A novel approach that enables long range hybrid plasmonic modes to be supported in asymmetric structures will be discussed. Examining the modal behavior of an asymmetric hybrid plasmonic waveguide (AHPW) reveals that field symmetry on either side of the metal is the only necessary condition for plasmonic structures to support long range propagation. In this talk we shall demonstrate that this field symmetry condition can be satisfied irrespective of asymmetry in waveguide structure, material, or even field profile. The versatility in the choice of parameters allows for long range hybrid plasmonic modes to be achieved in generic structures. Altering the existing limitations of these performance metrics (mode area and propagation losses) can have significant implications on the designs of active devices. As illustrative example, the utility of these waveguide designs is demonstrated when combined with novel material such as ITO to realize optoelectronic components such as filters, modulators and switches with record footprint, performance and insertion losses.
Plasmonic waveguides, which support surface plasmon polaritons (SPP)
propagating along metal-dielectric interfaces, offer strong field confinement and
are ideal for the design of integrated nano-scale photonic devices. However, due
to free-carrier absorption in the metal, the enhanced mode confinement inevitably
entails an increase in the waveguide loss. This lowers the device figure-of-merit
achievable with passive plasmonic components and in turn hinders the
performance of active plasmonic components such as optical modulators.
The trade-off between extinction ratio (ER), insertion loss (IL), and energy consumption (E) is a common bottleneck for existing integrated optical modulators. In this work, we report an indium tin oxide (ITO) based hybrid-plasmonic modulator, consisting of a Si/ITO/HfO2/Al/HfO2/ITO/Si stack, that can alleviate such trade- off in device metrics. This is achieved by first use field symmetry matching technique to engineer the waveguide to support long-range propagation. Then, by electrostatically inducing the ITO layers to enter an epsilon-near-zero state, strong carrier absorption as well as disturbance to the field symmetry will render the otherwise low-loss waveguide highly absorptive. Using this strategy, amplitude modulation with ER = 4.83 dB/μm, IL = 0.03 dB/μm, and E = 14.8 fJ is achieved. Moreover, with a triode-like biasing scheme, the modulator attributes can be further manipulated and the same device can be dynamically reconfigured for phase and 4-quadrature-amplitude modulation, with actively device length of only 5.53 μm and 17.78 μm respectively.
Plasmonic slot waveguide (PSW) provides unique ability to confine the light in few nanometers only. It also allows for near perfect transmission through sharp bends. These features motivate utilizing the PSW in various on chip applications that require nanoscale manipulation of light. The main challenge of using these PSWs are the associated high losses that allow for propagation length of ~10 μm only. However, this constraint plays a minimal rule for circuits designed to have footprint in the order of few micrometers only. Thus, designing PSW with compact size and superior performance is of prime essential. Finite difference time domain (FDTD) is usually utilized for modeling of such networks. This technique is, however, inefficient as it requires very fine grid and carful manipulation of the boundary condition to avoid spurious reflections. In the paper, we present our recent equivalent circuit model that is capable of accurately modeling the various junctions including T and X shapes. This model is highly efficient and allows for obtaining a closed form expression of the response of any network of PSW with accuracy comparable to the FDTD results.
In this paper, we discuss the recent achievements in realizing plasmonic networks, which are compatible
with silicon photonics platform. Obtaining good coupling between plasmonic gap and silicon waveguides is
necessary for these networks to be practical. We report our experimental realization of novel wide band,
and non-resonant coupling scheme between plasmonic gap and silicon waveguides.