Snigdharaj Kumar Mishra

Large effective area fiber

Refractive-index nonlinearities have negligible effect on the performance of short-haul fiber-optic communication links utilizing electronic repeaters. However, in long optical fiber links, nonlinearities can cause severe signal degradations. To mitigate nonlinear effects, new generation of fibers, referred to as large effective-area fibers, have been introduced in recent years. This paper reviews the latest research and development work on these fibers conducted by several research groups around the world. Attention is focused on a class of large effective-area fibers that are based on a depressed-core multiple-cladding design. Transmission properties, including dispersion, dispersion slope, effective area, mode-field diameter, bending loss, polarization-mode dispersion, and cutoff wavelength are discussed. Dispersion-shifted, non-zero dispersion-shifted, and dispersion-flattened designs are addressed. Design optimization, particularly with regard to effective area, bending loss, and polarization-mode dispersion, is elaborated upon. The trade-off between effective-area and bending loss is emphasized. Results for dispersion-shifted and non-zero dispersion-shifted large effective-area fibers with zero polarization-mode dispersion and low bending loss at 1.55 micrometer wavelength are presented.

Transmission of 32-Tb/s Capacity Over 580 km Using RZ-Shaped PDM-8QAM Modulation Format and Cascaded Multimodulus Blind Equalization Algorithm

In this paper, we propose a novel synthesizing method for high-speed 8-ary quadratic-amplitude modulation (QAM) optical signal generation using commercial optical modulators with binary electrical driving signals. Using this method, we successfully generated 114-Gb/s pulse-duration modulation (PDM)-8QAM optical signals. Intradyne detection of PDM-8QAM optical signals with robust blind polarization demultiplexing has been demonstrated by using a new cascaded multimodulus equalization algorithm. With return-to-zero-shaped PDM-8QAM modulation and the proposed blind polarization demultiplexing algorithm, we demonstrate transmission of a record 32-Tb/s fiber capacity (320 × 114 Gb/s) over 580 km of ultralow-loss single-mode fiber-28 fiber by utilizing C+L-band erbium-doped fiber-amplifier-only optical amplification and single-ended coherent detection technique at an information spectral efficiency of 4.0 bit/s·Hz.

17 Tb/s (161×114 Gb/s) PolMux-RZ-8PSK transmission over 662 km of ultra-low loss fiber using C-band EDFA amplification and digital coherent detection

Employing PolMux-RZ-8PSK modulation and coherent detection, we demonstrate 25 GHz-spaced, 161times114 Gb/s DWDM transmission through eight spans of ultra-low-loss fiber (average span length/loss of 82.75 km/14.6 dB) with a record capacity of 17 Tb/s (spectral efficiency 4.2 b/s/Hz) within the C-band EDFA bandwidth (4.025 THz).

32Tb/s (320×114Gb/s) PDM-RZ-8QAM transmission over 580km of SMF-28 ultra-low-loss fiber

Employing PDM-RZ-8QAM modulation, digital coherent detection and EDFA-only amplification, we demonstrate 25 GHz-spaced, 320×114Gb/s DWDM transmission through seven spans of ultra-low-loss fiber (average span length/loss of 82.8 km/14.6 dB) with a record capacity of 32Tb/s.

40 × 112 Gb/s transmission over an unrepeatered 365 km effective area-managed span comprised of ultra-low loss optical fibre

We experimentally demonstrate transmission of 40 × 112 Gb/s PM-QPSK channels over a 365 km unrepeatered span enabled by ultra-low loss fibres in an effective area-managed configuration using only backward-pumped Raman with 25 dB gain and EDFA amplification.

Long-haul quasi-single-mode transmissions using few-mode fiber in presence of multi-path interference.

We study long-haul Quasi-Single-mode (QSM) systems in which signals are transmitted in the fundamental modes of a few-mode fiber (FMF) while keeping other system components such as amplifiers and receivers are kept single-moded. The large-effective-area nature of the FMF fundamental modes improves system nonlinear tolerance in the expense of mode coupling along FMF transmissions which induces multi-path interference (MPI) and needs to be compensated. We analytically investigate 6-spatial-polarization mode QSM transmission systems in presence of MPI and show that in the weak coupling regime, the QSM channel is a Gaussian random process in frequency. MPI compensation filters are derived and performance penalties due to MPI and signal loss from higher-order modes are characterized. We also experimentally demonstrate 256 Gb/s polarization multiplexed (PM)-16-QAM QSM transmissions over a record distance of 2600 km with 100-km span using decision directed least mean square (DD-LMS) algorithm for MPI compensation.

Transmission of 112 Gb/s PM-QPSK signals over 7200 km of optical fiber with very large effective area and ultra-low loss in 100 km spans with EDFAs only

We experimentally investigate transmission of 16×112 Gb/s PM-QPSK signals over an optical fiber with effective area of 134 µm2 and attenuation of 0.162 dB/km. We demonstrate transmission over 7200 km with 100 km span lengths.

112 Gb/s PM-QPSK transmission up to 6000 km with 200 km amplifier spacing and a hybrid fiber span configuration

We demonstrate transmission of 112 Gb/s PM-QPSK signals up to 6000 km with 200 km spans. A hybrid fiber span configuration is used that combines two ultra-low loss fibers, one having very large effective area.

Quasi-Single-Mode Fiber Transmission for Optical Communications

The transmission of a single fundamental mode in a fiber with cutoff wavelength above the transmission band is studied as a means of allowing a larger fiber effective area and reducing fiber nonlinearity. The reduction of nonlinear impairments is achieved at the expense of a potential new linear impairment in the form of multipath interference (MPI). We use a power-coupled-mode formalism to analyze the growth of MPI, and the effects of fiber and cable attributes on its magnitude and the required complexity of digital signal processing to combat the MPI. Hybrid fiber spans comprised partially of a quasi-single-mode fiber are also analyzed using a modification of the Gaussian noise model of coherent systems to predict optimal configurations, and results from transmission experiments are presented that demonstrate very high spectral efficiencies and performance surpassing that of a purely single-mode fiber system.

256 Gb/s PM-16-QAM quasi-single-mode transmission over 2600 km using few-mode fiber with multi-path interference compensation

We experimentally demonstrate 256 Gb/s PM-16-QAM transmission up to 2600 km by using 100-km spans of few-mode fibers (FMF) operating in quasi-single-mode (QSM) transmission and using a DD-LMS algorithm to compensate multi-path interference (MPI).