JPH01194487A - Optical system of phase synchronous semiconductor laser array - Google Patents

Abstract

PURPOSE:To effectively utilize an output of a phase synchronous semiconductor laser array and to make a visible radiation having a single humped FFP due to a secondary higher harmonic to be generated efficiently, by providing both the phase synchronous semiconductor laser array which is oscillated by two wave surfaces which are 180 deg. out-of-phase, and a diffraction grating coupler which has a period substantially equal to the wavelength of a pair of lights which are half a period out-of-period. CONSTITUTION:The lights emitted from a laser array are converted into parallel rays by a collimator lens 2, and the parallel rays 2 are then applied to a diffraction grating optical coupler 4. In this connection, the laser beams 11, which are made the parallel rays by the collimator lens 2, becomes a double-humped far field pattern(FFP) 12. Two humped FFP components constituting the FFP 12 are applied to diffraction grating couplers 4a and 4b, respectively, which are half a period out-of-period. The light applied from the diffraction grating coupler 4a to an optical waveguide 5a is 180 deg. out of phase with the light applied from the diffraction grating coupler 4b which is half a period out of period with the coupler 4a to an optical waveguide 5b. Therefore, all the lights emitted from the semiconductor laser array 1 are applied to an optical waveguide 5 with being in phase. Thus, secondary higher harmonic lights 13 emitted from the two optical waveguides 5a, 5b are in phase each other, and therefore the FFP becomes a single-humped pattern as indicated by sign 14.

Description

[Detailed Description of the Invention] <Technical Field of the Invention> The present invention converts the output of a 180° phase-locked semiconductor laser array comprising two or more mutually coherently coupled optical co-imagers into one wavefront of equal phase. It relates to an optical system used for converting and inputting light into an optical waveguide.

<Prior art> A phase-locked semiconductor laser array in which multiple laser co-imagers are coherently coupled to each other has a low optical density at the end face and can be operated up to high output, making it suitable for use with optically pumped lasers that require high excitation intensity, etc. It is important as an excitation light source for harmonic generation. In particular, optical waveguides are often used to generate harmonics in order to utilize excitation light as efficiently as possible.

However, the output of such a semiconductor laser array mainly oscillates in a mode in which two wavefronts with a phase difference of 180° exist simultaneously. The far-field image of this mode is divided into two light beams corresponding to wavefronts with different phases. Even if these lights are guided into an optical waveguide using a coupler using a normal diffraction grating or prism, there is already a method using a half-wave plate as a means to bring two wavefronts with a phase difference of 180° into the same phase. It has been proposed (Japanese Patent Application Laid-Open No. 62-98320).

<The culmination of the problem to be solved by the invention> However, in the method using the half-wave plate described above, it is difficult to miniaturize the device, and in particular, integration with an optical waveguide is impossible.

<Purpose of the Invention> The present invention has been made in view of the above-mentioned problems, and aims to convert the output of a phase-locked semiconductor laser array whose phase is shifted by 180° into a single wavefront having an equal phase and guide it into an optical waveguide. The purpose is to provide an optical system that can perform

<Summary of the Invention> The present invention provides a phase-locked semiconductor laser array that has a plurality of laser resonators that are coherently coupled to each other and oscillates with two wavefronts that are 180° out of phase with each other, and a phase-locked semiconductor laser array that is provided on an optical waveguide. , and a diffraction grating coupler having a period comparable to the wavelength of a pair of light beams shifted by a half period from each other.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an optical system according to an embodiment of the present invention. It is a phase-locked semiconductor laser array in which 10 resonators are coherently coupled.The light emitted from the laser array is converted into parallel light by a collimator lens 2, and then enters a diffraction grating optical coupler 3. The laser beam 11 made into parallel light by the collimator lens becomes a double-peaked far-field pattern (FFP) 12 as shown in the figure, and each beam is shifted by a half period from each other. are incident on each. The light incident on the optical waveguide 5a from the diffraction grating optical coupler 4a and the light incident on the optical waveguide 5h from the diffraction grating optical coupler 4b, which is shifted by half a period, are out of phase by 180°, so the light exiting the semiconductor laser array 1 all enter the optical waveguide 5 with the same phase.

In this embodiment, a lithium niobate (LiNbO3) substrate 3
After depositing aluminum (not shown) on one side of
Using a photoresist mask and warm phosphoric acid (~60°C) as an etchant, a width of 1.5
The optical waveguide 5 was etched into micron stripes and immersed in a lithium benzoate solution as a mask to produce two parallel stripe-shaped optical waveguides 5 @2 μm and 0.5 μm deep by pronto exchange. After removing the photoresist, a Si3N4 film was deposited using a vacuum evaporation method, an electron beam resist (not shown) was applied, a diffraction grating optical coupler pattern was created by electron beam writing, and HF:N
A diffraction grating optical coupler 4 was fabricated by etching with a mixed solution of H4F=1:20. The period of the diffraction grating optical coupler 4 is determined by, for example, "optical integrated circuit" (Nishihara et al.).

The output of the laser array is determined to be incident on the waveguide 5 based on the oscillation wavelength of the semiconductor laser, the incident angle, and the propagation constant of the waveguide, as detailed in Ohmsha Publishing).As a phase-locked semiconductor laser array, the oscillation wavelength is 850 nm. , maximum output 2
00 mW, the laser beam is made into parallel light by a collimator lens and guided into the above optical waveguide through a diffraction grating optical coupler, thereby producing a second harmonic of 425 nm in wavelength.
3 was obtained.

The second harmonic lights 13 emitted from the two optical waveguides 5a and 5b were in phase with each other, and the FFP became a single peak like 14.

FIG. 2 is another embodiment of the present invention, and is a block diagram when the present invention is applied to a slave plate optical waveguide. Due to the diffraction grating optical coupler, all the lights emitted from the semiconductor laser array had the same phase, so no interference occurred in the optical waveguide, and a single peak second harmonic output was obtained as in the above embodiment.

FIG. 3 is a configuration diagram showing still another embodiment of the present invention,
(a) is a plan view, and (b) is a side view. In this example, the diffraction grating optical coupler was formed into a shape having light condensing properties, for example, as described in the Optical and Quantum Electronics Study Group Report 0QE84-109. Also in this case, the diffraction grating optical couplers 3a and 3b are shifted by half a period from each other. In this embodiment, a collimator lens as shown in the above two embodiments is unnecessary, and the apparatus can be further miniaturized.

<Effects of the Invention> According to the present invention, although stable operation is possible with high output, FFP
It is possible to efficiently generate visible light having a single peak FFP due to second harmonics by effectively utilizing the output of a phase-locked semiconductor laser array, which tends to have double peaks. Also,
By efficiently coupling a semiconductor laser and an optical waveguide, it is possible to significantly reduce the size of the device, and it can be used as a light source for optical pickups for high-density optical disks, etc., and has a great effect on business. can.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical system of one embodiment of the present invention.
(a) is a plan view, and (b) is a side view. FIGS. 2 and 3 each represent another embodiment of the invention. Yusei, f21 ~ Yo 3.44, 4 - Poison Luck Moe Vinegar Figure 51...
- Phase-locked semiconductor laser array, 2... collimator lens, 3... condensing diffraction grating optical coupler. 4... Diffraction grating optical coupler 5... Proton exchange optical waveguide 11... Phase-locked semiconductor laser array light beam 12...
Far-field image of phase-locked semiconductor laser array beam 13...
2nd harmonic output 14... Far-field image of 2nd harmonic output Agent Patent attorney Takeshi Sugiyama (1 other person) //
4b F, 2゛-3

Claims (1)

[Claims] 1. In an optical system of a phase-locked semiconductor laser array comprising a phase-locked semiconductor laser array, a diffraction grating optical coupler that receives light beams whose phases are shifted by 180° from the semiconductor laser array, and an optical waveguide, the diffraction grating light The coupler is composed of diffraction gratings having identical grating patterns whose periods are shifted from each other by half a period, and whose phases are 180 degrees with respect to each other.
An optical system for a phase-locked semiconductor laser array, characterized in that the optical fluxes shifted by degrees are converted into the same phase and input into the optical waveguide.