Multiplexing temperature-compensated open-cavity Fabry-Perot sensors at a fiber tip.

We investigate multiplexing of four highly sensitive Fabry-Perot (FP) microresonators at the tip of a single-mode optical fiber for refractive index (RI) measurements with simultaneous temperature compensation. The individual sensing elements for RI or temperature consist of either open-cavity FP resonators or solid fiber core regions fabricated by diamond-blade dicing of single-mode optical fibers, respectively. The reflectivity of the open resonators is further enhanced by matched dielectric coatings. At the same time, the solid core resonators formed by the fiber pieces between the open cavities are used as thermometers. This allows immediate compensation for temperature cross-sensitivity during RI measurements. The general performance of the sensor is demonstrated by measuring the RI of sucrose solutions, where we use phase tracking of the characteristic Fourier transform components of the backreflected optical spectrum for evaluation. The temperature sensitivity is on average 20±/∘C with an accuracy of 0.01°C, fully sufficient for biomedical applications. Meanwhile, the four RI sensing (open) cavities show high sensitivity of approximately 1160 nm/RIU. Due to the compact size of the sensor, small spatial inhomogeneities of RI can be accurately detected. If the cavities are additionally filled with molecularly imprinted polymers or coated with thin functional layers, they could also be used for the detection of trace substances in biomedical laboratory-on-a-fiber applications.

Watt-level 775†nm SHG with 70% conversion efficiency and 97% pump depletion in annealed/reverse proton exchanged diced PPLN ridge waveguides.

We report on fabrication of ridge waveguides formed in congruent periodically poled lithium niobate substrates using annealed and reverse proton exchange followed by diamond blade dicing. 1 W of second-harmonic generation at 775 nm has been obtained in a single-pass in 50 mm long ridge waveguides with internal conversion efficiency of 70%. At this power level, 97% pump depletion has been reached. Although elevated temperature operation and ridge geometry help to mitigate photorefractive damage (PRD) effects, nevertheless, at even higher second harmonic outputs significant power drop with blue shift and distortion of the SHG tuning curve have been observed indicating an onset of PRD.

Fiber-optic sensor measuring spatial distributions of refractive index and temperature.

In this work, we present a fiber sensor designed to measure simultaneously spatial inhomogeneities of the refractive index and temperature in liquid media, for example, induced by biochemical reactions. The sensor's constituent elements are Fabry-Perot microresonators fabricated in standard single-mode optical fibers by diamond blade dicing. To allow simultaneous measurements of different refractive indices, the sensor comprises two open cavities approximately 2 mm apart. With a small Si inlay inserted into one of the resonators used for temperature measurements, the sensor allows for immediate compensation of crosstalk between temperature- and composition-induced fluids' refractive index changes. The measurements were evaluated by phase tracking of the characteristic Fourier transform components of the sensor's backreflected spectra. The temperature sensitivity of the Si inlay is 0.063 rad/°C (79 pm/°C), and an accuracy of 0.01°C is obtained. Meanwhile, the two refractive index sensing (open) cavities show a sensitivity of 1168 and 1153 nm/RIU for temperature-compensated measurements. Finally, the sensor performance to measure spatial distributions is demonstrated by measuring the diffusion behavior of sucrose in water, which allows precise monitoring of hydration effects and breaking of bonds at elevated temperatures.

Efficient Nd:Ti:LiNbO3 ridge waveguide lasers emitting around 1085 nm.

In this work, we report on efficient neodymium-doped titanium in-diffused ridge waveguide lasers in x-cut congruent LiNbO3 under excitation at 814 nm. For the sample fabrication we used our novel technique of three-side evaporation and in-diffusion for Nd and Ti incorporation into pre-defined ridges. Due to improved photorefractive damage resistance by indium tin oxide (ITO) coating we achieved stable laser operation at 1084.7 nm with a maximum output power of 108 mW and a slope efficiency of 34% exceeding the best literature values for Nd:Ti:LiNbO3 ridge waveguide lasers.

Dual parameter fiber-integrated sensor for refractive index and temperature measurement based on Fabry-Perot micro-resonators.

We report on a miniature all-fiber dual parameter sensor capable of simultaneous measurement of the refractive index (RI) and temperature of fluids and gases. The high-sensitivity sensing element is comprised of two Fabry-Perot (FP) micro-resonators fabricated in a single-mode fiber and has a total length of <100 µm. The RI sensing cavity is formed by diamond blade dicing, whereas a thinner silicon inlay glued into it serves as a temperature sensor. The sensor's performance was tested on sucrose solutions over a range of temperatures. For the evaluation of the backreflected FP spectra, phase tracking of the characteristic Fourier transform components was used. Good accuracy (0.01°C) and linearity of temperature measurement with Si inlay with sensitivity 0.097 rad/°C (85.2 pm/°C) were found, whereas the open cavity allowed for reliable temperature-compensated measurements of 10-3 RI steps with 290 rad/RIU (1130 nm/RIU) sensitivity.

Fiber-integrated refractive index sensor based on a diced Fabry-Perot micro-resonator.

We report on a fiber-integrated refractive index sensor based on a Fabry-Perot micro-resonator fabricated using simple diamond blade dicing of a single-mode step-index fiber. The performance of the device has been tested for the refractive index measurements of sucrose solutions as well as in air. The device shows a sensitivity of 1160 nm/RIU (refractive index unit) at a wavelength of 1.55 µm and a temperature cross-sensitivity of less than 10-7 RIU/°C. Based on evaluation of the broadband reflection spectra, refractive index steps of 10-5 of the solutions were accurately measured. The conducted coating of the resonator sidewalls with layers of a high-index material with real-time reflection spectrum monitoring could help to significantly improve the sensor performance.

Low loss ridge waveguides in lithium niobate thin films by optical grade diamond blade dicing.

We report on the fabrication and characterization of ridge waveguides in lithium niobate thin films by diamond blade dicing. The lithium niobate thin films with a thickness of 1 µm were fabricated by bonding a He-implanted lithium niobate wafer to a SiO(2)-coated lithium niobate wafer and crystal ion slicing. Propagation losses of 1.2 dB/cm for TE and 2.8 dB/cm for TM polarization were measured at 1550 nm for a 9.28 mm long and 2.1 µm wide waveguide using the Fabry-Perot method.

Spatiotemporal airy light bullets in the linear and nonlinear regimes.

We demonstrate the realization of intense Airy-Airy-Airy (Airy(3)) light bullets by combining a spatial Airy beam with an Airy pulse in time. The Airy(3) light bullets belong to a family of linear spatiotemporal wave packets that do not require any specific tuning of the material optical properties for their formation and withstand both diffraction and dispersion during their propagation. We show that the Airy(3) light bullets are robust up to the high intensity regime, since they are capable of healing the nonlinearly induced distortions of their spatiotemporal profile.

Enhanced third-order nonlinear effects in optical AlGaAs nanowires.

We report the first observation of enhanced third-order nonlinear effects in AlGaAs nanowires. AlGaAs nanowaveguides with widths varying from 100 to 600nm were fabricated and characterized. Nonlinear phase shifts of approximately pi were experimentally observed at 1.55mum with peak powers of 30-40W in 600mum long, 550nm wide guides.

Discrete surface solitons.

It is theoretically shown that discrete nonlinear surface waves are possible in waveguide lattices. These self-trapped states are located at the edge of the array and can exist only above a certain power threshold. The excitation characteristics and stability properties of these surface waves are systematically investigated.

Vector discrete nonlinear surface waves.

It is theoretically shown that multi-component discrete vector surface waves can exist in arrays of coupled waveguides. These mutually trapped surface states primarily reside in the first waveguide of a semi-infinite array. The existence and stability of such surface waves are systematically investigated.