Titulo

David Vasquez

8-815-292 frequency distributed-feedback (DFB) lasers, dozens of different wavelength codes must be manufactured and inventoried, and perhaps more importantly, dozens of different wavelength-specific line cards must be manufactured and inventoried. Since the cost of line cards is measured in multiples of $10 k, this can be a significant overhead. Thus, even for this lessglamorous application, the savings are finite, but as a result, today’s tunable laser solutions are compared to fixedfrequency DFBs for both cost and performance. Bearing all of this in mind, it is generally agreed that if tunable lasers with the same performance specs as DFBs were available, most systems companies would select them over DFBs for a small price premium. As we will show in this report, sometunable embodiments appear to have reached specification parity with DFBs, so the situation may indeed be favorable for tunables in future WDM networks.

TUNABLE LASER
Abstract— This paper presents the development of a fiber-pigtailed narrowlinewidth tunable laser that utilizes a retroreflective optical system to construct the external cavity. For wavelength selection, a fixed etalon isemployed to provide the International Telecommunication Union (ITU) grid with the 50-GHz spacing and a lead zirconate titanate-actuated tunable filter to select one ITU mode to resonate. The laser device measures a linewidth of 7 kHz, an output power of 14 dBm, a side mode suppression ratio (SMSR) 55 dB, a tuning range 40 nm, and a response speed ~2 ms. The superior performance well demonstrates theadvantages of external cavity construction for the narrow-line width tunable lasers and may find applications in the emerging digital coherent communications. I. INTRODUCTION

TUNABLE

lasers applications range from sources for fiber optic telecommunication systems to broadband sensors. About three or four years ago, the telecom application began to drive significant investments into this fieldto support the perceived need for dynamic networks and wavelength reconfigurability in wavelength division multiplexing(WDM)systems. Vast reductions in operational costs were predicted for such flexible fiber-optic networks that were thought to be necessary for the rapidly expanding demand for bandwidth. However, as many new companies joined this effort, there was a large overbuild of capacity, andthe need for the new networks vanished, or more accurately, was pushed back to least the present time. The good news for the industry is that the demand for bandwidth continues to nearly double each year. Although the potential to reduce operational costs with more dynamical networks still exists. Today, the main value for telecom networks appears to be in the areas of inventory reduction, bothin the manufacture and operation of WDM systems. With fixed

II. TYPES OF TUNABILITY There are many types and categories of tunable lasers. They exist in the gas, liquid, and solid state. Among the types of tunable lasers are excimer lasers, CO2 lasers, dye lasers (liquid and solid state), transition metal solid-state lasers, semiconductor crystal and diode lasers, and free electron lasers.Tunable lasers find applications in spectroscopy, photochemistry, atomic vapor laser isotope separation, and optical communications. Single line tuning Since no real laser is truly monochromatic, all lasers can emit light over some range of frequencies, known as the linewidth of the laser transition. In most lasers, this linewidth is quite narrow (for example, the 1064 -nm wavelength transition of aNd:YAG laser has a linewidth of approximately 120 GHz, corresponding to a 0.45 -nm wavelength range). Tuning of the laser output across this range can be achieved by placing

David Vasquez wavelength-selective optical elements (such as an etalon) into the laser's optical cavity, to provide selection of a particular longitudinal mode of the cavity. Multi-line tuning

8-815-292 To get wideband...