10Gbit=s transmitter based on directly modulated InGaAlAs laser operating up to 126 C

Introduction: Optical communication systems operating at 10 Gbit=s are becoming increasingly important even for short reach applications such as metro, access and data-link networks. In fact, approximately 40% of all commercial 10 Gbit=s interfaces to be deployed between 2003 and 2006 are expected to be short reach (<2 km) [1]. A key enabling technology for the development of such systems is a reliable, high-speed optical transmitter that can be produced at low cost. In this respect, directly modulated semiconductor Fabry–Perot lasers offer several advantages over DFB lasers, including higher yield and no need for optical isolators. Uncooled operation is required to further reduce the transmitter cost, size, and power consumption, which requires laser devices capable of maintaining a high level of performance over a wide temperature range. For high-temperature operation, use of an InGaAlAs multiquantum-well (MQW) active material is advantageous [2], primarily because of its larger conduction-band offset relative to the more traditional InGaAsP MQW system. This property results in a stronger electron confinement in the quantum wells, which in turn reduces the degradation in threshold current and relaxation frequency with increasing temperature. Introducing compressive strain in the quantum wells is also favourable for both high-temperature and high-speed performance. In the past few years, several InGaAlAs strained MQW lasers have been reported in the literature [2–5], showing superior static and dynamic properties at high temperatures. In particular, characteristic temperatures T0 in excess of 100K [3] have been demonstrated, as well as operation at 10 Gbit=s up to laser temperatures of over 100 C [4, 5]. However, most of the work reported so far in this area has focused on the performance of the individual diode lasers, while less attention has been paid to the high-temperature characteristics of the complete transmitter modules. In this Letter, we report on the operation of a 10 Gbit=s transmitter based on a directly modulated 1.3 mm InGaAlAs Fabry–Perot laser with the transmitter case temperature ranging from 10 to 109 C. Clear open eye diagrams were obtained with 7.5 dB extinction ratio, and meeting the ITU G.693 mask test over this entire temperature range. The upper limit of 109 C case temperature corresponds to a laser temperature of 126 C (as measured with a temperature sensor close to the laser in the package), which is the highest reported to date for successful large-signal modulation at 10 Gbit=s.