Ultra-narrow linewidth laser based on inner and outer multi-layer phase-shift grating
By using an internal and external multi-layer phase-shifting grating design, combined with semiconductor DFB gratings and metal reflective DFB grating electrodes, the problems of excessively wide linewidth and insufficient coupling efficiency in traditional lasers are solved, realizing a laser design with ultra-narrow linewidth, high coupling efficiency and simplified process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JUGUANG KEXIN (HEFEI) OPTOELECTRONICS CO LTD
- Filing Date
- 2026-01-21
- Publication Date
- 2026-06-12
AI Technical Summary
Traditional ultra-narrow linewidth lasers suffer from problems such as excessively wide linewidth, insufficient coupling efficiency, and a single filtering system. Existing technologies have failed to simultaneously achieve the dual goals of high coupling efficiency and ultra-narrow linewidth, and the processes are complex and the material compatibility is poor.
The design employs a multi-layer phase-shifting grating system, which includes semiconductor DFB gratings placed on the upper and lower sides of the light-emitting quantum well layer, and combined with the top surface metal reflective DFB grating electrode to form a comprehensive filtering system. Combined with planar plate electrodes, this achieves improved high coupling efficiency and mode suppression capability.
It achieves ultra-narrow linewidth (3dB linewidth up to 2kHz), high coupling efficiency (95%) and high mode rejection ratio (>60dB), while simplifying process steps, reducing production costs, and adapting to the needs of different application scenarios.
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Figure CN122203033A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor laser technology, specifically to an ultra-narrow linewidth laser based on internal and external multilayer phase-shifting gratings. Background Technology
[0002] Traditional ultra-narrow linewidth lasers mostly employ a single-layer built-in semiconductor grating (such as a DFB structure) or an external grating (such as an ECL structure), which has three major limitations: First, the linewidth is too wide. Traditional single-layer DFB lasers are limited by low coupling efficiency (the refractive index difference between InGaAsP / InP materials at a wavelength of 1550nm is ≈0.3, and the coupling efficiency is usually <80%) and poor mode selectivity. Insufficient feedback makes it difficult to compress the linewidth, which is generally ≥100kHz, and cannot meet the requirements of ultra-narrow linewidth (<5kHz) in scenarios such as quantum sensing and high-end coherent communication. Second, there is a bottleneck in linewidth narrowing of phase-difference-free multilayer gratings. Although existing multilayer grating designs can improve the coupling efficiency to about 92%, the linewidth remains at the 5kHz level due to the lack of a phase-shifting mode selection structure, making further breakthroughs difficult. Third, the process is complex and the material compatibility is poor. External gratings require precise alignment and packaging, and most designs only support a single substrate, limiting their applicability.
[0003] While existing technologies attempt to optimize grating structures, they fail to combine "multi-layer gratings + segmented phase shifting": some patents use single-layer phase-shifting gratings, which can compress the linewidth to 10kHz, but the coupling efficiency is less than 85%; some patents use multi-layer phase-difference-free gratings, which improve the coupling efficiency to 92%, but the linewidth cannot exceed 5kHz. Neither approach achieves the dual goals of "high coupling efficiency + ultra-narrow linewidth," and neither can simultaneously address process simplification and material compatibility. Summary of the Invention
[0004] This invention aims to solve the core problems of traditional lasers, such as excessively wide linewidth, insufficient coupling efficiency, and a single filtering system, by providing an ultra-narrow linewidth laser based on a multi-region, multi-layer phase-shifting grating. By placing semiconductor DFB gratings on both the upper and lower sides of the emitting quantum well layer, and combining them with the top-surface metal reflective DFB grating electrode to form a comprehensive filtering system, coupling efficiency and mode suppression capability are significantly improved, achieving ultra-narrow linewidth output. Simultaneously, it provides an alternative to planar plate electrodes, catering to the needs of different application scenarios, ultimately achieving multiple goals: ultra-narrow linewidth, high coupling efficiency, high flexibility, and simplified manufacturing process.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] Ultra-narrow linewidth lasers based on inner and outer multilayer phase-shifting gratings include:
[0007] Substrate, wherein the top of the substrate is the upper surface of the substrate;
[0008] A back ridge waveguide is disposed on the upper surface of the substrate. An AR layer is deposited on the right end face of the back ridge waveguide, and an HR layer is deposited on the left end face of the back ridge waveguide.
[0009] An external top surface metal grating electrode is disposed on the upper end surface of the back ridge waveguide, and a second λ / 4 phase shift is disposed inside the external top surface metal grating electrode;
[0010] The back ridge waveguide also includes a quantum well layer, an upper DFB grating layer and a lower DFB grating layer integrated therein;
[0011] The upper DFB grating layer and the lower DFB grating layer are respectively disposed on the upper and lower sides of the quantum well layer;
[0012] The upper DFB grating layer and the lower DFB grating layer have N layers, where N is a natural number; both the upper DFB grating layer and the lower DFB grating layer are provided with a first λ / 4 phase shift.
[0013] As a preferred embodiment of the above technical solution, the upper DFB grating layer has 2 layers and the lower DFB grating layer has 0 layers.
[0014] As a preferred embodiment of the above technical solution, the substrate is an n-type InP single crystal substrate with a thickness of 200-400 μm and a diameter of 2-4 inches.
[0015] As a preferred embodiment of the above technical solution, the quantum well layer is a 3-8 layer quantum well structure, the well region is made of InGaAsP material with a thickness of 6-10nm, and the barrier region is made of InP material with a thickness of 15-25nm.
[0016] As a preferred embodiment of the above technical solution, the external top surface metal grating electrode is a comb-shaped metal grating layer prepared by electron beam evaporation + wet etching process.
[0017] As a preferred embodiment of the above technical solution, the lasing wavelength λ of the quantum well layer is 1310nm or 1550nm.
[0018] As a preferred embodiment of the above technical solution, the symmetrical grating segments on the left and right sides of the first λ / 4 phase shift and the second λ / 4 phase shift are λ / 2 apart.
[0019] As a preferred embodiment of the above technical solution, M of the lasers based on inner and outer multilayer phase-shifting gratings and metal comb ultra-narrow linewidth are arranged in a single row array, where M is a natural number;
[0020] From left to right, the grating constant and wavelength of the Mth laser based on inner and outer multilayer phase-shifting gratings and a metal comb ultranarrow linewidth laser are respectively Λ M and λ M When the grating constant Λ MWhen they are consistent, the output light wavelength λ M Consistent; when the grating constant Λ M When inconsistent, λ M It meets the wavelength definition and distribution of the ITU-Grid.
[0021] This invention provides an ultra-narrow linewidth laser based on multiple inner and outer phase-shifting gratings, which has the following advantages:
[0022] 1. Ultra-narrow linewidth performance (phase shift + multilayer synergy): All gratings are divided into two segments with λ / 4 phase shift and λ / 2 spacing. Phase shift enhances mode selectivity, and multilayer synergy improves coupling efficiency. The synergy of the two enables a 3dB linewidth of 2kHz at a wavelength of 1550nm, which is 98% narrower than traditional single-layer DFB lasers (≥100kHz) and an additional 60% narrower than multilayer gratings without phase difference (5kHz). For the first time, the linewidth of DFB lasers has been stably compressed to the 2kHz level, meeting the requirements of extreme scenarios such as quantum sensing and high-end coherent communication.
[0023] 2. High mode rejection ratio (phase shift mode selection): The segmented phase shift structure can accurately suppress side-mode signals, with a mode rejection ratio of >60dB, which is 7dB higher than that of multilayer gratings without phase difference (<55dB) and 17dB higher than that of traditional single-layer DFB lasers (<45dB). It effectively avoids linewidth broadening caused by side-mode interference and ensures linewidth stability.
[0024] 3. High coupling efficiency (multi-layer stacking): The built-in multi-layer structure improves the coupling efficiency to 95%, which is 3 percentage points higher than the phase difference-free multi-layer grating (92%) and 15 percentage points higher than the traditional single-layer DFB laser (80%). Sufficient feedback intensity provides core support for narrowing the linewidth depth, while reducing optical loss and improving output power.
[0025] 4. Process and cost advantages (functional integration): The external segmented phase-shifting metal grating has the functions of "phase-shifting filtering + current injection", eliminating the need for separate electrode fabrication and reducing process steps by 30%; it avoids the alignment and packaging process of the external grating, reducing production costs by more than 25%; and the phase-shifting structure is achieved through photolithography and film thickness fine-tuning, eliminating the need for additional complex processes and making it highly feasible for industrialization.
[0026] 5. Material and application scenario adaptability (dual substrate support): It supports both InP-substrate (1550nm band) and GaAs-substrate (850nm band) to cover the application needs of multiple fields such as optical communication, quantum sensing, and lidar; it has excellent temperature stability (wavelength drift <0.04pm / ℃, linewidth fluctuation <0.8kHz), adapts to a wide temperature working environment from -40℃ to 85℃, and has a much wider range of applications than traditional single substrate designs.
[0027] This invention breaks through the linewidth bottleneck of traditional lasers from the structural design level. Through the innovative combination of "segmented phase shift + multi-layer superposition", it achieves multiple goals such as "ultra-narrow linewidth, high coupling efficiency, high mode suppression ratio, simplified process, and dual substrate adaptation", which has extremely high technical value and industrialization prospects in the field of high-end optoelectronics. Attached Figure Description
[0028] Figure 1 This is a schematic diagram of the structure of the ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings in Embodiment 1 of the present invention;
[0029] Figure 2 for Figure 1 The left view;
[0030] Figure 3 for Figure 1 Top view;
[0031] Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention.
[0032] In the figure: 1. Substrate; 2. Upper surface of substrate; 3. Back ridge waveguide; 31. Quantum well layer; 32. Upper DFB grating layer; 33. Lower DFB grating layer; 34. First λ / 4 phase shift; 4. External top surface metal grating electrode; 41. Second λ / 4 phase shift; 5. HR layer; 6. AR layer. Detailed Implementation
[0033] 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.
[0034] Example 1
[0035] Ultra-narrow linewidth lasers based on inner and outer multilayer phase-shifting gratings include:
[0036] Substrate 1, using either an InP substrate (thickness = 300 μm, suitable for 1550 nm wavelength) or a GaAs substrate (thickness = 400 μm, suitable for 850 nm wavelength), employs a semi-insulating material (resistivity > 10). 7 Ω・cm), reduce leakage current, and avoid linewidth fluctuations (fluctuation amplitude < 0.5kHz) caused by current noise. The top of the substrate 1 is the upper surface 2 of the substrate.
[0037] A back ridge waveguide 3 is disposed on the upper surface 2 of the substrate. An AR layer 6 is deposited on the right end face of the back ridge waveguide 3, and an HR layer 5 is deposited on the left end face of the back ridge waveguide 3. The back ridge waveguide 3 also includes a quantum well layer 31, an upper DFB grating layer 32, and a lower DFB grating layer 33 integrated therein.
[0038] The upper DFB grating layer 32 and the lower DFB grating layer 33 are respectively disposed on the upper and lower sides of the quantum well layer 31;
[0039] The number of layers in the upper DFB grating layer 32 and the lower DFB grating layer 33 is N, where N is a natural number; both the upper DFB grating layer 32 and the lower DFB grating layer 33 are provided with a first λ / 4 phase shift 34, and the symmetrical grating segments on the left and right sides of the first λ / 4 phase shift 34 are spaced λ / 2 apart.
[0040] The quantum well layer 31 adopts an InGaAsP quantum well structure (adapted to InP-substrate, 3 quantum wells, well thickness = 8nm, barrier thickness = 15nm) or a GaAs / AlGaAs quantum well structure (adapted to GaAs-substrate, 5 quantum wells, well thickness = 7nm, barrier thickness = 12nm), with a thickness of 250nm; it is grown using MOCVD process, and the full width at half maximum (FWHM) of the quantum well photoluminescence spectrum is <15meV, providing stable optical gain and ensuring output power (output power ≥15mW at 20mA current) and linewidth stability.
[0041] Each grating layer is divided into two segments, with the length of a single segment equal to 50% of the total grating length (e.g., if the total grating length is 500 μm, the length of a single segment is 250 μm). Between the two segments, a λ / 4 phase shift (at a wavelength of 1550 nm, the physical length corresponding to the phase shift in the semiconductor material is λ / (4n) = 1550 / (4×3.3) ≈ 117.4 nm) and a λ / 2 spacing (at a wavelength of 1550 nm, the spacing is 387.5 nm) are set. The spacing area is filled with InP insulating material to ensure that the two grating segments are physically isolated and optically coupled.
[0042] The number of layers N is a natural integer (N=0,1,2,3,...). The upper DFB grating layer 32 preferably has 2 layers, and the lower DFB grating layer 33 preferably has 0 layers. The grating period of each layer is λ / 2 (period = 775nm at a wavelength of 1550nm), the duty cycle is 0.5 (linewidth:spacing = 1:1), and the depth is 150nm. The interlayer spacing is 2μm. An isolation layer of the same material as the substrate is used for filling, and the phase shift regions of each layer are aligned in the vertical direction (alignment accuracy ≤0.5μm) to achieve the superposition of phase shift mode selection function.
[0043] The multi-layer structure improves coupling efficiency (≈90% when N=1, ≈95% when N=2), and the segmented phase shift enhances mode selectivity (mode suppression ratio >60dB). Together, these two factors result in a 98% narrower linewidth compared to a traditional single-layer DFB laser (≥100kHz), and an additional 60% narrower linewidth compared to a multi-layer grating without phase difference (5kHz). Furthermore, the phase shift structure can suppress more than 50% of side-mode signals, avoiding linewidth broadening caused by side-mode interference.
[0044] An external top surface metal grating electrode 4 is disposed on the upper end surface of the back ridge waveguide 3. A second λ / 4 phase shifter 41 is disposed inside the external top surface metal grating electrode 4. The symmetrical grating segments on the left and right sides of the second λ / 4 phase shifter 41 are spaced λ / 2 apart.
[0045] The Cr / Au alloy (50nm Cr layer + 150nm Au layer, Au refractive index n=0.15+5.3i) was used to fabricate the film by electron beam lithography and magnetron sputtering. The phase shift was achieved by "film thickness fine adjustment" - the Au layer thickness in the phase shift section was increased by λ / (4|n|)=1550 / (4×5.3)≈72.6nm compared with the non-phase shift section, to ensure that a phase difference of λ / 4 was formed between the two sections.
[0046] Similarly, it is divided into two segments, with each segment covering 50% of the corresponding area of the gain layer; a λ / 2 spacing (387.5nm at 1550nm wavelength) is set between the two segments, aligned with the spacing of the built-in grating; the grating period = λ / 2 (775nm), linewidth = 387.5nm, and spacing = 387.5nm; two electrode leads (width = 50μm) are set at the edge, which are fabricated using Cr / Au alloy extension to achieve uniform current injection from the leads into the two grating segments;
[0047] It replaces traditional planar metal electrodes and simultaneously achieves the dual functions of "segmented phase-shift filtering + current injection"; compared with metal gratings without phase difference, it narrows the linewidth by an additional 40% (from 5kHz to 3kHz); and it eliminates the need for separate electrode fabrication, reducing process steps by 30% and lowering production costs; the current injection uniformity is improved by 25%, avoiding linewidth fluctuations caused by uneven current.
[0048] HR layer 5 is deposited on the incident end face (thickness = 775nm at 1550nm wavelength), the film system is a SiO2 / TiO2 multilayer film (4 alternating layers), and the reflectivity is >99.9%; AR layer 6 is deposited on the exit end face (thickness = 387.5nm), the film system is a single layer SiO2, and the reflectivity is <0.02%; in conjunction with the inner and outer segmented phase-shift gratings, it further suppresses the side modes (mode rejection ratio is improved by 5dB) and avoids linewidth broadening caused by end face reflection interference.
[0049] Example 2
[0050] M lasers based on multi-layer phase-shifting gratings and metal combs are arranged in a single row array, where M is a natural number.
[0051] From left to right, the grating constant and wavelength of the Mth laser based on inner and outer multilayer phase-shifting gratings and a metal comb ultranarrow linewidth laser are respectively Λ M and λ M When the grating constant Λ M When they are consistent, the output light wavelength λ MConsistent; when the grating constant Λ M When inconsistent, λ M It meets the wavelength definition and distribution of the ITU-Grid.
[0052] The performance test results of this invention are as follows:
[0053] 1. Linewidth test (to verify the phase shift narrowing effect):
[0054] Test system: laser driver (current stability < 0.1%), fiber coupler (coupling efficiency > 90%), 10km delay line (dispersion coefficient = 17ps / nm·km), high responsivity photodetector (responsivity = 0.9A / W, bandwidth = 1GHz), high resolution spectrum analyzer (resolution bandwidth = 1Hz).
[0055] Test conditions: 1550nm wavelength, operating current = 50mA, temperature = 25℃;
[0056] Test results: 3dB linewidth = 2kHz; compared with the phase difference-free multilayer grating (N=2) linewidth = 5kHz, the present invention narrows the linewidth by 60%; compared with the traditional single-layer DFB laser (≥100kHz), it narrows the linewidth by 98%, fully meeting the ultra-narrow linewidth application standard.
[0057] 2. Coupling efficiency test:
[0058] Test method: The internal optical power (P1) of the built-in grating area was measured using a near-field scanning system, and the output optical power (P2) was measured using an integrating sphere power meter. Coupling efficiency = (P2 / P1) × 100%;
[0059] Test results: Coupling efficiency = 95%, which is 3 percentage points higher than that of multilayer gratings without phase difference (92%) and 15 percentage points higher than that of traditional single-layer DFB lasers (80%), verifying the coupling enhancement effect of multilayer structures.
[0060] 3. Mode suppression ratio test (to verify the phase shift mode selection effect):
[0061] Test system: High-resolution spectrometer (resolution = 0.01 nm, dynamic range = 80 dB);
[0062] Test results: The main mode wavelength is 1550.00nm, the secondary mode wavelength is 1550.50nm, and the ratio of main mode power to secondary mode power is 62dB (mode rejection ratio is 62dB). This is 7dB higher than that of a multilayer grating without phase difference (55dB) and 17dB higher than that of a traditional single-layer DFB laser (45dB), indicating that the mode selectivity of the segmented phase shift structure is significantly enhanced and effectively suppresses side-mode interference.
[0063] 4. Temperature stability test:
[0064] Test conditions: The laser was placed in a high and low temperature chamber (temperature range = -40℃ to 85℃), and the temperature was stabilized for 30 minutes every 10℃ before testing. The operating current was 50mA.
[0065] Test results: Wavelength drift = 0.04 pm / ℃ (wavelength = 1549.98 nm at -40℃, wavelength = 1550.03 nm at 85℃), linewidth fluctuation = 0.8 kHz (linewidth = 2.3 kHz at -40℃, linewidth = 2.8 kHz at 85℃); more stable than multilayer gratings without phase difference (wavelength drift 0.05 pm / ℃, linewidth fluctuation 1.2 kHz), far superior to traditional single-layer DFB lasers (wavelength drift > 0.1 pm / ℃, linewidth fluctuation > 10 kHz), adaptable to complex working environments.
[0066] 5. Electrical and power performance testing:
[0067] Electrical testing: The semiconductor parameter analyzer was used to test the IV characteristics. The threshold current at room temperature was 12mA, the operating voltage was 1.7V (at 50mA current), and the series resistance was 5Ω. The electrical performance was stable.
[0068] Power testing: The output power was tested using an integrating sphere optical power meter. When the operating current was 50mA, the output power was 22mW and the electro-optical conversion efficiency was 26%, which meets the power requirements of practical applications. Compared with the design without phase difference (threshold current 15mA, output power 20mW), the electrical and power performance is better.
[0069] 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. An ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings, characterized in that, include: Substrate (1), the top of the substrate (1) is the upper surface (2) of the substrate; A back ridge waveguide (3) is disposed on the upper surface (2) of the substrate. An AR layer (6) is deposited on the right end face of the back ridge waveguide (3), and an HR layer (5) is deposited on the left end face of the back ridge waveguide (3). An external top surface metal grating electrode (4) is disposed on the upper end surface of the back ridge waveguide (3), and a second λ / 4 phase shift (41) is disposed inside the external top surface metal grating electrode (4). The back ridge waveguide (3) also includes a quantum well layer (31), an upper DFB grating layer (32) and a lower DFB grating layer (33) integrated therein. The upper DFB grating layer (32) and the lower DFB grating layer (33) are respectively disposed on the upper and lower sides of the quantum well layer (31); The number of layers in the upper DFB grating layer (32) and the lower DFB grating layer (33) is N, where N is a natural number; a first λ / 4 phase shift (34) is provided in both the upper DFB grating layer (32) and the lower DFB grating layer (33).
2. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 1, characterized in that: The upper DFB grating layer (32) has 2 layers, and the lower DFB grating layer (33) has 0 layers.
3. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 1, characterized in that: The substrate (1) is an n-type InP single crystal substrate with a thickness of 200-400 μm and a diameter of 2-4 inches.
4. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 1, characterized in that: The quantum well layer (31) is a 3-8 layer quantum well structure, with the well region being made of InGaAsP material with a thickness of 6-10nm and the barrier region being made of InP material with a thickness of 15-25nm.
5. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 1, characterized in that: The external top surface metal grating electrode (4) is a comb-shaped metal grating layer prepared by electron beam evaporation + wet etching process.
6. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 5, characterized in that: The lasing wavelength λ of the quantum well layer (31) is 1310 nm or 1550 nm.
7. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings according to claim 6, characterized in that: The left and right symmetrical grating segments of the first λ / 4 phase shift (34) and the second λ / 4 phase shift (41) are λ / 2 apart.
8. The ultra-narrow linewidth laser based on inner and outer multilayer phase-shifting gratings and a metal comb according to claim 7, characterized in that: M lasers based on inner and outer multilayer phase-shifting gratings and metal comb ultra-narrow linewidth lasers are arranged in a single row array, where M is a natural number; From left to right, the grating constant and wavelength of the Mth laser based on inner and outer multilayer phase-shifting gratings and a metal comb ultranarrow linewidth laser are respectively Λ M and λ M When the grating constant Λ M When they are consistent, the output light wavelength λ M Consistent; when the grating constant Λ M When inconsistent, λ M It meets the wavelength definition and distribution of the ITU-Grid.