer, notebook computer, minicomputer, mainframe, multiprocessor system, network computer, e-reader, netbook computer, or tablet. The electronic device can be a smartphone or other mobile electronic device.

The computer can comprise an operating system. The operating system can be a real-time, multi-user, single-user, multi-tasking, single tasking, distributed, or embedded. The operating system (OS) can be any of, but not limited to, Android ^®, iOS ^®, Linux ^®, a Mac operating system and a version of Microsoft Windows ^®. Any apparatus, systems and methods described herein can be implemented in or upon computer systems. Equally, the processing device may be part of a computer system.

Computer systems can include various combinations of a central processor or other processing device, an internal communication bus, various types of memory or storage media (RAM, ROM, EEPROM, cache memory, disk drives, etc.) for code and data storage, and one or more network interface cards or ports for communication purposes. The apparatus, systems, and methods described herein may include or be implemented in software code, which may run on such computer systems or other systems. For example, the software code can be executable by a computer system, for example, that functions as the storage server or proxy server, and/or that functions as a user's terminal device. During operation the code can be stored within the computer system. At other times, the code can be stored at other locations and/or transmitted for loading into the appropriate computer system. Execution of the code by a processor of the computer system can enable the computer system to implement the methods and systems described herein.

The computer system, electronic device, or server can also include a central processing unit (CPU), in the form of one or more processors, for executing program instructions. The computer system, electronic device, or server can include an internal communication bus, program storage and data storage for various data files to be processed and/or communicated. The computer system, electronic device, or server can include various hardware elements, operating systems and programming languages. The electronic device, server or computing functions can be implemented in various distributed fashions, such as on a number of similar or other platforms.

Any processes of controlling the apparatus described herein can be implemented in computer software that can be stored in the computer systems or electronic devices including a plurality of computer systems and servers. These can be coupled over computer networks including the internet. This network may be the same or a different network to the PON that the electronic controller 4 serves. The methods and steps performed by components described herein can be implemented in resources including computer software such as computer executable code embodied in a computer readable medium, or in electrical circuitry, or in combinations of computer software and electronic circuitry. The computer-readable medium can be non-transitory. Non-transitory computer-readable media can comprise all computer-readable media, with the sole exception being a transitory, propagating signal. Computer readable media can be configured to include data or computer executable instructions for manipulating data. The computer executable instructions can include data structures, objects, programs, routines, or other program modules that can be accessed by a processing system Computer-readable media may include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media, hard disk, optical disk, magneto-optical disk), volatile media (e.g., dynamic memories) and carrier waves that can be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media, transmission media (e.g., coaxial cables, copper wire, fibres optics) or any combination thereof.

The terms processing, computing, calculating, determining, or the like, can refer in whole or in part to the action and/or processes of a processor, computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the system's registers and/or memories into other data similarly represented as physical quantities within the system's memories, registers or other such information storage, transmission or display devices. Users can be individuals as well as corporations and other legal entities. Furthermore, the processes presented herein are not inherently related to any particular computer, processing device, article or other apparatus. An example of a structure for a variety of these systems will appear from the description herein. Embodiments are not described with reference to any particular processor, programming language, machine code, etc. A variety of programming languages, machine codes, etc. can be used to implement the teachings as described herein.

An electronic device can be in communication with one or more servers. The one or more servers can be an application server, database server, a catalog server, a communication server, an access server, a link server, a data server, a staging server, a database server, a member server, a fax server, a game server, a pedestal server, a micro server, a name server, a remote access server (RAS), a live access server (LAS), a network access server (NAS), a home server, a proxy server, a media server, a nym server, network server, a sound server, file server, mail server, print server, a standalone server, or a web server. A server can be a computer.

One or more databases can be used to store information from an electronic device. The databases can be organized using data structures (e.g., trees, fields, arrays, tables, records, lists) included in one or more memories or storage devices. In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration various examples in which the claimed invention(s) may be practiced and provide for superior Optical apparatus. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. In addition, the disclosure includes other inventions not presently claimed, but which may be claimed in future.

Claims

1. An optical apparatus (2) comprising

I) one or more first optical reflectors (4);

II) one or more second optical reflectors (6);

III) a first semiconductor waveguide (8a) located between the one or more first optical reflectors (4) and the one or more second optical reflectors (6);

IV) a second semiconductor waveguide (8b) located between the one or more first optical reflectors (4) and the one or more second optical reflectors (6);

V) an optical filter (10) located between the one or more first optical reflectors (4) and the one or more second optical reflectors (6);

VI) a first laser cavity (12a): i) extending between the one or more first optical reflectors and the one or more second optical reflectors ii) extending through at least the first semiconductor waveguide and the optical filter;

VII) a second laser cavity (12b): iii) extending between the one or more first optical reflectors and the one or more second optical reflectors; iv) extending through at least the second semiconductor waveguide and the optical filter.

2. An optical apparatus as claimed in claim 1 wherein the light propagating within the first cavity is subject to a different optical frequency response of the optical filter than the light propagating within the second laser cavity.

3. An optical apparatus as claimed in claims 1 or 2 wherein: the optical filter comprises a first face for receiving light propagating within the first and second laser cavities; light propagating within the first laser cavity is incident upon the optical filter at a first angle relative to the normal of the first face; light propagating within the second laser cavity is incident upon the optical filter at a second angle relative to the normal of the first face; the first angle being different from the second angle.

4. An optical apparatus as claimed in any of preceding claim comprising a device comprising: a first waveguide path comprising the first semiconductor waveguide; and, a second waveguide path comprising the second semiconductor waveguide; the device comprising a facet from which light propagating within the first and second waveguide paths is output towards the optical filter; the angle that the first waveguide path subtends to the facet is different to the angle that the second waveguide path subtends to the facet.

5. An optical apparatus as claimed in claims 1 or 2 wherein: the optical filter is disposed non-parallel to the facet.

6. An optical apparatus as claimed in claim 5 wherein the first and second waveguide paths each comprise: a beginning length portion: starting at a further device facet; running in a first direction along the device; an end length portion: adjoining the beginning length portion; terminating at the facet; running in a direction different to the direction of the beginning portion.

7. An optical apparatus as claimed in claim 6 wherein: the device comprises opposing first and second edges, each running between the facet and further facet; the first waveguide end portion converges towards the first edge as it extends towards the facet; the second waveguide end portion converges towards the second edge as it extends towards the facet.

8. An optical apparatus as claimed in claim 6, wherein the device comprises opposing edges, each edge running between the facet and further facet; the first and second waveguide end portions converge towards a common edge as they extend towards the facet.

9. An optical apparatus as claimed in claim 7 wherein: the device comprises further waveguide paths; a first one or more of the further waveguide paths each having a waveguide end portion converging towards the first edge; a second one or more of the further waveguide paths each having a waveguide end portion converging towards the second edge.

10. An optical apparatus as claimed in claim 8 wherein the device comprises further waveguide paths each having waveguide end portions converging towards the common edge.

11. An optical apparatus as claimed in any of claims 9 or 10 wherein each of the first, second and further waveguide paths comprises waveguide end portions that each subtend a different absolute angle to the facet normal.

12. An optical apparatus as claimed in any preceding claim wherein: the first optical reflector is a partial optical reflector; the optical apparatus further comprises an optical combiner configured to: receive light output from the first laser cavity and the second laser cavity via the first optical reflector; combine the received light into a spatially combined optical output.

13. An optical apparatus as claimed in claim 12 further comprising an illumination assembly configured to output the combined light to illuminate an external object

14. An optical apparatus as claimed in any preceding claim wherein the optical filter comprises an athermalised optical thin film filter.

15. An optical apparatus as claimed in claim 14 wherein the optical filter comprises a substrate material having a wavelength shift with temperature below 2pm/K.

16. An optical apparatus as claimed in any preceding claim wherein: each of the first and second laser cavities comprises a gain section and a phase control section; the length of at least one of: the gain section; and, phase control section, of the first laser cavity, being different to the length of the corresponding gain section and phase control section of the second laser cavity.

17. An optical apparatus as claimed in claim 16 wherein: the first optical reflector is a partial optical reflector; the optical apparatus further comprises an optical combiner configured to: receive light output from the first laser cavity and the second laser cavity via the first optical reflector; combine the received light into a spatially combined optical output.

18. An optical apparatus as claimed in claim 17 further comprising an illumination assembly configured to output the combined light to illuminate an external object.

19. An optical apparatus as claimed in any of claims 16-18 wherein the optical filter comprises an athermalised optical thin film filter.

20. An optical apparatus as claimed in claim 19 wherein optical filter comprises a substrate material having a wavelength shift with temperature below 2pm/K.

21. A system comprising an optical apparatus as claimed in any preceding claim and one or more electronic controllers in electrical communication with at least the semiconductor waveguides.

22. A system as claimed in claim 21 comprising an optical detector for detecting light reflected from one or more objects illuminated by the light output from the optical apparatus.