JPS61189502A - Method and device for forming diffraction grating - Google Patents

Abstract

PURPOSE:To form diffraction gratings which have the same period and are out of phase with each other on the same substrate with good reproducibility by providing an optical path length varying means which varies the phase of light in an adjustable state at least one luminous flux side in luminous flux after splitting. CONSTITUTION:A mechanism for phase adjustment is provided at one of positions 21-23 or to a mirror 142 to obtain the diffraction gratings which has the same grating intervals and are out of phase on the same substrate. This mechanism for phase adjustment employs the rotation of an optical parallel plate 2a which differs in reflective index from an ambient atmosphere, the reflection of a multiple reflecting mirror 2b which moves in parallel, the parallel movement of a prism 2c, or the electrooptic effect of a dielectric 2d. Consequently, the diffraction gratings which has the same period and are out of phase with each other are formed on the same substrate with good reproducibility and a single longitudinal mode laser is obtained with good reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for forming a diffraction grating, and particularly to a D diffraction grating formed of a uniform diffraction grating for a light source of optical fiber communication.
FB (Distributed Feedback Type, Distributed Fee-
dback) The present invention relates to a method and apparatus for forming a diffraction grating by two-beam interference exposure, which is suitable for manufacturing a laser.

[Background of the invention]

The conventional DFB laser shown in FIG. 5 is described in Document 1. H6Kog
elnik, et. al., Journal of Applied Physics (J-A
ppl, Phys, ).

Vol, 43. p-p, 2327-2335.1
As shown at 972, since the threshold value degenerates for two different wavelengths λ (or propagation constant β), a two-wavelength shooting state is essentially taken. Therefore, the axle load -
Reference 2. T, Matsuoka
, et, al, Journal of the Japanese Society of Applied Physics (Jpn,
J. Appl. Phys.), Vol. 23.
As shown experimentally in p, p, L138-L 140.1984, relative position control of the interosseous plane and the diffraction grating was an essential condition. The positional accuracy to achieve this is on the order of ±100 A, and cannot be controlled by normal interosseous spacing. On the other hand, as shown in FIG. 4, by shifting the phase of the diffraction grating by π/2 at approximately the center of the element, single-axis mode oscillation can be stably obtained as described in Reference 3. H, A.

Haus, et al., Institute of Electrical and Electronics Engineers, Quantum Electronics Journal (IEEE J, Quantu
m Electronics, ), Vol, QE
-12, I), 1), 532-539.1976. The fabrication of a diffraction grating with such a phase shift is described in References 4, K, 5ekartedjo
, et, al, x L/Electron, Letters, 1933.
There is also a method using direct writing using an electron beam, as shown in Reference 5. Shigeyuki Inaba and others, Institute of Electronics and Communication Engineers Optical and Radio Division Western National Conference.

Nα265. In 1981, a method using both positive and negative resists was proposed. However, direct electron beam writing has the problem of inherently low throughput, and methods that use both positive and negative resists have a distribution in the thickness of the resist, which reduces the diffraction efficiency of the resulting diffraction grating. However, there was a problem in that the left and right sides of the device were asymmetric, and reproducibility was lacking in obtaining single mode operation.

Note that the symbols 1 to 9 and 8 in FIGS. 4 and 5]
, 82 will be described in detail in the Examples section below.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems in the prior art, to form diffraction gratings with the same period and different phases on the same substrate with good reproducibility, thereby making it possible to generate a single-longitudinal mode laser. It is an object of the present invention to provide a method and apparatus for forming a diffraction grating that can generate the diffraction grating with good reproducibility.

[Summary of the invention]

In order to achieve the above object, the present invention utilizes a photochemical reaction in which a laser beam is split into at least two beams and then combined to cause interference, and the speed or properties change depending on this interference. A method and apparatus for forming a diffraction grating on an object plane, for example, on a semiconductor substrate surface, wherein the formation method adjustably changes the phase of light on at least one side of the light beam after the above-mentioned splitting, and the above-mentioned after the splitting. A forming device is employed in which an optical path length variable means for adjusting the phase of light is disposed on at least one side of the light beam.

There are two mutually correlated beams of wavelength λ that are irradiated onto a certain sample surface, and the angle between them is 20. Further, if the angle between the midline direction of the angle and the normal to the sample surface is δ, then a striped pattern with the following period A is formed on the sample surface.

] The bright lines and dark lines of the interference pattern are 2, where N is an arbitrary integer.
This corresponds to the fact that the phase difference of the light flux is equal to 2Nπ, (2N+1)π. Therefore, by causing a phase delay on at least one side of the light beam, it is possible to reverse the bright lines and dark lines of the interference fringes. It is possible to obtain a diffraction grating on the sample surface by using a photochemical reaction using interference light, but it is also possible to obtain diffraction gratings with different phases on the sample surface by exposing the sample while changing the phase of the light using a mask. It becomes possible to obtain a grid. Note that the amount of change in the phase of light can be detected from the change in brightness of the moiré image.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described while comparing them with conventional examples. Fig. 1 is a schematic diagram of a phase delay interference exposure apparatus according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing various specific embodiments of phase delay, and Fig. 3 is a schematic diagram of a conventional interference exposure apparatus. be. In the conventional example shown in FIG. 3, a laser beam emitted from a laser light source 11 such as a He-Cd or Ar laser is split by a beam splitter 12, and the beam diameter of each beam is expanded by beam expanders 131 and 132. , respectively, by reflecting them with mirrors 141° and 142 to change the traveling direction and obtain a striped interference pattern on the surface of the sample 15. However, in this conventional method, since there is no mechanism for adjusting the phase of the two light beams, it is not possible to intentionally obtain diffraction gratings having different phases while maintaining the same grating spacing.

In the embodiment of FIG. 1 proposed by the present invention, the positions 21°, 22.
23 or the mirror 142, it becomes possible to obtain diffraction gratings with equal grating spacing and different phases on the same substrate. As the mechanism provided at the position 21, 22 or 23 for adjusting the phase, various systems shown in FIG. 2 can be used. That is, as shown in FIG. 2(a), it is caused by the rotation of an optical parallel plate 2a whose refractive index is different from that of the surrounding atmosphere, and as shown in FIG.
The effect of phase delay was confirmed for both the reflection of , the parallel movement of the prism 2C as in (C), and the electro-optic effect of the dielectric 2d as in (d).

Here, as an example, we will explain the case where an optical parallel plate made of quartz (thickness 1c+++ with anti-reflection film on both sides) is installed at position 21 in Figure 1, and rotation about the optical axis causes a phase delay. do. First, partial exposure is performed on the surface of the sample 15 through the screen mask 16 with the optical parallel plate 2a ((a) in FIG. 2) tilted by θ=2 degrees with respect to the optical axis. Partial exposure is performed on the surface of the sample 15 while moving in parallel and tilting the optical parallel plate 2a further by 0.05 degrees.
By tilting it by 0.5 degrees, the change in optical path difference was λ/2, and it was possible to reverse the interference angle at the exposure section. Inversion of interference pattern ii, e.g. screen mask 16
By installing a reference diffraction grating 17 above, the moiré pattern can be observed and read directly.

By using an InP substrate coated with an AZ-based resist as Sample 15, gratings with different phases could be obtained as a resist pattern on the surface developed using AZD. Use this resist as a mask
Br: HNOs: HzO (= 1: 1:
This grating is transferred onto the InP substrate by using the etching solution of 30). An InGaAsP optical guide layer 3 (Te doped, carrier concentration I x 1011
0l8 thickness approximately 0.1μm, bandgap wavelength 1.3μm
m), InGaAsP active layer 4 (undoped, thickness approximately 0
．． 1 ttm.

bandgap wavelength 1.5 μm), InGaAsP buffer layer 5 (Zn doped, carrier concentration 7
Cm-3+thickness approx. 0. ．． 1 μm, bandgap wavelength 1
．． 3 μm), p-type InP layer 6 (Zn doped, carrier concentration 7×1017 cm−3, thickness 3 μm), p-type InGaAsP cap layer 7 (Zn doped).

Carrier concentration 5 x 1018cm-3, thickness 0.4μ
m, hunt cap wavelength 1.5 μm), and then an n-type electrode 81 (Au/Cr) and an n-type electrode 82 (A
After depositing u/Sn) and placing it between the bones, a non-reflective film 9 is applied to the interosseous surface.
(SiN) was formed to produce a semiconductor laser device shown in FIG.

This element operated in an axial load mode at the Bragg wavelength, and the effect of phase shift was confirmed.

Note that as another method for producing a phase shift in interference exposure, a method of moving the mirror 142 in parallel as shown by the arrow 24 in FIG. 1 may also be used (the same effect was confirmed).

〔Effect of the invention〕

As described above, in the interference exposure method, by causing a light delay on one side of the light beam, it is possible to quantitatively change the bright and dark positions of the interference fringes, and furthermore, the amount of delay can be changed by changing the moiré pattern. I was able to quantify it. By utilizing the above effect and using multiple exposure using partial exposure, it becomes possible to form diffraction gratings with the same period and different phases on the same substrate with good reproducibility.
Longitudinal mode laser has good reproducibility (effects obtained).

[Brief explanation of the drawing]

FIG. 1 is a schematic top view of a phase delay type interference exposure apparatus according to the present invention, FIG. 2 is a schematic diagram showing various phase delay methods according to embodiments of the present invention, and FIG. 3 is a schematic top view of a conventional interference exposure apparatus. 4 are cross-sectional views of a phase-shifted DFB laser according to the present invention, and FIG. 5 is a cross-sectional view of a conventional DFB laser. Description of symbols> 11... Laser light source 12... Beam splitter 131, 132... Beam splitter 141, 142
...Mirror 15...Sample 16...Screen mask 17...Reference diffraction grating

Claims (8)

[Claims] (1) Laser light is split into at least two beams and then combined to create interference, and a diffraction grating is formed on the object plane using a photochemical reaction in which the speed or properties change according to this interference. A method for forming a diffraction grating, characterized in that the phase of light is adjustable on at least one side of the divided beam. (2) The method of changing the phase is a method of effectively changing the optical path length by rotating a substance inserted into the optical path and having a refractive index different from that of the surrounding atmosphere. A method for forming a diffraction grating according to scope 1. (3) Diffraction according to claim 1, wherein the method of changing the phase is a method of spatially changing the optical path length by parallel movement of a mirror or prism inserted in the optical path. How to form a lattice. (4) The method of changing the phase is a method of effectively changing the optical path length by an electro-optic effect of a dielectric inserted into the optical path.
Diffraction grating formation method described in . (5) A diffraction grating is formed on the object plane by using a photochemical reaction in which the laser beam is split into at least two beams and then combined to cause interference, and the speed or properties change according to this interference. A diffraction grating forming device characterized in that an optical path length variable means for adjustablely changing the phase of light is disposed on at least one side of the divided beam. (6) The optical path length variable means is any of a means for rotating a substance having a refractive index different from that of the surrounding atmosphere, a means for moving a mirror or a prism in parallel, or a means for changing the electro-optic effect of a dielectric. A diffraction grating forming apparatus according to claim 5, characterized in that: (7) Claim 5, characterized in that a mask for partially blocking light irradiation is provided on the side of light irradiation to the object surface.
Diffraction grating forming device as described in 2. (8) The diffraction grating forming device according to claim 5, further comprising a reference diffraction grating that generates a moiré pattern in a portion where the combined light is irradiated onto the object surface.