CN104568391B - Double light path switching mutually refers to high-precision A OTF performance test methods and device - Google Patents

Abstract

The invention discloses a dual optical path switching cross-reference high-precision AOTF performance testing method and device. This test method uses the optical path switching component to realize the stable switching of ±1 level of the detection optical path, and uses the detector rotation device to realize the stable alternating test of the optical path, effectively eliminating the influence of factors such as the instability of light energy and the inconsistent response of the energy meter probe on the test results. . The invention has the characteristics of compact test optical path, concise and easy-to-operate test steps, clear data processing method and flow, etc., and can realize high-efficiency test while improving test accuracy and system stability.

Description

Dual-optical path switching cross-reference high-precision AOTF performance test method and device

Technical field:

The invention relates to an optical measurement technology, in particular to a dual optical path switching cross-reference high-precision AOTF performance test method and device, which is used to realize high-precision acousto-optic tunable filter performance test.

Background technique:

Acousto-optic tunable filter (Acousto-optic tunable filter, AOTF) is a new type of dispersive spectroscopic device, which is based on the acousto-optic effect and can realize electrically tunable spectral filtering through radio frequency. It has excellent force and thermal characteristics; it has flexible spectral selection performance due to its electrically tunable spectral filtering; and it has the advantages of controllable spectral sampling interval and fast wavelength scanning. It is very suitable for the flexible and efficient data acquisition requirements of spectral detection. At present, this technology has been widely used in non-imaging and imaging spectral instruments and equipment.

Spectroscopy principle of AOTF: As shown in Figure 1, AOTF consists of an acousto-optic medium (generally TeO ₂ ), an acoustic wave absorber and a transducer. When a beam of polychromatic light passes through a high-frequency vibrating optically elastic crystal, the light vector and the acoustic wave vector of a certain wavelength satisfying the momentum matching will produce a nonlinear effect inside the crystal to generate a diffracted beam, which is transmitted from the crystal at a certain diffraction angle. The polychromatic light transmitted through the crystal and not diffracted is directly emitted from the crystal along the propagation direction of the original light, thus achieving the effect of light splitting. When the vibration frequency of the crystal changes, the wavelength of the diffracted monochromatic light also changes accordingly, thereby realizing electrically tunable optical filtering. The diffraction performance of AOTF includes diffraction efficiency, spectral resolution, etc., and its performance is related to the wavelength and the parameters of the crystal itself. The test of AOTF diffraction performance usually needs to achieve full band coverage.

It is one of the feasible means to use the laser as the light source and use the energy receiving system to measure and calculate the zero-order and diffracted light energy, so as to obtain the diffraction efficiency of the AOTF. However, due to the limitation of the monochromaticity of the laser, this method cannot meet the needs of continuous spectrum testing of AOTF. Utilizing wavelength tunable lasers as continuously adjustable light sources is another feasible solution (patent CN 101706361), as shown in Figure 2, this method uses continuous adjustable light sources and uses beam splitters to reduce light energy instability The impact on the test accuracy can achieve wide-band and high-precision testing. However, this method also has limitations, mainly as follows: (1) It is necessary to switch the beam splitter suitable for different spectral bands when testing a wide spectrum, and at the same time, to ensure the test accuracy, it is necessary to test the wavelength-beam splitting curve of the beam splitter, which is time-consuming Laborious; (2) After completing the test on one level (such as +1 level) of the ±1 level of the AOTF device, an additional installation clamp is required for the other level (such as -1 level), and the optical path must be readjusted , poor operability and consistency; (3) The deviation of the base vector and the performance stability of the beam splitter itself will affect the test accuracy. The patent (CN103913297) proposes an AOTF test method using the characteristics of the acousto-optic device itself to realize the light energy reference. As shown in Figure 3, this method alternately measures the light intensity of 0th-order light and diffracted light by exchanging the positions of the two energy meters, which can effectively eliminate the influence of the instability of the light source and the inconsistency of the detector response on the measurement. However, the position exchange process of the two energy meters described in this method will introduce alignment position deviation, thereby affecting the test accuracy; in addition, the position exchange of the energy meter and the operation of switching ±1-order light by the Glan prism will inevitably cause Subsequent changes in the test optical path have high requirements for operation and affect the stability of the instrument.

Invention content:

The purpose of the present invention is to provide a novel method and device for testing the performance of a high-precision AOTF optical splitting device by using a switchable component to realize mutual reference of two optical paths.

Among them, the optical path switching component (reflection moving mirror) realizes the stable and portable switching of the ±1-level test optical path; the detector rotating device realizes the cross-reference test of the double optical path. The present invention can effectively eliminate the influence of light energy instability and energy meter probe response inconsistency, realize the fast switching test of the ±1-level optical path, and eliminate the influence on the structure of the subsequent optical path system. Compared with the existing technology, there are significant improvements in the following aspects: 1) Provide a novel testing method and device, which can rotate to realize cross-reference detection of dual optical paths, form corresponding data processing formulas, eliminate light energy instability and AOTF diffraction performance test error caused by inconsistent energy meter probe response; 2) Provide a novel test method device to realize portable and stable switching of AOTF ± 1st order light diffraction performance test optical path. The invention has the characteristics of compact test optical path, concise and easy-to-operate test steps, clear data processing method and flow, etc., and can realize high-efficiency test while improving test accuracy and system stability.

Basic principle: As shown in Figure 1, according to the principle of acousto-optic interaction, when a beam of polychromatic light passes through the AOTF, the polychromatic light is divided into two beams of linearly polarized light, namely o light and e light. When the RF drive frequency is applied to the crystal, the e-light is diffracted to form +1-order diffracted light (o-light) and 0-order light; the o-light also diffracts to form -1-order diffracted light (e-light) and Class 0 light. The total amount of -1st-order light and 0th-order light energy after diffraction of the o-light of the AOTF crystal to be tested is consistent with the incident o-light, and the total amount of +1-order diffracted light and 0-order light energy after e-light diffraction is also consistent with the incident e-light Consistent characterization, diffraction performance can be tested.

Test method and device:

1) As shown in Figure 6, the test device includes a tunable laser (1), a neutral density filter (2), an aperture diaphragm (3), a Glan prism (4), and a two-dimensional motorized turntable (5) , AOTF crystal to be inspected and radio frequency driver (6), reflecting moving mirror (7), detector rotating device (8), first energy meter probe (8.1), second energy meter probe (8.2). The tunable laser (1) has a wavelength range of 210nm-2300nm and a power of 40mW-80mW. The attenuation range of the neutral density filter (2) is 10%-80%. The aperture of the aperture diaphragm (3) ranges from 0.05mm to 0.15mm. The reflection rate of the moving mirror (7) is greater than 99%. The detector responds to a wavelength of 210nm-2300nm, and the rotation angle range of the rotating device is 0°-180°.

During the test, the laser beam emitted by the wavelength tunable laser (1) passes through the neutral density filter (2), the pinhole diaphragm (3), and the Glan prism (4) to obtain a linearly polarized quasi-monochromatic laser and vertically On the incident AOTF (6), the RF driver applies a certain RF drive to the AOTF (6), and adjusts the angle of the reflective moving mirror (7), so that the 0th-order light and one of the first-order diffracted lights (such as -1 order) are reflected to the detector Rotate the device to perform the test.

Among them, when the detector rotation device (8) is at 0° and 180°, the first energy meter probe (8.1) and the second energy meter probe (8.2) can realize the portable and stable switching interaction of the 0th order light and the -1st order diffracted light respectively. detected by (η is the diffraction efficiency of the AOTF to be tested, E ₀ is the 0th order light energy when the first energy meter probe 8.1 receives the detector rotation device at 0°, E ₁ is the diffraction received by the second energy meter probe 8.2 at this time Light energy; E ₀ ' is the diffracted light energy received by the first energy meter probe 8.1 at 180° from the detector rotation device, E ₁ ' is the 0-level light energy received by the second energy meter probe 8.2 at this time) processing, through Dual optical path cross-reference detection eliminates the influence of light source instability and energy meter probe response inconsistency, and realizes high-precision testing of the diffraction efficiency of the acousto-optic tunable filter;

Among them, the reflective moving mirror (7) rotates and combines the rotation angle of the Glan prism (4) to change the polarization state of the incident light, and realizes the switching of AOTF-1 diffracted light to +1-order light and its detection optical path, and completes the AOTF-1 The test of order diffracted light efficiency.

2) The position and parameters of the reflective moving mirror in the test device are determined as follows, as shown in Figure 4, assuming that the diffraction angle is β, the distance between the center of the reflector and the exit position is L, and the vertical distance between the 0-order light and the detector is H, and M is the horizontal distance between the two detectors. When the crystal diffracted light is -1 order, the position of the mirror is A, and the angle between it and the horizontal direction is α; when the diffracted light is +1 order, the position of the mirror is B, and the angle between it and the horizontal direction is γ . The rotations of the two reflection moving mirrors are just enough to meet the reflection of the optical path to the center positions of the two energy meter probes. According to the principle of geometric optics, it should satisfy:

Diffraction angle β, the distance from the center of the reflector to the exit position is L, once the vertical distance H between the 0th order light and the detector is determined, for the -1st order diffracted light, the angle between it and the horizontal direction is α, satisfying α>45° +β/2, the size of M is determined by the above formula. When moving the reflective moving mirror, the angle γ between it and the horizontal direction satisfies the following equation:

tan(2α-90°)tan(2α-90°-β)+tan(90°-2γ)tan(β-90°+2γ)＝0

The position of the reflecting moving mirror and the angle of the two rotations are thus determined. Realize switching and measurement of ±1st order diffracted light.

3) The detector rotating device (8) and the detectors (8.1) and (8.2) in the test device have the following characteristics: the rotating shaft of the detector rotating device (8) passes through the direction of the photosensitive surface of the detector (8.1) and the detector (8.2). Center and perpendicular to the plane formed by the rotation of the detectors 8.1 and 8.2, it is convenient to switch and can effectively avoid the position deviation caused by the energy meter exchange; the size of the aperture diaphragm (3) in the test device is smaller than the size of the photosensitive surface of the detector, further Eliminate the impact of position switching on the test, and realize the stability of the optical path and measurement.

4) The test device adopts a wide-spectrum Glan prism and its rotating adjustment clamp to switch and fine-tune the phase of the incident ray polarization, which can meet the requirements of the ±1st order diffraction performance test for the light source while improving the optical efficiency and reduce the deviation of the polarization base vector. impact on test accuracy.

Specific analysis and explanation:

1) During the test, adjust the wavelength of the wavelength tunable laser, apply a certain radio frequency drive to AOTF6, rotate the Glan prism, rotate the reflective moving mirror to position A, and test the diffraction efficiency of -1 order diffracted light. The 0-level light energy received by the first energy meter probe 8.1 is E ₀ , and the diffracted light energy received by the second energy meter probe 8.2 is E ₁ ; the detector rotating device is rotated 180° to realize the pairing of two energy meter probes Light alternate measurement of light, that is, the 0-level light energy received by the second energy meter probe 8.2 is E ₀ ′, and the diffracted light energy received by the first energy meter probe 8.1 is E ₁ ′. The calculation formula of the diffraction efficiency is as follows:

The analysis is as follows: Considering that the energy of the wavelength tunable laser 1 is unstable, the responsivity of the two energy meter probes of the same model also has deviations, which will reduce the accuracy of the test results. Alternate measurement of light and calculation by the above formula can effectively improve the accuracy.

Assume that after a certain RF drive is applied to AOTF6, the actual energy of the 0th-order light is e ₀ , and the actual energy of the diffracted light is e ₁ , and the ideal diffraction efficiency is:

Let the influence factor coefficient caused by laser energy instability be β, the response coefficient of the first energy meter probe be a, the response coefficient of the second energy meter probe be a(1+Δx), and Δx be the inconsistent response of the two energy meter probes The resulting relative deviation. Then the light energy responses obtained by the two energy meter probes 8.1 and 8.2 are: E ₀ =βae ₀ , E ₁ =βa(1+Δx)e ₁ . Keep the driving frequency unchanged, rotate the detector rotation device 180°, and the two energy meter probes can alternately measure the 0th-order light and diffracted light. The light energy obtained by the two is: E ₀ '=βa(1+Δx)e ₀ , E ₁ '=βae ₁ , according to the diffraction efficiency formula can be obtained:

The calculation formula of AOTF6 diffraction efficiency is:

If the optical path exchange test is not performed, the limit error of the diffraction efficiency at this time is Δη′, and it can be known that:

Δη'=η ₁ -η _real 1-5

After the optical path switching test is carried out, the limit error of the diffraction efficiency at this time is Δη", it can be known that:

Formulas 1-5 and 1-6 can be deduced from formulas 1-2, 1-3 and 1-4 as:

Δη″=η-η _real =0

Accompanying drawing 5 is when η _real is respectively 0.1, 0.3 and 0.5, Δ _η (comprising Δ η ' and Δ η ") and Δ x relational graph (Δ x value range is between 0-5%). Can know by accompanying drawing: The theoretical limit error of the diffraction efficiency of the method of alternately testing the dual optical path switching energy meter probe rotating device is 0. Compared with the results without alternate testing, the test accuracy is greatly improved.

The advantages of the present invention are:

1) Based on the characteristics of the AOTF crystal, a novel testing method and device is provided. The detector rotating device is used to realize the cross-reference test of the double optical path; Portable switching: It can realize the fast switching test of the ±1-level optical path while effectively eliminating the influence of the instability of the light energy and the inconsistency of the probe response of the energy meter, and eliminate the impact on the structure of the subsequent optical path system.

2) Use the diffraction efficiency formula to calculate and process the obtained data. Through theoretical error analysis, the theoretical limit error of the diffraction efficiency is 0. Compared with the existing technology and processing methods, the accuracy of the test is greatly improved. The optical path test based on this model The method can also be used in other optical measurement fields, which has important application value and reference significance.

Description of drawings:

Figure 1 AOTF spectroscopic schematic diagram.

Fig. 2 Schematic diagram of the test system for the diffraction efficiency of the tunable laser method AOTF.

Fig. 3 Self-referencing device for testing the high-precision diffraction performance of the AOTF.

Fig. 4 Schematic diagram of reflecting moving mirror and detector rotating device.

Fig. 5 Theoretical error curves (η _real =0.1, 0.3, 0.5).

Figure 6. Schematic diagram of a high-precision AOTF performance test device for dual optical path switching cross-reference.

detailed description:

The following description is a preferred embodiment of the present invention according to FIG. 6, which is used to illustrate the structural features and implementation methods of the present invention, but not to limit the scope of the present invention.

The dual optical path switching cross-reference high-precision AOTF performance test device includes the following parts:

(1) Wavelength tunable laser 1: In this implementation method, EKSPLA NT342/1/UV wavelength tunable laser is selected as the light source. This laser can generate 210nm-2300nm continuous tunable laser beam with an output power of 50mW.

(2) Neutral density filter 2: Spiricon neutral density filter is selected in this embodiment.

(3) Aperture diaphragm 3: Daheng Optoelectronics GCM-57 variable diaphragm is selected for this implementation.

(4) Glan prism 4: Thorlabs' GL15Glan-Laser CalcitePolarizers are used in this embodiment, the extinction ratio is better than 10000:1, and the spectral range is between 350nm and 2300nm to achieve wide-spectrum testing.

(5) Two-position electric turntable 5: Lianyi 148×142 two-position electric turntable is selected in this implementation plan. The adjustment range is 360°, the transmission ratio of the motor is 1:360, the minimum reading of the scale is 0.1°, and the resolution of the full-step operation of the motor is 0.005°.

(6) Reflecting moving mirror 7: In this embodiment, Maofeng photoelectric silver film reflector OQAg-12.7 is selected, the wavelength covers visible light and infrared, the diameter is 12.7mm, and the reflectivity is greater than 99%.

(7) Detectors (8.1, 8.2) and detector rotating device (8): In this embodiment, EPM1000 energy meter probes from Coherent Company of the United States are selected, and the probes are J4-09 and J45LP-MB respectively. The customized rotating and fixed mirror frame is selected to realize the fixing and rotation of the energy meter probe.

The implementation plan selects the short-wave infrared AOTF6 developed by Zhongdian 26 as the acousto-optic crystal to be tested, and uses its matching RF driver 62 as the AOTF component. The short-wave infrared AOTF has a wavelength range of 900-2300nm. The test method contains the following steps:

1) Select the output wavelength of the wavelength tunable laser 1, adjust the two-dimensional electric turntable 5, the laser beam passes through the neutral density filter, the aperture diaphragm, and the Glan prism, and then vertically incident on the AOTF6 crystal, through the rotating Glan The prism adjusts the Glan prism holder and fine-tunes the phase of the incident ray polarized light so that the light incident on the crystal is linearly polarized light (e light);

2) The radio frequency driver applies the radio frequency drive of the corresponding frequency to the AOTF6, adjusts the reflective moving mirror to a specific angle, and the detector rotation device is placed at 0°, so that the optical path is reflected to the center of the two energy meter probes, and the first energy meter probe 8.1 Receive 0-level light energy, and the second energy meter probe 8.2 receives diffracted light (o light) energy;

3) Keep the driving frequency unchanged, rotate the detector rotation device 180°, and realize the alternate test of the optical path of the two detector probes, that is, the first energy meter probe 8.1 receives the diffracted light (o light) energy, and the second energy meter probe 8.2 Receive 0-order light energy; use the above formula (1-1) to calculate the diffraction efficiency of the AOTF;

4) After completing the test of the +1 order (o light) of the AOTF, the polarization state of the linearly polarized light incident to the AOTF6 is changed by rotating and adjusting the Glan prism holder and fine-tuning the phase of the polarized light of the incident ray, so that the diffracted light is switched to Another stage (e-light), and rotate the reflective moving mirror to a specific position, repeat the above steps 1-3, and complete the test of e-light diffraction efficiency.

The AOTF diffraction performance test method involved in the present invention is simple, the optical path is compact, the test steps are simple and easy to operate, and the stability is strong. Compared with the traditional AOTF diffraction efficiency test method, it effectively reduces the instability caused by the energy fluctuation of the laser light source and the energy meter. The impact of inconsistent probe response rates on test results greatly improves test accuracy. By introducing a reflective moving mirror, the fast switching test of the ±1-level optical path can be realized while eliminating the influence on the structure of the subsequent optical path system. By introducing the detector rotation device, the cross-reference detection of the optical path can be realized, the AOTF diffraction performance test error caused by the instability of the light energy and the inconsistent response of the energy meter probe can be eliminated, and the position deviation introduced in the process of exchanging the probe position can be effectively avoided. The impact of the test results is simple, reliable and stable; the test results are processed through the diffraction efficiency calculation formula to further improve the test accuracy and reduce the test error. In theory, it is an ideal device for testing the high-precision diffraction performance of the acousto-optic tunable filter.

Claims (4)

1. a kind of switching of double light path mutually refers to high-precision A OTF performance testing devices, it include Wavelength tunable laser (1), in Property density filters (2), aperture (3), Glan prism (4), two-dimentional electrical turntable (5), acousto-optic tunable filter to be checked And drive device (6), reflection index glass (7), detector rotating device (8), the first energy meter probe (8.1), the second energy meter are visited Head (8.2), it is characterised in that：

The laser beam of Wavelength tunable laser (1) outgoing successively passes through neutral-density filter (2), aperture (3), lattice Obtained after blue prism (4) on the quasi- one-wavelength laser of linear polarization and vertical incidence AOTF (6), radio driver applies one to AOTF (6) Fixed radio-frequency driven, the angle of adjustment reflection index glass (7) makes 0 grade of light and -1 order diffraction light reflex to the energy meter of detector first Pop one's head in (8.1) and the second energy meter probe (8.2), or 0 grade of light and+1 order diffraction light is reflexed to the energy meter of detector first Pop one's head in (8.1) and the second energy meter probe (8.2), realize test；

Described detector rotating device (8) rotates 180 ° and realizes that two energy meters probe is alternately measured two-way light.

2. a kind of double light path switching according to claim 1 mutually refers to high-precision A OTF performance testing devices, its feature exists In：The rotating shaft of described detector rotating device (8) is popped one's head in by the first energy meter probe (8.1) and the second energy meter thereon (8.2) center of photosurface and to rotate the plane to be formed vertical with energy meter probe (8.1,8.2) line, it is to avoid energy meter is exchanged The position deviation of generation.

3. a kind of double light path switching according to claim 1 mutually refers to high-precision A OTF performance testing devices, its feature exists In the aperture of described aperture (3) is less than detector photosurface size, eliminates influence of the position switching to test.

4. a kind of double light path switching based on described in claim 1 is mutually with reference to the AOTF diffraction of high-precision A OTF performance testing devices The method of testing of efficiency, it is characterised in that method is as follows：

Detector rotating device (8) can realize the first energy meter probe (8.1) and the second energy meter probe when being in 0 ° and 180 ° (8.2) stable switching interaction detection portable to 0 grade of light and -1 order diffraction light respectively, diffraction efficiency computational methods are as follows：

<mrow> <mi>&amp;eta;</mi> <mo>=</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mn>1</mn> <mrow> <msqrt> <mfrac> <mrow> <msub> <mi>E</mi> <mn>1</mn> </msub> <msubsup> <mi>E</mi> <mn>1</mn> <mo>&amp;prime;</mo> </msubsup> </mrow> <mrow> <msub> <mi>E</mi> <mn>0</mn> </msub> <msubsup> <mi>E</mi> <mn>0</mn> <mo>&amp;prime;</mo> </msubsup> </mrow> </mfrac> </msqrt> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow>

In formula：E₀0 grade of light energy when detector rotating device is in 0 °, E are received for the first energy meter probe (8.1)₁For this When the second energy meter probe (8.2) diffraction light energy for receiving；E₀' receive detector for the first energy meter probe (8.1) Rotating device is in 180 ° of diffraction light energy, E₁' it is 0 grade of light energy that now the second energy meter probe (8.2) is received, lead to Cross double light path and mutually eliminate the influence that flashing is qualitative and energy meter sonde response is inconsistent with reference to detection, realize acousto-optic tunable The high precision measurement of filter diffraction efficiency；Reflection index glass (7) rotational angle α or γ and combines Glan prism in the horizontal direction (4) the anglec of rotation changes the polarization state of incident light, realizes AOTF by -1 order diffraction light to+1 grade of light and its detects light path Switching, completes the test to AOTF-1 order diffraction light efficiencies；Reflect index glass (7) rotational angle α or γ determination sides in the horizontal direction Method is as follows：

Wherein：β be the AOTF angles of diffraction, L be mirror center from Exit positions with a distance from, H be 0 grade of light away from the vertical of detector Distance, M is the horizontal range of two detectors, and α meets 45 ° of+β/2, γ of α ＞ and meets equation：

Tan (2 α -90 °) tan (2 α -90 ° of-β)+tan (90 ° of -2 γ) tan (β -90 °+2 γ)=0 (3)

The angle for thereby determining that the position of reflection index glass and rotating twice, realizes the switching of ± 1 order diffraction light and measures.