Distributed Feedback Semiconductor Laser Diode, Application and Preparation Method

Abstract

The present invention discloses a distributed feedback semiconductor laser diode, an application thereof, and a preparation method, including: a semiconductor substrate, a lower cladding layer deposited on the semiconductor substrate and made of the same conductive material as the semiconductor substrate, a semiconductor active layer deposited on the lower cladding layer and containing a ridge waveguide and a multi-quantum well gain layer, an upper cladding layer deposited on the semiconductor active layer, a semiconductor cover layer deposited on the upper cladding layer, and a conductive layer deposited on the semiconductor cover layer; the conductive layer has a non-metallized region, forming three current-free injection regions; a diffraction grating region is arranged in the semiconductor active layer; a phase-shifted grating is arranged in the diffraction grating region; the three current-free injection regions are located near the front end face of the laser diode, near the rear end face, and directly above the phase-shifted grating respectively; the current-free injection regions coincide with the peak positions of the side modes distributed along the ridge waveguide.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to a distributed feedback semiconductor laser diode, applications and preparation methods. Background Art

[0002] In the field of optical communication, many devices need to reduce the relative intensity noise (RIN) and the associated noise figure (NF), and RIN and NF usually have a constant offset relationship. For example: for a Fabry-Perot laser, people reduce RIN by increasing the cavity length of the resonator or increasing the reflectivity of the end face; for a distributed feedback laser, people more often reduce RIN by increasing the grating coupling strength. For a specific drive current, RIN can also be reduced by optimizing the maximum output optical power. The specific optimization method is a combination of low threshold current, high slope efficiency and high electro-optical conversion efficiency.

[0003] In addition, an analog distributed feedback laser diode is usually required to have a very low RIN in the frequency range of 10 MHz to 3 GHz. In this frequency domain range, the noise figure is determined by the side mode competition in the spectrum. Therefore, increasing the side mode suppression ratio of the device can effectively reduce RIN and further reduce the noise figure in the low frequency domain.

[0004] However, the chirped phase shift grating design of the prior art can achieve a relatively high (about 80%) single-mode yield on the premise of a high grating intensity, and its simulation test is as Figure 1 shown. It contains five curves, which are 2 times, 3 times, 4 times, 5 times and 6 times the threshold current respectively. It can be seen from the figure that a higher grating intensity is beneficial to reducing RIN and improving the high-speed characteristics of the device. However, so far, there is still no way to further increase the side mode suppression ratio in the prior art, and the industry still faces a 20% loss in the low side mode suppression ratio.

[0005] Therefore, there is an urgent need to propose a distributed feedback semiconductor laser diode, applications and preparation methods with a simple structure and an increased side mode suppression ratio. Summary of the Invention

[0006] In view of the above problems, the purpose of the present invention is to provide a distributed feedback semiconductor laser diode, applications and preparation methods. The technical solution adopted by the present invention is as follows:

[0007] First part, the present technology provides a distributed feedback semiconductor laser diode, which includes: a semiconductor substrate, a lower cladding layer deposited on the semiconductor substrate and made of the same conductive material as the semiconductor substrate, a semiconductor active layer deposited on the lower cladding layer and containing a ridge waveguide and a multi-quantum well gain layer, an upper cladding layer deposited on the semiconductor active layer, a semiconductor cover layer deposited on the upper cladding layer, and a conductive layer deposited on the semiconductor cover layer; the conductive layer has a non-metallized area and forms three non-current injection areas; a diffraction grating area is arranged in the semiconductor active layer; a phase shift grating is arranged in the diffraction grating area; the three non-current injection areas are respectively located at the upper part of the front end face of the semiconductor substrate, directly above the phase shift grating, and at the upper part of the rear end face of the semiconductor substrate; the non-current injection areas coincide with the side mode peak areas distributed along the ridge waveguide.

[0008] Second part, the present technology provides an application of a distributed feedback semiconductor laser diode, and the distributed feedback semiconductor laser diode is a buried heterostructure and / or a ridge waveguide structure.

[0009] Third part, the present technology provides a preparation method of a distributed feedback semiconductor laser diode, which includes the following steps:

[0010] Provide a semiconductor substrate;

[0011] Deposit a lower cladding layer made of the same conductive material as the semiconductor substrate on the semiconductor substrate;

[0012] Deposit a semiconductor active layer containing a ridge waveguide and a multi-quantum well gain layer on the lower cladding layer;

[0013] Deposit an upper cladding layer on the semiconductor active layer;

[0014] Deposit a semiconductor cover layer on the upper cladding layer;

[0015] And deposit a conductive layer on the semiconductor cover layer; a diffraction grating area is arranged in the semiconductor active layer; a phase shift grating is arranged in the diffraction grating area; the conductive layer has a non-metallized area and forms three non-current injection areas; the three non-current injection areas are respectively located at the upper part of the front end face of the semiconductor substrate, directly above the phase shift grating, and at the upper part of the rear end face of the semiconductor substrate; the non-current injection areas coincide with the side mode peak areas distributed along the ridge waveguide.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention ingeniously adds a current-free injection region to a DFB laser with a phase-shifted grating, effectively improving the side-mode suppression ratio. The present invention introduces a loss region at the position where the side-mode intensity of the laser resonator is the largest, and by studying the optical mode loss and the change of the longitudinal optical mode intensity along the length of the resonator, it is confirmed that the yield of the side-mode suppression ratio is effectively improved. In summary, the present invention has the advantages of simple structure and improved side-mode suppression ratio, and has high practical value and popularization value in the field of semiconductor technology. Brief Description of the Drawings

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope of protection. For those skilled in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a simulation schematic diagram of the single-mode yield of the phase-shifted chirped grating when the grating intensity is 3 in the present invention.

[0020] Figure 2 It is a structural schematic diagram of the present invention.

[0021] Figure 3 It is a simulation fundamental mode curve diagram of the present invention.

[0022] Figure 4 It is a material gain comparison diagram of the laser diode along the length of the resonator in the present invention.

[0023] Figure 5 It is a refractive index comparison diagram of the laser diode along the length of the resonator in the present invention.

[0024] Figure 6 It is a first-order optical mode simulation curve diagram of the present invention.

[0025] Figure 7 It is a second-order optical mode simulation curve diagram of the present invention.

[0026] Figure 8 It is a simulation diagram of the side-mode suppression ratio with different lengths of the current-free injection region in the present invention.

[0027] Figure 9 It is a simulation diagram of the threshold current with different lengths of the current-free injection region in the present invention.

[0028] Figure 10 It is a simulation diagram of the output optical power with different lengths of the current-free injection region in the present invention.

[0029] Figure 11 It is a simulation result of the noise figure in the frequency domain in the present invention.

[0030] In the above-mentioned drawings, the component names corresponding to the reference numerals are as follows:

[0031] 1. Semiconductor substrate; 2. High-reflection film; 3. Lower cladding layer; 4. Phase-shift grating; 5. Semiconductor active layer; 6. Upper cladding layer; 7. Semiconductor covering layer; 8. Conductive layer; 9. Transparent film; 10. Diffraction grating region. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present application clearer, the present invention will be further described below with reference to the drawings and embodiments. The implementation manners of the present invention include but are not limited to the following embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the scope of protection of the present application.

[0033] In this embodiment, the term "and / or" only describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0034] The terms "first", "second", etc. in the description and claims of this embodiment are used to distinguish different objects rather than to describe a specific order of the objects. For example, the first target object and the second target object are used to distinguish different target objects rather than to describe a specific order of the target objects.

[0035] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0036] In the description of the embodiments of the present application, unless otherwise specified, the meaning of "a plurality of" refers to two or more. For example, a plurality of processing units refers to two or more processing units; a plurality of systems refers to two or more systems.

[0037] As Figures 2 to 11 shown, this embodiment provides a distributed feedback semiconductor laser diode. This embodiment solves the technical problem in the prior art that the single-mode yield of the chirped phase-shift grating can only reach about 80% on the premise of a high grating intensity. In this embodiment, a current-free injection region is added to a DFB laser with a phase-shift grating, and by studying the optical mode loss and the longitudinal optical mode intensity change along the length of the resonant cavity, it is confirmed that the side-mode suppression ratio yield is effectively improved.

[0038] Specifically, the distributed feedback semiconductor laser diode of this embodiment includes: a semiconductor substrate 1, a lower cladding layer 3 deposited on the semiconductor substrate 1 and made of the same conductive material as the semiconductor substrate, a semiconductor active layer 5 deposited on the lower cladding layer 3 and containing a ridge waveguide and a multi-quantum well gain layer, an upper cladding layer 6 deposited on the semiconductor active layer, a semiconductor cover layer 7 deposited on the upper cladding layer, and a conductive layer 8 deposited on the semiconductor cover layer; the conductive layer has non-metallized regions, forming three current-free injection regions; a diffraction grating region 10 is arranged in the semiconductor active layer; a phase shift grating 4 is arranged in the diffraction grating region; the three current-free injection regions are located near the front end face of the laser diode, near the rear end face, and directly above the phase shift grating respectively; the current-free injection regions coincide with the edge mode peak regions (i.e., Figure 3 the vertex of the peak region in the figure is located at about 22.5 microns on the abscissa).

[0039] Among them, the semiconductor substrate and the semiconductor active layer are made of different conductive materials; the semiconductor active layer, the upper cladding layer, the semiconductor cover layer, and the conductive layer are made of the same conductive material. For example: if the semiconductor substrate and the lower cladding layer are N-type, then the semiconductor active layer, the upper cladding layer, the semiconductor cover layer, and the conductive layer are P-type; conversely, if the semiconductor substrate and the lower cladding layer are P-type, then the semiconductor active layer, the upper cladding layer, the semiconductor cover layer, and the conductive layer are N-type. The distributed feedback semiconductor laser diode of this embodiment can be a buried heterostructure, or a ridge waveguide structure; it can also be a hybrid structure of a buried heterostructure and a ridge waveguide structure; a high reflection film 2 or a transparent film 9 is plated on the light output end face. In this embodiment, the high reflection film 2 is distributed on the rear end faces of the semiconductor substrate 1, the lower cladding layer 3, the semiconductor active layer 5, the upper cladding layer 6, and the semiconductor cover layer 7, and the transparent film 9 is on the front end faces of the semiconductor substrate 1, the lower cladding layer 3, the semiconductor active layer 5, the upper cladding layer 6, and the semiconductor cover layer 7.

[0040] In addition, the semiconductor active layer of this embodiment is an AlGaInAsP alloy. In addition, a diffraction grating 10 for generating a single longitudinal mode is arranged in the semiconductor active layer.

[0041] As Figure 2 shown, this embodiment is based on a DFB single-mode laser with a phase shift grating, the cavity length is 175um, the rear end face is plated with a high reflection film, and the front end face is plated with a transparent film of less than 0.5%. The diffraction grating has a phase shift structure with a length of 60um and a value of 7 / 10 pi, and its center is 110um away from the front end face.

[0042] In this embodiment, by adding three current-free injection regions to a DFB laser with a phase-shifted grating, the side mode suppression ratio can be improved. In an application example, the middle current-free injection region is located directly above the phase-shifted grating structure and has a length of 60 μm. The current-free injection regions on both sides can be placed near the front end face and / or the rear end face of the laser, with a length of 7.5 μm. Since the intensity of the fundamental optical mode is very low at the front and rear end faces of the laser, the presence of the current-free injection regions does not affect the device performance. Its simulation test is as Figure 3 shown. Figure 3 In the simulation device, the cavity length is 175 μm; -87.5 μm and 87.5 μm correspond to the positions of the front end face and the rear end face respectively. Figure 3 The peak center in it is located at the abscissa of 22.5 μm, corresponding to the center of the current-free injection region, 110 μm away from the front end face. As Figure 4 shown, the intensity of the side modes with lower power is higher at the front and rear end faces of the laser. Therefore, the current-free injection regions can suppress the side mode intensity. As Figures 5 to 7 shown, the current-free injection regions also have a relatively high refractive index, which can "pull" the side modes into the absorption region, which is also beneficial for improving the side mode suppression ratio.

[0043] As Figure 8 shown, by applying this method, for most end-face phase spaces with a side mode suppression ratio greater than 30 dB, the noise figure can be increased by more than 10 dB. Further, adding a current-free injection region at the rear end face of the laser also has a significant improvement for devices with an original side mode suppression ratio less than 30 dB. In this way, while reducing the RIN, the optical output power, threshold current, and high-speed characteristics do not decrease significantly, as shown in Figure 9 and Figure 10 shown. As Figure 11 shown, as the SMSR increases, the noise figure will also improve by several decibels.

[0044] The above embodiments are only the preferred embodiments of the present invention, and do not limit the protection scope of the present invention. Any changes made by adopting the design principle of the present invention and non-creative labor on this basis shall fall within the protection scope of the present invention.

Claims

1. Distributed feedback semiconductor laser diode, characterized in that, Comprising: A semiconductor substrate, a lower cladding layer deposited on the semiconductor substrate and made of the same conductive material as the semiconductor substrate, a semiconductor active layer deposited on the lower cladding layer and containing a ridge waveguide and a multi-quantum well gain layer, an upper cladding layer deposited on the semiconductor active layer, a semiconductor cover layer deposited on the upper cladding layer, and a conductive layer deposited on the semiconductor cover layer; The conductive layer has a non-metallized region and forms three current-free injection regions; a diffraction grating region is disposed in the semiconductor active layer; a phase-shift grating is disposed in the diffraction grating region; the three current-free injection regions are respectively located at the upper part of the front end face of the semiconductor substrate, directly above the phase-shift grating, and at the upper part of the rear end face of the semiconductor substrate; the current-free injection regions coincide with the edge mode peak regions distributed along the ridge waveguide.

2. The distributed feedback semiconductor laser diode according to claim 1, wherein The semiconductor substrate and the semiconductor active layer are made of different conductive materials; the semiconductor active layer, the upper cladding layer, the semiconductor cover layer and the conductive layer are made of the same conductive material.

3. The distributed feedback semiconductor laser diode according to claim 1 or 2, characterized in that, The semiconductor active layer is an AlGaInAsP alloy.

4. The distributed feedback semiconductor laser diode according to claim 1 or 2, characterized in that, The semiconductor active layer is provided with a diffraction grating containing a phase-shift grating for generating a single longitudinal mode.

5. The distributed feedback semiconductor laser diode according to claim 4, characterized in that, The light output end faces of the semiconductor substrate, the lower cladding layer, the semiconductor active layer, the upper cladding layer, the semiconductor cover layer and the conductive layer are coated with a high-reflection film or a transparent film.

6. A method for preparing a distributed feedback semiconductor laser diode, characterized in that, Including the following steps: Providing a semiconductor substrate; Depositing a lower cladding layer made of the same conductive material as the semiconductor substrate on the semiconductor substrate; Depositing a semiconductor active layer containing a ridge waveguide and a multi-quantum well gain layer on the lower cladding layer; Depositing an upper cladding layer on the semiconductor active layer; Depositing a semiconductor cover layer on the upper cladding layer; And depositing a conductive layer on the semiconductor cover layer; a diffraction grating region is disposed in the semiconductor active layer; a phase-shift grating is disposed in the diffraction grating region; the conductive layer has a non-metallized region and forms three current-free injection regions; the three current-free injection regions are respectively located at the upper part of the front end face of the semiconductor substrate, directly above the phase-shift grating, and at the upper part of the rear end face of the semiconductor substrate; the current-free injection regions coincide with the edge mode peak regions distributed along the ridge waveguide.

7. The manufacturing method of a distributed feedback semiconductor laser diode according to claim 6, characterized in that, Further comprising: Coating a layer of high-reflection film or transparent film on the light output end faces of the semiconductor substrate, the lower cladding layer, the semiconductor active layer, the upper cladding layer, the semiconductor cover layer and the conductive layer.

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