Brahm Pal Singh

High power subterahertz electromagnetic wave radiation from GaN photoconductive switch

The authors present apparently the observation of subterahertz electromagnetic wave emission from GaN based large aperture photoconductive switches (LA-PCSWs) excited by ultraviolet femtosecond laser pulses. The photoconductive layer of the GaN LA-PCSW is doped with carbon giving rise to a resistivity as high as 60MΩcm. The absolute energy of the emitted radiation pulses is measured to be 93.3pJ/pulse under 500V bias voltage. The Fourier spectrum of the measured pulse by the time-domain-spectroscopy shows the main components lie in 0.1–0.2THz regime.

Dual-Wavelength High-Power Laser Diodes Fabricated by Selective Fluidic Self-Assembly

We have developed dual-wavelength high-power laser diodes (LDs) with a hybrid integrated solution, in which a 660 nm (red) LD chip and a 780 nm (infrared) LD chip are mounted side-by-side on the same substrate. To achieve the required mounting position accuracy, i.e., the distance between two emitting points is limited to 110±3 µm, we have developed a novel mounting technique called selective fluidic self-assembly (S-FSA). In this technique, we used new self-locking structures of guest-host pairs. Bumps formed on the bonding surfaces of the LD chips are used as guests. A substrate with recesses whose shapes correspond to those of the bumps is used as the host. By forming bumps aligned along the waveguide and assigning a rotationally asymmetric shape for the bumps, an accurate and selective mounting is realized. Dual-wavelength LDs fabricated by this technique demonstrated the required positioning accuracy and high-power operation.