En-Kuang Tien

Pulse compression and modelocking by using TPA in silicon waveguides.

We demonstrate a novel broadband pulse compression and modelocking scheme in silicon waveguides. Experimentally we obtain 25 fold pulse compression and 400 ps modelocked pulses. Results are limited by the RC time constant of the diode.

Discrete parametric band conversion in silicon for mid-infrared applications

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.

Ultra-broadband one-to-two wavelength conversion using low-phase-mismatching four-wave mixing in silicon waveguides

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.

Ultrafast pulse characterization using cross phase modulation in silicon

Based on the high nonlinearity of the chip-scale silicon waveguide with small dispersion, a compact frequency-resolved optical gating system has been demonstrated using cross phase modulation for ultrafast pulse characterization. The principal component generalized projections algorithm is used to retrieve the amplitude and phase from the spectrogram. Amplitude and phase of a 540 fs pulse have been measured. The measured amplitude result is confirmed by the autocorrelation measurement.

Performance Evaluation of Nondegenerate Wavelength Conversion in a Silicon Nanowire Waveguide

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.

Experimental demonstration of bandwidth enhancement based on two-pump wavelength conversion in a silicon waveguide

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.

Electrical signal-to-noise ratio improvement in indirect detection of mid-IR signals by wavelength conversion in silicon-on-sapphire waveguides

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.

Pulse Compression and Modelocking by Using TPA in Silicon Waveguides

We demonstrate a novel broadband pulse compression and modelocking scheme in silicon waveguides. Experimentally we obtain 25 fold pulse compression and 400 ps modelocked pulses. Results are limited by the RC time constant of the diode.

Influence of nonlinear loss competition on pulse compression and nonlinear optics in silicon

Aggregate nonlinear response of silicon is determined by the competition between the free carrier absorption (FCA) and two-photon absorption (TPA). We show that the front end of optical pulses is always exposed to TPA dominated nonlinear regime, whereas the trailing edge can be seen at FCA dominated regime at high intensities. These two losses can be used for pulse compression if the center of the pulse is in FCA dominated nonlinear regime. To reach this operation regime, energy of 50ps wide pulses has to be larger than 50nJ (40GW∕cm2). Competition phenomenon is observed experimentally in a mode locked laser setup to generate 60ps pulse of 60nJ.

Quasi-phase matching in SOI and SOS based parametric wavelength converters

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.