Laser wavelength measurement system based on phase difference between double interference signals

Abstract

The invention discloses a laser wavelength measurement system based on phase difference between double interference signals, which belongs to the technical field of optical fiber sensing and comprises a reference laser, an interferometer device, an optical path difference modulator, a photoelectric detector and a processing module. Corresponding phase differences of reference light and to-be-measured light are respectively measured by utilizing the fact that corresponding phases and wavelengths of two beams of light in a certain distance are inversely proportional, and the wavelength of the to-be-measured light is calculated according to the ratio of the phase differences and the wavelength of the reference light. According to the invention, optical path difference adjustment is set, and more accurate wavelength measurement is realized by amplifying the difference of phase differences corresponding to light with two wavelengths.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a laser wavelength measurement system and a measurement method based on a double interference signal phase difference. Background Art

[0002] Wavelength measurement has wide applications and importance in many fields. In the field of optical communications, with the rapid development of optical fiber communications and the increasing amount of information, optical wavelength measurement technology has received unprecedented attention. Accurate measurement of optical wavelength is essential to ensure the stability and transmission efficiency of optical communication systems. In addition, wavelength measurement is also widely used in the fields of chemical industry, medicine, papermaking, instrumentation, environmental protection, as well as in many scientific research fields such as laser physics, spectroscopy, and astrophysics research.

[0003] Interference measurement is an important method for measuring optical wavelength. Existing devices that use interference measurement often use the width of interference fringes to obtain wavelength, and need to control the phase to be measured to be half a period, which is difficult to achieve in actual situations, and the resolution depends on the optical path difference control device, so it is difficult to achieve high resolution. The present invention proposes a device with a certain resolution and simple operation, which uses a phase demodulation method and an optical fiber optical path, has certain innovation, and reduces the impact of noise by using secondary measurements that increase the signal amplitude, and has certain practicality. Summary of the invention

[0004] The purpose of the present invention is to provide a laser wavelength measurement system based on double interference signal phase difference, providing a new wavelength measurement idea.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A laser wavelength measurement system based on the phase difference between dual interference signals, comprising: a reference laser, an interferometer device, an optical path difference modulator, a photodetector and a processing module;

[0007] A reference laser emits a reference laser and the laser to be measured enters the interferometer device successively;

[0008] An interferometer device, used for generating two interference signals by splitting and coupling the light beam signal emitted by the laser, wherein the interferometer device is provided with two interferometers, and each interferometer is provided with two interference arms, and the two interferometers share one interference arm, which is a shared arm, and the other arms are respectively a sensor arm and a reference arm;

[0009] An optical path difference modulator, used to change the optical path of the sensing arm;

[0010] The photoelectric detector is connected to two interferometers respectively through a coupler to convert the optical interference signal into an electrical signal;

[0011] The processing module is used to convert the two electrical signals into digital signals and demodulate the phase difference between the two signals, that is, the phase difference between the interference signals. The processing module is connected to the two photodetectors.

[0012] As a further solution of the present invention, the measuring method of the measuring system is:

[0013] Step 1, setting the value of the optical path difference L0 between the sensing arm and the reference arm;

[0014] Step 2: The reference laser generates light with a wavelength of λ′ and enters the system. The laser input optical path generates interference and outputs two interference signals. The two interference signals are converted into two electrical signals through a photoelectric detector. The two electrical signals are demodulated for phase difference, and the phase difference B1 of the two signals is obtained according to the demodulation result β1.

[0015] Step 3: Switch the optical switch to allow the light to be measured λ to enter the system. The phase difference B2 between the two signals is obtained based on the demodulation result β2. According to the formula Get the value of the wavelength to be measured for the first time λ A ;

[0016] Step 4: Increase the optical path difference between the sensor arm and the reference arm to L1, and control the optical switch so that the reference light and the light to be measured enter the optical path in sequence. According to the corresponding demodulation results β3 and β4, the phase difference B3 of the two reference light signals and the phase difference B4 of the two light signals to be measured are obtained. According to the formula Find the wavelength λ to be measured B .

[0017] As a further solution of the present invention, when setting the initial optical path difference L0 of the sensor arm and the reference arm in step 1, a wavelength measurement range is artificially defined so that the initial measured reference light phase difference B1 and the measured light phase difference B2 within the measurement range can both fall between (nπ, (n+1)π), and the relationship between n and the optical path difference is numerically equal to Round down.

[0018] As a further solution of the present invention, when the demodulation result β1 corresponding to B1 is demodulated in step 3, it is also necessary to obtain the number of half cycles N1 contained in B1 according to the initial optical path difference L0, which is numerically equal to When N1 is an odd number, B1=(N1+1)π-β1; when N1 is an even number, B1=N1π+β1. Similarly, B2 is obtained. Within the limited wavelength measurement range, the value of N2 is the same as that of N1.

[0019] As a further solution of the present invention, in step 4, when the demodulation result β3 corresponding to B3 is demodulated, the number of half cycles N3 contained in it needs to be determined according to the measured L1, and its value is equal to Round down, if N3 is an odd number, then B3=(N3+1)π-β3, if N3 is an even number, then B3=N3π+β3; and when demodulating the demodulation result β4 corresponding to B4, to obtain B4, it is necessary to first calculate Find the positive integer N4 that is rounded down. If N4 is an odd number, then B4=(N4+1)π-β4; if N4 is an even number, B4=N4π+β4.

[0020] Beneficial effects of the present invention:

[0021] The present invention provides a method for obtaining the wavelength of the light to be measured by demodulating the phase difference of the interference signal and determining the number of half-cycles contained in the phase according to the optical path difference between the two interference arms. The present invention innovatively uses the phase demodulation method to obtain the wavelength of the light to be measured, and proposes a method for increasing the change in the optical path difference to improve the measurement accuracy. This method plays a positive role in improving the sensitivity of light wavelength measurement and can achieve high-precision measurement of light wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 It is a schematic block diagram of the system structure of the present invention;

[0024] Figure 2 is a first example diagram of phase difference change of the present invention;

[0025] Figure 3 This is a second example diagram of phase difference change of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] See also Figure 1 , the present invention is an optical wavelength measurement system based on the phase difference between dual interference signals, comprising: a reference laser, an interferometer device, an optical path difference modulator, a photodetector and a processing module;

[0029] The reference laser and the laser to be measured enter the same device successively, and the structure adopts a double Mach-Zehnder interferometer structure.

[0030] An interferometer device, used for splitting and coupling the light beam signal emitted by the laser, wherein two interferometers are provided, respectively marked as interferometer 1 and interferometer 2, and each interferometer is provided with two interference arms, and the two interferometers share one interference arm, which is a shared arm;

[0031] An optical path difference modulator is used to change the optical path of the sensor arm to obtain the difference in phase difference under different optical path lengths;

[0032] In one embodiment of the present invention, the optical path difference modulator adopts a phase modulator, which acts on the shared arm on one hand, so that both phase inputs are a series of data to realize the ellipse fitting demodulation algorithm;

[0033] On the other hand, it is also used as a device to control the change of optical path difference.

[0034] Use photodetectors and optical paths to connect and convert optical signals into electrical signals for further demodulation;

[0035] The two photoelectric detectors are respectively connected to the two interferometers through optical couplers.

[0036] The processing module is used to demodulate the collected signals, perform phase difference demodulation based on the ellipse fitting algorithm on the two electrical signals, and obtain the phase difference of the two interference signals. The signal processing module is connected to the two photodetectors.

[0037] Combine the following Figure 1 Figure 2 The measuring method of the optical wavelength measuring system based on the phase difference of double interference signals of the present invention is described in detail. The measuring method comprises the following steps:

[0038] Step 1: Use a shifter to control the arm length difference of the interferometer, multiply the read arm length difference by the refractive index, and set the optical path difference L0 = 9.7 um.

[0039] Step 2: The reference laser and the laser to be measured generate two optical signals. The reference light with a wavelength of λ'=1550.12nm enters the system through an optical switch. At the same time, the light reaches the photodetector from the sensing arm and the shared arm, and from the shared arm and the reference arm, respectively, to generate two interference signals.

[0040] Step three, the phase modulator of the shared arm applies a sinusoidal signal to introduce a common phase change of more than π / 2, so that both signals are a series of changing data, which can be used for ellipse fitting.

[0041] Step 4: Convert the two interference signals into two electrical signals through a photoelectric detector. Perform phase difference demodulation on the two electrical signals through the processing module, and obtain the phase difference B1 corresponding to the reference light according to the demodulation result β1. Then switch the input light to the light to be measured with a wavelength of λ=1550.22nm, and obtain the phase difference B2 corresponding to the light to be measured according to the demodulation result β2. Calculate the unknown wavelength based on the two phase differences between the reference light and the light to be measured, and the known wavelength of one of the light beams. The formula is Get the initial measurement wavelength value λ A .

[0042] Step 5: Apply voltage to the phase modulator on the sensor arm to increase the optical path to L1 = 1.000 mm, and control the optical switch so that the reference light and the light to be measured enter the optical path in sequence. According to the corresponding demodulation results β3 and β4, the phase difference B3 of the two reference light paths and the phase difference B4 of the two light paths to be measured are obtained; the unknown wavelength λ to be measured is calculated according to the phase differences measured twice between the reference light and the light to be measured and the known wavelength of the reference light. B , the formula to be used is Since the difference between B3 and B4 is greater than the difference between B1 and B2, the influence of environmental noise is reduced. (This experiment is mainly affected by environmental noise and less affected by phase noise. Therefore, when the arm length difference is amplified and the phase difference is increased, the phase noise increases, but the effect is not obvious, and the unchanged environmental noise has a reduced impact on the signal.)

[0043] Specifically, the optical fibers and optical devices used in the entire optical path are all polarization-maintaining devices.

[0044] Example 2

[0045] Based on Example 1, in step 1, regarding the arm length difference control before the initial measurement, the sensor arm is adjusted so that the reference wavelength phase difference change amount reaches About, (n is a natural number, and the relationship between it and the optical path difference is numerically equal to Round down), so that the phase difference of the measured light will not go beyond (0, π), and the measurable wavelength range is established at this time. Because the phase detection range is within (nπ, (n+1)π), the half cycle contained in the phase difference of the measured wavelength needs to be the same as the reference phase difference. The artificially established lower limit of measurement and the upper limit of measurement are λ d , then the upper and lower limits of the optical path difference corresponding to the half-period number n are (nλ d / 2,(n+1)λ c / 2), in this embodiment, the wavelength measurement range is artificially specified as (1500nm, 1600nm), then the reference signal and the measured signal contain the same half period n<=14, and the optical path difference range needs to be controlled between (800n, 750n+750), in units of nm.

[0046] Example 3

[0047] On the basis of Example 1, in step 4, to demodulate the demodulation result β1 corresponding to B1 and obtain B1, it is necessary to obtain the number of half cycles N1 contained in B1 based on the measured initial optical path difference L0, which is numerically equal to When N1 is an odd number, B1=(N1+1)π-β1, when N1 is an even number, B1=N1π+β1, N2=N1, and B2 is obtained by the same logic. Figure 2 Let's see how to adjust the optical path difference. In terms of adjustment method, a step-by-step adjustment method can be used, that is, segmented modulation, each time adjusting a smaller amount. Whenever the phase changes in the opposite direction, it means that a cycle has been exceeded and it needs to be recorded to compensate. Continuous adjustment can also be used. If you have a certain amount of modulation experience, you can use a one-time adjustment method that directly refers to past experience.

[0048] Depend on Figure 2 When L0 = 9.7um, N1 = N2 = 12, B1 = 12π + 1.6184 = 39.3175rad, B2 = 12π + 1.6159 = 39.3150rad (in this embodiment, four decimal places are taken). Then λ A =1550.2186nm (the actual calculated result deviates from 1550.22nm by about 0.0014nm, a deviation of 0.000092%). Without considering the noise, λ A It still deviates from the true value because the experimental conditions limit the data to four decimal places, and the information after the fourth decimal place of B1 and B2 is omitted.

[0049] Example 4

[0050] On the basis of Example 1, in step 5, in order to obtain B3 and B4 based on the demodulation result β3 corresponding to B3 and the demodulation result β4 corresponding to B4, it is necessary to first calculate the approximate value of B3 and the half-period N3 contained therein according to the secondary optical path difference L1 using the formula, and then restore the real B3 based on β3, and then calculate Find the positive integer N4 that is rounded down. If N4 is an odd number, then B4=(N4+1)π-β4; if N4 is an even number, B4=N4π+β4.

[0051] For example Figure 3As shown, the reference wavelength is 1550.12nm, the initial measurement wavelength is 1550.2186nm, and when the optical path difference L1 is adjusted to 1.000mm, β3=0.6996rad, β4=0.4381rad are measured, and N3=N4=1290 is calculated, then B3=N3π+β3=4053.3541rad, B4=N4π+β4=4053.0926rad, and the secondary measurement wavelength is (The actual calculated result deviates from 1500.22nm by about 0.00001nm, a deviation of 0.00000075%). Since L1 (1mm) in this embodiment is about 103 times L0 (9.7um), the phase differences (B3, B4) corresponding to the second time are about 103 times the phase differences (B1, B2) corresponding to the first time, and Figure 2 In comparison, when the measured value is also retained to four decimal places, the number of effective digits retained by the phase difference signal changes from 6 digits (B1 = 39.3175rad, B2 = 39.3150rad) to 8 digits (B3 = 4053.3541rad, B4 = 4053.0926rad), and the percentage of deviation is reduced, thereby improving the measurement accuracy of the wavelength. It should be noted that this experiment is mainly affected by environmental noise and less affected by phase noise. While amplifying the arm length difference and increasing the phase difference, the environmental noise remains relatively unchanged, while the signal is enhanced, and the signal-to-noise ratio increases, making the measurement more accurate.

[0052] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A laser wavelength measurement system based on the phase difference between dual interference signals, characterized in that: include: Reference laser, interferometer device, optical path difference modulator, photodetector and processing module; A reference laser emits a reference laser and the laser to be measured enters the interferometer device successively; An interferometer device, used for generating two interference signals by splitting and coupling the light beam signal emitted by the laser, wherein the interferometer device is provided with two interferometers, and each interferometer is provided with two interference arms, and the two interferometers share one interference arm, which is a shared arm, and the other arms are respectively a sensor arm and a reference arm; An optical path difference modulator, used to change the optical path of the sensing arm; The photoelectric detector is connected to two interferometers respectively through a coupler to convert the optical interference signal into an electrical signal; The processing module is used to convert the two electrical signals into digital signals and demodulate the phase difference between the two signals, that is, the phase difference between the interference signals. The processing module is connected to the two photodetectors.

2. A laser wavelength measurement system based on the phase difference between dual interference signals according to claim 1, characterized in that: The measurement method of this measurement system is: Step 1, setting the value of the optical path difference L0 between the sensing arm and the reference arm; Step 2: The reference laser generates light with a wavelength of λ′ and enters the system. The laser input optical path generates interference and outputs two interference signals. The two interference signals are converted into two electrical signals through a photoelectric detector. The two electrical signals are demodulated for phase difference, and the phase difference B1 of the two signals is obtained according to the demodulation result β1. Step 3: Switch the optical switch to allow the light to be measured λ to enter the system. The phase difference B2 of the two signals is obtained based on the demodulation result β2. According to the formula Get the value of the wavelength to be measured for the first time λ A ; Step 4: Increase the optical path difference between the sensor arm and the reference arm to L1, and control the optical switch so that the reference light and the light to be measured enter the optical path in sequence. According to the corresponding demodulation results β3 and β4, the phase difference B3 of the two reference light signals and the phase difference B4 of the two light signals to be measured are obtained. According to the formula Find the wavelength λ to be measured B .

3. A laser wavelength measurement system based on the phase difference between dual interference signals according to claim 2, characterized in that: When setting the initial optical path difference L0 between the sensor arm and the reference arm in step 1, a wavelength measurement range is artificially defined so that the initial reference light phase difference B1 and the measured light phase difference B2 within the measurement range can both fall between (nπ, (n+1)π). The relationship between n and the optical path difference is numerically equal to Round down.

4. The laser wavelength measurement system based on the phase difference between dual interference signals according to claim 3, characterized in that: When demodulating the demodulation result β1 corresponding to B1 in step 3, it is also necessary to obtain the number of half cycles N1 contained in B1 based on the initial optical path difference L0, which is numerically equal to When N1 is an odd number, B1=(N1+1)π-β1; when N1 is an even number, B1=N1π+β1. Similarly, B2 is obtained. Within the limited wavelength measurement range, the value of N2 is the same as that of N1.

5. The laser wavelength measurement system based on the phase difference between dual interference signals according to claim 4, characterized in that: In step 4, when the demodulation result β3 corresponding to B3 is demodulated, the number of half cycles N3 contained in it needs to be determined based on the measured L1, and its value is equal to Round down, if N3 is an odd number, then B3=(N3+1)π-β3, if N3 is an even number, then B3=N3π+β3; and when demodulating the demodulation result β4 corresponding to B4, to obtain B4, it is necessary to first calculate Find the integer N4 that is rounded down. If N4 is an odd number, then B4=(N4+1)π-β4; if N4 is an even number, B4=N4π+β4.

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