Background
The inertial navigation system is an autonomous navigation device capable of providing real-time multi-azimuth information of a carrier, and does not need external information in the working process. The fiber-optic gyroscope, as one of the core devices of the inertial navigation system, has a great influence on the accuracy of the inertial navigation system, and the overall performance of the inertial navigation system is mainly dominated in most cases. Therefore, the high-precision inertial navigation system puts higher requirements on the precision and the performance of the used fiber-optic gyroscope. The fiber-optic gyroscope has the advantages of high theoretical precision, all solid state, high reliability and the like, and the high-precision fiber-optic gyroscope is widely applied to the fields of deep space, diving, strategy and the like as the first choice of the application of the high-precision inertial navigation system.
The fiber-optic gyroscope has undergone rapid development since birth, and a mature theory and technology system has been formed up to now. In order to meet the more complex and severe application requirements, especially military applications, researchers in various countries have conducted intensive research on the improvement of the precision of the fiber optic gyroscope. The traditional method for improving the precision of the fiber-optic gyroscope comprises two modes of hardware and software, wherein the hardware mode mainly comprises the steps of improving the stability of a light source, suppressing circuit noise, controlling a loop winding mode, shielding magnetic and the like, and the software mode mainly comprises the steps of calculating algorithm optimization, temperature compensation and the like. However, as the technology matures, the traditional methods have reached a bottleneck, and the contradiction between cost and effect is increasingly prominent.
In addition, the precision of the fiber-optic gyroscope can be improved to a certain extent by increasing the length of the optical fiber and the diameter of the optical fiber ring to accumulate the nonreciprocal phase difference generated by the angular velocity, but the fatal defect of increasing the length of the optical fiber is that the environmental adaptability to temperature and the like is greatly reduced, because the internal stress of the optical fiber ring is not uniform and the nonreciprocal phase difference is generated asymmetrically due to environmental factors after the longer optical fiber is wound into a ring, so that the improvement of the precision is limited. Therefore, there is a need for a device and a method for improving the precision of a fiber-optic gyroscope without reducing the environmental stability of the fiber-optic gyroscope, and maintaining the volume of the fiber-optic ring substantially unchanged, which have important engineering significance in the technical improvement of the fiber-optic gyroscope.
Disclosure of Invention
The invention aims to overcome the defects of poor stability and low precision of the existing fiber optic gyroscope, and provides a device and a method for multiple optical multiplication of a fiber optic gyroscope light path.
In order to achieve the purpose, the invention adopts the following technical scheme:
a multiple optical multiplication device of a fiber-optic gyroscope light path comprises a light source, a polarizer, a beam splitter, a first polarization beam splitter/combiner, a first polarization switch, a polarization-maintaining fiber sensitive coil, a second polarization switch and a second polarization beam splitter/combiner;
the polarization beam splitter/combiner comprises three ports: the device comprises an A port, a B port and a C port, wherein the slow axis or the fast axis of the A port is in coupling connection with the slow axis of the C port, and the slow axis or the fast axis of the B port is in coupling connection with the fast axis of the C port; the output end of the light source is sequentially connected with the polarizer and the beam splitter through a polarization-maintaining optical fiber, two output ports of the beam splitter are respectively connected with an A port of a first polarization beam splitter/beam combiner and an A port of a second polarization beam splitter/beam combiner through the polarization-maintaining optical fiber, a C port of the first polarization beam splitter/beam combiner and a C port of the second polarization beam splitter/beam combiner are respectively connected with the same side ports of the first polarization switch and the second polarization switch through the polarization-maintaining optical fiber, the other side ports of the first polarization switch and the second polarization switch are respectively connected with two ports of a polarization-maintaining optical fiber sensitive coil through the polarization-maintaining optical fiber, and a B port of the first polarization beam splitter/beam combiner is connected with a B port of the second polarization beam splitter/beam combiner in a 0-degree coupling mode.
As a preferred embodiment of the present invention, the light in the polarization maintaining optical fibers connected to the ports a and B of the first and second polarization beam splitters/combiners can only be transmitted along the fast axis or the slow axis thereof, and the light in the polarization maintaining optical fibers connected to the ports C can be transmitted along the fast axis and the slow axis simultaneously.
As a preferred embodiment of the present invention, the first polarization switch and the second polarization switch rotate or maintain the polarization of the optical signal by 90 ° by modulating the operating voltage.
The invention has the beneficial effects that:
(1) the device provided by the invention has the advantages that two 1 multiplied by 2 polarization beam splitters/combiners are added, the structure is simple, the cost is low, through the specific placement and coupling of the 1 multiplied by 2 polarization beam splitters/combiners, the light in the polarization-maintaining optical fibers connected with the ports A and B of the first polarization beam splitter/combiner and the second polarization beam splitter/combiner can only be transmitted along the fast axis or the slow axis, the light in the polarization-maintaining optical fibers connected with the ports C can be transmitted along the fast axis and the slow axis simultaneously, and the foundation is laid for multiplying the optical path of the optical signals transmitted in the sensitive coil;
(2) the invention respectively arranges the polarization switches on the clockwise and counterclockwise light paths, and can further control the polarization state of the optical signal by specifically modulating the voltage of the polarization switches, so that the optical signal which is directly output enters the light path again. The method specifically comprises the following steps: by changing the voltage of the polarization switch, 90-degree deflection of optical signals is realized, light originally transmitted along the fast axis is converted into light transmitted along the slow axis, and light originally transmitted along the slow axis is converted into light transmitted along the fast axis. Under the ideal condition of not considering loss and error, the optical signal can be infinitely circularly transmitted in the optical path, thereby achieving the effect of multiple multiplication. Aiming at the existing stable and mature fiber optic gyroscope, it is difficult to try to improve the precision through the breakthrough of hardware and software, and the device and the method provided by the invention can effectively improve the measurement precision of the fiber optic gyroscope on the premise of not increasing the length of the optical fiber, and have important significance in engineering application.
Detailed Description
The invention is further illustrated by the following figures and examples.
As shown in fig. 1, the polarization beam splitter/combiner can couple two beams of orthogonal polarized light into one optical fiber, or separate one input light into two beams of orthogonal linearly polarized light, and its working principle is: the optical signal transmitted along the slow axis (or fast axis) of the polarization-maintaining optical fiber can be emitted from the port C and transmitted along the slow axis of the polarization-maintaining optical fiber along the incident port A, the optical signal transmitted along the slow axis (or fast axis) of the polarization-maintaining optical fiber can be emitted from the port C and transmitted along the fast axis of the polarization-maintaining optical fiber along the incident port B, and the optical signal transmitted along the fast axis/slow axis of the polarization-maintaining optical fiber can be emitted along the exit port B/port A and transmitted along the slow axis (or fast axis) of the polarization-maintaining optical fiber along the incident port C. The light in the polarization maintaining optical fiber connected with the port A and the port B of the polarization beam splitter/combiner can be transmitted only along the fast axis or the slow axis, and the light in the polarization maintaining optical fiber connected with the port C can be transmitted along the fast axis and the slow axis simultaneously.
As shown in fig. 2, the multiple optical multiplication device of the optical fiber gyroscope includes a light source 1, a polarizer 2, a beam splitter 3, a first polarization beam splitter/combiner 4, a first polarization switch 5, a polarization maintaining optical fiber sensitive coil 6, a second polarization switch 7, and a second polarization beam splitter/combiner 8; the polarization beam splitter/combiner comprises three ports: the device comprises an A port, a B port and a C port, wherein the slow axis or the fast axis of the A port is in coupling connection with the slow axis of the C port, and the slow axis or the fast axis of the B port is in coupling connection with the fast axis of the C port; the light source is sequentially connected with the polarizer and the beam splitter through a polarization maintaining optical fiber, two output ports of the beam splitter are respectively connected with an A port of a first polarization beam splitter/beam combiner and an A port of a second polarization beam splitter/beam combiner through the polarization maintaining optical fiber, a C port of the first polarization beam splitter/beam combiner and a C port of the second polarization beam splitter/beam combiner are respectively connected with the same side ports of the first polarization switch and the second polarization switch through the polarization maintaining optical fiber, the other side ports of the first polarization switch and the second polarization switch are respectively connected with two ports of a polarization maintaining optical fiber sensitive coil through the polarization maintaining optical fiber, and a B port of the first polarization beam splitter/beam combiner is connected with a B port of the second polarization beam splitter/beam combiner in a 0-degree coupling mode.
In one embodiment of the present invention, the light in the polarization maintaining fiber connected to the port a and the port B of the polarization beam splitter/combiner can be transmitted only along the fast axis or the slow axis thereof, and the light in the polarization maintaining fiber connected to the port C can be transmitted along the fast axis and the slow axis simultaneously; the first polarization switch and the second polarization switch have the function of enabling the polarization of the passing optical signal to be rotated by 90 degrees or kept unchanged by modulating the working voltage of the first polarization switch and the second polarization switch. When the polarization switch does not exist, the optical signals can be directly output after being transmitted for two circles in the optical path of the fiber-optic gyroscope through the specific placement of the two polarization beam splitters/combiners, so that the effect of secondary multiplication is achieved. After the polarization switch is adopted, when the optical signal is transmitted for two circles and is ready to be output, control voltage is applied to the polarization switch, the voltage enables the lithium niobate to generate birefringence, the phase of the optical signal passing through the polarization switch is changed, the function of the optical signal is similar to that of an adjustable wave plate, the polarization state of the optical signal can be adjusted through the combination of multiple wave plates (such as a quarter wave plate, a half wave plate and a quarter wave plate), therefore, the optical signal transmitted through the polarization switch can be subjected to 90-degree polarization rotation through controlling the working voltage of the polarization switch, the optical signal is changed along the transmission axis of the optical fiber, the optical signal can enter the optical path again instead of being directly output, and the effect of multiple times of multiplication is achieved.
In one embodiment of the present invention, the first polarization switch and the second polarization switch are made of lithium niobate. The first polarization beam splitter/combiner 4 and the second polarization beam splitter/combiner 8 are made of fused optical fibers. The diameter of the polarization maintaining optical fiber sensing coil 6 is 90 mm.
The method for the beam bypassing of the multiple optical multiplication device of the optical path of the fiber-optic gyroscope comprises the following steps:
1) an optical signal emitted by a light source 1 is divided into two parts after passing through a polarizer 2 and a beam splitter 3, and is respectively transmitted to a first polarization beam splitter/combiner 4 and a second polarization beam splitter/combiner 8 through polarization-maintaining optical fibers; three ports of the first polarization beam splitter/combiner 4 are defined as a1Mouth, B1Mouth and C1A port, defining three ports of the second polarization beam splitter/combiner 8 as A2Mouth, B2Mouth and C2A mouth;
2) the optical transmission process of the clockwise optical path transmission is as follows:
(a) clockwise light is transmitted along the slow or fast axis of the polarization maintaining fiber from A1Enters the first polarization beam splitter/combiner 4 from the mouth and then passes through C1The light is emitted from the port and transmitted into a first polarization switch 5 along the slow axis of the polarization maintaining optical fiber, the voltage of the first polarization switch is modulated to ensure that the light signal passing through the first polarization switch does not generate polarization rotation at the moment, the output light enters a second polarization switch 7 after being transmitted for one circle along the slow axis of the polarization maintaining optical fiber through a sensitive coil 6 of the polarization maintaining optical fiber, and the voltage of the second polarization switch is modulated to ensure that the light signal passing through the second polarization switch generates 90-degree polarization rotation at the moment;
(b) the emergent light from the second polarization switch is transmitted along the fast axis of the polarization-maintaining optical fiber and enters the C of the second polarization beam splitter/combiner 82Oral, then from B2B for port transmission to first polarization beam splitter/combiner1From mouth C1The light signal enters a first polarization switch 5, the voltage of the first polarization switch is modulated at the moment to ensure that the light signal passing through the first polarization switch does not generate polarization rotation, and the output light enters a second polarization switch 7 after being transmitted for one turn again along the fast axis of the polarization maintaining optical fiber through a polarization maintaining optical fiber sensitive coil 6;
(c) modulating the voltage of the second polarization switch to enable the optical signal passing through the second polarization switch not to generate polarization rotation, and repeating the step (b);
(d) repeating step (c) n times as required;
(e) when the optical signal needs to be output, the voltage of the second polarization switch is modulated to enable the optical signal passing through the second polarization switch to generate 90-degree polarization rotation, emergent light from the second polarization switch is transmitted along the slow axis of the polarization-maintaining optical fiber and enters the C of the second polarization beam splitter/combiner 82Oral cavity, then from A2The port outputs to the beam splitter to complete the transmission of a clockwise optical path, and at the moment, the optical signal winds in the polarization maintaining optical fiber coil for n +1 times, so that the multiplication of the optical path n +1 is realized.
3) The light transmission process of the counterclockwise light path transmission is as follows:
(f) counterclockwise light is transmitted along the slow or fast axis of the polarization maintaining fiber from A2Enters the second polarization beam splitter/combiner 8 from the mouth and then passes through C2The light is emitted from the port and transmitted into a second polarization switch 7 along the polarization maintaining optical fiber slow axis, the voltage of the second polarization switch is modulated at the moment to ensure that the light signal passing through the second polarization switch does not generate polarization rotation, and the output light is transmitted for a circle along the polarization maintaining optical fiber slow axis through a polarization maintaining optical fiber sensitive coil 6 and then enters a first polarization switch 5 to modulate the voltage of the first polarization switch at the moment to ensure that the light signal passing through the first polarization switch generates 90-degree polarization rotation;
(g) the emergent light from the first polarization switch is transmitted along the fast axis of the polarization-maintaining optical fiber and enters the C of the first polarization beam splitter/combiner 41Oral, then from B1B for port transmission to second polarization beam splitter/combiner2From mouth C2The light signal is emitted from the port and transmitted along the fast axis of the polarization maintaining optical fiber, the light signal enters a second polarization switch 7, the voltage of the second polarization switch is modulated at the moment to ensure that the light signal passing through the second polarization switch does not generate polarization rotation, and the output light enters a first polarization switch 5 after being transmitted for one turn again along the fast axis of the polarization maintaining optical fiber through a polarization maintaining optical fiber sensitive coil 6;
(h) modulating the voltage of the first polarization switch to enable the optical signal passing through the first polarization switch not to generate polarization rotation, and repeating the step (g);
(i) repeating the step (h) m times as required;
(j) when an optical signal needs to be output, the voltage of the first polarization switch is modulated to enable the optical signal passing through the first polarization switch to generate 90-degree polarization rotation, emergent light from the first polarization switch is transmitted along the slow axis of the polarization-maintaining optical fiber and enters the C of the first polarization beam splitting/combining device2Oral cavity, then from A2The port outputs to the beam splitter to complete the transmission of a clockwise optical path, and at the moment, the optical signal winds in the polarization maintaining optical fiber coil for n +1 times, so that the multiplication of an optical path m +1 is realized. (ii) a
4) Clockwise and anticlockwise optical signals enter the polarizer to interfere at the same time, and the interference optical signals are detected by the detector after passing through the optical fiber coupler.
According to the beam bypassing method, the number of turns n +1 and m +1 of optical signals transmitted anticlockwise and clockwise around the polarization maintaining optical fiber sensitive coil is the same.
The first polarization beam splitter/combiner 4 and the second polarization beam splitter/combiner 8 may adopt any device having the working principle shown in fig. 1, in this example, a fused fiber polarization beam combiner/splitter from Thorlab corporation is adopted, and the polarization switch may adopt any device having the working principle, in this example, a lithium niobate polarization switch from photonic corporation is adopted.
The invention adopts two polarization beam splitting/combining devices and a polarization switch in the fiber-optic gyroscope, which are respectively positioned in a positive light path and a reverse light path at two ends of a polarization-maintaining fiber-optic sensitive coil. The polarization beam splitter/combiner is used for coupling two beams of orthogonal polarized light into one optical fiber or separating one input light into two beams of orthogonal linear polarized light for output, and the polarization switch can enable the linear polarized light passing through the polarization beam splitter/combiner to realize 90-degree polarization rotation or keep the polarization unchanged by controlling voltage. Through the specific placement and coupling of the two polarization beam splitters/combiners and the modulation of the polarization switch voltage, an incident light signal can be circularly transmitted along the polarization-maintaining optical fiber sensitive coil of the optical fiber gyroscope, so that the effect of optical multiplication for multiple times is achieved.
The above-described embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, the technical scheme obtained by adopting the mode of equivalent replacement or equivalent transformation is within the protection scope of the invention.