We designed and experimentally reported modified potential InGaAs/InAlAs coupled quantum wells. In this structure, a large blue shift of the absorption edge of more than 35 meV is obtained at a reverse bias of -4 V. This predicts that a large negative electrorefractive index change can be achieved at longer wavelength region of the absorption edge.
The optical waveguide switch utilizing the principle of total internal reflection (TIR) is a promising structure since its
merits such as compact size, digital response characteristic, insensitivity to wavelength and polarization, and so on. In
this paper the TIR switch is studied both in theory and in experiment. At first, we give a comprehensive analysis about
reflection mechanism in the TIR switch from the following three issues: the grazing incidence of a narrow beam in the
free space, the beam reflection in a bounded space, and the beam expansion induced by the reflection in a two-dimensional
gradient field of the refractive index decrease. Then based on the analytical works, we successfully fabricate
practical TIR switches by utilizing the thermo-optical effect of polymer and the carrier injection effect of GaAs (both the
current injection and the photon injection manners are employed). The testing results show that: the extinction ratio of
the thermo-optical TIR switch exceeds 35 dB at an power consumption of 80 mW; for the carrier injection TIR switch
utilizing the current injection manner, its operation speed is faster than 20 ns and its operation current is about 70 mA.
The modal expansion method is utilized to study the reflection mechanism in the total-internal-reflection (TIR) switch. Due to the confinement of the waveguide, the beam reflection within the TIR switch is completely different from that in the free space. Its essence is the degeneracy between the even and odd modes in the waveguide of the reflection region.
We propose a compact variable optical attenuator (VOA) based on the W type five-layer symmetric slab waveguide. Simulation result shows that: for the attenuator based on GaAlAs/GaAs epitaxial layers, with a refractive index change of -0.01 in the current injection region of 1000 &mgr;m long (corresponding to injected current of about 80mA), an attenuation of more than 30dB is achieved. The attenuation range can be scaled to fit the requirements by varying the electrode length.
We propose an analytical reflection model for the waveguide switch with total-internal-reflection structure, which is the grazing reflection of beam with narrow beamwaist. For such incidence condition, the output optical field is the superposition of incident and reflected fields, we deduce the effective reflection coefficient together with angular spectrum of the output field.