Semiconductor laser chip with high power and low intensity noise and laser

Abstract

The invention provides a high-power low-intensity-noise semiconductor laser chip and a laser, a lower waveguide layer is arranged above an N-type substrate, two optical limiting layers are arranged above the lower waveguide layer, an active layer is clamped between the two optical limiting layers, a grating layer is arranged on the optical limiting layers, and the grating layer is arranged on the N-type substrate. An upper cladding layer is arranged on the grating layer, and a contact metal layer is arranged on the upper cladding layer; the grating layer is integrated with a lambda / 4 phase shift structure; and the semiconductor laser chip adopts a ridge waveguide structure. Compared with a traditional narrow ridge waveguide DFB laser, the narrow ridge waveguide DFB laser has the advantages that under the short cavity length condition, the output power exceeding hundreds of milliwatts, low relative intensity noise, high side mode rejection ratio and the narrow line width of about hundreds of kHz are achieved, and meanwhile the relaxation oscillation frequency of the GHz level is achieved. The laser chip shows good power linearity and single-mode stability in a lower normal temperature range, and is suitable for the fields of high-speed optical fiber communication, microwave photonics and the like with strict requirements on power and noise performance.

Description

Technical Field

[0001] This invention relates to the field of information photonics, and more specifically to a high-power, low-intensity-noise semiconductor laser chip and a laser. Background Technology

[0002] High-power semiconductor lasers with wavelengths around 1550 nm have wide applications in free-space optical communication, silicon photonics co-packaging, coherent optical communication, lidar (LiDAR), and high-resolution spectroscopy. This is mainly due to the low transmission loss of this wavelength in optical fibers and the atmosphere, and its inclusion in the "eye-safe" band. Furthermore, for applications such as microwave photonics and analog signal transmission (e.g., CATV), the relative intensity noise (RIN) of the laser is a critical performance parameter; low noise is a prerequisite for ensuring the system's signal-to-noise ratio and dynamic range.

[0003] To achieve high power output, traditional semiconductor lasers typically employ narrow ridge waveguide structures to maintain stable single-mode operation, avoiding beam quality degradation and power instability caused by higher-order mode lasing. However, the narrow waveguide structure limits the size of the active layer and the saturation output level of optical power. While increasing the cavity length can improve power to some extent, this increases device size, series resistance, and cost, and may degrade high-frequency response characteristics. To overcome the power limitations imposed by narrow waveguides while maintaining single-mode characteristics, various approaches have been explored. One solution is to use asymmetric cladding or thick waveguide layers to push the optical field towards the n-type substrate side, reducing overlap with the p-type doped layer (the main source of optical absorption loss) and thus lowering internal losses. For example, several micrometers thick InGaAsP material is used as the n-side waveguide layer. However, the epitaxial growth of thick InGaAsP requires precise lattice-matching control, resulting in high processing difficulty and cost; furthermore, its thermal conductivity is much lower than that of InP, severely limiting the device's heat dissipation capacity and causing a sharp drop in power at high temperatures.

[0004] Therefore, there is a lack of laser chips in the existing technology that can effectively address multiple challenges such as high power, wide waveguide single-mode stability, low internal loss, and low intensity noise. Summary of the Invention

[0005] One of the objectives of this invention is to provide a high-power, low-intensity noise semiconductor laser chip to solve the problems of output power, wide waveguide single-mode stability, internal loss, and noise intensity imbalance in existing semiconductor laser chips.

[0006] The second objective of this invention is to provide a high-power, low-intensity-noise semiconductor laser to improve the performance of the laser.

[0007] One of the objectives of this invention is achieved as follows: A high-power, low-intensity-noise semiconductor laser chip comprises a lower waveguide layer disposed above an n-type substrate, two optical confinement layers disposed above the lower waveguide layer, an active layer sandwiched between the two optical confinement layers, a grating layer disposed on the optical confinement layers, an upper cladding layer disposed on the grating layer, and a contact metal layer disposed on the upper cladding layer; the grating layer integrates a λ / 4 phase shift structure; the semiconductor laser chip employs a ridge waveguide structure.

[0008] Furthermore, the lower waveguide layer is an n-type doped InGaAsP layer.

[0009] Furthermore, the κL of the grating layer is 1; where κ is the coupling coefficient and L is the cavity length.

[0010] Furthermore, the active layer adopts an InGaAsP multi-quantum-well structure.

[0011] Furthermore, buried heterojunctions are also disposed around the sides of the active layer, optical confinement layer and lower waveguide layer to enhance current confinement and thermal management.

[0012] Furthermore, an anti-reflective film is deposited on the front end of the semiconductor laser chip, and a high-reflective film is deposited on the rear end.

[0013] The second objective of this invention is achieved as follows: A high-power, low-intensity-noise semiconductor laser, comprising: A semiconductor laser chip is connected to a temperature feedback control module and a performance compensation module, respectively, to generate laser light; The temperature feedback control module is connected to both the semiconductor laser chip and the tunable driver and feedback module, and is used to monitor the temperature of the semiconductor laser chip. The photoelectric detection module is connected to the semiconductor laser chip and the tunable drive and feedback module respectively, and is used to monitor the output parameters of the semiconductor laser chip; The tunable drive and feedback module is connected to the semiconductor laser chip and the performance compensation module, respectively, and is used to adjust the operating parameters of the semiconductor laser chip. The semiconductor laser chip is the semiconductor laser chip described in one of the objectives of this invention.

[0014] This invention aims to propose a high-power, low-intensity-noise semiconductor laser chip. This solution fully utilizes the excellent optoelectronic properties of InGaAsP and InP material systems (high lattice matching, tunable bandgap, and good thermal conductivity), and combines innovative waveguide structures and heterojunction designs to integrate a high-gain multiple quantum well (MQW) active unit, an optically modulated composite waveguide, a single-mode guarantee grating, and a low-loss doped cladding into an integrated semiconductor laser chip. By leveraging a dual-waveguide synergistic structure to weaken lateral light confinement, fundamental mode stability is maintained within a wider waveguide size, avoiding mode jumps caused by higher-order mode excitation. Combined with a distributed feedback (DFB) grating containing a λ / 4 phase shift, spatial hole burning is effectively suppressed, achieving high side-mode suppression ratio (SMSR) single-longitudinal mode output. Simultaneously, the use of InP, a material with high thermal conductivity, optimizes the heat conduction path, alleviating heat accumulation in the active layer. This design solves the core problems of traditional high-power semiconductor lasers, such as the difficulty in balancing high power and low noise, the contradiction between wide waveguides and single-mode stability, and performance degradation due to heat accumulation. It improves the temperature adaptability and long-term reliability of the laser chip, providing a compact, efficient, and stable laser source solution for fields such as optical communication, lidar, and silicon photonics co-packaging.

[0015] This invention provides a high-power, low-intensity-noise semiconductor laser chip, proposing a novel approach of "wide waveguide, low-loss optical field management." By employing a dual-waveguide structure, it fundamentally overcomes the contradiction between "narrow waveguide for single-mode operation" and "high power requires wide waveguides" in traditional lasers. It achieves output power exceeding milliwatt levels, low relative intensity noise (RIN), high side-mode rejection ratio (SMSR), and approximately kiloHz-level narrow linewidth under micrometer-scale wide waveguide and short cavity length conditions. This results in the synergistic optimization of multiple key performance indicators, including high power, single-mode operation, and low noise.

[0016] The semiconductor laser chip of this invention utilizes the inherent advantages of this structure in reducing internal losses and improving thermal management through monolithic integration of dual waveguides and buried heterojunctions. This integrated design simplifies the structure of the laser chip and enhances stability while achieving high performance, providing a more reliable and efficient solution for addressing the demand for high-performance light sources in fields such as high-speed optical communication and microwave photonics. The high-power, low-intensity-noise semiconductor laser of this invention monitors the parameters of the semiconductor laser chip in real time through a temperature feedback control module and a photoelectric detection module, and adjusts the operating parameters of the semiconductor laser chip through a tunable drive and feedback module, further reducing the relative intensity noise of the semiconductor laser chip. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the present invention.

[0018] Figure 2Side view of the present invention.

[0019] Figure 3 Scanning electron microscope image of the present invention.

[0020] Figure 4 These are the measured current curves of this invention at different temperatures.

[0021] Figure 5 This describes the performance of the present invention within a temperature range of −10°C to 60°C.

[0022] Figure 6 This is the measured relative noise intensity spectrum of the present invention.

[0023] The components are: 1. Lower cladding layer; 2. Lower waveguide layer; 3. Optical confinement layer; 4. Active layer; 5. Grating layer; 6. Upper cladding layer; 7. Contact metal layer; 8. Front end face; 9. Rear end face. Detailed Implementation

[0024] like Figure 1 As shown, the high-power, low-intensity-noise semiconductor laser chip of the present invention includes a lower waveguide layer 2 disposed above an N-type substrate, two optical confinement layers 3 disposed above the lower waveguide layer 2, an active layer 4 sandwiched between the two optical confinement layers 3, a grating layer 5 disposed on the optical confinement layers 3, an upper cladding layer 6 disposed on the grating layer 5, and a contact metal layer 7 disposed on the upper cladding layer 6. The semiconductor laser chip adopts a ridge waveguide structure; the grating layer 5 integrates a λ / 4 phase shift structure for realizing single-longitudinal-mode lasing.

[0025] The lower cladding layer 1 is an N-type InP, which is epitaxially grown on the substrate by MOCVD. Its refractive index is lower than that of the lower waveguide layer and the active layer, which confines the light field in the vertical direction and prevents light from leaking into the substrate.

[0026] The lower waveguide layer 2 is a passive lower waveguide layer, and it is made of N-type InGaAsP. The lower waveguide layer 2 and the active layer 4 together form a dual waveguide structure, which distributes the energy of the optical field partially, or even primarily, to this layer. This reduces the overlap between the optical mode and the upper P-type doped region, thereby significantly reducing the internal loss caused by P-type material absorption. It also weakens the lateral confinement force of the ridge waveguide on the light, enabling the suppression of higher-order transverse modes and achieving stable single-mode operation even with a relatively wide ridge waveguide.

[0027] The optical confinement layer 3 effectively confines the generated light to the active layer 4 and its vicinity, and overlaps with the carrier distribution to ensure high optical gain. The active layer 4 adopts a multi-quantum well structure, with buried heterojunction structures on both sides of the active layer, which are composed of P-type and N-type InP layers.

[0028] The grating layer 5 integrates a λ / 4 phase shift structure. A λ / 4 phase shift introduces a phase abrupt change equivalent to a quarter wavelength at the center of the grating. The material of grating layer 5 is formed by etching a defined pattern onto the grating layer material with an electron beam, followed by reactive ion etching to create a periodic corrugated structure. Grating layer 5 provides distributed optical feedback and utilizes its mode selection properties to enable the laser chip to operate in a single longitudinal mode. The λ / 4 phase shift structure disrupts the grating's symmetry, ensuring the laser has a definite dominant mode near the Bragg wavelength, thus stabilizing single-mode output.

[0029] The value of κL in the grating layer is 1; where κ is the coupling coefficient and L is the cavity length.

[0030] The buried heterojunction is arranged around the sides of the active layer 4, the lower waveguide layer 2 and the optical confinement layer 3. The buried heterojunction is formed by alternating growth of p-type InP and n-type InP to form a current confinement channel, which guides the injected current to flow precisely to the active layer, reduces the threshold current and series resistance, and reduces the additional noise and heat accumulation caused by current loss.

[0031] The upper cladding layer 6 is P-type InP, which is grown on the grating layer via secondary epitaxial growth using MOCVD. The function of the upper cladding layer 6 is similar to that of the lower cladding layer 1, confining the optical field in the vertical direction. It also serves as the hole transport layer for current injection. The contact metal layer 7 is formed on the P+ contact layer through metallization processes such as evaporation and sputtering, and acts as the anode for the injected driving current.

[0032] The ridge waveguide consists of an upper cladding layer 6 and a contact metal layer 7 on top. The ridge's sides are etched at bevels or vertical surfaces using inductively coupled plasma etching (ICP-RIE) and selective wet etching to partially etch the upper cladding layer 6 and the contact metal layer 7, forming a protruding "ridge." Current is confined to a narrow region below the ridge, ensuring efficient carrier injection into the active layer. The effective refractive index difference between the ridge and the etched regions on either side constitutes a lateral optical waveguide, confining the light field to propagate below the ridge.

[0033] like Figure 2 As shown, an anti-reflection film is deposited on the front surface 8 of the semiconductor laser chip to minimize reflection and enable efficient laser output; a high-reflection film is deposited on the rear surface 9 of the semiconductor laser chip to maximize reflection, increase the photon density in the resonant cavity, and improve laser output efficiency and power.

[0034] like Figure 3As shown, the semiconductor laser chip exhibits a clear layered stacking and a distinct lateral waveguide morphology. The interfaces between layers are smooth and the thickness is uniform, indicating good controllability of the epitaxial growth and etching processes. At the bottom of the structure, the n-type InP substrate and its lower waveguide layer 2 are visible, with the active layer 4 above it, largely consistent with the design values, providing an effective region for optical gain. The buried heterojunction structure on the side of the active layer 4 effectively restricts lateral current diffusion. At the top, the upper cladding layer and contact metal layer of the p-type InP completely cover the ridge region. This cross-sectional structure demonstrates the advantages of the semiconductor laser chip of this invention in terms of material quality, interface control, and structural integrity, providing a reliable device foundation for achieving high-power, low-noise laser output.

[0035] The present invention also provides a high-power, low-intensity-noise semiconductor laser, specifically including a semiconductor laser chip and a temperature feedback control module, a photoelectric detection module, and a tunable drive and feedback module connected to the semiconductor laser chip. The temperature feedback control chip and the photoelectric detection module are both connected to the tunable drive and feedback module.

[0036] The temperature feedback module monitors the chip temperature in real time and transmits the temperature signal to the tunable drive and feedback module. The photodetector module integrates an InGaAs photodetector to detect the light intensity, spectrum, and relative intensity noise (RIN) signal output by the semiconductor laser chip in real time, and sends the detected signals to the tunable drive and feedback module. Based on the parameters detected by the temperature feedback module and the photodetector module, the tunable drive and feedback module adjusts operating parameters such as the injection current; it compensates for the laser's output power and spectral performance, achieving wavelength tunability and suppressing mode jumps caused by temperature drift. Simultaneously, by adjusting the grating coupling state and current injection accuracy through feedback, it stably controls the RIN at a low level, ensuring that the semiconductor laser chip can stably output high-power, low-intensity-noise laser signals under different temperature and power conditions, while maintaining good spectral characteristics.

[0037] like Figure 4 As shown, this invention utilizes a multi-temperature range testing module to comprehensively test semiconductor laser chips at different temperature environments ranging from -10℃ to 60℃. A power-current (PI) characteristic monitoring module is used to accurately capture the variation of laser output power with injection current at different temperatures. The figure clearly shows that as the temperature increases, the output power saturation value of the semiconductor laser chip decreases, and the current threshold for reaching saturation also changes, demonstrating the significant impact of temperature on the power output capability of the semiconductor laser chip.

[0038] like Figure 5As shown, this invention also uses a spectral characteristic monitoring module to detect the spectral output of the laser at different temperatures. The peak wavelength, spectral line intensity, and other characteristics of the laser spectrum differ at different temperatures. With temperature changes, the peak position of the spectrum shifts to a certain extent, and the intensity distribution of the spectral lines also varies, reflecting the regulatory effect of temperature on the laser's spectral characteristics. By comparing and analyzing the PI curves and spectra at different temperatures, these monitoring signals are fed back to the temperature optimization control unit, thereby adjusting the structural parameters of the semiconductor laser chip and the temperature control strategy during operation. This ensures that the semiconductor laser chip maintains good performance under different temperature environments, achieving stable high-power output and precise control of spectral characteristics over a wide temperature range.

[0039] like Figure 6 As shown, this invention utilizes a multi-injection current testing module to test semiconductor laser chips under different injection current conditions ranging from 200mA to 600mA. The RIN spectrum monitoring module accurately captures the variation of relative intensity noise of the laser with frequency under different injection currents. The figure clearly shows that the spectral distribution and intensity of the RIN differ significantly with changes in injection current; the peak position and amplitude of the RIN vary under different currents, demonstrating the significant impact of injection current on laser noise characteristics. Simultaneously, the noise characteristic analysis module performs in-depth analysis of these RIN spectra, extracting noise characteristics across different frequency bands. These monitored and analyzed signals are fed back to the current optimization control unit, which adjusts the injection current magnitude and control strategy to ensure that the semiconductor laser chip maintains good noise performance under different current conditions, achieving low-intensity noise laser output over a wide current range.

Claims

1. A high-power, low-intensity-noise semiconductor laser chip, characterized in that, A lower waveguide layer is disposed above an N-type substrate, two optical confinement layers are disposed above the lower waveguide layer, an active layer is sandwiched between the two optical confinement layers, a grating layer is disposed on the optical confinement layer, an upper cladding layer is disposed on the grating layer, and a contact metal layer is disposed on the upper cladding layer; the grating layer integrates a λ / 4 phase shift structure; the semiconductor laser chip adopts a ridge waveguide structure.

2. The semiconductor laser chip according to claim 1, characterized in that, The lower waveguide layer is an n-type doped InGaAsP layer.

3. The semiconductor laser chip according to claim 1, characterized in that, The grating layer has κL=1; where κ is the coupling coefficient and L is the cavity length.

4. The semiconductor laser chip according to claim 1, characterized in that, The active layer adopts an InGaAsP multi-quantum-well structure.

5. The semiconductor laser chip according to any one of claims 1-4, characterized in that, Buried heterojunctions are also disposed around the sides of the active layer, optical confinement layer and lower waveguide layer to enhance current confinement and thermal management.

6. The semiconductor laser chip according to claim 1, characterized in that, An anti-reflective film is deposited on the front end of the semiconductor laser chip, and a high-reflective film is deposited on the rear end.

7. A high-power, low-intensity-noise semiconductor laser, characterized in that, include: A semiconductor laser chip is connected to a temperature feedback control module and a performance compensation module, respectively, to generate laser light; The temperature feedback control module is connected to both the semiconductor laser chip and the tunable driver and feedback module, and is used to monitor the temperature of the semiconductor laser chip. The photoelectric detection module is connected to the semiconductor laser chip and the tunable drive and feedback module respectively, and is used to monitor the output parameters of the semiconductor laser chip. The tunable drive and feedback module is connected to the semiconductor laser chip and the performance compensation module, respectively, and is used to adjust the operating parameters of the semiconductor laser chip. The semiconductor laser chip is the semiconductor laser chip according to any one of claims 1-6.

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