A small size, wideband, reflection suppression, large manufacturing tolerance integrated polarizer
By designing high-order mode filters and antisymmetric photonic crystal waveguides, the problems of large size, narrow bandwidth, and reflected light signals in silicon-based integrated optical waveguide polarizers were solved, realizing small-size, wide-bandwidth, and low-reflection optical polarizers, thus improving the performance stability of silicon-based photonic integrated circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEFEI UNIV OF TECH
- Filing Date
- 2024-09-30
- Publication Date
- 2026-07-07
AI Technical Summary
Existing silicon-based integrated optical waveguide polarizers suffer from problems such as large size, narrow bandwidth, and reflected light signals affecting system stability, making it difficult to meet the requirements of silicon-based photonic integrated circuits.
By employing a high-order mode filter and an antisymmetric photonic crystal waveguide design, and by designing periodic perturbations in the photonic crystal waveguide, the polarization state of the optical signal can be suppressed and converted within a specific wavelength range. Combined with chirp characteristics, an ultra-compact broadband polarizer can be realized.
This resulted in a small-size, wide-bandwidth, low-reflection optical polarizer, reducing system noise and improving manufacturing tolerance and performance stability.
Smart Images
Figure CN119291848B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of integrated optical polarizers, specifically an integrated optical waveguide polarizer that is small in size, has wide bandwidth, suppresses reflections, and has large manufacturing tolerances. Background Technology
[0002] Silicon-based photonics integration technology is widely considered a key solution for future information networks due to its outstanding advantages such as low power consumption, high speed, and high integration density. Silicon-based optical waveguides typically exhibit strong birefringence, resulting in strong polarization dependence in silicon waveguide devices. Various performance parameters, such as loss, operating wavelength, dispersion, and conversion efficiency, are highly correlated with polarization. Therefore, if the optical signal has a low polarization extinction ratio, the designed silicon optical device will fail to achieve its expected performance, further affecting the system's performance. Silicon waveguide polarizers can effectively address this problem. The main function of an optical polarizer is to allow only a specific polarization state of light to pass through the device, thereby significantly improving the polarization extinction ratio of the optical signal. This function makes integrated optical polarizers crucial in silicon photonic integrated circuits.
[0003] The main idea behind existing silicon-based integrated optical waveguide polarizer designs is to achieve high polarization-dependent loss, allowing one polarization state to be lost while enabling another polarization state to pass through without loss or with low loss. Key designs include waveguide Bragg gratings, thermally adiabatic bent waveguides, and asymmetric directional couplers. However, current polarizers based on these designs often have large dimensions, narrow operating bandwidths (less than 50 nm), or require complex fabrication processes. Furthermore, some common Bragg grating-based optical polarizers often generate high-energy reflected light signals, which can increase system noise and negatively impact the stability of the light source. Therefore, there is an urgent need to find compact, wide-spectrum, low-cost, and reflection-suppressive integrated optical polarizers for use in various silicon-based photonic integrated circuits. Summary of the Invention
[0004] This invention provides an integrated optical waveguide polarizer that is small in size, has a wide bandwidth, suppresses reflection, and has a large manufacturing tolerance, in order to solve the problems of large size, narrow bandwidth, and reflected light in existing optical polarizers.
[0005] The technical solution adopted in this invention is as follows:
[0006] An ultracompact broadband reflection suppression integrated optical waveguide polarizer includes a high-order mode filter and an antisymmetric photonic crystal waveguide. The high-order mode filter does not support the passage of high-order mode optical signals. The antisymmetric photonic crystal waveguide is a multimode optical waveguide with two rows of periodically distributed waveguide perturbations. The up and down waveguide perturbations are offset by half a period length along the optical transmission direction, exhibiting antisymmetric characteristics. This allows the photonic crystal to reflect the incident TE fundamental mode (TE0) or TM fundamental mode (TM0) and simultaneously convert it into odd-order high-order modes of TE or TM, respectively.
[0007] By designing the period length of the periodic waveguide perturbation in the photonic crystal, the reflection band of the photonic crystal for TM0 or TE0 covers the operating wavelength range of the device, thereby enabling the device to function as a TE-through or TM-through polarizer. The specific principle is as follows.
[0008] When the photonic crystal waveguide is designed such that its reflection band for TM0 covers the operating wavelength range of the device while its reflection band for TE0 is far from the operating wavelength range of the device, the TE0 incident light signal will pass through the higher-order mode filter and the photonic crystal waveguide without loss and will finally be output from the device. The TM0 incident light signal will be reflected as a TM higher-order mode signal when passing through the photonic crystal waveguide and will finally be filtered out by the higher-order mode filter. This forms a TE through-type waveguide polarizer with reflection suppression characteristics.
[0009] When the photonic crystal waveguide is designed such that its reflection band for TE0 covers the operating wavelength range of the device while its reflection band for TM0 is far from the operating wavelength range of the device, the TM0 incident light signal will pass through the higher-order mode filter and the photonic crystal waveguide without loss and will finally be output from the device. The TE0 incident light signal will be reflected as a TE higher-order mode signal when passing through the photonic crystal waveguide and will finally be filtered out by the higher-order mode filter. This forms a TM through-type waveguide polarizer with reflection suppression characteristics.
[0010] Furthermore, the periodic waveguide perturbation in the antisymmetric photonic crystal waveguide is an array of waveguide apertures periodically distributed along the optical transmission direction, with the refractive index inside the apertures being the same as the refractive index of the waveguide cladding.
[0011] Furthermore, in the antisymmetric photonic crystal waveguide, the period length of the periodic waveguide perturbation continuously increases or decreases along the optical transmission direction, i.e., it has a "chirp" characteristic.
[0012] Furthermore, the higher-order mode filter includes a single-mode narrow waveguide, an input tapered waveguide connected to one end of the single-mode narrow waveguide, and an output tapered waveguide connected to the other end of the single-mode narrow waveguide. The single-mode narrow waveguide does not support the transmission of higher-order modes. The input tapered waveguide is wider at the front and narrower at the back along the optical transmission direction, and the output tapered waveguide is narrower at the front and wider at the back along the optical transmission direction. The higher-order mode filter inputs optical signals through the input tapered waveguide and outputs optical signals to the photonic crystal waveguide through the output tapered waveguide.
[0013] Compared with the prior art, the advantages of the present invention are:
[0014] Thanks to the ultra-large coupling coefficient of photonic crystal waveguides and the periodic chirp used, the integrated optical waveguide polarizer proposed in this invention can simultaneously achieve ultra-small size and a wide operating bandwidth. Furthermore, unlike traditional optical polarizers based on reflection gratings, the integrated waveguide polarizer proposed in this invention has reflection suppression capabilities, which can reduce noise caused by reflected light and the potential adverse effects of reflected light on the light source. Finally, the integrated waveguide polarizer proposed in this invention has a large fabrication tolerance and is simple to process, thus exhibiting high performance stability and practicality. Attached Figure Description
[0015] Figure 1(a) is a schematic diagram of the integrated waveguide polarizer proposed in this invention.
[0016] Figures 1(b)-(c) are schematic diagrams of the TM through-type waveguide polarizer in the following embodiments of the present invention; wherein the upper and lower figures of Figure 1(b) are schematic diagrams of device transmission and transmission optical field when TE0 is incident, respectively, and the upper and lower figures of Figure 1(c) are schematic diagrams of device transmission and transmission optical field when TM0 is incident, respectively.
[0017] Figure 2 The following embodiments of the present invention represent the transmission responses of the TE0 and TM0 modes of the TM through-type waveguide polarizer.
[0018] Figure 3 This is a comparison of the operating bandwidth of the TM through-type waveguide polarizer in the following embodiments of the present invention when using chirped and unchirped antisymmetric photonic crystal waveguides.
[0019] Figure 4 This is a comparison of the device reflection response of the TM through-type waveguide polarizer in the following embodiments of the present invention with and without a high-order mode filter.
[0020] Figure 5 The following embodiments of the present invention show the transmission responses of the TE0 and TM0 modes of the TM through-type waveguide polarizer when the waveguide width fabrication error is ±60 nm. Detailed Implementation
[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.
[0022] This embodiment discloses a small-size, broadband, reflection-suppressive, and high-fabrication-tolerance TM-type integrated optical waveguide polarizer, the structure of which is shown in Figure 1(a), including a photonic crystal waveguide 2 and a high-order mode filter 1. The polarizer operates in the wavelength range of 1.42 μm to 1.62 μm. The device is constructed based on a silicon-based integrated waveguide, with silicon as the waveguide material and silicon dioxide as the cladding material.
[0023] The high-order mode filter 1 is located at the front of the entire polarizer and consists of a single-mode narrow waveguide 1b, an input tapered waveguide 1a connected to one end of the single-mode narrow waveguide 1b, and an output 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 tapered waveguide 1a is wider at the front and narrower at the back along the optical transmission direction, while the output tapered waveguide 1c is narrower at the front and wider at the back along the optical transmission direction.
[0024] The output tapered waveguide 1c of the high-order mode filter 1 is connected to one end of the photonic crystal waveguide 2. The input tapered waveguide 1a gradually transitions the optical signal waveguide width to match the single-mode narrow waveguide 1b, and the output tapered waveguide 1c gradually transitions the optical waveguide width to match the photonic crystal waveguide 2. TE0 or TM0 optical signals are input from the input tapered waveguide 1a of the high-order mode filter 1, pass through the single-mode narrow waveguide 1b, and are transmitted from the output tapered waveguide 1c to the photonic crystal waveguide 2.
[0025] Photonic crystal waveguide 2 is a chirped, antisymmetric, array-aperture type photonic crystal waveguide based on a multimode waveguide, located after the higher-order mode filter 1. Photonic crystal waveguide 2 features waveguide perturbations formed by a chirped periodic array of apertures. Each aperture is filled with silicon dioxide, and the positions of the upper and lower rows of apertures are staggered by half a period length along the light propagation direction, thus creating an antisymmetric characteristic. This allows it to reflect the incident TE fundamental mode (TE0) or TM fundamental mode (TM0) and simultaneously convert it into odd-order higher-order modes of TE or TM, respectively. The period of the chirped periodic array of apertures increases linearly along the light propagation direction. Specifically, along the light propagation direction, the period of the first row of apertures increases linearly. The waveguide aperture and the first The spacing between the waveguide apertures is ,in The spacing between the first and second waveguide apertures. The step size is the periodic variation. The second row of waveguide holes is offset from the first row of waveguide holes by half a cycle along the optical transmission direction, that is, the second row's... The waveguide aperture is relative to the first row of the first row. The waveguide apertures are offset along the direction of light transmission. .
[0026] In this embodiment, the width of the photonic crystal waveguide 2 is 0.8 μm, and the radius of each waveguide aperture in the chirped periodic array is approximately 0.215 μm. The period of the chirped periodic array apertures in the photonic crystal waveguide 2 increases linearly from 0.35 μm to 0.45 μm along the optical transmission direction. This period range ensures that the reflection band of the photonic crystal for the TE fundamental mode (TE0) covers the device's operating wavelength range (1.42 μm to 1.62 μm), while the reflection band of the photonic crystal for TM0 is far from the device's operating wavelength range. Therefore, the device in this embodiment is a TM through-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 a higher-order mode filter and reflected by the photonic crystal waveguide 2 into a higher-order TE odd-order mode, i.e., TE1 mode signal light. Since the high-order mode filter 1 connected to the input of the photonic crystal waveguide 2 is a narrow-width single-mode waveguide, it has a large loss for high-order modes. Therefore, 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 operating wavelength range of the device, it can pass through the polarizer and be output without loss. In summary, this embodiment can achieve the function of blocking TE0 and passing through TM0, while having no reflected light, that is, realizing a TM-passing waveguide polarizer with reflection suppression characteristics. The schematic diagram is shown in Figure 1(b)-(c).
[0027] Figures 2 to 5 Simulation results of the above embodiments of the present invention are presented (obtained by calculation using the three-dimensional finite-difference time-domain method (3D-FDTD)). In this embodiment, thanks to the ultra-large coupling coefficient caused by the periodic waveguide perturbation formed by the chirped periodic array apertures and the periodic chirp used, the photonic crystal waveguide in this embodiment has a length of only about 5 μm (with 13 periods) and can achieve an operating bandwidth of up to 0.2 μm, and its transmission spectrum is as follows. Figure 2 As shown. Figure 3 The TE0-TE1 mode conversion efficiency spectra of chirpless and chirped array aperture photonic crystal waveguides were compared, from... Figure 3 As can be seen, the use of a chirped photonic crystal in this embodiment can significantly increase its operating bandwidth.
[0028] The use of a higher-order mode filter enables this embodiment to suppress reflected signals. To verify this, Figure 4 The reflection energy spectrum was compared with and without the higher-order mode filter of the polarizer. Figure 4It can be seen that without the high-order mode filter, the device's reflection response is close to 0 dB across the entire operating wavelength range (1.42 μm to 1.62 μm). In contrast, with the addition of the high-order mode filter, the reflection response decreases to <-12.5 dB over the same wavelength range.
[0029] In addition, the waveguide polarizer in this embodiment has a large manufacturing tolerance. Figure 5 The propagation responses of the polarizer in TE and TM modes are presented for waveguide width errors of +60 nm and -60 nm. Figure 5 It can be seen that even with a waveguide width deviation as large as ±60 nm, the waveguide polarizer in this embodiment still has good working performance and a polarization suppression ratio of more than 20 dB within the operating wavelength range.
[0030] In practical applications, the overall period of the photonic crystal can be adjusted so that the reflection band corresponding to TM0 of the photonic crystal waveguide covers the working wavelength range, while the reflection band corresponding to TE0 is far from the working wavelength range, thus making the device a TE-through polarizer.
[0031] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.
[0032] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.
Claims
1. A small-size, broadband, reflection-suppressing, and high-manufacturing-tolerance integrated optical waveguide polarizer, characterized in that, It includes a waveguide high-order mode filter and an antisymmetric photonic crystal waveguide 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 perturbations, wherein the up and down periodic waveguide perturbations are staggered along the optical transmission direction, i.e., exhibiting antisymmetric characteristics; By designing the period length of the periodic waveguide perturbation in the photonic crystal, the reflection band of the photonic crystal for TM0 or TE0 modes can be made to fall within the operating wavelength range of the device. This allows the device to function as a TE-through or TM-through polarizer. The specific working principle is as follows: When the period size of the photonic crystal is designed such that its reflection band for TM0 covers the operating wavelength range of the device while its reflection band for TE0 is far from the operating wavelength range of the device, the TE0 incident light signal will pass through the higher-order mode filter and the photonic crystal without loss and will finally be output from the device. The TM0 incident light signal will be reflected into the TM higher-order mode when passing through the photonic crystal and will finally be filtered out by the higher-order mode filter, thus forming a TE through-type waveguide polarizer with reflection suppression characteristics. When the photonic crystal period is designed such that its reflection band for TE0 covers the device's operating wavelength range while its reflection band for TM0 is far from the device's operating wavelength range, the TM0 incident light signal will pass through the higher-order mode filter and the photonic crystal waveguide without loss and will eventually be output from the device. The TE0 incident light signal will be reflected as a TE higher-order mode signal when passing through the photonic crystal waveguide and will eventually be filtered out by the higher-order mode filter, thus forming a TM through-type waveguide polarizer with reflection suppression characteristics.
2. The small-size, broadband, reflection-suppressive, and high-manufacturing-tolerance integrated optical waveguide polarizer as described in claim 1, characterized in that, The periodic waveguide perturbation is an array of waveguide apertures periodically distributed along the optical transmission direction, with the refractive index inside the apertures being the same as the refractive index of the waveguide cladding.
3. A small-size, broadband, reflection-suppressing, and high-manufacturing-tolerance integrated optical waveguide polarizer according to any one of claims 1-2, characterized in that, The period length of the periodic waveguide perturbation in the photonic crystal increases or decreases continuously along the optical transmission direction, i.e., it has chirp characteristics.
4. The integrated optical waveguide polarizer with small size, wide bandwidth, reflection suppression, and large manufacturing tolerance according to claim 1, characterized in that, The high-order mode filter includes a single-mode narrow waveguide, an input tapered waveguide connected to one end of the single-mode narrow waveguide, and an output tapered waveguide connected to the other end of the single-mode narrow waveguide. The single-mode narrow waveguide does not support the transmission of high-order TE or TM modes. The input tapered waveguide is wider at the front and narrower at the back along the optical transmission direction, and the output tapered waveguide is narrower at the front and wider at the back along the optical transmission direction. The polarizer inputs the optical signal through the input tapered waveguide and outputs the optical signal to the photonic crystal waveguide through the output tapered waveguide.