Coherent techniques are expected to be used to meet the demand for higher data rates in short-reach optical links in the near future. Digital coherent receivers used for long haul applications are not suitable for short-reach links because of excessive power dissipation, size, and cost. The power consumption, size, and cost of the receiver can be drastically reduced by processing signals in the analog domain itself. A 100 Gbps dual-polarization quadrature phase shift keying receiver that uses analog domain signal processing is presented. The receiver, designed in 130 nm BiCMOS technology, consumes 3.5 W of power. Simulations show bit error rates of less than 10 −3 in the presence of dispersion up to 160 ps/nm, laser linewidths of up to 200 kHz, and a frequency offset of 100 MHz between the transmitter and the receiver lasers.

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We present the detailed architecture of an allanalog adaptive equalizer for low-power analog signal processing based coherent optical dual-polarization quadrature phase-shift keying transceivers. The proof of concept equalizer uses the constant modulus algorithm for weight coefficient update. The equalizer, implemented in a 130 nm SiGe BiCMOS technology for 100 Gb/s operation, occupies ∼1.4 mm × 1.35 mm area and draws 1 A current from a 2.5 V supply. Its functionality is validated experimentally for data rates up to 40 Gb/s and by using postlayout circuit simulations for data rates up to 100 Gb/s. The equalizer output after processing with a behavioral Costas loopbased carrier phase recovery and compensation module shows bit error rates well within the hard-decision forward error correction limit for 40 Gb/s single-mode fiber links of length up to 10 km. Performance and power consumption of the equalizer are expected to improve when implemented in advanced CMOS or FinFET technologies. The simple architecture of the analog domain equalizer makes it suitable for analog coherent shortreach interconnects with length less than 10 km and carrier wavelengths of either 1310 nm or 1550 nm.

Self-homodyne systems with polarization multiplexed carrier offer an LO-less coherent receiver with simplified signal processing requirement that can be a good candidate for high-speed short-reach data center interconnects. The practical implementation of these systems is limited by the requirement of polarization control at the receiver end for separating the carrier and the modulated signal. In this paper, effect of polarization impairments in polarization diversity based systems is studied and modeled. A novel and practical adaptive polarization control technique based on optical power feedback from one polarization is proposed for polarization multiplexed carrier based systems and verified through simulation results. The application of the proposed concept is experimentally demonstrated also for a QPSK system with polarization multiplexed carrier.