Tunable all-optical time-slot-interchange and wavelength conversionusing difference-frequency-generation and optical buffers

In this letter, we demonstrate a module that simultaneously performs optical time-slot interchange and wavelength conversion of the bits in a 2.5-Gb/s data stream to achieve a reconfigurable time/wavelength switch. Our switch uses difference-requency-generation (DFG) for wavelength conversion and fiber Bragg gratings as wavelength-dependent optical time buffers. This tunable technique employs high-extinction-ratio and low-additive-noise DFG     

Reduction of Light Signal Pulse Distortion in Cascaded SFG–DFG Wavelength Conversion: Segmented QPM Interleaved by Short Wavelength Cut Filters

Cascaded sum-frequency-generation (SFG) and difference-frequency-generation (DFG) can implement a wavelength conversion between arbitrary combinations of input and output signal wavelengths. By using a tunable wavelength pump light, the output wavelength can be tuned to a desired wavelength. As in many wavelength conversion devices using the nonlinear optical effect, the group velocity difference between light pulses with different wavelength causes a walk-off effect deforming the output pulse shape. Thus, the device length should be kept short to avoid the walk-off effect resulting in limited conversion efficiency. In this report, we propose a method, for quasi-phase matched device, to maintain the pulse shape of the SFG light pulse along the propagation distance. The output DFG light pulse deformation is suppressed and the conversion efficiency can be increased by extending the device length.      

Quasi-phase-matched (QPM) difference frequency generation in amirrorless counterpropagating configuration

We present a theoretical analysis of second-order nonlinear difference frequency generation (DFG) in a generalized mirrorless quasi-phase-matching (QPM) frame, aimed at a comparison of counterpropagating DFG configuration (CDFG) to other DFG schemes, in view of all-optical processing applications. Field nonlinear coupling equations have been numerically solved under the hypothesis of phase-matched interaction. The evolution of propagating fields within the material and the wavelength conversion efficiency have been calculated in dependence of operating parameters. The increased complexity in the evolution of amplitude and phase for fields interacting in CDFG with respect to forward-propagating DFG (FDFG) is at the basis of a dramatic increase in the wavelength conversion efficiency under particular settings of device parameters     

基于铌酸锂光波导的全光波长转换

研究了双脉冲泵浦情况下,在准相位匹配(QPM)的周期性极化反转的铌酸锂光波导(PPLN)中,基于级联二阶非线性效应--和频与差频效应(SFG DFG)的全光波长转换.推导了描述SFG DFG波长转换的理论模型.通过数值模拟,研究了波长转换过程,观察到脉冲传播过程中出现了走离效应与脉冲展宽.研究了器件长度、信号波长、脉宽等参数对波长转换效率的影响.     

Monolithically integrated 40-gb/s switchable wavelength converter

An all-optical switchable wavelength-converting module at 40 Gb/s line rate is demonstrated in a fully integrated InP chip. The device combines a semiconductor optical amplifier-based wavelength converter and a fast-tunable multifrequency laser. Sub-nanosecond switching among the eight channels of the integrated laser is shown, and error-free operation of the wavelength conversion process at 40 Gb/s for each wavelength is demonstrated. The applications of fast switching wavelength conversion for optical switching and packet routing are discussed.     

Experimental realization of 40 Gbit/s single-to-single and single-to-dual channel wavelength conversions in LiNbO3 waveguides with two-pump configuration

An all-optical 40 Gbit/s tunable single-tosingle channel wavelength conversion is experimentally realized based on cascaded sum- and difference-frequency generation (cSFG/DFG) in periodically poled LiNbO3 (PPLN) waveguides. By employing two tunable filters to effectively suppress the amplified spontaneous emission (ASE) noise, both wavelength down- and upconversions are simultaneously observed. We also propose and verify a novel cSFG/DFG-based single-todual channel wavelength conversion by setting two pumps (pumpl, pump2) close to each other or pump2 and the signal close to each other. For the latter, two kinds of cSFG/DFG schemes are both demonstrated The dependence of the conversion efficiencies of two channel idler waves on pumpl wavelength is discussed.The wavelength relationships between two channel idler waves and the three incident waves are investigated in detail theoretically as well as experimentally.     

Analysis of novel cascaded /spl chi//sup (2)/ (SFG+DFG) wavelength conversions in quasi-phase-matched waveguides

A novel cascaded second-order nonlinear interaction (/spl chi//sup (2)/), which is simultaneously based on sum frequency generation (SFG) and difference frequency generation (DFG) processes, is proposed and analyzed in quasi-phase-matched wavelength converters. Analytical expressions with clear physical insights are derived for the converted light. It is shown that the same conversion efficiency can be achieved by employing two pump sources with lower output power (P/sub p1/,P/sub p2/) in this novel scheme as compared with the conventional cascaded wavelength conversion technique based on second-harmonic generation and difference frequency generation (SHG+DFG) with a single higher power pump beam (P/sub p/=P/sub p1/+P/sub p2/). The theoretical results are consistent with the experimental ones. It is found that the pump wavelength difference can be separated by a span as large as 75 nm, while large 3-dB signal conversion bandwidth is retained. The results show that the novel cascaded /spl chi//sup (2)/ wavelength conversion scheme is very attractive for practical applications.     

Wavelength conversions in quasi-phase matched LiNbO/sub 3/ waveguide based on double-pass cascaded /spl chi//sup (2)/ SFG+DFG interactions

Based on the cascaded nonlinear interactions (/spl chi//sup (2)/:/spl chi//sup (2)/) of sum- and difference-frequency generation (SFG+DFG), a novel all-optical wavelength conversion scheme is proposed for the first time in periodically poled LiNbO/sub 3/ (PPLN) waveguide, in which a double-pass configuration is introduced. The performance of this scheme is thus different from the previous single-pass SFG+DFG scheme. The concept of the "balance condition" is presented to optimize the power and frequencies of the two pump sources. Under this condition, the energy is transferred irreversibly from the pump waves to the SF wave during the forward propagation. The equations describing the SFG can be solved analytically under this condition. Subsequently, the DFG equations are solved under the assumption that the SF wave would be constant during the backward propagation. Theoretical expressions are derived and are found to be consistent with numerical calculations. Compared with the conventional converter based on the cascaded /spl chi//sup (2)/:/spl chi//sup (2)/ interactions of second-harmonic generation and difference frequency generation SHG+DFG, the same conversion efficiency can be achieved in our scheme by employing two pump sources with lower power, or conversely higher conversion efficiency can be reached using two pump sources similar to that used in SFG+DFG scheme. The profile of the conversion efficiency can be further improved by adjusting the wavelengths of the two pump sources. In addition, compared with the single-pass SFG+DFG scheme, the main advantage of this new scheme rests on the fact that the conversion efficiency can be enhanced significantly. The advantages of the double-pass SHG+DFG scheme and the single-pass SFG+DFG scheme are combined in this new design to a great extent.     

An architecture for a wavelength-interchanging cross-connectutilizing parametric wavelength converters

This paper proposes an architecture for a wavelength-interchanging cross-connect (WIXC) that can be used as a switching node of strictly transparent and scalable networks with all-optical routing and all-optical wavelength conversion capabilities. This architecture utilizes all-optical parametric wavelength converters based on difference-frequency-generation (DFG) or four-wave mixing (FWM), although this work focuses only on the implementation using difference-frequency-generation wavelength converters. The proposed WIXC architecture exploits the unique wavelength mapping properties of parametric wavelength converters: mirror image mapping and simultaneous multichannel wavelength conversion. The derivation of this architecture involves application of a space/wavelength transformation to the classical Benes switch fabric. The connection setup for the resulting architecture follows the well established looping algorithm, and the architecture is scalable in both the ports and the wavelengths. The scaling occurs in an orderly fashion, which allows modular upgrades of WIXC's for cost-effective evolution of the networks. The unique properties of the parametric wavelength converter including transparent and multichannel conversion capabilities result in a WIXC architecture that requires fewer wavelength converters while maintaining scalability and transparency     

基于CWDM的波长转换器模块化设计

在研究粗波分复用（CWDM）技术和波长转换技术的基础上，设计了一个适用于CWDM系统的波长转换器模块。该模块支持8个CWDM信道，可工作于多速率状态。模块除内部具有3R功能还具有激光器偏流指示、发送功率指示、激光器关断控制、接收功率指示、低输入功率告警指示和速率选择等功能。实验结果表明，该模块较好地实现了波长的转换，具有较高的稳定度和实用性．     

A tunable wavelength conversion and wavelength add/drop scheme based on cascaded second-order nonlinearity with double-pass configuration

A selective and tunable wavelength conversion and wavelength add/drop scheme based on sum- and difference-frequency generation (SFG+DFG) is proposed, in which the concept of "double-pass" is introduced. An arbitrary channel can be dropped from a wavelength division multiplexing (WDM) signal and added to another WDM signal at arbitrary wavelength. The channel to be dropped is selected and depleted (dropped) by adjusting the pump 1 through sum frequency generation (SFG) during the forward propagation. Subsequently, the difference frequency generation (DFG), taking place during the backward propagation, is employed to convert (add) the dropped channel to another channel in another WDM signal by adjusting the pump 2. For the dropped and added channel, the phase matching of SFG and DFG are nearly perfect and the theoretical expressions are derived under the assumption that the two pumps are undepleted. The power of pump 1 is optimized to deplete the dropped channel completely, while that of pump 2 is chosen to maximize the output power of the added channel. Numerical calculations are performed to investigate the propagation of the other channels whose phase is mismatched. To suppress the crosstalk, the spacing of the WDM channels is chosen to be 0.2 nm (25 GHz). We have also compared our scheme with others (such as the single-pass scheme and the double waveguide scheme) and shown that ours possesses several distinct advantages.     

High-efficiency wavelength conversion using FWM in an SOAintegrated DFB laser

A wavelength converter that uses four-wave mixing (FWM) in an SOA-integrated distributed-feedback (DFB) laser was demonstrated. Lossless conversion up to 300-GHz detuning and a conversion efficiency of -5 dB at 1-THz detuning was achieved. The device exhibited low ASE (noise) level, and noise figure (NF) characteristics of 24 dB for 16-nm wavelength conversion was observed. This high-efficiency FWM wavelength conversion provided by a single device is promising for optical wavelength shifters in large-scale optical communication systems     

Mode overlap analyses of propagated waves in direct bonded PPMgLN ridge waveguide

Direct bonded periodically poled MgO doped lithium niobate (PPMgLN) ridge waveguide is a new wavelength converter with high conversion efficiency.The optical field distribution of the ridge waveguide is simulated by employing finite-difference method (FDM),the mode overlap of propagated waves in the ridge waveguide is calculated and the relationship between the overlap coefficient and the waveguide structure sizes is also investigated.The overlap coefficient to difference frequency generation (DFG) process conversion efficiency calculation is firstly introduced.     

Optical frequency conversions in nonlinear medium with periodicallymodulated linear and nonlinear optical parameters

A new method considering both linear and nonlinear optical parameter modulation and propagation loss is proposed to treat second-order nonlinear optical interactions in nonlinear media having periodic structures. Mathematical expressions are derived for difference frequency generation (DFG) and compared with those for second-harmonic generation (SHG). Wavelength conversions around 1.55 μm, which are very interesting in optical communication systems, are studied for semiconductor DFG devices with periodic structures. Semiconductor (e.g., AlGaAs) DFG devices of standard device lengths (several mm) and pump light intensities (10⁵ kW/cm²) are shown capable of practical level conversion efficiencies (~10%) and extremely wide bandwidths (⩾100 nm). Effects of propagation loss in DFG devices are also examined     

Temperature optimization for broad-band quasi-phase-matched difference frequency generation

The temperature-tuning prosperities of quasi-phase-matched (QPM) difference frequency generation (DFG) in a uniform periodically poled LiNbO/sub 3/ (PPLN) device are studied theoretically in the near degeneracy limit. Combining the theoretical and numerical analysis results, the paper shows that through the tuning of temperature, the conversion efficiency and bandwidth can be changed considerably. This paper proposes a PPLN device consisting of several segments of different temperature to obtain a more desirable performance for the QPM-DFG. The optimizations for temperature are studied in detail by the use of a cascading technique, and they show that broadening of the conversion bandwidth will reduce the conversion efficiency. A better performance of uniform PPLN can be obtained owing to the reconfigurable and adjustable abilities of multisection temperature tuning.     

Multiple quasi-phase-matched device using continuous phase modulation of /spl chi//sup (2)/ grating and its application to variable wavelength conversion

We propose a new multiple quasi-phase-matched wavelength converter based on the continuous phase modulation of a /spl chi//sup (2)/ grating for use in variable wavelength conversion. A numerical study shows that the proposed device exhibits a high conversion efficiency, flexible design, and robust fabrication tolerance. A waveguide device fabricated by annealed proton exchange agrees well with the numerical design. Fine-tuning the device enabled us to demonstrate variable wavelength conversion between signals on the standard optical frequency grid. Using the device, we also demonstrated fast (<100 ps) wavelength switching of 4-channel 40-Gb/s signals. The obtained results clearly show that the proposed multiple quasi-phase-matched devices will be useful when constructing future flexible photonic networks.     

Tunable wavelength converters of picosecond pulses based on periodically poled LiNbO3 waveguides

A tunable wavelength conversion between picosecond pulses is experimentally demonstrated by using cascaded sum- and difference-frequency generation (cSFG/DFG) in a periodically poled LiNbO3 (PPLN)waveguide. The pulsed signal with 40 GHz repetition rate and 1.57 ps pulse width is adopted. When the input signal and the first control wavelengths are kept at 1554.2 and 1532.5 nm, respectively, the output signal wavelength can be tuned from 1536.0 to 1545.2 nm as the second control wavelength varies from 1550.5 to 1541.0 nm. By varying the first control wavelength to satisfy the quasi-phase matching (QPM) condition for sum-frequency generation (SFG) and simultaneously adjusting the second control wavelength, the tunable output signal wavelength can also be obtained when the input signal wavelength is changed. In the experiment,the amplified spontaneous emission (ASE) noise from the erbium-doped fiber amplifier (EDFA) is effectively suppressed by employing two narrow band tunable filters. Therefore, the wavelength down- and up-conversions are simultaneously observed.     

Repeated wavelength conversion of 10 Gb/s signals and convertedsignal gating using wavelength-tunable semiconductor lasers

Repeated wavelength conversion of 10 Gb/s pseudorandom nonreturn-to-zero signals is demonstrated using semiconductor lasers that can be tuned wavelength over a broad range. Error-free tunable wavelength conversion with a very low power penalty can be achieved in both first and second wavelength conversion over a broad wavelength range from 1.486-1.573 μm. The converted signal can be switched rapidly within this wavelength region. High-speed converted signal gating controlled by adjusting the bias current to the device active region is also demonstrated     

Characterization of the chirp and intensity modulation propertiesof an SOA-MZI wavelength converter

Wavelength converters based on cross-phase modulation in semiconductor optical amplifiers (SOAs) in the arms of a Mach-Zehnder interferometer (MZI) provide a key network element for reconfigurable optical networks that incorporate wavelength routing. For system design purposes, the properties of the intensity and phase (chirp) modulation of the wavelength-converted signal for an SOA-MZI wavelength converter are important. In this paper, the small-signal α parameter, which characterizes the converter chirp, and the conversion frequency response are characterized experimentally for an integrated all-active SOA-MZI wavelength converter. For both co- and counterpropagating signals, the variation of the a parameter along the interference and conversion curves is considered in detail. Three optical modulators with quite different chirp properties are used to generate the modulated input signal to the wavelength converter. The results demonstrate that the chirp of the wavelength-converted signal is primarily determined by the device properties and the intensity of the modulated input signal. The a parameter of the wavelength-converted signal is negative for noninverting operation and positive for inverting operation. An important contribution of the paper is the detailed assessment of this key device characteristic. The experimental characterization of the wavelength converter is incorporated into a device model that can be used to obtain the pulse response. Calculated and measured results for the time dependence of the intensity and chirp of the wavelength-converted signal are in good agreement. The conversion frequency response for the intensity modulation is also measured along the conversion curve. The 3-dB bandwidth is found to be generally about 8-10 GHz