High-speed Photodetector Array Research Articles

Compact and scalable polarimetric self-coherent receiver using a dielectric metasurface

Polarimetric self-coherent systems using direct-detection-based Stokes-vector receivers (SVRs) are a promising technology to meet both the cost and capacity requirements of short-reach optical interconnects. However, conventional SVRs require a number of optical components to detect the state of polarization at high speed, resulting in substantially more complicated receiver configurations compared with the current intensity-modulation–direct-detection counterparts. Here, we demonstrate a simple and compact polarimetric self-coherent receiver based on a thin dielectric metasurface and a photodetector array (PDA). With a single 1.05-µm-thick metasurface device fabricated on a compact silicon-on-quartz chip, we implement functionalities of all the necessary passive components, including a 1×3 splitter, three polarization beam splitters with different polarization bases, and six focusing lenses. Combined with a high-speed PDA, we demonstrate self-coherent transmission of 20-GBd 16-ary quadrature amplitude modulation and 50-GBd quadrature phase-shift keying signals over a 25-km single-mode fiber. Owing to the surface-normal configuration, it can easily be scaled to receive spatially multiplexed channels from a multicore fiber or a fiber bundle, enabling compact and low-cost receiver modules for future highly parallelized self-coherent systems.

Optimization of an Optoelectronics-Based Plant Real-Time Discrimination Sensor for Precision Agriculture

We present a novel design for an optoelectronics- based real-time plant discrimination sensor, which enables a high signal-to-noise ratio, and hence a low false positive rate, to be attained. The sensor employs graded thin film coatings and a high-speed photodetector array in conjunction with a solar spectral filter and 3-wavelength sequentially driven laser module to generate multiple uniformly distributed laser spots of uniform optical power distribution. Plant discrimination is achieved through the measurements of the slope of the spectral response at discrete wavelengths as well as the Normalised Difference Vegetation Index (NDVI). The maximisation of the optical signal to noise ratio achieved by employing a custom designed optical band-pass filter minimises the daylight background noise saturating the photodetectors, thus enabling plant identification to be carried out with a background light intensity as high as 10,000 lux without implementing any shade construction.

Phase and time delays for microwave signals using photocarrier drift in a semiconductor

We present and experimentally demonstrate, at 1.6 GHz, the generation of phase and time delays on microwave signals in a photoconductive semiconductor. It takes advantage of the synchronous drift of photogenerated carriers with a moving interference pattern. Phase and time delays are controlled according to the relative orientation of the moving interference pattern with a high-speed photodetector array. Owing to the resonant principle, high sensitivity is available which is suitable for the control of signals in phased array antennas.