Spatial Hole Burning Effect Research Articles

Analysis, fabrication, and characterization of 1.55-μm selection-free tapered stripe DFB lasers

A new selection-free laser structure for monomode behavior based on an engineering of the stripe geometry is proposed. The structure is designed in order to eliminate facet phase effects and laser to laser variations. The effect of spatial hole burning is simulated and an enhancement of the sidemode suppression ratio (SMSR) with power is predicted and measured. Moreover, the sensitivity to technological fluctuations is theoretically analyzed. Experimentally, lasers having a 47-dB SMSR at 10 mW and an excellent homogeneity from laser to laser is obtained on a two inch wafer.

Simulating the modulation response of VCSELs: the effects of diffusion capacitance and spatial hole-burning

The comprehensive semiconductor laser simulator, Minilase, has been extended to simulate the dynamic response of vertical cavity surface emitting lasers (VCSELs). Unlike conventional rate equation approaches, Minilase is capable of correctly modelling nonlinear gain effects in the modulation response without the introduction of an empirical gain suppression factor. Various oxide-confined single-mode VCSEL structures are simulated with Minilase to examine the effects of real-space carrier transport on the modulation response in both vertical and lateral directions. It is demonstrated that a roll-off in the dynamic response is closely associated with the diffusion capacitance caused by vertical carrier leakage. By either grading the separate confinement regions or reducing the thickness of the SCH cavity, the vertical carrier leakage is shown to be greatly suppressed, and the modulation response is significantly improved. Simulations also reveal that the nonuniform HE11-like transverse optical intensity in the quantum well results in an overdamping of the relaxation oscillation, and this effect is greatly reduced by making the electrical aperture smaller than the optical aperture. Finally, a comparison with experimental results is presented and discussed.

Analysis of dual-wavelength oscillation in a broad-area diode laser operated with an external cavity.

Apodizing holographic gratings used in an external cavity have shown to be effective to control the modal content of multimode broad-area diode lasers, providing single longitudinal-mode and single lateral-mode emission. They can also be designed to provide Littrow reflection at two wavelengths. We observed stable oscillation at two wavelengths in a diode laser with an external cavity ended with such a grating. This is not a common behavior for homogeneously broadened gain media. We present simulations of the behavior of this laser based on a rate equation analysis. The effects of spatial hole burning and spontaneous emission are examined.

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

Concave tapered grating design of DFB laser at high power operation for reduced spatial hole-burning effect

Distributed feedback laser with concave tapered grating (CTG-DFB) is introduced and theoretical analysis of λ/4 phase-shifted CTC-DFB laser is presented. It is shown that, this structure has flat infra-cavity optical field and effectively reduces the spatial hole burning at high injection current. In addition, in this investigation the output power, linewidth and gain margin of the quarter wavelength phase-shifted distributed feedback (QWS-DFB) laser is compared with CTG-DFB laser. While the output power of proposed CTG structure is approximately equal to output power of QWS-DFB laser it has a smaller linewidth. The variation of lasing wavelength of CTG structure is very stable against the increase of injected current density.

Relaxation oscillations in a laser with a Gaussian mirror.

We present an analysis of the relaxation oscillations in a laser with a Gaussian mirror by taking into account the three-dimensional spatial field distribution of the laser modes and the spatial hole burning effect. In particular, we discuss the influence of the Gaussian mirror peak reflectivity and a Gaussian parameter on the damping rate and frequency of the relaxation oscillation for two different laser structures, i.e., with a classically unstable resonator and a classically stable resonator.

Extended Model of a VCSEL with Non-Uniform Laser Structure

Results of investigation of the oxide-confined vertical-cavity laser (VCSEL) including non-uniformity of diffusion processes, dynamical effects, and transparent cavity modes are presented. The influence of the spatial hole burning effect on laser characteristics is investigated and discussed. It was shown that decreasing of oxide mesa radius leads to increasing of the modulation bandwidth of the VCSEL. Obtained results allow optimizing laser properties by changing of geometrical parameters.

ELIMINATION OF CHAOS IN MULTIMODE, INTRACAVITY-DOUBLED LASERS IN THE PRESENCE OF SPATIAL HOLE-BURNING

In this paper possibilities of a stabilization of large amplitude fluctuations in an intracavity-doubled solid-state laser are studied. The modification of the cross-saturation coefficient by the effect of spatial hole-burning is taken into account. The stabilization of the laser radiation by an increase of the number of modes, as proposed in [James et al., 1990b; Magni et al., 1993], is analyzed. It is found that when the cross-saturation coefficient is modulated by the spatial hole-burning the stabilization is not always possible. We propose a new way of obtaining a stable steady-state configuration based on an increase of the strength of nonlinearity, which leads to a strong cancellation of modes, so that during the evolution all modes, but for a single one, are canceled. Such a steady-state solution is found to be stable with respect to small perturbations.

Mode-locking operation of Nd:LuYLF

We report mode-locked laser operation of a diode-pumped Nd:Lu:YLiF4 crystal. This new laser material allowed generation of pulses shorter than those obtained from the well-established laser me- dium Nd:YLiF4 in the same experimental configuration. The mode- locking regime was obtained by introducing a very weak acousto-optical modulation with Kerr-lens-induced pulse shaping. A suitable negative value of the intracavity group-velocity dispersion was introduced to en- hance the initiation and stabilization of the regime. Pulses as short as 4.5 ps were readily obtained, without troublesome optimization procedures. To allow comparison with previously reported results for Nd:YLiF4 sys- tems, we review the importance of spatial hole-burning effects in mode- locking operation. © 2001 Society of Photo-Optical Instrumentation Engineers.

Widely tunable pulse durations from a passively mode-locked thin-disk Yb:YAG laser

We demonstrate a passively mode-locked thin-disk Yb:YAG laser that generates solitonlike pulses with durations that are continuously tunable in a very wide range from 3.3 to 89 ps or from 0.83 to 1.57 ps. The average powers are typically ~12 W . Previously [Opt. Lett. 25, 859 (2000)], only pulse durations in a narrow range near 0.7 ps could be obtained from such lasers because of the effect of spatial hole burning. We achieved this much wider range by constructing a laser cavity with two different angles of incidence on the thin disk, which greatly reduces the effect of spatial hole burning.

Passive mode locking of thin-disk lasers: effects of spatial hole burning

We recently demonstrated that passive mode locking of a thin-disk Yb:YAG laser is possible and that this concept leads to sources of femtosecond pulses with very high average power. Here we discuss in detail the effect of spatial hole burning on the mode-locking behavior of such lasers. We have developed an efficient numerical model and arrive at quantitative stability criteria which agree well with experimental data. The main result is that stable soliton mode locking can in general be obtained only in a certain range of pulse durations. We use our model to investigate the influence of various cavity parameters and the situation for different gain media. We also consider several methods to reduce the effect of spatial hole burning in order to expand the range of possible pulse durations.

Effect of spatial hole burning on injection-locked vertical-cavity surface-emitting laser arrays

Injection locking of vertical-cavity surface-emitting laser arrays is analyzed at steady state, including the effect of spatial hole burning. A free-running laser array (i.e., without injection), that operates well-above threshold, can exhibit multimode oscillations. Consequently, each of the free-running modes (at different frequencies) needs a different locking injection power. For low pump levels, just above threshold, the array is single mode and, as expected, the results bear a close resemblance to those of the average gain analysis, which ignores spatial hole burning.

Impact of structural changes in the corrugation on the DFB laser characteristics

A reduction of the spatial hole-burning (SHB) effect may be achieved by a change of the structural parameters in DFB LDs. Lasers presenting phase-shift discontinuities along the corrugation (PS DFB) or changes in the grating height (DCC DFB), or both, are seen to be more attractive in the high-power regime than conventional DFB laser diodes. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 352–355, 2000.

Multi-wavelength Operation of an Er3+-doped Fiber Laser at Room Temperature with a Novel Optical Fiber Mach-Zehnder Interferometer

A novel multi-wavelength erbium-doped fiber laser with a double-pass Mach-Zehnder fiber interferometer acting both as a comb filter and as a reflection mirror is demonstrated. The spatial hole burning effect introduced by the standing wave cavity configuration enables the simultaneous operation of multiple wavelengths in the homogeneously broadened erbium-doped fiber at room temperature. In the experiment, simultaneous oscillation of four wavelengths at room temperature has been obtained.

Distributed feedback lasers with refractive-index-modulated upper cladding layer of the grating for reducing the spatial hole-burning effect

A refractive-index-modulated (RIM) DFB laser, in which the refractive index of the center region of the upper cladding layer of the grating is smaller than that of the side regions, is proposed to obtain an effective λ/4 phase shift in the center region and a distributed coupling coefficient effect simultaneously. Simulation results show that the single-mode gain difference of RIM–DFB lasers is larger than that of corrugation-pitch-modulated (CPM) DFB lasers over the whole range of injection current due to the distributed coupling coefficient effect. The variation of the lasing wavelength of RIM–DFB lasers as a function of injection current is small compared to that of quarter-wavelength-shifted DFB lasers and CPM–DFB lasers. In addition, the effect of the length of the center region of RIM–DFB lasers on the above-threshold characteristics is investigated. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 173–176, 2000.

Study of spatial hole burning in distributed phase-shifted distributed feedback semiconductor lasers

A new algorithm based on transfer matrix method is given to analyse a new distributed feedback (DFB) structure–the distributed phase- shifted (DPS) DFB laser. In the small signal analysis, a new model is proposed with this algorithm. Considering different structures of DFB laser diode, we define a spatial-hole-burning (SHB) factor to measure the SHB effect. Compared with the λ/4 phase-shifted DFB and 3 phase-shifted DFB, the DPS-DFB structure shows a superior characteristics both in static and dynamic behavior.

A wavelength-tunable curved waveguide DFB laser with an integrated modulator

A distributed-feedback (DFB) laser with a curved waveguide in the active region integrated with an electroabsorption modulator is studied experimentally and theoretically. The modulator controls the lasing wavelength of the DFB laser by acting as an optical phase shifter. Our model, which is based on the transfer matrix method, is used to simulate this multisection device with the curved waveguide, self-consistently including the effects of spatial hole burning (SHB). The model explains the features and wavelength-tuning behavior of the spectrum and shows good agreement with experimentally measured spectra. We also show theoretically that the curved waveguide suppresses the longitudinal photon density profile of the device compared with a straight waveguide case, which implies reduced SHB effects.

Spatial hole-burning effects in the amplified-spontaneous-emission spectrum of the nonlasing supermode in semiconductor laser arrays

The amplified spontaneous emission spectrum of the light field in the non-lasing supermode of two coupled semiconductor lasers is analyzed using linearized Langevin equations. It is shown that the interference betweeen the laser mode and the fluctuating light field in the non-lasing mode causes spatial holeburning. This effect introduces a phase sensitive coupling between the laser field and the fluctuations in the non-lasing mode. For high laser fields, this coupling splits the spectrum of the non-lasing mode into a triplet consisting of two relaxation oscillation sidebands which are in phase with the laser light and a center line at the lasing frequency with a phase shift of pi half relative to the laser light. As the laser intensity is increased close to threshold, the spectrum shows a continuous transition from the single amplified spontaneous emission line at the frequency of the laser mode to the triplet structure. An analytical expression for this transition is derived and typical features are discussed.

Computational model of Q-switch Nd:YAlO3 dual-wavelength laser

A rate equation model with spatial hole-burning effect is built to calculate the Q-switch Nd:YAlO3(Nd:YAP) simultaneous dual wavelength laser. We find that 1341.4 and 1079.5 nm lasers can be simultaneously generated in a linear cavity by controlling the output coupling rates of the two coherent radiations. In contrast, a Y cavity and devices to control relative Q-switch delay were necessary for the dual wavelength Nd:YAG laser in previous work. Also with this model, some optimum parameters’ relationships to pump energy are investigated.

1.1-W continuous-wave 1480-nm semiconductor lasers with distributed electrodes for mode shaping

Diffraction-limited high-power devices may suffer from self-focusing effects due to nonuniform gain saturation. In this letter, we propose the concept of the distributed electrode, which allows one to improve the modal behavior of these lasers and to reduce spatial-hole burning effects by preferentially localizing current injection in the center of the structure, therefore shaping the optical mode. Utilizing this concept, we have realized unstable cavity lasers exhibiting single-lobe far-field patterns. We report the first realization of flared unstable cavity lasers emitting at 1480 mm with maximum output powers up to 1.1-W continuous-wave and external efficiencies as high as 0.45 W/A.