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Key CLARITY technologies II – Four-Wave Mixing wavelength conversion

National and Kapodistrian University of Athens Department of Informatics and Telecommunications Photonics Technology Laboratory. Key CLARITY technologies II – Four-Wave Mixing wavelength conversion. Introduction - Wavelength conversion. Wavelength conversion device. λ i. λ o. λ. λ.

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Key CLARITY technologies II – Four-Wave Mixing wavelength conversion

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  1. National and Kapodistrian University of Athens Department of Informatics and Telecommunications Photonics Technology Laboratory Key CLARITY technologiesII – Four-Wave Mixingwavelength conversion

  2. Introduction - Wavelength conversion Wavelength conversion device λi λo λ λ • Many optical systems may not be naturally compatible with one another and require a means of converting photons of different energies. • Wavelength/frequency conversion is a technique used to alter the wavelength of an optical field. • The new wavelength can be within the same waveband or in a totally different waveband. • A variety of media can be used:- Passive (waveguides, optical fibers …)- Active (semiconductor lasers, amplifiers …)

  3. Introduction - Non-linear processes 1 • In an optical system non-linear response can occur when there is sufficiently intense illumination. • The nonlinearity is exhibited in the polarization of the material (P) which is often represented by a power series expansion of the total applied optical field (E): • Optical non-linearity usually occurs due to 2nd and 3rd susceptibility: χ(2), χ(3) • Different non-linear processes which depend on the material can occur:- Cross gain saturation • - Cross-phase modulation- Four-wave mixing

  4. Introduction - Non-linear processes 2 λ λ λ1 λ2 λ3 λ1 λ2 • In most techniques more than one optical fields are required: • - the field to be wavelength converted at λ1(“signal”) • - an optical pumping field at λ2 (“pump”) • The signal photons are scattered to a new energy due to a non-linear process present in the medium. • Four-Wave Mixing is a χ(3) process and can take place in many media • Different non-linear physical mechanisms can contribute to the FWM process: • - gain • - Kerr effect- two-photon absorption- … INPUT OUTPUT Non-linear process Four-Wave Mixing (FWM)Cross-Phase Modulation (XPM)Cross-Gain Modulation (XGM)

  5. Four-Wave Mixing 1 ω ω ωs ωp ωs ωp ωs ωi • In FWM process four optical fields are involved: • - at the input: the “signal” and the “pump” • - at the output: the “conjugate” or “idler” and the “satellite” • Consider two input frequencies present, a strong pump field at ωp, and asignal field at ωs (Ω = ωp – ωs). • New components are generated at the output due to the non-linear polarization proportional to the third order susceptibility: • - the idler at ωi, ωi = 2ωp - ωs = ωp + Ω • - the satellite at ωs, ωs= 2ωs - ωp = ωs - Ω • The idler is the phase conjugate of the signal and the satellite is the conjugate of the pump INPUT OUTPUT Four-Wave Mixing Ω

  6. Four-Wave Mixing 2 • The efficiency of the FWM process (strength of the new products) depends on the pump power. • In order to obtain high efficiency, the FWM process the phase matching condition is required (β is the propagation constant): • Conversion of a waveband is possible • FWM is an efficient wavelength conversion tool for wavelength-division multiplexed (WDM) telecommunication networks • But it plays a negative role in the propagation of multi-wavelength signals in optical fibers, as new undesired wavelengths are generated.

  7. Conversion from mid-IR to near-IR using FWM - The concept • Within CLARITY the FWM process will be used to convert optical signals from the mid-infrared (MIR) regime for detection to the near-IR (NIR) regime. • 3rd order non-linear materials will be used to realize broadband parametric amplification. • For conversion of the signal which lies within the MIR regime (3 – 5 μm) to the NIR regime (1.4 – 1.7 μm), the pump should be around 2 μm.

  8. Conversion from mid-IR to near-IR using FWM - Engineering issues Phase matching condition depends on: • Input wavelengths • Waveguide dispersion and non-linear properties • Input pump power High conversion efficiency and broadband operation can be achieved following specific design rules: • Engineering the waveguide geometry: - Small effective mode area at the pump wavelength regime is required in order to exploit the high power of the pump field (<1μm2) - Mode overlap close to 1 in order to maximize the non-linear interaction between the FWM fields • Engineering the waveguide dispersion: zero dispersion at the pump wavenegth regime • Proper selection of input wavelengths: pump tunability is required • High pump power: ~W range

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