KR20000031822A - Wavemeter of optical signal, fiber bragg grating sensor and method thereof using wave selection type optical detector - Google Patents

Abstract

PURPOSE: A wave meter of optical signal, a sensor of fiber bragg grating(FBG) and its method are provided to measure a wavelength change of a reflective light caused by a perturbation such as a temperature and a strain fed to the FBG using a wave dependence of a wave selection typed optical detector. CONSTITUTION: An optical signal emerged from a source of light(41) having a broadband spectrum width such as an ASE(Amplified Spontaneous Emission) noise of an LED(Light Emitting Diode), an SLD(Super Luminescence Laser Diode), or an EDFA(Erbium-doped Fiber Amplifier) is projected into a FBG(43) through an optical coupler(42) and a reflective light of narrow band fit for a condition of the FBG(43) is transferred to the other optical coupler(44) by diverging in the optical coupler(42). The optical coupler(44) distributes the reflective light to a usual optical detector(45) and a wavelength selection type optical detector(46), and the usual optical detector(45) and the wavelength selection type optical detector(46) converts the diverged optical signal to an electric signal. The signal converted to the electric signal is amplified, differentially amplified and divided in a processor of signal(47) and the amount of parameter fed in the FBG(43) is measured by referring to a lookup table corresponding to a stored changed amount of wave and a sensing parameter.

Description

Optical signal wavelength measuring device and optical fiber Bragg grating sensor device and method using wavelength selective photodetector

The present invention relates to an optical signal wavelength measuring apparatus using a wavelength selective photodetector having a wavelength dependency, and an optical fiber Bragg grating (FBG) sensor apparatus and a method thereof, and in particular, by using a wavelength selective photodetector having a wavelength dependency. And a simple and economical optical signal wavelength measuring device, an optical fiber Bragg grating (FBG) sensor device and a method for demodulating reflected optical signals from a narrow fiber spectrum Bragg grating (FBG) with a minimum number of optical elements required will be.

The optical fiber Bragg grating (FBG) is engraved with regular intervals of regular refractive index shifts in the optical fiber. It is a kind of optical filter element characterized by reflecting only the corresponding wavelength according to, and transmitting the signal of the remaining wavelength band.

In this case, changing the structural characteristics of the grating such as the refractive index and the interval changes the wavelength characteristics of the reflected optical signal. Currently, research into the optical fiber Bragg grating (FBG) optical sensor for measuring the temperature and strain, etc. has been actively conducted.

In order to accurately measure the amount of temperature and strain applied to the optical fiber Bragg grating (FBG), it is necessary to measure the wavelength change of the optical signal reflected from the optical fiber Bragg grating (FBG) through the optical fiber Bragg grating (FBG) demodulator . Conventional optical fiber Bragg grating (FBG) demodulation methods include a method using a monochromator or spectrometer, a method of scanning a variable optical filter, a method using an optical interferer, and a method using a wavelength dependent response characteristic of the optical filter.

1 is an exemplary configuration diagram of an optical fiber Bragg grating sensor device using a conventional monochromator or spectrometer, a method of measuring the wavelength value of the optical signal reflected from the optical fiber Bragg grating using a monochromator or spectrometer It is an illustration.

In the conventional method using a monochromator or spectrometer, as shown in FIG. 1, an optical signal having a wide-spectrum spectral width generated from the light source 11 is connected to the optical fiber Bragg grating (FBG) through the optical coupler 12 ( 13 is incident on the optical coupler (13) and simply reflected from the optical fiber Bragg grating (13) branched from the optical coupler (12) to enter the monochromator or spectrometer (14) to a personal computer (PC) or signal processor (15) Can be configured through a spatial optical technique using a spatial diffraction grating element, a Fabry-Perot interferometer. In other words, the monochromator may be composed of a spatial Fabry-Perot interferometer, and the spectrometer may be composed of a spatial optical diffraction grating element and a photodetector that spatially detects it.

"Fiber Bragg grating temperature sensor system for medical applications (In-Fiber)" published in Yun-Jiang Rao et al. In the Journal of Lightwave Technology Vol.15, No.5 pp779-785 in 1997. Some of the demodulation methods presented in "Bragg-Grating Temperature Sensor System for Medical Applications" are examples of such methods.

However, the conventional technology is not a good method because there is a problem in the size of the device according to the spatial configuration and the reliability of the external environment change.

FIG. 2 is an exemplary configuration diagram of an optical fiber Bragg grating sensor device using a conventional variable optical filter, and is an exemplary view illustrating a method of measuring a wavelength change of an optical signal reflected from a conventional optical fiber Bragg grating using a variable optical filter.

In the conventional method using a variable optical filter, an optical signal having a wide spectral width generated from the light source 21 is incident on the optical fiber Bragg grating (FBG) 23 through the optical coupler 22, and the optical fiber Bragg grating 23 ), The optical signal reflected from the optical waveguide is branched from the optical coupler 22 to be incident on a variable optical filter 24 such as an optical fiber Fabry-Perot interferer and an acoustic optical element, and the output is converted into an electrical signal using the photodetector 25. Next, the change of the wavelength is measured by the signal processor 26. In the signal processing method, the variable optical filter 24 is periodically scanned by the scanning controller 27 to measure the changed wavelength at a point on a time axis or a frequency axis, and must continuously scan the wavelength region expected at a constant speed.

Therefore, the conventional technology has a disadvantage in that the detection speed is limited, and the variable characteristics of the variable optical filter must be linear to measure an accurate amount, and the configuration is made by using an expensive variable optical filter and a controller for controlling the same. Complex and uneconomical

The demodulation method described in US Pat. No. 5,818,585 (Fiber Bragg grating interrogation system with adaptive calibration), which is registered in the United States as "M. A. Davis", is an example of such a conventional method.

3 is a configuration example of an optical fiber Bragg grating sensor device using a conventional optical filter having a wavelength dependency, a method of measuring the wavelength change of the optical signal reflected from the conventional optical fiber Bragg grating using an optical filter having a wavelength dependency This is an example of.

In the conventional method using an optical filter having a wavelength dependency, an optical signal having a broad spectral width generated from the light source 31 is incident on the optical fiber Bragg grating (FBG) 33 through the optical coupler 32, and the optical fiber Bragg The optical signal reflected from the grating 33 and branched from the optocoupler 32 is distributed by the other optocoupler 34 to two outputs, and two optical filters 35 and 36 that receive the respective divided outputs. And the photodetectors 37 and 38 detect the change in the wavelength of the optical fiber Bragg grating reflected light as the change in the electric intensity. The detected electrical signal is processed by the signal processor 39 to measure the amount of change in wavelength, which is converted into an amount of perturbation.

However, the conventional technique is also relatively complicated and economical in that it uses an optical filter.

"All-fibre Bragg grating strain sensor demodulation technique using a wavelength division coupler" published by "MA Davis" in "Electronic Letters, Vol. 30, No1 pp75-77" in 1994. Wavelength division coupler) and "SM Serge" and the like, US 5,319,435 (Method and apparatus for measuring the wavelength of spectrally narrow optical signal) demodulation method is an example of such a conventional method.

On the other hand, the method using the optical interferer is a method in which the optical signal reflected from the optical fiber Bragg grating (FBG) is incident on an asymmetric optical interferometer such as Mach-Zehnder, changing the minute change of the wavelength to the phase difference of the interferometer. This method has the advantage of showing high resolution characteristics because it can measure the minute wavelength change of the reflected light, but its configuration is complicated and the real-time correction function of the measurement data according to the external influence of the optical interferometer is required. In addition, since the amount of application causing a phase change of 2 [pi] or more can not be distinguished by using an interferer, the operating range is limited. An example of such a conventional method is Fibre-Grating-based sensing system with interferometric wavelength-shift detection (US Pat. No. 5,361,130) to which "A. D. Kersey" et al.

Looking at the technical characteristics of the conventional as described above, as follows.

First, a method using a spatial optical monochromator or spectrometer has disadvantages such as deterioration of reliability due to changes in the size and external environment of the device according to spatial configuration.

In addition, the scanning method of the variable optical filter has a disadvantage in that the detection speed is limited because the wavelength region expected to be continuously scanned at a constant speed is limited, and the variable amount of the variable optical filter may be linear to measure an accurate amount. . In addition, the configuration is complicated and uneconomical by using the variable optical filter.

In addition, the method using the asymmetric optical interferometer can measure a small wavelength change of the reflected light of the optical fiber Bragg grating (FBG), but has the advantage of showing high resolution characteristics, but the configuration is complicated and the measurement data according to the external influence of the optical interferometer Correction function is required. In addition, since the amount of application causing a phase change of 2 [pi] or more can not be distinguished by using an interferer, the operating range is limited.

The simplest method in the prior art is a method using the wavelength response characteristics of the optical filter, but this method is also relatively complicated and uneconomical in that it uses an optical filter.

The present invention devised to solve the above problems, the temperature applied to the optical fiber Bragg grating (FBG) using the wavelength dependence of the wavelength selective photodetector (characteristic that the output response changes linearly with wavelength) and Provided are an optical signal wavelength measuring device, an optical fiber Bragg grating (FBG) sensor device, and a method for measuring the amount of perturbation applied by converting a change in wavelength of reflected light due to perturbation such as strain into electrical intensity. The purpose is.

1 is an exemplary configuration diagram of an optical fiber Bragg grating sensor device using a conventional monochromator or spectrometer.

2 is an exemplary view of the configuration of an optical fiber Bragg grating sensor device using a conventional variable optical filter.

3 is an exemplary configuration diagram of an optical fiber Bragg grating sensor device using an optical filter having a conventional wavelength dependency.

4 is a configuration diagram of an optical fiber Bragg grating sensor device using a wavelength selective photodetector according to the present invention.

5 is a configuration diagram of an embodiment of a signal processor according to the present invention.

Figure 6 is a flow diagram of an embodiment of the optical fiber Bragg grating sensing method using a wavelength selective photodetector according to the present invention.

Figure 7 is a schematic diagram of one embodiment of a temperature sensor using the scheme of the present invention.

8 is a wavelength response characteristic diagram of a wavelength selective photodetector used in a temperature sensor experiment using the present invention.

9 is a characteristic diagram of a result of a temperature sensor experiment using the present invention.

* Explanation of symbols for the main parts of the drawings

41: light source 42,44: optocoupler

43: optical fiber Bragg grating 45: photodetector

46: wavelength selective photodetector 47: signal processor

An optical fiber Bragg grating sensor device of the present invention for achieving the above object, the optical fiber Bragg grating sensor device, comprising: optical signal generating means for generating an optical signal having a wide bandwidth spectrum; An optical fiber Bragg grating receiving the optical signal and reflecting the optical signal according to a setting parameter; Optical branch means for transmitting the optical signal of the optical signal generating means to the optical fiber Bragg grating, and for branching the reflected light of the optical fiber Bragg grating; Optical distribution means for distributing the optical signal branched from the optical branch means; Light detecting means for detecting and converting one output of the light distribution means into an electrical signal regardless of wavelength; Wavelength selective light detecting means for converting and detecting the other output of the light distribution means into an electrical signal according to the wavelength; And signal processing means for processing an electrical signal from the light detecting means and the wavelength selective light detecting means to measure an amount of a parameter applied to the optical fiber Bragg grating.

In addition, the optical fiber Bragg grating sensing method of the present invention, the optical fiber Bragg grating sensing method applied to the optical fiber Bragg grating sensor device, comprising: a first step of branching the optical signal reflected by the incident optical signal according to the setting parameter of the optical fiber Bragg grating; Distributing the branched optical signal; The optical signal of the divided one side is converted into an electrical signal according to a constant response characteristic irrespective of the wavelength, and the optical signal of the divided other side is converted into an electrical signal according to a linear response characteristic varying with the wavelength. A third step of doing; A fourth step of amplifying the signals converted into the electrical signals and then differentially amplifying the signals; A fifth step of normalizing the differentially amplified signal by dividing the differentially amplified signal into an electrical signal converted according to the constant response characteristic; And a sixth step of converting the normalized analog value into a digital value, and then measuring the amount of parameter applied to the optical fiber Bragg grating by comparing with a value that has been corrected and stored in advance.

On the other hand, the optical signal wavelength measuring apparatus of the present invention, the optical signal wavelength measuring apparatus, comprising: optical distribution means for receiving and distributing the optical signal to be measured; Light detecting means for detecting and converting one output of the light distribution means into an electrical signal regardless of wavelength; Wavelength selective light detecting means for converting and detecting the other output of the light distribution means into an electrical signal according to the wavelength; And signal processing means for processing the electric signals from the light detecting means and the wavelength selective light detecting means to measure the wavelength of the incident optical signal.

In addition, the optical signal wavelength measuring method of the present invention, the optical signal wavelength measuring method applied to the optical signal wavelength measuring apparatus, comprising: a first step of distributing the incident optical signal to be measured; The optical signal of the divided one side is converted into an electrical signal according to a constant response characteristic irrespective of the wavelength, and the optical signal of the divided other side is converted into an electrical signal according to a linear response characteristic varying with the wavelength. A second step of doing; A third step of amplifying the signals converted into the electrical signals and then differentially amplifying the signals; A fourth step of normalizing the differentially amplified signal by dividing the differentially amplified signal into an electrical signal converted according to the constant response characteristic; And a fifth step of measuring the wavelength of the incident optical signal by converting the normalized analog value into a digital value and then comparing it with a value that has been corrected and stored in advance.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a configuration diagram of an optical fiber Bragg grating sensor device using a wavelength selective photodetector according to the present invention, wherein the optical signal reflected from the optical fiber Bragg grating (FBG) is composed of a wavelength selective photodetector and a normal photodetector. The optical fiber Bragg grating sensor apparatus of the method of measuring a wavelength change is shown.

In the present invention, the pass band of the reflected light is changed by changing the refractive index of the optical fiber Bragg grating FBG and the distance between the gratings due to the temperature and strain applied to the optical fiber Bragg grating FBG 43. Using this function, the amount of perturbation applied to the optical fiber Bragg grating FBG is measured by a demodulator.

Looking at the configuration and operation of the optical fiber Bragg grating sensor device according to the present invention.

The optical signal from the light source 41 having a broad spectral width, such as a light emitting diode (LED), a super luminescence laser diode (SLD) or an amplified spontaneous emission (ASE) noise of an erbium-doped fiber amplifier (EDFA), Incident on the optical fiber Bragg grating (FBG) 43 through the 42, the narrow-band reflected light that meets the conditions of the optical fiber Bragg grating 43 is branched from the optical coupler (42) and transmitted to another optical coupler (44) do.

The optocoupler 44 distributes the reflected light to the ordinary photodetector 45 and the wavelength selective photodetector 46. In the ordinary photodetector 45 and the wavelength selective photodetector 46, the optical signal is electrically distributed. Convert each to a signal. In this case, the wavelength selective photodetector 46 has a characteristic that the response characteristic changes linearly with the wavelength, and the ordinary photodetector 45 has a constant response characteristic with the wavelength.

The signal converted into an electrical signal is subjected to amplification, differential amplification, and divider in the signal processor 47, and is referred to as a lookup table that corresponds to a wavelength change amount and a sensing parameter that are already corrected and stored. The amount of parameter applied to the Bragg grating 43 is measured.

As such, the method can be composed of only two photodetectors, two optocouplers, an optical fiber Bragg grating (FBG), and a light source, which is simpler, more reliable, and more economical than the conventional method. Can be.

In addition, an optical circulator may be used instead of the optical coupler 42.

5 is a configuration diagram of an embodiment of a signal processor according to the present invention.

After receiving a signal converted into an electrical signal from each of the photodetectors 45 and 46, the signal amplifier 51 amplifies the signal to an appropriate size, and differentially amplifies two outputs from the differential amplifier 52. The differential amplifier 52 is used to prevent the operating range from being limited by the signal saturation and the electrical characteristics.

The change in the output intensity of the light source may directly change the output intensity of the wavelength selective photodetector 46, resulting in an error in the measured value. To prevent this, the divider 53 divides the output of the differential amplifier 52 by the output of the ordinary photodetector 45 and normalizes it. After converting the normalized analog value to a digital value, the applied parameter amount is calculated by comparing it with the value of a lookup table 57 in which the pre-corrected value is recorded.

6 is a flowchart illustrating an optical fiber Bragg grating sensing method using a wavelength selective photodetector according to the present invention.

First, an optical signal from a light source having a broad spectrum width is incident on the optical fiber Bragg grating FBG, and after branching the reflected light of the narrow band reflected according to the conditions of the optical fiber Bragg grating 43 (61), the branched optical signal Is distributed to a normal photodetector and a wavelength selective photodetector (62). Thereafter, the divided optical signals are converted into electrical signals using an ordinary photodetector and a wavelength selective photodetector, respectively (63).

Thereafter, after amplifying the two signals converted into electrical signals to an appropriate size (64), the two amplified outputs are differentially amplified (65). The differentially amplified signal is then normalized by dividing the differentially amplified signal by the signal detected by a normal photodetector (66).

Thereafter, the normalized analog value is converted into a digital value (67), and then the amount of the applied parameter is measured by comparing the previously corrected value with a value of a recorded lookup table.

Figure 7 is a schematic diagram of an embodiment of a temperature sensor using the scheme of the present invention.

7 is similar to the configuration of FIG. 4, and a thermoelectric cooler (TEC) 74 is attached to the optical fiber Bragg grating 73 to apply a temperature to the optical fiber Bragg grating 73. In addition, the optical circulator 72 is used instead of the optical coupler to reduce the loss, and the optical coupler 76 uses a 95: 5 ratio optical coupler. The characteristic of the wavelength selective photodetector 77 used by this structure is shown in FIG. As shown in FIG. 8, linear response characteristics are shown from 1535 nm to 1550 nm. EDFA 71 was used as the light source, and the optical fiber Bragg grating 73 had a Bragg wavelength of 1545.7 nm at room temperature, and the reflectance was 99%. The temperature of the TEC 74 was controlled by a thermostat 75 with an accuracy of 0.01 ° C. Figure 9 shows the output of the sensor according to the temperature change between 5 ° C ~ 55 ° C, the change in the Bragg wavelength of the optical fiber Bragg grating (FBG) was measured by a wavemeter (wavemeter) and compared with the sensor output. This invention can be used not only for temperature but also for strain measurement.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

The present invention as described above, perturbation of the temperature and strain applied to the optical fiber Bragg grating (FBG), using the wavelength dependence of the wavelength selective photodetector, that is, the output response changes linearly with the wavelength By measuring the amount of perturbation applied by converting the wavelength change of reflected light due to the intensity into electric strength, the use of variable optical filters, optical interferometers, and monochromators required in the conventional fiber Bragg grating (FBG) demodulation method This unnecessary and simple photodetector can be used to easily construct an optical fiber Bragg grating (FBG) sensor, thereby making it possible to manufacture an economical fiber Bragg grating (FBG) sensor and improving reliability. have.

Claims (12)

An optical fiber Bragg grating sensor device, Optical signal generating means for generating an optical signal having a broadband spectral width; An optical fiber Bragg grating receiving the optical signal and reflecting the optical signal according to a setting parameter; Optical branch means for transmitting the optical signal of the optical signal generating means to the optical fiber Bragg grating, and for branching the reflected light of the optical fiber Bragg grating; Optical distribution means for distributing the optical signal branched from the optical branch means; Light detecting means for detecting and converting one output of the light distribution means into an electrical signal regardless of wavelength; Wavelength selective light detecting means for converting and detecting the other output of the light distribution means into an electrical signal according to the wavelength; And Signal processing means for processing an electrical signal from the light detecting means and the wavelength selective light detecting means to measure an amount of a parameter applied to the optical fiber Bragg grating Fiber Bragg grating sensor device comprising a. The method of claim 1, The wavelength selective light detecting means, An optical fiber Bragg grating sensor device comprising a wavelength selective photodetector in which the response characteristic changes linearly with wavelength. The method according to claim 1 or 2, The signal processing means, Amplifying means for amplifying an electrical signal from said photodetecting means and said wavelength selective photodetecting means; Differential amplifying means for differentially amplifying the signal amplified by the amplifying means; Division means for normalizing by dividing the output of the differential amplifying means by the output of the photodetecting means; Analog / digital conversion means for converting a normalized analog value into a digital value in said division means; Storage means for storing a parameter value with a pre-corrected value; And Central processing means for measuring an amount of a parameter applied to said optical fiber Bragg grating by comparing an output value of said analog / digital conversion means with a value stored in said storage means; Fiber Bragg grating sensor device comprising a. The method of claim 3, wherein The optical branch means, An optical fiber Bragg grating sensor device comprising an optocoupler. The method of claim 3, wherein The optical branch means, Optical fiber Bragg grating sensor device comprising an optical circulator. In the optical fiber Bragg grating sensing method applied to the optical fiber Bragg grating sensor device, A first step of branching the reflected optical signal according to the setting parameter of the optical fiber Bragg grating; Distributing the branched optical signal; The optical signal of the divided one side is converted into an electrical signal according to a constant response characteristic irrespective of the wavelength, and the optical signal of the divided other side is converted into an electrical signal according to a linear response characteristic varying with the wavelength. A third step of doing; A fourth step of amplifying the signals converted into the electrical signals and then differentially amplifying the signals; A fifth step of normalizing the differentially amplified signal by dividing the differentially amplified signal into an electrical signal converted according to the constant response characteristic; And A sixth step of measuring the amount of parameter applied to the optical fiber Bragg grating by comparing the normalized analog value to a digital value and then comparing it with a pre-corrected and stored value; Fiber Bragg grating sensing method comprising a. The method of claim 6, The process of converting into an electrical signal according to the linear response characteristic of the third step, Optical fiber Bragg grating sensing method characterized in that the optical signal is converted into an electrical signal by using a wavelength selective photodetector. In the optical signal wavelength measuring apparatus, Optical distribution means for receiving and distributing the optical signal to be measured; Light detecting means for detecting and converting one output of the light distribution means into an electrical signal regardless of wavelength; Wavelength selective light detecting means for converting and detecting the other output of the light distribution means into an electrical signal according to the wavelength; And Signal processing means for measuring the wavelength of said incident optical signal by processing electrical signals from said photodetection means and said wavelength selective photodetection means Optical signal wavelength measuring apparatus comprising a. The method of claim 8, The wavelength selective light detecting means, An optical signal wavelength measuring apparatus comprising a wavelength selective photodetector whose response characteristic changes linearly with wavelength. The method according to claim 8 or 9, The signal processing means, Amplifying means for amplifying an electrical signal from said photodetecting means and said wavelength selective photodetecting means; Differential amplifying means for differentially amplifying the signal amplified by the amplifying means; Division means for normalizing by dividing the output of the differential amplifying means by the output of the photodetecting means; Analog / digital conversion means for converting a normalized analog value into a digital value in said division means; Storage means for storing a parameter value with a pre-corrected value; And Central processing means for measuring the wavelength of the incident optical signal by comparing the output value of the analog / digital conversion means with the value stored in the storage means. Optical signal wavelength measuring apparatus comprising a. In the optical signal wavelength measuring method applied to the optical signal wavelength measuring apparatus, Distributing an incident optical signal to be measured; The optical signal of the divided one side is converted into an electrical signal according to a constant response characteristic irrespective of the wavelength, and the optical signal of the divided other side is converted into an electrical signal according to a linear response characteristic varying with the wavelength. A second step of doing; A third step of amplifying the signals converted into the electrical signals and then differentially amplifying the signals; A fourth step of normalizing the differentially amplified signal by dividing the differentially amplified signal into an electrical signal converted according to the constant response characteristic; And A fifth step of measuring the wavelength of the incident optical signal by converting the normalized analog value into a digital value and then comparing it with a pre-corrected and stored value Optical signal wavelength measurement method comprising a. The method of claim 11, The process of converting into an electrical signal according to the linear response characteristic of the second step, An optical signal wavelength measuring method comprising converting an optical signal into an electrical signal using a wavelength selective photodetector.