The Optical Communications Reference

3.3.2 Overview of optical properties

3.3.2.1 Introduction

This section broadly reviews the optical characteristics

that have been identified thus far in both classes of

microstructured optical fibers. As described in Section

3.3.1, HFs guide light due to the effective refractive

index difference between the solid core and the ar-

rangement of air holes that forms the cladding region.

The effect of the holes on the fiber properties depends on

the hole distribution and size(s) relative to the wave-

length of light guided in the fiber. Hence, the effective

refractive index of the structured cladding region (and

thus the fiber’s NA) can be a strong function of wave-

length in these fibers. For this reason, it is possible to

design fibers with spectrally unique properties not pos-

sible in conventional core-clad optical fibers. In addition,

the optical properties of microstructured fibers are de-

termined by the spatial configuration of air holes used to

form the cladding, and many different arrangements can

be envisaged within this flexible fiber type.

PBGFs guide light for use with a fundamentally dif-

ferent mechanism than conventional fibers, and so it is

not surprising that the optic al properties of modes

guided with these fibers can be radically different from

(c) (d)

(e) (f)

(a) (b)

Fig. 3.3.1 A representative selection of microstructured optical fibers. The images shown are all fibers fabricated at the ORC

(Southampton, UK). (a) Small-core nonlinear pure silica holey fiber. (b) Large-mode area pure silica holey fiber. (c) Air-cor e photonic

bandgap fiber. (d) Double-clad Yb3

þ

-doped large-mode area fiber. (e) Extruded highly nonlinear bismuth holey fiber. (f) One-dimensional

layered soft glass microstructured fiber.

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Microstructured optical fibers CHAPTER 3.3