A low-power broadband light source driven resonant fiber-optic gyroscope and a working method thereof

Abstract

The present application relates to the technical field of optical gyroscopes, and specifically relates to a resonant fiber-optic gyroscope driven by a low-power broadband light source and a working method thereof. The fiber-optic gyroscope comprises an ASE light source, a circulator, a Y waveguide, a fiber resonant cavity, a first coupler, a second coupler, a photoelectric detector, and a signal processing unit. The ASE light source is connected to the circulator, and the circulator is connected to the input port of the Y waveguide and the photoelectric detector. The first coupler and the second coupler each have four ports. The Y waveguide is connected to port 1 of the first coupler and port 1 of the second coupler. The fiber resonant cavity is composed of the first coupler, the second coupler, and a section of fiber coil. Port 2 of the first coupler and port 2 of the second coupler are through-arm ports, and port 2 of the first coupler and port 2 of the second coupler are connected by means of 90° polarization axis rotation fusion splicing polarization maintaining optical fiber. The present application can significantly improve the utilization rate of the light source, effectively improve the stability and sensitivity of the system, and has significant engineering application potential.

Description

Technical Field

[0001] This invention relates to the field of optical gyroscope technology, specifically to a low-power broadband light source driven resonant fiber optic gyroscope and its operating method. Background Technology

[0002] Gyroscopes are widely used in navigation, positioning, and inertial measurement technologies. Existing resonant fiber optic gyroscopes (RFOGs) typically employ narrow-linewidth light sources as their excitation source. Theoretical analysis shows that this structure is beneficial for improving system sensitivity and reducing dependence on fiber length. However, in practical applications, narrow-linewidth light sources easily introduce coherent noise, which adversely affects system stability and measurement accuracy, limiting the performance improvement and widespread application of resonant fiber optic gyroscopes.

[0003] The resonant fiber optic gyroscope driven by a broadband light source combines the technical features of resonant fiber optic gyroscopes and interferometric fiber optic gyroscopes, achieving relatively stable angular velocity output with a relatively simplified structure.

[0004] However, existing broadband light source-driven resonant fiber optic gyroscopes still suffer from shortcomings in power utilization efficiency. These solutions typically employ a transmission-type fiber optic resonator structure, in which some resonant and non-resonant light leaks from the idle ports of the fiber coupler, leading to a reduction in effective optical power utilization. Furthermore, to obtain a fiber optic resonator with a higher quality factor, a coupler with a smaller cross-coupling coefficient is required, which further limits the system's optical power transmission efficiency. Therefore, to achieve the same theoretical sensitivity, broadband light source-driven resonant fiber optic gyroscopes usually require higher input optical power. This dependence on high-power light sources reduces the system's environmental adaptability and stability to some extent, hindering its engineering and integrated applications. Summary of the Invention

[0005] To address the technical problems of low power utilization efficiency in existing broadband light source-driven resonant fiber optic gyroscopes, this invention proposes a low-power broadband light source-driven resonant fiber optic gyroscope and its operating method.

[0006] This invention achieves efficient utilization of input light by connecting the idle ports of two fiber couplers in a transmission resonant cavity using a 90° polarization axis rotation fusion splice of polarization-maintaining fibers. This method enhances optical power circulation within the resonant cavity and significantly suppresses the introduction of additional relative intensity noise. By simultaneously allowing the input light to enter the resonant cavity through two couplers, the utilization rate of the light source is effectively improved. This invention provides an innovative solution for realizing low-power, broadband light source-driven resonant fiber optic gyroscopes. This method significantly improves light source utilization, reduces dependence on high-power light sources, and effectively enhances system stability and sensitivity. This method has significant engineering application potential, especially suitable for fiber optic gyroscope systems requiring miniaturization and low power consumption.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a low-power broadband light source driven resonant fiber optic gyroscope, comprising an ASE light source, a circulator, a Y-waveguide, a fiber optic resonant cavity, a first coupler, a second coupler, a photodetector, and a signal processing unit;

[0009] The ASE light source is connected to port 1 of the circulator, port 2 of the circulator is connected to the input port of the Y waveguide, and port 3 of the circulator is connected to the photodetector.

[0010] The first coupler and the second coupler each have four ports, namely port 1, port 2, port 3 and port 4;

[0011] The Y-waveguide has one input port and two output ports. The two output ports of the Y-waveguide are respectively connected to port 1 of the first coupler and port 1 of the second coupler.

[0012] The fiber resonant cavity is composed of a first coupler, a second coupler, and a section of fiber coil; port 3 of the first coupler and port 3 of the second coupler are connected; port 4 of the first coupler and port 4 of the second coupler are respectively connected to the two ends of the fiber coil to form a closed optical circuit.

[0013] Port 2 of the first coupler and port 2 of the second coupler are straight-through arms. Port 2 of the first coupler and port 2 of the second coupler are connected by fusion splicing polarization-maintaining fiber with a 90° polarization axis rotation.

[0014] Furthermore, the center wavelength of the ASE light source is selected from 1520 nm to 1620 nm; the spectral width of the ASE light source is from 10 nm to 80 nm; and the output power of the ASE light source is from 1 mW to 100 mW.

[0015] Furthermore, the first coupler and the second coupler are 2×2 fiber optic couplers; the optical parameters of the first coupler and the second coupler are similar, and the difference in the splitting ratio of the first coupler and the second coupler is controlled within ±1%; the splitting ratio of the first coupler and the second coupler is selected from 90:10 to 99:1, preferably, the splitting ratio is from 95:5 to 98:2.

[0016] Furthermore, the fiber coil constituting the fiber resonant cavity is wound using a four-pole symmetrical winding method or an octole symmetrical winding method.

[0017] Furthermore, the ports 2 of the first coupler and the second coupler are connected by a 90° polarization axis rotation fusion splice of polarization-maintaining fiber. Specifically, the first coupler and the second coupler are connected by a polarization-maintaining fiber. At the connection point, the pigtail of the straight-through output port of the first coupler carrying the straight-through optical signal is orthogonally fused with the pigtail of the straight-through input port of the second coupler. During the fusion splicing operation, the slow axis of the output fiber of the first coupler is precisely aligned with the fast axis of the input fiber of the second coupler, or the fast axis of the output fiber of the first coupler is precisely aligned with the slow axis of the input fiber of the second coupler, so that the polarization direction of the beam is rotated by 90°.

[0018] The present invention also provides a method for operating a resonant fiber optic gyroscope driven by a low-power broadband light source, comprising the following steps:

[0019] Step 1: The broadband light source output from the ASE light source is split into two equal beams by the Y-waveguide after passing through the circulator. and Y-waveguide for light and Modulation;

[0020] Step 2, Definition The coupled light is Light entering the resonant cavity via ports 1 and 4 of the first coupler; definition The coupled light is Light entering the resonant cavity via ports 1 and 4 of the second coupler;

[0021] Coupled light and The coupled light propagates along the CW and CCW directions respectively, and then couples out of the resonant cavity from port 1 of the second coupler and the first coupler respectively, returning to the input port of the Y waveguide. After interference, it is detected by the PD.

[0022] Step 3, Definition The direct-through light is the light that passes through ports 1 and 2 of the first coupler but does not enter the resonant cavity; defined The direct light is Light that does not enter the resonant cavity via ports 1 and 2 of the second coupler;

[0023] direct light and After the direct light passes through the 90° polarization axis rotation fusion point, The direct light is divided into two parts. One part of the light is coupled into the resonant cavity again through ports 2 and 3 of the second coupler and resonates. This part of the light is defined as part a1. The other part is the direct light that is not coupled into the resonant cavity through ports 2 and 1 of the second coupler and is effectively filtered out by the Y waveguide. The direct light is also divided into two parts. One part of the light is coupled into the resonant cavity again through ports 2 and 3 of the first coupler and resonates. This part of the light is defined as b1 part of the light. The other part is the direct light that is not coupled into the resonant cavity through ports 2 and 1 of the first coupler and is effectively filtered out by the Y waveguide.

[0024] In step 4, the light a1 coupled from port 1 of the second coupler and the light b1 coupled from port 1 of the first coupler in step 3 have polarization directions perpendicular to the polarization direction of the Y waveguide. Therefore, this part of the resonant light will also be filtered out.

[0025] In steps 5 and 3, the light portions a1 and b1 from step 3 both pass through the 90° fusion point again, and are divided into two parts when they pass through the corresponding coupler again: one part is coupled into the resonant cavity again and participates in resonance, which are defined as the light portion a2 and the light portion b2 respectively; the other part is not coupled into the resonant cavity and is directly transmitted and output, and its polarization direction is consistent with the polarization direction of the Y waveguide.

[0026] Step 6: The a2 and b2 portions of light that were coupled back into the resonant cavity in Step 5 are used as the input for the next cycle. For any k-th cycle (k≥2), after the ak and bk portions of light pass through the 90° fusion point and the corresponding coupler again, they are divided into two parts: one part is coupled into the resonant cavity to form the a(k+1) and b(k+1) portions of light in the next cycle; the other part is the light that is not coupled into the resonant cavity and is output through the direct port of the corresponding coupler. When the cycle number k is even, the polarization direction of the output light is consistent with the polarization direction of the Y-waveguide and is effectively detected by the photodetector; when k is odd, its polarization direction is inconsistent with the polarization direction of the Y-waveguide and is suppressed and filtered out by the polarization selection unit Y-waveguide. The above process is repeated in cycles to form the a3 portion of light, the b3 portion of light, ..., the an portion of light, and the bn portion of light in sequence. The cycle terminates when the amplitude of the an portion of light and the bn portion of light decays to zero in the nth cycle.

[0027] Step 7: Calculate the angular velocity information of the fiber optic gyroscope by monitoring the change in total optical power detected by the photodetector.

[0028] Furthermore, the output light field of the ASE light source described in step 1 is expressed as:

[0029] (1)

[0030] in Represents the instantaneous amplitude of the light field. This represents the peak value of the light field amplitude. It is the center frequency of the ASE light source. Representing the independent variable of time, It is the initial phase of light. Denotes the base of the natural logarithm. It represents the imaginary unit.

[0031] Furthermore, in step 1, the method by which the Y-waveguide modulates the light is one of sinusoidal modulation, bipolar sawtooth wave modulation, triangular wave modulation, or square wave modulation.

[0032] Furthermore, in step 2, the optical wave vector returning to the input port of the Y-waveguide is in the form of:

[0033] (2)

[0034] (3)

[0035] in and These represent the instantaneous values ​​of the optical field amplitude coupled from the resonant cavity via ports 1 of the second and first couplers, respectively, from the CW and CCW directions. and These represent the input optical field amplitudes injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; This represents the summation of multiple beams. This indicates the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is the center frequency of the ASE light source. It is a Sagnac phase shift; It is the one-way transmission time of light; Represents the base of the natural logarithm; It represents the imaginary unit.

[0036] Furthermore, in step 6, the optical power effectively detected by the photodetector is expressed as:

[0037] (4)

[0038] in It is the amplitude of the light field at the detector. This represents the insertion loss of the circulator. This represents the insertion loss of the Y-waveguide. This represents the light field component propagating in the CW direction. The light field components propagating in the CCW direction are expressed as follows:

[0039] (5)

[0040] (6)

[0041] in and Let represent the total optical field amplitude that returns to the Y-waveguide input port after n resonances in the resonator along the CW and CCW directions, respectively. Its expression is:

[0042] (7)

[0043] (8)

[0044] Among them, the optical field amplitude corresponding to the first resonance and Represented as:

[0045] (9)

[0046] (10)

[0047] in and These represent the amplitudes of the input optical field injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; For multi-beam interference summation, This represents the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is a Sagnac phase shift; It is the one-way transmission time of light; It is the power coupling coefficient between the first coupler and the second coupler; Indicates the independent variable of time; It is the initial phase of light; Represents the base of the natural logarithm; Represents the imaginary unit;

[0048] The total optical power reaching the photodetector is expressed as:

[0049] (11)

[0050] in This represents the total optical power received by the photodetector. This represents the amplitude of the light field at the photodetector. express The complex conjugate, It is the frequency of light.

[0051] Compared with the prior art, the beneficial effects of the present invention are:

[0052] 1. Improve the efficiency of light source power utilization

[0053] This invention introduces a 90° polarization axis rotation fusion structure at two unused ports of a transmissive resonant cavity, allowing the optical signal that was originally output from the unused ports and was not effectively utilized to be reinjected into the input path of the resonant cavity after completing the polarization rotation. Since this reinjected optical signal can participate again in the coupling and propagation process of the resonant cavity, the output optical power of the light source is recycled. Therefore, without increasing the rated output power of the light source, the system's light source power utilization efficiency is significantly improved. Experiments show that the equivalent utilization efficiency of the light source can be increased by nearly 2 times.

[0054] 2. Improve the scaling factor and resolution of broadband light source-driven resonant fiber optic gyroscopes.

[0055] The increased power utilization efficiency of the light source leads to a higher effective optical power entering the resonant cavity and participating in detection. Simultaneously, the improved quality factor of the resonator results in a steeper resonance curve and a narrower linewidth. Therefore, this invention significantly enhances the system's sensitivity to minute phase or frequency changes. Based on these effects, this invention effectively optimizes the scaling factor of the resonant fiber optic gyroscope, improving the resolution and sensitivity of rotation signal detection.

[0056] 3. Avoid introducing additional relative intensity noise, thereby improving detection accuracy and system stability.

[0057] This invention constructs a highly reciprocal optical signal reinjection structure, which cyclically enhances the intracavity optical power and significantly suppresses the entry of additional relative intensity noise. The 90° polarization axis rotation structure adjusts the polarization direction before optical reinjection, ensuring that any through-light that fails to recouple into the cavity is completely filtered out upon reaching the Y-waveguide. Through this polarization conversion and noise suppression mechanism, this invention prevents excess optical power from entering the system, fundamentally suppressing the introduction of additional relative intensity noise and improving the signal-to-noise ratio, detection stability, and reliability of the resonant optical gyroscope in engineering applications.

[0058] 4. Improve the quality factor Q of the resonant cavity

[0059] The 90° polarization axis rotation re-entry structure employed in this invention ensures that the polarization state of the returning optical signal matches the coupling conditions of the resonant cavity, while retaining the original phase information. This allows the optical signal to be repeatedly re-entered into the resonant cavity. Because the optical field carrying phase information is repeatedly superimposed within the resonant cavity, the coherent accumulation effect of the intracavity optical field is enhanced, reducing equivalent energy loss. Therefore, the energy storage capacity of the resonant cavity is significantly improved, thereby enhancing the quality factor Q of the resonator. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the overall structure of the low-power broadband light source driven resonant fiber optic gyroscope of the present invention.

[0061] Figure 2 This is a schematic diagram comparing the transmission and demodulation characteristics of the present invention with those of conventional solutions.

[0062] in, Figure 2 (a) is a transmission curve graph. Figure 2 (b) is the demodulation curve diagram;

[0063] Figure 3 This is a schematic diagram illustrating the improvement effect of the resonator quality factor Q as a function of the coupling coefficient when using the structure of the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings.

[0065] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Specific Implementation Method 1

[0067] This invention provides a low-power broadband light source driven resonant fiber optic gyroscope, see [link to relevant documentation]. Figure 1 It includes an ASE light source, a circulator, a Y-waveguide, an optical fiber resonant cavity, a first coupler, a second coupler, a photodetector, and a signal processing unit.

[0068] The ASE light source is connected to port 1 of the circulator, port 2 of the circulator is connected to the input port of the Y waveguide, and port 3 of the circulator is connected to the photodetector.

[0069] The first coupler and the second coupler each have four ports, namely port 1, port 2, port 3 and port 4.

[0070] The Y-waveguide has one input port and two output ports. The two output ports of the Y-waveguide are connected to port 1 of the first coupler and port 1 of the second coupler, respectively.

[0071] The fiber optic resonant cavity consists of a first coupler, a second coupler, and a section of fiber optic coil. Port 3 of the first coupler is connected to port 3 of the second coupler. Port 4 of the first coupler and port 4 of the second coupler are respectively connected to the two ends of the fiber optic coil, forming a closed optical circuit.

[0072] Port 2 of the first coupler and port 2 of the second coupler are straight-through arms. Port 2 of the first coupler and port 2 of the second coupler are connected by a 90° polarization axis rotation fusion splice of polarization-maintaining fiber. Specifically, the first coupler and the second coupler are connected by a polarization-maintaining fiber. At the connection point, the pigtail of the straight-through output port (i.e., port 2 of the first coupler) of the first coupler carrying the straight-through optical signal is orthogonally fused with the pigtail of the straight-through input port (i.e., port 2 of the second coupler). During the fusion splicing operation, the slow axis of the output fiber of the first coupler is precisely aligned with the fast axis of the input fiber of the second coupler (or the fast axis of the output fiber of the first coupler is precisely aligned with the slow axis of the input fiber of the second coupler), so that the polarization direction of the beam is rotated by 90°.

[0073] The light source is an amplified spontaneous emission (ASE) source. To meet the needs of the system in different application scenarios, the center wavelength of the ASE source can be selected from 1520 nm to 1620 nm, preferably 1550 nm. The spectral width of the ASE source is preferably 10 nm to 80 nm to ensure sufficient spectral bandwidth to suppress coherent noise. In terms of power, the output power of the ASE source is configured to meet low-power drive conditions, and its range can be selected from 1 mW to 100 mW.

[0074] The first and second couplers are 2×2 fiber optic couplers, but in other embodiments, integrated optical waveguide couplers or other forms of optical beam splitters / combiners may also be used. Furthermore, to ensure system reciprocity and suppress non-reciprocity errors caused by optical path asymmetry, the optical parameters of the first and second couplers should be similar (the difference in the splitting ratio between the first and second couplers should be controlled within ±1%) to ensure that the CW and CCW beams experience similar coupling losses and phase shifts during transmission. The splitting ratio of the first and second couplers is selected in the range of 90:10 to 99:1, preferably 95:5 to 98:2.

[0075] The fiber optic resonant cavity is a closed optical circuit formed by interconnecting a first coupler, a second coupler, and a section of fiber optic coil. The length of the fiber optic coil can be selected from 50 m to 1000 m. The winding diameter of the fiber optic coil can be selected from 3 cm to 15 cm. Furthermore, in order to maintain the polarization state stability of the optical signal during transmission within the resonant cavity, the fiber optic coil is preferably wound with polarization-maintaining fiber, and the fiber optic coil constituting the fiber optic resonant cavity is wound using a four-pole symmetrical winding method or an octole symmetrical winding method to suppress non-reciprocity errors caused by changes in ambient temperature.

[0076] The Y-waveguide is preferably manufactured using an annealed proton exchange process with lithium niobate (N-N). A Y-waveguide is used to achieve single-polarization transmission characteristics. Given that the Y-waveguide is used as a high extinction ratio polarizer in this system to filter stray light signals perpendicular to the working axis, its polarization extinction ratio should preferably be above 30 dB.

[0077] The photodetector is used to convert the received optical signal into an electrical signal for subsequent demodulation and processing. Preferably, a PIN photodiode made of indium gallium arsenide (InGaAs) material is used.

[0078] The signal processing unit is used to receive the detected electrical signals and obtain the rotational angular velocity information through a digital demodulation algorithm.

[0079] It should be noted that, in Figure 1 In this diagram, ASE represents the ASE light source, CIR represents the circulator, C1 represents the first coupler, C2 represents the second coupler, PD represents the photodetector, and 1, 2, 3, and 4 represent port 1, port 2, port 3, and port 4. Specific Implementation Method Two

[0081] The present invention also provides a method for operating a resonant fiber optic gyroscope driven by a low-power broadband light source, comprising the following steps:

[0082] Step 1: The broadband light source output from the ASE light source is split into two equal beams by the Y-waveguide after passing through the circulator. and Y-waveguide for light and Modulation is performed.

[0083] The output light field of the ASE light source in step 1 can be expressed as:

[0084] (1)

[0085] in Represents the instantaneous amplitude of the light field. This represents the peak value of the light field amplitude. It is the center frequency of the ASE light source. Representing the independent variable of time, It is the initial phase of light. Denotes the base of the natural logarithm. It represents the imaginary unit.

[0086] The method of modulating light using a Y-waveguide is one of the following: sinusoidal modulation, bipolar sawtooth wave modulation, triangular wave modulation, or square wave modulation.

[0087] Step 2, Definition The coupled light is Light entering the resonant cavity via ports 1 and 4 of the first coupler; definition The coupled light is Light enters the resonant cavity through ports 1 and 4 of the second coupler.

[0088] Coupled light and The coupled light propagates along the CW (clockwise) and CCW (counterclockwise) directions respectively, and then couples out of the resonant cavity from port 1 of the second coupler and the first coupler respectively, returning to the input port of the Y waveguide. After interference, it is detected by the PD.

[0089] The optical vector returning to the input port of the Y-waveguide is in the form of:

[0090] (2)

[0091] (3)

[0092] in and These represent the instantaneous values ​​of the optical field amplitude coupled from the resonant cavity via ports 1 of the second and first couplers, respectively, from the CW and CCW directions. and These represent the amplitudes of the input optical field injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; This represents the summation of multiple beams. This indicates the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is the center frequency of the ASE light source. It is a Sagnac phase shift; It is the one-way transmission time of light; Represents the base of the natural logarithm; It represents the imaginary unit.

[0093] Step 3, Definition The direct-through light is the light that passes through ports 1 and 2 of the first coupler but does not enter the resonant cavity; defined The direct light is Light that does not enter the resonant cavity via ports 1 and 2 of the second coupler.

[0094] direct light and After the direct light passes through the 90° polarization axis rotation fusion point, The direct light is divided into two parts. One part is coupled back into the resonant cavity via ports 2 and 3 of the second coupler and resonates; this part is defined as part a1. The other part is the direct light that is not coupled into the resonant cavity via ports 2 and 1 of the second coupler. Since its polarization direction is perpendicular to the transmission axis of the Y-waveguide, this part of the direct light will be effectively filtered out by the Y-waveguide. Similarly, The direct light is also divided into two parts. One part of the light is coupled into the resonant cavity again through ports 2 and 3 of the first coupler and resonates. This part of the light is defined as the b1 part of the light. The other part is the direct light that is not coupled into the resonant cavity through ports 2 and 1 of the first coupler and is effectively filtered out by the Y waveguide.

[0095] Since the Y-waveguide is a single-axis optical device with a high polarization extinction ratio, it can effectively filter out optical signals whose polarization direction is perpendicular to its working axis. At this time, the direct light returning to the Y-waveguide via the first coupler port 1 and the second coupler port 1, having passed through the 90° polarization axis rotation fusion structure, has its transmission polarization direction rotated by 90°, becoming perpendicular to the working axis of the Y-waveguide. Therefore, this portion of the direct light that fails to couple back into the resonant cavity is effectively filtered out upon reaching the Y-waveguide and cannot enter the photodetector, thus preventing the introduction of additional relative intensity noise and significantly improving the detection stability of the system.

[0096] In steps 4 and 3, the light a1 coupled from port 1 of the second coupler and the light b1 coupled from port 1 of the first coupler have polarization directions perpendicular to the polarization direction of the Y waveguide. Therefore, this part of the resonant light will also be filtered out.

[0097] In steps 5 and 3, the light portion a1 (output from port 2 of the first coupler) and the light portion b1 (output from port 2 of the second coupler) both pass through the 90° fusion point again, and are divided into two parts when they pass through the corresponding coupler again: one part is coupled into the resonant cavity again and participates in resonance, and is defined as the light portion a2 and the light portion b2 respectively; the other part is not coupled into the resonant cavity and is directly transmitted and output, and its polarization direction is consistent with the polarization direction of the Y waveguide.

[0098] Step 6: The a2 and b2 portions of light, which were coupled back into the resonant cavity in Step 5, are used as the input for the next cycle. For any k-th cycle (k≥2), after the ak and bk portions of light pass through the 90° fusion point and the corresponding coupler again, they are divided into two parts: one part is coupled into the resonant cavity, forming the a(k+1) and b(k+1) portions of light for the next cycle; the other part, which is not coupled into the resonant cavity, is output through the direct port of the corresponding coupler. When the cycle number k is even, the polarization direction of the output light is consistent with the polarization direction of the Y-waveguide and can be effectively detected by the photodetector; when k is odd, its polarization direction is inconsistent with the polarization direction of the Y-waveguide and is suppressed and filtered out by the polarization selection unit Y-waveguide. The above process is repeated cycle by cycle, forming the a3 portion of light, the b3 portion of light, ..., the an portion of light, and the bn portion of light in sequence. The cycle terminates when the amplitude of the an portion of light and the bn portion of light decays to zero in the n-th cycle.

[0099] By employing a 90° polarization axis rotational fusion welding of the idle port of the transmission resonant cavity, the input and output light are re-entered in a loop, thereby improving both the utilization rate of the light source and the detection accuracy of the gyroscope. Returning to the Y-waveguide input port, the optical power effectively detected by the photodetector can be expressed as:

[0100] (4)

[0101] in It is the amplitude of the light field at the detector. This represents the insertion loss of the circulator. This represents the insertion loss of the Y-waveguide. This represents the light field component propagating in the CW direction. The light field components propagating in the CCW direction are expressed as follows:

[0102] (5)

[0103] (6)

[0104] in and Let represent the total optical field amplitude that returns to the Y-waveguide input port after n resonances in the resonator along the CW and CCW directions, respectively. Its expression is:

[0105] (7)

[0106] (8)

[0107] Among them, the optical field amplitude corresponding to the first resonance and Represented as:

[0108] (9)

[0109] (10)

[0110] in and These represent the amplitudes of the input optical field injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; For multi-beam interference summation, This represents the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is a Sagnac phase shift; It is the one-way transmission time of light; It is the power coupling coefficient between the first coupler and the second coupler; Indicates the independent variable of time; It is the initial phase of light; Represents the base of the natural logarithm; It represents the imaginary unit.

[0111] The total optical power reaching the photodetector can be expressed as:

[0112] (11)

[0113] in This represents the total optical power received by the photodetector. This represents the amplitude of the light field at the photodetector. express The complex conjugate, It is the frequency of light.

[0114] Step 7: Calculate the angular velocity information of the fiber optic gyroscope by monitoring the change in total optical power detected by the photodetector.

[0115] Due to the Sagnac effect, the detected optical power changes. Therefore, the angular velocity information of the fiber optic gyroscope can be calculated by monitoring the changes in optical power detected by the photodetector.

[0116] Example:

[0117] The specific implementation methods are further described below with reference to the embodiments.

[0118] Example 1:

[0119] A low-power broadband light source driven resonant fiber optic gyroscope includes an ASE light source, a circulator, a Y-waveguide, a fiber optic resonant cavity, a first coupler, a second coupler, a photodetector, and a signal processing unit.

[0120] The ASE light source is connected to port 1 of the circulator, port 2 of the circulator is connected to the input port of the Y waveguide, and port 3 of the circulator is connected to the photodetector.

[0121] The first coupler and the second coupler each have four ports, namely port 1, port 2, port 3 and port 4.

[0122] The Y-waveguide has one input port and two output ports. The two output ports are connected to port 1 of the first coupler and port 1 of the second coupler, respectively.

[0123] The fiber optic resonant cavity consists of a first coupler, a second coupler, and a polarization-maintaining fiber coil. Specifically, ports 3 and 4 of the first coupler are connected to the two ends of the fiber coil, and ports 3 and 4 of the second coupler are also connected to the two ends of the fiber coil, forming a closed optical circuit.

[0124] Port 2 of the first coupler and port 2 of the second coupler are straight-through arms, connected by a section of polarization-maintaining fiber. Crucially, this connection employs a 90° polarization axis rotation fusion splice, whereby at the splice point, the slow axis of the output fiber of the first coupler is precisely aligned with the fast axis of the input fiber of the second coupler, rotating the polarization direction of the transmitted light by 90°.

[0125] An amplified spontaneous emission (ASE) light source is used. In this embodiment, the center wavelength of the ASE light source is set to 1550 nm, the spectral width is approximately 35 nm, and the output power is set to 7 mW. This configuration satisfies the low-power drive requirements while providing sufficient spectral bandwidth to suppress coherent noise.

[0126] The circulator uses a clockwise circulator.

[0127] Both the first and second couplers are 2×2 polarization-maintaining fiber couplers. In this embodiment, the splitting ratio of both the first and second couplers is 95:5, meaning that 95% of the energy is at the through end and 5% of the energy is coupled into the resonant cavity.

[0128] The fiber optic coil is approximately 200 m long and has a winding diameter of approximately 7.5 cm. The coil uses polarization-maintaining fiber and is wound using a four-pole symmetrical winding method to reduce Shupe errors caused by changes in ambient temperature.

[0129] The Y-waveguide is a lithium niobate waveguide manufactured using an annealed proton exchange process. It has a polarization extinction ratio of 40 dB and is used for beam splitting, phase modulation of optical signals, and as a polarizer to filter out stray light perpendicular to the working axis.

[0130] The photodetector PD uses an InGaAs PIN photodiode adapted to the 1550 nm band to convert interference optical signals into electrical signals.

[0131] Under the condition of keeping the input conditions such as light source power and modulation depth the same, a comparative experiment was conducted between the low-power broadband light source driving scheme proposed in this invention and the traditional resonant gyroscope scheme. Experimental results show that, compared with the traditional scheme, the transmission efficiency of the proposed scheme is improved by approximately two times. Figure 2 As shown in (a), the demodulation curves corresponding to the two schemes are as follows: Figure 2 As shown in (b), compared with the conventional solution, the demodulation sensitivity of the present invention is improved by about two times. The present invention also achieves nearly a two-fold improvement in both the output optical power and the system scaling factor, two key performance indicators.

[0132] The aforementioned performance improvement is primarily attributed to the 90° polarization axis rotational fusion structure employed in this invention. This structure enables the modulation of the light polarization state, thereby suppressing the relative intensity noise introduced by the direct-pass light and enhancing the effective signal using re-entry light, thus improving the system's signal-to-noise ratio. Through this technical solution, the system can still achieve high detection sensitivity and measurement accuracy even under low-power broadband light source driving conditions.

[0133] Example 2:

[0134] A simulation experiment was conducted based on the working method of the resonant fiber optic gyroscope driven by a low-power broadband light source in Specific Implementation Method Two. The insertion loss of the circulator was also considered. The insertion loss of the Y-waveguide is 0.2 dB. The total loss is 0.2 dB, consisting of the fiber intrinsic attenuation and the coupler insertion loss. It is 0.1 dB. Under this condition, the power coupling coefficient of the first coupler and the second coupler is... The Q-factor enhancement coefficient was simulated and analyzed when it varied in the range of 0.05 to 0.5. Figure 3 The Q-factor boost coefficient and the power coupling coefficient of the first and second couplers are given under specific loss conditions. The simulation results show the relationship between the two. As shown in the figure, under the above loss conditions, the Q-factor improvement coefficient is always greater than 1, indicating that the proposed structure can improve the Q-factor of the resonant cavity. When the coupling coefficient changes from 0.05 to 0.5, the Q-factor can be improved by about 3% to 57%.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-power broadband light source driven resonant fiber optic gyroscope, characterized in that, The resonant fiber optic gyroscope includes an ASE light source, a circulator, a Y-waveguide, a fiber optic resonant cavity, a first coupler, a second coupler, a photodetector, and a signal processing unit. The ASE light source is connected to port 1 of the circulator, port 2 of the circulator is connected to the input port of the Y waveguide, and port 3 of the circulator is connected to the photodetector. The first coupler and the second coupler each have four ports, namely port 1, port 2, port 3 and port 4; The Y-waveguide has one input port and two output ports. The two output ports of the Y-waveguide are respectively connected to port 1 of the first coupler and port 1 of the second coupler. The fiber resonant cavity is composed of a first coupler, a second coupler, and a section of fiber coil; port 3 of the first coupler and port 3 of the second coupler are connected; port 4 of the first coupler and port 4 of the second coupler are respectively connected to the two ends of the fiber coil to form a closed optical circuit. Port 2 of the first coupler and port 2 of the second coupler are straight-through arms. Port 2 of the first coupler and port 2 of the second coupler are connected by fusion splicing polarization-maintaining fiber with a 90° polarization axis rotation.

2. The low-power broadband light source driven resonant fiber optic gyroscope according to claim 1, characterized in that, The center wavelength of the ASE light source is selected from 1520 nm to 1620 nm; the spectral width of the ASE light source is from 10 nm to 80 nm; and the output power of the ASE light source is from 1 mW to 100 mW.

3. The low-power broadband light source driven resonant fiber optic gyroscope according to claim 1, characterized in that, The first coupler and the second coupler are 2×2 fiber optic couplers; the optical parameters of the first coupler and the second coupler are similar, and the difference in the splitting ratio of the first coupler and the second coupler is controlled within ±1%; the splitting ratio of the first coupler and the second coupler is selected from 90:10 to 99:

1.

4. The low-power broadband light source driven resonant fiber optic gyroscope according to claim 1, characterized in that, The fiber optic coils constituting the fiber optic resonant cavity are wound using a four-pole symmetrical winding method or an octole symmetrical winding method.

5. The low-power broadband light source driven resonant fiber optic gyroscope according to claim 1, characterized in that, The first coupler's port 2 and the second coupler's port 2 are connected by a 90° polarization axis rotation fusion splice of polarization-maintaining fiber. Specifically, the first coupler and the second coupler are connected by a polarization-maintaining fiber. At the connection point, the pigtail of the straight-through output port of the first coupler carrying the straight-through optical signal is orthogonally fused with the pigtail of the straight-through input port of the second coupler. During the fusion splicing operation, the slow axis of the first coupler's output fiber is precisely aligned with the fast axis of the second coupler's input fiber, or the fast axis of the first coupler's output fiber is precisely aligned with the slow axis of the second coupler's input fiber, so that the polarization direction of the beam is rotated by 90°.

6. A method for operating a resonant fiber optic gyroscope driven by a low-power broadband light source, characterized in that, The working method includes the following steps: Step 1: The broadband light source output from the ASE light source is split into two equal beams by the Y-waveguide after passing through the circulator. and Y-waveguide for light and Modulation; Step 2, Definition The coupled light is Light entering the resonant cavity via ports 1 and 4 of the first coupler; definition The coupled light is Light entering the resonant cavity via ports 1 and 4 of the second coupler; Coupled light and The coupled light propagates along the CW and CCW directions respectively, and then is coupled out of the resonant cavity from port 1 of the second coupler and the first coupler respectively, returning to the input port of the Y waveguide. After interference, it is detected by the PD. Step 3, Definition The direct-through light is the light that passes through ports 1 and 2 of the first coupler but does not enter the resonant cavity; defined The direct light is Light that does not enter the resonant cavity via ports 1 and 2 of the second coupler; direct light and After the direct light passes through the 90° polarization axis rotation fusion point, The direct light is divided into two parts. One part of the light is coupled into the resonant cavity again through ports 2 and 3 of the second coupler and resonates. This part of the light is defined as part a1. The other part is the direct light that is not coupled into the resonant cavity through ports 2 and 1 of the second coupler and is effectively filtered out by the Y waveguide. The direct light is also divided into two parts. One part of the light is coupled into the resonant cavity again through ports 2 and 3 of the first coupler and resonates. This part of the light is defined as b1 part of the light. The other part is the direct light that is not coupled into the resonant cavity through ports 2 and 1 of the first coupler and is effectively filtered out by the Y waveguide. In step 4, the light a1 coupled from port 1 of the second coupler and the light b1 coupled from port 1 of the first coupler in step 3 have polarization directions perpendicular to the polarization direction of the Y waveguide. Therefore, this part of the resonant light will also be filtered out. In steps 5 and 3, the light portions a1 and b1 from step 3 both pass through the 90° fusion point again, and are divided into two parts when they pass through the corresponding coupler again: one part is coupled into the resonant cavity again and participates in resonance, which are defined as the light portion a2 and the light portion b2 respectively; the other part is not coupled into the resonant cavity and is directly transmitted and output, and its polarization direction is consistent with the polarization direction of the Y waveguide. Step 6: The a2 and b2 portions of light that were coupled back into the resonant cavity in Step 5 are used as the input for the next cycle. For any k-th cycle (k≥2), after the ak and bk portions of light pass through the 90° fusion point and the corresponding coupler again, they are divided into two parts: one part is coupled into the resonant cavity to form the a(k+1) and b(k+1) portions of light in the next cycle; the other part is the light that is not coupled into the resonant cavity and is output through the direct port of the corresponding coupler. When the cycle number k is even, the polarization direction of the output light is consistent with the polarization direction of the Y-waveguide and is effectively detected by the photodetector; when k is odd, its polarization direction is inconsistent with the polarization direction of the Y-waveguide and is suppressed and filtered out by the polarization selection unit Y-waveguide. The above process is repeated in cycles to form the a3 portion of light, the b3 portion of light, ..., the an portion of light, and the bn portion of light in sequence. The cycle terminates when the amplitude of the an portion of light and the bn portion of light decays to zero in the nth cycle. Step 7: Calculate the angular velocity information of the fiber optic gyroscope by monitoring the change in total optical power detected by the photodetector.

7. The operating method of the low-power broadband light source driven resonant fiber optic gyroscope according to claim 6, characterized in that, The output light field of the ASE light source mentioned in step 1 is expressed as follows: (1) in Represents the instantaneous amplitude of the light field. This represents the peak value of the light field amplitude. It is the center frequency of the ASE light source. Representing the independent variable of time, It is the initial phase of light. Denotes the base of the natural logarithm. It represents the imaginary unit.

8. The operating method of the low-power broadband light source driven resonant fiber optic gyroscope according to claim 6, characterized in that, In step 1, the method by which the Y-waveguide modulates the light is one of sinusoidal modulation, bipolar sawtooth wave modulation, triangular wave modulation, or square wave modulation.

9. The operating method of the low-power broadband light source driven resonant fiber optic gyroscope according to claim 6, characterized in that, In step 2, the optical wave vector returning to the input port of the Y-waveguide is in the form of: (2) (3) in and These represent the instantaneous values ​​of the optical field amplitude coupled from the resonant cavity via ports 1 of the second and first couplers, respectively, from the CW and CCW directions. and These represent the amplitudes of the input optical field injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; This represents the summation of multiple beams. This indicates the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is the center frequency of the ASE light source. It is a Sagnac phase shift; It is the one-way transmission time of light; Represents the base of the natural logarithm; It represents the imaginary unit.

10. The operating method of the low-power broadband light source driven resonant fiber optic gyroscope according to claim 6, characterized in that, In step 6, the optical power effectively detected by the photodetector is expressed as: (4) in It is the amplitude of the light field at the detector. This represents the insertion loss of the circulator. This represents the insertion loss of the Y-waveguide. This represents the light field component propagating in the CW direction. The light field components propagating in the CCW direction are expressed as follows: (5) (6) in and Let represent the total optical field amplitude that returns to the Y-waveguide input port after n resonances in the resonator along the CW and CCW directions, respectively. Its expression is: (7) (8) Among them, the optical field amplitude corresponding to the first resonance and Represented as: (9) (10) in and These represent the amplitudes of the input optical field injected into the resonant cavity from the CW and CCW directions, respectively. It is the transmission coefficient; For multi-beam interference summation, This represents the number of times light circulates within the fiber optic resonant cavity; For round-trip transmission coefficient, express Round-trip transmission coefficient; It is a Sagnac phase shift; It is the one-way transmission time of light; It is the power coupling coefficient between the first coupler and the second coupler; Indicates the independent variable of time; It is the initial phase of light; Represents the base of the natural logarithm; Represents the imaginary unit; The total optical power reaching the photodetector is expressed as: (11) in This represents the total optical power received by the photodetector. This represents the amplitude of the light field at the photodetector. express The complex conjugate, It is the frequency of light.

Images