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Analysis of volatile organic compounds (VOCs) for medical and industrial applications typically requires complex and expensive mass spectrometric systems to achieve the desired sensitivity and specificity. Raman spectroscopy enables specific compound identification based on distinct spectral fingerprints but traditionally has low sensitivity. We have developed a novel Raman system that provides VOC detection in the low ppm range. VOCs from the gas phase are absorbed and enriched in a thin polymer film coated on the surface of an optical sensor element. The VOC enriched polymer film is probed with evanescent wave excitation and optimized Raman signal collection. The herein described Raman sensor is low-cost, robust, readily manufacturable, and capable of providing high sensitivity without the nanostructured sensors required for surface enhanced Raman spectroscopy. To suppress background noise and interfering spectral features while improving our ability to resolve VOC mixture spectra, we applied two-dimensional (2D) correlation analysis to time series spectra acquired during VOC absorption into the polymer film. We established proof of principle through analysis of known VOC biomarkers for selected bacterial pathogens. The system enabled VOC detection with significantly higher sensitivity than commercial Raman probes. We observed good agreement between spectra of VOCs in the thin film obtained after 2D correlation analysis, and of pure VOCs using a commercial probe. Mixture spectra were further de-convoluted based on the off-diagonal peaks observable in the 2D Raman spectrum in conjunction with segmented data analysis. We anticipate that this system can be applied to a variety of medical, industrial, and biodefense applications.

A monolithic CMOS compatible process has been developed to realize vertically integrated devices in silicon. The method involves the implantation of an oxygen into a patterned silicon substrate to form buried guiding structures. These buried devices are separated from a surface silicon layer by an intervening layer of silicon dioxide formed through the implantation process. Photolithography and etching is used to define devices on the surface silicon layer. The method has been utilized to realize the vertically coupled microdisk resonators and a variety of microresonator-based integrated optical elements. A new method for extraction of the unloaded Q of a cavity from its measured spectrum is also described.

A modified separation by implantation of oxygen process has been developed to sculpt vertically coupled microdisk resonators in silicon. The approach involves the implantation of oxygen ions into a silicon substrate, patterned with thermal oxide, to define waveguides on the bottom silicon layer, and photolithography and reactive ion etching to define the microdisk resonators on the top silicon layer. The top and the bottom silicon layers are separated by the oxide layer that was formed after the oxygen implantation. Fabricated microdisk resonators show resonances with a Q value of 10 300 and a free spectral range of 5.4nm.

Nonlinear losses limit supercontinuum efficiency in silicon. This fundamental limitation can be relaxed and higher energy efficiency and a more stable output can be obtained by stimulating modulation instability with an off-resonant weak seed.

In silicon devices, the spectral bandwidth of coherent anti-Stokes Raman scattering (CARS) is limited by the narrowband nature of the Raman process in this medium. In this Letter, we report the observation of broadband wavelength conversion in silicon through CARS enhanced by the self-phase-modulation-induced spectral broadening of the optical pump. The CARS conversion over a bandwidth substantially greater than the intrinsic Raman linewidth is demonstrated yielding conversion efficiencies as high as 1%. Numerical simulations are performed to explain the spectral features observed in the spectrum of the anti-Stokes signal.

Broadband coherent antistokes Raman scattering (CARS) is observed experimentally in silicon, facilitated by self‐phase modulation induced spectral broadening of the pump. Numerical modeling reveals the strong influence of free carrier dynamics on the CARS process.

We experimentally demonstrate unprecedented wavelength conversion efficiency of 58% from coherent anti-Stokes Raman scattering (CARS) in a silicon waveguide. CARS is modeled by incorporating Raman scattering and free carrier effects into the nonlinear Schrodinger equation.

Spectral broadening in silicon is studied numerically as well as experimentally. Temporal dynamics of the free carriers generated during the propagation of optical pulses, through the process of two-photon absorption (TPA), affect the amplitude and phase of the optical pulses, thereby determining the nature and extent of the generated spectral continuum. Experimental results are obtained by propagating pico-second optical pulses in a silicon waveguide for intensities that span two orders of magnitude (1-150 GW/cm2). These results validate the conclusions drawn from numerical simulations that the continuum generation has a self-limiting nature in silicon., Comment: 16 pages, 6 figures

An attempt at creating a multi-wavelength silicon light source is reported. Self phase modulation is used to broaden the spectrum of an off-chip seed pulse. The spectrum is filtered into discrete channels using vertically-coupled microresonators.

A novel approach to three-dimensionally (3-D) integrate nanophotonic and electronic devices in silicon is described. The method is based on the SIMOX (Separation by Implantation of OXygen) process, to realize three-dimensionally (3-D) integrated devices in a monolithic fashion. In this approach, photonic and electronic devices are realized on vertically stacked layers of silicon, separated from each other by a dielectric layer of silicon dioxide formed through the process of oxygen implantation. Opto-electronic integration is demonstrated by realizing photonic circuits in a subterranean silicon layer and Metal-Oxide-Semiconductor (MOS) transistors on a surface layer of silicon. Optical and electronic functionalities are thus separated into two different layers of silicon, paving the way towards dense three-dimensional opto-electronic integration. This has the significant advantage that photonic devices do not consume any of the expensive silicon real estate required for CMOS circuitry. The versatility of the technique of SIMOX 3-D sculpting in obtaining complex optical circuitry is also demonstrated by synthesizing a cascaded microdisk structure that may be utilized to tailor the passband characteristics of optical filters.

The integration of photonics and electronics on a single silicon substrate requires technologies that can add optical functionalities without significantly sacrificing valuable wafer area. To this end, we have developed an innovative fabrication process, called SIMOX 3-D Sculpting, that enables monolithic optoelectronic integration in a manner that does not compromise the economics of CMOS manufacturing. In this technique, photonic devices are realized in subsurface silicon layers that are separated from the surface silicon layer by an intervening SiO2 layer. The surface silicon layer may then be utilized for electronic circuitry. SIMOX 3-D sculpting involves (1) the implantation of oxygen ions into a patterned silicon substrate followed by (2) high temperature anneal to create buried waveguide-based photonic devices. This process has produced subterranean microresonators with unloaded quality factors of 8000 and extinction ratios >20dB. On the surface silicon layers, MOS transistor structures have been fabricated. The small cross-sectional area of the waveguides lends itself to the realization of nonlinear optical devices. We have previously demonstrated spectral broadening and continuum generation in silicon waveguides utilizing Kerr optical nonlinearity. This may be combined with microresonator filters for on-chip supercontiuum generation and spectral carving. The monolithic integration of CMOS circuits and optical modulators with such multi-wavelength sources represent an exciting avenue for silicon photonics.

Three-dimensional optoelectronic integration can be achieved in SOI wafers using the process of SIMOX 3D sculpting. Micro-resonators, with unloaded Q of 8000 and extinction ratio >20 dB, were fabricated in a buried silicon layer and MOS transistor structures were fabricated on the surface silicon layer using a patterned SIMOX process.

Stimulated Raman scattering in SOI waveguides has received significant attention recently with the demonstration of pulsed, continuous wave Raman lasers and high gain Raman amplification. However, the limited bandwidth of the Raman signal in silicon (/spl sim/105GHz) renders this scheme unsuitable for broadband WDM amplification unless multi-pumping scheme is employed. Large pulsed gain and lasing have been reported in GeSi waveguides. The SiGe on SOI platform represents a Raman medium with a flexible gain spectrum.

Three-dimensionally integrated microdisk resonators have been employed to realize Vernier filters in Silicon. Cascaded configuration of vertically-coupled microdisk resonators with dissimilar radii increases the free spectral range of filters from 5.5 nm to 23 nm.

Monolithic integration of photonics and electronics has been achieved in silicon by vertically integrating metal-oxide-semiconductor field-effect transistors and waveguide-coupled microdisk resonators in a double-layer silicon-on-insulator wafer, thus paving the way towards dense three-dimensional optoelectronic integration.

This paper presents recent breakthroughs and applications of Raman based silicon photonics such as silicon Raman amplifiers and lasers. These lasers would extend the wavelength range of III-V laser to mid-IR where important applications such as laser medicine, biochemical sensing, and free space optical communication await the emergence of a practical and low cost laser.

Although the Raman effect is nearly two orders of magnitude stronger than the electronic Kerr nonlinearity in silicon, under pulsed operation regime where the pulse width is shorter than the phonon response time, Raman effect is suppressed and Kerr nonlinearity dominates. Continuum generation, made possible by the non-resonant Kerr nonlinearity, offers a technologically and economically appealing path to WDM communication at the inter-chip or intra-chip levels. We have studied this phenomenon experimentally and theoretically. Experimentally, a 2 fold spectral broadening is obtained by launching ~4ps optical pulses with 2.2GW/cm2 peak power into a conventional silicon waveguide. Theoretical calculations, that include the effect of two-photon-absorption, free carrier absorption and refractive index change indicate that up to >30 times spectral broadening is achievable in an optimized device. The broadening is due to self phase modulation and saturates due to two photon absorption. Additionally, we find that free carrier dynamics also contributes to the spectral broadening and cause the overall spectrum to be asymmetric with respect to the pump wavelength.

A new process has been developed to create vertically-integrated photonic and optoelectronic circuits in silicon. The approach is the 3-D extension of the SIMOX process where buried SiO2 sections can be selectively created by using oxygen implantation, through a mask, followed by annealing. By controlling the implant energy, dose, mask area and thickness, arbitrary 3-D arrangements of Silicon/SiO2 can be created. The process has been used to create vertically coupled microdisk resonators and add-drop wavelength multiplexers on a silicon wafer.

This paper presents the design and operation of Si and GeSi Raman lasers and amplifiers. Different laser applications in various practical fields are also discussed.

Nonlinear optical devices, with silicon-on-insulator material system as platform for their fabrication are discussed. Third order nonlinearity in silicon offers active functionalities in silicon by taking advantage of the high index contrast and tight beam confinement. Among the third order effects; Raman, Kerr nonlinearity, two-photon absorption are particularly strong

We demonstrate all-optical switching based on cross phase modulation in silicon waveguides. Switching of a 1537 nm CW signal by a pulsed pump at 1560 nm and with extinction of 13 dB is demonstrated.

This paper reports the fabrication and characterization of add-drop filters based on vertically coupled microdisk resonators in silicon. SIMOX 3-D sculpting is the technique used to fabricate monolithically integrated filters based on microdisk resonator structures that show adjacent channel cross talk suppression as high as 15 dB for channels that are separated by 1.5 nm.

In this paper we report the demonstration of vertically coupled microdisk resonator structures on SOI substrates, using the technique of SIMOX 3-D sculpting.

In this paper, fabrication of three dimensionally integrated nano-optical structures in silicon-on-insulator (SOI) substrates using the process of separation by implantation of oxygen (SIMOX) is reported. Buried rib waveguides with lowest ever loss with the SIMOX process, reported with the fabrication of vertically integrated structures using conventional lithography and etching process, demonstrate the capability to sculpt 3-D integrated optical devices.

Vertically coupled microdisk resonator structures have been synthesized on Silicon utilizing a modified Separation by Implantation of Oxygen (SIMOX) technique. Resonances are observed with Q values of 6300 and free spectral range of 5.4 nm.

The polarization state of an optical signal is important for optical communication systems, but standard single mode fibers do not maintain the input polarization state.

We demonstrate that stimulated supercontinuum generation alleviates restrictions on spectral broadening in silicon waveguides. At telecommunications wavelengths, two-photon and free-carrier absorption typically deplete the pump before large broadening factors can be achieved. However, broadening via modulation instability (MI) can be enhanced by seeding, which also substantially improves the energy efficiency of spectral broadening in media with nonlinear loss. Coherent seeding also generates a stable output spectrum, in contrast to conventional approaches where broadening starts from noise. The combination of self-phase modulation and stimulated modulation instability generates broadening factors in excess of 40-fold at moderate intensity levels, with >15-times better energy efficiency.

Raman gain is a useful nonlinear phenomenon that has made optically pumped silicon lasers and amplifiers a reality. Unfortunately, the bandwidth of Raman gain in silicon is normally rather limited, owing to the narrow Raman linewidths typical of crystalline materials. Here, we report Raman amplification in silicon with a spectrum that is modified by the simultaneous occurrence of self-phase-modulation. This combined nonlinear action produces a broad Raman gain spectrum from a narrowband pump source.

Self-phase modulation is utilized to generate a continuum of wavelengths on a silicon chip. The propagation of near transform-limited, picosecond pulses (3ps) through a micron sized silicon waveguide results in the generation of a spectral continuum. This spectral continuum is then carved by microdisk resonators that are integrated three dimensionally on the same chip, resulting in multiple wavelength channels, with the farthest channel being around 3.1nm away from the center wavelength of the seed pulse. This technique can potentially enable wavelength division multiplexing at the chip level using a single off-chip laser.

Monolithic integration of photonics and electronics has been achieved in silicon by three-dimensionally integrating metal-oxide-semiconductor field-effect transistors and waveguide-coupled microdisk resonators. Implantation of oxygen ions into a silicon-on-insulator substrate with a patterned thermal oxide mask followed by a high temperature anneal was utilized to realize the buried photonic structures. This results in the formation of vertically stacked silicon layers separated from each other by an intervening oxide layer. Transistors are fabricated on the surface silicon by conventional processing techniques. Optical and electronic functionalities are thus separated into two different layers of silicon, paving the way toward dense three-dimensional optoelectronic integration.

Laterally-coupled silicon microresonators are fabricated beneath the surface of a silicon-on-insulator substrate using a modified separation by implantation of an oxygen technique. Implantation of oxygen ions into a substrate with patterned thermal oxide mask was utilized to realize buried waveguiding structures. Microdisk resonators in the buried silicon layer show loaded quality factors of 2000, with extinction ratios in excess of 20dB. The process also results in the formation of a silicon layer on the surface of the wafer that is suitable for the fabrication of electronic devices, thereby paving the way for three-dimensional monolithic integration of electronics and photonics in silicon.

Add-drop filters, based on vertically coupled microdisk resonators, have been realized in silicon, using a modified separation by implantation of oxygen process. Buried rib waveguides in the bottom-layer silicon, of a two-layer structure, are coupled to microdisk resonators in the top-layer silicon through a silicon dioxide layer formed by oxygen implantation. The radii of the microdisk structures were varied suitably to obtain resonators with slightly shifted resonance wavelengths. The average adjacent channel crosstalk suppression of these filters exhibits an upper limit of 12.11dB and a lower limit of 6.2dB over the wavelength band under consideration.

We describe the first observation of spontaneous Raman emission, stimulated amplification, and lasing in a SiGe waveguide. A pulsed optical gain of 16dB and a lasing threshold of 25 W peak pulse power (20 mW average) is observed for a Si1-xGex waveguide with x=7.5%. At the same time, a 40 GHz frequency downshift is observed in the Raman spectrum compared to that of a silicon waveguide. The spectral shift can be attributed to the combination of composition- and strain-induced shift in the optical phonon frequency. The prospect of Germanium-Silicon-on-Oxide as a flexible Raman medium is discussed.

First demonstration of cross phase modulation based interferometric switch is presented in silicon on insulator waveguides. By using Mach-Zehnder interferometric configuration we experimentally demonstrate switching of CW signal ~25 nm away from the pump laser. We present the effect of free carrier accumulation on switching. Additionally, we theoretically analyze the transient effects and degradations due to free carrier absorption, free carrier refraction and two photon absorption effects. Results suggest that at low peak power levels the system is governed by Kerr nonlinearities. As the input power levels increase the free carrier effects becomes dominant. Effect of free carrier generation on continuum generation and power transfer also theoretically analyzed and spectral broadening factor for high input power levels is estimated.