Micro-integrated coherent balance detector and detection method

Abstract

The invention belongs to the technical field of integrated photonic devices, optical communication and optical detection, and particularly relates to a micro-integrated coherent balance detector and a detection method, and the detector comprises a packaging substrate, a frequency mixer passive chip, a balance detector active chip, and an inter-chip coupling micro transmission-reflection mirror group. The top of the packaging substrate is designed to be of a stepped staggered layer structure, the frequency mixer passive chip is located on a high level, and the balance detector active chip is located on a low level. The inter-chip coupling micro-transmitting-reflecting mirror group comprises a first group of micro-lenses, a micro-reflecting mirror and a second group of micro-lenses, the first group of micro-lenses are used for collimating light beams output by the frequency mixer passive chip, the micro-reflecting mirror is used for deflecting the light beams by 90 degrees, and the second group of micro-lenses are used for collimating the deflected light beams and vertically projecting the light beams to a photosensitive surface of the balance detector active chip. The problems of low optical coupling efficiency, complex optical path adjustment and high manufacturing difficulty are solved, the optical coupling efficiency is improved, mode mismatch and scattering loss are reduced, the system manufacturing complexity and cost are reduced, and the multi-scene application requirement is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated photonic devices, optical communications and optical detection, and in particular, relates to a micro-integrated coherent balanced detector and a detection method. Background Art

[0002] In the fields of optical communication, optoelectronic measurement, and lidar, coherent detection technology is an important method for detecting optical signals. Compared with traditional direct detection technology, coherent detection technology can significantly improve the sensitivity and signal detection capability of the system by coherently mixing the signal light with the local oscillator light. Therefore, coherent detection has become a key technology for modern high-performance optical systems. The core component of coherent detection is the coherent balanced detector, which mixes the signal light with the local oscillator light through a mixer to output a differential optical signal, and uses a photodetector to achieve photoelectric conversion. The key advantage of the coherent balanced detector is that it can significantly suppress the local oscillator noise and the thermal noise of the receiver, so that the receiving sensitivity of the system is increased by about 20dB compared with the traditional direct detection method, thereby achieving high-sensitivity detection of weak optical signals.

[0003] Existing coherent balanced detectors are usually composed of an input optical system, a mixer, a photodetector, a signal processing module, and a system integration method. The input optical system uses a diffraction microlens or a grating coupler to introduce spatial signal light and local oscillator light into a silicon-based waveguide system to achieve efficient coupling. The mixer uses a multimode interference coupler or a 3-dB coupler to mix the signal light with the local oscillator light, and outputs two optical signals with a phase difference of 180°. The photodetector uses a waveguide balanced detector to receive differential optical signals, complete photoelectric conversion, and output differential photocurrents. The signal processing module amplifies, digitizes, and optimizes the signal through a differential amplifier and an analog-to-digital converter. The system integration method usually uses three-dimensional integration, TSV (through silicon via) technology, or CMOS (Complementary Metal-Oxide-Semiconductor process) technology to achieve full integration.

[0004] Although existing technologies have made some progress in coherent detection, there are still the following major technical challenges in practical applications:

[0005] 1. Insufficient optical coupling efficiency: Existing diffraction microlenses are limited by light wavelength and incident angle, resulting in high optical energy loss; the coupling efficiency of grating couplers is usually only 50%-70%, and its performance is affected by design parameters and waveguide structure.

[0006] 2. Low interconnection efficiency: The mixer and the balanced detector are connected by a waveguide, and there are additional losses in the waveguide material and structural design. At the same time, manufacturing errors lead to deviations in optical signal transmission, affecting detection accuracy. The inconsistency of the photodiode in the balanced detector (such as differences in response speed or sensitivity) can also cause signal distortion and zero offset problems.

[0007] 3. Complex optical path adjustment: The optical path design is highly dependent on the waveguide system and fixed coupler structure, with high processing accuracy and alignment requirements and low fault tolerance, making it difficult to meet the application requirements of multiple scenarios.

[0008] 4. Insufficient flexibility in system integration: Although 3D integration, TSV technology and CMOS process have improved device integration, they limit the independent optimization of optical modules, detector modules and signal processing modules, making it difficult to adapt to multi-wavelength and multi-scenario requirements.

[0009] 5. Poor control of beam quality and signal loss: Waveguide balanced detectors and multimode interference couplers are prone to introduce mode mismatch and mode dispersion, resulting in reduced beam quality and increased signal loss, thereby reducing detection efficiency.

[0010] 6. High difficulty in manufacturing and adjustment: Diffractive microlenses and grating couplers are highly sensitive to manufacturing process errors, and uneven nano-scale processing leads to optical aberrations and energy loss. In addition, system adjustment requires high-precision alignment, high manufacturing costs, and complex processes, which affect performance consistency and yield.

[0011] In summary, the existing coherent balanced detection technology is limited by low optical coupling efficiency, poor system flexibility, and complex optical path adjustment in practical applications in the fields of optical communication, optoelectronic measurement, and lidar. These technical bottlenecks provide a clear research direction for further optimizing the performance of coherent detectors, and also lay the foundation for the development of new coherent detection technologies. Summary of the invention

[0012] In view of the defects of the prior art, the present invention proposes a micro-integrated coherent balanced detector and a detection method. In view of the technical problems of the existing coherent balanced detectors such as low optical coupling efficiency, complex optical path adjustment, and insufficient system integration flexibility, more efficient light field coupling, more flexible modular design and better system performance are achieved through improved structural design and material selection.

[0013] On the one hand, the present invention provides a micro-integrated coherent balanced detector, including a packaging substrate, a mixer passive chip, a balanced detector active chip and an inter-chip coupling micro-transmitter-reflector group;

[0014] The top of the packaging substrate is a staircase staggered structure, the mixer passive chip is arranged on the top high level of the packaging substrate, and the balanced detector active chip is arranged on the top low level of the packaging substrate;

[0015] The inter-chip coupling micro-lens-mirror group includes a first group of micro-lenses, a micro-mirror, and a second group of micro-lenses, wherein: the first group of micro-lenses is arranged at the output port of the mixer passive chip, and is used to collimate the light beam output by the mixer passive chip; the micro-mirror is arranged directly behind the first group of micro-lenses, and is used to deflect the collimated light beam by 90°; the second group of micro-lenses is arranged directly below the micro-mirror, and is used to collimate the deflected light beam and vertically project it to the photosensitive surface of the balanced detector active chip;

[0016] The light beam output by the mixer passive chip is collimated by the first group of microlenses, deflected by 90 degrees by the micromirror and collimated by the second group of microlenses, and then vertically projected to the photosensitive surface of the balanced detector active chip to realize the balanced detection function.

[0017] In a preferred implementation, further, the mixer passive chip comprises a mode field conversion structure; the mode field conversion structure is arranged at an output port of the mixer passive chip and matches the first group of micro lenses.

[0018] In a preferred implementation, further, the first group of microlenses includes a first microlens and a second microlens; one side of the first microlens and the second microlens is fixed to the output port of the mixer passive chip by an optically transparent adhesive, and the other side of the first microlens and the second microlens is optically connected to the micro-mirror by bonding transparent glue; the optical axes of the first microlens and the second microlens coincide with the center of the output light beam corresponding to the mixer passive chip.

[0019] In a preferred implementation, further, the second group of microlenses includes a third microlens and a fourth microlens; the third microlens and the fourth microlens are located directly above the photosensitive surface of the active chip of the balanced detector, and are fixed to the bottom surface of the micromirror by an optically transparent adhesive.

[0020] In a preferred implementation, further, the mixer passive chip has two input ports and two output ports, the two input ports respectively input the signal light to be measured and the local oscillator light, and the two output ports are respectively provided with mode field conversion structures, and the first microlens and the second microlens are respectively connected to the corresponding mode field conversion structures; the balanced detector active chip includes two detector array elements, each detector array element includes a photosensitive surface, and the third microlens and the fourth microlens are respectively arranged directly above the photosensitive surface of the corresponding detector array element.

[0021] In a preferred implementation, further, the micro-mirror includes an incident surface, a reflecting surface and an exit surface; the incident surface is located directly in front of the exit light beams of the first micro-lens and the second micro-lens; the reflecting surface is inclined at 45° and is located inside the propagation path of the incident light beam, and is used to deflect the light beam by 90°; the exit surface is located at the bottom of the micro-mirror and is perpendicular to the reflected light beam, and its bottom surface is used to connect to the third micro-lens and the fourth micro-lens.

[0022] In a preferred implementation, further, the third microlens and the fourth microlens are located 0.1-0.3 mm above the photosensitive surface of the active chip of the balanced detector.

[0023] In a preferred implementation, further, the material of each microlens is resin, and its three-dimensional size is in the range of 0.5-1.5 mm×0.5-1.5 mm×0.2-0.6 mm.

[0024] On the other hand, the present invention further provides a detection method based on any one of the above-mentioned micro-integrated coherent balanced detectors, the method comprising:

[0025] Step 1: The signal light to be measured and the local oscillator light are coupled into the mixer passive chip through two input ports of the mixer passive chip respectively, and the signal light and the local oscillator light are coherently mixed in the mixer passive chip to generate a mixing signal containing characteristic information of the signal light to be measured;

[0026] Step 2: The mixed signal is transmitted to the output port of the mixer passive chip through the on-chip waveguide in the mixer passive chip, and the beam mode field of the mixed signal is expanded at the output port through the mode field conversion structure;

[0027] Step 3: The mixed signal after expanding the beam mode field is collimated and deflected 90° through an inter-chip coupled micro-transmitter-reflector group to achieve spatial light transmission;

[0028] Step 4: The mixed light beam deflected by 90° is projected onto the first photosensitive surface and the second photosensitive surface of the balanced detector respectively, and the photosensitive surface absorbs the light signal and generates a photocurrent, and the current signal is collected by the metal electrode and transmitted to the signal processing circuit;

[0029] Step 5: The signal processing circuit receives the two photocurrent signals transmitted by the balanced detector, extracts the intensity, frequency, phase and dynamic characteristics of the signal light to be measured over time through differential amplification and filtering, and outputs the processing results digitally.

[0030] In a preferred implementation, further, step 3 includes:

[0031] Step 3.1: The mixed signal after expanding the light beam mode field passes through a first microlens and a second microlens at the mode field conversion structure of two output ports of the mixer passive chip, and the output mixed light signal is collimated into a parallel light beam;

[0032] Step 3.2: The two collimated light beams are horizontally projected onto the reflective surface of the micro-mirror, which is inclined at 45° to the horizontal plane, and a 90° deflection of the light beams is achieved through reflection;

[0033] Step 3.3: The light beam deflected by the micromirror is further collimated by the third microlens and the fourth microlens at the bottom of the micromirror, and is vertically projected onto the photosensitive surface of the balanced detector.

[0034] The beneficial effects of the present invention are:

[0035] First, the micro-integrated coherent balanced detector of the present invention adopts a stepped staggered structure on the packaging substrate, arranges the mixer passive chip and the balanced detector active chip at different levels, and cooperates with the inter-chip coupling micro-lens-mirror group to realize efficient optical path coupling. Through the combination of the first group of microlenses, the micro-mirrors and the second group of microlenses, the collimation, deflection and high-precision projection of the light beam are realized, which greatly reduces the optical path loss and error, saves space, improves the system integration and detection sensitivity, and provides a small size and excellent performance solution for high-precision optical detection applications.

[0036] Second, in a preferred implementation, the present invention can effectively optimize the mode field distribution of the optical signal by setting a mode field conversion structure at the output port of the mixer passive chip and matching it with the first group of microlenses, thereby improving the optical coupling efficiency and reducing the insertion loss. At the same time, the design can improve the quality of optical transmission, reduce the energy loss in the optical system, and improve the overall performance and stability of the system.

[0037] Third, in the preferred implementation, the cooperation between the first group of microlenses and the mode field conversion structure of the present invention optimizes the mode matching of the output light beam and reduces optical loss; the second group of microlenses is positioned directly above the photosensitive surface of the detector array element, which effectively improves the collection efficiency of the optical signal and the optical alignment accuracy, and further improves the detection sensitivity and signal quality of the system. In addition, the microlenses are fixed by optically transparent adhesives, with a compact structure, high reliability, and easy assembly and integration, thereby improving the overall performance and practicality of the device.

[0038] Fourth, in a preferred implementation, the present invention provides a micro-mirror, whose incident surface faces the outgoing light beams of the first micro-lens and the second micro-lens, to ensure accurate incident light beams; the reflecting surface is arranged at a 45° tilt, so that the light beam is deflected 90° in the propagation path, effectively changing the direction of the light path; the exit surface is perpendicular to the reflected light beam and connected to the third micro-lens and the fourth micro-lens, to ensure that the light beam is emitted at an optimized angle.

[0039] Fifth, in a preferred implementation, the material of the microlens of the present invention is resin, which has excellent light transmittance and processability, and its three-dimensional size is controlled within a reasonable range, which not only ensures the optimization of the optical path, but also takes into account the compact structure and processing cost;

[0040] Sixth, the detection method of the micro-integrated coherent balanced detector provided by the present invention realizes efficient coherent mixing of the signal light to be measured and the local oscillator light in the mixer passive chip, and combines the signal transmission of the on-chip waveguide, the beam expansion of the mode field conversion structure, and the beam collimation and deflection design of the micro-transmitter-mirror group to ensure the high-quality transmission of the mixing signal and the precise positioning of the mixed signal on the photosensitive surface of the balanced detector. This method has high integration and low optical path transmission loss, can significantly improve the sensitivity and stability of signal detection, and at the same time has the advantages of small size and compact structure, and is suitable for high-precision and miniaturized optical detection application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a simplified structural diagram of a micro-integrated coherent balanced detector according to an embodiment of the present invention;

[0042] Figure 2 It is a flow chart of a detection method of a micro-integrated coherent balanced detector according to an embodiment of the present invention.

[0043] Among them, 1 is a packaging substrate; 2 is a mixer passive chip; 3 is a balanced detector active chip; 301 is a first photosensitive surface; 302 is a second photosensitive surface; 401 is a first microlens; 402 is a second microlens; 403 is a third microlens; 404 is a fourth microlens; 5 is a micromirror. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0045] In the description of this application, the terms "first", "second", and "third" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance; the term "plurality" refers to two or more, unless otherwise expressly defined. Terms such as "installed", "connected", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0046] In the description of the present application, it should be understood that the directions or positional relationships indicated by the terms "up", "down", "left", "right", "front", "back", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific orientation, and therefore, should not be understood as a limitation on the present application.

[0047] In the description of this specification, the description of the terms "one embodiment / method", "some embodiments / methods", "specific embodiments / methods", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment / method or example are included in at least one embodiment / method or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment / method or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments / methods or examples in a suitable manner.

[0048] As the instruction manual Figure 1The present invention records a micro-integrated coherent balanced detector, including a packaging substrate 1, a mixer passive chip 2, a balanced detector active chip 3 and an inter-chip coupling micro-transmitter-mirror group. The inter-chip coupling micro-transmitter-mirror group includes a first group of micro-lenses, a second group of micro-lenses and a micro-mirror 5. The top of the packaging substrate 1 is a stepped staggered structure, the mixer passive chip 2 is arranged on the top high-level surface of the packaging substrate 1, and the balanced detector active chip 3 is arranged on the top low-level surface of the packaging substrate 1. One end of the mixer passive chip 2 is two input ports for input signal light and local oscillator light, and the other end is an output port for the mixed signal light and local oscillator light, and a first group of micro-lenses is arranged at the output port, and the first group of micro-lenses is used to collimate the light output by the mixer. The top of the balanced detector active chip 3 has a photosensitive surface, and a second group of micro-lenses is arranged directly above the photosensitive surface. A micromirror 5 is provided directly above the second group of microlenses and directly behind the first group of microlenses. The micromirror 5 is used to deflect the collimated light beam projected by the first group of microlenses by 90° and then project it to the second group of microlenses. The second group of microlenses is used to collimate the light beam deflected by 90° and then project it vertically onto the photosensitive surface of the balanced detector active chip 3 for balanced detection.

[0049] The packaging substrate 1 is used to support all devices and realize module packaging. The material of the packaging substrate 1 is metal or aluminum nitride, and the thickness of the top of the substrate is divided into two parts: the side with a thickness of 4-6mm (preferably 5mm) is used to mount the mixer passive chip; the side with a thickness of 1-3mm (preferably 2mm) is used to mount the balanced detector chip.

[0050] The mixer passive chip 2 can be fixed to the thick edge of the package substrate 1 by bonding, welding or mechanical clamping. Adhesive fixation is to use conductive glue to fix the mixer passive chip 2 to the thick edge of the package substrate 1; if the mixer passive chip 2 and the package substrate 1 support welding technology, they can be soldered or eutectic welded together; mechanical clamping is to use a micro-clamp or screw to fix the chip on the substrate, which is suitable for scenes that require repeated adjustments. The mixer passive chip 2 is provided with two input ports, two output ports, a mixer, an on-chip waveguide and a waveguide auxiliary structure. Among them, the two input ports and the output port are used to realize 3-dB mixing of signal light and local oscillator light. The mixer is a 3-dB coupler, and a multi-mode interference coupler (preferred) or other types of couplers can be used. In the preferred implementation of the present application, the mixer adopts a multi-mode interference coupler structure, and its material is selected from silicon, silicon dioxide, indium gallium arsenide or lithium niobate according to the requirements of the wavelength of light. On-chip waveguides are micro-nanoscale and are used to guide signal light and local oscillator light from the input port to the mixer and from the mixer to the output port.

[0051] The waveguide auxiliary structure is a mode field conversion structure. The two output ports of the mixer passive chip 2 correspond to the two input ports of the signal light and the local oscillator light. A mode field conversion structure is provided at each input and output port. The mode field conversion structure is used to expand the micro-nano scale optical mode field in the on-chip waveguide, improve the matching degree with the optical mode field of devices such as off-chip optical fiber or microlens, and increase the coupling efficiency. The mode field conversion structure can adopt a tapered waveguide structure, and gradually increase or decrease the waveguide width to gradually expand the on-chip micro-nano scale optical mode field to match the mode field diameter of the off-chip optical device (such as a microlens). The material of the mode spot converter is silicon or silicon nitride, and the mode spot converter can be prepared by photolithography, dry etching or electron beam etching process. The mode spot converter uses a silicon-based tapered waveguide as an example: first, photoresist is coated on the mixer passive chip 2, and the initial mask pattern of the tapered waveguide is generated using photolithography technology. The silicon layer is accurately removed using a dry etching process to form a tapered area, and the waveguide width is controlled to gradually expand. Then, a silicon dioxide or silicon nitride cladding is added to optimize the mode field expansion and transmission characteristics, and finally, cleaning and surface passivation are performed to reduce scattering loss and reflection. The selection of the above materials and processes can ensure that the mode spot converter can achieve efficient light field matching, improve overall coupling efficiency and reduce transmission loss.

[0052] The first group of microlenses includes a first microlens 401 and a second microlens 402. The optical axis is the geometric center line of the microlens and is also the propagation path of the light beam when passing through the microlens. The optical axes of the first microlens 401 and the second microlens 402 respectively coincide with the center of the light beam of the output port corresponding to the mixer passive chip 2 to avoid light beam deviation or scattering loss. Specifically, the coincidence of the optical axis of the microlens and the output port is achieved through physical position and optical path design. The physical position design is to use high-precision alignment equipment to measure and mark the physical center point of the bottom of the microlens and the center point of the output port of the pattern spot converter, so that the physical center point of the bottom of the microlens should coincide with the center point of the output port of the pattern spot converter, and then use optical design software (such as Zemax or Lumerical) to simulate the propagation path of the light beam from the pattern spot converter to the microlens, verify the feasibility of optical axis alignment, optimize the radius of curvature and position of the microlens, and ensure beam collimation.

[0053] The first microlens 401 and the second microlens 402 are respectively arranged on the spot converter at the two output ports of the mixer passive chip 2 by bonding, mechanical clamping or direct processing. Adhesive fixation is to apply an optically transparent adhesive (such as epoxy resin or UV curing glue) between the output port of the spot converter and the microlens. Mechanical clamping is to design a mechanical clamp around the output port of the spot converter to fix the position of the microlens. Direct processing is to directly process the microlens near the output port of the spot converter or to directly form the microlens on the chip by additive manufacturing (such as nanoimprint technology). In the preferred implementation of the present application, the adhesive fixation method is adopted.

[0054] One side of the first microlens 401 and the second microlens 402 is connected to the mode spot converter through an optically transparent adhesive, and the other side is connected to the micromirror 5 through an optically transparent adhesive. The micromirror 5 is a rectangular parallelepiped structure, and its material is resin. If the light beams transmitted by the first microlens 401 and the second microlens 402 require a certain propagation distance to complete the mode field expansion, the spacing of 0.1-0.2mm is achieved by controlling the thickness of the optically transparent adhesive. The micromirror 5 includes an incident surface, a reflecting surface, an exiting surface and a supporting side surface. The incident surface is located directly in front of the exiting light beams of the first microlens 401 and the second microlens 402, perpendicular to the optical axis after the light beams are collimated. The incident surface allows the light beam to directly enter the reflecting surface to maintain the energy transmission of the light beam. The reflecting surface is located inside the propagation path of the incident light beam, inclined at 45°, and is used to deflect the light beam by 90°. The reflecting surface must completely cover the cross section of the incident light beam to ensure no optical loss. The reflecting surface has a high reflectivity coating (such as a metal film or a dielectric film). The exit surface is perpendicular to the reflected light beam, located at the bottom of the micro mirror 5, and directly connected to the third micro lens 403 and the fourth micro lens 404. The exit surface allows the deflected light beam to enter the second group of micro lenses without attenuation for convergence.

[0055] The second group of microlenses includes a third microlens 403 and a fourth microlens 404. The third microlens 403 and the fourth microlens 404 have the same structure and installation method as the first microlens 401 and the second microlens 402, and are fixed to the bottom surface of the micromirror 5 by an optically transparent adhesive. The alignment platform ensures that the deflected optical axis of the micromirror 5 is aligned with the center of the third microlens 403 and the fourth microlens 404 respectively. The spacing between the third microlens 403 and the fourth microlens 404 and the micromirror 5 can be achieved by controlling the thickness of the optically transparent adhesive.

[0056] In a preferred implementation of the present application, the material of the first microlens 401, the second microlens 402, the third microlens 403 and the fourth microlens 404 are resins, and are in the shape of thin cuboids, with three-dimensional dimensions in the range of (0.5-1.5mm)×(0.5-1.5mm)×(0.2-0.6)mm, preferably 1mm×1mm×0.4mm. The first microlens 401 and the second microlens 402 are 0-0.4mm away from the edge of the mixer passive chip 2, preferably 0.2mm. The three-dimensional dimensions of the micromirror 5 are in the range of (1-3mm)×(1-3mm)×(2-4)mm, preferably 2mm×2mm×3mm. The third microlens 403 and the fourth microlens 404 after installation are located 0.1-0.3mm directly above the top photosensitive surface of the balanced detector active chip 3, preferably 0.2mm.

[0057] The balanced detector active chip 3 includes two detector array elements, and the detector array element includes a first photosensitive surface 301 and a second photosensitive surface 302 arranged on the top of the balanced detector active chip 3, a metal electrode, a substrate layer and an internal connection structure. The first photosensitive surface 301 and the second photosensitive surface 302 are used to receive incident light signals and generate photocurrents. The first photosensitive surface 301 and the second photosensitive surface 302 are made of semiconductor materials, such as silicon (Si) or gallium arsenide (GaAs), and are usually designed to be rectangular or circular. The metal electrode covers the metal layer around or on the back of the photosensitive surface, which is used to collect the photocurrent and transmit it to the signal processing circuit. The material is aluminum (Al), gold (Au) or platinum (Pt). The signal processing circuit is located in the back-end electronic module of the balanced detector system, and is not directly integrated on the balanced detector active chip 3, but is connected to the balanced detector chip through an internal connection structure. In the implementation method of the present application, the signal processing circuit can be partially embedded in the packaging substrate 1 to form an integral module to further reduce the loss and noise of signal transmission. The signal processing circuit is used to amplify, differentially calculate, filter and extract features of the photocurrent generated by the photosensitive surface, and finally output the characteristic information of the signal light to be measured. The substrate layer is used to support the structural layer of the entire detector array element, and has electrical isolation and heat conduction functions. It is usually made of silicon (Si) or sapphire (Sapphire) material with high thermal conductivity and mechanical stability. The internal connection structure uses micro-wires or metal interconnect structures to transmit the electrical signals output by the detector array element to the subsequent processing circuit of the balanced detector.

[0058] In a preferred implementation of the present application, the size of the detector array element is in the range of (1-3 mm)×(2-4 mm), with a preferred value of 2 mm×3 mm.

[0059] Example 1

[0060] By comparing the coherent balanced detector in the prior art with the coherent balanced detector structure of the present invention, the advantages of the coherent balanced detector of the present invention are explained.

[0061]

[0062]

[0063]

[0064] Example 2

[0065] The coherent balanced detector of the present invention shows excellent performance in two typical scenarios, optical communication and laser radar. For optical communication systems, it supports high-sensitivity, multi-wavelength fiber communication signal detection, adapts to the needs of DWDM (dense wavelength division multiplexing) technology, and covers a wavelength range of 1260nm to 1620nm. For laser radar systems, it supports high-precision, broadband optical signal detection for vehicle-mounted laser radar and environmental monitoring, and adapts to laser radar signals with a wavelength of 1550nm.

[0066] Design of key components:

[0067] The waveguide width design range of the mode spot converter is 200nm to 500nm, which can flexibly adapt to signal light of different wavelength ranges. In optical communication scenarios, the mode spot converter optimizes the matching of standard single-mode optical fiber (mode field diameter 10.4μm) and the micro-nano mode field of the on-chip waveguide. In the lidar scenario, the mode spot converter matches the wide beam laser signal to improve the beam collimation effect.

[0068] The radius of curvature and material parameters of the micro-lens group are adjusted to adapt to the efficient coupling of multi-wavelength signals. The lens material is made of low-dispersion quartz glass or high-performance resin to ensure high transmittance (≥98%) in the wavelength range of 1260nm to 1620nm. The reflective surface of the micro-mirror group is coated with a broadband high-reflectivity coating (such as a multi-layer dielectric film) with a reflectivity of ≥98%, which is adapted to the efficient deflection of signal lights of different wavelengths.

[0069] The photosensitive surface material is made of gallium arsenide (GaAs) or indium gallium arsenide (InGaAs), and the response spectrum range is 1000nm to 1700nm, which meets the detection requirements of optical communication signals and lidar signals. The photosensitive surface diameter of the balanced detector is optimized to 20μm, which can meet the detection requirements of both narrow-beam optical communication signals and wide-beam lidar signals.

[0070] Multi-wavelength detection performance test:

[0071] In the optical communication scenario, the DWDM system was used to test the detection performance of multiple wavelength signals (such as 1310nm and 1550nm) in the detector of the present invention. The results showed that the system sensitivity was improved by 20dB, and the coupling loss was controlled below 0.5dB, meeting the signal detection requirements of 100Gbps and above.

[0072] In the LiDAR scenario, the detection performance of Doppler frequency shift signals and weak reflection signals was tested at a wavelength of 1550nm. The results showed that the common mode noise suppression rate reached 40dB, the signal-to-noise ratio was significantly improved, and long-distance (>200m) weak signal detection was supported.

[0073] Experiments have shown that high optical coupling efficiency and high-sensitivity detection are achieved in multiple scenarios. The common-mode noise suppression function of the balanced detector enhances the robustness of the system and is suitable for high-performance optical signal detection needs in complex environments. The modular design supports fast switching and flexible adaptation of optical communication and lidar applications, providing an integrated solution for multiple scenario requirements.

[0074] The present invention also records a detection method for a micro-integrated coherent balanced detector, which includes five stages: optical signal input, light field coupling and mixing, light beam collimation and deflection, photoelectric conversion and signal processing. High-sensitivity coherent detection of weak optical signals is achieved through coupling, mixing, collimation, deflection and photoelectric signal conversion of signal light and local oscillator light.

[0075] Methods include:

[0076] Step 1: The signal light to be measured and the local oscillator light are coupled into the mixer passive chip through the two input ports of the mixer passive chip respectively, and the signal light and the local oscillator light are coherently mixed in the mixer passive chip to generate a mixing signal containing characteristic information of the signal light to be measured.

[0077] The purpose of step 1 is to achieve efficient mixing of the signal light to be measured and the local oscillator light, laying the foundation for subsequent signal extraction and processing. Through the design of passive chips, the system power consumption can be reduced and the integration of mixing devices can be improved, thereby improving the overall performance and reliability of the optical system.

[0078] Specifically, the signal light is the target light to be measured in the mixing system, and usually carries optical information that needs to be measured or analyzed, such as modulation information (such as changes in phase, amplitude or frequency), spectral characteristics (such as the presence of a specific wavelength), and dynamic changes (such as Doppler shift or time correlation). The purpose of mixing is to extract the information in the signal light. After the signal light is mixed with the local oscillator light, its phase, frequency or intensity characteristics are converted into electrical signals or other forms of easy-to-read output. The local oscillator light is an important light source for providing a reference signal in the mixing process. Its main functions include: 1. Providing a stable phase and frequency reference for coherent mixing with the signal light to be measured, thereby extracting the characteristic information of the signal light to be measured (such as frequency, phase or amplitude); 2. In the mixing process, the intensity of the local oscillator light directly affects the power and signal-to-noise ratio of the mixing signal; 3. The frequency position of the local oscillator light determines the frequency distribution of the signal light after mixing, so that the characteristic information of the signal light is transferred to the intermediate frequency or radio frequency range that is easy to measure, which is convenient for subsequent processing.

[0079] The signal light to be measured is input by an external light source (such as an atmospheric detection signal or an optical communication signal) and enters the first input port of the mixer passive chip through the input optical fiber or free space coupling. The mixer passive chip requires that the wavelengths of the signal light and the local oscillator light are close to ensure efficient coherent mixing. The coherence condition is that the wavelength difference (or frequency difference) between the signal light and the local oscillator light needs to be within the bandwidth range of the chip design to ensure the phase consistency of the light field and form a stable interference signal. The working bandwidth of the chip is usually limited, and the wavelengths of the signal light and the local oscillator light need to fall within this range. For example, if the chip is designed in the C band (1530nm-1565nm), the wavelengths of the two beams of light need to be within this range.

[0080] The local oscillator light is generated by a local oscillator light source (such as a narrow linewidth laser), and after the frequency is adjusted by a frequency stabilization controller, it is connected to the second input port of the mixer passive chip through a single-mode optical fiber or waveguide. The mixer passive chip integrates an optical waveguide for transmitting the signal light and the local oscillator light respectively. Inside the mixer passive chip, the signal light waveguide and the local oscillator light waveguide are merged into a common mixing region. The mixing region is designed as a Mach-Zehnder interferometer (MZI), a microring resonator or a cross-waveguide structure, and the specific form is selected according to the application. The crossing angle and waveguide spacing are optimized to reduce crosstalk and improve mixing efficiency. The mixing operation is achieved through nonlinear optical effects (such as quadratic nonlinear effects, four-wave mixing) or interference superposition effects.

[0081] Step 2: The mixed signal is transmitted to the output port of the mixer passive chip through the on-chip waveguide in the mixer passive chip, and the beam mode field of the mixed signal is expanded at the output port through the mode field conversion structure.

[0082] The purpose of step 2 is to transfer the mixing signal from the mixing area to the output port through efficient transmission of the on-chip waveguide, and at the same time use the mode field conversion structure to optimize the mode field distribution of the output light beam, enhance the coupling efficiency of the output signal with the external optical device, reduce insertion loss, and improve the optical signal transmission quality and overall performance of the system.

[0083] In step 2, the process of optimizing the mode field distribution of the output light beam by the mode field conversion structure is taken as an example of a tapered waveguide used in the mode field conversion structure, and the restrictions of the mode field and the waveguide wall (waveguide boundary) are reduced by gradually increasing the geometric dimensions of the waveguide (such as width and height). Because the mode field is the electromagnetic field distribution of light in the waveguide, for common optical waveguides (such as silicon-based waveguides), the mode field is mostly concentrated in the core area of ​​the waveguide and may partially extend to the outside of the waveguide, while the waveguide wall constrains the light in the waveguide through the difference in refractive index. The restriction of the waveguide wall will cause the lateral expansion of the mode field to be suppressed, making the mode field distribution highly concentrated in the waveguide. The mode field size of the external single-mode optical fiber is usually large (such as about 10μm), and the small mode field in the waveguide is prone to mismatch when coupling with it, increasing insertion loss. However, this limitation is reduced by using a mode field conversion structure, allowing the mode field to expand more smoothly from the core area of ​​the waveguide to the periphery, so that the light beam mode field is expanded from the small mode field of the on-chip waveguide (usually sub-micron level) to a diameter that matches the external optical fiber mode field, thereby reducing the mode field mismatch of the light beam and reducing coupling loss.

[0084] Step 3: After the mode field of the beam is expanded, the mixed signal is collimated and deflected by 90° through an inter-chip coupled micro-transmitter-reflector group to achieve spatial light transmission.

[0085] The purpose of step 3 is to collimate the beam and adjust the spatial direction of the mixing signal through the inter-chip coupled microlens group and micromirror group to ensure efficient transmission of the signal light and precise matching of the spatial path; by vertically projecting to the photosensitive surface of the balanced detector, high-sensitivity detection of the signal is achieved to maximize the output signal-to-noise ratio and system performance.

[0086] Step 3.1: The mixed signal after expanding the light beam mode field passes through a first microlens and a second microlens at the mode field conversion structure of the two output ports of the mixer passive chip, and the output mixed light signal is collimated into a parallel light beam.

[0087] In step 3.1, the beam collimation effect is expressed by the focal length formula of the lens:

[0088]

[0089] Where: θ represents the divergence angle of the light beam; λ represents the wavelength of the light; ω 0 Represents the mode field radius of the beam at the focus.

[0090] When a microlens is used to focus the light beam into parallel light, the mode field radius ω 0 The relationship with the focal length f of the lens is:

[0091]

[0092] Where: d It represents the mode field radius of the beam at the input end of the lens.

[0093] From formulas (1)-(2), it can be seen that the microlens optimizes the lens focal length f and the input mode field radius ω d , and then adjust the mode field radius ω of the beam at the focus 0 , making the divergence angle θ extremely small, usually less than 0.1°, the directionality of the collimated beam is significantly improved, and the power dispersion caused by the divergence of the beam energy loss is greatly reduced.

[0094] Coupling effect: The collimated parallel beam can be transmitted into the micromirror with high efficiency, reducing the coupling loss caused by divergence. Typical loss value L 1 ≤0.1dB.

[0095] Step 3.2: The two collimated light beams are horizontally projected onto the reflective surface in the micro-mirror, which is inclined at 45° to the horizontal plane, and a 90° deflection of the light beams is achieved through reflection.

[0096] In step 3.2, the reflective surface of the micromirror is inclined at 45° to the horizontal plane. The reflection of the micromirror follows the law of reflection:

[0097] θ i =θ r (3)

[0098] Where: θ i represents the incident angle of the light beam; θ r Represents the reflection angle of the light beam.

[0099] Since the reflective surface of the micromirror is inclined at 45° to the horizontal plane, the horizontally incident light beam will be deflected at an angle of 90° and turned to the vertical direction. The beam path changes as follows: horizontal light beam → micromirror reflective surface (45°) → vertical light beam.

[0100] The surface of the micro-mirror in this application is plated with a high-reflectivity metal coating (such as silver or aluminum), and its reflectivity R is close to 1 (typical value is R ≥ 0.98), and the reflection loss is dominated by surface absorption and scattering loss:

[0101] L 反射 =-10log 10 (R)(4)

[0102] When R=0.98, the reflection loss in formula (4) is only ≤0.1dB.

[0103] High-precision micromachining ensures that the angular error of the reflective surface is controlled within ±0.05°, ensuring small deviation of the beam path and reducing power loss caused by scattering.

[0104] Coupling effect: The micro-mirror achieves efficient conversion of the beam direction, maintaining the beam's directionality and energy concentration. Typical loss value L 2 ≤0.1dB.

[0105] Step 3.3: The light beam deflected by the micromirror is further collimated by the third microlens and the fourth microlens at the bottom of the micromirror, and is vertically projected onto the photosensitive surface of the balanced detector.

[0106] In step 3.3, the focusing of the microlens follows the Gaussian beam propagation theory, and the radius of the focused beam ω f The mode field radius ω of the detector photosensitive surface d Matching, the coupling efficiency can be described by the following formula:

[0107]

[0108] Where: f Represents the mode field radius of the focused beam (determined by the focal length of the lens and the input beam); ω d represents the mode field radius of the detector's photosensitive surface; d represents the offset distance between the light beam and the center of the photosensitive surface.

[0109] By designing the focal length of the microlens, ω f ≈ω d , and aligning the beam center to control the offset d≈0, a high coupling efficiency η≥0.89 can be achieved.

[0110] Coupling effect: The secondary collimation of the microlens focuses the beam energy on the photosensitive surface of the detector, further reducing the mode mismatch loss and insertion loss. Typical loss value L 3 ≤0.1dB.

[0111] Through the step-by-step optimization of the above structure, the total insertion loss is:

[0112] L total =L 1 +L 2 +L 3 ≤0.5dB (6)

[0113] By collimating the light beam with a microlens to reduce divergence loss, the efficient reflection of the micromirror to achieve beam direction conversion, and the high coupling efficiency of secondary collimation and focusing, a coupling loss of less than 0.5dB between the mixer passive chip and the balanced detector chip was successfully achieved. This structural design significantly improves system performance, especially in terms of the optimization effect of optical signal transmission efficiency.

[0114] Step 4: The mixed light beam deflected by 90° is projected onto the first photosensitive surface and the second photosensitive surface of the balanced detector respectively. The photosensitive surface absorbs the light signal and generates photocurrent. The current signal is collected by the metal electrode and transmitted to the signal processing circuit.

[0115] The purpose of step 4 is to achieve efficient conversion of optical signals to electrical signals by projecting the deflected mixed light beams onto the photosensitive surfaces of the balanced detectors, thereby ensuring the detection sensitivity and signal integrity of the mixed signal. By utilizing the structural characteristics of the balanced detector, common mode noise can be effectively suppressed and the signal-to-noise ratio can be improved, providing high-quality input signals for subsequent signal processing.

[0116] The first photosensitive surface and the second photosensitive surface are located at the two input ends of the balanced detector chip, and their sizes match the mode field diameter of the incident light beam, which is typically 10μm to 20μm. The light beam is completely aligned with the photosensitive surface in the vertical direction, so that the offset error d of the beam on the photosensitive surface is controlled within the range of ±1μm to reduce energy loss and maximize light absorption efficiency.

[0117] It should be noted that in step 2-4, the two mixed signals output from the mixer passive chip 2 after mixing pass through the inter-chip coupling micro-transmitter-mirror group and are received by the first photosensitive surface and the second photosensitive surface of the balanced detector. The two mixed signals are used in the subsequent steps to perform differential calculation on the photogenerated currents of the two signals. The differential calculation can offset the common mode noise and improve the signal-to-noise ratio of the signal light.

[0118] Step 5: The signal processing circuit receives the two photocurrent signals transmitted by the balanced detector, extracts the intensity, frequency, phase and dynamic characteristics of the signal light to be measured over time through differential amplification and filtering, and outputs the processing results digitally.

[0119] The purpose of step 5 is that the signal processing circuit extracts the characteristic information of the signal light to be measured (such as intensity, frequency, phase and its dynamic changes) from the photocurrent signal transmitted by the balanced detector through differential amplification and filtering, eliminates common-mode noise and useless frequency components, improves the signal-to-noise ratio, and finally outputs the signal digitally to meet the high-precision requirements of multiple scenarios such as communication, sensing and analysis.

[0120] Specifically, the first photosensitive surface and the second photosensitive surface of the balanced detector respectively receive the incident two-way mixing signal to generate two-way photogenerated current signal I 1 and I 2 , the two signals are transmitted to the signal processing circuit through the internal connection structure. The signal processing circuit uses a differential amplifier to perform differential calculation on the two photocurrent signals. The differential calculation can effectively offset the common mode signal (such as local oscillator light intensity fluctuation and environmental noise) and improve the signal-to-noise ratio. The formula for differential calculation is:

[0121] I out =G·(I 1 -I 2 ) (7)

[0122] Where: G represents the gain of the amplifier.

[0123] Furthermore, the differential electrical signal is filtered to remove irrelevant frequency components and noise, a high-pass filter is used to remove low-frequency noise or DC bias, a band-pass filter is used to extract specific frequency components of the signal light, and a low-pass filter is used to remove high-frequency noise. After filtering, the output signal only contains effective characteristic information of the signal light to be measured.

[0124] Then, the intensity, frequency, phase and dynamic change characteristic information of the signal light to be measured are extracted from the filtered signal. The intensity information is used to reflect the optical power or light intensity of the signal light to be measured, the frequency is obtained by using spectrum analysis or fast Fourier transform (FFT) method, the phase information is restored by the phase shift information in the mixing signal, and the dynamic change information is extracted by time domain analysis to extract the modulation information or dynamic characteristics of the signal light.

[0125] Finally, an analog-to-digital converter (ADC) is used to convert the extracted analog signal into a digital signal, which is then transmitted to an external device through a standard communication interface (such as I2C, SPI, or UART), or directly used for display, storage, or further analysis.

[0126] The micro-integrated coherent balanced detector of the present invention realizes efficient integration of the mixer passive chip and the balanced detector active chip by adopting a stepped staggered structure combined with mode field conversion, on-chip waveguide, and beam collimation and deflection design of a micro-transmitter-mirror group, thereby improving the optical path coupling efficiency, signal detection sensitivity and system stability. At the same time, it has the advantages of small size, compact structure and low optical path loss, providing an excellent performance solution for high-precision, miniaturized optical detection applications.

[0127] The above is only an embodiment of the present invention, and the common sense such as the known specific structure and characteristics in the scheme is not described in detail here. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the attached claims rather than the above description, so it is intended to include all changes within the meaning and scope of the equivalent elements of the claims. Any figure mark in the claims should not be regarded as limiting the claims involved.

Claims

1. A micro-integrated coherent balanced detector, characterized in that: It comprises a packaging substrate (1), a mixer passive chip (2), a balanced detector active chip (3) and an inter-chip coupling micro-transmitter-reflector group; The top of the packaging substrate (1) is a stair-stepped structure, the mixer passive chip (2) is arranged on a high-level surface at the top of the packaging substrate (1), and the balanced detector active chip (3) is arranged on a low-level surface at the top of the packaging substrate (1); The inter-chip coupling micro-lens-mirror group comprises a first group of micro-lenses (4), a micro-mirror (5) and a second group of micro-lenses (6), wherein: the first group of micro-lenses (4) is arranged at the output port of the mixer passive chip (2) and is used to collimate the light beam output by the mixer passive chip (2); the micro-mirror (5) is arranged directly behind the first group of micro-lenses (4) and is used to deflect the collimated light beam by 90 degrees; the second group of micro-lenses (6) is arranged directly below the micro-mirror (5) and is used to collimate the deflected light beam and vertically project it onto the photosensitive surface of the balanced detector active chip (3); The light beam output by the mixer passive chip (2) is collimated by a first group of microlenses (4), deflected by a micromirror (5) by 90 degrees and collimated by a second group of microlenses (6), and then vertically projected onto the photosensitive surface of the balanced detector active chip (3), thereby realizing a balanced detection function.

2. The micro-integrated coherent balanced detector according to claim 1, characterized in that: The mixer passive chip (2) comprises a mode field conversion structure; the mode field conversion structure is arranged at an output port of the mixer passive chip (2) and matches the first group of micro lenses (4).

3. The micro-integrated coherent balanced detector according to claim 1, characterized in that: The first group of microlenses (4) comprises a first microlens (401) and a second microlens (402); one side of the first microlens (401) and the second microlens (402) is fixed to the output port of the mixer passive chip (2) by means of an optically transparent adhesive, and the other sides of the first microlens (401) and the second microlens (402) are optically connected to the micro-mirror (5) by means of a bonding transparent adhesive; and the optical axes of the first microlens (401) and the second microlens (402) coincide with the center of the output light beam corresponding to the mixer passive chip (2).

4. The micro-integrated coherent balanced detector according to claim 3, characterized in that: The second group of microlenses (6) includes a third microlens (403) and a fourth microlens (404); the third microlens (403) and the fourth microlens (404) are located directly above the photosensitive surface of the balanced detector active chip (3) and are fixed to the bottom surface of the micromirror (5) by an optically transparent adhesive.

5. The micro-integrated coherent balanced detector according to claim 4, characterized in that: The mixer passive chip (2) has two input ports and two output ports, the two input ports respectively input the signal light to be measured and the local oscillator light, and the two output ports are respectively provided with a mode field conversion structure, and the first microlens (401) and the second microlens (402) are respectively connected to the corresponding mode field conversion structure; the balanced detector active chip (3) comprises two detector array elements, each detector array element comprises a photosensitive surface, and the third microlens (403) and the fourth microlens (404) are respectively arranged directly above the photosensitive surface of the corresponding detector array element.

6. The micro-integrated coherent balanced detector according to claim 4, characterized in that: The micro-mirror (5) comprises an incident surface, a reflection surface and an exit surface; the incident surface is located directly in front of the exit light beams of the first micro-lens (401) and the second micro-lens (402); the reflection surface is inclined at 45° and is located inside the propagation path of the incident light beam, and is used to deflect the light beam by 90°; the exit surface is located at the bottom of the micro-mirror (5) and is perpendicular to the reflected light beam, and its bottom surface is used to connect to the third micro-lens (403) and the fourth micro-lens (404).

7. The micro-integrated coherent balanced detector according to claim 4, characterized in that: The third microlens (403) and the fourth microlens (404) are located 0.1-0.3 mm above the photosensitive surface of the balanced detector active chip (3).

8. The micro-integrated coherent balanced detector according to claim 4, characterized in that: The material of each microlens is resin, and its three-dimensional size is in the range of 0.5-1.5mm×0.5-1.5mm×0.2-0.6mm.

9. A detection method based on the micro-integrated coherent balanced detector according to any one of claims 1 to 8, characterized in that: include: Step 1: The signal light to be measured and the local oscillator light are coupled into the mixer passive chip through two input ports of the mixer passive chip respectively, and the signal light and the local oscillator light are coherently mixed in the mixer passive chip to generate a mixing signal containing characteristic information of the signal light to be measured; Step 2: The mixed signal is transmitted to the output port of the mixer passive chip through the on-chip waveguide in the mixer passive chip, and the beam mode field of the mixed signal is expanded at the output port through the mode field conversion structure; Step 3: The mixed signal after expanding the beam mode field is collimated and deflected 90° through an inter-chip coupled micro-transmitter-reflector group to achieve spatial light transmission; Step 4: The mixed light beam deflected by 90° is projected onto the first photosensitive surface and the second photosensitive surface of the balanced detector respectively, and the photosensitive surface absorbs the light signal and generates a photocurrent, and the current signal is collected by the metal electrode and transmitted to the signal processing circuit; Step 5: The signal processing circuit receives the two photocurrent signals transmitted by the balanced detector, extracts the intensity, frequency, phase and dynamic characteristics of the signal light to be measured over time through differential amplification and filtering, and outputs the processing results digitally.

10. The detection method according to claim 9, characterized in that: Step 3 includes: Step 3.1: The mixed signal after expanding the light beam mode field passes through a first microlens and a second microlens at the mode field conversion structure of two output ports of the mixer passive chip, and the output mixed light signal is collimated into a parallel light beam; Step 3.2: The two collimated light beams are horizontally projected onto the reflective surface of the micro-mirror, which is inclined at 45° to the horizontal plane, and a 90° deflection of the light beams is achieved through reflection; Step 3.3: The light beam deflected by the micromirror is further collimated by the third microlens and the fourth microlens at the bottom of the micromirror, and is vertically projected onto the photosensitive surface of the balanced detector.

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