We propose to study and harness a new form of supercontinuum generation to produce novel sources of broadband radiation with high stability and/or low power generation requirements. Such sources would have a significant impact on applications, including imaging, communications, and spectroscopy.
Intellectual Merit: Recent experiments have identified a new phenomenon known as optical rogue waves, highly-rare, brief pulses of intense, broadband light mathematically and physically analogous to infamous ocean waves,propagating through optical fiber [Solli et al., Nature 450, 1054 (2007)]. Real-time capture of these events has shown they follow extreme-value statistics. Subsequent work has shown that optical rogue waves can be actively controlled to produce enhanced broadband light sources through stimulated supercontinuum generation [Solli et al., Phys. Rev. Lett. 101, 233902 (2008)].
Broader Impact: There is a practical and functional technology gap in available supercontinuum sources, particularly at visible and near-IR wavelengths. Existing sources either produce unstable supercontinuum or are difficult to deploy outside of regulated laboratory environments. This research aims to utilize stimulated supercontinuum generation, a new physical concept inspired by nature, to produce high-quality, compact, and potentially low-cost white light sources at visible/near-IR wavelengths. This research also seeks to apply stimulated supercontinuum generation in silicon waveguides in order to overcome physical effects that have significantly limited chip-scale spectral broadening.
This research effort involves cutting-edge optical and electronic experimental work, simulations, and theoretical analysis. It will provide students and postdoctoral scholars with versatile skills that are highly desirable in both the industrial and academic workplaces.
A beam of white light is actually a combination of many other colors, and these colors can be split apart with a prism or by water droplets, seen as a rainbow. Normally, a single color of light remains a single color. However, when extremely bright light (more than a million times brighter than the sun), travels far enough through certain materials, a single color may turn into a continuous stream of colors called white light continuum, and may even encompass colors beyond those that you and I can see. Although it may seem impossible to create such brilliant light, one way is to shine pulsed lasers into optical fibers (extremely thin and long pieces of glass that carry virtually all Internet and voice data around the globe). White light continuum has a myriad of uses. These many colored, (often pulsed) light sources can be used to stabilize atomic clocks to within one second in a million years; such timing precision is invaluable for the Global Positioning System. In addition, the swathe of colors can be used to differentiate chemicals, proteins and cells for use in chemical and biological research as well as medicine. In telecommunications, each color can also carry a separate channel of information to send around the world using optical fibers (and perhaps someday, on your personal computers, tablets and smartphones, too). Yet another application of white light continuum is as a light source for optical coherence tomography. Also known as "optical ultrasound", optical coherence tomography is a technique for measuring features underneath a material’s surface to make volumetric photos, e.g., to find features in tissue for medicine. It turns out that a phenomenon discovered in our laboratory called optical rogue waves—optical waves that are extraordinarily large compared to most other occurrences—can help us generate broadband, stable white light continuum. These are the optical analogues of oceanic rogue waves, colossal waves capable of destroying a vessel or swallowing it beneath the sea, and then disappearing without a trace. Studies reveal that optical rogue waves are generated by just the right kind of random starting conditions. Since determining the conditions that create such a rare occurrence, one can now stimulate or "tame" these optical rogue waves with a second much weaker seed light. This process stabilized generation of white light continuum, guaranteeing broad, repeatable pulses of white light. The work done here determined that one can control and stabilize the light, and how to do so. Because of the way white light continuum is made, more broadening results in more instability. Experiments and simulations show that this weak seed can stabilize the white light continuum more by than 1,000 times under a variety of conditions, including a range of input luminosities. Another result is that the seed must be the right color and be aligned in time with the original pulse. In some cases, one will only want bright light at a certain newly created color beyond the original; a method to control where to put a significant amount of power in a desired color was also found. As the techniques for generation of white light continuum mature, high-volume production dictates that such a multi-colored source be very inexpensive, fault-tolerant, and preferably small and integrated into existing fabrication processes. Silicon, the material of choice for integrated electronics, has proven itself as a viable platform for integrated optics, and is just such a material for white light continuum. Through this grant, we also discovered that taming rogue wave phenomena aids the brightness and stability of white light continuum generation on silicon, tolerant to a wide range of conditions. In addition, the breadth of colors made by stimulating rogue waves in silicon cannot be matched without stimulation, even if one increases the input brightness significantly.
