CN101706361B - System and method for testing diffraction efficiency of acousto-optic tunable filter - Google Patents

Abstract

The invention discloses a system for testing the diffraction efficiency of an acousto-optic tunable filter (AOTF). The system comprises a wavelength tunable laser, a neutral density filter, a diaphragm orifice, a beam splitting mirror, a two-dimensional electric turnplate and an energy meter. The wavelength tunable laser can generate laser beams with continuously adjustable wavelength, the laser beams after passing through the neutral density filter and the diaphragm orifice are split into two beams of lasers with fixed beam splitting ratio by the beam splitting mirror, and the energy of reflecting beams is used as reference energy; transmission beams enter the AOTF, the energy of diffracted light is received when radio-frequency drive is applied to the transmission beams, and energy with direct penetration is received when the drive is not applied to the transmission beams, thereby calculating the diffraction efficiency of the AOTF. Meanwhile, the measurement of an aperture angle can be realized by changing the angle of incident light through the two-dimensional electric turnplate. The device has the characteristics of simple principle and strong operability, can meet the requirement of testing the continuous wavelength of the AOTF and can also enhance the testing accuracy greatly by utilizing reference beams generated by the beam splitting mirror.

Description

Diffraction efficiency of acousto-optic tunable filter test macro and method of testing

Technical field:

The present invention relates to optical measuring technique, specifically refer to a kind of diffraction efficiency of acousto-optic tunable filter test macro and method.

Background technology:

(Acousto-optic tunable filter AOTF) is a kind of arrowband tunable optical filter to acousto-optic tunable filter, and it is the light-splitting device of making according to the acousto-optic interaction principle.The frequency that is applied to radio-frequency driven on the crystal by change is selected the branch optical wavelength, thereby realizes length scanning.This technology has been widely used in non-imaging and imaging spectral instrument at present.

The light-dividing principle of AOTF: shown in accompanying drawing 1, accompanying drawing 2, when a branch of polychromatic light by a dither have the flexible crystal of optics the time, the monochromatic light of a certain wavelength will produce diffraction at crystals, from crystal, transmit at a certain angle, the polychromatic light that diffraction does not take place is then crossed crystal along the direct transmission of former light ray propagation direction, reaches the purpose of beam split thus.When the crystal vibration frequency changes, the also corresponding change of the monochromatic wavelength of transmissive.Isotropy and anisotropy Bragg diffraction can both be used for filtering device, but adopt isotropic body to make optical filter practicality extreme difference, it requires harsh (subtended angle is in the per mille radian) for the collimation of incident light, small deviation also can cause spectral band-width significantly to be widened, and the angle of diffraction of different wave length correspondence is also different, therefore, AOTF adopts birefringece crystal anisotropy Bragg diffraction.In anisotropy AOTF, the angle of incidence of light that incides AOTF has a little change δ θ _iThe time, because double refraction amount has compensated the momentum mismatch that causes because of the angle variation just with the variation of angle, so still can keep the approximate establishment of momentum matching condition, acoustooptic diffraction changes not very sensitive in certain angle to incident light, thereby can make the AOTF of big angular aperture.

The measuring technology of AOTF diffraction efficiency: according to the light-dividing principle of AOTF, the collimation and the beam diameter of incident beam had higher requirements,, require the diameter of light beam and emission angle as far as possible little for satisfying certain measuring accuracy.And need realize that to the test of AOTF diffraction efficiency all band covers.

At present, the domestic method that the AOTF diffraction efficiency is tested mainly concentrates on and adopts continuous wide spectrum light source (for example halogen tungsten lamp), carries out the spectral characteristic test of emergent light by the spectrum receiving system, and its proving installation synoptic diagram is seen accompanying drawing 3.At first the light source collimation utilizes polaroid to produce orthogonal polarized light incident, utilizes spectrometer to receive 0 grade of light spectrum.If the spectral intensity of 0 grade of light is I when not adding radiofrequency signal ₀, add that 0 grade of light minimum value is I after the radio-frequency driven, diffraction efficiency T=(I ₀-I)/I ₀Under the situation that driving power is fixed, change AOTF radio-frequency driven frequency, can carry out spectral scan.The defective of this method is, because the light source collimation back depth of parallelism does not have laser good, and the laser of different angles incident can produce bigger variation to the test result of AOTF diffraction efficiency, so result who tests with this method and the diffraction efficiency of actual AOTF have difference.

If adopt laser as light source, then only need to utilize the energy receiving system just can carry out the measurement and the calculating of luminous energies at different levels easily, thereby draw the AOTF diffraction efficiency.But adopt this kind method of testing, the laser instrument of single wavelength can't satisfy the demand of the continuous spectral coverage of AOTF test, and this kind method of testing to the stability requirement of energy of lasers than higher.So, only utilize laser to carry out the test of AOTF diffraction efficiency at present as light source in indivedual fixed band, can't satisfy the demand of AOTF all band test.

Summary of the invention:

The device that the purpose of this invention is to provide a kind of AOTF of measurement diffraction efficiency solves energy of lasers instability, the inconsistent technical matters that causes measuring error of energy meter sonde response.

As shown in Figure 4, the present invention is as testing light source with EKSPLA NT342/1/UV Wavelength tunable laser 1, light beam incides beam splitter 4 after by neutral density filter 2 and aperture 3, by beam splitter 4 incident light is divided into the fixedly transmitted light and the reflection reference light of splitting ratio.Adjust light path, make transmitted light vertically enter AOTF71 to be measured, 72 couples of AOTF71 apply driving frequency by the AOTF driver.Energy meter probe 61 receives the beam energy that sees through AOTF71, and energy meter probe 62 receives the energy of reference beam synchronously.

Concrete grammar: adjust laser wavelength, AOTF71 is added certain radio-frequency driven, the energy meter probe 61 diffraction light energy that receive are E ₁, the energy meter probe 62 reference beam energy that receive synchronously are E ₂, work as E ₁/ E ₂Be to diffraction centre wavelength that should the RF driving frequency when maximum.

Do not add under the radio-frequency driven the direct emergent light ENERGY E of energy meter probe 61 AOTF that receive ₁', energy meter probe 62 reflected beam energy that receive synchronously are E ₂', formula for calculating diffraction efficiency is as follows:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="H2009102264978E00021.png"\; state="\{\{state\}\}">E</figure-callout>}}_1}{\mathrm{\&eta;}{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="H2009102264978E00021.png"\; state="\{\{state\}\}">E</figure-callout>}}_2}=\frac{{{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="H2009102264978E00021.png"\; state="\{\{state\}\}">E</figure-callout>}}_1}^{\&prime;}}{{{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="H2009102264978E00021.png"\; state="\{\{state\}\}">E</figure-callout>}}_2}^{\&prime;}},$ Then $\mathrm{\&eta;}=\frac{E_1{E_2}^{\&prime;}}{E_2{E_1}^{\&prime;}}---(1-1)$

Rotate the incident angle of light that can change AOTF71 by two-dimentional electrical turntable 5, work as E ₁/ E ₂The angle variation that drops to maximal value one half correspondence is the crystal aperture angle.

Wavelength tunable laser 1: 210～2300nm is provided continuous adjustable laser wavelength, and laser beam divergence is less than 0.5mrad, and the sweep spacing of 210～709nm band spectrum is 0.1nm, and the sweep spacing of 710～2300nm band spectrum is 1nm.

Neutral density filter 2 and aperture 3 may command incident light energy, and the size of limit laser hot spot.The effect of beam splitter 4 is to produce reference beam, realizes the significantly raising of measuring accuracy.Wavelength tunable laser energy instability, the energy value comparability of single measurement is low.Two energy meter sonde response rates are inconsistent, and need the number of wavelengths of testing more in the test, so will demarcate certain difficulty to the sonde response coefficient under each wavelength.The beam splitter that adds in the optical system for testing can produce reflected reference beam, and its energy is monitored, and the splitting ratio of beam splitter under specified wavelength is steady state value, so it is constant to enter energy and the reference beam energy ratio of AOTF71.Beam splitter plays the effect that improves measuring accuracy.Because AOTF71 logical optical efficiency under specified wavelength is constant, so can replace directly test diffraction light energy by the ratio of diffraction light energy and reference beam energy.

Two dimension electrical turntable 5 can be adjusted the angle of incident light, and one is used for the light path adjustment, and two are used for aperture angle measures.

The advantage of this patent is:

1) the present invention as incident light source, can satisfy the demand of AOTF needs high density, closely-spaced wavelength measurement with Wavelength tunable laser.

2) the present invention utilizes beam splitter to carry out the beam splitting of incident light energy,, offsets energy of lasers instability and the inconsistent test error that causes of energy meter sonde response rate, thereby significantly improves AOTF diffraction efficiency measuring accuracy as monitoring by the reference beam energy.

Description of drawings:

Fig. 1 anisotropy AOTF polar plot.

Fig. 2 AOTF beam split synoptic diagram.

Fig. 3 is wide light source AOTF diffraction efficiency test macro synoptic diagram.

Fig. 4 is an AOTF diffraction efficiency test macro synoptic diagram.

Embodiment:

Be a better embodiment of the present invention who provides according to Fig. 4 below, in order to architectural feature of the present invention and implementation method to be described, rather than be used for limiting scope of the present invention.

The diffraction efficiency of acousto-optic tunable filter test macro comprises following several sections:

1) Wavelength tunable laser 1: select EKSPLA NT342/1/UV Wavelength tunable laser 1 as light source in the present embodiment.This laser instrument can produce 210～2300nm continuously adjustable laser beam.

2) neutral density filter 2: select the Spiricon neutral density filter in the present embodiment.

3) aperture 3: the present embodiment is selected the photoelectricity GCM-57 of Daheng iris for use.

4) beam splitter 4: present embodiment selects fixedly that splitting ratio is 1: 1 (beam splitter of 600～1200nm) for use.Can change in its all band splitting ratio, but at certain fixed wave length, the device splitting ratio is constant.

5) two-dimentional electrical turntable 5: present embodiment is selected friendship ties 148 * 142 two-dimentional electric rotary tables for use, 360 ° of range of adjustment, the ratio of gear of motor 1: 360,0.1 ° of scale least count, 0.005 ° of motor synchronizing operation resolution.

6) the energy meter probe 61,62: present embodiment is selected the U.S. EPM1000 of Coherent company energy meter gauge outfit for use, and probe is selected J4-09 and J45LP-MB for use.

Present embodiment select for use U.S. Brimrose visible/near infrared AOTF71 and supporting radio driver 72 be as the AOTF assembly.Selected laser wavelength is regulated two-dimentional electrical turntable 5, makes Wavelength tunable laser 1 emission light beam by neutral density filter 2, aperture 3, beam splitter 4 back vertical incidence AOTF71, is received the reference beam of beam splitter reflection by energy meter probe 62.When AOTF 71 is not added driving, behind AOTF71, receive 0 grade of luminous energy by energy meter probe 61; When AOTF71 is applied driving, behind AOTF71, receive the diffraction light energy by energy meter probe 61.In test process, two energy meter probes 61,62 receive synchronously.Calculate the diffraction efficiency of AOTF71 by the formula (1-1) of aforementioned calculation diffraction efficiency.

As mentioned above, the method for testing of this test macro is simple, workable, is comparatively desirable AOTF diffraction efficiency proving installation.

Claims (3)

1. acousto-optic tunable filter AOTF diffraction efficiency test macro, it comprises light source, neutral density filter (2), aperture (3), beam splitter (4), two-dimentional electrical turntable (5), first energy meter probe (61), second energy meter probe (62), it is characterized in that: the described light source in the described test macro adopts Wavelength tunable laser (1); The laser beam that described Wavelength tunable laser (1) sends is successively by neutral density filter (2), aperture (3) back is divided into the fixedly transmitted light and the reflection reference light of splitting ratio by beam splitter (4) with incident light, transmitted light vertical incidence AOTF to be measured (71), by AOTF driver (72) AOTF (71) is applied radio-frequency driven, receive the beam energy that sees through AOTF (71) by first energy meter probe (61), second energy meter probe (62) receives the energy of reflected reference beam synchronously, and the laser energy that second energy meter probe (62) is measured reflected reference beam is used to compensate laser energy unstable and first energy meter probe (61) and the inconsistent measuring error that causes of second energy meter probe (62) response.

2. a kind of acousto-optic tunable filter AOTF diffraction efficiency test macro according to claim 1, it is characterized in that: described Wavelength tunable laser (1) adjustable laser wavelength coverage continuously is 210～2300nm, laser beam divergence is less than 0.5mrad, the sweep spacing of 210～709nm band spectrum is 0.1nm, and the sweep spacing of 710～2300nm band spectrum is 1nm.

3. acousto-optic tunable filter AOTF diffraction efficiency method of testing based on the described system of claim 1 is characterized in that may further comprise the steps:

A. adjust laser wavelength, AOTF (71) is added certain radio-frequency driven, measure the diffraction light ENERGY E of measuring on the light path by first energy meter probe (61) ₁, measure reflected beam energy E on the reference path by second energy meter probe (62) simultaneously ₂

B. do not add under the radio-frequency driven, measure by first energy meter probe (61) and measure direct emergent light ENERGY E on the light path ₁', measure reflected beam energy E on the reference path by second energy meter probe (62) simultaneously ₂';

C. calculate the AOTF diffraction efficiency, computing formula is as follows:

$\mathrm{\&eta;}=\frac{E_1{E_2}^{\&prime;}}{E_2{E_1}^{\&prime;}}---\left(1\right).$

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