This PDF file contains the front matter associated with SPIE Proceedings Volume 12573, including the Title Page, Copyright information, Table of Contents and Conference Committee lists.

Tilted fibre Bragg gratings (TFBGs), especially ones with a tilt angle of 45o, are very promising and effective fibre elements that can act as polarizing elements Therefore, a TFBG in conjunction with an isolator, a coupler and polarisation control can creat an all-fibre mode-locked laser. A TFBG is based on the Brewster angle principle, which couples out of the fibre the s-polarisation of the light while maintaining the transmission of p-polarisation through the fibre core with minimal losses. In other words, the 45o -TFBGs are behaving as in-fibre polarisers. Compared with other types of polarisers TFBGs have a higher polarisation extinction, low insertion loss, broadband responsivity, wavelength tunability and, can be adapted to any type of fibres. Moreover, from a fibre laser perspective, TFBGs being an all-in fibre components, do not require coupling in and out of the fibre or collimation within the laser resonators, resulting in more robust and stable fibre laser systems, with minimal maintenance. In this paper we describe our recent progress on developing high polarising and low loss tilted fibre Bragg grating. The grating is inscribed in a ZBLAN passive fibre for potential use as a polarising element for future mid-infrared mode locked laser. The inscription was performed using the plane-by-plane method utilising femtosecond pulses at 517 nm. The polarising elements were characterised in transmission in terms of polarisation dependent loss, transmission loss and bandwidth. The results show significantly improved characteristics compared to previous works and is a significant step towards a monolithic mode-locked mid-infrared lasers at the 3.5 µm band.

CYTOP-XYLEX fibre Bragg grating (FBG) sensors’ response to relative humidity (RH) changes is investigated in this work. The intensive research on CYTOP polymer optical fibre sensors relies on their lower optical attenuation compared with the standard poly(methyl) methacrylate (PMMA) based polymer optical fibre sensors. However, CYTOP is a hydrophobic polymer and cannot be used as a standalone material in humidity-sensing applications. A hydrophilic material is required to be used as fibre over-cladding for RH detection; the water swelling occurring in the over-cladding material can strain the FBG structure located in the CYTOP core. In this work, a novel CYTOP fibre with a XYLEX over-cladding material is used to investigate the humidity responsivity of FBG sensors. A femtosecond laser system and the plane-by-plane inscription method were utilised to fabricate the FBG sensors through the fibre over-cladding. The FBG sensors were placed in a climatic chamber with controlled temperature and RH, and their response to RH changes was monitored. The RH sensitivity was evaluated for different temperatures. The results show that the RH sensitivity increases with temperature, whereas the reported RH sensitivity of PMMA-based sensors decreases with temperature. We also report that by applying a pre-strain on the fibre, the RH sensitivity can be eliminated for cross-sensitivity compensation purposes.

An array of four fiber Bragg gratings (FBGs) is inscribed at the same spot with a single uniform phase-mask (PM). The inscription setup consists of an 800 nm femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The wavelength tunability of the center Bragg wavelength is achieved by a defocusing lens, and by PM translation. An FBG is inscribed, followed by three cascaded FBGs, which are inscribed exactly at the same spot, only after a movement of the PM. The second order Bragg grating array at ~1.55 µm transmission spectra of these four FBGs is measured, showing a spectral shift of ~1.8 nm between each one, and a total spectral shift of ~5.4 nm. The transmission dip of each FBG is approximately −6 dB. The third order Bragg grating array at ~1.04 µm transmission spectra shows a transmission dip of approximately −3 dB, a wavelength separation of ~1.2 nm between each one, and a total wavelength shift of ~3.6 nm.

Submarine optical fibers are nowadays the core backbone of international communications, carrying over 99% of the intercontinental data traffic. These critical infrastructures for communications have also recently demonstrated to have strong potential for geophysical monitoring in the bottom of the oceans. In this paper, we show that submarine optical fiber cables can be used to gain knowledge on the planet and its dynamics, including more accurate estimations of currents and other water mixing phenomena that have strong impact in climate change estimations. Among other things, we show that internal waves, a large-scale phenomenon generated by the interaction of barotropic tides with bathymetric changes in the sea-bottom, can be very accurately observed by deploying chirped-pulse Distributed Acoustic Sensing (DAS) technology over these cables.

We propose a new light management mechanism in graded index (GRIN) multimode fibers (MMFs) that allow to control the spectral mode distribution of the propagated beam. The effect is achieved through longitudinal non-Hermitian modulations of the complex refractive index, i.e. the refraction index (for instance, a modulation of the core radius) and a periodic gain/loss profile. The applied potential holding a longitudinal spatial period close to the intermodal beat frequency of the parabolic index profile, to strongly influence the transverse mode dynamics. The non-Hermitian potential introduces a unidirectional and controllable coupling between the transverse modes. In turn, the spatial shift between the real and imaginary components of the modulation controls the unidirectional coupling either to higher or lower order modes. The effect is simultaneously demonstrated by solving a (2+1) D Linear Schrodinger Equation (two transverse plus one longitudinal spatial coordinates) as well as it is predicted by a simplified model for an oscillating Gaussian beam ansatz, leading to a system of ordinary differential equations. We demonstrate, both analytically and numerically, a mode cleaning effect, i.e. the improvement of the spatial structure of light in its propagation along the modulated MMFs; in an ideal case resulting in single-mode spatially coherent output. On the contrary, when inducing the coupling towards higher order modes, pulsing is enhanced, which may eventually contribute to super-continuum generation. The proposed scheme could lead to actual applications as it could be experimentally realized within the current nanofabrication technologies.

The possibility to control Rayleigh scattering in glass single-mode optical fibers opens important perspectives in the field of distributed sensing. Optical backscatter reflectometry (OBR), operating in the time domain, makes use of scattering events occurring in optical fibers as sensing methods. The possibility of forming nanoparticles during the fiber drawing process, which results in an increase of the backscattered power even up to 50 dB over standard single-mode fibers, increments the backscattered power and enables multi-fiber sensing architectures, suitable in medical devices. In this contribution, we turn our attention to the possibility of using the augmented elastic scattering in novel systems for biosensing, characterized by a simple fabrication. We present two methods based on reflector-less sensing, and on distributed interferometry, to achieve biosensing and we discuss the application in the detection of cancer biomarkers. Reflector-less biosensors make use of a fiber taper or etching without the need to fabricate any reflector; so far, sensitivity ratings up to ~1 nm/RIU (refractive index units) have been reported; however, detection limits of sub-picomolar levels are reported, due to the precise tracking of the OBR. Distributed interferometers turn a high-scattering fiber into a series of mirrors, which can be simply terminated by a fiber cleave. Even with a simple fabrication, we show the possibility to achieve sensitivity in the order of 60-100 dB/RIU and detection limit as low as few attomolars.

Chalcogenide glasses are known for their large transparency in the mid-infrared and their high non linear optical properties. Different methods have developed to prepare the microstructured chalcogenide preforms and fibers. In this context, various chalcogenide PCFs operating in the MIR range have been elaborated in order to associate the high non-linear properties of these glasses and the original PCF properties. For example, small core fibers have been drawn to enhance the non linearities for telecom applications and generation of supercontinuum sources. In the 2-12 µm window, single mode fibers, polarization maintaining fibers and exposed core fibers have been realized for Gaussian beams propagation and sensors applications.

Lasers emitting in the visible find applications in biology and medicine. Considering the success of near-infrared fiber lasers, the possibility to optically pump rare-earth-doped fibers in the blue to directly obtain visible emission is attractive. The recent progress in the field of GaN-based blue laser diodes offers new scopes. Dy3+-doped materials have received much interest because of their intense yellow emission originating from the 4F9/2→6H13/2 transition. An involvement of a glass matrix benefiting from enhanced thermo-mechanical properties would ease diode pumping. We report on the synthesis of a series of novel phosphate glasses in the system P2O5-Al2O3–BaO-K2O doped with Dy2O3. The Dy3+ concentrations were 0.05, 0.21, 0.83 and 2.5 [1020 ions/cm3]. The glasses were synthesized by the standard melt-quenching technique and thoroughly characterized in their physical, thermo-mechanical and optical properties. A Dy3+-doped optical fiber was drawn by preform drawing from the developed glasses, with the preform being obtained by rod-in tube technique, combining a cast core and an extruded cladding. Preliminary emission results in the visible from the fabricated fiber will be reported.

The interest in fiber lasers operating in the yellow range of the visible spectrum has greatly increased alongside the improvement of blue pump laser diodes, as well as the recent fabrication of high-quality Dysprosium-doped fluoride fibers, to be used as the active medium. In this work, a matrix-based simulation model which exploits the rate equations was applied to examine the influence of excited state absorption on the performances of a tunable yellow source. Simulation results provide useful guidelines to improve the tunability range of the yellow fiber laser, by properly selecting the reflectivity of the output mirror and the active fiber length.

In this work we explore using a carbon monoxide (CO) laser towards specialty optical fiber fabrication specifically targeting the use of unconventional core materials, such as semiconductors as well as other crystalline materials, surrounded by a silica glass cladding. With laser heating there is a near instantaneous temperature response with a change in laser power. Highly localized heating minimizes overall thermal exposure reducing the duration that the core and cladding material interact at elevated temperatures. Localized heating also results in large temperature gradient across the liquid-solid interface, which is beneficial for crystallization kinetics. Compared to using CO₂-lasers, the radiation from the CO-laser, which operates at 5.5 μm, has a much larger penetration depth in silica resulting in energy being deposited further into the material. This enables a more homogeneous transverse temperature distribution as well as a higher average temperature while minimizing surface vaporization. This talk covers the results from recent work using a CO laser for the fabrication of hybrid material optical fibers.

Fiber-based laser systems enable high output power in combination with diffraction limited beam quality. Their output power is generally limited by the onset of nonlinear effects. The chirally coupled core (CCC) fiber provides a large mode field diameter while also suppressing higher-order-modes. This is needed to further increase a laser’s output power and maintaining single-mode operation. However, the integration of specialty fibers in an all-fiber laser setup is in most cases not possible because suitable fiber components are not available. We report on the development of a cladding light stripper and a signal-pump combiner with integrated 34/250-µm CCC fibers which allow for the development of spliceless all-fiber amplifier systems. The cladding light stripper is manufactured by structuring the CCC-fiber’s cladding using a CO2-laser to interrupt pump light guiding within the cladding. The cladding light stripper enables a stripping efficiency of 19 dB and was tested up to a stripped optical power of 100W, which is sufficient to enable kW-class amplifier systems. The signal-pump combiner relies on a side-pumped design with four pump input fibers. Its characterization reveals a pump-to-signal fiber coupling efficiency of 90% and a signal-to-pump isolation of 30 dB. Component stability was tested at a pump input power of 500W. An S2 -measurement confirmed that the spatial mode content of the signal light propagating through the CCC-fiber-based signal-pump combiner remains unaffected. Furthermore, a signal-pump combiner was subjected to temperature cycles between -5 and 85 °C over a time period of <1000 h and showed no degradation.

Nowadays, the main limiting factor of power scaling of high-power thulium fiber lasers is high heat load causing thermal mode instability (TMI) and other thermally induced difficulties. Increased temperature of the fiber core also leads to large changes of its spectroscopic parameters. In this work, we present the experimental measurements of the temperature dependence of the fluorescence lifetime of the thulium-doped fibers. The results of the temperature-dependent fluorescence lifetime, absorption and emission cross-section spectra, and energy transfer coefficient k3011, which characterizes so-called “two-for-one” cross-relaxation process 3H4, 3H6 → 3F4, 3F4, were employed to develop a numerical model for simulation and optimization of high-power thulium-doped fiber lasers and amplifiers with temperature-dependent fiber characteristics.

We design and characterize ring core fibers supporting orbital angular momentum modes; our fibers are produced in-house at Universit´e Laval. These fibers are tested in a transmission system test bed to demonstrate the wide range of exploitation strategies that are supported. When combining specialty fiber with integrated, silicon photonic multiplexers the costs are kept low, and multiplexed signals can be easily inserted into systems and technologies with tributaries for signal mode operation. We have demonstrated polarization maintaining operation on 12 data channels (6 modes) at 1.3 km that has the simplest digital signal processing. We used coherent detection of QPSK across the C-band, for a capacity of 40 Tb/s. When employing simple, commercially available 2-by-2 multiple-input, multiple-output processing the capacity can be increased to 65 Tb/s by suppressing polarization crosstalk. The performance of these fibers is best suited for short-distance links such as those in data centers. The ability to support a wide palate of modes gives flexibility; up to 12 simultaneous channels has already been demonstrated. Modes can be lit gradually as needed, or from initial deployment. The modes are polarization maintaining and very low crosstalk so that simple digital signal processing can be used. No multiple-input, multiple-output processing is required at distances under a kilometer. Our solutions are compatible with a migration from the current single-wavelength direct-detection approach to more aggressive, higher bandwidth systems. As data center technology moves to multiple wavelengths and/or coherent detection, the modal multiplexing with orbital angular momentum can provide the flexibility that is unattainable with scalar, linearly-polarized modal multiplexing.

In this contribution, we focus on development of a thulium-doped fiber-optic amplifier working in spectral range from 1800 to 2050 nm. The amplifier is core-pumped using an erbium-doped fiber laser emitting at 1565 nm with maximum output power of ~2 W. We use in-house developed and manufactured silica-based thulium-doped fibers and commercially available optical components in the setup. A tunable thulium-doped fiber laser was used as signal source allowing us to cover the whole spectral range of interest. The basic parameters of the amplifier with respect to used configuration, fiber lengths, and spectral wavelength are presented and discussed.

In this work, a novel data driven approach towards modal analysis of multimode fibers is proposed. Key to this approach is a neural network which was trained to approximate the complex optical transfer function of a given fiber. Afterwards, it can be used to reconstruct the fiber modes. Hence, the network is able to provide approximated solutions to the underlying partial differential equations. Training data was generated by simulating the propagation of various synthetic test patterns through the fiber. During network training the inverse transfer function of the system is found. As the model topology mirrors deterministic approaches, the model is fully interpretable. The approximated eigenstates of the system and for this reason, the modes guided by the fiber, can be extracted from the trained network. These obtained fiber modes are compared to the theoretical modes which are obtained by calculation with finite difference method. This reconstruction was shown to be of high quality as a low mean squared error between the magnitudes of the deterministically calculated and the reconstructed modes was achieved. The influence of the used training data was investigated. It could be shown, that the convergence as well as the generalisation properties of the approach depend heavily on the statistical properties of the excitation amplitudes of the eigenstates in the training data

Here I will report on optical fibers that are interfaced with dielectric nanostructures and demonstrate their capabilities on the examples of achromatic light focussing and optical trapping. Both topics involve implementation of nanostructures on fibers through 3D nanoprinting. This has allowed for (i) the realization of an achromatic metasurface-based lens interfaced to a SMF-28, used for wavelength- and polarization-independent light focussing across the entire telecommunication range, and for (ii) trapping microspheres and bacteria with only one single-mode fiber containing a nanoprinted holographic metalens with a record-high numerical aperture of 0.88.

Lens-less 3D raster-scanning endomicroscopy via multicore fibers (MCFs) enables minimally invasive applications for instance auto fluorescent imaging for cancer diagnostics in the brain. However, it suffers from various issues: (i) periodic core arrangements, which result in higher diffraction orders and a limited field of view, (ii) bend-sensitive transfer functions which require constant on-line calibration, and (iii) inherent (static) differential path length differences of the individual fiber cores. To overcome these limitations, we present an MCF with 1200 aperiodically arranged cores, which is twisted to decrease dynamic bending sensitivity. Furthermore, diffractive optical elements (DOEs) were directly imprinted on the fiber facet using 2-Photon-Polymerization to compensate the inter-core-dispersion. As a first demonstration, a simple imaging system consisting only of a camera and an MCF with an integrated DOE for phase compensation and focusing is realized for direct imaging. As a result, a flexible phase preserving fiber waveguide is realized, that can easily be included in standard microscopes to extend their field of applications to deep tissue and in vivo imaging.

Due to their flexibility and robustness, polymer optical fibers represent a promising platform for the development of brain-compatible implantable devices with reduced risk of tissue inflammation. Furthermore, by combining different biocompatible materials it is possible to integrate multiple functionalities in a single hybrid optical fiber. This approach allows the fabrication of soft brain interfaces able to support multiple modalities of neural interrogation. Such interfaces capable of simultaneous light delivery and recording of neuronal activity with minimal tissue damage are currently lacking for infrared wavelengths in the strong water absorption region. This spectral region, in particular, is crucial for infrared neuromodulation, a promising technique for direct light-induced control of neural activity without genetic manipulation. Here we present novel infrared fiber-based neural interfaces developed by thermal drawing of soft, biocompatible optical polymers, which are able to simultaneously modulate and record neural activity, as validated experimentally in vivo.

Here, we demonstrate a new configuration of intracavity optical tweezers based on a ring cavity fiber laser. In this scheme, we placed the optical trapping system inside the Yb:doped fiber laser cavity operating with backward pumping. We use two counter-propagating inversely correlated beams, a pump at 976 nm from top to bottom and a signal at 1030 nm in the opposite direction. They are focused on the sample with a ultra-low numerical aperture (NA=0.088) aspheric lenses. Using this approach, counter-propagating intracavity optical tweezers (IOT), we are capable of 3D optical trapping of 1.98 µm-diameter polystyrene particles. Using such a low NA lens reduces the laser intensity on the trapped particle compared to the standard intracavity optical tweezers. The total average power on the particle is 885 µW, which corresponds to the average intensity of 21.2 µW µm⁻²

Recent advancements in optogenetics and brain interfacing technologies have significantly improved neuroscience research. However, developing user-friendly and efficient probes with high spatial and temporal resolution and specificity remains a challenge. Tapered Optical Fibers (TOFs) have emerged as an intriguing solution due to their unique properties. This work reviews the strategies developed to enable precise definitions of light delivery and collection sites along the TOF axis, incorporating additional functionalities such as electrical recording sites or exploiting alternative light-matter interactions for label-free applications. The latest progresses in TOF micro and nanostructuring are categorized based on these objectives, highlighting the benefits and limitations of each approach. This manuscript aims at providing a comprehensive overview of recent advancements in TOF micro and nanostructuring.

In this research, we inform about fabrication of special photonic crystal fibers (PCFs) for a lossy mode resonance realization, which were developed and fabricated in our facilities. The fibers were formed by a limited number of air channels in a silica matrix. In this case, PCF modes can leak from a fiber core and it is possible to obtain the resonance due to coupling between the modes of the PCF core and modes of a thin absorbing coating without deleting or polishing a silica cladding, or fiber tapering. The fibers give also a possibility of a single-mode operation of sensors based on these fibers. Examples of possible using the fibers for fiber optic sensors are discussed.

The Brillouin frequency spectrum profile is characterised by the Lorentzian or the Gaussian function, which is identical to the reflection spectrum of a fibre Bragg grating (FBG), while similarly the Brillouin frequency is linearly dependent on the amount of applied strain or the ambient temperature of the fibre. In this paper, we used the Zero-Crossing fibre Bragg grating demodulation algorithm to optimise the Brillouin frequency shift of a typical single-mode optical fibre, SMF28, in which static and dynamic strain steps are applied. We showed that the FBG demodulation algorithms could be used and improve the response from a Brillouin system even though the strain levels are below the measuring capability of the system.

We present our recent studies regarding the influence of ionized radiation when a monolithic Holmium fibre laser was exposed under a total dose of 350 Gy of γ-radiation. Since fibre lasers have many uses for space applications, it is important to study the robustness and the effects caused by ionized radiation. The optical fibre laser was characterized before and after the exposure using spectrum analysis and Raman spectrometry while the variations were quantified. Moreover, the fibre laser response and the FBG mirrors' temperature response were analyzed.

Hollow core anti-resonant fibers (HCAR) exploit the resonant structure of the cladding to decrease the propagation loss at specific transmission windows located in between resonance wavelengths. HCAR loss is usually computed by numerical methods such as finite elements or estimated by analytical formulas. Here, the semi-analytical method based on solution of the nonlinear dispersion equation is presented and discussed. The method employs the theory of propagation of electromagnetic waves in cylindrically-layered media and it is fully vectorial. Its reliability and efficiency is tested by comparison with results of numerical simulations of the HCAR structure using modal analysis in COMSOL.

The rapid increase of transfers in data center has led to increased demand for high-speed optical interfaces. The 100 Gb/s optical systems commonly deployed today will be replaced by systems with higher bit rates. The physical part of the optical network that include optical fiber, often does not change for decades or never. Older fiber optic links may contain a mixture of fibers (the optical path is not perfectly homogeneous, consisting of only one type of optical fiber) and replacing them may be problematic or practically impossible. Polarization mode dispersion (PMD) is one of their property, than can become stochastic over time. The ITU-T G.652 fibers are now commonly deployed, where the recommendation specifies a maximum PMD up to 0.2 ps.km^−1/2 . Older optical fibers did not have this parameter specified. These optical fibers were commonly manufactured before the introduction of induced polarization mode coupling. In this paper, we present an innovative method to exploit the system reserve for the purpose of reducing the impact of random phenomena such as PMD on link outage. The simulation model uses switching from the current channel to the backup channel. Depending on backup link parameters and the configuration of the switching algorithm, improvements ranging from units to tens of percent can be achieved. The switching algorithm can operate based on an evaluation of the opening of the eye diagram or based on the deteriorating bit error ratio. To simulating the effectiveness of the switching algorithm, we used data obtained from real measurements. The measurements were performed on an optical path that was partially exposed to external influences. Polarization-related parameters of optical fibers were measured.

Nanocrystalline holmium-doped titanates have been widely investigated for their luminescence properties. Low-phonon pyrochlore lattice supports the radiative energy transfers improving the efficiency of high-power lasers and amplifiers operating around 2 m. However, the chemical reactivity toward the silica prevents the incorporation of ceramic nanoparticles in common optical fibers. Deposition of active ceramic layer on the inner wall of capillary or hollow core fiber represents a promising alternative. We present a versatile sol-gel route to active capillary fibers doped by nanocrystalline (Ho0.05La0.95)2Ti2O7. Nanocrystalline films with tailored properties were prepared by sol-gel method. The sols were coated on silica glass slides to receive a set of reference samples and soaked into silica capillary fibers making the coatings on the inner capillary wall. The presented approach led to the formation of homogenous nanocrystalline (Ho0.05La0.95)2Ti2O7 films with tailored nanocrystal size up to 87 nm and refractive index of about 2.2. All prepared samples showed an intensive emission at 2.0 m under an excitation at 450 nm and the luminescence decay time of about 7.3 ms. The presented method enables the preparation of homogenous and highly transparent thin films with tailored properties. These films are suitable for preparation of bulk luminophores and planar active optical components operating at 2 μm.

Antiresonant negative curvature hollow-core optical fibers (NC-HCFs) have proven to have great potential for the delivery of high-energy pulses and for continuous wave Mid-infrared fiber gas laser (FGL) systems. However, following the drawing fiber conditions on the designed fiber geometry, the resulting position of transmission bands of the NC-HCFs needs to be matched to both pumping and lasing wavelengths for the FGL with the particular filled gas. In this work, we investigated experimentally the possibilities of adjusting the transmission bands of a short length of the fabricated NC-HCFs to both UV the Mid-infrared directions that would further enhance their usage in FGL. The investigation was based on two steps. The first step involves fabricating a few fibers from a single preform with different inner geometry dimensions concerning the applied pressure into the preform’s capillaries. This would help to calibrate the correlation of adjusted fibers’ transmission bands to the desired wavelength with respect to the applied pressure while drawing. Increasing the pressure into the capillaries from 300 to 400 mm H₂O while maintaining the pressure in the preform core at 30 mm H₂O the bands were gradually blue-shifted by ~16.5 % to have about 330 nm shift at the first transmission band. This is attributed to the decrease in core diameter, capillaries gaps, and wall-thickness while increasing the capillaries diameter. The second step involves processing a short length of drawn fibers through local heating and tapering for adjusting their transmission bands' positions using a CO₂ laser fusion splicer. Processing the whole length of a short fiber segment ~5 cm shows a complete redshift by ~12.2 % and a blueshift by ~10.2 % after heating and tapering respectively. The first transmission band of the processed fiber was shifted about 200 nm after heating and 122 nm after tapering. The parameters of processing were optimized; thus, no insertion losses were observed. Such results urge us to further develop the mechanism of processing fibers to process long lengths of fibers in the future.

In addition to the well-known problem related to the growing demands in telecom fiber optical data transmission lines with extended bandwidth in recent years the researchers developed an interest in mode-locked fiber lasers of 1600-1700 nm spectral region in a number of biomedical applications. The known approach to get the generation in this range uses the Er-doped fiber mode-locked seed source of telecom range. The output ultrashort pulse then propagates in nonlinear optical fiber with anomalous dispersion undergoing the Raman shift to the longer wavelengths. We propose a method to control the characteristics of the output Raman soliton spectrum adjusting the polarization of the pump pulse at the input of the nonlinear fiber. We have shown that this method allows to tune the wavelength of the output spectrum maximum in the whole range (1600-1700 nm) while the output power remains constant. Our simulation results agree with experimental observations.

For applications in fiber lasers and amplifiers, silica glass remains a perspective host for rare-earth ions thanks to favorable material properties. However, the luminescence of RE ions is hindered by the high phonon energy of silica lattice and low solubility of RE ions, which cause luminescence quenching. Pure silica thus needs to be co-doped with suitable additives such as Al₂O₃, which form a beneficial low-phonon environment and increase the solubility of RE ions. Luminescence lifetime is one of the most important parameters to determine the suitability of RE-doped silica fibers for laser operation. Optical fibers with higher luminescence lifetime typically exhibit higher values of slope efficiency and lower laser threshold. It was previously shown that the environment of Tm³⁺, Ho³⁺ or Yb³⁺ ions and luminescence lifetime may be significantly affected by fabrication processing at high temperatures, probably due to the chemical changes occurring in the matrix. However, the effect of fabrication processing on the spectroscopic properties of another important RE ion, Er³⁺, is different to the other ions and remains unclear. In this contribution, we present a study on the fluorescence lifetime of a highly-doped optical fiber prepared by the MCVD method combined with nanoparticle-doping. The fluorescence lifetime of Er³⁺ was studied in several stages of fabrication processing. The influence of fabrication processing on the fluorescence lifetime of Er³⁺ ions was analyzed and discussed.

Recent evolution in nanoscience and nanotechnologies has brought novel possibilities in the development of optical fibers. Dual-wavelength fiber lasers have attracted scientific attention due to their prospective applications in fields including next-generation optical fiber communication, ranging systems, and spectroscopy. Nanostructurization has shown itself as a suitable method for preparing fiber lasers operating simultaneously at dual wavelengths. We report on the design of nanostructured or “pixelated” core fabricated by assembling erbium- and ytterbium elements, as well as on the optimization of the average concentration of rare earth elements using numerical modeling. Preliminary experimental results of erbium- and ytterbium-doped nanostructured-core fiber will be presented.

We present results from studying dynamic aspects of the pair-induced quenching (PIQ) process in holmium-doped optical fibers. The PIQ process is detrimental for the efficiency of Ho-doped fiber lasers operating in the eye-safe 2.1 μm wavelength regime, and has been suggested to be the dominating cause of efficiency degradation in such lasers. Time-resolved fluorescence experiments were used to determine the rate of the PIQ-related upconversion process occurring within pairs of Ho-ions, i.e. the lifetime of doubly-excited Ho-pairs. Measurements were performed on twelve different Ho-doped fibers varying by an order of magnitude in Ho-doping concentration. The lifetime of doubly-excited Ho-pairs was measured to be 460 ns on average, varying only slightly for the different fibers.

We demonstrate elimination of temperature sensitivity for fiber Bragg gratings (FBGs) in polymer perfluorinated (CYTOP) fiber by gamma radiation treatment. Several FBG samples inscribed line-by-line in a few-mode fiber with 20-µm CYTOP core and 250-µm XYLEX overclad received gamma radiation doses in the range from 80 to 520 kGy. Initially positive value of temperature sensitivity (19.6 pm/℃) decreased with received dose with subsequent change of sign from positive to negative. Among the irradiated samples, the one that received 200-kGy dose demonstrated the closest to zero temperature sensitivity (≈ 1 pm/℃). Along with a decrease of temperature sensitivity, we observed an increase of RH sensitivity with received dose from 13.3 pm/%RH for pristine FBG up to 56.8 pm/%RH for the case of 520 kGy dose. Thus, gamma radiation treatment of CYTOP FBGs provides decrease of their temperature sensitivity and increase of RH sensitivity simultaneously. Correct selection of the irradiation dose allows to eliminate temperature sensitivity for RH sensing application.