CN214750920U - Polarization conversion coupling structure, photonic integrated chip and optical component - Google Patents

Abstract

The application provides a polarization conversion coupling structure, a photonic integrated chip and an optical component. The coupling structure integrates a polarization beam splitting structure, a polarization rotation structure and a two-in-one coupling structure. The polarization light splitting structure is used for receiving the incident light and converting the incident light into two paths of orthogonal linearly polarized light for output; the polarization rotation structure is used for rotating the polarization state of one path of linearly polarized light into the polarization state consistent with that of the other path of linearly polarized light; the two-in-one coupling structure comprises at least one phase shifter and at least one coupler, wherein the phase shifter is used for adjusting the phase of one path of linearly polarized light; the coupler combines the two paths of linearly polarized light with the same polarization state into one path of linearly polarized light for output. The coupling structure converts incident light in a random polarization state into a path of optimized linearly polarized light, and then the coupling structure is combined with a photonic integrated chip and other polarization-sensitive optical systems, so that polarization-related loss can be effectively reduced.

Description

Polarization conversion coupling structure, photonic integrated chip and optical component

Technical Field

The application relates to the technical field of optical communication, in particular to a polarization conversion coupling structure, a photonic integrated chip and an optical component.

Background

With the rapid development of optical interconnection of data centers, the number of optical devices required in the optical communication industry is greatly increased, and in addition to the increasing requirement on transmission rate, the cost and the package size of the optical devices and chips are more and more important in the industrial competition. Accordingly, integrated chips based on silicon materials and iii-v materials are gradually emerging in the optical communication market and become the main development direction of the optical communication industry.

Due to the problems of the photolithography process and the material, the optical refractive indexes of different Polarization directions are different, the central wavelength is also shifted, the roughness of the waveguide horizontal and vertical directions is also different after photolithography, and the randomly polarized light directly enters the optical chip to generate a large Polarization Dependent Loss (PDL). PDL is an important performance index of an optical chip, and eliminating or reducing the influence of PDL becomes a problem of long-term development of integrated optical chips.

In addition, some polarization-dependent elements that are often employed in Optical components, such as Semiconductor Optical Amplifiers (SOAs), polarization-dependent isolators, polarization-dependent Optical circulators, polarization-maintaining fibers, or the like, also have a large PDL.

Disclosure of Invention

The application aims to provide a polarization conversion coupling structure, a photonic integrated chip and an optical component, which can effectively reduce polarization-dependent loss.

In order to achieve one of the above objects, the present application provides a polarization conversion coupling structure, which has a light incident port through which incident light of random polarization state is incident into the polarization conversion coupling structure; the polarization conversion coupling structure comprises a substrate, and a polarization light splitting structure, a polarization rotation structure and a two-in-one coupling structure are arranged on the substrate;

the polarization light splitting structure comprises an input waveguide and two output waveguides; the input waveguide extends to the light incident port and is used for receiving the incident light; the two output waveguides are respectively used for transmitting two paths of linearly polarized light with mutually vertical polarization states;

the polarization rotating structure is arranged in one of the two output waveguides and is used for rotating the polarization state of the linearly polarized light transmitted in the output waveguide to be consistent with the polarization state of the other path of linearly polarized light;

the two-in-one coupling structure comprises at least one phase shifter and at least one coupler; the coupler comprises two input ports and an output port, wherein the two input ports are respectively connected with the two output waveguides; the phase shifter is arranged in one of the two output waveguides and used for adjusting the phase of linearly polarized light transmitted in the output waveguide;

the two-in-one coupling structure combines the two paths of linearly polarized light with consistent polarization states into one path of linearly polarized light to be output.

As a further improvement of the embodiment, the two-in-one coupling structure comprises two couplers and two phase shifters; the two couplers are respectively a first coupler and a second coupler, and the two phase shifters are respectively a first phase shifter and a second phase shifter;

the first coupler comprises two first input ports and two first output ports, and the second coupler comprises two second input ports and one second output port;

the two first input ports are respectively connected with the two output waveguides; the first phase shifter is arranged in one of the two output waveguides and used for adjusting the phase of linearly polarized light transmitted in the output waveguide where the first phase shifter is arranged, so that the phases of the two paths of linearly polarized light with the same polarization state are the same; the two second input ports are respectively connected with the two first output ports; the second phase shifter is arranged between one of the two first output ports and a second input port connected with the first output port, and is used for adjusting the phase of linearly polarized light output by the first output port where the second phase shifter is located, so that two paths of linearly polarized light output by the first coupler are combined into one path of linearly polarized light to be output after passing through the second coupler.

As a further improvement of the embodiment, a monitoring port is further disposed on one side of the second output port of the second coupler, and the monitoring port is connected to a monitoring detector.

As a further improvement of the embodiment, a monitoring port is further provided on the output port side of the coupler, and the monitoring port is connected to a monitoring detector.

As a further improvement of the embodiment, the polarization splitting structure is a mach-zehnder interferometer-based polarization splitter.

As a further improvement of the embodiment, the polarization rotating structure is a polarization rotator based on asymmetric waveguides.

As a further improvement of the embodiment, the coupling region of the coupler is also provided with a phase shifter.

The application also provides a photonic integrated chip, which comprises the polarization conversion coupling structure of any one of the embodiments.

As a further improvement of the embodiment, the photonic integrated chip is also provided with a light detector or a light modulator; the optical detector or the optical modulator is connected with the output port of the two-in-one coupling structure.

The present application further provides a polarization converting coupling structure, comprising:

the polarization light splitting structure is used for splitting incident light in a random polarization state into two paths of linearly polarized light with mutually vertical polarization states;

the polarization rotating structure is used for rotating the polarization state of one path of linearly polarized light of the two paths of linearly polarized light into the polarization state consistent with that of the other path of linearly polarized light;

a two-in-one coupling chip comprising two input waveguides, at least one phase shifter, and at least one coupler; the coupler comprises two input ports and an output port, wherein the two input ports are respectively connected with the two input waveguides; the phase shifter is arranged in one of the two input waveguides and used for adjusting the phase of linearly polarized light transmitted in the input waveguide where the phase shifter is arranged;

the linearly polarized light which is changed into two paths of linearly polarized light with the same polarization state through the polarization rotating structure respectively enters the two-in-one coupling chip through the two input waveguides, and the two-in-one coupling chip combines the linearly polarized light with the same polarization state into one path of linearly polarized light and outputs the path of linearly polarized light through the output port.

As a further refinement of the embodiment, the polarization splitting structure is a walk-off crystal; or the polarization light splitting structure comprises a polarization light splitting prism and a reflecting mirror, and the reflecting mirror is used for reflecting one path of linearly polarized light output by the polarization light splitting prism to be transmitted in parallel with the other path of linearly polarized light.

As a further improvement of the implementation manner, the polarization rotation structure includes a half-wave plate, and the half-wave plate is located in the optical path of one of the two linearly polarized light beams with mutually perpendicular polarization states, which are output by the polarization splitting structure.

As a further improvement of the implementation manner, the polarization rotation structure further includes an optical path compensator, and the optical path compensator and the half-wave plate are respectively located in the optical paths of the two linearly polarized light paths.

As a further improvement of the embodiment, a coupling structure is further arranged between the polarization rotation structure and the two-in-one coupling chip; the coupling structure comprises coupling lenses respectively positioned in the two paths of light paths of the linearly polarized light, or the coupling structure comprises a light path offset element and a coupling lens

The present application further provides an optical assembly comprising a polarization converting coupling structure and a polarization sensitive optical system as described in any of the above embodiments. The polarization conversion coupling structure converts incident light in a random polarization state into a path of linearly polarized light matched with the polarization sensitive optical system, and then the linearly polarized light is coupled into the polarization sensitive optical system.

As a further improvement of the embodiment, the polarization-sensitive optical system is one or more of a photonic integrated chip, a semiconductor optical amplifier, a polarization-dependent isolator, a polarization-dependent optical circulator and a polarization-maintaining optical fiber; the optical assembly further comprises a coupling lens, and linearly polarized light output by the polarization conversion coupling structure is coupled into the polarization sensitive optical element through the coupling lens;

or, the polarization sensitive optical system is an external cavity laser, and the polarization conversion coupling structure is arranged in a resonant cavity of the external cavity laser.

The beneficial effect of this application: the polarization-dependent loss reduction method has the advantages that incident light in a random polarization state is subjected to polarization splitting and polarization rotation and then synthesized into a beam of optimized linearly polarized light through the low-loss two-in-one coupling structure, and then the beam of optimized linearly polarized light is combined with the photonic integrated chip and other polarization-sensitive optical systems, so that the polarization-dependent loss of the photonic integrated chip or the optical component can be effectively reduced.

Drawings

Fig. 1 is a schematic structural diagram of a polarization conversion coupling structure in embodiment 1 of the present application;

FIG. 2 is a schematic diagram of a polarization splitting structure and its internal polarization state change in embodiment 1;

FIG. 3 is a schematic diagram of another structure of a polarization splitting structure;

FIG. 4 is a schematic cross-sectional view of a polarization rotation structure employed in example 1;

fig. 5 is a schematic structural diagram of a modified polarization conversion coupling structure according to embodiment 1 of the present application;

fig. 6 is a schematic structural diagram of a polarization conversion coupling structure according to embodiment 2 of the present application;

FIG. 7 is a schematic diagram showing a modified structure of the polarization conversion coupling structure of embodiment 2;

fig. 8 is a schematic structural diagram of a polarization conversion coupling structure according to embodiment 3 of the present application;

fig. 9 is a schematic structural diagram of a photonic integrated chip according to embodiment 4 of the present application;

FIG. 10 is a schematic view of a polarization conversion coupling structure in embodiment 5 of the present application;

fig. 11 is a schematic diagram of a variation of the polarization conversion coupling structure according to embodiment 5 of the present application;

fig. 12 is a schematic structural diagram of an optical assembly according to embodiment 6 of the present application.

Detailed Description

The present application will now be described in detail with reference to specific embodiments thereof as illustrated in the accompanying drawings. These embodiments are not intended to limit the present application, and structural, methodological, or functional changes made by those skilled in the art according to these embodiments are included in the scope of the present application.

In the various illustrations of the present application, certain dimensions of structures or portions may be exaggerated relative to other structures or portions for ease of illustration and, thus, are provided to illustrate only the basic structure of the subject matter of the present application.

Also, terms used herein such as "upper," "above," "lower," "below," and the like, denote relative spatial positions of one element or feature with respect to another element or feature as illustrated in the figures for ease of description. The spatially relative positional terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. When an element or layer is referred to as being "on," or "connected" to another element or layer, it can be directly on, connected to, or intervening elements or layers may be present.

Example 1

As shown in fig. 1, this embodiment provides a polarization converting coupling structure 100 that converts incident light of random polarization states into desired TM or TE light. The polarization conversion coupling structure 100 has a light entrance port 101a, and incident light of random polarization state enters the polarization conversion coupling structure 100 through the light entrance port 101 a. The polarization conversion coupling structure 100 includes a substrate 101, and a polarization splitting structure 110, a polarization rotation structure 120, and a two-in-one coupling structure 130 are disposed on the substrate 101. In this embodiment, the Polarization conversion coupling structure 100 is based On a Silicon-On-Insulator (SOI) structure design, and includes a Silicon substrate, a buried oxide layer, and a top Silicon layer, which are stacked in sequence, and the Polarization Beam Splitter (PBS) 110, the Polarization Rotator (PR) 120, and the two-in-one coupling structure 130 are all formed by etching the top Silicon layer, and an insulating protection layer may also cover the top Silicon layer. In other embodiments, the polarization conversion coupling structure may also be based on a semiconductor chip structure made of a group iii-v material, such as a lithium niobate chip.

In this embodiment, the polarization splitting structure 110 includes one input waveguide 111 and two output waveguides 112. The input waveguide 111 extends to the light entrance port 101a of the polarization conversion coupling structure 100 to receive incident light. The two output waveguides 112 are respectively used for transmitting two linearly polarized lights with mutually perpendicular polarization states, such as TE light and TM light. The polarization rotating structure 120 is disposed in one of the two output waveguides 112, and is configured to rotate the polarization state of the linearly polarized light transmitted in the output waveguide to be consistent with the polarization state of the other linearly polarized light. The two-in-one coupling structure 130 includes at least one phase shifter 131 and at least one coupler 132, and is configured to combine two linearly polarized lights with the same polarization state into one linearly polarized light for output. In this embodiment, the two-in-one coupling structure 130 includes a phase shifter 131 and a coupler 132. The coupler 132 includes two input ports 132a and one output port 132b, and the two input ports 132a are respectively connected to the two output waveguides 112. The phase shifter 131 is disposed in one of the two output waveguides 112, and is configured to adjust a phase of the linearly polarized light transmitted in the output waveguide where the phase shifter is disposed, so that the phase of the linearly polarized light is consistent with a phase of the linearly polarized light transmitted in the other output waveguide, and two paths of linearly polarized light having the same phase and the same polarization state are combined into one path of linearly polarized light by the coupler 132 and output by the output port 132b of the coupler 132.

As shown in fig. 2, in this embodiment, the polarization splitting structure 110 is a mach-zehnder interferometer-based polarization splitter. The polarization splitting structure 110 includes two 2 × 2 couplers and two connecting arms 113 and 114, and the two connecting arms 113 and 114 connect the two 2 × 2 couplers. One of the two incident arms of one of the 2 × 2 couplers serves as an input waveguide 111 of the polarization splitting structure, and the two output arms of the other 2 × 2 coupler respectively serve as two output waveguides 112 of the polarization splitting structure. In this embodiment, the widths d1 and d2 of the two connecting arms 113 and 114 are different, and the widths d1 and d2 of the two connecting arms 113 and 114 are designed to realize polarization splitting, so that incident light with random polarization states is split into TE light and TM light, which are output by the two output waveguides 112. In other embodiments, as shown in fig. 3, as the polarization splitting structure 110', the mach-zehnder interferometer may also be designed such that the lengths of the two connecting arms 115 and 116 are different, and polarization splitting is implemented by designing the length difference Δ L between the two connecting arms 115 and 116, so that incident light in a random polarization state is split into TE light and TM light, which are output by the two output waveguides respectively. As shown in fig. 4, in this embodiment, the polarization rotating structure 120 is an asymmetric waveguide based polarization rotator. The asymmetric waveguide comprises a ridge waveguide 121 and a partially planar waveguide 122 located on one side of the ridge waveguide 121.

As shown in fig. 1, taking the example of converting the incident light in the random polarization state into a beam of TM light, the incident light in the random polarization state may be one or a combination of natural light, elliptically polarized light, or linearly polarized light (in this embodiment, non-TM light) with a polarization direction that is not optimal. Incident light of random polarization state is incident into the input waveguide 111 of the polarization splitting structure 110 through the light incident port 101a of the polarization conversion coupling structure 100, and is split into TM light and TE light by the polarization splitting structure 110, and the TM light and the TE light are output by the two output waveguides 112. In this embodiment, the polarization rotation structure 120 and the phase shifter 131 are both disposed in the output waveguide 112 for transmitting TE light, the polarization rotation structure 120 converts the TE light transmitted in the output waveguide 112 into TM light for output, and then the phase shifter 131 adjusts the phase of the TM light after being rotated in the output waveguide 112, so that the TM light and the TM light transmitted in another output waveguide 112 are combined into one path of TM light in the coupler 132 with minimum loss and output by the output port 132a of the coupler 132. In other embodiments, the phase shifters and polarization rotating structures may also be provided in the two output waveguides, respectively. Assuming that it is necessary to convert incident light of random polarization state into a beam of TE light, a polarization rotation structure is provided in an output waveguide transmitting TM light to convert TM light transmitted in the output waveguide into TE light output.

As shown in fig. 5, in the above embodiment 1, another phase shifter 132c may be further disposed in the coupling region of the coupler 132 for adjusting the splitting ratio of the coupler 132, so as to couple two linearly polarized light beams with arbitrary amplitudes and the same phase and the same polarization state into the same optical waveguide.

Example 2

This embodiment also provides a polarization converting coupling structure 100' that converts incident light of a random polarization state into desired TM or TE light, as shown in fig. 5. The polarization conversion coupling structure 100' includes a substrate 101, and a polarization splitting structure 110, a polarization rotation structure 120, and a two-in-one coupling structure 130 are disposed on the substrate 101. Unlike embodiment 1, in this embodiment, the two-in-one coupling structure 130 includes two couplers and two phase shifters; the two couplers are a first coupler 134 and a second coupler 136, respectively, and the two phase shifters are a first phase shifter 133 and a second phase shifter 135, respectively. Wherein the first coupler 134 comprises two first input ports 134a and two first output ports 134b, and the second coupler 136 comprises two second input ports 136a and one second output port 136 b. The two first input ports 134a of the first coupler 134a are respectively connected to the two output waveguides 112 of the polarization splitting structure 110, and the first phase shifter 133 is disposed in one of the two output waveguides 112 and is used for adjusting the phase of the linearly polarized light transmitted in the output waveguide where the first phase shifter is disposed, so that the phases of the two linearly polarized light paths with the same polarization state are the same. The two second input ports 136a of the second coupler 136 are connected to the two first output ports 134b of the first coupler 134, respectively. The second phase shifter 135 is disposed between one of the two first output ports 134b and the second input port 136a connected to the first output port, and the second phase shifter 135 is configured to adjust a phase of the linearly polarized light output by the first output port where the second phase shifter 135 is located, so as to change a splitting ratio of the second coupler 136, and thus two paths of linearly polarized light output by the first coupler 134 are combined into one path of linearly polarized light to be output after passing through the second coupler 136. That is, the splitting ratio of the second coupler 136 is adjusted by the second phase shifter 135, so as to couple two linear polarized lights with arbitrary amplitude and the same phase and the same polarization state into the same optical waveguide, and then output the linear polarized lights from the second output port 136b of the second coupler 136. In this embodiment, the second coupler 136 is a directional coupler. In other embodiments, the second coupler may also be a Y-type coupler or a multi-mode interference coupler, etc.

Similarly, taking the example of converting the incident light in the random polarization state into one beam of TM light, the incident light in the random polarization state is incident into the input waveguide 111 of the polarization splitting structure 110 through the light incident port 101a of the polarization conversion coupling structure 100', and is split into TM light and TE light by the polarization splitting structure 110, and the TM light and the TE light are output by the two output waveguides 112, respectively. In this embodiment, the polarization rotation structure 120 and the first phase shifter 133 are both disposed in the output waveguide 112 transmitting the TE light, the polarization rotation structure 120 converts the TE light transmitted in the output waveguide 112 into TM light output, and then the first phase shifter 133 adjusts the phase of the TM light after being rotated in the output waveguide 112 to be identical to the phase of the TM light transmitted in the other output waveguide. After being coupled by the first coupler 134, the two TM lights with the same phase are output by two first output ports 134b of the first coupler 134, and after the phase of one TM light is adjusted by the second phase shifter 135, the one TM light is coupled with the other TM light in the second coupler 136 into one TM light, and the one TM light is output by a second output port 136b of the second coupler 136. The splitting ratio of the second coupler 136 is adjusted by the second phase shifter 135, so that two paths of TM light with any amplitude are coupled into the same optical waveguide and output by the second output port 136b of the second coupler 136, so that the two paths of TM light can be combined into one path of TM light output with smaller loss, and the coupling loss is reduced.

As shown in fig. 6, in the polarization rotation coupling structure 100' of embodiment 2, a monitoring port 136c and a monitoring Detector (MPD) 137 may be further disposed on one side of the second output port 136b of the second coupler 136, and the monitoring Detector 137 is disposed at the monitoring port 136c to Monitor the coupling loss of the two-in-one coupling structure 130, so that when the two linearly polarized light beams are combined into one linearly polarized light beam for output, the minimum loss is achieved. Similarly, a monitoring port and a monitoring detector may be disposed on one side of the output port of the two-in-one coupling structure in embodiment 1, and the monitoring detector is disposed at the monitoring port to monitor the coupling loss of the two-in-one coupling structure.

Example 3

This embodiment also provides a polarization converting coupling structure 100 "that converts incident light of random polarization states into desired TM or TE light, as shown in fig. 7. The polarization conversion coupling structure 100' includes a substrate 101, and a polarization splitting structure 110, a polarization rotation structure 120, and a two-in-one coupling structure 130 are disposed on the substrate 101. Unlike embodiment 2, in this embodiment, the second coupler 138 of the two-in-one coupling structure 130 is a Y-type coupler. The second coupler 138 includes two second input ports 138a and one second output port 138 b.

In this embodiment, for example, incident light in a random polarization state is converted into a beam of TE light, the incident light in the random polarization state is incident into the input waveguide 111 of the polarization splitting structure 110 through the light incident port 101a of the polarization conversion coupling structure 100 ″, and the TM light and the TE light split by the polarization splitting structure 110 are output by the two output waveguides 112. In this embodiment, the polarization rotation structure 120 is provided in the output waveguide 112 transmitting TM light, and the first phase shifter 133 is provided in the output waveguide 112 transmitting TE light. The polarization rotating structure 120 converts TM light transmitted in the output waveguide 112 into TE light to be output, and the first phase shifter 133 adjusts the phase of TE light in the other output waveguide 112 to be identical to the phase of TE light after being rotated by the polarization rotating structure 120. Two paths of TE light with the same phase are input through two first input ports 134a of the first coupler 134, coupled by the first coupler 134, and then output two paths of TE light with any amplitude through two first output ports 134b of the first coupler 134, where one path of TE light is coupled with the other path of TE light at the second coupler 138 after the phase of the TE light is adjusted by the second phase shifter 135, and is output through a second output port 138b of the second coupler 138. The splitting ratio of the second coupler 138 is adjusted by the second phase shifter 135 to couple the two TE lights with any amplitude into the same optical waveguide, and the two TE lights are output by the second output port 138b of the second coupler 138, so that the two TE lights can be combined into one TE light output with smaller loss, and the coupling loss is reduced.

Example 4

As shown in fig. 8, this embodiment provides a photonic integrated chip that integrates the polarization conversion coupling structure in embodiments 1 or 2 or 3 described above, and fig. 8 exemplifies the polarization conversion coupling structure 100' in integrated embodiment 2. In this embodiment, the photonic integrated chip further has a light detector 200, and the light detector 200 is connected to the output port 136b of the two-in-one coupling structure 130 of the polarization conversion coupling structure 100'.

When the incident light in the random polarization state directly enters the optical detector in the photonic integrated chip, the incident light in the random polarization state can generate large polarization-dependent loss after entering the photonic integrated chip, and the performance of the optical detector is affected. The photonic integrated chip of this embodiment converts incident light in a random polarization state into linearly polarized light with a lower loss in the dominant polarization direction in the chip, such as TE light or TM light, by integrating the polarization conversion coupling structure 100', and then enters the optical detector 200, thereby effectively reducing polarization-dependent loss.

In other embodiments, the photonic integrated chip may also integrate an optical modulator, which is connected to the output port of the two-in-one coupling structure of the polarization conversion coupling structure. The photonic integrated chip converts incident light in a random polarization state into linearly polarized light with lower loss in an advantageous polarization direction in the chip, such as TE light or TM light, by integrating the polarization conversion coupling structure, and then the linearly polarized light enters the optical modulator, so that the polarization-related loss can be effectively reduced.

Of course, in other embodiments, the photonic integrated chip may also integrate other optical components, such as a wavelength division multiplexer, etc.

Example 5

As shown in fig. 9, this embodiment provides a polarization conversion coupling structure, and unlike embodiments 1 to 3, all of the structures of embodiments 1 to 3 are integrated in a photonic integrated chip, and the polarization conversion coupling structure of this embodiment employs a combination of a partial free space structure and a chip. Specifically, in this embodiment, the polarization conversion coupling structure 300 includes a combination of the polarization splitting structure 310 and the polarization rotating structure 320 of the free space structure, and the two-in-one coupling chip 330. The polarization beam splitting structure 310 is configured to split incident light in a random polarization state into two linearly polarized light paths with polarization states perpendicular to each other; the polarization rotating structure 320 is used for rotating the polarization state of one path of linearly polarized light to be consistent with the polarization state of the other path of linearly polarized light. The two-in-one coupling chip 330 is similar to the two-in-one coupling structure in the polarization conversion coupling structures of embodiments 1 to 3, in which the two-in-one coupling chip 330 includes two input waveguides 331, at least one phase shifter and at least one coupler. The coupler comprises two input ports and an output port, wherein the two input ports are respectively connected with two input waveguides; the phase shifter is arranged in one of the two input waveguides and is used for adjusting the phase of the linearly polarized light transmitted in the input waveguide where the phase shifter is arranged. The two paths of linearly polarized light with the same polarization state respectively enter the two-in-one coupling chip 330 through the two input waveguides 331, and the two paths of linearly polarized light with the same polarization state are combined into one path of linearly polarized light by the two-in-one coupling chip 330 to be output.

In this embodiment, the polarization splitting structure 310 is a walk-off crystal, and based on the walk-off effect of the birefringent crystal, the incident light with random polarization state is split into two parallel light beams with mutually perpendicular polarization states, and the two parallel light beams are output. In other embodiments, the polarization beam splitter structure may also employ a combination of a polarization beam splitter Prism (PBS) and a mirror. The polarization beam splitter prism divides incident light in a random polarization state into two paths of linearly polarized light with mutually vertical polarization states and outputs the linearly polarized light, wherein one path of linearly polarized light is reflected by the reflector and then is transmitted in parallel with the other path of linearly polarized light.

The polarization rotation structure 320 includes a half-wave plate 321, and the half-wave plate 321 is located in the optical path of one of the two linearly polarized light paths with polarization states perpendicular to each other output by the polarization splitting structure 310, and is configured to rotate the polarization state of the linearly polarized light in the optical path where the half-wave plate is located to be consistent with the polarization state of the other linearly polarized light path. In this embodiment, the polarization rotation structure 320 further includes an optical path compensator 322, and the optical path compensator 322 and the half-wave plate 321 are respectively located in the optical paths of the two linearly polarized light beams. Namely, the half-wave plate 321 is located in the optical path of one of the linearly polarized light beams, and the optical path compensation plate 322 is located in the optical path of the other linearly polarized light beam. The optical path compensation sheet 322 may be a transparent optical flat sheet, such as a glass sheet.

In this embodiment, the two-in-one coupling chip 330 includes two couplers and two phase shifters; the two couplers are a first coupler 333 and a second coupler 335, respectively, and the two phase shifters are a first phase shifter 332 and a second phase shifter 334, respectively. Wherein the first coupler 333 includes two first input ports 333a and two first output ports 333b, and the second coupler 335 includes two second input ports 335a and one second output port 335 b. The two first input ports 333a are connected to the two input waveguides 331, respectively; the first phase shifter 332 is disposed in one of the two input waveguides 331, and the first phase shifter 332 is configured to adjust the phase of the linearly polarized light transmitted by the input waveguide 331 where the first phase shifter 332 is located, so that the phases of the two linearly polarized light paths with the same polarization state are the same. The two second input ports 335a are connected to the two first output ports 333b, respectively; the second phase shifter 334 is disposed between one of the two first output ports 333b and the second input port 335a connected thereto, so as to change the splitting ratio of the second coupler 335, and thus two linearly polarized light beams output by the first coupler 333 are combined into one linearly polarized light beam to be output after passing through the second coupler 335. That is, the splitting ratio of the second coupler 335 is adjusted by the second phase shifter 334, so as to couple two linear polarized lights with arbitrary amplitude and the same phase and polarization state into the same optical waveguide, and then output the linear polarized lights from the second output port 335b of the second coupler 335. In this embodiment, the second coupler 335 is a Y-type coupler. In other embodiments, the second coupler may also be a directional coupler or a multi-mode interference coupler, etc.

In this embodiment, a coupling structure 340 is further disposed between the polarization rotation structure 320 and the two-in-one coupling chip 330; the coupling structure 340 includes coupling lenses respectively located in the optical paths of the two linearly polarized light beams. The two linearly polarized light beams with the same polarization state output by the polarization rotation structure 320 are coupled to the two input waveguides 331 of the two-in-one coupling chip 330 through the two coupling lenses.

Taking the example of converting the incident light with random polarization state into a beam of TE light, the incident light with random polarization state is incident into the polarization beam splitting structure 310, and is split into TM light and TE light by the polarization beam splitting structure 310 for output. In this embodiment, the half-wave plate 321 of the polarization rotation structure 320 is disposed in the optical path of the TM light to rotate the TM light into TE light, and the other linearly polarized TE light is directly output through the optical path supplement plate. The two paths of TE light are respectively coupled into the two-in-one coupling chip through two coupling lenses. The first phase shifter 332 adjusts the phase of one of the TE lights to be identical to the phase of the other TE light. Two paths of TE light with the same phase are input through two first input ports 333a of the first coupler 333, coupled by the first coupler 333, and output through two first output ports 333b of the first coupler 333, wherein one path of TE light is phase-adjusted by the second phase shifter 334, and then coupled with the other path of TE light in the second coupler 335 to form one path of TE light, which is output through the second output port 335b of the second coupler 335. The splitting ratio of the second coupler 335 is adjusted by the second phase shifter 334 to couple the two TE lights with any amplitude into the same optical waveguide, and then the two TE lights are output by the second output port 335b of the second coupler 335, so that the two TE lights can be combined into one TE light output with smaller loss, and the coupling loss is reduced.

As shown in fig. 10, a deformation structure of the polarization conversion coupling structure in fig. 9 is different from the polarization conversion coupling structure shown in fig. 9 in that, in this embodiment, the coupling structure 340 includes a light path shifting element 342 and a coupling lens 342, the light path shifting element 342 is located in one path of linearly polarized light, and shifts the linearly polarized light where it is located toward the other path of linearly polarized light, so that the distance between the two paths of linearly polarized light becomes smaller, and then the two paths of linearly polarized light are respectively coupled into the two input waveguides 331 of the two-in-one coupling chip 330 through the same larger coupling lens 342. Here, the optical path deviation element 342 is a wedge plate.

Example 6

As shown in fig. 11, this embodiment provides an optical assembly including the polarization converting coupling structure and the polarization sensitive optical system 400 of the above embodiment 1 or 2 or 3 or 5, and the polarization converting coupling structure 100' of embodiment 2 is exemplified in fig. 11. In this embodiment, the optical assembly further includes a coupling lens 500, and the linearly polarized light output from the two-in-one coupling structure 130 of the polarization converting coupling structure 100' is coupled into the polarization sensitive optical system 400 through the coupling lens 500.

In this embodiment, the polarization sensitive optical system 400 is another photonic integrated chip that integrates a light modulator. The polarization conversion coupling structure 100' converts incident light in a random polarization state into linearly polarized light with a dominant polarization direction (matched with a polarization sensitive optical system) with low loss in a chip, such as TE light or TM light, and then the linearly polarized light enters into the optical modulator of the photonic integrated chip, so that the polarization-dependent loss can be effectively reduced.

In other embodiments, the polarization sensitive optical system may also be a combination of one or more of a semiconductor optical amplifier, a polarization dependent isolator, a polarization dependent optical circulator, or a polarization maintaining fiber. Alternatively, the polarization sensitive optical system may be an external cavity laser, and the polarization conversion coupling structure is disposed in a resonant cavity of the external cavity laser.

The above list of details is only for the concrete description of the feasible embodiments of the present application, they are not intended to limit the scope of the present application, and all equivalent embodiments or modifications that do not depart from the technical spirit of the present application are intended to be included within the scope of the present application.

Claims (16)

1. A polarization conversion coupling structure is provided with a light entrance port, and incident light in a random polarization state enters the polarization conversion coupling structure through the light entrance port; the method is characterized in that: the polarization conversion coupling structure comprises a substrate, and a polarization light splitting structure, a polarization rotation structure and a two-in-one coupling structure are arranged on the substrate;

the polarization light splitting structure comprises an input waveguide and two output waveguides; the input waveguide extends to the light incident port and is used for receiving the incident light; the two output waveguides are respectively used for transmitting two paths of linearly polarized light with mutually vertical polarization states;

the polarization rotating structure is arranged in one of the two output waveguides and is used for rotating the polarization state of the linearly polarized light transmitted in the output waveguide to be consistent with the polarization state of the other path of linearly polarized light;

the two-in-one coupling structure comprises at least one phase shifter and at least one coupler; the coupler comprises two input ports and an output port, wherein the two input ports are respectively connected with the two output waveguides; the phase shifter is arranged in one of the two output waveguides and used for adjusting the phase of linearly polarized light transmitted in the output waveguide;

the two-in-one coupling structure combines the two paths of linearly polarized light with consistent polarization states into one path of linearly polarized light to be output.

2. The polarization converting coupling structure of claim 1, wherein: the two-in-one coupling structure comprises two couplers and two phase shifters; the two couplers are respectively a first coupler and a second coupler, and the two phase shifters are respectively a first phase shifter and a second phase shifter;

the first coupler comprises two first input ports and two first output ports, and the second coupler comprises two second input ports and one second output port;

the two first input ports are respectively connected with the two output waveguides; the first phase shifter is arranged in one of the two output waveguides and used for adjusting the phase of linearly polarized light transmitted in the output waveguide where the first phase shifter is arranged, so that the phases of the two paths of linearly polarized light with the same polarization state are the same; the two second input ports are respectively connected with the two first output ports; the second phase shifter is arranged between one of the two first output ports and a second input port connected with the first output port, and is used for adjusting the phase of linearly polarized light output by the first output port where the second phase shifter is located, so that two paths of linearly polarized light output by the first coupler are combined into one path of linearly polarized light to be output after passing through the second coupler.

3. The polarization converting coupling structure of claim 2, wherein: and one side of the second output port of the second coupler is also provided with a monitoring port, and the monitoring port is connected with a monitoring detector.

4. The polarization converting coupling structure of claim 1, wherein: and one side of the output port of the coupler is also provided with a monitoring port, and the monitoring port is connected with a monitoring detector.

5. The polarization converting coupling structure of claim 1, wherein: the polarization light splitting structure is a polarization light splitter based on a Mach-Zehnder interferometer.

6. The polarization converting coupling structure of claim 1, wherein: the polarization rotating structure is a polarization rotator based on asymmetric waveguides.

7. The polarization converting coupling structure of claim 1, wherein: the coupling area of the coupler is also provided with a phase shifter.

8. A photonic integrated chip, comprising: the photonic integrated chip comprises the polarization converting coupling structure of any one of claims 1 to 7.

9. The photonic integrated chip of claim 8, wherein: the photonic integrated chip is also provided with a light detector or a light modulator; the optical detector or the optical modulator is connected with the output port of the two-in-one coupling structure.

10. A polarization converting coupling structure, comprising:

the polarization light splitting structure is used for splitting incident light in a random polarization state into two paths of linearly polarized light with mutually vertical polarization states;

the polarization rotating structure is used for rotating the polarization state of one path of linearly polarized light of the two paths of linearly polarized light into the polarization state consistent with that of the other path of linearly polarized light;

a two-in-one coupling chip comprising two input waveguides, at least one phase shifter, and at least one coupler; the coupler comprises two input ports and an output port, wherein the two input ports are respectively connected with the two input waveguides; the phase shifter is arranged in one of the two input waveguides and used for adjusting the phase of linearly polarized light transmitted in the input waveguide where the phase shifter is arranged;

the linearly polarized light which is changed into two paths of linearly polarized light with the same polarization state through the polarization rotating structure respectively enters the two-in-one coupling chip through the two input waveguides, and the two-in-one coupling chip combines the linearly polarized light with the same polarization state into one path of linearly polarized light and outputs the path of linearly polarized light through the output port.

11. The polarization converting coupling structure of claim 10, wherein: the polarization light splitting structure is a walk-off crystal; or the polarization light splitting structure comprises a polarization light splitting prism and a reflecting mirror, and the reflecting mirror is used for reflecting one path of linearly polarized light output by the polarization light splitting prism to be transmitted in parallel with the other path of linearly polarized light.

12. The polarization converting coupling structure of claim 10, wherein: the polarization rotation structure comprises a half-wave plate, and the half-wave plate is positioned in the light path of one path of linearly polarized light of the two paths of linearly polarized light with mutually vertical polarization states output by the polarization light splitting structure.

13. The polarization converting coupling structure of claim 12, wherein: the polarization rotation structure further comprises a light path compensation plate, and the light path compensation plate and the half-wave plate are respectively positioned in the light paths of the two paths of linearly polarized light.

14. A polarization converting coupling structure according to any one of claims 10 to 13, wherein: a coupling structure is also arranged between the polarization rotation structure and the two-in-one coupling chip; the coupling structure comprises coupling lenses respectively positioned in the two paths of light paths of the linearly polarized light, or the coupling structure comprises a light path offset element and a coupling lens.

15. An optical assembly, comprising: comprising the polarization converting coupling structure of any one of claims 1-7 or 10-14 and a polarization sensitive optical system; the polarization conversion coupling structure converts incident light in a random polarization state into a path of linearly polarized light matched with the polarization sensitive optical system, and then the linearly polarized light is coupled into the polarization sensitive optical system.

16. The optical assembly of claim 15, wherein:

the polarization sensitive optical system is one or a combination of a plurality of photon integrated chips, semiconductor optical amplifiers, polarization related isolators, polarization related optical circulators or polarization maintaining optical fibers; the optical assembly further comprises a coupling lens, and linearly polarized light output by the polarization conversion coupling structure is coupled into the polarization sensitive optical element through the coupling lens;

or, the polarization sensitive optical system is an external cavity laser, and the polarization conversion coupling structure is arranged in a resonant cavity of the external cavity laser.

Images