Uncooled Lasers And 40 Gbit/s Modulators (Research Review)
Considerable research effort is being expended on high-speed components to meet the requirements of next-generation networking applications for greater bandwidth and wider temperature range. With this aim, Mitsubishi Electric is developing 40 Gbit/s electroabsorption modulators, in addition to 1300 nm FabryPerot lasers operating at 10 Gbit/s. 40 Gbit/s modulator At the recent Optical Fiber Communication conference (1924 March, Anaheim, CA), K Takagi and colleagues from Mitsubishi described a 40 Gbit/s electroabsorption modulator. The device contains an InGaAsP MQW structure as the absorption layer. Transparent InGaAsP waveguides are integrated either side of this layer to shorten the modulator length to 75 m and provide a total device dimension of 300 m. The modulator was grown on a semi-insulating InP:Fe substrate, which reduced the parasitic capacitance to 0.07 pF and afforded higher bandwidth performance. The device featured a 15 dB extinction ratio at an operating wavelength of 1553 nm. Accelerated aging tests were used to confirm a reliability of more than 17 million hours at 25 C. 10 Gbit/s FabryPerot laser Mitsubishi s T Kadowaki and colleagues provided details of the company s 10 Gbit/s FabryPerot laser at the same meeting. Based on a ridge waveguide structure, the company s device operates uncooled at 1300 nm and provides 5 mW of output power. To increase the operating frequency, Mitsubishi has increased the laser s front and rear facet reflectivity and decreased the cavity length to 200 m. The active regions are a modification of the usual InGaAsP QWs, employing five AlGaInAs wells to improve the laser s temperature dependence on threshold current and slope efficiency. A low power consumption of 1.4 dB (at 1E10 BER) was achieved, with a dispersion characteristic for singlemode transmission of +10.3 ps/nm. The results hold promise for an FP laser suitable for uncooled operation at OC-192 data rates for applications such as 10 Gigabit Ethernet over 3 km distances. Reliability testing was also used to determine the effect of aluminum in the QW structure on the catastrophic optical damage (COD) limit. A device with a 200 m cavity length and front and rear facet reflectivities of 65 and 90% was tested at 10 mW output power and a temperature of 85 C. Stable operation was obtained for more than 6500 hours, leading to an estimated lifetime of 200 000 h. Mitsubishi says this result equals the performance of conventional FabryPerot lasers employing InGaAsP active regions. No deterioration in COD limit was noted during the test, and a pulsed output power of more than 200 mW could be sustained without fluctuation for up to 1300 h.