Band-edge Bilayer Plasmonic Nanostructure for Surface Enhanced Raman Spectroscopy

Spectroscopic analysis of large biomolecules is critical in a number of applications, including medical diagnostics and label-free biosensing. Recently, it has been shown that Raman spectroscopy of proteins can be used to diagnose some diseases, including a few types of cancer. These experiments have however been performed using traditional Raman spectroscopy and the development of the Surface enhanced Raman spectroscopy (SERS) assays suitable for large biomolecules could lead to a substantial decrease in the amount of specimen necessary for these experiments. We present a new method to achieve high local field enhancement in surface enhanced Raman spectroscopy through the simultaneous adjustment of the lattice plasmons and localized surface plasmon polaritons, in a periodic bilayer nanoantenna array resulting in a high enhancement factor over the sensing area, with relatively high uniformity. The proposed plasmonic nanostructure is comprised of two interacting nanoantenna layers, providing a sharp band-edge lattice plasmon mode and a wide-band localized surface plasmon for the separate enhancement of the pump and emitted Raman signals. We demonstrate the application of the proposed nanostructure for the spectral analysis of large biomolecules by binding a protein (streptavidin) selectively on the hot-spots between the two stacked layers, using a low concentration solution (100 nM) and we successfully acquire its SERS spectrum

Sub-microsecond thermal reconfiguration of silicon photonic devices

© 2009 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.DOI: 10.1109/LEOS.2009.5343159Using the experimental data we show the possibility of sub-microsecond reconfiguration of silicon photonics microresonators through pulse shaping of micro-heater excitation. Also, a novel heater structure based on small microdisk resonators with sub-hundred-nanosecond reconfiguration speed is proposed and investigated theoretically

Power handling of silicon microring modulators

Silicon photonic wavelength division multiplexing (WDM) transceivers promise to achieve multi-Tbps data rates for next-generation short-reach optical interconnects. In these systems, microring resonators are important because of their low power consumption and small footprint, two critical factors for large-scale WDM systems. However, their resonant nature and silicon’s strong optical nonlinearity give rise to nonlinear effects that can deteriorate the system’s performance with optical powers on the order of milliwatts, which can be reached on the transmitter side where a laser is directly coupled into resonant modulators. Here, a theoretical time-domain nonlinear model for the dynamics of optical power in silicon resonant modulators is derived, accounting for two-photon absorption, free-carrier absorption and thermal and dispersion effects. This model is used to study the effects of high input optical powers over modulation quality, and experimental data in good agreement with the model is presented. Two major consequences are identified: the importance of a correct initialization of the resonance wavelength with respect to the laser due to the system’s bistability; and the existence of an optimal input optical power beyond which the modulation quality degrades.Defense Advanced Research Projects Agency (DARPA) (Grant HR0011-11-C-0100

Low-power swept-source Raman spectroscopy

'Molecular fingerprinting' with Raman spectroscopy can address important problems-from ensuring our food safety, detecting dangerous substances, to supporting disease diagnosis and management. However, the broad adoption of Raman spectroscopy demands low-cost, portable instruments that are sensitive and use lasers that are safe for human eye and skin. This is currently not possible with existing Raman spectroscopy approaches. Portability has been achieved with dispersive Raman spectrometers, however, fundamental entropic limits to light collection both limits sensitivity and demands high-power lasers and cooled expensive detectors. Here, we demonstrate a swept-source Raman spectrometer that improves light collection efficiency by up to 1000× compared to portable dispersive spectrometers. We demonstrate high detection sensitivity with only 1.5 mW average excitation power and an uncooled amplified silicon photodiode. The low optical power requirement allowed us to utilize miniature chip-scale MEMS-tunable lasers with close to eye-safe optical powers for excitation. We characterize the dynamic range and spectral characteristics of this Raman spectrometer in detail, and use it for fingerprinting of different molecular species consumed everyday including analgesic tablets, nutrients in vegetables, and contaminated alcohol. By moving the complexity of Raman spectroscopy from bulky spectrometers to chip-scale light sources, and by replacing expensive cooled detectors with low-cost uncooled alternatives, this swept-source Raman spectroscopy technique could make molecular fingerprinting more accessible

High-speed polysilicon CMOS photodetector for telecom and datacom

Absorption by mid-bandgap states in polysilicon or heavily implanted silicon has been previously utilized to implement guided-wave infrared photodetectors in CMOS compatible photonic platforms. Here, we demonstrate a resonant guided-wave photodetector based on the polysilicon layer that is used for the transistor gate in a microelectronic SOI CMOS process without any change to the foundry process flow (“zero-change” CMOS). Through a combination of doping mask layers, a lateral pn junction diode in the polysilicon is demonstrated with a strong electric field to enable efficient photo-carrier extraction and high-speed operation. This photodetector has a responsivity of more than 0.14 A/W from 1300 to 1600 nm, a 10 GHz bandwidth, and 80 nA dark current at 15 V reverse bias.United States. Defense Advanced Research Projects Agency (Award HR0011-11-C-0100)United States. Defense Advanced Research Projects Agency (Contract HR0011- 11-9-0009

Compact and high-precision wavemeters using the Talbot effect and signal processing

Precise knowledge of a laser’s wavelength is crucial for applications from spectroscopy to telecommunications. Here, we present a wavemeter that operates on the Talbot effect. Tone parameter extraction algorithms are used to retrieve the frequency of the periodic signal obtained in the sampled Talbot interferogram. Theoretical performance analysis based on the Cramér–Rao lower bound as well as experimental results are presented and discussed. With this scheme, we experimentally demonstrate a compact and high-precision wavemeter with below 10 pm single-shot estimation uncertainty under the 3–σ criterion around 780 nm

Non-paraxial Talbot Effect for Building Compact Spectrometers

We explore the possibility of utilizing mid-field Talbot effect under non-paraxial diffraction for building compact spectrometers. Our experiment demonstrates nanometer resolution with a bandwidth over at least 100 nm for a Talbot spectrometer built using a standard 1-D transmission grating and a commercial CMOS imager

Photonic Readout of Superconducting Nanowire Single Photon Counting Detectors

Scalable, low power, high speed data transfer between cryogenic (0.1–4 K) and room temperature environments is essential for the realization of practical, large-scale systems based on superconducting technologies. A promising approach to overcome the limitations of conventional wire-based readout is the use of optical fiber communication. Optical fiber presents a 100–1,000x lower heat load than conventional electrical wiring, relaxing the requirements for thermal anchoring, and is also immune to electromagnetic interference, which allows routing of sensitive signals with improved robustness to noise and crosstalk. Most importantly, optical fibers allow for very high bandwidth densities (in the Tbps/mm2 range) by carrying multiple signals through the same physical fiber (Wavelength Division Multiplexing, WDM). Here, we demonstrate for the first time optical readout of a superconducting nanowire single-photon detector (SNSPD) directly coupled to a CMOS photonic modulator, without the need for an interfacing device. By operating the modulator in the forward bias regime at a temperature of 3.6 K, we achieve very high modulation efficiency (1,000–10,000 pm/V) and a low input impedance of 500 Ω with a low power dissipation of 40 μW. This allows us to obtain optical modulation with the low, millivolt-level signal generated by the SNSPD