The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jérôme Faist - One of the best experts on this subject based on the ideXlab platform.
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Negative free Carrier Absorption in terahertz quantum cascade lasers
Applied Physics Letters, 2016Co-Authors: Camille Ndebeka-bandou, Mattias Beck, Keita Ohtani, Markus Rösch, Jérôme FaistAbstract:We analyze the peculiar case where the free Carrier Absorption arising from LO phonon Absorption-assisted transitions becomes negative and therefore turns into a gain source for quantum cascade lasers. Such an additional source of gain exists when the ratio between the electronic and the lattice temperatures is larger than one, a condition that is usually fulfilled in quantum cascade lasers. We find a gain of few cm$^{-1}$'s at 200K. We report the development of a terahertz quantum cascade laser operating in the negative free Carrier Absorption regime.
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wallplug efficiency of quantum cascade lasers critical parameters and fundamental limits
Applied Physics Letters, 2007Co-Authors: Jérôme FaistAbstract:Fundamental limits in the wallplug efficiency of quantum cascade lasers are derived in a rate equation model that uses global effective parameters. Free Carrier Absorption and thermal population of the lower state force a strong downward trend of this efficiency with increasing wavelength, that agrees well with experimental data taken from literature.
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measurement of far infrared waveguide loss using a multisection single pass technique
Applied Physics Letters, 2001Co-Authors: Michel Rochat, Jérôme Faist, Mattias Beck, U OesterleAbstract:Waveguide loss measurements based on a multisection single-pass technique have been performed for both mid-infrared and far-infrared quantum cascade structures. The far-infrared quantum cascade structures are based on a vertical transition active region emitting at λ≈76 μm, embedded in a double-plasmon waveguide. The measured waveguide loss of 42±20 cm−1 agrees well with the calculated one based on free Carrier Absorption.
Irina Veretennicoff - One of the best experts on this subject based on the ideXlab platform.
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effect of photon energy dependent loss and gain mechanisms on polarization switching in vertical cavity surface emitting lasers
Journal of The Optical Society of America B-optical Physics, 1999Co-Authors: B Ryvkin, Krassimir Panajotov, A Georgievski, Jan Danckaert, Michael Peeters, Guy Verschaffelt, Hugo Thienpont, Irina VeretennicoffAbstract:We have analyzed the effect of the photon energy and temperature dependence of both the gain and the total losses inside the cavity to understand the polarization behavior of vertical-cavity surface-emitting lasers. The assumption that the losses are dominated by free-Carrier Absorption in the p-doped mirror is made. Developing a new theoretical approach, we are able to predict different polarization switching regimes in which switching occurs from the high- to the low-frequency mode, from the low- to the high-frequency mode, or both consecutively. All these predictions have been experimentally verified by our measurements on GaAs/AlGaAs proton-implanted vertical-cavity surface-emitting lasers.
Shinichi Takagi - One of the best experts on this subject based on the ideXlab platform.
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novel ge waveguide platform on ge on insulator wafer for mid infrared photonic integrated circuits
Optics Express, 2016Co-Authors: Jian Kang, Mitsuru Takenaka, Shinichi TakagiAbstract:We present Ge rib waveguide devices fabricated on a Ge-on-insulator (GeOI) wafer as a proof-of-concept Ge mid-infrared photonics platform. Numerical analysis revealed that the driving current for a given optical attenuation in a Carrier-injection Ge waveguide device at a 1.95 μm wavelength can be approximately five times smaller than that in a Si device, enabling in-line Carrier-injection Ge optical modulators based on free-Carrier Absorption. We prepared a GeOI wafer with a 2-μm-thick buried oxide layer (BOX) by wafer bonding. By using the GeOI wafer, we fabricated Ge rib waveguides. The Ge rib waveguides were transparent to 2 μm wavelengths and the propagation loss was found to be 1.4 dB/mm, which may have been caused by sidewall scattering. We achieved a negligible bend loss in the Ge rib waveguide, even with a 5 μm bend radius, owing to the strong optical confinement in the GeOI structure. We also formed a lateral p-i-n junction along the Ge rib waveguide to explore the capability of Absorption modulation by Carrier injection. By injecting current through the lateral p-i-n junction, we achieved optical intensity modulation in the 2 μm band based on the free-Carrier Absorption in Ge.
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strain induced enhancement of plasma dispersion effect and free Carrier Absorption in sige optical modulators
Scientific Reports, 2015Co-Authors: Mitsuru Takenaka, Takenori Osada, Masahiko Hata, Shinichi TakagiAbstract:The plasma dispersion effect and free-Carrier Absorption are widely used to change refractive index and Absorption coefficient in Si-based optical modulators. However, the weak free-Carrier effects in Si cause low modulation efficiency, resulting in large device footprint and power consumption. Here, we theoretically and experimentally investigate the enhancement of the free-Carrier effects by strain-induced mass modulation in silicon-germanium (SiGe). The application of compressive strain to SiGe reduces the conductivity effective mass of holes, resulting in the enhanced free-Carrier effects. Thus, the strained SiGe-based optical modulator exhibits more than twice modulation efficiency as large as that of the Si modulator. To the best of our knowledge, this is the first demonstration of the enhanced free-Carrier effects in strained SiGe at the near-infrared telecommunication wavelength. The strain-induced enhancement technology for the free-Carrier effects is expected to boost modulation efficiency of the most Si-based optical modulators thanks to high complementary metal-oxide-semiconductor (CMOS) compatibility.
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strain induced enhancement of plasma dispersion effect and free Carrier Absorption in sige optical modulators
arXiv: Optics, 2013Co-Authors: Mitsuru Takenaka, Takenori Osada, Masahiko Hata, Shinichi TakagiAbstract:The plasma dispersion effect and free-Carrier Absorption are widely used for changing refractive index and Absorption coefficient in Si-based optical modulators. However, these free-Carrier effects in Si are not large enough for making the footprint of the Si modulators small. Here, we have theoretically and experimentally investigated the enhancement of the plasma dispersion effect and free-Carrier Absorption by strain-induced mass modulation in silicon-germanium (SiGe). The application of compressive strain to SiGe reduces the conductivity hole mass, resulting in the enhanced free-Carrier effects. Thus, the strained SiGe-based optical modulator exhibits more than twice modulation efficiency as large as that of the Si modulator. To the best of our knowledge, it is the first demonstration of the enhanced free-Carrier effects in strained SiGe at the near-infrared telecommunication wavelength. The strain-induced enhancement technology for the free-Carrier effects is expected to boost the modulation efficiency of the most Si-based optical modulators thanks to high complementary metal-oxide-semiconductor (CMOS) compatibility.
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strain engineering of plasma dispersion effect for sige optical modulators
IEEE Journal of Quantum Electronics, 2012Co-Authors: Mitsuru Takenaka, Shinichi TakagiAbstract:The plasma dispersion effect and free-Carrier Absorption in strained SiGe are analyzed using the six-band k·p method and the Drude model. Since the hole conductivity mass of SiGe is decreased by applying compressive strain, enhancement of the plasma dispersion effect, and free-Carrier Absorption in strained SiGe is expected. We predict that Si0.5Ge0.5 coherently grown on Si will exhibit three times higher plasma dispersion and four times higher free-Carrier Absorption than Si. The modulation characteristics of SiGe quantum well metal-oxide-semiconductor (MOS) optical modulators are also analyzed by technology computer-aided design simulation and finite-difference optical mode analysis. An extremely small VπL of 0.033 V-cm is predicted in the case of a compressively strained Si0.5Ge0.5 quantum well in conjunction with a high-k gate dielectric MOS structure. The enhancement of free-Carrier Absorption in the SiGe high-k MOS modulator also makes in-line intensity modulation feasible and an intensity modulation efficiency of 9 dB/mm/V is predicted.
Kent D. Choquette - One of the best experts on this subject based on the ideXlab platform.
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Cold-cavity measurement of optical loss from oxide-confined vertical-cavity surface-emitting lasers
Applied Physics Letters, 2014Co-Authors: Stewart T. M. Fryslie, Dominic F. Siriani, Kent D. ChoquetteAbstract:Microcavity laser design and performance optimization requires a quantitative knowledge of the cavity optical losses. A generalized method using sub-threshold spectral measurements matched to model calculations is demonstrated to determine optical loss in microcavity lasers. Cold-cavity spectral characteristics are used to extract the size-dependent optical loss for small diameter oxide-confined vertical-cavity surface emitting lasers. For oxide aperture diameters less than 4 μm, the oxide scattering loss can be greater than 10 cm−1, similar to the typical values of free Carrier Absorption loss.
B Ryvkin - One of the best experts on this subject based on the ideXlab platform.
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effect of photon energy dependent loss and gain mechanisms on polarization switching in vertical cavity surface emitting lasers
Journal of The Optical Society of America B-optical Physics, 1999Co-Authors: B Ryvkin, Krassimir Panajotov, A Georgievski, Jan Danckaert, Michael Peeters, Guy Verschaffelt, Hugo Thienpont, Irina VeretennicoffAbstract:We have analyzed the effect of the photon energy and temperature dependence of both the gain and the total losses inside the cavity to understand the polarization behavior of vertical-cavity surface-emitting lasers. The assumption that the losses are dominated by free-Carrier Absorption in the p-doped mirror is made. Developing a new theoretical approach, we are able to predict different polarization switching regimes in which switching occurs from the high- to the low-frequency mode, from the low- to the high-frequency mode, or both consecutively. All these predictions have been experimentally verified by our measurements on GaAs/AlGaAs proton-implanted vertical-cavity surface-emitting lasers.