J.E. Carroll

Dynamic analysis of radiation and side-mode suppression in a second-order DFB laser using time-domain large-signal traveling wave model

In this paper, we have developed a relatively simple algorithm to calculate the large-signal dynamic response of DFB lasers by solving the time-dependent coupled wave equations directly in the time domain. The spontaneous emission noise, longitudinal variations of carrier (hole burning) and photon densities as well as that of the refractive index are taken into consideration. To demonstrate the power of this straightforward algorithm, the model shows how the side-mode suppression ratio in devices with high /spl kappa/L and a /spl lambda4: phase shift is significantly affected by the radiation in the second-order DFB laser. The time-dependent radiation pattern in grating-coupled surface-emitting lasers is also calculated for the first time. >

Large-signal dynamic model of the DFB laser

A computer model is proposed to analyze the characteristics of distributed feedback (DFB) lasers. The model is based on time-dependent coupled wave equations, with spontaneous emission taken into account. In order to avoid uncertain phase factors in spontaneous emission, a method of converting field equations to power equations in a matrix format before computation is introduced. The steady-state LI curve and transient response to the pulse excitation are calculated in the lambda /4 phase-shifted DFB lasers. The longitudinal variations of the carrier and photon densities as well as of the refractive index are considered in the model. >

Dynamics of monolithic passively mode-locked semiconductor lasers

Monolithic colliding pulse mode-locking (CPM) in semiconductor lasers is compared with self colliding pulse mode-locking (SCPM) through a large signal dynamic computer model which incorporates most of the significant features of semiconductor lasers. These include gain saturation, spontaneous emission, the gain-frequency relation, and the line-width enhancement factor. This new model replicates many of the published experimental results and also gives additional insight into the internal operation of the device. In particular, gain saturation combined with the standing waves created by colliding pulses within the saturable absorber produce a transient gain grating. This is found to have significant effects in locking either the even or the odd modes together in CPM. A performance comparison between CPM and SCPM is completed and some key design parameters of both configurations are explored. >

Ultrafast switching in polarization-bistable laser diodes

A new form of pitchfork-bifurcation-like polarization bistability in laser diodes that has major speed advantages over conventional S-shaped polarization bistability is reported. From the rate-equation analysis, it is shown that flip-flop operation with bit rates of higher than 50 Gbits/s may be achieved.

Multiport homodyne detection near the quantum noise limit

A detailed description of a multiport detection experiment operating close to the quantum noise limit is presented. Simultaneous phase and amplitude measurements were made on signals of only five photons energy with a signal-to-noise ratio that was accountable to within 2 dB of the quantum limit. Statistical examination of the noise showed excellent agreement with the gaussian distribution predicted by both the semiclassical and fully quantum theories.

The effect of cavity length on picosecond pulse generation with highly rf modulated AlGaAs double heterostructure lasers

We report the generation of picosecond pulses with oxide‐isolated‐stripe, double heterostructure GaAlAs laser diodes of varying lengths. A pulse width of 15 ps at a repetition frequency of 1 GHz is achieved with a 60‐μm‐long device. The experiments indicate a linear relation between pulse width and laser length.

Semiconductor 1.55 /spl mu/m laser source with gigabit/second integrated electroabsorptive modulator

A 1.55 /spl mu/m laser source with low chirp and high speed can be achieved when a single-mode DFB laser is modulated by an integrated quantum-confined Stark effect electroabsorptive modulator. The dynamic characteristics of such a device are simulated by a time domain, large signal dynamic model. The simulation demonstrates that the frequency chirp has two components: 1) changes of the refractive index induced by variation of the absorption coefficient during the modulation and 2) changes in the lasing frequency caused by changes in the effective residual facet reflection as the external modulator is switched on and off. Optimization by choice of the operating wavelength and coupling coefficient in the lasing section is discussed. >

Autocorrelation systems for the measurement of picosecond pulses from injection lasers

The paper reviews briefly the different structures, alignment techniques and performance of autocorrelation systems for the measurement of picosecond pulses generated by injection lasers suitable for optical communications. The interpretation of results obtained with such systems is also discussed. Specific reference is made to a system operating at 1-3 μm wavelength. The aim is to provide a helpful account of such systems for those starting in the field of picosecond electronics. In order to illustrate the technique some new results are presented on mass-transport injection lasers with low thresholds.

A low-frequency analog for a Gunn-effect oscillator

After a brief introduction to the Gunn effect and an explanation of the proposed equivalent circuit of the Gunn diode, a low-frequency (5 Hz) lumped-circuit analog is described. The analog is able to simulate the initiation and circuit quenching of the domain, the transit time of a dipole domain, and the dynamic negative-resistance characteristic associated with the domain. Thus the analog can qualitatively account for many properties of the dipole domain modes. A short section also shows how, within certain limitations, the LSA mode can be investigated by means of the analog. The analog enables the behavior of the Gunn diode to be studied under various forms of loading, and the results to be related to a wide range of actual diodes in microwave circuits by a simple scaling process. The sciencies of various modes can be compared. Photographs are presented of an oscilloscope display showing the relevant current and voltage waveforms (including the domain voltage) for a pure resistive load, a parallel resonant load, and a series inductive load. The provision for a direct display of domain voltage means that a particularly clear visual distinction is possible between transit-time and circuit-quenched modes of oscillation. Tuning by variation of the external load is demonstrated; the importance of the semiconductors current peak-to-valley ratio and of the choice of transit time in determining the efficiency in a given mode is illustrated. A possible explanation for the reported observation of subharmonics is provided by the analog, on the basis of alternate modes, i.e., a cycle of circuit-quenched operation followed by a cycle of transit-time operation. The limitations of the analog are discussed together with ways in which some of them could be overcome.

Chirp reduction using push-pull modulation of three-contact lasers

Low-chirp modulation of three-contact distributed-feedback (DFB) lasers is experimentally demonstrated, using a push-pull modulation scheme. When the laser was modulated with a 2.0-Gb/s pseudorandom bit sequence, the -20-dB linewidth was measured to be 0.055 nm after deconvolving the measurement equipments response. The results are simulated using a large-signal time-domain model that illustrates the mechanisms responsible for the low chirp. The grating structure is shown to have a significant effect on the performance of the device under push-pull modulation.<<ETX>>