DBR semiconductor laser with highly consistent lasing performance in full tuning range

Abstract

The application discloses a DBR semiconductor laser with highly consistent lasing performance in a full tuning range, and belongs to the technical field of semiconductor optoelectronic devices. The laser is stacked into an epitaxial stack structure along a material growth direction, and is sequentially divided into a rear grating area, a first isolation area, a phase area, a second isolation area, a gain area, a third isolation area and a front grating area along a resonant cavity length direction; the rear grating area and the front grating area are both engraved with multi-period sampled gratings with unequal reflection peak wavelength intervals, wavelength tuning is realized based on a vernier effect, and the sampling duty cycles of the two sampled gratings are both less than 10% to realize reflection spectrum flattening; a multi-layer quantum well or quantum dot structure with different structure parameters is adopted for the active layer to widen the gain bandwidth. The application realizes the cooperation of grating reflection spectrum flattening and wide gain active area, so that key parameters such as output power, threshold current and side mode suppression ratio remain highly consistent in the full tuning range, is compatible with conventional semiconductor processing technology, has strong manufacturability, and is suitable for the fields of optical communication, optical sensing, optical measurement and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of semiconductor optoelectronic devices, and particularly relates to a wide-tunable DBR semiconductor laser. Background Technology

[0002] In the fields of optical communication, optical sensing, and optical measurement, tunable semiconductor lasers can dynamically adjust their output wavelength according to actual needs. They are key components for realizing core functions such as wavelength routing, wavelength division multiplexing, spectral analysis, and fiber optic sensing, possessing significant application value and broad market prospects. Currently, common tunable semiconductor lasers mainly include tunable external cavity lasers, tunable distributed feedback (DFB) laser arrays, and tunable distributed Bragg reflection (DBR) lasers. Among these, tunable external cavity lasers are typically large in size and have complex mechanical structures, making integration difficult; tunable DFB laser arrays require multiple independent lasers with wavelength selection switches, resulting in high system costs and limited tuning speed. Compared to these two solutions, tunable DBR lasers offer advantages such as relatively simple structure, wider tuning range, and faster switching speed, thus demonstrating greater potential in practical applications.

[0003] Tunable DBR lasers operate based on the vernier effect, and a typical structure includes a front sampling grating region, a gain region, a phase region, and a back sampling grating region. By applying different injection currents to the front and back sampling grating regions, their effective refractive indices can be changed, thereby shifting the position of their reflection peaks. Utilizing the vernier effect generated by the slight difference in the interval between the two grating reflection peaks, a wide range of tuning of the reflection peaks can be achieved, thus controlling the lasing wavelength of the laser. This mechanism enables tunable DBR lasers to have continuous or quasi-continuous tuning capabilities over a wide wavelength range.

[0004] However, existing tunable DBR lasers still suffer from significant performance defects in practical applications. On one hand, there is a large reflectivity difference, typically exceeding 20%, between the reflection peak at the center wavelength and the reflection peak at the edge wavelengths within the tuning range of the sampling grating. On the other hand, the gain spectrum of the active material in the laser exhibits an inherent distribution characteristic of high gain at the center wavelength and low gain at the wavelengths on both sides. Under the combined effect of these two factors, the lasing characteristics (including key parameters such as output power, threshold current, side-mode rejection ratio, and linewidth) of current tunable DBR lasers differ significantly between the center wavelength and the edge wavelengths of the tuning range. This inconsistency prevents the laser from maintaining stable and balanced performance output across the entire tunable wavelength range, making it difficult to meet the stringent requirements for lasing performance consistency across the entire tuning range in fields such as optical communication, optical sensing, and optical measurement. Although methods such as superstructure gratings can be used to flatten the reflection spectrum, these grating structures are complex, require extremely high manufacturing standards, and are difficult to mass-produce. Therefore, improving the uniformity of lasing characteristics across the entire tuning range of tunable DBR lasers has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] Existing tunable DBR lasers exhibit significant differences in lasing characteristics (including key parameters such as output power, threshold current, side-mode rejection ratio, and linewidth) between the center wavelength and the edge wavelengths of the tuning range. This makes it difficult to maintain stable and balanced performance across the entire tunable wavelength range, failing to meet the stringent requirements for consistent lasing performance across the entire tuning range in fields such as optical communication, optical sensing, and optical measurement. This invention proposes a DBR semiconductor laser with highly consistent lasing performance across the tuning range. On one hand, it optimizes the sampling grating structure by flattening the reflection peaks of the front and rear gratings, reducing the reflectivity difference between the center and edge wavelengths. On the other hand, it improves the active region structure design, extending its 3dB gain bandwidth and mitigating the adverse effects of a high center and low sides in the active region gain spectrum.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A DBR semiconductor laser with highly consistent lasing performance across the entire wavelength tuning range includes a substrate, an epitaxial stacked structure formed on the substrate, and N-electrodes and P-electrodes respectively disposed on the back side of the substrate and the top of the epitaxial stacked structure; the epitaxial stacked structure includes, from bottom to top, a buffer layer, a lower confinement layer, a grating layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a P-type ohmic contact layer.

[0008] The DBR semiconductor laser is divided into the following regions along the length of the resonant cavity: rear grating region, first isolation region, phase region, second isolation region, gain region, third isolation region, and front grating region.

[0009] Furthermore, the rear grating region, serving as the rear-end reflector of the laser cavity, is etched with a multi-period sampling grating. Its characteristic is to reflect a series of laser beams with fixed wavelength intervals (Δλ1). Injecting current into this region can alter the effective refractive index of the material in this region, thereby shifting the wavelengths of a series of reflection peaks.

[0010] Furthermore, the front grating region, acting as the front-end reflector of the laser cavity, is also etched with a multi-period sampling grating, thus reflecting a series of laser beams with fixed wavelength intervals (Δλ2, and Δλ1≠Δλ2). Injecting current into this region can alter the effective refractive index of the front grating region, thereby shifting the wavelengths of a series of reflection peaks. When a reflection peak of the front and rear sampling gratings aligns at a certain wavelength, the reflectivity at that wavelength is highest, satisfying the laser oscillation condition and generating lasing. At this point, by changing the current injected into the front and rear gratings respectively, their effective refractive indices can be altered, causing the entire comb-like spectrum of their reflection peaks to shift. Since Δλ1≠Δλ2, after the relative shift of the reflection peaks, they will realign at a new wavelength, while the reflection peaks at other wavelengths remain misaligned. In this way, the lasing wavelength "jumps" from the previous alignment point to the next alignment point, achieving wavelength tuning.

[0011] Furthermore, the phase region material structure is the same as that of the front and rear grating regions, but without the grating structure. The current injected into this region changes the effective refractive index of the material, thereby fine-tuning the optical path within the laser cavity. This ensures that the longitudinal mode of the laser cavity is precisely aligned with the reflection peaks of the front and rear gratings, achieving continuous wavelength tuning.

[0012] Furthermore, the purpose of the gain region is to provide optical amplification. By injecting current into this region, electrons and holes recombine, generating stimulated emission optical amplification, which provides energy for the entire laser.

[0013] Furthermore, the isolation region serves to achieve electrical isolation between the various functional areas. This region is typically formed into a high-resistance area through methods such as physical etching or ion implantation, ensuring that the current injected into each area (such as the gain region, phase region, and grating region) is independent of each other. This is the basis for achieving independent and precise control.

[0014] The key feature of achieving highly consistent lasing performance across the entire wavelength tuning range is:

[0015] (a) Design of sampling grating for flattening the reflection spectrum

[0016] To achieve highly consistent lasing performance across the entire tunable wavelength range, this invention employs a flattened reflection spectrum design for the pre-sampling grating region and the post-sampling grating region. Specifically, the pre-sampling grating region and the post-sampling grating region are designed to have a flattened reflection spectrum, ensuring that the reflectivity difference between the reflection peak at the center wavelength and the reflection peak at the edge wavelengths (e.g., the wavelengths corresponding to ±5th order reflection peaks) does not exceed 5% across the entire tunable wavelength range of the DBR laser. In contrast, this difference is typically above 20% for conventional sampling gratings, which is a major cause of non-uniformity in lasing characteristics across the entire wavelength range.

[0017] To achieve the aforementioned flattened reflection spectrum, both the pre-sampling grating region and the post-sampling grating region employ a small sampling duty cycle, preferably less than 10%, and preferably 4% to 6%. A small duty cycle significantly broadens the main lobe width of the reflection spectrum envelope and reduces the relative amplitude differences between different order reflection peaks, thus keeping the reflectivity difference between the 0th-order reflection peak and higher-order reflection peaks within 5% throughout the entire tuning range. It should be noted that reducing the sampling duty cycle decreases the grating coupling coefficient. Therefore, this invention increases the refractive index modulation amplitude by increasing the grating etching depth and appropriately increases the total length of the sampling grating, thereby compensating for the peak reflectivity and ensuring that the laser threshold current and output power are not affected.

[0018] Through the above design, the reflection spectrum envelopes of the front and rear sampling grating regions are significantly flattened. During vernier effect tuning, the grating reflectivity remains essentially consistent regardless of whether the lasing wavelength is located at the center or edge of the tuning range. This structure eliminates the need for excessively complex structures such as superstructure gratings and is fully compatible with conventional semiconductor fabrication processes.

[0019] (II) Active region design to extend 3dB gain bandwidth

[0020] The active region is designed to have an extended 3dB gain bandwidth, with its gain spectrum 3dB bandwidth being at least 70% wider than that of a conventional DBR laser active region. The 3dB bandwidth of a conventional active region is typically around 40nm, while the 3dB bandwidth of the active region in this invention can reach over 70nm, or even wider.

[0021] To achieve the aforementioned extended bandwidth, the active layer is a multi-layer stacked structure, and the structural parameters of each functional sublayer are not completely identical.

[0022] Furthermore, the active region employs a multi-quantum-well structure, and by adjusting the well layer thickness, barrier layer thickness, and strain of the quantum wells, its gain spectrum exhibits high gain flatness. Specifically:

[0023] Material system: InAlGaAs or InGaAsP material system is selected, which has good gain characteristics over a wide wavelength range;

[0024] Well layer thickness: designed to be 5–10 nm;

[0025] Debris layer thickness: designed to be 8–12 nm;

[0026] Strain introduction: Different compressive strains (e.g., 0.5%–1.5%) are introduced into different quantum wells to change the band structure, enhance the separation effect between light and heavy holes in the valence band, and thus expand the gain spectrum width; at the same time, different tensile strains are introduced into different barrier layers to further increase the band shift and broaden the gain bandwidth.

[0027] Number of cycles in multiple quantum wells: The number of cycles can be set to 5 to 10 cycles to balance the gain and bandwidth.

[0028] Similarly, to achieve extended bandwidth, the active region employs a multi-quantum dot structure, and by adjusting the size uniformity and strain of the quantum dots, its gain spectrum exhibits high gain flatness. Specifically:

[0029] Material system: InAs / GaAs quantum dot material system is selected;

[0030] Size inhomogeneity control: By introducing appropriate quantum dot size inhomogeneity (size fluctuation ±10%~15%), the ground state transition energies of each quantum dot are distributed in a gradient, and after superposition, a broad and flat gain spectrum is formed.

[0031] Strain engineering: By introducing appropriate compressive strain into the quantum dot layer and tensile strain into the spacer layer, the energy level distribution is further adjusted to suppress the filling effect of higher-order states, thereby ensuring uniform gain and stable saturated output power over a wide tuning range.

[0032] Multi-quantum dot cycle number: The number of cycles can be set to 5 to 10 cycles to balance the gain and bandwidth.

[0033] (III) Collaborative and Coordinated Working Method

[0034] During device operation, by applying different injection currents to the front and rear sampling grating regions, their effective refractive indices are altered. The vernier effect is used to continuously change the alignment position of the reflection peaks of the two gratings, thus achieving continuous tuning of the lasing wavelength. Simultaneously, a pump current is applied to the active region to provide optical gain. Since the reflection spectra of the front and rear sampling gratings are flattened, and supported by the wide gain bandwidth of the active region, even if the lasing wavelength shifts to the edge of the tuning range, the decrease in reflectivity and material gain is significantly suppressed. This ensures that key lasing characteristics such as output power, threshold current, side-mode rejection ratio, and linewidth remain highly consistent throughout the entire tuning range.

[0035] The technical solution provided by this invention does not rely on complex processes such as superstructure gratings that require high precision and high cost. It can significantly improve the full-wavelength tuning performance consistency of tunable DBR lasers by means of small sampling duty cycles and multi-quantum well composition / thickness adjustment, which can be achieved by conventional semiconductor processes. It has good manufacturability and repeatability.

[0036] The beneficial effects of this invention are:

[0037] (1) This invention significantly reduces the reflectivity difference between the center wavelength and the edge wavelength from over 20% to less than 5% by flattening the reflection spectrum of the sampling grating. Simultaneously, by expanding the 3dB gain bandwidth of the active region, the conventional 40nm 3dB bandwidth is broadened to over 70nm, effectively overcoming the inherent defect of high gain at the center and low gain at both sides of the active region. The synergistic effect of these two factors ensures that the DBR laser maintains high stability in key parameters such as output power, threshold current, side-mode rejection ratio, and linewidth across the entire range from the shortest to the longest tuning wavelength, meeting the stringent requirements for balanced performance across the entire wavelength range in optical communication, optical sensing, and optical measurement.

[0038] (2) This invention avoids the use of high-precision, high-cost reflectance spectrum flattening schemes such as superstructure gratings. The small-sampling duty cycle grating design adopted can be realized through conventional semiconductor processes such as holographic exposure or step lithography combined with reactive ion etching, with a wide process window and good repeatability. At the same time, the structural adjustment of the active region is a conventional technology in the field of semiconductor lasers and does not involve additional complex growth steps. The technical solution maintains excellent performance without increasing the substantial process difficulty, and has high industrialization feasibility.

[0039] (3) This invention maintains the basic multi-zone structure of the tunable DBR laser without introducing additional optical components, external cavity structures or multi-laser arrays. The device is fully monolithically integrated, with small size and high mechanical stability; a single laser can achieve wide-range continuous tuning, avoiding the system complexity and high cost brought about by multi-device integration, and maintaining the original structural and cost advantages of the tunable DBR laser.

[0040] (4) The present invention uses the current tuning mechanism, and the tuning speed can reach the microsecond or even nanosecond level, which is much faster than mechanically tuned external cavity lasers. It is suitable for application scenarios that require fast wavelength switching, such as optical packet switching, fast spectral scanning, and dynamic wavelength allocation in wavelength division multiplexing networks.

[0041] (5) The technical solution of the present invention is not limited to a specific material system or working band. It can be used to make O-band, C-band and L-band devices using InP-based material system, or O-band or other special band devices using GaAs-based material system. By adjusting the parameters, it can be extended to multiple bands to meet the application needs of different fields. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the planar structure of the tunable DBR semiconductor laser described in this invention;

[0044] Figure 2 This is a schematic diagram of the sampling grating described in this invention;

[0045] In the diagram: 101, rear grating region; 102, first isolation region; 103, phase region; 104, second isolation region; 105, gain region; 106, third isolation region; 107, front grating region; 201, grating groove.

[0046] Figure 3 This is a schematic diagram of the material structure of the active region of the multi-quantum well in Example 1.

[0047] Figure 4 This is a simulated reflection spectrum of the quantum well DBR semiconductor laser from Example 1.

[0048] Figure 5 This is a graph showing the relationship between the reflectivity and grating length of the quantum well DBR semiconductor laser in Example 1.

[0049] Figure 6 The simulated gain spectrum of the active region of the quantum well in Example 1 is shown.

[0050] Figure 7 The simulated reflection spectrum of the quantum well DBR semiconductor laser is shown in Comparative Example 1.

[0051] Figure 8 The simulated gain spectrum of the active region of the quantum well is shown in Comparative Example 1.

[0052] Figure 9 This is a simulated reflection spectrum of the quantum dot DBR semiconductor laser in Example 2.

[0053] Figure 10 The simulated reflection spectrum of the quantum dot DBR semiconductor laser is shown in Comparative Example 2. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The planar structure of the DBR semiconductor laser described in this invention is as follows: Figure 1 As shown, the resonant cavity is divided into a rear grating region 101, a first isolation region 102, a phase region 103, a second isolation region 104, a gain region 105, a third isolation region 106, and a front grating region 107 along its length. The front and rear ends of the laser are coated with high-reflection films to suppress FP cavity lasing and achieve single-mode output.

[0056] The device, from bottom to top, consists of an N-electrode, substrate, buffer layer, lower confinement layer, grating layer, lower waveguide layer, active layer, upper waveguide layer, upper confinement layer, P-type ohmic contact layer, and P-electrode. Among these:

[0057] The gain region 105 contains a complete active layer structure. The corresponding region grating layer has no grating etched. Electron-hole recombination is achieved by injecting current, generating stimulated emission light amplification to provide energy for the laser.

[0058] The rear grating region 101 and the front grating region 107 are engraved with multi-period sampling gratings in the grating layer, which serve as the rear and front reflectors of the laser cavity, respectively. The injected current can change the effective refractive index of the material in the region, causing the wavelength of the reflection peak to shift.

[0059] The material layer stacking structure of phase region 103 is the same as that of rear grating region 101 and front grating region 107, but its grating layer has not been etched with grating structure. The injected current can finely adjust the optical path in the cavity to ensure that the longitudinal mode is precisely aligned with the grating reflection peak and achieve continuous wavelength tuning.

[0060] The first isolation region 102, the second isolation region 104, and the third isolation region 106 are high-resistivity structures, which are fabricated through physical etching or ion implantation processes to achieve electrical isolation between each functional region and ensure independent current control in each region.

[0061] The structure of the sampling grating described in this invention is as follows: Figure 2As shown, 201 is the grating groove, Λ is the seed grating period, Ls is the sampling period, Lg is the grating length within a single sampling period, and the sampling duty cycle is Lg / Ls. The sampling grating can reflect a series of lasers with fixed wavelength intervals. The wavelength interval between the reflection peaks of the rear grating region and the front grating region is Δλ1≠Δλ2. Wavelength tuning is achieved based on the vernier effect: when a certain reflection peak of the front and rear sampling gratings is aligned at a specific wavelength, that wavelength satisfies the laser oscillation condition to generate lasing. By injecting current into the front and rear grating regions respectively to change the effective refractive index, the comb-like spectra of the two sets of reflection peaks can be moved relative to each other and realigned at the new wavelength, thus achieving the switching of the lasing wavelength.

[0062] This invention achieves a flattened reflection spectrum by setting the sampling duty cycle to less than 10%, which broadens the main lobe width of the reflection spectrum envelope and reduces the amplitude differences of each order of reflection peaks. At the same time, by adjusting the grating etching depth and the total grating length to compensate for the peak reflectivity, the device threshold and power performance are ensured to be unaffected by the reduction in duty cycle.

[0063] Example 1

[0064] This embodiment describes a DBR laser employing a planarized sampling grating and a wide-gain multi-quantum-well active region. The device is fabricated on an InP substrate, with a central lasing wavelength of 1550 nm and a seed grating period of 237.01 nm. The wavelength intervals of the reflection peaks in the rear and front grating regions are 4.3 nm and 4.7 nm, respectively, with sampling periods of 80.22 μm and 73.39 μm, respectively. The sampling duty cycles are both 0.04, and the number of sampling periods are 32 and 18, respectively, corresponding to total grating lengths of 2567 μm and 1321 μm, respectively. By increasing the total grating length and optimizing the etching depth, the decrease in coupling coefficient caused by the small duty cycle is compensated, ensuring that the peak reflectivity meets the device's lasing requirements.

[0065] The active region employs a 5-period graded parameter AlGaInAs multi-quantum-well structure, such as... Figure 3 As shown, the quantum well thicknesses from the p-side to the n-side are 6 nm, 8 nm, 10 nm, 8 nm, and 6 nm, respectively; the quantum well compressive strain is 12000 ppm, the barrier layer thickness is 10 nm, and the tensile strain is -3000 ppm. The gain peak positions of each quantum well are controlled by varying the well thickness, and the superposition of multiple peaks achieves gain bandwidth expansion. The remaining structural parameters of the device are consistent with Comparative Example 1: the active region length is 700 μm, the phase region length is 150 μm, the lengths of each isolation region are 40 μm, and the chip width is 300 μm.

[0066] The reflection spectrum of the sampling grating in this embodiment is as follows: Figure 4 As shown, within the wavelength range of 1520nm-1570nm, the difference in reflectivity of each order of the reflection peaks of the rear and front sampling gratings is controlled within 5%, and the flatness of the reflection spectrum is significantly improved. Figure 5The reflectance variation curves for the 0th, ±5th, and ±6th order reflection peaks under different sampling period numbers are shown. It can be seen that as the sampling period number increases, the reflectance of each order reflection peak increases synchronously, and the difference in reflectance between orders remains within a small range under the same period number. The active region gain spectrum of this embodiment is shown below. Figure 6 As shown, its 3dB gain bandwidth is approximately 80nm, representing an improvement of over 120% compared to Comparative Example 1, effectively covering the entire tuned wavelength range. This embodiment achieves high consistency in key parameters such as output power, threshold current, side-mode rejection ratio, and linewidth across the entire tuned range through the synergistic effect of a flattened reflective grating and a wide-gain active region.

[0067] Comparative Example 1

[0068] This comparative example uses a tunable DBR laser with a conventional sampling grating and a uniform quantum well active region as a benchmark for comparing the quantum well scheme of this invention. The device is fabricated on an InP substrate, with a central lasing wavelength of 1550 nm and a seed grating period of 237.71 nm. The wavelength intervals of the reflection peaks in the rear and front grating regions are 4.3 nm and 4.7 nm, respectively, with sampling periods of 80.74 μm and 73.87 μm, sampling duty cycles of 0.12 and 0.10, and sampling periods of 8 and 6, respectively. The corresponding total grating lengths are approximately 646 μm and 443 μm, respectively. The active region employs a 5-period uniform parameter AlGaInAs quantum well structure, with all quantum wells having a thickness of 6 nm and a compressive strain of 12000 ppm, and all barrier layers having a thickness of 10 nm and a tensile strain of -3000 ppm. Other structural parameters of the device: active region length is 700μm, phase region length is 150μm, each isolation region length is 40μm, and chip width is 300μm.

[0069] The sampled grating reflection spectrum of this comparative example is as follows: Figure 7 As shown, within the wavelength range of 1520nm-1570nm, the reflectivity differences between the rear and front sampling gratings are approximately 50% and 20%, respectively; the active region gain spectrum is as follows. Figure 8 As shown, its 3dB gain bandwidth is approximately 36nm. The strong wavelength dependence of reflectivity and gain together leads to significant differences in lasing characteristics such as output power, threshold current, and linewidth between the center and edge wavelengths of the device.

[0070] Example 2

[0071] This embodiment describes a DBR laser employing a planarized sampling grating and a wide-gain multi-quantum dot active region. The device is fabricated on a GaAs substrate, with a central lasing wavelength of 1300 nm and a seed grating period of 198.26 nm. The wavelength intervals of the reflection peaks in the rear and front grating regions are 4.3 nm and 4.7 nm, respectively, with sampling periods of 58.18 μm and 53.23 μm, respectively. The sampling duty cycles are both 0.04, and the number of sampling periods are 50 and 25, respectively, corresponding to total grating lengths of 2909 μm and 1331 μm, respectively. By increasing the total grating length and optimizing the etching depth, the decrease in coupling coefficient caused by the small duty cycle is compensated, ensuring that the peak reflectivity meets the device's lasing requirements.

[0072] The active region employs a 5-period InAs / GaAs quantum dot structure, with quantum dot size fluctuations ranging from ±10% to ±15%. This size inhomogeneity creates a gradient distribution of ground-state transition energies among the quantum dots, resulting in a broad and flat gain spectrum. Compressive strain is introduced into the quantum dot layers, and tensile strain is introduced into the spacer layers between adjacent quantum dot layers, further modulating the energy level distribution, suppressing higher-order state filling effects, and ensuring uniform gain and stable saturated output power over a wide tuning range. The remaining structural parameters of the device are consistent with Comparative Example 2: the active region length is 700 μm, the phase region length is 150 μm, the lengths of each isolation region are 40 μm, and the chip width is 300 μm.

[0073] The reflection spectrum of the sampling grating in this embodiment is as follows: Figure 9 As shown, within the wavelength range of 1270nm-1320nm, the difference in reflectivity of each order of the reflection peaks of the rear and front sampling gratings is controlled within 5%, the flatness of the reflection spectrum is significantly improved, and the consistency of lasing characteristics across the entire wavelength range is greatly improved.

[0074] Comparative Example 2 (Pre-existing Quantum Dot DBR Laser)

[0075] This comparative example uses a tunable DBR laser with a conventional sampling grating and a uniform quantum dot active region as a benchmark for the quantum dot scheme of this invention. The device is fabricated on a GaAs substrate, with a central lasing wavelength of 1300 nm and a seed grating period of 198.26 nm. The wavelength intervals of the reflection peaks in the rear and front grating regions are 4.3 nm and 4.7 nm, respectively, with sampling periods of 58.18 μm and 53.23 μm, respectively. The sampling duty cycles are both 0.10, and the number of sampling periods are 25 and 13, respectively, corresponding to total grating lengths of approximately 1454 μm and 692 μm, respectively. The active region adopts a 5-period InAs / GaAs quantum dot structure, with high quantum dot size uniformity and no deliberate size fluctuation design. Other structural parameters of the device are: active region length of 700 μm, phase region length of 150 μm, length of each isolation region of 40 μm, and chip width of 300 μm.

[0076] The sampled grating reflection spectrum of this comparative example is as follows: Figure 10 As shown, in the wavelength range of 1270nm-1320nm, the difference in reflectivity between the rear and front sampling gratings is approximately 29% and 26%, respectively, which directly leads to significant differences in the lasing characteristics of the center and edge wavelengths.

[0077] In summary, this invention, through the synergistic effect of a small duty cycle sampling grating planarization design and a wide-gain active region structure, significantly reduces the fluctuations in reflectivity and gain within the tuning range without introducing complex processes. This ensures that key lasing characteristics such as output power, threshold current, side-mode rejection ratio, and linewidth remain highly consistent across the entire tuning range. The solution is compatible with conventional semiconductor processing techniques, exhibits excellent manufacturability and repeatability, and possesses significant application value and industrialization prospects.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A DBR semiconductor laser with highly consistent lasing performance across its entire tuning range, comprising a substrate, an epitaxial stacked structure formed on the substrate, and N-electrodes and P-electrodes respectively disposed on the back side of the substrate and the top of the epitaxial stacked structure; the epitaxial stacked structure, from bottom to top, comprises a buffer layer, a lower confinement layer, a grating layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a P-type ohmic contact layer; characterized in that, The DBR semiconductor laser is divided into a rear grating region, a first isolation region, a phase region, a second isolation region, a gain region, a third isolation region, and a front grating region along the length of the resonant cavity. Multi-period sampling gratings are etched within the grating layers of the corresponding regions of the rear and front grating regions. The wavelength interval of the reflection peaks of the sampling gratings in the rear grating region is Δλ1, and the wavelength interval of the reflection peaks of the sampling gratings in the front grating region is Δλ2, where Δλ1 ≠ Δλ2. The sampling duty cycle of the sampling gratings in both the rear and front grating regions is less than 10%. The active layer is a multi-layer stacked structure, and the structural parameters of each functional sublayer within it are not entirely the same.

2. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The sampling duty cycle of the sampling gratings in both the rear and front grating regions is 4% to 6%, and the etching depth and total length of the sampling gratings are matched with the sampling duty cycle.

3. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The epitaxial stacking structure of the phase region is consistent with the epitaxial stacking structure of the front grating region and the rear grating region, and the grating layer in the corresponding area of ​​the phase region is not etched with a grating.

4. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The first isolation region, the second isolation region, and the third isolation region are all high-resistance structures used for electrical isolation.

5. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 4, characterized in that, The high-resistivity structure is formed by physical etching or ion implantation.

6. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The active layer is a multi-quantum-well structure, and the material system is InAlGaAs or InGaAsP.

7. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The multi-quantum well structure has a well layer thickness of 5–10 nm, a barrier layer thickness of 8–12 nm, and a period number of 5–10.

8. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 7, characterized in that, In the multi-quantum-well structure, the compressive strain and thickness of each quantum well are not exactly the same, and the tensile strain and thickness of each barrier layer are not exactly the same.

9. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 1, characterized in that, The active layer is a multi-quantum dot structure, and the material system is InAs / GaAs quantum dots; the number of periods of the multi-quantum dot structure is 5 to 10, and the size fluctuation range of the quantum dots is ±10% to ±15%.

10. The DBR semiconductor laser with highly consistent lasing performance across the entire tuning range according to claim 9, characterized in that, In the multi-quantum dot structure, the dimensions of each quantum dot layer are not exactly the same, each quantum dot layer has compressive strain, and the spacer layer between adjacent quantum dot layers has tensile strain.

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