High-extinction-ratio optical fiber acousto-optic modulator, light modulation method and optical fiber sensing system

Abstract

The invention discloses a high-extinction-ratio optical fiber acousto-optic modulator, a light modulation method and an optical fiber sensing system. The modulator comprises a base, an input end optical fiber collimator, an acousto-optic medium, a polarization splitting prism, two output end optical fiber collimators, a matching network and a radio frequency socket. And a transverse wave transducer is bonded on a sound transmission surface of the acousto-optic medium and is connected with the radio frequency socket through a matching network. During working, the transducer is driven by a radio-frequency signal to excite transverse ultrasonic waves in the acousto-optic medium, so that abnormal Bragg diffraction of incident laser occurs. 0-level light and 1-level diffraction light which are output after diffraction are separated by the polarization splitting prism and then are respectively coupled to the first output end optical fiber collimator and the second output end optical fiber collimator to be output. The structure effectively increases the separation angle of two light beams, significantly inhibits 0-level optical crosstalk, realizes high extinction ratio in a single device, and has the advantages of compact structure, low insertion loss and low power consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic technology, in particular to a high-extinction-ratio fiber-optic acousto-optic modulator, an optical modulation method and a fiber-optic sensing system. BACKGROUND

[0002] A distributed fiber-optic sensing system uses an optical fiber as a signal transmission medium and a sensing unit, and can continuously sense the spatial distribution and change information of external parameters along the optical fiber in a long distance and a large range. Among them, a distributed fiber-optic sensing system based on a phase-sensitive optical time domain reflectometer (OTDR) has become an important branch of distributed fiber-optic sensing technology due to its wide sensing range, high spatial resolution, compact structure and rapid response. At present, this technology has been widely used in the fields of power monitoring, perimeter security, oil and gas exploration and seismic wave detection.

[0003] A fiber-optic acousto-optic modulator is a core device of an OTDR, and requires that the optical pulse entering the sensing optical fiber has a high enough extinction ratio. Otherwise, there will be obvious crosstalk between the sensing signals, which will affect the accuracy of sensing. At present, the limit value of the extinction ratio of a single acousto-optic modulator is 60 dB. Usually, a cascaded mode of two fiber-optic acousto-optic modulators is used to improve the extinction ratio, but this mode will significantly increase the product size, increase the insertion loss and power consumption, and is not conducive to the development of fiber-optic sensing systems towards low power consumption and miniaturization, thereby limiting the further application of the system. SUMMARY

[0004] In view of the above problems in the prior art, the purpose of the present application is to provide a fiber-optic acousto-optic modulator with high extinction ratio, which solves the problems of large size, complex structure, high insertion loss and high power consumption of the existing acousto-optic modulator.

[0005] Further, a method for optical modulation using the above modulator and a fiber-optic sensing system comprising the above modulator are provided.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions: A high-extinction-ratio fiber-optic acousto-optic modulator comprises a base and the following components mounted on the base: an input-end fiber collimator, an acousto-optic medium, a polarization beam splitter prism, a first output-end fiber collimator, a second output-end fiber collimator, a matching network, and a radio frequency socket arranged on one side of the base; The acousto-optic medium is located on the exit light path of the input-end fiber collimator, and the relative positions of the exit angle of the input-end fiber collimator and the light transmission surface of the acousto-optic medium satisfy the abnormal Bragg diffraction condition; a transverse wave transducer is bonded on the sound transmission surface of the acousto-optic medium, the transverse wave transducer is electrically connected to the matching network through a wire, and the matching network is electrically connected to the radio frequency socket through a wire; The polarization beam splitting prism is located on the light path of the acousto-optic medium, and is used for separating the 0-order light and the 1-order diffraction light output after the abnormal Bragg diffraction of the acousto-optic medium in space and coupling the 0-order light and the 1-order diffraction light to the first output fiber collimator and the second output fiber collimator, respectively.

[0007] Further, the input fiber collimator is used for receiving the incident light of horizontal polarization.

[0008] Further, the 0-order light maintains the horizontal polarization state and is transmitted by the polarization beam splitting prism to the first output fiber collimator for output, and the 1-order diffraction light becomes the vertical polarization state and is reflected by the polarization beam splitting prism to the second output fiber collimator for output.

[0009] Further, an anti-reflection film is coated on the light passing surface of the acousto-optic medium.

[0010] Further, the acousto-optic medium is a tellurium dioxide crystal.

[0011] An optical modulation method, which uses the above acousto-optic modulator for modulation, comprises the following steps: (1) coupling the incident light of horizontal polarization into the acousto-optic medium through the input fiber collimator; (2) exciting the transverse wave ultrasonic wave in the acousto-optic medium through the transverse wave transducer, so that the incident light is subjected to abnormal Bragg diffraction, and the 1-order diffraction light is generated and is the vertical polarization light; (3) separating the 0-order horizontal polarization light and the 1-order diffraction vertical polarization light by using the polarization beam splitting prism, transmitting the 0-order horizontal polarization light to the first output fiber collimator for output, and reflecting the 1-order diffraction vertical polarization light to the second output fiber collimator for output, that is, completing the optical modulation.

[0012] Further, the angle of the polarization beam splitting prism is adjusted to maximize the power of the output 1-order diffraction vertical polarization light.

[0013] An optical fiber sensing system comprising the above acousto-optic modulator.

[0014] Compared with the prior art, the present application has the following beneficial effects: 1. The application provides a high extinction ratio fiber acousto-optic modulator, which realizes the function of optical switch with high extinction ratio by skillfully utilizing the polarization state rotation caused by abnormal Bragg diffraction and combining with a polarization beam splitter. Specifically, after the incident laser with horizontal polarization undergoes abnormal Bragg diffraction with a transverse wave ultrasonic wave in the acousto-optic medium, the 0-order light maintains the original horizontal polarization state, while the 1-order diffraction light is rotated to the vertical polarization state. Then, the polarization beam splitter transmits the 0-order light (horizontal polarization) to the first output end fiber collimator for output according to the orthogonal polarization difference, and reflects the 1-order diffraction light (vertical polarization) to the second output end fiber collimator for output. This design greatly increases the separation angle of the 1-order diffraction light and the 0-order light, effectively reduces the probability of the 0-order light entering the second output end fiber collimator, thereby improving the extinction ratio, reducing the signal crosstalk of the 0-order light, and enhancing the sensing accuracy. Compared with the traditional two-fiber acousto-optic modulator cascade mode, the structure of the application is more simple, the volume, insertion loss and power consumption are significantly reduced, the cost is also lower, and an extinction ratio of up to 80 dB can be achieved, which lays a solid foundation for the development of fiber sensing system in the direction of miniaturization and low power consumption.

[0015] 2. The application also provides a method for modulating light using the above-mentioned acousto-optic modulator. First, the incident light with horizontal polarization is precisely coupled into the acousto-optic medium through the input fiber collimator; then the polarization beam splitter is used to act on the light, so that the 0-order light is directly transmitted through the polarization beam splitter and output through the first output end fiber collimator, while the 1-order diffraction light is reflected by the polarization beam splitter and then output by the second output end fiber collimator; in this way, efficient modulation of light is realized, which meets the special needs of fiber sensing system for light signal processing, and the operation is simple and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Fig. 1 is a structural schematic diagram of the high extinction ratio fiber acousto-optic modulator of the application; Figure 2 Fig. 2 is a light path schematic diagram of the high extinction ratio fiber acousto-optic modulator of the application.

[0017] In the figure, 1 is a base, 2 is an input end fiber collimator, 3 is an acousto-optic medium, 4 is a polarization beam splitter, 5 is a first output end fiber collimator, 6 is a second output end fiber collimator, 7 is a matching network, 8 is a radio frequency socket, and 9 is a transverse wave transducer. DETAILED DESCRIPTION

[0018] The application will be further described below with reference to the accompanying drawings. EMBODIMENT

[0019] As Figure 1As shown, the present invention provides a high extinction ratio fiber optic acousto-optic modulator, including a base 1, and the following components mounted on the base 1: an input fiber optic collimator 2, an acousto-optic medium 3, a polarizing beam splitter 4, a first output fiber optic collimator 5, a second output fiber optic collimator 6, a matching network 7, and an RF socket 8 disposed on one side of the base 1. The acousto-optic medium 3 is located on the output optical path of the input fiber collimator 2, and the relative position of the output angle of the input fiber collimator 2 and the light-transmitting surface of the acousto-optic medium 3 satisfies the anomalous Bragg diffraction condition; a transverse wave transducer 9 is bonded to the acoustic surface of the acousto-optic medium 3, and the transverse wave transducer 9 is electrically connected to the matching network 7 through a wire, and the matching network 7 is electrically connected to the radio frequency socket 8 through a wire. The polarization beam splitter 4 is located in the light output path of the acousto-optic medium 3, and is used to spatially separate the 0th order light and the 1st order diffracted light output after anomalous Bragg diffraction of the acousto-optic medium 3, and couple them to the first output fiber collimator 5 and the second output fiber collimator 6 respectively.

[0020] In specific implementation, the input fiber collimator 2 is used to receive horizontally polarized incident light. The 0th-order light maintains its horizontal polarization state and is transmitted by the polarizing beam splitter 4 to the first output fiber collimator 5 for output. The 1st-order diffracted light becomes vertically polarized and is reflected by the polarizing beam splitter 4 to the second output fiber collimator 6 for output. Its optical path diagram is as follows: Figure 2 As shown.

[0021] In practice, an antireflection film is coated on the light-transmitting surface of the acousto-optic medium 3. This can significantly reduce insertion loss and improve the overall optical efficiency of the device.

[0022] In a specific implementation, the acousto-optic medium 3 is tellurium dioxide (TeO2) crystal. Tellurium dioxide crystal has an extremely high figure of merit in acousto-optics, enabling it to achieve extremely high diffraction efficiency with extremely low radio frequency drive power, thereby reducing device power consumption and improving device performance.

[0023] Working principle: The radio frequency signal is transmitted to the matching network 7 through the radio frequency socket 8, driving the transducer 9 to excite transverse wave ultrasonic waves in the acousto-optic medium 3, thereby causing anomalous Bragg diffraction of the horizontally polarized incident laser beam calibrated by the input fiber collimator 2. After diffraction, the 0th order light retains its original horizontal polarization state, while the polarization state of the 1st order diffracted light is rotated to vertical polarization. The polarization beam splitter 4 utilizes the orthogonal polarization characteristics to effectively separate the two beams: the 0th order light is transmitted to the first output fiber collimator 5, while the 1st order diffracted light is reflected to the second output fiber collimator 6, thus completing the optical modulation.

[0024] The present invention also provides an optical modulation method, which uses the above-mentioned acousto-optic modulator for modulation, and includes the following steps: (1) The horizontally polarized incident light is coupled into the acousto-optic medium through the input fiber collimator; (2) Transverse wave ultrasound is excited in the acousto-optic medium by transverse wave transducer, causing the incident light to undergo anomalous Bragg diffraction; first-order diffracted light is generated and is vertically polarized light; (3) Use a polarizing beam splitter to separate the 0th order horizontally polarized light from the 1st order diffracted vertically polarized light; and transmit and couple the 0th order horizontally polarized light to the output of the first output fiber collimator, and reflect and couple the 1st order diffracted vertically polarized light to the output of the second output fiber collimator, thus completing the optical modulation.

[0025] In practice, by adjusting the angle of the polarizing beam splitter, the power of the output first-order diffracted vertically polarized light can be maximized.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A high extinction ratio fiber optic acousto-optic modulator, characterized in that, Includes a base, and the following components mounted on the base: an input fiber collimator, an acousto-optic medium, a polarizing beam splitter, a first output fiber collimator, a second output fiber collimator, a matching network, and an RF socket disposed on one side of the base. The acousto-optic medium is located in the output optical path of the input fiber collimator, and the relative position of the output angle of the input fiber collimator and the light-transmitting surface of the acousto-optic medium satisfies the anomalous Bragg diffraction condition; a transverse wave transducer is bonded to the acoustic surface of the acousto-optic medium, the transverse wave transducer is electrically connected to the matching network through a wire, and the matching network is electrically connected to the radio frequency socket through a wire. The polarization beam splitter is located in the light output path of the acousto-optic medium and is used to spatially separate the 0th order light and the 1st order diffracted light output after anomalous Bragg diffraction of the acousto-optic medium and couple them to the first output fiber collimator and the second output fiber collimator, respectively.

2. The high extinction ratio fiber optic acousto-optic modulator according to claim 1, characterized in that, The input fiber collimator is used to receive horizontally polarized incident light.

3. The high extinction ratio fiber optic acousto-optic modulator according to claim 2, characterized in that, The 0th-order light remains horizontally polarized and is transmitted by the polarizing beam splitter to the first output fiber collimator. The 1st-order diffracted light becomes vertically polarized and is reflected by the polarizing beam splitter to the second output fiber collimator.

4. The high extinction ratio fiber optic acousto-optic modulator according to claim 1, characterized in that, An antireflective film is coated on the light-transmitting surface of the acousto-optic medium.

5. The high extinction ratio fiber optic acousto-optic modulator according to claim 1, characterized in that, The acousto-optic medium is tellurium dioxide crystal.

6. A method for optical modulation, characterized in that, Modulation using any one of the acousto-optic modulators described in claims 1 to 5 includes the following steps: (1) The horizontally polarized incident light is coupled into the acousto-optic medium through the input fiber collimator; (2) Transverse wave ultrasound is excited in the acousto-optic medium by transverse wave transducer, causing the incident light to undergo anomalous Bragg diffraction; first-order diffracted light is generated and is vertically polarized light; (3) Use a polarizing beam splitter to separate the 0th order horizontally polarized light from the 1st order diffracted vertically polarized light; and transmit and couple the 0th order horizontally polarized light to the output of the first output fiber collimator, and reflect and couple the 1st order diffracted vertically polarized light to the output of the second output fiber collimator, thus completing the optical modulation.

7. The method according to claim 6, characterized in that, It also includes adjusting the angle of the polarizing beam splitter to maximize the power of the output first-order diffracted vertically polarized light.

8. A fiber optic sensing system, characterized in that, Includes the acousto-optic modulator described in any one of claims 1 to 5.

Images