JPS63164382A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To remove the oscillation of a Fabry-Perot mode and unstable two mode oscillation, which have been at issue in a distributed feedback semiconductor laser with a conventional cleavage plane, simultaneously, and to enable stable single longitudinal mode oscillation by forming a laser resonator to a ring shape and shaping a diffraction grating along the resonator. CONSTITUTION:An N-type InP buffer layer 8, an InGaAsP active layer 9, an InGaAsP waveguide layer 10, a diffraction grating 11 and a P-type clad layer 12 are laminated onto an N-type InP substrate 7 in succession, and a ring-shaped resonator 15, the surface and the rear of which have electrodes 13, 14, is formed. The diffraction grating 11 is shaped smoothly to be connected along the ring- shaped resonator 15. Accordingly, light emission in the active layer 9 is confined into the ring resonator 15, and the loss only of a mode simultaneously satisfying conditions determined by the period of the diffraction grating in modes satisfying a large number of ring resonance conditions is reduced selectively, thus acquiring a semiconductor laser performing stable single longitudinal mode oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a single longitudinal mode oscillation semiconductor laser device suitable as a light source for an optical integrated circuit for optical fiber communication.

In conventional optical fiber communications, since optical fibers have chromatic dispersion, if the light source has spectral broadening, the transmission band is significantly limited. For this reason, long-distance, large-capacity transmission systems require a single longitudinal mode oscillation semiconductor laser as a light source.

As a semiconductor laser that performs single longitudinal mode oscillation, there is a distributed feedback semiconductor laser in which an active layer and a diffraction grating are integrated, as shown in FIG. In FIG. 3, 1 is M-type InP
Buffer layer, 2 is InGa SP active layer, 3 is InGa
AsP waveguide layer, 4 is a diffraction grating, and 6 is a p-type InP cladding layer. Such lasers oscillate in a single longitudinal mode at a wavelength determined by the period of the diffraction grating.

However, since the cleavage plane of the crystal is normally used as the output end face 6, a 7-abry bellows resonator is formed on both end faces, and when a high current is injected or due to a large temperature change, the wavelength determined by the diffraction grating is independent of the wavelength determined by the diffraction grating. , it often oscillates even in the Fapley bellows resonator mode. In addition, the oscillation wavelength determined by the diffraction grating changes depending on the position of the cleavage plane on the diffraction grating, and oscillation at two wavelengths or mode skipping between two wavelengths often occurs. There were few oscillations in a stable single mode.

Problems to be Solved by the Invention As mentioned above in the prior art section, when a distributed feedback semiconductor laser has a cleavage plane, two-mode oscillation or Fapley-Perot mode oscillation occurs, and single longitudinal mode oscillation occurs. Yield was poor.

The present invention solves the above-mentioned conventional problems, and by forming the laser resonator in a ring shape and forming the diffraction grating so as to smoothly connect along the resonator, stable single longitudinal mode oscillation can be achieved. The aim is to obtain a semiconductor laser.

Means for Solving the Problems The semiconductor laser device of the present invention includes an active region of a semiconductor laser including at least an active layer and a confinement layer partially formed on a semiconductor substrate, and a semiconductor laser device in the vicinity of the active region. The structure includes a diffraction grating formed along the resonator of the semiconductor laser, and an optical waveguide capable of extracting light emitted from the active region as an output, and the resonator of the semiconductor laser is formed in a ring shape, and the resonator of the semiconductor laser is formed in a ring shape. This configuration is such that a diffraction grating is formed so as to be smoothly connected along the ring-shaped resonator to perform single longitudinal mode oscillation.

Operation The present invention is a distributed feedback type laser/grazer with the above-described configuration. The oscillation wavelength of a distributed feedback semiconductor laser (DFB laser) is given by the following oscillation condition.

λ1 −・N=a ・・・・・・・・・・・・(1
) n Here, N is the order of the diffraction grating and is a natural number, a is the interval between the diffraction gratings, λ1 is the wavelength in vacuum, and n is the refractive index of the laser medium.

The oscillation wavelength mode of a DFB laser having a normal cleavage plane includes, in addition to the DFB mode given by equation (1), a 77 Prie-Perot mode with a wavelength interval of λ2/2nl. The DFB mode and the 71 Preperot mode are independent and their wavelengths do not match. Therefore, if the oscillation threshold gains of both modes are approximately equal, oscillation will occur in both modes.

In contrast, in the present invention, the diffraction grating is formed so as to be smoothly connected along the ring-shaped resonator.
The ring resonator length l is an integer multiple of the spacing a of the diffraction gratings, and the resonant wavelength of the ring resonator satisfies the following equation, where m is an integer.

λ −・m=1l ・・・・・・・・・・・・・・・
(2) There are many n ring resonance mode intervals of λ2/2nl, but from equations (1) and (2), the conditions for the DFB mode and the ring resonance mode are simultaneously satisfied.

Therefore, among a large number of ring resonant modes with almost no difference in loss, only the light of the wavelength selected by the diffraction grating has a small loss, and single mode oscillation is performed in this mode.

Embodiment FIG. 1 shows a sectional view of a semiconductor laser constituting an embodiment of the present invention. B is a plan view, and B is a side view. In the figure,
7 is an n-type 1nP substrate, 8 is an n-type 1nP backing layer, 9 is an InGaM 8P active layer, 10 is an InGaAsF waveguide layer, 11 is a diffraction grating, 12 is a p-type cladding layer, 13.14
A ring-shaped resonator 15 is formed with electrodes. Further, 16 is an optical waveguide for determining the optical output range.

The light emission within the active layer e is confined within the ring resonator 16, and among the many modes satisfying the S/G resonance condition,
Only a mode that simultaneously satisfies the conditions determined by the period of the diffraction grating has a selectively reduced loss and oscillates as a laser.

FIG. 2 shows a top view of a second embodiment of the invention.

In FIG. 1, a diffraction grating is formed along the ring-shaped resonator on the surface of the optical waveguide layer, but in FIG. 2, a diffraction grating 17 is formed along the side surface of the ring-shaped resonator. Except for this, it has the same configuration as the case of FIG.

In this example, the material is an InGaAgP crystal on an InP substrate, but the structure of the present invention can be applied to other compound semiconductor materials, such as AlGaAs crystal on a GaAs substrate, depending on the desired oscillation wavelength. It can be easily achieved.

Effects of the Invention As described above, the present invention solves the problems encountered in conventional distributed feedback semiconductor lasers having a cleavage plane by forming a ring-shaped laser resonator and forming a diffraction grating along the resonator. It is possible to obtain stable single longitudinal mode oscillation by simultaneously removing the Fabry-Perot mode oscillation and unstable bimode oscillation, which has been associated with long-distance, large-capacity optical transmission.
It is particularly effective as a light source for optical integrated circuits.

[Brief explanation of the drawing]

FIG. 1(B) is a top view of a semiconductor laser device constituting the first embodiment of the present invention, and FIG. 1(B) is a cross-sectional view of the same device.
FIG. 2 is a top view of a second embodiment of the present invention, and FIG. 3 is a front view of a conventional distributed feedback semiconductor laser. 7...Substrate, 9...Active layer, 11.1
7...Diffraction grating, 16...S/G resonator. Name of agent: Patent attorney Toshio Nakao and 1 other person7-
a certain uncle

Claims (1)

[Claims] an active region of a semiconductor laser including at least an active layer and a confinement layer partially formed on a semiconductor substrate; a diffraction grating formed along a resonator of the semiconductor laser in proximity to the active region; and an optical waveguide capable of extracting light emitted from the active region as an output, the resonator of the semiconductor laser is formed in a ring shape, and the diffraction grating is smoothly connected along the ring-shaped resonator. A semiconductor laser device formed to perform single longitudinal mode oscillation.