JP2008216131A - Infrared imaging/laser range finder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared imaging/laser range finder without reducing imaging performance, without causing an aberration, even when sharing an objective lens of two optical systems of an infrared imaging optical system and a laser range finding receiving optical system. <P>SOLUTION: This infrared imaging/laser range finder shares the objective lens of the two optical systems of the infrared imaging optical system and the laser range finding receiving optical system, and has a dichroic mirror 6 using an objective diffraction lens 5 having a diffraction surface on one surface or both surfaces, arranged in the rear of the objective diffraction lens 5, reflecting infrared radiation for imaging and transmitting a range finding laser beam, as the objective lens. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical system of an infrared imaging / laser ranging device having an infrared imaging device and a laser ranging device.

  In an infrared imaging / laser ranging device having an imaging device for target detection and a laser ranging device for ranging, an imaging optical system, a transmission optical system for laser ranging, and a receiving optical system are used. (For example, refer to Patent Document 1).

  The optical system of the imaging device and the transmission optical system and the reception optical system of the laser distance measuring device are configured with different optical systems depending on the required field of view, wavelength band used, transmitter used, detector, etc. Often done.

  In an infrared imaging / laser distance measuring device having an imaging device and a laser distance measuring device, in order to increase the detection distance and the distance measuring distance, the imaging optical system of the imaging device and the receiving optical system of the laser distance measuring device are It is necessary to use an objective lens having a large aperture for each optical system. However, the increase in the diameter of the two objective lenses increases the size of the entire apparatus, which limits the equipment and operating conditions on which the infrared imaging / laser ranging device can be mounted.

  On the other hand, as means for reducing the size of an infrared imaging / laser ranging apparatus having an imaging apparatus and a laser distance measuring apparatus, the objective lens of the imaging optical system and the receiving optical system is shared, and then wavelength separation means such as a dichroic mirror is used. There is a method of guiding light of two wavelengths for imaging and ranging to respective optical systems (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 7-181260 (FIG. 7) Japanese Patent Laid-Open No. 5-107501 (FIG. 2)

  However, when using an infrared imaging device for the imaging device and sharing the objective lens of the imaging optical system and the receiving optical system for laser distance measurement, it is necessary to use a lens material that transmits both wavelengths. The lens materials that can be produced are limited. Due to the limited use of lens materials, imaging optical systems that use a wide range of wavelengths cannot correct chromatic aberration by using multiple lens materials. As a result, the imaging optical system collects light. Degradation of imaging performance, such as an increase in the spot diameter of the generated light, occurs.

  The present invention has been made in view of the above-described points. Even if the objective lens of the two optical systems, that is, the infrared imaging optical system and the laser distance receiving optical system is shared, no aberration occurs, and the imaging performance is improved. An object of the present invention is to obtain an infrared imaging / laser distance measuring device that does not deteriorate.

  An infrared imaging / laser distance measuring device according to the present invention is an infrared imaging / laser ranging device sharing an objective lens of two optical systems of an infrared imaging optical system and a laser distance receiving optical system, As the lens, an objective diffractive lens having a diffractive surface on one side or both sides is used, and a dichroic mirror that is disposed behind the objective diffractive lens and reflects infrared rays for imaging and transmits laser beams for distance measurement is provided. It is characterized by that.

  According to the present invention, it is possible to obtain an infrared imaging / laser distance measuring device in which aberration does not occur and imaging performance does not deteriorate.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of an optical system of an infrared imaging / laser distance measuring apparatus according to Embodiment 1 of the present invention. Infrared imaging / laser distance measuring devices include infrared light receiving elements, signal processing circuits that have been converted and output to electrical signals by laser receiving elements, laser transmitter control circuits, and drive mechanisms and drives for adjusting the focus of each optical system. Although a control circuit and the like are provided, the configuration shown in FIG.

  In FIG. 1, a laser beam 3 emitted from a laser transmitter 1 is emitted to a target through a transmission optical system 2. The laser beam 3 is reflected by the target, passes through the objective diffraction lens 5, the wedged dichroic mirror 6, and the receiving optical system 7, and forms an image on the laser receiving element 8. Infrared light 4 emitted from the target and its periphery passes through the objective diffractive lens 5, reflects off the surface of the dichroic mirror 6 with wedge, passes through the imaging optical system 9, and then forms an image on the infrared light receiving element 10. . Here, the wavelengths of the laser light 3 and the infrared light 4 are different wavelengths, and the infrared light 4 has a wide wavelength range. As an example, the wavelength of the laser beam 3 is 1.5 μm and the wavelength of the infrared light 4 is 3 to 5 μm.

  Here, first, the objective diffraction lens 5 will be described. In FIG. 1, laser light 3 and infrared light 4 coming from a target are incident on an objective diffraction lens 5 together. The objective diffractive lens 5 is a lens having a diffractive surface on one side or both sides. Since the infrared light 4 has a wavelength range of 3 to 5 μm, in the case of a normal single lens having no diffractive surface, a shorter wavelength is refracted more greatly due to a difference in refractive index depending on the wavelength of the lens material. Further, chromatic aberration occurs and the imaging performance is deteriorated.

  In general, in order to correct chromatic aberration, chromatic aberration is corrected by combining a positive lens with a negative lens made of a material having different dispersion. In the case of an infrared optical system of 3 to 5 μm, a combination of Si for the positive lens and Ge for the negative lens is often used. However, since Ge does not transmit light having a wavelength of 1.5 μm, it transmits laser light 3 of 1.5 μm. In the case of the objective lens to be corrected, it is impossible to correct the chromatic aberration by the combination of the Si and Ge lenses.

  As means for correcting chromatic aberration, in the first embodiment, an objective diffractive lens having a diffractive surface is used. Since light that has passed through the diffractive surface is refracted as the wavelength increases, providing the lens with a diffractive surface makes it possible to correct chromatic aberration with a single lens and obtain high imaging performance. Since the laser light 3 is a single wavelength light, no chromatic aberration occurs.

Further, the amount of light that is transmitted varies depending on the wavelength depending on the diffraction surface and diffraction efficiency. The relationship between the diffraction efficiency and the transmitted wavelength λ is expressed by η = sinc ² (λ ₀ / λ−k). Here, sinc is the sink function, η is the diffraction efficiency, λ ₀ is the wavelength of light indicating the optical path difference of the diffraction surface, λ is the wavelength of the transmitted light, k is the order of the diffracted light (0, 1, 2,...・）

In order to obtain high diffraction efficiency when transmitting infrared light 4 and laser light 3 having different wavelengths, the objective diffractive lens 5 has a light wavelength λ ₀ indicating the optical path difference of the diffracting surface and the order k of the diffracted light. λ ₀ / λ _L −k ₂ | ≦ | λ _min −k ₁ | or | λ ₀ / λ _L −k ₂ | ≦ | λ _max −k ₁ |, and in addition, λ ₀ / λ _max −k ₁ It is set so as to satisfy the relationship of ≦ 0 ≦ λ _min −k ₁ . Here, k ₁ and k ₂ are the orders of the diffracted light, λ _L is the wavelength of the laser light 3, and λ _min and λ _max are the minimum wavelength and the maximum wavelength of the infrared light 4. When λ _L is 1.5 μm, λ _min is 3.0 μm, and λ _max is 5.0 μm, λ ₀ is 3.3 μm, k ₁ is 1, and k ₂ is 2. A design example is shown in FIG.

  Next, the dichroic mirror 6 with a wedge will be described. A dichroic mirror is an optical component that separates an optical path of light according to a wavelength by reflecting and transmitting a specific wavelength. The light that has passed through the objective diffraction lens 5 enters the dichroic mirror 6 with a wedge as a condensed light beam. The light that has passed through the parallel-shaped medium placed obliquely on the light path to be condensed has astigmatism, and the imaging performance is deteriorated. Also, the amount of astigmatism that occurs when passing through a medium placed obliquely varies depending on the incident angle of light incident on the objective diffraction lens 5.

  For infrared light 4 for imaging purposes, light from a wide field of view including the target must be imaged on the infrared light receiving element 10, while for laser light 3, light reflected by the target is required. Only a narrow field of view may be formed on the laser light receiving element 8.

  Therefore, the infrared light 4 with a wide field of view is reflected by the surface of the dichroic mirror 6 with a wedge, thereby preventing astigmatism from occurring over the entire wide field of view. For the laser beam 3 with a narrow field of view, when the dichroic mirror passes through the dichroic mirror by applying a wedge instead of a parallel plate, the astigmatism generated on the entrance surface is canceled by the astigmatism generated on the exit surface. Correct and maintain imaging performance.

The wedge is tilted about an axis perpendicular to the surface normal to the surface on which the laser beam 3 is incident and the plane including the chief ray of the laser beam, and the angle 12 of the incident surface of the dichroic mirror 6 with the wedge with respect to the chief ray 11 is set to θ _i , If the exit surface of the angle 13 and theta _o, holds the relationship of θ _i> θ _o, the angle, material of the wedge with the dichroic mirror 6, the thickness, the angle of the incident light, the distance between the objective diffraction lens 5 Optimized to correct aberrations.

  Therefore, according to the first embodiment, in the infrared imaging / laser distance measuring apparatus that shares the objective lenses of the two optical systems, that is, the infrared imaging optical system and the laser ranging reception optical system, one or both surfaces are used as the objective lens. In addition, an objective diffractive lens having a diffractive surface is used, and a dichroic mirror that is disposed behind the objective diffractive lens, reflects infrared rays for imaging, and transmits laser light for distance measurement, so that no aberration occurs. Thus, it is possible to obtain an infrared imaging / laser ranging device in which the imaging performance does not deteriorate.

It is a block diagram which shows the structure of the optical system of the infrared imaging and laser distance measuring device by Embodiment 1 of this invention. It is a figure which shows the example of a design of the diffraction efficiency of the objective diffraction lens 5 by Embodiment 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser transmitter, 2 Transmission optical system, 3 Laser light, 4 Infrared light, 5 Objective diffraction lens, 6 Dichroic mirror with a wedge, 7 Reception optical system, 8 Laser receiving element, 9 Imaging optical system, 10 Infrared light receiving element, 11 Chief ray, 12 angle 慮_i of incident surface of dichroic mirror with respect to chief ray, 13 angle 慮_o of exit surface of dichroic mirror with respect to chief ray.

Claims (3)

An infrared imaging / laser distance measuring apparatus that shares the objective lens of two optical systems, an infrared imaging optical system and a laser ranging reception optical system,
As the objective lens, while using an objective diffractive lens having a diffractive surface on one side or both sides,
An infrared imaging / laser ranging apparatus, comprising a dichroic mirror disposed behind the objective diffractive lens and reflecting infrared rays for imaging and transmitting laser beams for ranging. In the infrared imaging / laser ranging device according to claim 1,
The objective diffractive lens has a wavelength λ ₀ indicating diffraction optical path difference and diffraction orders k ₁ and k ₂ .
| Λ ₀ / λ _L −k ₂ | ≦ | λ _min −k ₁ | or | λ ₀ / λ _L −k ₂ | ≦ | λ _max −k1 | and λ ₀ / λ _max −k ₁ ≦ 0 ≦ λ _min −k ₁
Where λ ₀ is the wavelength indicating the optical path difference of diffraction
λ _L is the wavelength of the laser beam
λ _min is the minimum wavelength of infrared light
λ _max is the maximum wavelength of infrared light
Infrared imaging / laser ranging apparatus characterized in that k ₁ and k ₂ are set so as to satisfy the relationship of diffraction orders. The infrared imaging / laser distance measuring device according to claim 1 or 2,
The dichroic mirror is tilted about an axis perpendicular to the surface normal to the surface on which the laser beam is incident and the plane containing the principal ray of the laser beam, and the angle between the principal ray and the exit surface with respect to the angle between the principal ray and the incident surface. An infrared imaging / laser ranging device characterized by having a wedge shape with a small diameter.

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