All-optical Wavelength Conversion Research Articles

InP Photonic Integrated All-Optical Wavelength Conversion of 128 GBaud DP-16QAM Signals Using XGM in SOAs

InP Photonic Integrated All-Optical Wavelength Conversion of 128 GBaud DP-16QAM Signals Using XGM in SOAs

Impact of the reconfigurable optical add-drop multiplexer architecture on the design of multi-band C+L+S optical networks

The main advantage of multi-band (MB) networks is to provide more capacity than C-band networks by using other unused bands like the L- and S-bands and, in this way, postpone the announced optical network capacity crunch. However, MB nodes have a more complex structure than C-band nodes, impacting their cost and enhancing their induced physical layer impairments (PLIs). The main goal of this paper is to analyze the impact of several MB node architectures (namely baseline, common-band and compact MB node architectures) on the total network capacity and total network cost-per-bit, using a routing, modulation format, and spectrum assignment (RMSA) network planning tool based on a Monte–Carlo simulation that also incorporates the impact of network PLIs. When the PLIs are neglected, the common-band architecture presents the lowest cost-per-bit compared to the remaining MB architectures, since only lower cost C-band components are used. However, with the PLIs impact, the common-band architecture leads to the lowest total network capacity and highest cost-per-bit due to additional noise coming from all-optical wavelength converters. In particular, the common-band total network capacity is less than half the baseline and compact total network capacities for a blocking probability of 1%, considering the best channel launch power. Also, the common-band cost-per-bit is almost twice the baseline and compact cost-per-bit due to the PLIs-induced degradation.

Efficient and Broadband All-Optical Wavelength Conversion between C and O Bands in Nanophotonic Lithium Niobate Waveguides

Efficient and Broadband All-Optical Wavelength Conversion between C and O Bands in Nanophotonic Lithium Niobate Waveguides

Design and Characterization of Dispersion-Tailored Silicon Strip Waveguides toward Wideband Wavelength Conversion

One of cost-effective ways to increase the transmission capacity of current standard wavelength division multiplexing (WDM) transmission systems is to use a wavelength band other than the C-band to transmit in multi-band. We proposed the concept of multi-band system using wavelength conversion, which can simultaneously process signals over a wide wavelength range. All-optical wavelength conversion could be used to convert C-band WDM signals into other bands in a highly nonlinear fiber (HNLF) by four-wave mixing and allow to simultaneously transmit multiple WDM signals including other than the C-band, with only C-band transceivers. Wavelength conversion has been reported for various nonlinear waveguide materials other than HNLF. In such nonlinear materials, we noticed the possibility of wideband transmission by dispersion-tailored silicon-on-insulator (SOI) waveguides. Based on the CMOS process has high accuracy, it is expected that the chromatic dispersion fluctuation could be reduced in mass production. As a first step in the investigation of the broadness of wavelength conversion using SOI-based waveguides, we designed and fabricated dispersion-tailored 12 strip waveguides provided with an edge coupler at both ends. Each of the 12 waveguides having different widths and lengths and is connected to fibers via lensed fibers or by lenses. In order to characterize each waveguide, the pump-probe experimental setup was constructed using a tunable light source as pump and an unmodulated 96-ch C-band WDM test signal. Using this setup, we evaluate insertion loss, input power dependence, conversion bandwidth and conversion efficiency. We confirmed C-band test signal was converted to the S-band and the L-band using the same silicon waveguide with 3 dB conversion bandwidth over 100-nm. Furthermore, an increased design tolerance of at least 90 nm was confirmed for C-to-S conversion by shortening the waveguide length. It is confirmed that the wavelength converters using the nonlinear waveguide has sufficiently wide conversion bandwidth to enhance the multi-band WDM transmission system.

2-μm short data pulse all-optical wavelength converter based on MXene microfiber

We demonstrate the all-optical wavelength conversion of short pulse signals at 2-μm using MXene-assisted microfiber. The process involves an actively mode-locked thulium-holmium co-doped fiber laser, which is synchronously modulated by a digital signal and coupled with continuous light for the conversion process. The converted light is generated via four-wave mixing (FWM) with in the MXene-assisted microfiber. The conversion efficiency reaches −38.98 dB. For a wavelength tuning range of 6.08 nm–1.04 nm, the conversion efficiency is increased by 10.44 dB. The wavelength conversion efficiency fluctuation during 130 min is only 0.512 dB. The converter enables the successful transmission of 489 Mb/s data carried by the converted light. The results show that the MXene-assisted microfiber carrier wavelength converter has a high conversion efficiency and excellent stability. This study aligns with the development trend of all-optical wavelength conversion and explores the characteristics of highly nonlinear optical materials. The utilization of MXene-assisted microfiber enables significant advancements in all-optical wavelength conversion, particularly in the context of processing 2-μm short data pulse signals for nonlinear optics applications.

TiN/Ti3C2 Heterojunction Microfiber-Enhanced Four-Wave Mixing-Based All-Optical Wavelength Converter

As a novel nanomaterial, the TiN/Ti3C2 heterojunction has been demonstrated to possess exceptional optoelectronic properties, offering significant potential for applications in fields such as communication, optical sensors, and image processing. The rapid evolution of the internet demands higher communication capacity and information processing speed. In this context, all-optical wavelength conversion, a pivotal technique in all-optical signal processing, holds paramount importance in overcoming electronic bottlenecks, enhancing wavelength utilization, resolving wavelength competition, and mitigating network congestion. Utilizing the idle light generated through the four-wave mixing (FWM) process accurately mimics the bit patterns of signal channels. This process is inherently rapid and theoretically capable of surpassing electronic bottlenecks with ease. By placing an optical filter at the fiber output end to allow idle light passage while blocking pump and signal light, the output becomes a wavelength-converted replica of the original bitstream. It has been verified that TiN/Ti3C2 heterojunction-coated microfiber (THM) exhibits outstanding third-order nonlinear coefficients. Building upon this, we achieved a THM-enhanced FWM all-optical wavelength converter, resulting in a ~4.48 dB improvement in conversion efficiency. Compared to conventional high-nonlinear fibers, this compact device significantly reduces fiber length and can be easily integrated into current high-speed optical communication networks. It demonstrates broad prospects in the realms of all-optical signal processing, robotic applications, ultra-high-speed communication, and beyond.

All-optical wavelength and format conversion of DQPSK-to-PAM4 using DLI and pump assisted NOLM

An all-optical wavelength and format conversion scheme of 20 Gbps differential quadrature phase shift keying (DQPSK)-to-4-ary pulse amplitude modulation (PAM4) signals based on the delay line interferometer (DLI) and the pump assisted nonlinear optical loop mirror (NOLM) is proposed and numerically simulated. The input DQPSK signal is converted into two star-16-ary quadrature amplitude modulation (star-16QAM) signals (namely, star-16QAM-I and star-16QAM-Q) using DLI with the time delay of 1-symbol and different linear phase shifts of π/4 and −π/4, respectively. The star-16QAM signals are converted into the on-off keying (OOK) signals (namely, OOK-I and OOK-Q) using the pump assisted NOLM based on the self-phase modulation (SPM) and the cross-phase modulation (XPM) in the highly nonlinear fiber (HNLF). The two OOK signals can be aggregated into different types of PAM4 signals by adjusting their power ratio (PR) and relative phase shift (RPS) flexibly. Error vector magnitude (EVM) and bit error rate (BER) for the input and output optical signals are calculated to verify the scheme performance. Compared to the DQPSK signal with an input optical signal-to-noise ratio (OSNR) of 30 dB, there are about 2.5 dB penalty of receiver OSNR for the converted OOK-I and OOK-Q signals. For the corresponding aggregated equidistant PAM4 and equiamplitude PAM4 signals, they have about 6.3 dB and 12.1 dB penalty of receiver OSNR. The proposed scheme of DQPSK-to-PAM4 can be deployed at the all-optical gateway to bridge the long-hual and short-reach optical networks.

Impact of wideband wavelength conversion on the performance of optical networks

In this paper, it is proposed and numerically tested a 4 −THz guard-band-less integrated all-optical wavelength converter (iAOWC) with two four-wave mixing (FWM) stages. The nonlinear media used in each stage is a waveguide with a tellurite core that is buried into a SiO2 substrate. The core is shaped as two interleaved spirals connected in their centers by two arcs of a circle to minimize bend loss. The iAOWC can continuously shift a 4 −THz WDM bandwidth from the C- to the L-band and vice versa. In the physical layer simulations, 80×28−GBaud, as DP-QPSK and DP-16QAM, 50-GHz-WDM signals were propagated, respectively, through typical distances found in ultra-long-haul and long-haul transmission systems. For up to four wavelength conversions, the penalties imposed on the signals bit-error-ratios by the iAOWCs were negligible. In the network layer simulations, blocking probabilities were estimated in the CORONET and PANEUR topologies supposing an incremental traffic scenario. Physical layer results were fundamental for the parameters (route lengths, wideband conversion, and spectral shift) considered in the network layer analysis. All network links could carry up to 160 wavelengths that extended from C- to L-band. It is shown that by using an iAOWC with bandwidth of 4-THz instead of 1-THz, both with the same spectral shift capability, to match the blocking probabilities achieved with OEOWCs, this would lead to a reduction of 50% and 40% in the number of required devices for the CORONET and PANEUR topologies, respectively. Finally, this is the first time that it is reported a joint analysis of the physical and network layers regarding the impact of wideband wavelength conversion on the performance of optical networks, specially using an integrated all-optical device and under real-world traffic scenarios.

Hybrid Silicon Nitride Photonic Integrated Circuits Covered by Single-Walled Carbon Nanotube Films.

The integration of low-dimensional materials with optical waveguides presents promising opportunities for enhancing light manipulation in passive photonic circuits. In this study, we investigate the potential of aerosol-synthesized single-walled carbon nanotube (SWCNT) films for silicon nitride photonic circuits as a basis for developing integrated optics devices. Specifically, by measuring the optical response of SWCNT-covered waveguides, we retrieve the main SWCNT film parameters, such as absorption, nonlinear refractive, and thermo-optic coefficients, and we demonstrate the enhancement of all-optical wavelength conversion and the photoresponse with a 1.2 GHz bandwidth.

Cascaded four-wave mixing all-optical wavelength converter based on highly nonlinear fiber deposited graphene oxide

The all-optical wavelength conversion using cascaded four-wave mixing (FWM) phenomena with graphene oxide (GO) and a highly nonlinear fiber (HNLF) device is demonstrated experimentally. GO has a strong third-order nonlinear effect and is an excellent nonlinear optical material for nonlinear optical wavelength conversion. The group velocity matching of pump and signal, HNLF, and GO amplification promote the cascaded nonlinear frequency mixing process. From the experimental and analytical results, the maximum spacing between signal and pump is 21 nm, and specifically, the order of cascaded FWM light increases from order 1 to order 2 with increasing GO, and the first-order FWM conversion efficiency increases to a maximum of −14.5 dB. To the best of our knowledge, this is the first time that cascaded FWM-based all-optical wavelength conversion in HNLF–GO with wide wavelength selectivity is investigated with combined pump and signal light. Our findings not only provide an effective method for achieving all-optical wavelength conversion in cascaded FWM but also offer the possibility of fabricating high-performance nonlinear optical devices.

100-Gbps per-channel all-optical wavelength conversion without pre-amplifiers based on an integrated nanophotonic platform

Abstract All-optical wavelength conversion based on four-wave mixing attracts intense interest in many areas, especially in optical fiber communications, due to the advantages of femtosecond response, modulation-format transparency, and high flexibility in optical network management. In this paper, we present the first optical translation of 32-GBaud 16QAM signals with an integrated Si3N4 nonlinear nanophotonic waveguide. An on-chip continuous-wave conversion efficiency of up to −0.6 dB from S band to C band is achieved in the dispersion-engineered low-loss Si3N4 nonlinear waveguide that is back-end compatible with complementary metal–oxide–semiconductor processes. The high conversion efficiency avoids the use of external optical amplifiers for signal demodulation. The converted idler is successfully received with a sensitivity penalty of less than 0.5 dB. Moreover, pre-amplifier-free multichannel wavelength conversion of over-100-Gbps coherent signals in C band is also demonstrated using the same Si3N4 nanophotonic waveguide via changing the pump wavelength, which shows good flexibility in all-optical signal processing. Additionally, wavelength conversion with a bandwidth over 100 nm can be expected by optimizing the current Si3N4 nanophotonic waveguide, which is promising for commercial coherent fiber communications and has bright prospects in various areas including optical signal processing, imaging, optical spectroscopy, and quantum optics.

Optimization and Performance Evaluation of Single-Mode SOI Waveguides for Ultra-Broadband C-to-S Wavelength Conversion

In order to keep up with expected growth in data traffic, using multiple bands beyond the C band is an appealing solution as it can partly reuse deployed optical fibers. One way of handling multi-band data generation and reception is by using all-optical wavelength converters (AOWCs) to translate to or from the C band, where commercial equipment is easily available. In this work, we therefore designed and realized an AOWC targeting C-to-S band conversion. To respect the requirements of commercial applications, we aimed for a low-complexity high-bandwidth implementation with reasonably low power consumption, tolerance for typical process variations and potential for further integration. Thus we implemented the AOWC as a strip waveguide in a Silicon-on-insulator (SOI) technology. An optimization of the conversion bandwidth was conducted during design and initial characterizations confirmed a conversion efficiency of -32.8 dB and a high bandwidth of about 35 nm with grating couplers and likely beyond 50 nm for edge couplers. Using the fabricated converters, we were able to demonstrate a marginal 0.3 dB optical signal-to-noise ratio (OSNR) penalty for a back-to-back (b2b) transmission of a single-channel single-polarization 32 GBd quadrature-phase-shift keying (QPSK) signal converted from C to S band. Additionally, this converted signal was successfully transmitted over 100 km of standard single-mode fiber (SSMF). Finally, crosstalk issues arising in multi-channel conversion were investigated.

Two-dimensional material integrated micro-nano fiber, the new opportunity in all-optical signal processing

Abstract With the development of all-optical networks, all-optical devices have become a research hotspot in recent years. Two-dimensional materials, represented by graphene and black phosphorus, have attracted great interest in the scientific community due to their excellent optical, electrical, magnetic, and mechanical properties. Bridging the gap between fiber optics and nanotechnology, microfibers can interact with light and matter at the micro or even nanoscale. By combining two-dimensional materials with microfibers, composite waveguides can be formed. They have the advantages of high nonlinear effect, all-fiber structure, and high damage threshold, etc. The composite waveguide can be directly applied to optical fiber communication systems, and plays an important role in the field of all-optical signal processing with a huge application prospect. In this review, the properties of typical 2D materials are first introduced. Next, the preparation methods of the relevant equipments are introduced and compared. Then, the all-optical signal processing technology based on 2D material-integrated microfiber composite waveguide is reviewed. The latest developments of all-optical modulators, all-optical wavelength converters, all-optical logic gates and all-optical thresholding devices are presented. Finally, the challenges and opportunities for the future development of 2D materials-integrated microfiber optoelectronic devices are summarized.

Highly Efficient Multi-Band Optical Networks with Wavelength-Selective Band Switching

Multi-band transmission technologies promise to cost-effectively expand the capacity of optical networks by exploiting low-loss spectrum windows beyond the conventional band used in already-deployed fibers. While such technologies offer a high potential for capacity upgrades, available capacity is seriously restricted not only by the wavelength-continuity constraint but also by the signal-to-noise ratio (SNR) constraint. In fact, exploiting more bands can cause higher SNR imbalance over multiple bands, which is mainly due to stimulated Raman scattering. To relax these constraints, we propose wavelength-selective band switching-enabled networks (BSNs), where each wavelength channel can be freely switched to any band and in any direction at any optical node on the route. We also present two typical optical node configurations utilizing all-optical wavelength converters, which can realize the switching proposal. Moreover, numerical analyses clarify that our BSN can reduce the fiber resource requirements by more than 20% compared to a conventional multi-band network under realistic conditions. We also discuss the impact of physical-layer performance of band switching operations on available benefits to investigate the feasibility of BSNs. In addition, we report on a proof-of-concept demonstration of a BSN with a prototype node, where C+L-band wavelength-division-multiplexed 112-Gb/s dual-polarization quadrature phase-shift keying signals are successfully transmitted while the bands of individual channels are switched node-by-node for up to 4 cascaded nodes.

Four-channel all-optical wavelength conversion unit based on nonlinear effect of three-section monolithically integrated semiconductor lasers.

A simple and highly efficient four-channel all-optical wavelength conversion based on four-wave mixing effect of the directly modulated three-section monolithically integrated semiconductor laser is proposed and experimentally investigated. For this wavelength conversion unit, the spacing of the wavelength can be adjusted by tuning the bias current of the lasers and setting it to be 0.4nm (50GHz) as a demonstration is this work. A 50Mbps 16-QAM signal centers at 4-8GHz is experimentally switched to a targeted path. Up- or downconversion depends on a wavelength-selective switch, and the conversion efficiency can reach up to -2 to 0dB. This work provides a new technology for photonic radio-frequency switching matrix and contributes to the integrated implementation of satellite transponders.

Broadband Wavelength Conversion for Hybrid Multiplexing Signals Based on a Parallel Dispersion-Engineered Silicon Waveguide

Broadband all-optical wavelength conversion (AOWC) for hybrid wavelength- and mode-division multiplexing (WDM-MDM) signals is experimentally demonstrated based on degenerate four-wave mixing in a silicon chip with a parallel dispersion-optimized multimode nonlinear waveguide and mode (de)multiplexers. By simultaneously coupling two modes into the waveguide using an optical fiber array, the intermodal crosstalk is measured to be as low as −25.9 dB for the fundamental mode of the transverse electric mode (TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) (or −23.6 dB for the first-order mode TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ), and the conversion efficiency is −25.4 dB for TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (or −26.3 dB for TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) mode. A wide conversion bandwidth of ∼68 nm is measured except for the influence of the crosstalk, which is the first time to experimentally demonstrate the broadband wavelength conversion for MDM signal. Using a 4 × 10 Gbit/s on-off keying (OOK) hybrid WDM-MDM signal, four AOWC channels are obtained on the idlers and the power penalty of each channel is less than 2.7 dB at the bit-error-ratio of 1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> .

Pulse distortion caused by waveguide inhomogeneity in nonlinear optical wavelength converters

Low-noise integrated all-optical wavelength converters that can be operated in short pulse regime are essential tools to overcome contention resolution in a modern communication network, based on wavelength division multiplexing. Any imperfect functionality in such devices causes non-ideal optical power transfer to the converted data pulses. All imperfections during the preparation and operation of the wavelength converters can be addressed to the waveguide inhomogeneity which distorts data pulses to be converted. This paper reports different waveguide inhomogeneity effects on the pulse distortion while using periodically poled lithium niobate waveguide as wavelength converters. Three types of chi ^{(2)}-based nonlinear optical processes, including second harmonic generation, difference frequency generation, and cascaded second harmonic generation/difference frequency generation are numerically studied to show that any constant, linear, and quadratic waveguide inhomogeneity causes short pulse (down to 1 ns) distortion in such wavelength converters. In addition, it is shown that the reconstruction of textrm{sech}^2-shaped generated pulses is possible, when suitable upside-down quadratic variations of obtained inhomogeneity are deliberately induced in the waveguide. Notably, for pulsed second harmonic generation, the generated pulse can be compressed using an upside-down quadratic phase mismatch.

Wideband Simultaneous Wavelength Conversion of Multiple WDM Channels Using Silicon-Rich Nitride Waveguide

The triple-band (S+C+L) transmission system using only C-band transceivers and all-optical wavelength conversions (AOWCs) without S- and L-band optical transceivers have been proposed. Although an AOWC employs highly nonlinear fibers, it is not applicable to photonic integrated circuits (PICs). For a device with successful wavelength conversion, a silicon-rich nitride (SRN) waveguide provides superior performance, as it is applicable to PIC and facilitates a higher Kerr nonlinearity than conventional stoichiometric silicon nitride waveguides. Thus, in this study, we propose an all-optical simultaneous wavelength conversion method that can be cost-effectively fabricated on a PIC based on four-wave mixing in SRN waveguides. Following an explanation regarding the design of an SRN waveguide for wideband AOWC, the successful operation of a double-stage AOWC of 64-channel 64-Gb/s QPSK signals between the C+L bands and the S-band is demonstrated, which is useful for wideband transmission systems.

Wide Wavelength Selectable and High Frequency Precision of All-Optical Wavelength Conversion Using Pump Light Generated from Optical Combs and SSB Modulation

All-optical wavelength conversion based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF) with wide wavelength selectivity and highly precise frequency controllability was investigated in combination with pump light generated from optical combs and single-side-band (SSB) modulation. Using multiple carriers, optical combs generated using LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase modulators and an SSB phase modulator, pump lights were precisely controlled with a frequency range of 580 GHz and frequency shift of 1.25 GHz. The frequency difference of the pump lights from the ideal one was less than the resolution of an optical spectrum analyzer FWM was performed for single-polarized 10 Gbaud NRZ-QPSK signals in combination with the generated pump lights, and clear eye-openings and constellations for idler signals were achieved. Moreover, a bit error rate (BER) of <3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> for all idler lights was achieved. Conversely, in the case of the 1.25 GHz controlled pump light, the constellation was distorted, and the BER was saturated at 2.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . In addition, the limit of wavelength convertible bandwidth was investigated to determine the condition for selecting the frequency of wavelength conversion applicable to wavelength defragmentation in the metro/core networks. From the experimental and analytical results, the maximum frequency spacing between the signal and pump was found to be 1403.125 GHz, limited by the wavelength conversion efficiency of the HNLF, whereas the minimum frequency spacing was found to be 25 GHz, restricted by the crosstalk between the signal and pump light that could not be eliminated using the bandpass filter.

Spectral shaped PAM4 signal based on nonlinear differential coding for AOWC system with Self-pumping structure

Spectral shaped 4-level pulse amplitude modulation (PAM4) signal based on nonlinear different coding (NLDC) is proposed in an all-optical wavelength conversion (AOWC) system with self-pumping structure. Laser-driven Mach-Zehnder modulator generates multiple spectra and forms self-pumping structure by selecting signal and pump light, which can ignore the laser phase conversion noise. However, uniform PAM4 signal is severely distorted by nonlinear effects of the practical bandwidth-limited and power-limited AOWC systems. In order to effectively reduce nonlinear interference and fully evaluate the performance of the AOWC systems with self-pumping structure, the PAM4 signal based on NLDC is proposed and demonstrated in two AOWC systems based on parallel pump and vertical pump structures. Compared with the uniform PAM4 signal, the bit error rate (BER) of converted light with NLDC can be reduced by two orders of magnitude, two pump structures can reach 3.496 × 10−5 and 2.85 × 10−4, respectively. The two structures can obtain bandwidth tolerance gains of 3.45 GHz and 3.7 GHz, respectively. When the bandwidth is 18 GHz, this scheme can obtain more than 10Gbit/s data rate gain. In addition, NLDC can make PAM4 signal insensitive to the injection current of semiconductor optical amplifier, which proves that the proposed scheme has high tolerance to the nonlinear effect and is suitable for high-capacity AOWC system.