JPH0199017A - Equalizing device for gaussian distribution light beam in optical system - Google Patents

Abstract

PURPOSE:To convert to a light beam having uniform light intensity distribution by forming a convex lens of lenses in a system by selecting a material whose transmittivity is lower than that of an ordinary lens material in a wavelength area of a light beam emitted from a light source, and allowing it to execute a light intensity distribution correction, as well. CONSTITUTION:A convex lens 40 for changing a light beam 3a radiated from a semiconductor laser 2 being a light source to parallel rays 3b is formed by a material whose transmittivity in a wavelength area of the light source is lower enough than that of an ordinary lens material, for instance, a material having transmittivity being equal to that of an ND filter, as a lens for executing a light intensity distribution correction, as well. A light intensity distribution of a light beam which is transmitted through the convex lens 40 is corrected by the product of the radiation intensity of a semiconductor laser light which is made incident on each position on the lens surface and the transmittivity of the convex lens, and with respect to an intensity difference between the maximum value and the minimum value of a cross sectional area distribution of a Gaussian beam before it is subjected to a correction by the convex lens 40, the intensity difference in the cross sectional area distribution which has passed through the convex lens 40 drops, and in the process that the radiated Gaussian beam passes through the convex lens 40, the light intensity distribution can be equalized.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention corrects the light intensity distribution of a Gaussian beam emitted from a light source to create a uniform light intensity distribution in an optical system for a laser photoelectric switch, etc. Concerning a device that converts light into light.

[Conventional technology]

First, as an example of an optical system to which the present invention is applied, the configuration of the laser photoelectric switch shown in FIG. 6 is shown. In the figure, 1 is a semiconductor laser 2 as a light source. and a light projecting section incorporating a lens system 4 that converts a light beam 3a emitted from a semiconductor laser into a parallel light beam 3b and emits it; 5 has a photodiode (not shown) built therein; This is a light receiving section with a light receiving slit 6 opened. Such a photoelectric switch detects the amount of light blocked when a detected object 7 placed on the optical path between the light emitter 1 and the light receiver 6 blocks the parallel light beam 3b from the change in the amount of light received by the light receiver 6, and detects the amount of light being detected. Detected object 7
The dimension d of is determined.

[Problem that the invention seeks to solve]

By the way, in the photoelectric switch described above, in order to always detect the dimensions of the detected object 7 with high accuracy regardless of the position of the detected object 7, light is emitted from the light projecting section 1 toward the light receiving section 5. It is necessary that the light intensity distribution in a cross section perpendicular to the optical axis of the parallel light rays 3 is uniform.

Therefore, in the light emitting section of the photoelectric switch shown in FIG. 7, which combines the semiconductor laser 2 and a convex lens as the lens system 4, the light beam 3a emitted from the semiconductor laser 2 is first
As shown in the figure, this is a Gaussian beam with a distribution approximated by a Gaussian distribution in which the light intensity is highest at the center of the beam and decreases as the radiation angle increases. Therefore, in the region of parallel light rays 3b shown in FIG. 7, the light intensity distribution in a cross section perpendicular to the optical axis also exhibits a non-uniform intensity distribution corresponding to the radiation intensity distribution shown in FIG. For this reason, when measuring and determining the dimensions of the object 7 to be detected using the photoelectric switch shown in FIG. A difference occurs in the amount of light received by the light receiving section 5, and therefore the amount of light blocked by the object to be detected 7, and this difference directly becomes a measurement error.

In addition to the examples above, semiconductor lasers are used by being incorporated into optical systems for various purposes, such as laser printers, but depending on the optical system, there are many cases where a light beam with a uniform light intensity distribution is required as described above. .

On the other hand, as a means of converting a Gaussian beam emitted from a laser into a light beam with a uniform light intensity distribution in a laser printer, etc.
After the laser beam is made into parallel light beams using a collimator, etc., special reflecting mirrors, prisms, etc. are placed in the middle of the optical path to change the direction of the light beams in the outer region of the beam, where the light intensity is low, so that they are superimposed on the center region of the beam.

Alternatively, a method has been reported in which the light intensity distribution is made uniform by combining specially shaped aspherical lenses to disperse the light rays in the central region of the beam, where the light intensity is high, to the peripheral region. However, such a system requires complicated optical parts, and since these parts are interposed in the optical path, the optical system becomes large and its position adjustment is troublesome.

This invention was made in view of the above points, and its purpose is to create a Gaussian distribution by slightly changing the lens characteristics of some of the lenses that make up the optical system, without installing any additional special optical components. An object of the present invention is to provide a simple device capable of converting a light beam exhibiting a uniform light intensity distribution into a light beam having a uniform light intensity distribution.

[Means for solving problems]

In order to solve the above problems, according to the present invention, in an optical system including a light source that emits light rays exhibiting a Gaussian distribution and a convex lens arranged on the optical axis of the light source, at least one of the lenses in the system The convex lens is a lens that also serves as a light intensity distribution correction lens, and the convex lens is constructed by selecting a lens material that has lower transmittance than a normal lens material in the wavelength range of the light beam emitted from the light source.

[Effect]

With the above configuration, the convex lens that also serves as light intensity distribution correction has a transmittance of about 30 to 85%, which is much lower than the transmittance of normal lens materials, which is 99.7 to 99.9%. It is made from the same lens material. On the other hand, a convex lens has a structure in which the thickness is thick at the center of the lens and becomes thinner toward the periphery. Moreover, the rate of attenuation of light intensity that occurs during the process of light rays passing through a lens increases as the thickness of the lens increases.
Therefore, among the light beams that pass through the convex lens, the attenuation of the light intensity is large for the light that passes through the center of the lens, and the attenuation of the light that passes through the peripheral portion is small.

From this, in a convex lens made of a normal lens material with a transmittance close to 100%, the difference in the amount of attenuation of light rays due to the difference in thickness between the center and the periphery of the lens is extremely small and can be ignored. However, by aligning the optical axis and making the Gaussian beam incident on a convex lens made of a lens material with low transmittance as described above, the light rays in the central region of the beam are greatly attenuated within the convex lens. On the other hand,
The attenuation rate of the light beam in the beam circumference is small, and as a result, the light intensity distribution of the light beam emitted from the convex lens in a cross section perpendicular to the optical axis becomes uniform.

〔Example〕

1 to 3 each show a different embodiment of the present invention. First, FIG. 1 shows an embodiment corresponding to the optical system shown in FIG. 7, in which a convex lens 40 that changes a light beam 3a emitted from a semiconductor laser 2 as a light source into a parallel light beam 3b is used for light intensity distribution correction. As a lens that also serves as
Lens material 1 whose transmittance in the wavelength range of the light source is sufficiently lower than that of ordinary lens materials; for example, it is made of a material having a transmittance equivalent to that of an ND filter.

Here, the effective diameter of the convex lens 40 is 10 mm, and the focal length is 12.
5mm, and if a lens is manufactured by selecting a lens material whose transmittance for the wavelength of the semiconductor laser 2 is 70% per 1mm of lens thickness, the distribution of relative transmittance with respect to the light incident position of the convex lens 40 is shown in FIG. It comes to be expressed as If the transmittance distribution of the convex lens 40 shown in FIG. 4 is compared with the light intensity distribution of the laser beam emitted from the semiconductor laser shown in FIG. 8 on the same scale, the result will be as shown in FIG. . The curve in the figure is the radiation intensity of the semiconductor laser, and ■ is the transmittance of the convex lens.As is clear from this figure, the region of low transmittance in the zero curve corresponds to the beam center region with high light intensity in the zero curve. , conversely, a region of high transmittance on the zero curve corresponds to a beam peripheral region of low radiation intensity on the zero curve. Here, the light intensity distribution of the light beam transmitted through the convex lens 40 (the cross-sectional intensity distribution along the cross section It is corrected by the product of , and becomes like the black line in FIG. That is, before correction by the convex lens 40, the intensity difference ΔE between the maximum value and the minimum value of the cross-sectional intensity distribution of the Gaussian beam is 26%, whereas after passing through the convex lens 40, the intensity in the cross-sectional intensity distribution is 26%. The difference ΔE decreases to 2% or less, and as a result, the Gaussian beam emitted from the semiconductor laser 2 passes through the convex lens 40 which also serves as a light intensity distribution correction.
It can be seen that the light intensity distribution is made more uniform by a factor of 10 or more during the process of transmitting the light.

Here, the transmittance per unit thickness of the lens material for the convex lens 40 should be more appropriately selected in the range of 30 to 80%, and the shape of the lens surface should be selected as much as possible within the allowable aberrations of the optical system. By forming a curved surface close to a Gaussian distribution, it is possible to further improve the accuracy of correcting the light intensity distribution.

FIG. 2 shows an embodiment of an optical system that converts a light ray 3a emitted from a light source into a parallel light ray 3b through a lens system 4 consisting of a plurality of lenses 40.4L 42, in which at least one convex lens 40 of the lens system As described in the previous embodiment, the lens also serves as a lens for correcting light intensity distribution, and is made of a lens material having a lower transmittance than a normal lens material. Furthermore, in the embodiment of FIG.
A plurality of lenses 40 are included in the optical path of the parallel rays emitted from the
．． 41, one convex lens 40 of the lens system is configured as a lens that also serves as a lens for correcting light intensity distribution, as in the previous embodiment. , each of these embodiments can achieve the same effects as the embodiment shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, in an optical system including a light source that emits light rays exhibiting a Gaussian distribution and a convex lens arranged on its optical axis, at least one convex lens among the lenses in the system is used to emit light. As a lens that also serves as an intensity distribution correction lens, the convex lens is constructed by selecting a lens material that has a lower transmittance than a normal lens material in the wavelength range of the light rays emitted from the light source, thereby exhibiting a Gaussian distribution emitted from the light source. The light beam can be corrected by the convex lens so that the light intensity distribution in a cross section perpendicular to the optical axis becomes uniform. Moreover, compared to the conventional light intensity distribution uniformization correction method described above, there is no need for special additional parts or troublesome adjustments to install the additional parts, and it is possible to eliminate the need for some convex lenses, which are the constituent elements of the optical system. By simply manufacturing the lens from a lens material with low transmittance, the Gaussian distribution light rays emitted from the light source can be corrected to a uniform light intensity distribution while maintaining the original function of the convex lens.

[Brief explanation of the drawing]

1, 2, and 3 are system diagrams of optical systems according to different embodiments of the present invention, FIG. 4 is a transmittance distribution diagram of a convex lens that also serves as a light intensity distribution correction, and FIG. An explanatory diagram for making the intensity distribution uniform. FIG. 6 is a configuration diagram of a laser photoelectric switch as an example of the implementation target of the present invention. FIG. 7 is a schematic diagram of the light projecting section in FIG. 6. FIG. FIG. 3 is a radiation intensity distribution diagram of a semiconductor laser. In each figure, 1: light projector, 2: semiconductor laser as a light source, 3a: Gaussian distributed light rays emitted by the light source, 3b = parallel rays, 4: lens system, 40: convex lens for correcting light intensity distribution. ■ Figure 1 Figure 2

Claims (1)

[Claims] In an optical system including a light source that emits light rays exhibiting a Gaussian distribution and a convex lens arranged on its optical axis, at least one convex lens among the lenses in the system is used as a lens that also serves as a lens for correcting light intensity distribution, and the convex lens A device for homogenizing Gaussian distributed light in an optical system, characterized in that the lens is constructed by selecting a lens material having a lower transmittance than a normal lens material in the wavelength range of the light emitted from the light source.