High-slope efficiency surface grating surface emitting laser

Abstract

The utility model relates to the technical field of lasers, and discloses a high-slope-efficiency surface grating surface emitting laser which comprises a substrate, a lower waveguide layer, an active layer and an upper waveguide layer from bottom to top along the cross section. A ridge-shaped waveguide is formed in the middle area of the uppermost layer of the upper waveguide layer, and a Bragg grating is etched on the surface of the ridge-shaped waveguide; the Bragg grating comprises a section of second-order grating located in the middle and two sections of first-order gratings located at the two ends; a lambda / 4 phase shift is arranged in the second-order grating; the lambda / 4 phase shift is located in an etching area or a non-etching area of the first-order grating closest to the second-order grating; when the lambda / 4 phase shift is located in the etching region of the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is maximum, and the downward diffraction light power is minimum; when the lambda / 4 phase shift is located in the non-etching area of the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is minimum, and the downward diffraction light power of the second-order grating is maximum. According to the invention, high-slope efficiency lasing can be realized.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and in particular to a high slope efficiency surface grating surface emitting laser. Background Art

[0002] A typical example of a surface-emitting laser is the vertical-cavity surface-emitting laser (VCSEL), which is widely used in optical communications, optical sensing, optical pumping and other application scenarios due to its advantages such as low cost, low power consumption and circular spot. The resonant cavity of the VCSEL is along the direction of epitaxial growth, and the cavity length is very short, which makes the longitudinal mode spacing of the VCSEL naturally large and has excellent single longitudinal mode characteristics; however, due to the cylindrical table structure of the VCSEL itself, it lacks lateral restrictions on the light field, making it very difficult for the VCSEL to achieve a single transverse mode. Single-mode lasers, due to their high coherence, narrow spectral width, and wavelength stability, can improve the transmission rate and transmission distance in optical communications, improve the resolution and response speed in optical sensing, and improve the pumping efficiency in optical pumping.

[0003] Especially for the huge market of short-distance communications for data centers, as data capacity increases, higher requirements are placed on the data transmission rate and transmission distance of VCSELs. However, due to its wider spectral width compared to single-mode lasers, existing multi-mode VCSELs are extremely difficult to maintain the original transmission distance of the multi-mode optical fiber link in the data center while increasing the transmission rate. On the other hand, multi-mode VCSELs are prone to high-order transverse modes when the injection current increases. The appearance of high-order transverse modes will limit the direct modulation bandwidth of the laser (YC Hang, et al., "High-efficiency, high-speed VCSELs with 35Gb / s error-free operation," Electron. Lett., vol. 43, no. 19, pp. 1022-1023, Sep. 2007.). Therefore, single-mode surface emitting lasers have huge application potential.

[0004] By shrinking the oxide aperture of the VCSEL, the area of ​​the optical mode can be reduced, and at the same time, the area of ​​current injection can be reduced, limiting the generation of high-order transverse modes, thereby achieving single longitudinal mode lasing and achieving high modulation bandwidth (N. Ledentsov Jr., L. Chorchos, M. Agustin, NN Ledentsov and JP Turkiewicz, "850nm single-mode VCSEL for error-free 60Gbit / s OOK operation and transmission through 800mof multi-mode fiber," in Optical Fiber Communication Conference, paper. W3A.2, 2019.). However, an overly small oxide aperture can lead to excessively high injection current density, causing reliability issues. Etching a surface relief of the distributed Bragg reflector (DBR) on the VCSEL can introduce additional losses to the high-order transverse modes, thereby achieving single transverse mode lasing with a relatively large oxide aperture (E.Haglund, M.Jahed, JSGustavsson, A.Larsson, J.Goyvaerts, R.Baets et al. High-power single transverse and polarization mode VCSEL for silicon photonics integration. Optics Express, 2019, 27(13): 18892-18899.), but the surface relief is extremely sensitive to the etching depth, which requires extremely high etching precision and poor consistency. Replacing the upper DBR of a VCSEL with a high-contrast grating that provides sufficient feedback only for the fundamental mode can filter out high-order transverse modes and achieve single-transverse-mode lasing (CJ Hasnain, W. Yang. High-contrast gratings for integrated optoelectronics. Advances in Optics and Photonics, 2012, 4(3): 379-440.). However, this high-contrast grating is a suspended grating structure. Suspended structures are not only difficult to manufacture but also suffer from stress issues, and may have stability issues in actual packaging applications.

[0005] In addition to vertical cavity surface emitting lasers, horizontal cavity surface emitting lasers can also be used to make surface emitting lasers. Usually, horizontal cavity surface emitting lasers use the excellent single-mode characteristics of distributed feedback DFB laser structure or DBR laser structure, plus an additional vertical diffraction body to achieve single-mode surface emission. This diffraction body mainly includes 45° reflector (Martin et al.,"1300-nm Horizontal-Cavity Surface-Emitting BH-DFB Lasers for Uncooled Operation."IEEE Photonics Technology Letters,vol.18,pp.962-964,1995.) and a second-order Bragg grating. Single-mode surface emission can be achieved by combining a DFB structure with a second-order Bragg grating (N.Eriksson,M.Hagberg,and A.Larsson,"Highly efficient grating-coupled surface-emitters with single outcouplingelements."IEEE Photonics Technology Letters,vol.7,pp.1394-1396,1995.). However, due to the relatively large volume of this type of horizontal cavity, its threshold is relatively large, which results in high laser power consumption. Horizontal-cavity surface-emitting lasers can also reduce the active region volume by oxidizing the aperture to reduce the threshold current and power consumption (Liu C, Zhang P, Xiang M, et al. Single mode surface-emitting DFB lasers with a large-area oxidized aperture based on surface grating. Optics Letters, 2020, 45(13): 3573.), but this type of laser usually has low slope efficiency.

[0006] In summary, existing vertical cavity surface emitting lasers have difficulty in single transverse mode lasing, while existing horizontal cavity surface emitting lasers have problems with low slope efficiency and output power. Utility Model Content

[0007] The purpose of the present application is to provide a high-slope-efficiency surface grating surface-emitting laser, which is based on a DFB laser structure, adopts a first-order Bragg grating to provide feedback and longitudinal mode selection, and utilizes a ridge waveguide structure to limit the transverse mode, resonates the laser at the Bragg wavelength through a λ / 4 phase shift, utilizes a second-order grating to vertically diffract light, and finally, by designing the position of the λ / 4 phase shift at the second-order grating, greatly increases the proportion of the second-order grating's upward diffracted light power to the total diffracted light power, thereby achieving high-slope-efficiency lasing.

[0008] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0009] A high-slope-efficiency surface grating surface-emitting laser comprises, from bottom to top along a cross-section, a substrate, a lower waveguide layer, an active layer, and an upper waveguide layer; a ridge waveguide is formed in the middle region of the uppermost layer of the upper waveguide layer, and a Bragg grating is etched on the surface of the ridge waveguide; the Bragg grating comprises a second-order grating in the middle and two first-order gratings at both ends; a λ / 4 phase shift is provided in the second-order grating, and the Bragg grating is filled with a low-refractive-index medium;

[0010] The λ / 4 phase shift is located in the etched area or the non-etched area of ​​the first-order grating closest to the second-order grating; when the λ / 4 phase shift is located in the etched area of ​​the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is maximum, and the downward diffraction light power is minimum; when the λ / 4 phase shift is located in the non-etched area of ​​the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is minimum, and the downward diffraction light power is maximum.

[0011] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, the slope efficiency of the laser is determined according to the number of second-order grating periods.

[0012] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, the low refractive index medium is filled in the Bragg grating by spin-on glass, plasma enhanced chemical vapor deposition growth of silicon oxide or silicon nitride, atomic layer deposition growth of silicon oxide, aluminum oxide, silicon nitride or tetraethoxysilane deposition of silicon oxide, etc.

[0013] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, a lower ohmic contact layer and a lower electrode layer are sequentially provided between the substrate and the lower waveguide layer; an upper ohmic contact layer and an upper electrode layer are sequentially provided at the upper end of the upper waveguide layer.

[0014] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, the lower waveguide layer is P-type or N-type doped, the active layer is undoped, and the upper waveguide layer is N-type or P-type doped.

[0015] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, the lower waveguide layer comprises one or more high resistance regions; and the active layer comprises one or more quantum well structures and one or more optical confinement layer structures.

[0016] Preferably, in the above-mentioned high slope efficiency surface grating surface emitting laser, the upper waveguide layer and the active layer are connected via one or more high conductivity layers.

[0017] The beneficial effects of this application are:

[0018] This application designs the position of the λ / 4 phase shift at the second-order grating, controls the relative position of the longitudinal standing wave field and the grating, increases the proportion of light power diffracted vertically upward by the second-order grating, and greatly improves the slope efficiency of the laser without introducing additional losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure shows a structural diagram of a high slope efficiency surface grating surface emitting laser according to an embodiment of the present application.

[0020] Figure 2 A schematic diagram of the cross-sectional structure of the laser active DFB region and the passive DBR reflection region under the high aluminum composition oxide layer limiting current injection scheme according to an embodiment of the present application is shown; wherein, (A) is the laser active DFB region; (B) is the passive DBR reflection region.

[0021] Figure 3 A schematic diagram of the longitudinal structure of a high slope efficiency surface grating surface emitting laser according to an embodiment of the present application is shown.

[0022] Figure 4 The light field distribution diagram is shown when the λ / 4 phase shift is located in the first-order grating etched area adjacent to the second-order grating according to an embodiment of the present application.

[0023] Figure 5 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the first period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0024] Figure 6 The light field distribution diagram is shown when the λ / 4 phase shift is located in the etched area of ​​the first period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0025] Figure 7 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the second period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0026] Figure 8 The light field distribution diagram is shown when the λ / 4 phase shift is located in the etched area of ​​the second period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0027] Figure 9 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the third period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0028] Figure 10 The light field distribution diagram is shown when the λ / 4 phase shift is located in the etched area of ​​the third period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0029] Figure 11 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the fourth period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0030] Figure 12 The light field distribution diagram is shown when the λ / 4 phase shift is located in the etched area of ​​the fourth period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0031] Figure 13 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the fifth period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0032] Figure 14 The light field distribution diagram is shown when the λ / 4 phase shift is located in the etched area of ​​the fifth period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0033] Figure 15 The light field distribution diagram is shown when the λ / 4 phase shift is located in the non-etched area of ​​the fifth period of the second-order grating according to an embodiment of the present application (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0034] Figure 16 A simulation structure diagram of a high slope efficiency surface grating surface emitting laser according to an embodiment of the present application is shown.

[0035] Figure 17A diagram showing the relationship between the vertically upward and downward normalized optical power of the second-order grating and the ratio of the vertically upward diffracted optical power of the second-order grating to the total diffracted optical power and the λ / 4 phase shift position according to an embodiment of the present application is shown; wherein, (A) is the relationship between the vertically upward and downward normalized optical power of the second-order grating and the λ / 4 phase shift position; (B) is the relationship between the ratio of the vertically upward diffracted optical power of the second-order grating to the total diffracted optical power and the λ / 4 phase shift position.

[0036] Figure 18 A graph showing the vertical upward output optical power of a laser according to an embodiment of the present application as a function of the injected current is shown. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0038] The specific implementation of the present application is further described in detail below with reference to the accompanying drawings and examples.

[0039] Figure 1 The structure diagram of a high slope efficiency surface grating surface emitting laser according to an embodiment of the present application is shown. The lateral, transverse and longitudinal directions of the laser are respectively marked as x, y and z directions, and all schematic diagrams use the same spatial coordinate system and markings. The embodiment of the present application provides a high slope efficiency surface grating surface emitting laser. Figure 1 As shown, the high slope efficiency surface grating surface emitting laser includes a substrate 1, a lower ohmic contact layer 2, a lower electrode layer 3, a lower waveguide layer 4, a high resistance region 5, an active layer 6, a conductive layer 7, an upper waveguide layer 8, an upper ohmic contact layer 9, and an upper electrode layer 10 along the cross section from bottom to top. Among them, the lower waveguide layer 4 is P-type or N-type doped, the active layer 6 is undoped, and the upper waveguide layer 8 is N-type or P-type doped. The upper waveguide layer 8, the active layer 6 and the lower waveguide layer 4 together constitute a NiP or PiN structure. The lower ohmic contact layer 2 is heavily doped with P-type or N-type, and the doping concentration range is 10 18 ~10 19 cm -3, used to form an ohmic contact. The lower waveguide layer 4 contains one or more high resistance regions 5, which are mainly used to limit the injection area of ​​current. The active layer 6 contains one or more quantum well structures and one or more light confinement layer structures, which are used to provide gain for light. The quantum well structure of the active layer 6 can also be replaced by a bulk material, quantum wire, or quantum dot structure that also has a gain effect. The upper waveguide layer 8 and the active layer 6 are connected by one or more layers of high conductivity layer 7. A ridge waveguide 11 structure is etched on the upper waveguide layer 8. A grating structure is etched on the ridge waveguide 11 structure, including a second-order grating 13 in the middle for coupling out light and first-order gratings 12 on both sides for providing feedback.

[0040] Figure 2 FIG. 1 shows a schematic cross-sectional structure diagram of the laser active DFB region 16 and the passive DBR reflection regions 14 and 15 under the scheme of limiting current injection using a high aluminum content oxide layer according to an embodiment of the present application. Figure 2 As shown in (A), there is a high-aluminum current confinement layer 5 in the lower waveguide layer 4 of the laser near the active layer 6. The aluminum content of this layer is higher than 80%, and it can be oxidized to an insulating (AlGa) under high temperature and high humidity conditions. x O y The oxidation process is from the outside to the inside along the edge of the mesa. The oxidized part will form a high resistance area, and the unoxidized part will form a rectangular current injection aperture as a whole, so that the current can only be injected from the unoxidized aperture. Figure 2 As shown in (B), the epitaxial structure of the passive DBR reflective regions 14 and 15 is identical to that of the active DFB region 16, except that their mesa width is narrower than the latter. The high-aluminum composition layer of the passive DBR reflective regions 15 and 16 will also oxidize from the outside inward under high temperature and high humidity conditions. Due to their narrower mesas, when the active DFB region 16 partially oxidizes to form a current injection limiting aperture, the high-aluminum composition layer 5 of the passive DBR reflective regions 14 and 15 will be completely oxidized to an insulating (AlGa) layer. x O y , preventing current injection into this region and providing only optical feedback. The overall passive DBR-active DFB-passive DBR three-section structure restricts current injection to the current-injection-limiting aperture directly below the 16-ridge waveguide in the active DFB region, improving injection efficiency and reducing the active region volume.

[0041] The upper waveguide layer 8 is etched to a depth of H. r The ridge waveguide 11 has an etching depth of H gThe surface grating includes a first-order grating 12 that provides feedback and a second-order grating 12 located in the middle of the first-order grating for vertically diffracting light. In order to obtain high feedback, the ridge waveguide 11 should be as thin as possible so that most of the light field is confined to the ridge waveguide, thereby having sufficient overlap with the grating. In order to avoid the absorption of the light field in the ridge waveguide 11 by the upper ohmic contact layer 9 and the upper electrode layer 10, the upper electrode layer 10 is made on both sides of the ridge waveguide 11 in the active DFB region 16, separated by a groove greater than 500nm in the middle, and no electrodes are made in the passive DBR reflection regions 14 and 15 at both ends. The upper electrode layer 10 is grown on the upper ohmic contact layer 9. The grating etching depth Hg and the ridge waveguide height Hr can be adjusted according to actual needs. Grating etching depth H g The deeper the ridge waveguide, the greater the coupling coefficient of the grating, and the stronger the optical feedback provided by the grating. r The thinner it is, the more concentrated the light field distribution is in the ridge waveguide, the stronger the interaction with the grating, the larger the coupling coefficient of the grating, and the stronger the feedback ability of the grating. g It should not be too deep. g This will cause the confinement of the ridge waveguide to weaken, the light field will leak to both sides, and the loss will increase.

[0042] Because this laser uses a surface grating structure, a low-refractive-index medium must be used to fill the grating to ensure its stability and protect it from external environmental influences. Possible filling methods for the Bragg grating include: spin-on-glass (SOG); plasma-enhanced chemical vapor deposition (PECVD)-grown silicon oxide or silicon nitride; and atomic layer deposition (ALD)-grown silicon oxide, aluminum oxide, or silicon nitride.

[0043] Figure 3 FIG. 5 shows a schematic diagram of the longitudinal structure (zy plane) of a high slope efficiency surface grating surface emitting laser according to an embodiment of the present application. Figure 3 As shown, a first-order grating 12 is engraved on the surface of the ridge waveguide 11, and a second-order Bragg grating 13 of several periods is inserted in the center of the first-order grating. The period of the first-order grating 12 is Λ=λ B / 2n eff , the period of the second-order grating 13 is Λ=λ B / n eff , the etching depth is H g . Where λ B is the Bragg wavelength, n effThe effective refractive index is λ / 4. The phase shift region is inserted into the second-order grating 13 to ensure that the laser can stably operate at the Bragg wavelength λ. B At the same time, the light field is concentrated at the second-order grating 13 to facilitate vertical diffraction of light. The more the number of second-order gratings 13, the stronger its vertical diffraction ability is, but the more loss is introduced. The number of second-order gratings 13 can be determined according to the actual performance requirements of the laser. Figure 3 The second-order grating 13 is located in the center of the active DFB region 16, with first-order gratings 12 on both sides. The DBR reflection regions 14 and 15 at both ends are first-order gratings 12. The upper electrode layer 10 is made on both sides of the ridge waveguide 11 of the active DFB region 16, and the high aluminum component layer 5 directly below it is in an unoxidized state. Carriers can be injected from the unoxidized area directly below the ridge waveguide 11 along the upper electrode layer 10 on both sides. The passive DBR reflection regions 14 and 15 do not have electrodes, and the high aluminum component layer 5 directly below the ridge waveguide 11 is completely oxidized to (AlGa). x O y , there is no current injection, it only provides feedback to reduce the threshold current.

[0044] The position of the λ / 4 phase shift region at the second-order grating will affect the distribution of the standing wave field at the second-order grating, thereby affecting the vertical diffraction light characteristics of the second-order grating. Figures 4 to 15 The figures show the longitudinal schematic diagrams and light field distribution diagrams of 12 cases where the λ / 4 phase shift region is located in the etched area and non-etched area of ​​the first-order grating at five different periods of the second-order grating and one adjacent period. The 12 cases are:

[0045] Case 1: λ / 4 phase shift located in the first-order grating etched area adjacent to the second-order grating

[0046] Case 2: The λ / 4 phase shift is located in the non-etched region of the first period of the second-order grating (the etched region adjacent to the first-order grating is defined as the first period of the second-order grating).

[0047] Case 3: The λ / 4 phase shift is located in the etched area of ​​the first period of the second-order grating (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0048] Case 4: The λ / 4 phase shift is located in the non-etched region of the second period of the second-order grating (the etched region adjacent to the first-order grating is defined as the first period of the second-order grating).

[0049] Case 5: The λ / 4 phase shift is located in the etched area of ​​the second period of the second-order grating (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0050] Case 6: The λ / 4 phase shift is located in the non-etched region of the third period of the second-order grating (the etched region adjacent to the first-order grating is defined as the first period of the second-order grating).

[0051] Case 7: The λ / 4 phase shift is located in the etched area of ​​the third period of the second-order grating (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0052] Case 8: The λ / 4 phase shift is located in the non-etched region of the fourth period of the second-order grating (the etched region adjacent to the first-order grating is defined as the first period of the second-order grating).

[0053] Case 9: The λ / 4 phase shift is located in the etched area of ​​the fourth period of the second-order grating (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0054] Case 10: The λ / 4 phase shift is located in the non-etched region of the fifth period of the second-order grating (the etched region adjacent to the first-order grating is defined as the first period of the second-order grating).

[0055] Case 11: The λ / 4 phase shift is located in the etched area of ​​the fifth period of the second-order grating (the etched area adjacent to the first-order grating is defined as the first period of the second-order grating).

[0056] Case 12: The λ / 4 phase shift is located in the non-etched area of ​​the first-order grating adjacent to the five-period second-order grating.

[0057] Phase shift at different positions will affect the overall longitudinal standing wave field distribution, thereby affecting the antinode or node of the light field under the second-order grating etching area as the standing wave field. When the antinode of the standing wave field is located directly below the second-order grating etching area, light is more likely to leak upward, thereby increasing the proportion of upward diffraction. When the node of the standing wave field is located directly below the second-order grating etching area, light is not easy to leak upward, thereby increasing the proportion of downward diffraction of the second-order grating. In order to further illustrate the influence of the λ / 4 phase shift position on the diffraction performance of the second-order grating, the time-domain finite difference method (FDTD) is used to perform the following simulation: the longitudinal (along the z propagation direction) first-order grating period is set to 128nm, the number of periods is 1200, the second-order grating 13 is inserted in the middle of the first-order grating, the period is 256nm, and the number of periods is 5; the corresponding Bragg wavelength is 850nm; the waveguide fundamental mode light source is input from the left end; the light output power at the top and bottom of the second-order grating 13 under different phase shift conditions is monitored, as shown in FIG. Figure 16 shown. Figure 17 (A) shows the normalized diffracted light power of the second-order grating at different phase shift positions. Figure 17 (B) shows the ratio of the second-order grating's upward diffracted light power to the total diffracted light power at different phase shift positions. Figure 5It can be seen that when the number of standing wave field antinodes in the second-order grating etched area is greater, the proportion of the second-order grating's upward diffraction power is greater; when the number of standing wave field nodes in the second-order grating etched area is greater, the proportion of the second-order grating's downward diffraction power is greater. Among them, in case 1, the λ / 4 phase shift is located in the etched area of ​​the first-order grating adjacent to the second-order grating. In this case, the proportion of the second-order grating's upward diffraction is the largest. The laser with the phase shift in the position of case 1 can obtain the maximum upward vertical surface emission slope efficiency. In case 12, the λ / 4 phase shift is located in the non-etched area of ​​the first-order grating adjacent to the second-order grating. In this case, the proportion of the second-order grating's upward diffraction is the smallest, that is, the proportion of the downward diffraction is the largest. The laser with the phase shift in the position of case 12 can obtain the maximum downward vertical surface emission slope efficiency. In this case, the laser can achieve high slope efficiency substrate light emission. In actual conditions, the phase shift position can be designed according to the laser performance requirements to control the light field distribution.

[0058] Figure 18 FIG. 1 shows a graph showing the vertical upward output optical power of a laser according to an embodiment of the present application as a function of the injection current. Figure 18 As shown in the figure, when the number of second-order gratings is constant and the phase shift position design is different, the slope efficiency of the laser is different. When the laser uses a five-period second-order grating, the slope efficiency is 0.2mW / mA under the phase shift design of case 1, and the slope efficiency is 0.06mW / mA under the phase shift design of case 12. The slope efficiency of the laser using the phase shift design of case 1 is increased by 3.4 times compared to the laser using the phase shift design of case 12, which greatly improves the output efficiency of the laser. Similarly, the number of periods of the second-order grating 13 can also be increased to increase the slope efficiency of the laser. As shown in the figure, under the same phase shift position design of case 1, the slope efficiency of the second-order grating with 7 periods is 0.27mW / mA; the slope efficiency of the second-order grating with 9 periods is 0.3mW / mA. On the other hand, increasing the number of second-order gratings also increases the laser threshold. When the second-order grating period is 5, the threshold current is approximately 2 mA; when the second-order grating period is 7, the threshold current is approximately 2.2 mA; and when the second-order grating period is 9, the threshold current is approximately 2.4 mA. The appropriate number of second-order gratings is designed based on the actual requirements for threshold and slope efficiency. This shows that the laser achieves both low threshold and high slope efficiency.

[0059] It should be noted that the design of the λ / 4 phase shift located at the second-order grating in this application is not limited to a specific material system or wavelength. For surface-emitting DFB lasers that use a second-order Bragg grating in the center for surface emission and first-order Bragg gratings on both sides for feedback, the design of the λ / 4 phase shift located at the second-order grating in this application can regulate the slope efficiency of the laser.

[0060] The above implementation modes are only used to illustrate the present application and are not intended to limit the present application. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, all equivalent technical solutions also fall within the scope of the present application, and the scope of patent protection of the present application shall be defined by the claims.

Claims

1. A high slope efficiency surface grating surface emitting laser, characterized in that: The laser comprises, from bottom to top along a cross section, a substrate, a lower waveguide layer, an active layer, and an upper waveguide layer; a ridge waveguide is formed in the middle region of the uppermost layer of the upper waveguide layer, and a Bragg grating is etched on the surface of the ridge waveguide; the Bragg grating comprises a second-order grating in the middle and two first-order gratings at both ends; a λ / 4 phase shift is provided in the second-order grating; and the Bragg grating is filled with a low-refractive-index medium; The λ / 4 phase shift is located in the etched area or the non-etched area of ​​the first-order grating closest to the second-order grating; when the λ / 4 phase shift is located in the etched area of ​​the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is maximum, and the downward diffraction light power is minimum; when the λ / 4 phase shift is located in the non-etched area of ​​the first-order grating closest to the second-order grating, the upward diffraction light power of the second-order grating is minimum, and the downward diffraction light power is maximum.

2. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: The slope efficiency of the laser is determined by the number of second-order grating periods.

3. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: The low refractive index medium is filled in the Bragg grating by spin-on glass, plasma enhanced chemical vapor deposition growth of silicon oxide or silicon nitride, atomic layer deposition growth of silicon oxide, aluminum oxide, silicon nitride or tetraethoxysilane deposition of silicon oxide.

4. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: A lower ohmic contact layer and a lower electrode layer are sequentially arranged between the substrate and the lower waveguide layer; an upper ohmic contact layer and an upper electrode layer are sequentially arranged on the upper end of the upper waveguide layer.

5. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: The lower waveguide layer is doped with P type or N type, the active layer is undoped, and the upper waveguide layer is doped with N type or P type.

6. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: The lower waveguide layer includes one or more high resistance regions; the active layer includes one or more quantum well structures and one or more light confinement layer structures.

7. The high slope efficiency surface grating surface emitting laser according to claim 1, wherein: The upper waveguide layer and the active layer are connected via one or more high conductivity layers.

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