Multimode Semiconductor Laser Research Articles

Step-tunable all-optical wavelength conversion using cavity-enhanced four-wave mixing

Step tuning of a wavelength converter using cavity-enhanced four-wave mixing in a multimode semiconductor laser is experimentally and theoretically demonstrated. The converter is modulation-format transparent and is shown experimentally to have a high conversion efficiency (>-10 dB) and to be step-tunable over a large conversion range (>2.5 THz). A mathematical model of the wavelength converter is derived and is used to simulate step tuning of this device and to examine the relationship between conversion efficiency and information bandwidth of the converter.

Dual-wavelength superfluorescent fiber emitter

The feasibility of constructing a dual-wavelength, spatially single-mode, superfluorescent fiber emitter on the basis of erbium optical fibers with pumping by multimode semiconductor lasers is demonstrated. The emitter is fabricated by all-fiber technology and has a power output in excess of 10 mW, an average emission wavelength of 1.54 μm, and a spectral resolution of 27.5 nm at component linewidths of 3 nm and 9 nm. The depolarization of the radiation from the emitter as it propagates in an anisotropic, single-mode fiber waveguide is investigated.

Visualization of 50 MHz Surface Acoustic Wave Propagation Using Stroboscopic Phase-Shift Interferometry

A Stroboscopic phase-shift interferometry has been developed to visualize surface acoustic wave (SAW) propagation on SAW devices quantitatively. The developed interferometry is a Fizeau-type one with a multi-mode semiconductor laser diode and an optical isolator. With the laser light illuminating stroboscopically, observed interference intensity gives information about average displacements of the vibrations. Fifty MHz SAW propagation on the surface of the SAW device has been measured with the interferometry. Distribution of the SAW along the propagation path has been observed, whose amplitude is 3 nm (p-p). Repetition accuracy evaluated with the root mean square method is 1/2500 of the laser wavelength. The system is useful for estimating and improving performances of micro-devices.

Five wavelength interrogation technique for miniature fibre optic Fabry-Pérot sensors

Five equally spaced wavelengths from a multimode semiconductor laser diode source are used to provide five phase shifted intensity outputs from a low finesse Fabry-Pérot interferometer, from which the absolute phase, modulo 2π, can be determined. The use of five measurements is shown to reduce the phase errors arising from multiple reflections by two orders of magnitude compared to techniques using two or three intensity outputs. In addition, errors arising from miscalibration of the cavity are also reduced by up to two orders of magnitude compared to two, three and four phase shifted intensity outputs. Phase errors are discussed and the technique is demonstrated for temperature measurement. A 70°C range and 0.07°C resolution are obtained.

The dependence of carrier lifetime on spectral width in multimode semiconductor lasers

Comprehensive measurements of the dependence of the carrier lifetime, eye pattern, and power penalty on the spectral width in multimode semiconductor lasers for a gigabit lightwave transmission system are presented. The results show that the carrier lifetime, eye pattern, and power penalty caused by mode partition noise (MPN) are strongly dependent on the source spectral width. The lasers with shorter carrier lifetimes exhibit a narrow spectral width, and hence show less MPN, a better eye opening, and a lower power penalty. A theoretical calculation of the MPN-induced power penalty is in good agreement with the measured system penalties. The likely cause for narrow spectral width with shorter carrier lifetime of the lasers is due to the smaller linewidth enhancement factor a caused by a higher doping concentration in the lasers.

Dispersion-compensated 333-km 10-Gb/s transmission using mid-span spectral inversion in an injection-locked InGaAsP V-groove laser

We have demonstrated a 1.5-μm, 333-km, 10-Gb/s transmission system in conventional 1.3-μm zero-dispersion-wavelength single-mode fiber, using mid-span spectral inversion In a multi-mode semiconductor laser. The inverted spectrum was generated via cavity-enhanced highly-nondegenerate four-wave mixing, for which the resonant gain in the injection-locked V-groove laser yields higher conversion efficiencies relative to those of travelling-wave amplifiers. The bit-rate×distance product of 3330 Gb-km/s is more than an order of magnitude better than the best previous result employing a semiconductor conjugator.

Effect of carrier lifetime on mode partition noise in multimode semiconductor lasers

The dependence of mode partition noise (MPN), and its association with the eye diagram and power penalty, on carrier lifetime in 1.3 μm InGaAsP multimode semiconductor lasers for a 1.2 Gbit/s lightwave transmission system was investigated. It was found that lasers with shorter carrier lifetimes showed less MPN, and hence, a better eye opening and a lower power penalty, than the lasers with longer carrier lifetimes. The significant dependence of MPN, eye opening, and power penalty on carrier lifetime in multimode semiconductor lasers suggests that the carrier lifetime of the laser, which depends on the laser design, can be used as an important parameter for characterizing the performance of high-speed lightwave transmission systems.

Optical-feedback-induced chaos and its control in multimode semiconductor lasers

The effects of optical feedback in multilongitudinal mode semiconductor lasers are studied through computer simulations. Two separate regimes are found based on the length of the external cavity. For long external cavities (external-cavity mode spacing larger than the relaxation-oscillation frequency), the laser follows a quasi-periodic route to chaos as feedback is increased. For short external cavities, the laser can undergo both quasi-periodic and period doubling routes to chaos. When the laser output becomes chaotic, the relative-intensity noise is greatly increased (by more than 20 dB) from its solitary-laser value. Considerable attention is paid to the effects of optical feedback on the longitudinal-mode spectrum. The stabilization of the mode spectrum and the reduction of the feedback-induced noise through current modulation are studied and compared with experimental results. Current modulation eliminates feedback-induced chaos when the modulation frequency and depth are suitably optimized. This technique of chaos control has applications in optical data recording. >

Circuit modelling of multimode semiconductor lasers and study of pulse broadening effect

A circuit model for the semiconductor laser based on multimode rate equations is developed. This extends the available results based on circuit models for singlemode lasers. The effect of fibre dispersion on the longitudinal modes is investigated by using the model in the simulation of a digital optical link.

Quantum correlation between longitudinal-mode intensities in a multimode squeezed semiconductor laser.

The intensity-noise properties of a constant-current-driven multimode semiconductor laser were studied theoretically and experimentally. It was shown that the total intensity noise of a pump-noise-suppressed multimode semiconductor laser was reduced to below the standard quantum limit even though the intensity noise of each individual mode had large excess intensity noise. This discovery stems from negative quantum correlations between longitudinal-mode intensities.

A low-cost surface laser light scattering spectrometer

A low-cost surface laser light scattering spectrometer for measuring interfacial tension and viscosity has been built and tested. The spectrometer is based on a cheap multimode semiconductor laser and an ordinary Si photodiode. In the case of fluids with moderate viscosities (e.g. hexane, ethanol and water) the spectrometer provides an accuracy as least as good as that obtained with the high-cost light scattering spectrometers proposed so far. Possible improvements of the spectrometer for expanding its range into the high viscosity region are discussed.

Laser mode partition noise in lightwave systems using dispersive optical fiber

Semiconductor laser mode partition noise (LMPN) can impair analog optical systems, but this phenomenon has not previously been well-characterized. Theoretical expressions for the noise spectra that result when light from a nearly single-mode or strongly multimode semiconductor laser is passed through a length of dispersive optical fiber are presented and have been tested experimentally. A widely used model is found to greatly overestimate the partition noise of a DFB laser; a model for the strongly multimode case is found to match experimental results for a multimode laser. It is observed that partition noise can be significant even for multimode lasers operating near the fiber dispersion minimum.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analytical expressions for the intensity and frequency noise of an individual mode in a multimode semiconductor laser with external optical feedback

Analytical expressions are derived for the intensity and frequency noise of each individual mode in a multimode semiconductor laser with external optical feedback. It is shown that in a two-mode laser the side-mode effect on the intensity noise is enhanced by the optical feedback which gives the maximum linewidth narrowing.

Amplification of semiconductor laser radiation in the wavelength range 1.24–1.3 μm by stimulated Raman scattering in an optical fiber

An investigation was made of the influence of weak semiconductor laser radiation on the spectrum of stimulated Raman scattering in a single-mode optical waveguide pumped by a YAG:Nd3+ laser emitting at 1.06 μm. The scattered radiation power increased by a factor exceeding 10 at the semiconductor laser wavelength. A small-signal dynamic gain reached 47 dB. Simultaneous amplification was observed of several modes of multimode semiconductor laser radiation with an intermode spectral interval of 1.3 nm.

Gain saturation in fiber Raman amplifiers due to stimulated Brillouin scattering

The effects of stimulated Brillouin scattering (SBS) on Raman gain are explored. Measurements of gain in a fiber Raman amplifier show a saturation at low gain levels. Experimental data and a theoretical model are presented, demonstrating that this saturation is due to pump depletion by SBS. This effect also leads to Raman gain fluctuations arising from mode partitioning in a multimode pump laser. Two ways to avoid the deleterious effects of SBS on the performance of Raman amplifiers are suggested. One is to use a multimode semiconductor laser with a modal linewidth of the order of a few hundred megahertz, which leads to a strongly reduced Brillouin gain coefficient. The second approach is to use very short pump pulses in a backward configuration. >

Dispersion penalty for 1.3 mu m lightwave systems with multimode semiconductor lasers

The effect of fiber dispersion on the performance of lightwave systems is analyzed for the case where multimode semiconductor lasers operating near the zero-dispersion wavelength of the single-mode fiber are used as sources. Both the intersymbol interference and the mode-partition noise are considered in the discussion of dispersion-induced power penalties. The theory is in agreement with an experiment in which the bit error rate is measured for lasers at various bit rates. The tolerable limits on the deviation of the laser wavelength from the zero-dispersion wavelength are obtained for a 1.3- mu m system operating at 1.7 Gb/s. Monte Carlo simulations are used to predict the effect of mode-partition noise on the performance of such high-speed lightwave communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Eye-length measurement by interferometry with partially coherent light

With a multimode semiconductor laser we have been able to measure the optical length of the eye within a precision of 0.03 mm. A first series of in vivo measurements acoustically determined eye length.

Coherence multiplexing using a parallel array of electrooptic modulators and multimode semiconductor lasers

The paper presents a rather new approach of electrooptic modulation of light suitable for coherence multiplexing N transmission channels. A parallel array of N electrooptic multiplexers powered by multimode semiconductor lasers is used for imprinting the signals on light simultaneously. It is shown that the electrooptic multiplexers have to generate optical time delays whose optimal values are ruled by the sequence 1/2N \cdot \delta f, 1/N \cdot \delta f, 3/2N \cdot \delta f , etc., where \delta f is the intermodal separation of the laser longitudinal modes. The performance of the system is discussed in terms of crosstalk, number of possible channels, and signal power. The demonstration of the method is reported in the area of optical communications with the transmission of base-band video signals.

Analysis of mode separation in multichannel branching waveguides

Spatial separation of modes is important in multiport switching and wavelength multiplexing for integrated optics, and in controlling the spatial modes in multimode semiconductor laser structures. It has been recently shown that the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> normal modes of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> - mode channel waveguide can be separated by branching into <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> single-mode channels whose propagation constants are all different. By means of examples, we answer two questions about this mode separation scheme. 1) How widely separated must the channels be in order for each mode to be concentrated in a different one of the channels? 2) How small must the branching angle be in order for the power to remain in the launched mode? The effects of wavelength, dimensions, and refractive index step are discussed. Important conclusions are that the branching angle must be rather small, of the order of a few milliradians, and that it is helpful to have the largest possible difference in the widths of the guiding channels, thereby giving them the largest possible difference in uncoupled propagation constants.

Gain nonlinearities in semiconductor lasers: Theory and application to distributed feedback lasers

The gain spectrum in semiconductor lasers is affected by the intensity-dependent nonlinear effects taking place due to a finite intraband relaxation time of charge carriers. We obtain an analytic expression for the nonlinear gain in multimode semiconductor lasers using the density-matrix formalism. In general, the nonlinear gain is found to consist of the symmetric and asymmetric components. The asymmetry does not have its origin in the carrier-induced index change, but is related to details of the gain spectrum. The general expression for the nonlinear gain is used to discuss the range of single-longitudinal-mode operation of distributed feedback lasers. It is also used to obtain an analytic expression for the self-saturation coefficient and to compare the predicted value to the experimental value for both GaAs and InGaAsP lasers. The agreement between the theoretical and the experimental values supports the hypothesis that spectral hole burning is the dominant mechanism for the gain nonlinearities in semiconductor lasers.