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Optics Express

Properties of power dependence on low-crosstalk waveband conversion with an apodized multiperiod-QPM LiNbO_3 device

Isao Tomita, Takeshi Umeki, Osamu Tadanaga, Hongbin Song, Masaki Asobe, Hirokazu Takenouchi

Published Jun 13, 2014• 2 citations
Publisher

Abstract

Quasi-phase-matched (QPM) LiNbO₃ devices having a multiperiod-periodically-poled structure, which we call multiperiod-QPM LiNbO₃ devices, are capable of shifting the idler waveband during waveband conversion via cascaded difference-frequency generation (cascaded DFG). However, these multiperiod-QPM devices have a problem that they produce extra ripples between QPM peaks in the phase-matching curve. These ripples cause crosstalk between wavebands arising from sum-frequency generation (SFG) between the signal and idler wavebands and subsequent DFG between the SFG wavelength and the signal waveband. To decrease the size of the ripples and thus that of the crosstalk, an apodized multiperiod-QPM device is developed. In demonstrating waveband conversion for low crosstalk with this device, we measure the dependence of the idler power, the crosstalk power, and their ratio on the signal power. This measurement shows that it agrees well with theoretical prediction and that the obtained feature of crosstalk reduction is kept even for decreased signal power.

DOI
10.1364/oe.22.015232

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Journal of the Optical Society of America B•May 1, 2003•15 citations
Quasi-phase-matched (QPM) LiNbO₃ devices having a multiperiod-periodically-poled structure, which we call multiperiod-QPM LiNbO₃ devices, are capable of shifting the idler waveband during waveband conversion via cascaded difference-frequency generation (cascaded DFG). However, these multiperiod-QPM devices have a problem that they produce extra ripples between QPM peaks in the phase-matching curve. These ripples cause crosstalk between wavebands arising from sum-frequency generation (SFG) between the signal and idler wavebands and subsequent DFG between the SFG wavelength and the signal waveband. To decrease the size of the ripples and thus that of the crosstalk, an apodized multiperiod-QPM device is developed. In demonstrating waveband conversion for low crosstalk with this device, we measure the dependence of the idler power, the crosstalk power, and their ratio on the signal power. This measurement shows that it agrees well with theoretical prediction and that the obtained feature of crosstalk reduction is kept even for decreased signal power.
Cascaded second-order nonlinear interaction (&chi(2));based wavelength conversion technique has attracted much attention due to its unique characteristics such as low noise and broadband, which are critical in fiber communication networks. In this report, wavelength conversions based on the newly proposed SFG-DFG (sum frequency generation - difference frequency generation) and conventional SHG-DFG (second harmonic generation - difference frequency generation) are studied and compared both experimentally and theoretically in a LiNbO3 quasi-phase matched (QPM) waveguide. It is shown that the same conversion efficiency can be achieved by employing two pump sources with only half power each (P1, P2) in the SFG-DFG scheme as compared with the SHG-DFG scheme with a single higher power pump beam (P=P1+P2). It is shown that the cascaded SFG-DFG based wavelength conversion has a larger 3-dB pump tolerance bandwidth. The theoretical results are consistent well with the experimental ones. It is found that the pump wavelength difference can be separated by a span as large as 75 nm, while 3-dB signal conversion efficiency is retained in a 45 mm-long device. It is also exhibited that tolerance of temperature for the cascaded SFG-DFG remains the same as that of the cascaded SHG-DFG based devices. The results show that the SFG-DFG wavelength conversion scheme is very attractive for practical applications.
The principle of all-optical wavelength conversion based on the cascaded sum and difference frequency generation (SFG+DFG) in quasi-phase-matched (QPM) periodically poled LiNbO3 (PPLN) waveguides is introduced. The conversion efficiency of the wavelength converter is calculated. The influences of the powers and span of two pumps on the conversion efficiency are analyzed. Bandwidth of one pump wavelength is discussed. The tuning is about 0.5 nm. The signal pulse width is compressed about 0.68 times.
We investigate response flatting of cascaded sum- and difference- frequency generation (SFG/DFG)-based wavelength conversion in quasi-phase-matched (QPM) periodically poled lithium niobate waveguides for wavelength division multiplexing optical communication systems. The cascaded SFG/DFG-based configuration shows more robustly combined properties than conventional DFG-based and cascaded second-harmonic generation and DFG (SHG/DFG)-based configurations. The response fluctuation, generated while enhancing the conversion bandwidth, can be efficiently reduced by the method of pump detuning or QPM period detuning.
Wavelength conversion based on the cascaded sum-frequency generation and difference-frequency generation (cSFG+DFG) process in quasi-phase-matched (QPM) periodically poled lithium niobate (PPLN) waveguides has the advantage of no pump occupation in the communication band, compared to the traditional cascaded second-harmonic generation (SHG) and DFG process. In cSFG+DFG-based wavelength conversion, two pump waves and a signal wave are required. The input pulse train, as a carrier of information, can be applied to either the signal or one of the two pump waves. Though the converted wave is in the form of pulses, its temporal and spectral characteristics are dependent on the arrangement of the pulsed wave. In this work, we target the wavelength conversion of 40-GHz picosecond pulse trains, and systematically analyze the temporal and spectral characteristics of the pump, signal, converted, and sum-frequency waves during their propagations in PPLN waveguides by using numerical simulation. In particular, pulse shapes, optical spectra, phases and conversion efficiency are compared when the picosecond pulse train is used as the signal and pump waves, respectively.
Difference-frequency generation (DFG) and cascaded second-order nonlinear interaction (χ(2)) based wavelength conversions in LiNbO3 quasi-phase-matched waveguides were studied systematically. The characteristics of the two conversion methods, such as conversion efficiency, conversion bandwidth, pump-wavelength tolerance, and temperature stability, were compared with both experimental and theoretical results of MgO-doped quasi-phase-matched waveguides. It was found that for shorter device length and lower pump power, DFG based wavelength converters had higher conversion efficiency, and the cascaded χ(2) based wavelength conversions had slightly wider 3-dB signal-conversion bandwidth. The 3-dB signal wavelength-conversion bandwidth decreased exponentially with an increase in device length. For long devices and high pump power, however, the efficiency difference between the cascaded χ(2) based conversions and DFG based ones was minor. Tolerance of pump wavelength for the cascaded χ(2) based wavelength conversions was approximately two times that of DFG-based ones, which decreases with the increase of device length. In both cases, the tolerance of pump wavelength exponentially decreased with an increase of device length. It was found that the temperature stability of the cascaded χ(2) based conversions was identical to that of DFG based conversions. These results are very helpful in choosing suitable wavelength converters for practical optical communication systems.