CN102519712B - One-eighth wave plate phase retardation measurer and measuring method - Google Patents

Abstract

Disclosed are a one-eighth wave plate phase retardation measurer and a measuring method. The measurer comprises a collimating light source, and is characterized by successively consisting of a polarization spectroscope, a one-fourth wave plate, a one-eighth wave plate inserting opening and a reflector along an advancing direction of a light beam emitted from the collimating light source, a first photoelectric detector is placed on the polarization spectroscope in a light beam reflecting direction, a second photoelectric detector is placed in a direction which is perpendicular to incident light and opposite to the first photoelectric detector, output ends of the first photoelectric detector and the second photoelectric detector are connected with an input end of a signal processing unit, and an angle formed between a fast axis of the one-fourth wave plate and a light transmission axis of the polarization spectroscope is 45 degrees. Experiments show that the one-eight wave plate phase retardation measurer and the measuring method have the advantages of simple structure, fast measurement speed and high measurement precision.

Description

/ 8th retardation of wave plate measurement mechanism and measuring methods

Technical field

The present invention relates to polarized-light technique field, is a kind of 1/8th retardation of wave plate measurement mechanism and measuring methods.

Background technology

/ 8th wave plates are widely used in the applications such as immersion lithographic illuminator, nonlinear optical system, light time multiplex system, optical sensor, Particular Intervention instrument, synchro phase shifter./ 8th wave plates are conventionally placed in reflected light path and make twice linearly polarized light through it convert circularly polarized light to realize the change of polarization state.In the use procedure of 1/8th wave plates, phase-delay quantity error has a strong impact on its result of use, therefore need to accurately measure its phase-delay quantity.Generally the phase retardation of 1/8th wave plates is not indicated, requires phase-delay quantity measurement result and phase retardation irrelevant.

Formerly technology [1] is (referring to Zhu Linling, Zeng Aijun, Li Fanyue etc. with irrelevant 1/8th retardation of wave plate method for real-time measurement of quick shaft direction. Chinese laser, Vol.38,0508002-1-0508002-4,2011) described a kind of device that can measure 1/8th retardation of wave plates, this device is mainly comprised of light source, circular polarizer, two-dimensional quadrature grating, analyzer array and photodetector array.In measuring process, first utilize circular polarizer to form circularly polarized light and form light beam to be measured through 1/8th wave plates to be measured, measuring beam forms four bundle diffracted beams by two-dimensional quadrature raster beam-splitting, utilizes four intensity signals that analyzer array and detector array detect can measure in real time the phase-delay quantity of 1/8th wave plates.But this measurement mechanism has used the unconventional optical element such as two-dimensional grating, analyzer array and photodetector array, make it have the deficiencies such as complex structure, resetting difficulty be large, adopt sine function to solve phase-delay quantity simultaneously, be difficult to improve measuring accuracy.

Summary of the invention

The object of the invention is to overcome above-mentioned the deficiencies in the prior art, a kind of 1/8th retardation of wave plate real-time measurement apparatus and measuring methods are provided, this device has simple structure, measuring beam makes for twice phase-delay quantity double by 1/8th wave plate to be measured, utilizes cosine function to solve phase-delay quantity and has improved measuring accuracy.

Technical solution of the present invention is as follows:

A kind of measurement mechanism of 1/8th retardation of wave plates, comprise collimated light source, feature is that its formation is: in the light beam working direction of sending along described collimated light source, polarization spectroscope successively, quarter-wave plate, the socket of 1/8th wave plates, catoptron, in the folded light beam direction of described polarization spectroscope, place the first photodetector, perpendicular to incident light the direction contrary with the first described photodetector, placing the second photodetector, the input end of the output termination signal processing unit of the first described photodetector and the second photodetector, the light transmission shaft angulation of the fast axle of described quarter-wave plate and described polarization spectroscope is 45 °.

Described collimated light source is the assembly of laser instrument, light emitting diode and collimation lens assembly, white light source and the optical filter of output collimated light beam.

Described polarization spectroscope is the block prism of birefringece crystal prism, plating polarization spectro-film.

Described quarter-wave plate is crystalline material type quarter-wave plate, multi-component compound quarter-wave plate, reflection rib build quarter-wave plate or birefringent film type quarter-wave plate.

Described catoptron is plane mirror, can be also secondary reflection prism.

Described the first photodetector and the second photodetector have identical performance parameter, are photodiode, phototriode, photomultiplier or photoelectric cell.

Described signal processing unit is formed with the computing machine of corresponding data processing, analysis software by the multi-channel high-speed degrees of data capture card with A/D translation function, or is consisted of signal processing circuit and the microprocessor with respective handling function.

7, utilize 1/8th described retardation of wave plate measurement mechanisms to measure the method for 1/8th retardation of wave plates, it is characterized in that the method comprises the following steps:

1. 1/8th wave plates to be measured inserted in described 1/8th wave plate sockets (4) to be measured and adjust light path;

2. the first photodetector (6) described in the first described detector and the second photodetector (7) record respectively light intensity I1 and light intensity I2 and send into described signal processing unit (8);

3. the formula that described signal processing unit (8) calculates phase-delay quantity δ by following formula is:

$\mathrm{\δ}=\frac{1}{2}\arccos (K_1{I}_2/K_2{I}_1-1)$

Wherein: the instrument constant that K1, K2 are measurement mechanism, the first detector recording during unmeasured 1/8th wave plate in device normalization process and the light intensity of the second photodetector.

Compare with technology formerly, technique effect of the present invention is as follows:

1, improved the measuring accuracy of phase-delay quantity.Twice of measuring beam be by 1/8th wave plates to be measured, and the detectable signal after utilizing phase-delay quantity to double solves the phase-delay quantity of 1/8th wave plates, and measuring accuracy is doubled.

2, measurement mechanism is simple in structure.Light splitting and analyzing multiplexing functions in this 1/8th retardation of wave plates real-time measurement apparatus, without inserting special-purpose spectroscope and analyzer, can obtain simple structure.

3, experiment shows, the feature that the present invention has is simple in structure, measuring speed is fast and measuring accuracy is high.

Accompanying drawing explanation

Fig. 1 is the structured flowchart of the phase-delay quantity real-time measurement apparatus embodiment of a kind of 1/8th wave plates of the present invention

Embodiment

Below in conjunction with embodiment and accompanying drawing, the invention will be further described, but should not limit the scope of the invention with this.

First refer to Fig. 1, Fig. 1 is the structured flowchart of the phase-delay quantity real-time measurement apparatus embodiment of the present invention's 1/8th wave plates.As seen from Figure 1, the measurement mechanism embodiment of the present invention's 1/8th retardation of wave plates, comprise collimated light source 1, in the light beam working direction of sending along described collimated light source 1, polarization spectroscope 2 successively, quarter-wave plate 3, the socket 4 of 1/8th wave plates, catoptron 5, in the folded light beam direction of described polarization spectroscope 2, place the first photodetector 6, perpendicular to incident light the direction contrary with the first described photodetector 6, placing the second photodetector 7, the input end of the first described photodetector 6 and the output termination signal processing unit 8 of the second photodetector 7, the light transmission shaft angulation of the fast axle of described quarter-wave plate 3 and described polarization spectroscope 2 is 45 °.

Described collimated light source 1 is the assembly of laser instrument, light emitting diode and collimation lens assembly, white light source and the optical filter of output collimated light beam.

Described polarization spectroscope 2 is the block prism of birefringece crystal prism, plating polarization spectro-film.

Described quarter-wave plate 3 is crystalline material type quarter-wave plate, multi-component compound quarter-wave plate, reflection rib build quarter-wave plate or birefringent film type quarter-wave plate.

Described catoptron 5 is plane mirror, can be also secondary reflection prism.

Described the first photodetector 6 and the second photodetector 7 have identical performance parameter, are photodiode, phototriode, photomultiplier or photoelectric cell.

Described signal processing unit 8 is formed with the computing machine of corresponding data processing, analysis software by the multi-channel high-speed degrees of data capture card with A/D translation function, or is consisted of signal processing circuit and the microprocessor with respective handling function.

In 1/8th wave plate sockets to be measured that 1/8th wave plates 4 to be measured insert between quarter-wave plate 3 and catoptron 5.

The collimated light beam of collimated light source 1 outgoing forms two bunch polarized lights through polarization spectroscope 2 successively, wherein be polarized the direction of vibration of spectroscope 2 reflections perpendicular to the linearly polarized light formation reference beam of the plane of incidence, reference beam is received by the first photodetector 6, and its light intensity is I ₁, have:

I ₁＝aI ₀ (1)

Wherein a is reflective light intensity coefficient, I ₀for initial light intensity.The linearly polarized light formation measuring beam that is parallel to the plane of incidence by the direction of vibration of polarization spectroscope 2, the light intensity I of measuring beam ₁' be:

I ₁′＝bI ₀ (2)

Wherein b is transmitted light intensity coefficient.

Measuring beam is reflected mirror 5 reflections successively after quarter-wave plate 3,1/8th wave plates 4 to be measured, the measuring beam that is reflected mirror 5 reflections is again polarized spectroscope 2 reflections, analyzing and is received by the second photoelectric detector 7 after 1/8th wave plates 4 to be measured, quarter-wave plate 3, and its light intensity is I ₂.

The direction of thoroughly the shaking angle at 45 ° of the quick shaft direction of quarter-wave plate 3 and polarization spectroscope 2.Collimated laser beam becomes linearly polarized light after polarization spectroscope 2, its Jones matrix can be expressed as

E wherein ₀it is the amplitude of circularly polarized light.Quarter-wave plate 3, its Jones matrix can be expressed as

$G_{\frac{\mathrm{\λ}}{4}}=\left(\begin{array}{cc}1& 0\\ 0& i\end{array}\right).---\left(4\right)$

The Jones matrix of 1/8th wave plates 4 to be measured can be expressed as

$G_{\frac{\mathrm{\λ}}{8}}=\left(\begin{array}{cc}\cos \frac{\mathrm{\δ}}{2}-i\sin \frac{\mathrm{\δ}}{2}\cos \left(2\mathrm{\θ}\right)& -i\sin \frac{\mathrm{\δ}}{2}\sin \left(2\mathrm{\θ}\right)\\ -i\sin \frac{\mathrm{\δ}}{2}\sin \left(2\mathrm{\θ}\right)& \cos \frac{\mathrm{\δ}}{2}+i\sin \frac{\mathrm{\δ}}{2}\cos \left(2\mathrm{\θ}\right)\end{array}\right),---\left(5\right)$

Wherein δ is the phase-delay quantity of 1/8th wave plates 4 to be measured and approaches 45 °, and θ is the phase retardation of 1/8th wave plates 4 to be measured, and its variation range is 0 °～180 °.The Jones matrix of catoptron 5 is

$G_{\mathrm{ref}}=\left(\begin{array}{cc}-1& 0\\ 0& 1\end{array}\right).---\left(6\right)$

Jones matrix during 2 pairs of measuring beam analyzings of polarization spectroscope is expressed as

Therefore the Jones vector after polarization spectroscope 2 analyzings is expressed as

The interference light intensity I that the second photodetector 7 receives ₂for

By formula (1) and (9), can be obtained

cos2δ＝2aI ₂/bI ₁-1。(10)

In device normalization process, unmeasured 1/8th wave plates 4 to be measured obtain instrument constant and are just equivalent to make δ equal zero in formula (9), now the light intensity K on the first detector 6 of record ₁with the light intensity K on the second photodetector 7 ₂be respectively

K ₁＝aI ₀ (11)

K ₂＝bI ₀，(12)

Utilize formula (11) and (12) to obtain:

a/b＝K ₁/K ₂(13)

Formula (13) substitution formula (10) can be obtained:

cos2δ＝2K ₁I ₂/K ₂I ₁-1(14)

Utilize formula

$\mathrm{\δ}=\frac{1}{2}\arccos (K_1{I}_2/K_2{I}_1-1)---\left(15\right)$

Calculate the value of phase-delay quantity δ between 0 °～90 °, obtained the phase-delay quantity of 1/8th wave plates to be measured.

The first photodetector 6 and the second photodetector 7 at synchronization respectively by the light intensity I detecting ₁and I ₂change electric signal into, this electric signal carries out high speed processing by signal processing system 8, so this device can be realized the real-time measurement of the phase-delay quantity of 1/8th wave plates 4 to be measured.Twice of measuring beam be by 1/8th wave plates 4 to be measured, the detectable signal I after utilizing phase-delay quantity to double ₁, I ₂the phase-delay quantity that solves 1/8th wave plates, is doubled measuring accuracy.Polarization spectroscope 2 has been realized light splitting and analyzing multiplexing functions simultaneously, makes measurement mechanism can obtain simple structure without inserting special-purpose spectroscope and analyzer.

As shown in Figure 1, its concrete structure and parameter are as follows for the structure of most preferred embodiment of the present invention:

Collimated light source 1 is the semiconductor laser with collimation lens, and its optical maser wavelength is 635nm.Polarization spectroscope 2 is the block prism of plating polarization spectro-film.The zero level quartz wave-plate that quarter-wave plate 3 is λ/300 for phase delay accuracy of measurement.Catoptron 5 is plane mirror.The first photodetector 6 and the second photodetector 7 are PIN photodiode.Signal processing system 8 forms by multi-channel synchronous data acquisition card with the computing machine of data processing, analysis software.

Utilize 1/8th wave plates to be measured that above-described embodiment is 45 ° to phase-delay quantity to measure, experimental result shows that the measuring accuracy of the phase-delay quantity of 1/8th wave plates to be measured is 0.5 °.Experiment shows, the feature that the present invention has is simple in structure, measuring speed is fast and measuring accuracy is high.

Claims (7)

1. the measurement mechanism of a retardation of wave plate, comprise collimated light source (1), be characterised in that its formation is: in the light beam working direction of sending along described collimated light source (1), polarization spectroscope (2) successively, quarter-wave plate (3), the socket of 1/8th wave plates (4), catoptron (5), in the folded light beam direction of described polarization spectroscope (2), place the first photodetector (6), perpendicular to incident light the direction contrary with described the first photodetector (6), placing the second photodetector (7), the input end of described the first photodetector (6) and the output termination signal processing unit (8) of the second photodetector (7), the light transmission shaft angulation of the fast axle of described quarter-wave plate (3) and described polarization spectroscope (2) is 45 °.

2. the measurement mechanism of 1/8th retardation of wave plates according to claim 1, is characterized in that described polarization spectroscope is the block prism of birefringece crystal prism or plating polarization spectro-film.

3. the measurement mechanism of 1/8th retardation of wave plates according to claim 1, is characterized in that described quarter-wave plate (3) is for crystalline material type quarter-wave plate, multi-component compound quarter-wave plate, reflection rib build quarter-wave plate or birefringent film type quarter-wave plate.

4. the measurement mechanism of 1/8th retardation of wave plates according to claim 1, is characterized in that described catoptron (5) is plane mirror, or secondary reflection prism.

5. the measurement mechanism of 1/8th retardation of wave plates according to claim 1, it is characterized in that described the first photodetector and the second photodetector have identical performance parameter, is photodiode, phototriode, photomultiplier or photoelectric cell.

6. the measurement mechanism of 1/8th retardation of wave plates according to claim 1, it is characterized in that described signal processing unit (8) is formed with the computing machine of corresponding data processing, analysis software by the multi-channel high-speed degrees of data capture card with A/D translation function, or formed by signal processing circuit and the microprocessor with respective handling function.

7. utilize 1/8th described retardation of wave plate measurement mechanisms to measure the method for 1/8th retardation of wave plates, it is characterized in that the method comprises the following steps:

1. 1/8th wave plates to be measured inserted in described 1/8th wave plate sockets (4) to be measured and adjust light path;

2. the first photodetector (6) described in the first described detector and the second photodetector (7) record respectively light intensity I1 and light intensity I2 and send into described signal processing unit (8);

3. the formula that described signal processing unit (8) calculates phase-delay quantity δ by following formula is:

$\mathrm{\δ}=\frac{1}{2}\arccos (K_1{I}_2/K_2{I}_1-1)$

Wherein: the instrument constant that K1, K2 are measurement mechanism, the first detector recording during unmeasured 1/8th wave plate in device normalization process and the light intensity of the second photodetector.