Passive lightwave conversion module and corresponding method for converting an incident lightwave with undefined polarization into a lightwave with defined polarization

Abstract

A passive lightwave conversion module is provided for converting an incident lightwave having an undefined polarization into a lightwave having a defined polarization, which is either transverse electric (TE) polarization or transverse magnetic (TM) polarization, the passive lightwave conversion module comprising: an optical splitter for splitting the incident light; two 50% input polarization converters that convert the power of the incident polarization to 50%, the input polarization converters being connected to the optical splitter; at least one 50% output polarization converter that converts the power of the polarization to 50%; and a bimodal phase shifter for introducing a phase shift between the TE polarization and the TM polarization, the bimodal phase shifter being connected to the two 50% input polarization converters and the at least one 50% output polarization converter.

Description

[Technical Field]

[0001] The present disclosure relates to the field of photonics, and more particularly to the field of converting an incident light wave having an undefined polarization state into a light wave having a defined polarization state. [Background technology]

[0002] One of the challenges in photonic integrated circuits (PICs) is the handling of polarization. PICs have a planar geometry, and therefore light waves behave differently when their polarization is in the plane of the chip, i.e., "TE" polarization, than when it is perpendicular to the plane of the chip, i.e., "TM" polarization. This creates problems if the chip is intended to process optical signals of undefined and even varying polarization, such as those transmitted by optical fibers. As a result, the chip's behavior becomes unpredictable without further measures.

[0003] Previous solutions to making PICs polarization independent rely on either the use of special waveguides or special circuit designs. The drawback is that these solutions imply a compromise in chip performance. Another idea is to use polarization diversity, which involves splitting the TE and TM polarizations and then processing them separately. Naturally, this takes up extra space on the chip surface.

[0004] All these solutions furthermore have difficulty addressing several polarization-related issues in optical communications, such as polarization mode dispersion (PMD) and polarization-sensitive detection. In this disclosure, another solution is proposed that can be used to mitigate PMD and facilitate polarization-sensitive detection, which does not have the drawbacks of the mentioned techniques. Summary of the Invention

[0005] It would be advantageous to achieve a passive light wave conversion module for converting an incident light wave having an undefined polarization into a light wave having a defined polarization, which may be either transverse electric (TE) polarization or transverse magnetic (TM) polarization. It would also be advantageous to have a corresponding method and optical device.

[0006] In a first aspect of the present disclosure, there is provided a passive light wave conversion module for converting an incident light wave having an undefined polarization into a light wave having a defined polarization, which is either transverse electric (TE) polarization or transverse magnetic (TM) polarization, the passive light wave conversion module comprising: an optical splitter for splitting the incoming light; - two 50% input polarization converters that convert the power of the input polarization to 50%, the input polarization converters being connected to an optical splitter; - at least one 50% power polarization converter that converts the power of the polarized light to 50%; a bimodal phase shifter for introducing a phase shift between TE and TM polarized light, the bimodal phase shifter being connected to two 50% input polarization converters and at least one 50% output polarization converter; Equipped with.

[0007] A passive lightwave conversion module can be configured to convert, for example, TE-polarized light to TE-polarized light and TM-polarized light to TE-polarized light, etc. Passive lightwave conversion modules do not need to know the polarization state of the incident light, as the output will always be in a specific polarization state.

[0008] In the following, the passive lightwave conversion module is described with respect to a TE output, however, the passive lightwave conversion module may also operate to provide a TM output.

[0009] The required function of the passive lightwave conversion module may imply polarization conversion of the TM part of the incident mode to TE while keeping the TE part of the incident mode as TE.

[0010] This may not be achieved with a simple polarization converter, since polarization conversion is a reversible process, as with all linear, non-magnetic, and time-independent couplers.

[0011] Therefore, the addition of a polarization converter is necessary, which can lead to relevant differences between the propagation of the incident TE and TM modes.

[0012] One example of a proposed solution for a waveguide uses birefringence and dispersion by adding a bimodal phase-shifting section, which may allow four different modes to propagate: TE00, TM00, TE01, and TM01, where the second index refers to the corresponding in-plane direction of the chip.

[0013] This section can be designed by setting the width and length of the conversion module, more specifically the bimodal phase shifter, so that the phase shift between TE00 and TM01 is an odd number π and the phase shift between TM00 and TE01 is an even number π.

[0014] The combination of TE00 and TM01 can be produced from a TE mode input using two parallel partial polarization converters, i.e., 50% conversion, while for a TM mode input, these two conversion modules result in a combination of TM00 and TE01.

[0015] In one example, each of the polarization converters is configured to convert half the power of the TE polarization to the TM polarization and half the power of the TM polarization to the TE polarization of the corresponding light wave.

[0016] In a further example, each of the polarization converters is configured to introduce a relative phase shift between the TE and TM polarizations.

[0017] In another example, a bimodal phase shifter can have four different modes, i.e. - TE00, which is the TE polarization produced by two 50% input polarization converters based on an incident light wave with TE polarization; - TM01, which is TM polarization produced by two 50% input polarization converters based on an incident light wave with TE polarization; - TE01, which is TE polarization produced by two 50% input polarization converters based on an incident light wave with TM polarization; - TM00, which is the TM polarization produced by two 50% input polarization converters based on an incident light wave with TM polarization; configured to guide the The bimodal phase shifter is configured to introduce an odd number of π radians of phase shift between TE00 and TM01, and an even number of π radians of phase shift between TE01 and TM00.

[0018] In one example, the passive lightwave conversion module comprises two 50% output polarization converters.

[0019] In another example, two 50% input polarization converters are configured such that the output converted light of the two 50% input polarization converters is shifted by π radians.

[0020] In yet another example, the passive lightwave conversion module includes two 50% output polarization converters, and the two 50% output polarization converters are configured such that the output converted light of the two 50% output polarization converters is shifted by π radians.

[0021] In another example, the width and length of the bimodal phase shifter are modified to achieve an odd number of π radians of phase shift between TE00 and TM01, and an even number of π radians of phase shift between TE01 and TM00.

[0022] A mathematical description can be provided using transfer matrices, where each section of the circuit is represented by a matrix. These act on vectors whose elements are the complex amplitudes of each mode involved. Four amplitudes are required (for the TE and TM modes of both the upper (first and third) and lower (second and fourth) polarization converters, and for the four modes of the bimodal phase shift section). The following parts can be distinguished:

[0023] a) Input. Here, there is a combination of TE and TM modes with unknown amplitudes and relative phases. To simplify the description, the polarization state is normalized so that the TE mode has amplitude "1" and phase "0". Therefore, the input vector can be expressed as:

[0024]

number

[0025] b) A splitter, where the input modes are combined into an upper branch and a lower branch, which is represented by the following matrix:

[0026]

number

[0027]

number

[0028] c) Dual 50% polarization converter section. The converter modules of the two branches are upside down, with their angled sides facing each other. This means that they give the same (50%) conversion, but with antiphase in the converted mode. This operation can be described as follows:

[0029]

number

[0030] d) Connection to a bimodal phase shifter. The fields from the dual polarization section build modes in the phase shifter section. However, the phase shifter section requires a different definition of the rows and columns of the matrix. Here, the four rows / columns are the 1st to 4th, respectively. 00 , T.E. 01 , TM 00 and TM 01 Each of these modes may be constructed from a combination of two modes from the PC section, depending on the polarization and phase relationship of the latter. The connection matrix is:

[0031]

number

[0032] e) Bimodal phase section, where TE 00 and TM 01 There is a phase shift (π) between 00 and T.E. 01 There is a phase shift (2π) between the matrix and the vector.

[0033]

number

[0034] f) Connection to the second PC section. This is the inverse operation of the operation described in d). Therefore, the matrix is ​​the same. M Conn2 =M Conn1 (6)

[0035] g) A second double 50% polarization converter section, which is identical to the first, so that M PC2 =M PC1 (7) Here, the total operation of the circuit is described as a multiplication of all these matrices. V out =M PC2 M Conn2 M Bimod M Conn1 M PC1 M split V in (8) When evaluated with the above matrix, we get:

[0036]

number

[0037] In a second aspect of the present disclosure, there is provided a method for converting an incident light wave having an undefined polarization into a light wave having a defined polarization, which is either transverse electric (TE) polarization or transverse magnetic (TM) polarization, using a passive light wave conversion module according to any of the previous examples, the method comprising: - splitting the incoming light by an optical splitter; - converting the power of the incident light to 50% by two 50% input polarization converters; - converting the power of the polarized light to 50% by at least one 50% power polarization converter; - introducing a phase shift between TE and TM polarizations by means of a bimodal phase shifter; The steps include:

[0038] It should be noted that the same advantages discussed with respect to the first embodiment, which is a passive lightwave conversion module, are also applicable to the second embodiment, which is a method of operating such a passive lightwave conversion module.

[0039] In one example, the method comprises: - introducing a relative phase shift between the TE and TM polarized light by each of the polarization converters.

[0040] In a further example, the method comprises: - guiding, by a bimodal phase shifter, TE00, which is TE polarization generated by two 50% input polarization converters based on an incident light wave having TE polarization; - guiding, by a bimodal phase shifter, TM01, which is TM-polarized light generated by two 50% input polarization converters based on an incident light wave with TE polarization; - guiding, by a bimodal phase shifter, TE polarization TE01 generated by two 50% input polarization converters based on an incident light wave with TM polarization; - guiding, by a bimodal phase shifter, TM00, which is TM polarization generated by two 50% input polarization converters based on an incident light wave having TM polarization; The method includes the steps of: A phase shift of an odd number of π radians is generated between TE00 and TM01, and a phase shift of an even number of π radians is generated between TE01 and TM00.

[0041] In another example, the step of converting the power of the incident light to 50% by two 50% input polarization converters includes: - It involves shifting the output converted light of two 50% input polarization converters by π radians.

[0042] In yet another example, the passive lightwave conversion module includes two 50% output polarization converters, and the step of converting the power of the polarized light to 50% by at least one 50% output polarization converter includes: - It involves shifting the output converted light of two 50% output polarization converters by π radians.

[0043] In a further example, the width and length of the bimodal phase shifter are modified to achieve an odd number of π radians of phase shift between TE00 and TM01, and an even number of π radians of phase shift between TE01 and TM00.

[0044] In a third aspect of the present disclosure, there is provided an optical device including a passive lightwave conversion module according to any of the examples provided above.

[0045] The present disclosure will be described in conjunction with the accompanying drawings. It is emphasized that, according to standard industry practice, various features are not drawn to scale. In fact, dimensions of various features may be arbitrarily increased or reduced for clarity of illustration.

[0046] In the accompanying figures, similar components and / or features may have the same reference label. Additionally, various components of the same type may be distinguished by following the reference label with a dash and a second label that distinguishes among the similar components. When only a first reference label is used herein, the description applies to any similar component with the same first reference label, regardless of the second reference label.

[0047] These and other aspects disclosed herein will be apparent from and elucidated with reference to the examples described hereinafter. [Brief explanation of the drawings]

[0048] [Figure 1] An example of a passive polarization converter is disclosed. [Figure 2] The TE mode fraction in the polarization of the guided modes is disclosed as a function of the waveguide width. [Figure 3] The effective refractive index of the waveguide modes is disclosed as a function of the waveguide width. [Figure 4]An example of a passive lightwave conversion module according to the present disclosure is disclosed. DETAILED DESCRIPTION OF THE INVENTION

[0049] It should be noted that in the description of the figures, the same reference numbers refer to the same or similar components that perform the same or essentially similar functions.

[0050] A more detailed description will now be provided with reference to certain examples, some of which are illustrated in the accompanying drawings to enable a more detailed understanding of the features of the present disclosure. It should be noted that the drawings are merely representative examples and therefore should not be considered to limit the scope of the claimed subject matter. The drawings are included to facilitate understanding of the disclosure and, therefore, are not necessarily drawn to scale. Advantages of the claimed subject matter will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings.

[0051] The above description that follows provides only preferred exemplary embodiment(s) and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the following description of the preferred exemplary embodiment(s) will provide those skilled in the art with an effective description for implementing the preferred exemplary embodiments of the present disclosure, and it will be understood that various changes may be made in the function and arrangement of elements, including combining features from different embodiments, without departing from the scope of the present disclosure.

[0052] Unless the context clearly requires otherwise, throughout this description and claims, words like "comprise," "comprising," and the like should be construed in an inclusive sense, i.e., "including, but not limited to," rather than an exclusive or exhaustive sense. As used herein, the terms "connected," "coupled," or any variation thereof, mean any direct or indirect connection or coupling between two or more elements. The coupling or connection between elements may be physical, logical, electromagnetic, or a combination thereof. Furthermore, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural may also include the plural or singular, respectively. The word "or" in reference to a list of two or more items includes all of the following interpretations of that word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0053] These and other changes can be made to the technology in light of the following detailed description. The description sets forth specific examples of the technology and describes the best mode contemplated, but no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system, while encompassed by the technology disclosed herein, may vary significantly in specific implementations thereof.

[0054] As mentioned above, specific terms used in describing particular features or aspects of the present technology should not be interpreted as being redefined herein to be limited to the particular characteristics, features, or aspects of the technology with which the terms are associated. In general, the terms used in the following claims should not be interpreted as limiting the technology to the specific examples disclosed herein, unless such terms are explicitly defined in the Detailed Description section. Therefore, the actual scope of the present technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology based on the claims.

[0055] FIG. 1 discloses an example of a passive polarization converter.

[0056] The design of the polarization converter is described below.

[0057] The polarization converter can be constructed using a special asymmetric waveguide with one sidewall that is tilted and forms an angle with the chip surface. A cross section of the converter module is shown in Figure 1. This results in a tilt of the waveguide mode.

[0058] For the correct width of the transformation module waveguide, the tilt shown is π / 4 radians. If this waveguide is placed between normal straight sidewall waveguides, the incident polarization mode (e.g., TE) will excite both tilted modes in equal proportions. After propagation through the angled waveguide, the cumulative phase difference between the tilted modes determines the reconfiguration of the output waveguide.

[0059] This results in an integrated version of the retardation plate. The proportion of TE and TM excitation modes depends directly on the waveguide width and the angle of the sloped sidewalls. The thickness of the upper cladding is set to 1.5 μm to achieve the same height as a typical platform-based waveguide.

[0060] Due to the crystal planes that act as stopping surfaces during wet etching, the sidewall angle can be equal to 54 degrees. Therefore, the waveguide width is swept to find a 50 / 50 excitation of the TE and TM modes.

[0061] The results are shown in Figure 2. As shown, the TE fraction is 50% at a width of 1.625 μm, which means the tilt mode angle is π / 4 radians. Therefore, based on equation (10) above, the complete polarization conversion length can be 132.1 μm.

[0062] Figure 3 shows the propagation of TE mode injection through the conversion module. As shown, the TE mode is completely converted to TM mode. Based on these simulations, the mode conversion efficiency is 99%.

[0063] The bimodal phase section is described below.

[0064] An eigenmode solver is performed to calculate the effective refractive index of the different modes as a function of the MMI width. As previously mentioned, for device operation, it is desirable to have an odd π between the TE0 and TM1 modes and an even π between the TM0 and TE1 modes. Any ratio that adheres to this rule can be used. In this exemplary design, the widths of the MMI sections are selected to provide a phase difference of 3π between TE0 and TM1 and a phase difference of 2π between TM0 and TE1.

[0065] FIG. 4 discloses an example of a passive lightwave conversion module according to the present disclosure.

[0066] To reduce the number of claims, certain aspects of the present technology are presented below in certain claim forms, but the applicant contemplates various aspects of the present technology in any number of claim forms. For example, while some aspects of the present technology may be recited as computer-readable medium claims, other aspects may also be embodied as computer-readable medium claims, or may be embodied in other forms, such as means-plus-function claims.

[0067] In the above description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the disclosed technology.

[0068] However, it will be apparent to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

[0069] Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting their scope.

Claims

1. 1. A passive light wave conversion module for converting an incident light wave having an undefined polarization into two light waves having defined polarizations, which are either transverse electric (TE) polarization or transverse magnetic (TM) polarization, comprising: an optical splitter for splitting the incoming light; two 50% input polarization converters that convert the power of the incident polarization to 50%, said input polarization converters being connected to said optical splitter; at least two 50% power polarization converters that convert the power of said polarization to 50%; a bimodal phase shifter for introducing a phase shift between the TE and TM polarizations, said bimodal phase shifter being connected to the two 50% input polarization converters and to the two 50% output polarization converters; The passive lightwave conversion module.

2. 2. The passive lightwave conversion module of claim 1, wherein each of the polarization converters is configured to convert half of the power of the TE polarization to the TM polarization and convert half of the power of the TM polarization to the TE polarization of the corresponding lightwave.

3. 10. A passive lightwave conversion module according to any preceding claim, wherein each of the polarization converters is configured to introduce a relative phase shift between the TE and TM polarizations.

4. The bimodal phase shifter has four different modes: - TE polarized light generated by the two 50% input polarization converters based on an incident light wave with TE polarized light. ００ , TM polarization, which is the TM polarization generated by the two 50% input polarization converters based on an incident light wave with TE polarization. ０１ , TE, the TE polarization produced by the two 50% input polarization converters based on an incident light wave with TM polarization. ０１ , TM polarization, which is the TM polarization generated by the two 50% input polarization converters based on an incident light wave with TM polarization. ００ , configured to guide the The bimodal phase shifter is a TE ００ and TM ０１ and TE ０１ and TM ００ 10. A passive lightwave conversion module according to any preceding claim, configured to produce a phase shift of an even number of π radians between

5. The bimodal phase shifter has four different modes: - TE polarized light generated by the two 50% input polarization converters based on an incident light wave with TE polarized light. ００ , TM polarization, which is the TM polarization generated by the two 50% input polarization converters based on an incident light wave with TE polarization. ０１ , TE, the TE polarization produced by the two 50% input polarization converters based on an incident light wave with TM polarization. ０１ , TM polarization, which is the TM polarization generated by the two 50% input polarization converters based on an incident light wave with TM polarization. ００ , configured to guide the The bimodal phase shifter is a TE ００ and TM ０１ and TE ０１ and TM ００ 10. A passive lightwave conversion module according to any preceding claim, configured to produce a phase shift of an odd number of π radians between

6. 10. A passive lightwave conversion module according to any of the preceding claims, wherein the two 50% input polarization converters are configured such that the output converted light of the two 50% input polarization converters is shifted by π radians.

7. 7. The passive lightwave conversion module of claim 6, wherein the two 50% input polarization converters are mirrored to each other and have slope outputs of 30 to 45 degrees and -30 to -45 degrees, respectively, so that the corresponding converted signals are shifted by π radians at the input of the bimodal phase shifter by the polarization converters.

8. The width and length of the bimodal phase shifter are ００ and TM ０１ is an odd number of π radians, and TE ０１ and TM ００ 5. The passive lightwave conversion module of claim 4, wherein the phase shift between

9. The width and length of the bimodal phase shifter are ００ and TM ０１ is an even number of π radians, and TE ０１ and TM ００ 6. The passive lightwave conversion module of claim 5, wherein the phase shift between

10. 1. A method for converting an incident light wave with undefined polarization into two light waves with defined polarizations, either transverse electric (TE) polarization or transverse magnetic (TM) polarization, comprising using a passive light wave conversion module according to any of the preceding claims, - splitting the incoming light by means of said optical splitter; - converting the power of said incident light to 50% by said two 50% input polarization converters; - converting the power of said polarized light to 50% by said two 50% output polarization converters; - introducing a phase shift between the TE and TM polarizations by means of the bimodal phase shifter; The method includes the steps of:

11. 11. The method of claim 10, the method comprising the step of introducing, by each of the polarization converters, a relative phase shift between the TE polarization and the TM polarization.

12. The method according to any one of claims 9 to 10, - guiding, by said bimodal phase shifter, the TE polarization TE00 produced by said two 50% input polarization converters on the basis of an incident light wave with TE polarization; - guiding, by said bimodal phase shifter, the TM polarization TM01 produced by said two 50% input polarization converters on the basis of an incident light wave with TE polarization; - guiding, by said bimodal phase shifter, the TE polarization TE01 produced by said two 50% input polarization converters on the basis of an incident light wave with TM polarization; - guiding, by said bimodal phase shifter, the TM polarization TM00 produced by said two 50% input polarization converters based on an incident light wave with TM polarization; The method includes the steps of: The method of the present invention, wherein a phase shift of an odd number of π radians is produced between TE00 and TM01, and a phase shift of an even number of π radians is produced between TE01 and TM00.

13. The method according to any one of claims 9 to 10, - guiding, by said bimodal phase shifter, the TE polarization TE00 produced by said two 50% input polarization converters on the basis of an incident light wave with TE polarization; - guiding, by said bimodal phase shifter, the TM polarization TM01 produced by said two 50% input polarization converters on the basis of an incident light wave with TE polarization; - guiding, by said bimodal phase shifter, the TE polarization TE01 produced by said two 50% input polarization converters on the basis of an incident light wave with TM polarization; - guiding, by said bimodal phase shifter, the TM polarization TM00 produced by said two 50% input polarization converters based on an incident light wave with TM polarization; The method includes the steps of: The method of the present invention, wherein an even number of π radians of phase shift is produced between TE00 and TM01, and an odd number of π radians of phase shift is produced between TE01 and TM00.

14. said step of converting the power of said incident light to 50% by said two 50% input polarization converters comprises: A method according to any of claims 10 to 13, comprising shifting the output converted light of the two 50% input polarization converters by π radians.

15. said step of converting the power of said polarized light to 50% by said at least one 50% output polarization converter comprises: A method according to any of claims 10 to 14, comprising shifting the output converted light of the two 50% output polarization converters by π radians.

16. 13. The method of claim 12, wherein the width and length of the bimodal phase shifter are modified to achieve that the phase shift between TE00 and TM01 is an odd number of π radians and the phase shift between TE01 and TM00 is an even number of π radians.

17. 14. The method of claim 13, wherein the width and length of the bimodal phase shifter are modified to achieve that the phase shift between TE00 and TM01 is an even number of π radians and that the phase shift between TE01 and TM00 is an odd number of π radians.

18. An optical device comprising the passive lightwave conversion module according to any one of claims 1 to 9.

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