An integrated micro-opto-electromechanical system accelerometer based on ridge waveguide

Abstract

The application discloses a kind of integrated micro-optical mechanical system accelerometers based on ridge waveguide, including ridge waveguide structure, photonic crystal waveguide structure, photonic crystal resonant cavity, mass block;Photonic crystal resonant cavity includes two photonic crystal plates and the air slot between;Ridge waveguide structure includes first wide ridge waveguide 1a, first tapered ridge waveguide 2a, second tapered ridge waveguide 2b and second wide ridge waveguide 1b, first / two tapered ridge waveguide 2a / 2b connects first / two wide ridge waveguide 1a / 1b and first / two photonic crystal waveguide 3a / 3b, first photonic crystal waveguide 3a and second photonic crystal waveguide 3b are coupled by photonic crystal waveguide-microcavity coupling structure 4a;First photonic crystal waveguide 3a, second photonic crystal waveguide 3b and photonic crystal waveguide-microcavity coupling structure 4a are located on photonic crystal plate A;Photonic crystal plate B is etched on mass block.The application utilizes ridge waveguide technology to realize high sensitivity and high integration, while maintaining the advantages of simple structure and low-cost manufacturing.

Description

Technical Field

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

[0002] With the rapid development of microelectromechanical systems (MEMS) technology, optomechanical sensors have attracted widespread attention due to their superior noise performance and potential for cross-application in emerging sensor technologies. These sensors utilize a variety of materials, including silicon nitride, silicon, and lithium niobate, and employ a variety of structural designs, such as Zipper cavities, photonic crystal cavities, microdisks, and Fabry-Pérot cavities, all of which have demonstrated high-performance detection capabilities. However, the integration of these sensors into MEMS systems has been relatively slow, particularly due to challenges in compatibility and integration efficiency.

[0003] While microaccelerometers are widely used in various fields due to their small size, low cost, and low power consumption, traditional MEMS microaccelerometers still need to be improved in terms of sensitivity, resolution, and integration. Most existing accelerometers rely on mechanical or electrical detection methods, which can lead to insufficient sensitivity and strong environmental interference.

[0004] The SOI-based cavity optomechanical micro-opto-electromechanical system (MOEMS) accelerometer not only has the advantages of MEMS sensors such as small size, light weight, and low energy consumption, but also has the ultra-low noise and ultra-high precision characteristics of optical measurement. It is also compatible with mature semiconductor processes to a certain extent and has huge application potential. Cavity optomechanical MOEMS accelerometers require coupling lasers into optical microcavities when performing acceleration measurements. The traditional method of using micro-concave optical fibers to achieve optical microcavity coupling is not stable enough and is not conducive to the integrated packaging of accelerometer chips. When using silicon waveguides to integrate with accelerometers to achieve optical microcavity coupling, due to the structural characteristics of the waveguides, when the dry gas etching of the accelerometer chip is performed to leave the mass block suspended, the silicon dioxide below the waveguides will also be etched, causing the waveguides 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) accelerometers due to silicon waveguide collapse, and to provide an integrated micro-opto-electromechanical system (MOEMS) accelerometer based on ridge waveguides. 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 includes two photonic crystal plates and an air slot located between the two photonic crystal plates;

[0008] 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 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 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.

[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 to the functional layer of the SOI substrate via at least four cantilever beams to form a mechanical resonant structure, wherein there is 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] This accelerometer, based on ridge waveguide integration, utilizes ridge waveguide technology to achieve high sensitivity and high integration while maintaining the advantages of a simple structure and low-cost manufacturing. By integrating it with a detection device, this design can be applied to a wider range of fields, particularly those requiring high-precision and high-stability acceleration measurements.

[0015] 2. While the ridge waveguide has excellent optical transmission, due to the structural characteristics of the ridge waveguide, the etched grooves on both sides will not etch through the top silicon of the 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 Schematic diagram of the overall structure of the ridge waveguide integrated accelerometer of the present invention;

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

[0018] Figure 3 Schematic diagram of the structure of the ridge waveguide;

[0019] Figure 4 Schematic diagram of the structure of the 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 with reference to the accompanying drawings.

[0022] An integrated micro-opto-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 and formed 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 located 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 respectively arranged at the incident and emission ends of the laser; 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, as shown in FIG. 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 an optical fiber through a 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, the 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 effect 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, this ultimately enables analysis and detection of the optical modes of the photonic crystal microcavity and the mechanical modes of the mechanical oscillator. The connection between the laser source and the optical fiber, as well as the optical signal conditioning circuitry, can be added or removed based on the desired functionality.

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

[0030] This invention designs a ridge waveguide integrated accelerometer capable of detecting triaxial acceleration. The device comprises a ridge waveguide, a mass, an optomechanical coupling structure, a light source, and a photodetector, integrated using an SOI (silicon-on-insulator) substrate. Acceleration acts on the suspended mass, inducing minute deformations in the photonic crystal resonant cavity, which in turn results in changes in the optical signal. The accelerometer of this invention is fabricated as follows:

[0031] (1) Material and process preparation: An 8-inch SOI wafer was selected as the substrate. The thickness of the top silicon layer on the substrate was about 500 nm, and the thickness of the silicon dioxide (SiO2) intermediate layer was 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 ( Figure 3 The Si thickness is 350nm. The silicon dioxide layer beneath the mass block is then removed through a dry etching process, leaving the suspended mass suspended in the air. Supported by the cantilever beam, the mass block forms a mechanical oscillator. Air holes are removed from the photonic crystal plate A to create a light path, 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) Accelerometer integration: Assemble the modules according to the structure of the integrated accelerometer of the present invention. The laser is input from the first wide ridge waveguide 1a, 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, and couples the laser into the photonic crystal microcavity, causing it to resonate, and drives 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 optomechanical 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, ultimately realizing the analysis and detection of the optical mode of the photonic crystal microcavity and the mechanical mode of the mechanical oscillator.

[0035] (5) Signal processing and output: The photodetector output signal 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. 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 calibration, the output of the device is measured to verify the accuracy of the three-axis detection.

[0037] Transmission efficiency simulations show that the bus waveguide loss is close to the typical loss of silicon waveguide transmission, which is 1 to 1.5 dB / cm. The ridge waveguide loss primarily stems from the tapered transition from the coupling facet to the bus waveguide. The coefficient for the facet-to-bus waveguide transition is m = 1.15. Combined with the simulation results for facet coupling, it is concluded that a ridge thickness of 100 nanometers and a facet width close to the beam's mode field size of 2 microns is a reasonable choice, balancing performance and practical processing conditions.

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

[0039] This design enables the accelerometer to respond to external acceleration signals along three axes. When the acceleration causes the mass to vibrate, minute deformations in the photonic crystal cavity cause changes in optical frequency, phase, and intensity, which the photodetector converts into electrical signals. After amplification and filtering by the signal processing unit, accurate acceleration values ​​are 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 it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. An integrated micro-ophthalo-electromechanical system accelerometer based on a 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 includes two photonic crystal plates and an air slot located between the two photonic crystal plates; The ridge waveguide structure comprises 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; 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 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 via 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 laser is coupled to the first wide ridge waveguide (1a) through an optical fiber, and 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 a change in the optical signal; 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; The ridge waveguide structure is formed on the functional layer of the SOI substrate through photolithography and etching processes; an SOI wafer is selected as the substrate, and the thickness of the top silicon on the substrate is 500nm; the ridge waveguide and the mass block structure are etched on the top silicon using a photolithography process, and the thickness of the ridge waveguide is 350nm.

2. The ridge waveguide-based integrated micro-ophthalo-electromechanical system accelerometer 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.

3. The integrated micro-ophthalo-electromechanical system accelerometer based on ridge waveguide according to claim 1, 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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