Integrated polarizer with small size, broadband, reflection suppression and large manufacturing tolerance

Abstract

The invention discloses an integrated optical waveguide polarizer which is small in size, wide in band, capable of achieving reflection suppression and large in manufacturing tolerance. The integrated optical waveguide polarizer comprises a high-order mode filter and a photonic crystal waveguide. The high-order mode filter does not support optical signal transmission in a high-order mode. The photonic crystal waveguide is a multi-mode optical waveguide with two rows of periodically distributed waveguide disturbances, uplink and downlink periodic waveguide disturbances are mutually staggered along the optical transmission direction, and the anti-symmetric waveguide structure can reflect an incident fundamental mode and convert the incident fundamental mode into a high-order mode. The period of the photonic crystal can be designed, so that a reflection band of the photonic crystal for a TM fundamental mode or a TE fundamental mode covers the operating wavelength range of the device, and a TE pass-through type polarizer or a TM pass-through type polarizer is realized respectively. The integrated optical polarizer disclosed by the invention has an ultra-small size and a large working bandwidth at the same time, has a reflection suppression function, and can reduce noise caused by reflected light of a system and possible adverse effects of the reflected light on a light source.

Description

Technical Field

[0001] The invention relates to the field of integrated optical polarizers, in particular to an integrated optical waveguide polarizer with small size, broadband, reflection suppression and large manufacturing tolerance. Background Art

[0002] Silicon-based photonic integration technology is generally considered to be one of the key solutions for future information networks due to its outstanding advantages such as low power consumption, high speed and high integration. Silicon-based optical waveguides usually have a strong birefringence effect, which makes silicon optical waveguide devices usually have a strong polarization correlation. Its various performance parameters, such as loss, operating wavelength, dispersion, conversion efficiency, etc., have a strong correlation with polarization. Therefore, if the optical signal has a low polarization extinction ratio, the designed silicon optical device will not be able to perform as expected, which will further affect the performance of the system. The use of silicon optical waveguide polarizers can better solve this problem. The main function of the optical polarizer is to allow only optical signals of a certain polarization state to pass through the device, thereby greatly improving the polarization extinction ratio of the optical signal. This function makes the integrated optical polarizer occupy an important position in silicon optical integrated circuits.

[0003] The main idea of ​​the existing design scheme of silicon-based integrated optical waveguide polarizers is to design with large polarization-dependent loss, so that a certain polarization state is lost and the other polarization state is passed losslessly or with low loss. The main schemes include waveguide Bragg gratings, adiabatic curved waveguides, asymmetric directional couplers, etc. However, the polarizers based on existing schemes often have large sizes, narrow working bandwidths (less than 50 nm), or require more complex manufacturing processes. In addition, some common optical polarizers based on Bragg gratings often generate reflected light signals with large energy, which may increase system noise and adversely affect the stability of the light source. Therefore, there is an urgent need to find integrated optical polarizers that are compact, wide-spectrum, low-cost to process and implement, and have reflection suppression for use in various silicon-based photonic integrated circuits. Summary of the invention

[0004] The invention provides an integrated optical waveguide polarizer with small size, broadband, reflection suppression and large manufacturing tolerance, so as to solve the problems of large size, narrow bandwidth and reflected light existing in the existing optical polarizer.

[0005] The technical solution adopted by the present invention is: An ultra-compact broadband reflection suppression integrated optical waveguide polarizer includes a high-order mode filter and an antisymmetric photonic crystal waveguide, wherein the high-order mode filter does not support the passage of optical signals in high-order modes. The antisymmetric photonic crystal waveguide is a multimode optical waveguide with two rows of periodically distributed waveguide disturbances, wherein the uplink and downlink waveguide disturbances are staggered by half a period length along the light transmission direction, i.e., they present an antisymmetric characteristic, which enables the photonic crystal to reflect the incident TE fundamental mode (i.e., TE0) or TM fundamental mode (i.e., TM0) and simultaneously convert them into odd-order high-order modes of TE or TM, respectively.

[0006] By designing the period length of the periodic waveguide disturbance in the photonic crystal, the reflection band of the photonic crystal for TM0 or TE0 covers the working wavelength range of the device, so that the device can be used as a TE pass type or TM pass type polarizer. The specific principle is as follows.

[0007] When the photonic crystal waveguide is designed so that its reflection band for TM0 covers the device operating wavelength range and its reflection band for TE0 is far away from the device operating wavelength range, the TE0 incident light signal will pass through the high-order mode filter and the photonic crystal waveguide in sequence without loss and finally be output from the device, while the TM0 incident light signal will be reflected as a TM high-order mode signal when passing through the photonic crystal waveguide and finally be filtered out by the high-order mode filter, thereby forming a TE through-type waveguide polarizer with reflection suppression characteristics; When the photonic crystal waveguide is designed so that its reflection band for TE0 covers the device operating wavelength range and its reflection band for TM0 is far away from the device operating wavelength range, the TM0 incident light signal will losslessly pass through the high-order mode filter and the photonic crystal waveguide in sequence and finally be output from the device, while the TE0 incident light signal will be reflected as a TE high-order mode signal when passing through the photonic crystal waveguide and finally be filtered out by the high-order mode filter, thereby forming a TM-passing waveguide polarizer with reflection suppression characteristics.

[0008] Furthermore, the periodic waveguide perturbation in the antisymmetric photonic crystal waveguide is a waveguide hole array periodically distributed along the light transmission direction, and the refractive index in the hole is the same as the refractive index of the waveguide cladding.

[0009] Furthermore, the period length of the periodic waveguide disturbance in the antisymmetric photonic crystal waveguide continuously increases or decreases along the light transmission direction, that is, it has a "chirp" characteristic.

[0010] Furthermore, the high-order mode filter includes a single-mode narrow waveguide, an input-end tapered waveguide connected to one end of the single-mode narrow waveguide, and an output-end tapered waveguide connected to the other end of the single-mode narrow waveguide, wherein the single-mode narrow waveguide does not support the transmission of high-order modes, the input-end tapered waveguide is wide at the front and narrow at the back along the light transmission direction, and the output-end tapered waveguide is narrow at the front and wide at the back along the light transmission direction. The high-order mode filter inputs an optical signal through the input-end tapered waveguide, and outputs the optical signal to the photonic crystal waveguide through the output-end tapered waveguide.

[0011] Compared with the prior art, the present invention has the following advantages: Thanks to the ultra-large coupling coefficient of the photonic crystal waveguide and the periodic chirp used, the integrated optical waveguide polarizer proposed in the present invention can have both ultra-small size and wide working bandwidth. In addition, unlike the traditional optical polarizer based on reflection grating, the integrated waveguide polarizer proposed in the present invention has a reflection suppression function, which can reduce the noise caused by the reflected light in the system and the adverse effects that the reflected light may have on the light source. Finally, the integrated waveguide polarizer proposed in the present invention has a huge manufacturing tolerance and is simple to process, so it has high performance stability and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1( a ) is a schematic diagram of the structure of the integrated waveguide polarizer proposed in the present invention.

[0013] Figures 1 (b)-(c) are schematic diagrams of the principles of a TM-passing waveguide polarizer in the following embodiments of the present invention; the upper and lower figures of Figure 1 (b) are respectively a schematic diagram of device transmission and a transmission light field diagram when incident on TE0, and the upper and lower figures of Figure 1 (c) are respectively a schematic diagram of device transmission and a transmission light field diagram when incident on TM0.

[0014] Figure 2 1 is the transmission response of TE0 and TM0 modes of the TM-pass waveguide polarizer in the following embodiment of the present invention.

[0015] Figure 3 The following is a comparison of the working bandwidths of the TM-pass waveguide polarizer in the following embodiments of the present invention when using chirped and non-chirped antisymmetric photonic crystal waveguides.

[0016] Figure 4 The following is a comparison of the device reflection response of the TM-pass waveguide polarizer in the following embodiments of the present invention when there is a high-order mode filter and when there is no high-order mode filter.

[0017] Figure 5 1 is the transmission response of the TE0 and TM0 modes of the TM-pass waveguide polarizer in the following embodiment of the present invention when the waveguide width manufacturing error is ± 60 nm. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention will be further described below through specific examples in conjunction with the accompanying drawings.

[0019] This embodiment discloses a TM-passing integrated optical waveguide polarizer with small size, broadband, reflection suppression and large manufacturing tolerance, the structure of which is shown in FIG1(a), and includes a photonic crystal waveguide 2 and a high-order mode filter 1. The operating wavelength range of the polarizer is 1.42 um to 1.62 um. The device is constructed based on a silicon-based integrated waveguide, the waveguide material is silicon, and the cladding material is silicon dioxide.

[0020] The high-order mode filter 1 is located at the front of the entire polarizer, and is composed of a single-mode narrow waveguide 1b, an input-end tapered waveguide 1a connected to one end of the single-mode narrow waveguide 1b, and an output-end tapered waveguide 1c connected to the other end of the single-mode narrow waveguide 1b. The single-mode narrow waveguide 1b does not support the transmission of high-order modes, the input-end tapered waveguide 1a is wide at the front and narrow at the back along the light transmission direction, and the output-end tapered waveguide 1c is narrow at the front and wide at the back along the light transmission direction.

[0021] The output-end tapered waveguide 1c of the high-order mode filter 1 is connected to one end of the photonic crystal waveguide 2. The optical signal waveguide width is gradually changed to match the single-mode narrow waveguide 1b through the input-end tapered waveguide 1a, and the optical waveguide width is gradually changed to match the photonic crystal waveguide 2 through the output-end tapered waveguide 1c. The TE0 or TM0 optical signal is input from the input-end tapered waveguide 1a of the high-order mode filter 1, passes through the single-mode narrow waveguide 1b, and is transmitted to the photonic crystal waveguide 2 from the output-end tapered waveguide 1c.

[0022] The photonic crystal waveguide 2 is a chirped, anti-symmetric, arrayed hole photonic crystal waveguide based on a multimode waveguide, and the photonic crystal waveguide 2 is located after the high-order mode filter 1. The photonic crystal waveguide 2 has a waveguide perturbation formed by a chirped periodic array of holes. Each waveguide hole is made of silica material, and the positions of the waveguide holes in the upper and lower rows are staggered by half a period length along the light transmission direction, thereby forming an upper and lower anti-symmetric characteristic, which enables it to reflect the incident TE fundamental mode (i.e., TE0) or TM fundamental mode (i.e., TM0) and simultaneously convert it into odd-order higher-order modes of TE or TM, respectively. The period of the chirped periodic array of holes increases linearly along the light transmission direction. Specifically, along the light transmission direction, the first row of the first hole has a period of 100. The waveguide hole and The spacing between the waveguide holes is ,in is the distance between the first and second waveguide holes, is the step length of the periodic change. The second row of waveguide holes is staggered with the first row of waveguide holes by half a period along the light transmission direction, that is, The waveguide holes are located relative to the first row. The waveguide holes are staggered along the light transmission direction. .

[0023] In this embodiment, the width of the photonic crystal waveguide 2 is 0.8 um, and the radius of each waveguide hole in the chirped periodic array hole is about 0.215 um. The period of the chirped periodic array hole of the photonic crystal waveguide 2 increases linearly from 0.35 um to 0.45 um along the light transmission direction. This period range makes the reflection band of the photonic crystal for the TE fundamental mode (TE0) cover the device operating wavelength range (1.42 um to 1.62 um), and at the same time, the reflection band of the photonic crystal for TM0 is far away from the device's operating wavelength range, so that the device of this embodiment is a TM pass-type waveguide polarizer. At this time, when the incident light signal is TE0, the light signal will be coupled to the photonic crystal waveguide 2 by the high-order mode filter, and reflected by the photonic crystal waveguide 2 as a high-order TE odd-order mode, that is, TE1 mode signal light. Since the high-order mode filter 1 connected to the input end of the photonic crystal waveguide 2 is a single-mode waveguide with a narrow width, it has a large loss for the high-order mode, so the reflected TE1 mode signal light will be filtered out when passing through the high-order mode filter. When the incident light signal is TM0, since the reflection band of the photonic crystal for TM0 is not within the designed device operating wavelength range, it can pass through the polarizer and output without loss. In summary, this embodiment can achieve the function of blocking TE0 and passing TM0, and there is no reflected light, that is, a TM-passing waveguide polarizer with reflection suppression characteristics is realized, and the principle schematic diagram is shown in Figure 1 (b)-(c).

[0024] Figures 2 to 5 The simulation results of the above embodiment of the present invention are shown (calculated by three-dimensional finite difference time domain method (3D-FDTD)). In this embodiment, thanks to the ultra-large coupling coefficient caused by the periodic waveguide disturbance formed by the chirped periodic array holes and the periodic chirp used, the photonic crystal waveguide in this embodiment has a length of only about 5 um (with 13 periods) and can achieve a working bandwidth of up to 0.2 um. Its transmission spectrum is as follows: Figure 2 shown. Figure 3 The TE0-TE1 mode conversion efficiency spectra of chirp-free and chirped hole array photonic crystal waveguides are compared. Figure 3 It can be seen that the chirped photonic crystal used in this embodiment can significantly increase its working bandwidth.

[0025] The use of the high-order mode filter enables this embodiment to have the function of suppressing reflected signals. To verify this, Figure 4 The reflected energy spectra of the polarizer including and excluding the high-order mode filter are compared. Figure 4It can be seen that without adding a high-order mode filter, the device reflection response is close to 0 dB in the entire operating wavelength range (1.42 um to 1.62 um). In contrast, when a high-order mode filter is added, the reflection response is reduced to <-12.5 dB in this wavelength range.

[0026] In addition, the waveguide polarizer of this embodiment has a huge manufacturing tolerance. Figure 5 The transmission responses of the polarizer in TE mode and TM mode when the waveguide width error is +60nm and -60nm are given. Figure 5 It can be seen that even if the waveguide width deviation is as large as ± 60 nm, the waveguide polarizer of this embodiment still has good working performance and still has a polarization suppression ratio greater than 20 dB within the working wavelength range.

[0027] In practical applications, the size of the overall period of the photonic crystal can be adjusted so that the reflection band of the photonic crystal waveguide corresponding to TM0 covers the working wavelength range, while the reflection band corresponding to TE0 is far away from the working wavelength range, thereby making the device a TE-passing polarizer.

[0028] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. The various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction, and such combinations should also be regarded as the contents disclosed in the present disclosure as long as they do not violate the concept of the present invention. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0029] The present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention and without departing from the design concept of the present invention, various modifications and improvements made to the technical solution of the present invention by technical personnel in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A small size, broadband, reflection suppression, integrated optical waveguide polarizer with large manufacturing tolerance, characterized in that: It includes a waveguide high-order mode filter and an antisymmetric photonic crystal based on a multimode waveguide; the high-order mode filter does not support the passage of high-order mode optical signals, and the antisymmetric photonic crystal waveguide is a multimode optical waveguide with two rows of periodically distributed waveguide disturbances, wherein the upstream and downstream periodic waveguide disturbances are staggered along the light transmission direction, that is, they present an antisymmetric characteristic; By designing the period length of the periodic waveguide perturbation in the photonic crystal, the reflection band of the photonic crystal for the TM fundamental mode (i.e., TM0 mode) or the TE fundamental mode (i.e., TE0 mode) can fall within the working wavelength range of the device, so that the device can be used as a TE pass-through or TM pass-through polarizer. The specific working principle is as follows: When the period size of the photonic crystal is designed so that its reflection band for TM0 covers the device operating wavelength range and its reflection band for TE0 is far away from the device operating wavelength range, the TE0 incident light signal will pass through the high-order mode filter and the photonic crystal in sequence without loss and finally be output from the device, while the TM0 incident light signal will be reflected as a TM high-order mode when passing through the photonic crystal and finally be filtered out by the high-order mode filter, thereby forming a TE-through waveguide polarizer with reflection suppression characteristics; When the period size of the photonic crystal is designed so that its reflection band for TE0 covers the device operating wavelength range and its reflection band for TM0 is far away from the device operating wavelength range, the TM0 incident light signal will losslessly pass through the high-order mode filter and the photonic crystal waveguide in sequence and finally be output from the device, while the TE0 incident light signal will be reflected as a TE high-order mode signal when passing through the photonic crystal waveguide and finally be filtered out by the high-order mode filter, thereby forming a TM-passing waveguide polarizer with reflection suppression characteristics.

2. The antisymmetric photonic crystal waveguide based on multimode waveguide according to claim 1, characterized in that: The periodic waveguide disturbance is a waveguide hole array periodically distributed along the light transmission direction, and the refractive index in the hole is the same as the refractive index of the waveguide cladding.

3. A small-size, broadband, reflection-suppressing, integrated optical polarizer with a large manufacturing tolerance according to any one of claims 1 to 2, characterized in that: The period length of the periodic waveguide disturbance in the photonic crystal increases or decreases continuously along the light transmission direction, that is, it has a chirp characteristic.

4. An integrated optical polarizer with ultra-small size, large bandwidth, reflection suppression and large manufacturing tolerance according to claim 1, characterized in that: The high-order mode filter comprises a single-mode narrow waveguide, an input-end tapered waveguide connected to one end of the single-mode narrow waveguide, and an output-end tapered waveguide connected to the other end of the single-mode narrow waveguide, wherein the single-mode narrow waveguide does not support the transmission of high-order TE or TM modes, the input-end tapered waveguide is wide at the front and narrow at the back along the light transmission direction, and the output-end tapered waveguide is narrow at the front and wide at the back along the light transmission direction. The polarizer inputs an optical signal through the input-end tapered waveguide, and outputs the optical signal to the photonic crystal waveguide through the output-end tapered waveguide.

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