Why does it matter? Supercontinuum (SC) lasers are broadband lasers that cover a wide wavelength spectral range. SC lasers combine the broadband attributes of lamps with the spatial coherence and high brightmess of lasers. SC lasers are advantageous for various applications in defense, metrology and healthcare.  For example, the mid-infrared spectrum of SC lasers overlaps with the black body radiation and thus can be used to spectrally emulate a hot body. In addition, the broad bandwidth and high power is also attractive for spectrosopy applications, such as stand-off explosives detection, etc. In metrology, the broad bandwidth of the SC lasers allow precise depth resolution in a 3D interferometer setup and can be used to form 3D  maps of surfaces[1]. In addition, the spectral dependence of the reflected light can be used to measure properties like roughness of the surface [2].  As an example in healthcare, the carbon-hydrogen bonds that form the building blocks of fats/lipids ovelaps with the SC spectrum and thus can be used to perform diagnostics/therapeutics [3].

What  is our solution? Up to now, SC lasers have been primarily used in a laboratory settings and often use a modelocked laser to pump the nonlinear optical fibers. In our approach, we replace the modelocked lasers with laser diodes and gain fibers used in the mature telecommunications industry. While modelocked lasers output small duration pulses with high peak power, we utilize a phenomenon called modulation instability (MI) to break up the laser diode pump pulses to obtain smaller pulses with high peak powers.The main advantage of our setup is the scalability of the average power by increasing the pulse repetition rate and the pump powers. We have built SC sources in the visible to the mid-infrared (~0.45-4.5 microns) using this architecture [4,5,6]. We have also scaled up the  time average power up to ~10 W in  a mid-infrared SC [6].  We are also exploring the various gain fibers to improve the SC generation efficiency for the various wavelengths of interest. Thus, by exploiting the physics in the fiber, we have been able to eliminate the need for a modelocked laser and build all-fiber integrated high power SC sources using only commercially available off-the-shelf parts.

[1] M. Kumar, M.N. Islam, J.F.L. Terry, C.A. Aleksoff, and D. Davidson, High resolution line scan interferometer for solder ball inspection using a visible supercontinuum source. Opt. Express 18 (2010).
[2] V.V. Alexander, H. Deng, M.N. Islam, J.F.L. Terry, R.B. Pittman, and T. Valen, Surface roughness measurement of flat and curved machined metal parts using a near infrared super-continuum laser. Opt. Eng 50 (2011).
[3] K. Ke, C. Xia, M.N. Islam, M.J. Welsh, and M.J. Freeman, Mid-infrared absorption spectroscopy and differential damage in vitro between lipids and proteins by an all-fiber-integrated supercontinuum laser. Opt. Express 17 (2009) 12627-12640.
[4] M. Kumar, C. Xia, X. Ma, V.V. Alexander, M.N. Islam, J.F.L. Terry, C.A. Aleksoff, A. Klooster, and D. Davidson, Power adjustable visible supercontinuum generation using amplified nanosecond gain-switched laser diode. Opt. Express 16 (2008).
[5] O.P. Kulkarni, V.V. Alexander, M. Kumar, M.J. Freeman, M.N. Islam, J.F.L. Terry, M. Neelakandan, and A. Chan, Supercontinuum generation from ~1.9 to 4:5 μm in ZBLAN fiber with high average power generation beyond 3:8 μm using a thulium-doped fiber amplifier. J. Opt. Soc. Am. B 28 (2011) 2486-2498.
[6] C. Xia, Z. Xu, M.N. Islam, J.F.L. Terry, M.J. Freeman, A. Zakel, and J. Mauricio, 10.5 W time-averaged power mid-IR supercontinuum generation extending beyond 4 um with direct pulse pattern modulation. IEEE J. Sel. Top. Quantum. Electron 15 (2009) 422-434