**6. Acknowledgments**

Most of work presented in this chapter was carried out within COST Action 299 "FIDES". Research at NIT was financially supported by Polish Ministry of Science and Higher Education as special research project COST/39/2007.

#### **7. References**

198 Photonic Crystals – Introduction, Applications and Theory

Conditions Sample loss (dB) Splice loss (dB)

Loss with finished splice 1 3.19 (reference) Fibers cleaved and aligned 8.98 5.79 Lens-tipped fibres aligned 5.37 2.18 Fibres spliced 4.61 1.42 After heating No. 1 4.38 1.19 After heating No. 2 4.28 1.09 After heating No. 3 4.17 0.98

Table 4. Loss of IPHT 252b5 sample measured during making of splice No. 2 (1558 nm).

In contrast to work presented in the preceding section, fusion splicing of small-core, thin PCF to SMF was complicated and time-consuming. However, attempts to fuse the same fibres without pre-forming resulted in very high splice loss (15.5 dB for 2 PCF-SMF splices)

Arc fusion splicing of most microstructured silica-based fibres to SMFs with conventional equipment and tools is possible, with loss acceptable for purposes like PCF characterization. Unfortunately, splicing procedure must be tailored to each PCF and is labour intensive. In many cases, a trade-off between achieving low loss and high strength of the splice

PCF to PCF splicing is more demanding in term of equipment and work procedures, because of need for rotational alignment of fibres, not available in most fusion splicing machines, and increased length of collapsed holes. The latter problem can be reduced by adopting fusion time shorter than 0.3 s, but at the expense of compromised

Most of work presented in this chapter was carried out within COST Action 299 "FIDES". Research at NIT was financially supported by Polish Ministry of Science and Higher

Fig. 30. Splice after additional heating No. 2 (left) and No. 3 (right).

and frequent entrapment of small gas bubble in the centre of splice.

**5. Conclusions** 

exists.

splice strength.

**6. Acknowledgments** 

Education as special research project COST/39/2007.

Bang, O. (2010). PCFs, mPOFs and THz fibers. *Proc. 2nd Workshop on Specialty Optical Fibers and their Applications (WSOF 2010)*, ISBN: 978-0-8194-8360-7, Oaxaca City, Mexico, October 13-15, 2010. Available from

http://www.cio.mx/WSOF2010/archivos/Ole%20Bang.pdf


http://www.us.schott.com/english/download/technical\_glass\_guide\_us.pdf

**0**

**10**

*Japan*

**Optical Solitons from a Photonic Crystal Fiber**

A photonic crystal fiber (PCF) is a fiber that contains the regular (usually hexagonal) arrays of air holes in the propagation direction of an optical fiber. At the center position, the core is created by not making an air hole and the light wave propagates at the core position since the effective refractive index of the core is higher than that of the photonic crystal clad surrounding the core. Photonic crystal fibers of this type have been used to generate ultrabroadband optical pulses by propagating femtosecond optical pulses in these fibers (Ranka et al., 2000). The core diameter of a PCF for the generation of ultrabroadband optical pulses using a Ti:sapphire laser (center wavelength ∼800 nm) is about 1-2 *μ*m if it is assumed that the silica core is surrounded by regular air holes. Due to the waveguide dispersion, the group velocity dispersion (GVD) becomes negative at 800 nm. Because of the small core diameter and the negative GVD, nonlinear effects are enhanced and optical solitons are generated in a PCF. Theoretical calculations for elucidating the mechanism of the ultrabroadband pulse generation in a PCF have been performed (Husakou & Herrmann, 2001) and the generation of fundamental soliton pulses by the fission of an input higher-order soliton pulse due to the third and higher order dispersion as well as the higher-order nonlinear effects including the Raman effects are found to be important for the spectral broadening. Supercontinuum generation in a PCF is reviewed in (Dudley et al., 2006). The center wavelength of the generated fundamental soliton pulse becomes longer as it propagates in a PCF due to soliton self-frequency shift and its center wavelength can be changed by the peak power or the chirp of an input pulse. Recently, it was used as a variable-wavelength light source in various applications including coherent anti-Stokes Raman scattering (CARS) spectroscopy and optical coherence tomography (OCT). The present article describes the properties of the fundamental solitons from a PCF and its applications studied in our

It is well known that the soliton pulse, which does not change its shape as it propagates in a fiber, can be created when the pulse propagates in the anomalous dispersion region (Agrawal, 2007; Hasegawa, 1992). If we consider the electric field (considered to be scalar) that depends on only time *t* and propagation position *z* such that *E*(*z*,*t*) = *Re*[*A*(*z*, *t*)*ei*(*β*0*z*−*ω*0*<sup>t</sup>*)], where *Re* shows the real part, *ω*<sup>0</sup> is the central angular frequency, and *β*<sup>0</sup> is the propagation constant at *ω*<sup>0</sup> (*β*<sup>0</sup> = *β*(*ω*0)) of a pulse, the slowly varying envelope approximation (SVEA) equation for

**1. Introduction**

laboratory.

**2. Fundamental soliton pulse**

**and Their Applications**

Naoki Karasawa and Kazuhiro Tada *Chitose Institute of Science and Technology*

