Design of high-speed driver ics for direct modulation of VCSELs and DFB-LDs

Abstract

This thesis focuses on two most important issues for the implementations of a short distance optical communication system and an emerging optical access network technology: a 10Gb/s driver IC consuming low power for direct modulation of VCSEL (vertical-cavity surface-emitting laser) and a 1.25Gb/s burst-mode DFB-LD driver IC``s design having a function of compensating temperature dependency. First of all, this paper explains the employing electric technology for improving a bandwidth characteristic and the electric equivalent circuit of a commercial VCSEL. Turning one``s attention to these two points, we designed and fabricated a 10Gb/s driver IC for direct modulation of 850nm VCSEL diodes by using InGaP/GaAs heterojunction bipolar transistor technology with a cut-off frequency of 45GHz and an emitter area of $6\mum^2$. The driver IC consists of the CML (current mode logic) interface for the high-speed operation and an ER (extinction ratio)-controllable terminal using a variable resistor. In this work, the fiber-launched optical output signal of the VCSEL driven by the fabricated driver IC exhibits rise/fall times of 29.4/39psec and a controllable extinction ratio at a 3.3V supply voltage with $250mV_{pp}$ input data sequence. The VCSEL driver IC exhibits the small dc power consumption of 65mW as well. This paper also demonstrates the other 10Gb/s VCSEL driver IC designed and fabricated using $0.18\mum$ CMOS technology. Even though the HBT VCSEL driver IC have an ER-controllable terminal, it is difficult to manipulate ER of the optical output signal of a VCSEL because the pre-bias current and modulation current could not be controlled individually. The improved VCSEL driver IC using CMOS technology has two control terminals to adjust pre-bias and modulation current for meeting the requirements of each application and attempts a cascode topology for progressing wideband performance. The improved VCSEL driver IC exhibits rise/fall time of 32.8/43.2psec, dc powe...