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Air Force

High-power laser in the 1100-1500nm region with a controllable linewidth

This laser will open up opportunities for guide star (1178nm), remote water sensing (1240nm), and expansion of telecommunications bandwidth into the O, E, and S bands (1300–1500nm)

Photonics

In general, there is a lack of efficient, high-power lasers in the 1100-1500nm region with a controllable linewidth. Lasers in this spectral region are difficult to obtain, since many materials don’t give off coherent light in this region and those that lase in parts of this region, such as bismuth co-doped silica or Yb-doped silica, do so inefficiently. One way of obtaining photons in this spectral region is through the nonlinear process of Stimulated Raman Scattering (SRS), which acts to shift the initial pump wavelength out to longer wavelengths. This process, which occurs at high optical intensities, involves the coupling of light propagating through the nonlinear medium to the vibrational modes of the medium. The result is re-radiated light, which is shifted to a different wavelength. Light upshifted in wavelength is commonly referred to as a Stokes line, whereas light downshifted in wavelength is referred to as an anti-Stokes line. To date, a controllable linewidth, high-power Raman laser with output powers approaching 100W has not been reported.

Air Force researchers have developed a Raman amplifier controllable by a seed source to address the above shortcoming in the field. In this invention, a rare-Earth-doped Raman amplifier is spliced directly onto a Raman resonator system. The amplifier can be seeded with both the initial signal (zeroth order Stokes) and the desired output signal (Nth order Stokes) through a wavelength division multiplexer (WDM). Because of power limitations associated with the WDM, the initial signal is amplified to the desired level downstream from the WDM, consisting of one or multiple stages, each stage being pumped with diodes. The two signals can then be injected into the resonator(s), which generates multiple orders of Stokes in one or more amplifiers. The desired output signal passes through the system and the N-1th order Stokes signal amplifies it. To increase the efficiency of the system, a highly reflective Bragg grating centered at the pump wavelength can be included downstream from the Raman fiber to enable reflection of any unused pump light back through the Raman fiber.

This application is a division of US patent 9,502,855 filed on Mar. 7, 2016, which is a division of US patent 9,293,889, filed on Jun. 6, 2015 and issued on Mar. 22, 2016, which is a division of US patent 9,054,499, filed on Jun. 23, 2014 and issued on Jun. 9, 2015, which is a division of US patent 8,761,210, filed on Jun. 13, 2013 and issued on Jun. 24, 2014, which is a division of US patent 8,472,486, filed on Aug. 17, 2011 and issued on Jun. 25, 2013, and claims the benefit of the foregoing filing date.

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