Nir Sheffi

Tilted Gaussian Beams Multiplexer for Graded-Index Multimode Fiber in Data-Centers Interconnections

In recent years, there has been an explosive growth of data traffic in data-center interconnections. A significant amount of the installations within data centers are graded-index multimode fibers (GI-MMFs). These fibers enable the use of mode-division multiplexing to increase the fibers capacity. The heart of such a multiplexing scheme is a spatial multiplexer. In this paper, we propose a simple tilted Gaussian beam multiplexer for GI-MMF using low-cost commercially available lenses. We derive an analytical expression for the power coupling coefficients using a tilted Gaussian beam launch into a GI-MMF. We use the analytical expression to perform an optimization algorithm for tilted Gaussian beams as a spatial multiplexer with GI-MMF. The optimization was performed for 3 × 3, 4 × 4, and 5 × 5 multiple-input-multiple-output (MIMO) systems. Typical power coupling matrices exhibit maximum crosstalk of -12.5 dB with strong coupling efficiency that is greater than -0.6 dB.

Energy-Efficient VCSEL Array Using Power and Offset Allocation of Spatial Multiplexing in Graded-Index Multimode Fiber

In recent years, we exhibit an exponential data traffic and electrical power consumption growth in high-performance computing (HPC) interconnects. Thus, Green Photonics, which tries to minimize the Joule/bit ratio, becomes a major subject of both public and scientific interest. A significant amount of the installations within these HPCs are graded-index multimode fibers using parallel rack-to-rack optical interconnects. These fibers enable the use of mode division multiplexing to increase the fibers capacity. In this paper, we theoretically derive a power and offset allocation method for an intensity modulated optical multiple-input-multiple-output system with incoherent single-mode vertical cavity surface emitting laser array, which minimizes the electrical power consumption for a required bit rate and allowed bit error rate. This method outperforms simple equal bit and power allocation scheme, achieving a 45–55% electrical power save with a typicalrequired bit error rate of 10−6.

Direct modulation and coherent detection optical OFDM

Optical orthogonal frequency division multiplexing (O-OFDM) with a novel direct modulation and coherent detection system at 34.3 Gb/s and 16 QAM is proposed. Electronic pre-compensation of laser frequency response is applied at the transmitter. Following homodyne coherent detection and analog to digital conversion, digital signal processing compensates the DFB laser frequency chirp and chromatic dispersion (CD). Mathematical results and numerical simulation show that the proposed system achieves 10−3 BER with 10.5 Eb/N0, similar to a standard single carrier system.

Advanced modulation formats and digital signal processing for next generation fiber optics networks

Advanced modulation formats are proposed and analysed for next generation optical networks. The new evolving optical networks data rates of 100G and above require real time analog-to-digital conversion followed by real time digital signal processing. This is in order to allow increased spectral efficiency and full compensation of amplitude and phase distortion imposed by the optical channel in such high bitrates. Various approaches are presented, including discrete multi-tone and optical OFDM.

Low cost direct modulation and coherent detection optical OFDM for metro applications

High speed transmission systems (> 10 Gb/s) for cost-sensitive applications such as metropolitan network have attracted extensive interest due to the explosive data traffic growth in such applications. Optical orthogonal frequency division multiplexing (OFDM) based on direct modulation and direct detection for single-mode fiber (SMF) and multi-mode fiber (MMF) without optical amplification and chromatic dispersion (CD) compensation was proposed. Recent research has also shown that optical OFDM can be used with electronic dispersion compensation using direct detection in SMF. However, laser frequency chirp has been identified as a key limiting factor of capacity-versus-reach performance. In this paper, we present a novel concept of low cost optical OFDM with direct modulation of distributed feedback (DFB) lasers and coherent detection at 51.4 Gb/s and 64 QAM. A comprehensive theoretical model of the proposed system is developed. The proposed optical OFDM system concept and performance is based upon using electronic precompensation of laser frequency response, and electronic post compensation of DFB laser frequency chirp and CD. A numerical simulation of the transmission performance of the aforementioned system is conducted using different fiber lengths (40 km, 60 km, 120 km) and chirp parameters, which shows its attractiveness for access and metro applications.