In the first stage, an 8-cm long LMA PCF (LMA35, NKT Photonics) with a mode field diameter of 26 μm was employed.
The laser output is coupled into a large-mode-area photonic crystal fibre (PCF) of 26 μm mode field diameter and 8 cm length for spectral broadening via self-phase modulation.
By the means of mode field diameter (MFD) variation as a sensor indirect parameter, the common problems of intensity modulated optical sensors are overcome.
The 10.5 μm beam diameter of each core of the multicore fiber is collimated to a large Gaussian mode field diameter of 78 μm.
Universal fiber is a multimode fiber that has an LP01 mode field diameter approximately matched to that of standard single-mode fiber.
Mode field diameter (MFD) of the fiber is selected as the indirect parameter for strain sensing task and investigating the MFD behaviour of the fiber, the strain sensitivity is augmented through independent adjustment of the structural parameters.
The fiber has flat modal field over the central part of the core, which provides large mode field diameter (8.3 μm at λ0=1550 nm) leading to the relatively large effective area (Aeff=56.1 μm2) required to reduce nonlinear effects.
The dependence of structural parameters on the effective index of the fundamental guided mode, effective index of the fundamental cladding mode, mode field diameter, confinement loss, effective mode area, and chromatic dispersion in PCF have been studied, respectively.
The mode field diameter is 9.6 μm in the horizontal direction and 6.0 μm in the vertical direction, respectively, indicating an excellent overlap with a standard single-mode fiber.
In both cases, the field diameter of the system is 20 mm, macro- and micrometric focusing (graduated 0.002 mm) wth coaxial controls.
As in other rodents, neither soma size nor dendritic field diameter showed significant variation with retinal eccentricity (Fig. 2G,H).
