This PDF file contains the front matter associated with SPIE Proceedings Volume 9009, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

A flexible and efficient channel bandwidth assignment is highly required for next optical generation networks. Among various techniques to enhance the wavelength routing capability, wavelength conversion plays an important role on improving network reconfigurability. In this paper, we experimentally demonstrate a sub-band wavelength conversion of a wide-band optical orthogonal frequency-division multiplexing (OFDM) signal based on four-wave mixing (FWM) using high-nonlinear fiber (HNLF) to solve the spectrum conflicts in the flexible coherent optical OFDM (CO-OFDM) networks. Combining with the wavelength selective switch (WSS) in a reconfigurable optical add/drop multiplexer (ROADM), some spectrum-overlapped sub-bands are successfully relocated to ‘seamlessly’ form a new wide-band signal, which efficiently eliminates the spectrum conflicts, and achieves a good spectral efficiency.

We propose a PLC-based multi/demultiplexer (MUX/DEMUX) with a mode conversion function for mode division multiplexing (MDM) transmission applications. The PLC-based mode MUX/DEMUX can realize a low insertion loss and a wide working wavelength bandwidth. We designed and demonstrated a two-mode (LP₀₁ and LP₁₁ modes) and a three-mode (LP₀₁, LP₁₁, and LP₂₁ modes) MUX/DEMUX for use in the C-band.

I propose and demonstrate a novel and simple optical exclusive OR circuit for binary signals, which is composed of a balanced photo-detector and a Mach-Zehnder intensity modulator. Two input optical signals into the photo-detector produce an electrical signal to drive the modulator. The modulator outputs an optical exclusive OR signal of the two input optical signals. I report the configuration, operating principle, and primary experimental results using 10 Gbit/s binary signals to demonstrate that the exclusive OR circuit operates properly. The proposed simple circuit is suitable for the future hybrid integration of photonics and electronics.

We present a novel non-data-aided algorithm that uses only the magnitude of the received signal for accurate estimation of the signal-to-noise ratio (SNR) in M-QAM optical coherent digital receivers. The Koay inversion method that only works with constant-modulus signals, is extended through analytically exact expressions so as to allow application to any multi-level, complex modulation scheme. Performance is evaluated via simulation for formats up to 64-QAM and is shown to be superior than the decision-directed error vector magnitude (EVM) method at low SNR, while outperforming schemes based on the method of moments at high SNR.

Few-mode fiber (FMF) transmission system has become an emerging technology to overcome next capacity crunch. To compensate the large accumulated differential mode group delay (DMGD) and random mode coupling in FMF transmission systems, frequency domain least mean square (FD-LMS) algorithm has been proposed and proven as the most hardware efficient approach. Except for the hardware complexity, convergence speed is another major consideration of adaptive FD-LMS algorithm, especially in FMF system with large accumulated DMGD. We propose two algorithms to improve the convergence speed of the adaptive FD-LMS in FMF transmission systems. One is signal power spectrum density (PSD) dependent adaptive algorithm, which adopts variable step size that is the reciprocal of the power level in each frequency bin. The other is noise power directed adaptive FD-LMS algorithm, which adopts the step size of each frequency bin rendering the posterior errors that will converge to background noise in additive white Gaussian noise channel. Our simulation results show that, in a 3000 km FMF transmission system with 35-ps/km DMGD and optical signal to noise ratio (OSNR) of 14 dB, the noise power directed algorithm and PSD dependent algorithm can improve the convergence speed by 54% and 35% over conventional adaptive FD-LMS algorithm with negligible increase in hardware complexity. We also proposed a complexity reduced single-stage adaptive equalizer for compensating both chromatic dispersion (CD) and DMGD simultaneously. The single-stage method can save 6% complex multiplication over conventional two-stage equalization method in a 1000 km FMF transmission system with 76-ps/km DMGD.

The need for software-defined transmissions raises new challenges for the transceiver design: multiple modulation formats have to be supported to accommodate for varying bandwidth demand and physical characteristics of different optical paths. In order to keep the receiver complexity and cost low, most of the digital signal processing functionalities should be shared by the different formats.

In this paper we address the problems of carrier frequency and phase recovery as well as the tracking of fast polarization rotations for arbitrary constellations in two or four dimensions. We first report how not only carrier frequency recovery but also ADC sampling error correction can be performed using a modulation-format independent frequency-domain approach. We then report a framework where the combined impact of phase error and fast polarization rotation can be described by a rotation in a four-dimensional space and show how to efficiently estimate and compensate this rotation. We finally investigate the dynamic performance of the reported algorithms for polarization-switched QPSK and 4D 32QAM constellations using numerical simulations.

We propose an all-optical regeneration scheme for 16-QAM signal. An incoming signal is 50/50 split into I and Q arms. Each arm contains three phase sensitive amplifiers (PSAs); between the PSAs the signal propagates through highly nonlinear fiber (HNLF) and acquires nonlinear phase shift due to self-phase modulation (SPM). At the end, another 50/50 coupler combines the regenerated I and Q signals.

In each arm, the first PSA is used to amplify one quadrature of incoming signal and deamplify the other quadrature in order to squeeze the phase noise. Since data encoded on the deamplified quadrature is also erased by the first PSA, signal in each arm retains only the data on amplified quadrature. After the first PSA, only amplitude noises remain on the two power levels of each signal.

The amplitude noise is regenerated by the SPM in the HNLF, followed by the PSA. The SPM converts the amplitude noise to the phase noise and thus causes rotation of the uncertainty (noise) ellipse around the signal phasor in the complex plane. For a proper nonlinear phase shift, the long axis of the noise ellipse can be significantly compressed by the PSA. To suppress the noise on both signal levels with 1:9 power ratio, there are two HNLF+PSA combinations in each arm.

Our modeling shows better than 4 dB noise reduction for all constellation points. Moreover, the higher signal levels experience even greater noise suppression, which is beneficial for their nonlinear propagation through the transmission fiber.

Pulse-shaping is a powerful tool to increase the spectral efficiency of signals transmitted over optical fiber. Two main contenders, namely OFDM and Nyquist signaling have emerged as promising candidates for future optical networks. As a third option, DFT-spread OFDM combines the two techniques. Although all techniques are well-known in wireless and wireline communications, the extremely high data rates are challenging when designing real-time optical transmitters and receivers, particularly in view of the special impairments imposed by the optical transmission channel. After giving a theoretical overview on OFDM and Nyquist signals, we show the system design for the three pulse-shaping techniques and discuss the processing requirements and the potential performance in terms of spectral efficiency and out-of-band signal suppression. We further investigate the impact of modulator nonlinearity and limited resolution of DACs and ADCs on the different signals. Finally, we demonstrate real-time OFDM and Nyquist pulse generation with data rates beyond 100 Gbit/s transmitted on a single optical carrier and in a single polarization.

Space-division multiplexing (SDM) systems transmit over multiple spatial-paths to increase capacity or photon efficiency. In these links, coupling between the spatial paths scramble each input signal across all the output channels. This scrambling is described by a N × M frequency dependent transfer matrix which can be undone using multiple-input multiple-output processing. Using a swept-wavelength interferometer with spatial diversity, we can completely characterize the amplitude and phase transmission between each input and output across the entire C-band in a single 100-ms scan. Matrix eigenanalysis of the transfer matrix enables extraction of the system's insertion loss, mode-dependent loss, and the principle-states of polarization. Results will include transfer matrix measurements of few-mode fibers, coupled-core fibers, photonic lantern spatial-multiplexers, and SDM compatible wavelength routing components such as a wavelength selective switch.

We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable to compensate DMD in wide wavelength range. All fabricated TMFs composed of a graded index core and a depressed inner claddings have low DMD slopes of less than |0.15| ps/km/nm, low optical loss of less than 0.21 dB/km for LP₀₁ and LP₁₁ modes respectively and low mode coupling ratio of less than -35 dB at the wavelength of 1550 nm. All TMFs have the similar effective area of 120 μm² for LP₀₁ mode and 160 μm² for LP₁₁ mode at 1550 nm. Moreover, it is clarified that a DMD compensation transmission line composed of the fabricated TMFs can successfully achieve the DMD of below |4.0| ps/km in the C+L band and mode conversion ratio of less than -30 dB at splice points.

A novel approach of using multi-element fiber (MEF) technology in space-division multiplexing (SDM) systems is presented. This paper reviews the progress in fabrication and characterization of MEF based both ultralow crosstalk transmission and amplifier fibers. Passive 3-element MEFs have been successfully demonstrated for application in telecommunications. An active 5-element MEF amplifier has also been demonstrated in a novel multiport cladding-pumped configuration, in which a central un-doped multi-mode pump fiber-element is surrounded by four Er/Yb-doped active fiber-elements. MEF is compatible with current WDM systems, and there is no need to develop specialized multiplexing/demultiplexing components. Moreover, it offers a smooth upgrade to SDM systems.

Due to the ever increasing capacity demands for optical communication links, single-mode fibers will soon not be able to support the exponential growth of data rates. A strong candidate to overcome the upcoming capacity crunch is spacedivision multiplexing (SDM) where different parallel paths in one fiber are used to transmit independent data streams. Suitable candidates for SDM are e.g. multi-mode fibers (MMF), where different orthogonal modes are independently addressed. In this paper, we discuss nonlinear interaction between signals that propagate in different fiber modes. Based on the nonlinear effect of four-wave mixing, phase-matching between spectral components that propagate in different fiber modes is studied. With the knowledge of intra- and intermodal four-wave mixing, all Kerr-effect based nonlinearities can be expressed in an analytical way. We propose a method to calculate the maximal achievable Optical Signal to Noise Ratio (OSNR) for each mode, based on the assumption that the nonlinear interference can be taken into account for by an additive noise term.

We analyzed a sample transmission link that uses a 55-mode graded-index multi-mode fiber, aiming to minimize the group-delay differences between signals that travel in different fiber modes. It is shown that each of the 55 modes can achieve an equal or higher OSNR compared to a standard single-mode fiber.

The steady increase of bandwidth demand in worldwide communications has revived the interest about multimode optical bers and their use in spatial division multiplexed systems. Roughly speaking, in these systems transmission capacity is increased by using modes as separate channels, resorting to either special ber with negligible mode coupling, or to MIMO technology to compensate mode dispersion. In this framework, understanding the mechanisms that originate mode coupling is of crucial importance, for it would lead to the development of more accurate propagation models and optimized ber designs. The paper analyzes the most common sources of mode coupling and their e ects.

The traffic carried by core optical networks grows at a steady but remarkable pace of 30-40% year-over-year. Optical transmissions and networking advancements continue to satisfy the traffic requirements by delivering the content over the network infrastructure in a cost and energy efficient manner. Such core optical networks serve the information traffic demands in a dynamic way, in response to requirements for shifting of traffics demands, both temporally (day/night) and spatially (business district/residential). However as we are approaching fundamental spectral efficiency limits of singlemode fibers, the scientific community is pursuing recently the development of an innovative, all-optical network architecture introducing the spatial degree of freedom when designing/operating future transport networks. Spacedivision- multiplexing through the use of bundled single mode fibers, and/or multi-core fibers and/or few-mode fibers can offer up to 100-fold capacity increase in future optical networks. The EU INSPACE project is working on the development of a complete spatial-spectral flexible optical networking solution, offering the network ultra-high capacity, flexibility and energy efficiency required to meet the challenges of delivering exponentially growing traffic demands in the internet over the next twenty years. In this paper we will present the motivation and main research activities of the INSPACE consortium towards the realization of the overall project solution.

We demonstrate a flexible multi-format vector modulator for coherent passive optical network (PON) architectures based on a non-interferometric cascade of a Semiconductor Optical Amplifier (SOA) and an Electro-Absorption Modulator (EAM) that exhibits increased simplicity and high energy-efficiency at low cost. 12- and 16- Quadrature Amplitude Modulation (QAM) constellations are generated, achieving modulation efficiencies of 3.6 and 4 bits/symbol respectively. The presented results demonstrate successful transmission over 25 km of fiber below the Forward Error Correction (FEC) limit, with sufficient compatible loss-budgets, making the proposed modulator concept an attractive candidate for urban network deployments, where high user density demands spectrally efficient formats. In addition, we describe the operation principle of the proposed modulator in detail and finally, the complete set of the digital signal processing (DSP) functionalities and algorithms that follow the standard coherent detection scheme is given, emphasizing on novel methods for QAM signal demodulation with uncommon constellation diagrams.

The implementations of super-Nyquist pulse generation, both in a digital field using a digital-to-analog converter (DAC) or an optical filter at transmitter side, are introduced. Three corresponding signal processing algorithms at receiver are presented and compared for high spectral-efficiency (SE) optical systems employing the spectral prefiltering. Those algorithms are designed for the mitigation towards inter-symbol-interference (ISI) and inter-channel-interference (ICI) impairments by the bandwidth constraint, including 1-tap constant modulus algorithm (CMA) and 3-tap maximum likelihood sequence estimation (MLSE), regular CMA and digital filter with 2-tap MLSE, and constant multi-modulus algorithm (CMMA) with 2-tap MLSE. The principles and prefiltering tolerance are given through numerical and experimental results.

We describe a novel all-optical hybrid mode-division multiplexing (MDM) -optical code division multiplexing (OCDM) architecture for future flexible access network. We successfully demonstrate, for the first time, an asynchronous on-off keying (OOK) modulation, 2 mode x 4 code x 10 Gbps transmission over 2km two mode fiber (TMF), without dispersion compensation at single wavelength, by using 16-chip (200 Gchip/s), 16-phase-shift keyed (PSK) optical codes (OC) generated by a multiport encoder/decoder (E/D) and an optical mode multiplexer/demultiplexer (MMUX/MDeMUX). We also analytically and experimentally evaluate the mode crosstalk tolerance as a function of the LP₀₁ and LP₁₁ modes.

We made two types of three-mode multiplexers with three single-mode input cores and one enlarged output core. Light in each input core evolved adiabatically into just one of the LP₀₁, even-LP₁₁ and odd-LP₁₁ modes of the output core. In the first type, the transition between inputs and output was formed by the controlled collapse of selected holes in a photonic crystal fibre with three cores in an equilateral triangular array. In the second type, three standard single-mode fibres were made dissimilar and tapered together within a fluorine-doped silica capillary. In both cases the output light patterns matched the LP₀₁ and LP₁₁ distributions as expected, with broadband operation across at least 100 nm in the near-IR, low insertion losses and mode purities exceeding 10 dB.

A multicore Er³⁺-doped fiber amplifier (MC-EDFA) can be realized by using an amplification medium such as bundled or multi-element Er³⁺-doped fiber (EDF) and multicore EDF, and employing a discrete pumping or cladding pumping method. In this paper, we report three recently developed MC-EDFAs, which represent all the amplification forms realizable using the amplification medium and pumping method. We also report the importance of an MC-EDFA for constructing a practical long-haul multicore fiber transmission system based on the facts of the progress made on the transmission experiments, and describe further progress on the MC-EDFA.

The optical transfer function of a pulsed local oscillator coherent receiver is derived. We point out that the transfer function is the amplitude of the spectral envelope of the locked optical modes of the pulsed local oscillator source. Using quantum theory of homodyne detection, and assuming an additive Gaussian circular optical noise, with a spectral density hν/2, at each optical input port of the optical mixer, a general discussion on the fundamental limit of the Signal-to-Noise Ratio of a pulsed coherent receiver is provided. It includes the influence of the time jitter of the sampling pulses. Results are numerically discussed in the context of time equivalent under sampling technique, but may be obviously extended to any real time sampling of optical signals.

We introduce an optical delay line based on the nonlinear birefringence effects in a polarization-maintaining fiber Bragg grating (PMFBG). A 92 ps delay (approximate 360° phase shifts at 10 GHz) is demonstrated with independent of the optical wavelength drifting by tuning the polarization angle of the polarization controller (PC) from 0 to 90°.

The paper will present a compression algorithm that will allow for both random and non-random sequential binary strings of data to be compressed for storage and transmission of media information. The compression system has direct applications to the storage and transmission of digital media such as movies, television, audio signals and other visual and auditory signals needed for engineering practicalities in such industries.

We consider design and modeling of hardware realizations of reconfigurable multifunctional continuous logic devices (R MCL D) as advanced components of the next generation high-performance MIMO-systems for the processing and interconnection. The R MCL D realize function of two-valued and continuous logics with current inputs and current outputs on the basis of CMOS current mirrors and circuits which realize the limited difference functions. We show advantages of such elements consisting in encoding of variables by the photocurrent levels, that allows easily providing optical inputs (by photo-detectors (PD)) and optical outputs (by LED). The conception of construction of R MCL D consists in the use of a current mirrors realized on 1.5μm technology CMOS transistors. Presence of 55÷65 transistors, 1 PD and 1 LED makes the offered circuits quite compact and allows their integration in 1D and 2D arrays. In the presentation we consider the capabilities of the offered circuits, show the simulation results and possible prospects of application of the circuits in particular for time-pulse coding for multivalued, continuous, neuro-fuzzy and matrix logics. The simulation results of NOT, MIN, MAX, equivalence (EQ) and other functions, that implemented R MCL D, showed that the level of logical variables can change from 1 μA to 10 μA for low-power consumption variants. The base cell of the R MCL D have low power consumption <1mW and processing time about 1÷11μS at supply voltage 2.4÷3.3V. Modeling of such cells in OrCad is made.