CN1264000C - Self-injection locking fibre-optical laser circulator - Google Patents

Abstract

The present invention relates to an optical gyroscope, particularly to an optical fiber laser gyroscope. The present invention is composed of an optical fiber laser, a detector and a difference frequency signal processing circuit. The present invention is characterized in that the optical fiber laser is composed of a semiconductor laser with tail fiber, a unifrequent distributed feedback optical fiber laser DFB, optical fiber rings and an optical fiber coupler, wherein each optical fiber ring is composed of a wavelength division multiplexer, an isolator, gain optical fiber and an optical fiber coupler, the two optical fiber rings with gain optical fiber form two respectively independent resonant cavities, the DFB injects seed laser respectively into the resonant cavities to lock the work wavelengths of the resonant cavities, the isolator makes the laser works in a unidirectional traveling-wave mode, and the laser transmission direction is clockwise in one ring and is counterclockwise in the other ring. The present invention eliminates the phenomenon of spatial hole burning in homogeneous broadening gain media and the locking effect caused by backward scattering, and the laser in the two annular resonant cavities works in a stable single longitudinal mode with narrow linewidth. The difference frequency signals can be used for detecting.

Description

Self-injection-locked fiber laser gyroscope

Technical field:

The invention relates to an optical gyroscope, in particular to a fiber laser gyroscope.

Background technique:

As an important sensor, the gyroscope has important applications in military and civilian applications such as positioning, orientation, and navigation of satellites, aircraft, ships, and automobiles. A new generation of optical gyroscopes based on the Sagnac effect (such as laser gyroscopes, interferometric fiber optic gyroscopes, etc.) has attracted people's research interest. As the first generation of products, the laser gyroscope has entered practical application in the field of medium and low precision. It adopts the difference frequency signal detection method, the electronic processing is more convenient, and the signal processing accuracy is higher; but the discrete optical components and defects such as short life, large volume, and heavy weight affect the application of laser gyroscopes in high-precision fields. As the second generation of interferometric fiber optic gyro, its fully solidified structure has aroused great interest. At the same time, it also has the advantages of low power consumption, long life, small size, light weight, etc., and has a good development in the application fields with low and medium precision requirements; however, the interferometric fiber optic gyroscope uses phase detection, and the electronic processing is relatively complicated. , Problems such as noise, stability, dynamic range and scale factor linearization limit the further improvement of the performance of fiber optic gyroscopes, and also affect the application of interferometric fiber optic gyroscopes in high-precision fields. With the development of fiber lasers, people hope to combine the advantages of full solidification of fiber optic gyroscopes with the advantages of laser gyroscope difference frequency signal processing to develop high-performance fiber laser gyroscopes to meet higher precision applications (such as inertial navigation) requirements.

There are two key requirements for high-performance fiber laser gyroscopes: ① the gain medium should be able to provide directional gain to avoid gain competition between the oppositely transmitted lasers; ② the backscattering must be negligible to eliminate the latch-up effect. The fiber laser gyro that has been proposed so far, such as the Chinese patent application CN1320821A "Ring Fiber Laser Gyro", its core is a narrow-linewidth single-frequency fiber laser, which uses Mach-Zenger interferometer multi-stage filtering to realize the single-frequency operation of the fiber laser , to separate the two signal lasers in space to avoid the competition between the clockwise and counterclockwise signal lasers due to the shared gain. However, the filtering bandwidth of a single-stage Mach-Zenger interferometer is relatively wide, and a multi-stage Mach-Zenger interferometer and a cavity length controller are required, which makes the structure of the ring cavity more complicated, and the accuracy and sensitivity are affected.

Invention content:

The purpose of the present invention is to provide a new optical gyroscope, that is, self-injection locking fiber laser gyroscope, which can not only solve the problems of gain competition and locking effect, but also make the structure simple, small in size, and improve the accuracy and sensitivity of the gyroscope.

The present invention is realized in the following ways:

The self-injection-locked fiber laser gyro is composed of a fiber laser, a detector, and a difference frequency signal processing circuit. The fiber laser is composed of a semiconductor laser with a pigtail, a single-frequency distributed feedback fiber laser DFB, a fiber ring, and a fiber coupler. It is composed of a wavelength division multiplexer, an isolator, a gain fiber and a fiber coupler. The specific structure is: two semiconductor lasers LD ₁ and LD ₂ with pigtails are respectively passed through the wavelength division multiplexer WDM ₁ and WDM ₂ and The two ends of DFB are connected; then WDM ₁ and WDM ₂ are respectively connected with isolators I ₁ and I ₂ , gain fibers GF ₁ and GF ₂ , and I ₁ and I ₂ , GF ₁ and GF ₂ are respectively connected with fiber coupler C ₁ Connect with C ₂ separately to form two optical fiber loops with gain and opposite directions; one output end of fiber coupler C ₁ and C ₂ is respectively connected with two input ends of fiber coupler C ₃ , and the output end of C ₃ The two output terminals are respectively connected to the detectors PD ₁ and PD ₂ , and PD ₁ or PD ₂ is connected to the difference frequency signal processing circuit.

That is to say, the present invention constitutes the fiber laser gyroscope through the topological structure of the fiber laser with self-injection locking, that is, the fiber laser as the core component of the fiber laser gyroscope is a bidirectional self-injection-locked single-frequency fiber laser (its specific structure as the picture shows). It uses two semiconductor lasers LD ₁ and LD ₂ with pigtails as pumping sources to provide pumping power for the single-frequency distributed feedback fiber laser DFB, and then injects them into a fiber ring from opposite directions, and then injects them into a fiber ring in the opposite direction. The running and locked signal laser is extracted from the fiber optic ring for detection and processing. The pumping power of the two fiber rings is also provided by LD ₁ and LD ₂ respectively. LD ₁ and LD ₂ are respectively connected to both ends of DFB through wavelength division multiplexers WDM ₁ and WDM _2. The wavelength of LD ₁ and LD ₂ depends on the absorption of the working material in the gain fiber (or active fiber) used by DFB. Depending on the peak, the usual pump wavelengths are 650nm, 780nm, 800nm, 915nm, 980nm and 1480nm, etc. The output power is generally selected to be greater than 100mW; DFB is directly produced on the gain fiber, and the gain fiber should be highly doped Rare earth-doped fiber or other doped fiber (such as Erbium-doped or Ytterbium-doped fiber with a doping amount of more than 800ppm), its length is generally about 3-10cm, and can provide phase-stable single longitudinal mode seeds to the two fiber rings Laser (the spectral line half-width of the DFB output wavelength should be smaller than the longitudinal mode spacing of the fiber ring); WDM ₁ and WDM ₂ have the same characteristic parameters, which are selected for the pump source wavelength and the working wavelength of the signal laser. The wavelength division multiplexer WDM ₁ , the isolator I ₁ , the fiber coupler C ₁ and the gain fiber GF ₁ are connected through a single-mode fiber to form a fiber ring 1, the wavelength division multiplexer WDM ₂ , the isolator I ₂ , The fiber coupler C ₂ and the gain fiber GF ₂ are also connected through a single-mode fiber to form another fiber ring 2, and the two fiber rings each form a ring cavity with gain, and their directions are opposite, that is, the direction of the isolator makes The signal lasers generated in the two fiber rings run in opposite directions. Among them, the two isolators I ₁ and I ₂ also have the same characteristic parameters, and their return loss exceeds 60dB for the wavelength of the signal laser; the gain fiber used in the two fiber rings is the same as that in the DFB, and its length is generally based on Depending on the characteristics of the fiber and the specific application environment, you can choose from a few centimeters to a few meters, as long as the signal laser can be generated in the fiber ring; the length of the fiber ring (that is, the ring cavity) is adjusted through the single-mode fiber, generally from A few meters to tens of meters can meet higher application accuracy requirements (the cavity lengths of the two ring cavities should be slightly different, so that there is a frequency difference between the laser operating frequencies in the two cavities). One output end of the fiber coupler _C1 and _C2 in the two fiber rings is respectively connected with the two input ends of another fiber coupler _C3 , and the two output ends of _C3 are respectively connected with the detector _PD1 It is connected with PD ₂ , and PD ₁ or PD ₂ is connected with the difference frequency signal processing circuit. The coupling ratios of C ₁ and C ₂ are both 98:2, and the coupling ratio of C ₃ is 1:1, that is, 3dB; the detector can be a common PIN photodetector or an avalanche photodetector.

The clear working process is as follows:

Under the pumping of two semiconductor lasers, two fiber rings with gain fibers form two independent resonant cavities. The seed lasers are respectively injected into the two fiber rings through the DFB, and the working wavelengths in the two resonators are locked. The wavelength of the locked signal laser is determined by the resonance conditions of the two ring cavities and the wavelength of the DFB; the isolators added to the two fiber ring cavities make the signal laser work in a unidirectional traveling wave state, and the laser transmission in a ring The direction is clockwise, and the transmission direction of the laser in the other ring is counterclockwise; the unidirectional traveling wave operation of the signal laser eliminates the space hole burning phenomenon caused by the uniformly broadened gain medium (that is, the gain fiber) in the fiber ring, and adds The injection locking of the upper DFB makes the laser in the two ring cavities work in a stable single longitudinal mode state with a narrow line width; and because the return loss of the isolator can be greater than 60dB, it can well eliminate the backscattering resulting in a latch-up effect. The single longitudinal mode signal lasers output by the two ring cavities keep the phase constant due to the injection locking of the DFB, and become two coherent lights, so the difference frequency signal can be used for detection; the operating frequency of the two signal lasers is slightly different due to the slight difference in the length of the fiber ring cavity. There is a frequency difference, and this initial frequency difference can be used to eliminate the measurement blind area caused by the signal laser itself having a certain line width to improve the measurement accuracy, and can also be used to judge the direction of the rotational angular velocity.

Assuming that the operating frequency of the signal laser in one ring is v ₁ and the operating frequency of the signal laser in the other ring is v ₂ at rest, then when the ring rotates clockwise at an angular velocity of Ω, according to the Sagnac effect, the frequencies of the two signal lasers will become:

v ₁ ′＝v ₁ +(2A ₁ /λ ₀ L ₁ )Ω 〔1〕

v ₂ ′＝v ₂ -(2A ₂ /λ ₀ L ₂ )Ω 〔2〕

In the formula, A ₁ and L ₁ are the area and length of ring 1, respectively, A ₂ and L ₂ are the area and length of ring 2, respectively, λ ₀ is the wavelength of the laser in vacuum (because the initial frequency difference between the two lasers is very small , thinking that they work at the same wavelength at rest).

Then after the rotation, the frequency difference between the two signal lasers is:

Δv=v ₂ ′-v ₁ ′

＝(v ₂ -v ₁ )-(2A ₂ /λ ₀ L ₂ +2A ₁ /λ ₀ L ₁ )Ω 〔3〕

When the fiber ring rotates counterclockwise at an angular velocity of Ω, the frequency of the two signal lasers becomes:

v ₁ ″＝v ₁ -(2A ₁ /λ ₀ L ₁ )Ω 〔4〕

v ₂ ″＝v ₂ +(2A ₂ /λ ₀ L ₂ )Ω 〔5〕

Then the frequency difference between the two signal lasers is:

Δv=v ₂ "-v ₁ "

＝(v ₂ -v ₁ )+(2A ₂ /λ ₀ L ₂ +2A ₁ /λ ₀ L ₁ )Ω 〔6〕

It can be seen from the two formulas [3] and [6] that the rotational angular velocity can be measured by detecting the frequency difference of the two lasers through the difference frequency; moreover, the frequency difference is not the same when the rotation direction is different, so the rotation direction can also be judged according to the frequency difference .

The advantages of the present invention are:

1. The seed laser injection generated by DFB generates single-frequency laser in clockwise and counterclockwise directions respectively. Not only the two phase-transmitted signal lasers are separated in space, so that there is no common gain, and a stable two-way signal laser output can be generated; moreover, the phase of the two signal lasers is kept constant by using injection locking, and they are mutually coherent light, so that The difference frequency detection can be used.

2. The isolator is used to suppress backscattering (more than 60dB), which can eliminate the blocking effect, and also eliminate the space hole burning effect of the gain medium, narrow the working line width of the signal laser, thereby improving the sensitivity and measurement accuracy of the gyroscope .

3. By adjusting the length difference between the two optical fiber rings, the frequency shift of the fiber laser gyroscope can be directly realized without other additional components. The direction of rotation is judged according to the frequency difference; and the structure of the gyroscope is greatly simplified.

4. Due to the injection locking of DFB, the frequency change slope of the signal laser is large and the sensitivity is high. It only takes a few meters to meet the navigation requirements (for example, the measurement accuracy of 10 ^-3 can be achieved with a fiber ring cavity length of 5m), so the detection accuracy is high. , Large dynamic range.

5. The entire gyroscope is a full-fiber solidified structure, and the components used are all common parts without special requirements, so the structure is simple, easy to manufacture, and has low power consumption, long life, small size and light weight.

6. Due to the short cavity length, the drift caused by uneven temperature distribution can be ignored, and the influence of mechanical vibration is very small, so it has high stability.

The present invention can be applied to the orientation, positioning and navigation of satellites, airplanes, ships and automobiles. Because of its high precision, sensitivity and stability, it is suitable for satellite inertial navigation and flight attitude adjustment; it can also be used as an important inertial navigation device or device for high-precision autonomous orbit determination and automatic navigation of aerospace vehicles.

Description of drawings:

Accompanying drawing 1 is the structural representation of the present invention.

Detailed ways:

Embodiments of the present invention will be described below in conjunction with the accompanying drawings. It can be seen from the figure that the semiconductor laser LD is a pump laser usually used in an erbium-doped fiber amplifier, the model is QLM9S470-915, the working wavelength is 980nm, and the output power is 150mW; the DFB is a single-frequency fiber laser doped with erbium. The bidirectional output power is 0.25mW, the wavelength is 1.546μm, and the line width is 2MHz; the length of the two optical fiber ring cavities is about 4m, and the distance between the longitudinal modes is about 50MHz. Optical fiber, the gain is 15dB/m; the isolator adopts CASIX products (Class A), the return loss is 65dB, and the peak isolation is 42dB; the coupling ratio of coupler C ₁ and C ₂ is 98:2, of which 2% is from the Lead out as a detection signal, the coupling ratio of C ₃ is 1:1 (ie 3dB) to make the difference frequency interference between the two lasers; the WDM of the wavelength division multiplexer is 980/1550nm, and the isolation is greater than 30dB; the two optical fiber rings are overlapped together. The detector is a PIN photodetector with a peak wavelength of 1550nm. The entire gyroscope is fully fiber optic and solidified on an indium steel plate.

Claims (1)

1, a kind of self-injection locking fibre-optical laser circulator, form by fiber laser and detector, difference frequency signal treatment circuit, it is characterized in that fiber laser is made up of semiconductor laser, single-frequency distributed feedback optical fiber laser DFB, fiber optic loop, the fiber coupler of magnetic tape trailer fibre, fiber optic loop then is made up of wavelength division multiplexer, isolator, gain fibre and fiber coupler, and concrete structure is: with the semiconductor laser LD of two magnetic tape trailer fibres ₁And LD ₂Respectively by wavelength division multiplexer WDM ₁And WDM ₂Be connected with the two ends of DFB; Wavelength division multiplexer WDM then ₁, isolator I ₁, fiber coupler C ₁And gain fibre GF ₁Between link to each other wavelength division multiplexer WDM successively by single-mode fiber ₂, isolator I ₂, fiber coupler C ₂And gain fibre GF ₂Between also link to each other successively by single-mode fiber, form band two fiber optic loop gain, that direction is opposite; Fiber coupler C ₁And C ₂Output terminal more respectively with fiber coupler C ₃Two input ends be connected C ₃Two output terminals respectively with detector PD ₁And PD ₂Link to each other PD ₁Or PD ₂Be connected with the difference frequency signal treatment circuit again.

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