METHOD AND SYSTEM FOR EXPANDING THE DYNAMIC RANGE OF MACH-ZEHNDER SENSOR BASED ON THE CALCULATION OF OPTICAL LENGTH

Abstract

A method and system are for expanding a measuring range of a Mach-Zehnder sensor based on the calculation of optical length; the method includes: (1) performing calibration according to a known parameter to complete calibration of a Mach-Zehnder pressure sensor; and (2) for an unknown parameter, testing the unknown parameter first using the Mach-Zehnder sensor to acquire discrete data; processing the discrete data using a peak and valley synthesis algorithm to restore a diffraction order m; calculating an optical length value of the unknown parameter; and restoring, according to a calibrated relationship curve between the optical length and the parameter, the unknown parameter, thus expanding the measuring range of the Mach-Zehnder sensor to enable the Mach-Zehnder sensor to break through the limitation of the FSR and the spectral width of a light source. The measuring range can be theoretically expanded to infinitely great.

Claims

1. A method for expanding a measuring range of a Mach-Zehnder sensor based on the calculation of optical length, comprising: (1) making an asymmetric Mach-Zehnder sensor, an input end of the asymmetric Mach-Zehnder sensor being connected with a light source, and an output end of the Mach-Zehnder sensor being connected with an optical measuring device; (2) for several known parameters, testing the known parameters first using the asymmetric Mach-Zehnder sensor to acquire discrete data, the discrete data being optical power corresponding to different wavelengths; processing the discrete data using a peak and valley synthesis algorithm, and restoring a diffraction order m; calculating an optical length value of the known parameters to obtain a correction relationship curve between the optical length value and a measured parameter; and completing the calibration of the asymmetric Mach-Zehnder sensor; and (3) for unknown parameters, testing the unknown parameters using the asymmetric Mach-Zehnder sensor to acquire discrete data; processing the discrete data using the peak and valley synthesis algorithm, and restoring a diffraction order m; calculating an optical length value of the unknown parameters; restoring the unknown parameters according to the calibrated relationship curve between the optical length and the parameter in step (2), thus expanding the measuring range of the asymmetric Mach-Zehnder sensor to enable the asymmetric Mach-Zehnder sensor to break through the limitation of the FSR of the instrument and the spectral width of the light source.

2. The method for expanding the measuring range of the Mach-Zehnder sensor based on the calculation of optical length according to claim 1, wherein in step (1), the spectral width of the light source selected by the asymmetric Mach-Zehnder sensor is greater than half of the FSR, so that the discrete data output by the asymmetric Mach-Zehnder sensor has at least one valley value and one peak value at the same time.

3. The method for expanding the measuring range of the Mach-Zehnder sensor based on the calculation of optical length according to claim 1, wherein in step (2) and step (3), the discrete data is processed using the peak and valley synthesis algorithm to restore the diffraction order m, specifically as follows: the diffraction order m is calculated using the peak and valley synthesis algorithm, that is, using ratios of different peak wavelengths or valley wavelengths; when the acquired discrete data simultaneously contains one peak wavelength .sub.2 and one valley wavelength .sub.1, and .sub.1<.sub.2: $\begin{array}{cc}\frac{{}_1}{{}_2}=\frac{n_{{}_1}}{n_{{}_2}}.Math.\frac{2m}{2m+1},& \left(\mathrm{VI}\right)\end{array}$ when the acquired discrete data contains both a peak wavelength .sub.1 and a valley wavelength .sub.2, and .sub.1<.sub.2: $\begin{array}{cc}\frac{{}_1}{{}_2}=\frac{n_{{}_1}}{n_{{}_2}}.Math.\frac{2m-1}{2m},& \left(\mathrm{VII}\right)\end{array}$ in formulas (VI) and (VII), m is the diffraction order; n.sub.1 is the effective refractive index of a waveguide corresponding to wavelength .sub.1; n.sub.2 is the effective refractive index of a waveguide corresponding to wavelength .sub.2; .sub.1 and .sub.2 are measured by the optical measuring device; n.sub.1 and n.sub.2 are obtained according to the empirical formula; adjacent peak wavelengths and valley wavelengths in the discrete data, as well as n.sub.1 and n.sub.2 are substituted into formula (VI) or formula (VII), thus obtaining the diffraction order m.

4. The method for expanding the measuring range of the Mach-Zehnder sensor based on the calculation of optical length according to claim 1, wherein in step (2) and step (3), the specific process of calculating the optical length value of the known parameters or the unknown parameters is as follows: first performing translation and scaling transformation on the discrete data such that the amplitude of the discrete data is 1; and calculating an arc-cosine function to obtain a phase value; and superimposing 2m to obtain a total optical length value.

5. An implementation system for expanding a measuring range of a Mach-Zehnder sensor based on the calculation of optical length, which is used for implementing the method for expanding the measuring range of the Mach-Zehnder sensor based on the calculation of optical length according to claim 1, wherein the system comprises a light source, an asymmetric Mach-Zehnder sensor, a discrete data acquisition module, an optical length acquisition module, and a physical-quantity-to-be-measured acquisition module which are connected in sequence; the discrete data acquisition module comprises an optical measuring device, used for measuring acquired discrete data; the optical length calculation module is used for processing the discrete data using a peak and valley synthesis algorithm, restoring a diffraction order m, and calculating an optical length value of parameters; and the physical-quantity-to-be-measured calculation module is used for restoring unknown parameters according to a calibrated relationship curve between the optical length value and the parameter, thus calculating a physical quantity to be measured.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 is an output spectral image of an asymmetric Mach-Zehnder sensor;

[0049] FIG. 2 is a definition diagram of error E;

[0050] FIG. 3 is a schematic diagram of the impact of fluctuations of peaks or valleys on error E;

[0051] FIG. 4 is a schematic diagram of the impact of fluctuations of the effective refractive index of a waveguide at a wavelength of 1550 nm on error E;

[0052] FIG. 5 is a schematic diagram of the impact of fluctuations of a wavelength-varying coefficient d.sub.n of the refractive index of a material on error E;

[0053] FIG. 6 is a schematic structural diagram of an asymmetric Mach-Zehnder sensor based on a lithium niobate waveguide provided in Embodiment 1;

[0054] FIG. 7 is discrete data of the Mach-Zehnder sensor acquired by an optical measuring device in Embodiment 1;

[0055] FIG. 8 is a schematic diagram of the impact of errors at various diffraction orders m on error E; and

[0056] FIG. 9 is comparison between final test results of the asymmetric Mach-Zehnder sensor in Embodiment 1 and theoretical results.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] The present invention is further described below in combination with the embodiments and the drawings of the specification, but is not limited to this.

Embodiment 1

[0058] A method for expanding a measuring range of a Mach-Zehnder temperature sensor based on the calculation of optical length includes the following steps: [0059] (1) An asymmetric Mach-Zehnder temperature sensor based on a lithium niobate waveguide is manufactured; the asymmetric Mach-Zehnder sensor is bonded to an aluminum alloy; and a phase difference between two arms in the asymmetric Mach-Zehnder sensor is changed using a stress caused by a temperature. The structure of the sensor is as shown in FIG. 6. The waveguide structure is made by a proton exchange process, which ensures that there is only one polarization state and improves the measuring accuracy. The asymmetric Mach-Zehnder sensor includes an input coupler, two sensing arms with different lengths, and an output coupler, which are connected in sequence; an input end of the asymmetric Mach-Zehnder sensor is connected with a light source; and an output end of the Mach-Zehnder sensor is connected with an optical measuring device. [0060] (2) The asymmetric Mach-Zehnder sensor is first used to test known parameters to acquire discrete data. The discrete data is the optical power corresponding to different wavelengths. The obtained discrete data is as shown in FIG. 7, and the discrete data includes the optical power corresponding to different wavelengths. The discrete data is processed using a peak and valley synthesis algorithm to restore a diffraction order m; an optical length value of the known parameters is calculated, thus obtaining a correction relationship curve between an optical length and the measured parameters. In this embodiment, the measured parameter is temperature, and a temperature-varying coefficient d.sub.t of the obtained optical length is corrected; and the calibration of the asymmetric Mach-Zehnder sensor is completed. The relationship curve between the optical length and the measured parameter is as shown in FIG. 9, in which the solid line represents a theoretical calculation result, and the other line represents a calibrated result.

[0061] As shown in FIG. 7, the valley wavelength is .sub.1=1535.915 nm, and the peak wavelength is .sub.2=1559.432 nm. When the wavelength is 1550 nm, the effective refractive index of the lithium niobate waveguide is 2.17, and the wavelength-varying coefficient of the effective refractive index is d.sub.n=0.031. In this embodiment, the parameter tested by the Mach-Zehnder sensor is temperature. The arm difference of the Mach-Zehnder structure is different due to different structural deformations at different temperatures. Mathematically, the arm difference is considered to be the same, and the length of an actual change of the arm difference is converted into the change of the refractive index, so that it is relatively simple during processing. At this time, the calculation formula of the effective refractive index of the lithium niobate waveguide along with wavelength and temperature is n.sub.=n.sub.1.55+d.sub.n.Math.(1.55)+d.sub.t.Math.(tt.sub.0) (X), where t.sub.0 is an initial temperature, and d.sub.t is a temperature-varying coefficient of the effective refractive index. Therefore, from which n.sub.1 and n.sub.2 can be calculated.

[0062] When the temperature is 26.5 C., the peak wavelength of the discrete data is .sub.1=1528.3 nm, and the valley wavelength is .sub.2=1552.4 nm; when the temperature is 28.6 C., the peak wavelength of the discrete data is .sub.1=1545.9 nm, and the valley wavelength is .sub.2=1570.6 nm; and n.sub.1 and n.sub.2 are calculated according to formula (X). .sub.2=1552.4 nm and .sub.2=1570.6 nm, as well as n.sub.1 and n.sub.2, are brought into

[00007]$\begin{array}{cc}\frac{{}_1}{{}_2}=\frac{n_{{}_1}}{n_{{}_2}}.Math.\frac{2m}{2m+1}.& \left(\mathrm{VI}\right)\end{array}$

After optimization, when n.sub.1.55=2.17, d.sub.n=0.025 RIU/m, 13 C., and d.sub.t=0.128 RIU/ C., the errors at the various diffraction orders m are as shown in FIG. 8. Since this is a calibration process, it is known that a difference between the diffraction orders m at two temperatures is 1, which belongs to a reasonable determining range. From this, it can be determined that n.sub.1.55=2.17, d.sub.n=0.025 RIU/m, t.sub.0=13 C., and d.sub.t=0.128 RIU/ C.

[0063] The optical length value of the known parameters is calculated according to the diffraction order m, and then the correction relationship curve between the optical length value and the measured parameter is obtained, thus completing the calibration of the asymmetric Mach-Zehnder sensor.

[0064] (3) Measurement is performed. Temperature t is unknown at this time. For an unknown parameter, i.e. temperature t, discrete data is acquired first using the asymmetric Mach-Zehnder sensor; the discrete data is processed using the peak and valley synthesis algorithm according to relevant parameters of the effective refractive index obtained in step (2), so as to restore a diffraction order m; and an optical length value of the unknown parameter is calculated to restore the unknown parameter, i.e. temperature t.

[0065] In this embodiment, in step (2), a measuring curve can be obtained by calibrating 26.5 C. and 28.6 C.

[0066] In step (3), m is first determined through the spectrum of the unknown temperature; the optical length is then calculated; and the correction measuring curve obtained in step (2) is queried, thus obtaining the temperature value.

[0067] In this embodiment, the sensitivity of the sensor is about 16 nm/ C., and the spectral width of the light source is 50 nm. If the temperature is determined according to the traditional method and a peak position, the measuring range is only 50/16=3.125 C. However, by using the method provided in the present invention, the measuring range can exceed this limit. In this embodiment, only the measuring range of 4 C. is shown. It is unnecessary to describe a larger measuring range.

Embodiment 2

[0068] A method for expanding a measuring range of a Mach-Zehnder pressure sensor based on the calculation of optical length is different from Embodiment 1 in that: [0069] (1) A high-sensitivity pressure sensor based on an asymmetric Mach-Zehnder interference principle. [0070] (2) Calibration is performed according to a known pressure to obtain an optical length value at the known measured parameter, so that a correction relationship curve between the optical length and the measured parameter, i.e. the pressure, is obtained, thus completing the calibration of the Mach-Zehnder pressure sensor. [0071] (3) According to the calibrated value of d.sub.n, for an unknown pressure, the value of m is determined; the spectrum is moved and stretched to plus and minus 1; an arc-cosine function is used to obtain a phase value which is superimposed with am to obtain a total optical length value; and the total optical length value is compared with the calibrated value to restore a measured pressure value.

Embodiment 3

[0072] A method for expanding a measuring range of a Mach-Zehnder refractive index sensor based on the calculation of optical length is different from Embodiment 1 in that: [0073] (1) A high-sensitivity refractive index sensor based on an asymmetric Mach-Zehnder interference principle. [0074] (2) Calibration is performed according to a known liquid or gas refractive index to obtain an optical length value at the known measured parameter, so that a correction relationship curve between the optical length and the measured parameter, i.e. liquid or gas, is obtained, thus completing the calibration of the Mach-Zehnder pressure sensor. [0075] (3) According to the calibrated value of d.sub.n, for an unknown liquid or gas refractive index, the value of m is determined; the spectrum is moved and stretched to plus and minus 1; an arc-cosine function is used to obtain a phase value which is superimposed with 2m to obtain a total optical length value; and the total optical length value is compared with the calibrated value to restore a measured refractive index.

Embodiment 4

[0076] A system for expanding a measuring range of a Mach-Zehnder sensor based on the calculation of optical length is used for implementing the method for expanding the measuring range of the Mach-Zehnder sensor based on the the calculation of optical length provided in any one of Embodiments 1-3, and includes a light source, an asymmetric Mach-Zehnder sensor, a discrete data acquisition module, an optical length acquisition module, and a physical-quantity-to-be-measured acquisition module which are connected in sequence.

[0077] The discrete data acquisition module includes an optical measuring device, used for measuring acquired discrete data; and the optical measuring device includes a spectrometer or an optical power meter.

[0078] The optical length calculation module is used for processing the discrete data using a peak and valley synthesis algorithm, restoring a diffraction order m, and calculating an optical length value of parameters.

[0079] The physical-quantity-to-be-measured calculation module is used for restoring unknown parameters according to a calibrated relationship curve between the optical length value and the parameter, thus calculating a physical quantity to be measured.