A NEW TUNABLE LASER USING A SINGLE ELECTROABSORPTION TUNING SUPER STRUCTURE GRATING FOR SUBNANOSECOND SWITCHING APPLICATIONS

A new tunable laser structure using a single electro-absorption (EA) t uning super structure grating (SSG) section for fast wavelength switch ing operation is reported. Instead of index change by carries density or by thermal variation, the tuning mechanism of this absorption chang e (AC) distributed Bragg reflector (DBR) laser is based on a localized absorption variation induced in a Franz-Keldysh EA SSG section used a s Bragg reflector. According to a simulation which takes into account the absorption and refractive index variations of the SSG section vers us voltage and wavelength, an optimized device theoretically allows a wide tuning range of up to 11 nm with nine regularly spaced wavelength channels. Over this whole tuning range, the variation of the AC-DBR l aser threshold gain is lower than 2 cm(-1). Compared to a standard DBR laser exhibiting an 8-cm(-1) threshold gain variation for the same wa velength shift, this AC-DBR laser would present extremely low threshol d current and emitted power variations under tuning. Owing tea its tun ing mechanism, the switching time of the AC-DBR laser is independent o f the wavelength shift, and only limited by the parasitic capacitance of the SSG ridge section. A test structure, easier to realize, with on ly a theoretical tuning range of 3 nm over four regularly spaced chann els has been fabricated. These devices exhibiting a tuning range of 2. 5 nm with three modes, present threshold current and output power vari ations under tuning of less than 8 mA and 1.2 dB, respectively. A swit ching time between two successive wavelength channels shorter than 250 ps has been observed, in agreement with typical capacitances of 0.8 p F/100 mu m measured an the SSG section.