Alexandros Kapsalis

FWM-based wavelength conversion of 40 Gbaud PSK signals in a silicon germanium waveguide

We demonstrate four wave mixing (FWM) based wavelength conversion of 40 Gbaud differential phase shift keyed (DPSK) and quadrature phase shift keyed (QPSK) signals in a 2.5 cm long silicon germanium waveguide. For a 290 mW pump power, bit error ratio (BER) measurements show approximately a 2-dB power penalty in both cases of DPSK (measured at a BER of 10(-9)) and QPSK (at a BER of 10(-3)) signals that we examined.

Optical properties of silicon germanium waveguides at telecommunication wavelengths

We present a systematic experimental study of the linear and nonlinear optical properties of silicon-germanium (SiGe) waveguides, conducted on samples of varying cross-sectional dimensions and Ge concentrations. The evolution of the various optical properties for waveguide widths in the range 0.3 to 2 µm and Ge concentrations varying between 10 and 30% is considered. Finally, we comment on the comparative performance of the waveguides, when they are considered for nonlinear applications at telecommunications wavelengths.

High peak-power picosecond pulse generation at 1.26 µm using a quantum-dot-based external-cavity mode-locked laser and tapered optical amplifier

In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm - 1.3 μm spectral range.

Investigation on the Multimode Dynamics of InGaAsP–InP Microring Lasers

A multimode model based on the rate equation approximation is presented in order to simulate the mode dynamics of 1.55-mum InGaAsP-InP microring lasers. A detailed characterization is performed including calculated optical spectra, time traces and relative intensity noise spectra. Different operation regimes are observed, bidirectional multimode with/without alternate oscillations, unidirectional single mode, bidirectional single mode and mode hopping. The boundaries of the above operation regimes are investigated with respect to the current level, bus waveguide reflectivity and ring radius. Varying the current level a transition from multimode to single mode and eventually mode hopping operation is observed. Increasing the bus waveguide reflectivity a transition from unidirectional to bidirectional operation is revealed, while the use of nonequal reflectivities between the two facets, promotes unidirectional operation. Moreover, the ring radius is proved to be a critical parameter for the extent of each operation regime since it directly influences the modal wavelength separation

Broadband telecom to mid-infrared supercontinuum generation in a dispersion-engineered silicon germanium waveguide.

We demonstrate broadband supercontinuum generation (SCG) in a dispersion-engineered silicon-germanium waveguide. The 3 cm long waveguide is pumped by femtosecond pulses at 2.4 μm, and the generated supercontinuum extends from 1.45 to 2.79 μm (at the -30  dB point). The broadening is mainly driven by the generation of a dispersive wave in the 1.5-1.8 μm region and soliton fission. The SCG was modeled numerically, and excellent agreement with the experimental results was obtained.

Widely Tunable All-Active Microring Lasers

A tunable laser based on an InGaAsP-InP microring resonator with multimode interference coupler is demonstrated. Tuning ranges from 18 to 30 nm are achieved and mappings of the tunable operation are experimentally produced and analyzed. The observed tunability is the result of the interaction between counterpropagating ring modes through back-reflection from the device facets

7Gb/s Direct Modulation of Vertically Coupled Microring Lasers

We report on the properties of directly modulated active-passive integrated microring lasers fabricated using full wafer bonding techniques. Bit rates up to 7 Gb/s are reported for the first time, together with a 50 km SMF transmission.

Towards nonlinear conversion from mid- to near-infrared wavelengths using Silicon Germanium waveguides

We demonstrate the design, fabrication and characterization of a highly nonlinear graded-index SiGe waveguide for the conversion of mid-infrared signals to the near-infrared. Using phase-matched four-wave mixing, we report the conversion of a signal at 2.65 µm to 1.77 µm using a pump at 2.12 µm.

All-optical phase regeneration with record PSA extinction ratio in a low-birefringence silicon germanium waveguide

We report a low-power continuous wave-pumped phase sensitive amplifier (PSA)-based phase regenerator implemented in a passive silicon-based waveguide. A polarization assisted-PSA, consisting of two orthogonally-polarized pumps and a phase-locked signal copolarized to one of them, was implemented in a low-birefringence silicon germanium (SiGe) waveguide. The strong TE/TM modal symmetry of the waveguide and its large nonlinear coefficient enabled the achievement of an extremely large phase sensitive extinction ratio of approximately 29 dB for a total input power of only 21.3 dBm. This SiGe-based PSA was used to demonstrate phase regeneration on a 20 Gb/s differential phase-shift keying signal, thereby reducing its error vector magnitude and phase error by three and six times respectively and enabling a bit-error ratio improvement of up to 2 dB.

Tunable Master-Oscillator Power-Amplifier Based on Chirped Quantum-Dot Structures

A broadly tunable master-oscillator power-amplifier (MOPA) picosecond optical pulse source is demonstrated, consisting of an external cavity passively mode-locked laser diode with a tapered semiconductor amplifier. By employing chirped quantum-dot structures on both the oscillators gain chip and amplifier, a wide tunability range between 1187 and 1283 nm is achieved. Under mode-locked operation, the highest output peak power of 4.39 W is achieved from the MOPA, corresponding to a peak power spectral density of 31.4 dBm/nm.