In this paper we numerically study the coherence properties of the supercontinuum generated in a lead-silicate
microstructured fiber taper, with an increasing core radius along the propagation distance which tailors the
dispersion property. Simulations are conducted by adding quantum noise into the input pulse at 1.55 μm, and
the complex degree of first-order coherence function and the overall spectral coherence degree are both
calculated. Although the spectral broadening is comparable, the coherence degree is shown to vary with
different pumping conditions. It decreases with higher peak power and longer duration due to the significant
competition between the soliton-fission process and the noise-seeded modulation instability. By controlling the
input pulse parameters, it is possible to generate perfectly coherent supercontinuum with a flat broadened
spectrum extending to ~5μm in this fiber taper.
A fiber ring laser which generates ~ 570 ps wide pulse train at 40 GHz has been demonstrated using a photonic crystal
fiber as a nonlinear optical loop mirror (NOLM). Theoretical simulation of the NOLM transmission has been carried out
using the split-step Fourier method.
Semiconductor optical amplifiers are important for wide range of applications in optical networks, optical tomography
and optical logic systems. For many of these applications particularly for optical networks and optical logic, high speed
performance of the SOA is important. All optical Boolean operations such as XOR, OR, AND and NOR has been
demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has
been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop
devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds. An optical pseudo-random
bit stream (PRBS) generator is important for all-optical encryption circuits. A model of a PRBS generator using SOAMZI
based devices has been developed. We show that a PRBS generator can work @ 80 Gb/s using regular SOAs and
@ ~ 250 Gb/s or at higher speeds using two-photon absorption based processes in SOAs.
When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an
associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using twophoton
absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input
data signals with high intensity, configured in the form of a Mach-Zehnder interferometer has been solved. The input
intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change.
The model shows that both XOR operation and pseudorandom binary sequence generation at 250 Gb/s with good signal to
noise ratio is feasible.
Semiconductor optical amplifiers are important for wide range of applications including optical networks, optical
tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic
high speed performance of the SOA is important. The speed of operation of SOA is limited by the gain and phase
recovery times in the SOA. We have demonstrated higher speed operation (i) for SOAs with a carrier reservoir layer, (ii)
for SOAs with a multi-quantum well modulation doped active region, and, (iii) for SOAs with a quantum dot (QD)
active region. The multi-quantum well SOA has been integrated with InGaAsP/InP based waveguides to build Mach-
Zehnder interferometers (MZI). XOR optical logic has been demonstrated at 80 Gb/s using these SOA-MZI structures.
XOR operation has been analyzed by solving the rate equation of the SOA, for SOAs with both regular and QD active
region. Mach-Zehnder interferometers fabricated using SOA with quantum dot active region (QD-SOA) can be used for
XOR operation at 250 Gb/s. Pseudo random bit stream (PRBS) generation using both regular and QD-SOA have been
studied and their performance modeled. The model shows QD-SOA based devices can be used to produce PRBS
generators that operate near 250 Gb/s.
Proc. SPIE. 7211, Physics and Simulation of Optoelectronic Devices XVII
KEYWORDS: Ultrafast phenomena, Semiconductor optical amplifiers, Modulation, Quantum dots, Signal processing, Signal analysis, Picosecond phenomena, Four wave mixing, Electronic support measures, Global system for mobile communications
A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot
semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to
simulate the carrier density modulation in the system, results show that the existence of QD excited state
contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the
QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with
small intensity modulation probe signal injected is simulated using this model, a set of coupled wave
equations describing the evolution of all frequency components in the active region of QD-SOA are derived
and solved numerically. Results show that better FWM conversion efficiency can be obtained compared
with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning
between pump and probe lights is 0.5 nm.
Proc. SPIE. 7211, Physics and Simulation of Optoelectronic Devices XVII
KEYWORDS: Signal to noise ratio, Logic, Semiconductor optical amplifiers, Mach-Zehnder interferometers, Logic devices, Picosecond phenomena, Hole burning spectroscopy, Electronic support measures, Global system for mobile communications, Beam controllers
A scheme to realize fiber-based all-optical Boolean logic functions including XOR, AND, OR and NOT
based on a semiconductor optical amplifier with a closely stacked Stranski-Krastanow InAs/GaAs quantum
dot layers is proposed. Rate equations is given to describe the population dynamics of the carrier in the
device, as well as the nonlinear dynamics including carrier heating and spectral hole-burning. The model is
used to simulated the cross gain and cross phase modulation in the device that are related to the logic
processes. Results show with QD excited state serving as a carrier reservoir, this type of QD device is
suitable for high speed operations with ultra fast carrier and phase relaxation. All optical logic operation
can be carried out at up to 250 Gb/s.
We simulated the evolution of self-similar parabolic pulses (similaritons) in a normally dispersive
fiber amplifier. The rate of development of a Gaussian pulse into the asymptotic parabolic regime
has been studied. The model has been applied to an optical transmission system with a fiber
amplifier. By calculating the Q-factor, we numerically determined the signal to noise performance of
the pulse train along fiber length. For the parameters we used, a 6m long fiber amplifier with 20 dB
gain is capable of amplifying 200Gb/s initial chirp-free Gaussian pulses of duration 0.4ps with no
distortion and additional noise. The trade-off between pulse width and amplifier length has been
A scheme for high speed clock and data recovery using an electroabsorption modulated laser and a
semiconductor optical amplifiers arranged in an optical-electrical-optical (OEO) loop has been
demonstrated. By injecting the 80Gb/s optical data into the OEO ring, the 10GHz clock tone is traced
and amplified in the loop. A 10GHz electrical clock and, a 10 GHz optical clock are recovered
We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, pump
wavelength, signal input power, and fiber length. The absorption coefficient of Yb varies ( by a factor of ~ 5) with the
pump wavelength in the range of 910 to 990 nm. However, semiconductor lasers may be available only at certain
wavelengths. Thus it is important to calculate optical gain and amplified output power as a function of pump wavelength.
The calculation shows that significant optical gain and amplified output power can be obtained even if the pump laser
wavelength is not at the peak absorption wavelength. The gain decreases with increasing input signal. We show that a
high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is
not unexpected since the input pump causes population inversion in Yb. More than 100 W of amplified power can be
obtained using 24m long fiber with 300 W of total pump power by using side-pumping method. Side pumping increases
the efficiency over end pumping for high output power.