Widely-Tunable Transmitters and Photonic Integrated Circuits Larry A. Coldren, James W. Raring, Jonathon S. Barton, Matt Sysak, and Leif Johansson Electrical &Computer Engineering and Materials Departments, University of California Santa Barbara, CA 93106 and Agility Communications, Inc., 475 Pine Ave, Santa Barbara, CA 93117 Ph: (805) 893-4486; Fax: (805) 893-4500; email: - INVITED PAPER Abstract: Widely-tunable lasers and single-chip transmitters, in which such lasers are integrated with modulators and semiconductor-optical-amplifiers, have recently become the core of practical modules that are gaining wide-spread use in new wavelengh-division-multiplexed systems. More advanced photonic ICs have been demonstrated for use in advanced communication and sensor systems. 1. Introduction Despite a significant downturn in the market for telecommunication products, certain new enabling components are enjoying rapid market growth as their capabilities to reduce operational costs gain acceptance. One such example is the widely-tunable laser and derivative products that provide a 'one-size-fits all' solution in dense wavelength division multiplexed (DWDM) communication systems. In the future, such devices may also find use in reconfigurable optical add-drop multiplexers (ROADMs), photonic switch architectures, and other elements in dynamically reconfigured networks. In this paper, we shall summarize recent advances with InP-based single-chip photonic integration techniques that are gaining wide acceptance for such applications[1,2]. Such photonic integration has long been sought after as the next big step toward low-cost, low-size, and low-power dissipation chips with increased capability. Although efforts in this area have been ongoing for decades, only within the past several years have practical photonic integrated circuits (PICs) emerged. Key to the active PICs to be discussed here are having seamless transitions in absorption edge, so that the various amplifying, modulating, splitting, and passive interconnecting waveguides can be integrated together without loss or reflections. As illustrated in Fig. 1 various approaches have been developed. The first, butt-joint regrowth, requires an extra regrowth, but the waveguide properties can be chosen nearly arbitrarily. The other three require no regrowths, but are somewhat restricted due to the inherent relationships between the sections. Nevertheless, such approaches are being widely used because of the relative simplicity of the fabrication process and the fact that relatively good properties for the various elements of many PICs can be obtained. /4: ?skE t~ATIYE Acfrne MI I tsp t () I PAi WE" Figure 1. Schematics of active-to-passive waveguide integration techniques. In principle, there is no limit to the scale of the PICs that can be created, once waveguides of about three or four different different bandgaps can be integrated with high yield. The PICs to be discussed also achieve a high level of 0-7803-9040-7/05/$20.00 02005 IEEE I11