Width-modulated silicon waveguide is investigated as a means of quasi-phase-matching to enhance the bandwidth of wavelength conversion based on four-wave-mixing. A conversion bandwidth enhancement of ~40% is achievable in a 5mm sinusoidally modulated SOI waveguide.

Electric control of the pulse reshaping and compression is demonstrated using the two-photon absorption (TPA) and TPA-induced free-carrier absorption in an intracavity silicon waveguide. A forward bias is applied to the silicon waveguide to tune the free-carrier lifetime and density, hence enhancing the pulse compression effect. A pulse compression of about 30% is experimentally verified using a 3.3 V forward bias.

L'invention concerne des techniques et des dispositifs pour produire des impulsions laser courtes, et consistant a generer des impulsions laser ultracourtes en separant un traitement non lineaire des impulsions laser via une modulation de phase automatique (SPM) non lineaire dans un milieu optique non lineaire a partir d'un traitement lineaire ulterieur des impulsions laser pour obtenir des impulsions laser ultracourtes.

Four-wave mixing (FWM) in silicon waveguides is considered to be a promising effect to realize the wavelength conversion function for wavelength-division-multiplexing optical communication systems. Compared to the degenerate FWM with a single pump, the nondegenerate FWM with two pumps shows more flexibility in phase-matching condition and has more opportunities to acquire broader conversion bandwidth. The bandwidth enhancement is theoretically analyzed for the two-pump FWM and an enhancement of 25% is experimentally demonstrated. Also, an ultra-broadband wavelength conversion is presented based on two-pump FWM by fixing one pump near the signal and scanning the other pumps.

The electrical control of pulse width in a two-photon absorption-based silicon pulse compressor is demonstrated. Approximately 30% improvement in pulse compression rate is experimentally measured under a forward voltage of 3.3 V.

We analyzed the noise performance of time stretched analog to digital converter with both lumped and distributed amplification cases. We show that distributed amplification provides up to 16dB higher SNR corresponding to ~2.5 bit higher resolution.

In this study, we demonstrate method for quasi phase matched silicon-on-sapphire waveguides suitable for MWIR wavelength conversion to achieve higher conversion efficiency than that can be achieved in uniform waveguide geometries. In particular we show that periodic change in waveguide width by 0.5μm and hence periodic change in waveguide dispersion can to reset phase accumulation and provide ever-increasing gain profile. With the fabrication flexibility of large cross-section of MWIR waveguides, the possibility of using quasi-phase-matching can provide >30dB conversion efficiency enhancement and increase the conversion bandwidth by 2 times. Such improvement may facilitate the fabrication of parametric oscillators that can improve the conversion efficiency by 50dB.

With a transparency window up to 6 μm, sapphire can serve as a platform to support silicon photonic integrated circuit in MWIR. Planar waveguide devices based on silicon-on-sapphire (SOS) are emerging as a bridge between MWIR and SWIR through frequency band conversion process. While these devices are widely proposed to amplify MWIR signals and generate MWIR source, it can also be inversely utilized to achieve MWIR light detection. Here MWIR signals are down-converted to telecommunication wavelength (1.55 μm) through SOS waveguides and indirectly detected by SWIR detectors. Since detectors at telecommunication wavelengths exhibit superior performances in terms of speed, noise and sensitivity, the indirect detection scheme can be a promising candidate to improve the detection performance. In this report, we analyze performance of the indirect detection of MWIR signals by wavelength conversion in SOS waveguides. Particularly we modeled and compared the noise performance of the indirect detection with direct detection using state-of-the-art MWIR detectors. We show that, in addition to advantages of room temperature and high speed operation, the proposed indirect detection can improve the electrical signal-to-noise ratio up to 50dB, 23dB and 4dB compared to direct detection by PbSe, HgCdTe and InSb detectors respectively. The improvement is more pronounced in detection of weak MWIR signals.

We investigate synchronous first and second order pulsed Raman lasers that can achieve frequency spacing of up to 1000 cm(-1) for CARS microscopy applications. In particular, we focus on analytical and numerical analysis of pulsed stability derived for Raman lasers by using dispersion-managed telecom fibers and pumping at near 1530 nm telecom wavelengths. We show the evolution of the first and second order Stokes signals at the output for different peak pump power and the net anomalous dispersion combinations. We determine the stability condition for dispersion-managed synchronous Raman lasers up to second order. The results show that the stable second order Raman Stokes pulses with 0.02 W to 0.1 W peak power and 1 ps to 2.1 ps pulse width can be achieved in proposed dispersion-managed systems. (C) 2011 Optical Society of America

Planar waveguide devices based on silicon-on-sapphire are emerging as a bridge between mid-infrared (IR) and near-IR wavelength through frequency conversion process. We analyze the limits of indirect detection of mid-IR signals by wavelength conversion in such waveguides and investigate signal-to-noise ratio improvement that is attainable with respect to direct detection using state of the art commercial detectors. Our calculation shows that, in addition to room temperature and high speed operation, the proposed indirect detection can improve the electrical signal-to-noise ratio up to 40 dB compared to direct detection by PbSe, HgCdTe, and InSb detectors, especially in detection of weak mid-IR signals.

Wavelength tunable synchronous pulse sources are highly desirable for spectroscopy and optical diagnostics. The common method to generate short pulses in the fiber is the use of nonlinear induced spectral broadening which result in soliton shaping in anomalous dispersion regime. However, to generate ultra-short pulses, broadband gain mechanism is also required. In recent years, Raman fiber lasers have retrieved strong interest due to their capability of serving as pump sources in gain-flattened amplifiers for optical communication systems. The fixed-wavelength Raman lasers have been widely studied in the last years, but recently, much focus has been on the multi wavelength tunable Raman fiber lasers which generate output Stokes pulses in a broad wavelength range by so called cascaded stimulated Raman scattering. In this paper we investigate synchronous 1st and 2nd order pulsed Raman lasers that can achieve frequency spacing of up to 1000cm-1 that is highly desired for CARS microscopy. In particular, analytical and numerical analysis of pulsed stability derived for Raman lasers by using dispersion managed telecom fibers and pumped by 1530nm fiber lasers. We show the evolution of the 1st and 2nd order Stokes signals at the output for different pump power and SMF length (determines the net anomalous dispersion) combinations. We investigated the stability of dispersion managed synchronous Raman laser up to second order both analytically and numerically. The results show that the stable 2nd order Raman Stokes pulses with 0.04W to 0.1W peak power and 2ps to 3.5ps pulse width can be achieved in dispersion managed system.

Mid-infrared has great potential for silicon photonics. Engineering the dispersion by IR compatible cladding materials and waveguide dimensions enable broadband discrete wavelength conversion. We show that >1.2μm discrete wide-band conversion is achievable at 4μm pumping.

Nonlinear silicon photonics has been an immense research subject in the past several years with promising prospects of delivering chip scale signal modulation, shaping and characterization tools. In particular, broadband parametric process has been considered for applications ranging from wideband light amplifiers to signal characterization and signal shaping tools. Although underlying nonlinear effect, Kerr phenomena, in silicon has generated promising result of wavelength conversion, the success of these devices have been challenged by the presence of nonlinear losses such as two photon absorption and the two photon generated free carrier absorption. Experimental demonstrations were limited to conversion efficiencies below -10dB. Here, we present the prospect of ultra wide discrete band conversion schemes and the prospect of parametric process at mid-infrared wavelengths where nonlinear losses are not present. In particular, we explore the parametric wavelength conversion scheme at mid-wave infrared wavelength (2μm~6μm) by four-wavefixing process in silicon waveguides with new cladding materials, such as sapphire, that can provide transparency up to 6μm and facilitate phase matching condition for discrete wavelength bands as far as 60THz away from each other. Design criteria include the optimization of mode overlap integrals and dispersion engineering for an ultra-wide band signals. The particular results of wavelength conversion between 2μm bands and 5μm bands, and between 1.8μm bands and >4μm bands will be presented. Prospects of frequency band conversion in generation of new infrared signals and low noise, room temperature detection of mid-infrared signals will also be discussed.

We experimentally demonstrate the bandwidth enhancement of wavelength conversion in a silicon waveguide based on four-wave mixing (FWM) with two continuous-wave pumps. Our measurement results show 25% bandwidth improvement from 29.8 nm to 37.4 nm in a 17-mm-long silicon waveguide with a pump spacing of 14.9 nm as compared to a single-pump FWM. The experimental results are verified by theoretical calculations and >40% bandwidth enhancement is predicted by further wavelength separation of the two pumps.

An ultra-broadband wavelength conversion is presented and experimentally demonstrated based on nondegenerate four-wave mixing in silicon waveguides. Two idlers can be generated and their wavelengths can be freely tuned by using two pumps where the first pump is set close to the signal and the second pump is wavelength tunable. Using this scheme, a small phase-mismatch and hence an ultra-broad conversion bandwidth is realized in spite of the waveguide dispersion profile. We show that the experimental demonstrations are consistent with the theoretical estimations. Total conversion bandwidth is estimated to reach >500 nm and it can provide a feasible approach to realize one-to-two wavelength conversion among different telecommunication bands between 1300 nm and 1800 nm.

We experimentally demonstrate the C-band wavelength conversion using four-wave mixing in a 17-mm-long silicon-on-insulator waveguide pumped by a dispersed mode-locked femtosecond laser pulse. The idler can be observed with an incident average pump power lower than 4 dBm, and about 35 nm of conversion bandwidth from 1530 nm to 1565 nm is measured by using a 1550-nm pump wavelength. The pulse-pumped efficiency is demonstrated to be higher, by more than 22 dB, than the cw-pumped efficiency. The conversion efficiency variations with respect to the pump and signal powers are also investigated.

Silicon waveguides integrated with doped dielectric gain media may allow the design of planar light sources with electronic control. In this paper, the effects of design geometries and nonlinear losses on the gain in crystalline silicon waveguides with erbium-doped regions are investigated. We show that by using multitrench geometries, the power confinement can be increased and higher gain-to-nonlinear-loss ratio achieved. Net gain can be improved as much as 0.38 dB/cm in multitrench waveguides compared to single-trench waveguides.

The performance of wavelength conversion based on nondegenerate four-wave mixing (FWM) with two pumps is theoretically evaluated in a silicon nanowire waveguide. A theoretical model is developed to take into the limitations of nonlinear loss parameters on conversion bandwidth, efficiency, and uniformity. Analysis shows that the conversion bandwidth of two-pump nondegenerate FWM is >30% broader than the conversion bandwidth of the degenerate FWM without compromising the conversion efficiency under the same pump power level. Also the results indicate that the improvement originates from efficient phase matching over broader bandwidth range due to two-wavelength pumps.