An optical resonant accelerometer based on a broadband light source

Abstract

This invention discloses an optical resonant accelerometer based on a broadband light source, comprising a broadband light source, an optical reference cavity, a sensitive optical cavity, an electro-optic modulator, a photodetector, a circuit module, and a first equilateral triangular prism and a second equilateral triangular prism with identical structures. The broadband light source is incident perpendicularly onto the first side of the first equilateral triangular prism, then splits into two optical paths. The two optical paths pass through the optical reference cavity and the sensitive optical cavity respectively, and are coupled in the second equilateral triangular prism. The coupled beam is detected by the photodetector, which is connected to the circuit module. This invention features a simple structure, low cost, minimal susceptibility to environmental interference signals, and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of optical acceleration sensing technology, specifically designing an optical resonant accelerometer based on a broadband light source. Background Technology

[0002] Inertial navigation systems, as autonomous navigation systems that do not rely on external information, hold extraordinary importance in national defense and military applications, with wide applications in aircraft navigation, tactical and strategic missiles, and spacecraft. Accelerometers are a crucial component of inertial navigation systems, typically used to measure the acceleration of a carrier. Traditional accelerometers are usually electromechanical, relying heavily on piezoelectric, capacitive, and piezoresistive conversion methods, including piezoelectric materials, strain gauges, and capacitive sensors, to measure the displacement of a mass block relative to a local reference, converting this displacement into an output voltage or other types of electrical signals. However, this conversion method is significantly limited in sensitivity and precision, making it unsuitable for many applications requiring higher accuracy. Optical accelerometers, however, can overcome this limitation of traditional accelerometers. Optical resonant accelerometers, as an important type of optical accelerometer, typically employ a highly precise optical Fabry-Perot cavity (FP cavity) as the sensing element. The FP cavity provides high accuracy while also enabling highly sensitive measurement of minute displacements. Using a mass block and a fixed end as the two reflecting surfaces of an FP cavity, the displacement of the mass block caused by acceleration leads to a displacement of the mass block in the FP cavity, thereby causing a frequency shift in the transmission spectrum of the FP cavity. The optical frequency shift of the FP cavity is proportional to the acceleration. In addition to its own advantages of high precision and high sensitivity, optical resonant accelerometers are smaller, lighter, and have higher accuracy and sensitivity compared to conventional systems, but their cost is relatively high and they are not easy to mass-produce.

[0003] However, the complexity of the environments in which accelerometers are used often means that they are affected by factors such as temperature, air pressure, and other vibrations in the environment. Therefore, environmental factors can significantly interfere with the measurement results, affecting the accuracy of the accelerometer measurements and introducing substantial errors. Thus, reducing the impact of environmental factors on accelerometer measurement results has become a major challenge in improving accelerometer performance.

[0004] Furthermore, for optical resonant accelerometers, to improve detection accuracy, existing technologies typically require the use of narrow-linewidth lasers and frequency-locking techniques. Most existing optical accelerometers use narrow-linewidth lasers as their light source. However, while using a laser as the accelerometer's light source can achieve high accuracy and sensitivity, it necessitates a complex demodulation system, which undoubtedly increases the complexity of the entire sensing system, inevitably increasing the accelerometer's size and significantly raising costs. In addition, to avoid the influence of slowly changing environmental factors such as temperature and humidity on the test results, frequency locking of the laser and resonant cavity is often required, further increasing the overall system complexity and cost. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problem that improving the measurement accuracy of optical resonant accelerometers in the prior art requires high cost, this invention proposes an optical resonant accelerometer with simple structure, low cost and high accuracy. This invention provides an optical resonant accelerometer based on a broadband light source.

[0006] Technical Solution: An optical resonant accelerometer based on a broadband light source includes a broadband light source, an optical reference cavity, a sensitive optical cavity, an electro-optic modulator, a photodetector, a circuit module, and two identical equilateral triangular prisms, a first equilateral triangular prism and a second equilateral triangular prism. Both the first and second equilateral triangular prisms include a first included angle, a first side, and a second side. The first side is an adjacent side of the first included angle, and the second side is the opposite side of the first included angle. A 50-50 unpolarized beam splitter is embedded within each equilateral triangular prism. One end of the 50-50 unpolarized beam splitter is fixed to the first included angle, and the other end is fixed to the midpoint of the second side. The second side of the first equilateral triangular prism and the second side of the second equilateral triangular prism are... For the placement, taking the line where the 50-50 unpolarized beam splitter is located as the axis, an optical reference cavity and an electro-optic modulator are sequentially arranged above the axis between the first and second equilateral triangular prisms, and a sensitive optical cavity is arranged below the axis; both the optical reference cavity and the sensitive optical cavity are FP cavities, and both are parallel to the second sides of the first and second equilateral triangular prisms; a broadband light source is incident perpendicularly onto the first side of the first equilateral triangular prism, and then splits into two optical paths. The two optical paths pass through the optical reference cavity and the sensitive optical cavity respectively, and are then coupled in the second equilateral triangular prism. The coupled beam is detected by a photodetector, which is connected to a circuit module.

[0007] Furthermore, the sensitive optical cavity includes a first cavity mirror, a vertical connecting part, a horizontal connecting part, a mass block, and a cantilever beam. The horizontal connecting part is connected to the first cavity mirror through the vertical connecting part. The two ends of the mass block are connected to the horizontal connecting part through the cantilever beam. One end of the cantilever beam is connected to the horizontal connecting part, and the other end of the cantilever beam is connected to the mass block. The cantilever beam is made of silicon nitride, and the mass block can vibrate under the connection of the cantilever beam. The first cavity mirror is a plane mirror, and the surface of the mass block opposite to the first cavity mirror is a plane mirror.

[0008] Furthermore, the optical reference cavity includes a first cavity mirror, a second cavity mirror, and a connecting part. The two ends of the first cavity mirror and the second cavity mirror are connected by the connecting part. Both the first cavity mirror and the second cavity mirror are plane mirrors. The first cavity mirror, the second cavity mirror of the optical reference cavity, the first cavity mirror of the sensitive optical cavity, and the surface of the mass block opposite to the first cavity mirror are made of the same material. The optical reference cavity and the sensitive optical cavity have the same cavity length.

[0009] Furthermore, the first side of the first equilateral triangular prism and the second equilateral triangular prism includes a near-angle portion and a far-angle portion, the outer surface of the near-angle portion is coated with an anti-reflection coating, and the outer surface of the far-angle portion is coated with a high-reflection coating; the first equilateral triangular prism and the second equilateral triangular prism also include a third side, the third side includes a near-angle portion and a far-angle portion, and at least the outer surface of the far-angle portion of the third side is coated with a high-reflection coating.

[0010] Furthermore, the circuit module includes an operational amplifier, an analog-to-digital converter, a demodulation circuit, and a PC terminal connected in sequence, with the output terminal of the electro-optic modulator connected to the input terminal of the operational amplifier.

[0011] Furthermore, it does not include a PDH frequency locking circuit.

[0012] Compared with existing technologies, the optical resonant accelerometer based on a broadband light source provided by this invention has the following advantages:

[0013] (1) The light source adopts a broadband light source instead of a narrow linewidth laser, eliminating the need for a complex demodulation system. The entire accelerometer has a simple structure, small size, and low cost.

[0014] (2) The optical FP cavity, as a reference optical cavity, can eliminate or suppress the interference of other factors in the environment on the acceleration signal to be measured. It is less affected by environmental factors and has higher accuracy.

[0015] (3) A dual-optical-path structure is adopted, one of which serves as a reference optical path. However, only one photodetector is needed for the whole structure, which is simple and has a low cost. Attached Figure Description

[0016] Figure 1This is a schematic diagram of an optical resonant accelerometer based on a broadband light source.

[0017] Figure 2 This is a schematic diagram of the sensing element of an optical resonant accelerometer.

[0018] Figure 3 (a) is the transmission spectrum of the optical reference cavity signal;

[0019] Figure 3 (b) is the transmission spectrum of the sensitive optical cavity when there is no acceleration signal;

[0020] Figure 3 (c) is the transmission spectrum of the sensitive optical cavity when there is an acceleration signal;

[0021] Figure 3 (d) is the transmission spectrum after interference between the optical reference cavity signal and the sensitive optical cavity signal;

[0022] In the figure, 1 is a broadband light source, 2 is an optical reference cavity, 3 is a sensitive optical cavity, 4 is an electro-optic modulator, 5 is a photodetector, 6 is a circuit module, 7 is a first equilateral triangular prism, 8 is a second equilateral triangular prism, 9 is a first side, 10 is a second side, 11 is a 50-50 unpolarized beam splitter, 12 is a first cavity mirror, 13 is a vertical connecting part, 14 is a horizontal connecting part, 15 is a mass block, 16 is a cantilever beam, 17 is a near-angle part, 18 is a far-angle part, and 19 is a third side. Detailed Implementation

[0023] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0024] An optical resonant accelerometer based on a broadband light source, such as Figure 1As shown, it includes a broadband light source (ASE light source) 1, an optical reference cavity 2, a sensitive optical cavity 3, an electro-optic modulator (EOM) 4, a photodetector (PD) 5, a circuit module 6, and a first equilateral triangular prism 7 and a second equilateral triangular prism 8 with the same structure; the first equilateral triangular prism 7 and the second equilateral triangular prism 8 each include a first included angle, a first side 9 and a second side 10, the first side 9 is an adjacent side of the first included angle, and the second side 10 is the opposite side of the first included angle. A 50-50 unpolarized beam splitter 11 is embedded in the equilateral triangular prism to divide the prism into two 30-60-90 prisms. One end of the 50-50 unpolarized beam splitter 11 is fixed at the first included angle, and the other end is fixed at the midpoint of the second side 10. The second side of the first equilateral triangular prism 7 and the second side of the second equilateral triangular prism 8 are placed opposite each other. Taking the line where the 50-50 unpolarized beam splitter is located as the axis, an optical reference cavity 2 and an electro-optic modulator 4 are sequentially arranged above the axis between the first equilateral triangular prism 7 and the second equilateral triangular prism 8, and a sensitive optical cavity 3 is arranged below the axis. Both the optical reference cavity 2 and the sensitive optical cavity 3 are FP cavities. The reference cavity 2 and the sensitive optical cavity 3 are both parallel to the second side of the first equilateral triangular prism 7 and the second equilateral triangular prism 8. The light emitted by the broadband light source 1 is incident perpendicularly to the first side 9 of the first equilateral triangular prism 7, and then splits into two light paths. The two light paths pass through the optical reference cavity 2 and the sensitive optical cavity 3 respectively, and are coupled in the second equilateral triangular prism 8. The reference light path needs to be modulated by an electro-optic modulator after passing through the optical reference cavity 2. The coupled beam is detected by the photodetector 5, which is connected to the circuit module 6.

[0025] The sensitive optical cavity 3 includes a first cavity mirror 12, a vertical connecting part 13, a horizontal connecting part 14, a mass block 15, and a cantilever beam 16. The horizontal connecting part 14 is connected to the first cavity mirror 12 through the vertical connecting part 13. The two ends of the mass block 15 are connected to the horizontal connecting part 14 through the cantilever beam 16. One end of the cantilever beam 16 is connected to the horizontal connecting part 14, and the other end of the cantilever beam 16 is connected to the mass block 15. The cantilever beam 16 is made of silicon nitride. The mass block 15 is not directly connected to the horizontal connecting part 14, and the part between them is suspended. The mass block 15 can vibrate under the connection of the cantilever beam 16. The first cavity mirror 12 is a plane mirror, and the surface of the mass block 15 opposite to the first cavity mirror 12 is a plane mirror.

[0026] The optical reference cavity 2 includes a first cavity mirror, a second cavity mirror, and a connecting part. The two ends of the first cavity mirror and the second cavity mirror are connected by the connecting part. Both the first cavity mirror and the second cavity mirror are plane mirrors. The first cavity mirror, the second cavity mirror of the optical reference cavity, the first cavity mirror of the sensitive optical cavity, and the surface of the mass block opposite to the first cavity mirror are made of the same material. The optical reference cavity and the sensitive optical cavity have the same cavity length.

[0027] The first side 9 of the first equilateral triangular prism 7 and the second equilateral triangular prism 8 includes a near-angle portion 17 and a far-angle portion 18. The outer surface of the near-angle portion 17 is coated with an anti-reflection (AR) coating, and the outer surface of the far-angle portion 18 is coated with a high-reflection (HR) coating, used to reflect signals from the reference optical path. The first and second equilateral triangular prisms also include a third side 19, which is the other adjacent side of the first angle. The third side 19 includes a near-angle portion and a far-angle portion, and at least the outer surface of the far-angle portion of the third side is coated with a high-reflection coating, used to reflect signals from the measurement optical path.

[0028] The optical resonant accelerometer based on a broadband light source in this embodiment adopts a dual-optical-path structure. One optical path is the optical path of the sensing unit, and the other is the reference optical path. Both the optical reference cavity 2 and the sensing optical cavity 3 are FP cavities. To ensure effective suppression of interference signals in the environment, the optical reference cavity 2 and the sensing optical cavity 3 not only adopt the same structure, but also maintain the same materials and cavity lengths. The only difference is that the two cavity mirrors of the optical reference cavity are fixed, while one side of the FP cavity of the sensing optical cavity is a vibrating mass suspended by a cantilever beam, and the other side is a plane mirror, the same as the cavity mirror of the optical reference cavity.

[0029] During measurement, such as Figure 1 The dashed line represents the optical path. A broadband light source is incident perpendicularly onto the first side of the first equilateral triangular prism 7, passing through the AR coating near the included angle of the first side before entering the prism. After passing through the 50-50 unpolarized beam splitter 11, the beam becomes two optical paths. These two paths are reflected by the HR coatings at the far included angles of the first and third sides of the prism, respectively, and then incident perpendicularly into the optical reference cavity 2 and the sensitive optical cavity 3. The optical path containing the optical reference cavity 2 serves as the reference signal path. After passing through the optical reference cavity, the reference signal path passes through an electro-optic modulator (EOM) to modulate the transmission spectrum of the optical reference cavity before reaching the second equilateral triangular prism 8. The optical path containing the sensitive optical cavity 3 serves as the measurement signal path. After passing through the sensitive optical cavity 3, the measurement signal path reaches the second equilateral triangular prism 8. The second equilateral triangular prism 8 couples the two optical paths into a single optical path, which is then detected by a photodetector 9. Finally, the detected optical signal is demodulated, and the output of the photodetector is connected to circuit module 6. This circuit module includes an operational amplifier, an analog-to-digital converter, an FPGA demodulation circuit, and a PC connected in sequence. Data analysis is performed on the PC to determine the change in acceleration. The circuit module does not contain a PDH frequency-locking loop.

[0030] Working principle of sensitive optical cavity: such as Figure 2As shown, the light path is incident from above. When an acceleration signal arrives, the mass block will resonate vertically. At this time, the cavity length of the FP cavity formed by the mass block and the first cavity mirror will change, thus causing a change in the cavity resonant frequency. The magnitude of the detected acceleration signal is determined by the proportionality of the frequency shift of the transmission spectrum resonant frequency to the acceleration signal.

[0031] The incident light path is first split into two paths, one for measurement and the other as a reference. These two paths then converge through a prism and interfere with each other. When there is no acceleration signal, the transmission spectrum of the optical reference cavity is as follows (…). Figure 3 (a) and the transmission spectrum of the sensitive optical cavity ( Figure 3 (b) When the prisms are superimposed, the power of the signal detected by the PD is at its maximum value, such as... Figure 3 As shown in (d), Figure 3 (d) Point A is the point of maximum power. When there is an acceleration signal, the transmission spectrum of the optical path containing the sensitive optical cavity undergoes a frequency shift, such as... Figure 3 As shown in (c), the frequency shift is -Δf1 or Δf1. However, the transmission spectrum of the optical path containing the optical reference cavity remains unchanged. Therefore, after the transmission spectra of the two optical paths are superimposed again through the prism, the power of the signal detected by the PD will decrease, as shown in (c). Figure 3 As shown in (d), points B and C are the power points detected when the transmission spectrum of the sensitive optical cavity undergoes a frequency shift of -Δf1 or Δf1. This is used to determine the received acceleration signal. However, without modulation, the slope of the highest point of the transmission spectrum is 0, resulting in low sensitivity and inability to distinguish the direction of the acceleration signal. Therefore, an EOM is used to apply a sine wave or sawtooth wave modulation to the signal of the optical reference cavity, causing a corresponding frequency shift in the transmission spectrum, thus placing the wavelength at the position of maximum slope. This improves the measurement sensitivity and also allows for the determination of the direction of the acceleration signal.

[0032] This embodiment uses a simple and low-cost broadband light source to replace the complex and expensive narrow-linewidth laser light source used in most optical accelerometers. This not only greatly reduces the cost of the optical resonant accelerometer, but also eliminates the need for the subsequent PDH frequency locking circuit, making the accelerometer system simpler overall.

[0033] In addition, to eliminate the influence of external environmental interference, an optical reference cavity is introduced into the system. Both the optical reference cavity and the sensitive optical cavity are FP cavities, maintaining consistency in parameters such as structure, materials, and cavity length. Interference between the transmission spectra of the optical reference cavity and the sensitive optical cavity suppresses interference factors in the environment, reducing the impact of factors other than the measured acceleration signal on the measurement results and thus making the results more accurate.

Claims

1. An optical resonant accelerometer based on a broad spectrum light source, characterized in that, The application relates to a sensitive optical cavity and an optical reference cavity, and belongs to the field of optical fiber communication.

2. The optical resonant accelerometer based on a broadband light source according to claim 1, characterized in that, The sensitive optical cavity comprises a first mirror, a vertical connecting part, a horizontal connecting part, a mass block and a cantilever beam, the horizontal connecting part and the first mirror are connected through the vertical connecting part, the two ends of the mass block are connected with the horizontal connecting part through the cantilever beam, one end of the cantilever beam is connected with the horizontal connecting part, and the other end of the cantilever beam is connected with the mass block, the cantilever beam is made of silicon nitride, and the mass block can vibrate under the connection of the cantilever beam; the first mirror is a plane mirror, and the surface opposite to the first mirror of the mass block is a plane mirror.

3. The optical resonant accelerometer based on a broadband light source according to claim 1 or 2, characterized in that, The optical reference cavity comprises a first mirror, a second mirror and a connecting part, the two ends of the first mirror and the second mirror are connected through the connecting part, and the first mirror and the second mirror are plane mirrors; the first mirror and the second mirror of the optical reference cavity and the first mirror and the surface opposite to the first mirror of the mass block of the sensitive optical cavity adopt the same material, and the cavity lengths of the optical reference cavity and the sensitive optical cavity are the same.

4. The optical resonant accelerometer based on a broadband light source according to claim 1 or 2, characterized in that, The first edge of the first equilateral triangular prism and the second equilateral triangular prism comprises a near-angle part and a far-angle part, the outer side surface of the near-angle part is coated with an anti-reflection coating, and the outer side surface of the far-angle part is coated with a high-reflection coating; the first edge of the first equilateral triangular prism and the second equilateral triangular prism further comprises a third edge, the third edge comprises a near-angle part and a far-angle part, and the outer side surface of at least the far-angle part of the third edge is coated with a high-reflection coating.

5. The optical wide-spectrum light source based resonant accelerometer according to claim 1 or 2, c h a r a c t e r i z e d in that, The circuit module comprises an operational amplifier, an analog-to-digital converter, a demodulation circuit and a PC end which are sequentially connected, and the output end of the electro-optical modulator is connected with the input end of the operational amplifier.

6. The optical wide-spectrum light source based resonant accelerometer according to claim 1 or 2, characterized in that, The PDH frequency-locked loop is not included.

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