Simultaneous Wavelength Conversion Research Articles

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.

Versatility of Stimulated Raman Scattering Based Power Combining of Multiple Fiber Lasers

We demonstrate the versatility of our recently demonstrated technique of Stimulated Raman Scattering induced simultaneous wavelength conversion and power combining of multiple Ytterbium (Yb) doped fiber lasers in terms of number of input pump sources and the wavelength spacing between them. We experimentally show that this technique works when the Raman gain coefficient between the input chosen pump sources is 1) negligible, i.e., when pump sources are separated in wavelength by as small as 5nm, 2) approximately half of the peak value, and 3) more than half of the peak value. Our experiments also show that the technique works for more than two Ytterbium-doped fiber lasers. Experimental results were shown for power combining of 1074nm and 1079nm lasers, 1088nm and 1117nm lasers, and 1074nm, 1088nm and 1117nm lasers with >80% of the power in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5~\mu \text{m}$ </tex-math></inline-formula> band in each case. Also, through simulations, we elucidate the reasons for asymmetric Raman gain that is responsible for power combing and show power combining of 6 pump sources, with arbitrary wavelength spacing showing the versatility of this technique.

Simultaneous nonlinear wavelength and mode conversion for high-brightness blue sources

We investigate frequency doubling of focused Bessel-like higher order fiber modes in a one-dimensionally quasi-phase matched structured KTP crystal. A single higher-order fiber mode, L P 0 , 7 , was generated at 971 nm using a fiber optical parametric amplifier pumped by sub-nanosecond pulses at 1064 nm. Frequency doubling to 485.5 nm was achieved with a maximum conversion efficiency of 48%, which produced a highly structured blue beam without any brightness improvement with respect to the fundamental beam. By optimizing the phase mismatch, we also experimentally demonstrate clean on-axis conversion—resulting from cascaded χ ( 2 ) : χ ( 2 ) processes, which is in good agreement with our numerical simulations, that give rise to brightness enhancement.

Multiple spatial and wavelength conversion operations based on a frequency-degenerated intermodal four-wave mixing process in a graded-index 6-LP few-mode fiber

We report on the experimental observation of a simultaneous threefold wavelength and spatial conversion process at telecommunication wavelengths taking place in a 6-LP-mode graded-index few-mode fiber. The physical mechanism is based on parallel and phase-matched frequency-degenerated intermodal four-wave mixing (FD-IFWM) phenomena occurring between the fundamental mode and higher-order spatial modes. More precisely, a single high-power frequency-degenerated pump wave is simultaneously injected in the four spatial modes L P 01 , L P 11 , L P 02 , and L P 31 of a 1.8-km long graded-index few-mode fiber together with three independent signals in the fundamental mode. By means of three parallel phase-matched FD-IFWM interactions, these initial signals are then simultaneously spatially and frequency-converted from the fundamental mode to specific high-order modes. The influence of the differential modal group delay is also investigated and shows that the walk-off between the spatially multiplexed signals significantly limits the bandwidth of the conversion process for telecom applications.

Multiple modal and wavelength conversion process of a 10-Gbit/s signal in a 6-LP-mode fiber.

We demonstrate experimentally a simultaneous threefold modal and wavelength conversion process of a 10-Gbit/s On/Off keying signal in a 1.8-km long graded-index 6-LP-mode fiber. The principle of operation is based on a phase-matched inter-modal four-wave mixing phenomenon occurring between the fundamental mode and 3 higher-order modes of the fiber. The converted signals show well-opened eye-diagrams and error-free processing.

Simultaneous wavelength and format conversion in SDN/NFV for flexible optical network based on FWM in SOA

We propose an all-optical wavelength and format conversion model (CM) for a dynamic data center interconnect node and coherent passive optical network (PON) optical network unit (ONU) in software-defined networking and network function virtualization system based on four-wave mixing in a semiconductor optical amplifier. Five wavelength converted DQPSK signals and two format converted DPSK signals are generated; the performances of the generated signals for two strategies of setting CM in the data center interconnect node and coherent PON ONU, which are over 10 km fiber transmission, have been verified. All of the converted signals are with a power penalty less than 2.2 dB at FEC threshold of 3.8 × 10 − 3, and the optimum bias current of SOA is 300 mA.

Investigation of nonlinear effects in few-mode fibers

In this work, nonlinear optical effects are exploited for future implementations of space-division multiplexing fiber systems. The paper first presents the fundamentals of intermodal nonlinear phenomena over few-mode fibers, such as cross-phase modulation, four-wave mixing (FWM), stimulated Brillouin scattering and stimulated Raman scattering. Second, the potential applications of few-mode nonlinear effects are discussed for sensing and optical signal processing. We demonstrated how fiber mode symmetries and linear mode coupling affect intermodal power transfer and spectral broadening. Lastly, the paper proposes a ultrafast all-optical simultaneous wavelength and mode conversion scheme based on intermodal FWM, with the capability of switching state of polarization and mode degeneracy orientation. Under this scheme, cross-polarization modulation and cross-mode modulation can be achieved.

All-optical ultrafast wavelength and mode converter based on inter-modal four-wave mixing in few-mode fibers

An ultrafast all-optical simultaneous wavelength and mode conversion scheme is purposed based on intermodal four-wave mixing (IM-FWM), with the capability of switching state of polarization (SOP) and mode degeneracy orientation (MDO) in few-mode fibers (FMF). The relation among the conversion efficiency, pump power and phase matching conditions is investigated in theory analysis and simulation. Using this scheme, cross-polarization modulation (XPolM) and cross-mode modulation (XMM) can be achieved, by in the best case up to 50% conversion efficiency. Furthermore, numerical results further indicate that the proposed configuration has the potential application for generating doughnut modes by the mixing of three characteristic spatial frequencies.

Parametric Amplification, Wavelength Conversion, and Phase Conjugation of a 2.048-Tbit/s WDM PDM 16-QAM Signal

We demonstrate polarization-independent parametric amplification of a 2.048-Tbit/s 8-WDM PDM 16-QAM signal and simultaneous wavelength conversion and phase conjugation in a highly nonlinear fiber. Two high-power continuous-wave pumps with orthogonal polarizations and counter-phase modulation are used in the fiber optical parametric amplifier (FOPA) to achieve broadband flat gain, polarization independence, and high-quality idler generation. The polarization-independent FOPA is amplitude and phase preserving and has ~10 dB on-off gain for the signal and ~9 dB conversion efficiency for the idler with a 1-dB bandwidth of ~16 nm. Compared to the back-to-back case, the amplified signals and the wavelength-converted conjugates have mean Q <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> penalties of only 0.6 and 0.4 dB, respectively, with variances of Q <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factors across all the wavelength-division-multiplexed channels of only 0.3 dB. This demonstration shows the great promise of optical signal processing techniques to simultaneously process large-capacity multiple-channel multilevel signals with almost no latency and potentially low power consumption.

Parametric laser pulse shortening.

We report simultaneous laser pulse shortening and wavelength conversion based on spectral-temporal correlation in high-gain optical parametric generation (OPG). By spectrally filtering the off-peak signal energy, we shortened a 560 ps pump pulse at 1064 nm to an 80 ps signal pulse at 1.5 μm from a 45 mm long PPLN optical parametric generator with 60 μJ pump energy from a passively Q-switched Nd:YAG laser. Using the same technique, we further demonstrated a 3.6 time shortened laser pulse at 1072 nm from noncollinearly phase matched OPG in a 44 mm long lithium niobate crystal with 3 mJ amplified pump energy from the same Nd:YAG laser.

Polarization-Independent All-Optical Regenerator for DPSK Data

We demonstrate polarization-independent simultaneous all-optical phase-preserving amplitude regeneration and wavelength conversion of NRZ differential phase shift keying (DPSK) data by four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). The dependence upon polarization state of the signals is eliminated by using a co-polarized dual-pump architecture. Investigation on the regenerative capability vs. pumps detuning shows significant BER threshold margin improvement over 6 nm conversion range.

Simultaneous brightness enhancement and wavelength conversion to the eye‐safe region in a high‐power diamond Raman laser

AbstractBrightness enhancement in an external cavity diamond Raman laser designed for high power conversion of a neodymium (1064 nm) laser to the eye‐safe spectral region is reported. Using a multimode input beam pulsed at 36 kHz pulse repetition frequency, 16.2 W with 40% overall conversion efficiency was obtained at the second Stokes wavelength of 1485 nm. The output beam had a quality factor of which is a factor of 2.7 times lower than that of the input beam, resulting in a higher overall brightness. The output power, brightness, and brightness enhancement obtained represent significant advances in performance for Raman lasers as well as other competing kHz‐pulsed eye‐safe technologies.

Dual SOA-MZI Wavelength Converters Based on III-V Hybrid Integration on a $\mu{\rm m}$-Scale Si Platform

We report on the simultaneous wavelength conversion operation of a dual-element semiconductor optical amplifier-Mach–Zehnder interferometer (SOA-MZI) array hybridly integrated on a 4- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}$</tex> </formula> silicon-on-insulator (SOI) waveguide platform through thermocompression bonding. The SOAs are part of a six-element SOA array with both facets coupled on SOI through vertical and horizontal alignments. The device achieves almost two orders of magnitude reduction in footprint compared with state-of-the-art hybridly integrated SOA-MZI structures. We present for the first time experimental proof of the successful operation of a dual-element SOA-MZI device based on III-V technology on SoI that serves as a wavelength converter, with one SOA-MZI yielding error-free performance with a 0.8-dB power penalty at 12.5 Gb/s and the second SOA-MZI operating error-free at 10 Gb/s with a 2-dB power penalty.

Multichannel Wavelength Conversion Using Four-Wave Mixing in Semiconductor Ring Lasers

We theoretically study all-optical simultaneous wavelength conversion of multiple channels by four-wave mixing in semiconductor ring lasers. Locking the semiconductor ring laser to a holding beam allows us to achieve large conversion efficiencies with good signal-to-noise ratio in several channels at multi-Gb/s bit rates. Cross-talk between signals, arising from the peculiar four-wave mixing cascade of modes in semiconductor ring lasers and their cross-gain saturation, is studied in detail. We show that it can be controlled by adjusting the intensity of the holding beam, the bias current of the laser, and the number, intensity, and wavelength of signals that one wants to convert.

Simultaneous DPSK demodulation and wavelength conversion scheme for Rayleigh backscattering noise mitigation in WDM-PON

We propose a scheme for mitigating Rayleigh backscattering noise and demodulating differential phase-shift keying (DPSK) signals in wavelength-division-multiplexed passive optical networks (WDM-PONs) with injection-locked Fabry-Perot laser diodes (FP-LDs). Signal demodulation and wavelength conversion are simultaneously realized on the basis of the frequency deviation and red shift of longitude modes in the FP-LDs. Experimental results demonstrate that the demodulation and wavelength conversion of 2.5-Gb/s DPSK signals are achieved. A power penalty of about 1.6 dB at a bit error rate of 10-9 is measured after transmission over 25-km single mode fiber.

Intermodal Čerenkov radiation in a higher-order-mode fiber

We demonstrate an intermodal Čerenkov radiation effect in a higher-order-mode (HOM) fiber with a mode crossing (i.e., two guided modes having the same propagation constant at the same wavelength). A frequency-shifted soliton in the vicinity of the mode-crossing wavelength emits a phase-matched dispersive wave in a different propagation mode. We develop a theoretical explanation for this nonlinear optical effect and demonstrate that the mode crossing in HOM fibers can be utilized to achieve simultaneous wavelength and mode conversion; the strength of this intermodal nonlinear interaction can be tuned by controlled fiber bending.

All-Optical Switching of QPSK Signals for 100 G Coherent Systems

We propose a novel method for signal processing of phase-modulated signals suitable for 100 G coherent systems. By exploiting a single semiconductor optical amplifier Mach-Zehnder interferometer, all-optical selective switching with simultaneous wavelength conversion of bursts of data in the original signal is demonstrated. The operation is suitable for dynamic wavelength routing and/or add/drop operation in multichannel coherent systems, thus enabling flexible network resources optimization. The operation has been demonstrated for single-channel single-polarization, dual-channel (DC) single-polarization, and DC polarization-multiplexed (PM) 28 GBaud quadrature phase shift key-modulated signals. By exploiting coherent detection strategy and digital signal processing, an error rate below 10-3 prior to forward error correction has been observed for all the experiments; the corresponding optical signal-to-noise ratio penalty has been measured to be almost negligible in the single-polarization case whereas a maximum penalty below 1.5 dB for the PM one is reported.

All-optical simultaneous drop and wavelength conversion of DPSK data

We demonstrate an all-optical scheme for the simultaneous drop and wavelength conversion of bursts of data from a continuous stream of differential phase-shift keyed (DPSK) signals. This function is obtained in a single semiconductor optical amplifier Mach-Zehnder interferometer thanks to proper nonlinear interaction of the data stream and an optical gate signal at different wavelength. Fast switching-time enabling wavelength shifting operation on continuous DPSK data stream at 10 and 40 Gb/s without any bit loss is reported. Corresponding measured power penalties are negligible at 10 Gb/s and about 1.7 dB at 40 Gb/s.

40-Gb/s NRZ-to-RZ and OOK-to-BPSK Format and Wavelength Conversion on a Single SOA-MZI for Gridless Networking Operations

We propose and experimentally demonstrate simultaneous format and wavelength conversion at 40 Gb/s exploiting a single commercial semiconductor optical amplifier Mach-Zehnder interferometer. Conversion from nonreturn-to-zero (NRZ) to a 2-ps return-to-zero (RZ) on-off keying (OOK) format suitable for grooming onto a 160-Gb/s optical time-division-multiplexing frame is achieved. Furthermore, for the first time to the best of our knowledge, 40-Gb/s conversion from RZ OOK to RZ binary phase-shift keying (BPSK) is achieved. The effectiveness of the proposed scheme is demonstrated by means of bit-error-rate measurements. Error-free operations are reported, with a power penalty of 0.5 dB for the case of NRZ-to-RZ OOK conversion and of 3 dB (comprehensive of the degradation due to the wavelength conversion used to generate the probe signal) for the case of OOK-to-BPSK conversion.

Field-Trial of an All-Optical PSK Regenerator/Multicaster in a 40 Gbit/s, 38 Channel DWDM Transmission Experiment

The performance of future ultra-long haul communication systems exploiting phase-encoded signals is likely to be compromised by noise generated during signal transmission. One potential way to mitigate such noise is to use Phase Sensitive Amplifiers (PSAs) which have been demonstrated to help remove phase as well as amplitude noise from phase-encoded signals. Recently, we showed that a PSA-based signal regenerator based on degenerate four-wave mixing can be implemented in a network-compatible manner in which only the (noisy) signal is present at the device input (black-box operation). The developed regenerator was also able to perform simultaneous wavelength conversion and multicasting, details/analysis of which are presented herein. However, this scheme was tested only with artificial noise generated in the laboratory and with the regenerator placed in front of the receiver, rather than in-line where even greater performance benefits are to be expected. Here, we address both theoretically and experimentally the important issue of how such a regenerator, operating for convenience in a multicasting mode, performs as an in-line device in an installed transmission fiber link. We also investigate the dispersion tolerance of the approach.