Dispersion management in soft glass all-solid photonic crystal fibres R. BUCZYNSKI *1,2,3 , J. PNIEWSKI 2 , D. PYSZ 1 , R. STEPIEN 1 , R. KASZTELANIC 2 , I. KUJAWA 1 , A. FILIPKOWSKI 1,3 , A.J. WADDIE 3 , and M.R. TAGHIZADEH 3 1 Institute of Electronic Materials Technology (ITME), 133 Wólczyńska Str., 01–919 Warsaw, Poland 2 Faculty of Physics, University of Warsaw, 7 Pasteura Str., 02–093 Warsaw, Poland 3 School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK The development of all-solid photonic crystal fibres for nonlinear optics is an alternative approach to air-glass solid core photonic crystal fibres. The use of soft glasses ensures a high refractive index contrast (> 0.1) and a high nonlinear coeffi- cient of the fibres. We report on the dispersion management capabilities in all-solid photonic crystal fibres taking into ac- count four thermally matched glasses which can be jointly processed using the stack-and-draw fibre technique. We present structures with over 450 nm broadband flat normal dispersion and ultra-flat near zero anomalous dispersion below 5 ps/nm/km over 300 nm dedicated to supercontinuum generation with 1540 nm laser sources. The development of an all-solid photonic crystal fibre made of F2 and NC21 glasses is presented. The fibre is used to demonstrate supercontinuum genera- tion in the range of 730–870 nm (150 nm) with flatness below 5 dB. Keywords: fibres' dispersion, photonic crystal fibres, microstructured fibres, soft glass, supercontinuum generation. 1. Introduction The tailoring of the group velocity dispersion (GVD) of an optical fibre is critical to the successful utilization of nonli- near optical properties in applications such as superconti- nuum generation, harmonic generation and wavelength con- version via stimulated Raman scattering. One of the optical structures that can be used to tailor the GVD is holey or photonic crystal fibre (PCF), e.g., a microstructured fibre with longitudinal holes in the cross-section. Due to the high refractive index contrast between glass and air, along with freedom of choice of the holes’ geometrical parameters, one can precisely control dispersion behaviour and nonlinearity of the fibres [1]. However, this approach has serious techno- logical drawbacks resulting in unintended distortions of the lateral profile that influence the dispersion properties of the fibres [2]. By using soft glasses for fabrication of the PCFs, one can combine the unique properties of that class of glasses, such as high nonlinearity, gain and transmission in the near infrared with the wave guiding properties of PCFs, namely single mode guidance for large mode areas and tight mode confinement [3,4]. Heavy metal oxide glasses such as SF6 and SF57 offer a large Raman shift and high nonlinearity [5,6]. Highly nonlinear PCFs made of such glasses have been used successfully for broadband supercontinuum ge- neration with a low intensity input pulses [7–9]. All-solid photonic crystal fibres (APCFs) are an alterna- tive approach to the more popular air-glass solid core pho- tonic crystal fibres (PCFs). In ACPFs, the air holes are replaced with glass microrods of a refractive index different from that of the background glass. Index guiding and pho- tonic bandgap guiding mechanisms can exist in APCFs depending on the refractive index of the core. The develop- ment of the first all-solid PCF with a high index core was reported by Feng at al. [10] with the APCF having a high index core (n = 1.76) with the photonic cladding of a lower refractive index (n = 1.53). With this approach a highly non- linear PCF was realized (230 W –1 km –1 at 1.55 μm with the attenuation of 5 dB/m at 1.55 μm). Several successful exam- ples of the theoretical and practical development of all-solid photonic bandgap fibres with a low index core have also been reported in soft and pure silica glasses [11–14]. For index guided fibres different cross-section profiles are pro- posed, e. g., hexagonal lattice of microrods [1,12,13,15,16] W-type rings [17–20] and chirped Bragg-like geometry [21]. The advantages of all-solid PCFs, as compared to the air hole based PCFs, are relatively simple fabrication and a po- ssibility to glue or splice nonlinear fibres with standard opti- cal fibres. Moreover, the fibre parameters’ control during the drawing process is much simpler and the development of parameters similar to the designed ones is straightfor- ward. In addition, the APCFs have unique spectral and dis- persion properties that are suitable for applications in low- -loss fibre lasers, nonlinear optics, birefringent fibres [22] and fibres with reduced bending and confinement losses [16]. The possibility of maintaining single-mode operation through the suppression of higher modes has also been stu- Opto-Electron. Rev., 20, no. 3, 2012 R. Buczynski 207 OPTO-ELECTRONICS REVIEW 20(3), 207–215 DOI: 10.2478/s11772-012-0033-y * e-mail: rbuczyns@igf.fuw.edu.pl