Integrated micro-opto-electro-mechanical system accelerometer based on ridge waveguide

Abstract

The invention discloses an integrated micro-opto-electro-mechanical system accelerometer based on a ridge waveguide. The integrated micro-opto-electro-mechanical system accelerometer comprises a ridge waveguide structure, a photonic crystal waveguide structure, a photonic crystal resonant cavity and a mass block, the photonic crystal resonant cavity comprises two photonic crystal plates and an air slot between the two photonic crystal plates; the ridge waveguide structure comprises a first wide ridge waveguide 1a, a first gradual change ridge waveguide 2a, a second gradual change ridge waveguide 2b and a second wide ridge waveguide 1b, the first / second gradual change ridge waveguide 2a / 2b is connected with the first / second wide ridge waveguide 1a / 1b and the first / second photonic crystal waveguide 3a / 3b, and the first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b are coupled through the photonic crystal waveguide-microcavity coupling structure 4a; the first photonic crystal waveguide 3a, the second photonic crystal waveguide 3b and the photonic crystal waveguide-microcavity coupling structure 4a are located on the photonic crystal plate A; and the photonic crystal plate B is etched on the mass block. According to the invention, high sensitivity and high integration level are realized by using the ridge waveguide technology, and the advantages of simple structure and low manufacturing cost are maintained at the same time.

Description

Technical Field

[0001] The present invention relates to micro-opto-electro-mechanical systems (MOEMS) and sensor integration technology, in particular to a high-sensitivity, multi-dimensional integrated MOEMS accelerometer based on ridge waveguide integration. Background Art

[0002] With the rapid development of micro-electromechanical systems (MEMS) technology, optomechanical sensors have attracted widespread attention due to their excellent performance in noise performance and their potential for cross-application in emerging sensor technologies. These sensors use a variety of materials, including silicon nitride, silicon and lithium niobate, and a variety of structural designs, such as Zipper cavity, photonic crystal cavity, microdisk and Fabry-Pérot cavity, all of which have demonstrated high-performance detection capabilities. However, the integration of these sensors with MEMS systems has been relatively slow, especially in terms of compatibility and integration efficiency.

[0003] Although micro accelerometers are widely used in many fields due to their advantages such as small size, low cost and low power consumption, traditional MEMS micro accelerometers still need to be improved in terms of sensitivity, resolution and integration. Most existing accelerometers rely on mechanical or electrical detection methods, which have problems such as insufficient sensitivity and strong environmental interference.

[0004] The cavity optomechanical micro-opto-electromechanical system (MOEMS) accelerometer based on SOI not only has the advantages of small size, light weight and low energy consumption of MEMS sensors, but also has the ultra-low noise and ultra-high precision characteristics of optical measurement, and is compatible with mature semiconductor processes to a certain extent, and has great application potential. The cavity optomechanical MOEMS accelerometer needs to couple the laser into the optical microcavity when measuring acceleration. The traditional method of using micro-concave optical fiber to achieve optical microcavity coupling is not stable enough, which is not conducive to the integrated packaging of accelerometer chips. When the optical microcavity coupling is achieved by integrating silicon waveguide with accelerometer, due to the structural characteristics of the waveguide, when the dry gas etching of the accelerometer chip is performed to make the mass block suspended, the silicon dioxide under the waveguide will also be etched, which will cause the waveguide to collapse, and the processing success rate is very low. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem of low chip processing yield of traditional strip waveguide integrated cavity optomechanical MOEMS accelerometer due to silicon waveguide collapse, and to provide an integrated micro-opto-electromechanical system accelerometer based on ridge waveguide. The ridge waveguide technology is used to greatly improve the processing success rate. While ensuring the high sensitivity and high integration of the accelerometer, it has the advantages of simple structure and low-cost manufacturing.

[0006] The object of the present invention is achieved through the following technical solutions: an integrated micro-opto-electromechanical system accelerometer based on a ridge waveguide, comprising a ridge waveguide structure, a photonic crystal waveguide structure, a photonic crystal resonant cavity, and a mass block;

[0007] The photonic crystal resonant cavity comprises two photonic crystal plates and an air slot located between the two photonic crystal plates;

[0008] The ridge waveguide structure comprises a first wide ridge waveguide 1a, a first tapered ridge waveguide 2a, a second tapered ridge waveguide 2b and a second wide ridge waveguide 1b arranged along the injection and emission directions of the photonic crystal resonant cavity; the first wide ridge waveguide 1a and the second wide ridge waveguide 1b have the same structure and are symmetrically arranged, and are arranged at the injection and emission ends of the laser, respectively; the first tapered ridge waveguide 2a and the second tapered ridge waveguide 2b have the same structure and are symmetrically arranged; the first tapered ridge waveguide 2a connects the first wide ridge waveguide 1a and the first photonic crystal waveguide 3a, and the second tapered ridge waveguide 2b connects the second photonic crystal waveguide 3b and the second wide ridge waveguide 1b;

[0009] The photonic crystal waveguide structure comprises a first photonic crystal waveguide 3a and a second photonic crystal waveguide 3b, wherein the first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b have the same structure and are symmetrically arranged; the first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b are coupled through a photonic crystal waveguide-microcavity coupling structure 4a; wherein the first photonic crystal waveguide 3a, the second photonic crystal waveguide 3b and the photonic crystal waveguide-microcavity coupling structure 4a are located on a photonic crystal plate A;

[0010] The mass block is fixed on the functional layer of the SOI substrate through a cantilever beam, and the photonic crystal plate B is etched on the mass block.

[0011] The ridge waveguide structure is formed on the functional layer of the SOI substrate through photolithography and etching processes.

[0012] The mass block is fixed on the functional layer of the SOI substrate through at least four cantilever beams to form a mechanical resonance structure, wherein there is a strong coupling between the optical mode of the photonic crystal resonant cavity and the mechanical vibration mode of the mass block.

[0013] The beneficial effects of the present invention are:

[0014] 1. The accelerometer based on ridge waveguide integration of the present invention achieves high sensitivity and high integration by using ridge waveguide technology, while maintaining the advantages of simple structure and low-cost manufacturing. Through integration with detection devices, the design can be applied more widely, especially in fields that require high-precision and high-stability acceleration measurement.

[0015] 2. While the ridge waveguide has excellent optical transmission, due to the structural characteristics of the ridge waveguide, the etching grooves on both sides will not etch through the top silicon of SOI. Therefore, when the accelerometer chip is dry-etched with gas, the silicon dioxide under the ridge waveguide will not be etched by the hydrogen fluoride gas, thereby effectively preventing the collapse of the long-distance silicon waveguide. Therefore, the ridge waveguide structure will not be destroyed, which can greatly improve the processing success rate of the integrated silicon waveguide accelerometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the ridge waveguide integrated accelerometer of the present invention;

[0017] Figure 2 This is a partial enlarged view of the photonic crystal resonant cavity;

[0018] Figure 3 is a schematic diagram of the structure of the ridge waveguide;

[0019] Figure 4 is a schematic diagram of the structure of a photonic crystal waveguide structure;

[0020] Figure 5 Schematic diagram of the integrated detection device. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0022] An integrated micro-optical electromechanical system accelerometer based on a ridge waveguide includes a ridge waveguide structure, a photonic crystal waveguide structure, a photonic crystal resonant cavity, and a mass block; Figure 1 As shown in the figure, the purple part in the middle is the ridge waveguide structure, and there are mass blocks on the upper and lower sides. The upper mass block is a fixed mass block (the photonic crystal plate A is processed on the fixed mass block); the lower mass block is a movable mass block, which can achieve resonance (unless otherwise specified, the mass blocks referred to in the following text are all movable mass blocks).

[0023] The photonic crystal resonant cavity includes two photonic crystal plates and an air slot between the two photonic crystal plates. Figure 2 As shown;

[0024] The ridge waveguide structure includes a first wide ridge waveguide 1a, a first gradient ridge waveguide 2a, a second gradient ridge waveguide 2b and a second wide ridge waveguide 1b arranged along the injection and emission directions of the photonic crystal resonant cavity. Figure 3As shown; the first wide ridge waveguide 1a and the second wide ridge waveguide 1b have the same structure and are symmetrically arranged, and are arranged at the laser input and output ends respectively; the first gradient ridge waveguide 2a and the second gradient ridge waveguide 2b have the same structure and are symmetrically arranged; the first gradient ridge waveguide 2a connects the first wide ridge waveguide 1a and the first photonic crystal waveguide 3a, and the second gradient ridge waveguide 2b connects the second photonic crystal waveguide 3b and the second wide ridge waveguide 1b;

[0025] The photonic crystal waveguide structure includes a first photonic crystal waveguide 3a and a second photonic crystal waveguide 3b. The first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b have the same structure and are symmetrically arranged. The first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b are coupled through a photonic crystal waveguide-microcavity coupling structure 4a. The first photonic crystal waveguide 3a, the second photonic crystal waveguide 3b and the photonic crystal waveguide-microcavity coupling structure 4a are located on a photonic crystal plate A, such as Figure 4 As shown;

[0026] The mass block is fixed on the functional layer of the SOI substrate through a cantilever beam, and the photonic crystal plate B is etched on the mass block;

[0027] The integrated detection device using the accelerometer of the present invention includes a laser source, a polarization controller, an accelerometer, a photodetector, and a signal conditioning circuit. The laser emitted by the laser source is connected to the optical fiber through the polarization controller (FPC), and the laser is coupled to the first wide ridge waveguide 1a through the optical fiber. Figure 3 As shown in the figure, Fiber Core is an optical fiber; then the first wide ridge waveguide 1a inputs the light into the first photonic crystal waveguide 3a, and the first photonic crystal waveguide 3a couples the light into the photonic crystal resonant cavity; the photomechanical coupling of the photonic crystal resonant cavity drives the mass block to resonate, causing a slight deformation of the photonic crystal resonant cavity, thereby causing the optical signal to change; the laser carrying the photomechanical coupling information passes through the second photonic crystal waveguide 3b, the second gradient ridge waveguide 2b and the second wide ridge waveguide 1b in sequence, and is input into the photodetector by the optical fiber; the optical signal output by the photodetector is separated into a high-frequency optical signal and a low-frequency radio frequency signal, which are respectively input into the signal conditioning circuit. The signal conditioning circuit includes attenuators, spectrum analyzers, power meters, frequency meters, DAQ, host computers and other equipment, such as Figure 5 As shown. Finally, the analysis and detection of the optical mode of the photonic crystal microcavity and the mechanical mode of the mechanical oscillator are realized. The connection method between the laser source and the optical fiber, as well as the optical signal conditioning circuit can be increased or decreased according to the actual function to be detected.

[0028] The ridge waveguide structure is formed on the functional layer of the SOI substrate through photolithography and etching processes.

[0029] The mass block is fixed on the functional layer of the SOI substrate through at least four cantilever beams to form a mechanical resonance structure, wherein there is a strong coupling between the optical mode of the photonic crystal resonant cavity and the mechanical vibration mode of the mass block.

[0030] The present invention designs a ridge waveguide integrated accelerometer capable of detecting triaxial acceleration. The device comprises a ridge waveguide, a mass block, an optomechanical coupling structure, a light source and a photodetector, and is structurally integrated using an SOI (silicon on insulator) substrate. Acceleration acts on the suspended mass block, causing a slight deformation of the photonic crystal resonant cavity, thereby causing an optical signal change. The preparation steps of the accelerometer of the present invention are:

[0031] (1) Material and process preparation: An 8-inch SOI wafer is selected as the substrate. The thickness of the top silicon layer on the substrate is about 500 nm, and the thickness of the silicon dioxide (SiO2) middle layer is 3 μm.

[0032] (2) Structural processing of ridge waveguide, photonic crystal waveguide and mass block: The ridge waveguide and mass block structure are etched on the top silicon layer using photolithography. The thickness of the ridge waveguide is ( Figure 3 The Si thickness is 350nm; the silicon dioxide layer under the mass block is etched away by dry etching process to make the suspended mass block suspended in the air, and the mass block forms a mechanical oscillator under the support of the cantilever beam. A part of the air holes are removed from the photonic crystal plate A to form a path through which light can pass, forming a photonic crystal waveguide and a photonic crystal waveguide-microcavity coupling structure.

[0033] (3) Integration of detection module: A micro laser source is integrated at one end of the ridge waveguide and a photodetector is integrated at the other end to detect the optical signal passing through the photonic crystal cavity.

[0034] (4) Integration of accelerometer: Assemble each module according to the structure of the integrated accelerometer of the present invention. The laser is input from the first wide ridge waveguide 1a, and passes through the first gradient ridge waveguide 2a, the first photonic crystal waveguide 3a, and the photonic crystal waveguide-microcavity coupling structure 4a in sequence, coupling the laser into the photonic crystal microcavity to make it resonate, and driving the detection mass block to resonate through the photomechanical coupling effect. The first photonic crystal waveguide 3a then couples the light into the photonic crystal resonant cavity; the mass block is driven to resonate through the photomechanical coupling effect of the photonic crystal resonant cavity; the laser carrying the photomechanical coupling information passes through the second photonic crystal waveguide 3b, the second gradient ridge waveguide 2b, and the second wide ridge waveguide 1b in sequence, and is input into the photodetector through the optical fiber; the optical signal output by the photodetector is separated into a high-frequency optical signal and a low-frequency radio frequency signal, which are respectively input into the signal conditioning circuit, and finally the optical mode of the photonic crystal microcavity and the mechanical mode of the mechanical oscillator are analyzed and detected.

[0035] (5) Signal processing and output: The output signal of the photodetector is transmitted to the signal processing unit, which performs real-time analysis and amplification of acceleration signals in different directions. The signal processing unit can filter out environmental noise, compensate for temperature drift, and ensure the stability of the accelerometer in complex environments.

[0036] (6) Testing and calibration: The accelerometer is placed on a vibration table with known acceleration for calibration, and the sensitivity of the ridge waveguide is adjusted to ensure that the detection accuracy in the X, Y, and Z directions meets the predetermined requirements. After the calibration is completed, the output results of the measurement device are measured to verify the accuracy of the three-axis detection.

[0037] In terms of transmission efficiency simulation, the simulation results show that the bus waveguide loss is close to the normal loss of silicon waveguide transmission, that is, 1 to 1.5 dB / cm, while the ridge waveguide loss mainly comes from the tapered transition of the coupling end face to the bus waveguide. The coefficient of the end face gradual transition to the bus waveguide is m = 1.15. Combined with the simulation results of the end face coupling, it is concluded that a ridge thickness of 100 nanometers and an end face width close to the spot mode field size of 2 microns is a reasonable choice, taking into account both performance and actual processing conditions.

[0038] The final designed ridge waveguide achieved a transmission efficiency of 82% to 94% in the 1480-nanometer to 1630-nanometer band, and a transmission efficiency of 82.9% at a wavelength of 1550 nanometers, which is typical for optomechanical sensing applications, and an end-face coupling efficiency of 46.3%.

[0039] Through the above design, the accelerometer can respond to the acceleration signal applied by the outside world in three-axis directions. When the acceleration causes the mass block to vibrate, the slight deformation of the photonic crystal cavity causes the optical frequency, phase and intensity to change, and the photodetector converts it into an electrical signal. After amplification and filtering by the signal processing unit, an accurate acceleration value can be obtained.

[0040] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. An integrated micro-ophthalomechanical system accelerometer based on ridge waveguide, characterized in that: Including ridge waveguide structure, photonic crystal waveguide structure, photonic crystal resonant cavity, and mass block; The photonic crystal resonant cavity comprises two photonic crystal plates and an air slot located between the two photonic crystal plates; The ridge waveguide structure includes a first wide ridge waveguide 1a, a first tapered ridge waveguide 2a, a second tapered ridge waveguide 2b and a second wide ridge waveguide 1b arranged along the injection and emission directions of the photonic crystal resonant cavity; The first wide ridge waveguide 1a and the second wide ridge waveguide 1b have the same structure and are symmetrically arranged, and are arranged at the laser input and output ends respectively; the first gradient ridge waveguide 2a and the second gradient ridge waveguide 2b have the same structure and are symmetrically arranged; the first gradient ridge waveguide 2a connects the first wide ridge waveguide 1a and the first photonic crystal waveguide 3a, and the second gradient ridge waveguide 2b connects the second photonic crystal waveguide 3b and the second wide ridge waveguide 1b; The photonic crystal waveguide structure comprises a first photonic crystal waveguide 3a and a second photonic crystal waveguide 3b, wherein the first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b have the same structure and are symmetrically arranged; the first photonic crystal waveguide 3a and the second photonic crystal waveguide 3b are coupled through a photonic crystal waveguide-microcavity coupling structure 4a; wherein the first photonic crystal waveguide 3a, the second photonic crystal waveguide 3b and the photonic crystal waveguide-microcavity coupling structure 4a are located on a photonic crystal plate A; The mass block is fixed on the functional layer of the SOI substrate through a cantilever beam, and the photonic crystal plate B is etched on the mass block.

2. The integrated micro-o-electromechanical system accelerometer based on ridge waveguide according to claim 1, characterized in that: The ridge waveguide structure is formed on the functional layer of the SOI substrate through photolithography and etching processes.

3. The integrated micro-o-electromechanical system accelerometer based on ridge waveguide according to claim 1, characterized in that: The mass block is fixed on the functional layer of the SOI substrate through at least four cantilever beams to form a mechanical resonant structure.

4. The integrated micro-o-electromechanical system accelerometer based on ridge waveguide according to claim 3, characterized in that: There is a strong coupling between the optical mode of the photonic crystal resonator and the mechanical vibration mode of the mass block.

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