JPS59218786A - Single axial mode semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a single axial mode semiconductor laser capable of oscillating in a single axial mode and single axial mode oscillation to a high output level by forming a an irregular period structure having a specific period in a boundary between a photowaveguide layer and an intermediately layer and a resonator structure which suppresses the Fabry-Perot mode oscillation of a semiconductor laser. CONSTITUTION:Two slots which reach an intermediate layer are opened in a composite semiconductor layer 9 having a photowaveguide layer 1, an intermediate layer 2, an active layer 3 and a clad layer 4 on a (100) azimuth N type InP wafer 10, and a mesa stripe is formed. A periodic structure of the period substantially equal to the value of lambda0/(2Xneff), where neff is equivalent refractive index of a composite photowaveguide layer of a mesa stripe in a boundary between the layer 1 and the layer 2 and lambda is the wavelength of the oscillating light in a free space is formed in 0-11 direction. A P type InP first current block layer 5 and an N type InP second current block layer 6 are grown except on the mesa stripe on the layer 9. The first end 20 is perpendicular cleaved surface, and the second end 21 is an oblique surface. Since these ends 20, 21 do not substantially form Fabry-Perot resonator, the Fabry-Perot mode is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single-axis mode semiconductor laser that oscillates in a single-axis mode and is used in optical communications, and particularly to a single-axis mode semiconductor laser that is suitable for high-output oscillation.

In recent years, the wavelength of 1.5 μm, which is the lowest loss region of optical fiber
There has been remarkable progress in the research and development of single-axis mode semiconductor lasers, which are intended for application as light sources in the band. This is because single-axis mode oscillation is not affected by the material dispersion of the optical fiber.
This is because long-distance optical fiber communication becomes a reality. However, conventional single-axis mode oscillation lasers have problems with high-power oscillation characteristics, and improvements have been desired. One of them is that the light exit end face was made with an open valve, so the Fabry-Perot mode oscillated at high output, resulting in complete single-axis mode oscillation. Similar to normal Fabry-Bello semicircular body lasers, an oblique transverse mode occurs.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a single-axis mode semiconductor laser capable of single-axis mode and early mode oscillation up to high output levels.

The uniaxial mode semiconductor laser of the present invention includes a semiconductor substrate of a first conductivity type, a first waveguide layer of a quaternary conductivity type epitaxially grown on the semiconductor substrate, and an intermediate waveguide layer of a first conductivity type. In order to form a mesa stripe for laser oscillation, in the composite semiconductor layer including the active layer, the active layer, the second quaternary cladding layer, and the cladding layer, a depth at least reaches the intermediate layer on both sides of the mesa stripe to form a mesa stripe for laser oscillation. After forming two 6I# layers, a second 4-type first current blocking layer and a first conductivity type second current blocking layer are grown by primary epitaxial growth except for the upper side of the mesa stripe, and In the semiconductor laser comprising the mesa stripe and the buried layer and contact layer epitaxially grown on the second current blocking layer, the optical waveguide layer has a bandgap wavelength shorter than the oscillation wavelength, and the intermediate layer is a crystal layer having a lower refractive index than the optical waveguide layer, and furthermore, at the boundary between the optical homowave layer and the intermediate layer, there is a crystal layer having an isolateral refractive index, H, and an oscillation wavelength λ of the semiconductor laser. , Ohji The resonator structure is characterized by forming a concave-convex periodic structure having a period Δ given by the following equation, and having a resonator structure that suppresses the 7-application-pero one mode oscillation of the semiconductor laser.

In the present invention, laser oscillation is performed in a composite optical waveguide layer consisting of an active layer, an intermediate layer, and a waveguide layer located in and below the mesa stripe, but the periodic structure that causes distributed feedback has a maximum light intensity. Since it is formed at the boundary between the intermediate layer and the optical waveguide layer, which is close to . In addition, in the present invention, since the active layer is not grown directly on the optical waveguide layer in which the periodic structure is formed, but a single intermediate layer is interposed, in addition to the advantage that the active layer has good crystallinity, The refractive index change between the layer and the active layer has the advantage that the refractive index change of the periodic structure can be large.

Further, in the present invention, due to the structure in which the composite optical waveguide includes a crystal layer having a lower refractive index than the optical waveguide layer, an intermediate layer and By adopting the stripe loading guide format on which the active layer has a mesa stripe width, the isolateral refractive index of the composite optical waveguide 1fiJ is low. For this reason,
The width of the mesa stripe can be increased without maintaining the fundamental transverse mode oscillation, which increases the ease of fabrication and prevents optical damage to the end face due to optical density.In addition, the resonator structure has a 7-plane bellows mode. A configuration that suppresses (
For example, since an oblique end face, an anti-reflection vapor layer treatment, etc.) are used, Fabry-Perot mode oscillation does not occur.

Due to the synergistic effect of the above-mentioned structural features, the single-axis mode semiconductor laser of the present invention can consistently perform distributed feedback oscillation up to high output levels while maintaining single-axis mode and single-transverse mode oscillation. be.

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a cross-sectional view of a single-axis mode semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of a mesa stripe portion of FIG. 1. (An optical waveguide layer 1, an intermediate layer 2, an active layer 3, and a cladding layer 4 are epitaxially grown in sequence on an n-InP wafer 10 with a 1(10) plane orientation.The optical waveguide layer 1 has a forbidden band wavelength of 1 .30 μm n InCL72
GA (L28 Asg, 61 PL59 quaternary mixed crystal 1 intermediate layer 2 is n-InP, active layer 3 has a bandgap wavelength of 1.55
/'F7j Inα59Gaa41Asn, es+ P
The nu quaternary mixed crystal and cladding layer are p-InP. The thickness of each layer is 0.3pm, 0.1pm, 0.1pm respectively
, 1pm. A mesa stripe with a width of 4 μm is formed by cutting two grooves in the composite semiconductor layer 9 made up of each of these layers until it reaches the intermediate layer. Optical waveguide layer 1
At the boundary of the intermediate layer 2, the isolateral refractive index of the composite optical waveguide layer of the mesa stripe is approximately equal to the value of λ./(2Xn e!f), where the wavelength of the oscillation light in free space is λ. Equal periods (“art” 3 in the example)
．． 27, λ, -1,5511Wl, 1: h 23
70X) The O-circumference IJJ structure is formed in the (oir) direction. On the composite semiconductor layer 9, p-InP
A first current blocking layer 5 of n-4nP and a second current blocking layer 6 of n-4nP are grown except on top of the mesa stripe, and then a buried layer 7 and a contact layer 8 are grown on the second current blocking layer 6 and the mesa stripe. is growing. The buried layer 7 is p-InP, and the contact layer 8 has a bandgap wavelength of 1.201.
1m p In(L78Gan22 Asα48P
It is a quaternary mixed crystal of o, 52. The first electrode 11 is Au −
The p1 second electrode 12 is a negative electrode of Ge-Ni.
It is a positive electrode of i /P t . A first end face 20 on one side of the mesa stripe is a vertical cleavage face, and a second end face 21 is a slightly etched oblique face.

The operation of the embodiment having the above configuration will be explained.

When a current is passed from the first electrode 12 to the second electrode, luminescent recombination occurs in the active layer 3, but the first and second end faces 20,
21 does not substantially constitute a 7-application Perot resonator, the Fabry-Perot mode is suppressed. Of the spontaneously emitted light emitted from the active layer 3, the wavelength λ equal to 2×n, ffxA is subjected to a feedback effect by the periodic structure, and therefore increases significantly as the current increases, causing distributed feedback oscillation.

In this example, the threshold current is 3 ohmA at room temperature.

The optical output at an injection current of 100 mA is approximately 20 ysW, and within this range, single-axis to de-excavation and single-transverse mode (
fundamental mode) oscillation. According to the present invention, a single-axis mode, single-transverse mode high-output semiconductor laser can be obtained relatively easily.

Although the embodiments of the present invention have been described above, various modifications can be made in addition to the embodiments. The n-InP wafer 10 has p
However, in this case, the conductivity type of each layer must be reversed to that of the embodiment. Also,
The crystal structure of the embodiment may be other than InP and InGaAsP, and the oscillation wavelength is also 55 μm.
Of course, the wavelength is not limited to , and other wavelengths may be used. Furthermore, since the purpose of forming the second end face obliquely is to suppress the occurrence of Fabry-Perot modes, any means that produces the same effect may be used.

For example, the second end surface 21 may be inclined when viewed from above the mesa stripe. In addition, the first end surface 2
An anti-reflection film may be formed on the surface of the substrate 0 to improve light extraction efficiency. Further, the depth of the two grooves forming the mesa stripe may be set to a depth that reaches the leading wave layer l.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are a cross-sectional view and a vertical cross-sectional view of a mesa stripe portion of an embodiment of the present invention. In the figure, 1... optical waveguide layer, 2... intermediate layer, 3...
- active layer, 4... cladding layer, 5, 6... current blocking layer, 7... buried layer, 8... contact layer, 9
...Composite semiconductor layer, 1 (1=InP wafer, 11.
12... Electrode, 2.0.21... End surface, 30...
It is a periodic structure. ,? Bottom, -K(ii,・舅74iri%”F:I
Knee 4 (

Claims (1)

[Claims] A semiconductor substrate of a first conductivity type, an optical waveguide layer of a first conductivity type epitaxially grown on the semiconductor substrate,
A composite semiconductor layer including an intermediate layer of a first conductivity type, an active layer, and a cladding layer of a second conductivity type has a depth that reaches at least the intermediate layer. A first current blocking layer of a second conductivity type and a second current blocking layer of a first conductivity type, comprising a mesa stripe sandwiched by two grooves, and epitaxially grown in sequence on the mesa stripe except for the upper part of the mesa stripe. a buried layer and a contact layer epitaxially grown on the mesa stripe and the second current blocking layer; further, the optical waveguide layer has a bandgap wavelength that is shorter than the oscillation wavelength; The layer is a crystal layer having a refractive index lower than that of the optical waveguide layer, and furthermore, at the boundary between the optical waveguide layer and the intermediate layer, there is a crystal layer having an isolateral refractive index "@ff" and an oscillation wavelength λ of the semiconductor element. , has an uneven periodic structure with a period A given by the following formula %), and
A single-axis mode semiconductor laser characterized by having a resonator structure that suppresses noopibel mode oscillation.