Assaad Baz

Single-Mode, Large Mode Area, Solid-Core Photonic BandGap Fiber With Hetero-Structured Cladding

We theoretically and experimentally analyze the benefit of hetero-structured cladding in Solid-Core Photonic BandGap fibers so as to increase the loss ratio between high order modes and fundamental mode. This property is applied to the realization of 19-cells core fibers practically single-mode around 1050 nm. When designed to operate in the 4th BandGap, a new design is proposed which permits to obtain mode field diameter of 44 μm whereas, for operation in the 3rd BandGap, a mode field diameter of 33 μm is obtained with 20 cm bending radius. The impact of the shape of hetero-structure on single-mode behavior is discussed.

Pixelated high-index ring Bragg fibers.

A new type of Anti Resonant Reflecting Optical Waveguide (ARROW) fiber with a low refractive index contrast is reported. This waveguide is similar to a Bragg fiber for which the high index rings are replaced by discontinuous rings made of circular High Index Inclusions (HII). As compared to conventional Bragg fibers, such a new structure enables true Photonic BandGap (PBG) guidance and limits the number of cladding modes located within the high index regions, thus enhancing the guiding properties. A Mode Field Diameter (MFD) of 26 μm is reported at a wavelength of 1400 nm. Single Mode (SM) behavior is also observed beyond 1400 nm for a 1 m-long fiber.

Design and realization of flexible very large mode area pixelated Bragg fibers

A new Pixelated Bragg Fiber design showing improved optical performances in terms of single-mode behavior and effective area is presented. The cladding is made of 3 rings of cylindrical high refractive index rods (pixels) in which some pixels are removed to act as a modal sieve for an improved rejection of Higher Order Modes (HOMs). Two half-wave-stack conditions are used to increase the confinement losses of the 3 first HOMs: LP11 and LP02-LP21 guided core modes. The realized fiber exhibits a core diameter of 48.5 μm with an effective single-mode behavior observed from 1000 nm to beyond 1700 nm even for a 1-m-long straight fiber. Losses prove to be low with a minimum value of 25  dB/km between 1200 and 1500 nm. Bending radius of 22.5 cm is reported for this structure without any significant extra-losses above a wavelength of 1350 nm.

UV-induced Bragg grating inscription into single-polarization all-solid hybrid microstructured optical fiber.

We demonstrate a single-polarization all-solid hybrid microstructured optical fiber with a UV-induced Bragg grating. A strong (∼20 dB) UV-induced Bragg grating was inscribed within the 30 nm-wide single-polarization window of the fiber, producing polarized Bragg reflection. The sharp band-edge cutoff allows a large polarization-extinction ratio of the Bragg reflection. The hybrid structure of the fiber enabled minimal UV exposure to the high-index regions and the location of the single-polarization window was maintained after the grating was inscribed.

Very large mode area Solid-Core Photonic BandGap fiber laser with hetero-structured cladding and Yb-doped Sol-Gel core

Single-Mode Large Mode Area (SM-LMA) fibers are highly demanded for high power laser applications, due to the quality of the beam they deliver together with reduced impairments caused by non-linear effects. Even though LMA fibers demonstrated large progress during the last decade, the need for flexible, active or passive LMA fibers still persists. Besides this, fiber-integrated functionalities, like spectral filtering or chromatic dispersion control can be needed. In this context, Solid-Core Photonic BandGap (SC-PBG) fibers appear as good candidates for the realization of LMA structures. Recently, based on the concept introduced by Murao et al. in 2009 [1], we experimentally demonstrated that High Order Modes (HOM) can be removed by hetero-structuring the cladding in SC-PBG fibers. Thus, by introducing 6 outer cores around the central one, it has been possible to fabricate passive LMA fiber with a mode field diameter (MFD) of 44 μm when working in the 4th PBG and a MFD of 33 μm when working in the 3rd PBG [2]. In the present work, this concept is extended to double-clad active fiber.

Recent advances in the design of photonic bandgap and hybrid fibers: from LMA to HNL fibers

Solid-Core Photonic BandGap Fibers (SC-PBGF) belongs to the family of microstructured optical fibers whereby the cladding is made of high refractive index inclusions as compared to that of the fiber core. In such fibers, light is confined to the core by an anti-resonant mechanism and several high transmission windows separated by high loss regions compose the transmission spectrum. Guiding mechanism is then identical to the one observed in Hollow-Core PBGF (HC-PBGF) except that a solid core can be exploited. Such PBGFs have proven to be good candidates for single-mode high power delivery and for controlling the spectral extension of supercontinuum generation. Mixing different types of resonators in the cladding or mixing PBG with modifed-Total Internal Reection (m-TIR) mechanism also lead to original and more exible fiber designs. Recent developments in the design and realization of Large Mode Area (LMA) and Highly NonLinear (HNL) fibers are presented, including single-mode ring-structured Bragg _bers, LMA fibers exhibiting a fundamental mode with a flat-top profile, and hybrid fibers for supercontinuum generation or frequency conversion.

Pixelated Bragg fibers

We report on a new Bragg Fiber design for which the high index rings are replaced by discontinuous rings made of circular high index rods. Advantages of this new kind of fibers are presented