CN102735430B - Method and device for detecting phase delay - Google Patents

Abstract

The invention belongs to the technical field of laser detection, and relates to a method for detecting phase delay of an optical element by using a laser weak feedback orthogonal light intensity phase difference effect. According to method, the phase delay of the element is detected by using the phase difference effect existing between two paths of light intensity signals output by a laser in an orthogonal direction under the condition with anisotropy outer cavity laser weak feedback. The method does not have special requirements on a detected sample, and according to a detection principle, the phase delay of the detected sample is amplified, so that the sensitivity is high.

Description

Phase delay detection method and detection device

technical field

The invention belongs to the technical field of laser detection, and relates to a method and a detection device for detecting the phase delay of an optical element by utilizing the phase difference effect of laser weak feedback orthogonal light intensity.

Background technique

Phase delay detection is mainly used in the detection of birefringent optical elements or the birefringence effect caused by stress and other reasons. Among them, the most typical application is the detection of wave plate phase delay. Waveplates are widely used in optical systems, especially in systems related to polarized light, such as optical isolators, optical filters, optical pickups for optical discs, laser heterodyne interferometers, and ellipsometers. The accuracy of the phase delay of the wave plate itself will affect the use effect of the entire system. If you want to process a high-precision wave plate or must determine the actual phase delay of the wave plate with high precision, you need to have an accurate detection method for the wave plate. Another typical application is to detect the internal stress of glass. Glass materials often have residual stress unavoidably during processing. In addition, glass materials also have residual stress when combined with other materials. These residual stresses will cause non-negligible effects in some applications, so it is necessary to have a precise method Such residual stresses are detected. The detection of residual stress can actually be transformed into the detection of phase retardation caused by stress birefringence.

At present, the methods widely used in the detection of wave plate phase retardation include rotational extinction method and ellipsometry. These two methods have the problems of insufficient detection accuracy or complicated operation. The rotating extinction method needs to add a standard 1/4 wave plate in the optical path, the error of this standard 1/4 wave plate will affect the detection accuracy of the system, and this error cannot be detected and eliminated by the rotating extinction method system itself. The light source used in the ellipsometry is a wide-spectrum light source, and the required wavelength of the detection light is obtained by splitting light. The central wavelength error of the detection light obtained in this way is relatively large, thereby introducing detection errors.

Contents of the invention

To sum up, it is indeed necessary to provide a phase delay detection method and a detection device thereof with high precision and easy operation.

A phase delay detection method, comprising the following steps: providing a detection device, the detection device includes a laser, a laser weak feedback external cavity, and a data acquisition and processing system, the initial polarization state of the laser generated by the laser is linear polarization, and the The laser weak feedback external cavity is used to accommodate the measured sample, and the data acquisition and processing system includes a Wollaston prism; the measured sample is placed in the laser weak feedback external cavity, so that the fast axis of the measured sample and the The direction of the slow axis corresponds to the direction of the two optical axes of the o-ray and e-ray of the Wollaston prism, and forms an included angle with the initial polarization direction of the laser; Finally, the laser forms light intensity signals in the direction of the fast and slow axes of the sample to be measured, and separates them through a Wollaston prism, and there is a phase difference between the two light intensity signals; The light intensity signals of the measured sample in the direction of the fast and slow axes output by the Wollaston prism are compared and processed to obtain the phase delay.

A phase delay detection device, comprising: a laser, the laser is composed of a cavity concave reflector, a gain tube, an anti-reflection window, and a cavity plane output mirror, wherein: the cavity concave reflector is fixed on the The upper end of the gain tube, the upper end of the gain tube is fixed to the inner cavity concave reflector, the lower end is fixed to the anti-reflection window, the anti-reflection window is fixed to the lower end of the gain tube, and the inner cavity plane output mirror is located at the bottom of the anti-reflection window Below and at intervals with the anti-reflection window; a laser weak feedback external cavity, the laser weak feedback external cavity includes an inner cavity plane output mirror, a beam expander collimating lens group, a sample holder, and an outer cavity plane weak reflection mirror. Set at intervals from top to bottom; a data acquisition and processing system, the data acquisition and processing system includes a Wollaston prism, a first photodetector, a second photodetector, an analog/digital converter and a computer, Among them: the Wollaston prism divides the output light of the laser into two orthogonally polarized components along the fast and slow axes of the measured sample; the first photodetector and the second photodetector are located above the Wollaston prism, respectively detecting The light intensity signal on the orthogonal direction is converted into a voltage signal; the analog/digital converter converts the voltage signal output by the photodetector into a digital signal and outputs it to a computer; the input terminal of the computer is connected to the analog/digital converter The output terminal is connected to receive the digital signal for comparison and calculation processing.

The invention uses a semi-external cavity laser and an external plane reflector to form a laser feedback system, and uses the phase difference effect of the light intensity curve to detect the phase delay of the optical element. The direction of the optical axis of the Wollaston prism coincides with the direction of the fast (slow) axis of the sample to be measured, so that the light output by the laser is divided into two parts. There is a phase difference between the two light intensity signals, and this phase difference has a linear relationship with the phase delay of the measured sample. By measuring the phase difference between the light intensity signals in two orthogonal directions, the phase delay of the sample under test can be obtained. This detection method is simple to operate, has no special requirements for the sample to be tested, and has the potential to be applied to small stress detection requirements such as residual stress.

Description of drawings

Fig. 1 is a schematic diagram of a device for detecting phase delay using laser weak feedback orthogonal light intensity phase difference effect according to an embodiment of the present invention;

Figure 2 is a schematic diagram of the positional relationship between the direction of the fast and slow axis of the measured sample, the initial polarization direction of the laser and the direction of the optical axis of the Wollaston prism;

Figure 3 is a schematic diagram of the phase difference effect of laser weak feedback orthogonal light intensity;

Fig. 4 is an experimental diagram of the phase difference effect of laser weak feedback orthogonal light intensity.

Description of main component symbols

first photodetector 1 second photodetector 2 Wollaston Prism 3 Cavity Concave Mirrors 4 gain tube 5 AR Windows 6 Cavity Plane Output Mirror 7 Internal Cavity Piezoelectric Ceramics 8 Beam expander collimator lens group 9 sample holder 10 External Cavity Plane Weak Mirror 11 External Cavity Piezoelectric Ceramics 12 Analog/Digital Converter 13 computer 14 Internal cavity piezoelectric ceramic drive module 15 External cavity piezoelectric ceramic drive module 16

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

Detailed ways

The phase delay detection method and detection device provided by the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1 , the first embodiment of the present invention provides a phase delay detection device and its method. The device includes a laser, a weak laser feedback external cavity, and a data acquisition and processing system.

The laser not only serves as a light source to provide detection light, but also serves as a sensor for receiving laser feedback. It has a semi-outer (inner) cavity structure, its initial polarization state is linear polarization, single longitudinal mode, and fundamental transverse mode output. The laser type can be gas laser, semiconductor lasers and solid state lasers.

The laser is composed of a cavity concave reflector 4 , a gain tube 5 , an anti-reflection window 6 , a cavity plane output mirror 7 and a cavity piezoelectric ceramic 8 . The gain tube 5 stores a laser gain medium; the inner cavity concave reflector 4 is fixed on the upper end of the gain tube 5; the anti-reflection window 6 is fixed on the lower end of the gain tube 5; the inner cavity The plane output mirror 7 is located below the anti-reflection window 6, and is spaced apart from the anti-reflection window 6; the inner cavity piezoelectric ceramic 8 is located at the lower end of the inner cavity plane output mirror 7, and is connected to the The inner cavity plane output mirror 7 is fixedly arranged. By controlling the voltage change on the inner cavity piezoelectric ceramic 8, the inner cavity piezoelectric ceramic 8 can push the inner cavity planar output mirror 7 to move along the axis of the laser within a range of microns to stabilize the laser output mode . It can be understood that the inner cavity piezoelectric ceramic 8 can also be replaced by other micro-movement elements, as long as the inner cavity plane output mirror 7 can be pushed to move along the axis of the laser on a micron level.

The laser weak feedback external cavity is composed of an internal cavity plane output mirror 7, a beam expander collimating lens group 9, a sample holder 10, an external cavity plane weak reflection mirror 11, and an external cavity piezoelectric ceramic 12 arranged in sequence from top to bottom. The beam expander and collimator lens group 9 is composed of a concave lens and a convex lens, located below the inner cavity piezoelectric ceramic 8, and is spaced apart from the inner cavity piezoelectric ceramic 8; the beam expander collimator lens group 9 can output the laser The light is expanded and collimated, so that the laser beam covers a certain area on the sample surface; the position between the two lenses of the beam expanding and collimating lens group 9 and between the lens group and the laser inner cavity plane output mirror 7 You can adjust. The laser weak feedback external cavity is used to accommodate the sample to be tested, and the laser output by the plane output mirror 7 of the laser cavity can be incident on the sample to be tested; There is a phase difference in the axial direction, which is determined by the phase delay of the measured sample.

The sample holder 10 is located below the beam expander collimator lens group 9, and is spaced apart from the beam expander collimator lens group 9, and the laser incident surface of the sample holder 10 can rotate perpendicular to its surface normal direction; the sample The sample to be measured is placed on the upper end of the seat 10, and there is a light hole in the middle through which the laser can pass through the hole during detection; the sample to be tested can rotate along with the sample seat 10 perpendicular to the axis of the laser.

The external cavity plane weak reflector 11 is located below the sample seat 10 and is spaced from the sample seat 10 to reflect the laser light passing through the sample. Preferably, the external cavity planar weak reflector 11 is connected to the inner cavity The distance between the planar output mirrors 7 is an integer multiple of the distance between the inner cavity planar output mirror 7 and the inner cavity concave mirror 4, so as to reduce the speckle effect existing when semiconductor lasers are used.

The external cavity piezoelectric ceramic 12 is fixed with the external cavity flat weak reflector 11, and is at the lower end of the external cavity flat weak reflector 11; by controlling the voltage loaded on the external cavity piezoelectric ceramic 12, the external cavity voltage The electroceramic 12 can push the planar weak reflector 11 of the external cavity to reciprocate along the laser axis direction, so as to generate continuous feedback waveform signals that can be used to detect the phase relationship.

The data acquisition and processing system is used to receive light intensity signals in the direction of the fast and slow axes, and perform comparison calculation processing to obtain phase delay; output control signals to adjust the length of the laser inner cavity and the length of the laser weak feedback outer cavity. In the present invention, the "up" and "down" are based on the structure, direction and positional relationship shown in FIG. 1 .

The data acquisition and processing system includes a Wollaston prism 3, a first photodetector 1, a second photodetector 2, an analog/digital converter 13, an inner cavity piezoelectric ceramic drive module 15, an outer cavity piezoelectric ceramic The drive module 16 and the computer 14 form together, wherein:

The Wollaston prism 3 is located above the inner cavity concave reflector 4, the surface of the Wollaston prism 3 near the inner cavity concave reflector 4 is its incident surface, and the incident surface from the incident surface The laser is divided into two orthogonally polarized components along the fast and slow axes of the sample to be measured, and its specific position can be selected according to actual needs, as long as the laser can be incident from the incident surface;

The first photodetector 1 and the second photodetector 2 are located above the Wollaston prism 3, respectively detect the light intensity signal output by the Wollaston prism 3 and convert it into a voltage signal;

The analog/digital converter 13 converts the voltage signal output by the first photodetector 1 and the second photodetector 2 into a digital signal and outputs it to the computer 14;

The inner cavity piezoelectric ceramic drive module 15 receives the control signal output by the computer 14 to control the expansion and contraction of the inner cavity piezoelectric ceramic 8, thereby driving the inner cavity plane output mirror 7 to move slightly in the direction of the laser axis to stabilize the laser output mode;

The piezoelectric ceramic drive module 16 of the external cavity receives the control signal output by the computer 14, and controls the expansion and contraction of the piezoelectric ceramic 12 of the external cavity, thereby driving the planar weak reflector 11 of the external cavity to reciprocate along the laser axis.

In the computer 14, its input terminal is connected to the output terminal of the analog/digital converter 13, and the digital signal is received for comparison calculation processing; its output terminal is connected to the inner cavity piezoelectric ceramic drive module 15 and the outer cavity piezoelectric The input end of the ceramic driving module 16 is connected to control the movement of the piezoelectric ceramic. It can be understood that the data acquisition and processing system is not limited to the above-mentioned components, and can be changed according to the experimental environment and specific requirements.

It can be understood that the specific distance and positional relationship of the various components can be selected according to the needs, as long as the laser light emitted by the laser can be irradiated on the sample surface and reflected back into the laser cavity by the plane weak mirror 11 of the external cavity, Wollaston The prism 3 separates the laser output along the fast-slow axis of the measured sample, and it only needs to be received by the first photodetector 1 and the second photodetector 2 . Preferably, the inner cavity concave reflector 4, the gain tube 5, the antireflection window 6, the inner cavity plane output mirror 7, the inner cavity piezoelectric ceramic 8, the beam expanding collimating lens group 9, the sample holder 10, the outer cavity The planar weak reflector 11 and the external cavity piezoelectric ceramic 12 are coaxially arranged along the axis of the laser.

The present invention further provides a detection method of phase delay, comprising the following steps:

First, a detection device is provided, the detection device includes a laser, a laser weak feedback external cavity and a data acquisition and processing system, the laser is used to generate laser light, and the initial polarization state of the laser is linear polarization, and the laser weak feedback external cavity The cavity includes an external cavity planar weak reflector, which reflects laser light to generate laser feedback, and the data acquisition and processing system is used to collect and process data. The data acquisition and processing system includes a Wollaston prism to convert incident The laser of the Raston prism is divided into two beams along the optical axis of its o-ray and e-ray;

Secondly, the sample to be tested is placed in the laser weak feedback external cavity, so that the directions of the fast axis and the slow axis of the sample to be tested are consistent with the directions of the two optical axes of the o-ray and e-ray of the Wollaston prism;

Again, irradiate the measured sample with the laser light emitted by the laser, and after feedback, the laser forms light intensity signals in the direction of the fast and slow axes of the measured sample, and outputs them through the Wollaston prism, and the two light intensities There is a phase difference between the signals;

Finally, the light intensity signals in the direction of the fast and slow axes of the measured sample output through the Wollaston prism are respectively received by the data acquisition and processing system, and are compared and processed to obtain the phase delay.

Specifically, the method for detecting phase delay using the phase difference effect of laser weak feedback orthogonal light intensity described in the present invention may include the following steps:

Step 1, the initial output state of the laser is set to single longitudinal mode, linearly polarized light, the laser is incident from the incident surface of the Wollaston prism 3, and the incident surface of the Wollaston prism 3 is rotated perpendicular to the axis of the laser to make it One of the two optical axis directions is parallel to the initial polarization direction of the laser, and at this time, there is only one spot of outgoing light behind the Wollaston prism 3;

In the 2nd step, the incident surface of the Wollaston prism 3 is rotated perpendicular to the laser axis direction, and the outgoing light behind the Wollaston prism 3 has two light spots. Preferably, the incident surface of the Wollaston prism 3 Rotate 45° perpendicular to the laser axis. At this time, the initial polarization direction of the laser and the two optical axes of the Wollaston prism 3 form an included angle of 45°. The vibration direction of the light field corresponding to the two light points is orthogonal, so it is called orthogonal light intensity;

Step 3, aligning the first photodetector 1 and the second photodetector 2 with the aforementioned two light spots respectively;

Step 4: Put the sample to be measured on the sample seat 10 of the weak feedback external cavity, rotate the sample seat 10 perpendicular to the axis of the laser, so that the fast (or slow) axis of the sample to be measured is parallel to the initial polarization direction of the laser , the light intensity signals received by the first photodetector 1 and the second photodetector 2 are in phase;

Step 5: Rotate the sample holder 10 carrying the sample to be tested, so that the direction of the fast and slow axes of the sample to be tested is consistent with the direction of the two optical axes of the o-light and e-light of the Wollaston prism 3, and is consistent with the initial polarization direction of the laser form an angle

It can be understood that the correspondence between the direction of the fast and slow axes and the two optical axes of o-light and e-light is not limited, it may be that the fast axis corresponds to the o-optical axis, and the slow axis corresponds to the e-axis, or it may be the slow axis Corresponding to the o optical axis, the fast axis corresponds to the corresponding way of the e optical axis. The included angle between the Wollaston prism 3 and the initial polarization direction of the laser light is sufficient, and the size of the angle is not limited. At the same time, the angle at which the incident surface of the Wollaston prism 3 rotates perpendicular to the axis of the laser is not limited, as long as the emitted light forms two light spots. In this embodiment, preferably, the sample to be tested is rotated by 45°. At this time, the direction of the fast and slow axes of the sample to be tested is at an angle of 45° to the initial polarization direction of the laser. The components are respectively received by the first photodetector 1 and the second photodetector 2, and there is a phase difference Δφ between the two light intensity signals. There is the following relationship between the phase difference Δφ and the phase delay δ of the measured sample:

(*)

In the formula, θ _c can be regarded as the detection compensation amount, and can be obtained by detecting the standard wave plate. It can be seen from the formula (*) that the phase difference between the two orthogonal light intensity signals is twice the phase delay of the measured sample, so the resolution is improved.

In step 6, the light intensity signals are collected by the analog/digital converter 13 and the computer 14 and compared and calculated to obtain the phase difference Δφ of the two light intensity signals, and then calculate the phase delay δ of the measured sample:

(**).

During the above steps, the computer 14 outputs the control voltage to the piezoelectric ceramics 12 through the external cavity piezoelectric ceramic drive module 16, thereby driving the external cavity flat weak reflector 11 to reciprocate along the laser axis direction, and through the internal cavity pressure The electroceramic driving module 15 controls the inner cavity piezoelectric ceramic 8 to stabilize the laser output state. Preferably, the reflector 4, the gain tube 5, the antireflection window 6, the inner cavity plane output mirror 7, the inner cavity piezoelectric ceramic 8, the beam expander collimating lens group, the sample holder, the outer cavity plane weak reflector, The piezoelectric ceramics in the external cavity are coaxially arranged, thereby improving the accuracy of the detection results.

As shown in Figure 2, after completing the fifth step above, the schematic diagram of the positional relationship between the direction of the fast and slow axes of the measured sample, the direction of the optical axis (o-axis and e-axis) of the Wollaston prism, and the initial polarization direction E _i of the laser, The first photodetector and the second photodetector respectively receive the components E _s and E _f of the laser output in the fast-slow axis direction of the measured sample.

Figure 3 shows the schematic diagram of the phase difference effect of laser weak feedback orthogonal light intensity. From the figure, it can be seen that there is a phase difference Δφ between the two light intensity signals, and this phase difference is determined by the phase delay of the measured sample;

Figure 4 shows the experimental diagram of the phase difference effect of laser weak feedback orthogonal light intensity. From the figure, it can be seen that there is an obvious phase difference between the two light intensity signals, and the phase difference varies with the phase delay of the wave plate. And change, and with the different motion directions of the piezoelectric ceramics in the external cavity, the phase relationship between the two light intensity signals is exchanged.

The laser weak feedback in the present invention belongs to a kind of laser feedback phenomenon. Laser feedback (laser feedback), also known as laser self-mixing interference (self-mixing interference) or back-scattering modulation (back-scattering modulation), means that the output beam of the laser is reflected (or scattered) by an external mirror (or object) Back into the laser cavity, it interacts with the light field in the cavity, causing the output light field of the laser to change.

Specifically, as a specific embodiment of the detection device, the laser adopts a semi-external-cavity helium-neon laser, and the reflectivity _R1 and _R2 of the inner cavity concave reflector and the inner cavity plane output mirror are 99.6% and 99%, respectively, The distance between them, that is, the length of the laser cavity is L=180mm; the gain tube is filled with helium-neon mixed gas, and the gas filling ratio is He ³ :Ne ²⁰ :Ne ²² =9:0.5:0.5; the anti-reflection window is fixed at the gain One end of the tube; the inner cavity piezoelectric ceramic is fixed on the above-mentioned inner cavity plane output mirror, under the action of the input voltage, it can push the inner cavity plane output mirror to move along the laser axis direction, so that the laser output state is stable; the outer cavity plane weak reflection The reflectivity _R3 of the mirror is 4%; the external cavity piezoelectric ceramic is fixed on the external cavity plane weak reflector, and the external cavity plane weak reflector can be pushed to reciprocate along the laser axis direction under the action of the driving voltage; The material of the wave plate to be tested is quartz, with a diameter of 11mm. The wave plate is placed on the sample holder. The sample holder can rotate perpendicular to the axis of the laser to drive the wave plate to rotate. There is a light hole in the center of the sample holder, and the laser passes through the hole during detection. Pass.

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 (10)

1. a detection method for bit phase delay, comprises the following steps:

One pick-up unit is provided, described pick-up unit comprises laser instrument, the weak feedback exocoel of laser and data Collection & Processing System, the laser original state of polarization that described laser instrument produces is linear polarization, described laser weak feedback exocoel comprises the weak catoptron of an exocoel plane, the weak catoptron of described exocoel plane is arranged at the below of described laser instrument, and described data acquisition and processing system comprises the top that a wollaston prism is arranged at described laser instrument;

Sample is arranged in the weak feedback exocoel of laser, make the o light of the fast axle of sample and slow-axis direction and described wollaston prism and e light two optical axis directions corresponding consistent, and to have angle with laser initial polarization direction shape;

The laser sent with laser instrument irradiates described sample, after the weak catoptron feedback of exocoel plane, laser instrument forms light intensity signal respectively on the fast and slow axis direction of described sample, and exports through wollaston prism, between two-way light intensity signal, form phasic difference;

Receive the light intensity signal of described sample on fast and slow axis direction exported through wollaston prism with data Collection & Processing System respectively, and compare computing, obtain bit phase delay.

2. the detection method of bit phase delay according to claim 1, is characterized in that, described laser instrument comprises inner chamber concave mirror, gain tube, anti-reflection window, inner chamber flat output mirror and inner chamber piezoelectric ceramics, wherein:

Inner chamber concave mirror is fixed on the upper end of described gain tube;

Gain tube upper end and inner chamber concave mirror are fixed, and lower end and anti-reflection window are fixed;

Anti-reflection window is fixed on the lower end of described gain tube;

Inner chamber flat output mirror is positioned at the below of described anti-reflection window, and and described anti-reflection window interval arrange;

Inner chamber piezoelectric ceramics and described inner chamber flat output mirror are fixed, and in inner chamber flat output mirror lower end.

3. the detection method of bit phase delay according to claim 2, is characterized in that, described laser weak feedback exocoel comprises inner chamber flat output mirror, beam-expanding collimation lens combination, specimen holder, the weak catoptron of exocoel plane, exocoel piezoelectric ceramics, wherein:

Beam-expanding collimation lens combination, is positioned at below inner chamber piezoelectric ceramics, and and described inner chamber piezoelectric ceramics interval arrange;

Specimen holder, is positioned at below beam-expanding collimation lens combination, and and described beam-expanding collimation lens combination interval arrange;

The weak catoptron of exocoel plane is positioned at below specimen holder, and and described beam-expanding collimation lens combination interval arrange;

Exocoel piezoelectric ceramics and the weak catoptron of described exocoel plane are fixed, and in the weak catoptron lower end of exocoel plane.

4. the detection method of bit phase delay according to claim 3, it is characterized in that, described data Collection & Processing System comprises wollaston prism, the first photodetector, the second photodetector, A/D converter, inner chamber Piezoelectric Ceramic module, exocoel Piezoelectric Ceramic module and computing machine, wherein:

The output light of laser instrument is divided into the component of two cross polarizations by wollaston prism along sample fast and slow axis direction;

First photodetector, the second photodetector, be positioned at above wollaston prism, detects the light intensity signal on orthogonal directions respectively and convert voltage signal to;

A/D converter, converts digital signal to by the voltage signal that photodetector exports and exports to computing machine;

Inner chamber Piezoelectric Ceramic module, the control signal that receiving computer exports, controls the flexible of inner chamber piezoelectric ceramics, thus drives inner chamber flat output mirror trace on laser axis direction mobile;

Exocoel Piezoelectric Ceramic module, the control signal that receiving computer exports, controls the flexible of exocoel piezoelectric ceramics, thus drives the weak catoptron of exocoel plane along the to-and-fro movement of laser axis;

Computing machine, its input end is connected with the output terminal of described A/D converter, receives digital signal and compares computing; Its output terminal is connected with the input end of described inner chamber Piezoelectric Ceramic module and exocoel Piezoelectric Ceramic module, controls the motion of inner chamber piezoelectric ceramics and exocoel piezoelectric ceramics.

5. the detection method of bit phase delay according to claim 4, is characterized in that, comprises the steps: further

1st step, rotated perpendicular to laser axis by the wollaston prism plane of incidence, make one of the o light of wollaston prism and e light two optical axis directions parallel with laser initial polarization direction, now after wollaston prism, emergent light only has a luminous point;

2nd step, the wollaston prism plane of incidence is rotated 45 ° perpendicular to laser axis, make two optical axis directions angle all at 45 ° of laser initial polarization direction and wollaston prism, now after wollaston prism, emergent light has two luminous points, the light field direction of vibration that these two luminous points are corresponding is orthogonality relation, forms orthogonal light intensity;

3rd step, aligns described two luminous points respectively by the first photodetector, the second photodetector;

4th step, sample is arranged at the specimen holder of the weak feedback exocoel of described laser, and specimen holder is rotated perpendicular to its plane of incidence normal direction, make the fast of sample or slow-axis direction parallel with laser initial polarization direction, the now light intensity signal coordination phase that arrives of the first photodetector and the second photoelectric detector;

5th step, the laser entrance face of sample is rotated 45 ° perpendicular to plane of incidence normal direction direction, make the fast and slow axis direction of sample and laser initial polarization direction angle all at 45 °, and the fast and slow axis direction of sample is consistent with two optical axis directions of wollaston prism, on sample fast and slow axis direction, two components of Laser output are received respectively by the first photodetector and the second photodetector, occur phasic difference between the light intensity signal of described two components this phasic difference and there is following relation between the bit phase delay δ of sample:

θ in formula _cbe detect compensation rate, and obtained by examination criteria wave plate;

6th step, compares calculating by A/D converter and computer acquisition light intensity signal, obtains the phasic difference of two light intensity signals and then calculate the bit phase delay δ of sample:

6. the detection method of bit phase delay according to claim 5, it is characterized in that, in above-mentioned steps process, computing machine exports control voltage by exocoel Piezoelectric Ceramic module to exocoel piezoelectric ceramics, thus drive the weak catoptron of exocoel plane along the to-and-fro movement of laser axis direction, and control inner chamber piezoelectric ceramics by inner chamber Piezoelectric Ceramic module, stabilized lasers output state.

7. the detection method of bit phase delay according to claim 2, is characterized in that, the distance between described inner chamber flat output mirror and the weak catoptron of exocoel plane is the integral multiple of the spacing of described inner chamber flat output mirror and described inner chamber concave mirror.

8. the detection method of bit phase delay according to claim 3, it is characterized in that, described inner chamber concave mirror, gain tube, anti-reflection window, inner chamber flat output mirror, inner chamber piezoelectric ceramics, beam-expanding collimation lens combination, specimen holder, the weak catoptron of exocoel plane, the coaxial setting of exocoel piezoelectric ceramics.

9. a pick-up unit for bit phase delay, comprising:

One laser instrument, described laser instrument comprises inner chamber concave mirror, gain tube, anti-reflection window, inner chamber flat output mirror, wherein: inner chamber concave mirror is fixed on the upper end of described gain tube, gain tube upper end and inner chamber concave mirror are fixed, lower end and anti-reflection window are fixed, anti-reflection window is fixed on the lower end of described gain tube, inner chamber flat output mirror be positioned at described anti-reflection window below and and described anti-reflection window interval arrange;

The weak feedback exocoel of one laser, described laser weak feedback exocoel comprises the interval setting successively from top to bottom of inner chamber flat output mirror, beam-expanding collimation lens combination, specimen holder, the weak catoptron of exocoel plane;

One data Collection & Processing System, described data Collection & Processing System comprises wollaston prism, the first photodetector, the second photodetector, A/D converter and computing machine, wherein:

The output light of laser instrument is divided into the component of two cross polarizations by wollaston prism along sample fast and slow axis direction;

First photodetector, the second photodetector, be positioned at above wollaston prism, detects the light intensity signal on orthogonal directions respectively and convert voltage signal to;

A/D converter, converts digital signal to by the voltage signal that photodetector exports and exports to computing machine;

Computing machine, its input end is connected with the output terminal of described A/D converter, receives digital signal and compares computing.

10. the pick-up unit of bit phase delay as claimed in claim 9, is characterized in that, comprise further:

One inner chamber Piezoelectric Ceramic module, the control signal that receiving computer exports, controls the flexible of inner chamber piezoelectric ceramics, thus drives inner chamber flat output mirror to carry out micron-sized movement on laser axis direction;

One exocoel Piezoelectric Ceramic module, the control signal that receiving computer exports, controls the flexible of exocoel piezoelectric ceramics, thus drives the weak catoptron of exocoel plane along the to-and-fro movement of laser axis.