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.
We present the study of domain growth in congruent LiNbO
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crystals with planar soft proton exchanged waveguides (CLN SPE). The spatial distribution of H ions was measured by confocal Raman ...microscopy. The growth of elongated irregular shape domains followed by slow domain widening was obtained. Domain approaching led to a change in the growth directions. Domain widening represented formation of submicron domains with depth of tens microns in front of the domain walls. Low threshold field is attributed to the surface composition gradient. The suppression of hexagonal domain growth is related to existence of the surface dielectric layer.
The periodical domain structure with period 2 μm was created in 1-mm-thick MgO doped lithium niobate single crystals by electron-beam irradiation. The second harmonic generation (SHG) around 370 nm ...was obtained during pumping the crystals by 100 mW continuous wave tunable Ti:Sapphire laser. The normalized efficiency was 0.05%/W. The dependence of the SHG power on the pump beam position has indicated that the periodical domain structure depth is about 300 μm. The obtained results have demonstrated that the electron-beam poling can be used for creation of the short pitch periodical domain structures for light frequency conversion.
Microfluidic separation of magnetic particles is based on their capture by magnetized microcollectors while the suspending fluid flows past the microcollectors inside a microchannel. Separation of ...nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bioanalysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregation that amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increases nanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficient capture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickel micropillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as 6-10 kA/m, and experiments were carried out at flow rates ranging between 0.3 and 30 μL/min. Nanoparticle capture is shown to be mostly governed by the Mason number Ma, while the dipolar coupling parameter α does not exhibit a clear effect in the studied range, 1.4 < α < 4.5. The capture efficiency Λ shows a strongly decreasing Mason number behavior, Λ∝Ma^{-1.78} within the range 32 ≤ Ma ≤ 3250. We have proposed a simple theoretical model which considers destructible nanoparticle chains and gives the scaling behavior, Λ∝Ma^{-1.7}, close to the experimental findings.
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.
•We propose a focused ion-beam irradiation for periodical poling in lithium niobate waveguides.•The ion-beam irradiation is realized after waveguide creation by soft proton exchange method.•This ...method allowed to create the 1-mm-long 2-μm-period domain structure in a channel waveguide.•The obtained second harmonic generation efficiency for pulsed 756–378 nm wavelength conversion was up to 6·107% W−1 cm−2 for average power.
The lithium-niobate-based waveguides have emerged as one of the key platforms for enabling integrated optical technologies. The most common method for creating waveguides in lithium niobate is soft proton exchange (SPE) method. The range of the waveguides applications can be expanded further by creation of near-surface periodical structure of stripe ferroelectric domains within a waveguide (periodical poling) to realize various types of nonlinear optical interactions for creation of frequency conversion devices. However, the joint use of these two procedures (SPE and periodical poling) remains a challenging task. In this paper, we propose a focused ion beam (i-beam) periodical poling technique realized after SPE process for creation of an integrated optical frequency conversion device. The choice of i-beam poling parameters is based on the study of the features of domain structure evolution in lithium niobate after SPE process. We have found that SPE process leads to formation of shallow structure of isolated nanodomains. The revealed isotropic domain growth was caused by the sideways domain wall motion by step generation as a result of merging with these nanodomains. This type of domain kinetics is preferable for periodical poling as it decreases the probability of fast merging of stripe domains due to formation of fast domain walls. Eventually, we have created the 1-mm-long 2-μm-period domain structure in a channel waveguide. The obtained second harmonic generation efficiency for pulse pumping at 756 nm was up to 6·107% W−1 cm−2 for average power and 300 % W−1 cm−2 for peak power indicating the high quality of periodical poling.
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