Among various integration technologies, single-chip integration has broad application prospects in future high-capacity, high cost, and high energy consumption applications. For applications such as wavelength division multiplexing (WDM) systems, coherent optical communication, and next-generation data center interconnection, it is necessary to provide laser sources with wide spectral coverage. At present, on-chip light source solutions mainly focus on Butt Couple FC、Hbrid(bonding or MTP)， The first two mass production capabilities rely on equipment, among which Butt Couple is more common in domestic universities, FC and Hbrid are gradually becoming popular in fab, such as AMF/GF FC, Intel/Tower/HPE bonding, IMEC/NTT MTP. At the same time, various research institutes are also exploring new technologies. For example, EPFL is exploring erbium-doped waveguide lasers, and this year's performance has greatly improved compared to last year. UCSB and AIM are collaborating to manufacture III-V laser materials in grooves on silicon optical chips, which can achieve local placement of light sources on a single integrated chip. If we look at the development in recent years, we can find that direct epitaxy is no longer a bottleneck, and even reliability performance continues to break records. What was quite surprising this time was IMEC's nanoridge engineering method for achieving direct epitaxial lasers. Although the performance was not very good, at least two pieces of information were seen: first, exploring new epitaxial technologies that are not limited to UCSB's traditional V-groove structure, and Hong Kong Science and Technology's transverse nanowires. IMEC's nanoridge structure still has some ideas. Second, direct epitaxial technology is becoming well-known and its performance will continue to improve. Various commercial fabs are also collaborating on research, and like Hybrid bonding, it is believed that it will also be commercially available in the future. 1. Butt Couple, led by Professor Chen from Tsinghua University, presents a hybrid integrated III-V/Si3N4 laser with wide range wavelength switching function, as shown in the figure. This ECL is composed of a docking coupling of an InGaAP SOA chip and two Si3N4 external cavity chips.

The length of SOA is 2.5mm, and the beam exit angle of its output port waveguide is 19.5 ° to suppress end face reflection. The thickness of the Si3N4 waveguide is 100 nm, and the input waveguide is tilted 13 ° at the coupling surface to match the SOA waveguide. The purpose of manufacturing PZT actuators on a circular waveguide is to utilize its fast photoelastic tuning effect. The usual photoelastic efficiency is low (with a tuning efficiency of 0.67 pm/V), and the tuning range of piezoelectric actuation is limited. To improve tuning efficiency, the radius of the external MRR is set to 592 μ m and 593 μ m to form a Vernier filter. And cascade SDA-MRR with a-MZI to provide sufficient side mode suppression. SDA-MRR is structurally similar to all pass MRR, but its uniqueness lies in the etching of rectangular subwavelength hole defects with a size of 0.54 μ m × 0.2 μ m in the annular waveguide, resulting in mutual coupling of cavity anti propagation modes and exhibiting a stronger reflection spectrum than traditional MRR reflectors, with a typical Q of 1.56e6. To further enhance SMSR, a-MZI with FSR twice that of SDA-MRR FSR is used to suppress the first adjacent side mode of the Vernier filter. The measured output power of ECL on a single-mode chip at 1536.5 nm is 9.2 mW, with an inherent linewidth of 8.92 Hz. By driving a bias voltage on the PZT actuator, tuning from 1513.37 nm to 1559.53 nm at 46.16 nm is achieved, which is limited by the saturation voltage and the low photoelastic efficiency of the PZT actuator. The voltage applied to the PZT actuator varies linearly with the laser wavelength, and the tuning efficiency is increased to 0.38 nm/V. The final demonstrated ECL achieved a record breaking 21.35nm wavelength switching range in the C-band, with a switching time of less than 4 μ s. 2. A 450 nm InGaN laser achieved by passive alignment flip chip bonding of Flip chip AMF on a visible light silicon platform. This platform has alignment structures and mechanical stops defined by photolithography on chips and LDs, achieving up to 9.6 mW of continuous waveplate optical power. The semiconductor laser has the potential to further integrate thermal optical switches and silicon photodetectors. The wafer structure includes a 220 nm thick Si photodiode, a 120 nm thick SiN waveguide, and metal. SiO2 and Si etching define flip chip bonding sockets, mechanical stops (for height alignment), and alignment marks (for in-plane alignment), as shown in the figure. SiN reverse tapered edge coupling (150 nm tip width) achieves optical coupling between silicon optical chips and bonded LDs. Measure the LIV curve, and when operating continuously at 50 mA and 120 mA, the on-chip optical power reaches 4.6 mW and 9.6 mW, respectively, corresponding to WPEs of 1.9% and 1.6%, respectively. Based on the alignment marks visible through the transparent LD substrate, the estimated X - and Y-misalignment is less than 0.3 µ m. The coupling loss from LD to SiN waveguide is calculated to be 4.8 dB, while the simulated optimal alignment coupling loss is 2.7 dB. As a proof of concept, InGaN LD is connected to a power monitor and an optical switch, which includes a 328um long phase shifter with an output of ER 22.0dB and Ppi 12.8 mW. 3. Hbrid (MTP) Ghent University imec implements an integrated tunable laser with a tuning range exceeding 45nm and a waveguide output power of 5mW based on MTP, as shown below. The gain region is a 1.2mm long InP/InAlGaAs SOA waveguide structure, which introduces a dual ridge structure. Two InP/InAlGaAs active ridges are defined at the top of the Si waveguide using photolithography and ICP etching, with each ridge width of 3 µ m and a distance of 20 µ m. Silicon waveguides are manufactured on the 400nm SiPh platform of IMEC. The BCB adhesive layer has a thickness of 100-150nm and is accurately transferred into the designated grooves using a wafer level micro transfer printer (Amicra Nano). The resistance of the dual ridge laser is 8.1 ohms (two SOA in parallel). When the current is 200mA and at 20 ℃, the waveguide coupling output power reaches 5mW. By using a thermally adjustable Sagnac loop mirror and phase shifter to optimize the reflectivity of the output coupling mirror, the laser achieves a wide tuning range of 1530.0 nm to 1577.2 nm, exceeding 45 nm. The instantaneous linewidth at 1540.8 nm is 3.93 kHz. 4. Erbium doped waveguide EPFL achieves a tunable erbium-doped waveguide laser with a wavelength tuning range of 40 nm and an output power of 10 mW by using chip level high-energy ion implantation in ultra-low loss 700 nm thick silicon nitride. Compared with waveguide lasers based on erbium-doped Al2O3 and erbium-doped LiNbO3, the performance is greatly improved. Erbium based laser is formed by a 17cm long erbium-doped spiral waveguide and tunable ring mirrors at both ends. Use integrated micro heaters for tuning. A passive Si3N4 waveguide with ultra-low loss of about 2 dB/m was prepared using a subtraction process based on DUV. After dry etching, it was annealed at 1200 ℃ for 11 hours to remove excess H2 and break Si-H and N-H bonds. Selective erbium ion implantation with a maximum beam energy of 500 keV was performed in a spiral waveguide, and the chip was annealed at 1000 ℃ in nitrogen gas to activate erbium ions and repair implantation defects. The wavelength can be tuned to over 91 nm, with an SMSR of 75 dB, covering the entire C-band and most of the L-band. The output power of the off chip laser is as high as 10 mW. Can work at a high temperature of 125 ℃. The Lorentz linewidth is 95 Hz, as shown in the figure. 5. The direct epitaxial QD laser O-band InAs quantum dot (QD) laser provides a scalable and cost-effective approach for the application of next-generation optical data communication in 300 mm silicon optical monolithic integration. During the material growth process, a 5-10 µ m etching gap is generated between the laser facet and the waveguide input, forming an optical scattering tilted gap. The coupling loss is in the range of 10-30 dB, making laser to waveguide coupling a challenge. UCSB reduces the laser waveguide gap size to 3 µ m through a mixed III-V growth method, and fills the gap with BCB polymer (refractive index of 1.56) to reduce beam divergence, reducing the coupling loss between the laser and silicon nitride waveguide to 6 dB. Made on AIM Photonics. The following figure shows a complete pocket laser coupled to a waveguide, with the sample including an edge coupler, a ring resonator for wavelength filtering, and a DBR reflector for single-mode laser output. Test the photocurrent characteristics of FP laser at 20 ° C. By comparing the measurement results of optical fiber and integrating sphere, the coupling loss is calculated to be below 6 dB. Add silicon nitride DBR gratings at both ends of the gain region of a standard pocket QD laser to verify single-mode characteristics. Within the temperature range of 21 ° C to 24 ° C, the SMSR is 26 dB. In the future, further performance optimization is needed to achieve scalable production of on-chip single-mode light sources by integrating DBR lasers on a single chip. IMEC demonstrated the fabrication of electrically driven GaAs lasers on 300 mm CMOS using nanoridge engineering methods. The failure time (TTF) distribution of two degradation mechanisms observed in aging tests at different temperatures and current densities was studied, and a statistical model for life prediction was established to provide design criteria for the synergistic optimization of electro-optical performance and reliability. Using MOVPE technology, InGaAs/GaAs nanoridge lasers were selectively grown on a 300 mm (001) Si substrate. The high aspect ratio grooves reduced the defect density in the active region, and the nanoridge engineering method precisely controlled the shape and size of the nanoridges. Study the reliability of a laser with a plug spacing of 4.8 µ m and compare it with an LED with a plug spacing of 1.6 µ m. Study its reliability by applying constant current density stress. The conditions are JNR=5 kA/cm2 and T=25 ° C. In the early stages of aging, laser Jth gradually increases, but SE remains almost unchanged. Degradation is caused by enhanced Shockley Read Hall recombination, which shortens the non radiative carrier lifetime. When the stress time is prolonged, rapid failure occurs, and Jth and SE degrade sharply. Under moderate aging conditions (JNR=1.5 kA/cm2), Jth significantly increased even after 1000 hours of stress. Degradation is related to high current density at the metal/p-GaAs contact (Jp con). Due to the higher Jp con, it degrades faster in lasers than in LEDs. It is speculated that impurities diffuse from the p-GaAs layer and/or the metal/p-GaAs interface. The temperature and current density dependence of the laser failure time (TTF, defined as a 30% reduction in output power) distribution is shown in the figure. The cumulative failure function F (t) consists of two statistical distributions: the lognormal distribution describes gradual degradation, and the Weibull distribution describes rapid failure. Using maximum likelihood estimation to simultaneously fit all stress conditions, the obtained fitting parameters show good consistency with experimental data, as shown in the figure. Using models to estimate the TTF of two mechanisms separately, laying the foundation for obtaining reliable InGaAs/GaAs nanowire lasers. At different temperatures, the median lifetime (t50%) of the device is a function of Jp con. With the goal of a 10-year service life at 85 ° C, it is necessary to reduce the Jp con to below 20 kA/cm2, which is equivalent to a p-contact plug spacing of 0.3 µ m.