Widely tunable multichannel wavelength conversion using multiple wavelength quasi-phase-matched LiNbO/sub 3/ waveguide

Widely tunable multichannel wavelength conversion using a multiple wavelength quasi-phase-matched LiNbO/sub 3/ waveguide is proposed. Simultaneous conversion of four-channel signals with a tunable range of more than 35 nm is successfully demonstrate for the first time.     

Low crosstalk and variable wavelength conversion using multiple QPM LiNbO3 waveguide module

A multiple quasi-phase matched LiNbO₃ device in a four-port fibre-pigtail module for variable difference frequency generation (DFG) is described. The module structure realises DFG pumped by second-harmonic light that results in wavelength conversion with low crosstalk. The module is also used to demonstrate polarisationinsensitive conversion. This device technology will be useful for future photonic networks that employ a grouped wavelength path.     

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.     

准相位匹配LiNbO3波导全光波长变换的理论研究

对周期性极化LiNbO3(PPLN)光波导实现准相位匹配全光波长变换进行了理论研究,得出了提高准相位匹配和全频光波长变换效率的有效途径,为准相位匹配全光波长变换器的研制提供了理论指导。     

High-Quality Grouped-Wavelength Conversion and Dynamic Switching Using Multiple-QPM LiNbO $_{3}$ and TLA

We demonstrate dynamic grouped-wavelength conversion using multiple quasi-phase-matched LiNbO$_{3}$ modules and a tunable laser diode array. A high signal-to-noise ratio of larger than 45 dB is obtained for the converted signals. The power penalty of the wavelength converter is confirmed to be less than 0.2 dB.      

A five-order mode converter for multimode waveguide

A numerical model of five-order mode converter that converts the order of modes in an integrated-optic multimode waveguide is proposed. Such a structure is useful in optical guiding wave devices for mode control and mode shuffling. The dimensions and index profile of the device are well within the capabilities of the state of the art of integrated optics technology. We have successfully optimized the structural design of the device for propagation loss of less than 13.1 dB at an operating wavelength of 1.55 /spl mu/m. A cascaded form of the five-order mode converter is also proposed for selective mode conversion without the need of restructuring the connection within the device.     

Integrated-optic digital-to-analogue converter for recognising multiwavelength pulse patterns

A planar lightwave circuit based device is proposed that can recognise optical multiwavelength pulse patterns based on digital-to-analogue conversion. The device consists of a splitter with variable splitting ratios, delay lines and an arrayed-waveguide grating based wavelength multiplexer, and requires no optical gates. 80 Gbit/s and four-bit label recognition experiments were successfully carried out with the device.     

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.     

Highly Efficient +5-dB Parametric Gain Conversion Using Direct-Bonded PPZnLN Ridge Waveguide

We fabricated a 50-mm-long ZnO-doped quasi-phase-matched LiNbO ridge waveguide by employing the direct bonding and dry etching techniques. We obtained a second-harmonic generation conversion efficiency of 2400%/W and a second-harmonic output power of 148 mW with a pump power of 160 mW. We demonstrated 1.55-m-band wavelength conversion based on a cascade scheme. A parametric conversion gain of 5 dB was successfully achieved.     

Third harmonic generation of Nd:YAG laser light in periodicallypoled LiNbO3 waveguide

The authors propose and first demonstrate an LiNbO₃ waveguide device with cascading quasi-phase-matched second harmonic generation and quasi-phase-matched sum-frequency generation for generation of a third harmonic wave. Ultraviolet light of 355 nm wavelength, which was the shortest value ever reported for LiNbO₃ waveguide wavelength-convertors, was obtained with Nd:YAG laser light     

Analysis of Ultrafast All-Optical OTDM Demultiplexing Based on Cascaded Wavelength Conversion in PPLN Waveguides

Ultrafast all-optical optical time-division multiplexing demultiplexing based on the cascaded second-harmonic generation and difference-frequency generation wavelength conversion in quasi-phase-matched periodically poled lithium niobate waveguides are studied theoretically. For a typical 160- to 10-Gb/s demultiplexing process, conversion efficiency, pulse shape, time delay, phase variation, and crosstalk are investigated in two different arrangements of the 160-Gb/s signals, and both the wavelength conversion and pulse reshaping can be realized     

Tunable Wavelength Conversion of ps-Pulses Exploiting Cascaded Sum- and Difference Frequency Generation in a PPLN-Fiber Ring Laser

Tunable wavelength conversion of picosecond (ps)-pulses based on cascaded sum- and difference frequency generation is proposed and demonstrated by use of a fiber ring laser incorporating a periodically poled lithium niobate waveguide and two parallel-arranged tunable filters (TFs). The pulsed signal with 40-GHz repetition rate and 1.57-ps pulsewidth is employed. No external pump and control sources are required in the wavelength converter. By properly adjusting two TFs to change the lasing pump and control wavelengths, flexible wavelength conversion from a changeable input signal wavelength to a variable output idler wavelength is achieved.     

All-optical wavelength conversions based on MgO-doped LiNbO/sub 3/ QPM waveguides using an EDFA as a pump source

We propose and demonstrate cascaded /spl chi//sup (2)/ wavelength conversion in an MgO-doped LiNbO/sub 3/ quasi-phase-matched waveguide at reduced pump cost by using only an erbium-doped fiber amplifier (EDFA) as the exclusive pump source in a fiber-ring resonator. A fiber Bragg grating in conjunction with an optical circulator isolates the pump light and confines it to the resonator. A conversion efficiency of -30 dB was obtained with a 3-dB gain-saturation output power of only +12 dBm from the EDFA. It is anticipated that -14-dB conversion efficiency is possible, if an EDFA with a 3-dB gain-saturation output power of +20 dBm is used.     

Section-wise-exact coupled-mode theory of waveguidequasi-phase-matched second-harmonic generation

We derive exact mathematical expressions for both the amplitude and phase evolution of optical waves due to linear and nonlinear interactions in a waveguide device and propose a section-wise-exact coupled-mode theory analysis for quasi-phase-matched second-harmonic generation in the waveguide. Section-wise-exact coupled-mode theory is readily applicable to nonuniform quasi-phase-matched gratings and can be useful as a quantitative method in their analysis and design. Using the method, several numerical results are presented for second-harmonic generation in periodically poled LiNbO₃ channel waveguides. In addition, we introduce a split-step method which takes propagation losses into account and which can include linear and two-photon absorption and waveguide losses     

Integrated QPM sum-frequency generation interferometer device forultrafast optical switching

An all-optical switching device consisting of a LiNbO₃ waveguide Mach-Zehnder interferometer with a quasi-phase-matched (QPM) sum-frequency generation (QPM-SFG) section, and a thermooptic phase shifter in the arms was designed and fabricated. Picosecond gate switching of signal wave by control pulses both in 1.5-μm wavelength band is demonstrated in a device having a QPM-SFG section of 5-mm length     

半导体激光器实现波长转换的理论和实验分析

作为自动交换光网络中的核心器件,全光波长转换器在网络中发挥着重要作用。建立了半导体激光器实现波长转换的理论模型,利用速率方程,数值求解了半导体激光器进行波长转换的特性;自行搭建了一套利用光纤光栅外腔半导体激光器进行全光波长转换的实验平台,并对实验结果进行了研究。发现试验结果和理论分析结果是相当吻合的。分析表明,降低光子寿命,优化外腔结构将是该器件在未来智能光网中实用的关键。     

Wide-range all-optical wavelength conversion usingdual-wavelength-pumped fiber Raman converter

A wavelength conversion scheme based on a fiber Raman converter is proposed, in which an externally injected high power pump laser and the associated Stokes laser are used to assist the Raman conversion process of signal light coded with optical information. Because the Raman gain spectrum in fibers is extremely broad, a wavelength conversion device with wide-range tunability is feasible. We numerically demonstrate that wavelength conversion from 1.31 to 1.42 μm can be realized using a fiber Raman converter at up to 10 Gb/s with an efficiency of 18%. It is also demonstrated that wide range conversion from 1.31 to 1.55 μm for optical fiber communication is feasible at up to 5 Gb/s when the fiber Raman converters are cascaded twice     

All-optical wavelength conversion using a pulse reformatting optical filter

We introduce a general concept for the design of all-optical wavelength converters with pulse reformatting functionality. The novel wavelength converters are based on a single semiconductor optical amplifier followed by an optical filter. A microelectromechanical system-based realization is shown and simultaneous 40 Gb/s wavelength conversion, switching and signal format conversion is demonstrated. The new pulse reformatting optical filter device outperforms current schemes with respect to input-power requirements, input-power dynamic range and signal quality.     

Theoretical analysis of wavelength conversion based on four-wave mixing in light-holding SOAs

We propose to use an additional injection beam of short wavelength to enhance the wavelength conversion that utilizes the four-wave-mixing (FWM) effect in a semiconductor optical amplifier (SOA). With this scheme, the assist light can increase the saturation intensity without sacrificing the gain of an SOA, and this leads to an increase in conversion efficiency. A numerical method dealing with various FWM mechanisms, such as amplified spontaneous emission (ASE) noise, longitudinal spatial hole burning, and wavelength-dependent gain spectrum, is developed to predict the static characteristics of our scheme. The carrier densities are nonuniformly distributed along the longitudinal direction of the SOA as a result of the ASE effect, which affects the measurement of the wavelength-dependent transparent current. The effects of an assist light on saturation output power and conversion efficiency are analyzed in detail. The analysis shows that using an assist light can improve both the conversion efficiency and signal-to-background-noise ratio (SBR) for SOAs of different lengths. The degree of improvement depends on the bias condition, assist light wavelength, and the device geometry. The study for the device optimization reveals that a compromise between conversion efficiency and SBR must be made to choose the device length.     

Quasi-phase-matched second harmonic generation: tuning andtolerances

The theory of quasi-phase-matched second-harmonic generation is presented in both the space domain and the wave vector mismatch domain. Departures from ideal quasi-phase matching in periodicity, wavelength, angle of propagation, and temperature are examined to determine the tuning properties and acceptance bandwidths for second-harmonic generation in periodic structures. Numerical examples are tabulated for periodically poled lithium niobate. Various types of errors in the periodicity of these structures are then analyzed to find their effects on the conversion efficiency and on the shape of the tuning curve. This analysis is useful for establishing fabrication tolerances for practical quasi-phase-matched devices. A method of designing structures having desired phase-matching tuning curve shapes is also described. The method makes use of varying domain lengths to establish a varying effective nonlinear coefficient along the interaction length