CN102435213A - Fiber grating wavelength demodulating device based on Fresnel holographic wavelength division multiplexer - Google Patents

Abstract

The invention discloses a fiber Bragg grating wavelength demodulation device based on a Fresnel holographic wavelength division multiplexer, and relates to a fiber Bragg grating wavelength demodulation device. The device is provided with a circulator, a Fresnel holographic wavelength division multiplexer, a photoelectric detector, a data acquisition card and a computer. The circulator is provided with a light source light input port, a light source light output port and a fiber Bragg grating reflected light output port, the light source light input port is externally connected to a light source, and the light source light output port is externally connected to a fiber Bragg grating group. The input end of the Fresnel holographic wavelength division multiplexer is connected to the fiber Bragg grating reflected light output port of the circulator, and the Fresnel holographic wavelength division multiplexer is provided with multiple channels, each of which is provided with a photoelectric detector. The output end of each photoelectric detector is connected to the input end of a data acquisition card, and the output end of the data acquisition card is connected to a computer. The invention has the advantages of low cost and strong applicability, can simultaneously perform wavelength demodulation on multiple fiber Bragg gratings, and can be used for combined measurement of dynamic and static parameters.

Description

Fiber Bragg Grating Wavelength Demodulation Device Based on Fresnel Holographic Wavelength Division Multiplexer

technical field

The invention belongs to the technical field of optical fiber sensing, and relates to an optical fiber grating wavelength demodulation device, in particular to an optical fiber grating wavelength demodulation device based on a Fresnel holographic wavelength division multiplexer.

Background technique

Fiber Bragg grating sensors have the advantages of high sensitivity, anti-electromagnetic interference, work based on wavelength coding, and the ability to realize multi-point distributed measurement, so they have become a research hotspot in the field of sensing. Fiber Bragg grating wavelength demodulation is the key technology to realize fiber Bragg grating sensing. Many demodulation methods have been proposed one after another, each of which has its own advantages and disadvantages. In contrast, the edge filter method (see S.M.Melle, K.Liu, and R.M.Measures, IEEE Photonics Technology Letters, 1992, 4(5): 516-518) is not only low in cost, more convenient to use, and more stable Good, and it has the advantages of fast response speed and is suitable for static parameter measurement and dynamic parameter measurement, but this method is only suitable for wavelength demodulation of a single fiber grating. The arrayed waveguide grating (AWG) demodulation method (see JP 2000-180270, SANO YASUKAZU) uses the AWG wavelength division multiplexer as the filter, overcomes the above-mentioned shortcomings of the edge filter method, and can simultaneously perform wavelength resolution on multiple fiber gratings. Tune. However, the production of AWG adopts standard semiconductor process, the cost is relatively high, and there may be a problem that the channel transmission spectrum does not match the wavelength range of the fiber Bragg grating reflection spectrum. Therefore, searching for new filters for fiber grating wavelength demodulation has important application value.

The Fresnel holographic wavelength division multiplexer (see Chinese patent CN 1256821C) is a new type of wavelength division multiplexer with an off-axis Fresnel lens structure proposed in recent years. The wavelength division multiplexer is made by laser holography technology, and is suitable for mass production by replication technology (see X.Ren, S.Liu, X.Zhang, and S.Li, Proceedings of SPIE, 2008, 6832: 68322M-1-68322M-8), so it has the characteristics of low cost and high production rate. In addition, since the wavelength division multiplexer is an angular dispersion device, it can separate the multi-wavelength optical signals multiplexed in one optical fiber in space according to wavelength, and each wavelength corresponds to a unique diffraction angle in space, thus changing the output The wavelength range of the transmission spectrum of the channel can be changed by the position of the receiving fiber at the end. The above characteristics show that using the Fresnel holographic wavelength division multiplexer as a filter can realize simultaneous wavelength demodulation of multiple fiber gratings at low cost; and it can easily solve the wavelength range mismatch that may exist in the AWG demodulation method problem, the applicability is strong. However, there is no report on the technology of using Fresnel holographic wavelength division multiplexer to demodulate the wavelength of fiber grating.

Contents of the invention

The purpose of the present invention is to provide a Fresnel holographic wavelength division multiplexer based on Fresnel holographic wavelength division multiplexer with low cost and strong applicability, which can simultaneously demodulate the wavelength of multiple fiber gratings, and can be used for combined measurement of dynamic and static parameters. Fiber Bragg grating wavelength demodulation device.

To achieve the above object, the present invention adopts the following technical solutions:

The invention is provided with a circulator, a Fresnel holographic wavelength division multiplexer, a photoelectric detector, a data acquisition card and a computer; The optical input port is connected to an external light source, and the optical output port of the light source is connected to an external fiber grating group; the input port of the Fresnel holographic wavelength division multiplexer is connected to the output port of the fiber grating reflected light of the circulator, and the Fresnel holographic wavelength division multiplexer There are multiple channels, each channel only filters the reflected light of one fiber grating, each channel is equipped with a photodetector, the output of each photodetector is connected to the input of the data acquisition card, and the output of the data acquisition card is connected to the computer .

Working principle of the present invention and beneficial effect are as follows:

Through the combination of Fresnel holographic wavelength division multiplexer, photodetector, data acquisition card and computer, the wavelength demodulation of multiple fiber gratings can be realized at the same time: Fresnel holographic wavelength division multiplexer is used for receiving The reflected light of the fiber grating acts as a multi-channel filter. The transmission spectrum of the channel is approximately Gaussian. The reflected light of each fiber grating is filtered through two adjacent channels. The overlapping part of the adjacent channel transmission spectrum corresponds to The wavelength range is the effective range of wavelength demodulation. Each channel only filters the reflected light of one fiber grating to avoid crosstalk; the photodetector is used to measure the output optical power of the channel, and its number is the same as the number of channels; data acquisition The card is used to collect the output electrical signal of each photodetector; the computer is used to divide the output of adjacent photodetectors and take the logarithm of the result, as well as the calculation result and the peak wavelength of the fiber grating reflection spectrum. The linear relationship shows the results of wavelength demodulation. The division operation eliminates the influence of light source power unevenness and fluctuation, and the logarithm is taken to make the operation result and the peak wavelength of the reflection spectrum of the fiber grating linearly related (see Chinese patent CN 2745045Y).

The present invention has the following outstanding advantages:

1. Low cost. The filter used in the present invention, that is, the Fresnel holographic wavelength division multiplexer is made by laser holographic technology, and is suitable for mass production through replication technology, and has the characteristics of low cost and high production rate, so the present invention is adopted The cost of the optical fiber grating wavelength demodulation device is relatively low.

2. Strong applicability. The filter used in the present invention, that is, the Fresnel holographic wavelength division multiplexer belongs to the angular dispersion device, and the wavelength range of the channel transmission spectrum can be changed by changing the position of the receiving optical fiber at the output end, which can conveniently solve the problem of using an arrayed waveguide grating (AWG ) The demodulation device may have the problem that the channel transmission spectrum does not match the wavelength range of the fiber Bragg grating reflection spectrum, so the applicability of the present invention is significantly enhanced.

Description of drawings

FIG. 1 is a schematic diagram of the structural composition and application of an embodiment of the present invention (a schematic diagram of a system for simultaneously performing wavelength demodulation on multiple fiber gratings). In Figure 1: 1 is a broadband light source, 2 is a circulator, 3 is a fiber grating group (a fiber grating group is a plurality of fiber gratings connected in series), 4 is a Fresnel holographic wavelength division multiplexer, and 5 is a Fresnel The channel of the Seoul holographic wavelength division multiplexer, 6 is a photodetector, 7 is a data acquisition card, and 8 is a computer.

Detailed ways

As shown in FIG. 1 , light emitted by a broadband light source 1 is input from port A of a circulator 2 , and output from port B through the circulator 2 to enter a plurality of fiber gratings 3 connected in series. The fiber Bragg grating 3 perceives the change of the physical quantity to be measured at the location, and converts it into the change of the peak wavelength of the reflection spectrum, and the reflection spectrum is approximately Gaussian. The reflected light of the fiber grating 3 is output from the port C through the circulator 2, and enters the Fresnel holographic wavelength division multiplexer 4 which acts as a multi-channel filter. The transmission spectrum of the channel 5 of the Fresnel holographic wavelength division multiplexer 4 is approximately Gaussian, the reflected light of each fiber grating 3 is filtered by two adjacent channels 5, and the overlapping part of the transmission spectrum of the two adjacent channels The corresponding wavelength range is the effective range of wavelength demodulation, and each channel only filters the reflected light of one fiber Bragg grating 3 to avoid crosstalk. The photodetector 6 is connected to the channel 5 of the Fresnel holographic wavelength division multiplexer 4 for measuring the output optical power of the channel 5 , and the number of the photodetector 6 is the same as that of the channel 5 . The data acquisition card 7 is connected to the electrical signal output terminals of the photodetectors 6 for collecting the output electrical signals of each photodetector 6 . The computer 8 is connected with the output end of the data acquisition card 7, and is used for dividing the output of the adjacent photodetector 6 and taking the logarithm of the result, and the linearity formed according to the calculation result and the peak wavelength of the fiber grating reflection spectrum. The relationship shows the result of wavelength demodulation, the division operation eliminates the influence of light source power unevenness and fluctuation, and the logarithm is taken to make the operation result and the peak wavelength of the reflection spectrum of the fiber Bragg grating linearly related.

Claims (1)

1. Based on the fiber grating wavelength demodulation device of Fresnel holographic wavelength division multiplexer, it is characterized in that being provided with circulator, Fresnel holographic wavelength division multiplexer, photodetector, data acquisition card and computer; The circulator is provided with a light source light input port, a light source light output port and a fiber grating reflected light output port, the light source light input port is connected to an external light source, and the light source light output port is connected to an external fiber grating group; It is connected with the fiber grating reflected light output port of the circulator, and the Fresnel holographic wavelength division multiplexer has multiple channels, each channel only filters the reflected light of one fiber grating, and each channel is equipped with a photodetector ; The output terminals of each photoelectric detector are connected to the input terminals of the data acquisition card, and the output terminals of the data acquisition card are connected to the computer.

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