A polarization-insensitive optical waveguide detector
By introducing an edge coupler, a polarization conversion module, and an optical resonant cavity structure into the optical waveguide detector, the problems of low polarization sensitivity and low optical responsivity of two-dimensional material optical waveguide detectors are solved, realizing a polarization-insensitive optical waveguide detector, improving the detector's responsivity and reducing dark current.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANGHAI UNIV
- Filing Date
- 2023-08-18
- Publication Date
- 2026-07-31
AI Technical Summary
Existing two-dimensional material heterogeneous integrated optical waveguide detectors suffer from polarization sensitivity and low optical responsivity, which cannot meet the needs of optical communication and optical ranging.
By introducing edge couplers, polarization conversion modules, mode spot converters, beam combiners, and optical resonant cavity structures, polarization conversion and enhanced absorption of optical signals are achieved. Black phosphorus/MoTe2 or black phosphorus/MoS2 heterojunction structures are used to improve detector responsivity and reduce dark current.
A polarization-insensitive optical waveguide detector was realized, which improved the optical responsivity and reduced the dark current, meeting the needs of applications such as optical communication and optical ranging.
Smart Images
Figure CN117055149B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of integrated optoelectronic chips and devices, and in particular to a polarization-insensitive optical waveguide detector. Background Technology
[0002] Compared to electronic integrated circuits, photonic integrated circuits offer advantages such as low transmission loss, wide transmission bandwidth, high transmission speed, and strong resistance to electromagnetic interference, making the development of photonic chips an inevitable outcome. To integrate with existing electronic devices, photodetectors that convert optical signals into electrical signals are a crucial component. Over the past few decades, silicon-based integrated optoelectronic chips based on the SOI (Silicon-on-insulator) platform have achieved significant development, but also exhibit obvious application limitations. For example, their centrosymmetric crystal structure is unsuitable for second-order nonlinear photonic devices; their optical transparency window is larger than 1.1 μm, limiting their application in the visible light band. In recent years, novel photonic platform materials such as lithium niobate (LiNbO) and aluminum nitride (AlN) have gained widespread attention due to their high nonlinearity and wide transparency window. Integrated photonic devices based on lithium niobate and aluminum nitride materials, such as optical waveguides, gratings, microring resonators, beam splitters, and modulators, have achieved considerable development, demonstrating excellent photonic performance. However, lithium niobate and aluminum nitride materials have poor conductivity, and their band gaps are larger than the photon energy of infrared light, making them unsuitable for direct use in photodetector fabrication. Heterogeneous integration of two-dimensional materials with good light absorption and conductivity (such as black phosphorus and graphene) into integrated photonic platforms is a common method for fabricating integrated optical waveguide detectors. However, two-dimensional materials are typically anisotropic and highly polarization-sensitive, exhibiting good absorption characteristics only for light of a specific polarization. Furthermore, for on-chip integrated optical waveguide devices, the vertical and horizontal dimensions of the photonic chip usually differ significantly, and transverse electric waves (TE waves) and transverse magnetic waves (TM waves) have large refractive index differences; therefore, the optical waveguide itself exhibits significant polarization dependence. However, to meet the needs of optical communication, optical interconnection, and optical ranging, polarization-insensitive integrated optical waveguide detectors are required. Therefore, suppressing or eliminating the polarization sensitivity of on-chip integrated optical waveguide detectors is an important research topic in the field of integrated optoelectronic chips.
[0003] Another problem with heterogeneous integrated optical waveguide detectors made of two-dimensional materials is their low optical responsivity. The signal light in the waveguide enters the two-dimensional material above the waveguide via evanescent wave coupling, requiring a certain transmission distance for complete absorption. However, two-dimensional materials such as black phosphorus are mechanically exfoliated, resulting in a device length generally smaller than the required absorption length. Furthermore, while choosing smaller two-dimensional material detectors is beneficial for improving device integration and reducing dark current, this reduces the absorption of signal light by the two-dimensional material. Summary of the Invention
[0004] The purpose of this invention is to provide a polarization-insensitive optical waveguide detector that can improve responsivity by enhancing light absorption through a resonant cavity and overcome polarization sensitivity through a polarization conversion module.
[0005] To achieve the above objectives, the present invention provides the following solution:
[0006] A polarization-insensitive optical waveguide detector, comprising:
[0007] An edge coupler is used to couple optical signals from an optical fiber into a lithium niobate / aluminum nitride optical waveguide on a polarizer to obtain coupled transmission light; the coupled transmission light includes TM0 light and TE0 light.
[0008] A polarization conversion module is disposed on the transmission optical path of the coupled transmission light, used to convert the TMO light into TEO light, and to split the original TEO light and the converted TEO light into a single beam for output.
[0009] A mode converter is placed on the transmission optical path of the TEO light output by the two-beam splitter to adjust the size of the original TEO light and the converted TEO light to obtain two TEO lights of the same size; the size of the two TEO lights is the mode size under single-mode waveguide conditions.
[0010] A beam combiner is placed on the transmission optical path of two TE0 beams of the same size to combine two TE0 beams of the same size into the same TE0 single-mode waveguide and output single-mode waveguide TE0 light.
[0011] An optical resonant cavity is disposed in the transmission optical path of the single-mode waveguide TEO light, and is used to uniformly distribute the light intensity of the single-mode waveguide TEO light within the cavity.
[0012] A photodetector is disposed in the cavity of the optical resonant cavity and is used to absorb the light intensity of the single-mode waveguide TEO light by utilizing the light-absorbing two-dimensional material and convert it into an electrical signal.
[0013] Optionally, the edge coupler may have an inverted cone, a regular cone, or a double cone structure.
[0014] Optionally, the polarization conversion module employs a first polarization rotation device or a second polarization rotation device; the first polarization rotation device includes a polarization beam splitter and a polarization rotator arranged sequentially along the transmission optical path; the second polarization rotation device is a polarization beam splitter rotator.
[0015] Optionally, the polarization beam splitter rotator is composed of a tapered waveguide structure and an asymmetric directional coupler structure.
[0016] Optionally, the mode converter employs a tapered waveguide structure.
[0017] Optionally, the structure of the beam combiner can be a Y-branch, directional coupler, or multimode interferometer structure.
[0018] Optionally, the optical resonant cavity adopts a one-dimensional resonant cavity structure or a two-dimensional photonic crystal resonant cavity structure; the one-dimensional resonant cavity structure includes a half-reflecting mirror and a total reflecting mirror arranged sequentially along the transmission optical path.
[0019] Optionally, both the semi-reflecting mirror and the total reflecting mirror are constructed from periodically arranged circular holes.
[0020] Optionally, both the semi-reflecting mirror and the total reflecting mirror adopt a distributed Bragg reflector structure or a Bragg grating structure.
[0021] Optionally, the light-absorbing two-dimensional material adopts a black phosphorus / MoTe2 heterojunction structure or a black phosphorus / MoS2 heterojunction structure.
[0022] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:
[0023] This invention discloses a polarization-insensitive optical waveguide detector. The detector includes an edge coupler for coupling optical signals from an optical fiber into a lithium niobate / aluminum nitride optical waveguide on a polarizer; a polarization conversion module for optical conversion, splitting the original TEO light and the converted TEO light into beams; a mode converter for adjusting the light size to obtain two TEO beams of the same size; a beam combiner for combining the light to output single-mode waveguide TEO light; an optical resonant cavity for uniformly distributing the intensity of the single-mode waveguide TEO light within the cavity; and a photodetector for absorbing the intensity of the single-mode waveguide TEO light using a two-dimensional light-absorbing material and converting it into an electrical signal. This detector structure enhances responsivity by using a resonant cavity to increase light absorption and overcomes polarization sensitivity through a polarization conversion module. Attached Figure Description
[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0025] Figure 1 This is a schematic diagram of the polarization-insensitive optical waveguide detector of the present invention.
[0026] Figure label:
[0027] 1. Edge coupler; 2. Polarization conversion module; 3. Mode converter; 4. Beam combiner; 5. Optical resonant cavity; 6. Half-reflector; 7. Total reflection mirror; 8. Photodetector. Detailed Implementation
[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0029] The purpose of this invention is to provide a polarization-insensitive optical waveguide detector that can improve responsivity by enhancing light absorption through a resonant cavity and overcome polarization sensitivity through a polarization conversion module.
[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0031] Edge coupler 1 is used to couple optical signals in optical fiber into lithium niobate / aluminum nitride optical waveguides on polarizers to obtain coupled transmission light; the coupled transmission light includes TM0 light and TE0 light.
[0032] Polarization conversion module 2 is disposed on the transmission optical path of the coupled transmission light, and is used to convert the TMO light into TEO light, and to split the original TEO light and the converted TEO light into a single beam for output.
[0033] The mode converter 3 is set on the transmission optical path of the TEO light output by the two beams and is used to adjust the size of the original TEO light and the converted TEO light to obtain two TEO lights of the same size; the size of the two TEO lights is the mode size under the single-mode waveguide condition.
[0034] The beam combiner 4 is placed on the transmission optical path of two TE0 beams of the same size to combine two TE0 beams of the same size into the same TE0 single-mode waveguide and output single-mode waveguide TE0 light.
[0035] An optical resonant cavity 5 is disposed in the transmission optical path of the single-mode waveguide TEO light, and is used to uniformly distribute the light intensity of the single-mode waveguide TEO light within the cavity.
[0036] The photodetector 8 is disposed in the cavity of the optical resonant cavity 5 and is used to absorb the light intensity of the single-mode waveguide TEO light by utilizing the light-absorbing two-dimensional material and convert it into an electrical signal.
[0037] In this embodiment, the edge coupler 1 adopts an inverted cone, a regular cone, or a double cone structure. The polarization conversion module 2 adopts a first polarization rotation device or a second polarization rotation device; the first polarization rotation device includes a polarization beam splitter and a polarization rotator arranged sequentially along the transmission optical path; the second polarization rotation device is a polarization beam splitter rotator. The polarization beam splitter rotator is composed of a tapered waveguide structure and an asymmetric directional coupler structure. The mode converter 3 adopts a tapered waveguide structure. The beam combiner 4 adopts a Y-branch, directional coupler, or multimode interferometer structure. The optical resonant cavity 5 adopts a one-dimensional resonant cavity structure or a two-dimensional photonic crystal resonant cavity structure; the one-dimensional resonant cavity structure includes a half-reflecting mirror 6 and a total reflecting mirror 7 arranged sequentially along the transmission optical path. The light-absorbing two-dimensional material adopts a black phosphorus / MoTe2 heterojunction structure or a black phosphorus / MoS2 heterojunction structure.
[0038] As a specific embodiment of the reflector, both the semi-reflective mirror 6 and the total reflective mirror 7 are composed of periodically arranged circular holes.
[0039] As another specific implementation of the reflector, both the semi-reflective mirror 6 and the total reflective mirror 7 adopt a distributed Bragg reflector structure or a Bragg grating structure.
[0040] Based on the above technical solution, the following embodiments are provided.
[0041] In this embodiment, to overcome the polarization sensitivity of optical waveguide detectors integrated on polarizers (especially two-dimensional material heterojunction optical waveguide detectors), a polarization rotating beamsplitter optical waveguide detector scheme is proposed. The input TM0 light is converted into TE0 light through the polarization rotating beamsplitter, effectively solving the polarization dependence of the two-dimensional material detector. To overcome the low responsivity of the optical waveguide detector, reflectors are introduced at both ends of the two-dimensional material detector to form an optical resonant cavity 5, which is used to confine the light field energy, allowing photons to interact with the absorbing material multiple times, thereby improving the detector's optical responsivity. To overcome the problems of large dark current and slow response speed in traditional photoconductive detectors, a detector structure based on a black phosphorus / MoTe2 or black phosphorus / MoS2 two-dimensional material heterojunction pn junction is proposed. The components of each part are described separately.
[0042] Edge coupler 1 couples the optical signal in the optical fiber into the on-chip lithium niobate / aluminum nitride optical waveguide. The edge coupler 1 can adopt structures such as inverted cone, positive cone and double cone.
[0043] Polarization conversion module 2 can first use a polarization splitter (PS) to separate the TE and TM light in the waveguides into two beams, and then use a polarization rotator (PR) to convert the TM polarized light into TE polarized light, so that the polarization states of the optical signals in the first and second waveguides are the same. Alternatively, it can be implemented directly using a polarization splitter-rotator (PSR). Figure 1 This is a polarization beam splitter rotator based on the principle of mode evolution. The polarization beam splitter rotator employs a tapered waveguide and an asymmetric directional coupler (ADC) structure. As the waveguide width changes from narrow to wide, a transition from TM0 to TE1 occurs, known as mode hybridization. First, the TM0 light is converted to TE1 light using mode hybridization. Then, the difference in effective refractive index between different modes is used to separate the TE1 mode into another adjacent waveguide and convert it back into TE0 light, while the original TE0 mode continues to propagate forward in that waveguide. The distance between the two beams after splitting should be much larger than the width at which mode coupling occurs.
[0044] The mode converter 3 adopts a tapered waveguide structure to convert the split TEO light into mode size under single-mode waveguide conditions, thereby reducing transmission loss and preventing inter-mode crosstalk.
[0045] The beam combiner 4 combines the TE0 light from the two waveguides into the same TE0 single-mode waveguide and inputs it into the optical resonant cavity 5. Possible structures include Y-branch, directional coupler (DC), and multimode interferometer (MMI).
[0046] The optical resonant cavity 5 can greatly confine the energy of the light field within the cavity, thereby allowing the light to interact with the light-absorbing material multiple times, greatly enhancing light absorption. Figure 1 The diagram shows a one-dimensional resonant cavity consisting of a half-reflecting mirror 6 and a total reflecting mirror 7. The mirrors are formed by etching a series of periodically arranged circular holes in the waveguide. The light field incident end is the half-reflecting mirror 6, and the other end is the total reflecting mirror 7 (reflectivity required to be above 90%). A light-absorbing two-dimensional material (such as a black phosphorus / MoTe2 heterojunction pn junction) is placed above the waveguide at the center of the cavity. A relatively uniform light intensity distribution can be obtained within this resonant cavity. Its resonant wavelength is determined by the cavity's refractive index and cavity length. Since the two-dimensional material is placed within the cavity, only a slight change in the cavity's overall refractive index slightly alters the resonant wavelength, making it easier to design. In this embodiment, the mirrors can also employ a distributed Bragg reflector (DBR) structure or a Bragg grating structure. Furthermore, the resonant cavity can also employ a two-dimensional photonic crystal resonant cavity structure.
[0047] The photodetector 8 converts optical signals into electrical signals for subsequent electrical processing. Figure 1 The photodetector 8 shown is a black phosphorus / MoTe2 heterojunction structure. Compared to black phosphorus-based photoconductors and MSM structures, this heterojunction structure has lower dark current and faster response speed. By adjusting the thickness of the black phosphorus, black phosphorus with a bandgap as low as 0.3 eV can be obtained, and the detectable wavelength range includes the communication band to the mid-infrared band. In this embodiment, after the waveguide and resonant cavity structures are fabricated, metal electrodes are first deposited on both sides of the waveguide using photolithography and film deposition methods. Then, the black phosphorus and MoTe2 heterojunction is integrated onto the lithium niobate or AlN optical waveguide by mechanical transfer. MoTe2 can also be replaced by other n-type two-dimensional materials such as MoS2.
[0048] Based on the above embodiments, the following beneficial effects are achieved:
[0049] This embodiment addresses the polarization dependence of TE and TM light in a two-dimensional material photodetector integrated on a lithium niobate and aluminum nitride optical waveguide. By introducing a polarization beam splitter rotator structure, the TE0 signal light is converted into a TM0 signal light for detection, which effectively reduces its polarization dependence and yields a polarization-insensitive optical waveguide detector.
[0050] To address the low absorption efficiency of evanescent wave coupled two-dimensional material photodetectors, an optical resonant cavity structure is introduced to confine the light field, enabling the detector to absorb the signal light multiple times, thereby improving the absorption rate and the detector's photoresponsivity.
[0051] To address the issues of high dark current and slow response speed in traditional photoconductive detectors, an electrical structure based on a two-dimensional heterojunction pn junction is proposed. This structure effectively reduces the dark current of the detector and improves the response speed and sensitivity of the photodetector.
[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.
[0053] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.
Claims
1. A polarization-insensitive optical waveguide detector, characterized by, include: An edge coupler is used to couple optical signals from an optical fiber into a lithium niobate / aluminum nitride optical waveguide on a polarizer to obtain coupled transmission light; the coupled transmission light includes TM0 light and TE0 light. A polarization conversion module is disposed on the transmission optical path of the coupled transmission light, used to convert the TMO light into TEO light, and to split the original TEO light and the converted TEO light into a single beam for output. A mode converter is placed on the transmission optical path of the TEO light output by the two-beam splitter to adjust the size of the original TEO light and the converted TEO light to obtain two TEO lights of the same size; the size of the two TEO lights is the mode size under single-mode waveguide conditions. A beam combiner is placed on the transmission optical path of two TE0 beams of the same size to combine two TE0 beams of the same size into the same TE0 single-mode waveguide and output single-mode waveguide TE0 light. An optical resonant cavity is disposed in the transmission optical path of the single-mode waveguide TEO light, and is used to uniformly distribute the light intensity of the single-mode waveguide TEO light within the cavity. A photodetector is disposed in the cavity of the optical resonant cavity and is used to absorb the light intensity of the single-mode waveguide TEO light by utilizing the light-absorbing two-dimensional material and convert it into an electrical signal.
2. The polarization-insensitive optical waveguide detector of claim 1, wherein, The edge coupler has an inverted cone, a regular cone, or a double cone structure.
3. The polarization-insensitive optical waveguide detector of claim 1, wherein, The polarization conversion module employs either a first polarization rotation device or a second polarization rotation device; the first polarization rotation device includes a polarization beam splitter and a polarization rotator arranged sequentially along the transmission optical path; the second polarization rotation device is a polarization beam splitter rotator.
4. The polarization-insensitive optical waveguide detector of claim 3, wherein, The polarization beam splitter rotator is composed of a tapered waveguide structure and an asymmetric directional coupler structure.
5. The polarization-insensitive optical waveguide detector of claim 1, wherein, The mode converter adopts a tapered waveguide structure.
6. The polarization-insensitive optical waveguide detector according to claim 1, characterized in that, The structure of the beam combiner can be a Y-branch, directional coupler, or multimode interferometer.
7. The polarization-insensitive optical waveguide detector according to claim 1, characterized in that, The optical resonant cavity adopts a one-dimensional resonant cavity structure or a two-dimensional photonic crystal resonant cavity structure; the one-dimensional resonant cavity structure includes a half-reflecting mirror and a total reflecting mirror arranged sequentially along the transmission optical path.
8. The polarization-insensitive optical waveguide detector according to claim 7, characterized in that, Both the semi-reflecting mirror and the total reflecting mirror are constructed from periodically arranged circular holes.
9. The polarization-insensitive optical waveguide detector of claim 7, wherein, Both the semi-reflecting mirror and the total reflecting mirror adopt a distributed Bragg reflector structure or a Bragg grating structure.
10. The polarization-insensitive optical waveguide detector of claim 1, wherein, The light-absorbing two-dimensional material adopts a black phosphorus / MoTe2 heterojunction structure or a black phosphorus / MoS2 heterojunction structure.