JP4881085B2 - Optical adjustment method of optical element - Google Patents

Description

The present invention relates to a method for optically adjusting a lens or other optical element.

As a method for evaluating the result of optical adjustment of the lens, there is a method using interference fringe analysis. In this evaluation method, a lens that has been optically adjusted in advance is set in a known interferometer, and the wavefront aberration of the optical element is obtained from interference fringes obtained from the reflected light from this lens and the reflected light from the reference surface. Thus, the result of optical adjustment of the lens was quantitatively evaluated.
Japanese Patent Laid-Open No. 2000-214048

However, in the above-described conventional evaluation method, since it takes time to analyze interference fringes, it is difficult to evaluate the optical adjustment repeatedly performed by a normal optical element every time the adjustment is performed. Therefore, the evaluation using the interference fringe analysis was only performed after all the optical adjustments were completed. That is, it is difficult to readjust the result of interference fringe analysis and readjust the optical element.

In order to solve the above-described problems, the optical adjustment method of the present invention transmits reflected light reflected by a reference surface of a standard flat plate and a test optical element disposed at a predetermined position after passing through the standard flat plate. This is a method for measuring the optical performance of the test optical element by observing the interference fringes obtained by the test light that is folded back by the concave mirror and transmitted again through the test optical element and the reference plane of the reference plane plate. The step of setting the inclination angle of the reference surface with respect to the incident light, the reflected light from the reference surface of the set inclination angle, and the test light transmitted through the test optical element have a spatial carrier. an interference fringe formation step of forming an interference pattern in real time, an interference fringe analysis step of analyzing the interference fringes formed in the interference fringes formed step to real time, the analysis result of the interference fringe analysis step Based on the optical adjustment step of performing optical adjustment of the test optical element continuously provided with, during the formation of interference fringes due to the interference fringes formed step, analysis of the interference fringes in the interference fringe analysis step And the adjustment of the optical element to be tested in the optical adjustment step are continuously executed a required number of times .

The analysis result may be Zernike expanded, and optical adjustment may be performed based on at least one coefficient of the expanded polynomial.

According to the present invention, by tilting the reference surface by a predetermined angle with respect to the incident light, the same effect as obtaining a plurality of interference fringe images by changing the position of the reference surface can be obtained. It becomes possible to do . Then, during the formation of the interference fringes in the interference fringe formation step, the interference fringe analysis is performed by continuously executing the interference fringe analysis in the interference fringe analysis step and the adjustment of the optical element to be tested in the optical adjustment step as many times as necessary. The optical adjustment using the result can be repeated. That is, not only can optical evaluation be performed after all repeated adjustments have been completed, but each of the repeated adjustments can be evaluated in real time using the results of interference fringe analysis. .

Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. In the present embodiment, the test lens 80 is an object of optical adjustment, but the present invention can also be applied to other optical elements.

First, an optical adjustment device used for carrying out the optical adjustment method according to the present invention will be described. The optical adjustment device includes an optical adjustment unit 10, an interference fringe forming unit 20, and an interference fringe analysis unit 42.

The optical adjustment unit 10 shown in FIG. 1 includes a holding unit 11 that holds a test lens 80 and an adjustment driving unit 12 that drives the holding unit. The holding unit 11 is, for example, an electric XYZθ stage, and can adjust the arrangement and inclination of the test lens 80. The holding unit 11 operates according to the drive current supplied from the adjustment drive unit 12 connected thereto. The adjustment drive unit 12 supplies a predetermined drive current to the holding unit 11 based on the control signal output from the control unit 43 connected thereto. In the holding unit 11, optical adjustment of the test lens 80 can be performed based on an analysis result of interference fringes described later. For example, when the test lens 80 is a lens system composed of a plurality of lenses, the eccentricity of the lens system can be adjusted by moving an arbitrary lens in the horizontal direction (arrow in FIG. 1). A known lens holding device can be used as the holding unit 11.

As the interference fringe forming unit 20, a known interferometer can be used. In this embodiment, as shown in FIG. 1, a semiconductor laser (LD) (light source) 21 and an interference fringe observation CCD (charge coupled device) 41 are used. , And an optical system 30 is used. The optical system 30 includes a collimator lens 31, a mirror 32, a half mirror 34, a condenser lens 35, a reference plane plate 36, a pinhole 37, and a reflection reference concave mirror 38.

The semiconductor laser 21 is driven by a driver 22 and emits a predetermined laser beam as reference light. The driver 22 supplies a drive current to the semiconductor laser 21 based on a control signal output from the control unit 43 connected thereto. In the traveling direction of the laser light emitted from the semiconductor laser 21, a collimator lens 31 and a mirror 32 are arranged in order from the semiconductor laser 21 side. Laser light emitted from the semiconductor laser 21 is collimated by a collimator lens 31 and reflected by a mirror 32 disposed at an inclination of 45 degrees with respect to the optical path, whereby the traveling direction is bent by 90 degrees.

On the optical path of the reflected light by the mirror 32, a half mirror 34, a reference plane plate 36, a lens 80 to be tested, and a reflection reference concave mirror 38 are arranged in this order from the mirror 32 side. The light reflected by the mirror 32 is transmitted through a half mirror 34 disposed at an inclination of 45 degrees with respect to the optical path, and is incident on a reference plane plate 36.

The reference flat plate 36 is a flat glass plate whose surface is polished with high accuracy, and a reference surface 36 a is provided on a surface far from the half mirror 34. The reference surface 36a has a property of transmitting part of the light incident on the reference flat plate 36 and reflecting the rest. Using this property, it is possible to obtain interference fringes between the light reflected by the reference surface 36a and the light that has passed through the reference surface 36a and then passed through the lens to be examined and reflected by the reflection standard concave mirror.

The reflected light from the reference surface 36 a is reflected by the half mirror 34, passes through the condenser lens 35, and then enters the CCD 41 through the pinhole 37 disposed on the optical path. Instead of the CCD 41, other imaging devices (for example, CMOS (Complementary Metal Oxide Semiconductor)) can be used.

On the other hand, the light that has passed through the reference surface 36 a passes through the lens 80 to be examined, is reflected by the reflective reference concave mirror 38, and passes through the reference flat plate 36 again. The transmitted light is reflected by the half mirror 34 and then enters the CCD 41 through the condenser lens 35 and the pinhole 37. This light and the reflected light from the reference surface 36a interfere to form interference fringes. The formed interference fringes are converted into electrical signals by the CCD 41 and input to the interference fringe analysis unit 42.

The reference flat plate 36 is held by a support device (for example, an electric θ stage) 51. The support device 51 is connected to the control unit 43 via a reference plane plate driving unit 52. The reference plane plate drive unit 52 that has received the drive signal output from the control unit 43 supplies a predetermined drive current to the support device 51, and the support device 51 thereby causes the optical axis (reference) of the reference plane plate 36 . The direction perpendicular to the surface 36a can be inclined by an arbitrary angle (predetermined angle) θ with respect to the traveling direction of the incident light on the reference plane plate 36. By inclining the reference plane plate 36 (reference surface 36a) in this way, interference fringes (space carriers, tilt fringes) corresponding to the inclination angle are generated, and the reference plane plate 36 is not inclined. The phase distribution of the test lens 80 can be obtained by analyzing the interference fringes obtained by superimposing the interference fringes representing the shape of the test lens 80 that sometimes occurred.

As shown in FIG. 2, the interference fringe analysis unit 42 includes an A / D converter 421, a frame memory 422, a D / A converter 423, and a calculation unit 424 therein. For example, a personal computer can be used as the interference fringe analysis unit 42, but the A / D converter 421, the frame memory 422, the D / A converter 423, and the calculation unit 424 are configured as independent devices. Also good.

Signal charges (interference fringe image signals) accumulated in each pixel are sequentially input from the CCD 41 to the A / D converter 421. In the A / D converter 421, each input analog signal is converted into a digital signal (interference fringe image data). The interference fringe image data is stored at an address corresponding to the pixel of the CCD 41 in the frame memory 422 connected to the A / D converter 421.

The interference fringe image data stored in the frame memory 422 is converted into an analog signal by the D / A converter 423 connected to the frame memory 422. The converted analog signal is displayed on an output unit 44 (for example, a monitor, a CRT display, a liquid crystal display, or a printer) provided outside the interference fringe analysis unit 42. Conventional interference fringe analysis can be performed by the display on the output unit 44.

On the other hand, a calculation unit 424 is also connected to the frame memory 422. The arithmetic unit 424 can obtain the phase distribution of the test lens 80 by analyzing the interference fringe image data output from the frame memory 422 using the spatial phase shift method described below, and thereby the wavefront. It is possible to analyze aberrations and other surface conditions of the test lens 80. Furthermore, optical adjustment of the test lens 80 can be performed using wavefront aberration as an analysis result of interference fringe analysis.

A control unit 43 is connected to the calculation unit 424, and an input unit 45 (for example, a keyboard and a mouse), a reference plane plate driving unit 52, and an adjustment driving unit 12 are connected to the control unit 43. The control unit 43 changes the attitude of the reference plane plate 36 with respect to the reference plane plate drive unit 52 or the adjustment drive unit 12 based on a signal input from the calculation unit 424 (interference fringe analysis unit 42) or the input unit 45. Alternatively, a control signal necessary for optical adjustment of the test lens 80 is output. Based on this control signal, the reference plane plate driving unit 52 supplies a driving current necessary for changing the attitude of the reference plane plate 36 to the support device 51. The adjustment driving unit 12 supplies a driving current necessary for optical adjustment of the test lens 80 to the holding unit 11 based on a control signal from the control unit 43.

Here, an analysis method using the spatial phase shift method will be described.
When the optical axis of the reference plane plate 36 is inclined by an angle θ (a predetermined angle depending on the wavelength λ of the semiconductor laser 21) with respect to the traveling direction of the incident light on the reference plane plate 36, the calculation by the calculation unit 424 Based on the interference fringe image data output from the frame memory 422, if attention is paid to one period with interference fringes, a spatial signal intensity distribution I (x) represented by the following expression A can be calculated. . In Formula A, y is omitted for one-dimensional display.
<Formula A>
I (x) = a + b · cos [φ + 2πνx]
Here, a is the average intensity distribution, b is the amplitude, ν is the spatial frequency of the spatial carrier, and φ is the initial phase at a certain point.

この式により被検レンズ８０の各点における位相を求めることができ、２次元的にこれを繰り返せば、被検レンズ８０の波面収差を定量的に求めることができる。 Regarding the formula (A), assuming that a and b have constant values, the initial phase φ is expressed by the following formula B where the signal strengths of the four pixels described above are I ₀ , I ₁ , I ₂ , and I ₃ , respectively. It is represented by
<Formula B>

With this equation, the phase at each point of the test lens 80 can be obtained, and if this is repeated two-dimensionally, the wavefront aberration of the test lens 80 can be obtained quantitatively.

On the other hand, as a method for calculating the initial phase, the distance between the reference plane plate 36 and the test lens 80 is moved in the optical axis direction by the amount scanned by one period (2π) of the interference fringes, and at the same time, the interference fringes. In some cases, each time is scanned by 2π / N (N is an integer), an image is captured N times in total, and an initial phase is calculated from a change in brightness of each image (temporal phase shift method or fringe scan method). However, in this method, a mechanism for changing the distance between the reference plane plate 36 and the lens 80 to be examined is necessary, and an image has to be captured N times.

On the other hand, in the present embodiment, it is only necessary to capture an image once, and if the inclination angle of the reference plane plate 36 is determined, it is necessary to change the interval between the reference plane plate 36 and the test lens 80. Absent. Therefore, interference fringe analysis can be performed at low cost and in a short time, and it is possible to obtain wavefront aberration and other information of the test lens 80 each time the interference fringe analysis is performed. As a result, in the optical adjustment of the test lens 80 that often repeats fine adjustment, interference fringe analysis can be performed in real time to obtain quantitative information of wavefront aberration, so that only the final adjustment result can be obtained. In addition, the result of fine adjustment in the middle can be evaluated at any time. In other words, practically, interference fringe analysis can be performed, and optical adjustment and evaluation of the result (progress) can be performed integrally and continuously.

Here, performing the interference fringe analysis in real time means that the period is faster than the period in which the observer can observe through the output unit 44 (for example, a time corresponding to one drive period of the interference fringe analysis unit 42 (for example, 1/500). ))). When interference fringe analysis is performed at such a period (speed), for example, when the output unit 44 performs interlace processing, the time for displaying one frame (1/30 seconds in the NTSC system) is the interference fringe. Since it is much longer than the drive period of the analysis unit 42, the person who observes the output unit 44 feels that interference fringe analysis is being performed simultaneously with the work he / she has performed. It becomes.

Note that the wavefront aberration calculated from the phase obtained as described above is used for interference fringe analysis. However, if the wavefront aberration is expanded by Zernike in the calculation unit 424, more detailed analysis can be performed. In other words, each coefficient of the polynomial after Zernike expansion indicates the aberration information of the lens 80 to be measured in detail for each type of aberration, and the larger the number, the more information that can be obtained. Therefore, when these coefficients are analyzed, the aberration of the test lens 80 can be analyzed in more detail.

Next, the flow of the operation of interference fringe analysis and optical adjustment of the test lens 80 will be described with reference to FIG.
First, of the light perpendicularly incident on the reference plane plate 36, the light transmitted through the reference plane plate 36, reflected by the reflective reference concave mirror 38, and again transmitted through the reference plane plate 36, and the light reflected by the reference plane plate 36 The components of the semiconductor laser 21, the CCD 41, and the optical system 30 are arranged so as to follow the same optical path and enter the CCD 41, and the operation of interference fringe analysis and optical adjustment is started (step S100). Since it is confirmed by a well-known method whether or not it has entered along the same optical path, the description thereof is omitted here.

Subsequently, when the operator operates the input unit 45 to input the tilt angle value θ, the control unit 43 outputs a control signal to the reference plane plate drive unit 52, and the reference plane plate drive unit 52 that receives the control signal supports it. A drive current necessary for the reference flat plate 36 to be inclined by an angle θ with respect to the optical path of the incident light is supplied to the device 51 (step S101). As a result, the reference flat plate 36 is inclined at an angle θ with respect to the optical path of the incident light.

Next, the reference light is emitted from the semiconductor laser 21 by operating the driver 22 (step S102). The emitted light is reflected by the mirror 32 through the collimator lens 31, passes through the half mirror 34, and enters the reference flat plate 36. A part of the incident light is reflected by the reference surface 36 a of the reference plane plate 36, reflected by the half mirror 34, and then enters the CCD 41 through the condenser lens 35 and the pinhole 37. The light that has not been reflected by the reference surface 36a passes through the test lens 80 and then enters the reflection reference concave mirror 38. If the test lens 80 is correctly arranged, the light is reflected so as to follow the same optical path as the incident light. The reflected light from the reflective reference concave mirror 38 passes through the test lens 80 and the reference flat plate 36 again, is reflected by the half mirror 34, and then enters the CCD 41 through the condenser lens 35 and the pinhole 37 (step S103). ). As described above, the CCD 41 receives the reflected light from the reference surface 36a and the light that has been transmitted through the reference plane plate 36 and then transmitted through the lens 80 and reflected by the reflective reference concave mirror 38. Interference fringes are formed in real time by light.

Here, the formation of interference fringes in real time means that the interference fringes are formed at a period earlier than the period in which the observer can observe through the output unit 44, as in the above-described interference fringe analysis in real time. Means that.

The formed interference fringes can be analyzed by display on the output unit 44, and detailed and quantitative analysis can also be performed by calculating the phase in the interference fringe analysis unit 42 (step S104). The formation of the interference fringes, the display on the output unit 44, and the calculation of the phase in the interference fringe analysis unit 42 are performed continuously unless the operator stops the operation of the interference fringe forming unit 20, and the phase distribution (wavefront aberration) ) Is stored in a storage area (not shown) in the control unit 43. If it is not necessary to calculate the phase, the interference between the reflected light and the transmitted light by the reference surface 36a can be obtained by setting the reference surface inclination angle θ to zero and eliminating the interference fringes generated according to the reference surface inclination angle. Displaying only the stripes on the output unit 44 is preferable because analysis becomes easy.

In the optical adjustment, the operator operates the input unit 45 during the formation of interference fringes and / or analysis of the interference fringes, so that the control unit 43 outputs a control signal to the adjustment drive unit 12 and receives it. The adjustment driving unit 12 can supply the driving current for optically adjusting the test lens 80 to the holding unit 11 at any time. During the optical adjustment, the light transmitted through the reference plane plate 36 is incident on the lens 80 to be tested, and the formation of interference fringes and the analysis of interference fringes can be continued. When the operator wants to evaluate the result of the optical adjustment (YES in step S105), the operator operates the input unit 45, so that the phase distribution stored in the storage area of the control unit 43 at the time of the operation. The calculation result of (wavefront aberration) is referred to (step S106). The optical adjustment of the test lens 80 can be quantitatively evaluated based on the phase distribution or the change from the phase distribution at the previous evaluation.

When the operator does not wish to continue the interference fringe analysis after the evaluation of the optical adjustment is completed or while the evaluation of the optical adjustment is not desired (NO in step S105), the operator By operating the input unit 45, the operation of the optical adjustment device is stopped (step S108). In contrast, while the operator does not perform an operation for stopping the operation of the optical adjustment device (YES in step S107), the emission of the reference light is continued (step S102), and the interference fringes incident on the CCD 41 are analyzed. Is continued (steps S103 and S104). During this time, the optical adjustment result is evaluated as needed according to the wishes of the operator.

The optical adjustment device according to the present embodiment can automatically perform optical adjustment according to the evaluation result of the optical adjustment result. That is, in the storage area of the control unit 43, data related to the allowable range of optical adjustment based on the specifications of the lens 80 to be tested is stored in advance, and the control unit 43 stores these data and the optical adjustment result. When the evaluation results are compared and it is determined that the optical adjustment result is not within the allowable range, a control signal is sent from the control unit 43 to the adjustment driving unit 12 to operate the holding unit 11 so as to be within the allowable range. The adjustment driving unit 12 that has received the output changes the position and inclination of the lens constituting the lens 80 to be tested with respect to the holding unit 11. The result adjusted in this way is evaluated again by the next interference fringe analysis, it is determined whether or not the optical adjustment is within the allowable range based on the specification of the lens 80 to be tested, and the optical adjustment is repeated until it enters. Therefore, optical adjustment can be performed. In the present invention, since the interference fringe analysis can be performed in a short time by the spatial phase shift method, the optical adjustment using the result of the interference fringe analysis can be easily repeated.

Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment, and can be improved or changed within the scope of the purpose of the improvement or the idea of the present invention.

It is a figure which shows the structure of the optical adjustment apparatus used for the optical adjustment method which concerns on embodiment of this invention. It is a figure which shows the structure of the analysis part which concerns on embodiment of this invention. It is a flowchart which shows the flow of the optical adjustment method which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical adjustment part 11 Holding | maintenance part 12 Adjustment drive part 20 Interference fringe formation part 21 Semiconductor laser 30 Optical system 36 Reference plane board 36a Reference surface 38 Reflection reference concave mirror 41 CCD
42 Interference fringe analysis unit 43 Control unit 44 Output unit 45 Input unit 80 Test lens (optical element)
422 Frame memory 424 Calculation unit θ Inclination angle (predetermined angle)

Claims (2)

The reflected light reflected by the reference plane of the reference plane plate and the reference plane plate are transmitted, then the test optical element arranged at a predetermined position is transmitted and folded back by the concave mirror, and again the test optical element and the reference plane plate A method of measuring optical performance of a test optical element by observing interference fringes obtained by test light transmitted through a reference surface,
Setting an inclination angle of the reference surface with respect to incident light;
An interference fringe forming step for forming an interference fringe having a spatial carrier in real time by the reflected light from the reference surface at the set inclination angle and the test light transmitted through the test optical element ;
An interference fringe analysis step for analyzing the interference fringes formed in the interference fringe formation step in real time;
Based on the analysis result in the interference fringe analysis step, an optical adjustment step of continuously performing optical adjustment of the optical element to be tested,
With
During the formation of the interference fringes by the interference fringe forming step, the analysis of the interference fringes in the interference fringe analysis step and the adjustment of the optical element to be tested in the optical adjustment step are continuously performed a required number of times. An optical adjustment method for an optical element. The optical adjustment method according to claim 1, wherein the analysis result is subjected to Zernike expansion, and optical adjustment is performed based on at least one coefficient of the polynomial after expansion.

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