Effective Lifetime Of Free Carriers Research Articles

Measurement of the Nonlinear Loss and Effective Free Carrier Lifetime in Silicon Microring Resonators

Measurement of the Nonlinear Loss and Effective Free Carrier Lifetime in Silicon Microring Resonators

Numerical investigation into the output performance of a silicon Raman laser based on a silicon-on-insulator waveguide pumped by 2 µm lasers

We numerically analyze the characteristics of a mid-infrared continuous-wave (CW) Raman laser in silicon-on-insulator (SOI) photonics circuits including standing-cavity and ring resonator configurations, which are pumped by lasers at 2 µm. The dependence of cascaded Raman laser performance on the cavity length, effective free carrier lifetime, and the power transmission is investigated for the optimization of CW Raman silicon standing-cavity lasers. In addition, the mid-infrared Raman laser in the ring resonator is also presented under different parameters; in particular, the coupling strengths between the bus waveguide and the ring resonator for both the pump and Raman lasers are crucial to the laser performance. The numerical simulation results also reveal that the position of the coupler for extracting the Raman light from the ring resonator plays an important role in optimizing the structures of such Raman lasers.

Mid-infrared soliton and Raman frequency comb generation in silicon microrings.

We numerically study the mechanisms of frequency comb generation in the mid-infrared spectral region from cw-pumped silicon microring resonators. Coherent soliton comb generation may be obtained even for a pump with zero linear cavity detuning, through suitable control of the effective lifetime of free carriers from multiphoton absorption, which introduces a nonlinear cavity detuning via free-carrier dispersion. Conditions for optimal octave spanning Raman comb generation are also described.

Schottky MSM junctions for carrier depletion in silicon photonic crystal microcavities

Collection of free carriers is a key issue in silicon photonics devices. We show that a lateral metal-semiconductor-metal Schottky junction is an efficient and simple way of dealing with that issue in a photonic crystal microcavity. Using a simple electrode design, and taking into account the optical mode profile, the resulting carrier distribution in the structure is calculated. We show that the corresponding effective free carrier lifetime can be reduced by 50 times when the bias is tuned. This allows one to maintain a high cavity quality factor under strong optical injection. In the fabricated structures, carrier depletion is correlated with transmission spectra and directly visualized by Electron Beam Induced Current pictures. These measurements demonstrate the validity of this carrier extraction principle. The design can still be optimized in order to obtain full carrier depletion at a smaller energy cost.

TUNABLE ASYMMETRIC FANO LINESHAPES IN SILICON-BASED MICRORING RESONATORS WITH FEEDBACK

We theoretically examine the Fano lineshapes of silicon-based compound microring resonators consisting of a single resonator channel dropping filter linked to a loop as a feedback structure. All possible optical effects for the continuous-wave operating regime, such as linear absorption or scattering, two-photon absorption, free-carrier absorption and dispersion, thermo-optics, are simultaneously considered. We show that sharp Fano resonances can be tuned by variation in the coupling coefficients, length of feedback loop, effective free carrier lifetime and the temperature inside the device. Tunable Fano lineshapes open up opportunities for applications in sensing, computing, and communications.

Measurement of surface recombination velocity and bulk lifetime in Si wafers by the kinetics of excess thermal emission

A contactless nondestructive technique for measuring recombination parameters (surface recombination velocity and bulk and effective lifetime of free carriers) in Si wafers is proposed. The technique is based on the analysis of the relaxation kinetics of excess thermal emission of a wafer beyond the Si intrinsic absorption edge (λ > 3 μm) after excitation by a short laser pulse with a photon energy higher than the Si band gap. Experimental results for wafers 300 μm and 2 mm thick, excited by laser radiation with wavelengths of 0.96 and 1.06 μm at above-room temperatures are presented. The surface and bulk components of the effective lifetime are separated by extrapolating the final portion of the kinetics of excess thermal emission relaxation to the intersection with the y coordinate axis.

Effect of free carriers on pump-to-signal noise transfer in silicon Raman amplifiers

We study noise transfer from pump to signal in silicon Raman amplifiers, with particular emphasis on the regimes of strong cumulative free-carrier absorption and heavy pump depletion. We calculate the relative intensity noise (RIN) transfers in copumped and counterpumped amplifiers and provide intuitive explanations for RIN peculiarities. We show that noise transfer at low frequencies may be suppressed by carefully choosing the pump intensity, effective free-carrier lifetime, or amplifier length, but only at the expense of a rise in noise at high frequencies.

Silicon Raman Amplifiers With Ring-Resonator-Enhanced Pump Power

In this paper, design rules for optimal silicon Raman amplifiers operating at standard telecommunications wavelengths are formulated. For given material and waveguide parameters, and a specified upper pump-power limit, explicit expressions are derived for the optimal length and maximum possible gain of single-pass-pumped amplifiers. For ring-resonator (RR) amplifiers, the optimization problem is reduced to finding a zero of a fifth-order polynomial. Due to resonant pump-power enhancement, RR amplifiers with positive gain can be realized for any pump power, however small it is. Finally, for small pump powers, the maximum possible gain is most effectively increased by reducing the linear waveguide losses as opposed to the effective area or the effective free-carrier lifetime.

Parametric Raman wavelength conversion in scaled silicon waveguides

The benefits of using submicrometer modal-dimension silicon waveguides in realizing high-efficiency parametric Raman wavelength conversion are demonstrated theoretically and experimentally. The combined effects of Raman nonlinearities and free-carrier losses induced by two-photon absorption (TPA) are analyzed using the coupled-mode theory. The analysis indicates that scaling down the lateral dimensions increases the conversion efficiency of the Raman process and reduces the effective lifetime of free carriers and hence ameliorates the free-carrier losses. The feasibility of data conversion is demonstrated by coherent transfer of the analog radio-frequency (RF) signal from Stokes to anti-Stokes channels. The conversion efficiency, and hence signal-to-noise ratio (SNR), and bandwidth of the conversion process are found to be limited by the phase mismatch between the pump, Stokes, and anti-Stokes fields. The dispersion properties of submicrometer waveguides are also studied from the point of view of achieving phase matching and enhancing the conversion efficiency.

Injection dependent long carrier lifetimes in high quality CVD diamond

Abstract In this paper we report an experimental study of photocurrent mobility×lifetime products and free carrier lifetimes in CVD grown polycrystalline diamond of various qualities. The investigated samples are low impurity samples, nitrogen content ∼10 15 cm −3 , with an average grain size ranging from 25 μm up to 110 μm. This large difference in average grain size makes it possible to distinguish effects due to lifetime limiting trapping and recombination defect centers inside the grains from effects caused by defect centers at grain boundaries. At low carrier densities, 13 cm −3 , the effective free carrier lifetime is in the sub-nanosecond to nanosecond range in all samples due to intra-grain trapping and recombination centers. At high carrier densities, >10 13 cm −3 , the intra-grain centers becomes saturated and the effective lifetime becomes predominately given by carrier diffusion to and recombination at the defects related to the grain boundaries. Hence, the effective lifetime at high carrier densities is strongly related to the average grain size and increases up to several tens of nanoseconds, in samples with a large average grain size, whereas it remains in the nanosecond range for samples with small average grain size. In addition, we observe a lower mobility×lifetime product and decay constant with increasing nitrogen content, clearly showing the negative influence of nitrogen and nitrogen-related defects on these important material parameters.