S. Chandrasekhar

2.5 Tb/s (64/spl times/42.7 Gb/s) transmission over 40/spl times/100 km NZDSF using RZ-DPSK format and all-Raman-amplified spans

We report 2.5 Tb/s (64 /spl times/ 42.7-Gb/s) WDM transmission over 4000 km (forty 100-km spans) of non-zero dispersion-shifted fiber. This capacity /spl times/ distance record of 10 petabit-km/s for 40-Gb/s systems is achieved in a single 53-nm extended L band using return-to-zero differential-phase-shift-keyed modulation, balanced detection, and distributed Raman amplification.

112-Tb/s Space-division multiplexed DWDM transmission with 14-b/s/Hz aggregate spectral efficiency over a 76.8-km seven-core fiber

We describe a new multicore fiber (MCF) having seven single-mode cores arranged in a hexagonal array, exhibiting low crosstalk among the cores and low loss across the C and L bands. We experimentally demonstrate a record transmission capacity of 112 Tb/s over a 76.8-km MCF using space-division multiplexing and dense wavelength-division multiplexing (DWDM). Each core carries 160 107-Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels on a 50-GHz grid in the C and L bands, resulting in an aggregate spectral efficiency of 14 b/s/Hz. We further investigate the impact of the inter-core crosstalk on a 107-Gb/s PDM-QPSK signal after transmitting through the center core of the MCF when all the 6 outer cores carry same-wavelength 107-Gb/s signals with equal powers, and discuss the system implications of core-to-core crosstalk on ultra-long-haul transmission.

448-Gb/s Reduced-Guard-Interval CO-OFDM Transmission Over 2000 km of Ultra-Large-Area Fiber and Five 80-GHz-Grid ROADMs

We propose a novel coherent optical orthogonal frequency-division multiplexing (CO-OFDM) scheme with reduced guard interval (RGI) for high-speed high-spectral-efficiency long-haul optical transmission. In this scheme, fiber chromatic dispersion is compensated for within the receiver rather than being accommodated by the guard interval (GI) as in conventional CO-OFDM, thereby reducing the needed GI, especially when fiber dispersion is large. We demonstrate the generation of a 448-Gb/s RGI-CO-OFDM signal with 16-QAM subcarrier modulation through orthogonal band multiplexing. This signal occupies an optical bandwidth of 60 GHz, and is transmitted over 2000 km of ultra-large-area fiber (ULAF) with five passes through an 80-GHz-grid wavelength-selective switch. Banded digital coherent detection with two detection bands is used to receive this 448-Gb/s signal. Wavelength-division multiplexed transmission of three 80-GHz spaced 448-Gb/s RGI-CO-OFDM channels is also demonstrated, achieving a net system spectral efficiency of 5.2 b/s/Hz and a transmission distance of 1600 km of ULAF.

Experimental investigation on the performance of closely spaced multi-carrier PDM-QPSK with digital coherent detection

We experimentally investigate the performance of a spectrally efficient multi-carrier channel consisting of two or more optical carriers spaced around the baud rate, with each carrier modulated with polarization division multiplexed (PDM) quadrature phase shift keyed (QPSK) format. We first study the performance of a 100-Gb/s 2-carrier PDM-QPSK channel with each carrier modulated at 12.5 Gbaud as a function of various design parameters such as the time alignment between the modulated carriers, the frequency separation between the carriers, the oversampling factor at the receiver, and the bandwidth of the digital pre-filter used for carrier separation. While the measurements confirm the previously reported observations, they also reveal some interesting additional features. The coherent crosstalk between the modulated carriers is found to be minimized when these carriers are symbol aligned. Spacing the carriers at the baud rate, corresponding to the orthogonal frequency-division multiplexing (OFDM) condition, leads to a local maximum in performance only for some specific cases where large oversampling (>2 x ) is applied. It is found that 4 x oversampling, together with a constant modulus algorithm (CMA) based digital equalizer having multiple quarter-symbol (T/4) spaced taps, gives much better overall performance than 2 x oversampling with a CMA-based equalizer having T/2 spaced taps. In addition, using a T/4-delay-and-add filter (DAF) as a pre-filter for assist carrier separation is found to give better performance than the commonly used T/2-DAF. In addition, it is possible to set the carrier spacing to be as small as 80% of the baud rate while incurring negligible penalty at BER approximately 10(-3). 3-carrier and 5-carrier PDM-QPSK channels at 12.5-Gbaud with frequency-locked carriers spaced at 12.5 GHz and 4 x oversampling are also studied, and shown to perform reasonably well with small relative penalties. Finally, increasing the baud rate of the 2-carrier PDM-QPSK to 25 Gbaud and 28 Gbaud is investigated. It is found that with a fixed sampling speed of 50 Gsamples/s, scaling from 12.5 Gbaud to 25 and 28 Gbaud causes excess crosstalk penalties of about 2.8 dB and 4.8 dB, respectively, indicating the need to increase the sampling speed and transmitter bandwidth in order to support these high-data-rate channels without excessive coherent crosstalk.

100-Gb/s DQPSK Transmission: From Laboratory Experiments to Field Trials

We discuss the generation, detection, and long-haul transmission of single-polarization differential quadrature phase shift keying (DQPSK) signals at a line rate of 53.5 Gbaud to support a net information bit rate of 100 Gb/s. In the laboratory, we demonstrate 10-channel wavelength-division multiplexed (WDM) point-to-point transmission over 2000 km on a 150-GHz WDM grid, and 1200-km optically routed networking including 6 reconfigurable optical add/drop multiplexers (ROADMs) on a 100-GHz grid. We then report transmission over the commercial, 50-GHz spaced long-haul optical transport platform LambdaXtremereg. In a straight-line laboratory testbed, we demonstrate single-channel 700-km transmission, including an intermediate ROADM. On a field-deployed, live traffic bearing Verizon installation between Tampa and Miami, Florida, we achieve 500-km transmission, with no changes to the commercial system hardware or software and with 6 dB system margin. On the same operational system, we finally demonstrate 100-Gb/s DQPSK encoding on a field-programmable gate array (FPGA) and the transmission of real-time video traffic.

Demonstration of 42.7-Gb/s DPSK receiver with 45 photons/bit sensitivity

A record sensitivity of -36.2 dBm at 1552.5-nm wavelength (45 photons/bit) is reported for an optically preamplified receiver operating at 42.7 Gb/s. The transmission format is return-to-zero differential phase-shift keying. The receiver employs a delay-interferometer demodulator followed by balanced-photodiode detection and electronic demultiplexing to 10.7 Gb/s.

Monolithic Polarization and Phase Diversity Coherent Receiver in Silicon

In this paper, we realized a monolithic silicon photonic integrated circuit (PIC) for polarization and phase diversity coherent detection. The PIC includes two polarization beam splitters, two 90° optical hybrids, and four pairs of balanced photodiodes implemented as integrated germanium detectors. We tested the PIC using polarization-division multiplexed quadrature phase-shift keyed signals at 43 and at 112 Gb/s.

High-speed monolithic p-i-n/HBT and HPT/HBT photoreceivers implemented with simple phototransistor structure

Monolithic photoreceivers, using the base-collector junction of an InP/InGaAs phototransistor structure for a p-i-n photodetector, have been fabricated for the first time. Bandwidths as high as 3 GHz and bit rates as high as 5 Gb/s, with sensitivities of -22.5 dBm and -21.5 dBm for light focused on the p-i-n or on the first stage transistor of the preamplifier, respectively, have been achieved. These results represent the highest operating speed demonstrated for any phototransistor-based receiver.<<ETX>>

Generation and 1,200-km transmission of 448-Gb/s ETDM 56-Gbaud PDM 16-QAM using a single I/Q modulator

We generate 56-Gbaud PDM 16-QAM using electronic time-division multiplexing (ETDM) and a four-level-driven I/Q modulator. The 448-Gb/s line-rate signal is transmitted over 1,200 km of ultra-large-area fiber and coherently received by two 32.5-GHz oscilloscopes with >5.5 effective bits.

Spectrally Efficient Long-Haul WDM Transmission Using 224-Gb/s Polarization-Multiplexed 16-QAM

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 224-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 28 Gbaud. We measure a required optical signal-to-noise ratio of 23.4 dB (0.1-nm reference bandwidth; 10-3 bit-error ratio), 3.4-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 2000-km single-channel transmission. We also demonstrate 1200-km WDM transmission on a 50-GHz grid (4-b/s/Hz spectral efficiency), including three passes through a wavelength-selective switch.