Distributed feedback (DFB) lasers that are widely used in high-speed communication nowadays usually use end-facet coating in order to seek a balance between fabrication difficulty and device performance. This paper investigates DFB lasers with a partial grating structure that is immune to the phase uncertainties at the end-facet with high-reflection (HR) film and the improvement of its output chirp characteristics. It is found that, after parameter optimization, the carrier concentration and photon density distribution along the partial grating DFB(PG-DFB) laser cavity can be more uniform, which helps to obtain a better production yield. In addition, a compromised choice of the length of grating region and non-grating region can ensure stable single-mode output, as well as sub-10 mA threshold and high slope efficiency (SE). We also find that the PG-DFB laser can reduce the transient chirp by about 5 GHz compared to conventional DFB laser with uniform grating.
All-optical wavelength conversion of differential phase-shift keyed (DPSK) signals based on SOA in a Mach-Zehnder interferometer (SOA-MZI) configuration is simulated and analyzed using the transfer function of MZI and a wideband dynamic model of SOA. The operation principle is analyzed and operation point selection, influence of SOA physical parameters, different signal format and operation speed are discussed in detail.
The results of 10Gb/s operation show that SOA-MZI is compatible with both non-return-to-zero (NRZ) and return-to-zero (RZ) formatted signals. However, the conversion performance is sensitive to the operation point of the involved SOAs. To maximize the Q value of the demodulated conversion signal, the power and wavelength of the original DPSK signal and the probe light should be optimized to obtain approximately π phase difference between the upper and lower arms of MZI in the middle of each bit. Besides, SOA with short carrier lifetime and large linewidth enhancement factor is preferred for wavelength conversion applications. 40Gb/s operation is also simulated with SOA carrier lifetime of 100ps, and the results strongly suggests 40Gb/s operation with RZ formatted signals and relatively large input powers of the clock signal.
Based on a Mach-Zehnder interferometer and optical temporal time delay (OTDL), we propose and demonstrate
experimentally an all-optical 40-Gb/s RZ-DPSK to ASK-Manchester format conversion. This obtained ASK-Manchester
signals have the phase changes due to the demodulation of RZ-DPSK, which is called as phase-incorporated
ASK-Manchester signal. Compared with pure Manchester signal, the simulated results show that the phase-incorporated
ASK-Manchester signal has a compact optical spectrum and lower power at the low radio frequency (RF) frequencies, which
presents high tolerance on chromatic dispersion and little the cross-talk between payload and label. Moreover, the efficiency
and the BER performance of conversion and the dynamic range of fiber input power, transmission length, and chromatic
dispersion tolerance of the converted ASK-Manchester are detailed discussed. Less than 1-dB power penalty over 50-km
SMF transmission is observed.
This paper proposes and numerically investigated a novel high-speed wavelength-division-multiplexed passive optical
network (WDM-PON) architecture with colorless user terminals based on the use of a different modulation scheme for
downstream and upstream transmission. In the central office (CO), based on the carrier suppressing functionality of
Mach-Zehnder modulator (MZM) and differential-phase-shift-keying to amplitude-shift-keying conversion using
Mach-Zehnder delay interferometer, 40-Gb/s optical frequency shift keying (FSK) is generated and employed for
transmitting the downstream data. In the remote node (RN) or optical network unit (ONU), the upstream data is
re-modulated at 2.5-Gb/s by an intensity modulator and sent back to CO with the same fiber. Since only one light source
is needed for each WDM channel, and the MZM to generate carrier suppressed signal can be shared by all the channels, a
centralized 40-Gb/s WDM-PON access system with low-cost configuration is realized. Error free transmission over
20-km SMF can be observed for both downstream and upstream signals in our simulation.
We propose and demonstrate a novel orthogonal optical labeling scheme based on 40-Gbit/s optical frequency-shift keying (FSK) payload and 2.5-Gbit/s intensity-modulated (IM) labeling. Using the technology of carrier-suppressed modulation and conversion of differential phase-shift keying to IM, only one light source is needed to generate the optical FSK signal. The system performance, including range of IM modulation depth, bit error ratio, and dispersion limitation, is carefully investigated by numerical simulation. With IM modulation depth of 0.4, the 40 Gbit/s FSK payload and 2.5-Gb/s IM label are transmitted over a 50-km standard single mode fiber (SMF) with 0.87 and 0.92 dB penalty and show immunity to input power range upto 11 and 15 dB, respectively. Optimal methods to improve the system performance are also proposed and discussed. After optimization, the IM modulation depth can be reduced to 0.2.
A thorough simulation and evaluation of phase noise for optical amplification using semiconductor optical
amplifier (SOA) is very important for predicting its performance in differential phase shift keyed (DPSK) applications.
In this paper, standard deviation and probability distribution of differential phase noise are obtained from the statistics of
simulated differential phase noise. By using a full-wave model of SOA, the noise performance in the entire operation
range can be investigated. It is shown that nonlinear phase noise substantially contributes to the total phase noise in case
of a noisy signal amplified by a saturated SOA and the nonlinear contribution is larger with shorter SOA carrier lifetime.
Power penalty due to differential phase noise is evaluated using a semi-analytical probability density function (PDF) of
receiver noise. Obvious increase of power penalty at high signal input powers can be found for low input OSNR, which
is due to both the large nonlinear differential phase noise and the dependence of BER vs. receiving power curvature on differential phase noise standard deviation.
Gain-transparent semiconductor optical amplifier (GT-SOA) can be used as optical phase-modulators in
Mach-zehnder interferometer configuration for 2R or 3R regeneration, wavelength conversion of differential phase
modulated signals and all-optical format conversion from on-off keying (OOK) to binary phase shift keying (BPSK).
Numerical simulation of the phase modulation effect of GT-SOA is performed using a wideband dynamic model and the
performance is evaluated using the differential-phase-Q factor. Performance improvement by holding light injection is
analyzed and non-return-to-zero (NRZ) and return-to-zero (RZ) modulation formats of the OOK signal are considered.
The input power dynamic range and switching speed of an optical switch matrix based on cascaded semiconductor optical amplifier (SOA) gates with holding-light injection were studied numerically using the carrier-density rate equation of the SOA and a dynamic bit-error-rate calculation method. It is shown that holding-light injection can effectively extend the input power dynamic range to high signal input powers, on account of the suppression of the patterning effect in the presence of holding light. Moreover, cascaded SOA gates tend to provide a more linear output-input relation with holding-light injection. A useful by-product of holding-light injection is the enhanced switching speed of the SOA. The switch-on time with holding light is always shorter than that without, owing to a shorter carrier lifetime in the presence of holding light.
This paper aims at numerically simulating gain recovery enhancement effect in SOAs when a CW pump light is applied. An effective carrier lifetime model was given and used to investigate the pump power and wavelength dependence of SOA effective carrier lifetime. Effective carrier lifetime reduction behaviors and gain saturation curves at the signal wavelength were simulated. Gain dynamics introduced by short pulse amplification in a CW pumped SOA were also simulated to visualize the recovery enhancement effect.
We investigated the window properties of SOALOM (Semiconductor optical amplifier in a loop mirror) used as a 3R regenerator using simulation method. A multi-section model of SOA (semiconductor optical amplifier) was used in our simulation. The switching pulse was assumed to be a noisy Gaussian pulse with finite ER (Extinction Ratio). The influence of some system parameters such as the pulse width and peak power of the switching pulse, the applied current to SOA, and SOA displacement in the loop on the window properties was discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.