This Conference Presentation, Composite material glass photonics: from 2D materials to catalysts inside active optical fibres, was recorded at Photonics Europe Strasbourg France.
The possibility of fabricating all-fiber nonlinear devices based on periodically poled silica fibers allows for overcoming most of the issues of free space nonlinear optics, such as thermal instabilities and high costs of nonlinear crystals. In this talk the most recent results related to the topic are presented, including some interesting applications of periodically poled fibers, such as the generation of high harmonics and of Frequency Combs when exploited in cavity configuration.
We have recently developed a novel electro-optic modulator via external electrical gating of 2D MoS2 bilayers deposited within the inner regions of a silica hollow core anti-resonant fiber. The MoS2 film acts as the electro-optically active material, responding with increased absorption of waveguided modes when in the presence of an externally applied electric field. The bilayer is formed via a liquid phase deposition method, in which the single source precursor ammonium tetrathiomolybdate is thermally decomposed into MoS2. The device has to date demonstrated modulation depths of >3.5dB, at an operating DC voltage of 1500 V with an optical insertion loss of 7.5dB. We have thus developed a novel, active, composite material anti-resonant fiber (CM-ARF) technology platform, which despite high voltage requirements, show excellent potential for all-fiber electro-optical design and operation.
Thermal poling, a technique to create permanently effective second-order susceptibility in silica optical fibers, has recently been improved by the discovery of an “induction poling” technique1 and the adoption of liquid electrodes2, allowing for poling fibers of any length and geometry. Nevertheless, the nonlinearity created via thermal poling is always limited by the 𝜒(3)of the optical fiber material and by the maximum electric field that can be frozen inside the glass. For these reasons research is ongoing to determine routes for further improving the nonlinear effects due to the thermal poling process. In this work, we propose to enhance the effects of the thermal poling by exploiting the intrinsic nonlinear properties of some 2D materials3, which are deposited inside the cladding holes of a twin-hole silica fiber. The materials we focused on are 2D Transition Metal Chalcogenide (2D TMDC) MoS2 and WS2 and the technique adopted to realize the deposition inside the cladding channels of a twin-hole step index silica fiber consists of a thermal decomposition process4 of the precursor ammonium tetrathiomolybdate (NH4)2MoS4 in 6% H2/Ar flow. The technique has allowed us to uniformly coat the two cladding channels for a length of ≈25 cm with a film nominally consisting in a bi-layer of the 2D materials. A Raman based analysis has been used to test the morphology of the coating. The fiber deposited with 2D materials was later thermally poled and periodically erased via exposure to UV light to reach the QPM condition at a wavelength of ≈1550 nm. The effective 𝜒(2) of the fiber was measured via SHG for both the deposited and the pristine fiber, showing an enhancement of the nonlinearity in favor of the deposited one. The phenomenon can be explained by the exploitation of a higher 𝜒(3) seen by the pump wave due to the presence of the 2D layer deposited inside the cladding holes and opens the possibility of exploiting the higher intrinsic material 𝜒(2), in case of a periodic patterning/synthesis of the TMDC.
Hollow Core Anti-resonant fibers allow for guidance of mid-infrared light at low attenuation and can be used for a variety of applications, such as high power laser transmission and gas sensing. Recent work has seen the integration of silicon into such fibers with linear losses potentially as low as 0.1dB/m. Due to the change in refractive index difference of silicon via for example the free carrier plasma dispersion effect, the prospect of an all optical modulator using such a fiber has been proposed. Here, further work has been undertaken on the integration of functional materials inside hollow core fibers via the deposition of the TMD semiconductor material MoS2, in its few-layered form. Through the use of a liquid precursor, a high quality MoS2 film can be deposited over 30cm length of fiber, as confirmed via Raman spectroscopy. The transmission spectra of these novel composite material hollow core fibers has also been analysed, showing additional loss of around 5dB/m, despite being only around 2nm in thickness. This implies that the refractive index of the integrated material is potentially able to modify the guidance properties of the fiber sample. We will present a comparison of the composite material hollow core fibers we have fabricated to date and discuss the prospects for using these novel waveguides in the active manipulation of light, including optical switching, sensing and frequency generation.
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