Low power consumption continuously tunable DBR laser and control method thereof

Abstract

The application discloses a low-power continuous tunable DBR laser, which comprises an InP substrate, a short active region, a front passive region, a rear passive phase region and a rear passive region which are sequentially formed along the optical axis direction, a grating region is arranged above or below the short active region and a uniform Bragg grating is integrated, the short active region is designed in an asymmetric eccentric mode, a deep layer electric isolation groove is arranged between the first electrode and the second electrode and between the second electrode and the rear passive region and penetrates to the lower waveguide layer, and transverse thermal drift and current blocking are realized. The first electrode is continuously swept, the second electrode synchronously outputs a feedforward phase compensation current, the double electrodes cooperatively maintain the constant phase resonance condition, the mode jump-free continuous tuning in the specified waveband is realized, and the steady-state power consumption is reduced by about 44% compared with the traditional structure. The holographic grating one-time forming process and the double-electrode isolation design are adopted, an external temperature-sensitive controller is not needed, the structure is simplified, the process compatibility is good, and the preparation cost and the system complexity are reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronics technology, specifically to a low-power continuously tunable distributed Bragg reflector (DBR) laser, which is particularly suitable for laser gas sensing, fiber optic communication, spectral analysis and other fields, and can meet the application requirements of low power consumption, high stability and fast tuning for portable devices. Background Technology

[0002] Tunable semiconductor lasers, with their advantages of small size, high efficiency, and strong integrability, are widely used in fiber optic communication systems, laser gas sensing, and spectral analysis. Distributed Bragg reflector lasers, as the mainstream type of tunable laser, have their lasing wavelength determined by both the grating period and the effective refractive index of the waveguide. Conventional techniques often achieve wavelength tuning by changing the carrier concentration in the grating region through current injection, thereby controlling the effective refractive index.

[0003] With the development of optical communication and laser gas sensing technologies, stringent requirements have been placed on the power consumption, tuning range, tuning stability, tuning speed, and fabrication cost of DBR lasers. However, existing DBR lasers generally suffer from several drawbacks: First, they often employ three-electrode or multi-electrode structures, lacking effective isolation design between electrodes, which easily leads to current and thermal crosstalk, resulting in low tuning precision. Furthermore, mode-hopping occurs frequently during tuning, and the initial phase range control precision is insufficient, limiting the tuning range and making it difficult to achieve wide-range, mode-hopping-free continuous tuning. Second, high-performance DBR lasers often combine docking regeneration growth processes with electron beam λ / 4 phase-shifting gratings, which... The first problem is the high complexity and high manufacturing cost of DBR lasers, which also leads to poor compatibility with semiconductor mass production processes. Secondly, some structures require the integration of redundant components such as temperature-sensitive controllers, increasing both device complexity and system cost, and making them unsuitable for miniaturized, low-cost portable applications. Thirdly, traditional DBR lasers have high operating current and power consumption, and a long active region, resulting in a narrow non-mode-hopping tuning range that cannot meet the low-power, wide-tuning requirements of battery-powered portable devices. Fourthly, some existing non-mode-hopping DBR lasers rely on a single tuning current, which simplifies control but results in insufficient tuning stability and difficulty in balancing low power consumption and fast tuning characteristics.

[0004] Furthermore, among existing mode-hopping-free tuning technologies, vertical-cavity surface-emitting lasers (VCSELs) suffer from limited tuning speeds. While distributed feedback (DFB) laser arrays can achieve wide tuning ranges, their tuning speeds are slow due to thermal tuning mechanisms, failing to meet the demands of high-speed optical communication and other applications. To address these issues, there is an urgent need to develop a low-power, continuously tunable DBR laser with a simplified structure, excellent electrode isolation, low fabrication cost, stable tuning performance, fast tuning speed, and no need for complex temperature control. This would overcome the shortcomings of existing technologies and promote its large-scale application in fields such as laser gas sensing and optical communication. Summary of the Invention

[0005] The purpose of this invention is to provide a low-power continuously tunable DBR laser and its wavelength tuning control method. By combining short active region design and dual-electrode collaborative control technology, it solves the technical problems of existing DBR lasers, such as high power consumption, narrow tuning range, easy mode jumping during tuning, slow tuning speed, complex process, and dependence on temperature control components. It achieves continuous tuning of ≥4nm without mode jumping, while reducing device fabrication cost and system complexity, improving process compatibility, and meeting the application requirements of portable devices.

[0006] Technical solution To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A low-power continuously tunable DBR laser includes: an InP substrate; and a short active region, a front passive region, a rear passive phase region, and a rear passive region sequentially formed along the optical axis in an epitaxial layer of the InP substrate; a grating region is provided above or below the short active region, and a uniform Bragg grating is integrated within the grating region; the physical length of the short active region is less than that of the rear passive region, and the waveguide geometric center of the short active region is asymmetrically offset from the overall physical center of the laser along the optical axis, tending to be closer to the front exit cavity surface of the laser; the short active region, the front passive region, the rear passive phase region, and the rear passive region exhibit a step-by-step epitaxial growth interface in their physical structure; wherein, the grating region is a continuous first-order epitaxial layer formed on the surface of the InP substrate. The short active region is a secondary epitaxial layer embedded in or covering a specific region of the primary epitaxial layer. The passive waveguide group formed by the front passive region and the rear passive phase region is a tertiary epitaxial layer physically connected to the end face of the short active region along the optical axis. The upper surfaces of the short active region and the passive waveguide group are covered by four consecutive P-type epitaxial regions. The upper surface of the short active region is covered by a first electrode, and the upper surface of the rear passive phase region is covered by a second electrode. Electrically isolated grooves that cut off the upper cladding and penetrate to the interface of the lower waveguide layer are formed between the first electrode and the second electrode, and between the second electrode and the upper surface of the rear passive region. The electrically isolated grooves are filled with an insulating medium to form a lateral blocking structure against thermal drift and current diffusion in the active region.

[0007] The short active region is an InGaAsP multi-quantum-well structure with a length of 5-40 μm. By shortening the active region length and combining it with a high-coupling-coefficient grating design, the mode-hopping-free tuning range is significantly expanded, while optical field transmission loss is reduced and response speed is improved. The waveguide center point of the short active region is offset from the physical center of the laser and is closer to the front exit cavity surface of the laser, increasing the output power of the laser's front cavity surface and adapting to the application requirements of unidirectional light output. To compensate for the increased threshold gain caused by the short active region, a thick-layer design is adopted to achieve high mode gain. The short active region structure can be of two types: containing a grating region above or below it, or having no grating region above or below it.

[0008] The grating period of the high-coupling-coefficient uniform Bragg grating is set according to the target Bragg wavelength and is fabricated using a one-step holographic exposure process, eliminating the need for electron beam lithography and reducing process complexity and fabrication costs. The grating region supports two growth methods: first growing the lower grating and then growing the short active region, or first growing the short active region and then growing the upper grating. This allows for flexible selection based on actual process requirements, improving process compatibility. The coupling coefficient of the grating can be adjusted according to the tuning range requirements, preferably 150~300 cm⁻¹. - ¹, balancing tuning range and device stability.

[0009] The front passive region is made of InGaAsP waveguide material, and the rear passive phase region and the rear passive region are both made of InGaAsP waveguide material or other similar materials, with lengths of 10~50μm, 5~50μm, and 100~280μm, respectively. Each passive region adopts a bulk material or waveguide layer structure that matches the InGaAsP multi-quantum-well structure of the short active region. By adjusting the molar ratio of In, Ga, As, and P elements and the epitaxial layer thickness in the passive region and the short active region, the intrinsic absorption bandgap width of the passive region is made greater than the lasing photon energy of the short active region, so as to construct an equivalent refractive index matching structure for aligning the waveguide docking interface, and control the refractive index step difference between the two sides at the lasing wavelength within a preset tolerance range, thereby reducing mode mismatch and reducing intracavity loss.

[0010] The electrically isolated groove is formed by dry or wet etching, with a width of 3~10μm and a depth penetrating from the upper cladding to the lower waveguide layer. The groove is filled with an insulating medium, which can achieve complete electrical and thermal isolation between the first and second electrodes, effectively blocking current crosstalk and thermal crosstalk, improving the current control accuracy, and avoiding phase shift during tuning that could lead to mode skipping.

[0011] When the InP substrate is an N-type substrate, the first electrode and the second electrode are double P electrodes; when the InP substrate is a P-type substrate, the first electrode and the second electrode are double N electrodes. Both electrodes are Ti / Pt / Au multilayer metal structures, and the area of ​​the upper surface covered by the electrodes is 60%~80%, which ensures uniform current injection, improves the uniformity and stability of regulation, and reduces electrode contact resistance and power consumption.

[0012] The antireflection coating has a transmittance of more than 99% at the laser's operating wavelength. Its core purpose is to eliminate the uncontrollable parasitic reflection mode of the FP cavity introduced by the random cleavage position of the cleavage surface, completely cut off the random interference of the external end face to the initial phase inside the cavity, so that the initial lasing wavelength is completely controlled by the grating period and the injected current in the phase region, thereby improving the laser output stability and providing a guarantee for mode-hopping-free tuning.

[0013] This invention also provides a mode-skipping-free dynamic compensation wavelength tuning method for the above-mentioned low-power continuously tunable DBR laser, comprising the following coordinated control steps: Step A: Establish the correspondence between feedforward compensation: calibrate the intracavity background phase shift caused by the first electrode when it is tuned within the set current range, and generate the correspondence between the tuning current and the refractive index drift in the passive phase region. Step B: Asymmetric excitation and fundamental wavelength anchoring: Inject initial tuning current into the first electrode near the front emitting cavity surface, and use the high gain characteristics of the short active region set asymmetrically to lasing out the fundamental wavelength. Step C: Continuous Wavelength Sweep and Feedforward Phase Shift Compensation: During the process of continuously applying a sweeping tuning current to the first electrode to change the effective refractive index of the active region, the corresponding relationship in Step A is extracted simultaneously, and the corresponding phase compensation current is output to the second electrode simultaneously. After being driven by this phase compensation current, the passive phase region generates an inverse phase difference that matches the wavelength drift, so that while the laser continuously changes the output wavelength, it maintains the phase resonance condition between the feedback phase of the Bragg grating and the optical length of the phase region, thereby achieving continuous tuning without mode skipping within a specified wavelength band.

[0014] This control method eliminates the need for an external temperature-sensitive controller. It achieves laser thermal stability control through dual-current coordinated regulation, with a laser tuning range of ≥4nm, a side-mode rejection ratio of >35dB, and power consumption reduced by more than 35% compared to traditional DBR lasers, making it suitable for high-speed optical communication scenarios.

[0015] III. Beneficial Effects Compared with the prior art, the present invention has the following beneficial effects: 1. Low power consumption, wide tuning range, and continuous output without mode hopping: Combining a short active region with a high coupling coefficient grating design, and through dual-electrode coordinated control, continuous tuning without mode hopping (≥4nm) is achieved with a side-mode suppression ratio (SMR) >35dB, meeting the wide tuning range requirements of fields such as gas detection and covering the absorption spectra of various gases. The core physical mechanism for achieving low power consumption in this application lies in the synergy of "high coupling feedback and ultra-short gain volume". On the one hand, the active region length is shortened to 5~40μm, greatly reducing the effective emission volume of the active region, thereby significantly reducing the absolute values ​​of the transparency current and threshold current required to achieve population inversion; on the other hand, to compensate for the gain loss caused by the short cavity, this application incorporates a 150~500cm... - The high-coupling-coefficient grating provides extremely high optical reflectivity and intracavity feedback. This strong feedback allows the laser to establish stable oscillations even at relatively low injected carrier concentrations. Combined with the leakage current effect eliminated by the deep electrically isolated trench, the internal quantum efficiency of converting injected current into photons is significantly improved, ultimately resulting in a substantial reduction in overall power consumption on a macroscopic scale. This makes it suitable for battery-powered portable laser gas detection devices.

[0016] 2. Short cavity high coupling design improves device performance: The total cavity length of the laser is controlled at 200~300μm. The short cavity design effectively reduces optical field transmission loss and improves response speed; the grating area is integrated at 150~500cm. - ¹ A high-coupling-coefficient uniform Bragg grating enables efficient optical feedback, further improving the tuning performance and operational stability of the laser. At the same time, the short active region design expands the mode-hopping-free tuning range.

[0017] 3. Electrode Isolation Design to Eliminate Crosstalk and Improve Accuracy: Compared to the simple surface markings of traditional DBR lasers, the depth of the electrical isolation trench in this invention is strictly configured to penetrate the upper cladding and reach the lower waveguide layer. Combined with the asymmetric eccentric design of the short active region, this deep trench structure cuts off the lateral thermal conduction grid and carrier lateral diffusion channels in the InP epitaxial layer caused by the high current injection of the first electrode. When the first electrode performs a large-range step wavelength tuning current, the high thermal impedance wall generated by the deep electrical isolation trench ensures that the refractive index fine-tuning in the passive phase region is not affected by the crosstalk of the transient thermal effects of the active region. It is precisely because of this physical barrier jointly constructed by the epitaxial layer structure and the depth of the isolation trench shown in the attached figure that the effective refractive index control of the grating waveguide and the phase compensation of the phase region can be absolutely decoupled, thereby eliminating the fundamental mode drift during the tuning process from a physical source.

[0018] 4. Simplified process and significantly reduced manufacturing cost: The uniform Bragg grating adopts a one-time holographic exposure molding process, which eliminates the need for electron beam lithography and is fully compatible with existing semiconductor mass production processes; it supports two grating growth methods, with good process compatibility; it eliminates the need for redundant components such as external temperature controllers, reducing process steps by 20%, shortening the manufacturing cycle, and improving device yield; it can be integrated on a single chip to form a multi-channel array, further expanding the tuning range.

[0019] 5. Initial phase range locking, adaptable to multiple application scenarios: By depositing a high-transmittance antireflection film to eliminate cavity surface phase interference, an initial phase range of 0 < φ < π is introduced and locked, ensuring that the mode-hopping point is outside the operating current range; the laser operates in the wavelength range of 635nm to 2330nm, covering a variety of gas absorption spectra and optical communication bands, suitable for multiple fields such as laser gas sensing, optical communication, and spectral analysis, especially suitable for portable devices; at the same time, it can be monolithically integrated to form a multi-channel array, achieving a wider range of wavelength tuning, and adapting to WDM optical communication systems.

[0020] 6. Compact structure and easy integration: The overall structure is simplified, with no redundant temperature control components. The chip size is miniaturized, making it easy to integrate with other optoelectronic devices such as photodetectors and signal processing units. It can be applied to integrated optoelectronic systems, further expanding its application scenarios. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the side view of the low-power continuously tunable DBR laser of the present invention along the cavity length direction; Figure 2 This is a schematic diagram of the side view of the low-power continuously tunable DBR laser of the present invention along the cavity length direction; Figure 3 This is a flowchart of the wavelength tuning control method for the low-power continuously tunable DBR laser of the present invention; Figure 1 Marking explanation: 1-InP substrate, 2-grating region, 3-short active region, 4-front passive region, 5-back passive region, 5'-back passive phase region, 6-first electrode (short active region electrode), 7-second electrode (phase control electrode), 8-electric isolation groove, 9-antireflection film; Figure 2 Marking explanation: Same Figure 1 The markings are as follows: 1-InP substrate, 2-grating region, 3-short active region, 4-front passive region, 5-back passive region, 5'-back passive phase region, 6-first electrode (short active region electrode), 7-second electrode (phase control electrode), 8-electric isolation groove, 9-antireflection film. Figure 3Step description: Step A - Establish feedforward compensation correspondence; Step B - Asymmetric excitation and basic wavelength anchoring; Step C - Continuous wavelength sweep and feedforward phase shift compensation. The proportions of the components in the attached drawings are for illustrative purposes only and do not represent the actual size proportions of the devices; identical or similar markings represent identical or similar components. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the specific embodiments and accompanying drawings. The processes, conditions, experimental methods, etc., for implementing the present invention are obviously only some embodiments of this application, not all embodiments. Except for the content specifically mentioned below, all are common knowledge and general knowledge in the art. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1: Laser fabrication (growing the grating first, then growing the active region) The low-power continuously tunable DBR laser in this embodiment uses semi-insulating InP as the substrate and is fabricated by first growing the lower grating and then regrowing the short active region. The specific steps are as follows: 1. Grating Growth: A grating is grown on an InP substrate using a one-step holographic exposure process to fabricate a uniform Bragg grating with a period of approximately 239 nm and a coupling coefficient of 300 cm⁻¹. - ¹.

[0025] 2. Selective Region Growth: Using selective region growth technology, a 20μm long InGaAsP multi-quantum-well short active region (thick layer design to compensate for the threshold gain increase problem), a 20μm long InGaAsP waveguide material front passive region, a 15μm long InGaAsP waveguide material rear passive phase region, and a 170μm long InGaAsP waveguide material rear passive region are sequentially formed on the chip, with a total laser cavity length of 225μm. The waveguide center point of the short active region is offset from the physical center of the laser and is closer to the front output cavity surface.

[0026] 3. Creation of ridge waveguide and deep isolation trench: After forming the ridge waveguide by photolithography and dry etching, an electrical isolation trench (e.g., 1.5 μm deep and 10 μm wide) is etched between the first electrode and the second electrode, and between the second electrode and the upper surface of the passive region. The trench is filled with SiO2 insulating medium to construct a lateral thermal blocking barrier.

[0027] 4. Electrode fabrication: A Ti / Pt / Au multilayer metal electrode is fabricated, with the electrode covering 70% of the area of ​​the corresponding upper surface. Since the substrate is N-type, the first and second electrodes are double P electrodes.

[0028] 5. Anti-reflection coating: An anti-reflection coating is deposited on the front and rear ends of the laser, with a transmittance > 99%.

[0029] Example 2: Laser fabrication (active region grown first, then grating grown) The low-power continuously tunable DBR laser in this embodiment is fabricated using semi-insulating InP as the substrate and employs a method of first growing gratings onto the active regions of varying lengths. The specific steps are as follows: 1. Selective region growth: Using selective region growth technology, a 25μm long InGaAsP multi-quantum-well short active region, a 30μm long InGaAsP waveguide material front passive region, a 20μm long InGaAsP waveguide material back passive phase region, and a 175μm long InGaAsP waveguide material back passive region are sequentially formed on the InP substrate, resulting in a total laser cavity length of 250μm. The waveguide center point of the short active region is offset from the physical center of the laser and is closer to the front output cavity surface.

[0030] 2. Grating Growth: A grating is grown on the back side of the short active region. A uniform Bragg grating is fabricated using a one-step holographic exposure process. The grating period is approximately 240 nm, and the coupling coefficient is 200 cm⁻¹. - ¹.

[0031] 3. Creation of ridge waveguide and deep isolation trench: Similar to Example 1, after etching to form the ridge waveguide, an electrical isolation trench (e.g., 8 μm wide and 1.4 μm deep) is formed between the first electrode and the second electrode, and between the second electrode and the upper surface of the passive region, extending to the interface of the lower waveguide layer, and filled with SiO2 insulating medium.

[0032] 4. Electrode fabrication: A Ti / Pt / Au multilayer metal electrode is fabricated, with the electrode covering 70% of the area of ​​the corresponding upper surface. Since the substrate is N-type, the first and second electrodes are double P electrodes.

[0033] 5. Anti-reflection coating: An anti-reflection coating is deposited on the front and rear ends of the laser, with a transmittance > 99%.

[0034] In summary, Embodiments 1 and 2 respectively demonstrate two specific implementations where the grating region is located below and above the active region. Although the epitaxial growth order differs, both achieve the core objective of low power consumption and wide-range mode-hopping-free continuous tuning of this invention by vertically integrating a high-coupling-coefficient uniform Bragg grating with a short active region, supplemented by dual-electrode isolation and initial phase range locking technology. Those skilled in the art will understand that both structures are typical representatives of the inventive concept, and any adjustment to the stacking order based on the inventive concept should be considered within the protection scope of this invention.

[0035] Example 3: Factors Affecting Wavelength Tuning Performance 1. Structure of epitaxial materials Equation (1) shows the formula for the reflection center wavelength of the Bragg grating in a DBR laser: (1) In formula (1) For the grating period, This represents the effective refractive index of the grating region waveguide. The lasing wavelength of the laser is determined by this Bragg wavelength and the phase condition of the resonant cavity.

[0036] Wavelength tuning of a DBR laser can be achieved by changing the effective refractive index of the grating region or phase region. When the injection current increases, the plasma effect of charge carriers causes the refractive index to decrease, thus blue-shifting the lasing wavelength; conversely, it red-shifts. By adjusting the current injected into the grating region, wavelength drift caused by changes in ambient temperature can also be compensated for, locking the laser wavelength to the target absorption peak.

[0037] Equation (2) shows the bandgap (reflection peak bandwidth) of a uniform Bragg grating in a DBR laser. The approximate formula is: (2) In formula (2), κ is the grating coupling factor. For the grating Bragg wavelength, Let κ be the group refractive index of the grating region waveguide. From equation (2), it can be seen that the larger the grating coupling factor κ, the wider the grating bandgap of the DBR laser. The larger the value, the greater the tunable range of the laser's wavelength.

[0038] In this embodiment, the value of the grating coupling factor is designed based on the expected requirements for the grating bandgap and wavelength tuning range. As shown in formula (2), the coupling factor is proportional to the bandgap; therefore, under the same conditions, increasing κ helps to obtain a wider bandgap. By setting a coupling factor higher than that of conventional DBR lasers, a larger grating bandgap can be obtained, thereby supporting a wider range of wavelength and current tuning capabilities.

[0039] The coupling factor of a grating can be controlled in various ways, including optimizing the grating layer material, adjusting the grating layer thickness, changing the grating duty cycle, and modifying the grating morphology. In some embodiments, the coupling factor κ can be adjusted by optimizing the material or adjusting the thickness while keeping the grating duty cycle and morphology constant. Optionally, the value of κ can be set to be greater than 150 cm⁻¹. - ¹, for example, 200 cm - ¹.

[0040] 2. Setting the initial phase In practical applications, a suitable initial phase is essential for a sensing DBR laser to achieve continuous single-mode emission within the required tuning range and to reach the desired side-mode suppression ratio (SMR). The positions of the left and right modes in the spectrum of a sensing DBR laser correspond to phases 0 and π, respectively. If the initial phase is too small, insufficient SMR will occur when the current in the tuning segment increases from near zero. However, if the initial phase is too large, the tuning range of the sensing DBR laser will be too small when the current in the tuning segment increases from near zero. Therefore, this application proposes introducing an initial phase greater than 0 and less than π in the sensing DBR laser. As one embodiment, a value within the range of π / 4 ± π / 8 can be introduced as the initial phase. This ensures that the SMR meets the usage requirements without mode hopping, while also avoiding the problem of an excessively small laser wavelength tuning range. Of course, in practical applications, the initial phase range can be comprehensively set based on the requirements for both SMR and wavelength tuning range. It should be noted that due to the nanoscale randomness of semiconductor wafer cleaving processes, the physical initial phase of the device after fabrication is uncertain. To ensure that the device operates within the optimal initial phase range of 0 < φ < π during each power-on, this application employs an electrical preset position compensation mechanism: During the power-on initialization phase, the laser rapidly scans the injection current of the second electrode (phase control electrode) via an internal detection circuit (e.g., a small current scan of 0~5mA) and monitors the side-mode suppression ratio of the output spectrum. Since injecting current into the passive phase region linearly changes its effective refractive index, it effectively changes the optical path difference (i.e., changes the phase φ). The control system detects the point where the side-mode suppression ratio reaches its maximum value, indicating that the synthesized phase has been fine-tuned and anchored within the ideal range of 0 < φ < π. Subsequently, this preset position current is applied as a constant DC bias to the second electrode, serving as the "zero point" for subsequent wide-range wavelength tuning, thus completely solving the phase randomness problem caused by the manufacturing process.

[0041] 3. The position and length of the tuning section and the longitudinal mold spacing In DBR lasers, as the tuning current increases, the plasma effect causes the laser frequency to rise rapidly within nanoseconds; simultaneously, the injected current causes the chip temperature to gradually increase, thereby suppressing frequency rise. In the embodiments of this application, the position and length of the tuning section (short active region) in the DBR laser also affect the temperature distribution under current injection, thus affecting the phase tuning rate and overall tuning performance. By optimizing the length and position of the tuning section, better thermal stability and tuning efficiency can be achieved.

[0042] Formula (3) shows the formula for calculating the longitudinal mode spacing of a DBR laser: (3) In formula (3), For the grating Bragg wavelength, Let L be the effective refractive index of the waveguide with grating, and L be the total resonant cavity length. From formula (3), it can be seen that the smaller the total resonant cavity length of the laser (including the combined length of the short active and passive regions), the lower the effective refractive index within the cavity. The combined effect of these factors results in the longitudinal modulus spacing of its FP cavity. The larger the value, the more precise the laser cavity length. This application strictly controls the total cavity length of the laser to 200-300 μm, resulting in a significant widening of the lasing longitudinal mode spacing (e.g., greater than 2 nm). Simultaneously, in conjunction with formula (2), this application uses a length greater than 150 cm. - The high coupling coefficient κ of the ¹b broadens the bandgap L of the grating reflection spectrum (for example, to more than 10 nm). The core mechanism is that, through the synergy of the parameters of the two, it ensures that only one main longitudinal mode satisfies the lasing phase condition within the extremely wide grating bandgap, completely suppressing the oscillation competition between adjacent longitudinal modes, thereby achieving absolutely mode-free continuous output within a current tuning range of up to 4 nm.

[0043] It should be noted that both the front and rear end faces are coated with antireflection films with a transmittance greater than 99%. The core purpose of this is to eliminate uncontrollable parasitic reflection modes in the Fabry-Perot cavity introduced by the random cleavage positions of the cleavage surface. In this invention, the core resonant feedback of the laser does not rely on end-face reflection, but rather on a high coupling coefficient (150~500 cm⁻¹). - The strong distributed reflection formed by the uniform Bragg grating (¹) combined with the built-in reflection / scattering mechanism of the passive region maintains the lasing threshold. Thus, the end-face antireflection film completely cuts off the random interference of the external end-face phase on the initial phase inside the cavity, so that the initial lasing wavelength is precisely controlled by the grating period and the injected current in the phase region.

[0044] Example 4: Verification of Laser Wavelength Tuning Performance Comparative example: A conventional DBR laser was fabricated as a comparative example, which has the same material system as Example 1, but its active region length is 300 μm and its grating coupling coefficient is 50 cm⁻¹. - ¹, and only conventional shallow surface isolation is used between the electrodes. Under the same output power conditions, the total injection current required for the laser in this embodiment 1 to reach rated output is 25mA, while the comparative laser, due to its large size and severe leakage current, requires an injection current as high as 45mA. Actual measurements with a power meter show that the steady-state power consumption of the device of this invention is indeed reduced by approximately 44% (conservatively stated as more than 35%) compared to the comparative example.

[0045] The low-power continuously tunable DBR laser prepared in Example 1 was tested at room temperature (25°C) without the need for an external temperature controller. The test process and results are as follows: 1. Preset position locking test: The injection current (0~5mA) of the second electrode is scanned by the internal detection circuit to monitor and capture the maximum value of the side mode suppression ratio, lock the optimal initial preset position current, and eliminate the phase blind zone caused by the randomness of the cleavage position; 2. Dynamic Feedforward Compensation Tuning Test: A continuous wavelength sweep was initiated, injecting a 3-35mA sweep tuning current into the first electrode. Simultaneously, based on a pre-established feedforward compensation correspondence, the system synchronously outputs a dynamic phase compensation current to the second electrode. The laser wavelength was continuously and smoothly tuned from 1647.0nm to 1651.2nm, a tuning range of 4nm, strictly meeting the resonant phase matching condition throughout, completely eliminating mode hopping. 3. During tuning, phase shift is compensated by fine-tuning the Iphase, maintaining a side-mode rejection ratio >35dB throughout the process; 4. Power consumption test: According to comparative tests, the steady-state power consumption of this device is reduced by about 44% compared with the comparison (conservatively stated as more than 35%), and the thermal stability is excellent.

[0046] The scope of protection of this invention is not limited to the above embodiments. Any variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in this invention and are protected by the appended claims.

Claims

1. A low-power continuously tunable DBR laser, characterized in that, include: InP matrix; The laser comprises a short active region, a front passive region, a rear passive phase region, and a rear passive region sequentially formed along the optical axis in the epitaxial layer of the InP substrate; a grating region is provided above or below the short active region, and a uniform Bragg grating is integrated within the grating region; characterized in that the physical length of the short active region is less than that of the rear passive region, and the waveguide geometric center of the short active region is asymmetrically offset from the overall physical center of the laser along the optical axis, and tends to be closer to the front exit cavity surface of the laser; the short active region, the front passive region, the rear passive phase region, and the rear passive region exhibit a step-by-step epitaxial growth interface in physical structure; wherein, the grating region is a continuous primary epitaxial layer formed on the surface of the InP substrate, and the short active region... As a secondary epitaxial layer embedded or covering a specific region of the primary epitaxial layer, the passive waveguide group formed by the front passive region and the rear passive phase region is a tertiary epitaxial layer physically connected to the end face of the short active region along the optical axis; the upper surface of the short active region and the passive waveguide group is jointly covered by four consecutive epitaxial P-type regions; the upper surface of the short active region is covered with a first electrode, and the upper surface of the rear passive phase region is covered with a second electrode; electrical isolation grooves that sink and cut off the upper cladding and penetrate to the interface of the lower waveguide layer are formed between the first electrode and the second electrode, and between the second electrode and the upper surface of the rear passive region, and the electrical isolation grooves are filled with insulating medium to form a lateral blocking structure against thermal drift and current diffusion in the active region.

2. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The short active region is an InGaAsP multi-quantum-well structure with a length of 5~40μm. By shortening the length of the active region, the mode-hopping-free tuning range is expanded. The waveguide center point of the short active region is offset from the physical center of the laser and is closer to the front exit cavity surface of the laser.

3. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The short active region includes a grating region above or below it.

4. The low-power continuously tunable DBR laser according to claim 1, characterized in that, There is no grating region above or below the short active region.

5. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The grating period of the high-coupling-coefficient uniform Bragg grating is set according to the target Bragg wavelength and is fabricated using a one-step holographic exposure process.

6. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The grating region is located between the short active region and the InP substrate.

7. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The short active region is located between the grating region and the InP substrate.

8. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The preceding passive region is made of InGaAsP waveguide material with a length of 10-50 μm; the following passive phase region is made of InGaAsP waveguide material or other similar material with a length of 5-50 μm; the following passive region is made of InGaAsP waveguide material or other similar material with a length of 100-280 μm; the preceding passive region, the following passive phase region, and the following passive region all adopt bulk material or waveguide layer structure that matches the InGaAsP multi-quantum-well structure of the short active region; by adjusting the molar ratio of In, Ga, As, and P elements and the epitaxial layer thickness in the passive region and the short active region respectively, the intrinsic absorption bandgap width of the passive region is made greater than the lasing photon energy of the short active region, so as to construct an equivalent refractive index matching structure for aligning the waveguide docking interface, and control the refractive index step difference between the two sides at the lasing wavelength within a preset tolerance range.

9. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The electrical isolation trench is fabricated by dry or wet etching, with a width of 3~10μm and a depth penetrating from the upper cladding to the lower waveguide layer. The trench is filled with an insulating medium.

10. The low-power continuously tunable DBR laser according to claim 1, characterized in that, When the InP substrate is an N-type substrate, the first electrode and the second electrode are double P electrodes; when the InP substrate is a P-type substrate, the first electrode and the second electrode are double N electrodes; both electrodes are Ti / Pt / Au multilayer metal structures, and the area of ​​the upper surface covered by the electrodes accounts for 60% to 80% of the corresponding region.

11. The low-power continuously tunable DBR laser according to claim 1, characterized in that, The antireflection film has a transmittance of more than 99% at the laser's operating wavelength and is used to eliminate cavity surface phase interference and assist in locking the initial phase range.

12. A mode-hopping-free dynamic compensation wavelength tuning method based on the low-power continuously tunable DBR laser of claim 1, characterized in that, This includes the following coordinated control steps: Step A: Establish the correspondence between feedforward compensation: calibrate the intracavity background phase shift caused by the first electrode when it is tuned within the set current range, and generate the correspondence between the tuning current and the refractive index drift in the passive phase region. Step B: Asymmetric excitation and fundamental wavelength anchoring: Inject initial tuning current into the first electrode near the front emitting cavity surface, and use the high gain characteristics of the short active region set asymmetrically to lasing out the fundamental wavelength. Step C: Continuous Wavelength Sweep and Feedforward Phase Shift Compensation: During the process of continuously applying a sweeping tuning current to the first electrode to change the effective refractive index of the active region, the corresponding relationship in Step A is extracted simultaneously, and the corresponding phase compensation current is output to the second electrode simultaneously. After being driven by this phase compensation current, the passive phase region generates an inverse phase difference that matches the wavelength drift, so that while the laser continuously changes the output wavelength, it maintains the phase resonance condition between the feedback phase of the Bragg grating and the optical length of the phase region, thereby achieving continuous tuning without mode skipping within a specified wavelength band.

13. The wavelength tuning control method according to claim 12, characterized in that, No external temperature-sensitive controller is required; the thermal stability of the laser is controlled through dual-current coordinated regulation. The side-mode rejection ratio is >35dB, and the power consumption is reduced by more than 35% compared with traditional DBR lasers.

14. The wavelength tuning control method according to claim 12, characterized in that, Before performing step B, an electrical preset position compensation step is also included: during the power-on initialization phase, the current injected into the second electrode is scanned through the internal detection circuit, and the side-mode rejection ratio of the output spectrum is monitored; the current point corresponding to the maximum value of the side-mode rejection ratio is captured, and the preset position current is applied to the second electrode as the initial DC bias to anchor the physical initial phase in the ideal range of 0 < φ < π.

15. The wavelength tuning control method according to claim 12, characterized in that, In step C, the phase compensation current synchronously output to the second electrode and the frequency sweep tuning current of the first electrode are strictly synchronized in the time domain to ensure that the side-mode rejection ratio of the device remains stable during the continuous wavelength sweep process, and the steady-state power consumption is significantly reduced compared with the conventional fixed bias mode.

16. The low-power continuously tunable DBR laser according to any one of claims 1 to 11, characterized in that, Multiple lasers are monolithically integrated to form a multichannel array.

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