Broadband optical fiber light source

Abstract

The invention relates to a broadband optical fiber light source which is composed of a 980 nm pump laser, a wavelength division multiplexer, an erbium-doped optical fiber, a band-pass filter, a reflector, an isolator, a gain flattening filter, a first coupler, a second coupler, a single-mode optical fiber collimator, a wavelength tracking module, a photoelectric detector, an electric control adjustable attenuator and a light source driving circuit board. The wavelength tracking module is arranged in the light source, the average wavelength change is sensed in real time through the wavelength tracking module and is used as a feedback signal for controlling the driving current of the pump laser, and the driving current of the pump laser is adjusted to control the pump power, so that the average wavelength closed-loop control is realized, and the average wavelength stability of the broadband optical fiber light source can be greatly improved; in addition, the output end of the light source is provided with an electrically-controlled variable attenuator and a photoelectric detector, the light emitting power change condition of the light source is monitored in real time based on the photoelectric detector, the attenuation of the attenuator is synchronously changed, and the effect of stable light output power of the light source is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic gyroscopes, and in particular to a broadband fiber optic light source for a fiber optic gyroscope. Background Art

[0002] The fiber optic gyroscope is a fully solid-state gyroscope based on the Sagnac effect. It has the characteristics of high reliability, long life, wide dynamic range, resistance to impact and vibration, small size, light weight, wide precision coverage, and suitability for mass production. It has been widely used in sea, land, air, and space fields and has become one of the mainstream inertial instruments in contemporary times.

[0003] Broadband fiber light source technology is one of the technical driving forces behind the successful engineering application of fiber optic gyroscopes. Its short coherence length can suppress the amplitude noise and drift of the fiber optic gyroscope caused by the Kerr effect, backscattering and polarization coupling, making the noise level as low as acceptable for engineering applications.

[0004] The broadband fiber light source for fiber gyroscope is a broadband light source based on spontaneous radiation amplified by erbium-doped gain fiber. Compared with the broadband light source of superluminescent diode (SLD), its output has the characteristics of high stability of average wavelength, wide spectrum, high output power, etc., and is suitable for high-precision fiber gyroscope.

[0005] However, the inherent optical properties of broadband fiber light sources also bring difficult-to-overcome performance drawbacks to fiber gyros. The average wavelength stability level under a wide spectrum makes it difficult for fiber gyro scale factor stability to be comparable to that of laser gyros using narrow linewidth light sources. For optical gyros based on the Sagnac effect, the average wavelength of the light source affects the scale factor of the optical gyro.

[0006] The average wavelength stability of the light source directly reflects the stability of the scale factor of the fiber optic gyroscope, so the average wavelength stability is a key indicator of the light source for the fiber optic gyroscope. The main reason for the change of the average wavelength of the broadband fiber light source for the fiber optic gyroscope is the change of the ambient temperature, which has three main sources, as shown in formula (1).

[0007]

[0008] The first term is the inherent average wavelength caused by the temperature characteristics of erbium-doped fiber. The second and third terms are the pump wavelength λ p and the pump power P p The change in average wavelength caused by this; T is the ambient temperature.

[0009] It can be seen that the full-temperature average wavelength change of the broadband fiber optic light source is jointly determined by three temperature-related factors, not a single linear relationship. Therefore, the average wavelength stability of the broadband fiber optic light source shows a certain nonlinear correlation with the temperature change, and this nonlinear relationship with the temperature change cannot be removed in the subsequent fiber optic gyroscope scale factor temperature compensation linear model, which limits the further improvement of the fiber optic gyroscope scale factor stability and becomes a bottleneck problem in the development of fiber optic gyroscope technology. Summary of the invention

[0010] In view of the deficiencies in the prior art, the present invention proposes a broadband optical fiber light source which can significantly improve the average wavelength stability of the broadband optical fiber light source.

[0011] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0012] A broadband optical fiber light source, comprising:

[0013] A pump laser, used to emit 980nm pump light;

[0014] A wavelength division multiplexer, wherein the 980nm pump light is transmitted to the erbium-doped optical fiber through a 980 / 1550nm common port of the wavelength division multiplexer to generate forward and backward 1550nm super-fluorescence;

[0015] A bandpass filter for filtering out residual pump light in the forward superfluorescence;

[0016] The reflector is used to reflect and filter out the forward super fluorescence of the residual pump light, so that the forward super fluorescence passes through the bandpass filter and the erbium-doped optical fiber in sequence and reaches the 1550nm port of the wavelength division multiplexer together with the backward super fluorescence;

[0017] An isolator is connected to the 1550nm port of the wavelength division multiplexer, and is used to allow the forward and backward super-fluorescence to pass sequentially and eliminate the return light;

[0018] A gain flattening filter is connected to the output end of the isolator and is used to achieve spectrum flattening and shaping;

[0019] A first coupler, whose input end is connected to the output end of the gain flattening filter, is used to achieve superfluorescence light splitting output in a ratio of 2:98;

[0020] a single-mode optical fiber collimator connected to the 2% splitting port of the first coupler and used to project light into the wavelength tracking module;

[0021] The wavelength tracking module is connected to the output end of the single-mode fiber collimator to form two anti-phase interference signals that can characterize the average wavelength change, and complete the photoelectric conversion and send them to the light source driving circuit board;

[0022] The second coupler is connected to the 98% splitting port of the first coupler, and is used to achieve super-fluorescence splitting output according to a 2:98 ratio, wherein 2% of the split light is photoelectrically converted by the photodetector and sent to the light source driving circuit board, and 98% of the split light is output after passing through the electrically controlled adjustable attenuator;

[0023] The light source driving circuit board is used to perform signal differential processing on the two anti-phase interference signals output by the wavelength tracking module, and use the difference between the real-time voltage value after differentiation and the preset voltage value as the feedback signal for adjusting the pump laser driving current to realize the closed-loop control of the average wavelength of the light source; and is used to detect the light source optical power fluctuation caused by the wavelength closed-loop control according to the output signal of the photodetector, and adjust the preset attenuation of the attenuator according to the degree of optical power fluctuation detected by the photodetector, so as to realize the stability of the light source output power.

[0024] Moreover, the wavelength tracking module adopts a 50:50 special-shaped beam splitter. During the light splitting process, there is a phase difference of π between the two horizontal interference light waves, and the phases of the vertical and horizontal interference light waves remain inverted.

[0025] The present invention has the following advantages and positive effects:

[0026] 1. The broadband fiber light source for fiber optic gyroscope proposed by the present invention is provided with a wavelength tracking module in the light source, and the wavelength tracking module senses the average wavelength change in real time, and uses the average wavelength change signal as a feedback signal for the pump laser drive current control, and adjusts the pump laser drive current to control the pump power. The pump power affects the average wavelength change of the broadband fiber light source to achieve closed-loop control of the average wavelength, which can greatly improve the stability of the average wavelength of the broadband fiber light source, thereby helping to solve the bottleneck problem that the stability of the fiber optic gyroscope scale factor is limited by the stability of the average wavelength of the broadband fiber light source. In addition, the output end of the light source is equipped with an electrically controlled variable attenuator and a photodetector, which monitors the change of the light output power of the light source in real time based on the photodetector, and synchronously changes the attenuation of the attenuator to achieve the effect of stabilizing the output light power of the light source.

[0027] 2. The broadband fiber optic light source of the present invention adopts the average wavelength closed-loop control technology, which can improve the average wavelength stability of the broadband fiber optic light source by an order of magnitude, and help to significantly improve the stability of the fiber optic gyroscope scale factor.

[0028] 2. This broadband fiber optic light source has a closed-loop control function for output optical power. The average wavelength closed-loop control process does not cause fluctuations in the output optical power of the light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram showing the composition of a broadband optical fiber light source of the present invention;

[0030] In the figure: 1. Pump laser; 2. Wavelength division multiplexer; 3. Erbium-doped fiber; 4. Bandpass filter; 5. Reflector; 6. Isolator; 7. Gain flattening filter; 8. First coupler; 9. Single-mode fiber collimator; 10. Wavelength tracking module; 11. Second coupler; 12. Photodetector; 13. Electrically controlled adjustable attenuator; 14. Light source driver circuit board;

[0031] Figure 2 is a schematic diagram of a wavelength tracking module of the present invention;

[0032] Figure 3 This is a comparison diagram of the average wavelength change at full temperature before and after the wavelength closed-loop control of the present invention;

[0033] Figure 4 This is an enlarged view of the average wavelength change at all temperatures after the wavelength closed-loop control of the present invention; DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0035] Figure 1 It is a schematic diagram of the broadband fiber light source, which consists of a 980nm pump laser, a wavelength division multiplexer, an erbium-doped fiber, a bandpass filter, a reflector, an isolator, a gain flattening filter, a first coupler, a second coupler, a single-mode fiber collimator, a wavelength tracking module, a photodetector, an electrically controlled adjustable attenuator and a light source driver circuit board.

[0036] The light source driver circuit board drives the pump laser to emit a near 980nm pump light, which is transmitted to the 980nm / 1550nm common port of the wavelength division multiplexer through the 980nm port of the wavelength division multiplexer. The pump light then enters the erbium-doped fiber to excite the energy level transition of the bait ion, generating forward (in the same direction as the pump light) and backward (in the opposite direction of the pump light) near 1550nm super fluorescence, wherein the forward super fluorescence is filtered out by a bandpass filter to avoid disturbing the pump power component in the erbium-doped fiber, thereby affecting the closed-loop control effect of the average wavelength of the light source. Subsequently, the forward super fluorescence is reflected by a reflector and then passes through the bandpass filter, the erbium-doped fiber and the backward super fluorescence in sequence to reach the 1550nm port of the wavelength division multiplexer. Subsequently, the forward and backward super fluorescence pass through the isolator and the gain flattening filter in sequence to achieve return light elimination and spectrum flattening shaping respectively. The ultimate effect of spectrum flattening shaping is to improve the symmetry of the broadband light source spectrum. The superfluorescent light with a flat spectrum passes through the 2:98 first coupler, and a single-mode fiber collimator is provided at the end of the 2% splitting port optical fiber to project the light into the wavelength tracking module to sense the change in the average wavelength of the light source. The wavelength tracking module forms two anti-phase interference signals to characterize the change in the average wavelength, and completes the photoelectric conversion and sends it to the light source driver circuit board for signal differential processing. The difference between the real-time voltage value after the difference and the preset voltage value is used as a feedback signal for adjusting the pump laser driving current to achieve closed-loop control of the average wavelength of the light source. At this time, 98% of the split light passes through the 2:98 second coupler, and 2% of the split light is photoelectrically converted by the photodetector and sent to the light source driver circuit board to detect the fluctuation of the light source optical power caused by the wavelength closed-loop control. 98% of the split light then passes through the electrically controlled adjustable attenuator to achieve the final average wavelength stable flat wide-spectrum light energy output. The light source driver circuit board adjusts the preset attenuation of the attenuator according to the degree of optical power fluctuation detected by the photodetector to achieve the stability of the light source output power.

[0037] The light source driving circuit board is composed of an adjustable constant current source circuit, a temperature control circuit, a differential amplifier circuit and an adjustable constant voltage source circuit. The adjustable constant current source circuit can provide an adjustable constant driving current for the pump laser, so that the pump laser can emit light continuously and stably. The temperature control circuit uses the built-in temperature sensor of the pump laser as feedback to control its built-in heating and cooling device, so that the temperature of the pump laser can be stabilized within a precise range. The differential amplifier circuit performs differential amplification processing on the two electrical signals from the wavelength tracking module, which can improve the tracking accuracy of wavelength changes. The adjustable constant voltage source circuit uses the light source output optical power fluctuation voltage signal detected by the photodetector as feedback, and provides an adjustable and stable voltage input to the electrically controlled adjustable attenuator to compensate for the optical power fluctuation caused by adjusting the output wavelength of the light source by changing the constant current source, thereby achieving stable output of the light source optical power.

[0038] Figure 2: The figure is a schematic diagram of the wavelength tracking module. The wavelength tracking module adopts a 50:50 special-shaped beam splitter design. The input light wave is divided into two beams on the reflection / transmission surface and transmitted in the vertical and horizontal directions respectively. The vertical and horizontal ends of the special-shaped beam splitter are triangular reflection structures. Both the vertical and horizontal light beams are reflected back and divided into four light waves at the same position of the reflection / transmission surface. The two vertical light waves interfere and are received by the photoelectric detector in the vertical direction and converted into voltage signals. The two horizontal light waves interfere and are received by the photoelectric detector in the horizontal direction and converted into voltage signals. The two vertical interference light waves are reflected once and transmitted once on the reflection / transmission surface. The beam splitting process does not produce a phase difference between the two vertical interference light waves. One of the two horizontal interference light waves is reflected twice on the reflection / transmission surface, and the other is transmitted twice. Reflection causes a π / 2 phase delay in the light wave. Therefore, the beam splitting process causes a π phase difference between the two horizontal interference light waves. The phases of the vertical and horizontal interference signals always remain inverted. Differential processing of the two interference signals can improve the wavelength change tracking accuracy.

[0039] The 50:50 special-shaped beam splitter is slightly longer in the horizontal direction than in the vertical direction to ensure that there is a certain optical path difference Δl between the light waves propagating in the horizontal direction and the light waves propagating in the vertical direction. When the average wavelength is 1550nm, this optical path difference forms a phase difference of π / 2. Therefore, the above two interference signals will work at the maximum slope, which can improve the sensitivity of wavelength change perception.

[0040] The interference signal of one channel can be expressed as formula (2). When the average wavelength of the light source is When the phase of the interference signal changes The amplitude of the interference signal will also change. By monitoring the amplitude change of the interference signal, the change of the average wavelength of the light source can be determined. The difference between the voltage signal representing the amplitude of the interference signal and the preset voltage value is used as the feedback signal for adjusting the driving current of the pump laser to achieve closed-loop control of the average wavelength of the light source.

[0041]

[0042] In the formula, I 1 and I 2 are the light intensity of the light wave propagating in the horizontal direction and the light intensity of the light wave propagating in the vertical direction, n is the refractive index, Δl is the optical path difference between the two light waves, is the average wavelength of the light source.

[0043] Figure 3This is a comparison of the average wavelength change at all temperatures before and after wavelength closed-loop control. Under the temperature range of -40°C to 60°C and a temperature change rate of 1°C / min, for the same broadband fiber optic light source, the average wavelength change at all temperatures before wavelength closed-loop control is 202.56ppm, and the average wavelength change at all temperatures after wavelength closed-loop control is 2.65ppm. It can be seen that the average wavelength stability of the broadband fiber optic light source has been improved by orders of magnitude.

[0044] Figure 4 This is an enlarged view of the full-temperature average wavelength change after wavelength closed-loop control. After wavelength closed-loop control, the full-temperature average wavelength change has a trend of continuous slight ups and downs, which is a normal phenomenon caused by the closed-loop control adjustment process. The overall full-temperature average wavelength change fluctuation of the broadband fiber light source is already at an extremely low level.

[0045] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A broadband fiber optic light source, Features: include: A pump laser, used to emit 980nm pump light; A wavelength division multiplexer, wherein the 980nm pump light is transmitted to the erbium-doped optical fiber through a 980 / 1550nm common port of the wavelength division multiplexer to generate forward and backward 1550nm super-fluorescence; A bandpass filter for filtering out residual pump light in the forward superfluorescence; The reflector is used to reflect and filter out the forward super fluorescence of the residual pump light, so that the forward super fluorescence passes through the bandpass filter and the erbium-doped optical fiber in sequence and reaches the 1550nm port of the wavelength division multiplexer together with the backward super fluorescence; An isolator is connected to the 1550nm port of the wavelength division multiplexer, and is used to allow the forward and backward super-fluorescence to pass sequentially and eliminate the return light; A gain flattening filter is connected to the output end of the isolator and is used to achieve spectrum flattening and shaping; A first coupler, whose input end is connected to the output end of the gain flattening filter, is used to achieve superfluorescence light splitting output in a ratio of 2:98; a single-mode optical fiber collimator connected to the 2% splitting port of the first coupler and used to project light into the wavelength tracking module; The wavelength tracking module is connected to the output end of the single-mode fiber collimator to form two anti-phase interference signals that can characterize the average wavelength change, and complete the photoelectric conversion and send them to the light source driving circuit board; The second coupler is connected to the 98% splitting port of the first coupler, and is used to achieve super-fluorescence splitting output according to a 2:98 ratio, wherein 2% of the split light is photoelectrically converted by the photodetector and sent to the light source driving circuit board, and 98% of the split light is output after passing through the electrically controlled adjustable attenuator; The light source driving circuit board is used to perform signal differential processing on the two anti-phase interference signals output by the wavelength tracking module, and use the difference between the real-time voltage value after differentiation and the preset voltage value as the feedback signal for adjusting the pump laser driving current to realize the closed-loop control of the average wavelength of the light source; and is used to detect the light source optical power fluctuation caused by the wavelength closed-loop control according to the output signal of the photodetector, and adjust the preset attenuation of the attenuator according to the degree of optical power fluctuation detected by the photodetector, so as to realize the stability of the light source output power.

2. The broadband fiber optic light source according to claim 1, Features: The wavelength tracking module adopts a 50:50 special-shaped beam splitter; during the light splitting process, there is a phase difference of π between the two horizontal interference light waves, and the phases of the vertical and horizontal interference light waves remain inverted.

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