GB2545912A

GB2545912A - Interferometry

Info

Publication number: GB2545912A
Application number: GB1523035.2A
Authority: GB
Inventors: Bitauld David; Rønnow Troels; Martin-Lopez Enrique
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2015-12-29
Filing date: 2015-12-29
Publication date: 2017-07-05
Also published as: GB201523035D0

Abstract

An interferometer chip comprising a semiconductor substrate 102, a laser 110 configured to provide light for at least one pair of paths including a delay path 130 and a sample path 120, and at least one detector 140 configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path is provided by a light guide (160, Fig. 3) formed from the semiconductor substrate. The light guide may be a channel wave guide. The delay path may be less than 3mm in length. There may be silicon micro lenses 172 having a refractive index greater than 2 and a focal length of less than 1mm in each of the sample paths for directing light towards a sample 200. The chip may comprise a plurality of pairs of paths and detectors, each pair of paths comprising a different sample path associated with a sensor and delay path. The sensors may be arranged as a 1D array over which the sample is swiped. The interferometer chip may be used as a biometric sensor comprising a curved reflector (302, Fig. 7) over which a sample is swiped.

Description

TITLE

Interferometry TECHNOLOGICAL FIELD

Embodiments of the present invention relate to interferometry of a sample. BACKGROUND

An interferometer used for interferometry of a sample, typically has a delay path and a sample path. Light is split into the delay path and the sample path. The light of the sample path interacts with the sample and is then combined with light of the delay path that has not interacted with the sample. The combined light signal depends upon interference between the light from the two different paths. This interference is dependent upon a phase shift introduced by the sample and is detected by a detector.

Interferometers are often large and bulky systems.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided an interferometer chip comprising: a semiconductor substrate; a laser configured to provide light for at least one pair of paths of an interferometer including a delay path and a sample path; and at least one detector configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path is provided by a light guide formed from the semiconductor substrate.

According to various, but not necessarily all, embodiments of the invention there is provided an interferometer chip comprising: multiple pairs of paths of an interferometer for receiving light from a laser, each pair of paths including a delay path and a different sample path; at least one detector associated with each pair of paths configured to detect interference of light returning from the associated pair of paths, and at least one micro lens in each of the one or more sample paths for directing light towards a sample.

According to various, but not necessarily all, embodiments of the invention there is provided a photonic integrated circuit comprising: a semiconductor substrate; a laser integrated within the semiconductor substrate configured to provide light for at least one pair of paths of an interferometer including a delay path and a sample path; and at least one detector configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path is provided by a light guide formed from the semiconductor substrate.

According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the brief description, reference will now be made by way of example only to the accompanying drawings in which:

Fig 1 illustrates operation of an interferometer similar to those illustrated in the other figures;

Fig 2 illustrates an example of an interferometer chip;

Fig 3 illustrates an example of a light guide;

Fig 4 illustrates an example of an interferometer chip;

Fig 5 illustrates an example of an interferometer chip;

Fig 6 illustrates an example of a tunable laser;

Fig 7 illustrates use of an interferometer chip in a biometric sensor system;

Fig 8 illustrates an example of an interferometer chip;

Fig 9 illustrates use of the interferometer chip in Fig 8 in a biometric sensor system; Fig 10 illustrates an example of a sensor apparatus comprising an interferometer chip. DETAILED DESCRIPTION

The figures 1 to 6 illustrate an interferometer chip 100 comprising: a semiconductor substrate 102; a laser 110 integrated within the semiconductor substrate 102 configured to provide light 112 for at least one pair of paths of an interferometer including a delay path 130 and a sample path 120; and at least one detector 140 configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path 130 is provided by a light guide 160 formed from the semiconductor substrate 102.

The formation of the delay path 130 from the semiconductor substrate 102 enables the delay path 130 to be entirely on-chip and short allowing the sample path 120 to a sample 200 to also be short and the sample 200 to be very close to the chip 100.

Fig 1 illustrates operation of an interferometer similar to those illustrated in the other figures. The features described in relation to Figure 1 are applicable to the interferometers illustrated in the other figures.

The interferometer uses a single delay path 130 and a single sample path 120. The interferometer is arranged in Michelson configuration where a single optical arrangement 150 is used to split light into the delay path 130 and a single sample path 120 and to recombine light from the delay path 130 and the single sample path 120 for detection. A laser 110 is configured to provide light 112 to the optical arrangement 150. The optical arrangement 150 splits the light 112 into two different paths- the delay path 130 and the sample path 120.

The light entering the delay path 130 travels the length of the delay path 130 and is reflected, for example by a mirror or other optical element returning light in the opposite direction, to return along the delay path 130. This journey introduces a delay.

The light entering the sample path 120 travels the length of the sample path 120 and is reflected by a sample 200 to return along the sample path 120. This journey introduces a delay at least partially dependent upon the interaction of the light at the sample 200.

The optical arrangement 150 combines the light received from the two different paths-the delay path 130 and the sample path 120. This combined light signal 104 depends upon interference between the light returning from the two different paths. This interference is dependent upon the phase shift introduced by the different journeys experienced by light along the two different paths, which is dependent upon the optical characteristics of the sample 200. A detector 140 is configured to detect the combined light signal 104.

By varying the wavelength of light produced by the laser 110 it is possible to sweep the source in the spectral domain, that is detected combined light signals 104 at different wavelengths. This sweep of the sample 200 in the spectral domain may be converted to an image in the spatial domain by, for example, using a Fourier or other suitable transform.

By using multiple sample paths 120 simultaneously it is possible to extend the imaging of the sample 200 from a single point to multiple simultaneous points. In some configurations the multiple sample paths 120 may be paired with a common single delay path 130 to create multiple different combined light signals 104. In other configurations, for example as illustrated in Fig 2, each of the multiple sample paths 120 may be paired with a different one of multiple delay paths 130 to create multiple different combined light signals 104.

Fig 2 illustrates an example of an interferometer chip 100 comprising: a laser 110 configured to provide light for at least one pair of paths of an interferometer including a delay path 130 and a sample path 120; and at least one detector 140 configured to detect interference of light returning from the at least one pair of paths 120, 130 of the interferometer.

The interferometer chip 100 in this example, but not necessarily all examples, comprises multiple sample paths 120 that may be used simultaneously to extend the imaging of the sample 200 from a single point to multiple simultaneous points. Each of the multiple sample paths 120 is paired with a different one of multiple delay paths 130 to create simultaneously multiple different combined light signals 104 each of which is detected simultaneously using a different detector 140.

The output 112 of the laser 110 is split by optical element 164 into N different light signals, each of which is provided as an input to one of N optical arrangements 150. The optical element 164 may, for example, be a star coupler or a 1xM multi mode interference coupler or a tree-like structure of 1x2 splitters.

Each pairing of delay path 130 and sample path 120 is coupled to an optical arrangement 150 that is configured to split received light and provide it in a forward direction along both the delay path 130 and the sample path 120 and to recombine light received, in the return direction, from the delay path 130 and the sample path 120 for detection by a detector 140. The optical arrangement 150, in this example, may be a 2x2 multi mode interference coupler.

The interferometer chip 100 comprises sensors 170 for outputting light from the interferometer chip 100 towards the sample 200 and for receiving light reflected from the sample 200. Each sensor 170 is part of a different sample path 120 and is used to image a different part of the sample 200.

In this example, each sensor 170 comprises a micro lens 172. A micro lens 172 is therefore within each of the N sample paths 120 and is used to direct light from the interferometer chip 100 along the sample path 120 in the forward direction towards the sample200. In this example the multiple micro lenses 172 are arranged in a rectilinear line with separation (pitch) of 0.25mm or less and preferably less than 0.05mm. The multiple micro lens 172 therefore form a one dimensional array.

The diameter of the micro lenses 172 may be the same as the pitch between the micro lenses 172 in order to leave little space between them.

The lenses may be configured so that the light output from the array of lenses 172 is collimated to minimize the light beam divergence in the measured sample volume. In order to do so, the surface of interferometer chip 100 should be close to the focal plane of the micro lenses 172. The focal length of the micro lenses 172 is chosen so that the light beam coming out of the interferometer chip 100 has a diameter that is smaller but comparable to the diameter of the micro lenses 172.

Each micro lens 172 is formed of a transparent material with a curved surface, which can be spherical or aspherical. The transparent material could be an insulator (n~1.4-2) or a semiconductor (n~3-4). The volume between a surface of the interferometer chip 100 and the micro lenses 172 could be made of the same material as the micro lenses in a single piece. Part of this volume could also be empty (air) or filled with a solid spacer made of another transparent material.

In the case of a spherical surface, the radius of curvature determines the focal length. If the micro lenses 172 and the volume between them and the surface of the interferometer chip 100 is the same material, the focal length is defined by: F=n/(n-1)R, with f the focal length, n the lenses’ material refractive index and R the radius of curvature.

The higher the refractive index n, the larger the radius of curvature can be in order to obtain a given focal length. As it is currently more difficult or impossible to fabricate lenses with a high aspect ratio, which corresponds to a small radius of curvature for a given lens diameter, the micro lenses 172 may be formed from high index material such as silicon (n~3.4).

Depending on the optical output divergence of the interferometer chip 100 and the material of the micro lenses 172, the distance between the interferometer chip 100 surface and the furthest point of the micro lenses 172 from the interferometer chip 100 could range from approximately 0.05mm to 5mm. A typical case would be a silicon (n=3.4) micro lens array with its surface directly in contact with the interferometer chip 100. For a D=3 micron optical output, the divergence is θ=4*λ/(π*Ο*η)=0.19 with λ the wavelength (1.55 microns). The focal length is calculated to let the beam expand almost to the diameter of the micro lenses: f=0.2/0.19=1.05mm. This focal length is achieved with a radius of curvature R=0.75mm.

Thus in some examples, each micro lens 172 may be formed from material having a refractive index greater than 2 or greater than 3.. Each micro lens 172 may have the same focal length, which may be less than 2mm. A light guide 160 is used to interconnect the laser 110 and the optical element 164. Each of N outputs from the optical element 164 is interconnected to an input of a different one of N optical arrangements 150 using N separate light guides 160. Each optical arrangement 150 has an output interconnected to a light guide 160 that forms the delay path 130 and has an output interconnected to a light guide 160 that forms the portion of the sample path 120 between the optical arrangement 150 and the sensor 170 (micro lens 172) in the sample path 120. Each optical arrangement 150 has an input interconnected to the optical element 164 via a light guide 160 (as previously described) and an input interconnected to a detector 140 via a light guide 160.

Some of the light guides 160 may optionally and additionally comprise a semiconductor optical amplifier or slave laser 162. For example, each of the N light guides 160 between the optical element 164 and an optical arrangement 150 may comprise a semiconductor optical amplifier or slave laser 162. For example, each of the N light guides 160 forming part of a sample path 120 an optical arrangement 150 and sensor 170 may comprise a semiconductor optical amplifier or slave laser 162.

Some or all of the optical components of the interferometer chip 100 including the laser 110, optical element 164, optical arrangements 150, light guides 160, detectors 140 and semiconductor optical amplifier or slave laser 162 (if present) maybe integrally formed from or within the substrate 102.

The semiconductor substrate 102 may be a monolithic semiconductor substrate 102.

The semiconductor substrate 102 may be a homogenous or non-homogenous epitaxial substrate. An epitaxial substrate is one where a film or epitaxial layer of crystalline material is deposited onto a substrate layer of crystalline material. A homogenous epitaxial substrate is one where the epitaxial layer and the substrate layer are the same material. A non-homogenous epitaxial substrate is one where the epitaxial layer and the substrate layer are different material.

In this example but not necessarily all examples, the substrate 102 is a compound semiconductor substrate 102. That is the substrate 102 comprises a compound semiconductor formed different elements. In this example but not necessarily all examples, the substrate 102 is a lll-V semiconductor substrate 102. That is the substrate 102 comprises a compound semiconductor formed from one or more Group III elements (e.g. Al, Ga, In) and one or more Group V elements (e.g. P, As). Examples of lll-V semiconductor substrates include gallium arsenide GaAs, indium phosphide InP. The lll-V semiconductor substrate 102 may be a monolithic lll-V semiconductor substrate 102. The lll-V semiconductor substrate 102 may comprise an epitaxial layer of lll-V semiconductor substrate 102 on a bulk semiconductor. The bulk semiconductor may be the same or a different lll-V semiconductor or another material or semiconductor such as, for example, silicon.

Some or all of the optical components of the interferometer chip 100 including the laser 110, optical element 164, optical arrangements 150, light guides 160, detectors 140 and semiconductor optical amplifier or slave laser 162 (if present) may be integrally formed from or within the semiconductor substrate 102, for example, within epitaxial layers of the semiconductor substrate 102. For example, the optical element 164 may be formed as a 1xM multi-mode interference coupler and each of the optical arrangements 150 may be formed as a 2x2 multi mode interference coupler. For example a majority of a length of the delay path 130, for example all of the delay path 130, may be provided by a light guide 160 formed from the semiconductor substrate 102.

As an example, the substrate 102 may comprise epitaxial layers of semiconductor grown on bulk lll-V semiconductor. The optical components of the interferometer chip 100 including the laser 110, optical element 164, optical arrangements 150, light guides 160, detectors 140 and semiconductor optical amplifier or slave laser 162 (if present) may be integrally formed from or within the lll-V epitaxial layers of the semiconductor substrate 102. For example, the optical element 164 may be formed as a 1xM multi-mode interference coupler and each of the optical arrangements 150 may be formed as a 2x2 multi mode interference coupler. The laser 110 may be integrated within the lll-V semiconductor substrate 102. Other parts of the interferometer may, for example, also be integrated within the lll-V semiconductor substrate 102. For example a majority of a length of the delay path 130, in this example all of the delay path 130, is provided by a light guide 160 formed from the lll-V semiconductor substrate.

The physical length L of the delay path 130 may be less than 3mm or 2 mm in physical length. The light therefore travels a distance L in a forward direction along the delay path 130 and a distance L in a return direction along the delay path 130.

In this example, the delay path 130 is formed in a straight line. However, in other examples the delay path 130 may be curved.

Fig 3 illustrates a light guide 160. The light guide 160 comprises a strip of the semiconductor substrate 102. The strip is defined by absence or a different height of adjacent semiconductor substrate 102 on at least two opposing sides 163, 165s of the strip. The absence or height difference of semiconductor may or may not be filled with another material of lower refractive index such as silicon oxide, silicon nitride or polymer.

The light guide 160 illustrated in Fig 3 forms the delay path 130. , The light guide 160 is a channel light guide. A channel light guide has containment, which may be strong or weak, in the transverse direction of the light guide. Examples of channel light guides suitable for use as the delay path 130 include, for example, a covered-core light guide (high-index light guiding core buried or formed in a low-index surrounding medium), a strip-loaded light guide (high-index light guide is loaded by an overlying strip of lower-index material forming a light guiding core beneath the strip), a ridge light guide (lower-index material has an overlying strip of high-index material forming the light guiding core), a rib light guide (high-index planar light guide has an overlying strip of the same high-index material that together form the light guiding core).

The particular channel light guide 160 illustrated in Fig 3 is a rib waveguide, however, other types of channel light guides 160 may be used. The light guide 160comprises a strip of the semiconductor substrate 102. The strip is defined by absence of adjacent semiconductor substrate 102 on at least three sides 161, 163, 165 of the strip.

The delay path 130 comprises at a terminal end 167 of the light guide 160 an end surface 161 for reflecting light incident on the surface 161 in a forward direction from the delay path 130 back along the delay path in a return direction. The light guide 160 provides in a single structure both a forward part of the delay path 130 and a return part of the delay path 130.

The end surface 161 defines a boundary from the higher refractive index semiconductor substrate 102 to a lower refractive index medium such as air. The reflection could also be introduced by an MMI reflector or a 1x2 splitter with the two outputs connected with each other.

Fig 4 illustrates an example of an interferometer chip 100 similar to that illustrated in Fig 2 and similar references are used to refer to similar features which will not be described again.

The interferometer chip 100 illustrated in Fig 4 is different to the interferometer chip 100 illustrated in Fig 2 in that it does not use a single detector 140 for a single combined light signal 104 but instead produces multiple (two) combined light signals 104 and measured both simultaneously using a balanced detector configuration. A balanced detector configuration may, for example, use two detectors 140, for example two photodiode detectors in a back-to-back series connection. The balanced reflector configuration is used to cancel or diminish the constant effect of back reflections and enhance the effect of interference.

The interferometer chip 100 illustrated in Fig 4 is different to the interferometer chip 100 illustrated in Fig 2 in that the optical components interconnected to the multiple outputs of the optical element 164 are different and the optical components interconnected to the multiple inputs of the optical arrangements 150 are different.

Each of the multiple outputs of the optical element 164 is interconnected via a light guide 160 to an optical arrangement 180. The optical arrangement 180 operates as a splitter. It may, for example, be a 1x2 multi mode interference coupler.

Each of the two outputs of the optical arrangement 180 is interconnected via a light guide 160 to different ones of a pair an optical arrangements 182.

Each of the two outputs of the optical arrangement 180 is interconnected via the light guide 160 to one of the inputs of each of the pair of an optical arrangements 182. The other one of the inputs of each of the pair of an optical arrangements 182 is connected as a return port to one of a pair of detectors 140 arranged as balanced detectors. Each optical arrangement 180 operates as a splitter. It may, for example, be a 2x1 multi mode interference coupler.

The output of each of the pair of optical arrangements 182 is interconnected via a separate light guide 160 to one of the inputs to the optical arrangement 150.

The optical arrangement 150 combines the light received in the return direction from the two different paths- the delay path 130 and the sample path 120 to produce two combined light signals 104 that depend upon interference between the light returning from the two different paths. One of the combined light signals 104 is provided through one of the pair of optical arrangements 182 to one of the balanced detectors 140 and the other one of the combined light signals 104 is provided through the other one of the pair of optical arrangements 182 to the other one of the balanced detectors 140.

In Fig 2, each optical arrangement 150 is configured to direct light into one pair of paths 130, 120 of the interferometer and also configured to direct light returning from the one pair of paths 130, 120 of the interferometer to one detector. The optical arrangement 150 comprises as one of its inputs a return port configured to provide light returning from the at least one pair of paths 130, 120 of the interferometer to a respective detector 140. For each return port, there is a corresponding forward port, as one of the inputs, configured to receive light for direction forward into the at least one pair of paths 130, 120 of the interferometer.

In Fig 4, each optical arrangement 182 is configured to direct light into one pair of paths 130, 120 of the interferometer and also configured to direct light returning from the one pair of paths 130, 120 of the interferometer to one detector. The optical arrangement 150 comprises as one of its inputs a return port configured to provide light returning from the at least one pair of paths 130, 120 of the interferometer to a respective detector 140. For each return port, there is a corresponding forward port, as one of the inputs, configured to receive light for direction forward into the at least one pair of paths 130, 120 of the interferometer. There is therefore symmetrical injection of light into the pair of optical arrangement 182 that provide signals to the back-to-back balanced detectors 140.

Fig 5 illustrates an example of an interferometer chip 100 similar to that illustrated in Fig 2 and similar references are used to refer to similar features which will not be described again.

The interferometer chip 100 illustrated in Fig 5 is different to the interferometer chip 100 illustrated in Fig 2 in that it does not use a single detector 140 for a single combined light signal 104 but instead produces multiple combined light signals 104 and measures them simultaneously using multiple detectors 140.

The interferometer chip 100 illustrated in Fig 5 is different to the interferometer chip 100 illustrated in Fig 2 in that the detector 140 interconnected to the optical arrangement 150 is replaced by a hybrid coupler 190 which interconnects the optical arrangement 150 to multiple detectors 140. In addition the delay path 130 originates in the forward direction from the optical arrangement 150 but returns to an input of the hybrid coupler 190. A different hybrid coupler 190 is interconnected at one of its inputs, via a different light guide 160, to each of the optical arrangements 150. The other input to the hybrid coupler 190 is interconnected to a return leg of the delay path 130. Each of the multiple outputs of the hybrid coupler 190 is interconnected to a different detector 140.

In this example, but not necessarily all examples, each hybrid coupler 190 is an NxN multi-mode interference coupler that introduces a phase shift of 2ττ/η between the N outputs and thus measures interference at different phase shifts. In the illustrated example N is 4 but it could alternatively be 2 or 3 or another number.

In some but not necessarily all examples, the laser 110 is configured to operate as a swept-source, tunable laser. The laser 110 may be configured to be tuned to a tuned wavelength and configured to have a linewidth smaller than 1nm with a high selectivity, greater than 20dB, at the tuned wavelength. The laser 110 may be configured to be tuned to multiple different tuned wavelengths separated by a range greater than 40nm.

The laser 110 illustrated in Fig 6 is an example of a tunable laser 110.

The laser 110 comprises semiconductor optical amplifier (SOA) 113 providing optical gain, a tuneable optical band-pass filter 114 (controllable wavelength selective filter) and a multi mode interference coupler (MMI) 115. The components are connected by light guides 160 in a ring.

In this example but not necessarily all examples the tuneable optical band-pass filter 114 comprises a cascaded sequence of asymmetric Mach-Zehnder interferometers (AMZI) 116 at least some of which are tuned using voltage controlled phase modulators e.g. voltage controlled electro-refractive phase modulators. This tunable laser 110 has a wavelength of 1.5um (1525nm) tunable within a range of 60nm. At the tuned wavelength it has a gain of 40dB relative to the nearest maxima at a separation (free spectral range) 0.05nm. A feedback loop 119 is configured to control laser 110 operation. The feedback loop comprises the laser output 112 to the optical element 164. An additional output of the optical element 164 provides a portion of the laser output into the feedback loop 119. The laser output is measured within the feedback loop 119 at block 118. A control signal 117 is generated to adjust the wavelength of the laser 110. In this way the wavelength of the laser output can be accurately controlled allowing a smooth scan through a range of wavelengths.

Some or all of the optical components of the interferometer chip 100 including the laser 110, optical element 164, optical arrangements 150, light guides 160, detectors 140 and semiconductor optical amplifier or slave laser 162 (if present), feedback loop 119, optical arrangements 180, 182 (if present), hybrid couplers 190 (if present) may be integrally formed from or within the substrate 102.

Fig 7 illustrates use of the interferometer chip 100 as a biometric sensor system 300. The sensors 170 are arranged as a one dimensional array 174 (into the page) over which the sample 200, a user’s finger in this example, is swiped. The biometric sensor system 300 comprises a curved parabolic reflector 302 associated with a sensing area 304 over which a sample 200 is swiped 201. This curved reflector 302 bends the sample path 120 at right angles allowing the sensing area 304 to be offset from the sensors 170 and for the direction of swipe 201 to be rotated through 90 degrees so that it is parallel to a plane of the substrate 102.

The biometric sensor system 300 may, for example, be used to image an external finger print, an internal finger print, sweat ducts and glands, melanoma, moles.

The biometric sensor system 300 may, for example, be used for optical coherence tomography (OCT).

In the preceding paragraphs reference has been made to an interferometer chip. It may alternatively be referred to as a photonic integrated circuit.

Fig 8 illustrates a an example of an interferometer chip 100 similar to that illustrated in Fig 2 and similar references are used to refer to similar features which will not be described again.

The interferometer chip 100 illustrated in Fig 8 is different to the interferometer chip 100 illustrated in Fig 2 in that it uses vertical couplers 175 arranged in a two-dimensional array as sensors 170. In this configuration, a curved parabolic reflector 302 for use in a biometric sensor system 300 and swiping of the sample 200 may not be required to produce a two-dimensional image as illustrated in Fig 9. In Fig 9, the sensors 170 comprise vertical couplers and each of the vertical couplers has an associated micro lens 170 as previously described in relation to Fig 2.

Fig 10 illustrates an example of a sensor apparatus 400 comprising the interferometer chip 100. In this example, but not necessarily all examples, the sensor apparatus 400 is a mobile or hand held device. A handheld device is one that can be grasped within the palm of a hand and is sized to fit within most normal inside jacket pockets.

In some, but not necessarily all examples, the sensor apparatus 400 may be a mobile communication device or a handheld communications device such as for example a mobile cellular telephone.

The apparatus 400 comprises processing circuitry 402 for processing output from the detectors 140 of the chip 100.

The apparatus 400 comprises an output interface 404 for communicating the results of the processing. In some embodiments the interface 404 may comprise a display for displaying the results of the processing locally. The display may be any suitable display that provides a visual image to a user. In some embodiments the interface 404 may comprise communication circuitry for communicating the results of the processing remotely. The communication circuitry 404 may be configured to communicate wirelessly. It may for example comprise a radio transmitter and/or radio transceiver.

In some but not necessarily all embodiments the processing circuitry 402 is configured to process output from the detectors 140 of the chip 100 to produce a two or three dimensional image of the sample 200.

In some but not necessarily all embodiments the processing circuitry 402 is configured to process output from the detectors 140 of the chip 100 to classify the sample 200 using for example image classification methods.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one.” or by using “consisting”.

In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class ora property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a features described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. l/we claim:

Claims

1. An interferometer chip comprising: a semiconductor substrate; a laser configured to provide light for at least one pair of paths of an interferometer including a delay path and a sample path; and at least one detector configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path is provided by a light guide formed from the semiconductor substrate.

2. An interferometer chip as claimed in claim 1, wherein all of the delay path is formed from the semiconductor substrate.

3. An interferometer chip as claimed in claim 1 or 2, wherein the light guide is a channel light guide.

4. An interferometer chip as claimed in any preceding claim, wherein the delay path is less than 3mm in physical length.

5. An interferometer chip as claimed in any preceding claim, wherein the light guide provides in a single structure a forward part of the delay path and a return part of the delay path.

6. An interferometer chip as claimed in any preceding claim, wherein the delay path comprises at a terminal end of a light guide a surface for reflecting light incident on the surface in a direction from the delay path back along the delay path.

7. An interferometer chip as claimed in any preceding claim, comprising a micro lens in each of the one or more sample paths for directing light from the interferometer chip towards a sample.

8. An interferometer chip as claimed in claim 7, comprising multiple micro lens arranged in a line with separation of less than 0.05mm.

9. An interferometer chip as claimed in claim 7 or 8, where the each micro lens is formed from material having a refractive index greater than 2.

10. An interferometer chip as claimed in claim 7, 8 or 9, wherein each micro lens is formed from silicon.

11. An interferometer chip as claimed in claim 7, 8, 9, or 10 wherein each micro lens has a focal length less than 1mm.

12. An interferometer chip as claimed in any preceding claim, comprising at least one optical arrangement configured to direct light into the at least one pair of paths of the interferometer and also configured to direct light returning from the at least one pair of paths of the interferometer to one or more detectors, wherein the optical arrangement comprises one or more return ports configured to provide light returning from the at least one pair of paths of the interferometer to one or more respective detectors and wherein, for each of the one or more return ports, there is a corresponding forward port configured to receive light for forward direction into the at least one pair of paths of the interferometer.

13. An interferometer chip as claimed in claim 12, wherein each optical arrangement comprises one or more multi-mode interference couplers integrated within the ll-V semiconductor substrate.

14. An interferometer chip as claimed in any preceding claim, wherein the laser is configured to operate as a swept-source, tunable laser.

15. An interferometer chip as claimed in any preceding claim, wherein the laser is a tunable laser configured to be tuned to tuned wavelength and configured to have high selectivity, greater than 20dB, at the tuned wavelength.

16. An interferometer chip as claimed in any preceding claim, wherein the laser is a tunable laser configured to be tuned to multiple tuned wavelengths separated by a range greater than 40nm.

17 An interferometer chip as claimed in any preceding claim, wherein the laser comprises a cascaded sequence of asymmetric Mach-Zehnder interferometers.

18. An interferometer chip as claimed in any preceding claim, wherein a feedback loop comprising measurement of the laser output is configured to control laser operation.

19. An interferometer chip as claimed in any preceding claim, comprising a plurality of sensors for providing light to and receiving light from a sample, wherein the interferometer chip comprises a plurality of pairs of paths of an interferometer each pair comprising a different sample path associated with a particular sensor and a delay path; and detectors configured to detect separately interference of light returning from each of the multiple pairs of paths of the interferometer, wherein the laser is configured to provide light for the plurality of pairs of paths simultaneously and wherein each delay path and at least part of each sample path is provided by a separate light guide formed from the semiconductor substrate.

20. An interferometer chip as claimed in claim 19, wherein the sensors are arranged as a one dimensional array over which the sample is swiped.

21. An interferometer chip as claimed in any preceding claim, where the semiconductor substrate is a monolithic epitaxial semiconductor substrate comprising, formed from the semiconductor substrate, the laser, the one or more delay paths, at least part of the one or more sample paths, one or more detectors, and one or more multimode interferometers each coupling a delay path and a sample path to the laser and to at least one detector.

22. A biometric sensor system comprising an interferometer chip as claimed in any preceding claim.

23. A biometric sensor system as claimed in claim 22 comprising a curved reflector associated with a sensing area over which a sample is swiped.

24 An interferometer chip comprising: multiple pairs of paths of an interferometer for receiving light from a laser, each pair of paths including a delay path and a different sample path; at least one detector associated with each pair of paths configured to detect interference of light returning from the associated pair of paths, and at least one micro lens in each of the one or more sample paths for directing light towards a sample.

25. A photonic integrated circuit comprising: a semiconductor substrate; a laser integrated within the semiconductor substrate configured to provide light for at least one pair of paths of an interferometer including a delay path and a sample path; and at least one detector configured to detect interference of light returning from the at least one pair of paths of the interferometer, wherein at least a majority of a length of the delay path is provided by a light guide formed from the semiconductor substrate.