Contents I. Introduction
The fast development of optical digital coherent systems over the past 10 years, initially for 40 Gb/s, then 100 Gb/s and nowadays for up to 400 Gb/s
http://www.alcatel-lucent.com/press/2013/002786.
, has set a new standard symbol rate typically around 28–32 GBd, depending on the overhead from the forward error correction (FEC) codes. Despite the great capacity growth enabled by the improvement of spectral efficiency, as allowed by coherent technologies, further increase is needed, such that pushing the symbol rate to ever higher levels remains a prime challenge [1]. In this field, most of the work has been carried out on signal generation with high speed digital to analog converters [2] and signal detection [3] with off-line or quasi-real-time digital signal processing. In this context, low-noise amplification of received signals is not needed, due to the use of digital storage oscilloscopes with sensitive front-end headshttp://teledynelecroy.com/100ghz/.
. However, such an analog function will be needed as soon as ADC-based true-real-time implementations will be sought, as already happened for the 28-32-GBd generation. In practice, a transimpedance amplifier with gain control is required to provide a low-noise linearly-amplified and constant-amplitude signal to drive the following ADC in its full dynamic range. Leading edge implementations, targeting 28-32-GBd applications, have been reported in InP [4] and SiGeInphi IN3250TA 32 Gb/s Dual Differential Input Linear Amplifier.
. In this paper, we report the first TIA-VGA (Fig. 1) compatible with 60-GHz-class applications, with a - 3-dB bandwidth and differential transimpedance gain reaching respectively 68 GHz and 59 dBΩ, along with wide gain and bandwidth controls.TIA-VGA microphotograph (chip size: .
