Spectral Hole Burning Effects Research Articles

Lasing Mode Hysteresis Characteristics in Semiconductor Ring Lasers

Wavelength and directional hysteresis due to increasing and decreasing current and temperature have been investigated. Measurements indicate that lasing direction hysteresis associated with changes in injection current can be attributed to the resulting shift in the linear gain peak which is due to the change in device temperature. Interaction between the linear gain spectrum and the asymmetric nonlinear gain spectrum results in contrasting behavior for increasing and decreasing temperature and current. The phenomena are modeled using a nonlinear time domain model including the carrier density pulsation (CDP), carrier heating (CH) and spectral hole burning (SHB) effects. The numerically reproduced hysteresis loop is in close agreement to the experimental observation. Our work further shows that mode hops to longer wavelength non lasing modes are quicker than those to shorter wavelength lasing modes due to the lack of four wave mixing (FWM) mode coupling in the non-lasing mode. The same model can be used to study the dynamics during switching of lasing directions triggered by other means, such as optical injection.

Numerical modeling of optical coherent transient processes with complex configurations—III: Noisy laser source

A previously developed numerical model based on Maxwell–Bloch equations was modified to simulate optical coherent transient and spectral hole burning processes with noisy laser sources. Random walk phase noise was simulated using laser-phase sequences generated numerically according to the normal distribution of the phase shift. The noise model was tested by comparing the simulated spectral hole burning effect with the analytical solution. The noise effects on a few typical optical coherence transient processes were investigated using this numerical tool. Flicker and random walk frequency noises were considered in accumulation process.

Linewidth Enhancement Factor of Quantum-Dot Optical Amplifiers

The linewidth enhancement (alpha-) factor of quantum-dot (QD) semiconductor optical amplifiers in the small signal gain and nonlinear regimes is theoretically investigated. A microscopic polarization equation and a wave equation are used to model subpicosecond pulse propagation in the nonlinear regime. In addition, a population equation that takes into account spectral hole burning and carrier heating effects is used. A novel approach to obtain the alpha-factor from the output pulse amplitude and phase in the dynamic nonlinear regime is presented. An in-depth study reveals that the presence of excited states (ES) limits the alpha-factor to values greater than 1 except when the energy separation between the ground state and ES is large. The alpha-factor dependence on QD inhomogeneous broadening, carrier density, carrier temperature, energy level separation, and input pulse energy is analyzed. We find that these can change the alpha-factor considerably. In particular, the alpha-factor increases with increasing input pulse energy and can be greater than 10 for input pulse energies larger than the amplifier's input pulse saturation energy. In the light of our calculations, the optimum device engineering required to obtain a low alpha-factor is discussed

Theory of semiconductor quantum-dot laser dynamics

A theory for describing nonequilibrium dynamics in a semiconductor quantum-dot laser is presented. This theory is applied to a microcavity laser with a gain region consisting of an inhomogeneous distribution of quantum dots, a quantum-well wetting layer, and injection pumped bulk regions. Numerical results are presented and the effects of spectral hole burning, plasma heating, and many-body effects are analyzed.

Linear and nonlinear mode interactions in a semiconductor ring laser

In order to understand and explain recently reported nonlinear behaviors in semiconductor ring lasers (SRLs) and to further design novel functional devices, a multimode model has been developed for linear and nonlinear interactions between modes in an SRL lasing unidirectionally. The model includes population pulsation, spectral hole burning, carrier heating, and four-wave mixing effects. Heterodyne detection has been used to make high-resolution measurements of the lasing spectra of an SRL in which the individual resonances associated with the coupled eigenvalues can be observed. By fitting these high-resolution spectra to the model, we have extracted a number of key parameters characterizing the coupling mechanisms in the device and the semiconductor gain medium. Using these parameters, the model generates device characteristics in very good agreement with experimental results, which validate its use for future device design and optimization.

Ultraslow light propagation in a solid

With the spectral hole-burning effect resulting from coherent population oscillation in the homogenously broadened material， the ultraslow light propagation phenomenon with the group velocity as slow as 27.55±0.05m/s at room temperature in a ruby crystal is observed. And the group velocity in ruby crystal depends on the amplitude modulation frequency, the power of laser beam and the orientation of the crystal lattice. Lower frequency or higher power leads to slower group velocity.

On high-speed cross-gain modulation without pattern effects in quantum dot semiconductor optical amplifiers

In the regime with maximum linear gain in a quantum dot (QD) semiconductor optical amplifier (SOA), instantaneous gain modulation by change of the photon density is possible due to spectral hole burning effects. This, in turn, leads to the opportunity of ultrafast cross-gain modulation (XGM) without pattern effects at modulation bit-rates much higher than the interband relaxation rate. The maximum bit-rate for this pattern-effect-free XGM grows with increasing pump current density of the QD SOA.

Modeling and measurement of the wavelength-dependent output properties of quantum-well optical amplifiers: Effects of a carrier-dependent escape time

We present a model for quantum-well (QW) semiconductor optical amplifiers (SOAs) that considers bidirectional field propagation and the carrier densities in the barrier and QW regions. Carrier capture from the barriers into the QWs and carrier escape from the QWs to the barriers are included by means of effective capture and escape times. The model incorporates the wavelength dependence of the optical response of the active region and the effects of spectral hole burning via an analytical approximation to the susceptibility of the active material, which allows one to very effectively include the wavelength dependence of the output properties of the SOA. The model is used to analyze the experimental results obtained for a multiquantum-well SOA. The simulations results show a good agreement with the experimental data when a carrier-density dependent escape time from the QW to the barrier regions is considered.

Spectral hole burning in erbium-doped fiber amplifiers

A new theoretical/numerical model of the spectral hole burning (SHB) effect in erbium-doped fiber amplifiers (EDFAs) is suggested. A new measurement technique for SHB measurement is developed. Experiments are conducted to identify the particular mechanism of SHB. A computer simulation program is developed using this approach. The shape and depth of the spectral hole are in accordance with the suggested theory.

Optical characterization of spherical fine particles of glassy Eu 3+ doped yttrium basic carbonates

Spherical fine particles of glassy Eu 3+ doped yttrium basic carbonate, whose sizes are about 300 nm in diameter, are prepared by a co-precipitation method using urea as a precipitation generator. The optical properties concerned with the f–f transitions of Eu 3+ are investigated for the as-prepared powder and the powder samples calcined at 300 and 550 °C. As the calcination temperature becomes high, the absorption band (charge-transfer band) due to the electron transfer from O 2− to Eu 3+ shifts to lower energy. The forced electric dipole 5 D 0– 7 F J ( J=0,2,3,4) transition strengths and the inhomogeneous width of the 5D 0– 7F 0 luminescence spectrum of Eu 3+ increase with calcination temperature. From these results, the local structure around Eu 3+ is compared among the three powder samples. The persistent spectral hole burning (PSHB) effect is observed at 10, 70, and 120 K in the 7F 0– 5D 0 transition of Eu 3+ in all the samples. It is found that, at these temperatures, the burning reaction rate decreases with increasing calcination temperature. Probable PSHB mechanisms of the three samples are discussed.

Analytical description of spectral hole-burning effects in active semiconductors

An analytical description of the effects of spectral hole burning on the optical properties of active semiconductor materials is developed for fields that are slow compared to intraband relaxation times. Nonlinear gain compression and four-wave mixing effects are discussed.

Lateral-cavity spectral hole burning in quantum-dot lasers

Spectral hole burning effects are observed as strong spectral intensity modulations in the emission spectra of broad and narrow stripe quantum-dot lasers with ridge waveguide. The modulation is attributed to lateral-cavity resonances burning holes in the inhomogeneously broadened spectral gain profile of the quantum dots. Lateral cavity engineering is expected to be crucial for optimizing quantum-dot laser performance and for potential realizing of wavelength-stabilized devices.

Polarization peculiarity and its operation mechanism of the single longitudinal mode oscillation in a 633‐nm He‐Ne laser with internal mirrors

AbstractWe measured the polarization characteristics of laser tubes having the same specification for single mode oscillation in an internal‐mirror 633‐nm He‐Ne laser. From these results, we found that as the resonance conditions were continuously changed by the thermal variations in the laser tube length, the polarization could be classified into polarization that maintains a constant polarization direction and polarization whose direction continuously switches with its orthogonal direction. To explain this operation mechanism, we simulated a two‐mode equation that accounts for the orthogonal polarization mode. From this result, we showed that the two polarization (natural) axes produced by the presence of minute loss and phase anisotropies in the laser tube generate a peculiar polarization property caused by quantitative differences in these anisotropies. We also found that the spatial hole burning effect between the two modes exists to the same degree as the spectral hole burning effect. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(7): 48–56, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10019

Theoretical analysis of spectral hole burning and relaxation oscillation in all-optical gain stabilized multichannel erbium-doped fiber amplifier (EDFA)

The spectral hole burning effects and gain dynamics of all-optical gain clamped multichannel erbium-doped fiber amplifiers (EDFAs) are modeled. The two-level laser model is used to write the propagation and rate equations of the inhomogeneous laser medium. The governing equations are an uncountable system of partial differential equations (PDEs). After some mathematical manipulations, averaging over the fiber length and introducing an approximation method, the system of PDEs is converted to a finite system of ordinary differential equations (ODEs). The gain dynamics and hole burning of an all-optical stabilized multiwavelength EDFA and the transient response of an optical fiber inverter are analyzed by the solution of the system of ODEs. Theoretical results are in good agreement with the published experimental result.

Preparation and optical properties of capped-CdSe nanocrystals

Capped-CdSe nanocrystals were synthesized by colloidal method and almost monodisperse nanocrystals were obtained by size selective precipitation. Persistent spectral hole-burning (PSHB) effects of the CdSe nanocrystals suspended in an organic solvent glass matrix were examined at liquid-He temperature. Prominent spectral changes were not observed for the irradiation of the burning light of 15 mW/cm 2 at the peak position of the exciton absorption band. In single nanoparticle spectroscopy of dilute CdSe samples, the fluorescence emitted by small aggregates of the nanocrystals were observed and vanished continuously by the irradiation of strong laser beam. Detection of the single dot itself is not realized, mainly due to the background noise.

Spectral hole burning effects on partially loaded,19 nm bandwidth, 6246 km longEDFA lightwave transmission system

Spectral hole burning (SHE) is a significant phenomenon for wide-bandwidth EDFA-based lightwave transmission systems. For the first time the effects are reported of SHB on the Q-performance for a partially loaded, 19 nm bandwidth, 6246 km system. Idler tones are shown to both flatten the gain shape and improve the performance for such a system.

Wavelength- and Angle-Selective Optical Memory Effect by Interference of Multiple-Scattered Light

We report observations of a new optical memory effect in Sm-doped ZnS nanocrystals and elucidate its mechanism. One of the salient properties of this effect is that the incident angle as well as the wavelength of incoming light is memorized with high resolution. We show that this effect is not based upon spectral selection of homogeneous absorption lines as in the persistent spectral hole-burning effect but upon recording of interference patterns of multiple-scattered light in disordered media.

Simple dynamic model of all-optical gain-clamped erbium-doped fiber amplifiers

A simple dynamic model of laser-gain clamped erbium-doped fiber amplifiers (EDFAs) using ordinary differential equations is presented. The model not only provides a fast means of calculating EDFA gain dynamics, but also shows explicitly how the laser relaxation oscillation frequency and damping constant are affected by design parameters through analytical expressions. It is shown that the dynamic power excursion caused by relaxation oscillations can be reduced by increasing the oscillation frequency. The simplified model has two limitations: first, the amplified spontaneous emission (ASE) spectrum is not fully resolved and the noise figure can not be studied; second, the effect of spectral hole burning, which also causes gain excursion, can not be modeled. The first limitation can be removed by ASE-resolved modeling, where the concept of average inversion is also utilized to save computing time.

Amplification of strong picosecond optical pulses in semiconductor optical amplifiers

Numerical simulations have been undertaken to investigate the amplification of strong picosecond optical pulses in semiconductor optical amplifiers (SOAs), taking into account carrier heating, spectral holeburning, two-photon absorption (TPA) and ultrafast nonlinear refraction (UNR) effects. It is shown that both the TPA and UNR play important roles in determining the output pulse properties if the pulse energy is larger than ~0.5 pJ, and that these effects can be significantly enhanced with increased pulse energy and decreased pulse width as well as with higher small signal gain of the SOA. Results also indicate that, for larger input pulse energy, the symmetry of the amplified optical pulse can be controlled simply by adjusting the injected current.

Optically induced polarization rotations in CdTe/CdMnTe multiple quantum wells

We report large polarization state rotations of a weak pulsed beam in CdTe/CdMnTe quantum wells photoinduced by intense circularly polarized pulsed pump beam. Time-resolved analysis of the effect shows that, at moderate pump fluences, the polarization state rotation is due to the combined effect of many-body interactions and spectral hole burning at early times and to photoinduced magnetization at longer ones. At higher pump fluences, space filling and degenerate four-wave mixing become important. At low pump fluences (few μJ/cm2) already the polarization rotation photoinduced at early times can be as large as a few degrees making these multiple quantum wells potential candidates for applications.