Optical Signal Regeneration Research Articles

Transparent vs Translucent Multi-Band Optical Networking: Capacity and Energy Analyses

Multi-band optical fiber transmission is generally proposed for capacity upgrades in optical transport networks. To comprehensively assess the potential of multi-band transmission, key metrics such as the potential capacity increase, energy consumption, and the number of required interfaces must be evaluated for different transmission scenarios. We consider progressive spectral exploitation, starting from the C-band only and up to C+L+S+U-band transmission, for both transparent and translucent solutions that exploit optical signal regeneration. By considering accurate state-of-the-art physical layer models, we derive a networking performance metric that enables the comparison of different solutions in terms of capacity allocation and energy consumption. For a translucent network design, different regenerator placement algorithms are compared, with the aim of minimizing energy consumption. The proposed network-wide numerical analysis shows that, for spectral occupations exceeding the C+L-band, translucent solutions can significantly increase network capacity, while leading to a similar energy consumption per transmitted bit as in the transparent design case, but they require the deployment of additional line interfaces. Significantly, these results provide evidence that the transparent exploitation of an additional transmission band produces a capacity increment that is at least comparable to that of a translucent solution based on already-in-use bands. Since this is attained at the expense of fewer line interfaces, it is a key finding suggesting that extending the number of bands supported is a cost-effective approach to scaling the capacity of existing fiber infrastructures.

A Mach–Zehnder modulator based novel regenerator for employment in relays used in free space optical communication

AbstractRelay nodes that are proposed for extending the length of free space optical links are generally based upon simple optical amplifiers. In this article, we have proposed an all‐optical relay that performs regeneration of optical signals along with the conventional optical amplification. Our proposed regenerator is based upon a dual‐drive Mach–Zehnder modulator. The optical pulsed signal received at the input of the regenerator is divided into two outputs using an optical splitter. One of the splitter outputs is converted into an electrical signal while the signal in the other path is given as input to the optical modulator. The negative slope of the modulator is used to compress intensity fluctuations over the pulsed optical signal by combining the converted electrical signal with the bias voltage of the modulator. We have compared the performance of our proposed regeneration scheme with the conventional optical amplifier based relay nodes in a free space optical link that is modeled by the Gamma–Gamma channel model. To simulate the effect of medium and strong turbulence of the free space optical link, the refractive index structure parameters chosen for the Gamma–Gamma channel model are and , respectively. It was observed that our proposed dual‐drive Mach–Zehnder modulator based relay significantly improves the receiver sensitivity by 4 dB under strong turbulence conditions and by 0.7 dB under medium turbulence conditions, respectively.

Modeling and design of enhanced all optical signal regeneration technique

Optical Signal regeneration in all-optical domain has played a vital in role for long haul optical communication systems. On contrary, the electronic regeneration systems have limitations in terms of real-time infeasibility for high data rate transmission with quality performance. The existing all-optical signal regeneration techniques remain in challenges for its complex design, testing and modeling prospective. The proposed all-optical signal regeneration technique is the new signal regeneration technique that is modeled and designed efficiently in order to regenerate high data rate signal that is degraded during transmission. The proposed all-optical signal regeneration technique is developed using single- pump Phase Sensitive Amplification, designed Optical Frequency Locked Model and noise mitigation model. The PSA performance is examined using various aspects i.e. signal power, noise figures, and phase error detection and correction. The proposed system will add a new dimension for signal regeneration schemes to develop more efficient regeneration systems with better performance analysis approach.

Phase Sensing Technology Based Optical Signal Regeneration for 40 Gb/s Optical System

In this paper, phase sensing technology based optical signal regeneration system is designed and developed for 40 Gb/s optical system. The designed technique has achieved the low bit error rate (BER) and high Q-factor for the long haul optical system of 200 km. In comparison to the existing systems, the proposed technique have achieved the low BER and high Q-factor for long noisy fiber link. In this work, the HNLF configuration based that varies the phase sensing during the optical signal regeneration for high-speed 40 Gb/s degraded optical system is developed. The designed phase sensing based optical signal regeneration system has achieved the BER of 10−21 with high Q-factor. The designed system can be used in the existing regeneration system to provide the noiseless communication for long haul optical systems.

Signal reshaping and noise suppression using photonic crystal Fano structures.

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

Analysis of photonic noise generated due to Kerr nonlinearity in silicon ring resonators.

The Kerr effect in silicon ring resonators (RRs) is widely used for switching and regeneration of optical communications signals. In addition, it has been shown to considerably limit the performance of refractive index sensors based on high quality-factor RRs. While the Kerr effect's impact on output signals of silicon RRs is well known, its influence on the properties of the output noise is yet to be explored. In this work, we analytically and numerically analyze the noise properties of Kerr effect in silicon RRs. We show that the input power, RR's bandwidth, and input optical signal to noise ratio (OSNR) have significant influence on the power and distribution of the output noise. We use the developed noise model to evaluate the RR's noise figure and output noise distribution for optical communications and sensing applications. These noise properties can be used for the design and performance evaluation of optical communications systems and sensors using silicon photonic RRs.

A New All-Optical Signal Regeneration Technique for 10 GB/S DPSK Transmission System

<p>The transmission of high power inside the optical fiber, produce amplitude noise, phase noise and other transmission impairments that degrade the performance of optical communication system. The signal regeneration techniques are used to mitigate these nonlinear impairments in the electrical or in the optical domain. All-optical signal regeneration techniques are one of the solutions to mitigate these nonlinear transmission impairments in the optical domain without converting the signal from optical to electrical domain. The existing techniques are not capable enough to attain the Bit Error Rate (BER) less than 10<sup>-10</sup> with the power penalty less than – 9dBm. In this paper, a new all-optical signal regeneration technique is developed that mitigate amplitude and phase noises in the optical domain. The new optical signal regeneration technique is developed by combining the two existing technique one is 3R (Reshaping, Reamplification and Retiming) regeneration and other is Phase Sensitive Amplification (PSA). The 10Gb/s Differential Phase shift Keying (DPSK) noisy transmission system is used to verify the features of developed technique. The developed technique successfully mitigates the nonlinear impairments from the noisy DPSK system with significant improvement in BER at low power penalty with the additional feature of high Q-factor and an eye open response for the regenerated signal. It is determined that BER of 10<sup>-12</sup> is achieved at the power penalty of -14 dBm with Q-factor of 42 and an eye opened response. The developed technique in the DPSK system is realized using commercial software package Optisystem. The designed technique will be helpful to enhance the performance existing high-speed optical communication by achieving the minimum BER at low power penalty.</p>

InP Microdisk Lasers Integrated on Si for Optical Interconnects

We review recent theoretical and experimental work on InP membrane microdisk lasers heterogeneously integrated on SOI and coupled to a Si bus waveguide. The lasers can now be fabricated with very high yield, have typical threshold currents of 0.5 mA and output powers of tens of μW, while the total power consumption is restricted to 5 mW. First, we describe various improvements in the fabrication technology and interesting results on the uniformity in device characteristics. In a second part, unidirectional behaviour and reflection sensitivity are briefly discussed. The third part is focused on optical signal regeneration with microdisk lasers. The last part contains a brief summary of optical interconnects based on heterogeneously integrated microdisk lasers and heterogeneously integrated photodetectors.

Genetic Approach for Optimizing the Placement of All-Optical Regenerators in WSON

In wavelength switched optical networks (WSONs), the placement of opto-electronic regenerators has always been optimized to keep the cost and power consumption contained, while ensuring the quality of transmission (QoT) for the optical signals. Nowadays, with the increase of the transmission rates and the spectral efficiency of the modulation formats, optical signal regeneration is still relevant for ensuring QoT. The progress in integrated photonics makes possible the realization of integrated optical regenerators that can replace the traditional opto-electronic regenerators. All-optical regenerators enable a reduction of size and energy consumption. However, differently from opto-electronic regenerators, recently fabricated integrated optical regenerators neither perform wavelength conversion nor regenerate multiple lightpaths at the same wavelength. Thus, novel constraints and limitations are introduced to the conventional regenerator placement problem, which has been well studied in the past for opto-electronic regenerators. This paper addresses the all-optical regenerator placement (ORP) problem in WSONs with guaranteed QoT. A genetic algorithm (GA) is proposed for optimizing the ORP while jointly solving the routing and wavelength assignment problem. GA results are compared with the optimal solutions found by solving a binary linear programming (BLP) formulation. When properly tuned, GA is able to quickly achieve the optimal solutions found by the BLP solver. The performance analysis indicates that the additional constraints have a negligible impact on the overall number of regenerators, compared to the case with opto-electronic regenerators.

Simultaneous frequency conversion, regeneration and reshaping of optical signals

Nondegenerate four-wave mixing in fibers enables the tunable and low-noise frequency conversion of optical signals. This paper shows that four-wave mixing driven by pulsed pumps can also regenerate and reshape optical signal pulses arbitrarily.

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Enhanced Properties in Single-Walled Carbon Nanotubes Based Saturable Absorber for All Optical Signal Regeneration

Ultrafast relaxation dynamics of photogenerated carriers in nanostructure based saturable absorber (SA) are investigated using a degenerate cross-polarized pump–probe experiment at 1.55 µm operating wavelength. Single-walled carbon nanotubes (SWNT) encased in micelles are studied and compared to bundled ones as well as to iron doped InGaAs/InP multiple quantum wells (MQW). SA parameters for all optical signal regeneration (AOSR) are extracted from the normalized differential transmission. Although all samples show the same order of recombination time, SWNT in micelles present a much higher contrast ratio associated to a lower level of saturation fluence as compared to their bundled and MQW counterparts.

A direct comparison of single-walled carbon nanotubes and quantum-wells based subpicosecond saturable absorbers for all optical signal regeneration at 1.55 μm

Subpicosecond optical transmission experiments are used to compare saturable absorber (SA) based on bundled single-walled carbon nanotubes (SWNT) and iron-doped InGaAs/InP epitaxial multiple quantum wells (MQW) at 1.55 μm telecom wavelength. The SA key parameters (contrast ratio, saturation fluence, and recovery time) relevant for high speed all optical signal regeneration (AOSR) are extracted from the normalized differential transmission (NDT). Although both SA exhibit good contrast ratios, SWNT show a full signal recovery as well as a much faster response time than MQW. This original work on SA shows that SWNT are excellent candidates for future low cost AOSR.

Design of photonic crystal fibers with highly nonlinear glasses for four-wave-mixing based telecom applications

A fully-vectorial mode solver based on the finite element method is employed in a combination with the downhill simplex method the dispersion optimization of photonic crystal fibers made from highly nonlinear glasses. The nonlinear fibers are designed for telecom applications such as parametric amplification, wavelength conversion, ultra-fast switching and regeneration of optical signals. The optimization is carried in terms of the zero dispersion wavelength, dispersion magnitude and nonlinear coefficient and confinement loss in the wavelength range around 1.55 microm. We restrict our work to the index-guiding fiber structures a small number of hexagonally arrayed air holes.

Large signal-to-noise-ratio enhancement of ultrashort pulsed optical signals using a power-symmetric Nonlinear Optical Loop Mirror with output polarisation selection

A numerical study of a fibre-based scheme for the regeneration of ultrashort-pulsed optical signals is presented. The setup is made of a power-symmetric Nonlinear Optical Loop Mirror (NOLM) followed by a polariser. The NOLM operates through nonlinear polarisation rotation, and includes twisted, anomalous-dispersion fibre and a quarter-wave retarder. When the orientations of the linear input polarisation and of the output polariser are properly adjusted, the output energy characteristic flattens at high power, a property that can be used to eliminate large amplitude fluctuations on the logical ones of an optical signal. When the input pulse parameters closely match those of fundamental solitons or of stable elliptically polarised solitary waves, a wide and flat plateau is obtained, allowing the reduction of ∼30% amplitude fluctuations to less than 1%. Very large amplitude fluctuations beyond 50% can also be reduced down to a few %. Although the output pulses are slightly chirped, they are free of pedestal, thanks to the zero low-power transmission of the NOLM, which also allows the simultaneous regeneration of logical zeros. We believe that this setup will be useful for the regeneration of highly degraded signals in future ultrafast transmission networks.

A passive all-optical semiconductor device for level amplitude stabilization based on fast saturable absorber

A high-speed saturable-absorber-based device (response time below 2.5ps) providing a significant amplitude stabilization is demonstrated. The experimental results allow estimating that the amplitude fluctuations of the output should be reduced by about 90% compared to the input fluctuations, within the input power range of (5–18μJ∕cm2). This device has been studied in view of its possible use for bit-1 noise reduction. When combined with a state-of-art saturable absorber device, this could provide a simple and compact scheme for the complete reamplification and reshaping regeneration of digital optical signals.

Recent Advances in Optical Processing Techniques Using Highly Nonlinear Bismuth Oxide Fiber

We report our recent studies on nonlinear processing of optical signals using a 35-cm highly nonlinear bismuth oxide fiber (Bi-NLF). Our findings are based on self-phase modulation, cross-phase modulation, and four-wave mixing in the Bi-NLF. We demonstrate applications of the nonlinear techniques in optical signal regeneration, tunable optical delay, stabilization of multiwavelength laser source, tunable optical pulse generation, microwave photonic carrier frequency multiplication, and all-optical wavelength conversion.

An Optical Parametric Amplified Fiber Switch for Optical Signal Processing and Regeneration

An optical parametric amplified (OPA) fiber switch is described in this paper. This device switches input signals without shifting the wavelength by changing the polarization state of the signal using optical parametric amplification. The OPA fiber switch features ultra-broadband, highly efficient switching with a high contrast ratio. We experimentally test the prototype of the OPA fiber switch, which uses a highly nonlinear fiber. Optical demultiplexing of 160 Gb/s differential phase-shift keying (DPSK) signals is demonstrated in the whole C-band and shows that it provides almost penalty-free optical detection. The application of amplitude noise suppression with the OPA fiber switch by using parametric gain saturation is then proposed and demonstrated for a 160 Gb/s DPSK signal. When it is set to an amplitude-limiting condition, the OPA fiber switch successfully increases the optical signal-to-noise ratio by 4 dB and effectively suppresses the phase deterioration in 160 Gb/s DPSK transmission by increasing the system margin by more than 5 dB.

Performances of a Fully Integrated All-Optical Pulse Reshaper Based on Cascaded Coupled Nonlinear Microring Resonators

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We propose a simple way to design a fully integrated and passive all-optical pulse reshaper in the aim of reamplifying and reshaping (2R) regeneration of optical digital signals. The device could be achieved from a coupled microresonator structure with Kerr nonlinearity. By using time-domain simulation, we show that we can obtain a clear nonlinear power transfer that is capable of improving signal-to-noise ratio and reducing bit error rate for digital signals. The reshaping performances are estimated by calculating <formula formulatype="inline"><tex>$Q$</tex> </formula>-factor enhancement. Since we take benefit from field enhancement at resonance, this integrated reshaper could be much smaller than other gates based on nonlinear fibers or waveguides. </para>

Broad-band optical parametric gain on a silicon photonic chip

Developing an optical amplifier on silicon is essential for the success of silicon-on-insulator (SOI) photonic integrated circuits. Recently, optical gain with a 1-nm bandwidth was demonstrated using the Raman effect, which led to the demonstration of a Raman oscillator, lossless optical modulation and optically tunable slow light. A key strength of optical communications is the parallelism of information transfer and processing onto multiple wavelength channels. However, the relatively narrow Raman gain bandwidth only allows for amplification or generation of a single wavelength channel. If broad gain bandwidths were to be demonstrated on silicon, then an array of wavelength channels could be generated and processed, representing a critical advance for densely integrated photonic circuits. Here we demonstrate net on/off gain over a wavelength range of 28 nm through the optical process of phase-matched four-wave mixing in suitably designed SOI channel waveguides. We also demonstrate wavelength conversion in the range 1,511-1,591 nm with peak conversion efficiencies of +5.2 dB, which represents more than 20 times improvement on previous four-wave-mixing efficiencies in SOI waveguides. These advances allow for the implementation of dense wavelength division multiplexing in an all-silicon photonic integrated circuit. Additionally, all-optical delays, all-optical switches, optical signal regenerators and optical sources for quantum information technology, all demonstrated using four-wave mixing in silica fibres, can now be transferred to the SOI platform.