# All-Analog Adaptive Equalizer for Coherent Data Center Interconnects

## TL;DR

This paper introduces the first all-analog adaptive equalizer for coherent optical data center interconnects, demonstrating reduced power consumption and complexity compared to digital solutions at 40 Gb/s over 10 km fiber.

## Contribution

It presents a novel all-analog adaptive equalizer architecture using the constant modulus algorithm, implemented in 130 nm SiGe BiCMOS technology for the first time.

## Key findings

- Successfully demonstrated 40 Gb/s data processing over 10 km fiber.
- Achieved blind adaptation of the equalizer in the analog domain.
- Showed potential for lower power consumption in advanced CMOS technologies.

## Abstract

In a high-speed coherent optical transmission system, typically the signals obtained at the receiver front-end are digitized using very high-speed ADCs and then processed in the digital domain to remove optical channel impairments. In this work, we show that these signals can instead be processed in the analog domain itself, which can significantly reduce the power consumption as well as the complexity of the receiver. The first all-analog adaptive equalizer for receivers of coherent dual-polarization optical links has been presented with its detailed architecture and measurement results. The proof-of-concept equalizer uses the constant modulus algorithm for blind adaptation of its weight coefficients to implement a 4x4 2-tap FIR filter in 130 nm SiGe BiCMOS technology. Its functionality is evaluated experimentally for 40 Gb /s data rate and 10 km standard single-mode fiber channel. This demonstration shows that the use of all-analog processing for short-reach data-center interconnects is feasible and is a much simpler solution than the use of the high-speed ADC+DSP based approach. Moreover, when implemented in advanced CMOS or FinFET technologies, the power consumption of the equalizer is expected to be significantly lower than the DSP based implementations in similar process technologies.