IEEE Photonics Technology Letters

In this letter, we numerically study the relationship between 40-Gb/s-based dense wavelength-division-multiplexing (DWDM) transmission performance and chromatic dispersion in two different transmission lines. We show that the optimum chromatic dispersion region for improving the DWDM transmission performance varies with the type of transmission line. We also show that a hybrid transmission line has a greater potential to resist any change in the dispersion slope compensation characteristics than a single fiber transmission line with a dispersion compensation fiber module. Finally, we show that chromatic dispersion of more than 12 ps/nm/km in a hybrid transmission line is optimum for a 40-Gb/s-based DWDM transmission system by taking the design of a dispersion compensating fiber into account.

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.

Oxide-confined top-emitting vertical-cavity surface-emitting-laser (VCSEL) 8 × 8 arrays were designed and fabricated with ultralow thresholds. The arrays were flip-chip bonded onto sapphire substrates and mounted in pin-grid-array packages as optical transmitter arrays. By using the offset-contact bonding process, we were able to obtain very high yield for hybridized devices without damaging the VCSEL mesas. Room-temperature lasing thresholds below 70 μA were found from some of these packaged VCSELs with measured oxide apertures 2.6 μm in diameter. The emission spectrum at an injection current of 70 μA showed a full-width at half-maximum linewidth of less than 2.5 A. Polarization properties were also confirmed from the output of the device. The superior performance was attributed to the optimized size and placement of the confinement aperture and the precise alignment of the gain profile of the active region to the mode of the resonant cavity.

A simulation method that targets all possible combinations of first- and second-order polarization-mode dispersion (PMD) is described. Use of this method in importance-sampled Monte Carlo simulations yields a more comprehensive determination of PMD-induced system penalties than first-order biasing alone and significantly speeds up the calculation of outage probabilities, particularly when PMD compensation is employed. The technique is demonstrated by using it to calculate the probability distribution function (pdf) of second-order PMD and the joint pdf of the magnitude of first- and second-order PMD.

In this letter, we present the study of the small signal modulation response of a monolithic twin ridge laterally coupled diode lasers. Such structures have been extensively theoretically studied for their promising characteristics as high-speed optical sources for optical communications, and in this work we demonstrate the increase of the small signal bandwidth beyond the relaxation oscillation frequency with the appearance of a second peak in the small signal response due to the laterally mode locking of these two emitters.

The authors carry out a numerical and experimental comparison between three different techniques for chromatic dispersion compensation on a terrestrial 40-Gb/s system. They are: periodic dispersion compensation at the amplifier places; the same but with initial prechirp; and dispersion compensation all at the end of the system by means of highly dispersed pulses. Numerical results are consistent with experimental ones and suggest the most convenient compensation technique with respect to fiber type (G.652 or G.655) and pulsewidth (3-10 ps).

We demonstrate a new concept for InGaAsP-InP 1.55-μm Fabry-Perot lasers integrated with spot size converters using type-A antiresonant reflecting optical waveguides. The fabrication of such devices allows to avoid the growth of thick layers of quaternary material with low Ga and As fraction, which are difficult to achieve and grow. Reduced far-field divergence angles (10/spl deg/ × 27/spl deg/) and improved coupling to cleaved standard single-mode fibers (2.6-dB coupling loss) are achieved. The proposed device is compatible with conventional epitaxial techniques and lithographic methods.

We analyze the ultimate performances of an all-optical sampler based on ultrafast bulk GaAs saturable absorbers created by ion irradiation. The ion irradiation technique provides a unique way to adapt the sampler resolution to the optical pulse width since the absorber relaxation time can be adjusted over more than three decades with the irradiation dose. Subpicosecond time resolutions with pulse contrast of /spl sim/100 are achievable by using high irradiation doses. In standard conditions, the sampler noise performances are limited by the detector noise and sampling pulse amplitude fluctuations. Picosecond laser diode pulses with an average power of less than one microwatt are already measurable. The ultimate limit is imposed by the absorber luminescence shot noise.

InP vertically coupled microdisk resonator/waveguide switching devices with an electroabsorptive (EA) active region are demonstrated for the first time. The devices exhibit single-mode operation, large free spectral range of 10.5 nm and a high quality factor of 5700. The EA effect provides a way of loss-trimming the resonant characteristics. Active switches, routers, and fast modulators based on these devices are envisioned as part of a WDM system.

In all-optical gate switches that employ the cascaded second-order nonlinear effect in quasi-phase-matched (QPM) LiNbO/sub 3/ devices, walkoff between the fundamental and second harmonic pulses is very large. The authors experimentally show that crosstalk of the switch induced by such walkoff limits the switching speed, but that the switching speed can significantly be enhanced by walkoff compensation. Using a 20-mm-long QPM LiNbO/sub 3/ waveguide device, the authors switch one of twin pulses separated by 6.25 ps without crosstalk, showing the possibility of switching a 160-Gb/s signal.