On-chip optical interconnection using integrated germanium light emitters and photodetectors.

Germanium (Ge) is an attractive material for monolithic light sources and photodetectors, but it is not easy to integrate Ge light sources and photodetectors because their optimum device structures differ. In this study, we developed a monolithically integrated Ge light emitting diode (LED) that enables current injection at high density and a Ge photodiode (PD) having low dark current, and we fabricated an on-chip optical interconnection system consisting of the Ge LED, Ge PD, and Si waveguide. We investigated the properties of the fabricated Ge LED and PD and demonstrated on-chip optical interconnection.

Optical net gain measurement in n-type doped germanium waveguides under optical pumping for silicon monolithic laser.

Silicon (Si) monolithic lasers are key devices in large-scale, high-density photonic integrated circuits. Germanium (Ge) is promising as an active layer due to the complementary metal-oxide semiconductor process compatibility with Si. A net optical gain from Ge is essential to demonstrate lasing operation. We fabricated Ge waveguides and investigated the n-type doping effect on the net optical gain. The estimated net gain of the n-Ge waveguide increased from -2200 to -500/cm, namely reducing loss, under optically pumped condition.

GaInAsP/InP lateral-current-injection distributed feedback laser with a-Si surface grating.

We fabricated a novel lateral-current-injection-type distributed feedback (DFB) laser with amorphous-Si (a-Si) surface grating as a step to realize membrane lasers. This laser consists of a thin GaInAsP core layer grown on a semi-insulating InP substrate and a 30-nm-thick a-Si surface layer for DFB grating. Under a room-temperature continuous-wave condition, a low threshold current of 7.0 mA and high efficiency of 43% from the front facet were obtained for a 2.0-µm stripe width and 300-µm cavity length. A small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA.

Lateral current injection GaInAsP/InP laser on semi-insulating substrate for membrane-based photonic circuits.

A room-temperature pulsed operation was demonstrated using lateral current injection-type lasers composed of a 400-nm-thick GaInAsP core layer with compressively strained 5 quantum wells. A threshold current of 105 mA and corresponding density of 1.3 kA/cm(2) (260 A/cm(2) per well) were obtained with the stripe width of 5.4 microm and the cavity length of 1.47 mm. A fundamental transverse mode operation was obtained with the narrower stripe device of 2.0 microm and the cavity length of 805 microm, while the threshold current and corresponding density were 49 mA and 3.0 kA/cm(2), respectively.

Electrically-pumped compact hybrid silicon microring lasers for optical interconnects.

We demonstrate an electrically-pumped hybrid silicon microring laser fabricated by a self-aligned process. The compact structure (D = 50 microm) and small electrical and optical losses result in lasing threshold as low as 5.4 mA and up to 65 degrees C operation temperature in continuous-wave (cw) mode. The spectrum is single mode with large extinction ratio and small linewidth observed. Application as on-chip optical interconnects is discussed from a system perspective.

GaInAsP/InP membrane BH-DFB lasers directly bonded on SOI substrate.

A room-temperature continuous-wave operation under optical pumping was demonstrated with GaInAsP/InP membrane buriedheterostructure (BH) distributed-feedback (DFB) laser directly bonded on an SOI substrate. A threshold pump power of 2.8 mW and a sub-mode suppression ratio of 28 dB were obtained with a cavity length of 120 microm and a stripe width of 2 microm.