Rama Raj

Ultrafast dynamics of the third-order nonlinear response in a two-dimensional InP-based photonic crystal

We report experimental demonstration of very fast nonlinear response around 1.5μm in an InP-based two-dimensional photonic crystal. The nonlinearity produced by low pump powers via carrier induced nonlinear refractive index, leads to an efficient wavelength shift of a photonic crystal resonance observed in reflectivity. Thus we show that it is possible to obtain round the clock (rise and recovery) switching times shorter than 10ps with contrast ratio higher than 80%.

Hybrid III-V semiconductor/silicon nanolaser

Heterogeneous integration of III-V compound semiconductors on Silicon on Insulator is one the key technology for next-generation on-chip optical interconnects. In this context, the use of photonic crystals lasers represents a disruptive solution in terms of footprint, activation energy and ultrafast response. In this work, we propose and fabricate very compact laser sources integrated with a passive silicon waveguide circuitry. Using a subjacent Silicon-On-Insulator waveguide, the emitted light from a photonic crystal based cavity laser is efficiently captured. We study experimentally the evanescent wave coupling responsible for the funneling of the emitted light into the silicon waveguide mode as a function of the hybrid structure parameters, showing that 90% of coupling efficiency is possible.

All-optical bistable band-edge Bloch modes in a two-dimensional photonic crystal

We demonstrate experimentally all-optical bistable operation in an InP-based two-dimensional photonic crystal slab lying on top of a Bragg reflector. Bistability is obtained around 1550nm, using a low group velocity mode at the band edge of the photonic dispersion characteristic. The origin of the bistable regime is shown to be the fast (275ps relaxation time), electronically induced nonlinear refraction index. A low intensity threshold of 4kW∕cm2 was observed, with a contrast of 65% between the high and low reflectivity states.

Heterogeneous integration and precise alignment of InP-based photonic crystal lasers to complementary metal-oxide semiconductor fabricated silicon-on-insulator wire waveguides

The integration of two-dimensional III-V InP-based photonic crystal and silicon wire waveguides is achieved through an accurate alignment of the two optical levels using mix-and-match deep ultraviolet (DUV)/electron beam lithography. The adhesively bonded structures exhibit an enhancement of light emission at frequencies where low group velocity modes of the photonic crystal line defect waveguides occur. Pulsed laser operation is obtained from these modes at room temperature under optical pumping. The laser light is coupled out of the Si waveguide via grating couplers directly to single mode fiber.

Direct observation of high-order optical susceptibilities via angularly-resolved multiwave mixing

Abstract A new method of monitoring specific high-order optical susceptibilities of nonlinear media via angularly-resolved emission in a phase-matched multiwave mixing configuration is presented. This technique, which can be viewed as the creation by two optical beams of a strongly anharmonic absorption or index grating, and the simultaneous exploration of higher Bragg-diffraction orders by a third wave, is demonstrated here in the case of gas media near optical resonance.

Continuous-wave operation of photonic band-edge laser near 1.55 μm on silicon wafer

We report on the continuous-wave operation of a band edge laser at room temperature near 1.55 μm in an InGaAs/InP photonic crystal. A flat dispersion band-edge photonic mode is used for surface normal operation. The photonic crystal slab is integrated onto a Silicon chip by means of Au/In bonding technology, which combines two advantages, efficient heat sinking and broad band reflectivity.

Tuning a two-dimensional photonic crystal resonance via optical carrier injection

We report on wide wavelength tuning through optical injection of carriers of a photonic resonance observed in reflectivity at 1543 nm in an InP-based two-dimensional photonic crystal slab. An 8-nm blueshift, which represents 20 times the resonance linewidth, is observed when a 4-kW/cm2 intense optical pump is incident on the sample. An analytical model that we developed, based on a coupled-mode nonlinear approach, allows us to describe this phenomenon in detail.

Ultrafast all-optical switching and error-free 10 Gbit/s wavelength conversion in hybrid InP-silicon on insulator nanocavities using surface quantum wells

Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mW switching powers.

Hybrid InP-based photonic crystal lasers on silicon on insulator wires

We report on InP-based photonic crystal lasers operating at 1.585 μm at room temperature, integrated with and evanescently coupled to silicon on insulator (SOI) waveguides. By optically pumping at 1.18 μm through the SOI wires, pulsed laser emission from line defect photonic crystal waveguides accurately aligned (<30 nm) to the silicon circuitry is demonstrated.

Field localization and enhancement of phase-locked second- and third-order harmonic generation in absorbing semiconductor cavities

We predict and experimentally observe the enhancement by three orders of magnitude of phase mismatched second and third harmonic generation in a GaAs cavity at 650 and 433 nm, respectively, well above the absorption edge. Phase locking between the pump and the harmonics changes the effective dispersion of the medium and inhibits absorption. Despite hostile conditions the harmonics resonate inside the cavity and become amplified leading to relatively large conversion efficiencies. Field localization thus plays a pivotal role despite the presence of absorption, and ushers in a new class of semiconductor-based devices in the visible and uv ranges.