JPH028284B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for the holographic fabrication of blazed gratings. As the reliability of laser equipment has improved, laser beam scanning has come to be used to form or read figures, and has already been put to practical use in laser faxes, laser printers, and laser point of sales (POS). There is. These practical devices scan a screen with a laser beam and modulate the laser beam to form an image, or scan a figure with a laser beam and read the figure from the strength of the reflected light. ing. In this case, a rotating polygon mirror or an optical scanning device combining a galvanometer mirror and a lens is used for laser beam scanning. In recent years, it has been proposed to use a hologram as a means for scanning a laser beam without using a rotating polygon mirror. Although an inexpensive optical scanning device can be realized by using holograms,
There is a problem in terms of conversion efficiency. The method of optically producing a hologram is to record interference fringes with different pitches on the circumference of a disk, and the pitch of the interference fringes changes discontinuously for each hologram unit.
When a laser beam is incident on the interference fringes, diffracted light is obtained, and as the interference fringes rotate, the diffracted light also rotates to draw an arc. Since the interference fringe pitches of the holograms recorded on the disk circumference are different, the diffracted light from each hologram draws different arcs, forming a group of scanning lines. The interference fringes of a hologram have a sinusoidal profile, and it is theoretically difficult to achieve a conversion efficiency of more than 30%. If a volume-type material (dichromate gelatin, photopolymer, etc.) is used as the recording material, it is possible to increase the conversion efficiency to nearly 90%, but it is not possible to obtain multiple conversion efficiencies. Next, the method of obtaining an optical scanning disk using a computer hologram makes it possible to obtain any interference fringes, but since the shape of the interference fringes is a digital line drawing, the efficiency is low at a few percent. It is difficult to draw large-area interference fringes using a computer output device in terms of recording time and recording resolution. Therefore, a method of blazing a holographic grating is desired in terms of conversion efficiency, but the conventional fabrication method using ion milling can only produce a simple grating composed of identical pitches, and it is possible to fabricate a holographic grating with arbitrary curvature. It is not possible to blaze a lattice.

It is an object of the invention to provide a method of fabricating a holographic grating with high conversion efficiency to a scanning beam.

According to the present invention, in a method for manufacturing a holographic grating that records interference fringes formed by interference of a plurality of monochromatic lights on a recording material, the light intensity and spatial position of sharpened interference fringes are continuously adjusted. A method for producing a holographic grating characterized by recording overlappingly while changing the holographic grating is obtained.

This invention will be described in detail below with reference to the drawings. FIG. 1 shows the spatial intensity distribution of interference fringes holographically obtained by a conventional method. The intensity distribution is sinusoidal, and the diffracted light conversion efficiency obtained from a holographic grating recording this intensity distribution is low, at a maximum of 33%. Second
The figure shows a method of manufacturing a blazed grating by ion milling, in which a grating pattern 2 is formed holographically on a substrate 1 using photoresist. An ion beam is irradiated obliquely onto this grating pattern to perform ion beam etching on the substrate 1. The photoresist forming the grating pattern 2 is also etched, but because the amount of etching on the base portion under the photoresist is small, the blazed grating 3 with a sawtooth wave shape as shown in FIG. 3 is formed.
is obtained. When the blaze condition of the blazed grating 3 is satisfied, a conversion efficiency close to 100% can be obtained.
The angle of the slope of the grating (blaze angle) is determined by the incident angle of the ion beam in FIG. Therefore, all blazed gratings produced by ion beam etching have the same blaze angle, and only simple gratings can be blazed.

A holographically formed grating, particularly a grating used for optical scanning, has interference fringes whose pitch changes continuously. The blaze angle is a function of the lattice pitch; the smaller the pitch, the larger it becomes. Fourth
The figure shows a blazed grating in which the pitch of interference fringes changes continuously, which is the object of this invention.
It cannot be manufactured by conventional methods such as ion milling.

Next, a method for manufacturing a holographic blazed grating according to the present invention will be described. FIG. 5 shows the intensity distribution of interference fringes used in grating fabrication, and is a sharpened version of the intensity distribution of interference fringes obtained by holography. Sharpening is possible by using repeated reflections by an etalon or nonlinearity of the recording material. As shown in FIG. 6, the amount of light of the recorded interference fringes is increased over time to provide exposure for t seconds. FIG. 7 shows the exposure dose distribution on the surface of the recording material. As the light intensity of the interference fringes increases with time, the interference fringes are simultaneously moved within one wavelength and recorded. That is, the interference fringe 4 is t
The light moves to the position of the interference fringe 4' per second as the amount of light increases, and is recorded integrally on the recording material. The resulting light intensity distribution becomes a 4° sawtooth wave. At this time, if the interference fringes remain as sine waves, the combined wavefront is only a sine wave, so sharpened interference fringes are required. Movement of the interference fringes can be easily achieved by inserting an optical wedge into a single monochromatic beam. Since the movement of the interference fringes by the optical wedge is carried out at the same rate for all grating pitches, the above effect can be produced simultaneously on all continuously changing gratings. Moreover, the smaller the pitch, the steeper the angle formed by the 4° sawtooth slope, allowing the blazed angle to be matched to the pitch of each grating. Furthermore, another feature of this method is the 8th
The point is that it is possible to blaze a holographic grating with a two-dimensional curved surface as shown in the figure.
Since the movement of the interference fringes by the optical wedge is always carried out in the direction perpendicular to the fringes, it is possible to blaze the interference fringes with a two-dimensional pattern by the above method.

The holographic grating with the density distribution of the sawtooth wave thus obtained is transferred and recorded onto a photoresist recording material, and if a grating with the same relief distribution as the density distribution is obtained, the final result is a blazed grating with high conversion efficiency. A holographic grating is obtained.

FIG. 9 shows an example of a grating manufacturing apparatus using the blazed holographic grating manufacturing method of the present invention. Monochromatic light 20 from the laser 5 passes through the optical modulator 6, is reflected by the mirror, and is divided into object light 21 and reference light 22 by the half mirror 8. The object light 21 is incident on the recording plate 13 as a wavefront formed by lenses 9, 10, and 11, and the reference beam 22 is also transmitted through the optical wedge 14 and enters the recording plate 13 as a wavefront diverging at the lens 12. As the optical modulator 6, an ultrasonic modulator, an electro-optic modulator, or a disc-shaped temperature filter can be used, and the optical wedge 4 can be a transparent solution cell with a spacer of several μm at one end, a glass wedge, etc. Can be used. As shown in FIGS. 10a and 10b, the recording plate 13 is configured to utilize a repetition effect. In a, the recording material 16 is covered with a semi-transparent mirror 17 and a reflecting mirror 18.
placed between. In b, the recording material 19 is applied onto the semi-transparent mirror 17 and is set opposite the reflecting mirror 18. In both cases, the interval between the semi-transparent mirror 17 and the reflecting mirror 18 is determined so that an etalon effect can be obtained at the center value of the incident angle of the incident lights 21 and 22. In FIG. 9, the exposure amount is changed by the light conversion adjuster 6, and at the same time, the optical wedge 14 is moved by the minute movement mechanism 15, and the phase amount of the reference beam 22 is changed to move and record the interference fringes. By this method, a holographic grating with a sawtooth concentration distribution can be fabricated.

As described above in detail, the present invention provides a method of manufacturing a holographic grating with high conversion efficiency into a scanning beam.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams for explaining the conventional method of manufacturing a blazed grating, with Figure 1 showing the intensity distribution of interference fringes, and Figure 2 showing the method of manufacturing a blazed grating by ion milling. FIG. 3 is a diagram showing a blazed grating. Figures 4 to 8 are diagrams for explaining the method of manufacturing a blazed grating according to the present invention. Figure 4 is a diagram showing the blazed grating targeted by the present invention, and Figure 5 is a diagram showing the intensity distribution of interference fringes. 6 is a diagram showing changes in the light amount of recorded interference fringes, FIG. 7 is a diagram showing the exposure amount distribution on the surface of the recording material, and FIG. 8 is a diagram showing a holographic grating with a two-dimensional curved surface. FIG. FIG. 9 is a diagram showing an example of a grating manufacturing apparatus using the blazed holographic grating manufacturing method of the present invention.
FIG. 0 is a diagram showing the configuration of a recording plate. In the figure, 4 and 4' are interference fringes, 6 is an optical modulator,
13 is a recording material, and 14 is an optical wedge.

Claims (1)

[Claims] 1. A method for manufacturing a holographic grating for recording interference fringes formed by interference of monochromatic light on a recording material using a two-beam interference optical system, wherein an etalon plate and an optical wedge are provided in the two-beam interference optical system. the interference fringes are sharpened by the etalon plate, the spatial position of the interference fringes is continuously changed by moving the optical wedge, and the light intensity of the interference fringes is temporally changed while overlapping recording is performed. A method for producing a holographic lattice characterized by: