A laser wavelength measurement system based on phase difference between two interference signals

Abstract

The application discloses a laser wavelength measurement system based on phase difference between double interference signals and belongs to the technical field of optical fiber sensing. The system comprises a reference laser, an interferometer device, an optical path difference modulator, a photoelectric detector and a processing module. The application utilizes the inverse proportion between the phase and the wavelength size corresponding to two beams of light at a distance, respectively measures the phase difference corresponding to the reference light and the to-be-measured light, and calculates the wavelength of the to-be-measured light according to the ratio of the phase difference and the wavelength of the reference light. The application sets the optical path difference adjustment, amplifies the difference between the phase differences corresponding to two wavelengths of light, and realizes more accurate wavelength measurement.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a laser wavelength measurement system and method based on the phase difference of dual interference signals. Background Technology

[0002] Wavelength measurement has wide applications and is of great importance in many fields. In the field of optical communication, with the rapid development of fiber optic communication and the continuous increase in information volume, optical wavelength measurement technology has received unprecedented attention. Accurate measurement of optical wavelength is crucial to ensuring the stability and transmission efficiency of optical communication systems. In addition, wavelength measurement is also widely used in chemical engineering, medicine, papermaking, instrumentation, environmental protection, and many scientific research fields such as laser physics, spectroscopy, and astrophysics.

[0003] Interferometry is an important method for measuring optical wavelength. Existing interferometric devices often determine the wavelength by measuring the width of interference fringes, requiring the measured phase to be controlled at half a period, which is difficult to achieve in practice. Furthermore, the resolution depends heavily on the optical path difference control equipment, making high resolution challenging. This invention proposes a device with a certain resolution and simple operation, employing phase demodulation and an optical fiber path. It is innovative and reduces the impact of noise by using a secondary measurement that increases the signal amplitude, thus demonstrating practicality. Summary of the Invention

[0004] The purpose of this invention is to provide a laser wavelength measurement system based on the phase difference of dual interference signals, which provides a new approach to wavelength measurement.

[0005] The objective of this invention can be achieved through the following technical solutions:

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

[0007] A reference laser is emitted, and the laser to be tested enters the interferometer device sequentially.

[0008] An interferometer device is used to split and couple a laser beam signal to generate two interference signals. The interferometer device is equipped with two interferometers, and each interferometer is equipped with two interference arms. The two interferometers share one interference arm, which is a shared arm. The other arms are a sensing arm and a reference arm, respectively.

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

[0010] The photodetector is connected to two interferometers via couplers, converting optical interference signals into electrical signals.

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

[0012] As a further aspect of the present invention, the measurement method of the measurement system is as follows:

[0013] Step 1: Set the value of the optical path difference L0 between the sensing arm and the reference arm.

[0014] Step 2: Light with wavelength λ′ generated by the reference laser enters the system, and interference is generated in the laser input optical path, resulting in two interference signals. The two interference signals are converted into two electrical signals by a photodetector, and the two electrical signals are demodulated by phase difference. The phase difference B1 between the two signals is obtained based on the demodulation result β1.

[0015] Step 3: Switch the optical switch to allow the light to be measured, λ, to enter the system. Calculate the phase difference B2 between the two signals based on the demodulation result β2, and then use the formula... The initial measurement value λ of the wavelength to be measured is obtained. A ;

[0016] Step four: Adjust and increase the optical path difference between the sensing arm and the reference arm to L1, and control the optical switch to allow the reference light and the light under test to enter the optical path sequentially. Based on their corresponding demodulation results β3 and β4, obtain the phase difference B3 between the two signals of the reference light and the phase difference B4 between the two signals of the light under test. Then, use the formula... Find the wavelength λ to be measured B .

[0017] As a further aspect of the present invention, when setting the initial optical path difference L0 between the sensing arm and the reference arm in step one, a wavelength measurement range is first artificially defined so that the initial measurement of the reference light phase difference B1 and the measurement range of the measured light phase difference B2 can simultaneously fall between (nπ, (n+1)π), where n and the optical path difference are numerically equal to... Rounding down.

[0018] As a further aspect of the present invention, when demodulating the demodulation result β1 corresponding to B1 in step three, 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 Rounding down, when N1 is odd, B1 = (N1+1)π-β1, and when N1 is even, B1 = N1π+β1; similarly, B2 is derived. Within the limited wavelength measurement range, the value of N2 is the same as that of N1.

[0019] As a further aspect of the present invention, in step four, when the demodulation result β3 corresponding to B3 is demodulated, the number of half-cycles N3 contained therein needs to be determined based on the measured L1, and its value is equal to Rounding down, if N3 is odd, then B3 = (N3+1)π - β3; if N3 is even, then B3 = N3π + β3. When demodulating the 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 odd, then B4 = (N4+1)π - β4. If N4 is even, then B4 = N4π + β4.

[0020] The beneficial effects of this invention are:

[0021] This invention provides a method for determining the wavelength of the light under test by demodulating the phase difference of the interference signal and determining the number of half-cycles contained in the phase based on the optical path difference between the two interference arms. This invention innovatively uses a phase demodulation method to determine the wavelength of the light under test and proposes a method to increase the change in optical path difference to improve measurement accuracy. This method plays a positive role in improving the sensitivity of optical wavelength measurement and enables high-precision measurement of optical wavelength. Attached Figure Description

[0022] The invention will now be further described with reference to the accompanying drawings.

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

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

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

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] Please see Figure 1 The present invention is an optical wavelength measurement system based on the phase difference between two 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 tested enter the same device one after the other, and the structure adopts a double Mach-Zehnder interferometer structure.

[0030] An interferometer device is used to split and couple the beam signal emitted by a laser. Two interferometers are provided, labeled as interferometer 1 and interferometer 2, and each interferometer is provided with two interferometer arms. The two interferometers share one interferometer arm, which is a shared arm.

[0031] An optical path difference modulator is used to change the optical path of the sensing arm in order to obtain the phase difference under different optical paths.

[0032] In one embodiment of the present invention, the optical path difference modulator employs a phase modulator, which acts on the shared arm so that both phase inputs are a series of data, thereby realizing the elliptic fitting demodulation algorithm.

[0033] On the other hand, it also serves as a device for controlling changes in optical path difference.

[0034] A photodetector and an optical path are used to connect the optical signal and convert it into an electrical signal, which facilitates further demodulation.

[0035] The two photodetectors are connected to two interferometers respectively via optical couplers.

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

[0037] The following is combined with Figure 1 Figure 2 The measurement method of the optical wavelength measurement system based on the phase difference of dual interference signals according to the present invention is described in detail. The measurement method includes the following steps:

[0038] Step 1: Use a displacement device 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 μm.

[0039] Step 2: The reference laser and the laser under test generate two optical signals. The reference light with wavelength λ' = 1550.12nm is allowed to enter the system through an optical switch. At the same time, the light reaches the photodetector from the sensing arm and the shared arm, and the shared arm and the reference arm, respectively, generating two interference signals.

[0040] Step 3: Apply a sinusoidal signal to the phase modulator of the shared arm, introducing a shared 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 four: The two interference signals are converted into two electrical signals using a photodetector. The processing module demodulates the phase difference of these two electrical signals, and the phase difference B1 corresponding to the reference light is obtained based on the demodulation result β1. Then, the input light is switched to the test light with a wavelength λ = 1550.22 nm, and the phase difference B2 corresponding to the test light is obtained based on the demodulation result β2. The unknown wavelength is calculated based on the two phase differences between the reference light and the test light, and the known wavelength of one of the beams. The formula is as follows: The initial measured wavelength value λ was obtained. A .

[0042] Step 5: Apply voltage to the phase modulator on the sensing arm to increase the optical path to L1 = 1.000 mm, and control the optical switch to allow the reference light and the light under test to enter the optical path sequentially. Calculate the phase difference B3 between the two paths of the reference light and the phase difference B4 between the two paths of the light under test based on their corresponding demodulation results β3 and β4. Calculate the unknown wavelength λ to be measured based on the two phase differences measured from the reference light and the light under test, and the known wavelength of the reference light. B The formula needs to be used. 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, while increasing the phase difference by varying the amplification arm length increases the phase difference, the phase noise increases, but this effect is not noticeable, while the influence of the constant environmental noise on the signal is reduced.)

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

[0044] Example 2

[0045] Based on Example 1, in step one, regarding the control of the arm length difference before the initial measurement, the sensing arm is adjusted so that the change in the reference wavelength phase difference reaches... Left and right, (n is a natural number, and its relationship with the optical path difference is numerically equal to) (Rounding down) ensures that the phase difference of the light being measured will not exceed (0, π). This establishes the measurable wavelength range, because the phase detection range is within (nπ, (n+1)π), and the half-cycle contained in the phase difference of the measured wavelength must be the same as the reference phase difference. The lower limit of measurement is artificially established, and the upper limit is λ. d Then the upper and lower limits of the optical path difference corresponding to the half-cycle number n are (nλ) d / 2,(n+1)λ c / 2), In this embodiment, the wavelength measurement range is artificially defined as (1500nm, 1600nm). Then, the reference signal and the signal under test contain the same half-cycle n<=14. The optical path difference range needs to be controlled between (800n, 750n+750) in nm.

[0046] Example 3

[0047] Based on Example 1, in step four, to obtain B1 by demodulating the demodulation result β1 corresponding to B1, it is necessary to calculate the number of half-cycles N1 contained in B1 based on the measured initial optical path difference L0, which is numerically equal to Rounding down, when N1 is odd, B1 = (N1+1)π - β1; when N1 is even, B1 = N1π + β1, N2 = N1. Similarly, B2 can be derived. (Combined...) Figure 2 Let's look at how to adjust the optical path difference. In terms of adjustment methods, a step-by-step adjustment method can be used, that is, segmented modulation, adjusting a small amount each time. Whenever the phase reverses, it means that a cycle has been exceeded and needs to be recorded to compensate back. Continuous adjustment can also be used. If there is some modulation experience, the method of adjusting all at once by directly referring to past experience can be used.

[0048] Depend on Figure 2 When L0 = 9.7 μm, N1 = N2 = 12, B1 = 12π + 1.6184 = 39.3175 rad, B2 = 12π + 1.6159 = 39.3150 rad (in this embodiment, four decimal places are used). Therefore, λ A = 1550.2186nm (the actual calculated result deviates from 1550.22nm by approximately 0.0014nm, a deviation of 0.000092%). Ignoring noise, λ A The results still deviate from the true values ​​because the experimental conditions limit the number of decimal places to four. Information beyond the fourth decimal place in B1 and B2 is omitted.

[0049] Example 4

[0050] Based on Example 1, in step five, regarding the demodulation of B3 and B4 from the demodulation results β3 and β4 corresponding to B3, it is necessary to first calculate the approximate value of B3 and its contained half-period N3 using the formula based on the secondary optical path difference L1, then reconstruct the true B3 based on β3, and finally calculate... Find the positive integer N4 that is rounded down. If N4 is odd, then B4 = (N4 + 1)π - β4. If N is even, then 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 increased to 1.000mm, β3 = 0.6996rad and β4 = 0.4381rad are measured. N3 = N4 = 1290 is calculated, therefore B3 = N3π + β3 = 4053.3541rad and B4 = N4π + β4 = 4053.0926rad. The second measurement wavelength... (The actual calculation result has a deviation of approximately 0.00001nm, or 0.00000075%, from 1500.22nm). Since L1 (1mm) in this embodiment is approximately 103 times L0 (9.7um), the phase differences (B3, B4) corresponding to the second iteration are approximately 103 times the phase differences (B1, B2) corresponding to the first iteration, and... Figure 2 In comparison, when the measured values ​​are also retained to four decimal places, the number of effective bits retained in the phase difference signal increases from 6 bits (B1 = 39.3175 rad, B2 = 39.3150 rad) to 8 bits (B3 = 4053.3541 rad, B4 = 4053.0926 rad), reducing the percentage of deviation and thus improving the measurement accuracy of the wavelength. It should be noted that this experiment is mainly affected by environmental noise, with less influence from phase noise. While increasing the phase difference by varying the amplification arm length, the environmental noise remains relatively constant, while the signal is enhanced, increasing the signal-to-noise ratio and thus making the measurement more accurate.

[0052] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A laser wavelength measurement system based on the phase difference between two interference signals, characterized in that, include: Reference laser, optical switch, interferometer device, optical path difference modulator, photodetector and processing module; A reference laser is emitted, and the laser to be tested enters the interferometer device sequentially. An interferometer device is used to split and couple a laser beam signal to generate two interference signals. The interferometer device is equipped with two interferometers, and each interferometer is equipped with two interference arms. The two interferometers share one interference arm, which is a shared arm. The other arms are a sensing arm and a reference arm, respectively. Optical path difference modulator, used to change the optical path of the sensing arm; The photodetector is connected to two interferometers via couplers, converting optical interference signals into electrical signals. The processing module is used to convert the two electrical signals into digital signals and demodulate the phase difference between the two signals, i.e. the phase difference between the interference signals. The processing module is connected to two photodetectors. The measurement method of this measurement system is as follows: Step 1: Set the value of the optical path difference L0 between the sensing arm and the reference arm. Step 2, the reference laser generation wavelength is When light enters the system, interference occurs in the laser input optical path, resulting in two interference signals. These two interference signals are converted into two electrical signals by a photodetector. Phase difference demodulation is then performed on these two electrical signals, and the results are analyzed based on the demodulation parameters. The phase difference B1 between the two signals is obtained; Step 3: Switch the optical switch to allow the light to be measured (λ) to enter the system, and then analyze the demodulation results. The phase difference B2 between the two signals is obtained, according to the formula. The initial measurement value of the wavelength to be measured was obtained. ; Step four: Adjust and increase the optical path difference between the sensing arm and the reference arm to L1, and control the optical switch to allow the reference light and the light under test to enter the optical path sequentially, based on their respective demodulation results. The phase difference B3 between the two signals of the reference light and the phase difference B4 between the two signals of the test light are obtained, according to the formula. Determine the wavelength to be measured ; In step one, when setting the initial optical path difference L0 between the sensing arm and the reference arm, a wavelength measurement range is first defined so that the initial measurement of the reference light phase difference B1 and the measurement range of the target light phase difference B2 can simultaneously fall between (nπ, (n+1)π), where n and the optical path difference are numerically equal to... Rounding down; In step three, the demodulation result corresponding to B1 is obtained. At the same time, it is also necessary to determine the number of half-cycles N1 contained in B1 based on the initial optical path difference L0, which is numerically equal to The integer part, when N1 is odd. π- When N1 is even, B1 = ; Similarly, it can be concluded that within the limited wavelength measurement range, the value of N2 is the same as that of N1; In step four, when the demodulation result corresponding to B3 is obtained... At that time, the number of half-cycles N3 contained in L1 needs to be determined based on the measured L1, and its value is equal to If N3 is an odd number, then... If N3 is even, then ; When the demodulation result corresponding to B4 is obtained... To obtain B4, you need to first calculate... Find its integer value when rounded down. ,if If it is an odd number, then π- If N4 is even, .

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