In the past few decades, several methods concerning optical thin films have been established to facilitate the development of integrated optics. This paper provides a brief depiction of different techniques for implementing optical waveguide thin films that involve chemical, physical, and refractive index modification methods. Recent advances in these fabrication methods are also been presented. Most of the methods developed for the realization of the thin-films are quite efficient, but they are expensive and require sophisticated equipment. The major interest of the scientists is to develop simple and cost-effective methods for mass production of optical thin films resulting in the effective commercialization of the waveguide technology. Our research group is focused on developing a silica-titania optical waveguide platform via the sol-gel dip-coating method and implementing active and passive optical elements via the wet etching method. We are also exploring the possibility of using nanoimprint lithography (NIL) for patterning these films so that the fabrication process is efficient and economical. The recent developments of this platform are discussed. We believe that silica-titania waveguide technology developed via the sol-gel dip-coating method is highly attractive and economical, such that it can be commercialized for applications such as sensing and optical interconnects.

This paper presents a linear dependence of temperature sensitivity in Rayleigh scattering-based optical frequency domain reflectometry (OFDR) on the concentration of germanium in the fiber core. Eight different commercially available single-mode fibers have been investigated and compared with the standard SMF-28 Corning fiber. We have experimentally analyzed the influence of germanium concentration in the fiber core, the protective coating, the degree of reduction of the fiber cladding's diameter, and the amount of humidity on Rayleigh backscatter in response to temperatures ranging from 10-90°C. Maximum sensitivity was 1.343 GHz/°C for 20.78 mol % of the germanium-doped bare fiber and it does not depend on changes in humidity. The experimental results were compared and qualitatively agreed with the numerical simulations.

We report the design of a microstructured silica-based fiber for widely tunable soliton self-frequency shift, suitable for pumping with two most common fiber laser wavelengths: 1.04 and 1.55 μm. Depending on the pump source, the output spectrum can be continuously tuned up to 1.67 (pump at 1.04 μm) or 1.95 μm (pump at 1.55 μm) in the same 1.5 m-long fiber sample, with pump-to-soliton conversion efficiency higher than 20%. The fiber is highly birefringent, which results in an excellent polarization extinction ratio of the soliton, reaching 26 dB. The shifted solitons have a high degree of coherence confirmed by pulse-to-pulse interference measurement. The available soliton tuning range covers the wavelengths inaccessible for fiber lasers, e.g., 1.3 μm and 1.7, highly important for multi-photon microscopy and imaging. Our work shows that it is possible to design and fabricate one universal optical fiber that supports soliton shift when pumped at two different wavelengths separated by over 500 nm.

We present a comprehensive study of an in-line Mach-Zehnder intermodal interferometer fabricated in a boron-doped two-mode highly birefringent microstructured fiber. We observed different interference signals at the output of the interferometer, related to the intermodal interference of the fundamental and the first order modes of the orthogonal polarizations and a beating of the polarimetric signal related to the difference in the group modal birefringence between the fundamental and the first order modes, respectively. The proposed interferometer was tested for measurements of hydrostatic pressure and temperature for different alignments of the input polarizer with no analyzer at the output. The sensitivities to hydrostatic pressure of the intermodal interference signals for x- and y-polarizations had an opposite sign and were equal to 0.229 nm/MPa and −0.179 nm/MPa, respectively, while the temperature sensitivities for both polarizations were similar and equal 0.020 nm/°C and 0.019 nm/°C. In the case of pressure, for the simultaneous excitation of both polarization modes, we observed a displacement of intermodal fringes with a sensitivity depending on the azimuth of the input polarization state, as well as on the displacement of their envelope with a sensitivity of 2.14 nm/MPa, accompanied by a change in the fringes visibility. Such properties of the proposed interferometer allow for convenient adjustments to the pressure sensitivity of the intermodal fringes and possible applications for the simultaneous interrogation of temperature and pressure.

We present a highly birefringent silica fiber with normal dispersion up to 2334 nm, designed to control a net-cavity dispersion of pulsed fiber lasers at different wavelengths. The fiber is characterized by a large normal dispersion, slowly growing from -87 ps/nm/km at 1200 nm to -42 ps/nm/km at 2000nm, and high phase birefringence exceeding 1.9 × 10⁻⁴ in this spectral range which ensures a polarization extinction ratio as high as 28 dB for a 1 m long fiber section. The industrially fabricated fiber was examined in two all-polarization-maintaining mode-locked fiber oscillators operating at central wavelengths of 1560 nm and 1980nm. We confirmed the ability to manage the dispersion of the oscillators, which worked in both anomalous and normal dispersion, maintaining stable mode-locking. Employing the developed fiber with normal dispersion has resulted in a broadening of spectral full width at half maximum from 7.8 to 44.3 nm and from 5.5 to 25.8 nm for the erbium and thulium lasers, respectively. The ability to support operation in the range of tens of MHz allows for the application of the developed laser sources in systems reducing the repetition rate via e.g. pulse picking.