Jin-Wei Shi

Design and demonstration of ultra-fast W-band photonic transmitter-mixer and detectors for 25 Gbits/sec error-free wireless linking.

A 25 Gbits/s error-free on-off-keying (OOK) wireless link between an ultra high-speed W-band photonic transmitter-mixer (PTM) and a fast W-band envelope detector is demonstrated. At the transmission end, the high-speed PTM is developed with an active near-ballistic uni-traveling carrier photodiode (NBUTC-PD) integrated with broadband front-end circuitry via the flip-chip bonding technique. Compared to our previous work, the wireless data rate is significantly increased through the improvement on the bandwidth of the front-end circuitry together with the reduction of the intermediate-frequency (IF) driving voltage of the active NBUTC-PD. The demonstrated PTM has a record-wide IF modulation (DC-25 GHz) and optical-to-electrical fractional bandwidths (68-128 GHz, ~67%). At the receiver end, the demodulation is realized with an ultra-fast W-band envelope detector built with a zero-bias Schottky barrier diode with a record wide video bandwidth (37 GHz) and excellent sensitivity. The demonstrated PTM is expected to find applications in multi-gigabit short-range wireless communication.

III-Nitride-Based Cyan Light-Emitting Diodes With GHz Bandwidth for High-Speed Visible Light Communication

A large reduction (from 17 to 5 nm) is made in the thickness of the barrier layers in the multiple-quantum-well region of III-nitride-based cyan light-emitting diodes (LEDs) grown on patterned sapphire substrates. This is shown to lead to a simultaneous improvement in the modulation speed, differential quantum efficiency, and maximum output power of the LEDs under both room temperature and 110 °C operation. With our novel device structure, we achieve a moderate output power (1.7 mW) with a record high 3-dB electrical-to-optical (E-O) bandwidth (1 GHz). The over twofold enhancement in the E-O bandwidth (~1 versus ~0.5 GHz) compared with that previously reported visible LEDs can be attributed to the more uniform distribution of injected carriers within the MQW region and the aggressive downscaling of the thickness of the total active layer, which leads to a shortening of the spontaneous recombination time.

Fully integrated microwave frequency synthesizer on heterogeneous silicon-III/V

We demonstrate a photonic microwave generator on the heterogeneous silicon-InP platform. Waveguide photodiodes with a 3 dB bandwidth of 65 GHz and 0.4 A/W responsivity are integrated with lasers that tune over 42 nm with less than 150 kHz linewidth. Microwave signal generation from 1 to 112 GHz is achieved.

Monolithically integrated InAs/InGaAs quantum dot photodetectors on silicon substrates

We report InAs/InGaAs quantum dot (QD) waveguide photodetectors (PD) monolithically grown on silicon substrates. A high-crystalline quality GaAs-on-Si template was achieved by aspect ratio trapping together with the combined effects of cyclic thermal annealing and strain-balancing layer stacks. An ultra-low dark current of 0.8 nA and an internal responsivity of 0.9 A/W were measured in the O band. We also report, to the best of our knowledge, the first characterization of high-speed performance and the first demonstration of the on-chip photodetection for this QD-on-silicon system. The monolithically integrated waveguide PD shares the same platform as the previously demonstrated micro-ring lasers and can thus be integrated with laser sources for power monitors or amplifiers for pre-amplified receivers.

Type-II GaAs0.5Sb0.5/InP Uni-Traveling Carrier Photodiodes With Sub-Terahertz Bandwidth and High-Power Performance Under Zero-Bias Operation

We successfully demonstrate ultrafast uni-traveling carrier photodiodes (PD) with sub-terahertz bandwidth (∼170 GHz) and high-power performance under zero bias and at 1.55-μm optical wavelength operation. By using a type-II (GaAs_0.5Sb_0.5/InP) absorption-collector interface and inserting an n-type (1 × 10¹⁸ cm⁻³⁾ charge layer in the collector, the current blocking (Kirk) effect can be greatly minimized. A stack of undoped Al<italic>_x</italic>In_0.52Ga_0.48−xAs layers with different Aluminum mole fractions (<italic>x</italic>: 0.2 to 0.08) and bandgaps is adopted as the collector layer. This graded-bandgap design can provide a built-in electric field and further shorten the internal collector transit time. The demonstrated PD structure achieves a 3-dB optical-to-electrical bandwidth of 170 GHz and subterahertz output power −11.3 dBm at 170 GHz, a record among all the reported zero-bias PDs.

Heterogeneously integrated InP based evanescently-coupled high-speed and high-power p-i-n photodiodes on silicon-on-insulator (SOI) substrate

We demonstrate InP based evanescently-coupled p-i-n photodiodes heterogeneously integrated onto silicon-on-insulator substrate. Using advanced waveguide structures and fabrication processes, it simultaneously achieves 67 GHz O-E bandwidth (RC-free), broad optical window (1520-1600nm) with 0.5 A/W internal responsivity, and high saturation currents (9 mA at 70 GHz).

GaSb-Based p-i-n Photodiodes With Partially Depleted Absorbers for High-Speed and High-Power Performance at 2.5-

We first demonstrate a novel high-speed and highpower p-i-n photodiode with a cutoff wavelength at ~2.5 μm. This device is composed of a partially depleted p-type Ga_0.8In_0.2As_0.16Sb_0.84 photo-absorption layer grown on GaSb substrate in order to enhance its speed and saturation power performance. With proper passivation processes, a low dark current (~0.7 μA) and wide (6 GHz) optical-to-electrical (O-E) bandwidth can be simultaneously achieved with a miniaturized size of active mesa diameter (~8 μm) under 1.55-μm optical wavelength excitation. The electron/hole drift-velocity and electron mobility across the Ga_0.8In_0.2As_0.16Sb_0.84 active layer can further be estimated based on the extracted internal response time and device modeling technique. Using the heterodyne-beating setup at 1.55-μm wavelength, the demonstrated device shows a saturation current at ~3.6 mA (at 6-GHz operating frequency), which is mainly limited by the space-charge (electron/hole) induced screening effect at the depleted absorption region.

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By combing Si/Ge avalanche photodiodes based electrical comb-line generators with photonic-transmitter-mixers, millimeter-wave short-pulse generations for photonic ultra-wideband linking at W-band with wireless transmission distance up to 12 meter and error-free 1.5Gbps data rate are demonstrated.