Semiconductor Laser Amplifier Research Articles

Wavelength conversion in tapered‐waveguide laser diode amplifiers

AbstractWavelength conversion using cross‐gain modulation (XGM) in linear tapered‐waveguide semiconductor laser amplifiers (SLAs) has been investigated theoretically and compared with the nontapered semiconductor laser amplifier. For example, we have found that for the linear tapered‐waveguide SLA with a 450‐μm cavity length, a higher signal power is required to achieve an extinction ratio similar to that obtained by the conventional SLA with the same cavity length. However, a similar extinction ratio is observed for both conventional and linear tapered‐waveguide with the cavity length of 1200 μm. The difference between the extinction ratios for up and down conversions is less severe in a linear tapered‐waveguide SLA as compared to that for a conventional SLA. The rise time for the linear tapered‐waveguide is observed to be higher than that for the conventional SLA. It is possible to attain extinction‐ratio conservation using XGM for both up and down conversions in an SLA with a very long cavity length of 2400 μm. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 134–142, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20748

Acceleration of a Gain-Clamped Semiconductor Optical Amplifier by the Optical Speed-Up at Transparency Scheme

The optical speed-up at transparency principle has been successfully applied to a gain-clamped semiconductor optical amplifier yielding a remarkable acceleration in the gain recovery of the device as well as to the disappearance of the typical relaxation oscillations stemming from the coupling between the internal lasing mode and the carrier density. A record gain recovery time of 13 ps has been measured with an available gain of still 16 dB. A small-signal analysis of the semiconductor laser amplifier rate equations properly reproduces the acceleration of the recovery time and the disappearance of the relaxation oscillations. These results apply to semiconductor lasers in general.

Amplification and wave mixing of induced and spontaneous emission in semiconductor laser amplifiers

We theoretically describe and experimentally investigate the spatio-spectral wave mixing of induced and spontaneous emission in large-area InGaAs-semiconductor laser amplifiers. The dynamic light-matter-coupling is described by a spatially resolved theory based on Maxwell–Bloch–Langevin equations, taking into account many-body-carrier interactions, energy transfer between the carrier and phonon systems and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and the noise caused by spontaneous emission. Our numerical model reveals the fundamental physical processes which are responsible for the spectral power distribution of the amplified laser light and predicts the emission properties of high-power semiconductor laser amplifiers, such as emission spectra and input power–output power characteristics.

Wavelength Conversion in Tapered-waveguide Laser Diode Amplifiers

Wavelength conversion using cross-gain modulation (XGM) in linear tapered-waveguide semiconductor laser amplifiers (SLAs) has been investigated theoretically and compared with the non-tapered semiconductor laser amplifier. For example, we have found that for the linear tapered-waveguide SLA with a 450 pm cavity length, a higher signal power is required to achieve a similar extinction ratio as obtained by the conventional SLA with the same cavity length. However, a similar extinction ratio is observed for both conventional and linear tapered-waveguide with the cavity length of 1200 pm. The difference between the extinction ratio for up and down conversion is less severe in a linear tapered-waveguide SLA as compared to that for a conventional SLA. The rise time for linear tapered-waveguide is observed to be higher than that for conventional SLA. It is possible to attain extinction ratio conservation using XGM for both up and down conversions in a SLA with a very long cavity length of 2400 μm.

Optical packet switching and buffering by using all-optical signal processing methods

We present a 1 /spl times/ 2 all-optical packet switch. All the processing of the header information is carried out in the optical domain. The optical headers are recognized by employing the two-pulse correlation principle in a semiconductor laser amplifier in loop optical mirror (SLALOM) configuration. The processed header information is stored in an optical flip-flop memory that is based on a symmetric configuration of two coupled lasers. The optical flip-flop memory drives a wavelength routing switch that is based on cross-gain modulation in a semiconductor optical amplifier. We also present an alternative optical packet routing concept that can be used for all-optical buffering of data packets. In this case, an optical threshold function that is based on a asymmetric configuration of two coupled lasers is used to drive a wavelength routing switch. Experimental results are presented for both the 1 /spl times/ 2 optical packet switch and the optical buffer switch.

Performance analysis on semiconductor laser amplifier loop mirrors

Operating characteristics of the semiconductor laser amplifier loop mirror (SLALOM) in optical time-division multiplexing (OTDM) applications are investigated in theory. The injection current of the semiconductor laser amplifier (SLA) should be adjusted to realize a flat and high switching window. The channel crosstalk induced by the finite carrier lifetime and the signal timing jitter should be balanced. The optimal switching window width should be slightly wider than half of the OTDM signal bit interval. The control pulse should be narrower than one-third of the OTDM bit interval in order not to deteriorate the bit error rate (BER) performance. Further discussion indicates that the nonlinear gain compression in the SLA becomes a crucial limit for the SLA-based all-optical switches to be used in the terahertz applications.

Comparison of interferometric all-optical switches for demultiplexing applications in high-speed OTDM systems

We have investigated three interferometric all-optical switches based on cross-phase modulation (XPM) in semiconductor optical amplifiers (SOAs), the semiconductor laser amplifier in a loop mirror (SLALOM) switch, the Mach-Zehnder interferometer (MZI) switch, and the ultrafast nonlinear interferometer (UNI) switch. Switching windows with different widths are measured under similar conditions for all three switching configurations. We introduce the integrated contrast ratio (ICR) as a measure to evaluate the performance of a switch from switching windows. Using the ICR, the switches are compared and their application is discussed as demultiplexer in optical time division multiplexing (OTDM) systems for data rates of 40, 80, and 160 Gb/s.

Optical mixing of microwave signals in a nonlinear semiconductor laser amplifier modulator

In this paper we propose and evaluate the optical mixing of RF signals by means of exploiting the nonlinearity of a SLA modulator. The results show the potential for devices with low conversion losses (and even gain) and polarization insensitivity and reduced insertion losses.

Multiple-output all-optical header processingtechnique based on two-pulse correlation principle

A serial all-optical header processing technique based on a two-pulse correlation principle in a semiconductor laser amplifier in a loop mirror (SLALOM) configuration that can have a large number of output ports is presented. The operation is demonstrated experimentally at a 10 Gbit/s Manchester encoded data stream. Experimental evidence is provided in the case of two different output ports.

Cross-talk analysis of optical time-division demultiplexer

We have developed a simulation model to investigate the demultiplexing of all-optical-time-division-multiplexed data, employing an optical time-division demultiplexer. Particular attention is paid to the cross-talk performance when selected parameters of the system are varied. The system used to demultiplex the data is the asymmetric semiconductor laser amplifier loop mirror (ASLALOM), which is capable of selecting high-speed optical pulses within a data train. The authors use a model of the ASLALOM that includes a time and space analysis of a traveling-wave semiconductor laser amplifier. Our investigation shows that this system produces cross talk that is dependent on the data rate, control pulse energy, and control pulse rate.

All-optical serial header processing based on two-pulsecorrelation

An all-optical serial header processor is demonstrated using a semiconductor laser amplifier in a loop mirror configuration (SLALOM). The operation of the header processor is discussed and it is experimentally demonstrated with a 10 Gbit/s Manchester encoded (information rate of 5 Gbit/s) packet stream. The operation of the header processor is based on the correlation function of the SLALOM. The header processor can be utilised in devising all-optical packet switches.

Spatio-temporal dynamics of light amplification and amplified spontaneous emission in high-power tapered semiconductor laser amplifiers

We investigate the spatio-temporal light field dynamics in high-power semiconductor lasers with continuous-wave optical injection. The amplification processes that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially dependent gain and refractive index variations. Those are shown to be determined by dynamic interactions between the light fields and the active charge-carrier plasma. This microscopic light-matter-coupling is described by a spatially resolved microscopic theory based on Maxwell-Bloch-Langevin equations taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and noise. Results of our numerical modeling visualize the dynamic spatio-spectral beam shaping experienced by the propagating light in amplifiers of tapered geometry. This reveals the microscopic physical processes that are responsible for the particular amplitude and spatial shape of the light beam at the output facet.

Wavelength-tunable 40 GHz pulse-train generationusing 10 GHz gain-switched Fabry-Perot laser and semiconductor optical amplifier

A simple novel method is described for generating a wavelength-tunable 40 GHz pulse-train from a fibre ring laser with a semiconductor laser amplifier using 10 GHz electronics and optical repetition-rate multiplication. The 40 GHz pulses can be tuned over a 20 nm range with a pulsewidth of /spl sim/8 ps.

Saturation behavior and self-phase modulation of picosecond pulses in single-stripe and tapered semiconductor laser amplifiers

We experimentally investigate and theoretically describe the amplification of ultrashort optical pulses in a double-stage InGaAs-semiconductor laser amplifier system consisting of a double-pass single-stripe diode laser and a tapered amplifier. The pulses were generated by a mode-locked single-stripe laser in an external-resonator configuration. On amplification in a tapered amplifier, pulses exhibited both spectral broadening and distortion, depending on the tapered amplifier current and the injected optical pulse power. This behavior originates from the dynamic nonlinear carrier induced spatiospectral gain and index changes as well as gain saturation and leads to self-phase modulation. The origin of the observed behavior is revealed by a spatially resolved microscopic theory based on Maxwell–Bloch–Langevin equations that takes into account many-body interactions, energy transfer between carrier and phonon systems, and, in particular, the spatiotemporal interplay of stimulated and amplified spontaneous emission and noise.

Circuit model for traveling wave semiconductor laser amplifiers

A circuit model of a traveling wave semiconductor laser amplifier is presented for the circuit level simulation of single device or Optoelectronics Integrated Circuit (OEIC) included amplifiers. To verify the model, the simulated results are compared with the experimental results.

Use of a SLALOM as an optical frequency multiplier and pulse compressor

A SLALOM (semiconductor laser amplifier in the loop mirror) for optical frequency multiplication and pulse compression is presented theoretically. The influence of the relatively slow turn-on transition of the SLA and the window size to the switching window is discussed, and is neglected, instead of the sudden step for the transition in the short control pulse case in a previous paper 1. We make use of the two windows, which are created by the appropriate parameters of the proposed configuration, to multiply the optical pulse rate in the relatively long control pulse case. When the second window disappears in the short control pulse case, the device can be used as a pulse compressor. Analysis demonstrates that the 10 Gbit/s optical clock signal can be doubled to 20 Gbits/s, and a 100 ps pulse can be compressed to 34 ps at a rate of 2.5 Gbits/s with this device. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 187–191, 2000.

Use of a SLALOM as an optical frequency multiplier and pulse compressor

A SLALOM (semiconductor laser amplifier in the loop mirror) for optical frequency multiplication and pulse compression is presented theoretically. The influence of the relatively slow turn-on transition of the SLA and the window size to the switching window is discussed, and is neglected, instead of the sudden step for the transition in the short control pulse case in a previous paper 1. We make use of the two windows, which are created by the appropriate parameters of the proposed configuration, to multiply the optical pulse rate in the relatively long control pulse case. When the second window disappears in the short control pulse case, the device can be used as a pulse compressor. Analysis demonstrates that the 10 Gbit/s optical clock signal can be doubled to 20 Gbits/s, and a 100 ps pulse can be compressed to 34 ps at a rate of 2.5 Gbits/s with this device. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 187–191, 2000.

Influence of carrier transport on performance of SLALOM with a polarization-independent MQW SLA

The switching performance of the semiconductor laser amplifier in a loop mirror (SLALOM) with a polarization-independent multiquantum-well SLA influenced by the carrier transport is discussed. It is shown that the switching window is polarization-dependent in the case of ultra-short pulses used as switching pulses because of the carrier transport effect between quantum wells. The influence of polarization can be suppressed by modifying the polarization state of local switching pulses.

Microscopic theory of spatiotemporal multiwave mixing in broad-area semiconductor laser amplifiers

We investigate the interplay of multiwave-mixing processes with the microscopically coupled spatiotemporal light field and charge carrier dynamics in broad-area semiconductor laser amplifiers. Our theoretical description is based on extended spatially resolved Maxwell-Bloch equations including on the microscopic level spatiotemporal multiwave-mixing processes. Performing a third-order expansion in terms of the microscopic carrier distribution, we include in our description both the effects of population pulsations of the total carrier density at the beat frequency and the spatiospectral interactions of the light fields leading to gain nonlinearities as well as spatial and spectral hole burning. Our simulations show that in a broad-area semiconductor laser amplifier, spatiotemporal wave-mixing processes occur in both transverse and propagation directions of the multifrequency optical beams employed in a typical excite-probe configuration.

Limitations on ultrafast optical switching in a semiconductor laser amplifier operating at transparency current

Ultrafast optical switching in a semiconductor laser amplifier (SLA) at transparency current is studied under a strong pump condition. The switch configuration is a nonlinear optical loop mirror with a SLA as the nonlinear element. We demonstrate optical switching with 2 ps recovery time and 60% nonlinear transmission at switching energy of 9 pJ. We find that the transparency current is pump power dependent and that the transparency current is different for uniform 7-bit input control pulses at 100 Gb/s. We believe these two outcomes are due to significant carrier generation via two photon absorption (TPA) at high pump intensity. To verify our hypothesis, we modify coupled propagation equations by including the carrier generation due to the TPA and solve the equations numerically. Good agreement between the experimental and simulation results is obtained. We conclude that to achieve complete pattern-independent 100 Gb/s optical switching using a SLA at transparency current, we have to avoid TPA or use the SLA with a transit time shorter than the control pulse width.