Bulk Semiconductor Optical Amplifier Research Articles

Phase modeling based on the α-factor in bulk semiconductor optical amplifiers

Different approaches based on the α-factor to model the phase of the optical fields in bulk semiconductor optical amplifiers are analyzed. Our time-domain numerical model is presented and it is calibrated by means of experimental characterizations of the device gain, of the amplified spontaneous emission spectra, and of the effective α-factor. We then compare the phase modulation at the SOA output for three cases. In the first one, the α-factor is always taken as constant. In the second case, the α-factor is set according to the SOA working point and then kept fixed. In the last case, we take into account the dependence of the α-factor on the carrier density and on the wavelength for every simulated time step. We shall identify when the first two approximations listed above deliver reliable results. In particular cases, the use of a constant value for the α-factor can lead to phase errors up to 50%.

Nonlinear polarization rotation in semiconductor optical amplifiers: theory and application to all-optical flip-flop memories

We present a model for polarization-dependent gain saturation in strained bulk semiconductor optical amplifiers. We assume that the polarized optical field can be decomposed into transverse electric and transverse magnetic components that have indirect interaction with each other via the gain saturation. The gain anisotropy due to tensile strain in the amplifier is accounted for by a population imbalance factor. The model is applied to a nonlinear polarization switch, for which results are obtained, that are in excellent agreement with experimental data. Finally, we describe an all-optical flip-flop memory that is based on two coupled nonlinear polarization switches.

Polarization-insensitive SOA with a strained bulk active layer for network device application

Current and wavelength characteristics for 1.55-/spl mu/m semiconductor optical amplifiers (SOAs) containing bulk active layers with various tensile strains were investigated. The strain dependence of the gain-difference between the TE-mode and TM-mode (/spl Delta/G/sub TE-TM/) was almost linear having a waveguide-width over 0.8-1.5 /spl mu/m. A -0.12% tensile-strained bulk SOA had very low /spl Delta/G/sub TE-TM/ of less than 0.8 dB for driving current ranging from 0 to 120 mA. The low-polarization-sensitive condition of SOAs with strained-bulk active layers was shown to yield very wide range in driving current and wavelength for network device applications.

Intraband gain dynamics in bulk semiconductor optical amplifiers: measurements and simulations

We investigate experimentally and numerically the gain recovery time and gain compression resulting from intraband effects induced by sub-picosecond optical pulses in bulk semiconductor optical amplifiers. With the help of data produced by pump-probe measurements, the dependence of the intraband gain dynamics on pulse energy, device bias current, and length is discussed. The simulation results show a good agreement with the experimental data.

Influence of buried structure on polarization sensitivity in strained bulk semiconductor optical amplifiers

In order to achieve an accurate design of polarization-insensitive semiconductor optical amplifiers based on tensile strained bulk InGaAsP, the reduction of strain in the active layer of the buried heterostructure and its influence on polarization sensitivity are analyzed numerically for the first time. The gain calculation, including the strain distribution in the active layer, is examined based on the k /spl middot/ p method for the different active layers. It is found that the strain introduced during the epitaxial growth is strongly reduced after regrowth of the burying layer. In an active layer having the aspect ratio of 1 : 4, the strain reduction causes more than a 0.5-dB deviation in the polarization sensitivity of the gain. From a comparison with the experimental results, it is shown that including the effect of the burying layer in the calculation gives an accurate determination of the amount of strain for the polarization independence.

All-optical demultiplexing/shifting of 40-Gb/s OTDM optical signal using dual-pump wave mixing in bulk semiconductor optical amplifier

In this letter, we demonstrate all optical demultiplexing of a 40-Gb/s optical time division multiplexed signal with simultaneous wavelength shift of 19 nm (2.3 THz) using dual-pump wave mixing in a bulk semiconductor optical amplifier. Bit-error-rate measurements of the four demultiplexed 10-Gb/s channels together with eye diagrams are reported and optimization procedures for the operation of the demultiplexer/shifter are discussed,.

Mechanisms of wave mixing and polarisation sensitivity of the wavelength conversion in semiconductor optical amplifiers using two parallel polarised pumps

We report on an experimental and theoretical study of wavelength conversion based on four wave mixing (FWM) in a bulk semiconductor optical amplifier (SOA), using two parallel polarised pumps. The mechanisms responsible for the generation of the frequency converted products of the input signal are discussed. It is shown that the polarisation sensitivity of this scheme depends strongly on the position of the signal wavelength relative to the pump wavelengths.

Frequency-domain model of multiwave mixing in bulk semiconductor optical amplifiers

We present a new steady-state frequency-domain model of highly nondegenerate four-wave mixing in bulk semiconductor optical amplifiers (SOA's). The model can handle a large number of interacting optical fields and situations in which the nonlinear interactions are complex. It accounts for the longitudinal dependence of the population inversion in the SOA and the spectral dependence of the gain. Carrier population pulsations, spectral-hole burning, and carrier heating, which dominate the nonlinear response over bandwidths into the terahertz range, are included. The model also includes output amplified spontaneous emission noise and allows important system parameters such as signal-to-noise ratio and noise figure to be estimated. A number of applications of the model are presented in which good agreement between theoretical and experimental results is demonstrated.

Bidirectional four-wave mixing in semiconductor optical amplifiers: theory and experiment

Bidirectional four wave mixing (FWM) is investigated in a bulk semiconductor optical amplifier (SOA) for dispersion compensation and for the clear/drop functionality in optical time division multiplexed (OTDM) systems. Good performance for bidirectional midspan spectral inversion (MSSI) is theoretically predicted for bit rates of 10, 20, and 40 Gb/s and is shown to be in agreement with measurements performed at 10 and 20 Gb/s. Measurements of the clear/drop functionality using the bidirectional technique show excellent performance for a 4/spl times/10 Gb/s signal and is again in good agreement with simulations. The clear/drop functionality is also simulated for 4/spl times/20 Gb/s and 4/spl times/40 Gb/s signals.

Performance of a reconfigurable wavelength converter based on dual-pump-wave mixing in a semiconductor optical amplifier

We report on a wavelength converter based on dual pump wave mixing in an 1-mm-long bulk semiconductor optical amplifier. Very high conversion efficiency (more than 0 dB) and signal-to-background-noise ratio (SBR) (16 dB), for large down- or up-wavelength shifts (30 mn) has been achieved using parallel polarized pumps with low optical power (-13 dBm). Orthogonal polarized pumps result in worse performance, having the advantage of polarization insensitivity for small wavelength spacing between them. The converter operates in a fixed input-tunable output or a tunable input-fixed output mode of operation. In each mode, the measured SBR is almost independent of the wavelength shift for either up- or down-conversion.

Polarization-insensitive wavelength conversion up to 10 Gb/s based on four-wave mixing in a semiconductor optical amplifier

Polarization-insensitive wavelength conversion at 2.5 and 10 Gb/s using four-wave mixing in a bulk semiconductor optical amplifier is reported. At 10 Gb/s, a conversion range from 6.4-nm wavelength downshift to 4.8-nm upshift has been demonstrated. The conversion efficiency and signal-to-noise ratio versus conversion range are also characterized.

Gain recovery of bulk semiconductor optical amplifiers

The gain recovery time of 1.55-μm bulk semiconductor optical amplifiers (SOA's) with lengths from 500 to 1500 μm has been measured with a continuous-wave (CW) probe in the time domain. It is shown to decrease with increasing length down to 60 ps for the longest SOA. This behavior is theoretically explained. A lower limit for the recovery time is observed and explained.

Improved performance of a wavelength converter based on dual pump four-wave mixing in a bulk semiconductor optical amplifier

Very high conversion efficiency (6.5 dB for 23.4 nm down-wavelength shift and 4.5 dB for 16 nm up-wavelength shift) is reported, using four-wave mixing in a bulk semiconductor optical amplifier. Based on a dual pump configuration where wavelength conversion is achieved by shifting one of the pumps, superior performance has been achieved in terms of both efficiency and the converted signal-to-background amplified spontaneous emission noise ratio, especially for very large wavelength shifts. Simple theoretical considerations are also discussed for the explanation of the improved performance of the converter.

Study of polarization-insensitive wave mixing in bulk semiconductor optical amplifiers

A detailed experimental investigation of polarization-insensitive dual-pump wave mixing in bulk, polarization-insensitive semiconductor optical amplifier (SOA) is reported. Measurements of the phase conjugated, polarization-insensitive four-wave mixing (FWM) efficiency are reported versus: (1) pump-signal wavelength spacing while keeping the wavelength spacing between the two orthogonally polarized pumps constant and (2) wavelength spacing between the pumps while keeping the signal wavelength constant. The achieved wavelength conversion bandwidth of the polarization-insensitive scheme is approximately 60 nm with efficiency between 8 and -20 dB. The obtained results are in good agreement with theoretical predictions.

Effect of birefringence in a bulk semiconductor optical amplifier on four-wave mixing

We present experimental results on birefringence effects in an InGaAsP bulk semiconductor optical amplifier (SOA). Although the gain of the device is polarization insensitive, we observed a strong variation of the four-wave mixing (FWM) efficiency if the parallel input polarization of pump and signal wave was changed with respect to the device structure. This variation, which is attributed to birefringence in the SOA, can be as high as 10 dB for frequency detunings of about 6 THz. Thus, it might strongly affect the various applications of FWM for optical signal processing and parameter extraction. In addition, we performed polarization resolved measurements of the amplified spontaneous emission demonstrating different group velocity indices for TE and TM polarized light.

Low-noise and very high-efficiency four-wave mixing in 1.5-mm-long semiconductor optical amplifiers

Very high four-wave mixing (FWM) efficiency and signal-to-background ratio (SBR) are obtained in a 1.5-mm-long bulk semiconductor optical amplifier. The FWM efficiency is measured to be 5 dB at 1-THz pump-signal detuning, which is the highest value reported to date. With a pump power of -1.4 dBm, the SBR is in excess of 20 dB in a bandwidth of 12.5 GHz, for a pump-signal detuning range as large as 2 THz and the efficiency is under the same conditions larger than -1 dB for a pump-signal detuning range as large as 1 THz. These results make FWM an attractive method for practical wavelength conversion. Some low-detuning measurements show a maximum efficiency around 8 GHz.

Terahertz four-wave mixing in semiconductor optical amplifiers: Experiment and theory

Highly nondegenerate four-wave mixing processes in bulk semiconductor optical amplifiers are analyzed by comparing experimental data at detuning frequencies up to 3 THz with numerical calculations based on semiclassical density-matrix equations. Carrier heating and spectral holeburning are found to be dominant in mediating wave mixing in the THz region and lead to comparable contributions to nonlinear gain suppression in semiconductor lasers.

Heterodyne pump–probe technique for time-domain studies of optical nonlinearities in waveguides

We describe a novel pump–probe technique in which pump and probe pulses are collinear and have parallel polarizations but are still distinguishable. This new technique is especially useful for femtosecond time-domain studies of waveguides. We present experimental results for bulk (V-groove) semiconductor optical amplifiers at 1.5 μm and compare them with results for orthogonally polarized pump–probe measurements. The comparison demonstrates differences that are due to anisotropy of the group velocity as well as of the waveguide nonlinearity.