Roosevelt People

Integrated tunable laser with mode-selection modulator

We theoretically and experimentally investigate a recently proposed integrated tunable laser which consists of a curved waveguide distributed-feedback (DFB) laser and a passive electroabsorption (EA) modulator-separated by an isolation section. The modulator provides wavelength selectivity in the integrated device. The facet at the laser side is anti- reflection (AR) coated to enhance the light output power, and the EA side facet is high-reflection (HR) coated to increase the coupling between the two sections. We have developed a transfer-matrix model based on the coupled-mode theory which takes into account the curved waveguide and above-threshold spatial hole burning effects. Using this model, we study the wavelength tuning behavior of the integrated device when a voltage bias is applied to the modulator section.

Process simulation of selective-area MOCVD growth for optoelectronic integrated circuits

MOCVD selective area growth is a simple and versatile process technique widely used in the fabrication of optical integrated circuits. A computational model for selective area growth is verified using a comprehensive suite of experimental measurements: atomic force microscopy, optical interference microscopy, micro-photoluminescence, and micro-Xray diffraction. The model then allows for constructive engineering of the material thickness and composition through manipulation of the oxide mask used in selective area growth. Examples demonstrating the accuracy of the model and its applicability to device design are provided.

Wavelength division multiplexed (WDM) electroabsorption modulated laser fabricated by selective area growth MOVPE techniques

This paper describes the fabrication techniques pertaining to the on-wafer lasing wavelength control of an electroabsorption modulated laser (EML) using both a direct approach and a tunable wavelength source. The direct approach utilizes multiple grating pitches to control the on-wafer lasing wavelength of the DFB arrays. High resolution E-beam lithography was used to generate a phase mask to produce seven grating pitches separated by 0.25 nm pitch intervals. In a tunable wavelength sources approach, we used a multi-electrodes DFB lasers integrated with a bent waveguide for the wavelength tuning. These fabrication techniques show a promising low cost way of mass producing either set of discrete DFB devices with different wavelengths or a more complicated integrated device with wavelength combiner and a modulator.

High-speed broadband tunable lasers

New enabling technologies are needed for optical communication systems to accommodate rapidly growing traffic demands. Wavelength conversion and high-speed optical packet switching/routing will be key technology components for realizing more flexible and efficient optical networks. Lasers capable of wide-band, high-speed wavelength tuning will be essential to support these advanced functions. Also, many applications will require high launch powers in order to access an increasing number of users, nodes, or base stations. Hence, laser transmitters capable of suppressing stimulated Brillouin scattering (SBS) would be highly desirable. We have developed an ultrafast, broadband tunable laser, based on an electroabsorption modulator laser (EML), which exhibits wavelength switching speeds as fast as 56 ps. Here, we report system performance results on wavelength conversion high-speed optical packet switching, and SBS suppression using this device. We have tested multiple wavelength conversion sequences and demonstrated penalty-free transmission through two cascaded wavelength conversion stages including 200 km of standard non-DS fiber. When used to perform packet switching at 2.5 Gb/s, the tunable laser allows switching between optical packets on 4 wavelength channels in less than 1 bit period, thereby requiring no significant guardband. The modulated data packets have been transmitted through 200 km of non-DSF and yield open eye diagrams. The tunable laser has also been used to perform SBS suppression. We have measured SBS thresholds of approximately 25 dBm on 4 separate WDM channels. The required modulation signal is very small, 95 mVpp, and the residual AM is only approximately 1%.