Hideo Arimoto

Stimulated emission of near-infrared radiation by current injection into silicon (100) quantum well

We describe the observation of stimulated emissions by current injections into a silicon quantum well. The device consists of a free standing membrane with a distributed feedback resonant cavity fabricated by state-of-the-art silicon processes. The emission spectra have multimode structures peaked in the near-infrared region above the submilliampere threshold currents at room temperatures. Consequently, electronics and photonics should be able to be converged on chips by using silicon quantum well laser diodes.

Whispering gallery mode resonances from Ge micro-disks on suspended beams

Ge is considered to be one of the most promising materials for realizing full monolithic integration of a light source on a silicon (Si) photonic chip. Tensile-strain is required to convert Ge into an optical gain material and to reduce the pumping required for population inversion. Several methods of strain application to Ge are proposed in literature, of which the use of free-standing beams fabricated by micro-electro-mechanical systems (MEMS) processes are capable of delivering very high strain values. However, it is challenging to make an optical cavity within free-standing Ge beams, and here, we demonstrate the fabrication of a simple cavity while imposing tensile strain by suspension using Ge-On-Insulator (GOI) wafers. Ge micro-disks are made on top of suspended SiO

A wavelength-tunable short-cavity DBR laser with active distributed Bragg reflector

_{2}

Experimental Demonstration of a Highly Reliable Multicore-Fiber-Based Optical Network

beams by partially removing the supporting Si substrate. According to Raman spectroscopy, a slight tensile strain was applied to the Ge disks through the bending of the SiO2 beams. Whispering-Gallery-Mode (WGM) resonances were observed from a disk with a diameter of 3um, consistent with the finite-domain time-difference simulations. The quality (Q) factor was 192, and upon increasing the pumping power, the Q-factor was degraded due to the red-shift of Ge direct-gap absorption edge caused by heating.

Multi-core fiber technology for optical-access and short-range links

The incorporation of an active single-quantum well in the tuning layer of a DBR laser is proposed as a way of compensating for optical loss and achieving stable single-mode operation during wavelength tuning. Experimental results demonstrate that the structure achieves these goals while maintaining the efficiency of tuning. In application to a short-cavity DBR laser with a gain region 35-µm long, continuous wavelength gtuning over a broad 4.8nm is achieved with stable lasing properties (more than 40dB of side-mode suppression). Fast wavelength switching less than 10ns to cross a wavelength spacing of 2nm is also confirmed.

Observation of optical gain in ultra-thin silicon resonant cavity light-emitting diode

A prototype optical switch unit with multi-core fibers was fabricated. It was experimentally demonstrated that this prototype can automatically restore optical paths when line failure occurs. The corresponding restoration time is 5 ms, which meets the time specified in the ITU-T standard .

Low-Loss Silicon Waveguides and Grating Couplers Fabricated Using Anisotropic Wet Etching Technique

To provide high-capacity/high-reliability optical-access and short-range links, a novel failure-recovery system utilizing protection optical switch units and multi-core fibers was developed. Configuring the proposed failure-recovery system, the developed multi-core fiber (MCF) connection technology (i.e., fan-in/-out modules and MCF connectors) and a protection optical-switch unit experimentally demonstrated automatic impairment-aware optical-switching.

Spin-on doping of germanium-on-insulator wafers for monolithic light sources on silicon

We have observed net optical gain by current injections to ultra-thin Si embedded in a resonant optical cavity. The cavity consists of a dielectric waveguide fabricated by CMOS and MEMS process. The photoluminescence (PL) spectra show narrow resonances peaked at the designed wavelength, and the electroluminescence (EL) intensity increases super-linearly with currents. The comparisons with first principle calculations suggest that the optical gain is originated from intrinsic material properties of ultra-thin Si due to quantum confinements.

A Light Source Using 1.3-

We report low-loss silicon waveguides and efficient grating coupler to couple light into them. By using anisotropic wet etching technique, we reduced the side wall roughness down to 1.2nm. The waveguides were patterned along the [112] direction on a [110] SOI substrate. The waveguide boundaries are decided by the [111] planes which are normal to the [110] surface. Fabricated waveguides show minimum propagation loss of 0.85 dB/cm for TE polarization and 1.08dB/cm for TM polarization. The fabricated grating couplers show coupling efficiency of -4.16dB at 1570nm with 3dB bandwidth of 46nm.

\mu{\rm m}

High electron doping of germanium (Ge) is considered to be an important process to convert Ge into an optical gain material and realize a monolithic light source integrated on a silicon chip. Spin-on doping is a method that offers the potential to achieve high doping concentrations without affecting crystalline qualities over other methods such as ion implantation and in-situ doping during material growth. However, a standard spin-on doping recipe satisfying these requirements is not yet available. In this paper we examine spin-on doping of Ge-on-insulator (GOI) wafers. Several issues were identified during the spin-on doping process and specifically the adhesion between Ge and the oxide, surface oxidation during activation, and the stress created in the layers due to annealing. In order to mitigate these problems, Ge disks were first patterned by dry etching followed by spin-on doping. Even by using this method to reduce the stress, local peeling of Ge could still be identified by optical microscope imaging. Nevertheless, most of the Ge disks remained after the removal of the glass. According to the Raman data, we could not identify broadening of the lineshape which shows a good crystalline quality, while the stress is slightly relaxed. We also determined the linear increase of the photoluminescence intensity by increasing the optical pumping power for the doped sample, which implies a direct population and recombination at the gamma valley.