CN205192936U - Dual optical path polarimeter - Google Patents

Abstract

The utility model relates to a double-light-path polarimeter, which comprises a light path part and a circuit part, wherein a light beam emitted by a frequency-adjustable semiconductor laser device is divided into two light beams after passing through a polarizer, a depolarization beam splitter prism and a depolarization reflector in sequence, and one light beam enters a photoelectric converter through a sample tube and an analyzer; the other light beam enters the photoelectric converter through the depolarization reflector and the analyzer, a high-frequency signal generated by the signal generating circuit is loaded on the frequency-adjustable semiconductor laser, a signal is sent out to drive the stepping motor, and the stepping motor drives the polarizer to rotate; the electric signal is input into the analog-digital conversion unit in the microprocessor unit after passing through the preamplifier circuit, the frequency selecting circuit, the envelope detection circuit and the amplitude limiting clamping circuit in sequence, the converted analog signal is output in a digital signal form and stored in the microprocessor data storage unit, and the digital signal in the storage unit is processed by the microprocessor data processing unit and then output to the digital display unit. The optical zero point can be accurately found out, and the measurement precision of the polarimeter is improved.

Description

Dual optical path polarimeter

technical field

The utility model relates to a detection polarimeter, in particular to a laser frequency-modulated dual-optical-path polarimeter based on a center-of-gravity algorithm and a measuring method.

Background technique

When linearly polarized light passes through some optically active compounds or their solutions, the phenomenon that the vibration plane will deflect around the optical axis is called optical rotation, and the angle of rotation is called optical rotation. Optical rotation analysis (abbreviated as optical rotation method) uses linearly polarized light to cause optical rotation when passing through a solution or liquid containing chemically active substances, so that the vibration plane of the passing polarized light rotates to the left or right. Therefore, under certain conditions, the optical rotation of certain compounds can be analyzed by detecting the direction and degree of vibration plane rotation after linearly polarized light passes through certain substances, or the impurities, purity and content of compounds can be detected. Instruments used to measure optical rotation are called polarimeters. Optical polarimetry is mostly used to determine the concentration of sugar. In recent years, optical polarimetry has also been gradually used in pharmaceutical, food processing, chemical and biochemical analysis and other fields.

According to Biot's theorem, the optical rotation of a substance is related to the temperature of the substance and the wavelength of linearly polarized light. The optical rotation of some substances increases with temperature, such as quartz. However, substances such as sucrose decrease with increasing temperature. In addition, the wavelength of linearly polarized light is different, and the corresponding optical rotation is also different.

The optical rotation a of the optically active quality (the angle at which the vibration plane of the linearly polarized light passes through the material and rotates along the propagation direction) is proportional to the volume percentage concentration c of the optically active substance solution and the length 1 of the solution through which the polarized light passes, a=kcl(1), Where c is g/100ml, and 1 is mm.

The schematic diagram of the structure and principle of a traditional polarimeter is shown in Figure 1. A sodium lamp is used as the light source 1, and a beam of relatively simple parallel light can be obtained after passing through the aperture diaphragm 2, the objective lens 3, and the filter 4, as shown in Figure 1. As shown, the parallel light becomes linearly polarized light after passing through the polarizer (I) 5, and its vibration plane is 00 as shown in Fig. 2(a). When the polarized light passes through the Faraday coil 6, the vibration of the linearly polarized light is The plane produces a 50Hz β angle reciprocating swing as shown in Figure 2 (b). The light passes through the analyzer (II) 8 and is projected onto the photoelectric converter 9 to generate alternating electrical signals. When passing through the sample tube 7 with the sample The vibration plane of polarized light is rotated by α ₁ degree as shown in Fig. 2(c). After the instrument display is balanced, the polarizer 5 is reversely rotated by α ₁ degree to compensate the optical rotation of the sample, as shown in Fig. 2(d). The photoelectric converter 9 receives The signal of the signal passes through the preamplifier 10, the automatic high-voltage circuit 11 and then outputs through the frequency selective amplifier 12 and the power amplifier 13 to drive the servo motor 14.

Figure 3 is a schematic diagram of the working principle of the Faraday coil in the prior art. As shown in Figure 3, the instrument takes the time when the optical axes of the two polarizers 5 and 8 are orthogonal (ie OO⊥PP) as the optical zero point, and no polarizer is placed in the sample tube. For optically active substances, α=0o at this time. The Faraday coil 6 produces a β-angle swing with a frequency of 50Hz (Fig. 3(a)), and a 100Hz electrical signal is obtained in the photoelectric converter (Fig. 3(d)). When the sample tube is placed with α ₁ degree or α ₂ The photoelectric converter gets a 50Hz electrical signal (Fig. 3(b), (c)) when the sample is in the same degree, but their phases are just opposite (Fig. 3(e), Fig. 3(f)). Therefore, a servo motor whose operating frequency is 50 Hz can be rotated. The servo motor 14 rotates the polarizer 5 through α (α=α ₁ or α=α ₂ ) through the worm gear 15, and the instrument returns to the optical zero point. Under the control of the 100Hz signal, the servo motor 14 reappears the balance indication.

In summary, this method of measuring optical rotation uses Faraday coils to modulate optical signals, but Faraday coils have high operating voltage, large power consumption, large volume, and the modulation frequency is 50Hz, which is low in frequency and is susceptible to power frequency interference. Seriously affect the measurement accuracy. In addition, the light source used in this method is a sodium lamp, which consumes a lot of power and is easy to age.

Contents of the invention

The utility model is aimed at the problems that the traditional polarimeter consumes a lot of power and the measurement accuracy is easily disturbed. It eliminates the unstable influence of the light source, realizes the function of real-time zero adjustment of the instrument, and realizes fully automatic digital control, which greatly reduces the error and improves the accuracy.

The technical scheme of the utility model is: a dual optical path polarimeter, including an optical path part and a circuit part. Composed of a polarizer and a photoelectric converter, the beam emitted by the frequency-tunable semiconductor laser passes through a polarizer, a depolarizing beam splitter, and a depolarizing mirror in turn, and then is divided into two beams, and one beam enters the photoelectric converter through a sample tube and an analyzer ; The other light beam enters the photoelectric converter through the depolarizing mirror and the analyzer, and the photoelectric converter is connected to the circuit part. circuit, a microprocessor unit and a stepping motor; the microprocessor unit includes a microprocessor analog-to-digital conversion unit, a microprocessor data storage unit, a microprocessor data processing unit, and a microprocessor digital display unit; the signal generation The high-frequency signal generated by the circuit is loaded on the frequency-tunable semiconductor laser, and a driving signal is sent to the stepping motor, and the stepping motor is connected to the polarizer to drive the rotation of the polarizer; Amplifying circuit, frequency selection circuit, envelope detection circuit, limiter clamping circuit are output to the analog-to-digital conversion unit in the microprocessor unit, and the converted analog signal is output and stored in the microprocessor data storage unit in the form of digital signal The microprocessor data processing unit processes the digital signal in the storage unit and outputs the resulting signal to the digital display unit.

The beneficial effect of the utility model is that: the dual-optical-path polarimeter of the utility model uses a depolarization beam-splitting prism to construct a dual-optical-path structure, which can eliminate the influence of instability of the light source, realize the function of real-time zero adjustment, and complete the measurement of the optical rotation angle. Small size, low cost, low power consumption, etc.; use the center of gravity algorithm to realize fully automatic digitization and greatly improve the measurement accuracy.

Description of drawings

Fig. 1 is the structural principle schematic diagram of prior art polarimeter;

Fig. 2 is the vibration situation of prior art polarized light

Fig. 3 is the curved schematic diagram of the working principle of the Faraday coil in the prior art;

Fig. 4 is a schematic diagram of the curve of the double optical path Malius' law;

Fig. 5 is a functional block diagram of the dual optical path polarimeter of the present invention.

detailed description

As shown in Figure 5, a polarimeter with two optical paths includes an optical path part and a circuit part, and the optical path part successively includes a frequency-tunable semiconductor laser light source 21, a polarizer 22, a depolarizing beamsplitter prism 23, a depolarizing mirror 24, and a sample tube 25 and large diameter analyzer 26. The light beam sent by the frequency-tunable semiconductor laser 21 passes through the polarizer 22, the depolarization beam splitter 23, and the depolarization reflector 24 successively and is divided into two beams, one beam passes through the sample tube 25, and the analyzer 26 enters the photoelectric converter A27; The beam enters the photoelectric converter B28 through the depolarizing mirror 24 and the analyzer 26, and the circuit part includes a photoelectric converter A27 and a photoelectric converter B28, a preamplifier circuit 29, a frequency selection circuit 30, an envelope detection circuit 31, Limiting and clamping circuit 32 , microprocessor unit 33 , stepping motor 44 , and signal generating circuit 35 . The microprocessor unit 33 comprises a microprocessor analog-to-digital conversion unit, a microprocessor data storage unit, and a microprocessor data processing unit; the high-frequency signal generated by the signal generation circuit 35 is loaded on the frequency-tunable semiconductor laser 21, and simultaneously moves to the stepping The motor 34 sends a drive signal, and the stepper motor 34 is connected to the polarizer 22 to drive the polarizer 22 to rotate; the electrical signal of the photoelectric conversion passes through the preamplifier circuit 29, the frequency selection circuit 30, the envelope detection circuit 31, and the limiter clamp successively. After the bit circuit 32 is input to the microprocessor analog-to-digital conversion unit in the microprocessor unit 33, after the microprocessor analog-to-digital conversion unit converts the analog signal into a digital signal, it is stored in the microprocessor data storage unit, and the microprocessor data The processing unit processes the signal stored in the storage unit and outputs the result to the digital display unit for display.

The frequency-tunable semiconductor laser 21 is selected to replace the sodium lamp light source, and the signal generating circuit 35 generates a square wave signal of high frequency f, which is loaded on the frequency-tunable semiconductor laser 21, and the output power of the laser can be adjusted. After the light with frequency f passes through the polarizer 22, it becomes linearly polarized light, and the linearly polarized light is divided into two beams of light after passing through the depolarizing beam splitter 23, and one beam of light is directly incident on the large-diameter analyzer after passing through the depolarizing mirror 24 26 , another beam of light rotates through the optically active substance in the sample tube 25 , and then passes through the analyzer 26 with a large aperture. The two beams of polarized light are respectively received by the photoelectric converter A27 and the photoelectric converter B28 through the large-aperture analyzer 26 . The frequency of the linearly polarized light after passing through the object to be measured and the polarizer 26 remains unchanged, so the photoelectric converter A27 and the photoelectric converter B28 convert the two beams of optical signals with a frequency of f into two sets of electrical signals with a frequency of f. The electrical signals are respectively input into the preamplifier circuit 29 in parallel, and the preamplifier unit 29 is used to amplify the electrical signals input from the photoelectric converter A27 and the photoelectric converter B28, amplify the electrical signal to drive the frequency selection circuit 30, and the frequency selection circuit 30 is used for Select the signal with frequency f and filter out other frequency signals to remove noise interference. After the signal passes through the envelope detection circuit 31 and the limiter clamp circuit 32, it is input to the microprocessor unit 33, and the microprocessor analog-to-digital conversion unit is used to convert the analog signal from the limiter clamp circuit 32 into a digital signal, and Two sets of signals are recorded by the microprocessor digital memory unit. Then the signal generating circuit 35 sends out a signal to drive the stepping motor 34 and drive the polarizer 22 to rotate. Every time the stepper motor 34 rotates one step, the polarization angles of the two groups of optical signals with a frequency of f will change with the angle of the polarizer 22, causing the amplitude of the optical signals passing through the large-diameter polarizer 26 to change. After photoelectric conversion, pre-amplification, frequency selection amplification, and analog-to-digital conversion, the real-time signals of the two beams of light are recorded by the microprocessor data storage unit, and stored in two groups of data. After the stepping motor 34 has turned one circle, the microprocessor carries out data processing to the recorded two groups of signals, firstly performing FFT fast Fourier decomposition, then through digital filtering, and finally obtaining two signals by envelope detection. The curve of the amplitude of the signal with frequency f and the rotation angle of the stepper motor. According to Marius' law I=I ₀ cos ² α, the curve should theoretically be two curves as shown in Figure 4. And use the center of gravity algorithm to calculate the angle values corresponding to the optical zero points on the two curves respectively. The difference between the two angles is the optical rotation angle of the substance. Then compare the angle with the known international standard through the data processing unit to calculate the concentration of the solution. Finally, the output results are displayed numerically.

The optical signal is modulated by the high-frequency signal generated by the signal generating circuit in order to obtain a high-frequency modulated signal and avoid power frequency interference. In the traditional polarimeter, the servo motor is used to drive the polarizer to automatically rotate to the optical zero position principle, but in the utility model, the signal generating circuit generates a signal to drive the stepping motor 14 to drive the polarizer 2 to rotate for one circle, and then the micro The processor processes the recorded two sets of signal data to obtain two curves about the light intensity and the rotation angle of the stepping motor, and then uses the center of gravity algorithm to calculate the optical rotation of the substance from the curves. Using the utility model to calculate the optical rotation angle, compared with the traditional technology, can eliminate the influence of motor return error and the like, accurately find out the optical zero point, and greatly improve the precision of the polarimeter. Moreover, the utility model adopts the depolarization beam splitter 4 to form a dual optical path structure, eliminates the influence of light source instability, realizes the real-time zeroing function, effectively avoids the zero point drift problem caused by aging factors such as light source or equipment, and greatly improves the measurement precision.

The method for measuring the optical rotation angle of an optically active substance, the steps are as follows: 1) Adjust the balance of the optical path so that the polarizer 22 and the large-diameter analyzer 26 are orthogonal and fixed; 2) After adding the optically active substance to the sample tube 25, the light passes through The optical path part forms a double optical path, and the two optical paths respectively reach the photoelectric converter A27 and the photoelectric converter B28 through the large-diameter polarizer 26, and two high-frequency AC signals are output from the two photoelectric converters; 3) two groups The AC signal is input to the analog-to-digital conversion unit of the microprocessor unit 33 after being amplified by the preamplifier circuit 29, frequency-selected by the frequency-selection circuit 30, envelope detection 31, and limiter clamp 32, and input to the microprocessor after the analog-to-digital conversion data storage unit. 4) The stepper motor 34 drives the polarizer 22 to rotate, the intensity of the AC signal of the photoelectric converter changes, and the microprocessor records each signal. The two curves are obtained by FFT and envelope detection, and finally the optical zero point of the two curves is calculated by the center of gravity algorithm, and the difference is obtained from the optical rotation angle to obtain the solution concentration.

Claims (1)

1. a kind of double optical path polarimeter, comprise optical path part and circuit part, it is characterized in that: described optical path part is made of frequency-tunable semiconductor laser (21), polarizer (22), depolarization beam splitter prism (23), depolarization reflector (24), sample tube (25), analyzer (26) and photoelectric converter, the light beam sent by the frequency-tunable semiconductor laser (21) passes through polarizer (22), depolarization beam splitter ( 23), the depolarizing mirror (24) is divided into two light beams, and one beam enters the photoelectric converter through the sample tube (25) and the analyzer (26); the other beam passes through the depolarizing mirror (24), the analyzer (26) Enter the photoelectric converter, the photoelectric converter is connected to the circuit part, and the circuit part is composed of a signal generation circuit (35), a preamplifier circuit (29), a frequency selection circuit (30), an envelope detection circuit (31), a limiter Clamping circuit (32), microprocessor unit (33) and stepper motor (34) form; Microprocessor unit (33) comprises microprocessor analog-to-digital conversion unit, microprocessor data storage unit, microprocessor data Processing unit, microprocessor digital display unit; The high-frequency signal that described signal generating circuit (35) produces is loaded on the frequency-tunable semiconductor laser (21), and sends drive signal to stepping motor (34), and stepping motor ( 34) Connect the polarizer (22) to drive the polarizer (22) to rotate; the electric signal of the photoelectric conversion passes through the preamplifier circuit (29), the frequency selection circuit (30), the envelope detection circuit ( 31), the limiter clamp circuit (32) is input to the microprocessor analog-to-digital conversion unit in the microprocessor unit (33), and the converted analog signal is output and stored in the microprocessor data storage unit in the form of a digital signal The microprocessor data processing unit processes the digital signal in the storage unit and outputs the resulting signal to the digital display unit.