JP2015135409A - Polarization separation element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization separation element small in size and low in cost.SOLUTION: The polarization separation element includes: a lower clad layer formed on a substrate; a first optical waveguide 110 and a second optical waveguide 120 formed on the lower clad layer; a first tapered taper part 111 tapered as approaching a top end formed in the first optical waveguide 110; a second tapered taper part 121 tapered as approaching the top end formed on the second optical waveguide 120; a second core 130 covering the first tapered taper part 111 in the first optical waveguide 110 and the second tapered taper part 121 in the second optical waveguide 120; and an upper clad layer formed on a top surface and a side surface of the second core 130. The first optical waveguide 110 and the second optical waveguide 120 are formed of a material having a refraction factor higher than that of the second core 130. The first tapered taper part 111 and the second tapered taper part 121 are arranged in series in a light propagation direction.

Description

  The present invention relates to a polarization separation element.

  As a method for performing high-speed and large-capacity signal transmission, there is optical communication, and a long-distance backbone communication system has already been put into practical use. In addition, optical communication has been put into practical use between information system devices such as computers in order to increase the speed of signal transmission. In the future, practical use in information system devices and between boards is in the field of view.

  In such optical communication, an optical fiber is used as a wiring member for transmitting an optical signal. Examples of components for processing optical signals include an optical transceiver, an optical coupler / splitter, an AWG (Arrayed Waveguide Grating), and the like, and these are preferably formed using an optical waveguide.

  On the other hand, in recent years, silicon photonics is being used as an optical waveguide component in optical communication. Silicon photonics has an advantage that an optical waveguide component can be formed in a very small region by microfabrication in a semiconductor manufacturing process. Therefore, silicon photonics is advantageous in downsizing an apparatus used for optical communication.

  Usually, in silicon photonics, silicon (n> 3) having a very high refractive index is used as a core, so that very strong light confinement is realized, which greatly contributes to miniaturization of optical waveguide components. . However, strong confinement of light in silicon photonics has a side effect that polarization (= polarization) dependence is large. For this reason, currently, optical waveguide components that operate only with one polarization are designed and manufactured. In general, silicon photonics operating in the TE (Transverse Electric) mode is the mainstream, but the operation in the TM (Transverse Magnetic) mode can also be applied.

  Since the polarization state of the optical signal propagating through the optical fiber is indefinite, a response is required for the optical waveguide component on the receiving side. In the conventional silica-based optical waveguide component, the difference in loss between the TE mode and the TM mode can be kept within the standard, and the optical fiber can be connected as it is. However, since silicon photonics currently operates with only one polarization as described above, the other polarization cannot be used even if an optical fiber is simply connected. Therefore, for example, when the received light from the optical fiber is in the TM state, the silicon photonics may not be able to receive the light.

  For this reason, a structure called polarization diversity is disclosed (for example, Non-Patent Document 1). In this method, received light from an optical fiber is coupled to a silicon optical waveguide by a spot size converter, and immediately separated into a TE mode and a TM mode using a polarization splitter (separator). Thereafter, the separated TM mode is converted into a TE mode by a polarization converter. Thereby, the received light from the optical fiber can be used as two TE modes.

  The spot size converter used at this time is formed by, for example, a tapered taper silicon optical waveguide whose tip portion is gradually narrowed and a second core that covers the silicon optical waveguide (for example, Patent Documents). 1-3).

JP 2002-122750 A JP 2004-133446 A JP 2004-157530 A

Yamada et al., Polarization Independence Technology for Ultra-Small Silicon Optical Circuits, NTT Technology Journal, 2009.12. p.16-19 M. Pu, et.al., "Ultra-low-loss inverted taper coupler for silicon-on-insulator ridge waveguide", Opt. Commun., Vol. 283, pp. 3678-3682 (2010)

  However, in the above-described polarization diversity, elements serving as three elements, that is, a spot size converter, a polarization splitter, and a polarization rotator are required, and are arranged as separate optical waveguide components. Since the elements serving as these elements have different optimum refractive indexes and three-dimensional structures, it is difficult to form them simultaneously. In other words, since they are formed of materials having different refractive indexes, a process for forming elements as respective elements is required, and the time required for manufacturing becomes long.

  Furthermore, it is generally difficult to form elements that are elements made of different materials close to each other, and it is necessary to secure a certain area for polarization diversity. End up. In other words, with a single optical fiber, the area to be secured is small, so this is not a problem. However, silicon photonics is often introduced to handle large volumes of data, and is inevitably used. The number of will also increase. For this reason, silicon photonics has one of the features that it can be reduced in size, but the size is increased without taking advantage of this feature.

  For this reason, if the elements that are a plurality of elements among the elements that are the three elements of the spot size converter, the polarization splitter, and the polarization rotator can be integrated, in miniaturization and simplification of the manufacturing process, It becomes advantageous and can be manufactured at low cost.

  Accordingly, there is a need for a small and low-cost polarization separation element such as a polarization separation element in which a spot size converter and a polarization splitter are integrated.

  According to one aspect of the present embodiment, a lower cladding layer formed on a substrate, a first optical waveguide and a second optical waveguide formed on the lower cladding layer, and the first optical waveguide A first taper taper portion that tapers as it approaches the tip formed in the optical waveguide, and a second taper taper portion that tapers as it approaches the tip formed in the second optical waveguide. A second core that covers the first tapered taper portion in the first optical waveguide and the second tapered taper portion in the second optical waveguide; and an upper cladding layer formed on the upper surface and side surfaces of the second core; The first optical waveguide and the second optical waveguide are made of a material having a refractive index higher than that of the second core, and the first tapered taper portion and the second tapered taper portion Light propagation Characterized in that it is arranged in series in the direction.

  According to the disclosed polarization separation element, the polarization separation element can be reduced in size and can be manufactured at low cost.

Illustration of optical fiber and spot size converter Structure diagram of polarization separation element in first embodiment Sectional drawing of the polarization splitting element in 1st Embodiment Process drawing (1) of the manufacturing method of the polarization splitting element in 1st Embodiment Process drawing (2) of the manufacturing method of the polarization splitting element in 1st Embodiment Explanatory drawing of the characteristics of the polarization beam splitting element in the first embodiment Structure diagram of polarization separation element in second embodiment Sectional drawing of the polarization splitting element in 2nd Embodiment Illustration of light propagating through the second core (1) Illustration of light propagating through the second core (2) Correlation diagram between length of polarization rotation unit and polarization conversion efficiency in the second embodiment

  The form for implementing is demonstrated below. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

[First Embodiment]
First, a spot size converter among the three elements used in the polarization diversity will be described with reference to FIG. The spot size converter 10 is used for joining the optical waveguide and the optical fiber 20 in silicon photonics. That is, the light propagating through the optical waveguide is made incident on the optical fiber 20 and the light propagating through the optical fiber 20 is made incident on the optical waveguide. In the optical fiber 20, a cladding 22 is formed around the core 21, and light propagates through the core 21. Since the optical waveguide formed in silicon photonics is narrower than the core 21 in the optical fiber 20, the spot size converter 10 that converts the spot size of light when the optical waveguide in the silicon photonics and the optical fiber 20 are joined. Is required. The core diameter of a general single mode optical fiber is about 8.2 μm, and the core diameter of a high NA single mode optical fiber having a small core diameter is about 2.4 μm.

  The spot size converter 10 is formed by a silicon optical waveguide 11 serving as a core, a second core 12 that covers the silicon optical waveguide 11, a silicon optical waveguide 11, and a clad (not shown) that covers the periphery of the second core 12. At the end of the silicon optical waveguide 11, a taper taper portion 11 a is formed which becomes narrower as the optical fiber 20 is approached. In this manner, by forming the tapered portion 11a in the silicon optical waveguide 11, the light propagating through the silicon optical waveguide 11 spreads to the second core 12, so that it can efficiently enter the core 21 of the optical fiber 20. Can do.

  In the silicon optical waveguide 11, TE mode light is generally propagated. However, in the optical fiber, both TE mode light and TM mode light are propagated. Therefore, when TM mode light is used, a polarization splitter that separates TE mode light and TM mode light, and a polarization rotator that converts TM mode light into TE mode light are required. Therefore, when the spot size converter 10 shown in FIG. 1 is used in the polarization diversity, a polarization splitter and a polarization rotator are arranged as separate components after the spot size converter 10.

(Polarization separation element)
The polarization separation element in the present embodiment will be described with reference to FIGS. The polarization separation element according to the present embodiment includes a spot size converter and a polarization splitter among elements that are three elements of a spot size converter, a polarization splitter, and a polarization rotator used in polarization diversity. It is an integrated one.

  The polarization separation element according to the present embodiment has a first silicon optical waveguide 110 and a second silicon optical waveguide 120 formed of silicon (Si) having a refractive index of about 3.48. At the end of the first silicon optical waveguide 110, a first taper taper portion 111 is formed which tapers as the optical fiber 20 is approached. The close part is the tip 111a. A second taper taper part 121 is formed at the end of the second silicon optical waveguide 120 so that the taper taper as it approaches the optical fiber 20. The close portion is the tip 121a.

  In addition, the region where the first tapered taper portion 111 formed in the first silicon optical waveguide 110 and the second tapered taper portion 121 formed in the second silicon optical waveguide 120 are formed is a second region. Covered by the core 130. The second core 130 has a square cross-sectional shape and is formed in a shape that extends long in the light propagation direction. In the present embodiment, the second core 130 is made of silicon oxynitride (SiON) having a refractive index of about 1.46. In addition, the value of the refractive index mentioned above is a value in light with a wavelength of 1550 nm.

As shown in FIG. 3, in the present embodiment, the first silicon optical waveguide 110 and the second silicon optical waveguide 120 are formed on the lower cladding layer 102 on the silicon substrate 101. Further, an upper clad layer 131 is formed so as to cover the first silicon optical waveguide 110, the second silicon optical waveguide 120 and the second core 130. The lower cladding layer 102 and the upper cladding layer 131 are formed of a silicon oxide (SiO ₂ ) film having a refractive index of about 1.44, and the upper cladding layer 131 and the lower cladding layer 102 form a cladding.

  In the polarization separation element according to the present embodiment, the tip 111a of the first taper taper 111 in the first silicon optical waveguide 110 is more than the tip 121a of the second taper taper 121 in the second silicon optical waveguide 120. Is also formed near the optical fiber 20. In addition, the first taper taper portion 111 in the first silicon optical waveguide 110 and the second taper taper portion 121 in the second silicon optical waveguide 120 are such that the extending direction is the light propagation direction. They are formed in series in the propagation direction.

  Further, the tip 111 a of the first tapered taper portion 111 in the first silicon optical waveguide 110 is formed wider than the tip 121 a of the second tapered taper portion 121 in the second silicon optical waveguide 120. That is, the selectivity of the TE mode light can be enhanced by widening the tip of the tapered portion at the end of the optical waveguide. Therefore, the width of the tip 111a of the first taper taper 111 in the first silicon optical waveguide 110 is 100 nm to 150 nm, and the width of the tip 121a of the second taper taper 121 in the second silicon optical waveguide 120 is 50 nm or less. It forms so that it becomes.

  As a result, among the light incident on the second core 130 from the optical fiber 20, the TE mode light is separated at the first tapered taper 111 in the first silicon optical waveguide 110, and the first silicon optical waveguide 110 is separated. Propagate. The remaining TM mode light propagating through the second core 130 enters the second silicon optical waveguide 120 from the second tapered taper 121 and propagates through the second silicon optical waveguide 120. Therefore, the polarization separation element according to the present embodiment can separate the TM mode light and the TE mode light propagating in the optical fiber 20, and thus has a function as a polarization splitter. .

  Further, since the first taper taper portion 111 in the first silicon optical waveguide 110 and the second taper taper portion 121 in the second silicon optical waveguide 120 are covered with the second core 130, each of them is subjected to spot size conversion. It also has a function as a vessel.

  Therefore, the polarization separation element in the present embodiment is an integration of the polarization splitter and the spot size converter, which is advantageous for downsizing and cost reduction. Note that the polarization separation element in the present embodiment has polarization diversity by providing a polarization rotator in the subsequent stage of the second silicon optical waveguide 120.

(Method for manufacturing polarization separation element)
Next, a method for manufacturing the polarization separating element in the present embodiment will be described with reference to FIGS. In the present embodiment, a case where a polarization conversion element is manufactured using an SOI (Silicon on Insulator) substrate will be described, but a manufacturing method for manufacturing without using an SOI substrate may be used.

First, as shown in FIG. 4A, a silicon oxide film 140a is formed on the SOI substrate 100, and a resist pattern 141 is formed on the silicon oxide film 140a. The SOI substrate 100 is a substrate in which a silicon oxide film to be a lower clad layer 102 is formed on a silicon substrate 101, and a silicon layer 103 is formed on a silicon oxide film to be a lower clad layer 102. . The formed silicon oxide film to be the lower clad layer 102 is called a buried oxide film or a BOX (Buried Oxide) layer and has a thickness of 3 μm. Further, the formed silicon layer 103 has a thickness of 250 nm. Specifically, a silicon oxide film 140a is formed on the silicon layer 103 in the SOI substrate 100 by film formation by CVD (Chemical Vapor Deposition). The silicon oxide film 140a formed in this way is for forming a hard mask 140 described later. When the silicon oxide film 140a is formed by CVD, SiH ₄ (20%) / He, N ₂ O, or the like is used as a source gas. Thereafter, a photoresist is applied on the silicon oxide film 140a, and exposure and development are performed by an exposure apparatus. Thus, a resist pattern 141 is formed on the silicon oxide film 140a in the region where the first silicon optical waveguide 110 and the second silicon optical waveguide 120 are formed.

Next, as shown in FIG. 4B, the hard mask 140 is formed by removing the silicon oxide film 140a in the region where the resist pattern 141 is not formed by dry etching. Specifically, the silicon oxide film 140a in the region where the resist pattern 141 is not formed is removed by dry etching such as RIE (Reactive Ion Etching) using CF ₄ or the like as an etching gas. Thereby, the hard mask 140 is formed by the remaining silicon oxide film 140a. Thereafter, the resist pattern 141 is removed with an organic solvent or the like.

  Next, as shown in FIG. 4C, by removing the silicon layer 103 in the region where the hard mask 140 is not formed by dry etching such as RIE, the first silicon optical waveguide 110 and the second silicon The optical waveguide 120 is formed. Specifically, the silicon layer 103 in the region where the hard mask 140 is not formed is removed by dry etching such as RIE using HBr or the like as an etching gas. As a result, the first silicon optical waveguide 110 and the second silicon optical waveguide 120 are formed by the remaining silicon layer 103. Thereafter, the hard mask 140 formed of silicon oxide is removed by wet etching or the like.

  Next, as shown in FIG. 5A, an SiON film 130a is formed on the lower cladding layer 102, the first silicon optical waveguide 110, and the second silicon optical waveguide 120 which are formed of a silicon oxide film. Then, a resist pattern 142 is formed on the SiON film 130a. The SiON film 130a is for forming the second core 130. Specifically, the SiON film 130a is formed by CVD or the like so that the film thickness is about 3 μm. The refractive index of the SiON film 130a formed at this time is 1.46. Thereafter, a photoresist is applied on the SiON film 130a, and exposure and development are performed by an exposure apparatus, whereby a resist pattern 142 is formed on the region where the second core 130 is to be formed.

  Next, as shown in FIG. 5B, by removing the SiON film 130a in the region where the resist pattern 142 is not formed by dry etching such as RIE, the second core 130 is formed by the remaining SiON film 130a. Form. Thereafter, the resist pattern 142 is removed with an organic solvent or the like.

  Next, as illustrated in FIG. 5C, a silicon oxide film is formed so as to cover the exposed portions of the second core 130, the first silicon optical waveguide 110, and the second silicon optical waveguide 120. Thus, the upper clad layer 131 is formed. The formed silicon oxide film to be the upper clad layer 131 is formed by CVD so that the film thickness becomes 1 μm. Thereby, a clad is formed by the lower clad layer 102 and the upper clad layer 131. As described above, the polarization conversion element in the present embodiment can be manufactured.

  Furthermore, in order to further improve the TE mode selection performance, the first silicon optical waveguide 110 may be formed to be thick. Specifically, a silicon layer having a thickness of 10 nm to 100 nm is formed only in a region where the first silicon optical waveguide 110 is formed on the silicon layer 103 in the SOI substrate 100. Thereafter, by performing the above-described steps, one silicon optical waveguide 110 can be formed thick. Alternatively, a method using an SOI substrate 100 in which the silicon layer 103 has a thickness of 300 nm may be used. In this case, except for the region where the first silicon optical waveguide 110 is formed, the thickness of the silicon layer 103 is removed by dry etching or the like up to 250 nm, and then the above-described steps are performed, whereby the first silicon optical waveguide 110 is obtained. Can be formed thick.

  Next, the TE mode light and TM mode light detected by the first silicon optical waveguide 110 and the second silicon optical waveguide 120 in the polarization separation element according to the present embodiment will be described with reference to FIG. . FIG. 6 shows a simulation result in the case where light is incident from the optical fiber 20 to the polarization separation element in the present embodiment. In the first silicon optical waveguide 110 and the second silicon optical waveguide 120, TM mode light and TE mode light can be separated with an extinction ratio of 10 dB or more. In other words, in the polarization separation element according to the present embodiment, most of the TE mode light propagates through the first silicon optical waveguide 110, and the TM mode light passes through the second silicon optical waveguide 120. Most are propagating.

[Second Embodiment]
Next, a second embodiment will be described. The present embodiment is a polarization separation element in which a spot size converter, a polarization splitter, and a polarization rotator, which are three elements in polarization diversity, are integrated.

  As shown in FIG. 7, the polarization separation element in the present exemplary embodiment includes a first taper taper portion 111 of the first silicon optical waveguide 110 and a second taper taper portion 121 of the second silicon optical waveguide 120. Between these, a polarization rotation unit 312 is provided. The polarization rotation unit 312 rotates the polarization of the light propagating through the second core 130. As will be described later, the polarization rotation unit 312 is formed with a predetermined length in the light propagation direction. Thus, TM mode light can be converted to TE mode light. As described above, the light converted from the TM mode to the TE mode in the second core 130 propagates as the TE mode light in the second silicon optical waveguide 120. In the present embodiment, the first silicon optical waveguide 110 is formed in the order of the first taper taper portion 111 and the polarization rotation portion 312 from the side where the optical fiber 20 is installed. The tip 111a of the first taper taper portion 111 is the end portion of the first silicon optical waveguide 110 on the side where the optical fiber 20 is installed.

  The polarization rotation unit 312 is formed in the vicinity of any of the four corners that are the peripheral part in the cross section of the second core 130. In this way, by forming the polarization rotation unit 312 in the vicinity of any of the four corners that are the peripheral part in the cross section of the second core 130, the second core 130 in the vicinity of the region where the polarization rotation unit 312 is formed can be obtained. The polarization of the propagating light can be rotated.

  Accordingly, among the light incident on the second core 130 from the optical fiber 20, the TE mode light is separated at the first tapered taper portion 111 in the first silicon optical waveguide 110 and propagates through the first silicon optical waveguide 110. To do. Thereafter, the remaining TM mode light propagating through the second core 130 is converted into TE mode light by the polarization rotation unit 312, and then the second tapered taper part 121 in the second silicon optical waveguide 120. And propagates through the second silicon optical waveguide 120. In other words, light converted from the TM mode to the TE mode propagates through the second silicon optical waveguide 120 in the region where the polarization rotation unit 312 of the second core 130 is formed. Therefore, TE mode light propagates through both the first silicon optical waveguide 110 and the second silicon optical waveguide 120.

  Therefore, in the present embodiment, the TM mode light can be converted to the TE mode without separately providing a polarization rotator, and the spot size converter which is an element that becomes three elements in the polarization diversity. The polarization splitter and the polarization rotator can be integrated.

(Polarization rotator)
Next, in order to describe the polarization rotation unit 312 in the present embodiment, the mode of light incident on the second core 130 will be described. As shown in FIG. 8A, when the polarization rotation unit 312 is not formed in the second core 130, the light propagates in the TE mode or the TM mode. FIG. 9A shows the light intensity distribution of the light propagating in the TE mode with contour lines in the second core 130 in which the polarization rotating unit 312 is not formed, and FIG. 9B shows the propagation in the TM mode. The light intensity distribution of the light is a contour line. An arrow indicates a mode axis.

  On the other hand, as shown in FIG. 8B, when the polarization rotation unit 312 is formed in the peripheral portion in the cross section of the second core 130, the light propagating through the second core 130 is shown in FIG. The mode axis is tilted. For example, in the case of TE mode light, the light is divided into two modes shown in FIGS. 10 (a) and 10 (b). Since the two modes have different phase velocities, the two modes are out of phase with the propagation of light. Thereby, the polarization of the light propagating through this portion rotates. Since such polarization rotation occurs in the portion where the polarization rotation unit 312 is formed, light of a desired mode can be obtained by adjusting the length of the polarization rotation unit 312. That is, by adjusting the length of the polarization rotating unit 312, it is possible to convert TE mode light into TM mode light.

  By the way, in order to perform stable polarization conversion, it is necessary that the equivalent refractive indexes in the modes match each other in a state where the second core 130 and the polarization rotation unit 312 exist independently. . Specifically, it is preferable that the equivalent refractive index of the mode in a state where the polarization rotating unit 312 exists alone is equal to or lower than the refractive index of the second core 130. Further, the equivalent refractive index of the mode can be adjusted by the size in the cross section of the polarization rotation unit 312. When the cross section of the polarization rotation unit 312 is reduced, the equivalent refractive index is reduced and approaches the refractive index of the cladding. Furthermore, when the cross section of the polarization rotating unit 312 is increased, the equivalent refractive index increases.

  FIG. 11 shows a result obtained by simulation regarding the relationship between the length in the polarization rotating unit 312 and the polarization conversion efficiency in the polarization conversion element of the present embodiment. The width of the polarization rotator 312 is 480 nm, and a higher-order mode in a state where the polarization rotator 312 exists alone is used. When the TE mode light is incident, the polarization conversion efficiency in the TM mode and the polarization conversion efficiency in the TE mode periodically change according to the length of the polarization rotation unit 312.

  As shown in FIG. 11, by setting the length of the polarization rotation unit 312 to about 500 μm, light incident in the TE mode can be converted into the TM mode with high efficiency. In this case, light incident in the TM mode is converted to the TE mode with high efficiency.

  In the description of the present embodiment, the case where the second core 130 is formed of SiON has been described. However, the second core 130 may be formed of a material other than SiON, and may be formed of quartz glass doped with Ge or the like or a resin material. May be. Further, although the case where the first silicon optical waveguide 110 or the like is formed of Si has been described, the first silicon optical waveguide 110 or the like may be formed of a material other than Si, or may be formed of SiN, SiON, or the like. Good.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
A lower cladding layer formed on the substrate;
A first optical waveguide and a second optical waveguide formed on the lower cladding layer;
A first tapered taper portion that tapers as it approaches the tip formed in the first optical waveguide;
A second taper taper that tapers as it approaches the tip formed in the second optical waveguide;
A second core covering the first tapered taper portion in the first optical waveguide and the second tapered taper portion in the second optical waveguide;
An upper cladding layer formed on the upper and side surfaces of the second core;
Have
The first optical waveguide and the second optical waveguide are made of a material having a higher refractive index than the second core,
The polarization separating element, wherein the first taper taper and the second taper taper are arranged in series in a light propagation direction.
(Appendix 2)
The polarization separation element is connected to an optical fiber,
The tip of the first taper taper portion is formed closer to the optical fiber than the tip of the second taper taper portion,
The polarization separation element according to appendix 1, wherein a width at a tip of the first taper taper portion is wider than a width at a tip of the second taper taper portion.
(Appendix 3)
The polarization separation element according to appendix 1 or 2, wherein TE mode light propagates through the first optical waveguide, and TM mode light propagates through the second optical waveguide.
(Appendix 4)
Between the first tapered taper portion and the second tapered taper portion, a polarization rotation portion is formed of the same material as the first optical waveguide and the second optical waveguide,
The polarization rotator is formed in a peripheral portion of the second core, and the light propagating through the second core rotates in the region where the polarization rotator is formed. 1. The polarization separation element according to 1.
(Appendix 5)
The polarization separation element according to appendix 4, wherein the polarization rotating unit converts the TM mode propagating through the second core into a TE mode and the TE mode into a TM mode.
(Appendix 6)
The polarization separation element according to appendix 4 or 5, wherein TE mode light propagates through the first optical waveguide, and TE mode light propagates through the second optical waveguide.
(Appendix 7)
The first optical waveguide and the second optical waveguide are made of a material containing silicon,
The polarization conversion element according to any one of appendices 1 to 6, wherein the lower clad layer and the upper clad layer are made of a material containing silicon oxide.

20 optical fiber 21 core 22 clad 100 SOI substrate 101 silicon substrate 102 lower clad layer 103 silicon layer 110 first silicon optical waveguide 111 first tapered taper portion 111a tip 120 second silicon optical waveguide 121 second tapered taper portion 121a tip 130 second core 131 upper clad layer

Claims (3)

A lower cladding layer formed on the substrate;
A first optical waveguide and a second optical waveguide formed on the lower cladding layer;
A first tapered taper portion that tapers as it approaches the tip formed in the first optical waveguide;
A second taper taper that tapers as it approaches the tip formed in the second optical waveguide;
A second core covering the first tapered taper portion in the first optical waveguide and the second tapered taper portion in the second optical waveguide;
An upper cladding layer formed on the upper and side surfaces of the second core;
Have
The first optical waveguide and the second optical waveguide are made of a material having a higher refractive index than the second core,
The polarization separating element, wherein the first taper taper and the second taper taper are arranged in series in a light propagation direction. The polarization separation element is connected to an optical fiber,
The tip of the first taper taper portion is formed closer to the optical fiber than the tip of the second taper taper portion,
2. The polarization separation element according to claim 1, wherein a width at a tip of the first taper taper portion is wider than a width at a tip of the second taper taper portion. Between the first tapered taper portion and the second tapered taper portion, a polarization rotation portion is formed of the same material as the first optical waveguide and the second optical waveguide,
The polarization rotation unit is formed in a peripheral portion of the second core, and the light propagating through the second core rotates in the region where the polarization rotation unit is formed. Item 2. The polarization separation element according to item 1.

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