Performance Of Wavelength Conversion Research Articles

Single-shot dual-wavelength telecentric in-line-and-off-axis hybrid digital holography with non-prior reconstruction

Dual-wavelength in-line-and-off-axis hybrid digital holography (iohDH) can achieve high-resolution holographic dynamic imaging. However, it requires the prediction of the diffraction distance and the complex amplitude of the reference beam, which is time consuming and results in complications and accuracy limitations. While telecentric imaging technique can obtain nondiffractive images without predicting the diffraction distance, it also can even eliminate spherical aberration and astigmatic aberration. Therefore, a dual-wavelength telecentric iohDH is proposed to realize non-prior high-resolution reconstruction in a single shot. Employing the dual-wavelength telecentric iohDH, our approach acquires the focused in-line-and-off-axis hologram using a color camera in a single shot. In this case, we perform wavelength conversion on the phase and low-frequency information about the off-axis hologram as constraints for in-line iteration. Then, the in-line amplitude constraints are performed in the spatial and frequency domains until the algorithm converges. Compared to the state-of-the-art dual-wavelength iohDH, our approach can streamline the reconstructed processes without demanding a priori information of the diffraction distance and the complex amplitude of the reference beam. More importantly, our approach enables higher quality and efficient reconstruction under the telecentric system. We verified our approach using simulations and experiments, and the results indicate that our approach can allow the amplitude and phase reconstruction with high resolution in a single shot.

Mid-infrared broadband all-optical wavelength converter in Ge20Sb15Se65 photonic crystal fiber with flattened dispersion

A chalcogenide photonic crystal fiber (PCF) with flattened dispersion and high nonlinearity in mid-infrared (mid-IR) based on a triangular and circular lattice hybrid cladding structure is proposed. The structural parameters of the PCF are optimized by the full-vectorial finite-difference method. The numerical simulation results show: when d1 = 0.4 µm, d2 = 0.16 µm, d3 = 0.04 µm, Ʌ1 = 0.88 µm, Ʌ2 = 0.8 µm, Ʌ3 = 0.5 µm, the flatten and low dispersion is obtained in the wavelength range of 3.8–5 µm. The dispersion value is between ± 1.2 (ps/nm/km), and the maximum nonlinear coefficient is as high as 2464.2 km-1 W-1 at 2.5 µm. Based on the four-wave mixing (FWM) effect in the proposed PCF, the all-optical wavelength conversion performance is numerically analyzed. When the pumping wavelength is 4.02 µm, the 3 dB conversion bandwidth can reach 4833 nm (from 2.737 µm to 7.57 µm), and the maximum wavelength conversion efficiency is 12.12 dB. The proposed all optical wavelength converter is having large bandwidth and high conversion efficiency in mid-IR band due to the flat dispersion and high nonlinearity of the PCF, which has potential application in future space optical communication network and mid-IR photonic.

Hybrid pulse propagation model and quasi-phase-matched four-wave mixing in multipass cells

We describe a nonlinear propagation model based on a generalized Schrödinger equation in the time domain coupled to Gaussian beam evolution through ABCD matrices that account for Kerr lensing in the spatial domain. This model is well suited to simulate propagation in mildly nonlinear systems such as multipass cells for temporal compression. It is validated against both a full ( x , y , z , t ) numerical model and recently reported experimental results in multipass cells, with excellent agreement. It also allows us to identify the physical mechanism for the recently reported parasitic appearance of spectral content in the 700–950 nm range in argon-filled multipass cells that are used to compress pulses at 1030 nm. We think this is due to a quasi-phase-matched degenerate four-wave mixing process. This process could be used in the future to perform wavelength conversion as is already done in fibers and capillaries.

Tunable four-wave mixing in AlGaAs waveguides of three different geometries

The AlGaAs material platform has been intensively used to develop nonlinear photonic devices on-a-chip, thanks to its superior nonlinear optical properties. We propose a new AlGaAs waveguide geometry, called half-core etched, which represents a compromise between two previously studied geometries, namely the nanowire and strip-loaded waveguides, combining their best qualities. We performed tunable four-wave mixing (FWM) experiments in all three of these geometries in the telecommunications C-band (wavelengths around 1550nm), with a pulsed pump beam and a continuous-wave (CW) signal beam. The maximum FWM peak efficiencies achieved in the nanowire, strip-loaded and half-core geometries were about −5dB, −8dB and −9dB, respectively. These values are among the highest reported in AlGaAs waveguides. The signal-to-idler conversion ranges were also remarkable: 161nm for the strip-loaded and half-core waveguides and 152nm for the nanowire. Based on our findings, we conclude that the half-core geometry is an alternative approach to the nanowire geometry, which has been earlier deemed the most efficient geometry, to perform wavelength conversion in the spectral region above the half-bandgap. Moreover, we show that the half-core geometry exhibits fewer issues associated with multiphoton absorption than the nanowire geometry.

An approach to multi-wavelength conversion based on cross-phase modulation effect in dual HNLFs for optical orthogonal modulation format

In this paper, a multi-wavelength converter based on cross-phase modulation (XPM) effect in dual highly nonlinear fibers (HNLFs) for 60 Gbps non-return to zero/differential quadrature phase shift keying (NRZ/DQPSK) orthogonally modulated signal has been proposed. In the proposed wavelength converter, orthogonal modulation formats are used to enhance the spectral efficiency of system for physical layer expandability of optical network. The merit of proposed scheme is that the configuration of wavelength converter is simple and easy to implement at higher data rate. The BER performance of all converted signal is greater than or equal to 5.36 × 10–24 and spectral efficiency of designed wavelength converter is 9.75 b/s/Hz which makes the system more cost effective and expandable. In addition, the proposed multi-wavelength converter has been validated at variable HNLF parameters to achieve optimum wavelength conversion performance.

Raman enhanced polarization-insensitive wavelength conversion based on two-pump four-wave mixing.

Backward Raman amplification is applied to improve the conversion efficiency of two-orthogonal-pump four-wave mixing (FWM) with polarization insensitivity. Wavelength conversion with ~0dB efficiency and negligible polarization dependency is demonstrated by using a common highly nonlinear fiber without pump dithering. The conversion efficiency is increased by ~29dB with Raman enhancement. We also discuss the impact of the Raman pump power and the FWM pump powers on the performance of wavelength conversion. The results indicate that moderate pump powers without inducing significant spontaneous noise and stimulated Brillouin scattering are favorable to ensure high conversion efficiency and low excess noise for performance optimization.

Wavelength conversion performance in a tellurite step-index optical fiber

We demonstrated in this work the wavelength conversion performance based on the four-wave mixing process in a new tellurite step-index fiber as short as 1m. The fiber was pumped by a femtosecond pulsed laser near the zero dispersion wavelength of the fundamental mode which was close to that of the material dispersion in the near-infrared region. When the pump and signal wavelengths were at 1795 and 1434nm, respectively, the generated idler was obtained at 2400nm and the conversion wavelength spacing could be as broad as 966nm. In addition, a 17.5-dB signal gain at 1550nm and 1.1-dB idler at 1757nm were obtained when the pump was tuned to 1647nm.

Broad-Band All-Optical Wavelength Conversion of Differential Phase-Shift Keyed Signal Using an SOA-Based Nonlinear Polarization Switch

Broad-band all-optical wavelength conversion of differential phase-shift keyed (DPSK) signal is experimentally demonstrated. This scheme is composed of a one-bit delay interferometer demodulation stage followed by a semiconductor optical amplifier (SOA) based nonlinear polarization switch. A wavelength converter for the 10 Gb/s DPSK signal is presented, which has a wide wavelength range of more than 30 nm. The converted signals experience small power penalties less than 1.4 dB compared with the original signal, at a bit error rate of 10−9. Additionally, the optical spectra, the measured waveforms and the open eye diagrams of the converted signals show a high quality wavelength conversion performance.

All Optical Wavelength Conversion of Nyquist-WDM Superchannels Using FWM in SOAs

In this paper, the performance of all-optical wavelength conversion (WC) of Nyquist-WDM superchannels is investigated for future implementation in optical networks. We consider advanced modulation formats of DQPSK and 16-QAM for the subchannel modulation format achieving raw bit rates of 448 and 896 Gb/s, respectively. We demonstrate through simulations the WC of Nyquist-WDM superchannel using degenerate and nondegenerate four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We consider the effects of raised cosine (RC) and root raised cosine (RRC) signal pulse shaping within the wavelength conversion process. We find that the performance of the converted superchannel is severely impaired by crosstalk due to cross-gain modulation of the pump by the superchannel. Optimum performance of the converted superchannel is achieved by setting the detuning between the continuous-wave pump and the central wavelength of the superchannel to be around 200 GHz and using pumps of double the gain saturation power of the SOA with 23 dB pump to signal power ratio.

Multi-Format Wavelength Conversion Using Quantum Dash Mode-Locked Laser Pumps

We investigate and compare the performance of wavelength conversion for two different non-return-to-zero (NRZ) modulation formats at 40 Gb/s: on off keying (OOK) and differential phase-shift keying (DPSK). To achieve wide wavelength coverage and integrability, we use a dual pump scheme exploiting four-wave mixing in semiconductor optical amplifiers. For phase stability, we use a quantum-dash mode-locked laser (QD-MLL) as a multi-wavelength source for the dual pumps, with tunability provided by the output filter. The significant sidelobes of the DPSK spectrum (relative to OOK) require the balancing of the pump proximity to the original signal (facilitating high conversion efficiency) with the signal degradation from the pump spectrum overlapping the converted DPSK signal. We achieve a conversion efficiency near –3.6 dB for OOK and –5.4 dB for DPSK across a 12 nm tuning range with low input powers (1 dBm). We measure bit error rate (BER) and obtain error free transmission (BER < 10−9) with a power penalty less than 2 dB for OOK and 3 dB for DPSK.

Wavelength Conversion of DP-QPSK Signals in a Silicon Polarization Diversity Circuit

Multichannel wavelength conversion is experimentally demonstrated for high-speed 128 Gb/s dual-polarization quadrature phase-shift keying signals using four-wave mixing in a polarization diversity circuit with silicon nanowires as nonlinear elements. The wavelength conversion performance is investigated for both single- and three-channel input signals, showing quality factors well >9.8 dB (corresponding to bit-error-ratios better than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) and with a negligible power penalty compared with the back-to-back case.

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.

Dispersion engineering of suspended silicon photonic waveguides for broadband mid-infrared wavelength conversion

Silicon photonics has much potential in the mid-infrared (MIR) band due to the broad low-loss window of silicon. The performance of wavelength conversion based on degenerate four-wave mixing is theoretically evaluated in suspended silicon waveguides, which are adopted to eliminate the strong absorption of silica in the MIR region. A theoretical model is formed for MIR wavelength conversion by taking the nonlinear loss into account, where three-photon absorption and related free-carrier absorption play dominant roles. The relationship of the dispersion and the waveguide dimensions is analyzed, and the dispersion is manipulated by tuning the cross section of the waveguide. The phase mismatch is effectively reduced, and a MIR band conversion bandwidth as broad as 706&#xA0;nm is obtained with a conversion efficiency of &#x2212;20.5&#x2009;&#x2009;dB in an 8&#xA0;mm long suspended silicon waveguide pumped by a light intensity as low as 0.1&#x2009;&#x2009;GW/cm2.

Enhanced performance of polarization-insensitive wavelength conversion by dynamic control of the optical phase

The gain-transparent stimulated Brillouin scattering (SBS) process has been successfully applied to dual-orthogonal-pump four-wave mixing (FWM) to enhance the performance of polarization-insensitive wavelength conversion. The Brillouin pump and Stokes waves control the optical phase of one of the FWM pumps to achieve phase matching to extend the wavelength conversion range. The experimental data show that the polarization-insensitive property is well preserved under gain-transparent SBS processing, and only 0.5dB output power variation is observed in the converted idler. A 5.1dB enhancement of the conversion efficiency is obtained through the phase control at large signal-pump spectral spacing. By applying this scheme for exclusive phase control, simultaneous polarization-insensitive and wideband wavelength conversion can be potentially realized in other configurations using two copolarized pumps or a polarization diversity loop.

Performance of fiber delay‐line buffers in asynchronous packet‐based optical switching networks with wavelength conversion

SummaryA major challenge in asynchronous packet‐based optical networks is packet contention, which occurs when two or more packets head to the same output at the same time. To resolve contention in the optical domain, two primary approaches are wavelength conversion and fiber delay line (FDL) buffering. In wavelength conversion, a contending packet can be converted from one wavelength to another in order to avoid conflict. In FDL buffering, contending packets can be delayed for a fixed amount of time. While the performance of wavelength conversion and FDL buffering has been evaluated extensively in synchronous networks with fixed‐sized packets, in this paper, we study the performance of FDL buffers in asynchronous packet‐based optical networks with wavelength conversion. An analytical model is proposed to evaluate the performance in terms of packet loss probability and average delay. Extensive simulation and analytical results show that, with appropriate settings, FDL buffers can perform much better in switches with wavelength conversion than in switches with no conversion. Copyright © 2014 John Wiley &amp; Sons, Ltd.

PPLN Poling Design Based on a Discrete Layer Peeling Algorithm Combined With a Deleted-Reversal Method

In this paper, we propose a method to design the poling pattern of periodically poled lithium niobate (PPLN) devices according to a target spectral response of the selected nonlinear interaction. This method combines a discrete layer peeling algorithm with the deleted-reversal method. The main advantages and limitations of the proposed method in terms of fabrication feasibility of the resulting poling patterns are discussed. The effectiveness of the proposed method is shown by designing PPLNs with two different types of spectral responses: quasi-rectangular bandpass filtering and multichannel filtering. We experimentally demonstrate the method by designing and producing a PPLN which allows performing wavelength conversion within a spectral response approximately given by a 400 GHz quasi-rectangular filter.

Simulations of an OSNR-Limited All-Optical Wavelength Conversion Scheme

We present simulations of a scheme to perform wavelength conversion of signals that eliminates phase-noise transfer from the pump to the converted signal. Nondegenerate four-wave mixing in a semiconductor optical amplifier is used to convert the signal to a new wavelength, and if an optical comb generator is used as the multiple-pump source, then the signal can be converted without incurring any phase-noise transfer from the pumps. We highlight the capabilities of this scheme by simulating the conversion of 16-QAM signals at 10 GBd and showing that errors due to phase-noise accumulation are eliminated, thus enabling conversion whose only impairment would be the total additive optical noise.

An InP Monolithically Integrated Unicast and Multicast Wavelength Converter

We experimentally demonstrate a novel Indium Phosphide monolithically integrated optical circuit for all-optical wavelength conversion. The circuit exploits two cascaded cross gain modulation (XGM) interactions in semiconductor optical amplifiers. In a first XGM stage, the input signal and a continuous wave light at the desired output wavelength generate a wavelength converted yet not ideal copy of the input signal, whereas, in the second XGM stage, the quality of the wavelength converted signal is significantly improved because of the cross gain compression effect. We report 10 Gb/s wavelength conversion performance for both the unicast (single output wavelength) and the multicast (multiple output wavelengths) conversion. Experimental results confirm the effectiveness of the present photonic integrated circuit in both cases, showing only a moderate bit error rate power penalty.

A Wavelength and Converter Assignment Scheme using Converter Usage History in Wavelength-Routed Networks

In wavelength-routed networks, wavelength conversion improves lightpath blocking probability by eliminating the wavelength-continuity constraint. Because wavelength converters remain expensive in the near future, we need a wavelength and converter assignment scheme that decreases blocking probability with a limited number of converters. In this paper, we propose a wavelength and converter assignment scheme for decreasing blocking probability. Our scheme avoids contention among multiple lightpath requests by making each node-pair to perform wavelength conversion at different intermediate nodes with more idle converters. Simulation results show that 1) our scheme decreases blocking probability by about between 44% and 83% and 2) our scheme needs one or two fewer wavelength converters per node to achieve near-optimal blocking probability compared with conventional schemes.

Performance Enhancement for Ultrashort-Pulse Wavelength Conversion by Using an Aperiodic Domain-Inverted Optical Superlattice

We propose a designed aperiodic domain-inverted optical superlattice structure, where the performance of ultrashort-pulse wavelength conversion, relative-broad and flat conversion band with high conversion efficiency, has been well-balanced and enhanced in comparison with those in periodical or linear-chirped optical superlattices. Using this structure, we present a 5.5-nm flat band with almost no pulse distortion for picosecond wavelength conversion in the C-band. Moreover, the uniformity of all inverted domains may provide more convenience for poling. The above benefits may bring promising applications in generating broadband continuous-variable entanglement source and terahertz source with equivalent generation rate.