JPH0743510A - Even-numbered multiple beam generating element and optical recorder - Google Patents

Abstract

PURPOSE:To provide a grating which generates the even number of multiple beams with uniform light intensity and an optical recorder with high speed and high resolution. CONSTITUTION:The grating in which a reference phase pattern 10 with structure in which rectangular patterns 8, 9 provided with nonuniform width and single phase height ay, ay are stacked in multiple layers are arranged repeatedly is used as an even number multiple beam generating element which generates the even number of multiple beams. Also, in the optical recorder, multiple beams emitted from the even numbed multiple beam generating element are made incident on a multi-channel acoustic optical device, and the angle of the multiple beams to which light intensity modulation is applied in the arranging direction is scanned by a rotary polygonal mirror after being rotated by a roof prism.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam generating element which divides a laser beam into a plurality of beams and processes a plurality of beams in parallel to realize high speed, and an optical recording apparatus using the same. is there.

[0002]

2. Description of the Related Art When laser light is incident on a grating element, many diffracted lights are generated. Utilizing this phenomenon,
The use as a multi-beam generating element has been proposed in the past and has been partially used. However, it has been difficult to increase the number of multi-beams and to efficiently generate uniform multi-beam light.

Recently, in the patent filed by the present inventor of Japanese Patent Application No. 4-130313 as a grating element for converting into a large number of multiple beams, a reference phase pattern constituting the grating is subdivided into rectangular patterns of non-uniform width. It is shown that even if the phase height is set to one step, if this nonuniform width is arbitrarily optimized and set, it is possible to realize a multibeam with high accuracy and high light utilization efficiency.
This method can be easily realized because the formation of a pattern of the coating material is sufficient for the production.

[0004]

However, in the above-mentioned conventional invention, as the design example is shown for the element which generates an odd number of beams from 3 beams to 9 beams, the example of the even number Could not generate multiple beams. The control circuit used together with the optical device is configured with information of 1 byte, that is, 8 bits, or the flip-flop circuit, counter circuit, etc. often used in the control circuit doubles or halves the electrical information. The basic operation is to convert to. Therefore, it is often desired that the number of multiple beams required by the optical device is an even number.

It is an object of the present invention to provide an even number multi-beam generating element having an even number of multi-beams to be generated and having a high uniform light use efficiency, and a high-speed, high-resolution optical recording device using the same. To do.

[0006]

To achieve the above object, in a grating in which reference phase patterns according to the present invention are repeatedly arranged, the reference phase patterns each have an unequal width and have a single phase height. It has a structure in which rectangular patterns are laminated in multiple layers, and is characterized by generating even beams.

In the case of an even multi-beam element which generates two beams, the reference phase pattern has a structure consisting of one layer of a rectangular pattern having an unequal width and a single phase height, and does not use 0th-order diffracted light. , -1st-order diffracted light and + 1st-order diffracted light are used.

[0008]

According to the present invention, the reference phase pattern of the grating has a structure in which rectangular patterns each having an unequal width and a single phase height are superposed on each other in a multilayer structure. It is possible to realize an even number of multiple beams having a uniform intensity.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.
In the grating, the reference phase pattern is the grating pitch p,
It is assumed that they are repeatedly arranged. The reference phase pattern 10 of the present invention is formed by stacking the phase patterns 8 and 9, and each of the phase patterns 8 and 9 has a single phase height and is composed of a rectangular pattern having an unequal width. There is. In this example, the phase pattern 8 is composed of a rectangular pattern of M portion and has an unequal width represented by y (1) to y (M). The phase height is ay. On the other hand, the phase pattern 9 is also composed of a rectangular pattern of the K portion,
It has an unequal width represented by z (1) to z (K). The phase height is az.

FIG. 2 shows an example in which the grating 7 as the even multiple beam generating element of the present invention generates four beams. The lens 3 is arranged such that the grating 7 is at the front focus position and the image formation position is at the rear focus position. When the laser light 1 is made incident on the grating 7 designed for four beams, four beams of −1st order, 0th order, 1st order, and 2nd order are generated in this example. The arrangement pitch q of the four beams on the image plane 4 is constant. Since the diffracted light is generated asymmetrically in this way, it is possible to generate an even beam. When the reference phase pattern is composed of only one layer of the phase pattern shown in FIGS. 1 and 8, a sufficient asymmetric diffraction pattern cannot be generated and even multiple beams of 4 beams or more cannot be generated. A symmetric diffraction pattern can be realized for an even number of two beams. That is, as shown in FIG. 3, the light intensity of the 0th-order diffracted light can be made substantially 0, and the -1st-order diffracted light and the + 1st-order diffracted light can be made into two beams. In this case, the reference phase pattern of the grating can be composed of only one phase pattern layer as shown in FIGS.

Next, a concretely designed procedure will be described. When the reference phase pattern is f (ξ) and the grating pitch of the grating is p, the light intensity distribution on the screen shown in FIGS. 2 and 4 is expressed by the following equation.

[0012]

[Equation 1]

However, s is a coordinate on the standardized screen 4, and s = 2πx / (λf). Further, λ is the wavelength of light, and N is the total number of reference phase patterns included in the grating 7. By calculating the equation (1), the following equation is obtained.

[0014]

[Equation 2]

However,

[0016]

[Equation 3]

[0017]

[Equation 4]

The function M (s) of the equation (4) is a function having an equal peak value at the diffraction position of the grating 7, as shown in FIG. In order for many diffracted lights from the grating 7 to have a uniform light intensity, the function F (s) of the equation (3) must have a uniform value for many diffracted lights. I won't. Therefore, the function f indicating the reference phase pattern
How to set (ξ) is important.

Next, an embodiment designed by calculating the equation (3) for the reference phase pattern of the present invention will be shown. by the way,
The phase heights ay and az do not change the value of the expression (3) regardless of whether the sign is + or −, and naturally, the result obtained does not change even if the value is increased or decreased by an integral multiple of 2π.

(1) Two-beam element y (1) /p=0.5 y (2) /p=0.5 ay = 3.142 (radian) (5) The element of this design example is shown in FIG. FIG. 5 shows a result of simulation in which reproduction is performed by the optical system. The vertical axis represents the light intensity. However, the incident light intensity is 1. The light intensity of the 0th-order diffracted light is set to 0, and the -1st-order and + 1st-order diffracted lights form two beams. The light intensity of the two beams as a whole is 81%, which is a high light use efficiency. Assuming that the light utilization efficiency of the two beams is acceptable up to 20%, the design value of the equation (5) is acceptable within the following range.

0.248 <y (1) / p <0.752 0.248 <y (2) / p <0.752 1.56 <| ay | <4.72 (6) (2) 4 beams About the element y (1) /p=0.372 y (2) /p=0.628 z (1) /p=0.254 z (2) /p=0.443 z (3) / p = 0 .146 z (4) /p=0.156 ay = 1.66 az = 1.13 (7) FIG. 6 shows a simulation result in which the element of this design example is reproduced by the optical system of FIG. The vertical axis represents the light intensity. However, the incident light intensity is 1. -1 order, 0
There are four beams of diffracted light of the 2nd, + 1st, and + 2nd orders. Four
The light intensity of the entire beam is 80%, which is a high light use efficiency. The uniformity of multiple beams is 50 times the average light intensity of multiple beams.
%, The design value of the equation (7) is acceptable within the following range.

0.254 <y (1) / p <0.47 0.48 <y (2) / p <0.76 0.17 <z (1) / p <0.34 0.26 <z (2) / p <0.55 0.046 <z (3) / p <0.28 0.105 <z (4) / p <0.23 1.34 <| ay | <2.12 0. 67 <| az | <1.59 (8) (3) Six-beam element y (1) /p=0.080 y (2) /p=0.059 y (3) /p=0.297 y (4) /p=0.565 z (1) /p=0.37 z (2) /p=0.255 z (3) /p=0.197 z (4) /p=0.178 ay = 1.344 az = 1.68 (9) FIG. 7 shows a simulation result in which the element of this design example is reproduced by the optical system of FIG. The vertical axis represents the light intensity. However, the incident light intensity is 1. -Second order,-
There are 6 beams of diffracted light of the 1st, 0th, + 1st, + 2nd, and + 3rd orders. The light intensity of the six beams as a whole is 77%, which is a high light use efficiency. Assuming that the uniformity of the multiple beams is acceptable up to 50% of the average light intensity of the multiple beams, the design value of the equation (9) is acceptable within the following range.

Y (1) / p <0.159 y (2) / p <0.133 0.212 <y (3) / p <0.368 0.504 <y (4) / p <0. 613 0.313 <z (1) / p <0.447 0.18 <z (2) / p <0.317 0.142 <z (3) / p <0.271 0.148 <z (4 ) / P <0.218 1.05 <| ay | <1.71 1.44 <| az | <1.97 (10) (4) For 8 beam elements y (1) /p=0.297 y (2) /p=0.143 y (3) /p=0.174 y (4) /p=0.179 y (5) /p=0.075 y (6) /p=0.132 z (1) /p=0.306 z (2) /p=0.155 z (3) /p=0.121 z (4) /p=0.418 ay = 1.360 az = 1.37 ( 11) For this design example FIG. 8 shows a result of simulation in which the element is reproduced by the optical system of FIG. The vertical axis represents the light intensity. However, the incident light intensity is 1. -3rd order,-
The 2nd-order, -1st-order, 0th-order, + 1st-order, + 2nd-order, + 3rd-order, and + 4th-order diffracted light forms eight beams. The light intensity of the entire 8 beams is 79%, which is a high light use efficiency. Assuming that the uniformity of multiple beams can be up to 50% of the average light intensity of multiple beams, the design value of equation (11) can be up to the following range.

0.233 <y (1) / p <0.359 0.086 <y (2) / p <0.242 0.086 <y (3) / p <0.23 0.101 <y (4) / p <0.24 0.015 <y (5) / p <0.149 0.098 <y (6) / p <0.178 0.236 <z (1) / p <0. 365 0.07 <z (2) / p <0.22 0.06 <z (3) / p <0.183 0.38 <z (4) / p <0.45 1.181 <| ay | <1.58 1.19 <| az | <1.59 (12) The above-described multi-beam generating grating element of the present invention can be easily manufactured by the existing optical material coating technology, etching technology, or the like. That is, in order to create the phase patterns shown in FIGS. 1 and 10, first, a pattern of an optical material having a predetermined film thickness is created so that the phase patterns shown in FIGS. )reference). Next, a pattern of an optical material is formed on the upper layer so as to realize the phase patterns shown in FIGS. 1 and 9 with a predetermined film thickness (see FIG. 9B). The resulting element of FIG. 9C realizes the phase pattern of FIGS. As described above, the structure of the grating of the present invention may be formed by superposing the patterns of the optical material by the number of layers, each having a predetermined film thickness.

The thickness e of the optical material to be coated
Can be easily set from the phase height a and the following relational expression.

A = (2π / λ) (n-1) e The substrate 25 is a glass material, and the coating material 26 is SiO 2.
₂ or MgF ₂ can be used.

FIG. 10 shows a laser printer apparatus for performing optical recording with multiple beams generated by the multiple beam generating element of the present invention. Since optical recording is performed with multiple beams at one time, a high-speed or high-resolution laser printer device can be realized. The laser beam 1 emitted from the laser device 11 is incident on the multi-beam generation element 2 of the present invention. As described above with reference to FIG. 2, the lens 3 collimates the generated multi-beams 5 into parallel beams 6 of light.
And has a function of narrowing down to a small spot in the multi-channel acousto-optic device 13. Since the spots are narrowed down to small spots in the multi-channel acousto-optic device 13, it is possible to shorten the transit time of ultrasonic waves that cross these small spots, and it is possible to perform high-speed optical modulation.

The outline of the operation of the multi-channel acousto-optic device 13 will be described with reference to FIG. A transducer 16 is used for acousto-optic medium such as one PbMoO ₄ crystal or TeO _2.
Are provided, and the incident multi-beam light 17 can be independently modulated. That is, when an independent electric signal is applied to each of the plurality of transducers 16, each signal independently propagates a sound wave in the crystal, and the corresponding light beam is diffracted and modulated by the sound wave. Reference numeral 18 in FIG. 11 denotes a modulated beam, which is used for optical recording. Reference numeral 19 denotes transmitted light, which is shielded at an appropriate place so as not to reach the optical recording material.

Reference numeral 25 denotes a circuit device for driving the multi-channel acousto-optic device 13. The light emitted from the multi-channel acousto-optic device 13 is converted into an appropriate beam diameter by a lens, passes through the Dove prism 20, and enters the rotating polygon mirror 21. The rotary polygon mirror 21 is rotating and simultaneously scans the photosensitive drum 24 with multiple beams. The lens 22 is for focusing the multi-beam light on the photosensitive drum 24 as minute multi-point spots.

By the way, the multi-beam light is made into a series of small spots in the multi-channel acousto-optic device 13.
This spot diameter is D and the transducer array pitch is T
Then, T / D is larger than 1. Therefore, the photosensitive drum 2
Multipoint spots on 4 will also be arranged at this ratio,
The spot arrangement pitch becomes larger than the spot diameter. The multi-point spots 15 are shown on the photosensitive drum 24 in FIG. 12 in order to prevent the non-illuminated areas from being formed during the scanning of the multi-point spots, that is, in order to make the scanning line pitch smaller than the interval between the multi-point spots. As described above, it is necessary to set the spot arrangement direction and the scanning direction to be oblique.

As a method for realizing this, there is a method in which the multi-channel acousto-optic element 13 and the multi-beam generating element 2 are simultaneously rotated with the optical axis direction as a rotation axis. Optical element 13
It is very difficult to maintain the accuracy of the incident position of light on the. In order to eliminate this difficulty, the dove prism 20 is used. In this method, the Dove prism 20 is rotated about the optical axis direction to adjust and set it in a predetermined spot arrangement direction. The image rotation mechanism itself of the Dove prism is well known. That is, as shown in FIG. 13, the light from the image 26 is converted into an image 27 by being totally reflected by the bottom surface of the Dove prism 20. Therefore, when the Dove prism 20 is rotated like 28, the image 27 is also rotated as shown by 29.

The photodetector 23 is for receiving multiple beams of light, generating signals corresponding to the respective lights, and using the signals as synchronizing signals for the corresponding lights.

[0033]

As described above, the even-number multi-beam generating element of the present invention can be prepared by performing a process of forming a rectangular pattern with an optical material having a constant film thickness a plurality of times, so that the rectangular pattern can be easily formed. It is possible to realize an even number of multiple beams with high light utilization efficiency and uniform light intensity by arbitrarily designing the width of.

Further, by using the generated multi-beams together with the multi-channel acousto-optic modulator, a high speed and high resolution optical recording device can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a grating reference phase pattern used in a multi-beam generation element of the present invention.

FIG. 2 is a diagram for explaining an optical system for generating multiple beams by grading.

FIG. 3 is a diagram for explaining an operation of an optical system that generates two beams.

FIG. 4 is a diagram for explaining a function M (s).

FIG. 5 is a schematic diagram of a multi-beam generation grating according to the present invention.
It is an example of calculation when a beam is generated.

FIG. 6 is a schematic diagram of the multi-beam generation grading according to the present invention.
It is an example of calculation when a beam is generated.

FIG. 7 is a graph of the multi-beam generation grating of the present invention.
It is an example of calculation when a beam is generated.

FIG. 8 is a graph of the multi-beam generation grating of the present invention.
It is an example of calculation when a beam is generated.

FIG. 9 is a diagram for explaining a method of manufacturing an even multiple beam generating element and a cross-sectional structure of the even multiple beam generating element of the present invention.

FIG. 10 is a diagram showing an optical recording device using an even multi-beam generating element.

FIG. 11 is an operation explanatory view of the multi-channel acousto-optic device.

FIG. 12 is a diagram showing how a multi-point spot scans.

FIG. 13 is a diagram illustrating the operation of the Dove prism.

[Explanation of symbols]

1 is a laser beam, 2 is an even multiple beam generating element, 3 is a lens, 8 is a phase pattern of the first layer, 9 is a phase pattern of the second layer, 10 is a reference phase pattern of the even multiple beam generating element, 13 Is a multi-channel acousto-optic device, 20 is a Dove prism, 21 is a rotating polygon mirror, 24 is a photosensitive drum, and 23
Is a light detector.

Claims (6)

[Claims] 1. A grating in which reference phase patterns are repeatedly arranged, wherein the reference phase patterns have a structure in which rectangular patterns each having an unequal width and a single phase height are stacked in multiple layers to generate an even beam. An even multi-beam generating element characterized in that 2. In a grating in which reference phase patterns are repeatedly arranged, the reference phase pattern is composed of two parts, and the widths y (1) and y (2) of the respective rectangular patterns are given by assuming that the grating pitch of the grating is p. , 0.248 <y (1) / p <0.752 0.248 <y (2) / p <0.752 The phase height ay allows an integral multiple of 2π, 1.56 < | Ay | <4.72, an even multi-beam generating element for generating two beams. 3. The reference phase pattern has a structure in which two layers are superposed, and the first layer is composed of a rectangular pattern of two parts,
The width of the rectangular pattern is y (1), y (2), and the phase height ay, and the second layer is composed of a rectangular pattern of four parts. The width of the rectangular pattern is z (1), z (2), z (3),
If z (4) and the phase height are az, then the grating pitch of the grating is p: 0.254 <y (1) / p <0.475 0.477 <y (2) / p <0.760 167 <z (1) / p <0.34 0.264 <z (2) / p <0.554 0.046 <z (3) / p <0.28 0.105 <z (4) / p <0.23 Further, the phase height is 1.34 <| ay | <2.12 0.67 <| az | <1.59, assuming that addition and subtraction of integer multiples of 2π are allowed. The even-number multi-beam generation element according to claim 1, wherein the four-beam generation is performed. 4. The reference phase pattern has a structure in which two layers are superposed, and the first layer is composed of a rectangular pattern of four parts,
The width of the rectangular pattern is y (1), y (2), y
(3), y (4), the phase height is ay, and the second layer is composed of a rectangular pattern of four parts, and the width of the rectangular pattern is z.
(1), z (2), z (3), z (4), phase height is a
Letting z be z, the grating pitch of the grating is p, and y (1) / p <0.159 y (2) / p <0.133 0.212 <y (3) / p <0.368 0.504 < y (4) / p <0.613 0.313 <z (1) / p <0.447 0.180 <z (2) / p <0.317 0.142 <z (3) / p <0 .271 0.148 <z (4) / p <0.218 Further, assuming that the phase height is allowed to be increased or decreased by an integral multiple of 2π, 1.05 <| ay | <1.71 1.44 <| az The even-number multi-beam generating element according to claim 1, wherein | <1.97. 5. The reference phase pattern has a structure in which two layers are superposed, and the first layer is composed of a rectangular pattern of 6 parts,
The width of the rectangular pattern is y (1), y (2), y
(3), y (4), y (5), y (6), the phase height is a
y, the second layer is composed of a rectangular pattern of four parts, and the width of the rectangular pattern is z (1), z (2), z (3), z
(4) Assuming that the phase height is az, the grating pitch of the grating is p, and 0.233 <y (1) / p <0.359 0.086 <y (2) / p <0.242 0. 086 <y (3) / p <0.229 0.101 <y (4) / p <0.240 0.015 <y (5) / p <0.149 0.098 <y (6) / p <0.178 0.236 <z (1) / p <0.365 0.071 <z (2) / p <0.222 0.059 <z (3) / p <0.183 0.38 < z (4) / p <0.453 Further, assuming that the phase height is allowed to be increased or decreased by an integer multiple of 2π, 1.181 <| ay | <1.583 1.191 <| az | <1.59 The even-number multi-beam generating element for generating eight beams according to claim 1, wherein 6. A grating in which reference phase patterns are repeatedly arranged, wherein each of the reference phase patterns has a structure in which rectangular patterns each having a non-uniform width and a single phase height are stacked in multiple layers to generate an even beam. It is an even multi-beam generating element, the multi-beam emitted from the even multi-beam generating element is made incident on a multi-channel acousto-optic modulator, and the angle of the array direction of the light intensity-modulated multi-beam is rotated by a dove prism. After that, an optical recording device characterized by scanning with an optical scanner.