Biophotonics_Concepts_to_Applications

3.7 Hard-Clad Silica Fibers.

A hard-clad silica (HCS) opticalfiber is a MMF structure consisting of a silica glass
core that is covered by a thin hard plastic cladding, which increasesfiber strength
[ 25 ]. Thesefibers also feature bend insensitivity, long-term reliability, ease of
handling, and resistance to harsh chemicals and humid environments [ 5 ]. Core
diameters of commercially available HCSfibers range from 200 to 1500μm.
Table3.2 lists some performance parameters of three selected HCS fibers.
A common HCSfiber for industrial and medical applications has a core diameter of
200 μm and a cladding diameter of 230μm, which results in a very strong optical
fiber with low attenuation (less than 10 dB/km or 0.01 dB/m at 820 nm), a
numerical aperture of 0.39, negligible bending-induced loss for bend diameters less
than 40 mm, and an extremely high core-to-clad ratio to enable efficient light
coupling into and out of thefiber. Thefibers are available in both high OH and low

Refractive index

Radius

Core

Inner cladding

Outer cladding

Buffer jacket

Fig. 3.11 Cross-sectional
representation of a typical
DCF and its index profile

Table 3.2 General specifications of selected HCSfibers (J. Biomed. Opt. 19(8), 080902 (Aug 28,
2014). doi:10.1117/1.JBO.19.8.080902)

HCSfiber 1 HCSfiber 2 HCSfiber 3

Core diameter (μm) 200 ± 5 600 ± 10 1500 ± 30

Cladding diameter (μm) 225 ± 5 630 ± 10 1550 ± 30

Wavelength range (high OH

content) (nm)

300 – 1200 300 – 1200 300 – 1200

Wavelength range (low OH

content) (nm)

400 – 2200 400 – 2200 400 – 2200

Maximum power capability

(CW) (kW)

0.2 1.8 11.3

Maximum power capability

(pulsed) (MW)

1.0 9.0 56.6

Maximum long term bend

radius (mm)

40 60 150

Max attenuation at 850 nm 10 dB/km

(0.010 dB/m)

12 dB/km

(0.012 dB/m)

18 dB/km

(0.018 dB/m)

76 3 Optical Fibers for Biophotonics Applications