Abstract

Next-generation fiber optic systems are developing transmit and receive modules utilizing 40 Gb/s bit rates to expand network capacity. Regardless of the use of WDM, OTDM or ETDM to implement such networks, the continually improving performance of semiconductor device technology has resulted in chipsets able to meet many of the specifications of 40 Gb/s systems. A few T/R module chipsets for 40 Gb/s have been demonstrated using InP HBTs.^1–4 The driver amplifier (DA) often has the most stringent requirements in the transmit module, due the need for wide bandwidth and large output voltage swing to drive the laser modulator. We selected a 0.15 µm GaAs pHEMT process to obtain a high gain-bandwidth product and allow for high-volume production. This pHEMT process allowed us sufficient breakdown voltage to design the DA for a linear gain characteristic to at least 3.4 Vp-p. This driving voltage is adequate for most electro-ab-sorbtion (EA) modulators. We also chose to design the DA with a distributed topology in order to maintain flat gain and group delay to very high frequencies. Lastly, we used the technique of gate capacitor division to obtain a 78 GHz 3-dB bandwidth that will enable formats such as 40 Gb/s RZ and even higher bit rates. To our knowledge, the gain-bandwidth product of 219 GHz is the best reported for a GaAs distributed amplifier and is surpassed only by InP-based designs in which the output drive capability is lower or not reported.^5–10

© 2002 Optical Society of America