Linear Photodetector Array Research Articles

An optoelectronic control of arc gap during formation of fullerenes and carbon nanotubes

An automated system for controlling the interelectrode gap of the carbon arc and positioning the plasma, constructed from commercially available components, is described. The core components of the system are the linear photodetector array, analog, and digital integrated circuits, and two direct current motors. It allows for both maintaining constant arc gap and its positioning against the optical axis of the plasma diagnostic arrangement. The method of operation is demonstrated via the production of fullerenes and carbon nanotubes. This control contrivance has been used for more than one year in bench scale with very satisfactory results. In addition, the design presented here has been found to be simple to construct from readily available components and has the merit of being quite inexpensive, too (the entire cost is under $2400).

A linear array of photodetectors with wide dynamic range and near photon quantum-noise limit

An array of light frequency sensors, fabricated using a standard CMOS process, with operation over seven decades of illumination is presented. Each photodiode is connected to a charge amplifier which ensures that the diode remains under constant reverse bias, keeping the optoelectronic properties independent of light level. Employing this technique, the photogenerated charge is stored on the integrator's feedback capacitor rather than in the depletion region of the photodiode. Using on-chip comparators and off-chip logic, a signal with frequency proportional to the light level on each pixel is obtained, exhibiting a dynamic range of 145 dB and a SNR of close to the quantum-noise limit of the incident light.

Parallel-slab division-of-amplitude photopolarimeter

A division-of-amplitude photopolarimeter (DOAP) is described that uses a dielectric parallel-slab (PS) beam splitter that is coated with a high-reflectance metal on one side at oblique incidence. The instrument matrix of the PS DOAP is nonsingular, hence all four Stokes parameters can be measured simultaneously over a broad (UV-visible-IR) spectral range. The parallel, evenly spaced, ref lected beams simplify interfacing of the PS DOAP with linear photodetector arrays for both single-wavelength and spectroscopic polarimetry. The PS DOAP has several degrees of freedom that can be controlled for optimum performance.

Demonstration of novel optical multichannel grating demultiplexer receiver (MGD) for HDWDM systems

A novel implementation of a multichannel grating demultiplexer receiver suitable for HDWDM applications is described. The prototype receiver, capable of 10-channel operation spaced at 4nm, uses a 16-element GalnAs/InP monolithic linear photodetector array and silicon preamplifier ICs. The sensitivity at the input to the demultiplexer is – 3 1 dBm at 200Mbit/s. Optical and electrical crosstalk measurements in the receiver are presented, and limited tests have shown that there is a negligible crosstalk penalty.

Photocapacitance characteristics of amorphous-silicon Schottky diode sensor arrays and their changes due to the Staebler–Wronski effect

The capacitance measurements on a-Si:H Schottky diodes reported in the literature refer to large-area (some 10-mm2) specimens and were carried out in the dark at frequencies typically around 10 Hz. The main interest in these publications is the determination of the density of states in the band gap. For linear photodetector array applications, however, interest centers around the voltage and frequency characteristics of the capacitance of small-area back-to-back Schottky diodes under illumination and at frequencies typically around 1 kHz. But photoinduced changes in the capacitance are also of significance with a view to possible read-out circuits and their long-term stability. The capacitance was therefore measured over the frequency range 0.2–20 kHz and over the voltage range −5 to +5 V. Whereas the dark capacitance exhibited no changes due to photoinduced degradation, significant differences between degraded and nondegraded states were observed in the voltage and frequency characteristics of the photocapacitance. During degradation under high bias voltage (−5 V), the maximum of the capacitance shifted from −0.1 to +0.4 V indium tin oxide bias voltage and the capacitance showed a distinct increase. The photoinduced changes observed for the photocapacitance characteristics could be minimized by ensuring that the elements adjacent to the sensor were at equipotential with the sensor. Full reversibility of the photoinduced changes due to thermal annealing could be verified. The changes of the C-V and C-ω characteristics can be explained by the occurence of the well-known Staebler–Wronski effect.

The use of solid-state image sensor technology to detect and characterize live mammalian cells growing in tissue culture.

Arguments are presented that approximately 30 000 cells have to be measured in a single experiment to measure radiobiological parameters in a low-dose survival assay. For this purpose, a fully automated device capable of detecting and recognizing individual live unstained mammalian cells at a rate of 1 cm2/min is required. Specifications of such a system are derived and evidence is presented which suggests that this can best be carried out using a solid-state image sensor in the form of a linear array of photodetectors. The outline of the design and other potential uses of such a device are discussed.

Spatial and temporal correlation of underwater sunlight fluctuations in the sea

A submerged linear array of photodetectors was used to measure sunlight irradiance fluctuations caused by ocean surface waves. Decorrelation times and lengths were found to be functions of depth. It was also found that the sensor depth selects a dominant temporal frequency from the random surface waves.

The Optical Array: An Alternative to Scattering or Extinction for Airborne Particle Size Determination

An electro-optical technique is described for the measurement of the size distributions of cloud and precipitation particles. The technique utilizes a linear array of photodetectors as a size measuring grid in a typical shadowgraph-type imaging system. Several instruments have been designed and are described in various stages of testing and development. A thorough description of one such instrument and preliminary field data are given.