Extensible waveguide external grating once epitaxial high power dfb-soa laser

Abstract

This invention relates to the field of semiconductor laser technology, specifically to a high-power DFB-SOA laser with scalable waveguide external grating single-stage epitaxy. The high-power DFB-SOA laser with scalable waveguide external grating single-stage epitaxy includes: a substrate; a DFB region disposed on the left side of the upper surface of the substrate, wherein the DFB region includes one or more combinations of the following structures: a single waveguide structure, a dual waveguide structure, and a multi-waveguide structure with two or more layers; when using a dual-waveguide or multi-waveguide structure, a high-refractive-index undoped slab layer can be disposed between adjacent waveguide layers; the DFB region contains 6-16 quantum wells; the cavity length of the resonant cavity in the DFB region is 1900 μm to 2100 μm. This invention does not strictly limit the active waveguide region, and different structures can be selected according to performance requirements and process complexity.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, specifically to a high-power DFB-SOA laser with scalable waveguide external grating single-stage epitaxy. Background Technology

[0002] With the explosive growth in demand for high-speed, high-capacity optical interconnects from AI data centers, optical modules are evolving towards 800G / 1.6T and even 3.2T / 6.4T, placing stringent requirements on light sources, including high power (≥400mW), narrow linewidth (≤100kHz), high side-mode rejection ratio (≥45dB), and high-temperature stability (operating at 85℃ without cooling). Traditional InP-based DFB lasers face the following technical bottlenecks:

[0003] 1. Power limitation: The conventional cavity length is only 600-800μm, the carrier density is high, and the output power is usually ≤200mW;

[0004] 2. Wide linewidth: Due to the absorption loss of the quantum well and insufficient cavity length, the typical linewidth is in the range of several hundred kHz to MHz;

[0005] 3. Difficulty in heat dissipation: The substrate is relatively thick (≥150μm), resulting in high thermal resistance and significant wavelength drift under high current.

[0006] 4. Complex process: Traditional DFB requires two epitaxial growths of the grating capping layer, and DFB+SOA integration requires three epitaxial growths;

[0007] 5. Concentrated burn-in: Single-phase shift (such as λ / 4) causes the standing wave peak to be fixed in the center of the cavity, resulting in severe local overheating;

[0008] 6. Material oxidation: High-power applications require AlInGaAs, but aluminum is easily oxidized, resulting in a mass production yield of approximately 55%-60%.

[0009] Furthermore, the material and manufacturing challenges of traditional high-power lasers are as follows:

[0010] 1. Material contradictions: The AlInGaAs system has a high light confinement factor and good temperature characteristics, but it is prone to oxidation due to its aluminum content, resulting in a yield of about 55%-60%; the InGaAsP system is aluminum-free and has a high yield (≥80%), but it is limited in power and has a wider linewidth.

[0011] 2. Process contradictions: The traditional DFB+SOA scheme requires two internal etching processes (grating layer and SOA exit active layer), which leads to secondary and tertiary epitaxy, resulting in a very high risk of aluminum exposure. Summary of the Invention

[0012] To address the problems mentioned in the background section, the present invention provides the following technical solution.

[0013] Scalable waveguide external grating one-stage epitaxial high-power DFB-SOA laser, including:

[0014] Substrate;

[0015] A DFB region is disposed on the left side of the upper surface of the substrate. The DFB region includes one or more combinations of the following structures: a single waveguide structure, a double waveguide structure, and a multi-waveguide structure with two or more layers. When a double waveguide or multi-waveguide structure is used, a high-refractive-index undoped Slab layer can be disposed between adjacent waveguide layers. The DFB region contains 6-16 quantum wells. The cavity length of the resonant cavity in the DFB region is 1900 μm to 2100 μm.

[0016] A weak grating coupling structure is disposed in the resonant cavity of the DFB region. The weak grating coupling structure includes a first-order or higher-order external grating located outside the DFB region, wherein the coupling coefficient of the external grating is κL≤1.5; the geometry of the external grating is selected from at least one of a one-dimensional linear grating or a two-dimensional grating; the period of the external grating is a uniform period or a varying period; the external grating is located outside the DFB region, so there is no need to perform internal etching of the DFB region or perform secondary epitaxy.

[0017] Meanwhile, this invention explicitly uses a traditional DFB semiconductor grating covering the inside of the waveguide and close to the quantum well layer as an equivalent solution; the optical feedback principle, dual λ / 8 phase shift logic, SOA slanted structure, and long cavity narrow linewidth mechanism of this internal grating solution are all consistent with this invention and are still within the protection scope of this invention. The only difference is that it requires secondary epitaxy and additional etching in the process, which leads to increased process complexity, cost, and aluminum oxidation risk.

[0018] Two λ / 8 phase shifts are arranged along the cavity length direction of the resonant cavity in the DFB region, and the λ / 8 phase shifts are located at 1 / 3 and 2 / 3 of the cavity length of the resonant cavity in the DFB region, respectively;

[0019] The semiconductor optical amplifier (SOA) region is connected to the DFB region. The SOA region is inclined at an angle of 15°-25° relative to the DFB region. The SOA region includes a short tapered transition waveguide section at the front end and a long uniform width waveguide section connected thereto. The tapered transition section has a length ≤50μm and a width that gradually increases from 3μm in the DFB region to 6μm in the uniform region. The uniform region has a length ≥3000μm and a width of 6μm.

[0020] A QWI transparent window (passive waveguide region) is set on the exit end face of the SOA region.

[0021] As a preferred embodiment of the above technical solution, an electrically isolated structure is etched at the boundary between the DFB region and the SOA region.

[0022] As a preferred embodiment of the above technical solution, the external grating is a second-order top-face Chinese character-shaped metal grating, which includes vertical grating strips perpendicular to the waveguide direction of the DFB region and horizontal metal strips parallel to the waveguide direction of the DFB region.

[0023] As a preferred embodiment of the above technical solution, the left end face of the DFB region is coated with a high reflectivity film with a reflectivity ≥ 90%; the right end face of the SOA region is coated with an antireflection film with a reflectivity ≤ 0.5%.

[0024] As a preferred embodiment of the above technical solution, the QWI transparent window depth is ≤1μm.

[0025] As a preferred embodiment of the above technical solution, the substrate is eutectic bonded to a heat sink and a TEC is mounted on it.

[0026] As a preferred embodiment of the above technical solution, the weak grating coupling structure can also adopt a traditional DFB semiconductor grating inside the waveguide and close to the quantum well layer. This internal grating scheme is consistent with the working principle of the present invention and can achieve resonant feedback and high-power narrow linewidth output. It still falls within the protection scope of the present invention, requiring only secondary epitaxy and additional etching. The process is more complex and the cost is higher. Moreover, the oxidation risk of the aluminum-containing material in the quantum well increases significantly during the secondary epitaxy and etching process.

[0027] This invention provides a scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser, which has the following significant advantages compared with the prior art:

[0028] 1. Scalable active waveguide region design:

[0029] This invention does not strictly limit the active waveguide region, and different structures can be selected according to performance requirements and process complexity: single waveguide (symmetric or asymmetric SCH), dual waveguide (symmetric or asymmetric ASLOC), and multi-waveguide structures with two or more layers. When using a dual-waveguide or multi-waveguide structure, a high-refractive-index undoped slab layer can be placed between adjacent waveguide layers. The active waveguide region contains 6-16 quantum wells. The symmetric ASLOC dual-layer waveguide + InGaAs slab layer is the preferred scheme of this invention, which can reduce the confinement factor to 0.07 and the aspect ratio of the beam to <1.2.

[0030] 2. DFB long cavity design:

[0031] The DFB resonator has a length of 2000 μm (1900-2100 μm), resulting in a lower average carrier density and a mirror loss reduced to approximately 2.5 cm⁻¹. -1 Line width ≤ 80kHz.

[0032] 3. Wide spine design:

[0033] A ridge width ≥3μm reduces carrier density and resistance.

[0034] 4. SOA structure design: It consists of a short conical transition section (length ≤ 50 μm, width gradually increases from 3 μm to 6 μm) and a long uniform waveguide section (length ≥ 3000 μm, width 6 μm). The SOA as a whole is tilted at 15°-25° relative to the DFB waveguide to suppress optical mode resonance interference and deviate the reflected light from the original optical path.

[0035] 5. First-order or higher-order design of external gratings:

[0036] The external grating is located outside the active region (top surface, side surface, or near-field coupling), and can be first-order (Λ=λ / (2n_eff)) or higher-order (Λ=m·λ / (2n_eff), m≥2). By designing the grating depth, duty cycle, etc., κL≤1.5 is achieved. Higher-order gratings have a larger fabrication tolerance and are preferred.

[0037] 6. Optimal selection of various external grating shapes and Chinese character types:

[0038] External gratings and internal gratings are equally protected. Although this invention preferably uses an external top-surface grating to simplify the epitaxial process, the scope of protection of this invention is not limited to external gratings. Any structure employing the same physical principles as this invention, such as dual λ / 8 phase shift, long cavity, oblique SOA, or QWI transparent window, regardless of whether the grating is placed outside or inside the waveguide, falls within the scope of protection of this invention. Internal grating schemes require secondary epitaxy and additional etching, resulting in a more complex process and a higher risk of aluminum oxidation, but this does not affect the definition of the scope of protection of this patent.

[0039] 7. Dual λ / 8 phase shift:

[0040] By applying a phase shift of λ / 8 at both L / 3 and 2L / 3, the hole-burning intensity factor decreased from 0.85 to 0.27 (a reduction of 68%). Definition: S_hole = ∫[I(z)-I_avg] 2 dz / [∫I(z) dz] 2 .

[0041] 8. Narrow the line width:

[0042] Combining a long cavity with low internal loss (α_i approximately 9 cm) -1 (Line width ≤ 80kHz, actual measured 65kHz with aluminum, 78kHz without aluminum).

[0043] 9. Low-absorption light field management and spot circularization (preferred solution):

[0044] When using a symmetrical ASLOC+ high-refractive-index Slab layer, the constraint factor decreases from 0.18 to 0.07, the beam aspect ratio is <1.2, and the fiber coupling efficiency is ≥85%.

[0045] 10. External grating (no secondary epitaxy required):

[0046] External gratings are fabricated outside the active region, eliminating the need for internal etching and secondary epitaxy. Specific forms include top-side metal / dielectric / semiconductor gratings, side-etched gratings, side-drilled gratings, and near-field coupling gratings. Fabrication methods can include direct vapor deposition and lift-off (top-side metal) or shallow trench filling, or electron beam lithography followed by etching (dielectric / semiconductor / side structure).

[0047] 11. Bar-level end-face ion implantation + QWI (avoiding tertiary epitaxy):

[0048] After completing the preceding process, the wafers are diced to form bar strips; multiple bar strips are closely arranged in a fixture, with their end faces facing upwards to form a continuous target surface; a scanning ion beam is injected from a direction perpendicular to the end face (phosphine ions, 300-400 keV, 1×10⁻⁶). 14 cm -2 Annealing (650-750℃, 10-60 seconds) disrupts the quantum wells at a depth of 0.5-1μm near the end face, forming a transparent window. The surface damage layer is <10nm, much smaller than the thickness of the AR film. It is compatible with end face coating fixtures and does not require three-stage epitaxy.

[0049] 12. Single epitaxy + aluminum-free / aluminum-containing options available:

[0050] The epitaxy is performed using only one MOCVD cycle. The quantum well layer can be either aluminum-free InGaAsP or aluminum-containing AlInGaAs; the remaining layers are all aluminum-free materials.

[0051] 13. Double-gain volume of double-layer waveguide (if used):

[0052] When using a symmetrical ASLOC double-layer waveguide, the gain volume is doubled. Attached Figure Description

[0053] Figure 1 : A front cross-sectional view of the present invention.

[0054] Figure 2 : A top view of the structure of the present invention.

[0055] Figure 3 Comparison of three extensional structures: (a) Traditional simple DFB; (b) Traditional asymmetric ASLOC; (c) Symmetric ASLOC+Slab of this invention.

[0056] Figure 4 : A magnified view of a section of a Chinese character-shaped metal grating.

[0057] Figure 5 Comparison of light field distribution and changes in the aspect ratio of the light spot.

[0058] Figure 6 Schematic diagram of bar-level end face QWI: Multiple bar end faces are closely arranged with the ion beam vertically implanted. Local magnification shows the comparison between the damage layer <10nm and the AR film thickness.

[0059] Figure 7 : Substrate thinning and diamond heat sink + TEC substrate mounting structure diagram.

[0060] Figure 8 : Double λ / 8 phase shift position and burn-in intensity distribution curve.

[0061] Figure 9 : Schematic diagram of various implementation methods of external grating.

[0062] Figure 10 Comparison of single-stage extension vs. triple-stage extension processes.

[0063] Figure 11 Power / linewidth / orifice factor curves for different DFB cavity lengths (including the optimal point at 2000μm).

[0064] Figure 12 : Radar chart comparing the patent features of this invention.

[0065] Figure 13 Comparison of standing wave intensity distribution between dual λ / 8 phase shift and single phase shift.

[0066] Figure 14 Comparison of traditional asymmetric ASLOC structure with the symmetric ASLOC structure of this invention and schematic diagram of circular light spot.

[0067] In the figure: 1. Substrate; 2. DFB region; 21. T-shaped metal grating; 211. λ / 8 phase shift; 212. Vertical grating strip; 213. Horizontal metal strip; 3. SOA region; 4. Electrically isolated structure; 5. High reflectivity coating; 6. Anti-reflection coating; 7. QWI transparent window; 8. Heat sink; 9. TEC. Detailed Implementation

[0068] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0069] Example 1 (Preferred: Aluminum-containing AlInGaAs quantum well, symmetrical ASLOC+Slab dual waveguide, second-order top-plane T-shaped metal grating, 1310nm)

[0070] Epitaxial structure (single MOCVD):

[0071] Lower cladding: n-InP, 0.4 μm, 5 × 10⁻⁶ 17 cm -3；

[0072] Lower quantum well: 6×AlInGaAs / InGaAsP (8nm / 12nm);

[0073] Slab layer: InGaAs, 0.2μm, undoped;

[0074] Upper quantum well: 6×AlInGaAs / InGaAsP;

[0075] Upper cladding: p-InP, 0.3 μm, 5 × 10⁻⁶ 17 cm -3 ;

[0076] Contact layer: p + -InGaAs, 0.1μm, 1×10 19 cm -3 ;

[0077] DFB region 2: cavity length 2000μm, ridge width 3μm.

[0078] SOA Region 3: Conical transition 40μm (3→6μm), uniform segment 3000μm, width 6μm, inclined at 20°.

[0079] Electrical isolation structure 4: An isolation trench (10 μm wide and extending to the Slab layer) is etched at the junction of DFB and SOA and filled with polyimide.

[0080] End face coating: DFB area 2, rear end face high reflectivity film 5 (reflectivity ≥ 90%); SOA area 3, output end face anti-reflection film 6 (reflectivity ≤ 0.5%).

[0081] External grating (second-order top-face Chinese character-shaped metal grating 21): Λ=400nm, duty cycle 50%, Chinese character-shaped (no transverse grating in the middle 1μm, 1.2μm transverse strips on each side, vertical stripe width 0.5μm), Ti / Pt / Au (5 / 5 / 20nm), electron beam stripping. λ / 8 phase shift 211 is introduced at L / 3 and 2L / 3.

[0082] QWI transparent window 7: Slicing forms bar strips, multiple bar strips are closely arranged with the end faces facing upwards, phosphorus ion 360keV / 1e14cm -2 Vertical injection, annealing at 700℃ for 30 seconds, transparent window depth 0.8μm.

[0083] Substrate 1 and package: thinned to 80μm, eutectic bonded to diamond heat sink 8, and mounted on TEC9.

[0084] Test results: 475mW@25℃, 420mW@85℃; linewidth 65kHz; SMSR 49dB; burn-in factor 0.27; thermal resistance 205K / W; beam aspect ratio 1.15; fiber coupling efficiency 87%; yield ≥75%.

[0085] Example 2 (Aluminum-free InGaAsP quantum well, symmetric ASLOC+Slab dual waveguide, second-order top-plane T-shaped metal grating, 1310nm)

[0086] Epitaxial structure: The quantum well is replaced with 6×InGaAsP (6nm / 10nm), and the rest is the same as in Example 1. DFB region 2, SOA region 3, grating, and QWI transparent window 7 are all the same.

[0087] Test results: 450mW@25℃, 390mW@85℃; linewidth 78kHz; SMSR 48dB; burn-in factor 0.28; thermal resistance 210K / W; beam aspect ratio 1.16; fiber coupling efficiency 86%; yield ≥80%.

[0088] Example 3 (shallow groove covering top surface metal grating, containing aluminum)

[0089] Based on Example 1, the external grating was modified to method B: first, a 50nm shallow trench was etched in the contact layer, then metal was deposited to fill and cover it. Test results: 468mW, 68kHz, SMSR 48dB.

[0090] Example 4 (1550nm aluminum-containing, symmetrical ASLOC+Slab dual waveguide, second-order alphanumeric shape)

[0091] Λ=484nm, the rest is the same as in Example 1. Test results: 460mW, 70kHz, SMSR 48dB.

[0092] Example 5 (1550nm aluminum-free, symmetrical ASLOC+Slab dual waveguide, second-order 'Z' shape)

[0093] Λ=484nm, the rest is the same as in Example 2. Test results: 435mW, 82kHz, SMSR 47dB.

[0094] Example 6 (First-order grating variant, containing aluminum)

[0095] Based on Example 1, the external grating was changed to first order (Λ=200nm), and the κL ≤ 1.5 was achieved by reducing the groove depth to 100nm and the duty cycle to 40%. Test results: 425mW, linewidth 88kHz, SMSR 46dB, aperture burn-in factor 0.33, and spot aspect ratio 1.17. This indicates that the first-order grating also falls within the scope of protection of this invention.

[0096] Example 7 (Optimization of different DFB cavity lengths)

[0097] 1000 265 185 0.50 1500 398 98 0.31 2000 475 65 0.27 2500 490 58 0.24 (for reference only, exceeding the preferred cavity length range)

[0098] 2000μm is optimal.

[0099] Example 8 (Comparison without Chinese characters)

[0100] Based on Example 1, the Chinese character shape was changed to a traditional straight bar shape (the horizontal grating bar spans the entire ridge width of 3μm). Results: 458mW, linewidth 78kHz, hole burning factor 0.33. Compared to Example 1 (0.27), the Chinese character shape further reduced hole burning by approximately 18%, demonstrating its ability to mitigate hole burning.

[0101] Example 9 (Single waveguide asymmetric SCH, verifying the scalability of waveguide structures)

[0102] Based on Example 1, the upper quantum well layer, Slab layer, and lower quantum well layer are removed, and a single waveguide is used instead: 8 periodic AlInGaAs / InGaAsP quantum wells, with confinement layers of 1.5 μm for n-InP and 0.2 μm for p-InP. The DFB, SOA, external grating (second-order alphanumeric), QWI, etc. are the same as in Example 1.

[0103] Test results: 385mW, linewidth 95kHz, SMSR 46dB, hole burning factor 0.35, beam aspect ratio approximately 1.6, fiber coupling efficiency 72%.

[0104] This embodiment demonstrates that even with the simplest single waveguide structure, performance superior to that of a conventional DFB laser (conventional 150mW / 1MHz) can still be achieved.

[0105] Example 10 (Chirped grating, verifying the scalability of a variable periodicity grating)

[0106] Based on Example 1, the grating period was linearly varied along the cavity length from 395 nm to 405 nm (400 nm at the center, 2.5% chirp). Results: 468 mW, linewidth 70 kHz, SMSR 47 dB, hole burn-in factor 0.29.

[0107] Example 11 (waveguide side-perforated grating, verifying non-top surface external grating)

[0108] Based on Example 1, the top metal grating was removed, and a periodic air hole array (hole diameter 150 nm, period Λ = 400 nm, hole depth 0.5 μm) was fabricated in the InP cladding 0.3 μm from the sidewalls on both sides of the ridge waveguide, with κL ≈ 1.2. Results (simulation): approximately 460 mW, linewidth 72 kHz, SMSR 48 dB, hole burn-in factor 0.28.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-power DFB-SOA laser with scalable waveguide external grating single-stage epitaxy, characterized in that, include: Substrate (1); DFB region (2) is disposed on the left side of the upper surface of the substrate (1). The DFB region (2) includes one or more combinations of the following structures: single waveguide structure, double waveguide structure and multi-waveguide structure with two or more layers. When a double waveguide or multi-waveguide structure is used, a high refractive index undoped Slab layer can be disposed between adjacent waveguide layers. The DFB region (2) contains 6-16 quantum wells. The cavity length of the resonant cavity of the DFB region (2) is 1900 μm to 2100 μm. A weak grating coupling structure is disposed in the resonant cavity of the DFB region (2). The weak grating coupling structure includes a first-order or higher-order external grating located outside the DFB region (2). The coupling coefficient of the external grating is κL≤1.

5. The geometry of the external grating is selected from at least one of a one-dimensional linear grating or a two-dimensional grating. The period of the external grating is a uniform period or a varying period. The external grating is located outside the DFB region (2), so there is no need to perform internal etching on the DFB region (2) or perform secondary epitaxy. Two λ / 8 phase shifters (211) are arranged along the cavity length direction of the resonant cavity in the DFB region (2), and the λ / 8 phase shifters (211) are located at 1 / 3 and 2 / 3 of the cavity length of the resonant cavity in the DFB region (2), respectively; The SOA region (3) is connected to the DFB region (2). The SOA region (3) is inclined at an angle of 15°-25° relative to the DFB region (2). The SOA region (3) includes a short conical transition waveguide section at the front end and a long uniform width waveguide section connected thereto. The length of the conical transition section is ≤50μm, and the width gradually increases from 3μm in the DFB region (2) to 6μm in the uniform region. The length of the uniform region is ≥3000μm and the width is 6μm. A QWI transparent window (7) is set on the exit end face of the SOA area (3).

2. The scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser according to claim 1, characterized in that: An electrically isolated structure (4) is etched at the junction of the DFB region (2) and the SOA region (3).

3. The scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser according to claim 2, characterized in that: The external grating is a second-order top-face Chinese character-shaped metal grating (21), which includes vertical grating strips (212) perpendicular to the waveguide direction of the DFB region (2) and horizontal metal strips (213) parallel to the waveguide direction of the DFB region (2).

4. The scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser according to claim 3, characterized in that: The left end face of the DFB area (2) is coated with a high reflectivity film (5) with a reflectivity ≥90%; the right end face of the SOA area (3) is coated with an antireflection film (6) with a reflectivity ≤0.5%.

5. The scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser according to claim 4, characterized in that: The depth of the QWI transparent window (7) is ≤1μm.

6. The scalable waveguide external grating single-stage epitaxial high-power DFB-SOA laser according to claim 5, characterized in that: The substrate (1) is eutectic bonded to the heat sink (8) and mounted with a TEC (9).

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