Miniaturized interrogator and distributed fiber optic sensing system

Abstract

The application relates to the technical field of optical fiber sensing, and discloses a miniaturized interrogator and a distributed optical fiber sensing system, which comprise a laser chip and an interrogator chip; the interrogator chip comprises a first optical port, a second optical port, a third optical port, a fourth optical port, a first polarization filter, a second polarization filter module, a selection switch, a beam splitter, a modulator, a polarization rotation beam splitter, a 1*2 multimode interference coupler, a first 2*4 multimode interference coupler, a second 2*4 multimode interference coupler, a first balanced detector, a second balanced detector, a third balanced detector and a fourth balanced detector. The integrated degree can be effectively improved, the system cost, volume and weight are reduced, the complex device coupling process is avoided, the production efficiency and consistency are improved, and the sensing performance is kept high.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more particularly to a miniaturized interrogator and a distributed fiber optic sensing system. Background Technology

[0002] Distributed fiber optic sensing technology utilizes optical fiber as the sensing medium, detecting the scattering effect of light during transmission through the fiber to achieve distributed monitoring of environmental parameters such as temperature, strain, and vibration. This technology boasts significant advantages, including long monitoring distances (up to tens of kilometers), high spatial resolution, and strong resistance to electromagnetic interference. It has been successfully applied in important fields such as energy pipeline integrity monitoring, seismic wave detection, border security protection, transportation infrastructure health monitoring, and marine environmental observation. A typical distributed fiber optic sensing system consists of sensing optical fibers, an interrogator, and a data processing unit. However, current mainstream distributed fiber optic sensing systems still face significant limitations in design and manufacturing: the interrogator usually requires multiple discrete optical functional modules, including key components such as narrow-linewidth laser sources, modulators, optical couplers, and balanced photodetectors. This discrete architecture not only leads to a large overall system size and significantly increased weight but also results in high system costs, severely restricting the widespread application of this technology in complex industrial environments and scenarios requiring large-scale deployment. Moreover, the various optical functional modules need to be interconnected through optical fibers. This complex coupling connection process not only increases the difficulty of system assembly but also reduces production consistency, becoming one of the bottlenecks restricting the industrial mass production of distributed optical fiber sensors.

[0003] In recent years, with the development of photonic integration technology, integrating functional devices such as lasers, modulators, and detectors onto a single chip has become an important approach to solving the aforementioned problems. Photonic integrated interrogators offer advantages such as miniaturization, low cost, and high stability, and are expected to accelerate the engineering and industrialization of distributed fiber optic sensing systems. However, most current integration solutions are still limited to silicon-based platforms or single-material systems, making it difficult to simultaneously meet multiple technical requirements such as narrow-linewidth light sources and low-loss waveguides. For example, while the SOI platform can achieve low-loss and compact waveguides, integrating its light source remains a major challenge; and although the InP platform can monolithically integrate all optical components, its waveguide loss and integration density are lower than the SOI platform, and its manufacturing process is relatively immature, resulting in high cost and low yield. Therefore, the integration of distributed fiber optic sensing systems needs to actively utilize the advantages of various material platforms. Summary of the Invention

[0004] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a miniaturized interrogator and a distributed fiber optic sensing system that can effectively improve integration, reduce system cost, size and weight, avoid complex device coupling processes, improve production efficiency and consistency, and maintain high sensing performance.

[0005] In a first aspect, embodiments of the present invention provide a miniaturized interrogator, including a laser chip and an interrogator chip, wherein the laser chip generates a narrow linewidth light source; and the interrogator chip includes an optical port module, a polarization filter module, a selection switch, a beam splitter, a modulator, a polarization rotation beam splitter, a multimode interference coupler module, and a balanced detector module. in: The optical port module includes a first optical port, a second optical port, a third optical port, and a fourth optical port; the first optical port is used to connect to the laser chip, the second optical port is used to connect to an external laser module, the third optical port is used to output probe light, and the fourth optical port is used to input scattered light. The polarization filter module includes a first polarization filter and a second polarization filter; the input terminal of the first polarization filter is connected to the first optical port, the input terminal of the second polarization filter is connected to the second optical port, the output terminals of the first polarization filter and the second polarization filter are respectively connected to the two input terminals of the selection switch, the output terminal of the selection switch is connected to the input terminal of the beam splitter, one output terminal of the beam splitter is connected to the input terminal of the modulator, and the output terminal of the modulator is connected to the third optical port. The multimode interference coupler module includes a 1×2 multimode interference coupler, a first 2×4 multimode interference coupler, and a second 2×4 multimode interference coupler; the other output terminal of the beam splitter is connected to the input terminal of the 1×2 multimode interference coupler, the fourth optical port is connected to the input terminal of the polarization rotation beam splitter, the two output terminals of the 1×2 multimode interference coupler are respectively connected to one input terminal of the first 2×4 multimode interference coupler and one input terminal of the second 2×4 multimode interference coupler, and the two output terminals of the polarization rotation beam splitter are respectively connected to the other input terminal of the first 2×4 multimode interference coupler and the other input terminal of the second 2×4 multimode interference coupler; The balanced detector module includes a first balanced detector, a second balanced detector, a third balanced detector, and a fourth balanced detector; the two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the first balanced detector, and the other two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the second balanced detector; the two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the third balanced detector, and the other two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the fourth balanced detector; The first optical port is coupled to the laser chip via spatial light. The second optical port, the third optical port, and the fourth optical port are fixedly coupled to the fiber array.

[0006] According to some embodiments of the present invention, the miniaturized interrogator is provided in which the laser chip is an InP distributed feedback laser chip with an external cavity, used to provide a light source with a linewidth of less than or equal to 3kHz and a wavelength including 1550nm.

[0007] According to some embodiments of the present invention, the miniaturized interrogator is provided in which the first optical port, the second optical port, the third optical port and the fourth optical port are implemented using an edge coupler.

[0008] According to some embodiments of the present invention, the miniaturized interrogator is provided in which the first polarization filter and the second polarization filter are implemented using a polarization beam splitter to filter out the TM component of the input light so that the output light is pure TE mode light.

[0009] According to some embodiments of the present invention, the miniaturized interrogator has a selection switch that is a 2×2 Mach-Zehnder interferometer, used to select the input light of the laser chip or the input light of the external laser module as the input light source of the beam splitter.

[0010] According to some embodiments of the present invention, the miniaturized interrogator is a Mach-Zehnder intensity modulator with a bandwidth greater than 1.5 GHz.

[0011] According to some embodiments of the present invention, in a miniaturized interrogator, the first 2×4 multimode interference coupler and the second 2×4 multimode interference coupler serve as 90° mixers to mix the intrinsic light output from the 1×2 multimode interference coupler with the scattered light output from the polarization rotating beam splitter to obtain a mixed beam.

[0012] According to some embodiments of the present invention, a miniaturized interrogator chip and an interrogator chip are coupled via a spatial optical coupling method based on micro-optical components. The micro-optical components include an isolator and two microlenses located on the front and rear sides of the isolator. The isolator does not perform polarization rotation on the input light provided by the laser chip.

[0013] According to some embodiments of the present invention, the miniaturized interrogator chip is fabricated using a 220nm SOI process, the fiber array includes a single-mode fiber and a polarization-maintaining fiber, the third optical port and the fourth optical port correspond to the single-mode fiber, and the second optical port corresponds to the polarization-maintaining fiber.

[0014] In a second aspect, embodiments of the present invention provide a distributed optical fiber sensing system, including discrete optical components, a laser controller, a signal generation module, a signal acquisition and processing module, and a miniaturized interrogator as described in the first aspect embodiment above, wherein: The discrete optical components include an optical amplifier, a circulator, and a sensing fiber; the fiber array is connected to the circulator and the optical amplifier respectively; the sensing fiber is connected to the circulator. The laser controller is connected to the laser chip and is used to drive the laser chip and control the temperature of the laser chip. The signal generation module includes a multi-channel low-speed signal generator, a high-speed signal generator, and an electrical amplifier; the output terminal of the high-speed signal generator is connected to the input terminal of the electrical amplifier, and the output terminal of the electrical amplifier is connected to the radio frequency input port of the modulator; the multi-channel low-speed signal generator is a voltage source with high voltage output capability, and the output terminal of the multi-channel low-speed signal generator is connected to the selection switch, the beam splitter, the tuning control signal input port of the modulator, and the bias input port of the modulator; The signal acquisition and processing module includes a transimpedance amplifier, an analog-to-digital converter, and a data processing module connected in sequence; the output terminals of the first balanced detector, the second balanced detector, the third balanced detector, and the fourth balanced detector are all connected to the input terminal of the transimpedance amplifier, and the signal acquisition and processing module is used to amplify the signal and convert the current signal into a voltage signal.

[0015] The miniaturized interrogator and distributed fiber optic sensing system provided by embodiments of the present invention have at least the following beneficial effects: By integrating the core optical components of the interrogator onto a silicon-based photonic chip using photonic integration technology, and achieving integration of the laser chip and the silicon photonic chip through a hybrid integration method, the problems of large size and unstable connection of external laser modules are avoided, thereby significantly improving the system's compactness and reliability; A passive solution is adopted in the polarization control and 90° mixing stages, eliminating the need for complex electronic control algorithms for polarization controllers and 90° mixers, reducing peripheral circuits and active control modules, further improving the system's stability and ease of use; The on-chip modulator can meet system requirements through flexible device structure design. For example, appropriately reducing the bandwidth can effectively improve modulation efficiency, especially in analytical applications where a modulator with a bandwidth of less than 5 GHz can meet the requirements, thereby significantly reducing device design difficulty and improving practicality.

[0016] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description and the drawings. Attached Figure Description

[0017] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments; Figure 1 This is a schematic diagram of the structure of a miniaturized interrogator provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the distributed optical fiber sensing system provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the IQ imbalance test system provided in an embodiment of the present invention; Figure 4 This is a comparison chart of the sideband suppression ratio before and after IQ imbalance compensation in the IQ imbalance test system provided in this embodiment of the invention; Figure 5 This is a waterfall diagram of the system provided in this embodiment of the invention near the vibration region at the end of the optical fiber; Figure 6 This is a statistical graph showing the strain resolution of each sensing channel at the end of the optical fiber within 1 km of the system provided in this embodiment of the invention. Detailed Implementation

[0019] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the number itself, while "above," "below," "within," etc. are understood to include the number itself. "At least one" refers to one or more, and "at least one of the following" and similar expressions refer to any combination of these items, including any combination of single or multiple items. If "first," "second," etc., are used in the description, they are only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0021] It should be noted that the terms "setting," "installing," and "connecting" in the embodiments of this invention should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of the above terms in the embodiments of this invention in conjunction with the specific content of the technical solution. For example, the term "connection" can be a mechanical connection, an electrical connection, or a connection that allows for mutual communication; it can be a direct connection or an indirect connection through an intermediate medium.

[0022] It should be noted that the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Distributed fiber optic sensing technology utilizes optical fiber as the sensing medium, detecting the scattering effect of light during transmission through the fiber to achieve distributed monitoring of environmental parameters such as temperature, strain, and vibration. This technology boasts significant advantages, including long monitoring distances (up to tens of kilometers), high spatial resolution, and strong resistance to electromagnetic interference. It has been successfully applied in important fields such as energy pipeline integrity monitoring, seismic wave detection, border security protection, transportation infrastructure health monitoring, and marine environmental observation. A typical distributed fiber optic sensing system consists of sensing optical fibers, an interrogator, and a data processing unit. However, current mainstream distributed fiber optic sensing systems still face significant limitations in design and manufacturing: the interrogator usually requires multiple discrete optical functional modules, including key components such as narrow-linewidth laser sources, modulators, optical couplers, and balanced photodetectors. This discrete architecture not only leads to a large overall system size and significantly increased weight but also results in high system costs, severely restricting the widespread application of this technology in complex industrial environments and scenarios requiring large-scale deployment. Moreover, the various optical functional modules need to be interconnected through optical fibers. This complex coupling connection process not only increases the difficulty of system assembly but also reduces production consistency, becoming one of the bottlenecks restricting the industrial mass production of distributed optical fiber sensors.

[0024] In recent years, with the development of photonic integration technology, integrating functional devices such as lasers, modulators, and detectors onto a single chip has become an important approach to solving the aforementioned problems. Photonic integrated interrogators offer advantages such as miniaturization, low cost, and high stability, and are expected to accelerate the engineering and industrialization of distributed fiber optic sensing systems. However, most current integration solutions are still limited to silicon-based platforms or single-material systems, making it difficult to simultaneously meet multiple technical requirements such as narrow-linewidth light sources and low-loss waveguides. For example, while the SOI platform can achieve low-loss and compact waveguides, integrating its light source remains a major challenge; and although the InP platform can monolithically integrate all optical components, its waveguide loss and integration density are lower than the SOI platform, and its manufacturing process is relatively immature, resulting in high cost and low yield. Therefore, the integration of distributed fiber optic sensing systems needs to actively utilize the advantages of various material platforms.

[0025] Based on this, embodiments of the present invention provide a miniaturized interrogator and a distributed fiber optic sensing system, realizing the integration of the core components of the distributed fiber optic sensing system, especially the hybrid integration of the laser chip and the interrogator chip; it can effectively improve the integration degree, reduce system cost, size and weight, avoid complex device coupling processes, improve production efficiency and consistency, and maintain high sensing performance.

[0026] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0027] Reference Figure 1 A first aspect of the present invention provides a miniaturized interrogator, comprising a laser chip and an interrogator chip, wherein the laser chip generates a narrow linewidth light source; the interrogator chip includes an optical port module, a polarization filter module, a selection switch, a beam splitter, a modulator, a polarization rotation beam splitter, a multimode interference coupler module, and a balanced detector module; wherein: The optical port module includes a first optical port, a second optical port, a third optical port, and a fourth optical port, which correspond to... Figure 1 The optical ports shown are 1, 2, 3, and 4; the first optical port is used to connect to the laser chip, the second optical port is used to connect to the external laser module, the third optical port is used to output the probe light, and the fourth optical port is used to input the scattered light. The polarization filter module includes a first polarization filter and a second polarization filter; the input terminal of the first polarization filter is connected to the first optical port, the input terminal of the second polarization filter is connected to the second optical port, the output terminals of the first polarization filter and the second polarization filter are respectively connected to the two input terminals of a selection switch, the output terminal of the selection switch is connected to the input terminal of a beam splitter, one output terminal of the beam splitter is connected to the input terminal of a modulator, and the output terminal of the modulator is connected to the third optical port. The multimode interference coupler module includes a 1×2 multimode interference coupler, a first 2×4 multimode interference coupler, and a second 2×4 multimode interference coupler; the other output of the beam splitter is connected to the input of the 1×2 multimode interference coupler, the fourth optical port is connected to the input of the polarization rotation beam splitter, the two outputs of the 1×2 multimode interference coupler are respectively connected to one input of the first 2×4 multimode interference coupler and one input of the second 2×4 multimode interference coupler, and the two outputs of the polarization rotation beam splitter are respectively connected to the other input of the first 2×4 multimode interference coupler and the other input of the second 2×4 multimode interference coupler; The balanced detector module includes a first balanced detector, a second balanced detector, a third balanced detector, and a fourth balanced detector; the two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the first balanced detector, and the other two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the second balanced detector; the two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the third balanced detector, and the other two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the fourth balanced detector; The first optical port is coupled to the laser chip via spatial optical coupling; The second, third, and fourth optical ports are fixedly coupled to the fiber array.

[0028] In some embodiments of the miniaturized interrogator provided by the present invention, the laser chip is an InP distributed feedback laser chip with an external cavity, used to provide a light source with a linewidth less than or equal to 3kHz and a wavelength including 1550nm. Specifically, in some embodiments, the interrogator chip is fabricated based on a 220nm SOI platform and has a size of 4.95mm × 2.80mm.

[0029] In the miniaturized interrogator provided in some embodiments of the present invention, the first optical port, the second optical port, the third optical port and the fourth optical port are implemented using edge couplers. Specifically, a cantilever beam edge coupler is used, and a special process is used to etch away the silicon at the bottom to reduce the loss caused by the light field leaking to the silicon substrate. The edge coupler coupled to the laser and the edge coupler coupled to the fiber array are arranged on opposite sides of the interrogator chip to provide sufficient space margin for the co-packaging of the laser and the packaging of the fiber array. The edge coupler provides a polarization-insensitive, low-loss coupling port.

[0030] In the miniaturized interrogator provided in some embodiments of the present invention, the first polarization filter and the second polarization filter are implemented using a polarization beam splitter to filter out the TM component of the input light so that the output light is pure TE mode light.

[0031] Specifically, in this embodiment, the light input from optical port 1 and optical port 2 first passes through a polarization filter. The polarization filter is implemented using a polarization beamsplitter, which in this embodiment is based on an asymmetric directional coupler. This polarization beamsplitter further filters the incident light, removing the TM component and obtaining a pure TE component. The optical transmission link employs a global polarization-maintaining and passive design, avoiding reliance on complex real-time polarization control algorithms, thereby simplifying the peripheral circuitry and improving the system's practicality. Simultaneously, the polarization beamsplitter ensures that the incident light within the chip maintains a pure TE polarization state.

[0032] In some embodiments of the present invention, the miniaturized interrogator is provided with a selection switch of 2×2 Mach-Zehnder interferometer, which is used to select the input light of the laser chip or the input light of the external laser module as the input light source of the beam splitter.

[0033] Specifically, the light output from the polarization filter enters a selection switch to select the light source for subsequent links. The selection switch is a 2×2 Mach-Zehnder interferometer, which consists of two 2×2 multimode interference couplers connected together. A thermo-optical phase shifter is placed on one arm to support the adjustment of the phase difference between the two arms, thereby supporting the selection of the light source. In this embodiment, the output of the laser chip is selected as the light source for subsequent links by a voltage signal applied to the thermo-optical phase shifter.

[0034] The output light from the selector switch is split into two beams by the beam splitter. One beam enters the transmitting branch as the probe light, and the other enters the receiving branch as the local light. The beam splitter is an adjustable beam splitter, which is a 1×2 Mach-Zehnder interferometer, consisting of a 1×2 multimode interference coupler and a 2×2 multimode interference coupler connected together. A thermo-optical phase shifter is placed on the arm to support the adjustment of the phase difference between the two arms, thereby supporting the continuous adjustment of the splitting ratio.

[0035] In some embodiments of the present invention, the miniaturized interrogator is a Mach-Zehnder intensity modulator with a bandwidth greater than 1.5 GHz.

[0036] Specifically, in the transmit branch, the modulator is a Mach-Zehnder intensity modulator. This modulator utilizes carrier dispersion and traveling-wave electrodes, employing a single-ended push-pull structure to simplify the input of the electrical signal. The modulator is configured at the null point for carrier-suppressed double-sideband modulation, using a small reverse-bias signal for bias to enhance modulation efficiency at the cost of a slight reduction in bandwidth. The probe light after passing through the modulator is a frequency-modulated pulse signal, which is output to the interrogator chip via optical port 3.

[0037] In addition, the backscattered light enters the interrogator chip through optical port 4. The backscattered light contains TE light and TM light with proportions that change over time. After passing through the polarization rotating beam splitter, it is split into two beams according to polarization. The TM light is converted into TE light, and the TE light remains as TE light.

[0038] In the miniaturized interrogator provided in some embodiments of the present invention, the first 2×4 multimode interference coupler and the second 2×4 multimode interference coupler are used as 90° mixers to mix the intrinsic light output from the 1×2 multimode interference coupler with the scattered light output from the polarization rotating beam splitter to obtain a mixed beam; and an IQ imbalance compensation algorithm is used at the data processing end to improve the performance of the 2×4 multimode interference coupler.

[0039] Specifically, the processed scattered light and local light are mixed together in a 2×4 multimode interference coupler. This 2×4 multimode interference coupler is a passive 90° mixer, requiring no electrical signal and exhibiting a degree of resistance to external disturbances. Compared to an active 90° mixer, the passive design eliminates the need for complex electrical control, further simplifying the system structure and significantly improving its practicality and stability.

[0040] The output signal of the 90° mixer is received by four balanced detectors; each balanced detector consists of two identical germanium photodetectors connected by a metal layer, with the N-doped port of one germanium photodetector connected to the P-doped port of the other germanium photodetector.

[0041] In some embodiments of the present invention, the laser chip and the interrogator chip are coupled by spatial light based on micro-optical components. The micro-optical components include an isolator and two microlenses located on the front and rear sides of the isolator. The isolator does not perform polarization rotation on the input light provided by the laser chip.

[0042] Specifically, the microlens performs effective mode field matching, the isolator prevents reflection and does not alter the polarization; the laser chip outputs TE mode light, which is coupled into the interrogator chip in TE mode through the microlens and isolator.

[0043] In some embodiments of the present invention, the miniaturized interrogator chip is fabricated using a 220nm SOI process. Optical ports 2, 3, and 4 of the interrogator chip are coupled and fixed to the fiber array. The fixing is achieved by UV curing and by using a suitable matching liquid to achieve maximum coupling efficiency. The fiber array includes single-mode fiber and polarization-maintaining fiber. The third and fourth optical ports correspond to single-mode fiber, and the second optical port corresponds to polarization-maintaining fiber.

[0044] It should be noted that, in addition to edge couplers, optical ports can also be implemented using grating couplers, fiber taper couplers, free-space couplers, and other methods. These methods have their own suitability for different scenarios such as silicon photonics chip testing and packaging. Grating couplers are a common optical port implementation method in silicon photonics chips. They achieve vertical coupling of light by utilizing the diffraction effect of gratings, meaning the optical fiber is typically located above the chip to handle optical signal input and output. They are compatible with automated large-scale testing at the wafer and chip levels, can be arrayed on the chip, and have strong compatibility with CMOS processes, reducing the difficulty of large-scale integration. However, their shortcomings are also significant, including narrow bandwidth, relatively high coupling loss, and the coupling effect being affected by polarization state, making packaging more challenging.

[0045] Fiber taper coupling achieves optical coupling through a specially designed fiber taper. During fabrication, the fiber is heated with a flame and simultaneously stretched, reducing its diameter from 125 micrometers to approximately 1 micrometer. This narrow fiber taper allows the evanescent tail of light to be brought close to devices under test, such as rings and photonic crystal resonators, thereby completing optical signal transmission. It is suitable for wafer-scale automated testing and can achieve high-density coupling, but it has stringent requirements for the device packaging environment. It requires silicon photonic devices to use air as a cladding, while conventional silicon photonics manufacturing processes often use oxides to encapsulate silicon, limiting its application scenarios.

[0046] Free-space coupling relies on optical components such as lenses and mirrors to transmit light signals between optical fibers and chips in free space, and is often used in special scenarios. These include low-temperature experiments where samples are placed in a vacuum, biosensors that need to operate in solvents, and situations where multiple light outputs need to be measured simultaneously using an infrared camera. In practical applications, light signals can be scanned using mirrors on a galvanometer, or images of the chip's emitted light can be captured by a camera. However, using a camera limits the imaging scanning rate, and the overall system is susceptible to interference from external factors such as dust and vibration.

[0047] The glass waveguide evanescent wave coupling method first forms a surface optical waveguide in the glass through ion exchange, and then uses the evanescent wave coupling principle to achieve optical field transfer between the glass waveguide and the silicon nitride chip waveguide. One end of the glass chip is coupled to the optical chip, and the other end is fabricated into a fan-out waveguide adapted to the fiber spacing and connected to the optical fiber. It can also be combined with mechanical structures and connectors to achieve pluggable functionality. Its coupling stability is relatively good, but the typical coupling loss at a wavelength of 1310nm is about 1.5dB, and the overall loss is relatively high.

[0048] The microprism + concave mirror combination coupling method modifies the beam propagation direction by mounting prefabricated microprisms on a silicon photonic wafer, and then uses a concave mirror in the Photonic-Plug to expand the beam, reducing the coupling alignment accuracy requirements. The beam is then reflected multiple times before finally entering the fiber array. This method transforms the coupling alignment problem of optical ports into a wafer-level processing problem, adapting to the requirements of pluggable optical ports. However, it requires high processing and assembly accuracy for the microprisms and concave mirrors.

[0049] Lens array-assisted coupling involves several methods. Some manufacturers glue lenses onto the fiber array to form MOLA connectors, which expand the beam and couple it to the optical structure on the chip's V-groove, significantly reducing alignment tolerance. Other manufacturers glue lenses directly to the end face of the optical chip and the fiber array. This method can improve the alignment tolerance of the optical port in the X / Y direction to ±6µm and keep insertion loss at a low level. However, the lens bonding process and packaging sealing design are more difficult, requiring additional sealing caps and other structures to prevent dust from affecting the coupling effect.

[0050] Understandably, the core requirement of polarization filters is to "allow only specific polarization states to pass through while suppressing orthogonal polarization states." Besides polarization beam splitters (PBS, essentially a combination of "splitting + filtering"), more common implementations are specifically designed for "single-path polarization screening," encompassing different principles such as material absorption, crystal birefringence, micro / nano structures, and electrical modulation. These are adaptable to various scenarios ranging from consumer electronics to optical communication and chip integration. The core principle of an absorption-type polarization filter is to use materials with "polarization-selective absorption," which have almost no absorption for the target polarization state (such as horizontal H) and allow it to pass through smoothly, while strongly absorbing (extincting) orthogonal polarization states (such as vertical V), thus directly achieving polarization selection. Its advantages are simple structure, low cost, and small size; its limitations are a moderate extinction ratio (usually 100:1 to 1000:1), and some materials (such as organic dyes) have poor high-temperature resistance, making them unsuitable for high-power laser scenarios.

[0051] The core principle of a birefringent crystal polarization filter is to utilize the "birefringence effect" of a crystal—natural light, upon incident, decomposes into o-ray (ordinary ray) and e-ray (extraordinary ray), which have different refractive indices. Through crystal cutting, phase matching, or combination structures, one of the polarization states is deflected out of the light path (or canceled out by interference), retaining only the target polarization state. Its advantages are high extinction ratio, high power tolerance, and strong stability; its limitations are higher cost, larger size, sensitivity to incident angle, and unsuitability for compact integration scenarios.

[0052] The core principle of micro / nano structure polarization filters is to utilize the "structure polarization dependence"—light of the target polarization state can pass smoothly through the structure using a periodic structure at the micro / nano scale (period ≤ wavelength of light), while orthogonal polarization states are suppressed due to scattering, reflection, or mode cutoff. This allows for integration onto chips, making them compatible with CMOS processes. Their advantages include extremely high integration density, compact size, and compatibility with semiconductor processes; limitations include high processing precision requirements (requiring nanoscale photolithography) and relatively narrow bandwidth in some structures.

[0053] The core principle of electrically controlled polarization filters is to dynamically switch the "allowed polarization state" by controlling the polarization response of the material through an electric field (such as the orientation of liquid crystal molecules or the birefringence of ferroelectric materials), thus achieving "switchable polarization filtering" rather than fixedly selecting a single polarization. Its advantages include dynamic switching of polarization states and high flexibility; its limitations include complex structure, high cost, and some types (such as liquid crystals) are not suitable for high-power applications.

[0054] The core principle of thin-film interferometric polarization filters is to deposit multiple dielectric thin films on a substrate. By utilizing the difference in reflection / transmission interference between different polarization states in the thin film, the target polarization state is almost fully transmitted, while orthogonal polarization states are suppressed due to destructive interference, thus meeting the requirements for high bandwidth and low loss. Its advantages are wide bandwidth, low loss, and strong stability; its limitations are complex thin-film deposition processes, high cost, and the need for special design to withstand temperature changes.

[0055] It is understandable that the beam splitting ratio of an tunable beamsplitter can be adjusted in real time through electrical, optical, or mechanical means. Its core principle is to adjust the ratio of reflected to transmitted light by changing the physical properties of the device (such as refractive index, phase, and coupling length). Typical types include electro-optic tunable beamsplitters (such as those based on lithium niobate or silicon-based electro-optic effects), thermo-optic tunable beamsplitters (commonly used in silicon-based chips), and mechanically tunable beamsplitters (such as rotating thin-film beamsplitters). Among these, electro-optic tunable beamsplitters have a fast response speed (nanosecond level) and are suitable for optical communication and optical switching; thermo-optic tunable beamsplitters change the refractive index of the waveguide by heating, and have low cost and moderate response speed (millisecond level); mechanically tunable beamsplitters have a simple structure, are suitable for experimental scenarios, but have a slow response speed.

[0056] Understandably, the core of a modulator is "loading an electrical / optical signal onto an optical carrier." Classified by the modulated object (the physical parameters of light), besides the most commonly used intensity modulator, there are core types such as phase modulators, frequency modulators, polarization modulators, and wavelength modulators. Furthermore, there are composite modulators that combine multiple parameters, adaptable to different scenarios such as optical communication, lidar, and spectral analysis. Among these: The core principle of a phase modulator (PM) is to change the refractive index of the modulation medium using an electrical signal (or optical signal) (e.g., through electro-optic, thermo-optic, or acousto-optic effects), causing the phase of the optical carrier to change with the modulation signal (the amplitude and intensity of the light remain unchanged, only the phase is modulated). For example, in an electro-optic phase modulator based on lithium niobate (LN), the refractive index of LN changes after a voltage is applied, and the phase delay of light propagating in the medium changes accordingly. Silicon-based phase modulators achieve phase modulation through thermo-optic effects (heating changes the refractive index of the silicon waveguide) or carrier injection effects. Its advantages include wide modulation bandwidth (up to tens of GHz), low insertion loss, and good linearity; its limitations are that it cannot be directly received by a detector (the signal needs to be restored through interferometric demodulation), and the system complexity is slightly higher.

[0057] The core principle of a frequency modulator (FM) is to linearly change the frequency of an optical carrier with respect to a modulating signal; essentially, it's "differential phase modulation" (the rate of change of phase over time is the frequency). Implementation methods include electro-optic frequency modulation (EMM), acousto-optic frequency modulation (AFM), and direct frequency modulation (FM). EFM utilizes the electro-optic effect to change the refractive index of a medium, indirectly altering the propagation frequency of light. AFM involves ultrasonic waves acting on an acousto-optic crystal, causing a periodic change in the crystal's refractive index, resulting in a Doppler frequency shift as light passes through, with the frequency changing according to the ultrasonic signal. Direct frequency modulation directly changes the oscillation frequency of a laser by controlling its injection current (this is "integrated light source modulation," requiring no additional independent modulator). The advantages of frequency modulators are strong anti-interference capabilities and high measurement accuracy (suitable for radar / sensing); the limitations are a relatively narrow modulation bandwidth (acousto-optic MFM is typically <1 GHz) and complex demodulation circuitry.

[0058] The core principle of a polarization modulator (POLM) is to control the birefringence of the modulation medium through electrical signals, thereby changing the polarization state of the optical carrier (e.g., switching from linear polarization to elliptic polarization or orthogonal linear polarization), so that the polarization state changes with the modulation signal. Common implementations include lithium niobate polarization modulators (using electro-optic effects to control birefringence), liquid crystal polarization modulators (using electric fields to control the orientation of liquid crystal molecules, changing the polarization state), and silicon-based polarization modulators (using carrier injection to control waveguide birefringence). Its advantage is that it can be combined with polarization multiplexing technology to improve communication capacity; its limitation is that it is sensitive to polarization stability and requires the use of a polarization controller.

[0059] The core principle of a wavelength modulator (WM) is to change the wavelength (color) of an optical carrier according to the modulation signal. Essentially, it's a "wavelength representation of frequency modulation" (wavelength is inversely proportional to frequency). Implementation methods include indirect modulation and direct modulation. Indirect modulation changes the refractive index of the modulation medium through electro-optic / thermo-optic effects, shifting the resonant wavelength of the light (e.g., wavelength modulators based on microring resonators). Direct modulation controls the injection current or temperature of the laser, directly changing the output wavelength of the laser (e.g., integrated modulation of distributed feedback DFB lasers). The advantages of wavelength modulators are adaptability to multi-channel transmission and high detection sensitivity; limitations include a limited wavelength tuning range (typically in the nanometer range) and relatively slow response speeds for some types (thermo-optic modulation in the millisecond range).

[0060] The core principle of a pulse modulator is to control the on / off state of light using electrical signals, converting continuous light into pulsed light. Essentially, it's a "special form of intensity modulation" (focusing only on the binary state of "light / no light"), but emphasizing the timing and width control of the pulses. Common implementations include electro-optic switches (fast on / off, nanosecond response), acousto-optic switches (medium-speed on / off, microsecond level), and mechanical shutters (low-speed on / off, millisecond level). Its advantages are simple structure and clear modulation logic; its limitations are that it is only suitable for pulsed signal scenarios and has weak continuous modulation capabilities.

[0061] Reference Figure 2 A second aspect of the present invention provides a distributed fiber optic sensing system, including discrete optical components, a laser controller, a signal generation module, a signal acquisition and processing module, and a miniaturized interrogator as described in the first aspect embodiment above, wherein: The discrete optical components include an optical amplifier, a circulator, and a sensing fiber; the fiber array is connected to the circulator and the optical amplifier respectively, and is used to detect the output of light and the input of scattered light; the sensing fiber is connected to the circulator; specifically, the sensing fiber can be ordinary single-mode fiber, stress-sensitive enhanced special fiber, or other fiber that meets the needs of actual application scenarios; for example, the sensing fiber is a standard G.652.D single-mode fiber. The laser controller is connected to the laser chip and is used to drive the laser chip and control its temperature. The signal generation module includes a multi-channel low-speed signal generator, a high-speed signal generator, and an electrical amplifier. The high-speed signal generator outputs chirped signals, coded signals, or other types of signals according to the modulation scheme. The output of the high-speed signal generator is connected to the input of the electrical amplifier, and the output of the electrical amplifier is connected to the RF input port of the modulator. The multi-channel low-speed signal generator is a voltage source with high voltage output capability. The output of the multi-channel low-speed signal generator is connected to the selection switch, beam splitter, and tuning control signal input port of the modulator to set the operating point, and is also connected to the bias input port of the modulator. The signal acquisition and processing module includes a transimpedance amplifier, an analog-to-digital converter, and a data processing module connected in sequence. The outputs of the first, second, third, and fourth balanced detectors are all connected to the input of the transimpedance amplifier. The signal acquisition and processing module amplifies the signal and converts the current signal into a voltage signal. The acquisition card acquires four voltage signals. , , , , representing the I / Q signals corresponding to X-polarized and Y-polarized signal light, respectively.

[0062] In the data processing module, the acquired signal undergoes IQ imbalance correction. The specific steps are as follows: Build an IQ imbalance testing system, such as Figure 3 As shown. The setup of this test system and the acquisition of IQ imbalance compensation are based on the setup as follows. Figure 2 Previously, the system only needed to be tested once, and the obtained compensation parameters could be used continuously in subsequent tests. Figure 2 In the IQ imbalance compensation of the sensing system, there is no need for repeated testing. For example... Figure 3 As shown, optical port 3 is connected to an acousto-optic frequency shifter. The acousto-optic frequency shifter receives the electrical signal generated by the high-speed signal generator and shifts the frequency of the output light from optical port 3 to achieve heterodyne reception. Positive and negative sidebands at this frequency can be observed in the spectrum of the received signal, and the intensity difference between them is used as a measure of IQ balance. The input of the polarization controller is connected to the acousto-optic frequency shifter, and the output of the polarization controller is connected to optical port 4. Manually adjusting the polarization controller adjusts the polarization state of the input light, making the intensities of the X and Y polarization components of the output light closer together. This avoids excessively weak light in one polarization state, which could lead to severe signal-to-noise ratio degradation and abnormal IQ imbalance compensation parameter extraction. The acquisition card acquires four signals. , , , .

[0063] Taking the compensation of an IQ signal with one polarization component as an example, the compensation operation for the other polarization component is the same.

[0064] The obtained , First, remove the DC bias: Use the following formula for fitting: In the formula and correspond , A, B, and C are the compensation parameters obtained from the fitting.

[0065] Use A, B, and C to... , Compensation will be provided.

[0066] First, remove the DC bias as well: Then, compensation is performed using compensation parameters: After compensation, the intensity and phase imbalance between the IQ components can be effectively suppressed.

[0067] Examples of the compensation effects of the above schemes are as follows: Figure 4 As shown, the sideband rejection ratio (SSR) of a complex signal composed of IQ signals is infinitely large under ideal conditions, but it is a finite value due to the actual balance of IQ signals, such as 21dB before compensation. Through compensation of IQ imbalance, the SSR can be improved to 53dB.

[0068] This system supports multiple modulation and demodulation schemes. The preferred scheme for sensing testing is based on chirped pulses and matched filtering. A laser chip generates a narrow linewidth light source below 3kHz. A high-speed signal generator produces chirped pulse signals with a pulse duration of [missing information]. The pulse period is The frequency was scanned from 10MHz to 410MHz. The RF signal was then amplified and applied to the RF input port of the modulator. The modulator operated at null, with a reverse bias voltage of -0.5V. The output double-sideband pulse signal from the modulator entered the sensing fiber. The sensing fiber was 10km long, with a sinusoidal vibration signal applied to its tail for testing. A four-channel analog-to-digital converter with a sampling rate of 1GSa / s was used for acquisition. Demodulation followed a standard procedure, using matched filtering and rotating vector averaging, without any other special optimization algorithms. The gauge length was set to 4m during demodulation.

[0069] Demodulation results are as follows Figure 5 and Figure 6 As shown, Figure 5 A waterfall plot near the vibration region at the fiber optic tail is shown, demonstrating that the vibration signal is correctly reproduced. Figure 6 A statistical chart showing the strain resolution of each sensing channel over a 1km fiber optic cable tail is presented. The 99th percentile is taken as the system's strain resolution. .

[0070] Understandably, without changing the hardware components, multiple modulation and demodulation schemes can be supported simply by changing the modulation signal output of the high-speed signal generator and the built-in algorithm of the data processing module. Optional modulation and demodulation schemes include chirped pulse schemes, Golay coding, Simplex coding, time division multiplexing, frequency division multiplexing, and combinations thereof.

[0071] The miniaturized interrogator and distributed fiber optic sensing system provided by embodiments of the present invention integrate the core optical components of the interrogator onto a silicon-based photonic chip using photonic integration technology. Furthermore, a hybrid integration approach is used to achieve the integration of the laser chip and the silicon photonic chip, avoiding the problems of large size and unstable connection of external laser modules, thereby significantly improving the system's compactness and reliability. A passive solution is adopted in the polarization control and 90° mixing stages, eliminating the need for complex electronic control algorithms for polarization controllers and 90° mixers, reducing peripheral circuits and active control modules, and further improving the system's stability and ease of use. A high-performance 90° mixer is achieved through a passive multimode interference coupler combined with an IQ imbalance compensation algorithm at the data processing end. Compared to active solutions, this approach maintains high performance while being passive and eliminating the need for setting control algorithms. The on-chip modulator can meet system requirements through flexible device structure design. For example, appropriately reducing the bandwidth can effectively improve modulation efficiency. Especially in analytical applications, a modulator with a bandwidth of less than 5GHz can meet the requirements, thereby significantly reducing device design difficulty and improving practicality.

[0072] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A distributed optical fiber sensing system, characterized in that, It includes discrete optical components, a laser controller, a signal generation module, a signal acquisition and processing module, and a miniaturized interrogator, among which: The miniaturized interrogator includes a laser chip and an interrogator chip; the laser chip generates a narrow linewidth light source; the interrogator chip includes an optical port module, a polarization filter module, a selection switch, a beam splitter, a modulator, a polarization rotation beam splitter, a multimode interference coupler module, and a balanced detector module; wherein: The optical port module includes a first optical port, a second optical port, a third optical port, and a fourth optical port; the first optical port is used to connect to the laser chip, the second optical port is used to connect to an external laser module, the third optical port is used to output probe light, and the fourth optical port is used to input scattered light. The polarization filter module includes a first polarization filter and a second polarization filter; the input terminal of the first polarization filter is connected to the first optical port, the input terminal of the second polarization filter is connected to the second optical port, the output terminals of the first polarization filter and the second polarization filter are respectively connected to the two input terminals of the selection switch, the output terminal of the selection switch is connected to the input terminal of the beam splitter, one output terminal of the beam splitter is connected to the input terminal of the modulator, and the output terminal of the modulator is connected to the third optical port. The multimode interference coupler module includes a 1×2 multimode interference coupler, a first 2×4 multimode interference coupler, and a second 2×4 multimode interference coupler; the other output terminal of the beam splitter is connected to the input terminal of the 1×2 multimode interference coupler, the fourth optical port is connected to the input terminal of the polarization rotation beam splitter, the two output terminals of the 1×2 multimode interference coupler are respectively connected to one input terminal of the first 2×4 multimode interference coupler and one input terminal of the second 2×4 multimode interference coupler, and the two output terminals of the polarization rotation beam splitter are respectively connected to the other input terminal of the first 2×4 multimode interference coupler and the other input terminal of the second 2×4 multimode interference coupler; The balanced detector module includes a first balanced detector, a second balanced detector, a third balanced detector, and a fourth balanced detector; the two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the first balanced detector, and the other two outputs of the first 2×4 multimode interference coupler are connected to the two inputs of the second balanced detector; the two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the third balanced detector, and the other two outputs of the second 2×4 multimode interference coupler are connected to the two inputs of the fourth balanced detector; The first optical port is coupled to the laser chip via spatial light. The second optical port, the third optical port, and the fourth optical port are fixedly coupled to the fiber array; The first polarization filter and the second polarization filter are implemented using polarization beam splitters to filter out the TM component of the input light so that the output light is pure TE mode light; The selection switch is a 2×2 Mach-Zehnder interferometer, used to select the input light of the laser chip or the input light of the external laser module as the input light source of the beam splitter; The first 2×4 multimode interference coupler and the second 2×4 multimode interference coupler serve as 90° mixers to mix the intrinsic light output from the 1×2 multimode interference coupler with the scattered light output from the polarization rotating beam splitter to obtain a mixed beam. The laser chip and the interrogator chip are coupled via a spatial optical method based on micro-optical components. The micro-optical components include an isolator and two microlenses located on the front and rear sides of the isolator. The isolator does not perform polarization rotation on the input light provided by the laser chip. The discrete optical components include an optical amplifier, a circulator, and a sensing fiber; the fiber array is connected to the circulator and the optical amplifier respectively; the sensing fiber is connected to the circulator. The laser controller is connected to the laser chip and is used to drive the laser chip and control the temperature of the laser chip. The signal generation module includes a multi-channel low-speed signal generator, a high-speed signal generator, and an electrical amplifier; the output terminal of the high-speed signal generator is connected to the input terminal of the electrical amplifier, and the output terminal of the electrical amplifier is connected to the radio frequency input port of the modulator; the multi-channel low-speed signal generator is a voltage source with high voltage output capability, and the output terminal of the multi-channel low-speed signal generator is connected to the selection switch, the beam splitter, the tuning control signal input port of the modulator, and the bias input port of the modulator; The signal acquisition and processing module includes a transimpedance amplifier, an analog-to-digital converter, and a data processing module connected in sequence; the output terminals of the first balanced detector, the second balanced detector, the third balanced detector, and the fourth balanced detector are all connected to the input terminal of the transimpedance amplifier, and the signal acquisition and processing module is used to amplify the signal and convert the current signal into a voltage signal.

2. The distributed optical fiber sensing system according to claim 1, characterized in that, The laser chip is an InP distributed feedback laser chip with an external cavity, used to provide a light source with a linewidth of less than or equal to 3kHz and a wavelength including 1550nm.

3. The distributed optical fiber sensing system according to claim 1, characterized in that, The first optical port, the second optical port, the third optical port and the fourth optical port are implemented using an edge coupler.

4. The distributed optical fiber sensing system according to claim 1, characterized in that, The modulator is a Mach-Zehnder intensity modulator with a bandwidth greater than 1.5 GHz.

5. The distributed optical fiber sensing system according to claim 1, characterized in that, The interrogator chip is fabricated using a 220nm SOI process. The fiber array includes single-mode fiber and polarization-maintaining fiber. The third optical port and the fourth optical port correspond to the single-mode fiber, and the second optical port corresponds to the polarization-maintaining fiber.

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