Tunable laser and manufacturing method thereof
阅读说明：本技术 可调谐激光器及其制作方法 (Tunable laser and manufacturing method thereof ) 是由 剌晓波 梁松 唐强 刘云龙 张立晨 朱旭愿 于 2020-06-29 设计创作，主要内容包括：一种可调谐激光器及其制作方法,所述可调谐激光器包括位于同一衬底上、等高且贴合的增益区和分布式布拉格反射区；其中,增益区和分布式布拉格反射区,分别为双台脊波导结构,包括下台脊波导和上台脊波导；所述增益区的下台脊波导和分布式布拉格反射区的下台脊波导分别自下而上依次包括光斑放大层、间隔层和有源层；所述增益区的上台脊波导和分布式布拉格反射区的上台脊波导分别自下而上包括包层和盖层；其中,所述增益区的上台脊波导为楔形波导；所述分布式布拉格反射区的上台脊波导为侧壁光栅波导。本发明的可调谐激光器在实现波长调谐的功能的同时可以放大激光器端面的光斑尺寸,提高激光器与光纤的耦合效率。(A tunable laser and its preparation method, said tunable laser includes locating on the identity substrate, equal height and gain area and distributed Bragg reflecting region that is laminated; the gain region and the distributed Bragg reflection region are respectively of a double-platform ridge waveguide structure and comprise a lower platform ridge waveguide and an upper platform ridge waveguide; the lower ridge waveguide of the gain region and the lower ridge waveguide of the distributed Bragg reflection region respectively comprise a light spot amplification layer, a spacing layer and an active layer from bottom to top in sequence; the upper ridge waveguide of the gain region and the upper ridge waveguide of the distributed Bragg reflection region respectively comprise a cladding and a cover layer from bottom to top; wherein, the upper ridge waveguide of the gain region is a wedge waveguide; the upper ridge waveguide of the distributed Bragg reflection region is a side wall grating waveguide. The tunable laser can amplify the spot size of the end face of the laser while realizing the function of wavelength tuning, and improves the coupling efficiency of the laser and the optical fiber.)
1. A tunable laser is characterized by comprising a gain region and a distributed Bragg reflection region which are positioned on the same substrate, have the same height and are attached; wherein the content of the first and second substances,
the gain region and the distributed Bragg reflection region are respectively of a double-platform ridge waveguide structure and comprise a lower platform ridge waveguide and an upper platform ridge waveguide;
the lower ridge waveguide of the gain region and the lower ridge waveguide of the distributed Bragg reflection region respectively comprise a light spot amplification layer, a spacing layer and an active layer from bottom to top in sequence; the upper ridge waveguide of the gain region and the upper ridge waveguide of the distributed Bragg reflection region respectively comprise a cladding and a cover layer from bottom to top; wherein the content of the first and second substances,
the upper ridge waveguide of the gain region is a wedge waveguide;
the upper ridge waveguide of the distributed Bragg reflection region is a side wall grating waveguide.
2. The tunable laser of claim 1, further comprising a phase region on the substrate, the phase region being contoured and conformable between the gain region and the distributed bragg reflector region;
the phase region is of a double-platform ridge waveguide structure and comprises a lower platform ridge waveguide and an upper platform ridge waveguide;
the lower ridge waveguide of the phase region sequentially comprises a light spot amplification layer, a spacing layer and an active layer from bottom to top; the upper ridge waveguide of the phase region comprises a cladding and a cover layer from bottom to top; wherein the upper land waveguide of the phase region is a straight waveguide.
3. The tunable laser of claim 2, wherein electrical isolation trenches are provided between the gain, phase and distributed bragg reflector regions of the cap layer for electrical isolation of the regions.
4. The tunable laser of claim 3, further comprising a front electrode and a back electrode, the front electrode formed on the cap layer of the gain, phase, distributed Bragg reflector regions; the back electrode is formed on the back surface of the substrate.
5. The tunable laser of claim 4, wherein the gain, phase, spot-expanding layer of the DBR region is a farfield reduction layer or a dilute waveguide layer.
6. The tunable laser of claim 5, wherein the active layers of the DBR and phase regions are formed using a P-ion induced quantum well intermixing method.
7. The tunable laser of claim 1, wherein the width of the sidewall grating waveguide of the distributed bragg reflector region varies periodically in the length direction;
the width of the straight waveguide of the phase region is constant in the length direction;
the width of the wedge waveguide of the gain region is gradually reduced along the direction far away from the distributed Bragg reflection region.
8. A method for manufacturing a tunable laser is characterized by comprising the following steps:
step 1: epitaxially growing a light spot amplification layer, a spacing layer, an active layer, a cladding and a cover layer on a substrate in sequence;
step 2: making the cladding and the cover layer into an upper ridge waveguide which comprises a wedge waveguide of a gain region and a side wall grating waveguide of a distributed Bragg reflection region;
and step 3: the active layer, the spacer layer and the spot amplifying layer are made as lower ridge waveguides of the gain region and the distributed Bragg reflection region.
9. The method of manufacturing according to claim 8,
in the step 2, the cladding and the cover layer are manufactured into an upper ridge waveguide which comprises a wedge waveguide of a gain area, a straight waveguide of a phase area and a side wall grating waveguide of a distributed Bragg reflection area;
in the step 3, the active layer, the spacing layer and the light spot amplifying layer are made into a lower ridge waveguide of a gain area, a phase area and a distributed Bragg reflection area;
after the step 3, the method also comprises a step 4 and a step 5:
and 4, step 4: manufacturing a front electrode on the cover layer;
and 5: and manufacturing a back electrode on the back of the substrate.
10. The method of manufacturing according to claim 9,
the step 1 comprises the following substeps:
substep 1.1: epitaxially growing a light spot amplification layer, a spacing layer, an active layer and a sacrificial layer on a substrate in sequence;
substep 1.2: injecting P ions into the sacrificial layers of the phase region and the distributed Bragg reflection region;
substep 1.3: carrying out rapid annealing treatment;
substep 1.4: removing the sacrificial layer by wet etching;
substep 1.5: sequentially epitaxially growing a cladding layer and a cover layer;
after the step 1 and before the step 2, a step of manufacturing an electric isolation groove on the cover layer and injecting He ions into the electric isolation groove is further included;
in the step 2, inductively coupled plasma etching is adopted to form an upper ridge waveguide on the cladding layer and the cover layer;
wherein the etching atmosphere is CH4/H2/O2The active layer is made of InGaAlAs and serves as an etching stop layer for dry etching of the upper ridge waveguide.
Technical Field
The invention relates to the field of optoelectronic devices, in particular to a tunable laser and a manufacturing method thereof.
Background
Laser, which is another great invention after computers and semiconductors for 20 th century, has the advantages of high brightness, good directivity, strong coherence, and the like. Long-distance, ultra-long distance, high-speed, ultra-large capacity optical fiber communication systems are a requirement for the development of modern information society. Both trunk networks and wide area networks for long-distance communications and local area networks, access networks, and short-range data-link optical switches for short-range communications require a large number of high-performance, low-cost optoelectronic devices to support the functionality of optical networks. Compared with other lasers, the semiconductor laser has the advantages of small volume, high efficiency, long service life, capability of batch production, direct modulation, monolithic integration and the like, and has led to wide research of domestic and foreign scholars.
Tunable lasers are one of the important components of wavelength division multiplexing systems for optical communications, and help to reduce the investment in system construction and maintenance. The use of the tunable laser can realize the colorless of the optical network unit in WDM-PON networking, which is beneficial to simplifying the system and reducing the system cost. DBR tunable lasers generally include three sections, a gain section, a phase section, and a distributed bragg reflector section (DBR section). By changing the injection current of the DBR section, the effective refractive index of the DBR section waveguide is changed, thereby realizing the tuning of the working wavelength of the laser. The phase area is loaded with current, so that the phase can be adjusted, and the continuous tuning of the laser is realized. The conventional DBR laser adopts a buried grating, and the scheme not only needs to increase the epitaxial growth times and influence the yield, but also has certain limitation on the material selection of an active layer. The surface coupling grating structure can reduce the epitaxial growth times, simplify the process steps and reduce the manufacturing cost.
The asymmetric epitaxial structure and the large refractive index difference of the semiconductor active device cause the end face of the active device to have small and elliptical near-field distribution. When light from a semiconductor active device is directly coupled into an optical fiber or light transmitted by an optical fiber is coupled into a semiconductor active device, the coupling loss may be as high as 10dB due to mode field mismatch between the optical fiber and the semiconductor active device. Coupling efficiency between them can be improved by means of lenses or tapered fibers, however these solutions still have the problem of mode field mismatch. These schemes only change the size of the mode field but not the shape of the mode field, with small alignment tolerances, which certainly increases the packaging cost.
Disclosure of Invention
It is therefore an object of the present invention to provide a tunable laser and a method for fabricating the same, which are intended to solve at least one of the above mentioned technical problems.
In order to achieve the purpose, the technical scheme of the invention is as follows:
as an aspect of the present invention, a tunable laser is provided, which includes a gain region and a distributed bragg reflector region located on a same substrate, and having equal heights and being attached to each other; wherein the content of the first and second substances,
the gain region and the distributed Bragg reflection region are respectively of a double-platform ridge waveguide structure and comprise a lower platform ridge waveguide and an upper platform ridge waveguide;
the lower ridge waveguide of the gain region and the lower ridge waveguide of the distributed Bragg reflection region respectively comprise a light spot amplification layer, a spacing layer and an active layer from bottom to top in sequence; the upper ridge waveguide of the gain region and the upper ridge waveguide of the distributed Bragg reflection region respectively comprise a cladding and a cover layer from bottom to top; wherein the content of the first and second substances,
the upper ridge waveguide of the gain region is a wedge waveguide;
the upper ridge waveguide of the distributed Bragg reflection region is a side wall grating waveguide.
As another aspect of the present invention, a method for manufacturing a tunable laser is also provided, including the following steps:
step 1: epitaxially growing a light spot amplification layer, a spacing layer, an active layer, a cladding and a cover layer on a substrate in sequence;
step 2: making the cladding and the cover layer into an upper ridge waveguide which comprises a wedge waveguide of a gain region and a side wall grating waveguide of a distributed Bragg reflection region;
and step 3: the active layer, the spacer layer and the spot amplifying layer are made as lower ridge waveguides of the gain region and the distributed Bragg reflection region.
Compared with the prior art, the invention has at least one or part of the following beneficial effects:
the traditional Distributed Bragg Reflection (DBR) laser adopts a buried grating structure, needs multiple epitaxial growth, has high requirements on epitaxial wafer cleanliness and epitaxial layer materials, adopts side-wall grating waveguide as the upper ridge waveguide of the distributed Bragg reflection region, and can reduce the times of epitaxial growth so as to improve the yield and reduce the cost; on one hand, the side wall grating of the distributed Bragg reflection region can provide necessary optical feedback for a gain region of the laser, and simultaneously, after current modulation is loaded on the DBR region, the output wavelength of the laser can be changed, and the wavelength tuning effect is realized; the wedge-shaped waveguide part of the gain area in the upper ridge waveguide of the laser can ensure the basic transverse mode work of the laser and can reduce the effective refractive index of the upper ridge waveguide, and in the process that the width of the waveguide is gradually narrowed, an Optical field is gradually coupled into the lower ridge waveguide of the lower wide platform from the upper ridge waveguide, the size of a light spot is amplified, the power density is reduced, the threshold value of the Optical Catastrophic Damage (COD) of the laser is improved, and the laser can work under the condition of high power; under the combined action of the far field reduction layer and the wedge-shaped waveguide, the optical field is coupled to the lower ridge waveguide, so that the overlapping of the optical field, the active layer and the p-type cladding layer is reduced, the absorption loss caused by doping is reduced, and the output power of the laser is increased; meanwhile, the far-field divergence angle of the laser is reduced, the coupling efficiency of the laser and the optical fiber is improved, and the packaging cost is reduced;
the active layer can adopt an InGaAlAs material with larger conduction band offset (delta Ec is 0.72 delta Eg, wherein the delta Ec refers to the energy difference of conduction bands of the InP material and the InGaAlAs material, and the delta Eg refers to the energy difference of forbidden bandwidths of the InP material and the InGaAlAs material), the material has stronger electron confinement capability, is beneficial to increasing the output power and the modulation bandwidth of a laser, and meanwhile, the laser linewidth of the material is narrower;
when the upper ridge waveguide structure is etched by Inductively Coupled Plasma (ICP), the InGaAlAs material of the active layer can be used as an etching stop layer for dry etching, so that the uniformity of the dry etching depth can be ensured.
Drawings
Fig. 1 is a schematic flow chart of a tunable laser manufacturing method according to embodiment 1 of the present invention;
FIG. 2 is a schematic view of the layer structure formed in step 1 of example 1 of the present invention;
FIG. 3 is a schematic view of the layer structure formed in step 2 of example 1 of the present invention;
FIG. 4 is a schematic view of the layer structure formed in step 4 of example 1 of the present invention;
FIG. 5 is a schematic perspective view of the layer structure formed in step 4 of example 1 of the present invention;
FIG. 6 is a schematic perspective view of the layer structure formed in step 6 of example 1 of the present invention;
fig. 7 is a schematic diagram of a tunable laser according to embodiment 1 of the present invention;
fig. 8 is a schematic diagram of a grating structure of a sidewall grating waveguide according to embodiment 1 of the present invention.
In the above figures, the reference numerals have the following meanings:
1: an n-type InP substrate; 2: an n-type InP buffer layer; 3: a light spot amplifying layer; 4: an InP spacer layer; 5: an InGaAlAs active layer; 6: an InP sacrificial layer; 7: a p-type InP cladding layer; 8: an InGaAs cap layer; 9: SiO 22A layer; 10: SiO 22A passivation layer; 11: a Ti/Au front electrode layer; 12: AuGeNi/Au back electrode layer.
Detailed Description
The invention relates to a manufacturing method of a Distributed Bragg Reflector (DBR-LD) semiconductor laser. The invention provides a tunable laser, which can amplify the spot size of the end face of the laser and improve the coupling efficiency of the laser and an optical fiber while realizing the function of wavelength tuning.
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.
As an aspect of the present invention, a tunable laser is provided, which includes a gain region and a distributed bragg reflector region located on a same substrate, and having equal heights and being attached to each other; wherein the content of the first and second substances,
the gain region and the distributed Bragg reflection region are respectively of a double-platform ridge waveguide structure and comprise a lower platform ridge waveguide and an upper platform ridge waveguide;
the lower ridge waveguide of the gain region and the lower ridge waveguide of the distributed Bragg reflection region respectively comprise a light spot amplification layer, a spacing layer and an active layer from bottom to top in sequence; the upper ridge waveguide of the gain region and the upper ridge waveguide of the distributed Bragg reflection region respectively comprise a cladding and a cover layer from bottom to top; wherein the content of the first and second substances,
the upper ridge waveguide of the gain region is a wedge waveguide;
the upper ridge waveguide of the distributed Bragg reflection region is a side wall grating waveguide.
In the embodiment of the invention, the tunable laser further comprises a phase region which is positioned on the substrate, the phase region has the same height and is positioned between the gain region and the distributed Bragg reflection region in a fitting manner;
the phase region is of a double-platform ridge waveguide structure and comprises a lower platform ridge waveguide and an upper platform ridge waveguide;
the lower ridge waveguide of the phase region sequentially comprises a light spot amplification layer, a spacing layer and an active layer from bottom to top; the upper ridge waveguide of the phase region comprises a cladding and a cover layer from bottom to top; wherein, the upper ridge waveguide of the phase area is a straight waveguide.
In an embodiment of the invention, an electrical isolation groove is respectively arranged among the gain region, the phase region and the distributed Bragg reflection region of the cover layer and used for electrical isolation of each region.
In the embodiment of the invention, the tunable laser further comprises a front electrode and a back electrode, wherein the front electrode is formed on the cover layers of the gain region, the phase region and the distributed Bragg reflection region; the back electrode is formed on the back surface of the substrate.
In the embodiment of the invention, the facula expanding layer of the gain region, the phase region and the distributed Bragg reflection region is a far field reduction layer or a diluting waveguide layer.
In the embodiment of the present invention, the speckle amplifying layer may be a far-field reduction layer, but is not limited thereto.
More specifically, in the embodiment of the present invention, when the far-field reduction layer is used as the spot amplifying layer, the thickness of the far-field reduction layer is thinner than that of other epitaxial layers of the laser. When the far-field reduction layer is made of InGaAsP material, the thickness is 40-60 nm; and the InGaAsP material has a lower index of refraction than other epitaxial layer materials (other than the InP material).
In other embodiments of the invention, when the spot amplification layer is a diluting waveguide layer, the diluting waveguide layer alternately grows for 3-5 periods by using an InGaAsP layer with a thickness of 60nm and an InP layer with a thickness of 300 nm.
In an embodiment of the invention, the active layers of the distributed bragg reflector region and the phase region are formed by a P-ion induced quantum well intermixing method.
In the embodiment of the present invention, the lower ridge waveguide of the gain region, the phase region, and the distributed bragg reflection region may be a straight waveguide, but is not limited thereto, and may also be a wedge waveguide or a trapezoid waveguide; as long as the minimum width of the lower ridge waveguide of the gain region, the phase region and the distributed bragg reflector region is greater than the maximum width of the upper ridge waveguide of the gain region, the phase region and the distributed bragg reflector region. However, the lower ridge waveguide of the gain region, the phase region and the distributed bragg reflector region of the preferred embodiment of the present invention is a straight waveguide for practical process considerations.
In an embodiment of the present invention, the width of the sidewall grating waveguide of the distributed bragg reflector region varies periodically in the length direction;
the width of the straight waveguide of the phase section is constant in the length direction.
The width of the wedge-shaped waveguide of the gain region is gradually reduced in a direction away from the distributed Bragg reflector region.
As another aspect of the present invention, a method for manufacturing a tunable laser is also provided, including the following steps:
step 1: epitaxially growing a light spot amplification layer, a spacing layer, an active layer, a cladding and a cover layer on a substrate in sequence;
step 2: making the cladding and the cover layer into an upper ridge waveguide which comprises a wedge waveguide of a gain region and a side wall grating waveguide of a distributed Bragg reflection region;
and step 3: the active layer, the spacer layer and the spot amplifying layer are made as lower ridge waveguides of the gain region and the distributed Bragg reflection region.
In the embodiment of the invention, in step 2, the cladding layer and the cover layer are made into the upper ridge waveguide, including the wedge waveguide of the gain region, the straight waveguide of the phase region and the side wall grating waveguide of the distributed Bragg reflection region.
In the embodiment of the invention, in the step 2, the upper ridge waveguide is formed on the cladding layer and the cover layer by adopting inductive coupling plasma etching;
wherein the etching atmosphere is CH4/H2/O2The active layer is made of InGaAlAs and serves as an etching stop layer for dry etching of the upper ridge waveguide.
In the embodiment of the invention, in
In the embodiment of the present invention, after
and 4, step 4: manufacturing a front electrode on the cover layer;
and 5: and manufacturing a back electrode on the back of the substrate.
In an embodiment of the present invention, step 1 comprises the following sub-steps:
substep 1.1: epitaxially growing a light spot amplification layer, a spacing layer, an active layer and a sacrificial layer on a substrate in sequence;
substep 1.2: injecting P ions into the sacrificial layers of the phase region and the distributed Bragg reflection region;
substep 1.3: carrying out rapid annealing treatment;
substep 1.4: removing the sacrificial layer by wet etching;
substep 1.5: and epitaxially growing a cladding layer and a cover layer in sequence.
In an embodiment of the present invention, after step 1 and before step 2 are performed, a step of fabricating an electrical isolation trench on the cap layer and injecting He ions into the electrical isolation trench is further included.
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.