CN103411689A - Laser wavelength direct measurement method and device based on single frequency orthogonal linearly polarized light - Google Patents

Abstract

The invention discloses a laser wavelength direct measurement method and device based on single-frequency orthogonal linearly polarized light. The laser light to be measured with a wavelength of λ _x passes through a polarizer and a quarter-wave plate to form circularly polarized light, and shoots to two sets of Michelson interferometers to form two-way interference signals of horizontally polarized and vertically polarized components; first, the PZT The driver modulates the reference corner cube to move back and forth, and measures the phase difference of the two interference signals

Then the reference corner cube is stationary, and the measurement corner cube moves a certain displacement ΔL, and the whole cycle number N of the horizontal polarization component interference signal is measured by the bidirectional counting module; the phase difference of the two interference signals at this time is measured by modulating the reference corner cube again

Depend on The fractional variation of the horizontal polarization component interference signal is obtained; according to the displacement ΔL and the measured integer cycle number N and fractional ε, the wavelength λ _x to be measured is calculated by the computer. The optical path of the invention has a simple structure, does not need a reference laser, has high measurement accuracy, and can realize large-scale measurement of wavelengths.

Description

Method and device for direct measurement of laser wavelength based on single-frequency orthogonal linearly polarized light

technical field

The invention relates to a laser wavelength measurement method and device, in particular to a laser wavelength direct measurement method and device based on single-frequency orthogonal linearly polarized light.

Background technique

Laser wavelength is used as a measurement reference value and is widely used in the measurement of length, speed, angle, flatness, straightness and verticality. It is an important measurement parameter in the fields of precision metrology, precision machinery and microelectronics industry. The size is the key to ensure the accuracy of geometric measurement and the traceability of the value. Laser wavelength measurement methods are generally divided into: 1. The measurement method of laser frequency (wavelength) based on the harmonic optical frequency chain. In the actual measurement process of this method, if the gap between the optical frequencies in the chain is too large (more than 10GHz), It is very difficult to build a bridge between the known optical frequency and any unknown optical frequency; 2. The optical frequency (wavelength) measurement method based on the optical frequency interval division (OFID) frequency chain, but a method that can cover the microwave segment to The OFID chain of hundreds of THz in the optical frequency band is still extremely complicated; 3. The optical frequency (wavelength) measurement method based on the optical frequency comb is very difficult to achieve high measurement accuracy by using this method. The higher the measurement accuracy, the greater the impact on the instrument. The higher the requirements are, the more complex the measurement system will be; 4. The laser wavelength measurement method based on the Michelson interference principle requires a reference laser as a reference light source, and the measurement accuracy is affected by the reference laser; 5. Based on the principle of virtual synthetic wavelength A laser frequency (wavelength) measurement method that involves phase comparisons between signals of different frequencies.

The direct measurement method of laser wavelength based on single-frequency orthogonal linearly polarized light does not require a reference light source, and there is no phase comparison between signals of different frequencies. It can realize continuous measurement of wavelengths in a large range with high measurement accuracy.

Contents of the invention

In order to meet the need for high-precision laser wavelength measurement, the purpose of the present invention is to provide a method and device for direct measurement of laser wavelength based on single-frequency orthogonal linearly polarized light, which converts the measurement of unknown wavelengths into full-period counting of interference fringe signals The measurement of the phase difference with the two-way interference signal does not require a reference light source, and can realize continuous and direct measurement of a large range of laser wavelengths.

The technical solution adopted by the present invention to solve its technical problems is:

1. A direct measurement method of laser wavelength based on single-frequency orthogonal linearly polarized light:

(1) The laser output wavelength of the laser to be tested is _λx to form linearly polarized light after passing through the polarizer, and to form circularly polarized light after being directed to a quarter-wave plate whose e-axis and the polarization direction of the linearly polarized light form an angle of 45°. Circularly polarized light is composed of single-frequency orthogonal linearly polarized light, which is sent to two sets of Michelson interferometers to form interference signals of horizontal polarization component and vertical polarization component, which are respectively received by their respective photodetectors;

PZT驱动器停止调制；(2) First measure that the corner cube does not move, and the PZT driver modulates the reference corner cube to move back and forth within a stroke of 5 μm, and the interference signal of the λ _x vertical polarization component and the interference signal of the λ _x horizontal polarization component are measured by the phase difference measurement module phase difference

PZT driver stops modulation;

(3) Then measure the movement of the corner cube ΔL=100mm, and measure the integer cycle number N of the λ _x horizontal polarization component interference signal change by the bidirectional counting module;

则λ_x水平偏振分量干涉信号的小数变化量ε为：(4) Modulate the reference corner cube again to move back and forth within a stroke of 5 μm, and the phase difference between the interference signal of the λ _x vertical polarization component and the interference signal of the λ _x horizontal polarization component measured by the phase difference measurement module is

Then the fractional change ε of the interference signal of the horizontal polarization component of λ _x is:

(5) According to the measured displacement ΔL of the cube-corner prism and the measured number of cycles N of the interference signal change of the λ _x horizontal polarization component and the fractional change ε, the wavelength of the laser to be measured is obtained as:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;L</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>}$

At this point, the wavelength of the laser to be tested is obtained.

2. A laser wavelength direct measurement device based on single-frequency orthogonal linearly polarized light:

The invention comprises a laser to be measured, a polarizer, a quarter wave plate, a first beam splitter, a PZT driver, a reference corner cube, a first polarizing beam splitter, a measuring corner cube, a second polarizing beam splitter, and a second beam splitter mirror, a first photodetector, a second photodetector, a third photodetector, a phase difference measurement module, a bidirectional counting module and a computer; the laser output wavelength of the laser to be measured is _λx to form linearly polarized light through a polarizer, and The circularly polarized light composed of single-frequency orthogonal linearly polarized light is formed behind the quarter-wave plate whose e-axis and the polarization direction of the linearly polarized light are at an angle of 45°, wherein the λ _x vertically polarized component is directed to the first beam splitter , the first set of Michelson interferometer that is installed on the reference corner cube prism on the PZT driver and the first polarized beam splitter, forms the interference signal of the vertically polarized component, and the λ _x horizontally polarized component shoots to the first beam splitter, the reference angle The second set of Michelson interferometer composed of axicon prism and measuring corner prism forms the interference signal of the horizontal polarization component; the interference signal of the vertical polarization component is received by the first photodetector after being reflected by the second polarization beam splitter, and the interference signal of the horizontal polarization component After the signal is transmitted by the second polarization beam splitter and split by the second beam splitter, it is respectively received by the second photodetector and the third photodetector; the two-way interference received by the first photodetector and the second photodetector The signal is sent to the phase difference measurement module, and the two-way interference signals received by the second photodetector and the third photodetector are sent to the bidirectional counting module, and the phase difference measurement module and the bidirectional counting module are connected to a computer.

The beneficial effects that the present invention has are:

The invention converts the measurement of the unknown wavelength into the whole cycle count of the interference fringe signal and the measurement of the phase difference of the two interference signals, and can realize the high-precision measurement of the laser wavelength. The optical path structure of the invention is simple, and no reference laser is needed. It is convenient and has high measurement accuracy, can realize a wide range of wavelength measurement, and can be widely used in the field of optical precision measurement technology.

Description of drawings

Figure 1 is a schematic diagram of direct measurement of laser wavelength based on single-frequency orthogonal linearly polarized light.

Fig. 2 is a schematic diagram of the phase difference change of the interference signal of the λ _x vertical polarization component and the λ _x horizontal polarization component before and after the measurement of the corner cube.

In the figure: 1. Laser to be tested, 2. Polarizer, 3. Quarter-wave plate, 4. First beam splitter, 5. PZT driver, 6. Reference corner cube, 7. First polarizing beam splitter, 8. Measuring corner cube, 9. Second polarization beam splitter, 10. Second beam splitter, 11. First photodetector, 12. Second photodetector, 13. Third photodetector, 14. Phase difference Measuring module, 15, two-way counting module, 16, computer.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the present invention comprises a laser to be measured 1, a polarizer 2, a quarter-wave plate 3, a first beam splitter 4, a PZT driver 5, a reference corner cube 6, a first polarizing beam splitter 7, and a measurement Corner cube prism 8, the second polarization beam splitter 9, the second beam splitter 10, the first photodetector 11, the second photodetector 12, the third photodetector 13, phase difference measurement module 14, bidirectional counting module 15 and computer16. The laser light output by the laser 1 to be tested with a wavelength of λ _x passes through the polarizer 2 to form linearly polarized light, and then shoots to a quarter-wave plate whose e-axis and the polarization direction of the linearly polarized light form an angle of 45° to form circularly polarized light. The polarized light is composed of single-frequency orthogonal linearly polarized light, wherein the λ _x vertically polarized component is directed to the first beam splitter 4, the reference corner cube prism 6 installed on the PZT driver 5 and the first polarizing beam splitter 7. Set Michelson interferometer, form the interference signal of vertically polarized component; Simultaneously, λ _x horizontally polarized component shoots to the second set of Michelson interferometer that is made up of first beam splitter 4, reference corner cube prism 6 and measuring corner cube 8 , forming the interference signal of the horizontal polarization component; the interference signal of the vertical polarization component is received by the first photodetector 11 after being reflected by the second polarization beam splitter 9, and the interference signal of the horizontal polarization component is transmitted through the second polarization beam splitter 9, and then After being reflected and transmitted by the second beam splitter 10, it is received by the second photodetector 12 and the third photodetector 13; the two-way interference signals received by the first photodetector 11 and the second photodetector 12 are sent into the phase The difference measurement module 14, the two interference signals received by the second photodetector 12 and the third photodetector 13 are sent to the bidirectional counting module 15, and the measurement results of the phase difference measurement module 14 and the bidirectional counting module 15 are sent to the computer 16.

Note that L ₀ is the initial optical path difference between the reference optical path and the measuring optical path of the first Michelson interferometer, and L ₁ is the initial optical path difference between the reference optical path and the measuring optical path of the second Michelson interferometer.

Before the measurement starts, the first detector 11 detects that the phase of the interference signal of the vertical polarization component is:

The phase of the horizontal polarization component interference signal detected by the second detector 12 is:

The initial phase difference between the two interference signals is:

Measure the displacement ΔL of the corner cube prism 8, and the phase of the interference signal of the horizontal polarization component becomes:

At this time, the phase difference of the two interference signals becomes:

The phase difference change of the two-way interference signals is shown in Figure 2. V(λ _x ) represents the interference signal waveform of the vertically polarized component of the wavelength λ _x , and V(λ _x|| ) represents the measurement before the corner cube moves. The interference signal waveform of the horizontally polarized component of λ _x , V(λ′ _{x | |} ) represents the interference signal waveform of the horizontally polarized component of λ _x after the measurement of the corner cube.

Subtract formula (3) from formula (5) to get:

In the formula: N is the whole cycle number of λ _x horizontal polarization component interference signal change, ε is the fractional variation of λ _x horizontal polarization component interference signal.

According to formula (6), the unknown wavelength _λx can be calculated as:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;\; L</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

The specific implementation steps of direct measurement of laser wavelength based on single-frequency orthogonal linearly polarized light are as follows:

(1) Before the measurement starts, the measurement corner cube 8 does not move, and the reference corner cube 6 is modulated by the PZT driver 5 to move back and forth within a stroke of 5 μm. At this time, the λ _x vertical polarization component measured by the first photodetector 11 is The interference signal and the interference signal of the λ _x horizontal polarization component measured by the second photodetector 12 are sent to the phase difference measurement module 14 (Agilent 53220A general frequency counter), and the measured phase difference is

(2) The PZT driver 5 stops the modulation, and the measurement corner cube 8 moves a certain displacement ΔL=100mm, and through the mechanical phase shifting method, the λ _x horizontal polarization component detected by the second photodetector 12 and the third photodetector 13 The two-way signal with a phase difference of 90° of the interference signal is sent to the bidirectional counting module 15 (HP HCTL-2020 type counter circuit chip), and the whole cycle number N of the λ _x horizontal polarization component interference signal is measured;

(3) Modulate the reference corner cube 6 to move back and forth within a stroke of 5 μm again. It is measured that the phase difference of the two interference signals becomes

和

得出λ_x水平偏振分量的干涉信号小数变化量ε：(4) According to the measurement of the phase difference of the two interference signals before and after the movement of the corner cube prism 8

and

The fractional change ε of the interference signal of the horizontal polarization component of λ _x is obtained:

(5) The computer 16 (Lenovo Qitian M7300 type) is based on the measured integer cycle number N of the λ _x horizontal polarization component interference signal, the fractional change of the interference signal ε, and the displacement ΔL of the measurement of the corner cube prism 8, according to the following formula The wavelength of the laser to be measured is calculated as:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;L</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Substituting typical values: the wavelength λ _x of the laser to be measured is 633nm, the displacement of the measurement corner cube prism 8 is ΔL=100mm, the whole cycle number N of the interference signal is 315955, and the fractional change of the interference signal ε is 0.7662. When the measurement corner cube prism moves The positioning accuracy of the displacement is 0.1 nm, and when the interference fringe subdivision coefficient is 1/4096, the measurement accuracy of the laser wavelength to be measured is 1.23×10 ^-9 .

The present invention has been completed thus far.

Claims (2)

1. A laser wavelength direct measurement method based on single-frequency orthogonal linearly polarized light, characterized in that: (1) The laser output wavelength of the laser to be tested is _λx to form linearly polarized light after passing through the polarizer, and to form circularly polarized light after being directed to a quarter-wave plate whose e-axis and the polarization direction of the linearly polarized light form an angle of 45°. Circularly polarized light is composed of single-frequency orthogonal linearly polarized light, which is sent to two sets of Michelson interferometers to form interference signals of horizontal polarization component and vertical polarization component, which are respectively received by their respective photodetectors; (2) First measure that the corner cube does not move, and the PZT driver modulates the reference corner cube to move back and forth within a stroke of 5 μm, and the interference signal of the λ _x vertical polarization component and the interference signal of the λ _x horizontal polarization component are measured by the phase difference measurement module phase difference

PZT driver stops modulation; (3) Then measure the movement of the corner cube ΔL=100mm, and measure the integer cycle number N of the λ _x horizontal polarization component interference signal change by the bidirectional counting module; (4) Modulate the reference corner cube again to move back and forth within a stroke of 5 μm, and the phase difference between the interference signal of the λ _x vertical polarization component and the interference signal of the λ _x horizontal polarization component measured by the phase difference measurement module is

Then the fractional change ε of the interference signal of the horizontal polarization component of λ _x is: (5) According to the measured displacement ΔL of the cube-corner prism and the measured number of cycles N of the interference signal change of the λ _x horizontal polarization component and the fractional change ε, the wavelength of the laser to be measured is obtained as: ${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;\; L</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>}$ At this point, the wavelength of the laser to be tested is obtained. 2. a kind of laser wavelength direct measuring device based on the single-frequency orthogonal linearly polarized light of method according to claim 1, it is characterized in that: comprise laser to be measured (1), polarizer (2), quarter-wave sheet (3), first beam splitter (4), PZT driver (5), reference corner cube (6), first polarizing beam splitter (7), measuring corner cube (8), second polarizing beam splitter ( 9), the second beam splitter (10), the first photodetector (11), the second photodetector (12), the third photodetector (13), phase difference measurement module (14), bidirectional counting module ( 15) and computer (16); the laser to be measured (1) output wavelength is that λ _x forms linearly polarized light through a polarizer (2), and shoots to a quarter of an angle of 45° between the e axis and the polarization direction of the linearly polarized light One of the wave plates (3) forms circularly polarized light composed of single-frequency orthogonal linearly polarized light, wherein the λ _x vertically polarized component is directed to the reference beam mounted on the PZT driver (5) by the first beam splitter (4) The first cover of Michelson interferometer that corner cube prism (6) and the first polarizing beam splitter (7) form forms the interference signal of vertically polarized component, and λ _x horizontally polarized component shoots to by the first beam splitter (4), reference The second set of Michelson interferometers formed by the corner cube (6) and the measuring corner cube (8) form the interference signal of the horizontal polarization component; the vertical polarization component interference signal is reflected by the second polarization beam splitter (9) and then reflected by the second polarization beam splitter (9). Received by a photodetector (11), the interference signal of the horizontal polarization component is transmitted by the second polarization beam splitter (9), split by the second beam splitter (10), and then detected by the second photodetector (12) and the third photoelectric detector respectively Device (13) receives; The described two-way interference signal that the first photodetector (11) and the second photodetector (12) receive sends phase difference measurement module (14), and the second photodetector (12) The two-way interference signals received by the third photodetector (13) are sent to a bidirectional counting module (15), and the phase difference measurement module (14) and the bidirectional counting module (15) are connected to a computer (16).

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