Fig. 1. Photonic band gap fiber laser. The fiber laser emits light in the transverse direction (propagation and polarization vectors shown as solid arrows and dashed lines, respectively) having a dipole-like wave front from an extended length of the fiber.

Fig. 2. Structure of the fiber laser cavity. (a), Cross-sectional SEM micrographs of the PBG multilayer structure at various magnifications. The PEI in the cladding and the layers appears black, and the As₂S₃ layers white. The PEI and As₂S₃ layers are 89 nm and 59 nm thick (except for the first and last As₂S₃ layers which are 29.5 nm thick; the first layer is not visible). The top left inset shows a cross-sectional fluorescence micrograph of the full cross-section of a PBG fiber with an R590 organic dye in the core and enveloped by a thick PEI protective cladding. (b), Projected band structure of a one dimensional photonic crystal consisting of alternating layers of As₂S₃ and PEI. Transverse-electric (TE) and transverse-magnetic (TM) propagating modes are in dark and light blue, respectively; evanescent modes are in white. Light incident normally to the structure (k=0) and axially propagating modes through the hollow core are shown as regions A and B, respectively. (c), Measured reflection band gap centered around 620nm (see ‘Optical characterization’ in methods) in black; fluorescence spectrum of LDS698 (500 ppm concentration) in red; and calculated dye-in-cavity emission obtained by multiplying the last two, dashed line.

Fig. 3. Lasing characteristics of an LDS698-doped PBG fiber. a, Emission spectra of the fiber laser for a dye concentration of 500 ppm and pump energy below threshold (A), 1.2E_th (B) and 1.8E_th (C), where E_th is the lasing threshold energy. Inset shows the spectral full-width at half-maximum as a function of input energy for 500 ppm (red line) and 50 ppm (dashed blue). b, Dependence of the laser energy on the pump energy showing threshold values of E_th = 86 nJ and E_th = 100 nJ for the 500 ppm and 50 ppm, respectively. c, High resolution spectral measurement reveals mode spacing of 2 nm and quality factor of 640.

Fig. 4 Geometric dependence of the emission for an LDS698-doped PBG fiber laser. (a), Angular intensity pattern of the bulk dye and fiber laser emission at a fixed location along the y-axis measured by rotating the input polarization. This measurement is equivalent to fixing the pump polarization while measuring the emission intensity around the fiber. (b), Polarization of light emitted from bulk dye (dashed blue) and dye in a fiber cavity (red line) having a ratio of intensities in the x- and y-directions of 0.22 and 0.6, respectively, measured by fixing the pump polarization in the x-direction and recording the intensity as a function of polarizer rotation about the direction of maximum emission (y-axis). (c), Emission spectra from large core (200- μm) PBG fiber laser measured along the fiber axis at 10-μJ pump energy measured by scanning a probe fiber along the fiber side. The upper panel shows a photograph of the fiber showing laser light emitted from a spatially extended region along the fiber (~ 5 mm).

Fig. 5. (a). A photograph of an R590-doped PBG fiber showing the pump (532 nm, green) guided in the hollow-core PBG fiber. Lasing at 576 nm (orange) occurs in the R590-doped region. (b). Lasing “MIT” made out of 12 PBG fibers doped with DCM (orange) and LDS698 (red) that are simultaneously pumped in both directions. This display design illustrates the ability to finely tune dye location, size, and concentration. (c). Laser emission spectra from fibers doped with nine different dyes. The lasers producing emission spectra 1-3 are constructed using the same hollow-core PBG fibers having a fundamental reflection band gap at 500 nm, and were pumped at 355 nm. The fibers used to produce emission spectrum 4 has a fundamental reflection band gap at 600 nm, while those used for spectra 5-9 have a fundamental reflection band gap at 690nm, and all were pumped at 532 nm. Photographs of the organic dye-doped PBG fiber lasers showing the individual laser colors (blue, green and red) emitting from the fiber surface.