Theodore J. Schmidt

Real-Time Single-Carrier Coherent 100 Gb/s PM-QPSK Field Trial

The development of 100 Gb/s transponder technology is progressing rapidly to meet the needs of next-generation optical/IP carrier networks. In this paper, we describe the upgrade of an installed 10 Gb/s field system to 100 Gb/s using a real-time single-carrier, coherent 100 Gb/s polarization-multiplexed quadrature-phase-shift keyed channel. Performance sufficient for error-free operation after forward-error-correction was achieved over installed 900 and 1800 km links, proving the viability of 100 Gb/s upgrades to most installed systems. Excellent tolerance to fiber polarization mode dispersion and narrowband optical filtering demonstrates the applicability of this technology over the majority of installed fiber plant and through existing 50 GHz reconfigurable optical add/drop multiplexers.

Field trial of a real-time, single wavelength, coherent 100 Gbit/s PM-QPSK channel upgrade of an installed 1800km link

We demonstrate a real-time, single-wavelength, coherent 100 G PM-QPSK upgrade of a field system. Performance sufficient for error-free operation after forward-error-correction was achieved over installed 900 km and 1800 km links, proving the viability of seamless 100 Gb/s upgrades.

Differential Phase-Shift Keying Receiver Design Applied to Strong Optical Filtering

We study, via simulation and experiments, the influence of the differential phase-shift keying decoder free spectral range (FSR) when strong optical filtering is considered for the nonreturn-to-zero and return-to-zero modulation formats and show that larger FSR can improve performance.

Design of coherent receiver optical front end for unamplified applications

Advanced modulation schemes together with coherent detection and digital signal processing has enabled the next generation high-bandwidth optical communication systems. One of the key advantages of coherent detection is its superior receiver sensitivity compared to direct detection receivers due to the gain provided by the local oscillator (LO). In unamplified applications, such as metro and edge networks, the ultimate receiver sensitivity is dictated by the amount of shot noise, thermal noise, and the residual beating of the local oscillator with relative intensity noise (LO-RIN). We show that the best sensitivity is achieved when the thermal noise is balanced with the residual LO-RIN beat noise, which results in an optimum LO power. The impact of thermal noise from the transimpedance amplifier (TIA), the RIN from the LO, and the common mode rejection ratio (CMRR) from a balanced photodiode are individually analyzed via analytical models and compared to numerical simulations. The analytical model results match well with those of the numerical simulations, providing a simplified method to quantify the impact of receiver design tradeoffs. For a practical 100 Gb/s integrated coherent receiver with 7% FEC overhead, we show that an optimum receiver sensitivity of -33 dBm can be achieved at GFEC cliff of 8.55E-5 if the LO power is optimized at 11 dBm. We also discuss a potential method to monitor the imperfections of a balanced and integrated coherent receiver.

Towards full band colorless reception with coherent balanced receivers

In addition to linear compensation of fiber channel impairments, coherent receivers also provide colorless selection of any desired data channel within multitude of incident wavelengths, without the need of a channel selecting filter. In this paper, we investigate the design requirements for colorless reception using a coherent balanced receiver, considering both the optical front end (OFE) and the transimpedance amplifier (TIA). We develop analytical models to predict the system performance as a function of receiver design parameters and show good agreement against numerical simulations. At low input signal power, an optimum local oscillator (LO) power is shown to exist where the thermal noise is balanced with the residual LO-RIN beat noise. At high input signal power, we show the dominant noise effect is the residual self-beat noise from the out of band (OOB) channels, which scales not only with the number of OOB channels and the common mode rejection ratio (CMRR) of the OFE, but also depends on the link residual chromatic dispersion (CD) and the orientation of the polarization tributaries relative to the receiver. This residual self-beat noise from OOB channels sets the lower bound for the LO power. We also investigate the limitations imposed by overload in the TIA, showing analytically that the DC current scales only with the number of OOB channels, while the differential AC current scales only with the link residual CD, which induces high peak-to-average power ratio (PAPR). Both DC and AC currents at the input to the TIA set the upper bounds for the LO power. Considering both the OFE noise limit and the TIA overload limit, we show that the receiver operating range is notably narrowed for dispersion unmanaged links, as compared to dispersion managed links.

Coherent 100 Gb/s PM-QPSK field trial

The development of 100 Gb/s transponder technology is progressing rapidly to meet the needs of next-generation optical/IP carrier networks. In this paper, we describe the upgrade of an installed 10 Gb/s field system to 100 Gb/s using a real-time single-carrier, coherent 100 Gb/s polarization-multiplexed quadrature-phase-shift keyed channel. Performance sufficient for error-free operation after forward-error-correction was achieved over installed 900 and 1800 km links, proving the viability of 100 Gb/s upgrades to most installed systems. Excellent tolerance to fiber polarization mode dispersion and narrowband optical filtering demonstrates the applicability of this technology over the majority of installed fiber plant and through existing 50 GHz reconfigurable optical add/drop multiplexers.

Cycle slip probability in 100G PM-QPSK systems

We estimate asymptotic probabilities of a cycle slip for a non-decision aided feedforward carrier synchronizer in dispersion-uncompensated optical lines with negligible nonlinear crosstalk.

Economics of 100Gb/s transport

Deploying spectrally-efficient 100 Gb/s coherent transponder technology in carrier networks can yield substantial CAPEX and OPEX savings. This paper discusses these economic gains and how a carrier can maximize their return on optical transport investment.

Implementation challenges of 100G coherent transponders

We present challenges associated with taking a proof of concept to a commercial transponder suitable for field deployment requires design decisions to optimize performance, margin, power consumption and manufacturing cost.

Tunable high order dispersion compensator for optimized 40Gb/s performance in 50GHz channel spacing

We analyse the penalty associated with high-order dispersion in concatenated optical filters for 40 Gb/s channels in 50 GHz spacing, and demonstrate a tunable high-order dispersion-compensator to mitigate this penalty. Less than 0.1 dB/ROADM of penalty is demonstrated.