Optical path length increasing optical fiber resonator and optical path operation method

Abstract

The application provides an optical path increased optical fiber resonator and an optical path operation method. In the optical path increased optical fiber resonator, the optical path in a single circulation period in the optical fiber resonator is doubled, the line width of a resonance peak is reduced, the frequency resolution of the optical fiber resonator is improved, the performance of the optical fiber resonator is enhanced, and the engineering application of the optical fiber resonator is facilitated.

Description

Technical Field

[0001] This application belongs to the field of optical fiber resonator technology, specifically relating to an optical fiber resonator with optical path lengthening and an optical path operation method. Background Technology

[0002] Optical resonant cavities are important optical devices widely used in filters, lasers, and spectrometers. Traditional optical resonant cavities have two structures: parallel cavities and ring cavities. Regardless of whether it is a parallel cavity or a ring cavity structure, the direction of light propagation is controlled by optical components, causing light waves to be reflected and transmitted multiple times within the resonant cavity, forming multi-beam interference, thereby achieving resonance.

[0003] An optical fiber resonator is an optical resonator that uses optical fibers wound into a loop. A light beam operating at its intrinsic frequency can circulate and propagate within the optical fiber resonator, achieving resonance. Optical fiber resonators can be used in filters, laser sources, and optical fiber sensors (such as resonant fiber optic gyroscopes), serving as core components of these systems.

[0004] Optical path length is a key parameter of a resonant cavity. A longer optical path length can reduce the resonant peak linewidth, enabling smaller linewidths in filters; achieving narrow linewidth operation in lasers; improving frequency resolution in spectral analysis; and enhancing sensitivity in fiber optic sensing. However, considering size and volume in practical applications, optical path length is limited. For example, the fiber optic resonant cavity is the core sensing device of a resonant fiber optic gyroscope, and the gyroscope's accuracy is related to the cavity length. However, a longer fiber would result in an excessively large gyroscope, hindering miniaturization.

[0005] Therefore, increasing the optical path length within a limited volume can improve the performance of the fiber optic resonator, effectively reducing its volume and facilitating its engineering application and promotion. Summary of the Invention

[0006] The objective of this invention is to propose a fiber optic resonator with an extended optical path length. This solution improves the performance of the fiber optic resonator by increasing the optical path length within a limited volume, effectively reducing the volume of the fiber optic resonator and facilitating its engineering application.

[0007] In a first aspect, this application provides an optical fiber resonant cavity with optical path length extension, including a substrate and an optical fiber, as well as a first port, a second port, a third port, a fourth port, a first beam splitter, a second beam splitter, a first reflector, a second reflector, and an optical rotation component on the substrate.

[0008] The fiber optic resonant cavity is used to operate clockwise and counterclockwise light simultaneously.

[0009] Preferably, the optical fiber is a polarization-maintaining fiber to maintain the polarization state of the transmitted beam; the length of the optical fiber is much greater than the optical path length of the beam transmission on the substrate.

[0010] Preferably, the first and second reflectors are total reflection mirrors with a reflective film coated on their surfaces, which can reflect both the first and second polarization states of the light beam, and have a reflectivity of more than 99%.

[0011] Preferably, the first beam splitter and the second beam splitter are partial reflectors, with a partial reflective film coated on their surfaces, so as to partially reflect both the first polarization state and the second polarization state of the beam, with a reflectivity of 1% to 10%.

[0012] Preferably, within a single cycle of the circulating light in the fiber resonator, the beam passes through the fiber twice, thereby increasing the optical path length of the fiber resonator. Since the fiber length is much greater than the optical path length of the beam transmission on the substrate, the optical path length increase is nearly twice the fiber length.

[0013] Preferably, the optical rotation component enables the light beam to enter the optical fiber for transmission through optical rotation, while maintaining the light beam polarization state of the input and output resonant cavities unchanged.

[0014] Preferably, the optical rotation component includes a first optical rotator, a Faraday optical rotator, a first polarizing beam splitter, a second polarizing beam splitter, and a second optical rotator;

[0015] Between the first reflector and the third port, a first optical rotator, a Faraday optical rotator, and a first polarizing beam splitter are arranged in sequence; between the second reflector and the fourth port, a first optical rotator, a Faraday optical rotator, and a second polarizing beam splitter are arranged in sequence; a second optical rotator is arranged between the first polarizing beam splitter and the second polarizing beam splitter.

[0016] Preferably, the first optical rotator is a reciprocal optical rotator. By setting the optical axis, the polarization state of the beam entering the optical fiber is rotated by +45 degrees, and the polarization state of the beam exiting the optical fiber is rotated by +45 degrees.

[0017] The Faraday rotator is a non-reciprocal optical rotator that utilizes the Faraday effect to rotate the polarization state of the beam entering the optical fiber by -45 degrees and rotates the polarization state of the beam exiting the optical fiber by +45 degrees.

[0018] The first polarizing beam splitter is set by a polarization axis, so that the first polarized beam is transmitted and the second polarized beam is reflected.

[0019] The second polarizing beam splitter is configured via a polarization axis so that the first polarized beam is reflected and the second polarized beam is transmitted.

[0020] The second optical rotator is a reciprocal optical rotator that rotates the polarization state of the passing light beam by 90 degrees by setting the optical axis.

[0021] Secondly, this application also provides an optical path operation method, the method comprising:

[0022] The input light of the counterclockwise light has a first polarization state. The beam enters from the first port, is partially reflected by the first beam splitter onto the first mirror, is reflected by the first mirror, passes through the optical rotator, enters the optical fiber through the third port, and then enters the optical rotator through the fourth port. After being processed by the optical rotator, it enters the optical fiber again through the third port, is transmitted through the optical rotator through the fourth port, reaches the second mirror, is reflected by the second mirror, passes through the second beam splitter and the first beam splitter in sequence, and is reflected again by the first mirror into the optical rotator, thus forming a counterclockwise circulating light. From the time the beam is reflected by the first mirror into the optical rotator until the light reflected by the second mirror reaches the first mirror, this is one cycle. The counterclockwise circulating light is partially reflected by the second beam splitter and exits the resonant cavity from the second port, forming a counterclockwise resonant cavity signal.

[0023] The input light of the clockwise light has a second polarization state. The beam enters from the second port, is partially reflected by the second beam splitter onto the second mirror, is reflected by the second mirror, passes through the optical rotator, enters the optical fiber through the fourth port, and then enters the optical rotator through the third port. After being acted upon by the optical rotator, it enters the optical fiber again through the fourth port, and is transmitted through the optical rotator through the third port to the first mirror. After being reflected by the first mirror, it passes through the first beam splitter and the second beam splitter in sequence, and is reflected again by the second mirror into the optical rotator, thus forming a clockwise circulating light. From the time the beam is reflected by the second mirror into the optical rotator until the light reflected by the first mirror reaches the second mirror, this is one cycle. The clockwise circulating light is partially reflected by the first beam splitter and exits the resonant cavity from the first port, forming a clockwise resonant cavity signal.

[0024] Preferably, the first polarization state is a polarization direction perpendicular to the paper surface, facing the light transmission direction; the second polarization state is a polarization direction parallel to the paper surface, facing the light transmission direction; the first polarization state and the second polarization state are orthogonal; and the third polarization state is a polarization direction at a 45-degree angle to the first polarization direction and the second polarization direction.

[0025] This application has the following technical effects:

[0026] The present invention provides an optical fiber resonator with optical path length increase, which doubles the optical path length within a single cycle while maintaining the consistency of the input and output polarization states of the optical fiber resonator. This reduces the linewidth of the resonance peak, improves the frequency resolution of the optical fiber resonator, enhances the performance of the optical fiber resonator, and is beneficial for the engineering application of optical fiber resonators. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a preferred structure of an optical fiber resonator for optical path lengthening according to the present invention.

[0028] Figure 2 This is a schematic diagram of the optical rotation component;

[0029] Figure 3 This is a schematic diagram of the polarization state of the light beam as it passes through the first optical rotator 7 and the Faraday optical rotator 8;

[0030] The components include a substrate 101, an optical fiber 102, a first port 201, a second port 202, a third port 203, a fourth port 204, a first beam splitter 3, a second beam splitter 4, a first reflector 5, a second reflector 6, a first optical rotator 7, a Faraday optical rotator 8, a first polarizing beam splitter 9, a second polarizing beam splitter 10, and a second optical rotator 11. Detailed Implementation

[0031] The present invention provides an optical fiber resonant cavity for optical path lengthening, comprising: a substrate 101 and an optical fiber 102, and a first port 201, a second port 202, a third port 203, a fourth port 204, a first beam splitter 3, a second beam splitter 4, a first reflector 5, a second reflector 6, a first optical rotator 7, a Faraday optical rotator 8, a first polarizing beam splitter 9, a second polarizing beam splitter 10, and a second optical rotator 11 on the substrate.

[0032] The fiber optic resonator can operate clockwise and counterclockwise light simultaneously.

[0033] The input light of the counterclockwise light has the first polarization state. The beam is incident from the first port 201, partially reflected by the first beam splitter 3 onto the first reflector 5. Reflected by the first reflector 5, it passes through the optical rotator assembly, enters the optical fiber 102 through the third port 203, and then enters the optical rotator assembly again through the fourth port 204. After being processed by the optical rotator assembly, it again enters the optical fiber 102 through the third port 203, and is transmitted through the optical rotator assembly through the fourth port 204, reaching the second reflector 6. After being reflected by the second reflector 6, it passes sequentially through the second beam splitter 4 and the first beam splitter 3, and is reflected again by the first reflector 5 into the optical rotator assembly, thus forming a counterclockwise circulating light. One cycle occurs from the beam being reflected by the first reflector 5 into the optical rotator assembly to the light reflected by the second reflector 6 reaching the first reflector 5. The counterclockwise circulating light is partially reflected by the second beam splitter 4 and exits the resonant cavity from the second port 202, forming a counterclockwise resonant cavity signal.

[0034] The input light of the clockwise light has a second polarization state. The beam is incident from the second port 202, partially reflected by the second beam splitter 4 onto the second mirror 6. Reflected by the second mirror 6, it passes through the optical rotator assembly, enters the optical fiber 102 through the fourth port 204, and then enters the optical rotator assembly again through the third port 203. After being processed by the optical rotator assembly, it enters the optical fiber 102 again through the fourth port 204, and is transmitted through the optical rotator assembly through the third port 203, reaching the first mirror 5. After being reflected by the first mirror 5, it passes sequentially through the first beam splitter 3 and the second beam splitter 4, and is reflected again by the second mirror 6 into the optical rotator assembly, thus forming a clockwise circulating light. One cycle occurs from the time the beam is reflected by the second mirror 6 into the optical rotator assembly until the light reflected by the first mirror 5 reaches the second mirror 6. The clockwise circulating light is partially reflected by the first beam splitter 3 and exits the resonant cavity from the first port 201, forming a clockwise resonant cavity signal.

[0035] The optical fiber 102 is a polarization-maintaining fiber, which can maintain the polarization state of the transmitted beam. The length of the optical fiber 102 is much greater than the optical path length of the beam transmission on the substrate 101.

[0036] The first reflector 5 and the second reflector 6 are total reflection mirrors with a reflective film coated on their surfaces. They can reflect both the first polarization state and the second polarization state of the light beam, and the reflectivity is higher than 99%.

[0037] The first beam splitter 4 and the second beam splitter 5 are partial reflectors, with a partial reflective film coated on their surfaces. They partially reflect both the first polarization state and the second polarization state of the beam, with a reflectivity of 1% to 10%.

[0038] Within a single cycle of the circulating light in the fiber resonator, the beam passes through the fiber 102 twice, thereby increasing the optical path length of the fiber resonator. Since the length of the fiber 102 is much greater than the optical path length of the beam transmitted on the substrate 101, the optical path length increase is nearly twice the length of the fiber 102.

[0039] The optical rotator assembly includes a first optical rotator 7, a Faraday optical rotator 8, a first polarizing beam splitter 9, a second polarizing beam splitter 10, and a second optical rotator 11. The first optical rotator 7, the Faraday optical rotator 8, and the first polarizing beam splitter 9 are sequentially arranged between the first reflector 5 and the third port 203. The first optical rotator 7, the Faraday optical rotator 8, and the second polarizing beam splitter 10 are sequentially arranged between the second reflector 5 and the fourth port 204. The second optical rotator 11 is positioned between the first polarizing beam splitter 9 and the second polarizing beam splitter 10. Through optical rotation, the optical rotator assembly allows the light beam to enter the optical fiber 102 twice for transmission, while maintaining the beam polarization state of the input and output resonant cavities unchanged.

[0040] The first optical rotator 7 is a reciprocal optical rotator. By setting the optical axis, the polarization state of the beam entering the optical fiber 102 is rotated by +45 degrees, and the polarization state of the beam exiting the optical fiber 102 is rotated by +45 degrees.

[0041] The Faraday rotator 8 is a non-reciprocal optical rotator. Utilizing the Faraday effect, it ensures that the polarization state of the beam entering the fiber 102 rotates by -45 degrees, and the polarization state of the beam exiting the fiber 102 rotates by +45 degrees.

[0042] The first polarizing beam splitter 9 is configured with a polarization axis so that the first polarized beam is transmitted and the second polarized beam is reflected.

[0043] The second polarizing beam splitter 10 is configured with a polarization axis so that the first polarized beam is reflected and the second polarized beam is transmitted.

[0044] The second optical rotator 11 is a reciprocal optical rotator that rotates the polarization state of the passing light beam by 90 degrees by setting the optical axis.

[0045] The first polarization state is a polarization direction perpendicular to the plane of the paper, facing the direction of light transmission; the second polarization state is a polarization direction parallel to the plane of the paper, facing the direction of light transmission; the first polarization state and the second polarization state are orthogonal. The third polarization state is a polarization direction at a 45-degree angle to the first polarization direction and the second polarization direction.

[0046] The working principle of the optical rotator is explained using counterclockwise light as an example. Within one cycle, the light beam is incident on the optical rotator three times. First, the first reflecting mirror 5 reflects the light in the first polarization state, which is then converted to the third polarization state by the first optical rotator 7. After passing through the Faraday optical rotator 8, it retains the first polarization state and is transmitted through the first polarizing beam splitter 9, entering the optical fiber 102 from the third port 203. Second, the first polarization state light beam emitted from the optical fiber 102 enters the optical rotator from the fourth port 204, is reflected by the second polarizing beam splitter 10, and then becomes the second polarization state light after passing through the second optical rotator 11. The beam is reflected by the first polarizing beam splitter 9 and transmitted through the optical rotator component, and then transmitted through the third port 203 to the optical fiber 102 for the second time. The third time, the beam of the second polarization state is emitted from the optical fiber 102 at the fourth port 204 and enters the optical rotator component. After being transmitted through the second polarizing beam splitter 10, it is transformed into a beam of the third polarization state by the Faraday rotator 8, and then transformed into the first polarization state consistent with the first polarization state when it is emitted into the resonant cavity by the first rotator 7 before being emitted out of the optical rotator component.

[0047] For other embodiments in this application, please refer to Figure 1This invention provides a preferred structural diagram of a miniaturized integrated resonant fiber optic gyroscope. The fiber optic resonant cavity of this invention, with an optical path lengthening capability, includes: a substrate 101 and an optical fiber 102, and on the substrate: a first port 201, a second port 202, a third port 203, a fourth port 204, a first beam splitter 3, a second beam splitter 4, a first reflector 5, a second reflector 6, a first optical rotator 7, a Faraday optical rotator 8, a first polarizing beam splitter 9, a second polarizing beam splitter 10, and a second optical rotator 11.

[0048] The fiber optic resonator can operate clockwise and counterclockwise light.

[0049] The input light of the counterclockwise light has the first polarization state. The beam is incident from the first port 201, partially reflected by the first beam splitter 3 onto the first reflector 5. Reflected by the first reflector 5, it passes through the optical rotator assembly, enters the optical fiber 102 through the third port 203, and then enters the optical rotator assembly again through the fourth port 204. After being processed by the optical rotator assembly, it again enters the optical fiber 102 through the third port 203, and is transmitted through the optical rotator assembly through the fourth port 204, reaching the second reflector 6. After being reflected by the second reflector 6, it passes sequentially through the second beam splitter 4 and the first beam splitter 3, and is reflected again by the first reflector 5 into the optical rotator assembly, thus forming a counterclockwise circulating light. One cycle occurs from the beam being reflected by the first reflector 5 into the optical rotator assembly to the light reflected by the second reflector 6 reaching the first reflector 5. The counterclockwise circulating light is partially reflected by the second beam splitter 4 and exits the resonant cavity from the second port 202, forming a counterclockwise resonant cavity signal.

[0050] The input light of the clockwise light has a second polarization state. The beam is incident from the second port 202, partially reflected by the second beam splitter 4 onto the second mirror 6. Reflected by the second mirror 6, it passes through the optical rotator assembly, enters the optical fiber 102 through the fourth port 204, and then enters the optical rotator assembly again through the third port 203. After being processed by the optical rotator assembly, it enters the optical fiber 102 again through the fourth port 204, and is transmitted through the optical rotator assembly through the third port 203, reaching the first mirror 5. After being reflected by the first mirror 5, it passes sequentially through the first beam splitter 3 and the second beam splitter 4, and is reflected again by the second mirror 6 into the optical rotator assembly, thus forming a clockwise circulating light. One cycle occurs from the time the beam is reflected by the second mirror 6 into the optical rotator assembly until the light reflected by the first mirror 5 reaches the second mirror 6. The clockwise circulating light is partially reflected by the first beam splitter 3 and exits the resonant cavity from the first port 201, forming a clockwise resonant cavity signal.

[0051] The optical fiber 102 is a polarization-maintaining fiber, which can maintain the polarization state of the transmitted light beam. The length of the optical fiber 102 is much greater than the optical path length of the light beam transmission on the substrate 101.

[0052] The first reflector 5 and the second reflector 6 are total reflection mirrors with a reflective film coated on their surfaces. They can reflect both the first polarization state and the second polarization state of the light beam, and the reflectivity is higher than 99%.

[0053] The first beam splitter 4 and the second beam splitter 5 are partial reflectors, with a partial reflective film coated on their surfaces. They partially reflect both the first polarization state and the second polarization state of the beam, with a reflectivity of 1% to 10%.

[0054] In the above device, the light beam passes through the optical fiber 102 twice in a single cycle, thereby increasing the optical path length of the optical fiber resonator. Since the length of the optical fiber 102 is much greater than the optical path length of the light beam on the substrate 101, the optical path length increase is nearly twice the length of the optical fiber 102.

[0055] Figure 2 This is a schematic diagram of the optical rotation component.

[0056] The optical rotator assembly includes a first optical rotator 7, a Faraday optical rotator 8, a first polarizing beam splitter 9, a second polarizing beam splitter 10, and a second optical rotator 11. The first optical rotator 7, the Faraday optical rotator 8, and the first polarizing beam splitter 9 are sequentially arranged between the first reflector 5 and the third port 203. The first optical rotator 7, the Faraday optical rotator 8, and the second polarizing beam splitter 10 are sequentially arranged between the second reflector 5 and the fourth port 204. The second optical rotator 11 is positioned between the first polarizing beam splitter 9 and the second polarizing beam splitter 10. Through optical rotation, the optical rotator assembly allows the light beam to enter the optical fiber 102 twice for transmission, while maintaining the beam polarization state of the input and output resonant cavities unchanged.

[0057] The first optical rotator 7 is a reciprocal optical rotator. By setting the optical axis, the polarization state of the beam entering the optical fiber 102 is rotated by +45 degrees, and the polarization state of the beam exiting the optical fiber 102 is rotated by +45 degrees.

[0058] The Faraday rotator 8 is a non-reciprocal optical rotator. Utilizing the Faraday effect, it ensures that the polarization state of the beam entering the fiber 102 rotates by -45 degrees, and the polarization state of the beam exiting the fiber 102 rotates by +45 degrees.

[0059] The first polarizing beam splitter 9 is configured with a polarization axis so that the first polarized beam is transmitted and the second polarized beam is reflected.

[0060] The second polarizing beam splitter 10 is configured with a polarization axis so that the first polarized beam is reflected and the second polarized beam is transmitted.

[0061] The second optical rotator 11 is a reciprocal optical rotator that rotates the polarization state of the passing light beam by 90 degrees by setting the optical axis.

[0062] The first polarization state is a polarization direction perpendicular to the plane of the paper, facing the direction of light transmission; the second polarization state is a polarization direction parallel to the plane of the paper, facing the direction of light transmission; the first polarization state and the second polarization state are orthogonal. The third polarization state is a polarization direction at a 45-degree angle to the first polarization direction and the second polarization direction.

[0063] The working principle of the optical rotator is explained using counterclockwise light as an example. Within one cycle, the light beam is incident on the optical rotator three times. First, the first reflecting mirror 5 reflects the light in the first polarization state, which is then converted to the third polarization state by the first optical rotator 7. After passing through the Faraday optical rotator 8, it retains the first polarization state and is transmitted through the first polarizing beam splitter 9, entering the optical fiber 102 from the third port 203. Second, the first polarization state light beam emitted from the optical fiber 102 enters the optical rotator from the fourth port 204, is reflected by the second polarizing beam splitter 10, and then becomes the second polarization state light after passing through the second optical rotator 11. The beam is reflected by the first polarizing beam splitter 9 and transmitted through the optical rotator component, and then transmitted through the third port 203 to the optical fiber 102 for the second time. The third time, the beam of the second polarization state is emitted from the optical fiber 102 at the fourth port 204 and enters the optical rotator component. After being transmitted through the second polarizing beam splitter 10, it is transformed into a beam of the third polarization state by the Faraday rotator 8, and then transformed into the first polarization state consistent with the first polarization state when it is emitted into the resonant cavity by the first rotator 7 before being emitted out of the optical rotator component.

[0064] Figure 3 This is a schematic diagram of the polarization state of the light beam as it passes through the first optical rotator 7 and the Faraday optical rotator 8.

[0065] The light in the first polarization state is converted into a third polarization state beam by passing from above and downward through the first optical rotator 7, and then remains in the first polarization state after passing through the Faraday optical rotator 8.

[0066] The light in the second polarization state passes from below and upward through the Faraday rotator 8 to become a beam in the third polarization state, and then passes through the first rotator 7 to become the same polarization state as the first polarization state.

[0067] In summary, the optical path lengthening fiber resonator of this invention doubles the optical path length within a single cycle while maintaining the consistency of the input and output polarization states of the fiber resonator. This reduces the linewidth of the resonance peak, improves the frequency resolution of the fiber resonator, enhances the performance of the fiber resonator, and facilitates the engineering of fiber resonators.

Claims

1. A fiber optic resonator with optical path length extension, characterized in that, It includes a substrate and an optical fiber, as well as a first port, a second port, a third port, a fourth port, a first beam splitter, a second beam splitter, a first reflector, a second reflector, and a light-rotating component on the substrate; The fiber optic resonant cavity is used to operate clockwise and counterclockwise light simultaneously.

2. The optical fiber resonator with optical path lengthening according to claim 1, characterized in that, The optical fiber is a polarization-maintaining fiber, which maintains the polarization state of the transmitted beam; the length of the optical fiber is much greater than the optical path length of the beam transmission on the substrate.

3. The optical fiber resonator with optical path length extension according to claim 2, characterized in that, The first and second reflecting mirrors are total reflection mirrors with a reflective film coated on their surfaces. They reflect both the first and second polarization beams, with a reflectivity of over 99%.

4. The optical fiber resonator with optical path length extension according to claim 3, characterized in that, The first and second beam splitters are partial reflectors, with a partial reflective film coated on their surfaces, achieving partial reflection of both the first and second polarization states of the beam, with a reflectivity of 1% to 10%.

5. The optical fiber resonator with optical path length extension according to claim 4, characterized in that, In a single cycle of the circulating light in the fiber optic resonator, the beam passes through the fiber twice, thus increasing the optical path length of the fiber optic resonator. Since the fiber length is much greater than the optical path length of the beam transmitted on the substrate, the optical path length increase is nearly twice the fiber length.

6. The optical fiber resonator with optical path length extension according to claim 5, characterized in that, The optical rotator allows the light beam to enter the optical fiber for transmission through optical rotation, while maintaining the light beam polarization state of the input and output resonant cavities unchanged.

7. The optical fiber resonator with optical path length extension according to claim 6, characterized in that, The optical rotation component includes a first optical rotator, a Faraday optical rotator, a first polarizing beam splitter, a second polarizing beam splitter, and a second optical rotator; Between the first reflector and the third port, a first optical rotator, a Faraday optical rotator, and a first polarizing beam splitter are arranged in sequence; between the second reflector and the fourth port, a first optical rotator, a Faraday optical rotator, and a second polarizing beam splitter are arranged in sequence; a second optical rotator is arranged between the first polarizing beam splitter and the second polarizing beam splitter.

8. The optical fiber resonator with optical path length extension according to claim 7, characterized in that, The first optical rotator is a reciprocal optical rotator. By setting the optical axis, the polarization state of the beam entering the optical fiber is rotated by +45 degrees, and the polarization state of the beam exiting the optical fiber is rotated by +45 degrees. The Faraday rotator is a non-reciprocal optical rotator that utilizes the Faraday effect to rotate the polarization state of the beam entering the optical fiber by -45 degrees and rotates the polarization state of the beam exiting the optical fiber by +45 degrees. The first polarizing beam splitter is set by a polarization axis, so that the first polarized beam is transmitted and the second polarized beam is reflected. The second polarizing beam splitter is configured via a polarization axis so that the first polarized beam is reflected and the second polarized beam is transmitted. The second optical rotator is a reciprocal optical rotator that rotates the polarization state of the passing light beam by 90 degrees by setting the optical axis.

9. A method for operating an optical path, characterized in that, The method includes: The input light of the counterclockwise light has a first polarization state. The beam enters from the first port, is partially reflected by the first beam splitter onto the first mirror, is reflected by the first mirror, passes through the optical rotator, enters the optical fiber through the third port, and then enters the optical rotator through the fourth port. After being processed by the optical rotator, it enters the optical fiber again through the third port, is transmitted through the optical rotator through the fourth port, reaches the second mirror, is reflected by the second mirror, passes through the second beam splitter and the first beam splitter in sequence, and is reflected again by the first mirror into the optical rotator, thus forming a counterclockwise circulating light. From the time the beam is reflected by the first mirror into the optical rotator until the light reflected by the second mirror reaches the first mirror, this is one cycle. The counterclockwise circulating light is partially reflected by the second beam splitter and exits the resonant cavity from the second port, forming a counterclockwise resonant cavity signal. The input light of the clockwise light has a second polarization state. The beam enters from the second port, is partially reflected by the second beam splitter onto the second mirror, is reflected by the second mirror, passes through the optical rotator, enters the optical fiber through the fourth port, and then enters the optical rotator through the third port. After being acted upon by the optical rotator, it enters the optical fiber again through the fourth port, and is transmitted through the optical rotator through the third port to the first mirror. After being reflected by the first mirror, it passes through the first beam splitter and the second beam splitter in sequence, and is reflected again by the second mirror into the optical rotator, thus forming a clockwise circulating light. From the time the beam is reflected by the second mirror into the optical rotator until the light reflected by the first mirror reaches the second mirror, this is one cycle. The clockwise circulating light is partially reflected by the first beam splitter and exits the resonant cavity from the first port, forming a clockwise resonant cavity signal.

10. The method according to claim 9, characterized in that, The first polarization state is a polarization direction perpendicular to the plane of the paper, facing the direction of light transmission; the second polarization state is a polarization direction parallel to the plane of the paper, facing the direction of light transmission; the first polarization state and the second polarization state are orthogonal; the third polarization state is a polarization direction at a 45-degree angle to the first polarization direction and the second polarization direction.

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