A passive coherent long-wave infrared radiation sensing photonic integrated device

Abstract

The present invention discloses a passive coherent long-wave infrared radiation sensing photon integrated device, belonging to the field of infrared sensor device technology. The device comprises a substrate layer, an optical isolation layer, an optical transmission layer, and a metal structure layer arranged from bottom to top; the optical isolation layer is a silicon oxide layer; the optical transmission layer is a lithium niobate layer, comprising a coupled grating structure, an optical beam splitter structure, a bus optical transmission waveguide structure, a coupled waveguide structure, and a ring resonant cavity structure; and the metal structure layer is a periodic metal grating structure. The device of the present invention has a layered structure, is simple in structure, and is compatible with the processing technology of integrated photonic devices. It can directly convert long-wave infrared radiation signals into near-infrared signals in the communication band, which can be connected to optical fiber communication systems for transmission. The self-reference structure of the device can achieve coherent beat frequency of the near-infrared signal, thereby obtaining a signal output in the radio frequency domain. This greatly reduces the system testing cost while ensuring high sensitivity, and is of great significance to the development of high-performance infrared radiation photon sensors.

Description

Technical Field

[0001] The present invention belongs to the technical field of infrared sensor devices, and more specifically, relates to a passive coherent long-wave infrared radiation sensing photon integrated device. Background Art

[0002] Long-wave infrared (8-14μm) technology is widely used in military and civilian applications, such as medical monitoring, environmental monitoring, night vision imaging, and precision guidance. Long-wave infrared radiation sensors play a vital role in signal detection and analysis, and are a core component of infrared systems. Traditional long-wave infrared radiation sensors generally rely on narrow-bandgap semiconductor materials or thermosensitive materials. The former utilizes the photoelectric effect of semiconductor materials for infrared detection, but the response wavelength is limited by the bandgap and requires low-temperature operation. The latter offers a broad spectrum response at room temperature, but its performance is limited. Currently, long-wave infrared sensors are developing towards uncooled, wavelength-selective, highly sensitive, and low-cost technologies, which poses challenges to traditional device solutions.

[0003] "Whispering-Gallery-Mode Optical Microshell Resonator Infrared Detector" (IEEE Sensors Journal, 2021, 21: 2634-2641) discloses a glass microshell optical resonator for long-wave infrared sensing, which uses the glass microshell to absorb infrared radiation energy to generate heat, thereby leading to thermo-optical effect and thermal expansion effect. This effect causes the effective refractive index of the near-infrared optical resonance mode propagating on the surface of the microshell cavity to change, and exhibits a frequency drift phenomenon in the transmission spectrum. This infrared radiation sensor based on an optical resonator can directly convert infrared radiation signals into near-infrared signals that can be transmitted in optical fiber communication systems. However, due to the large size of the device, it cannot be integrated into a mature photonic chip; and due to structural limitations, the device has a low absorption rate for infrared radiation, resulting in a low photothermal conversion efficiency of the device, which limits the device's responsiveness. In addition, this infrared sensor device still relies on expensive high-precision spectrometers or narrow-linewidth tunable lasers, which further limits the application value of the device. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a passive coherent long-wave infrared radiation sensing photonic integrated device, thereby solving the technical problems that the existing infrared sensors using optical resonant cavities have low energy utilization efficiency and rely on high-precision spectrometers or narrow-linewidth tunable lasers.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a passive coherent long-wave infrared radiation sensing photonic integrated device, comprising: a substrate layer, an optical isolation layer, an optical transmission layer, and a metal structure layer arranged from bottom to top;

[0006] The substrate layer is a single crystal silicon layer, the optical isolation layer is a silicon oxide layer, and the metal structure layer is a two-dimensional metal grating;

[0007] The optical transmission layer is a lithium niobate layer, including a first coupling grating, an optical beam splitter, a first bus optical transmission waveguide, a second bus optical transmission waveguide, a first coupling waveguide, a first ring resonant cavity, a second coupling waveguide, a second ring resonant cavity, a second coupling grating and a third coupling grating;

[0008] The first coupling grating is connected to the optical input end of the optical beam splitter, and the optical output end of the optical beam splitter is connected to the first bus optical transmission waveguide and the second bus optical transmission waveguide respectively; the first coupling waveguide is connected to the second coupling grating, and the second coupling waveguide is connected to the third coupling grating;

[0009] The first ring resonant cavity is respectively arranged adjacent to and in parallel with the first coupling waveguide and the first bus optical transmission waveguide, and coupling gaps are provided between the first ring resonant cavity and the first coupling waveguide, and between the first ring resonant cavity and the first bus optical transmission waveguide;

[0010] The second ring resonant cavity is adjacent to and parallel to the second coupling waveguide and the second bus optical transmission waveguide, and coupling gaps are provided between the second ring resonant cavity and the second coupling waveguide, and between the second ring resonant cavity and the second bus optical transmission waveguide.

[0011] Preferably, the single crystal silicon of the substrate layer has a 100 crystal orientation and a thickness greater than 50 μm.

[0012] Preferably, the silicon oxide of the optical isolation layer has a thickness of 1 μm to 10 μm and a refractive index of 1.44 to 1.46.

[0013] Preferably, the light transmission layer is an x-cut single crystal lithium niobate thin film with a thickness of 0.5 μm to 0.7 μm.

[0014] Preferably, the heights of the first coupling grating, optical beam splitter, first bus optical transmission waveguide, second bus optical transmission waveguide, first coupling waveguide, first ring resonant cavity, second coupling waveguide, second ring resonant cavity, second coupling grating and third coupling grating are the same, all of which are 0.25 μm to 0.35 μm.

[0015] Preferably, the widths of the first bus optical transmission waveguide, the second bus optical transmission waveguide, the first coupling waveguide, the first ring resonant cavity, the second coupling waveguide, and the second ring resonant cavity are the same, and are all 1 μm to 5 μm;

[0016] The coupling gaps between the first bus optical transmission waveguide and the first ring resonant cavity, the second bus optical transmission waveguide and the second ring resonant cavity, the first ring resonant cavity and the first coupling waveguide, and the second ring resonant cavity and the second coupling waveguide are all the same, which are 0.3 μm to 0.9 μm;

[0017] The first bus optical transmission waveguide and the second bus optical transmission waveguide have the same length, both of which are 300 μm to 500 μm;

[0018] The first coupling waveguide and the second coupling waveguide have the same length, both of which are 300 μm to 900 μm;

[0019] The circumferences of the first ring resonant cavity and the second ring resonant cavity are the same, both ranging from 1000 μm to 1200 μm.

[0020] Preferably, the first coupling grating, the second coupling grating and the third coupling grating have the same structure, and the circumference of the first coupling grating, the second coupling grating and the third coupling grating is 0.8μm to 1μm, the duty cycle is 30% to 70%, and includes 20 to 40 periods.

[0021] Preferably, the optical beam splitter has a length of 20 μm to 30 μm and a width of 4 μm to 6 μm.

[0022] Preferably, the metal structure layer is a two-dimensional grating structure with a thickness of 0.06 μm to 0.12 μm, a period of 4 μm to 6 μm, and 20 to 60 periods.

[0023] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0024] 1. The passive coherent long-wave infrared radiation sensing photonic integrated device proposed in the present invention comprises a substrate layer, an optical isolation layer, an optical transmission layer, and a metal structure layer arranged from bottom to top. Its operating principle is based on the thermo-optic effect. The absorber, consisting of a top metal metasurface structure and an underlying dielectric layer, absorbs long-wave infrared radiation, generating a temperature rise that diffuses into the waveguide region. Under the action of the thermo-optic effect, the refractive index of the lithium niobate material changes, thereby changing the effective refractive index of the mode transmitted within the lithium niobate waveguide. As a result, a frequency drift of the resonant mode can be observed at the download end of the microring resonator.

[0025] 2. The passive coherent long-wave infrared radiation sensing photonic integrated device proposed in the present invention can greatly simplify the manufacturing process because the designed multi-layer absorber structure is highly compatible with the lithium niobate waveguide structure material stack; the absorber proposed in the present invention has the advantages of high efficiency and a wide operating band, which can cover the entire 8-14μm band; the wide waveguide microring resonator proposed in the present invention uses Euler linear bending to suppress the excitation of high-order modes and thus reduce the loss of the transmission fundamental mode, thereby obtaining a microring resonator with a higher quality factor (Q); in addition, the highly integrated design reduces the loss of radiation-induced heating, and a portion of the heat field can be diffused within the lithium niobate material, thereby improving the response rate of the device.

[0026] 3. The passive coherent long-wave infrared radiation sensing photonic integrated device proposed in this invention utilizes a complementary microring resonator. Specifically, the absorber structure is integrated only in the signal ring, while the reference ring does not. This enables coherent sensing of radiation signals. Under irradiation, the differential radiation response between the signal and reference rings causes varying degrees of frequency drift in the download signal. This is then extracted in the RF domain through beat frequency analysis. This approach eliminates the reliance of resonant cavity sensing applications on high-precision spectrometers or high-precision tunable lasers, significantly enhancing the practical value of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional view of the passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention;

[0028] Figure 2 This is a top view of the structure of the passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention;

[0029] Figure 3 is an absorption spectrum of a metal metasurface absorption structure in one embodiment of a passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention;

[0030] Figure 4 This is a side view of the output spectrum of the download output end of one embodiment of the passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention;

[0031] Figure 5 1 is a side view of the radiation response of an embodiment of the passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention;

[0032] Figure 6 It is a side view of the radiation response of another embodiment of the passive coherent long-wave infrared radiation sensing photonic integrated device of the present invention.

[0033] In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein: 1-substrate layer; 2-optical isolation layer; 3-optical transmission layer; 301-second coupling grating; 302-first ring resonant cavity; 303-optical beam splitter; 304-second ring resonant cavity; 305-third coupling grating; 306-first coupling waveguide; 307-first bus optical transmission waveguide; 308-first coupling grating; 309-second bus optical transmission waveguide; 310-second coupling waveguide; 4-metal structure layer. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1 and Figure 2 As shown, the present invention proposes a passive coherent long-wave infrared radiation sensing photonic integrated device, comprising a substrate layer 1, an optical isolation layer 2, an optical transmission layer 3, and a metal structure layer 4 arranged from bottom to top. Specifically, the substrate layer 1 is a single crystal silicon layer, the optical isolation layer 2 is a silicon oxide layer, and the metal structure layer 4 is a two-dimensional metal grating. The optical transmission layer 3 is a lithium niobate layer and includes a first coupling grating 308, an optical beam splitter 303, a first bus optical transmission waveguide 307, a second bus optical transmission waveguide 309, a first coupling waveguide 306, a first ring resonant cavity 302, a second coupling waveguide 310, a second ring resonant cavity 304, a second coupling grating 301, and a third coupling grating 305. The first coupling grating 308 is connected to the optical input end of the optical beam splitter 303, and the optical output end of the optical beam splitter 303 is connected to the first bus optical transmission waveguide 307 and the second bus optical transmission waveguide 309, respectively. The first coupling waveguide 306 is connected to the second coupling grating 301, and the second coupling waveguide 310 is connected to the third coupling grating 305. The first ring resonator 302 is arranged adjacent to and parallel to the first coupling waveguide 306 and the first bus optical transmission waveguide 307, respectively. Coupling gaps are provided between the first ring resonator 302 and the first coupling waveguide 306, and between the first ring resonator 302 and the first bus optical transmission waveguide 307. The second ring resonator 304 is arranged adjacent to and parallel to the second coupling waveguide 310 and the second bus optical transmission waveguide 309, respectively. Coupling gaps are provided between the second ring resonator 304 and the second coupling waveguide 310, and between the second ring resonator 304 and the second bus optical transmission waveguide 309, respectively.

[0036] The technical solution of the present invention is further illustrated below through specific embodiments.

[0037] Example 1

[0038] The passive coherent long-wave infrared radiation sensing photon integrated device provided in Example 1 comprises, from bottom to top, a substrate layer 1, an optical isolation layer 2, an optical transmission layer 3, and a metal structure layer 4; a top view of the passive coherent long-wave infrared radiation sensing photon integrated device provided in this embodiment is shown in FIG. Figure 2 As shown; its optical transmission layer 3 includes a first coupling grating 308, an optical beam splitter 303, a first bus optical transmission waveguide 307, a second bus optical transmission waveguide 309, a first coupling waveguide 306, a first ring resonant cavity 302, a second coupling waveguide 310, a second ring resonant cavity 304, a second coupling grating 301 and a third coupling grating 305.

[0039] To further explain, the first coupling grating 308 is connected to the optical beam splitter 303, the optical beam splitter 303 is connected to the first bus optical transmission waveguide 307 and the second bus transmission waveguide 309; the first coupling waveguide 306 is connected to the second coupling grating 301, and the second coupling waveguide 310 is connected to the third coupling grating 305.

[0040] Further explanation, along the Figure 2 The cross-sectional view along the axis indicated by the dotted line A is as follows: Figure 1 As shown; the first bus optical transmission waveguide 307 is arranged parallel to and adjacent to the first ring resonant cavity 302, with a coupling gap between the two; the second bus optical transmission waveguide 309 is arranged parallel to and adjacent to the second ring resonant cavity 304, with a coupling gap between the two; the first ring resonant cavity 302 is arranged parallel to and adjacent to the first coupling waveguide 306, with a coupling gap between the two; the second ring resonant cavity 304 is arranged parallel to and adjacent to the second coupling waveguide 310, with a coupling gap between the two.

[0041] The present invention uses a commercial lithium niobate on insulator (LNOI) substrate to manufacture a photonic integrated device for passive coherent long-wave infrared radiation sensing. The commercial LNOI substrate is composed of a bottom layer of high-resistance silicon, an intermediate silicon oxide dielectric layer, and a top layer of lithium niobate. The bottom silicon layer serves as a substrate layer 1, the intermediate silicon oxide dielectric layer serves as a light isolation layer 2, and the top layer of lithium niobate is processed using electron beam evaporation (EBE), an electron beam exposure machine (EBL), and an inductively coupled plasma etcher (ICP) to serve as a light transmission layer 3. A metal structure layer 4 is manufactured on the light transmission layer 3 using EBE and EBL.

[0042] In this embodiment, the thickness of the substrate layer 1 is 525 μm, the thickness of the optical isolation layer 2 is 2 μm, the thickness of the optical transmission layer is 0.5 μm, and the thickness of the metal structure layer 4 is 0.1 μm.

[0043] Specifically, electron beam evaporation is used to first deposit a 0.1 μm thick layer of metal Cr on the surface of the LNOI substrate as a hard mask for etching lithium niobate. Then, electron beam exposure and inductively coupled plasma etching are used to etch the top layer of lithium niobate to form a first coupling grating 308, an optical beam splitter 303, a first bus optical transmission waveguide 307, a second bus optical transmission waveguide 309, a first coupling waveguide 306, a first ring resonant cavity 302, a second coupling waveguide 310, a second ring resonant cavity 304, a second coupling grating 301, and a third coupling grating 305.

[0044] In Example 1, the first coupling grating 308, the optical beam splitter 303, the first bus optical transmission waveguide 307, the second bus optical transmission waveguide 309, the first coupling waveguide 306, the first ring resonant cavity 302, the second coupling waveguide 310, the second ring resonant cavity 304, the second coupling grating 301, and the third coupling grating 305 have the same height of 0.28 μm; the first bus optical transmission waveguide 307, the second bus optical transmission waveguide 309, the first coupling waveguide 306, the first ring resonant cavity 302, the second coupling waveguide 310, and the second ring resonant cavity 304 have the same width of 5 μm; the coupling gaps between the first bus optical transmission waveguide 307 and the first ring resonant cavity 302, and between the first ring resonant cavity 302 and the first coupling waveguide 306 are the same, both of which are 0.5 μm; The coupling gaps between the linear optical transmission waveguide 309 and the first ring resonator 304, and between the second ring resonator 304 and the second coupling waveguide 310 are identical, both 0.5 μm. The first bus optical transmission waveguide 307 and the second bus optical transmission waveguide 309 have the same length, 500 μm. The first coupling waveguide 306 and the second coupling waveguide 310 have the same length, 800 μm. The first ring resonator 302 and the second ring resonator 304 have the same circumference, 1200 μm. The first coupling grating 308, the second coupling grating 301, and the third coupling grating 305 have the same structure, with a period of 0.96 μm, a duty cycle of 52%, and 40 periods. The metal structure layer 4 is a two-dimensional grating structure with a thickness of 0.1 μm, a period of 5.4 μm, and a total of 60 periods.

[0045] Further explanation, the passive coherent long-wave infrared radiation sensing photonic integrated device provided by the present invention has a metal structure layer, a lithium niobate layer, and an optical isolation layer forming a metasurface absorber for achieving efficient absorption of infrared radiation. The absorption spectrum thereof is as follows: Figure 3As shown, the peak absorption rate reaches 99.8%, the 3dB bandwidth exceeds 6μm, and can cover the entire 8-14μm infrared window.

[0046] To further illustrate, the photonic integrated device for passive coherent long-wave infrared radiation sensing provided by the present invention has a transmission spectrum test diagram of the output end of the first ring resonant cavity 302 and the second ring resonant cavity 304 as shown in FIG. Figure 4 As shown, in the absence of infrared radiation, the output of the first ring resonant cavity 302 forms a resonance peak at point a, while the output of the second ring resonant cavity 304 at the download end forms a resonance peak at point b; these two outputs realize light beat frequency through the optical mixer, thereby outputting a beat frequency signal in the RF domain, whose frequency is the difference between the two resonance peak frequencies.

[0047] To further illustrate, the present invention uses an existing infrared quantum cascade laser as the infrared radiation light source of the device, with a peak wavelength of 9.1μm. When the light source is irradiated onto the metasurface absorption structure, efficient photothermal conversion will occur, thereby changing the effective refractive index of the mode in the waveguide, thereby causing the drift of the resonance peak; the vertical irradiation power density of the light source is 20 to 100μW / mm 2 .

[0048] Further explanation, the passive coherent long-wave infrared radiation sensor photonic integrated device provided by the present invention has a radiation response test diagram as shown in FIG. Figure 5 As shown, in the absence of infrared radiation, the beat signal peak is located at point c1. When infrared radiation strikes the integrated device, since only the first ring resonator 302 has the metal absorption structure integrated on both sides of its straight waveguide, the absorbed infrared radiation is converted into heat, heating the first ring resonator 302. However, the second ring resonator 304, located further away from the absorption structure, is heated only slightly. Due to the thermo-optical effect, the frequency shift of its mode is positively correlated with the temperature rise. Therefore, the resonance peaks of the two resonators shift differently, resulting in the peak of their output beat signal shifting to point d1. This shift in the beat signal peak reflects the intensity of the incident infrared radiation. Therefore, this photonic integrated device can eliminate the reliance of traditional optical resonator-based infrared radiation sensors on tunable lasers or high-precision spectrometers.

[0049] Example 2

[0050] The structure and operating principle of the passive coherent long-wave infrared radiation sensing photonic integrated device provided in Example 2 are the same as those in Example 1, except for the coupling gaps between the bus waveguide and the ring resonant cavity and the coupling waveguide. In Example 2, the coupling gaps between the first bus optical transmission waveguide 307 and the first ring resonant cavity 302, and between the first ring resonant cavity 302 and the first coupling waveguide 306 are the same, both 0.4 μm; the coupling gaps between the second bus optical transmission waveguide 309 and the first ring resonant cavity 302, and between the second ring resonant cavity 304 and the second coupling waveguide 310 are the same, both 0.4 μm.

[0051] The radiation response of the passive coherent long-wave infrared radiation sensing photonic integrated device provided in Example 2 is as follows: Figure 6 As shown, in the absence of infrared radiation, the peak value of the beat signal output by the download end of the first ring resonant cavity 302 and the second ring resonant cavity 304 is located at point c2; when infrared radiation is incident on the integrated device, since only the metal absorption structure is integrated on both sides of the straight waveguide of the first ring resonant cavity, the absorbed infrared radiation is converted into heat, and the first ring resonant cavity 302 will be heated, while the second ring resonant cavity 304 is far away from the absorption structure and is therefore heated very weakly. Due to the thermo-optical effect, the frequency shift of its mode is positively correlated with the temperature rise, so the resonance peak drift of the two resonant cavities is different, and the peak value of the beat signal output by them is shifted to point d2.

[0052] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A passive coherent long-wave infrared radiation sensing photonic integrated device, characterized in that: include: A substrate layer (1), a light isolation layer (2), a light transmission layer (3) and a metal structure layer (4) are arranged from bottom to top; The substrate layer (1) is a single crystal silicon layer, the light isolation layer (2) is a silicon oxide layer, and the metal structure layer (4) is a two-dimensional metal grating; The optical transmission layer (3) is a lithium niobate layer, comprising a first coupling grating (308), an optical beam splitter (303), a first bus optical transmission waveguide (307), a second bus optical transmission waveguide (309), a first coupling waveguide (306), a first ring resonant cavity (302), a second coupling waveguide (310), a second ring resonant cavity (304), a second coupling grating (301), and a third coupling grating (305); The first coupling grating (308) is connected to the optical input end of the optical beam splitter (303), and the optical output end of the optical beam splitter (303) is respectively connected to the first bus optical transmission waveguide (307) and the second bus optical transmission waveguide (309); the first coupling waveguide (306) is connected to the second coupling grating (301), and the second coupling waveguide (310) is connected to the third coupling grating (305); The first ring-shaped resonant cavity (302) is respectively arranged adjacent to and in parallel with the first coupling waveguide (306) and the first bus optical transmission waveguide (307), and coupling gaps are provided between the first ring-shaped resonant cavity (302) and the first coupling waveguide (306), and between the first ring-shaped resonant cavity (302) and the first bus optical transmission waveguide (307); The second ring-type resonant cavity (304) is respectively arranged adjacent to and in parallel with the second coupling waveguide (310) and the second bus optical transmission waveguide (309), and coupling gaps are provided between the second ring-type resonant cavity (304) and the second coupling waveguide (310), and between the second ring-type resonant cavity (304) and the second bus optical transmission waveguide (309).

2. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The single crystal silicon of the substrate layer (1) has a 100 crystal orientation and a thickness greater than 50 μm.

3. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The silicon oxide thickness of the optical isolation layer (2) is 1 μm to 10 μm, and the refractive index is 1.44 to 1.

46.

4. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The light transmission layer (3) is an x-cut single crystal lithium niobate film with a thickness of 0.5 μm to 0.7 μm.

5. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The first coupling grating (308), the optical beam splitter (303), the first bus optical transmission waveguide (307), the second bus optical transmission waveguide (309), the first coupling waveguide (306), the first ring-type resonant cavity (302), the second coupling waveguide (310), the second ring-type resonant cavity (304), the second coupling grating (301), and the third coupling grating (305) have the same height, which is 0.25 μm to 0.35 μm.

6. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The first bus optical transmission waveguide (307), the second bus optical transmission waveguide (309), the first coupling waveguide (306), the first ring resonant cavity (302), the second coupling waveguide (310), and the second ring resonant cavity (304) have the same width, which is 1 μm to 5 μm. The coupling gaps between the first bus optical transmission waveguide (307) and the first ring-type resonant cavity (302), the second bus optical transmission waveguide (309) and the second ring-type resonant cavity (304), the first ring-type resonant cavity (302) and the first coupling waveguide (306), and the second ring-type resonant cavity (304) and the second coupling waveguide (310) are the same, all ranging from 0.3 μm to 0.9 μm. The first bus optical transmission waveguide (307) and the second bus optical transmission waveguide (309) have the same length, both of which are 300 μm to 500 μm; The first coupling waveguide (306) and the second coupling waveguide (310) have the same length, both ranging from 300 μm to 900 μm; The first ring-shaped resonant cavity (302) and the second ring-shaped resonant cavity (304) have the same circumference, both ranging from 1000 μm to 1200 μm.

7. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The first coupling grating (308), the second coupling grating (301) and the third coupling grating (305) have the same structure, and the perimeter of the first coupling grating (308), the second coupling grating (301) and the third coupling grating (305) is 0.8 μm to 1 μm, the duty cycle is 30% to 70%, and includes 20 to 40 periods.

8. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The optical beam splitter (303) has a length of 20 μm to 30 μm and a width of 4 μm to 6 μm.

9. The passive coherent long-wave infrared radiation sensing photonic integrated device according to claim 1, characterized in that: The metal structure layer (4) is a two-dimensional grating structure with a thickness of 0.06 μm to 0.12 μm and a period of 4 μm to 6 μm, including 20 to 60 periods.

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