Optimal suppression of higher-order modes (HOMs) in hollow-core antiresonant fibers comprising a single ring of thin-walled capillaries was previously studied, and can be achieved when the condition on the capillary-tocore diameter ratio is satisfied (d/D ≈ 0.68). Here we report on the conditions for maximizing the leakage losses of HOMs in hollow-core nested antiresonant node-less fibers, while preserving low confinement loss for the fundamental mode. Using an analytical model based on coupled capillary waveguides, as well as full-vector finite element modeling, we show that optimal d/D value leading to high leakage losses of HOMs, is strongly correlated to the size of nested capillaries. We also show that extremely high value of degree of HOM suppression (∼1200) at the resonant coupling is almost unchanged on a wide range of nested capillary diameter dN ested values. These results thus suggest the possibility of designing antiresonant fibers with nested elements, which show optimal guiding performances in terms of the HOM loss compared to that of the fundamental mode, for clearly defined paired values of the ratios dN ested/d and d/D. These can also tend towards a single-mode behavior only when the dimensionless parameter dN ested/d is less than 0.30, with identical wall thicknesses for all of the capillaries.
Multicore fiber enables a parallel optic data link with a single optical fiber, thus providing an attractive way to increase the total throughput and the integration density of the interconnections. We study and present photonics integration technologies and optical coupling approaches for multicore transmitter and receiver subassemblies. Such optical engines are implemented and characterized using multimode 6-core fibers and multicore-optimized active devices: 850-nm VCSEL and PD arrays with circular layout and multi-channel driver and receiver ICs. They are developed for bit-rates of 25 Gbps/channel and beyond, i.e. <150 Gbps per fiber, and also optimized for ruggedized transceivers with extended operation temperature range, for harsh environment applications, including space.
We demonstrate a high brightness, polarization maintaining 42+1 to 1 cascaded combiner system which consists of a tree architecture with one 6+1 to 1 pump-signal combiner pumped with six multimode pump combiners. The cascaded combiner system has a pump efficiency of 95%, high beam quality with greater than 20dB PER. In this work the higher brightness of the combiner system is driven by choice of optimized pump fibers and high efficiency of multimode pump combiners that operate at an average pump efficiency of 99%.
We report on improved spatial uniformity of sensor grating arrays in offset and multicore fibers. We show improvement over conventional side writing in such fibers, in which cores offset from the center of the fiber exhibit grating strength variations due to lensing at the fiber surface. Such strength variations can degrade the performance of sensing systems that rely on continuous scattering from offset cores along a fiber. Our improved system uses multicore fibers whose coating is UV transparent and applies index matching materials to mitigate lensing aberrations. We show that it is capable of continuously inscribing gratings over any length of fiber.
In this work we report on a fiber grating fabrication platform suitable for parallel fabrication of Bragg grating arrays over arbitrary lengths of multicore optical fiber. Our system exploits UV transparent coatings and has precision fiber translation that allows for quasi-continuous grating fabrication. Our system is capable of both uniform and chirped fiber grating array spectra that can meet the demands of medical sensors including high speed, accuracy, robustness and small form factor.
A robust, alignment-free monolithic 2.1 kW single-mode continuous wave fiber laser, operating at 1083 nm is demonstrated. The laser is pumped with commercial fiber pigtailed multimode diodes through all-fiber pump-signal power combiners in a MOPA architecture. The oscillator was formed with high reflector and output coupler fiber Bragg gratings written in 11/200 μm (mode field/cladding diameter) single-mode fiber. The gain medium was a 19m OFS commercial 11/200 μm double clad Yb-doped fiber (DCY). Pump light was coupled to the oscillator using two 11/200 μm pump-signal power combiners (PSC). A total of 20 commercially available 58W pump diodes at 915 nm were used to generate 800W of signal, as measured before the amplifier. The Raman power after the oscillator was more than 60 dB below the signal power. The amplifier was built using 13 m of 14/200 µm DCY and two (18+1)x1 PSC combiners with more than 95% pump and signal light transmission. A total of 2 kW of power was used to bi-directionally pump the amplifier. The output was measured after 3 m 14/200 μm fiber, and 10 m 100/360 μm delivery cable. Total signal output power was 2.1 kW, corresponding to an amplifier slope efficiency of 77%. The Raman power is more than 30 dB below the signal power. At maximum power, no modal instabilities, thermal effects, nor power rollover were observed. With higher power pumps, it is predicted that a power level of 2.6 kW can be achieved with the Raman level below 20 dB.
In this paper we report on the development of a complete integrated optical fiber assembly suitable for shape sensing.
Our shape sensor module consists of a length (>1m) of twisted multicore optical fiber with fiber Bragg gratings inscribed
along its length. Our fiber has a compact 180 micron coated diameter, a twist of 50 turns per meter and grating
reflectivities greater than 0.01% per cm of array, suitable for high efficiency scatter measurements over many meters of
fiber. Single core to multicore fanouts and low reflectivity fiber termination are used to terminate the end of the array.
We present for the first time a cascaded Raman fiber laser where the Yb-doped fiber laser and Raman fiber are combined
into a single fiber. We achieve 42.6 % slope efficiency at 1236 nm with respect to launched pump power.
We show that kinetics of Bragg grating formation are sensitive to the external stress applied on the fiber. This leads us to revisit the model of variable reaction pathway (VAREPA model) which accounts for the experimental index change power law. Conclusions are that a power law is still obtained for low sensitivity, just the pre-exponential factor is changed. This is consistent with the experiment. However, an isotropic strain dependent VAREPA model gives rise to an equivalent sensitivity on the mean index and on the modulation which is not consistent with the experiment. It is thus not excluded that another mechanism leading to stress redistribution was active.
The writing of gratings within heated hydrogen loaded, non H2 loaded germanosilicate or Ce3+ doped aluminosilicate fibers was carried out through UV exposure. The fibers were heated by means of a CO2 laser beam. The thermally induced change in the grating growth kinetics depends on the type of fiber used to write the grating. The thermal stability of gratings written in either heated or unheated germanosilicate fibers was investigated through isochronal annealing experiments. Difference between the thermal behaviors of gratings written in the H2 loaded and the non H2 loaded fibers was demonstrated. There exists strong evidence that structural changes are involved in the photosensitivity of the germanosilicate fibers.