Background
Fiber optic gyroscopes are one of the important devices in the field of inertia to measure angular rate of rotation. The annual output of the domestic optical fiber gyroscope exceeds 3 ten thousand axes at present, and the precision of the domestic optical fiber gyroscope is close to 0.0001 degree/h. An ASE light source is generally adopted in a high-precision fiber optic gyroscope, and a fiber isolator is an important device in the ASE light source.
The optical fiber isolator used at present is mainly designed for an optical communication system, and the existing index parameters cannot completely meet the requirements of an optical fiber gyroscope. For example, the spectral ripple index is not found in the index system of the existing optical fiber isolator, and an effective test method is not available. During production, the isolator is found to affect the spectral ripple. FIG. 1 shows the measured spectra of two ASE sources, the difference being simply the replacement of the isolator. The spectrum ripple in FIG. 1(a) is small, and belongs to qualified products; the spectrum of FIG. 1(b) has large ripple and belongs to unqualified products. And the two devices belong to qualified devices according to the existing system and screening method. If the spectrum is found to be unqualified after the ASE light source is assembled, the device and the tail fiber need to be reworked and disassembled, and the glue is removed and cleaned, so that the workload is large, the time is consumed, the production efficiency is influenced, and the device is easily damaged. Therefore, the device needs to be screened before assembly to ensure that the device is qualified.
The main test equipment of the existing optical fiber isolator is an insertion return loss instrument which is used for testing the insertion loss and the return loss of the optical fiber isolator but cannot reflect the spectral ripple characteristics of the optical fiber isolator. Although the spectral characteristics of the fiber isolator can be tested by the spectrometer, the measured spectral characteristics are different from the spectral characteristics accessed into the ASE light source system due to different application environments, and the spectral characteristics of the fiber isolator accessed into the ASE light source system cannot be accurately reflected.
In the existing ASE light source production process, the fault rate of the optical fiber isolator is high, so that the spectral ripple is large and the index is out of tolerance. At present, no effective means is available for rejecting unqualified devices. And the yield of ASE light source in the high-precision fiber-optic gyroscope is low. Therefore, it is necessary to build a set of test system for the spectral characteristics, especially the ripple characteristics, of the fiber isolator.
Disclosure of Invention
The invention provides a system and a method for testing spectral characteristics of an optical fiber isolator, which are used for solving the technical problem that the yield of ASE light sources in a high-precision optical fiber gyroscope is low because whether the spectral ripple of the optical fiber isolator for the optical fiber gyroscope is qualified cannot be tested in the prior art.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the system comprises a pumping light source, a wavelength division multiplexer, an erbium-doped optical fiber and a reflector which are sequentially connected through optical fibers, wherein the front end of the wavelength division multiplexer is also connected with a tail fiber used for connecting an isolator to be tested, and the system also comprises a spectrum analyzer used for connecting and testing the spectrum output by the isolator to be tested.
Preferably, the test system further comprises: and the optical power meter is used for testing the output optical power of the isolator to be tested.
Preferably, the test system further comprises a comparison unit, wherein the comparison unit is used for comparing a spectral curve output by the isolator to be tested and measured by the spectrum analyzer with a standard qualified curve, and when the offset or fluctuation of the spectral curve exceeds a threshold range, the isolator to be tested is judged to be unqualified; and when the offset or fluctuation amount of the spectral curve is within the threshold range, judging that the isolator to be tested is qualified.
Preferably, the pump light source is connected to a light source driver for providing a drive current and a temperature controlled current to the pump light source.
Preferably, the driving current is larger than the working current so that the optical power output by the isolator to be tested is larger than the optical power in operation.
The invention also provides a method for testing the spectral characteristics of the optical fiber isolator, which comprises the following steps: laser emitted by a pumping light source passes through the wavelength division multiplexer, the erbium-doped fiber and the reflector in sequence through the optical fiber, and then returns to a tail fiber at the front end of the wavelength division multiplexer through reflection;
and connecting the isolator to be tested to a tail fiber at the front end of the wavelength division multiplexer, and connecting and testing the spectrum output by the isolator to be tested by using a spectrum analyzer.
Preferably, a spectral curve output by the isolator to be tested and measured by the spectrum analyzer is compared with a standard qualified curve, and when the offset or fluctuation quantity of the spectral curve exceeds a threshold range, the isolator to be tested is judged to be unqualified; and when the offset or fluctuation amount of the spectral curve is within the threshold range, judging that the isolator to be tested is qualified.
Preferably, the output optical power of the isolator to be tested is measured using an optical power meter.
Preferably, the driving current of the light source driver for supplying current to the pumping light source is set and adjusted to be larger than the working current so that the optical power output by the isolator to be tested is larger than the optical power in operation.
The invention has the following beneficial effects:
1. the system for testing the spectral characteristics of the optical fiber isolator is simple to operate, under the condition of skilled operation, the testing time of each device is less than 5 minutes, the increased testing cost is very little, the problems of low yield and low efficiency in the manufacturing process of the optical fiber isolator and the production process of the ASE light source are effectively solved, the performances of the optical fiber isolator and the ASE light source are improved, the technical progress of the high-precision optical fiber gyroscope can be promoted, and the engineering application process of the optical fiber isolator can be accelerated.
2. In a preferred scheme, the method for testing the spectral characteristics of the optical fiber isolator can test the spectral ripples of the optical fiber isolator, can screen the spectral characteristics of the optical fiber isolator before the ASE light source is assembled, can remove unqualified devices, and greatly improves the production efficiency and the yield.
In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the accompanying drawings.
Detailed Description
The embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways as defined and covered by the claims.
The terms in this example are explained as follows:
optical fiber isolator: the optical fiber passive device is a common optical fiber passive device and is widely applied to the fields of optical fiber communication, optical fiber lasers, optical fiber sensing and the like. The working principle is based on the Faraday nonreciprocal effect, and light can only be transmitted in the forward direction and cannot be transmitted in the reverse direction.
The insertion loss and the isolation degree are two important indexes of the optical fiber isolator, and the insertion loss represents the loss of light in forward transmission and is generally less than 1 dB; the degree of isolation represents the loss of light in reverse transmission, typically greater than 40 dB.
Spectrum: the light intensity distribution of light in the frequency domain can be measured by a spectrometer. The main indexes include central wavelength, spectral width, spectral ripple and the like. The light source spectrum in the optical fiber gyroscope is wide, and the influence of the spectrum ripple index on the performance of the optical fiber gyroscope is large.
ASE light source: namely, the erbium-doped fiber light source is a wide-spectrum light source based on spontaneous radiation and is used for a high-precision fiber optic gyroscope.
Referring to fig. 2, the system for testing the spectral characteristics of the optical fiber isolator of the present invention includes a pump light source, a wavelength division multiplexer, an erbium-doped fiber, and a reflector, which are sequentially connected through an optical fiber, wherein the front end of the wavelength division multiplexer is further connected to a tail fiber for connecting to an isolator to be tested, and the system further includes a spectrum analyzer for connecting to and testing a spectrum output by the isolator to be tested. The spectrum analyzer is provided, the spectrum ripple indexes of the optical fiber isolator can be measured, the spectrum characteristics of the optical fiber isolator can be screened before the ASE light source is assembled, unqualified devices can be eliminated, and the production efficiency and the yield are greatly improved. The method is simple to operate, under the condition of skilled operation, the testing time of each device is less than 5 minutes, the increased testing cost is very little, but the problems of low yield and low efficiency in the manufacturing process of the optical fiber isolator and the production process of the ASE light source are effectively solved, the performances of the optical fiber isolator and the ASE light source are improved, the technical progress of the high-precision optical fiber gyroscope can be promoted, and the engineering application process of the high-precision optical fiber gyroscope is accelerated.
In this embodiment, while testing the spectrum ripple, the output power of the optical power meter testing device may also be used to test the output optical power of the isolator to be tested. Compared with the insertion loss tested by an insertion loss tester, the test of the output power is more direct, and the performance of the ASE light source can be reflected more truly.
In order to unify the test standard of the index for the spectrum ripple of the optical fiber isolator, the test system can also be provided with a comparison unit (the comparison is realized by inputting the measured parameters of the spectrum analyzer into a computer), the comparison unit is used for comparing the spectrum curve output by the isolator to be tested and measured by the spectrum analyzer with a standard qualified curve, and when the offset or fluctuation quantity of the spectrum curve exceeds the threshold range, the isolator to be tested is judged to be unqualified; and when the offset or fluctuation amount of the spectral curve is within the threshold range, judging that the isolator to be tested is qualified. The threshold range can be set according to the corresponding precision requirement of the fiber-optic gyroscope, and the specific numerical range can also be determined through experiments.
In this embodiment, the pump light source is a 980nm single-mode pump light source (980 pump source), the 980 pump source is fixed on the heat sink, and 6 pins are connected with the light source drive board. The 980 pump source is connected to a light source driver for providing a drive current and a temperature controlled current to the pump source. When the isolator is used, the driving current can be set between 100mA and 150mA and adjusted according to actual conditions so that the optical power output by the isolator to be tested is slightly larger than 10mW, and the driving current can be set to be a fixed value after being stabilized and is slightly higher than the current in actual use, so that the quality problem of the device can be more easily exposed. The temperature control current is automatically set and is determined by the ambient temperature. The system displays the magnitude of the driving current after being started and is used for indicating whether the system works normally or not. The input voltage of the light source driving board is 5V and is provided by a switching power supply, and the input of the switching power supply is 220V commercial power.
In this embodiment, all adopt the optical fiber butt fusion between pumping light source, wavelength division multiplexer, erbium-doped fiber and the speculum, and system output (the tail fiber that is used for connecting the isolator that awaits measuring that wavelength division multiplexer's front end still connects) is an optical fiber, and is the same with optical fiber isolator input end tail fiber model, also carries out the butt fusion through optical fiber splicer to guarantee minimum butt fusion loss. When the length of the optical fiber is not enough after the optical fiber is used for a certain number of times, the optical fiber can be spliced.
The invention also provides a method for testing the spectral characteristics of the optical fiber isolator, which comprises the following steps:
laser emitted by a pumping light source passes through the wavelength division multiplexer, the erbium-doped fiber and the reflector in sequence through the optical fiber, and then returns to a tail fiber at the front end of the wavelength division multiplexer through reflection;
the isolator to be tested is connected to the tail fiber at the front end of the wavelength division multiplexer, the spectrum analyzer is used for connecting and testing the spectrum output by the isolator to be tested, and the optical power meter can be used for measuring the output optical power of the isolator to be tested.
Before testing, the driving current of the light source driver for providing the pumping light source with the driving current and the temperature control current can be set and adjusted to be between 100mA and 150mA, so that the optical power output by the isolator to be tested is more than 10 mW.
The following illustrates the actual testing procedure:
1) the power supply of the test system is firstly turned on, and the spectrograph and the desk type optical power meter are simultaneously turned on. The spectrometer parameters were set as: the center wavelength is 1560nm, the spectrum width is 10nm, the resolution is 0.02, and the logarithmic coordinate is 0.1 dB/div; the optical power meter is provided with: wavelength 1550nm, logarithmic or linear coordinate.
2) And (3) fusing the system output optical fiber and the tail fiber of the input end of the optical fiber isolator to be detected by a common single-mode optical fiber fusion splicer.
3) And inserting the tail fiber of the output end of the optical fiber isolator to be measured into the optical fiber adapter, connecting the optical fiber adapter to the desk type optical power meter, and recording the optical power value. Whether the optical power value is stable or not can be monitored in the process, and if the optical power jumping amount is large, the device is treated as a unqualified device.
4) And taking the optical fiber adapter inserted with the tail fiber of the device to be tested out of the table type optical power meter and connecting the optical fiber adapter into the spectrometer. And (3) selecting proper coordinates by pressing an automatic amplitude key, recording and storing a spectrum curve, and judging whether the device is qualified. The following method may be preferably used to determine whether the product is acceptable:
comparing a spectral curve output by the isolator to be tested and measured by a spectrum analyzer with a standard qualified curve, and judging that the isolator to be tested is unqualified when the offset or fluctuation quantity of the spectral curve exceeds a threshold range; and when the offset or fluctuation amount of the spectral curve is within the threshold range, judging that the isolator to be tested is qualified.
5) And after the test is finished, storing the qualified device and the unqualified device respectively.
In summary, the invention simulates the optical path of the optical fiber isolator in the ASE light source system of the optical fiber gyroscope to reproduce the spectral ripple characteristics of the optical fiber isolator in the ASE light source system, so that the optical spectrum analyzer is used for testing the spectral ripple of the optical fiber isolator, the spectral characteristics of the optical fiber isolator can be screened before the ASE light source is assembled, unqualified devices can be removed, and the production efficiency and the yield are greatly improved. In addition, the invention can test the output power of the device while testing the characteristic of the spectral ripple. Compared with the insertion loss tested by an insertion loss tester, the test of the output power is more direct, and the performance of the ASE light source can be reflected more truly. The invention can also be configured to manufacturers of the optical fiber isolators, and the optical fiber isolators are screened before leaving factories after being produced, so that the devices leaving factories are qualified devices which can be used for ASE light sources.
Therefore, the test system is expected to become a necessary device in the production process of the optical fiber isolator and a key device in the research and production of the optical fiber gyroscope.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.