Frank R. Shepherd

Gain-coupled DFB integrated with a Mach-Zehnder modulator for 10 Gb/s transmission at 1.55 um over NDSF

We review recent progress at Nortel Technology on the monolithic integration of a truncated-well 1 .55 im gain-coupled DFB with a Mach-Zehnder (MZ) modulator. Integrated MZ designs for both positive and negative chirp are described and analyzed. Link tests at 10 Gbit/s over 80 km ofnon-dispersion-shifted fiber (NDSF) show a negative dispersion penalty of 1 .1 dB, and steep BER curves with no evidence of flooring. The receiver sensitivity is found to be independent of pattern length, and independent ofthe laser operating wavelength, indicating negligible thermal, optical, and electrical crosstalk. Keywords: Integration, Mach-Zehnder, Gain-Coupling

Effect of process-induced stress in InP/InGaAsP weakly confined waveguides

InP/InGaAsP weakly confined wave guides, are of interest for the fabrication of a variety of optoelectronic devices, including optical cross point switches. Previous studies have shown that stress from metallization alters the behavior of these waveguides and the strain-induced changes in refractive index have been investigated by studying the degree of polarization (DOP) from the facets of ridge waveguide (RWG) lasers. However, in devices intended for waveguide routing or switching, e-beam deposited TiPtAu contacts, caused broadening and splitting of the optical near field mode profile after thermal annealing and increased waveguide loss. In this paper, we report the results of a study of process-induced changes on the optical near field mode profile, for different dielectric depositions, metallizations and anneal cycles. It was found that the addition of a layer of the TiPtAu. This not only eliminated the mode splitting, but for sufficiently high values of compressive stress, was found to actually sharpen the mode and enhance the guiding. On the basis of these results stable waveguides, suitable for routing or switching were achieved for a range of device parameters, operating conditions and process parameter variations.

Compact strongly gain-coupled DFB laser array with integrated BFMA arrays for simultaneous 4-λ 2.5 Gb/s 100-km WDM transmission

A low cost and high performance 4-(lambda) WDM DFB laser array employing a new strong gain-coupling laser design and a novel compact package approach is developed for optical network application. The WDM4 laser array is capable of simultaneous operation with 2.5 Gb/s 100 km NDS fiber transmission.

A novel compact optical cross-point switch on InP

In this paper, we propose and demonstrate a novel compact optical cross point switch configuration using electrical current tuning. The device is made on InP/InGaAsP material. It has a digital switching characteristics, a switching current of 40 mA and switching speed of nanosecond. For NxN switches, only N electrodes are needed. The switching electrode is only 600-micrometers long. It has a cross-talk of -40 dB.

Small-signal microwave performance of gain-coupled DFB laser array elements at 1.3 μm

The small-signal microwave performance of 1.3 micrometer gain-coupled DFB lasers has been measured as a function of device parameters such as current and ridge width by treating the laser as a two port device. The s-parameters were measured over a frequency range from 0.5 GHz to 8 GHz. The simulation software LIBRA was used with S11 return loss measurements to extract equivalent circuit parameters according to Kan and Laus laser model. Results demonstrate that the parameters describing the input impedance of the laser undergo a discontinuity at the lasing threshold current, Ith. The measured optical intensity modulation (IM) response, (S21), was used to study the behavior of the relaxation oscillation frequency fr as a function of laser bias current. It has been demonstrated that at high laser bias current Ilaser, fr is independent of laser bias current (Ilaser). We have also used the equivalent circuit parameters obtained from the S11 data to predict values for fr based on equations derived. These were then compared to the fr values obtained from S21 measurements.

WDM laser arrays with 2-nm channel spacing fabricated using a grating phase mask

High density wavelength division multiplexing (DWDM) requires several channels with a fixed wavelength spacing of 1 - 2 nm. This can be achieved by fabricating arrays of distributed feedback (DFB) lasers, using a photomask method to print the gratings with a different period for each DFB laser in the array. The grating phase mask is fabricated first, using e-beam lithography and reactive ion etching. The parallel exposure of all gratings using such a mask is orders of magnitude faster than direct wafer writing, using e-beam lithography. The characteristics of 8-channel gain coupled DFB laser arrays designed for a 2 nm channel spacing are reported. The required performance, achievable yield (i.e. cost), packaging requirements and reliability will determine whether these arrays are suitable for use in DWDM systems.