CN104931142A - Temperature compensating crystal type polarization interference apparatus - Google Patents

Abstract

The invention discloses a temperature compensation crystal polarization interference device. The polarization interference device consists of a polarizer (3), a main wave plate (5), a compensation wave plate (6), an analyzer (4), a photodetector (7), and a temperature sensor (8) placed in sequence along the optical path. ) and a signal processing module (9), its working principle and characteristics are: after the input light (1) passes through the polarizer (3), the angle between its vibration direction and the optical axis of the main wave plate (5) is 45°; then Through the main wave plate (5) and its corresponding compensation wave plate (6), the detector (7) converts the interference signal output by the analyzer (4) into an electrical signal; the signal processing module (9) according to the temperature sensor ( 8) The obtained temperature information softly compensates the electrical signal to obtain the polarization interference output (2). The invention simultaneously uses the compensating wave plate and the soft compensation based on temperature measurement to improve the temperature stability of the crystal polarization interference device.

Description

A Temperature Compensation Crystal Type Polarization Interference Device

technical field

The invention relates to the field of optical devices, in particular to a temperature compensation crystal polarization interference device.

Background technique

The traditional crystal-type polarization interference device is composed of a pair of polarizers and a crystal wave plate between them, and its interference output characteristics depend on the birefringence of the wave plate material, the thickness of the wave plate, and the relationship between the optical axis of the wave plate and the light-passing direction of the polarizer. angle. Since the thickness of the crystal wave plate and the birefringence difference are related to temperature, the output of this polarization interference device changes with the ambient temperature, which limits its performance and scope of application.

Improving the temperature stability of the optical system through automatic temperature control is a common method, but this method also needs to configure the feedback control system to make the optical device work within the initially set temperature range while detecting the temperature of the optical device. , the system for realizing precise temperature control is complex and costly. Using two crystal wave plates with complementary temperature characteristics to form a composite wave plate is a commonly used temperature compensation method in the field of crystal optics. One of the wave plates is the main wave plate and the other is the compensation wave plate. This method can make the composite wave plate have good temperature stability at a specific wavelength, but due to factors such as material dispersion and processing errors, when the composite wave plate is used in a larger wavelength and temperature range, its temperature stability is still Can not meet the requirements of high-precision applications. It can be seen that each of the above-mentioned methods to achieve high-precision temperature compensation has its own obvious disadvantages.

Contents of the invention

The object of the present invention is to provide a crystal-type polarization interference device and a temperature compensation method with high temperature stability.

The temperature compensation crystal type polarization interference device in the present invention includes a polarizer, a composite wave plate (including a main wave plate and a compensation wave plate), an analyzer, a photodetector, a temperature sensor and a signal processing module placed sequentially along the optical path, It is characterized in that: the input light becomes linearly polarized light through the polarizer, and the angle between its vibration direction and the optical axis of the main polarizer in the compound wave plate is 45°; the compound wave plate is composed of at least a main wave plate and a compensation wave plate , the length ratio of the main wave plate and the compensation wave plate and the orientation relationship of the optical axis (orthogonal or parallel) depend on their thermal expansion coefficient and thermo-optic coefficient; the temperature sensor monitors the temperature of the composite wave plate, and the signal processing module based on the temperature information The output signal of the photodetector is corrected again, that is, soft compensation.

The temperature compensation crystal-type polarization interference device proposed by the present invention overcomes the deficiency of the existing polarization interference device in terms of temperature stability, so that the temperature stability of the crystal-type polarization interference device can meet engineering requirements in a larger temperature and wavelength range. application requirements.

Description of drawings

Fig. 1 is a schematic diagram of a temperature compensation crystal type polarization interference device proposed by the present invention.

Fig. 2 is a schematic diagram of the working principle of temperature compensation in the temperature compensation crystal type polarization interference device proposed by the present invention.

Fig. 3 is a schematic diagram of the structure and principle of an embodiment of the temperature compensation crystal type polarization interference device in the present invention.

The meanings of the labels in the above figure are: 1 is the input light, 2 is the electrical signal output by polarization interference, 3 and 4 are the polarizer and analyzer respectively, 5 is the main wave plate, 6 is the compensation wave plate, 7, 11 and 12 are photodetectors, 8 is a temperature sensor, 9 is a signal processing module, and 10 is a polarization beam splitter.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of the polarization interference device proposed by the present invention. After the input light 1 is polarized by the polarizer 3, it passes through the composite wave plate (consisting of the main wave plate 5 and the compensating wave plate 6) and the analyzer 4 in turn, and the photoelectric The detector 7 converts it into an electrical signal, and the electrical signal and the output of the temperature sensor 8 are simultaneously sent to the signal processing module 9 for processing to generate the final polarization interference output signal 2 . Among them, the angle between the light transmission direction of the polarizer 3 and the optical axis of the main wave plate 5 is 45°, whether the optical axes of the main wave plate 5 and the compensation wave plate 6 are parallel or orthogonal depends on the characteristics of the two selected crystals . If the sign of the birefringence of the crystal material corresponding to the main wave plate 5 and the compensation wave plate 6 changes with temperature is opposite, then the optical axes of the main wave plate 5 and the compensation wave plate 6 are required to be parallel, and the _lengths L1 and L ₂ satisfies the following relationship:

(1)

Among them, Δ n ₁ and Δ n ₂ are the birefringence indices of the crystal material of the main wave plate and the compensation wave plate respectively, α ₁ and α ₂ are the linear expansion coefficients of the crystal material of the main wave plate and the compensation wave plate in the beam propagation direction . For example, when the main wave plate 5 and the compensating wave plate 6 are composed of YVO ₄ and LiNbO ₃ crystals respectively, only when the optical axes of the two are parallel can effective temperature compensation be realized. If the sign of the birefringence of the crystal material corresponding to the main wave plate 5 and the compensation wave plate 6 is the same with temperature, then the optical axes of the main wave plate 5 and the compensation wave plate 6 are required to be orthogonal, and the _lengths L1 and L2 satisfies the following relation _:

(2)

It should be noted that the compensation wave plate can also be composed of wave plates of two or more materials, and the determination of the length ratio relationship of the main wave plate is similar to that shown in formula (1) or (2).

In order to further improve the temperature stability of the crystal-type polarization interference device, a temperature sensor 8 is used to monitor the temperature of the composite wave plate in Fig. 1 . After the monitoring results are input into the signal processing module 9, the output signal of the detector 7 is soft compensated.

The present invention can effectively enhance the temperature stability of the polarization interference device by using the compensating wave plate and the method of implementing soft compensation after monitoring the temperature at the same time. The principle of temperature compensation can be explained by FIG. 2 .

Figure 2 shows the relationship between the output results of polarization interference and temperature variation under different configurations of the device shown in Figure 1 when the power and wavelength of the input light 1 are constant, where the abscissa represents temperature ( T ) and the ordinate represents Normalized polarization interference signal intensity ( I ). It should be noted that the variation trend of each curve in Figure 2 is only a qualitative description of the device in Figure 1 under different configurations, and does not represent the specific experimental results.

Curve a in FIG. 2 represents the variation trend of the intensity of the output signal of the detector 7 with temperature when the compensation wave plate 6 is not used in FIG. 1 . At this time, because the length and birefringence of the main wave plate are sensitive to temperature, the output signal of the detector 7 has a large slope. Since no compensation wave plate is used in this configuration, the result of the polarization interference device is very sensitive to temperature.

Curve b in Figure 2 represents the configuration shown in Figure 1, that is, the intensity of the detector 7 output signal varies with temperature when the compensation wave plate is included. It can be seen that the slope of its change is greatly reduced compared with curve a, but in the entire temperature range There are still large ups and downs.

In order to further suppress the fluctuation of the output signal of the detector 7 in the entire working temperature range, send it and the temperature signal output by the temperature sensor 8 to the signal processing module 9 for soft compensation. A feasible method is shown in Fig. 2, that is, the The fluctuation of curve b in the entire working temperature range is subdivided according to the measurement accuracy of the temperature sensor to obtain curve c, so that in the whole working temperature range, the output fluctuation of the system is very small, showing good temperature stability.

Fig. 3 is a schematic diagram of the structure and principle of an embodiment of the temperature compensation crystal type polarization interference device in the present invention. Compared with the polarization interference device shown in Figure 1, the analyzer 4 is replaced by a polarization beam splitter 10, and the two orthogonally polarized light beams emitted by the polarization beam splitter 10 are respectively received by detectors 11 and 12, and converted into electrical The signal is then input to the signal processing module 9 . Wherein, soft compensation is implemented after normalizing the signals output by the detectors 11 and 12, so as to avoid the influence on the polarization interference result when the power of the input light 1 fluctuates.

Relevant technical contents not mentioned in the above methods can be realized by adopting or referring to existing technologies.

Claims (2)

1. A temperature compensation crystal type polarization interference device, comprising a polarizer, a main wave plate, a compensation wave plate, a polarizer and a photodetector placed sequentially along the optical path, as well as a temperature sensor and a signal processing module, is characterized in that, At the same time, it includes a temperature soft compensation subsystem composed of a compensation wave plate, a temperature sensor and a signal processing module. 2. A temperature compensation method adopted in a temperature compensation crystal type polarization interference device, characterized in that, in the signal processing module, the polarization interference signal compensated by the compensation wave plate is processed according to the temperature information of the combined wave plate monitored by the temperature sensor Then perform soft compensation.