Semiconductor Laser Amplifier Research Articles

Optical loop mirror with semiconductor laser amplifier

A nonlinear optical loop mirror is reported, employing a semiconductor laser amplifier (SLA). The input-output characteristic is distinctly nonlinear, and when operating as an optical correlator, an extinction ratio of 13 dB was achieved.

Crosstalk reduction in semiconductor laser amplifiers

One of the important deficiencies of semiconductor laser amplifiers, compared with fibre amplifiers, is the crosstalk that is created by four-wave mixing and gain saturation. If the electron density were controlled at all points along the amplifier, the crosstalk could be greatly reduced. The paper looks at the theory of optoelectronic feedback, using the spontaneous emission as a measure of the electron density and introducing both linear and differential feedback into the injected current, to control the electron density in an amplifier. The paper also examines the consequential reductions in four-wave mixing. It is concluded that it may be feasible to effect this, particularly in an integrated amplifier. Preliminary practical trials are under way.

A theoretical study of pulsed laser sampling photon amplifiers

Theoretical studies point to significant improvements in the performance of semiconductor laser amplifiers by injecting carriers with pulsed electric currents of sub-nanosecond duration. A pulsed Fabry-Perot amplifier (FPA) is most sensitive to input lightwave at the instant the carrier density is crossing the critical region, and gives a sharply pulsed sampling effect on the input lightwave signal. Compared with a FPA operating at subcritical electron density, the pulsed amplifier gives much higher gain, peak power, and bandwidth. In fact, pulsed operation of a FPA is also expected to give significantly higher gain and about the same peak output power as a traveling wave amplifier. Pulsed operation also improves the performance of a traveling wave amplifier by attenuating its internally reflected waves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparative study of some travelling-wave semiconductor laser amplifier models

Mathematical models for travelling-wave semiconductor laser amplifiers are compared in the steady state for a simplified case where the exact solution is easily obtained. The frequently used model with the photon density averaged over the length of the amplifier is examined together with a simple perturbation model and a new orthogonal function model. The photon density averaging model is the most accurate. The perturbation model is less reliable because of its simplifications. For the orthogonal function model, the complexity grows much faster than the accuracy and therefore this model is unpractical.

Monolithically integrated 4×4 InGaAsP/InP laser amplifier gate switch arrays

Monolithically integrated 4×4 semiconductor laser amplifier gate switch arrays comprising 24 integrated laser amplifiers have been fabricated and evaluated. Net positive optical gain between fibres, high extinction ratio, and low crosstalk are reported.

Monolithically integrated 2×2 InGaAsP/InP laser amplifier gate switch arrays

Monolithically integrated 2*2 semiconductor laser amplifier gate switch arrays have been fabricated and evaluated. Net positive chip gain, high extinction ratio, and high electrical isolation between the integrated laser amplifiers are reported.

Modulation properties of a near travelling-wave semiconductor laser amplifier

The amplitude and phase or frequency modulation properties for pump current modulation of a near travelling-wave semiconductor laser amplifier are examined. The investigations are performed numerically in the time domain with large-signal analysis and in the frequency domain with small-signal analysis. It is shown that the modulation bandwidth is increased by high pump current or high input power and that the small-signal modulation efficiency is increased by low pump current or low input power. The validity of the simulations is supported by experimental results.

Cross-phase modulation in a semiconductor laser amplifier determined by a dispersive technique

Cross-phase modulation in a semiconductor laser diode amplifier is reported. A simple expression for the chirp imparted on a weak signal pulse by the action of a strong pump pulse is derived. A novel dispersive technique for characterizing the resulting nonlinear chirp is introduced and used in the present experiment. A maximum frequency excursion of 16 GHz, due to the cross-phase modulation, was measured. A value of 6 was found for alpha /sub xpm/, which is a factor for characterizing the cross-phase modulation in a similar manner to the conventional linewidth enhancement factor alpha .< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Gain saturation and propagation characteristics of index-guided tapered-waveguide traveling-wave semiconductor laser amplifiers (TTW-SLAs)

A model is developed to investigate the propagation characteristics and gain saturation performances of tapered-waveguide traveling-wave semiconductor laser amplifiers (TTW-SLAs). The influences of several physical mechanisms are analyzed. Two taper geometries are studied in detail: the exponential TTW-SLA and the linear TTW-SLA. The first is shown to be more efficient for narrow tapers (output width <14 mu m), whereas the linear TTW-SLA becomes superior for wide-taper geometries because of its better adiabatic propagation characteristics. Both tapered structures can provide a consistent improvement in the saturation output power compared to the conventional TTW-SLA, reaching absolute values on the order of approximately 18 dBm and approximately 23 dBm for the exponential and linear TTW-SLAs, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A GaInAsP/InP tapered-waveguide semiconductor laser amplifier integrated with a 1.5 mu m distributed feedback laser

A GaInAsP/InP index-guided type tapered-waveguide traveling-wave semiconductor laser amplifier (TTW-SLA) with exponential taper structure was realized for the first time and its integration with a 1.5 mu m wavelength phase adjusted DFB laser was demonstrated. A reasonable amount of the single-pass gain, which was limited by the residual reflectivity at the output end of the amplifier region, was obtained with no serious problem with the lasing spectrum. A narrow beam divergence of FWHM=5.5 degrees and stable longitudinal mode operation were obtained with the output waveguide width of 20 mu m by adopting both a window structure and 7 degrees angled facets. This value agrees well with the theoretically calculated one and proves that single transverse-mode propagation can be attained by an exponentially tapered TTW-SLA with a very wide output end. >

Optical demultiplexing at 6 Gb/s using a semiconductor laser amplifier as an optical gate

A semiconductor laser amplifier (SLA) has been employed successfully for optical demultiplexing in two-channel optical time division multiplexed system experiments at 6 and 2 Gb/s. Demultiplexing of 6-Gb/s (2-Gb/s) signals was demonstrated with a power penalty of 1.6 dB (3.0 dB) at bit error rates of 10/sup -9/. It is also shown that a reduction of the generated amplified spontaneous emission can be obtained by optical gating/demultiplexing for systems incorporating inline amplifiers. A 0.5-dB improvement in sensitivity was achieved as a result of using an SLA for demultiplexing from 2.0 to 1.0 Gb/s in a system with one inline Er/sup 3+/-doped fiber amplifier. >

Pulsed laser sampling photon amplifier

The performance of semiconductor laser amplifiers can be significantly improved by injecting carriers with pulsed electric currents of subnanosecond duration. Pulsed operation is illustrated in a Fabry-Perot amplifier and in a traveling-wave amplifier. The resonant amplifier is most sensitive to an input light wave at the instant the carrier density is crossing over the critical region, giving a sharply pulsed sampling effect on the input light wave signal. Compared to a resonant amplifier operating at subcritical electron density, the pulsed amplifier gives much higher gain and peak power. In fact, pulsed operation of a resonant amplifier is also expected to give significantly higher gain than and about the same peak output power as a traveling-wave amplifier. Pulsed operation also improves the performance of a traveling-wave amplifier by attenuating its internally reflected waves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification

Abstract : Optical amplifiers are important devices for future optical fiber transmission and other photonic technologies. Semiconductor laser amplifiers are attractive candidates for these applications because of theirs high gain, compactness, possibility of integration with light source and so on. In comparison with fiber amplifiers such as Er+-doped fibers, the semiconductor laser amplifiers have a disadvantage which is large difference between TE and TM gain. Therefore, to control the TE/TM mode gain is a key item in the development of semiconductor amplifiers. For polarization insensitive amplification in the semiconductor laser amplifier, several approaches have been proposed by geometric designing of active layers. 1-3 In this paper, we describe an approach to the polarization insensitive optical amplifier in which active layer consisted of GaInAsP multiple quantum well structures with biaxially tensile strains within well layers. A group has reported a strained layer quantum well amplifier with tensed barriers. 4 In this work, we investigated the effects of biaxially tensile strain on amplification in the quaternary strained quantum well amplifiers. The polarization insensitive amplification was successfully demonstrated.

Simulation of multicarrier traveling-wave semiconductor laser amplifiers

A simulation approach is presented that permits an accurate description of the behavior of a traveling-wave semiconductor laser amplifier fed by a multicarrier signal. It is shown to be equivalent to an exact solution of the discretized rate equation governing the amplifier behavior. The method is general enough to handle realistic input signal carriers as in a numerical FDM (frequency division multiplexing) environment. Comparisons with previously proposed models confirm the accuracy and flexibility of the approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of nonlinear gain on four-wave mixing and asymmetric gain saturation in a semiconductor laser amplifier

Nearly degenerate four-wave mixing (NDFWM) and asymmetric gain saturation were studied in a 1.5 μm InGaAsP semiconductor laser amplifier at highly saturated conditions (Pout ≫ Psat) and frequency separations up to 500 GHz. Apart from modulation of the carrier density the data reveal a new mechanism of NDFWM with a characteristic time of about 650 fs which takes over when the frequency separation exceeds 100 GHz.

Model for noise processes in semiconductor laser amplifiers:

A model for the noise processes in a Fabry-Perot semiconductor laser amplifier is presented. This model is based on the application of perturbation techniques to the travelling-wave rate equations for the amplifier. The model includes the effects of end-facet reflections and the backwards-travelling wave into the amplifier. The noise power spectral densities for the intensity, electron density and phase noise are derived. The model can be applied to an arbitrary gain profile and does not require homogenization of the photon field over the length of the device.

Effect of gain dispersion on ultrashort pulse amplification in semiconductor laser amplifiers

The effect of gain dispersion in semiconductor laser amplifiers is discussed by considering an amplifier model that includes both gain saturation and gain dispersion. The saturated and unsaturated amplification regimes corresponding to whether the pulse energy is comparable to or much smaller than the saturation energy, are discussed separately. In the unsaturated regime, gain-induced group-velocity dispersion is found to play an important role. The amplified pulse can be compressed or broadened depending on whether the input pulse is chirped or unchirped. The pulse spectrum remains largely unaffected in the linear regime. In the saturation regime, self-phase modulation leads to considerable changes in the pulse spectrum. >

Calculation of photon and current fluctuations in traveling-wave semiconductor laser amplifiers

The noise properties of semiconductor laser amplifiers are calculated using the Heisenberg equations of motion. Photon noise as well as the recombination current noise are calculated with this formalism, and agreement with previously published results was found for the photon noise. The formalism also gave the conventional current shot noise in the appropriate limits, e.g., when using the amplifier reverse-biased as a detector. The method gives reasonable agreement with reported experimental results and the results for the current noise could be given a consistent physical explanation. Some concluding remarks concerning the relationship with the Langevin approach and the possibilities of minimizing the noise are given. >

Fundamental limits of sub-ps pulse generation by active mode locking of semiconductor lasers: the spectral gain width and the facet reflectivities

The authors present a numerical simulation of active mode locking of a semiconductor laser amplifier (SCLA) in an external cavity, which includes the finite spectral gainwidth. This is shown to be essential for introducing a lower limit of the pulsewidth, although the gain linewidth is about a factor of 10-50 broader than the inverse pulsewidth. This numerical treatment consistently explains the experimental findings that even SCLA facet reflectivities as low as 10/sup -4/ lead to trailing pulses with an intensity almost of the same order of magnitude as the leading one. This theory makes detailed predictions about the influence of the facet reflectivities, the spectral gainwidth, and the injection current on the picosecond pulse generation. >

Picosecond pulse generation from a 1.3 mu m distributed feedback laser diode using soliton-effect compression

An experimental demonstration of the soliton-effect pulse compression with a 1.3- mu m distributed feedback (DFB) semiconductor laser, a compression fiber, two traveling-wave optical amplifiers, and a soliton-effect compression fiber is presented. The experimental configuration and the details of the pulse generation from a gain-switched 1.3- mu m DFB laser diode are described. Results of temporal compression using a fiber of normal dispersion are presented where reduction of the pulsewidth to 2.45 ps is realized. The pulse amplification characteristics of a two-stage traveling-wave semiconductor laser amplifier are discussed with emphasis on the observed temporal broadening and spectral narrowing. After a brief description of the soliton-effect compression in an optical fiber, details of the experimental realization are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>