CN101650226A - Micro phase delay measuring device for optical element based on laser feedback - Google Patents
Micro phase delay measuring device for optical element based on laser feedback Download PDFInfo
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Abstract
本发明涉及一种基于激光回馈的光学元件微小位相延迟测量装置，属于激光测量技术领域，其特征是利用632.8nm的He－Ne激光器与外部反射镜和四分之一波片构成的双折射激光回馈系统来测量光学元件微小的位相延迟。被测光学元件安放在激光腔中，当外部反射镜沿激光轴线左右移动时，激光的偏振态将在两个正交的方向跳变。伴随着偏振跳变，激光模式两个本征态的频率是不同的，并且它们之间的频差与激光内腔的位相延迟的大小有关，根据这一原理可以实现光学元件微小位相延迟的测量。激光回馈光学元件微小位相延迟测量方法及其实现装置具有结构简单、装配调整容易、测量精度高、成本低的特点。
The invention relates to a micro-phase delay measurement device for optical elements based on laser feedback, which belongs to the technical field of laser measurement, and is characterized in that it uses a birefringent laser composed of a 632.8nm He-Ne laser, an external reflector and a quarter-wave plate Feedback system to measure tiny phase delays of optical components. The optical element under test is placed in the laser cavity. When the external mirror moves left and right along the laser axis, the polarization state of the laser will jump in two orthogonal directions. With the polarization jump, the frequencies of the two eigenstates of the laser mode are different, and the frequency difference between them is related to the phase delay of the laser cavity. According to this principle, the measurement of the small phase delay of the optical element can be realized . The method for measuring the tiny phase delay of the laser feedback optical element and its realization device have the characteristics of simple structure, easy assembly and adjustment, high measurement accuracy and low cost.
Description
Technical field
The present invention relates to a kind of micro phase delay measuring device for optical element, belong to the laser measuring technique field based on laser feedback.
Background technology
There is several factors can make optical element produce position phase anisotropy, as: the heterogeneity of unrelieved stress, birefringence, laser gain and film etc.At present, domestic and international high-precision optical element bit phase delay measuring method has many, but mostly is to measure quarter-wave plate, not to be specifically designed to measurement optical element micro phase delay method and apparatus.At present, more typical wave plate measuring method has following several.
1, rotation light extinction method
The fast axle and the angle at 45, the polarization direction of the polarizer of a standard quarter wave plate, the fast axle of tested quarter wave plate is identical with the direction of polarized light of the polarizer.The laser of HeNe laser emitting becomes a branch of linearly polarized light behind the polarizer, respectively by behind wave plate to be measured and the standard wave plate, become a linearly polarized light again again.The rotation analyzer can find an extinction position.At this moment the twice of the polarization direction angle of the polarization direction of analyzer and the polarizer is exactly differing of wave plate position.Here it is, and the rotation light extinction method is measured the ultimate principle of quarter-wave plate phasic difference, and wherein the differentiation of extinction position has determined the measuring accuracy of wave plate phasic difference.The method of range estimation extinction position can make the wave plate measuring accuracy reach 3 °-5 °, if use the penumbra analyzer to detect the measuring accuracy of wave plate is brought up to about 1 °.If think further to improve precision, need high-precision angular instrument carry out the measurement of angle, but this make the volume of measuring equipment and cost all very big, increased the complicacy of system.
2, electrooptical modulation method
The ultimate principle of electrooptical modulation method is identical with the rotation light extinction method, but adopted the KD*P electro-optic crystal, judge the extinction position with the electrooptical modulation detection method, improved the precision of judging the extinction position, the measuring accuracy of final optical element phasic difference can reach about 0.5 °.
3, Magnetooptic Modulation
Magnetooptic Modulation also is the rotation light extinction method in essence, has adopted the method for magneto-optic modulation when just judging the extinction position.Because Magnetooptic Modulation can accurately be judged the extinction position, judge that precision can reach 1 ", so the measuring accuracy of optical element phasic difference can reach 10 in theory ".In fact owing to reasons such as stability and degrees of regulation, measuring repeatability can reach about 0.1 °.This method structure is complicated, needs special temperature stabilization mechanism, and the operation of adjustment is many, it is high to require, and the precision of adjustment influences very big to measurement result, so can be subjected to a lot of restrictions during practical application.
4, rotation analyzer method
Allowing monochromatic source become linearly polarized light by the polarizer, is that an analyzer that rotates enters highly sensitive photodetector by optical element to be measured (fast axle at 45 with polarizer axle) and one with the light path again.λ/4 postpone if optical element to be measured has accurately, and then transmitted light should be circularly polarized light, and the light intensity signal that sees through the rotation analyzer is constant all the time.If postpone to have departed from λ/4, then transmitted light will become elliptically polarized light, and light intensity signal also becomes an oscillator signal, and its amplitude and average intensity are by the ellipticity decision of elliptically polarized light.Measure the average intensity and the light intensity change in oscillation amplitude of transmission, just can calculate the optical element phasic difference.The precision of this method generally can reach about 1 °.
5, optical heterodyne interferometric method
Vertically zeeman laser is exported a branch of two kinds of circularly polarized lights left-handed, that dextrorotation has small frequency difference that comprise, behind quarter-wave plate to be measured and polaroid (fast axle of wave plate and angle at 45, polaroid polarization direction), on the polarization direction of polaroid, form and interfere, receive by photodetector then.The output of detector is directly proportional with the light intensity of incident light, so the difference interference signal has the phasic difference information of tested wave plate.By measuring the amplitude of heterodyne signal of ac, just can determine the phase-delay quantity of wave plate.The measuring accuracy of this method is subject to the adjustment sum of errors voltage measurement precision of tested wave plate and polaroid direction, is generally 0.2 °-0.3 °.
6, laser frequency division mensuration
Optical element bit phase delay measurement based on the laser frequency splitting technique is that optical element is put into laser cavity, because birefringence effect, a pattern of laser will be split into two orthogonal polarization components.Frequency difference between these two polarized components is directly proportional with the phasic difference of optical element, so, by measuring the bit phase delay that frequency difference just can obtain optical element.The measuring accuracy of this method is very high, can reach 0.05 °, can measure the optical element of any bit phase delay in theory, and can be traceable to optical wavelength.But not enough is, but in the chamber the mutually anisotropic value in position hour because strong mode competition, zlasing mode can not split into two frequencies of vibrating simultaneously, be that synchronization has only a kind of polarization state to keep vibration and another polarization state is suppressed, can't measure frequency difference this moment.Therefore, the laser frequency splitting technique can't realize the small mutually anisotropic measurement in position of optical element.
From top analysis we as can be seen, though at present both at home and abroad more about the measuring method of optical element bit phase delay, the measuring equipment of these methods is comparatively complicated, to having relatively high expectations of deflection adjustment.The overwhelming majority needs accurate measurement of angle, and high-precision angular instrument volume is very big, and cost is also very high, and the equipment that also has in addition needs the high precision standard quarter-wave plate.This has just increased the complicacy of measuring system, because measurement links has been introduced more instrument error and orientation adjustment error, the further raising of measuring accuracy is restricted, and, mostly do not possess the measurement of optical element micro phase delay.
Summary of the invention
The present invention utilizes the double-refraction external cavity feedback can cause the ultimate principle of laser polarization saltus step, has proposed a kind of measuring method of new optical element micro phase delay, and has made up measuring system.Under double-refraction external cavity feedback condition, zlasing mode saltus step between two assertive evidence attitudes is accompanied by the polarization saltus step, and the frequency of two eigenstates of zlasing mode is different, and the frequency difference between them is relevant with the size of the bit phase delay of laser inner chamber.Though two eigenstates can not be vibrated simultaneously, if can make the retentivity time of eye of their duration greater than human eye, they will be similar to and appear at simultaneously on the oscillograph, so just can directly measure the frequency difference between them.When the phasic difference of feedback exocoel birefringence element equaled pi/2, two polarization states had the identical duration.For this reason, we adopt the quarter-wave plate feedback to make laser produce the polarization saltus step, and regulate the sweep frequency of exocoel, and two polarization states are appeared on the oscillograph simultaneously, so just can realize the measurement of micro phase delay in the laser cavity by the measurement frequency difference.This invention has solved in the laser cavity bit phase delay hour, because the difficult problem that strong mode competition makes zlasing mode divide and to measure.
The invention is characterized in that described wave plate measuring apparatus based on laser feedback contains:
A: the He-Ne laser instrument of the 632.8nm of half intracavity, described He-Ne laser instrument contains:
Resonator cavity, described resonator cavity comprises:
The first inner chamber catoptron 6, the described first inner chamber catoptron 6 is fixed on the other end of described gain tube 8;
The second inner chamber catoptron 11 is positioned at the other end of above-mentioned anti-reflection window 9;
First piezoelectric ceramics 31 is fixed on the above-mentioned second inner chamber catoptron 11, and under the input voltage effect, described piezoelectric ceramics 12 promotes the above-mentioned second inner chamber catoptron 11 and moves along the laser axis direction is left and right, changes the frequency of laser;
The measured optical unit 10 is placed between above-mentioned anti-reflection window 9 and the described second inner chamber catoptron 11;
B: the laser feedback exocoel, described laser feedback exocoel comprises:
Laser feedback exocoel catoptron 4 is fixed on the opposite side of the described first inner chamber catoptron 6, with the described first inner chamber catoptron 6 interval is arranged;
Quarter-wave plate 5 is placed between above-mentioned laser feedback exocoel catoptron 4 and the described first inner chamber catoptron 6;
Second piezoelectric ceramics 32 is fixed on the above-mentioned laser feedback exocoel catoptron 4, and under the input voltage effect, it promotes above-mentioned laser feedback exocoel catoptron 4 and moves along the laser axis direction is left and right;
The first inner chamber catoptron 6 is common in described laser feedback exocoel catoptron 4, wave plate 6, second piezoelectric ceramics 32 and the described He-Ne laser instrument constitutes described laser feedback exocoel;
C: measuring system, described measuring system comprises:
Scanning interferometer is positioned at the outside of the above-mentioned second inner chamber catoptron 11, near the above-mentioned second inner chamber catoptron 11;
Oscillograph links to each other with above-mentioned scanning interferometer, observation zlasing mode, and the frequency difference of two orthogonal polarisation state during the saltus step of Laser Measurement polarization;
The quartz container 7 of described He-Ne laser instrument, the measured optical unit 10, quarter-wave plate 5 are fixed on separately the support, second piezoelectric ceramics 32 is fixed on the two-dimensional adjustment frame 2, and described each support, two-dimensional adjustment frame 2 are fixed on the platform 12 that is contained in the cover 1 separately;
Description of drawings
Fig. 1: laser feedback system schematic;
Fig. 2: laser feed-back wave plate measuring apparatus synoptic diagram;
Fig. 3: angle is 0, the zlasing mode during unglazed feedback;
Fig. 4: angle is 0, the zlasing mode during the quarter-wave plate feedback;
Fig. 5 angle is 1.6 °, the variation of zlasing mode under the quarter-wave plate feedback condition;
Fig. 6 angle is 3 °, the variation of zlasing mode under the quarter-wave plate feedback condition;
Fig. 7 difference on the frequency is with the experiment and the matched curve of variable angle;
Fig. 8 difference on the frequency is with the theoretical curve of variable angle.
Embodiment
Experimental provision as shown in Figure 1,6 and 11 is respectively the first inner chamber catoptron and the second inner chamber catoptron of laser instrument, their reflectivity R
1And R
2Be respectively 99.8% and 98.8%, the distance between them, promptly laserresonator length is designated as L; 8 is laser gain pipe, in He, Ne mixed gas are arranged, ratio is 7: 1; The 9th, anti-reflection window is fixed on an end of above-mentioned gain tube; 6,8, the 9 and 11 He-Ne laser instruments that constituted half exocoel 632.8nm jointly.31 is first piezoelectric ceramics, and it is fixed on the above-mentioned second inner chamber catoptron 11, and under the input voltage effect, it promotes the above-mentioned second inner chamber catoptron and moves along the laser axis direction is left and right, makes laser work at the single mode state; 4 is laser feedback exocoel catoptron, reflectivity R
3=10%; 32 is second piezoelectric ceramics, and it is fixed on the above-mentioned laser feedback exocoel catoptron 4, and under the input voltage effect, it promotes above-mentioned laser feedback exocoel catoptron 4 and moves along the laser axis direction is left and right; 10 is the measured optical unit, two-sided anti-reflection, and thickness is h, and when its crystallographic axis and the angle theta of light when changing, corresponding variation also takes place the bit phase delay of the measured optical unit, therefore can simulate the value of different bit phase delays by regulating angle; 4,5 and 6 have constituted the laser feedback exocoel jointly, and exocoel length is designated as l.Measuring system comprises scanning interferometer and oscillograph, the frequency difference of two orthogonal polarisation state of zlasing mode when being used for the detecting polarization saltus step.
The device that laser feedback optical element micro phase delay is measured as shown in Figure 2.1 is system's outer cover; The 2nd, the two-dimensional adjustment frame is fixed together with second piezoelectric ceramics 32, is used to regulate the collimation of feedback mirror 4; 5 is quarter-wave plate; The 7th, the quartz container of laser instrument can reduce the influence of external environment to laser instrument; 12 is system backplane, is used for the various piece of system is linked into an integrated entity, and increases the stability of system, improves the ability of anti-external interference; The quartz container 7 of above-mentioned He-Ne laser instrument and other device fixed support of respectively hanging oneself is fixed on the mounting platform 13 that is contained in the cover.
Example: as the experimental system of Fig. 1 or Fig. 2, under quarter-wave plate feedback situation, when the long variation of exocoel, two polarization eigen states of zlasing mode will replace vibration on two orthogonal directionss, the long every change λ of exocoel/4, the polarization state saltus step once, and two polarization states have the identical duration at a laser intensity in modulation period.When feedback mirror 4 under the promotion of piezoelectric ceramics 3, during along laser axis move left and right, can regulate the change frequency that is added in the scanning voltage on the piezoelectric ceramics 3, the polarization state saltus step that makes every 10ms left and right sides laser once, so just can the polarization mode of two alternate oscillations be simultaneously displayed on the oscillograph, realize the measurement of frequency difference by scanning interferometer.
At first, observe in the zlasing mode that does not have under the laser feedback situation.Making the crystallographic axis of the measured optical unit of laser inner chamber and the angle of light is 0 degree, and the zlasing mode that experiment obtains as shown in Figure 3.Fig. 3 shows that when not having the light feedback, because strong mode competition, single-mode laser has only a polarization state vibration, therefore can't observe two frequency differences between the polarization state.If introduce the quarter-wave plate feedback, and during the scanning exocoel, the experimental result of Fig. 4 will be observed.Fig. 4 shows, after the feedback of adding quarter-wave plate, when adding the voltage of linear variation on piezoelectric ceramics 3, can observe two patterns by scanning interferometer and oscillograph.If insert a polaroid in the scanning interferometer front, the polarization state that can find two patterns is a quadrature.When scan period of feedback mirror during less than 10ms, two polarization states appear on the oscillograph simultaneously, and the frequency of two eigenstates is different.
If change the crystallographic axis of quartz crystal and the angle of light, equal 1.6 ° and 3 ° respectively, under quarter-wave plate feedback situation, zlasing mode is as shown in Figure 5 and Figure 6.Can find that along with the increase of angle, the frequency difference between two polarization states also increases.In the polarization saltus step process of having drawn among Fig. 7, the empirical curve that the difference on the frequency Δ v between two orthogonal polarisation state changes with θ.Fig. 7 shows, in polarization saltus step process, the trend that difference on the frequency between two orthogonal polarisation state has monotone variation with the crystallographic axis and the angle between the light of quartz crystal, along with the increase of angle between quartz crystal crystallographic axis and the light, the difference on the frequency between two orthogonal polarisation state also increases.
Laser instrument output frequency difference is provided by following formula:
When calculating when carrying out numerical value, to quartzy parameter n
0, n
eValue be n
o=1.54263, n
e=1.55169.The thickness of wafer is got 3mm.The difference on the frequency of Theoretical Calculation with the theoretical curve of variable angle as shown in Figure 8.
Compare Theoretical Calculation and experimental result as can be seen, the two coincide, and therefore, utilizes the principle of the polarization saltus step of laser feedback generation can measure the small bit phase delay of optical element.
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| CN102155916B (en) * | 2011-03-02 | 2012-10-10 | 清华大学 | System for measuring phase orthogonal double-frequency laser feedback displacement |
| CN102155916A (en) * | 2011-03-02 | 2011-08-17 | 清华大学 | System for measuring phase orthogonal double-frequency laser feedback displacement |
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| CN102507158B (en) * | 2011-11-21 | 2014-02-12 | 中国科学院上海光学精密机械研究所 | Quarter-wave plate phase retardation distribution real-time measurement device and measurement method |
| CN102507158A (en) * | 2011-11-21 | 2012-06-20 | 中国科学院上海光学精密机械研究所 | Real-time measuring device and measuring method of quarter wave plate phase delay distribution |
| CN103185665A (en) * | 2013-03-13 | 2013-07-03 | 清华大学 | Method for measuring optical axis of birefringence element |
| CN103185665B (en) * | 2013-03-13 | 2015-08-12 | 清华大学 | The measuring method of birefringence element optical axis |
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| CN105576495A (en) * | 2016-03-14 | 2016-05-11 | 中国科学院武汉物理与数学研究所 | Residual amplitude modulation stabilization device based on wedge angle electro-optic crystal |
| CN105576495B (en) * | 2016-03-14 | 2019-01-29 | 中国科学院武汉物理与数学研究所 | Residual amplitude modulation stabilising arrangement based on angle of wedge electro-optic crystal |
| CN107655599A (en) * | 2017-09-14 | 2018-02-02 | 电子科技大学 | A kind of measuring method of optical element minimal stress |
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| CN108760249A (en) * | 2018-05-30 | 2018-11-06 | 西北大学 | The detection method and device of a kind of wave plate face phase-delay quantity |
| CN108760249B (en) * | 2018-05-30 | 2019-09-24 | 西北大学 | The detection method and device of a kind of wave plate face phase-delay quantity |
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