Modern deep neural networks (DNNs) have been demonstrating a phenomenal success in many exciting appli- cations such as computer vision, speech recognition, and natural language processing, thanks to recent machine learning model innovation and computing hardware advancement. However, recent studies show that state-of- the-art DNNs can be easily fooled by carefully crafted input perturbations that are even imperceptible to human eyes, namely “adversarial examples”, causing the emerging security concerns for DNN based intelligent systems. Moreover, to ease the intensive computation and memory resources requirement imposed by the fast-growing DNN model size, aggressively pruning the redundant model parameters through various hardware-favorable DNN techniques (i.e. hash, deep compression, circulant projection) has become a necessity. This procedure further complicates the security issues of DNN systems. In this paper, we first study the vulnerabilities of hardware-oriented deep compressed DNNs under various adversarial attacks. Then we survey the existing mitigation approaches such as gradient distillation, which is originally tailored to the software-based DNN systems. Inspired by the gradient distillation and weight reshaping, we further develop a near zero-cost but effective gradient silence (GS) method to protect both software and hardware-based DNN systems against adversarial attacks. Compared with defensive distillation, our gradient salience method can achieve better resilience to adversarial attacks without additional training, while still maintaining very high accuracies across small and large DNN models for various image classification benchmarks like MNIST and CIFAR10.
Tunable silicon microring filters are used to demonstrate CMOS-compatible on-chip wavelength control of Er+ doped
fiber-lasers. The filter uses a 10 μm-diameter microring resonator based on single-mode silicon-on-insulator (SOI) strip
waveguides operating around the telecom range of 1.55 μm. A piece of Er+ doped fiber (EDF) serves as the gain media
which is pumped by a 980 nm laser diode. An on-chip Ni-Cr micro-heater consuming up to 38 mW is capable of tuning
the Si microring filter by 2.3 nm with a lasing linewidths narrower than 0.02 nm. This approach enables arbitrary
multiple wavelength generation on a silicon chip. Possible applications include on-chip and chip-to-chip densewavelength
division multiplexed communications, telecommunications and optical sensor interrogation.
A platform that enables optical coupling from fiber-ribbon connectors to planar lightwave circuits (PLCs) is described. Flexible optical waveguides are used to form a variable length directional coupler that inserts and extracts light from a waveguide located arbitrarily inside the chip. The contact length can be adjusted for optimal coupling allowing manufacturing variation in materials, widths and cladding thicknesses present on a chip. This approach may be ideal for packaging WDM devices as the 3dB bandwidth of the coupling covers the whole 1300 -1700 nm fiber-optic telecommunication range. Coupling length control in the range of 0.05-0.2 μm leads to maximum coupling in excess of 80% for the range of conditions investigated. Simulations of the performance are discussed and initial fabrication and optical coupling results are presented.
We designed a compact optical resonator with two distributed Bragg reflectors (DBR) embedded on single mode
polymer ridge waveguide structure towards micro-scale polymer lasers. Single DBR is made up of alternating layers
with λ/4 thickness of air and polymer. Numerical simulation of the device was carried out with 3D FDTD. We
investigated the reflectance of single DBR as a function of order and number of periods and found a maximum of 97.8%,
achieved for a TE mode with air cladding in material with low refractive index 1.54. Focused ion beam (FIB)
lithography was used to open periodic air gaps on a 3 um wide ridge waveguide consisting of 1 um thick polymer layer
doped with disperse red 1 (n=1.54) structure. Single DBR with five periods are optically characterized by observing the
transmission through the device.
Microstructure manipulation is a fundamental process to further the study of biology and medicine, as well as to advance micro- and nano-system applications. The manipulation of micro and nanostructures has been achieved through various microgripper devices developed recently, which lead to advances in single cell manipulation and micromachine assembly. However, the physical, mechanical, optical and chemical information about the microstructure under study is usually extracted from macroscopic instrumentation, such as confocal microscopy and Raman spectroscopy. In this paper we describe the design, simulation, fabrication and characterization (mechanical and optical) of a novel Micro-Opto-Electro-Mechanical-System (MOEMS) optical microgripper. This is the first device of this kind, which enables the direct manipulation, mechanical characterization, and simultaneous optical characterization of microstructures. Optical fluorescence measurements or identification, as well as absorption spectroscopy are possible with this new device. The device is implemented in SU-8 due to its suitable optical and mechanical properties. The current generation of the device was designed to manipulate structures with dimensions lower than ~5 μm.
Slot-waveguides have attracted considerable attention recently due to the high-intensity electric fields and power
densities that can be achieved in very small volumes of low-index materials. Latest applications of this concept have led
to new designs of photodetectors, modulators and CMOS-compatible light-emitting devices. However, the coupling of
light to and from fiber optics and slot-waveguides remains a challenge. In this paper we present the numerical analysis of
a slotted nanotaper for coupling between a fiber and the horizontal slot-waveguide. We used numerical simulations to
study the coupling process and found a minimum mismatch loss of 0.4 dB for a tip width of 105 nm. The mode
conversion from the tip of the coupler to the full width of the slot-waveguide was performed with a loss less than 0.2 dB
when the length was at least 80 microns. This inverse taper increases significantly the coupling efficiency, compared to
other approaches such as direct butt coupling and an improved rectangular silicon nanotaper.