Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
The invention discloses a distributed feedback laser, comprising:
the N-face electrode layer is used for forming ohmic contact;
a substrate layer disposed over the N-sided electrode layer;
the buffer layer is arranged above the substrate layer and plays a role in buffering;
a first waveguide layer disposed over the substrate layer for confining an optical field;
a multiple quantum well active layer disposed over the first waveguide layer for generating stimulated emission of light;
a second waveguide layer disposed over the multiple quantum well active layer for confining an optical field;
the grating layer is arranged on the second waveguide layer and used for mode selection;
the etching self-stopping layer is arranged on the grating layer and used for controlling the etching depth;
the cladding layer is arranged above the etching self-stopping layer and used for limiting the light field and the carrier diffusion;
an ohmic contact layer disposed on the cladding layer; and
a P-side electrode layer disposed on the ohmic contact layer for forming an ohmic contact;
and etching the cladding layer and the ohmic contact layer to form a ridge waveguide, wherein the ridge waveguide comprises a straight waveguide and a mode field diffusion structure.
In some embodiments of the invention, the mode field spreading structure is a tapered ridge waveguide structure, the tapered ridge waveguide structure being connected to a straight waveguide.
In some embodiments of the invention, the tapered ridge waveguide structure is flared;
in some embodiments of the invention, the converging angle of the converging ridge waveguide structure is 0.4 to 5 degrees;
in some embodiments of the invention, the length of the tapered ridge waveguide structure is from 20 microns to 80 microns;
in some embodiments of the present invention, the converging ridge waveguide structure is disposed at an end of the ridge waveguide near the light exit surface or the backlight surface.
In some embodiments of the present invention, the mode field spreading structure is a broken ridge structure, and the distance between the broken ridge structure and the light emitting surface or the backlight surface end surface is 5 micrometers to 40 micrometers.
In some embodiments of the present invention, the mode field diffusion structure is a film structure deposited on the end surface of the straight waveguide light-emitting surface or backlight surface.
In some embodiments of the invention, the film structure has a refractive index between 1 and 3;
in some embodiments of the invention, the material of the membrane structure comprises SiO2、Al2O3、MgF2Etc.;
in some embodiments of the invention, the membrane structure has a thickness of 0.5 to 3 microns.
In some embodiments of the present invention, the bottom of the ridge waveguide is disposed above the etching self-stop layer, and the P-side electrode layer covers the top of the ridge waveguide layer and is led out from a circular pad;
in some embodiments of the invention, the ridge waveguide has a width of 1 to 3 microns and a depth of 1.5 to 2.5 microns;
in some embodiments of the present invention, the ridge waveguide is formed by etching two channels on the cladding layer and the ohmic contact layer, and the width of the channel is 8 micrometers to 15 micrometers.
In some embodiments of the present invention, a back light surface of the distributed feedback laser is plated with a high reflection film, and a light emitting surface of the distributed feedback laser is plated with an antireflection film.
In some embodiments of the present invention, the material used for the substrate layer comprises InP;
in some embodiments of the present invention, the buffer layer is made of a material including silicon-doped InP;
in some embodiments of the present invention, the buffer layer has a thickness of 400 nm to 500 nm;
in some embodiments of the present invention, the material used for the first waveguide layer includes InGaAsP;
in some embodiments of the present invention, the material used for the second waveguide layer includes InGaAsP;
in some embodiments of the present invention, the multiple quantum well active layer adopts an InGaAsP multiple quantum well structure;
in some embodiments of the present invention, the grating layer is obtained by a holographic exposure method;
in some embodiments of the present invention, the P-side electrode is made of titanium platinum gold, and the N-side electrode is made of gold germanium nickel.
The invention also discloses application of the distributed feedback laser in the field of optical communication.
In one exemplary embodiment, the semiconductor laser of the present invention is a narrow ridge DFB laser having a mode field diffusion structure, and is a narrow ridge DFB laser having a mode field diffusion structure that improves an end surface damage threshold and improves output power.
The narrow ridge DFB laser structure is in order from bottom to top: the semiconductor device comprises an N-surface electrode layer, an InP substrate, a buffer layer, a lower waveguide layer (namely a first waveguide layer), a multi-quantum well active layer, an upper waveguide layer (namely a second waveguide layer), a grating layer, an etching self-stop layer, a cladding layer, an ohmic contact layer and a P-surface electrode layer. The laser optical waveguide structure includes a lower waveguide layer, a multiple quantum well active layer, and an upper waveguide layer. The grating layer is arranged on the middle upper part of the upper waveguide layer. Wherein the cladding layer and the ohmic contact layer constitute a ridge structure. The ridge structure comprises a straight waveguide part and a mode field diffusion structure, wherein the mode field diffusion part comprises the following three conditions: a, shrinking the ridge width in the horizontal direction, namely shrinking the ridge waveguide structure; b, breaking the end surface ridge, namely breaking the ridge structure; and c, depositing a low-refractive-index film structure on the end face, namely a film structure.
The ridge waveguide is shrunk on the light-emitting surface of the laser, namely the ridge waveguide of the laser is gradually shrunk in the direction of the light-emitting surface to form a closed-horn-shaped shape. The ridge width gradually shrinks at a position close to the light-emitting surface in the horizontal direction, the shrinkage angle theta is 0.4-5 degrees, the ridge waveguide is in a closed horn mouth structure at the light-emitting surface, and the length of the closed horn mouth structure is 20-80 microns.
The ridge breaking structure on the light emitting surface means that the ridge waveguide is broken at a position 5-40 microns close to the light emitting surface in the vertical direction, and the straight waveguide part is directly contacted with air.
Wherein, depositing a film structure at the light-emitting end face refers to depositing a low-refractive index material film with refractive index of 1-3, which can be SiO2(refractive index n is 1.44) and Al2O3(refractive index n: 1.75) and MgF2(refractive index n is 1.38), and the like, and the film of the low refractive index material is the mode field diffusion portion. The film is deposited at the end face of the waveguide portion to a thickness of 0.5 to 3 microns.
Wherein, the mode field diffusion part is also applicable to the backlight surface.
Wherein, the grating region is arranged at the middle upper part of the upper waveguide layer, and the multiple quantum well active region is an InP material system.
The backlight surface of the laser is plated with a high-reflection film, and the light-emitting surface of the laser is plated with an antireflection film.
Wherein, P-surface electrodes and N-surface electrodes are respectively sputtered on the ohmic contact layer and below the InP substrate layer. And the P-side electrode is led out through a circular pad.
The technical solution of the present invention is further illustrated by the following specific embodiments in conjunction with the accompanying drawings. It should be noted that the following specific examples are given by way of illustration only and the scope of the present invention is not limited thereto.
The narrow ridge DFB laser with the mode field diffusion structure comprises a stack of an N-surface electrode layer, an InP substrate 1, a buffer layer 2, a lower waveguide layer 3, a multi-quantum well active layer 4, an upper waveguide layer 5, a grating layer 6, an etching self-stop layer 7, a cladding layer 8, an ohmic contact layer 9 and a P-surface electrode layer from bottom to top in sequence. Wherein the cladding layer 8 and the ohmic contact layer 9 constitute a ridge waveguide 11.
As shown in fig. 1a to 1c, the cladding layer 8 and the ohmic contact layer 9 constitute a straight waveguide portion and a mode field diffusion portion, and are divided into a backlight surface and a light exit surface, and the arrow indicates the laser light exit direction. Fig. 2 is a front view schematic diagram of fig. 1a, and fig. 3 is a side view schematic diagram of fig. 1 a.
Fig. 4 a-4 c show top views of the narrow ridge DFB laser with mode field diffusion structure, where fig. 4a is a ridge waveguide horizontal constriction (i.e., a constricted ridge waveguide), fig. 4b is a ridge waveguide break-up structure, and fig. 4c is a deposited low index material thin film structure (i.e., a film structure). The ridge waveguide comprises a straight waveguide part and a mode field diffusion part, wherein one end of the left side is a light-emitting end face of the ridge waveguide, the right side is a backlight end face, and the mode field diffusion part is positioned on one side of the light-emitting face. As shown in fig. 4a, the narrow ridge structure of the light-emitting surface is in a shape that the width of the ridge waveguide gradually shrinks toward the light-emitting surface, and the horizontal divergence angle θ of the ridge waveguide flaring structure is 0.4 to 5 degrees. As shown in fig. 4b, the ridge waveguide cut-off structure is to cut off the ridge waveguide at a position 5 to 40 microns close to the light exit surface, and the straight waveguide portion is directly contacted with air. As shown in fig. 4c, the depositing of the low refractive index material film structure is to deposit a low refractive index material film structure on the end face of the straight waveguide portion.
In this embodiment, the narrow ridge DFB laser has a cavity length L of 150 to 250 microns and a width W of 250 microns, and the exit mode field spreading section L1 includes a shrinkage of the horizontal ridge width, b-facet ridge break-off and c-facet deposition of a thin film of low refractive index material, wherein the shrinkage length of the horizontal ridge width is 20 to 80 microns and the break-off length of the b-facet ridge is 5 to 40 microns, and the thickness of the thin film of c-low refractive index material is 0.5 to 3 microns. The structure increases the area of a mode field, reduces the optical power density on the light-emitting surface, and improves the damage threshold of the end face of the laser.
In this embodiment, the InP substrate layer 1 is made of an InP substrate material, and the buffer layer 2 is made of an InP material doped with Si and having a thickness of 450 nm. The upper waveguide layer 3 and the lower waveguide layer 4 are made of InGaAsP material. The multiple quantum well active layer 4 adopts an InGaAsP multiple quantum well structure, has 5 quantum wells, and has a lasing wavelength of 1310 nm. Compared with the common double heterostructure laser, the quantum well laser has the advantages of low threshold, large output power and high modulation rate. Tensile or compressive strain is introduced in the quantum well structure to increase differential gain, and the layer thicknesses of the well and barrier are optimized to reduce carrier transit time through the optical confinement layer and carrier escape from the active region.
The grating layer 6 is manufactured on the middle upper part of the upper waveguide layer 5, and the grating is obtained by adopting a holographic exposure method. And a high reflection film is plated on the backlight surface of the laser, and an antireflection film is plated on the light emitting surface.
After obtaining the grating by the holographic method, the etched self-stop layer 7, the cladding layer 8 and the ohmic contact layer 9 are obtained by secondary epitaxy. The ridge waveguide 10 is obtained by photoetching and etching, the width of the ridge waveguide 10 is 2 microns, the depth of the ridge waveguide 10 is 1.8 microns, and the width of a channel 11 on two sides of the ridge waveguide 10 is 12 microns. The ridge waveguide 10 functions to achieve a light confinement effect and obtain a single-mode output.
And finally, obtaining a P-surface electrode on the ohmic contact layer 9 by adopting a magnetron sputtering method, and obtaining an N-surface electrode below the InP substrate layer 1. The P-face electrode is made of TiPtAu (titanium platinum gold), and the N-face electrode is made of AuGeNi (gold germanium nickel). The P-side electrode is led out through a circular bonding pad.
It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. In addition, the above definitions of the various elements are not limited to the specific structures, shapes or modes mentioned in the embodiments, and those skilled in the art may easily modify or replace them, for example:
1. directional phrases used in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., refer only to the orientation of the drawings and are not intended to limit the scope of the present disclosure;
2. the embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e. technical features in different embodiments may be freely combined to form further embodiments.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.