We have studied the effect of waveguide alignment on the reflection spectrum of Bragg gratings fabricated using a multiple order phase mask. We have demonstrated that splitting of certain Bragg peaks observed in earlier experiments reported in literature is caused by formation of the gratings with different periodicities in the waveguide tilted with respect to the phase mask plane due to the interference of non-symmetrical diffraction orders. Analytical expressions for spectral separation of the split peaks have been derived and verified against the experimental data recently presented in literature. The analytical predictions were also confirmed by numerical simulations of intensity distributions behind the multiple order diffraction grating and its projection on the tilted waveguide.
We present a direct comparison between two types of femtosecond 2 µm sources used for seeding of an ultrafast thulium-doped fiber amplifier based on all-normal dispersion supercontinuum and soliton self-frequency shift. Both nonlinear effects were generated in microstructured silica fibers, pumped with low-power femtosecond pulses at 1.56 µm originating from an erbium-doped fiber laser. We performed a full characterization of both nonlinear processes, including their shot-to-shot stability, phase coherence, and relative intensity noise. The results revealed that the solitons show comparable performance to supercontinuum in terms of relative intensity noise and shot-to-shot stability, despite the anomalous dispersion regime. Both sources can be successfully used as seeds for Tm-doped fiber amplifiers as an alternative to Tm-doped oscillators. The results show that the sign of chromatic dispersion of the fiber is not crucial for obtaining a stable, high-quality, and low-noise spectral conversion process when pumped with sub-50 fs laser pulses.
Excitonic emission from single InAs/InGaAlAs/InP quantum dashes has been investigated in the context of degree of linear polarization by post-growth modification of its surrounding dielectric medium.We present optical spectroscopy measurements on a symmetric squared pedestal structures (mesas), and asymmetric rectangular ones oriented parallel or perpendicular to the main in-plane axis of the dashes [1-10].Polarization resolved microphotoluminescence shows a significant quantitative modification of the degree of linear polarization value from -20% up to 70%.These results have been confronted with calculations of the coupling between the exciton transition dipole moment and electromagnetic field distributed in the vicinity of a quantum dash inside a processed mesa.
Both for Karol Wojtyła, the future Pope John Paul II, and Józef Tischner, freedom is a key matter. However, freedom must be e x p e r i e n c e d ; it is not revealed in objective metaphysics or in science.For Wojtyła, it is an experience of the moral a c t : freedom is a condition and in-gredient of the moral act and responsibility for it. It enters into the composition of the essential structure of the person, which means “self-restraint,” or shaping oneself through free choices. Freedom has the power to create man through itself: referring to others in morality, I at the same time refer to myself, deciding who I will be. This existential weight of freedom – responsibility for oneself before others, God, and oneself – is the price of freedom which, let us add, is inevitable. Even the rejection of freedom or resignation from it is still an expression of freedom. For Wojtyła, freedom shapes man through an instinc-tive, completely not induced reference to the truth about values. However, in this reference and in acting the subject is dependent only on itself. The weight of the action, whose truth we decipher in our conscience, is what most impresses Wojtyła. The lack of a need for the concept of grace in this vision is striking. The subject is independent, autonomous, and thus responsible. With regards to this point, Wojtyła is close to Thomism and its respect for the innateness of creation.For Tischner, freedom is key and is also an innate value that is experienced. Its essence is above all freeing, liberating; thus Tischner does not hesitate to discern it in extra-moral phenomena such as dancing, which liberates beauty, and even extra-human ones, such as the beauty of an elk jumping across a brook. Beauty and good require freedom. However, the true liberation of freedom is opening oneself to the freedom of the other in encoun-ter, as thanks to this I can enter into a relationship of love and fidelity; I can s a c r i f i c e myself and through this fulfill the highest act of freedom, an act that is not induced by pre-established responsibility for the other, as in Levinas’ philosophy. Although it is not induced, this act assumes in an essential way the relationality of the subject and at the same time its finiteness.
In this paper, we investigate both experimentally and theoretically the two intermodal-vectorial four-wave-mixing processes in birefringent few-mode fibers, which are spectrally indistinguishable. We show that two four-wave-mixing processes involving the four polarization modes of different spatial distributions can overlap spectrally as long as the group refractive indices of the signal and idler modes intersect at the pump wavelength. The experimental confirmation of theoretical predictions is performed with PANDA fiber pumped with an Nd:YAG laser with 1064.3 nm wavelength. The spectral overlap enables the hybrid-entanglement of photons in spatial-polarization-frequency degrees of freedom. Moreover, we discuss that the spectral position of the overlapping FWMs can be tailored by: (i) the relative phase birefringence of the four modes participating in the FWM or (ii) the average chromatic dispersion of the signal/idler modes, allowing to move the process away from detrimental Raman scattering. Interestingly, in the $\pm$ 100 THz range from pump considered here, the gain of FWM depends primarily on the integral overlap between the modes participating in the process and is virtually wavelength-independent. This characteristic makes few-mode birefringent fibers a promising platform for developing flat-gain, spectrally tailored sources of photon pairs entangled in multiple degrees of freedom.
We calculate, using finite difference method, the dispersion relation of photons transmitting through a one-dimensional photonic quasicrystal arranged in a generalized Fibonacci, generalized Thue-Morse and double periodic sequence. The structure of dispersion curves clearly shows their self-similar structure. With this method of calculation, we can obtain distribution of the electric field and energy density, group velocity and effective refraction index for the structure. We discuss taking into consideration the dispersion in layer materials and negative index materials.
