JPS6066489A - Distributed feedback and distributed bragg reflector type semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the efficiency of the titled laser and to lessen the size thereof by a method wherein the first Bragg wavelength of the distributed feedback active layer part and the second Bragg wavelength of the distributed Bragg reflector optical guide layer part are substantially equalized. CONSTITUTION:A distributed feedback active layer part 100 has been formed into a structure, wherein current blocking layers 7 and 8 have been partially inserted in a multilayer crystal growth layer consisting of a substrate 1, an optical guide layer 4, an active layer 5, a buried layer 9 and a contact layer 10, while a distributed Bragg reflector optical guide layer part 200 has been formed into a structure, wherein the current blocking layers 7 and 8 have been partially inserted in a multilayer crystal growth layer consisting of the substrate 1, an optical guide layer 2, a clad layer 3, the optical guide layer 4, the active layer 5, a clad layer 6, the buried layer 9 and the contact layer 10. On the whole surface of the upper side (n) of the contact layer 10 has been formed an Si3N4 film, excluding a part of the upper side just above the distributed feedback active layer part 100 and its vicinity. Moreover, a positive electrode 13 has been evaporated on the Si3N4 film all over the surface thereof and a negative electrode 11 has been evaporated on the lower side of the substrate 1 all over the surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly efficient and small-sized single-axis mode semiconductor laser suitable for use in optical fiber communications and the like.

Semiconductor lasers are excellent as light-emitting elements for optical fiber communications, but they generally oscillate in multiple axial modes, which poses a problem when used for long-distance, high-capacity optical fiber communications. The solution to this problem is a single-axis mode semiconductor laser, and the one considered as a practical structure is a distributed feedback semiconductor laser (DFB-
LD) and distributed plug reflector semiconductor laser (DBR-
LD) etc. The former forms a periodic structure in the vicinity of the active layer that undergoes radiative recombination, and has the advantage that the manufacturing method is no different from that of a normal semiconductor laser and can be made using a small Ct method. However, since the DFB-1, 1) generally has two exit surfaces, it has the disadvantage that the light extraction efficiency from one surface is poor.

On the other hand, the latter is a method in which a periodic structure is formed in a light guide layer that does not include an active layer to serve as a distributed Bragg reflector and is connected to another light guide layer that includes an active layer, and the number and position of the distributed Bragg reflectors are By appropriately setting the reflectance and reflectance, there is an advantage that the light extraction efficiency when viewed from one side can be increased. However, DBR-LD has disadvantages in that its size is large, making it somewhat difficult to mount it in a package, etc., and it is not possible to manufacture a large number of wafers.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly efficient and small-sized single-axis mode semiconductor laser which eliminates the drawbacks of the semiconductor lasers described above.

According to the present invention, a first light guiding layer including an active layer that performs luminescent recombination, a first periodic structure disposed close to the first light guiding layer, and an electrode for current injection are provided. a second light guide layer that is connected to the distributed feedback active layer and does not include an active layer that performs luminescent recombination; and a second light guide layer that is disposed close to the second light guide layer. a first Bragg wavelength of the distributed feedback active layer and a second Bragg wavelength of the distributed Bragg reflector light guide layer. A distributed feedback distributed Bragg reflector half-quad laser is obtained which is characterized by substantially equal wavelengths.

In the present invention, the first
a distributed feedback active layer portion comprising a light guide layer, a first periodic structure disposed close to the first light guide layer, and an electrode for current injection; The equivalent refractive index net of the light guide layer and the period AI of the first periodic structure
The light with the first Bragg wavelength λB1 determined by the following formula λ8=n, l The light propagates to the second light guide layer selected within the guide layer, and is expressed by the following formula λam using the isolateral refractive index "es" of the second light guide 1- and the period A8 of the second periodic structure described in 61J. -n,,X
Since the second Bragg wavelength λBs determined by undergoes distributed Bragg reflection within the second light guide layer. Due to the synergistic effect of the distributed feedback amplification effect and the distributed Bragg reflection effect, the present invention provides the first Bragg wavelength λ.
nt (ie, second Bragg wavelength λ□) can be oscillated. Furthermore, since the reflectance of the distributed Bragg reflector can be set appropriately, the amount of light emitted from one end face, which was a mere loss in the conventional DFB-LD, can be reduced and the efficiency of the laser can be significantly increased. In addition, since the feedback necessary for laser beam oscillation is performed in both the distributed section fi amplification section and the distributed Bragg reflector light guide layer section, the conventional D
BR-LD can significantly shorten the overall tunnel length. In addition, in the present invention, 1. As a means for making the second black wavelengths substantially equal, the first. The period of the second periodic structure is equal and the period of the first periodic structure is equal. If the second isolateral refractive indexes are made equal, the periodic structure can be fabricated only once, which is convenient. 1st. There are various ways to make the second isolateral refractive indexes equal. For example, the thickness of the second light guide layer may be made slightly larger than the thickness of the first light guide layer, or 1. The film thickness of the second light guide layer may be approximately the same, and the forbidden band width of the second light guide layer may be slightly larger than that of the first light guide layer.

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

FIG. 1 is a perspective view of an embodiment of the present invention.

(100) plane orientation <011> on the surface of the n-InP substrate 10
A periodic structure 30 of 238 oX is formed over the entire surface. This periodic structure 30 has a wavelength of 3250
It was created using a three-beam interference exposure method in which a bisected beam of an X He-Cd laser is focused at an angle of approximately 43 degrees, and chemical etching. The substrate 1 having the period M structure 30 is divided into a first region where the distributed feedback active layer portion 100 is formed and a second region where the distributed Bragg reflector light guide 14 portion 200 is formed. Above the second region, a bandgap wavelength of 1.3/jFFj and a thickness of 0.35Pm C
) A second guide layer 2 of n-InGaA8P and a second cladding layer 3 of n-InP having a thickness of 4 μm are grown. On the first region and the second cladding layer 3, an n-In film with a bandgap wavelength of L3pm and a thickness of 0.15 μm is formed.
The first guide layer 4 is made of GaAsP and the bandgap wavelength is 1.
Non-doped InGaAsP with a thickness of 55μm and 01pm
A first cladding layer 6 of p-InP with an active layer 1-5 and a thickness of 2 ptn is grown. The first guide layer 4, the active layer 5, and the first cladding layer 603 are placed on the second guide layer 2 and the second cladding layer 3, and are substantially butt-connected. There is a heavenly manifestation. In the multilayer crystal growth layer up to the first cladding layer 6, a mesa stripe 20 is formed by two grooves 21 and 22. A first layer of p-InP is formed in the area just above the mesa stripe 20.
A current blocking layer 7 of n-InP and a second current blocking layer 8 of n-InP are sequentially grown, and then a buried layer 9 of p-InP and a p'' -InP contact layers 10 are grown sequentially. Therefore, the distributed feedback active layer section 100 is formed between the substrate 1 and the first contact layer 10.
It has a structure in which first and second current blocking layers 7 and 8 are partially inserted into a multilayer crystal growth layer consisting of an original guide layer 4, an active layer 5, a buried layer 9, and a contact layer 1O. Further, the distributed Bragg reflector light guide layer section 200 includes a substrate 1, a second light guide layer 2, a second cladding layer 3, a first light guide layer 4, an active layer 5, a first glue 2, and a rad layer 6. Embedded layer 9
and a contact layer io. It has a structure in which a second current blocking layer 7.8 is partially inserted. On the upper side of the contact layer 10, an 811N4 film with a thickness of 02 μm is formed on the entire surface except for the area directly above the distributed feedback active layer portion 100, and on top of that is a Ti/N4 film.
A positive electrode of Pt is vapor-deposited over the entire surface. Further, a negative electrode of AuGeNi is vapor-deposited over the entire surface of the lower part of the substrate 111. Distributed Bragg reflector light guide layer section 2
The side of 00 is tilted diagonally due to ion milling.
is formed.

In the above structure, the equivalent refractive index of the distributed feedback active part 1000 optical waveguide is about 3.26, and the equivalent refractive index of the distributed Bragg reflector light guide layer part 2000'yt and the waveguide is about 326. The values are the same. Therefore, the Bragg wavelength for the periodic structure 30 is about 1.55 μm, which is the same for the distributed feedback active layer portion 100 and the distributed Bragg reflector light guide layer portion 200. Of the light guided to the optical waveguide in the mesa stripe 20, the Bragg wavelength is 1.55.
The μm light receives distributed feedback and optical amplification in the distributed feedback active layer section 100, and receives distributed reflection in the distributed Bragg reflector light guide layer section 200, so that it starts to oscillate as the injected current increases. In this structure, a normal DFB-LD
The light from one end face that was wasted in the process is also returned to the active layer.
Therefore, it has the advantage of extremely high oscillation efficiency, and also has the advantage of being smaller in size than a normal DBR-L1).

The embodiments of the present invention can be modified independently in addition to the examples. The obliquely inclined beam 40 is for suppressing the 7-application Perot mode oscillation, and is not necessary if the reflectance of the distributed Bragg reflector light guide layer section 2000 is large.
Other means may also be used. An anti-reflection film may be applied to the output surface of the distributed feedback active layer section 100 to improve light extraction efficiency. The oscillation wavelength may be other than 155 μz, and the crystal composition may be other than InGaAsP mixed crystal.

Also, f-guy 111m2, 4. The thickness and composition of the active layer 5 may be changed as appropriate. Further, the periodic structure 30 is not limited to a first-order diffraction grating, but may be a second-order or higher-order diffraction grating. The conductivity types of the substrate l and the grown crystal layer are all the same as in the example.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention. In the figure, l...substrate, 2.4... light guide layer,
3゜6...R2 Rad layer, 5...Active layer, 7.8...
-Current block layer, 9...buried layer, IO...contact layer, 11.13...electrode, 12...Ss, N4
Membrane, 20...Mesast 2ig, 21.22...Existence,
30...periodic structure, 40...tilted surface, 100...
Distributed feedback active layer portion, 200 . . . distributed Bragg reflection light guide layer portion.

Claims (1)

[Claims] / a light guide layer of fPJl including an active layer that emits and recombines gold; and a first light guide layer disposed in close proximity to the first light guide layer.
a distributed feedback active layer portion having a periodic structure of and a second periodic structure disposed close to the guide layer. A distributed feedback distributed Bragg reflector semiconductor laser characterized in that a period of a periodic structure is determined.