Tirumala R. Ranganath

Photocurrent amplification in Schottky photodiodes

Up to 20 dB of photocurrent amplification with a frequency response of 2 GHz has been observed in GaAs Schottky photodiodes. The amplification may be caused by a reduction in Schottky built‐in potential under illumination. The device may find application in improving the sensitivity of optical receivers.

Continuously graded‐index separate confinement heterostructure multiquantum well Ga1−xInxAs1−yPy/InP ridge waveguide lasers grown by low‐pressure metalorganic chemical vapor deposition with lattice‐matched quaternary wells and barriers

Continuously graded‐index separate confinement heterostructure multiple quantum well (four wells, Lz ∼50 A) lasers fabricated in the Ga1−xInxAs1−yPy/InP system with lattice‐matched quaternary wells (bulk emission wavelength λg=1.39 μm) and barriers (λg=1.2 μm) are reported. A 5‐μm‐wide ridge waveguide laser operates with laser threshold current Ith=34 mA at room temperature (λ∼1286 nm) with an external differential quantum efficiency of ∼19% per facet and a temperature coefficient T0 ∼40 K. Large‐area threshold current density is measured at 1.1 kA/cm2 on a 40×300 μm2 device.

50 GHz Velocity-matched, broad wavelength LiNbO3 modulator with multimode active section

Improved velocity matching in LiNbO3 modulators has been achieved by several workers [1-4], using a combination of relatively thick (≥ 1 µm) SiO2 buffer layers and thick (typically ≥ 10 µm) plated electrodes. Utilizing this combination, microwave indices ≤ 2.5 have been achieved. However, increase in electrode thickness lowers device impedance, which raises drive power requirements and causes mismatch to most common 50 Ω sources. This decrease is partially compensated by the thicker buffer layer and by employing large gaps (typically 15 μm) between the hot and ground electrode(s), both of which maintain the impedance at a high value. They also increase the drive voltage, however, resulting in a larger voltage-length product relative to conventional modulators. To achieve closer velocity matching would require additional increases in electrode/buffer thicknesses, resulting in even higher voltages.