JPS62206583A - Production of hologram and phase shift diffraction grating - Google Patents

Abstract

PURPOSE:To reduce a transition area of a phase shift part with an easy process by irradiating the interference light between a diffraction wave front, which is obtained by projecting obliquely incident parallel rays of light to a phase plate which generates a desired phase shift, and a reference luminous flux to a photosensitive body layer to form a ruggedness due to the interference light on the photosensitive body layer. CONSTITUTION:Obliquely incident parallel rays 2 of light are projected to a phase plate 1 which generates a desired phase shift, and this transmitted light 3 is allowed to interfere with a coherent parallel reference rays 4 of light, and the the interference light is recorded on a photosensitive body layer 5 on a substrate 6. The phase plate 1 is provided with plural phase shift parts by etching a quartz through which light is transmitted. Thus, a phase shift diffraction grating which has small transition areas in phase shift parts and has an optional period is produced with the easy process.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a holographic phase shift diffraction grating, and particularly to a method for manufacturing a holographic phase shift diffraction grating, and in particular a method for manufacturing a DFB (distributed chit feedback) type semiconductor laser. The present invention relates to a method of manufacturing a phase shift diffraction grating used for uniaxial mode conversion.

[Prior art]

Unifying the longitudinal mode of a semiconductor laser is an extremely important issue in preventing waveform distortion due to wavelength dispersion in optical fiber communications, ultra-high-speed transmission through stable high-speed modulation, noise reduction, and optical applied measurement. However, semiconductor lasers with Fabry-Perot resonators do not have sufficient longitudinal mode selectivity, so a DFB laser with a built-in diffraction grating in the resonator was developed. Since a DFB laser having a uniform structure as a whole oscillates in two longitudinal modes, a method of using a diffraction grating with a phase shift equivalent to 1/4 wavelength added to the center of the diffraction grating is adopted.

One way to manufacture such a phase shift diffraction grating is to use two types of resist, positive and negative, and invert the phase of each of these regions to generate a phase shift equivalent to a quarter wavelength. be.

Another method is to use a quartz contact mask having a step corresponding to a phase shift. Literature regarding the former includes "Technical Report of the Institute of Electronics and Communication Engineers" by Katsuyuki Udaka et al., OQB Vol. 85-11, W, 69-7.
The article “λ/4 shift InGaAsP/1n” on page 6
``PDFB laser'', and the literature on the latter is ``IEICE Technical Report J, 0'' written by Masataka Shirasaki et al.
The paper written in volume QE85-60, pages 1E57-64 “
[For DFB laser]/Proposal of a method for forming a four-wavelength shift diffraction grating - Invention of a phase mask and its effects -''.

The problem that the invention seeks to solve The above-mentioned conventional technology has the following problems.

:The method for distinguishing JL1 positive and negative 28i type resists involves three steps each for resist coating, development, and etching.
There was a problem in that a very large number of process steps, ie, 100 times, were required as a membership fee, resulting in low yields. Furthermore, in the method using the second contact mask, the phase of the light changes due to the diffraction of the light in the contact mask, and the desired grating is not formed in the phase shift portion, resulting in the formation of a so-called transition region. Another problem was that a different contact mask had to be prepared for each period of the diffraction grating.

The purpose of this technique is to solve the problems of the conventional technology, to make the transition region of the phase shift part smaller with a simple process, and to create a hologram and phase that can be applied without changing the period of the diffraction grating. An object of the present invention is to provide a method for manufacturing a shifted diffraction grating.

[Means for solving the problem] The structure of the hologram construction method of the invention of $1 is that a diffraction wavefront and a reference light beam obtained by irradiating a phase plate that causes a desired phase shift with obliquely incident parallel light are used. The method is characterized in that the photoreceptor layer is irradiated with interference light with the interference light, and irregularities are formed on the photoreceptor layer by the interference light.

The structure of the method for manufacturing a phase shift diffraction grating according to the second invention is as follows:
A wLl step of manufacturing a hologram by interfering with a reference light beam a diffraction wavefront obtained by irradiating a phase plate that produces a desired phase shift with obliquely incident parallel light, and making the hologram conjugate with the reference light. The wavefront obtained by irradiating with a wavefront,
It is characterized by including the step of 2 in which a photoconductor provided on a wafer is irradiated with a parallel beam of light that interferes with the surface on which the phase plate is disposed, and a phase shift diffraction grating is formed on the photoconductor. do.

[Effect]

The operation and principle of the present invention are as follows.

In the present invention, in order to fabricate a diffraction grating, we use a binary beam interference achromatic method, and use the principle of holography in which 10,000 beams of this binary beam become phase-shifted wavefronts on the interference surface. The basic principle is to generate such a wavefront. Holograms have the ability to freeze wavefronts and reproduce them.

In the present invention, a hologram is first formed by irradiating a phase plate that produces a desired phase shift l with parallel light and causing the obtained wavefront to interfere with a reference wavefront. This hologram records the diffracted wavefront from the phase plate, so when the hologram is illuminated from the back side with illumination light that is conjugate to the reference wavefront when the hologram was manufactured, the backward wavefront of the wavefront from the phase plate is reproduced. Therefore, on the surface where the phase plate was placed during the hologram production, a reversed wavefront of a wavefront immediately after passing through the phase plate, that is, a wavefront with a desired phase shift, is obtained. Therefore, by interfering this wavefront with a parallel beam at an appropriate angle, phase-shifted interference fringes can be obtained, and it takes a lot of effort to record these interference fringes on a photoreceptor.
, a phase-shifted diffraction grating can be formed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In the following description, the steps of the phase plate and the grooves of the diffraction grating are schematically illustrated with their actual edges enlarged for ease of explanation.

The phase plate 1 that provides the following is irradiated with obliquely incident parallel light 2, and the transmitted wave 3 is caused to interfere with the coherent parallel reference light 4 and recorded on the photoreceptor N5 on the substrate 6.

In this example, He-Cd with a wavelength of 325 is used as a light source.
Since a laser was used, the phase plate l was formed by etching quartz that transmits light at a wavelength of 325 m2, and multiple 1/4 wavelength phase shift gratings were formed on the same web.
The phase plate 1 is provided with a plurality of phase shift parts. Also,
Photoresist AZ-1350 can be used for the photoresist layer 5, and the photoresist layer 5 can be used as a hologram as it is after development, but in order to use it for a long time, the recorded photoresist pattern must be masked. , it is preferable to transfer it to the quartz substrate 6 by etching. The groove depth of the photoresist when used as is and the groove depth when transferred to the quartz substrate 6 were both about 0.5μ, and a diffraction efficiency of about 30% was obtained. .

It is. In this figure, a hologram 7 is formed on a quartz substrate 6. When this hologram 7 is irradiated with a wavefront 8 that is conjugate to the wavefront at the time of manufacture (parallel light 4 in Figure 2) from the back side of the hologram 7, a diffracted wave 9 is generated. This diffracted wave 9 is a reversed wavefront of the phase plate transmitted wavefront (wavefront 3 in Figure 2) when the hologram was manufactured.

Therefore, in the position where the phase plate was located when the hologram was made,
Immediately after passing through the phase plate, a wavefront with a phase shift is created. A wafer 10 coated with a photoresist (photoresist) 1 is placed at this position, and an interference light beam 1 of -10,000
By interfering with 2, a phase shift grating can be formed.

In this example, in order to form a diffraction grating with a period of 0.2 μm for a semiconductor laser with a wavelength of 1.5 μm, the incident angles of the two light beams 9.12 with respect to the wafer 10 are each 50.7 μm.
° Toshitomo. Further, the incident angle of the light beam 90 is fixed, and the grating period can be changed by changing the incident angle of the light beam 12.

Furthermore, in this embodiment, if the phase plate 1 in which grooves are formed perpendicular to the surface as shown in FIG. 1 is used, the phase shift of the transmitted light at the stepped portion will not be steep, resulting Therefore, the transition region expands.

FIG. 3 is a side view of a preferred phase plate 13 of another embodiment of the present invention for WLl. In this embodiment, as shown in the figure, a phase plate 1 having grooved side surfaces parallel to an obliquely incident parallel light beam 2 is used.
3, it is possible to form a phase shift grating with a small transition region.

[Effects of the Invention] As explained above, if the present invention is implemented, a phase shift having a small transition region of a phase shift portion and an arbitrary period can be achieved with a simple process similar to the normal interferenceless light method. Diffraction gratings can be manufactured.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of an optical system to be explained in the implementation of IEI's invention, Fig. 2 is a cross-sectional view showing the optical system during the manufacture of the phase shift diffraction grating of $2's invention, and wL3 is an IEI invention. FIG. 2 is a cross-sectional view of a hologram mounting optical system for explaining a preferable phase plate used for the hologram. 1.13... Phase plate% 2.4.8.12...
...Parallel light flux, 3.9...Diffraction wavefront, 5.
11... Photoreceptor layer, 6... Quartz substrate,
7...Hologram, 10...Wafer. , Go-゛,

Claims (3)

[Claims] (1) A photoreceptor layer is irradiated with interference light between a diffraction wavefront obtained by irradiating obliquely incident parallel light onto a phase plate that produces a desired phase shift and a reference light beam, and the interference light is applied onto the photoreceptor layer. A method for manufacturing a hologram, characterized by forming unevenness by (2) A first step of fabricating a hologram by interfering with a reference beam a diffraction wavefront obtained by irradiating a phase plate that produces a desired phase shift with obliquely incident parallel light; The wavefront obtained by irradiation with a wavefront conjugate to is caused to interfere with a parallel beam on the surface where the phase plate was placed, and is irradiated onto a photoreceptor provided on a wafer, forming a phase shift diffraction grating on this photoreceptor. A method of manufacturing a phase shift diffraction grating, the method comprising: a second step of: (3) Claim 2, characterized in that the phase plate is a phase plate that generates a phase shift depending on the presence or absence of grooves, and the side surfaces of the grooves are substantially parallel to the beam of obliquely incident parallel light. A method of manufacturing the phase-shifted diffraction grating as described.