JPH01172903A - Diffraction grating forming device - Google Patents

Abstract

PURPOSE:To obtain a uniform and highly efficient holographic diffraction grating being free from speckle noise by bringing divergent light and divergent light which have been set to a special condition to interference. CONSTITUTION:The diffraction grating device is formed so that H/LXC/L being the product of a ratio H/L of a difference H between a middle point of an interval C of pin holes of two special filters 7, 8 and an object to be exposed and the interval C of the pin holes of two special filters 7, 8 and an object to be exposed and length L of a diameter or a long side of the object to be exposed, and a ratio C/L of the interval C of the pin holes of two special filters 7, 8 and the length L of the object to be exposed is >=32, and also, the intensity distribution of laser radiated to the object to be exposed becomes a uniform intensity distribution of >=80% against a peak value. In this state, the divergent light and divergent light of such an intensity distribution are brought to interference. In such a way, a uniform and highly efficient holographic diffraction grating being free from speckle noise can be obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a diffraction grating forming apparatus.

Diffraction gratings have been used in the field of spectroscopy as dispersive elements in spectrometers, but in recent years they have also been used in the field of optical communications as resonators in semiconductor lasers and dispersive elements in demultiplexers.

As a method for producing this diffraction grating, a mechanical scoring method using a ruling engine has traditionally been widely used, but in recent years, a method using holographic exposure has also come to be used.

Prior Art Methods using this holographic exposure method include a method in which plane waves are made to interfere with each other, and a method in which divergent waves are made to interfere with each other.

Planar linear holographic diffraction gratings have generally been formed by using a method in which two laser beams are made to interfere with each other, in which plane waves are made to interfere with each other for exposure.

There was also a method to perform holographic exposure by interfering divergent waves with one another, but this resulted in a hyperbolic diffraction grating and was not used to fabricate a planar linear holographic diffraction grating.

An example of the above-described conventional holographic diffraction grating forming apparatus will be described below with reference to the drawings.

5 and 6 show a conventional planar linear holographic diffraction grating forming apparatus.

In FIG. 5, after coating a photoresist 52 on a substrate 51, by three-beam interferometry holographic exposure,
The light beam emitted from the exposure laser 53 is divided into two by a half mirror 54.
The beam is separated into two beams, each beam is filtered with special filters 55 and 56 to remove noise, and then expanded, converted into parallel waves by lenses 57 and 58, and reflected by mirrors 59 and 6o. The light beams are caused to interfere on the sample to obtain a planar linear holographic diffraction grating with the required spacing.

(For example, Japanese Unexamined Patent Application Publication No. 189502/1982) In FIG. 6, after a photoresist 62 is applied on a substrate 61, a light beam emitted from an exposure laser 63 is passed through a lens 64 by three-beam interference method holographic exposure. The plane wave beam is expanded, converted into parallel light by a parabolic mirror 65, and reflected by mirrors 66 and 67, so that the two beams interfere with each other on the sample. A planar linear holographic diffraction grating 42 with a required spacing by interfering two plane waves on a substrate.
get.

(For example, Japanese Unexamined Patent Publication No. 61-281529) However, in the above-mentioned forming apparatus, even if the light flux of the laser beam is once noise removed by the special filter, the light flux of the laser beam is There was a problem in that speckle noise was generated by the subsequent optical system, making it difficult to obtain a uniform grating.

FIG. 7 shows a conventional apparatus for forming a diffraction grating by interfering divergent waves.

In FIG. 7, after coating a photoresist 72 on a substrate 71, by three-beam interferometry holographic exposure,
The light beam emitted from the exposure laser 73 is divided into two by a half mirror 74.
The beam is separated into two beams, each beam is reflected by mirrors 75 and 76, the beam is expanded by lenses 77 and 78, and the two beams are caused to interfere on the sample to obtain a holographic diffraction grating.

(For example, Japanese Patent Application Laid-Open No. 189502/1982) The diffraction grating made by interfering these divergent waves is shown in Fig. 8.
As shown in Figure 1, the grating is a hyperbolic grating and has not been used to fabricate a planar linear holographic diffraction grating.

[For example, E, Double OLF, Progrease
In Obtics CB, WOLF+ Progre
ssin 0ptics)
The present invention provides an apparatus for producing a uniform planar linear holographic diffraction grating without speckle noise.

Means for Solving the Problems In order to solve the above problems, the holographic diffraction grating forming apparatus of the present invention includes: an exposure laser beam; a half mirror that divides the exposure laser beam into two beams; Two sets of mirrors for reflecting each of the two divided light beams and causing the two light beams to interfere on the sample, and for removing noise from the laser light reflected from the mirrors and expanding the light beam into diverging light. It is equipped with two sets of special filters consisting of a pinhole and a lens, and the distance H between the midpoint of the pinhole interval C of the two special filters and the object to be exposed and the size (diameter) of the object to be exposed are Alternatively, the product H/LxC/L of the ratio H/L to the long side) and the ratio C/L between the distance C between the pinholes of the two special filters and the size L of the exposed object is 32 or more. This is a diffraction grating forming apparatus in which the intensity distribution of the laser beam hitting the object to be exposed becomes a uniform intensity distribution of 80% or more of the peak value.

Effects of the present invention The above-mentioned diverging light and diverging light set under special conditions are set in a special arrangement such that the hyperbola can be regarded as a straight line depending on the size of the object to be exposed, and the specs are adjusted. A uniform and highly efficient holographic diffraction grating without noise can be obtained.

EXAMPLE Hereinafter, a holographic diffraction grating forming apparatus according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an apparatus for manufacturing a holographic diffraction grating according to an embodiment of the present invention.

In FIG. 1, after coating a photoresist 2 on a square substrate 1 with one side L, a half mirror 4 is installed to separate the exposure laser beam 3 and the exposure laser beam into two beams. two sets of mirrors 5 and 6 for reflecting each of the light beams and causing the two light beams to interfere on the sample; and a mirror for removing noise from the laser light reflected from the mirrors and expanding the light beam into diverging light. It consists of two sets of special filters 7 and 8 consisting of a pinhole and a lens.

In the above configuration, interference fringes are formed on the resist 2 on the substrate 1 by two diverging waves, and a sinusoidal holographic diffraction grating with a required interval is obtained by two-beam interferometry holographic exposure.

As described above, in the present invention, after the beam noise is removed by the special filter, there is no optical system up to the exposure section, and no speckle noise is generated in the interference fringes.

The ratio H/L of the distance H between the midpoint of the pinhole interval C of the two special filters and the exposed object to the diameter or long side size L of the exposed object, and Interval C between pinholes and size L of the exposed object
The product of the ratio C/L, H/L x C/L, is 32 or more, and the intensity distribution of the laser hitting the exposed object is a uniform intensity distribution of 80% or more of the peak value. This is how it was done.

FIG. 2 shows the ratio H/L of the distance H between the midpoint of the pinhole interval C of two special filters and the exposed object to the diameter or long side size L of the exposed object, and The groove spacing of the diffraction grating was investigated based on the relationship of the ratio C/L between the pinhole spacing C of the two special filters and the size L of the exposed object.

It connects the points where the ratio of the difference between the groove spacing d in the center and the groove spacing at the end of the diameter or long side size (d-D/D) x 100% is 1% or less. . This curve is H
/L×C/L becomes a value of 32, and if it exceeds this value, the error falls within 1%, and there is no problem even if it is used as a substantially linear diffraction grating.

For example, when used in combination with a lens as an optical demultiplexer, if the focal length is 5 Tsuru, an error of 1% will result in 1
The error can be suppressed to 0 μm or less, and the light can be focused onto an optical fiber.

Further, as shown in FIG. 3, the laser intensity distribution becomes a Gaussian distribution, and in order to obtain a uniform diffraction grating, the laser intensity needs to have a uniform distribution of 80% or more.

With a uniform distribution of 80% or more, a diffraction efficiency of 50% or more can be obtained.

The ratio H/L of the distance H between the midpoint of the interval C between the pinholes of the two special filters and the exposed object to the diameter or long side size L of the exposed object, as described above; The product of the interval C between the pinholes of the two special filters and the ratio C/L of the size L of the exposed object, H/L×C/L, is 32
The interference fringes formed by the diverging waves and the diverging waves that are above and in which the intensity distribution of the laser hitting the object to be exposed is a uniform intensity distribution of 80% or more of the peak value are as follows:
A uniform and highly efficient planar linear diffraction grating with extremely clean interference fringes can be obtained.

The present invention will be explained in detail below.

After applying a positive photoresist to a thickness of about 1.5 μm at a rotation speed of 500 rpm on a square glass substrate with a side of 30 m, which is the size of the object to be exposed, a He-Cd laser with a wavelength of 441.6 m was applied. Holographic exposure was performed with light.

The objective lens of the special filter is 30
Two diverging waves expanded to a beam diameter of 140 m at an angle of 140 m, with the distance H between the midpoint of the pinhole interval C of the two special filters and the exposed object being 600 fl, and C
was set as 400 cranes.

At this time, C/L is 13, )(/L is 20, H/
L x C/L has a value of 260.

At this time, the ratio of the difference between the groove spacing d in the center and the groove spacing at the end of the side size L (d-D/D) This value is not a problem.

In addition, the intensity distribution of the laser hitting the object to be exposed at this time was made to have a uniform intensity distribution of almost 100% with respect to the peak value. A diffraction efficiency of 75% was obtained with the graphic grating. The part corresponding to a in Figure 3.

FIG. 4 is a diagram showing the relationship between laser intensity distribution and diffraction efficiency.

As shown in Figure 4, when the laser intensity distribution corresponding to b in Figure 3 is 80%, the diffraction efficiency is 58%, and C in Figure 3 is
When the laser intensity distribution is 60%, the diffraction efficiency is 38
%Met.

As described above, according to this example, it is possible to obtain a uniform lattice without speckle noise, and even when using a base material, by combining vertical ion etching and oblique ion etching, deep grooves can be etched with good quality. This is a forming device that facilitates the manufacture of preselected holographic diffraction gratings.

Effects of the Invention As described above, the present invention provides a method for adjusting the ratio H of the distance H between the midpoint of the interval C between the pinholes of two special filters and the exposed object to the diameter or long side size L of the exposed object. /L and the ratio C/L of the distance C between the pinholes of the two special filters and the size L of the exposed object, H/L×C/
L is 32 or more, and the intensity distribution of the laser hitting the object to be exposed is made to be a uniform intensity distribution of 80% or more of the peak value. Speckle noise is caused by interference between the diverging lights. It is possible to obtain a uniform and highly efficient holographic diffraction grating without any defects.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing a holographic diffraction grating forming apparatus in an embodiment of the present invention, and Fig. 2 shows the distance H between the midpoint of the interval C between the pinholes of two special filters and the object to be exposed. The relationship between the ratio H/L of the diameter or long side size L of the exposed object and the ratio C/L of the interval C between the pinholes of the two special filters and the size L of the exposed object, A graph examining the groove spacing of a diffraction grating, Figure 3 is a distribution diagram showing the laser intensity distribution, Figure 4 is a graph showing the relationship between the laser intensity distribution and diffraction efficiency, Figures 5 and 6
7 is an explanatory diagram of a conventional holographic diffraction grating forming apparatus, and FIG. 8 is a plan view showing a hyperbolic holographic diffraction grating. l...Substrate, 2...Photoresist, 3
...Laser beam for exposure, 4... Half mirror 15, 6... Mirror, 7, 8...
special filter. Name of agent Patent attorney Toshio Nakao 1 person Figure 2 Buttocks Figure 3 A Standing Figure 4 1θ0 δ0 60 40

Claims (1)

[Claims] an exposure laser beam, a half mirror that divides the exposure laser beam into two beams, and two sets of mirrors that reflect each of the two divided beams and cause the two beams to interfere on the sample. , comprising two sets of special filters consisting of a pinhole and a lens for removing noise from the laser beam reflected by the mirror and expanding the luminous flux into diverging light, and an interval C between the pinholes of the two special filters. The ratio H/L between the distance H between the midpoint and the exposed object and the diameter or long side size L of the exposed object, the interval C between the pinholes of the two special filters, and the exposed object. The product of the size L and the ratio C/L, H/L x C/L, is 32 or more, and the intensity distribution of the laser hitting the object to be exposed is a uniform intensity of 80% or more of the peak value. A diffraction grating forming device characterized in that it has a distribution.