Optical Saturable Absorption Research Articles

10 Gbit/s RZ transmission over 5000 km with gain-clampedsemiconductor optical amplifiers and saturable absorbers

By combining a gain-clamped semiconductor optical amplifier (GC-SOA) and a saturable absorber-semiconductor optical amplifier module, 10 Gbit/s RZ transmission over 5000 km (200 × 25 km) has been demonstrated in a fibre loop setup. It is shown that a GC-SOA could compensate for the patterning introduced by a conventional SOA.

Pulse shape measurements using differential optical gating of a picosecond free electron laser source with an unsynchronized femtosecond Ti:sapphire gate

We have measured the temporal pulse shape of a mid-infrared free electron laser using a 60 fs Ti:sapphire pulse as an optical gate. By employing a differential technique to simultaneously measure the instantaneous infrared intensity and its time derivative, we have reconstructed the pulse shape with sub-ps resolution, despite jitter the order of 50 ps between the two lasers. The experiment has been performed with two different types of gating methods: sum-frequency generation, which provides an instantaneous gate, and photo-induced plasma absorption, which supplies a step function gate. Differential optical gating can be generalized to include other gating methods, such as the optical Kerr effect or saturable absorption, thus permitting detailed pulse shape studies on a variety of optical processes, especially in the far-infrared, where conventional pulse shape measurement methods are more difficult to implement.

High density optical storage based on superresolution techniques employing optical path filtering and saturable absorption

Optical superresolution techniques to increase the density of data storage by source and medium modifications are explained. It is shown that the light distribution at the source can be modified using a phase filter. This results in overall energy efficiency and improvement in the frequency response of the optical read-out. The frequency response of the optical readout with source modification Is good at medium and high frequencies. The technique of superresolution through source modification, and with saturable absorber in the medium is proposed.

A superresolution optical disk with a combination of optical path filtering and saturable absorption techniques

Calculations have been done for the modulation transfer function of a superresolution optical disk with a combination of optical path filtering and saturable absorption techniques. The results reveal that optical path filtering alone can only equalize, to a certain degree, the spatial frequency response of the opticaldisk system, but it can not attain any response beyond the cutoff frequency. With an additional saturable absorption layer in-between the substrate and the information layer, it is found that the optical response both under and beyond the cutoff frequency can be greatly improved.

A superresolution optical disk with a combination of optical path filtering and saturable absorption techniques

A superresolution optical disk with a combination of optical path filtering and saturable absorption techniques

Soliton stability in optical transmission lines using semiconductor amplifiers and fast saturable absorbers.

Soliton stability has been examined in the cascaded transmission system based on the standard monomode fibers with in-line semiconductor optical amplifiers, sliding filters, and saturable absorbers (SAs). Stabilization of the pulse propagation in such a system can be achieved under a proper choice of the filter and SA parameters. Conditions of the stable propagation including a critical sliding rate are determined. Impact of the saturable absorber on the soliton stability has been investigated.

Photothermal grating spectroscopy study of nongeminate atom recombination of photodissociated iodine in liquids

Photothermal grating spectroscopy is applied to study the nongeminate atom recombination of photodissociated iodine in liquids. A theoretical model is developed to describe the time dependence of diffraction signals. The excitation intensity dependence of diffraction from the anharmonic thermal grating, created by saturated optical absorption, is used to estimate the quantum yield ofthephotodissociation, which is critical to determine the number of iodine atoms produced and hence to the recombination rate. The rateconstant of nongeminate atom recombination is extracted from the dependence of the time-resolved photothermal diffraction signals on the atom concentration. From the relative amplitudes of the diffraction transients, we can also derive the enthalpy of the recombination reaction.

Photoelectrochemical evidence for saturated optical absorption in electrolytic cuprous oxide

An illuminated cuprous oxide-covered electrode immersed in alkaline media exhibits a nonlinear dependence of photocurrent on the intensity of 488 nm laser illumination. Results from intensity modulation experiments show that the differential efficiency for converting photons to photocurrent in the p-type cuprous oxide thin film is inversely proportional to the square root of illumination intensity. A charge transfer model that includes intensity dependent optical absorption in the cuprous oxide layer is found to be consistent with the observed photocurrent response. Analysis of the experimental results using the charge transfer model shows that the saturation intensity for cuprous oxide is approximately 100 mW/cm.2 Photoelectrochemical charge transfer is found to be efficient in the potential region where the nonlinear photocurrent response is observed, with nearly all photoinjected minority carriers being consumed by the interfacial charge transfer reaction rather than by recombination.

Analyses of suppression of mode hopping in an AlGaAs laser by saturable absorber

A novel stochastic model based on a formulation by the Fokker-Planck equation was proposed to describe a drastic suppression of mode hopping in an AlGaAs laser, which has been observed when tellurium was doped in its n-type cladding layer. It was found that this suppression was caused by a decrease in the self-saturation coefficient of the laser oscillation due to saturable optical absorption by DX centers. Furthermore, the dependence of this suppression on the laser power confinement ratio in the active layer was evaluated. Calculated results obtained with this model agreed well with the experimental results.

Saturation of the optical absorption in chalcogenide glasses

This paper is a report on observations of the optical absorption in bulk chalcogenide glasses or films of the quarternary AsSSe x Te 1− x system under Nd: glass laser irradiation. The sample was placed outside the laser cavity, and the nonlinear effect of the light transmission varying with the laser power was observed, and the light transmission of the sample increased by about 30%. When the sample was placed inside the laser cavity, the modulated effect was observed. It is considered that the saturated optical absorption in the AsSSE x Te 1− x system is caused by a self-induced dynamic Burstein-Moss shift of the fundamental absorption edge.

Observations of negative resistance associated with superlinear emission characteristics of (Al, Ga) As double-heterostructure lasers

Observations are reported of the electrical and optical behavior exhibited by stripe-geometry, proton-bombardment-delineated, (Al, Ga)As double-heterostructure junction lasers, whose output power shows an abrupt, nearly discontinuous increase as a function of input current. When operated within this superlinear regime (in addition to exhibiting self-induced intensity pulsations) the output power averaged over many pulsations fluctuates randomly between levels corresponding to the intensities at either end of the superlinear range. A negative resistance which is light induced and associated with the lasing optical field accompanies the superlinearity, as does motion of the lasing filament along the junction plane. The low temperature behavior of the negative resistance shows that non-ohmic conduction mechanisms are present in the laser material. However, axially nonuniform changes in the luminescence observed through the substrate indicate that saturable optical absorption in the active layer at the laser mirror faces may be the predominate cause of the superlinearity and negative resistance. The development of these effects with aging may be arrested by mirror facet coatings applied before bonding.

Single-mode stabilization by traps in semiconductor lasers

Recently it has been observed that certain single-transverse-mode semiconductor lasers continue to emit light predominantly in a particular longitudinal mode even after the optical gain peak has shifted by one or more mode spacings due to changes in bias current or temperature [1], [2]. The purpose of this paper is to show that this type of mode stabilization can be caused by the saturable optical absorption resulting from deep-level states or traps, which have been observed in AlGaAs laser structures [3]-[7]. The mode-selection mechanism is due to the spatial variation in the optical loss created by the standing-wave pattern of the single predominant mode. This loss pattern results in a lower average loss for the creating mode and a higher loss for all other modes. It is possible that laser devices with greatly improved single-mode stability can be made by introducing traps of the proper type and density during fabrication.

Saturable optical absorption of the deep Te-complex center inAl0.4Ga0.6As

Saturable optical absorption of the deep Te-complex center in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Al</mml:mi></mml:mrow><mml:mrow><mml:mn>0.4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi></mml:mrow><mml:mrow><mml:mn>0.6</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>As

Saturable absorption and rotational relaxation in CO2

Experimental data demonstrating saturated optical absorption of HF P2(4) laser radiation by CO2 is presented and analyzed in terms of a simple kinetic model. Within the framework considered, relatively slow rotational relaxation in the (00°0) vibrational level of CO2 is shown to be responsible for saturated absorption. The relation between the rotational relaxation rate constant appropriate to these experiments and that determined in thermal experiments is discussed.

Spontaneous power and the coherent state of injection lasers

A proposed relation between spontaneous and coherent properties of injection lasers is applied to several published results. On experimental and theoretical grounds it is shown that the parameter 1+X, the ratio of conventional gain coefficient to prorated loss for the strongest cavity mode, can be determined from the spontaneous emission. Over a limited range above unity, 1+X is the ratio of spontaneous intensity at the operating point to its value at threshold. This supplies a needed experimental connection between spontaneous studies at frequencies higher than the lasing band and the coherent properties. Published data of the current dependence of spontaneous emission are discussed in this framework, and the information needed to intercompare their internal state is pointed out. In general, fundamental differences in laser dynamics should be evidenced by radically different values of the critical parameter P* of the nonlinearity associated with the power dependence of X. All published values of P* are of order 5 mW per cavity mode, as predicted, indicating a similarity in the nonlinearity for quite different types of material. The recent observation that P* is independent of facet area gives strong support to the idea that the source of the nonlinearity is saturable optical absorption in a strongly interacting system.

Effect of saturable absorption on the behavior of spontaneous emission in semiconductor lasers

A substantial reduction of the spontaneous emission intensity is observed at the onset of stimulated emission in some injection lasers. It is shown that this effect is caused by the saturation of optically absorbing traps present in the active region. It is suggested that saturable optical absorption is also responsible for previously unexplained similar reduction observed by Nicoll in bulk semiconductor lasers.

Saturable Optical Absorption in Phthalocyanine Dyes

Strong optical absorption lines have been almost totally saturated in two phthalocyanine molecules. A giant pulse ruby laser served as the source of intense resonance radiation. The qualitative behavior of the nonlinear absorption is in good agreement with theory.