Dan Lu

A monolithically integrated quantum‐well semiconductor mode‐locked laser (SMLL) is presented, incorporating an intracavity pulse picker (PP) between the gain and saturable absorber (SA) sections to realize low‐repetition‐rate pulse generation with two distinct operating regimes. It can selectively output ultrashort pulses at subharmonic rates or operate in a seed‐pulse regime to achieve continuous and arbitrary repetition rate tuning: (i) under a shallow reverse bias on both SA and PP, the device extracts ultrashort pulses (5.37–7.68 ps) from a stable mode‐locked train to produce tunable subharmonic (1/N) repetition rates (5.1 MHz–1.02 GHz); (ii) under a deep reverse bias on both SA and PP, intracavity resonance is suppressed, enabling a continuous arbitrary repetition rate pulsed output tuning from 5 MHz to 3.4 GHz. The pulse widths range from 58 to 103 ps, achieving an ultra‐low duty cycle of 1/1942 at 5 MHz—the lowest repetition rate reported to date for monolithically integrated SMLL. Furthermore, this laser allows direct observation of pulse evolution from a single‐round‐trip seed to a stable mode‐locked state, providing an experimental approach for investigating the fundamental dynamics of the mode‐locking process.

A C-band high-power, low-noise distributed feedback (DFB) laser is demonstrated. The epitaxial structure incorporates a high-refractive-index layer in the N-doped region to improve single-transverse-mode characteristics and reduce intrinsic loss, enabling single-mode operation at a ridge width of 5 µm with an intrinsic loss of 2 cm ^-1 . At a test temperature of 15 °C, the DFB laser with a cavity length of 3.5 mm delivered an output power of 750 mW in quasi-continuous-wave mode and 519 mW in continuous-wave mode, with a side mode suppression ratio over 60 dB. The device also exhibits a minimum intrinsic linewidth of 14.9 kHz and relative intensity noise of -166 dBc/Hz.

We propose and experimentally demonstrate a multi-wavelength differential coherent vibration (MDCV) measurement scheme using a monolithically integrated Fabry-Pérot mode-locked laser diode (FP-MLLD). The scheme leverages multiple mutually coherent laser modes generated from a single FP-MLLD to form multiple probing pairs, enabling multi-channel coherent detection. In the time domain, the probing and reference signals exhibit a short-pulse waveform, which delivers higher peak power and signal-to-noise ratio (SNR) compared to continuous-wave or dual-wavelength sine-wave schemes. Experimental results show that the proposed system achieves vibration frequency measurement over a range of 5 Hz to 800 Hz with an SNR of ∼20 dB. Multi-channel measurement capability is validated via three spectrally filtered wavelength channels, all of which accurately resolve the target vibration frequency. This scheme features a simplified architecture, low cost, and native multi-channel capability, showing potential for multi-target or multi-directional vibration measurement applications.

We propose and experimentally demonstrate a reconfigurable few-mode laser source through coupling a weak resonant-cavity Fabry-Perot laser diode (WRC-FPLD) to a microring resonator (MRR), in which the MRR is utilized as an external cavity to implement self-injection. For such a scheme, when the feedback strength from the MRR to the WRC-FPLD is strong enough, the laser can enter a stable single-mode self-injection locking (SIO) state. Continuously increasing the feedback strength, two-mode and three-mode lasing states can be realized. Furthermore, the wavelength of few-mode lasing can be adjusted within dozens of GHz by varying the temperature of the MRR. Additionally, under relatively weak feedback strength, the laser exhibits an unlocked single-mode lasing state, which undergoes quasi-periodic bifurcation to a chaotic state, and finally reaches SIO with the increase of feedback strength. Under an optimized feedback strength, the effective bandwidth of the chaotic state arrives at 12.81 GHz. Such a reconfigurable few mode laser source possesses some advantages, such as miniaturization, stability, and tunability, and it has application prospects in many fields, including mode-division multiplexing, optical sensing, and on-chip signal processing.

This work first establishes an 8-channel four pulse amplitude modulation (PAM-4) intensity modulation direct detection (IM-DD) optoelectronic transceiver system, with cascaded silicon Mach-Zehnder interferometer (MZI) lattice-filter technology, for high-speed and long reach (LR) (over 10 km) transmission scenario of modern data center interconnection (DCI). The compact silicon photonic (SiPh) traveling wave Mach-Zehnder modulators (TW-MZM) and silicon-germanium (SiGe) photodetectors (PD) (bandwidth > 49.5 GHz with a responsivity > 0.8 A/W) are homogeneously integrated with MZI lattice-filter based $8\times 1$ multiplexer (MUX) and $1\times 8$ demultiplexer (DeMUX), respectively, endowing the system with compact structure and tunable operating wavelengths. Finally, the novel SiPh transceiver system is elaborately integrated and applied into the local area network wavelength division multiplexing (LAN-WDM) LR8 circumstance, transmitting over 10 km standard single mode fiber (SSMF), with broad bandwidth (> 33 GHz), good channel response uniformity, and supports over 100 Gbps per lane for high-speed transmission, featuring proper system bit error rate (BER) performance in compliance with IEEE 802.3 standards.

An ultra-compact 1310/1550 nm wavelength division (de)multiplexer based on a channel-shaped multimode interference structure was proposed and fabricated on an InP platform. The device has been simulated and optimized with a low insertion loss of 0.1 dB at 1310 nm wavelength and 0.33 dB at 1550 nm wavelength. The device features a notably compact footprint with an MMI region just 48 μm in length. Measurements revealed extinction ratios of 7.1 dB at 1310 nm and 5.9 dB at 1550 nm, accompanied by insertion losses of 7.07 dB and 3.03 dB for these wavelengths.

A high operating temperature mid-wavelength pBn infrared detector based on InAs/InAsSb superlattices with electron block interfacial graded doping is demonstrated. The photodetector exhibits saturated quantum efficiency from 77 K to 250 K under zero bias, requiring a −80 mV bias to fully extract photocurrent at 290 K. Under zero bias, the device achieves a peak responsivity of 1.69A/W at 150 K, corresponding to a quantum efficiency of 59.4%, and a detectivity of 1.24 × 10¹²cm·Hz^1/2/W at a cutoff wavelength of 5.0 µm. The dark current density of the pBn detector decreases from generation-recombination current limited 5.94 × 10⁻⁵A/cm² to surface leakage current limited 2.95 × 10⁻⁵A/cm² via the interfacial graded doping layer, resulting in a fitted generation recombination dark current of 1.37 × 10⁻⁶A/cm². At 290 K, the cutoff wavelength extends to 6.2 µm, with a dark current density of 9.35 × 10⁻²A/cm² and a peak quantum efficiency of 61.8% at 3.5 µm, leading to a specific detectivity of 9.87 × 10⁹cm·Hz^1/2/W. The dark current of the interfacial graded doping device is lower than the prediction of Rule 07 at a temperature higher than 190 K, demonstrating the great potential of the InAs/InAsSb pBn photodetector for room temperature operation.

The rapid growth of artificial intelligence (AI) inference, training, and cloud computing has driven the continuous demands for data transmission bandwidth and rate, enlarging the modern data centers’ scale and quantities. While high-speed, long-reach (LR) (∼10 km) data center interconnection (DCI) faces significant performance degradation caused by device nonlinearity, optical link loss, channel interference, etc., when adopting a wavelength-division multiplexing (WDM) architecture. This work establishes an 8-channel multiplexer (MUX)/demultiplexer (DeMUX)-based optoelectronic transceiver scheme with high isolation, low inter-channel interference, and polarization-insensitive features to minimize the four-wave mixing (FWM) interference for Tbps DCI reliable transmission. What we believe to be a novel scheme is applied to an elaborately designed 8-channel intensity modulation direct detection (IM-DD) silicon photonic (SiPh) transceiver system for the LR8 Tbps DCI-Campus (∼10 km transmission) scenario. Experimental results demonstrate the significant performance promotion by 200 Gbps with a total 1.1 Tbps transmission rate, ultra-high channel isolation (>45 dB), thorough polarization-insensitive inter-channel interference suppression, high signal-noise ratio (SNR), as well as good channel response uniformity.