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For a wide range of the thicknesses of the charge and the multiplication layers, detection efficiency and dark count probability are numerically investigated for GaInAs/InP single photon detection avalanche photodiodes (APD’s) which are operated in the Geiger mode. Breakdown probability and dark currents are calculated to evaluate detection efficiency and dark count probability. The result shows that dark count probability can be significantly reduced by increasing the thickness of the charge layer, whereas detection efficiency is expected to decline steeply at some thickness of the charge layer. Moreover, increasing the thickness of the multiplication layer does not continue to reduce dark count probability, which increases when the multiplication layer is thicker than a critical thickness. Finally, we show a design guideline of single photon detection APD’s with higher detection efficiency and lower dark count probability. [ABSTRACT FROM AUTHOR]

This paper presents the high reliability of the guardring-free planar InAlAs avalanche photodiode (APD) and its degradation mode analysis. We have conducted long-term and high-temperature aging tests under 175degC, 200degC, 225degC, and 250degC. There were three degradation modes as follows: 1) the increase in the dark current; 2) the decrease in the breakdown voltage; and 3) short circuit. Their thermal activation energies were 0.96, 1.30, and 0.93 eV, respectively. Their estimated mean times to failures at 85 are 25, 100, and 22 million hours, respectively. Increased dark current is generated in the upper side of the absorbing layer. The breakdown voltage decreased with aging time because the depletion width in the absorbing layer shrinks from the region side. Any degradation mode on the surfaced p-n junction did not appear in spite of the 10 000-h aging test at a high temperature of 200degC. The guardring-free planar InAlAs APD has the advantage of high reliability because the electric field of a surfaced p-n junction is weakened by the underlying field control layer. [ABSTRACT FROM PUBLISHER]

We demonstrate a practical 2.5-Gb/s AlInAs avalanche photodiode (APD) and an AlInAs APD-based optical receiver with high sensitivity. The AlInAs APD has a simple guardring-free planar structure with high reliability. In addition to the inherent low excess noise of AlInAs, their simplicity and high yields are great advantages in production, even when contrasted with the planar InP APDs now on the market. The guardring-free AlInAs APDs achieve larger gain-bandwidth (GB) products and lower excess noise, with a maximum 3-dB bandwidth of 6.0 GHz and a GB product of typically 80 GHz, and have equal performance with InP APDs, which have a responsivity of 1.0 A/W and a multiplying dark current of 2.2 nA. An AlInAs APD-based 2.5-Gb/s optical receiver with a SiGe transimpedance amplifier has a sensitivity of -37.0 dBm at a bit-error rate of 10-10 [ABSTRACT FROM PUBLISHER]

A novel wavelength combiner using non-uniform refractive index distribution within a multimode interference device is proposed and simulated. The refractive index step creates separate localized modes with different effective refractive indices and two modes are strongly excited which form the basis of an interferometer. We applied the concept to 1.30/1.31 μm and 1.31/1.55 μm wavelength combiners on an InP substrate. The lengths of the devices are 1272 μm and 484 μm with simulated insertion losses of 0.6 dB and 0.67 dB respectively.

A novel polarization splitter on an InP substrate utilizing an MMI coupler loaded with a dielectric and gold layer pad is proposed and simulated. A tilted joint is used for adjusting the phases of TE and TM modes. The MMI section is less than 540 μm. Simulations show that the device has a polarization extinction ratio over 23 dB and an insertion loss below 0.7 dB over the entire C-band for both TE and TM polarizations. The device design was optimized to maximize the wavelength range and tolerance for manufacturing variations.

A mode-evolution-based polarization rotator-splitter built on InP substrate is proposed by combining a mode converter and an adiabatic asymmetric Y-coupler. The mode converter, consisting of a bi-level taper and a width taper, effectively converts the fundamental TM mode into the second order TE mode without changing the polarization of the fundamental TE mode. The following adiabatic asymmetric Y-coupler splits the fundamental and the second order TE modes and also converts the second order TE mode into the fundamental TE mode. A shallow etched structure is proposed for the width taper to enhance the polarization conversion efficiency. The device has a total length of 1350 µm, a polarization extinction ratio over 25 dB and an insertion loss below 0.5 dB both for TE and TM modes, over the wavelength range from 1528 to 1612 nm covering all C + L band. Because the device is designed based on mode evolution principle, it has a large fabrication tolerance. The insertion loss remains below 1 dB and the polarization extinction ratio remains over 17 dB with respect to a width variation of +/- 0.12 µm at the wavelength of 1570 nm, or +/- 0.08 µm over the entire C + L band., (© 2012 Optical Society of America)

A hybrid digital optical computing system is constructed, a variation of the optical parallel array logic system (OPALS). The OPALS is a general-purpose digital optical computing system based on optical array logic, in which image coding and 2-D correlation are used to achieve parallel logical operations. In the constructed system, 2-D correlation for optical array logic is performed optically with a modified multireflective correlator; the other procedures in optical array logic are achieved by electronics including a TV feedback system. We have verified correct execution of programs written by optical array logic on the system. Although the processing speed of the system is still slow because of the sequential process in electronics, it can be drastically improved by replacing the sequential processing devices with parallel ones.