Efficient Wavelength Conversion Research Articles

Simple techniques for highly efficient wavelength conversion with low polarization sensitivity by use of semiconductor optical amplifiers

Experimental investigations of two schemes for polarization-direction-insensitive spectral conversion by use of four-wave mixing in a semiconductor optical amplifier (SOA) are reported. One scheme that utilizes an SOA with a linearly polarized signal and a single copropagating circularly polarized pump is, as far as we are aware, the simplest such scheme that has been reported to date. A theoretical analysis of this novel scheme is also presented. Experimental investigations of that scheme are compared with measurements of the performance of a previously proposed scheme, which involves the use of a single SOA and two orthogonal counterpropagating pump beams. We observe that polarization-direction-insensitive conversion is far more efficient in the new scheme described here. Within the observed detuning range, the difference in efficiency between the two schemes is found to increase from 6 to 18 dB as the detuning is increased. The corresponding increase in the difference of the signal-to-background ratio between the two schemes is from approximately 2 to 16 dB.

Highly Efficient Arbitrary Wavelength Conversion Within Entire C-Band Based on Nondegenerate Fiber Four-Wave Mixing

Highly efficient tunable wavelength conversion based on nondegenerate fiber four-wave mixing is demonstrated. We apply simultaneous phase modulation to the two pump waves so that stimulated Brillouin scattering is suppressed without affecting the generated idler wave. The signal light is converted from an arbitrary wavelength to another arbitrary one within the entire C-band with a conversion efficiency higher than -10 dB.

Phase-matching and Nonlinear Optical Processes in Silicon Waveguides

The efficiency of four-wave-mixing arising from Raman and non-resonant nonlinear susceptibilities in silicon waveguides is studied in the 1.3 - 1.8microm regime. The wavelength conversion efficiency is dominated by the Raman contribution to the nonlinear susceptibility, and high conversion efficiencies can be achieved under the phase-matching condition. In this context, dispersion in silicon waveguides is analyzed and it is shown that phase-matching is achieved in properly engineered waveguides where birefringence compensates for material dispersion. Finally the sensitivity of the phase mismatch to fabrication-induced errors in waveguide dimensions is quantified.

Channel-selective wavelength conversion and tuning in periodically poled Ti:LiNbO3 waveguides

All-optical wavelength-selective single- and dual-channel wavelength conversion and tuning has been demonstrated in a periodically poled Ti:LiNbO(3) waveguide that has two second-harmonic phase-matching peaks by cascaded sum and difference frequency generation (cSFG/DFG). The wavelength conversion efficiency was measured to be -7 dB with coupled pump power of 233 mW.

Intracavity wavelength conversions employing a MgO-doped LiNbO_3 quasi-phase-matched waveguide and an erbium-doped fiber amplifier

Intracavity sum-frequency generation and cascaded χ(2) wavelength conversions in a fiber ring resonator using a MgO-doped LiNbO3 quasi-phase-matched waveguide and an erbium-doped fiber amplifier were proposed and demonstrated. In the proposed configuration, the resonator enhances the pump light, and efficient wavelength conversion is realized. Dependence of converted signal power upon the position of a coupler used to couple a signal into the resonator and upon the round-trip loss of the resonator was studied in detail. The proposed configuration provides efficient wavelength conversion over a wide range of input signal power and resonator round-trip loss. The configuration provides a cost-effective solution to enhance pump power, thus increasing wavelength-conversion efficiency for practical system applications.

Four-wave mixing based 10-Gb/s tunable wavelength conversion using a holey fiber with a high SBS threshold

We demonstrate a four-wave-mixing based wavelength converter using a 15-m highly nonlinear holey fiber (HF) with a high stimulated Brillouin scattering (SBS) threshold. Error-free efficient wavelength conversion of 10-Gb/s nonreturn-to-zero signal over a /spl sim/10-nm bandwidth is reliably achieved. Our 15-m HF has a nonlinearity coefficient /spl gamma//spl sim/70(/spl plusmn/10) W/sup -1//spl middot/km/sup -1/ and an SBS threshold of more than 130 mW. The high SBS threshold is achieved by applying structural variation to the HF along its length during the fabrication process. No modulational-instability-induced intensity noise on the converted signals is observed due to the normal dispersion of the HF.

Symmetric highly efficient (/spl sim/0 dB) wavelength conversion based on four-wave mixing in quantum dot optical amplifiers

Conversion efficiency to longer wavelengths in four-wave-mixing-based wavelength conversion in optical semiconductor amplifiers is generally much lower than that in the opposite direction. This study demonstrates experimentally that this feature is drastically improved, and the asymmetry between conversion directions is eliminated by using quantum dots in the active layer. We attribute this to a reduction in linewidth enhancement factor due to the discreteness of the electron states in quantum dots.

Raman-assisted fiber optical parametric amplifier and wavelength converter in highly nonlinear fiber

We present a continuous-wave pumped fiber optical parametric amplifier and wavelength converter in 1 km of highly nonlinear dispersion-shifted fiber. The reduced pump requirements of the fiber allowed a low-signal-loss configuration in which respective net gains and wavelength-conversion efficiencies of up to 8.6 dB and 5.9 dB were obtained with only 89 mW of pump power. These values were increased to 19.5 dB and 17.3 dB, respectively, when a counterpropagating 680-mW pump was used to assist the parametric process through Raman amplification. Raman assistance in highly nonlinear fiber further promotes parametric amplification and wavelength conversion as a viable technology for the future.

Two-Photon Pumped Lasing from a Two-Dimensional Photonic Bandgap Structure with Polymeric Gain Material

Two-photon pumped laser action in an organic surface-emitting laser structure, shaped as a circular-grating, is demonstrated. The device exhibits a narrow linewidth blue laser emission with a clear lasing threshold upon two-photon excitation, which indicates that the polymer has a large cross-section for both stimulated emission and two-photon absorption. The combination of the large cross-sections and the high fluorescence quantum yield in the solid state offers potential for nonlinear light-emitting devices and for efficient wavelength conversion.

Optical signal processing using nonlinear semiconductor microring resonators

Recent fabrication advances have enabled compact semiconductor microring resonators to be fabricated with high-finesse values and picosecond cavity lifetimes. These devices have potential applications in optical signal processing as all-optical switches, multiplexers and logic gates. Theoretical analysis shows a maximum reduction in the switching power proportional to the fourth power of the field enhancement in the microring. An enhancement in the wavelength conversion efficiency by four-wave mixing which is proportional to the eighth power of the field enhancement is also predicted and experimentally confirmed. Experimental results demonstrating bistability, picosecond switching using pump and probe excitation, optical time-division demultiplexing, spatial pulse routing and four-wave mixing in GaAs-AlGaAs microring resonators are reported. Apart from the bistable response, which was thermally induced, the nonlinear effects observed in the microrings were caused by the two-photon absorption process. Applications of microrings to realize all-optical logic gates are also proposed.

Widely tunable all-optical wavelength converter using a fiber ring cavity incorporating a semiconductor optical amplifier

We demonstrate wavelength conversion using broad-band orthogonal pumps four-wave mixing in a semiconductor optical amplifier placed in a fiber ring cavity. The widely tunable all-optical wavelength converter operates with only one external pump laser. The wavelength-conversion efficiency has a variation smaller than 3 dB over a 40 nm range. Our result shows that the converter can operate with any arbitrary input and output wavelengths within the range. The measured power penalty is only 1.5 dB for a 2.5 Gb/s signal at 10 −9 bit-error-rate.

Characteristic comparison of single-pumped L-band erbium-doped fiber amplified spontaneous emission sources

We experimentally investigate the single-pumped L-band (1570–1610 nm) erbium-doped fiber amplified spontaneous emission (ASE) source in four configurations with single-pass forward, single-pass backward, double-pass forward (DPF), and double-pass backward structures. The characteristics are examined and compared in terms of the output power, mean wavelength, spectral linewidth, and pumping conversion efficiency. Among them, only DPF configuration is satisfied, and other configurations are intrinsically hard to be an L-band ASE source for applications. Such results are significantly different as compared with their corresponding C-band counterparts.

Analysis of all optical cascaded XGM wavelength converter using CW-holding beam

In this paper, we propose and analyze a wavelength conversion using an cross-gain modulation (XGM) with two semiconductor optical amplifiers and CW-holding beam for improvement of wavelength conversion speed and frequency chirp characteristics. Wavelength conversion characteristics of the cascaded XGM with a CW-holding beam are investigated in time domain. From the simulation, we have observed that the proposed scheme provides a non-inverted efficient wavelength conversion and frequency chirp reduction at higher bit rate operation.

Continuous-wave-pumped Raman-assisted fiber optical parametric amplifier and wavelength converter in conventional dispersion-shifted fiber

We present a continuous-wave-pumped fiber optical parametric amplifier, operating near 1539 nm in conventional dispersion-shifted fiber, with maximum on-off gain and wavelength-conversion efficiency of 13.7 and 13.1 dB, respectively. In addition, we show a novel configuration based on Raman amplification assistance in the parametric gain fiber that further increases the gain and wavelength-conversion efficiencies to 16.7 and 16.2 dB, respectively.

Quasi-phase-matched (QPM) difference frequency generation in a mirrorless 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.

Near-IR comparative characterization of optical second-order nonlinearities in Te-based semiconductors

We have systematically characterized the second harmonic generation efficiency of Te-based binary and ternary II–VI compounds in the near-IR spectral region, namely at=1.5 m and=1.9 m. A phase mismatched technique has been employed, as a translation into the spectral domain of the Maker fringes method. By using sub-picosecond optical pulses, reliable results for the value of non second-order linear coefficientd and of chromatic dispersion have been obtained. We have performed a comparative evaluation of nonlinear wavelength conversion efficiency of Te-based semiconductors and GaAs. The ternary alloys Cd0.5Zn0.5Te and Cd0.78Mn0.22Te can be considered as the best performing basic materials for optical wavelength converters working in the third communication window, since they possess at the same time a highd coefficient, good transparency, and low chromatic dispersion.

Broad-band continuous-wave-pumped fiber optical parametric amplifier with 49-dB gain and wavelength-conversion efficiency

A broad-band continuous-wave (CW) pumped fiber-based parametric amplifier with 39 dB of internal gain and wavelength conversion efficiency, corresponding to a black box gain/efficiency of 38 dB, is demonstrated. Bit-error-rate (BER) measurements indicate performance comparable to erbium-doped fiber amplifiers (EDFAs). These amplifiers may thus find new applications in future lightwave systems.

Measurements of second-order susceptibility at λ=1.5 μm in CdTe-based ternary alloys for efficient wavelength conversion

We have characterized the second-order optical nonlinear response of II-VI semiconductor ternary compounds Cd0.8Zn0.2Te and Cd0.78Mn0.22Te at λ=1.5 μm. A spectrally resolved phase-mismatch second-harmonic generation (SHG) technique has been used on bulk single crystals, exploiting 10−13 s optical pulses and multichannel detection. The nonlinear d coefficient has been measured and chromatic dispersion parameters have been validated. By normalizing SHG results in view of applications to all-optical wavelength conversion, the tested compounds prove to be interesting alternatives to more renowned AlxGa1−xAs.

All-optical wavelength conversion and signal regeneration using an electroabsorption modulator

All-optical wavelength conversion and signal regeneration based on cross-absorption modulation in an InGaAsP quantum well electroabsorption modulator (EAM) is studied at different bit rates. We present theoretical results showing wavelength conversion efficiency in agreement with existing experimental results, and the signal regeneration capability of the device is investigated. In particular, we demonstrate the dependence of the extinction ratio of both the converted signal and the control signal on the device length and on the power level of the control signal. We also show how the sweep-out dynamics influences the results.

Characteristics of Wavelength Tunable Femtosecond Soliton Pulse Generation Using Femtosecond Pump Laser and Polarization Maintaining Fiber

We have investigated both experimentally and numerically the characteristics of wavelength tunable femtosecond soliton pulse generation using a pulse width variable fiber laser and two different types of polarization maintaining fibers. The generated soliton shows the feature of the pulsewidth becoming almost constant at - 250 fs under any conditions of the pump pulse for 220m fiber. High conversion efficiency from pump pulse to a generated soliton pulse accounting for as much as 73% can be obtained. This efficiency decreases with increase in the input power or wavelength shift. A superior conversion efficiency and broad wavelength shift can be obtained by using a more shortened pump pulse. In the numerical calculations, it is predicted that under a condition of constant power of pump pulse, the maximum wavelength shift is achieved when the soliton number N is -1.4. The difference of mode field diameter and the group velocity dispersion (GVD) coefficient β2 affect the wavelength shift and conversion efficiency. Using the fiber with small mode field diameter and small absolute value of GVD coefficient β2, a high conversion efficiency and large wavelength shift can be obtained.