CN103185665A - Method for measuring optical axis of birefringence element - Google Patents

Abstract

The invention provides a method for measuring the optical axis of a birefringent element, comprising the following steps: a semi-external cavity laser continuously outputs laser light in a single longitudinal mode; adjusting the polarizer so that the polarization direction of the polarizer is the same as that of the half The initial polarization direction of the output laser of the external cavity laser is vertical; the birefringence is arranged between the output cavity mirror and the external cavity plane mirror, and the birefringent element is on the optical path along the output laser of the half external cavity laser There are two relatively parallel planes, and the laser is incident along the direction perpendicular to the two planes; the birefringent element is rotated with the axis parallel to the output laser direction of the semi-external cavity laser as the rotation axis, and drives the The external cavity plane reflector reciprocates along the output laser direction; the birefringent element is continuously rotated, so that the display device appears in an extinction state, and the optical axis of the birefringent element is obtained.

Description

Measuring Method of Optical Axis of Birefringent Element

technical field

The invention relates to a method for measuring the optical axis of a birefringence element.

Background technique

Many materials, such as biological tissues, optical fibers, liquid crystals, and wave plates, exhibit strong optical birefringence. For these materials, the orientation of the optical axis affects the properties of the material. For some instrument systems with high requirements, there is also an urgent need to accurately measure the optical axis.

Many methods have been applied to the measurement of the optical axis, such as polarization-sensitive optical coherence tomography, etc. However, the instruments based on these measurement methods are complex in structure, expensive in price, and low in measurement accuracy, so they cannot be used in high-precision fields.

Contents of the invention

To sum up, it is indeed necessary to provide a method for measuring the optical axis of a birefringent element with low price and high precision.

A method for measuring the optical axis of a birefringent element, comprising the following steps: Step S10, providing a measuring device for the optical axis of a birefringent element, including half of an external cavity laser, a laser feedback unit, and a polarization detection system; the half of the external cavity laser It includes a high anti-cavity mirror, a gain tube, an anti-reflection window, and an output cavity mirror arranged along the output laser light path of the half-external cavity laser; the laser feedback unit includes an external cavity plane reflector, and the external cavity plane reflector is set On the optical path of the laser light emitted from the output cavity mirror, and set apart from the output cavity mirror; the polarization state detection system includes a polarizer, a photodetector and a display device along the reflection from the external cavity plane The laser light emitted by the mirror is set at intervals in sequence, the photodetector receives the laser light emitted from the polarizer to sense the change of the laser intensity, and the display device displays the change of the laser intensity; step S11, the semi-external cavity laser continuously outputs the laser light , the mode is a single longitudinal mode; step S12, adjusting the polarizer so that the polarization direction of the polarizer is perpendicular to the initial polarization direction of the output laser light of the semi-external cavity laser; step S13, setting the birefringent element to be measured in Between the output cavity mirror and the external cavity plane mirror, the birefringent element has two relatively parallel planes along the optical path of the semi-external cavity laser output laser light, and the laser light is perpendicular to the two planes incident in the direction of two planes; step S14, rotating the birefringent element with the axis parallel to the output laser direction of the semi-external cavity laser as the rotation axis, and driving the external cavity plane mirror to reciprocate along the output laser direction, so that the The display device appears in an extinction state, and the optical axis of the birefringent element is the same as the initial polarization direction of the output laser light of the semi-external cavity laser, and the optical axis of the birefringent element is obtained.

The method for measuring the optical axis of the birefringent element provided by the present invention is based on the principle of laser feedback and polarization hopping, by rotating the birefringent element, using the optical axis of the birefringent element and the polarization direction of the laser output from the semi-external cavity laser Simultaneously, the extinction phenomenon is generated to obtain the optical axis of the birefringent element. The measuring device has simple structure, low cost and higher measurement accuracy, so it has broader application prospects.

Description of drawings

Fig. 1 is a measurement device for the optical axis of a birefringent element according to an embodiment of the present invention.

Fig. 2 is the laser intensity variation curve during the rotation process of the birefringent element.

Fig. 3 is the laser intensity change curve when the optical axis of the birefringent element is consistent with the initial polarization direction of the laser output from the semiconductor laser.

Description of main component symbols

High mirror 1 gain tube 2 AR Windows 3 output cavity mirror 4 birefringent element 5 External Cavity Plane Mirror 6 External Cavity Piezoelectric Ceramics 7 Polarizer 8 Photodetector 9 display device 10 half external cavity laser 20 laser feedback unit 30 Polarization detection system 40

The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. For the convenience of description, the present invention first describes the measuring device for the optical axis of the birefringent element.

As shown in FIG. 1 , the first embodiment of the present invention provides a device for measuring the optical axis of a birefringent element. The device includes half of an external cavity laser 20 , a laser feedback unit 30 and a polarization detection system 40 .

The semi-external-cavity laser 20 is used to output laser light to form a laser optical path. The semi-external-cavity laser 20 is used as both a light source and a sensor to form laser feedback. The semi-external-cavity laser 20 is a semi-external-cavity structure. The laser output from the external cavity laser 20 is polarized light of a single longitudinal mode. The laser type can be a gas laser, a semiconductor laser, or a solid-state laser, etc. The semi-external cavity laser 20 includes a high reflection cavity mirror 1, a gain tube 2, an anti-reflection window 3 and an output cavity mirror 4, the high reflection cavity mirror 1, a gain tube 2, an anti-reflection window 3, an output cavity mirror 4 are arranged sequentially and coaxially along the axis of the output laser light. The high reflection cavity mirror 1 is fixedly connected to the end of the gain tube 2 away from the output cavity mirror 4 , and the antireflection window 3 is fixedly connected to the end of the gain tube 2 close to the output cavity mirror 4 . Both the high reflection cavity mirror 1 and the output cavity mirror 4 are coated with a high reflection film of laser wavelength (the reflectivity is above 98%), and the reflectivity of the former is higher than that of the latter. The anti-reflection window 3 is coated with an anti-reflection film (not shown) for the laser wavelength. In this embodiment, the laser is a helium-neon laser, the gain tube 2 is filled with He-Ne gas, the gas ratio is 9:1, the Ne isotope ratio is: Ne ²⁰ :Ne ²² =1:1, the height of the laser The reflectivity of the anti-cavity mirror 1 and the output cavity mirror 4 are 99.8% and 98.8% respectively.

The laser feedback unit 30 includes an external cavity plane mirror 6 . The external cavity plane reflector 6 is arranged on the output optical path of the half external cavity laser 20 , and is spaced apart from the output cavity mirror 4 to form a space for accommodating the sample to be tested. The external cavity plane reflector 6 is used to reflect the laser output from the half external cavity laser 20 back to the half external cavity laser 20 to form laser feedback. The laser feedback unit 30 may further include an external cavity piezoelectric ceramic 7, the external cavity piezoelectric ceramic 7 is connected with the external cavity plane reflector 6, and is used to drive the external cavity plane reflector 6 along the The direction of the output laser axis reciprocates. It can be understood that the external cavity piezoelectric ceramic 7 can also be replaced by other micro-movement elements to drive the external cavity plane mirror 6 to reciprocate.

The polarization state detection system 40 is used to determine the polarization state of the laser incident into the polarization state detection system 40 , and includes a polarizer 8 , a photodetector 9 and a display device 10 . The polarizer 8 and the photodetector 9 are arranged along the axis where the semi-external-cavity laser 20 outputs laser light. Specifically, the polarizer 8 is arranged on the optical path of the laser light emitted by the semi-external cavity laser 20 from the external cavity plane reflector, and is spaced apart from the external cavity plane reflector 6 to receive the external cavity plane reflector 6. Laser light transmitted by mirror 6. The photodetector 9 is arranged on the optical path of the laser light transmitted from the polarizer 8 to receive the laser light transmitted from the polarizer 8 and convert the intensity of the laser light into an electrical signal and input it to the display device 10 . The display device 10 can display the laser intensity in the form of a waveform. In this embodiment, the display device 10 is an oscilloscope.

The present invention further provides a method for measuring a birefringent element using the measuring device for the optical axis of the birefringent element, which specifically includes the following steps:

Step S11, the semi-external cavity laser 20 continuously outputs laser light in a single longitudinal mode;

Step S12, adjusting the polarizer 8 so that the polarization direction of the polarizer 8 is perpendicular to the initial polarization direction of the laser output from the semi-external cavity laser 20;

Step S13, setting the birefringent element 5 to be measured between the output cavity mirror 4 and the external cavity plane mirror 6, the birefringent element 5 has two relatively parallel planes along the optical path of the output laser ;

Step S14, rotating the birefringent element 5 at a certain angle with the axis parallel to the laser output direction as the rotation axis, and driving the external cavity plane reflector to reciprocate along the direction of the semi-external cavity laser 20 outputting the laser light;

Step S15, continue to rotate the birefringent element 5, so that the display device 10 appears in an extinction state, at this time, the optical axis of the birefringent element is the same as the initial polarization direction of the output laser light from the semi-external cavity laser 20, and a birefringent element is obtained. The optical axis of the refractive element 5 .

In step S13 , the birefringent element 5 has two relatively parallel planes in the direction in which the semi-external-cavity laser 20 outputs laser light. The laser light output by the semi-external cavity laser 20 is incident perpendicular to the plane of the birefringent element 5, and the optical axis of the birefringent element 5 is parallel to the plane. According to the difference of materials of the birefringent element 5, the The optical axis may be the fast axis or the slow axis of the birefringent element 5 . Further, the two planes of the birefringent element 5 can be coated with an anti-reflection film or a refractive index matching liquid, so as to reduce or eliminate the interference phenomenon on the surface of the birefringent element 5 .

In step S14, the birefringent element 5 is rotated about an axis parallel to the output laser direction. Since the laser output from the semi-external cavity laser 20 is incident perpendicularly to the surface of the birefringent element 5, the birefringent element 5 can be rotated with the output laser as the rotation axis. During the rotation process, a triangular wave voltage is input to the external cavity piezoelectric ceramic 7 at the same time, so that the external cavity plane reflector 6 reciprocates. The photodetector 9 detects the intensity change of the laser light emitted from the polarizer 8 , and then is displayed in a waveform by the display device 10 .

In step S15 , continue to rotate the birefringent element 5 , and at the same time drive the external cavity plane mirror 6 to reciprocate, and observe the change of the waveform in the display device 10 . As shown in Figure 2, in the process of rotation, as long as there is an included angle between the optical axis of the birefringent element 5 and the initial polarization direction of the laser light output by the semi-external cavity laser 20, the external cavity plane reflector 6 reciprocates During the movement, the laser output from the half-external-cavity laser 20 always exits after passing through the polarizer 8 and cannot be completely extinguished. At this time, the voltage output by the photodetector 9 will not have a zero point, that is to say, the intensity of the laser light received by the photodetector 9 is not zero all the time. As shown in Figure 3, when the waveform displayed by the display device 10 has a zero point, it can be known that the laser intensity received by the photodetector 9 is also zero, that is to say, the extinction state occurs in the display device 10, that is, the display device 10 10, if the received voltage is zero, it can be determined that the optical axis of the birefringent element 5 is consistent with the initial polarization direction of the output laser light from the semi-external cavity laser 20, and then the optical axis of the birefringent element 5 can be obtained .

The method for measuring the optical axis of the birefringent element provided by the present invention is based on the principle of polarization hopping, by rotating the birefringent element, when the optical axis of the birefringent element is the same as the polarization direction of the output laser light from the semi-external cavity laser The extinction phenomenon is generated, the optical axis of the birefringent element is obtained, and the measurement can be performed without complex equipment. The measuring device has a simple structure, low price, and high measurement accuracy, so it has broad application prospects.

In addition, those skilled in the art can also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included in the scope of protection claimed by the present invention.

Claims (8)

1. A method for measuring the optical axis of a birefringent element, comprising the following steps: Step S10, providing a device for measuring the optical axis of a birefringent element, including half of the external cavity laser, a laser feedback unit, and a polarization detection system; The semi-external-cavity laser includes a high-reflection cavity mirror, a gain tube, an anti-reflection window, and an output cavity mirror arranged along the output laser light path of the semi-external-cavity laser; The laser feedback unit includes an external cavity plane reflector, the external cavity plane reflector is arranged on the optical path of the laser light emitted from the output cavity mirror, and is spaced apart from the output cavity mirror; The polarization state detection system includes a polarizer, a photodetector and a display device arranged at intervals along the laser emitted from the external cavity plane mirror, and the photodetector receives the laser emitted from the polarizer to sense Measuring the change of laser intensity, the display device displays the change of laser intensity; Step S11, the semi-external cavity laser continuously outputs laser light in a single longitudinal mode; Step S12, adjusting the polarizer so that the polarization direction of the polarizer is perpendicular to the initial polarization direction of the laser output from the semi-external cavity laser; Step S13, disposing the birefringent element to be tested between the output cavity mirror and the external cavity plane reflector, the birefringent element has two relatively parallel planes along the optical path of the semi-external cavity laser output laser , and the laser is incident along a direction perpendicular to the two planes; Step S14, rotating the birefringent element with the axis parallel to the laser output direction of the semi-external cavity laser as the rotation axis, and driving the external cavity plane mirror to reciprocate along the output laser direction, so that the display device appears an extinction state , the optical axis of the birefringent element is the same as the initial polarization direction of the output laser light of the semi-external cavity laser, and the optical axis of the birefringent element is obtained. 2. The method for measuring the optical axis of a birefringent element according to claim 1, wherein the laser output from the laser is incident on the birefringent element along a direction perpendicular to the two planes. 3. The method for measuring the optical axis of a birefringent element according to claim 1, wherein the birefringent element rotates with the output laser as a rotation axis. 4. The method for measuring the optical axis of a birefringent element as claimed in claim 1, wherein an external cavity piezoelectric ceramic is connected with the external cavity plane reflector, and drives the external cavity plane reflector along the said external cavity plane reflector. The reciprocating movement in the direction of the laser output from the semi-external cavity laser. 5 . The method for measuring the optical axis of a birefringent element according to claim 4 , wherein the voltage input by the external cavity piezoelectric ceramic is a triangular wave voltage to drive the external cavity plane mirror to reciprocate. 5 . 6. The method for measuring the optical axis of a birefringent element as claimed in claim 1, wherein, when the waveform shown by the display device is in an extinction state, the laser intensity received by the photodetector is also zero, i.e. When the voltage received by the display device is zero, the optical axis of the birefringent element is consistent with the initial polarization direction of the laser output from the half-external-cavity laser. 7. The method for measuring the optical axis of a birefringent element according to claim 1, wherein the two planes of the birefringent element are coated with an anti-reflection film or a refractive index matching liquid. 8. the measuring method of birefringence element optical axis as claimed in claim 1, is characterized in that, described high reflection cavity mirror, gain tube, anti-reflection window plate, output cavity mirror are arranged successively along the axis of described output laser and Coaxial setup.

Images