Ultra-wideband tunable DFB laser array based on enhanced self-heating effect and design method thereof

Abstract

The invention discloses an ultra-wideband tunable DFB laser array based on an enhanced self-heating effect and a design method of the ultra-wideband tunable DFB laser array. The ultra-wideband tunable DFB laser array is composed of a plurality of DFB semiconductor lasers. Wherein the differential resistance of each DFB semiconductor laser is 10-15 ohm, and the pure current wavelength tuning range of the single DFB semiconductor laser is 5-7 nm. According to the broadband tunable DFB laser array, by reducing the material doping concentration of the p waveguide area of the DFB semiconductor laser, the differential resistance of the laser is improved, the heat effect caused by injection current change is enhanced, the current tuning range of the single DFB semiconductor laser is widened, the integration number of the DFB semiconductor lasers needed by the broadband tunable DFB laser array is greatly reduced, and the broadband tunable DFB laser array is achieved. According to the scheme of the invention, rapid wavelength switching can be realized through current injection.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technologies, and particularly to an ultra-wideband tunable DFB laser array based on enhanced self-heating effect and its design method. Background Art

[0002] With the development of advanced technologies such as artificial intelligence and the Internet of Things, tunable lasers with a wide wavelength tuning range have become crucial in future data centers, metropolitan area transmissions, and access networks employing dense wavelength division multiplexing systems. Tunable lasers can replace fixed-wavelength lasers, reducing the system volume and cost, while facilitating the achievement of high network capacity. Currently, various tunable lasers have been proposed in the prior art. Among them, tunable DFB laser arrays have attracted much attention due to their excellent single longitudinal mode characteristics and simple wavelength tuning mechanism.

[0003] In a tunable DFB laser array, coarse tuning is achieved by selecting the working laser, and fine tuning of the wavelength is achieved by adjusting the thermoelectric cooler (TEC) or the injection current. Conventionally, in the wavelength tuning process of a tunable DFB laser array, the temperature is usually adjusted by the TEC, but this process consumes a high amount of energy, and the wavelength stabilization time usually lasts for several seconds, which is not suitable for scenarios requiring rapid wavelength tuning. Therefore, wavelength tuning based on the injection current is more attractive due to its fast and low-power consumption characteristics. However, the current tuning wavelength range of a single DFB laser unit is limited, usually less than 1.5 nm. Theoretically, to achieve a wide wavelength tuning range such as 60 nm, about 40 DFB laser units need to be integrated, which will significantly increase the manufacturing complexity of the DFB laser array and reduce the yield rate. Therefore, expanding the current tuning range of a single DFB laser unit, reducing the number of integrated lasers, and achieving a wide wavelength tuning range are the current research focuses. Summary of the Invention

[0004] The objective of the present invention is to provide an ultra-wideband tunable DFB laser array based on enhanced self-heating effect and its design method. By optimizing the self-heating effect of the laser, a significant improvement in the wavelength tuning range of a single laser is achieved, the number of integrated laser units is reduced, the preparation complexity is lowered, and at the same time, the wavelength tuning speed and stability are improved.

[0005] To achieve the above objective, the technical solution provided by the present invention is:

[0006] The present invention is realized through the following technical solutions:

[0007] The first aspect of the present application provides an ultra-wideband tunable DFB laser array based on enhanced self-heating effect, and the ultra-wideband tunable DFB laser array is composed of a number of DFB semiconductor lasers; the differential resistance of each DFB semiconductor laser is 10-15 Ω, and the pure current wavelength tuning range of a single DFB semiconductor laser is 5-7 nm.

[0008] To optimize the above technical solution, the specific measures taken also include:

[0009] The doping concentration of the p-waveguide region of the DFB semiconductor laser is 5×10 16 ~5×10 17 / cm 3 .

[0010] Furthermore, the ultra-wideband tunable DFB laser array is composed of 8-12 DFB semiconductor lasers; the pure current wavelength tuning range of the ultra-wideband tunable DFB laser array is 40-70 nm.

[0011] Furthermore, the ultra-wideband tunable DFB laser array adopts a Y-shaped waveguide that shares the same active layer with the DFB semiconductor laser.

[0012] Furthermore, the grating of the DFB semiconductor laser adopts an equivalent π phase shift.

[0013] Furthermore, a semiconductor optical amplifier SOA is integrated at the output end of the ultra-wideband tunable DFB laser array, and compressive-strained multiple quantum wells and tensile-strained barriers are used to enhance the differential gain.

[0014] The second aspect of the present application provides a design method for an ultra-wideband tunable DFB laser array based on enhanced self-heating effect, including the following steps:

[0015] Determine the optimized value of the differential resistance of the DFB semiconductor laser;

[0016] Simulate the V-I curves of the DFB semiconductor lasers under different doping concentrations;

[0017] Determine the doping concentration required for the optimized value of the differential resistance of the DFB semiconductor laser through the simulated V-I curves;

[0018] Design the doping concentration of the material in the p-waveguide region of the DFB semiconductor laser according to the required doping concentration in the simulation results;

[0019] Fabricate the grating of the DFB semiconductor laser using the reconstructed equivalent chirp REC grating technology.

[0020] Further, the method for determining the optimized differential resistance value of the DFB semiconductor laser is to increase the differential resistance of the DFB semiconductor laser to enhance the thermal effect generated during current tuning. However, the value of the differential resistance cannot be increased indefinitely. An excessively large differential resistance will keep the junction temperature of the laser at a relatively high temperature range during operation, thereby reducing the quantum efficiency and causing a decrease in gain. At high temperatures, it will also lead to an enhanced non-radiative recombination effect, resulting in a decrease in optical power.

[0021] Further, in the grating of the DFB semiconductor laser fabricated by using the reconstructed equivalent chirp (REC) grating technology, high-precision gratings are fabricated through single holographic exposure and micron-level resolution lithography.

[0022] Further, it also includes integrating a semiconductor optical amplifier (SOA) at the output end of the ultra-wideband tunable DFB laser array to increase the optical power to more than 50 mW, while keeping the relative intensity noise (RIN) below -130 dB / Hz.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The current tuning principle of the DFB semiconductor laser comes from two aspects: the change in carrier concentration and the generation of Joule heat. Among them, Joule heat is the most important factor affecting wavelength change. The present invention reduces the doping concentration in the p-waveguide region, optimizes the differential resistance of the laser, and enhances the Joule heat effect.

[0025] The current tuning range of a single DFB semiconductor laser is improved; the pure current wavelength tuning range of a single DFB semiconductor laser of the present invention is four to five times that of a conventional DFB semiconductor laser; the method of the present invention greatly reduces the number of DFB semiconductor lasers required for an ultra-wideband tunable DFB laser array, significantly improves the yield rate, reduces the complexity of the integration process, and greatly reduces the cost; the solution of the present invention can achieve fast wavelength switching through current injection, without changing the laser temperature by any external heater, which helps to reduce the tuning power consumption and improve the wavelength tuning speed.

[0026] The solution of the present invention enables a single DFB semiconductor laser to achieve a larger pure current wavelength tuning range without adjusting the thermoelectric cooler (TEC); while achieving ultra-wideband wavelength tuning, it solves the problems of high power consumption and slow tuning speed caused by traditional temperature tuning using a thermoelectric cooler; the present invention can significantly improve the wavelength tuning speed, providing a new solution for high-speed optical networks, future data centers, metro transmission, and access networks using dense wavelength division multiplexing systems. Description of the Drawings

[0027] Figure 1Schematic diagram of an ultra-wideband tunable DFB laser array based on enhanced self-heating effect in the embodiment.

[0028] Figure 2 Optical power-injection current (P-I) curve and voltage-injection current (V-I) curve of a single DFB laser optimized by reducing the doping concentration of the material in the p-waveguide region.

[0029] Figure 3 Superposition diagram of the tuning spectra of a single DFB laser at 50 - 200 mA current after optimization by reducing the doping concentration of the material in the p-waveguide region.

[0030] Figure 4 (a) Superposition spectrum of the tuning wavelengths of each channel of an ultra-wideband tunable DFB laser array based on enhanced self-heating effect in the embodiment at 50 - 200 mA current, (b) Variation of the central wavelength of each channel with current.

[0031] Figure 5 Variation of the optical power with the injection current of the semiconductor optical amplifier when each channel is operating. Detailed implementation manners

[0032] The above content of the present invention will be further described in detail below in the form of specific implementation manners. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following embodiments. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention.

[0033] By reducing the doping concentration of the material in the p-waveguide region of the DFB semiconductor laser, the present invention increases the differential resistance of the laser, enhances the thermal effect caused by the change of the injection current, and improves the current tuning range of a single DFB semiconductor laser. The specific implementation scheme of the present invention is as follows:

[0034] The present invention provides an ultra-wideband tunable DFB laser array based on enhanced self-heating effect. The ultra-wideband tunable DFB laser array is composed of several DFB semiconductor lasers; the differential resistance of each DFB semiconductor laser is 10 - 15 Ω, the pure current wavelength tuning range of a single DFB semiconductor laser is 5 - 7 nm, and the pure current wavelength tuning range of the ultra-wideband tunable DFB laser array is 40 - 70 nm.

[0035] The doping concentration of the p-waveguide region of the DFB semiconductor laser is 5×10 16 ~5×10 17 / cm 3 .

[0036] The ultra-wideband tunable DFB laser array is composed of 8 to 12 DFB semiconductor lasers. The pure current wavelength tuning range of a single DFB semiconductor laser is 5 to 7 nm.

[0037] In some embodiments, the ultra-wideband tunable DFB laser array uses a Y-type waveguide that shares the same active layer as the DFB semiconductor laser; in terms of waveguide design, the semiconductor optical amplifier light outlet adopts a 7° angle bend and a tapered geometry (preferably, the waveguide width gradually transitions from 2 μm at the input end to 7 μm at the output end) to minimize reflection.

[0038] In some embodiments, the grating of the DFB semiconductor laser adopts an equivalent π phase shift to ensure the high single longitudinal mode SLM characteristics of the laser array.

[0039] In some embodiments, a semiconductor optical amplifier SOA is integrated at the output end of an ultra-wideband tunable DFB laser array, and compressively strained multiple quantum wells and tensile strained barriers are used to enhance differential gain and achieve high power output while maintaining low noise and high stability.

[0040] The present invention also provides a design method for an ultra-wideband tunable DFB laser array based on enhanced self-heating effect, comprising the following steps:

[0041] Determine the optimal value of differential resistance of DFB semiconductor laser;

[0042] Simulate the VI curve of DFB semiconductor laser under different doping concentrations;

[0043] Determine the doping concentration required for the optimal value of differential resistance of the DFB semiconductor laser through the simulated VI curve;

[0044] Design the doping concentration of the material in the p-waveguide region of the DFB semiconductor laser according to the required doping concentration in the simulation results;

[0045] The grating of DFB semiconductor laser is made by reconstructing equivalent chirp REC grating technology.

[0046] The present invention optimizes the series resistance of the laser and enhances the Joule heating effect by reducing the doping concentration in the p-waveguide region. The current tuning principle of the DFB semiconductor laser comes from the change in carrier concentration and the generation of Joule heat, among which Joule heat is the most important factor affecting the wavelength change. The larger the resistance, the greater the thermal effect generated under the same current; the greater the thermal effect, the larger the wavelength tuning range; but the larger the resistance is, the better. Excessive resistance will bring about problems such as reduced gain and decreased optical power. The method of the present invention achieves a significant improvement in the wavelength tuning range of a single laser by optimizing the self-heating effect of the laser, reduces the number of integrated laser units, reduces the complexity of preparation, and improves the wavelength tuning speed and stability.

[0047] In some embodiments, the present invention uses Crosslight simulation software to simulate the V-I curves of DFB semiconductor lasers at different doping concentrations. According to the simulation results, the doping concentration of the p-waveguide region is reduced from the original 7×10 17 ~2×10 18 / cm 3 to 1×10 17 ~3×10 17 / cm 3 ; correspondingly, the differential resistance of the fabricated ultra-wideband tunable DFB laser array increases from about 5Ω to about 10Ω.

[0048] In fabricating the grating of the DFB semiconductor laser using the reconstructed equivalent chirp (REC) grating technology, high-precision gratings are fabricated through single holographic exposure and micron-scale resolution lithography. Using the REC grating technology simplifies the grating manufacturing process, improves the grating accuracy, ensures the uniformity of the wavelength interval, with a deviation within ±0.2nm.

[0049] It also includes integrating a semiconductor optical amplifier (SOA) at the output end of the ultra-wideband tunable DFB laser array, increasing the optical power to more than 50mW, while keeping the relative intensity noise (RIN) below -130dB / Hz.

[0050] Through the above method, the current tuning range of a single DFB semiconductor laser is improved; it is measured that the pure current wavelength tuning range of a single DFB semiconductor laser can be increased from the traditional about 1.5nm to more than 5.8nm, which is four to five times that of a conventional DFB semiconductor laser; originally, a DFB laser array for realizing a broadband tuning of more than 60nm requires integrating about 40 DFB semiconductor lasers; and the more integrated, the more complex the process, the higher the cost, and the yield will decrease exponentially. The method of the present invention can reduce the number of DFB semiconductor lasers, greatly improve the yield, and significantly reduce the cost; through the solution of the present invention, only by integrating more than 8 DFB lasers can a pure current wavelength tuning range of more than 40nm be achieved, and fast wavelength switching can be realized through current injection.

[0051] The following further elaborates on the technical solution of the present invention with specific embodiments. Of course, the present invention is not limited to this structure:

[0052] To prove the feasibility of the above solution, a laser array with a 4×3 matrix structure is designed as an embodiment. The laser array of this embodiment adopts a ridge waveguide structure with a width of 2μm, and the epitaxial layer is grown by a two-step metalorganic chemical vapor deposition (MOCVD) process.

[0053] Simulate the V-I curves of DFB semiconductor lasers with different doping concentrations. By reducing the doping concentration of the material in the p-waveguide region, the doping concentration of the p-waveguide region is reduced from the original 7×10 17 ~2×10 18 / cm 3 to 1×10 17 ~3×10 17 / cm 3 , increase the differential resistance of the DFB semiconductor laser, enhance the thermal effect generated during current tuning, and increase the current tuning range of a single DFB semiconductor laser from the traditional 1.5 nm to more than 5.8 nm;

[0054] Fabricate the grating of the DFB semiconductor laser by using the reconstructed equivalent chirp (REC) grating technology; integrate a semiconductor optical amplifier (SOA) at the output end of the ultra-wideband tunable DFB laser array, which can amplify the optical power of all channels to more than 50 mW, and the relative intensity noise (RIN) < -130 dB / Hz.

[0055] The specific steps for fabricating the laser array in this embodiment are as follows:

[0056] ① First, grow an n-InP buffer layer, an n-InAlGaAs lower optical confinement layer, an InAlGaAs multiple quantum well (MQW) structure, a p-InGaAsP upper optical confinement layer, and a p-InGaAsP grating layer on an n-type InP substrate in sequence.

[0057] ② Subsequently, fabricate a sampling grating by using the traditional holographic exposure combined with photolithography and etching methods.

[0058] ③ Grow a p-InP cladding layer and a p-InGaAs contact layer on the structure.

[0059] ④ Form a ridge waveguide by etching two grooves with a width of 18 μm on both sides.

[0060] ⑤ Achieve electrical isolation between adjacent segments through shallow grooving.

[0061] ⑥ Open p-type metal contact windows, metallize, and perform wafer dicing to form the lasers.

[0062] The DFB laser array reduces the semiconductor conductivity by reducing the doping concentration of the material in the p-waveguide region, increases the differential resistance, and enhances the self-heating effect. Before chip processing, the differential resistance of the DFB laser at different doping concentrations was simulated by Crosslight semiconductor simulation software, and the doping concentration with a differential resistance of about 10 Ω was selected to dope the material in the p-waveguide region. As Figure 2As shown, the V-I curve of a single DFB laser after doping reduction shows that the actual differential resistance is 9.6 Ω, and the P-I curve shows that its threshold current is between 25 - 30 mA.

[0063] The monolithic laser array of this embodiment integrates 12 DFB semiconductor lasers. The laser Bragg center wavelength interval is set to a 5 nm spacing. Lasers with adjacent center wavelengths are arranged in parallel on different waveguides, ensuring that the center wavelength of the series-connected DFB lasers is greater than 20 nm, avoiding crosstalk between Bragg gratings. The laser array of this embodiment can achieve a pure current wavelength tuning range of more than 60 nm from 1515 to 1575 nm.

[0064] When the injection current of the DFB semiconductor laser changes, it will trigger the self-heating effect, which will lead to changes in the effective refractive index and Bragg wavelength. Therefore, enhancing the self-heating effect of the laser can expand its current tuning wavelength range. As Figure 3 Shown is the pure current wavelength tuning superposition spectrogram of a single DFB laser after optimization, and the single channel reaches 6.2 nm.

[0065] This embodiment uses a Y-type waveguide that shares the same active layer as the DFB laser. When working, injecting a small amount of current can compensate for material absorption, significantly reducing the manufacturing complexity compared with the butt-joint coupling technology.

[0066] Integrate a semiconductor optical amplifier (SOA) at the output end of the ultra-wideband tunable DFB laser array. Its epitaxial structure is the same as that of the DFB laser array, and compressive-strained multiple quantum wells and tensile-strained barriers are used to enhance the differential gain. In terms of waveguide design, the semiconductor optical amplifier uses a 7° angle bend and a tapered geometry (the waveguide width gradually transitions from 2 μm at the input end to 7 μm at the output end) to minimize reflection.

[0067] As Figure 4 Shown, when tuning by sequentially applying an injection current of 50 - 200 mA to each channel, each channel achieves a wavelength tuning range of more than 5.8 nm, and the tuning efficiency of the wavelength with respect to the current is approximately 0.039 nm / mA. To verify the amplification ability of the semiconductor optical amplifier for the wavelengths of each channel, the injection current of the laser and the injection current of the Y-type waveguide are both set to 180 mA, and the injection current of the semiconductor optical amplifier is changed from 0 to 230 mA, and the output optical power at each current is recorded. As Figure 5 Shown, it can be seen that the optical power of each channel is amplified to more than 50 mW. While ensuring a 60 nm pure current tuning range, it has a relatively high optical power.

[0068] The laser array of this embodiment realizes fast wavelength switching through current injection, and the tuning time is less than 350 microseconds, which is 10 times faster than the traditional TEC (thermoelectric cooler) method.5 times

[0069] The DFB laser array of the present invention improves the differential resistance and enhances the self-heating effect by reducing the material doping concentration in the p-waveguide region. When the injection current of the DFB laser changes, the self-heating effect will be triggered, resulting in changes in the effective refractive index and the Bragg wavelength. Therefore, enhancing the self-heating effect of the laser can expand its current tuning wavelength range.

[0070] The solution of the present invention can be applied to dense wavelength division multiplexing (DWDM) systems and fast optical networks. Without adjusting the TEC, a single DFB semiconductor laser can achieve a high pure current wavelength tuning range. The present invention can significantly improve the wavelength tuning speed, providing a new solution for high-speed optical networks, future data centers, metro transmission, and access networks using dense wavelength division multiplexing systems.

[0071] The present invention solves the technical bottlenecks of traditional laser arrays in broadband wavelength tuning, fast switching, and low-cost integration, providing an innovative solution for the technological development in the field of optical communication.

[0072] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. An ultra-wideband tunable DFB laser array based on enhanced self-heating effect, characterized in that: The described ultra-wideband tunable DFB laser array is composed of several DFB semiconductor lasers; among them, the differential resistance of each DFB semiconductor laser is 10 - 15 Ω, and the pure current wavelength tuning range of a single DFB semiconductor laser is 5 - 7 nm.

2. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 1, wherein: The doping concentration of the p-waveguide region of the DFB semiconductor laser is 5×10 16 ~5×10 17 / cm 3 .

3. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 1, wherein: The described ultra-wideband tunable DFB laser array is composed of 8 - 12 DFB semiconductor lasers; the pure current wavelength tuning range of the ultra-wideband tunable DFB laser array is 40 - 70 nm.

4. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 1, characterized in that: The described ultra-wideband tunable DFB laser array uses a Y-shaped waveguide that shares the same active layer with the DFB semiconductor laser.

5. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 1, wherein: The grating of the described DFB semiconductor laser uses an equivalent π-phase shift.

6. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 1, wherein: The output end of the described ultra-wideband tunable DFB laser array is integrated with a semiconductor optical amplifier SOA, which uses compressive-strained multiple quantum wells and tensile-strained barriers to enhance the differential gain.

7. The design method of the ultra-wideband tunable DFB laser array based on the enhanced self-heating effect according to claim 1, characterized in that It includes the following steps: Determine the optimized value of the differential resistance of the DFB semiconductor laser; Simulate the V-I curves of DFB semiconductor lasers with different doping concentrations; Determine the doping concentration required for the optimized value of the differential resistance of the DFB semiconductor laser through the simulated V-I curves; Design the doping concentration of the p-waveguide region material of the DFB semiconductor laser according to the required doping concentration in the simulation results; Fabricate the grating of the DFB semiconductor laser using the reconstructed equivalent chirp REC grating technology.

8. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 7, characterized in that: The way to determine the optimized value of the differential resistance of the described DFB semiconductor laser is to increase the differential resistance of the DFB semiconductor laser to increase the thermal effect generated during current tuning. However, the value of the differential resistance cannot be increased indefinitely. An overly large differential resistance will keep the junction temperature at a relatively high temperature range during the operation of the laser, thereby reducing the quantum efficiency and causing a decrease in gain. At high temperatures, it will also lead to an increase in the non-radiative recombination effect, resulting in a decrease in optical power. Therefore, a suitable value should be selected.

9. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 7, characterized in that: In the fabrication of the grating of the DFB semiconductor laser using the reconstructed equivalent chirp REC grating technology, high-precision gratings are fabricated through single holographic exposure and micron-level resolution lithography.

10. The ultra-wideband tunable DFB laser array based on enhanced self-heating effect according to claim 7, characterized in that: It also includes integrating a semiconductor optical amplifier SOA at the output end of the ultra-wideband tunable DFB laser array to increase the optical power to above 50 mW while keeping the relative intensity noise RIN below -130 dB / Hz.

Images