JPH01227123A - Coherent optical device - Google Patents

Abstract

PURPOSE:To form numerous Fourier transform patterns while a sufficient light quantity is secured by providing a 1st lens, a transmissive object, and a 2nd lens in the described order behind a very small lens array so that at least two or more Fourier transform patterns can be formed simultaneously behind the 2nd lens. CONSTITUTION:The 1st lens 9 of a single lens, a transmissive object 3, and the 2nd lens 10 of a single lens are arranged in the described order behind a very small lens array 8. The 1st lens 9 has a lens diameter which is sufficient to transmit at least two or more luminous fluxes of the coherent luminous fluxes from the lens array and the object 3 has an area which is simultaneously irradiated by at least two or more luminous fluxes of the luminous fluxes transmitted by the 1st lens 9. Moreover, the 2nd lens 10 has a lens diameter which is sufficient to transmit at least two or more luminous fluxes of the luminous fluxes transmitted by the 1st lens 9 and object 3. Then at least two or more Fourier transform patterns of the transmissive object 3 are simultaneously formed behind the 2nd lens 10. Therefore, numerous Fourier transform patterns having sufficient light quantities can be obtained without unnecessary overlapping noise light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical device for simultaneously obtaining a plurality of Fourier transform patterns of a transparent object under coherent light illumination.

[Conventional technology]

Optical information processing, or so-called "optical computing"
In the field called Some methods attempt to obtain a large number of transformations at the same time and have each of them perform a specific image operation.

In such a case, an optical device that can simultaneously obtain a large number of Fourier transform patterns of a transmitted object with a convenient configuration is required.

Conventionally, as this type of device, the one shown in FIG. 3 or 4 is known.

In FIG. 3, coherent light emitted from a HeNe laser (1) becomes a spatially expanded parallel light beam by a beam expander (2), and illuminates a transparent object (3).

A pinhole array (4) arranged two-dimensionally in a grid is placed immediately after the transparent object (3), and behind it a lens (
5) is located. The transparent object (3) is a lens (5
) is placed near the front focal plane. With this configuration, a transparent object (
3) A large number of Fourier transform patterns are obtained.

The complex transmittance of the transparent object (3) is f (
f (x, y) sampled in 4) is f (x
, y) Σ Σδ(X −mp, y−nQ) (
(1 formula) % formula % (p, q are pinhole pinches).

Therefore, the Fourier transform pattern of equation (1) obtained by lens (5) is F (ξ, η)* Σ Σδ (ξ -at/p', η
-n/q') @ =-000=-■ (Equation 2), and the Fourier transform F(ξ, η) of f (x, y) is the ξ, η plane, that is, the back focal point of the lens (5). You can get many on the surface.

In the above formula, * represents convolution. Also, 1/
p', l/q', is F(ξ, η) on the Fourier transform plane
represents the pitch formed by p and p' and q and q' are proportional. Therefore, the pitch of the pinhole array and the pinch of the Fourier transform pattern are inversely proportional.

On the other hand, FIG. 4 shows a second example of a conventional technique for obtaining a large number of Fourier transform patterns constructed using computer generated holograms.

A transparent object (3) is illuminated with a parallel coherent light beam obtained with a configuration similar to that shown in FIG. A computer generated hologram (7) is placed behind this transparent object (3).

The computer generated hologram (7) is coded to reproduce a point image array arranged in a matrix at a predetermined distance from the hologram surface when parallel coherent illumination is used as a reference light.

Specifically, as shown in FIG. 5, a pattern is recorded in which a large number of so-called Fresnel zone plates are shifted and overlapped. In addition, in Fig. 5, for convenience, 2
Only the pattern is shown.

With the above configuration, it is possible to obtain a Fourier transform pattern of the transparent object (3) centering on each point image reproduced by the computer generated hologram.

[Problem that the invention seeks to solve]

However, the disadvantage of the apparatus shown in FIG. 3 is that since the object is sampled through the pinhole, the amount of light passing through the pinhole is extremely small, and the resulting Fourier transform pattern is quite dark.

To avoid this, if the pinhole diameter is increased, the complex transmittance h(x
, y) is added, and (2) is rewritten as (32). In other words, when the pinhole h(x, y) becomes thick (the cutoff of its Fourier transform H(ξ, η) moves toward the lower frequency side, the resulting Fourier transform pattern is one in which high-frequency information is deleted). It has the disadvantage of becoming

In addition, in the configuration shown in Fig. 4, when a computer generated hologram in which a large number of Fresnel zone plates are stacked is used to obtain a large number of Fourier transform patterns, in addition to the +1st-order diffracted light necessary to obtain the Fourier transform patterns, , 0th order, -
Not only are unnecessary diffracted lights such as first-order and ±second-order diffracted lights generated, but also diffracted lights due to mutual interference of each zone plate (so-called moiré) are generated, and the noise pattern due to these unnecessary diffracted lights overlaps significantly on the Fourier transform pattern. There are drawbacks such as being cluttered.

[Means for solving problems]

Under coherent illumination, a microlens array in which a large number of microlenses are arranged one-dimensionally or two-dimensionally on the same plane is arranged, and behind this lens array there is a first single lens, a transparent object, and a second single lens. Arrange the lenses in this order.

The lens has a diameter sufficient to transmit at least two or more of the coherent light beams emitted from each microlens of the lens array.

Furthermore, the passing object is placed in an area where at least two or more of the light beams that have exited from each microlens of the lens array and have passed through the first lens are illuminated at the same time.

Furthermore, the second lens has a lens diameter sufficient to transmit at least two or more of the light fluxes that have been emitted from each microlens of the lens array and transmitted through the first lens and the transmitting object.

The optical system is configured as described above, and at least two Fourier transform patterns of a transparent object are simultaneously formed behind the second lens.

[For production]

According to the above configuration, a large number of Fourier transform patterns of a transparent object can be generated, ensuring a sufficient amount of light and eliminating unnecessary stray light noise.
A uniform spatial frequency distribution of each Fourier transform pattern can be obtained.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, a microlens array (8) consisting of a large number of microlenses arranged one-dimensionally or two-dimensionally within the same plane is illuminated by parallel coherent light. The lighting may be the same as the conventional device. The beam αa transmitted through the microlens array (8) is transmitted through each lens (8).
At A), each becomes convergent light, and after focusing once,
It becomes a diverging light. A first lens (9) is arranged behind the microlens array (8). The first lens (9) is placed so that the front focal plane of the first lens and the rear focal plane of the microlens array (8) almost match.

In addition, the pupil surface of the first lens (9) is the microlens array (
It has a size large enough to allow all of the light beams emitted from each of the lenses (8) and diverging toward the first lens to enter therein.

The beams α~ emitted from each lens of the microlens array (8) are collimated by the first lens (9) and spatially overlap at the back focal position of the first lens (9). A transparent object (3), which is an input image to be subjected to Fourier transformation, is placed at this position.

A second lens QOI is further placed behind the transparent object (3). The transparent object (3) is this second lens α0
and a second lens QO
The size of the pupil plane of I is large enough to allow all the light beams that have passed through each microlens and also passed through the first lens (9) and the transparent object (3) to enter.

By arranging each optical element as described above, a transparent object (
A large number of Fourier transform patterns 3) are simultaneously obtained at the Fourier transform surface αυ, that is, at the rear focal position of the second lens α0).

In addition, in the above-mentioned embodiment, the interval between each component is set to the first
For example, the distance between the transparent object (3) and the second lens OQ may be shortened (or the distance between the transmitting object (3) and the second lens OQ may be shortened to obtain the Fourier transform The arrangement of each component may be changed appropriately depending on the size of the pattern, the interval between the IJ conversion patterns, etc.

In addition, there are cases where it is desired to obtain a large number of duplicate images of an object under coherent illumination. By arranging the beams, it is possible to obtain a large number of coherent duplicate images of the transparent object (3) on the image plane a3 located at the rear focal point of the second microlens array beam.

〔Effect of the invention〕

According to the present invention, a clear Fourier transform pattern with sufficient visibility can be created without unnecessary noise and without using pinhole arrays, computer generated holograms, etc., which were conventionally indispensable to create a large number of Fourier transform patterns. can be obtained without overlapping.

The components can also be composed of two sets of lenses and a microlens array, and the microlenses can be made, for example, with a plastic mold or as a gradient index lens array in a glass plate using ion exchange technology. Therefore, it is much easier to produce than computer-generated holograms.

As described above, according to the present invention, a large number of high-quality and clear Fourier transform patterns can be obtained with a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing one embodiment of the present invention, Fig. 2 is a side sectional view showing another embodiment of the invention, Fig. 3 is a side sectional view showing an example of a conventional device, and Fig. 4. 5 is a side sectional view showing another example of the conventional device, and FIG. 5 is a front view showing a computer generated hologram used in the device shown in FIG. (3)... Transmissive object, (81, Q... Microlens array, 00)... First lens, 0υ... Fourier transform surface, Q31... Image plane. Figure 3 = Figure 4 Figure 5

Claims (1)

[Claims] A microlens array in which microlenses are arranged one-dimensionally or two-dimensionally is provided under coherent illumination, a first lens is provided behind the microlens array, and a transmittance or phase difference is provided behind the first lens. At least one side has a spatially distributed transmitting object arranged, and a second lens is provided behind the transmitting object, and the first lens is configured to control the coherent light flux emitted from each microlens of the microlens array. The transmitting object has a lens diameter that allows at least two or more light beams to pass through the first lens, and the transmitting object includes at least two or more of the light beams that are emitted from each of the microlenses and transmitted through the first lens. The second lens is placed in a region that is simultaneously illuminated by the light beams, and the second lens emits from each microlens,
At least two or more of the light beams transmitted through the first lens and the transmitting object are transmitted, and at least two or more Fourier transform patterns of the transmitting object are provided behind the second lens. A coherent optical device characterized by simultaneous formation.