We put forward and present a demonstration of an actively controlled optical beam steering optical wireless communication (OWC) system based on an integrated actively steerable optical phased array (OPA). We theoretically and experimentally analyze the emitted optical beam full-width-half-maximum (FWHM) divergence angle and field-of-view (FOV) of the proposed integrated actively steerable OPA. Experimental results show that the beam steering can be achieved over a range of 17° with a minimum optical beam FWHM divergence angle of 1.49°. Besides, the integrated OPA chip design, beam forming optimization, packaging, as well as temperature stabilization are also discussed. Genetic Algorithm (GA) is utilized to optimize the applied voltages for the 30 phase shifters to produce low-divergence optical beams in different directions. A proof-of-concept bit-error-rate (BER) measurement using 10 Gbit/s on-off-keying (OOK) signal is also carried out, and the beam steered optical signal satisfying the pre-forward error correction BER limit (pre-FEC BER = 3.8 × 10 ⁻³ ) is achieved.

A high-performance photonic sweeping-frequency (chirped) radio-frequency (RF) generator has been demonstrated. By use of a novel wavelength sweeping distributed-feedback (DFB) laser, which is operated based on the linewidth enhancement effect, a fixed wavelength narrow-linewidth DFB laser, and a wideband (dc to 50 GHz) photodiode module for the hetero-dyne beating RF signal generation, a very clear chirped RF waveform can be captured by a fast real-time scope. A very-high frequency sweeping rate (10.3 GHz/μs) with an ultra-wide RF frequency sweeping range (~40 GHz) have been demonstrated. The high-repeatability (~97%) in sweeping frequency has been verified by analyzing tens of repetitive chirped waveforms.

The design, analysis, and demonstration of flip-chip bonding packaged uni-traveling-carrier photodiodes (UTC-PDs) with THz (dc to 315 GHz) 3-dB bandwidth and high-power performance are reported. The high-frequency roll-off (up to 0.4 THz) of the flip-chip bonding structure and device heating under high power operation are both minimized through properly downscaling the area of the bonding pad and minimizing the solder distance to the active area of the miniaturized UTC-PD. In order to suppress the serious space-charge screening effect in miniaturized UTC-PDs under high-current density (~180 kA/cm ² ) operation, an n-type charge layer is inserted into the collector. The detailed dynamic measurement results of these packaged PD modules indicate that non-equilibrium electron transport plays an important role in determining the maximum speed and THz output power. In addition, a femtosecond (fs) optical pulse train generator with a ~300 fs pulse-width output and repetition rate up to ~0.3 THz is also developed to further boost the photo-generated THz-power. Compared with using an optical signal with a sinusoidal envelope for PD excitation, the short-pulse approach can offer a 3-dB enhancement in output power under the same output photocurrent and operating frequency (around 0.3 THz). By utilizing such an fs light source and our PD module, a continuous wave output power as high as 1 mW at an operating frequency of ~0.3 THz is successfully demonstrated.

Photonic technologies that support the low cost manufacturing needed for automotive sensors have experienced explosive developments in recent years. To date most commercially available lidar system have been direct detection time-of-flight (ToF) sensors operating at 905 nm using mechanical mirrors for beam steering. However, these sensors suffer from important drawbacks. One issue is eye-safety, which limits maximum laser powers and hence operating range. Direct detection systems must also content with potential interference issues when lots of cars operate lidar systems simultaneously. In addition, mechanical scanners are frequently bulky and may be difficult to integrate within the form factors allowed by modern vehicles.

In this work, we demonstrate a novel top-illuminated avalanche photodiode (APD) with high-speed and wide dynamic range performance for coherent lidar applications, which needs simultaneous processing of weak light reflections from the object and a strong optical local-oscillator (LO) signal at the receiving end. By taking advantage of a partially depleted p-type $\text{In}_{0.53} \text{Ga}_{0.47} \text{As}$ absorbing layer and a thin $\text{In}_{0.52} \text{Al}_{0.48} \text{As}$ multiplication layer (88 nm), the demonstrated APDs exhibit a wide optical-to-electrical bandwidth (16 GHz) and high responsivity (2.5 A/W at 0.9 $\text{V}_{\text{br}}$ ) near the saturation output current which is as high as >8 mA. Furthermore, the measured low excess noise (k=0.14) characteristics of this device ensure its wide dynamic range performance. In addition, it should be noted that the measured nonlinear behaviors of these APDs are quite different from those of typical fast p-i-n photodiodes (PDs), which always show serious degradation in their O-E bandwidths at their saturation output. On the other hand, the measured bias dependent 3-dB O-E bandwidth of the demonstrated APDs can be pinned at 16 GHz without any degradation at around the saturation current output. Such distinct nonlinear APD behaviors can be attributed to the space-charge-screening effect induced gain reduction under high-power operation.

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 _0.8 In _0.2 As _0.16 Sb _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 _0.8 In _0.2 As _0.16 Sb _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.