JPH01238082A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the yield of an element without necessitating an optical waveguide itself to be equipped with a diffraction grating, by joining a stripe like active region and optical waveguide by pads and mounting diffraction gratings at the end face which is away from the optical waveguide without mounting the above gratings at the main frame of the optical waveguide. CONSTITUTION:End faces at the far-edge side from a stripe like optical waveguide layer 5 are formed vertically with respect to a p-n junction which is formed between an active layer 2 and the second clad layer 3 and are formed slantwise with respect to the stripe like optical waveguide layer 5. Further, diffraction grating reflecting mirrors 12 are formed in the vertical direction with respect to the p-n junction at the end faces; besides, the relation among the energy band widths of Ea, Eg, and Ec is Ea>Eg>Ec. For operating a semiconductor laser, a current is caused to flow between a p-type electrode 10 and an n-type electrode 9 of the laser part. A laser oscillation beam lambda 19 is guided by the optical waveguide layer Eg 5 and only the beam having specific wavelength lambda is reflected by the diffraction grating reflecting mirrors 12 and is fed back to the optical waveguide layer 5 and the active layer 2. Thus, laser oscillations are caused by only the beam having specific wavelengths lambda.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field to which the invention pertains The present invention relates to a semiconductor laser having a diffraction grating and having a narrowed linewidth in a single longitudinal mode for use as a light source.

(2) Conventional technology and its problems Conventionally, a multi-electrode DFB laser or a multi-electrode DBR laser has been used as a narrow linewidth single longitudinal mode semiconductor laser, and in either case, diffraction occurs in the active region or optical waveguide region. It has a grid. However, crystal growth on a diffraction grating tends to cause crystal defects, causing deterioration of optical properties, making it difficult to manufacture with a high yield.

(For example, Murata, Mito: rl, 5 μm band wavelength variable DB
"Wavelength Tuning Range of R Laser": 1987 Institute of Electronics, Information and Communication Engineers, Semiconductor Materials Division National Conference Proceedings Proceedings Proceedings 287) (3) Purpose of the Invention The present invention has been made in view of the above points. The purpose is to provide a diffraction grating at the far end of the optical waveguide region, eliminating the need for a diffraction grating in the waveguide itself, improving device yield, and creating a narrow linewidth single mode with high multiplication performance. The purpose of the present invention is to provide a semiconductor laser of the type.

(4) Structure of the invention (4-1) Differences between the characteristics of the invention and the conventional technology The present invention has the following features:
The main feature is that the striped active region and the striped optical waveguide are butt jointed, and the diffraction grating is not provided in the active region or the optical waveguide body, but at the far end of the optical waveguide. . Conventional techniques require crystal growth on a diffraction grating, which poses manufacturing problems such as increased crystal defects and optical loss.

The present invention improves on this point, and unlike the conventional structure, it has a simple structure in which a diffraction grating is externally attached, so it has the advantage of being able to manufacture elements with high yield and high reliability.

(4-2) Example FIG. 1 is a perspective view showing a first example of the present invention,
1 is n-1nP first cladding layer (EC), 2 is u-
1nGaAsP active layer (Ea), 3 is p-1nP second layer
cladding layer (EC), 4 is a p-InGaAsP contact layer, 5 is a striped u-InGaAsP optical waveguide layer (Ea), 6 is a p-InP current blocking layer, 7 is an n
-InP current blocking layer, 8 is n-InP substrate, 9 is n
- electrode, 10 is a p-electrode, 11 is a proton injection insulating region, 12 is a diffraction grating reflector, 13 is a high reflection film, 14 is the pitch P of the diffraction grating, 15 is the tilt angle θ of the diffraction grating reflector, 1
6 is a laser section, 17 is a wavelength control section, and 19 is a laser oscillation light (λ). The end surface on the far end side of the striped optical waveguide layer 5 is perpendicular to the pn junction formed between the active layer 2 and the second cladding layer 3, and the striped optical waveguide It is formed diagonally to the layer. In addition, a diffraction grating reflector 1 is placed on the end face in a direction perpendicular to this p-n junction.
2, and has a relationship of Ea>Ea>Ec between the energy band widths Ea, Ea, and EC.

To operate this, the p-electrode 10 of the laser section and the n-
A current is passed between the electrodes 9 to cause the semiconductor laser to emit light.

The laser oscillation light (λ) 19 is guided to the optical waveguide layer (Ea) 5, and only light with a specific wavelength λ, which is the diffraction grating reflecting mirror 12, is reflected and returned to the optical waveguide layer 5 and the active layer 2. Therefore, laser oscillation occurs only with light of a specific wavelength λ.

That is, laser oscillation occurs only with the light λ selected by the diffraction grating, and the cavity is effectively lengthened by the low-loss optical waveguide layer 5, thereby narrowing the line width.

Here, the following relationship exists between the wavelength λ of the laser oscillation light and the pitch P of the diffraction grating.

θ is the tilt angle 15 of the diffraction grating reflector. naff is the effective refractive index. λ=1.55μm, θ=30°.

n*tt=3.25. When m = 1, the pi y+ of the diffraction grating must be P = 0.48 μm.

Further, the wavelength λ and the phase of the end face are controlled by the wavelength control section 17.
This is possible by applying a forward current to the waveguide layer 5, adjusting the number of carriers injected into the waveguide layer 5, and controlling the effective refractive index neff. The refractive index change Δn can be obtained as follows by differentiating the plasma oscillation equation.

#-6.7X10-" (am3) xΔN (am-
:I) -----■Where, n is the refractive index, C is the speed of light,
λ is the oscillation wavelength, ΔN is the carrier density change (C1l-')
, Tn@, 1'nk are the effective masses of electrons and holes, respectively, and ε. is the conductivity and e is the electron charge.

In this way, by injecting a current into the optical waveguide layer 5, the effective refractive index n*ff can be adjusted, so even if the pitch P of the diffraction grating is fixed, the oscillation wavelength λ and the end face phase can be controlled. can.

FIG. 2 is a sectional view showing a second embodiment of the invention. The difference from the first embodiment is that the diffraction grating reflector 12 is made oblique to the pn junction, and the direction of the diffraction grating is parallel to the pn junction.

FIG. 3 is a perspective view showing a third embodiment of the present invention. 1st. The difference from the second embodiment is that the electrode on the optical waveguide layer 5 is divided into a wavelength control section 17 and an end face phase control section 18, respectively. Thereby, there is a degree of freedom in which wavelength control and end face phase control can be performed independently.

(5) As described in detail of the invention, the conventional multi-electrode DFB or DBR
In semiconductor lasers, since a diffraction grating must be provided in the active region or the optical waveguide region, there are many problems during crystal growth, which causes a reduction in device yield and reliability. In contrast, the semiconductor laser of the present invention uses a dry etching method on the far end side of the striped optical waveguide layer to provide an external diffraction grating reflector, so there is no problem during crystal growth. It has the advantage of contributing to higher yield and higher reliability of devices.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of the first embodiment of the present invention, FIG. 2 is a sectional view showing the structure of the second embodiment of the invention, and FIG.
The figure is a perspective view showing the structure of a third embodiment of the present invention. 1...n-InP first cladding layer (Ec), 2
...u-1nGaAsP active layer (El), 3...p
-Second cladding layer (EC) of InP, 4-p-1nG
aAsP contact layer, 5 ・-u-1nGaAsP
Optical waveguide layer (Ea), 6...p-1nP current blocking layer, 7...n-InP current blocking layer, 8...n-
InP substrate, 9...n-electrode, 10...p=electroplating,
11... Proton injection insulating region, 12... Diffraction grating reflector, 13... High reflection film, 14... Pitch P of diffraction grating, 15... Tilt angle θ of diffraction grating reflector, 16・
... Laser section, 17... Wavelength control section, 18... Phase control section, 19... Laser oscillation light (λ). Patent applicant Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] (1) The energy band width formed on the semiconductor substrate is E
a first cladding layer of _c, an active layer on the first cladding layer having an energy band width of E_a and serving as a striped light emitting region, and a stripe on the first cladding layer having an energy band width of E_g. a second cladding layer having an energy band width of E_c on the active layer and the optical waveguide layer, and the striped active layer and the optical waveguide layer are in contact with each other in the second cladding layer. an insulating region formed on a portion thereof, a main electrode separated by the insulating region and formed on the light emitting region via a contact layer, and a wavelength and phase control electrode formed on the optical waveguide layer. In the semiconductor laser, a far end side end surface of the optical waveguide layer is connected to the active layer and the second semiconductor laser.
is formed perpendicularly to the p-n junction formed between the striped optical waveguide layer and the cladding layer, and obliquely to the striped optical waveguide layer, and a diffraction grating is provided on the end face in the direction perpendicular to the p-n junction. and energy band widths E_a, E_g, E
There is a relationship between E_a<E_g<E_c,
It is characterized in that it is configured to control the oscillation wavelength and end face phase by flowing a forward current through the p-n junction of the optical waveguide layer and adjusting the refractive index according to the concentration of injected carriers. semiconductor laser. (2) An end face on the far end side of the optical waveguide layer is formed perpendicular to the striped optical waveguide and obliquely to the p-n junction, and a diffraction grating is formed on the end face parallel to the p-n junction. A semiconductor laser according to claim 1, characterized in that the semiconductor laser is formed with: (3) The semiconductor laser according to claim 1 or 2, wherein each electrode is divided into three parts, each of which serves as a light emitting part, a phase control part, and a wavelength control part.