Gain coupling type semiconductor laser based on quantum well internal mixing

Abstract

The invention belongs to the field of semiconductor lasers, and particularly relates to a gain coupling type semiconductor laser based on quantum well internal mixing, which comprises a substrate and an epitaxial structure grown on the substrate, and is characterized in that the epitaxial structure comprises a lower cladding, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding and a cover layer which are sequentially stacked from bottom to top; and a periodic quantum well internal mixing structure with a gain spectrum range different from that of the active layer is prepared in the active layer. The periodic quantum well internal mixing structure is prepared in the active layer to obtain the periodic gain in the active layer, the innate gain contrast ratio is achieved, the gain contrast ratio exists no matter how heavy the current is, and therefore high-power single longitudinal mode lasing can be stably achieved, and higher single longitudinal mode output power and better device performance are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor lasers, and in particular relates to a gain-coupled semiconductor laser based on quantum well internal mixing. Background Art

[0002] With the rapid development of technologies such as big data, cloud computing, quantum communication, 5G communication, and lidar, the performance requirements for lasers are constantly increasing, such as high power, narrow linewidth, tunability, high stability, high reliability, and high modulation rate. Semiconductor lasers with advantages such as small size, long service life, and high energy conversion efficiency are increasingly valued. Compared with FP cavity semiconductor lasers with wide linewidth and multi-longitudinal mode lasing, distributed feedback Bragg (DFB) semiconductor lasers with narrow linewidth, single longitudinal mode lasing, and direct modulation are becoming the core of various active devices. Compared with FP cavity semiconductor lasers, DFB semiconductor lasers add a grating layer above or below the active layer. The grating achieves resonance selection of a specific wavelength by periodically perturbing the physical parameters (refractive index or gain / loss) of the laser waveguide and active layer. Based on the different internal feedback mechanisms of the semiconductor, DFB semiconductor lasers can be divided into refractive index-coupled DFB semiconductor lasers and gain-coupled DFB semiconductor lasers. The refractive index-coupled DFB semiconductor laser mainly realizes laser lasing by periodically changing the refractive index and then periodically modulating the real part of the effective refractive index of the light field, while the gain-coupled DFB semiconductor laser realizes single longitudinal mode lasing by periodically modulating the imaginary part of the effective refractive index of the light field.

[0003] However, the refractive index-coupled DFB laser with uniform grating period has dual-mode lasing during operation, and its single-mode yield is low even if the end-face reflective film is introduced. Although stable single-mode lasing can be achieved by using a phase-shifted grating structure for mode selection, the single-mode characteristics deteriorate and the line width widens under high power due to the influence of spatial hole burning. The gain-coupled DFB semiconductor laser has the unique characteristic of the intrinsic mode with the lowest gain threshold, so it can stably lasing in single mode during operation without the need for mode selection.

[0004] At present, there are two methods to achieve gain-coupled DFB semiconductor lasers. The first method is to use micro-nanoscale grating preparation process and secondary epitaxial growth process to achieve gain coupling by directly etching gratings in the active layer or making non-absorption gratings near the active layer. However, nano-scale etching and secondary epitaxial processes are complex and the preparation cost is very high. Etching gratings near the active layer will also reduce the reliability and stability of the laser, which seriously limits the large-scale application of gain-coupled DFB semiconductor lasers. The second method is to periodically inject current into the active layer, so that the active layer periodically gains and achieves the effect of gain coupling. Although this method simplifies the process, due to the surface process being far away from the quantum well, the carrier concentration in the quantum well is not much different, and the gain difference is low. Therefore, the line width is wide during single longitudinal mode lasing, and as the injection current increases, the gain threshold contrast inside the active layer decreases under high injection current. After the quantum well is saturated, it presents a multi-mode working state, making it difficult to achieve high-power single-mode lasing. Summary of the invention

[0005] In view of the above technical problems, the present invention aims to provide a gain-coupled semiconductor laser based on quantum well internal mixing. To solve the above technical problems, the present invention adopts the following technical solutions: A gain-coupled semiconductor laser based on quantum well internal mixing comprises a substrate and an epitaxial structure grown on the substrate, wherein the epitaxial structure comprises a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer and a cap layer stacked in sequence from bottom to top, and a periodic quantum well internal mixing structure having a gain spectrum range different from that of the active layer is prepared in the active layer.

[0006] Furthermore, the periodicity of the hybrid structure in the quantum well is a uniform period, a phase shift period, or an optical length of each period is an integer multiple of half of the selected lasing wavelength.

[0007] Furthermore, a grating is prepared in the upper waveguide layer.

[0008] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. The present invention prepares a periodic quantum well inner mixed structure in the active layer to obtain a periodic gain in the active layer, and has an inherent gain contrast. The gain contrast exists no matter how large the current is, so it can stably realize high-power single longitudinal mode lasing, obtain higher single longitudinal mode output power and better device performance.

[0009] 2. Prepare a grating in the upper waveguide layer to play a mode selection role and obtain a stable, high-power, narrow-linewidth, single longitudinal mode output without mode hopping. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1is a schematic structural diagram of a gain-coupled semiconductor laser based on quantum well internal mixing provided according to Embodiment 1 of the present invention; Figure 2 It is a schematic structural diagram of a gain-coupled semiconductor laser based on quantum well internal mixing provided according to Example 2 of the present invention.

[0011] The reference numerals include: substrate 1 , lower cladding layer 2 , lower waveguide layer 3 , active layer 4 , upper waveguide layer 5 , upper cladding layer 6 , cap layer 7 , periodic quantum well internal mixing structure 8 and grating 9 . DETAILED DESCRIPTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0013] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0014] In order to solve the problem that the traditional gain-coupled DFB semiconductor laser has a complicated preparation process and the internal gain threshold contrast of the active layer is reduced under high injection current, and it is impossible to achieve stable high-power single longitudinal mode lasing under large current injection. The present invention innovatively proposes to use quantum well internal mixing technology to periodically induce partial quantum well structure in the quantum well material to change its gain spectrum, thereby increasing the gain contrast of the active layer and improving the current range of single longitudinal mode operation. It can also cooperate with the grating structure for mode screening to obtain a high-power single longitudinal mode device. A new solution is provided for achieving high-power stable single-mode output gain-coupled DFB lasers.

[0015] Example 1 Figure 1 The structure of a gain-coupled semiconductor laser based on quantum well internal mixing provided according to Embodiment 1 of the present invention is shown.

[0016] like Figure 1 As shown, the gain-coupled semiconductor laser based on quantum well internal mixing provided by Example 1 of the present invention includes a substrate 1, on which a lower cladding layer 2, a lower waveguide layer 3, an active layer 4, an upper waveguide layer 5, an upper cladding layer 6 and a cap layer 7 are sequentially grown using MOCVD technology, and the lower cladding layer 2, the lower waveguide layer 3, the active layer 4, the upper waveguide layer 5, the upper cladding layer 6 and the cap layer 7 constitute an epitaxial layer.

[0017] By using the quantum well internal mixing technology, a periodic quantum well internal mixing structure 8 is prepared in the active layer 4. The periodic quantum well internal mixing structure 8 has a gain spectrum range different from that of the active layer 4. In this way, regardless of the current injection situation, the gains of the active layer 4 and the periodic quantum well internal mixing structure 8 for the selected lasing wavelength always remain different, achieving a higher gain contrast, thereby forming a gain coupling effect of periodic gain.

[0018] Quantum well intermixing technology can be implemented in different ways, including but not limited to impurity-free vacancy diffusion induction, ion implantation, light induction, impurity induction and many other methods.

[0019] In quantum well hybridization technology, the center wavelength difference between the unhybridized part and the hybrid part can reach >20nm~100nm, and the gain peak intensity changes significantly.

[0020] Quantum well hybrid technology is usually applied to the laser cavity surface to form a periodic quantum well internal hybrid structure near the laser cavity surface to protect the cavity surface. The present invention does not form a periodic quantum well internal hybrid structure near the laser cavity surface, but forms a periodic quantum well internal hybrid structure inside the laser. It is not used for cavity surface protection, but for obtaining periodic gain, thereby achieving the effect of mode selection and single-mode lasing.

[0021] It should be noted that the periodic quantum well internal mixing structure can be a uniform period, a period with a phase shift, or the optical length of each period is an integer multiple of half the selected lasing wavelength.

[0022] Example 2 like Figure 2 As shown, the gain-coupled semiconductor laser based on quantum well internal mixing provided by Example 2 of the present invention includes a substrate 1, on which a lower cladding layer 2, a lower waveguide layer 3, an active layer 4, and an upper waveguide layer 5 are sequentially grown using MOCVD technology, and an upper cladding layer 6, a cap layer 7, and a grating 9 are prepared by grating lithography, etching, and secondary epitaxial growth technology.

[0023] By using the quantum well internal mixing technology, a periodic quantum well internal mixing structure 8 is prepared in the active layer 4. The periodic quantum well internal mixing structure 8 has a gain spectrum range different from that of the active layer 4. In this way, regardless of the current injection situation, the active layer 4 and the periodic quantum well internal mixing structure 8 always maintain different gains for the selected wavelength, achieving a higher gain contrast, thereby forming a gain coupling effect of periodic gain. At the same time, the selected lasing wavelength can also be one of the two or more wavelengths corresponding to the grating 9, thereby assisting the grating 9 in playing a mode selection role and obtaining a stable high-power narrow linewidth single longitudinal mode output without mode hopping.

[0024] The present invention utilizes quantum well internal mixing technology to realize a gain-coupled DFB semiconductor laser, so that no matter how high the current injection is, the gain contrast in the quantum well always exists and is maintained at a high level. A high-power single-mode gain-coupled DFB semiconductor laser can be independently realized, and a single mode of refractive index coupling can be selected for lasing in conjunction with the refractive index coupling of a grating. Generally speaking, the single-mode yield of the gain-coupled DFB semiconductor laser is improved, thereby improving the single longitudinal mode working power of the device under high current operation.

[0025] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0026] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A gain-coupled semiconductor laser based on quantum well internal mixing, comprising a substrate and an epitaxial structure grown on the substrate, wherein the epitaxial structure comprises a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper cladding layer and a cap layer stacked in sequence from bottom to top, characterized in that: A periodic quantum well inner mixed structure having a gain spectrum range different from that of the active layer is prepared in the active layer.

2. The gain-coupled semiconductor laser based on quantum well internal mixing according to claim 1, characterized in that: The periodicity of the hybrid structure in the quantum well is a uniform period, a phase shift period, or an optical length of each period is an integer multiple of half of the selected lasing wavelength.

3. The gain-coupled semiconductor laser based on quantum well internal mixing according to claim 1 or 2, characterized in that: A grating is fabricated in the upper waveguide layer.

Images