Wavelength Conversion Scheme Research Articles

Enhancing the frequency response of cross-polarization wavelength conversion

This work presents a novel wavelength conversion scheme, differential cross-polarization modulation (DXPoM), using an extra birefringence delay to enhance the performance of the conventional cross-polarization modulation. Simulation and experimental results confirm that the predicted performance is enhanced. Using the proposed scheme improves rise time by over 300%, reduces timing jitter by 50%, and increases extinction ratio by 9%.

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.

Optimal scheduling algorithms in WDM optical interconnects with limited range wavelength conversion capability

Optical communication is a promising candidate for many emerging networking and parallel/distributed computing applications because of its huge bandwidth. Wavelength division multiplexing (WDM) is a technique that can better utilize the optical bandwidth by dividing the bandwidth of a fiber into multiple wavelength channels. In this paper, we study optimal scheduling algorithms to resolve output contentions in bufferless time slotted WDM optical interconnects with wavelength conversion ability. We consider the general case of limited range wavelength conversion with arbitrary conversion capability, as limited range wavelength conversion is easier to implement and more cost effective than full range wavelength conversion, and it also includes full range wavelength conversion as a special case. We first consider the conversion scheme in which each wavelength can be converted to multiple wavelengths in an interval of wavelengths and the intervals for different wavelengths are ordered. We show that the problem of maximizing network throughput can be formalized as finding a maximum matching in a bipartite graph. We then give an optimal scheduling algorithm called the first available algorithm that runs in O(k) time, where k is the number of wavelengths per fiber. We also study the case where the connection requests have different priorities. We formalize the problem as finding an optimal matching in a weighted bipartite graph and give a scheduling algorithm called the downwards expanding algorithm that runs in O(kD + Nklog(Nk)) time where N is the number of input fibers of the interconnect and D is the conversion degree. Finally, we consider the circular symmetrical wavelength conversion scheme and give optimal scheduling algorithms for nonprioritized scheduling in O(Dk) time and prioritized scheduling in O(k/sup 2/+Nklog(Nk)) time.

Tunable and self‐probed wavelength conversion in an SOA‐based fiber‐ring laser

AbstractTunable all‐optical wavelength converters have been regarded as key opto‐electronic devices in intelligent next‐generation optical networks. A novel scheme for tunable wavelength conversion, based on cross‐gain modulation (XGM) in a semiconductor optical amplifier (SOA)‐based fiber‐ring laser, is proposed. Then, theoretical model for this novel scheme is established. Conversion output characteristics are calculated theoretically and measured experimentally under different conditions. The experimental results coincide with the theoretical results. Tunable wavelength conversion at 2.5 and 10 Gb/s with a 40‐nm tuning range are demonstrated experimentally. Experimental and theoretical studies show that this novel scheme is worthy of further investigation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 237–241, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20104

Analysis of Novel Cascaded<tex>$chi^(2)$</tex>(SFG<tex>$+$</tex>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.

Cascaded wavelength conversions based on sum-frequency generation and difference-frequency generation.

A novel wavelength conversion scheme based on cascaded sum-frequency generation (SFG) and difference-frequency generation (DFG) is proposed and demonstrated in a MgO-doped LiNbO3 quasi-phase-matched waveguide. In this scheme, two pump wavelengths are set outside the communication band. It is shown that the same conversion efficiency can be achieved by use of two pump sources with lower output power (P1, P2) in this scheme compared with the conventional cascaded wavelength conversion technique based on second-harmonic generation and DFG with a single higher-power pump beam (P = P1 + P2) that is due to the use of a larger SFG nonlinear coefficient. The results significantly influence the selection of a suitable nonlinear interaction scheme for practical applications.

Theoretical and experimental investigations on a novel tunable all-optical wavelength converter

Tunable wavelength converters are key components in intelligent all-optical network. In this paper, a novel scheme for tunable wavelength conversion based on semiconductor-fiber ring laser is proposed. Probe laser in the conventional scheme could be left out and self-started tunable wavelength conversion could be achieved. Theoretical model for this novel scheme is also established and the output characteristics are calculated. Experimental results show good agreement with theoretical results. In experimental study, 2.5Gb/s tunable XGM wavelengthconversion with 40nm tuning range was demonstrated. Experimental and theoretical studies show that this novel scheme is worthy of further investigation.

7� 40 Gb/s base-rate RZ all-optical broadcasting utilizing an electroabsorption modulator

We experimentally demonstrate all-optical broadcasting through simultaneous 7 x 40 Gb/s base-rate wavelength conversion in RZ format based on cross absorption modulation in an electroabsorption modulator. In this experiment the original intensity-modulated information is successfully duplicated onto seven wavelengths that comply with the ITU-T proposal. The advantages of the proposed wavelength conversion scheme are also discussed.

Improving the Performance of All-optical WDM Networks based on Light-path Reservation

In this paper, three methods are proposed to improve the performance of all-optical WDM networks based on the light-path reservation scheme. These are wavelength conversion, multiple fibers and two-path routing. We begin by developing analytical models for static-routing networks based on the nonblocking centralized switch, bi-directional Manhattan Street network and de Bruijn network topologies. Analytical results show that in most cases, the multiple fibers and wavelength conversion schemes give the best performance, in terms of lowest blocking probability, for the nonblocking centralized network at light and heavy loads respectively. The reverse is true for the bi-directional Manhattan Street and de Bruijn networks. The choice depends on the values of the parameters such as network load and reservation level. The two-path routing method offers moderate improvement in performance for the de Bruijn network topology. In addition, there exist optimum reservation levels for attaining minimum blocking probabilities. The advantage of the three schemes is moderate in the centralized switch, and slightly less in the de Bruijn network. However, these schemes offer significant performance improvement for the bidirectional Manhattan Street network.

A tunable‐output wavelength converter based on a self‐seeded Fabry‐Perot laser diode with a chirped fiber grating

AbstractWe report a new all‐optical wavelength conversion scheme based on a self‐seeded Fabry–Perot laser diode with a chirped fiber grating as the external cavity. This converter can convert the wavelength of input optical signals into 14 discrete wavelengths with external RF modulation. We successfully demonstrate all‐optical wavelength conversion at 10 Mbps. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 35–36, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10817

Polarisation-insensitive widely tunable wavelength converter using polarisation-diversified SOA fibre-ring laser

An efficient scheme of wavelength conversion has been demonstrated using broadband-orthogonal-pumps four-wave mixing in a semiconductor optical amplifier (SOA) placed inside a polarisation-diversified fibre-ring cavity. The polarisation sensitivity of the converter is less than 0.5 dB. A 3 dB conversion range over 40 nm is obtained. The power penalty is 3 dB for a 10 Gbit/s converted signal at 10−9 bit error rate level.

Fiber parametric amplifiers for wavelength band conversion

By using a loop configuration formed by a polarization beam splitter, we experimentally demonstrate that the existing wavelength-division multiplexing (WDM) sources in C-band can be wavelength converted to the S-band with low polarization sensitivity and low crosstalk. Using a fiber parametric amplifier as a band converter, we achieve experimentally 4.7-dB conversion efficiency over 30-nm conversion bandwidth in 315 m of fiber. Compared to the conventional straight fiber wavelength conversion scheme, a more than 2-dB improvement in polarization sensitivity is measured. In addition to the polarization insensitivity, channel crosstalk is measured to be <-27 dB in 315 m of high nonlinearity fiber. In a detailed experimental study, the pattern of crosstalk in longer fiber lengths and the coupling between the polarization sensitivity and crosstalk are measured. For example, with a 430-m fiber length, we measure the degradation in polarization sensitivity to be /spl sim/4 dB for 12-dB increased signal power. The experimental results are also confirmed by theoretical calculations. Moreover, in a 32 channels systems simulation, the signal-to-noise ratio (SNR) of the converted signals after 800-km propagation is calculated to be only 0.8-dB degraded compared to using laser diodes with the same initial SNR values. Furthermore, we calculate the effect of pump noise and show that the relative intensity noise of the pump is transferred to the converted signals with an additional 8-dB/Hz degradation.

Polarization-insensitive wavelength conversion in a lithium niobate waveguide by the cascading technique

In this letter, we present a polarization-insensitive wavelength conversion scheme based on the cascading of two second-order processes. The nonlinear device exploits a double pass configuration in a titanium indiffused waveguide realized on a periodically poled lithium-niobate substrate. Polarization-independent conversion efficiency is obtained by rotating the signal polarization state by means of a Faraday mirror. A polarization sensitivity lower than 0.8 dB is experimentally demonstrated.

New directions in sub-10-fs optical pulse generation

Sub-10-fs pulse generation has reached a maturity and robustness that gave rise to a rapid increase of new ultrafast applications. Some of these novel applications rely on the octave-spanning spectral width, the coherence properties, or the extremely high peak intensity of femtosecond lasers, which sets them apart from the traditional use of femtosecond lasers in ultrafast spectroscopy. In this review, we concentrate on the sub-10-fs regime and first discuss the state of the art in ultrashort pulse generation. We then report on ultrabroadband wavelength conversion schemes and dispersion control by chirped mirrors. We also review advances in pulse characterization methods, with which we can measure pulse properties with much higher accuracy than simple autocorrelation methods and which support even a bandwidth in the single-cycle regime. With the recent demonstrations of pulses with a duration of merely two optical cycles, a regime is entered where the relative phase between the carrier and the envelope of the pulse starts to play a role. We discuss methods to measure and control the carrier–envelope phase and point out applications in frequency metrology. A wealth of further novel directions and developments in femtosecond research is reviewed in this article.

Architectural evolution and principles of optical terabit packet switches (OTPS)

To support all traffic types, terabit packet switches are required to satisfy the ever-increasing bandwidth explosion. In this paper, a brief review of recent activities on optical packet switches is presented. Two terabit optical interconnection networks implemented by small modular structures are proposed. Their comparison and performance evaluations are discussed. Alternatively, a novel optical terabit packet switch with small optical buffers is presented and its performance with respect to buffer size is discussed. Two possible wavelength conversion schemes are introduced, and their cascadability performance is discussed. In addition, a novel all-optical packet header replacement unit is proposed and its control is presented.

A novel scheme for XGM wavelength conversion based on single-port-coupled SOA

A novel scheme is proposed for wavelength conversion based on cross-gain modulation (XGM) in a single-port-coupled semiconductor optical amplifier (SOA), in which the input and output share one port. Experimental results and theoretical analysis show that this scheme can be achieved with simple implementation, high output extinction ratio and large input dynamic range. Based on this novel scheme, 2.5 Gbit/s wavelength up conversion with a 12.8 nm span has been demonstrated with the output extinction ratio as high as 15 dB.

All-optical wavelength conversion for 20-Gb/s RZ format data

We have successfully demonstrated an all-optical wavelength conversion scheme for high-speed return-to-zero (RZ) format data input by using a semiconductor-optical-amplifier (SOA) converter incorporated with a stabilized asymmetric Mach-Zehnder interferometer (AMZI). A bit-error-rate penalty of the converted signals less than 1.2 dB compared to that of the back-to-back signals was achieved for the entire wavelength conversion range from 1530 to 1560 nm with an AMZI. In this scheme, the conversion speed faster than the carrier recombination rate of the SOAs was possible. Noninverted wavelength conversion of 20-Gb/s RZ format data signals has been achieved.

Wavelength-tunable all-optical clock recovery using a fiber-optic parametric oscillator

We report a wavelength-tunable clock recovery scheme for all-optical 3R regeneration and simultaneous wavelength conversion. The scheme is based on a fiber-optic parametric oscillator, in which dynamic gain results from the four-wave mixing process in the fiber. In our implementation, 2.9 ps clock pulses are recovered from the incident pseudo-random data stream with the clock wavelength being tunable over the whole erbium-doped-fiber-amplifier bandwidth. RF spectrum measurements show that the recovered clock has less timing jitter than the incident data stream. We also present a two-channel clock recovery experiment, which demonstrates the feasibility of our scheme at 100 Gbit/s data rate.

Wavelength conversion based on cross-gain modulation of ASE spectrum of SOA

We propose and demonstrate a simple and new scheme of wavelength conversion in which the cross-gain modulation of amplified spontaneous emission of a semiconductor optical amplifier is used to convert the pump signal wavelength by means of the spectrum-spliced method. This technology allows pump wavelength to be converted into any other wavelength without using any probe light source.

1.31-to-1.55 μm wavelength conversion by optically pumping a distributed feedback amplifier

We demonstrate a new technique for all-optical wavelength conversion to 1.55 /spl mu/m by using a 1.3-/spl mu/m signal that directly pumps a distributed feedback semiconductor optical amplifier. Data polarity can be selected by tuning the probe wavelength to different regions of the Bragg resonance. Polarity-inverted signals exhibit a digital-like transfer function with an on-off ratio of 4 and 2.4 at 155.5 and 622 Mb/s, respectively. This simple wavelength-conversion scheme is insensitive to the direction and polarization of the 1.31-/spl mu/m signal, and should be affordable for local access and other cost-sensitive optical-network layers.