JPH0749417A - Interference filter assembly - Google Patents

Abstract

PURPOSE:To reduce the opening ratio without deteriorating the characteristic of a filter by providing an interference filter that is installed between both microlenses for passing substantially parallel rays of light being output from the front microlens. CONSTITUTION:The rays of light converged by a converging system 1 are focused in various positions on the front surface of a front-side microlens 4 in accordance with their converging angle. Accordingly, the opening ratio F up to this microlens 4 is reduced, and an optical system can be formed. The light rays given to the microlens 4 are turned here into nearly parallel rays and are sent to an interference filter 2. After a prescribed filtering action has been carried out in this interference filter 2, the rays are sent out to a microlens 5 situated behind while keeping parallel rays. In the microlens 5, the rays are converged in various positions on the surface of a detecting element array 3. Thus, even if the aperture ratio F up to the microlens 4 is small, the optical path difference can be reduced to a small amount, and a filter that is light and excellent in the narrow-band characteristic can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference filter assembly, and more particularly to a narrow band (bandpass) interference filter assembly for use in a multi-assembly image system, which is called a high sensitivity spectral imager.

An interference filter used in an optical system is required to have a characteristic that it does not attenuate the light level and has a narrow wavelength pass band.

[0003]

2. Description of the Related Art FIG. 4 (a) shows a conventionally known interference filter assembly.
When the light ray R is incident on the left side of the lens, the light ray R forms an image on the detection element array 3 at the focal position of the lens 1 via the filter 2 including the substrate 21 and the interference film 22.

The action of the filter 2 is that, as shown in FIG. 2B, the substrate 2 passes through a thin film (interference film) 22 having a thickness d.
1 and the film material, and the interference of multiple reflections caused by the difference in the refractive index between the film material and the air (vacuum) is used to pass only a light beam in a predetermined wavelength band (bandpass). .

When the aperture diameter of the lens 1 is D and the focal length is f, the aperture ratio is represented by F = f / D. The smaller F is, that is, the larger the aperture diameter D or the smaller the focal length f is. Since the incident energy is collected in a small area on the surface of the detection element array 3, the bright optical system has a small amount of attenuation.

[0006]

However, when the aperture ratio F is reduced, the filter characteristics deteriorate as described below.

When a bright optical system having a small aperture ratio F value is used, θ ₀ in the figure becomes large. On the other hand, of the rays R, the optical path difference in the case of the ray R0 passing through the central portion (θ = 0) is the optical path length difference between the one-time reciprocating light and the directly passing light when the light is reflected twice as multiple reflections. 2d, and this optical path length difference is 2
It is preferably fixed at d.

However, at the lens 1, the light incident at h from the center is incident on the surface of the sensing element array 3 at an angle θ = tan ⁻¹ h / f, but the optical path difference at this time is 2l = 2d / cos θ.

This is a large-diameter condenser system (for example, F = 0.
In the case of 7), -45 ° <θ <+ 45 °, and the optical path difference is dispersed between 2d and 2.8d. As a result, it has been found by an experiment conducted by the present inventor that the filter characteristic greatly changes depending on the value of the aperture ratio F (F = 1.0 to 3.0) as shown in FIG.

As described above, in order to maintain the narrow-band spectral characteristic of the visible portion of the multispectral imaging system for remote sensing, in the conventional method as described above, the optical path length passing through the filter 2 is equal to the aperture ratio F. When the value is small, as shown in Fig. 4 (a), the ray R at the center of the optical system
There is a large difference between 0 and the peripheral ray R1.
Since the transmission characteristics in the central wavelength, the pass band width, and the cutoff wavelength range largely deviate from the designed values (see FIG. 5), the value of the aperture ratio F generally exceeds "2". There was a problem.

Therefore, an object of the present invention is to provide an interference filter which can reduce the aperture ratio as much as possible without deteriorating the filter characteristics.

[0012]

In order to achieve the above object, an interference filter according to the present invention, as shown in FIG.
It is installed between two microlenses 4 and 5 which are installed at the focal position of the light converging system 1 at the front and at the position where the rear is formed at the position where an image is formed on the visible light detecting element array 3, and between the microlenses 4 and 5. The interference filter 2 that allows the substantially parallel light output from the front microlens 4 to pass therethrough.

In the above-described present invention, the interference filter 2 may have an interference film filter formed on the back surface of the front microlens 4 or the front surface of the rear microlens 5.

In the present invention, a flat plate self-occurring microlens can be used as the microlens.

[0015]

In FIG. 1, the light beam condensed by the condensing system 1 is
Depending on the converging angle, the front side (flat plate self-lock)
Images are formed at various positions on the front surface of the microlens 4. Therefore, the aperture ratio F up to the microlens 4 becomes small and a bright optical system is formed.

The light rays given to the microlens 4 are converted into substantially parallel light, and are sent to the interference filter 2.

The interference filter 2 performs a predetermined filtering operation, and then sends the parallel rays as they are to the rear microlens 5. The microlens 5 focuses the light beam at various positions on the surface of the detection element array 3.

In this way, the light passing through the interference filter 2 becomes substantially parallel light, which is a light beam with a large aperture ratio F (or infinite), so that the aperture up to the microlens 4 is increased. Even if the ratio F is small, the above-mentioned optical path length difference can be made small, and it is possible to maintain a bright filter having excellent narrow band characteristics.

[0019]

FIG. 2 shows a partially enlarged view of FIG. 1, and in particular, in this embodiment, the microlens 4 is 1.5
A flat plate Selfoc microlens having a width of λ (wavelength) is used.

In this embodiment, a light ray R from a condenser system (not shown) is focused on the front surface of the SELFOC microlens 4 and enters the microlens 4.

In the lens 4, the light rays meander, but 1.5
Since it has a width of λ (wavelength), it becomes an abdominal part on the rear surface of the lens 4 and is emitted as parallel light, and the substrate 2 of the interference filter 2
It is incident on 1.

The light rays passing through the substrate 21 and further through the interference film 22 constituting the interference filter 2 are parallel light rays and have a large aperture ratio F, so that the above-mentioned difference in optical path length is caused. The dispersion is small, the filter characteristic can be maintained close to the design value, and the characteristic corresponding to F ≧ 3.0 in FIG. 5 can be obtained.

Then, the light beam which has passed through the filter 2 is given to the rear microlens 5 in parallel, and after meandering as shown here, since it has a lens width of, for example, 1.2λ, it is at its focal position. An image is formed on the surface of the sensing element array 3.

FIG. 3 shows an embodiment in which a filter thin film is directly attached to the rear surface of the front microlens 4 to serve as a microlens and a filter. Also in this embodiment, the microlens 4 has a wavelength of 1.5λ (wavelength). ) Using a SELFOC microlens having a width of
Is used as a selfoc micro lens having a width of 1.2λ.

The filter thin film may be directly attached to the front surface of the rear microlens 5.

Also in this embodiment, the light ray R from the condensing system (not shown) forms an image on the front surface of the SELFOC microlens 4 and is incident on the microlens 4 and becomes an abdominal portion on the rear surface thereof and becomes parallel light. The light is emitted and made incident on the interference film 22.

Then, the sensing element array 3 passing through the interference film 22 and located at the focal position by the microlens 5 is used.
Will be imaged on the surface of.

[0028]

As described above, according to the interference filter of the present invention, one of the two microlenses is installed at the focal position of the condensing system and the other is located at the position where an image is formed on the visible light detecting element array. Since the incident light to the interference filter installed between both the microlenses is configured to be substantially parallel light, the aperture ratio F is set to a small value in order to make the optical system bright. Even if the optical system and the microlens are arranged, the rays passing through the filter become parallel to each other without deteriorating the filter characteristics, and it becomes possible to provide a preferable narrow band.

[Brief description of drawings]

FIG. 1 is a view showing the principle of an interference filter assembly according to the present invention.

FIG. 2 is a partially enlarged view of an embodiment of an interference filter assembly according to the present invention.

FIG. 3 is a partially enlarged view of another embodiment of the interference filter assembly according to the present invention.

FIG. 4 is a diagram for explaining a conventional example.

FIG. 5 is a graph showing transmission characteristics of a conventional interference filter assembly.

[Explanation of symbols]

 1 Condensing System (Lens) 2 Interference Filter 3 Sensing Element Array 4,5 Selfoc Microlens R Ray

Claims (4)

[Claims] 1. Two microlenses (4, 5), the front of which is installed at a focus position of the light-collecting system (1) and the rear of which is installed at a position where an image is formed on the visible light detecting element array (3), An interference filter (2), which is installed between both microlenses (4, 5) and passes substantially parallel light output from the front microlens (4), assembly. 2. The interference filter assembly according to claim 1, wherein the interference filter (2) is formed by forming an interference film filter on the back surface of the front microlens (4). 3. The interference filter assembly according to claim 1, wherein the interference filter (2) has an interference film filter formed on the front surface of a rear microlens. 4. The interference filter assembly according to claim 1, wherein the microlenses (4, 5) are flat plate self-occurring microlenses.