CN102944193A - Device and method for measuring phase and luminous intensity of splitting grating sub light beam array - Google Patents

Abstract

A method for measuring the phase and light intensity of a beam-splitting grating sub-beam array, which is characterized in that the incident laser light emitted by the laser is divided into two paths by the first beam splitter mirror: one path of transmitted light is collimated and expanded by the first collimated beam expander After forming a plane wave, the beam-splitting grating located on the front focal plane of the Fourier lens is irradiated vertically, reflected by the first mirror, then reflected by the second beam splitter, and finally enters the CCD camera; the other reflected light is reflected by the second mirror Finally, it first passes through the optical switch, then passes through the optical phase retarder, and then passes through the second collimated beam expander to become a plane reference light, transmits through the second beam splitter, and enters the CCD camera vertically. The CCD camera collects the light field intensity distribution and transmits the data to the computer for processing. When the optical switch is turned on, the phase of the beam-splitting grating sub-beam array can be obtained by phase-shifting interferometry; when the optical switch is turned off, the light intensity distribution of the beam-splitting grating sub-beam array can be directly obtained.

Description

Apparatus and method for phase and light intensity measurement of beam-splitting grating sub-beam array

technical field

The invention relates to a phase and light intensity measuring system, in particular to a phase and light intensity measuring device and method for a beam-splitting grating sub-beam array, which can measure the phase relationship between each diffraction order of the beam-splitting grating sub-beam array, At the same time, the light intensity distribution of each diffraction order can also be obtained.

Background technique

High-efficiency in-line multiple imaging by means of multiple phaseholograms[J].Opt.Commun.，1971，3(5)：312-315和L.A.Romero,and F.M.Dickey，"Theory of optimal beam splitting by phase gratings.I.One-dimensional gratings,"J.Opt.Soc.Am.A 24,2280-2295(2007).）因效率高，光束分布均匀性不受入射光强分布影响等优点成为目前最有效的分束器件之一。In many technical fields such as optical fiber communication, optical computing, image processing and optical disk storage, it is often required to convert the input of a single optical signal into the output of multiple signals, and optical beam splitting devices can realize the above requirements. There are many ways to realize the optical beam splitter, the beam splitting grating designed based on the principle of Fraunhofer diffraction (see H.Dammann, K.

High-efficiency in-line multiple imaging by means of multiple phase holograms[J].Opt.Commun., 1971, 3(5): 312-315 and LARomero, and FMDickey, "Theory of optimal beam splitting by phase gratings.I. One-dimensional gratings,"J.Opt.Soc.Am.A 24,2280-2295(2007).) Due to its high efficiency and the uniformity of beam distribution not affected by the distribution of incident light intensity, it has become one of the most effective beam splitting devices at present. one.

Traditional beam-splitting gratings, which can divide the incident light field into sub-beam arrays with equal intensity or specific intensity distribution (see S.X.Li, G.Yu, C.Y.Zheng, and Q.F.Tan, "Quasi-Dammann grating with proportional intensity array spots , "Opt.Lett.33, 2023-2025(2008)), the discussion of the beam splitting effect is limited to the light intensity of the sub-beam array (light intensity uniformity or consistency with the required specific light intensity distribution), while for The phase values of the sub-beam arrays are not discussed. The development of technology has also put forward requirements for the phase value of the beam splitting grating sub-beam array, for example, in coherent beam combining based on diffraction grating (see Yan Aimin, Liu Liren, Dai Enwen, Sun Jianfeng. Coherent array laser inverse Damman grating beam combining aperture filling device [Z].CN101592783,2009.), the processing of the phase compensation plate is based on the phase relationship between the sub-beam phase arrays of the beam splitting grating (see A.Yan, L.Liu, E.Dai et al..Simultaneous beam combination and aperture filling of coherent laser arrays by conjugate Dammann gratings[J].Opt.Lett., 2010, 35(8): 1251-1253 and D.Pab?uf, F.Emaury, S.de Rossi, R.Mercier, G.Lucas -Leclin, and P. Georges, "Coherent beam superposition of ten diode lasers with a Dammann grating," Opt. Lett. 35, 1515-1517 (2010)). At present, it is necessary to measure the phase and light intensity distribution of the beam-splitting grating sub-beam array.

Contents of the invention

The object of the present invention is to provide a phase and light intensity measuring device and method of a beam-splitting grating sub-beam array, the device can measure the phase and light intensity of the beam-splitting grating sub-beam array, and can measure the phase and light intensity are evaluated simultaneously.

Technical solution of the present invention is as follows:

A device for measuring the phase and light intensity of a beam-splitting grating sub-beam array, which is characterized in that its composition includes: the incident laser light emitted by the laser is divided into transmitted light and reflected light by a first beam splitter; After the collimated beam expander is collimated and expanded into a plane wave, it vertically irradiates the beam-splitting grating to be measured on the front focal plane of the Fourier lens. CCD camera, described CCD camera is positioned at the rear focal plane of described Fourier lens, and this CCD camera is connected with computer; After described reflected light is reflected by second reflection mirror, first passes through optical switch, then passes through optical phase The retarder then passes through the second collimated beam expander and becomes the plane reference light, which is transmitted through the second beam splitter and is vertically incident on the CCD camera.

The method for measuring phase and light intensity by using the above-mentioned measuring device for beam splitting grating sub-beam array phase and light intensity is characterized in that the method includes the following steps:

① Place the beam splitting grating to be measured on the front focal plane of the Fourier lens;

其中i=1、2、3、4，CCD相机采集四次干涉图像数据并传输到计算机中分别保存为I₁、I₂、I₃、I₄；②Turn on the optical switch, the two paths of light interfere on the receiving surface of the CCD camera, and adjust the phase of the optical phase retarder to move

Where i=1, 2, 3, 4, the CCD camera collects four interference image data and transmits them to the computer and saves them as I ₁ , I ₂ , I ₃ , I ₄ respectively;

③Computer according to the following formula Calculate the phase of the corresponding beam-splitting grating sub-beam array

④ When measuring the light intensity of the beam-splitting grating sub-beam array, turn off the optical switch, and the light intensity data collected by the CCD camera is the distribution of the light intensity of the beam-splitting grating sub-beam array to be measured.

Technical effect of the present invention:

The present invention proposes to measure the phase of the beam-splitting grating sub-beam array for the first time, and provides a measuring device and method for the phase and light intensity of the beam-splitting grating sub-beam array, which can measure the diffraction orders of the beam-splitting grating sub-beam array At the same time, the relative light intensity of each diffraction order can be obtained.

Description of drawings

Fig. 1 is the block diagram of phase and light intensity measuring device of beam-splitting grating sub-beam array of the present invention;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Referring to Fig. 1 first, Fig. 1 is a block diagram of the phase and light intensity measuring device of the beam-splitting grating sub-beam array of the present invention. The incident laser light emitted by the laser 1 is divided into two paths of transmitted light and reflected light by the first beam splitter 2: one path of transmitted light passes through the first collimated beam expander 3 and then vertically irradiates the beam splitting grating located on the front focal plane of the Fourier lens 5 4. After being transformed by the Fourier lens 5, the beam splitting grating 4 and the CCD camera 8 are respectively placed on the front and rear focal planes of the Fourier lens 5. Reflected by the first reflector 6, and then reflected by the second beam splitter 7 parallel to the first reflector to the CCD camera 8 positioned at the rear focal plane of the Fourier lens, the light of this path can pass behind the Fourier lens 5 The focal plane obtains the light field distribution of each diffraction order of the beam splitting grating 4;

CCD相机8采集四次两路光的干涉光场，并传输到计算机13中并分别保存为I₁、I₂、I₃、I₄，并根据公式计算出分束光栅4在傅里叶透镜5后焦面的子光束阵列的位相

When measuring the phase of the sub-beam array of the beam splitting grating 4, the other reflected light of the first beam splitter 2 is reflected by the second mirror 9 parallel to the first beam splitter, and then passes through the optical switch 10 (opened at this time), Then pass through the optical phase retarder 11, then pass through the second collimated beam expander 12 as a plane reference light, transmit through the second beam splitter 7, and finally vertically enter the CCD camera 8 and split the beam obtained with the first light The light fields of each diffraction order of the grating 4 interfere with each other; the optical phase retarder 11 moves four phases

The CCD camera 8 collects the interference light field of the two-way light four times, and transmits it to the computer 13 and saves it as I ₁ , I ₂ , I ₃ , and I ₄ respectively, and according to the formula Calculate the phase of the sub-beam array of the beam splitting grating 4 at the back focal plane of the Fourier lens 5

When measuring the light intensity distribution of the 4 sub-beams of the beam-splitting grating, the optical switch 10 in the second optical path is closed, and there is no reference light at this time, and the light intensity distribution collected by the CCD camera 8 is the light of the 4 sub-beam arrays of the beam-splitting grating. strong distribution.

Said laser 1 must be a laser capable of generating the working wavelength of the beam splitting grating 4 .

The relevant description of the beam splitting grating 4 to be tested is as follows:

The beam splitting grating 4 to be tested is a diffractive optical element that can split a beam of incident light into a beam array with a specific light intensity distribution and has a periodic amplitude transmittance function. Its amplitude transmittance can be written as:

${\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}{\overset{<span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}{\overset{<span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; mT</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; n</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>$

C_mn为复数，其值由分束光栅的透过率函数决定，其绝对值的平方即为分束光栅(m,n)衍射级次的光强，其幅角值即为分束光栅(m,n)衍射级次的位相值。Among them, T _g is the transmittance function of the whole grating, t _g is the amplitude transmittance function in a single period, Tx _{and Ty} are the period of the grating in the x, y direction. Its (m,n) level Fourier spectrum is

C _mn is a complex number, its value is determined by the transmittance function of the beam-splitting grating, the square of its absolute value is the light intensity of the diffraction order of the beam-splitting grating (m,n), and its argument value is the beam-splitting grating ( m,n) Phase values of diffraction orders.

The invention proposes to measure its phase value for the first time, and provides a measurement method, which can simultaneously measure the phase value and light intensity value of the light point array. The detailed derivation of formula used in the present invention is as follows:

其中a_g、

分别为分束光栅4子光束阵列的振幅和位相。参考光在CCD相机8面的光场分布为其中

为光学相位延迟器10产生的相移，a_r、

分别为参考光的振幅和位相。两光相干之后的光场分布为U_all=U_g+U_r，光强分布为：Assume that the field distribution of the spectrum of the beam splitting grating 4 on the back focal plane of the Fourier lens 5 (the surface of the CCD camera 8) is

where a _g ,

are the amplitude and phase of the beam-splitting grating 4 sub-beam arrays, respectively. The light field distribution of the reference light on the 8 surfaces of the CCD camera is in

is the phase shift produced by the optical phase retarder 10, a _r ,

are the amplitude and phase of the reference light, respectively. The light field distribution after the two lights are coherent is U _all =U _g +U _r , and the light intensity distribution is:

因此处采用平行参考光，所以上述公式可以简化为：

Therefore, parallel reference light is used here, so the above formula can be simplified as:

其中I_a=a_g ²+a_r ²，I_b=2a_ga_r。

Where I _a =a _g ² +a _r ² , I _b =2a _g a _r .

i=1、2、3、4.CCD相机8采集四次图像并分别保存I₁、I₂、I₃、I₄。The optical phase retarder 10 moves four phases respectively:

i=1, 2, 3, 4. The CCD camera 8 collects four images and saves I ₁ , I ₂ , I ₃ , and I ₄ respectively.

According to the relationship of trigonometric functions,

After simple calculation

Finally you can get:

From this, we obtained the formula for calculating the phase distribution of the beam-splitting grating with 4 sub-beam arrays.

Now take the measurement of the phase value and light intensity value of the 5×5 beam-splitting Damman grating sub-beam array suitable for 632.8nm wavelength as a specific example to further describe the present invention in detail, but this should not limit the protection scope of the present invention.

The 5×5 beam-splitting Damman grating can divide a beam of laser incident at 632.8nm into 5×5 lattices of equal light intensity, and the corresponding diffraction orders are (m,n), where m and n are respectively m=- 2,-1,0,1,2; n=-2,-1,0,1,2; these 25 diffraction orders have the same light intensity distribution, Table 1 is the theoretical phase of the 25 diffraction orders value.

The wavelength of the laser is a helium-neon laser with a wavelength of 632.8nm. The light emitted by it is divided into two paths by the first beam splitter: the transmitted light path is collimated and expanded by the collimator beam expander into parallel light, and then vertically irradiates the 5×5 beam splitter Daman placed on the front focal plane of the Fourier lens The grating, transformed by the Fourier lens, is reflected by the first mirror to the second beam splitter, and is reflected by the second beam splitter into the CCD camera, and the light field distribution is that of a 5×5 beam-splitting Damman grating Fourier spectrum Ug _; when measuring the phase value of the 5 × 5 beam splitting Damman grating sub-beam array, turn on the optical switch, the light reflected by the first beam splitter mirror is reflected by the second reflector parallel to it, and passes through After the optical switch, it passes through the optical phase retarder, and then collimates and expands the beam through the second collimator beam expander as the plane reference light U _r , passes through the second beam splitter, and is combined with the beam splitting grating The spectra interfere with each other at the receiving surface of the CCD camera (the back focal plane of the Fourier lens).

i=1、2、3、4.CCD相机8采集四次图像并分别保存I₁、I₂、I₃、I₄。最后根据公式

得到5*5分束光栅子光束阵列的位相分布。The optical phase retarder 10 moves four phases respectively:

i=1, 2, 3, 4. The CCD camera 8 collects four images and saves I ₁ , I ₂ , I ₃ , and I ₄ respectively. Finally according to the formula

The phase distribution of the 5*5 beam splitting grating sub-beam array is obtained.

When measuring the light intensity distribution of the beam-splitting grating sub-beam array, the optical switch in the second optical path is turned off, and there is no reference light at this time, and the light intensity distribution I _g of the beam-splitting grating sub-beam array can be directly obtained on the CCD surface.

Table 1 Theoretical value of phase value distribution of 5×5 beam-splitting Damman grating

Diffraction order -2 -1 0 1 2 -2 -1.8206π -0.8624π -0.9103π -0.9582π 0 -1 -0.8624π 0.0957π 0.0479π 0 0.9582π 0 -0.9103π 0.0479π 0 -0.0479π 0.9103π 1 -0.9582π 0 -0.0479π -0.0957π 0.8624π 2 0 0.9582π 0.9103π 0.8624π 1.8206π

Claims (2)

1. the position of a beam-splitting optical grating beamlet array mutually and the measurement mechanism of light intensity, it is characterized in that its formation comprises: the incident laser that laser instrument (1) sends is divided into transmitted light and reflected light through the first beam splitter (2): described transmitted light is after the first collimator and extender device (3) collimates and expands into plane wave, vertical irradiation is positioned at the beam-splitting optical grating to be measured (4) of fourier lense (5) front focal plane, after the first catoptron (6) reflection, through the second spectroscope (7), reflect again, finally enter CCD camera (8), described CCD camera (8) is positioned at the back focal plane of described fourier lense (5), this CCD camera (8) is connected with computing machine (13), described reflected light is after the second catoptron (9) reflection, first by photoswitch (10), then by optical phase delay device (11), then, by after the second collimator and extender device (12), becoming the plane reference light, the second spectroscope (7) described CCD camera of vertical incidence (8) is crossed in transmission.

2. utilize the measurement mechanism of beam-splitting optical grating beamlet array position phase claimed in claim 1 and light intensity to carry out position mutually and the measuring method of light intensity, it is characterized in that the method comprises the following steps:

1. beam-splitting optical grating to be measured (4) is placed in to described fourier lense (5) front focal plane;

2. open photoswitch (10), two-way light is interfered at described CCD camera (8) receiving plane, adjusts described optical phase delay device (11) travel(l)ing phase and is respectively

i=1,2,3,4 wherein, described CCD camera (8) gathers respectively the interference image data totally four times and be transferred in computing machine (13) and save as respectively I ₁, I ₂, I ₃, I ₄;

3. computing machine (13) utilizes following formula to calculate the position phase of corresponding beam-splitting optical grating (4) beamlet array

4. when measuring beam-splitting optical grating (4) beamlet array light intensity, close photoswitch (10), the light intensity data that described CCD camera (8) gathers is the distribution of the light intensity of beam-splitting optical grating to be measured (4) beamlet array.

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