The performance of electronic systems for radio-frequency (RF) spectrum analysis is critical for agile radar and communications systems, ISR (intelligence, surveillance, and reconnaissance) operations in challenging electromagnetic (EM) environments, and EM-environment situational awareness. While considerable progress has been made in size, weight, and power (SWaP) and performance metrics in conventional RF technology platforms, fundamental limits make continued improvements increasingly difficult. Alternatively, we propose employing cascaded transduction processes in a chip-scale nano-optomechanical system (NOMS) to achieve a spectral sensor with exceptional signal-linearity, high dynamic range, narrow spectral resolution and ultra-fast sweep times. By leveraging the optimal capabilities of photons and phonons, the system we pursue in this work has performance metrics scalable well beyond the fundamental limitations inherent to all electronic systems. In our device architecture, information processing is performed on wide-bandwidth RF-modulated optical signals by photon-mediated phononic transduction of the modulation to the acoustical-domain for narrow-band filtering, and then back to the optical-domain by phonon-mediated phase modulation (the reverse process). Here, we rely on photonics to efficiently distribute signals for parallel processing, and on phononics for effective and flexible RF-frequency manipulation. This technology is used to create RF-filters that are insensitive to the optical wavelength, with wide center frequency bandwidth selectivity (1-100GHz), ultra-narrow filter bandwidth (1-100MHz), and high dynamic range (70dB), which we will present. Additionally, using this filter as a building block, we will discuss current results and progress toward demonstrating a multichannel-filter with a bandwidth of < 10MHz per channel, while minimizing cumulative optical/acoustic/optical transduced insertion-loss to ideally < 10dB. These proposed metric represent significant improvements over RF-platforms.
We show simulation results of the integration of a nanoantenna in close proximity to the active material of a photodetector. The nanoantenna allows a much thinner active layer to be used for the same amount of incident light absorption. This is accomplished through the nanoantenna coupling incoming radiation to surface plasmon modes bound to the metal surface. These modes are tightly bound and only require a thin layer of active material to allow complete absorption. Moreover, the nanoantenna impedance matches the incoming radiation to the surface waves without the need for an antireflection coating. While the nanoantenna concept may be applied to any active photodetector material, we chose to integrate the nanoantenna with an InAsSb photodiode. The addition of the nanoantenna to the photodiode requires changes to the geometry of the stack beyond the simple addition of the nanoantenna and thinning the active layer. We will show simulations of the electric fields in the nanoantenna and the active region and optimized designs to maximize absorption in the active layer as opposed to absorption in the metal of the nanoantenna. We will review the fabrication processes.
Current infrared imaging systems monitor emission from a given scene over a broad spectral range, which results with "black and white" images. As a result, there is ever increasing emphasis on the development of new, on the pixel level, infrared imaging technology that can provide spectral information. Attempts at creating a robust imaging system with spectral information have been made through a network of external optics, which results with a high cost and large system package. Here, we propose a metamaterial design that resonantly couples to an infrared photodetector for enhanced performance.
We demonstrate the effects of integrating a nanoantenna to a midwave infrared (MWIR) focal plane array (FPA). We
model an antenna-coupled photodetector with a nanoantenna fabricated in close proximity to the active material of a
photodetector. This proximity allows us to take advantage of the concentrated plasmonic fields of the nanoantenna. The
role of the nanoantenna is to convert free-space plane waves into surface plasmons bound to a patterned metal surface.
These plasmonic fields are concentrated in a small volume near the metal surface. Field concentration allows for a
thinner layer of absorbing material to be used in the photodetector design and promises improvements in cutoff
wavelength and dark current (higher operating temperature). While the nanoantenna concept may be applied to any
active photodetector material, we chose to integrate the nanoantenna with an InAsSb photodiode. The geometry of the
nanoantenna-coupled detector is optimized to give maximal carrier generation in the active region of the photodiode, and
fabrication processes must be altered to accommodate the nanoantenna structure. The intensity profiles and the carrier
generation rates in the photodetector active layers are determined by finite element method simulations, and iteration
between optical nanoantenna simulation and detector modeling is used to optimize the device structure.
We review the physics of photon-phonon coupling in guided wave systems, and discuss new opportunities for
information transduction aorded by nanoscale connement of light and phonons within a novel class of optome-
chanical waveguide systems. We present a fundamental analysis of optical forces generated through nanoscale
light-matter interactions, and use these insights to develop new approaches for broadband signal processing via
optomechanics. Recent experimental results will also be discussed.
Recent advance in controlling optical forces using nanostructures suggests that nanoscale optical waveguides are capable
of generating coherent acoustic phonons efficiently through a combination of radiation pressure and electrostriction. We
discuss the critical roles of group velocity in such processes. This photon-phonon coupling would allow an acoustic
intermediary to perform on-chip optical delay with a capacity 105 greater than photonic delay lines of the same size.
Phononic crystals (PnCs) are acoustic devices composed of a periodic arrangement of scattering centers embedded in a homogeneous background matrix with a lattice spacing on the order of the acoustic wavelength. When properly designed, a superposition of Bragg and Mie resonant scattering in the crystal results in the opening of a frequency gap over which there can be no propagation of elastic waves in the crystal, regardless of direction. In a fashion reminiscent of photonic lattices, PnC patterning results in a controllable redistribution of the phononic density of states. This property makes PnCs a particularly attractive platform for manipulating phonon propagation. In this communication, we discuss the profound physical implications this has on the creation of novel thermal phenomena, including the alteration of the heat capacity and thermal conductivity of materials, resulting in high-ZT materials and highly-efficient thermoelectric cooling and energy harvesting.
We present a semi-analytical Green's function-based technique for analyzing propagation loss in photonic crystal
waveguides (PCWGs). The method only requires the complex band structure of the PCWG to calculate the transmission
(or loss) of the structure. The plane-wave expansion method was used in this work to calculate the complex band
behavior, and the power of this technique is demonstrated by comparing the results with the brute force simulation
results for a PCWG. The possibility of extending this technique to the more practical arrangement of a random
distribution of defects using a configurational average with coherent potential approximation theory will also be
We present a theoretical analysis of propagation losses in photonic crystal waveguides due to
fabrication imperfections. The analysis is performed using a Green's function-based technique
with the layer Korringa-Kohn-Rostoker method. This approach requires only the calculation of
the complex mode behavior of the photonic crystal structure, from which the loss of a given
mode is directly deduced. The accuracy and applicability of the method is discussed. The
method will be demonstrated using two-dimensional photonic crystals with line-defect
waveguides having a single fabrication defect.
A method for controlling the dispersion and thus group velocity of guided modes in photonic crystal (PC) waveguides using bi- and quasi-periodic lattices is presented. Rectangular lattice photonic crystals are proposed as possible candidates for implementing such control. However, these structures, and generally all bi-periodic lattices, develop undesirable characteristics as the perfect square lattice is perturbed. Thus, quasi-periodic photonic crystals, which have been shown to be promising in selective mode engineering, were examined next. A possible scheme for engineering of a single mode PC waveguide with guiding through the entire bandgap is presented.