ABSTRACT
We investigate the impact of the photorefractive effect on lithium niobate integrated quantum photonic circuits dedicated to continuous variable on-chip experiments. The circuit main building blocks, i.e. cavities, directional couplers, and periodically poled nonlinear waveguides, are studied. This work demonstrates that photorefractivity, even when its effect is weaker than spatial mode hopping, might compromise the success of on-chip quantum photonics experiments. We describe in detail the characterization methods leading to the identification of this possible issue. We also study to which extent device heating represents a viable solution to counter this effect. We focus on photorefractive effect induced by light at 775 nm, in the context of the generation of non-classical light at 1550 nm telecom wavelength.
ABSTRACT
Light routing and manipulation are important aspects of integrated optics. They essentially rely on beam splitters which are at the heart of interferometric setups and active routing. The most common implementations of beam splitters suffer either from strong dispersive response (directional couplers) or tight fabrication tolerances (multimode interference couplers). In this paper we fabricate a robust and simple broadband integrated beam splitter based on lithium niobate with a splitting ratio achromatic over more than 130 nm. Our architecture is based on spatial adiabatic passage, a technique originally used to transfer entirely an optical beam from a waveguide to another one that has been shown to be remarkably robust against fabrication imperfections and wavelength dispersion. Our device shows a splitting ratio of 0.52±0.03 and 0.48±0.03 from 1500 nm up to 1630 nm. Furthermore, we show that suitable design enables the splitting in output beams with relative phase 0 or π. Thanks to their independence to material dispersion, these devices represent simple, elementary components to create achromatic and versatile photonic circuits.
ABSTRACT
We demonstrate phase-matched second harmonic generation in gallium nitride on silicon microdisks. The microdisks are integrated with side-coupling bus waveguides in a two-dimensional photonic circuit. The second harmonic generation is excited with a continuous wave laser in the telecom band. By fabricating a series of microdisks with diameters varying by steps of 8 nm, we obtain a tuning of the whispering gallery mode resonances for the fundamental and harmonic waves. Phase matching is obtained when both resonances are matched with modes satisfying the conservation of orbital momentum, which leads to a pronounced enhancement of frequency conversion.
ABSTRACT
We have developed a nanophotonic platform with microdisks using epitaxial III-nitride materials on silicon. The two-dimensional platform consists of suspended waveguides and mushroom-type microdisks as resonators side-coupled with a bus waveguide. Loaded quality factors up to 80000 have been obtained in the near-infrared spectral range for microdisk diameters between 8 and 15 µm. We analyze the dependence of the quality factors as a function of coupling efficiency. We have performed continuous-wave second harmonic generation experiments in resonance with the whispering gallery modes supported by the microdisks.
ABSTRACT
A ridge waveguide technology exhibiting high polarization dependency is developed for new efficient multi-section passive polarization rotator applications. In the presented configuration, the calculated mode coupling between the waveguide sections is very efficient and allows a polarization rotation with a high extinction ratio at lambda=1,55 mum. Experimental results show efficient polarization rotation with low cross-talk levels (-16dB) and no significant excess losses between sections. However, the overall transmission efficiency is limited by propagation losses and coupling losses to standard optical fibers.
ABSTRACT
CAP1 encodes a basic region-leucine zipper (bZip) transcriptional regulatory protein that is required for oxidative stress tolerance in Candida albicans. Cap1p is a homologue of a Saccharomyces cerevisiae bZip transcription factor designated Yap1p that is both required for oxidative stress tolerance and localized to the nucleus in response to the presence of oxidants. Oxidant-regulated localization of Yap1p to the nucleus requires the presence of a carboxy-terminal cysteine residue (C629) that is conserved in Cap1p as C477. To examine the role of this conserved cysteine residue, C477 was replaced with an alanine residue. This mutant protein, C477A Cap1p, was analysed for its behaviour both in S. cerevisiae and C. albicans. Wild type and C477A Cap1p were able to complement the oxidant hypersensitivity of a Deltayap1 S. cerevisiae strain. Whereas a Yap1p-responsive lacZ fusion gene was oxidant inducible in the presence of YAP1, the C. albicans Cap1p derivatives were not oxidant responsive in S. cerevisiae. Introduction of wild type and C477A Cap1p-expressing plasmids into C. albicans produced differential resistance to oxidants. Glutathione reductase activity was found to be inducible by oxidants in the presence of Cap1p but was constitutively elevated in the presence of C477A Cap1p. Western blot assays indicate Cap1p is post-translationally regulated by oxidants. Green fluorescent protein fusions to CAP1 showed that this protein is localized to the nucleus only in the presence of oxidants while C477A Cap1p is constitutively nuclear localized. Directly analogous to S. cerevisiae Yap1p, regulated nuclear localization of C. albicans Cap1p is crucial for its normal function.
Subject(s)
Candida albicans/physiology , Gene Expression Regulation, Fungal , Oxidative Stress , Saccharomyces cerevisiae Proteins , Transcription Factors/genetics , Basic-Leucine Zipper Transcription Factors , Binding Sites , Candida albicans/genetics , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Fungal Proteins/chemistry , Fungal Proteins/metabolism , Genetic Complementation Test , Leucine Zippers , Phenotype , Recombinant Proteins/metabolism , Saccharomyces cerevisiae/physiology , Transcription Factors/chemistry , Transcription Factors/metabolismABSTRACT
We propose and analyze a novel geometry for all-optical processing of low-power signals that is based on a frequency-nondegenerate counterpropagating parametric amplifier. The stationary response in the cascading regime exhibits multivalued solutions with enhanced nonlinear phase shifts. Implementation in a quasi-phase-matched LiNbO(3) waveguide is discussed.
ABSTRACT
We present what is to our knowledge the first experimental observation by fluorescent visualization, of the evolution of the mode field profile in a periodically segmented waveguide. The experimental observations are then compared with the numerical results obtained by a finite-difference beam propagation method. Good agreement between experimental and numerical results is observed.
ABSTRACT
We report the spectral characterization of proton-exchanged lithium niobate (PE:LiNbO(3)) waveguides in terms of the variation of the refractive-index difference between the waveguiding layer and the substrate. The dispersion of the extraordinary refractive-index increase (deltan(e)) is measured from 405 to 1319 nm with several light sources. Two types of proton-exchanged waveguide, prepared under different conditions, are studied. These measurements should be of use in the optimization of PE:LiNbO(3) waveguides for nonlinear optical applications, particularly in second-harmonic generation in the blue-green wavelength region.
ABSTRACT
We present theoretical modeling of a novel configuration for quasi-phase-matched parametric amplification in which the pump and the signal fields form guided waves of a planar waveguide while the idler is radiated into the substrate. We follow a coupled-mode approach to study the parametric amplification in periodically domain-reversed proton-exchanged LiNbO(3) waveguides upon a Z-cut substrate and present numerical results relevant to the amplification process. In particular, for given pump and signal wavelengths we have studied the dependence of the gain coefficient on the periodicity of a grating formed by domain inversion. This configuration, which is referred to as the Cerenkov-idler configuration, is shown to provide a large signal gain bandwidth and is more tolerant to variations in pump frequency.
ABSTRACT
By using x-ray diffraction and optical waveguide characterization, it has been shown that proton-exchanged layers on Z-cut LiNbO(3) can have as many as seven different crystallographic phases that are stable at room temperature. This study allows us to establish some correlation between fabrication parameters and the crystalline structure, the index profiles, and the propagation losses of waveguides prepared by this process.
ABSTRACT
A rigorous numerical model, verified by experimental results, gives an explanation of the particular electromagnetic behaviors observed in x-cut proton-exchanged lithium niobate waveguides. This approach, which allows an exact calculation of the weights of the coupled ordinary and extraordinarywaves that make up the hybrid modes, provides deeper insight into the study of the strains induced by the proton-exchange process in the waveguide itself, showing that the optical axis of the exchanged layer is not parallel to the waveguide plane.
Subject(s)
Opioid-Related Disorders/mortality , Acute Disease , Adult , Age Factors , Female , Humans , Italy/epidemiology , Male , Opioid-Related Disorders/epidemiology , Seasons , Sex FactorsABSTRACT
We report efficient operation of a channel waveguide laser and a channel waveguide amplifier in Nd:MgO:LiNbO(3). For the laser a cw output power of 2.9 mW was obtained for 23.6 mW of absorbed pump power. The absorbed pump power at threshold was 1.5 mW, and a slope efficiency of 13% was achieved. For the amplifier a small-signal gain of 7.5 dB was achieved for 22 mW of coupled pump power.
ABSTRACT
We report the presence of a curious and highly reproducible effect in multimode lithium niobate waveguides fabricated by proton exchange (PE) in molten benzoic acid at temperatures ranging from 160 degrees C to approximately 250 degrees C. The spectral lines in the mode spectra of these guides (measured using a prism coupler) are anomalously side-shifted out of the expected geometrical plane. Transforming these measurements back into the plane of the waveguide, we find that the direction of scattering (relative to the crystal axis) is extremely precise (<1% deviation about a mean), and that the effect can be explained by postulating the existence of precisely oriented, stress-induced gratinglike structures (with irregular periods in the 10-70-microm range) in the guides.
ABSTRACT
We demonstrate the possibility of controlling, practically independently, the form and indices of proton-exchanged lithium niobate guides by means of guide annealing and proton exchange in lithium-rich solutions. Experimental results are presented that indicate how one can realize specific guide designs.
ABSTRACT
An extension of the fundamental wavelength phase-matching range for second-harmonic generation based on titanium-indiffused proton-exchanged lithium niobate guides has been demonstrated. Both the theoretical basis and experimental verification are presented.
