The field of fiber optics was born in 1950s, and the Nobel Prize in Physics 2009 was awarded to Charles K. Kao for groundbreaking achievements concerning the transmission of light in fibers for optical communication. The field of nonlinear fiber optics emerged around early 1970s, but has attracted considerable interest since the discovery of fiber supercontinuum generation (i.e., ultra-broadband nonlinear frequency generation) by Ranka and co-workers in 2000. Today, fiber nonlinear frequency generation has found widespread applications in frequency metrology, spectroscopy, and microscopy. Noticeably, John L. Hall and Theodor W. Hänsch were awarded the Nobel Prize in Physics 2005 for developing optical frequency comb technology based on fiber supercontinuum generation from photonic crystal fibers (PCF). For a comprehensive understanding of this topic, we refer to a review article (J. M. Dudely et al. Rev. Mod. Phys. 78, 1135, 2006) and a textbook (G. P. Agrawal, Nonlinear Fiber Optics, 4th edition, Academic Press, 2007).
The PCF-based nonlinear frequency generation has been one of the most active research topics in optics over the past few years, and its application has profoundly influenced microscopy and biophotonic imaging (see Table below). To summarize, the multispectral excitation of supercontinuum has overcome the limitation of the discrete laser lines in conventional laser scanning confocal microscopy (LCSM) while the pulsed nature of the supercontinuum enabled the capability of fluorescence lifetime imaging microscopy, an excellent tool for studying biomolecule interaction. Also, it allows multi-photon microscopy (MPM) to be performed at the excitation wavelengths inaccessible from the source laser, and coherent anti-Stokes Raman microscopy (CARS) to be performed with a single ultrafast laser. Furthermore, the spectrally-broadened supercontinuum facilitates the high-resolution optical coherence tomography (OCT) imaging. The broader the bandwidth, the higher the resolution.
- Gail McConnell, "Confocal laser scanning fluorescence microscopy with a visible continuum source," Opt. Express 12, 2844-2850 (2004).
- C. Dunsby et. al., "An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy," J. Phys. D 37, 3296 (2004).
- J. H. Frank, A. D. Elder, J. Swartling, A. R. Venkitaraman, A. D. Jeyasekharan, and C. F. Kaminski, "A white light confocal microscope for spectrally resolved multidimensional imaging," J. Microsc. 227, 203-215 (2007).
- G. McConnell and E. Riis, "Photonic crystal fibre enables short-wavelength two-photon laser scanning fluorescence microscopy with fura-2," Phys. Med. Biol. 49, 4757-4763 (2004).
- J. Palero, V. Boer, J. Vijverberg, H. Gerritsen, and H. J. C. M. Sterenborg, "Short-wavelength two-photon excitation fluorescence microscopy of tryptophan with a photonic crystal fiber based light source," Opt. Express 13, 5363-5368 (2005).
- Henrik Nrgaard Paulsen, et. al., "Coherent anti-Stokes Raman scattering microscopy with a photonic crystal fiber based light source," Opt. Lett. 28, 1123-1125 (2003).
- Tak W. Kee and M. T. Cicerone, "Simple approach to one-laser, broadband coherent anti-Stokes Raman scattering microscopy," Opt. Lett. 29, 2701-2703 (2004).
- V. P. Mitrokhin, et. al., "Coherent anti-Stokes Raman scattering microspectroscopy of silicon components with a photonic-crystal fiber frequency shifter," Opt. Lett. 32, 3471-3473 (2007).
- I. Hartl, et. al., "Ultrahigh-resolution optical coherence tomography using continuum generation in an air–silica microstructure optical fiber," Opt. Lett. 26, 608-610 (2001).
- Hyungsik Lim, Yi Jiang, Yimin Wang, Yu-Chih Huang, Zhongping Chen, and Frank W. Wise, "Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 µm," Opt. Lett. 30, 1171-1173 (2005).
- Hui Wang, Christine P. Fleming, and Andrew M. Rollins, "Ultrahigh-resolution optical coherence tomography at 1.15 μm using photonic crystal fiber with no zero-dispersion wavelengths," Opt. Express 15, 3085-3092 (2007).
- G. Mcconnell, "Sequential confocal and multiphoton laser scanning microscopy using a single photonic crystal fibre based light source," Appl. Phys. B 81, 783-786 (2005).
- D. Träutlein, F. Adler, K. Moutzouris, A. Jeromin, A. Leitenstorfer, E. Ferrando-May, "Highly versatile confocal microscopy system based on a tunable femtosecond Er:fiber source," J. Biophoton. 1, 53-61 (2008).