JPS60189702A - Information device using prism optical system - Google Patents

Abstract

PURPOSE:To prevent the property of geometrical optics from varying with the wavelength of luminous flux by sticking two kinds of prisms made of materials which differ in the wavelength dispersion of a refractive index together and satisfying a specific conditional equation. CONSTITUTION:The 1st prism 2A made of the 1st material with a refractive index n1 and the 2nd prism 2B made of the 2nd material with a refractive index n2 are stucked together on a surface M to form a composite prism 2; and light is incident on the composite prism 2 at an angle theta1 from an air layer and projected at an angle theta2, and then incident on the boundary surface M at an angle alpha1 and projected from the composite prism 2 at right angles to its projection surface. In this case, the equation I holds, where DELTAn1 and DELTAn2 are dispersion values of the refractive indexes. Consequently, the projection angle does not vary with the wavelength. When this prism optical system is applied to an optical information processor, even variation in the wavelength of a light source exerts no influence.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a prism optical system and an information device using the same, and particularly to a composite prism optical system suitable for changing the shape of a light beam having a two-dimensional distribution and the use thereof. The present invention relates to the optical information processing device used.

[Background of the invention]

Conventionally, there are two types of optical systems for changing the shape of the light beam.
Two types of optical systems are known: one in which two lenses are arranged confocal and the magnification is adjusted by the ratio of their focal lengths, and the other in which the difference in entrance and exit angles due to refraction of a triangular prism is used. The present invention corresponds to an improved version of the latter of the above two optical systems.

FIG. 1 shows the state of refraction by the triangular prism, in which a light beam is obliquely incident on one surface of the triangular prism 1. Let the entrance and exit angles at the boundary be θ
1. If θ2, sin θ, = n sin θ? There is a relationship (Snell's law). Here, n is the refractive index of the material constituting the triangular prism.

In addition, regarding the change in the diameter of the luminous flux due to the above refraction,
When the diameters of the emitted light beams are respectively D,, D2, D,/D1=cosO,,/cost.

There is a relationship, and this relationship is used to perform the above shape change. Note that the other surface of the prism allows the light flux to enter and exit perpendicularly, so that the diameter ratio of the light flux generated on the other surface is maintained.

The above relationship remains unchanged if the wavelength of the luminous flux is constant, but
When the wavelength changes, the refractive index of the material constituting the triangular prism changes, so the above 0 changes, which poses a problem of having a large effect on the device incorporating the triangular prism.

What is the change in wavelength above?

For example, this is caused by variations in the individual emission wavelengths of semiconductor lasers used as light sources, or by changes in these wavelengths over time.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to solve the above-mentioned problems in conventional prism optical systems or devices using the same, and to improve geometrical optical properties with respect to wavelength changes of light beams. An object of the present invention is to provide an unchanging prism optical system and an optical information processing device using the same.

[Summary of the invention]

The main points of the present invention are that the prism constituting the prism optical system □ is formed by bonding together two types of materials with different wavelength dispersion of refractive index, and that this is used in an optical information processing device. It is in.

[Embodiments of the invention]

EMBODIMENT OF THE INVENTION Hereinafter, after a detailed description of the present invention, embodiments will be described in detail based on the drawings.

FIG. 2 is a diagram for explaining the present invention in detail. In the figure, 2 is a first prism 2A made of a first material with a refractive index of n, and a second prism 2B made of a second material with a refractive index of 02. This is a composite prism bonded together at M.

In the following description, the case will be considered in which, as described above, a light beam that enters the composite prism 2 from the air layer at an angle θ is output from the composite prism 2 perpendicularly to its output surface. In order for the emitted light to be emitted perpendicularly from the emitting surface of the composite prism 2, the angle indicated by α2 in the figure need only be made so that it does not change with respect to changes in wavelength.

From the above 5-nell law, sin e, : n, sjnθ2'−・・−−
−・−−−・(1) n, sir+α, =n, s
ir+α2=・・・=・・・(2) holds true, and θ2+α,=C (constant)・・・・・・・・・(3
).

Refractive index n, ln2 with respect to wavelength change of incident light flux; angle α1. Changes in α2, 02, etc., are expressed as Δnll and Δn2, respectively.
;Δα1. Δα2. If it is expressed as Δθ2 etc. (the angle θ remains unchanged), then from equation (]) and from equation (2), Δn1sinα, tenn, cosα1Δα1−Δn2s
inα2=n 2 Q OSα2Δα2°1 (5) is obtained.

Since it is necessary that Δα2=0 with respect to the wavelength change, Δn, sinα, +n, cosα1−Δn2si from equation (5)
It is necessary that nα2;0...-(6) hold true.

Also, by differentiating both sides of equation (3), Δθ,=−Δα,・・・・・・・・・・・・・・・(
7) Therefore, from Equation 5(2) and Equation (6), the following can be obtained. Substituting the relationship shown in equation (7) into equation (8) and rearranging it.

bawl. Here, by substituting the relationship shown in equation (4) into equation (9) and eliminating Δ02, the following is obtained, which is further summarized as a condition that the emission angle does not change with respect to a change in wavelength.

Note that materials having a refractive index and wavelength dispersion that satisfy the above conditions can exist as shown below.

For example, given 02-α and n, :n, 2Δn,=Δn.

It is. According to the optical glass list of Ohara Optical Glass Manufacturing Co., Ltd., the values of An, /Δn, can be taken as follows.
Real systems are configurable.

Note that in the composite prism 2 configured as described above, since two prisms 2A and 2B are used, the number of refractive surfaces increases, resulting in an increase in reflection loss. In order to reduce this as much as possible, the materials constituting the above two prisms must be made at T1. =n
It should be selected so that t.

It goes without saying that the prism optical system described above operates in the same way even if the direction of incidence and direction of emission are reversed.

Next, an example in which the present invention is applied to an optical information processing device will be described.

FIG. 3 is a block diagram showing a writable optical disk device according to an embodiment of the present invention. In the figure, 11 is a semiconductor laser, 12 is a lens, and 13 is a composite prism having the configuration shown in FIG. 2, which is a characteristic part of this embodiment.
14 is a beam splinter, 15° and 17 are lenses, 1G is an optical disk, and 18 is a photodetector.

The operation of the optical disk device shown in this embodiment will be explained below.

The laser beam emitted from the semiconductor laser 11 is turned into a parallel beam by the lens 2, and passes through a prism (composite prism) 13 for shape shaping. As described above, this prism 13 is characterized in that there is no change in the angle of the luminous flux after exiting the prism due to a change in the wavelength of the laser light. Thereafter, the light flux emitted from the brism 13 passes through the beam splitter 14 and lens 15 and is irradiated onto the optical disc 16, and information from the optical disc 16 is received by the photodetector 18. Since this is the same as the optical disk device of 2.0, a detailed explanation will be omitted.

Note that the configuration shown in the above embodiment is particularly effective in a case where a wavelength change occurs due to a change in laser beam output between reading and writing, such as in an optical disk that allows additional writing and rewriting.

For example, two prisms (
(see Figure 2), the first prism was LaK]O (n, = 1.70889 at λ = 830 nm) manufactured by Ohara Optical Glass Manufacturing Co., Ltd., and the second prism was LaK]O manufactured by Ohara Optical Glass Manufacturing Co., Ltd. =1.63066)
, γ = 33.710 degrees, and θ, = 64.56 degrees, then 01 = 31.410 degrees, α1 = 40.10 degrees, and α2 = 32.90 degrees. Here, the wavelength λ is 80
Refractive index change Δr when changing from 0 nm to 860 nm
l+ +Δn2 are −0,001759 and −0,003+28, respectively, and under the conditions described above (page 7 (1
1) Formula) % Formula % When the wavelength actually changes from 830 nm to 800 nm, the output angle change is 0.000708 degrees, and when the wavelength changes from 830 nm to 860 nm, the output angle change is 0.0007 degrees.
It is 17 degrees, which is more than an order of magnitude smaller than before. Note that the luminous flux at this time becomes 2.19 times as large in the direction of change.

Therefore, when using a laser with an ellipse ratio of 1:2, 2.1
The ratio becomes 9:2, making it almost a perfect circle.

FIG. 4 is a block diagram showing a laser printer according to another embodiment of the present invention. In the figure, 11 to 13 indicate the same components as shown in FIG. 3, 21 is a polygon mirror, 22 is an Fθ lens, and 23 is a photosensitive drum.

In this embodiment, a laser beam emitted from a semiconductor laser 11 is converted into parallel light by a lens 12, passes through a prism 13 for shape shaping, and then passes through a polygon mirror 21.
The photosensitive drum 23 is scanned through the F'0 lens 22. At this time, conventionally, there was a problem that when the wavelength of the laser beam changed due to a change in wavelength, distortion occurred in the patterns, characters, etc. drawn on the surface of the photosensitive drum 23.
By using the prism 13 described above, this problem is solved.

〔Effect of the invention〕

As described above, according to the present invention, since the prism constituting the prism optical system is formed by bonding two types of materials with different wavelength dispersion of refractive index, the geometrical optical properties change with respect to wavelength changes. This has the remarkable effect of being able to realize a prism optical system that does not Furthermore, when the above prism optical system is applied to an optical information processing device,
This has the remarkable effect of making it possible to realize an information device that is unaffected even if the wavelength of the light source changes significantly.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the action of a conventional triangular prism, Fig. 2 is a diagram showing a composite prism that is an embodiment of the present invention, and Figs. 3 and 4 are diagrams showing the above-mentioned composite prism. FIG. 2 is a block diagram showing an example of an optical information processing device to which the method is applied. 2: composite prism, 2'A, 2B double prism, 11: semiconductor laser, 12, 15, 17: lens, 13: composite prism, 14: beam splitter, 16 dual optical disk. 18: Photodetector, 21: Polygon mirror, 22: FO lens, 23: Photosensitive drum. Patent applicant: Hitachi, Ltd. (and 1 other person) No. 1
Figure 2

Claims (3)

[Claims] (1) In a prism optical system that changes the shape of a light beam by refraction of light, two types of prisms made of materials with different wavelength dispersion of refractive index are bonded together, but Δn, l
Δn: wavelength dispersion of refractive index n1 y nz: refractive index at a specific wavelength 02: refraction angle αl at the light incident surface of the first prism: 1st. A prism optical system characterized in that it is configured to satisfy a condition of an incident angle at a boundary surface of a second prism. (2) Claim 1, characterized in that the material is made of a material having the same refractive index n1tn2 at the specific wavelength.
Prism optical system described in Section 2. (3) At least a writing light source and a beam collimating optical system. In an optical information processing device having a beam shape converting prism and a beam condensing optical system, the beam shape converting prism is made of materials having different wavelength dispersions of refractive indexes.
Pasting different types of prisms, however, Δnll Δn2
= wavelength dispersion of refractive index nIg n4 : refractive index at a specific wavelength θ2 : refraction angle α at the light incidence surface of the first prism, : 1st. An information device characterized by using a composite prism configured to satisfy a condition of an incident angle at a boundary surface of a second prism.