Shiming Gao

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.

Dispersion engineering of a silicon-nanocrystal-based slot waveguide for broadband wavelength conversion

A proposal for broadband wavelength conversion using four-wave mixing is presented based on a slot waveguide with silicon nanocrystals (Si-ncs) as the optical nonlinear material. The dispersion of the waveguide is engineered to realize a flat dispersion as well as a small effective mode area for better nonlinear interaction by optimizing the waveguide dimensions. The conversion performance is synthetically analyzed and numerical results show that a bandwidth of over 400 nm and an efficiency of -2.38 dB can be achieved using a pump power of 150 mW in a 4 mm long Si-nc slot waveguide with slot width of 50 nm, slab width of 310 nm, and height of 305 nm.

Polarization-Independent Wavelength Conversion Using an Angled-Polarization Pump in a Silicon Nanowire Waveguide

A proposal for polarization-independent wavelength conversion is presented based on four-wave mixing in a silicon nanowire waveguide using an angled-polarization pump. The principle of polarization independence is introduced and the theoretical model is established. The optimized incident pump polarization angle is obtained for different waveguide geometries, and a polarization-independent bandwidth of 64 nm is achieved with the efficiency fluctuation of less than 1 dB in a 285 nm × 650 nm silicon waveguide. The polarization-independent bandwidth is limited by the larger one of the TE- and TM-mode phase mismatches, and can be enhanced further by carefully tailoring the dispersion characteristics of the silicon nanowire waveguide.

OPTIMAL DESIGN OF A SILICON-ON-INSULATOR NANOWIRE WAVEGUIDE FOR BROADBAND WAVELENGTH CONVERSION

The broadband wavelength conversion based on four-wave mixing in a silicon nanowire waveguide is theoretically investigated by taking into account the influence of the waveguide loss and free-carrier absorption on the phase-matched condition. The lossy wavelength conversion is compared with the lossless one in terms of conversion efficiency and bandwidth. The size of the silicon-on- insulator nanowire waveguide is optimized to be 400 nm × 269 nm for broadband wavelength conversion by realizing a flattened dispersion. The pump wavelength is also optimized to 1538.7 nm in order to further enhance the conversion bandwidth. A 3-dB conversion bandwidth of over 280 nm is achieved in the optimized waveguide with the optimized pump wavelength.

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.

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.

All-optical multiple-channel logic XOR gate for NRZ-DPSK signals based on nondegenerate four-wave mixing in a silicon waveguide

We report an all-optical multiple-channel exclusive OR (XOR) gate for 10 Gbits/s non-return-to-zero differential phase-shift keying (NRZ-DPSK) signals using nondegenerate four-wave mixing in a silicon waveguide. The function of the logic XOR gate is experimentally demonstrated using 40 bit DPSK sequences. Also, the eye diagram of the XOR signal is clearly observed as the incident signals are both modulated by DPSK sequences originating from 2(31)-1 pseudorandom binary sequences.

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.

All-optical wavelength conversion and multicasting for polarization-multiplexed signal using angled pumps in a silicon waveguide

We report all-optical wavelength conversion and multicasting for a 20 Gb/s (2×10 Gb/s) polarization-multiplexed (Pol-MUX) nonreturn-to-zero amplitude-shift keying signal using four-wave mixing (FWM) in a silicon waveguide. The temporal waveforms and eye diagrams demodulated from both polarization channels of the converted idler are clearly observed. Moreover, the wavelength multicasting of the Pol-MUX signal is also demonstrated by using two incident pumps.