At present, optical fiber materials with ultra-broadband gain in the NIR, 1100–1500 nm, are of great interest for the development of compact, versatile, and high-brightness light sources in the low-loss transmission window of silica fiber, where no efficient active fiber exists.1 Applications for such a source are diverse, including communications in the 1300–1500 nm region, optical coherence tomography for medical imaging, generation of efficient yellow light by frequency-doubling for dermatology applications, satellite-based water sensing in vegetation, and laser guide star use (creating an energized layer of sodium atoms in the mesosphere used as a reference for telescope tuning). Existing sources in this wavelength range have either limited bandwidth or limited efficiency. In particular, rare earth (RE) doped glasses are generally limited to 100 nm bandwidth in the NIR, and the available RE transitions do not span 1150–1500 nm with high-efficiency. In general, there is a lack of efficient, high-power lasers in the 1100-1500 nm region with a controllable linewidth.
To address the above issues, Air Force researchers have developed a Raman amplifier having a novel design enabling high-Raman conversion efficiencies and output powers in addition to linewidths which are controllable by the seed source. In this invention, an RE-doped Raman amplifier is spliced directly onto a Raman resonator system. The RE-doped amplifier is both seeded with the initial signal and the desired output signal through a wavelength division multiplexer (WDM). Because of power limitations associated with the WDM, it is necessary to amplify the initial signal via a downstream amplifier. This amplifier may consist of one or multiple stages with each stage being pumped with diodes. The desired output signal and the amplified initial signal are then both injected into the Raman resonator(s) where multiple orders of Stokes are generated in one or more Raman amplifiers. The desired signal passes through the system and is amplified by the Stokes signal.
Parent filling is US patent 8,472,486 – Seeded Raman amplifier for applications in the 1100-1500 nm spectral region, filed on Aug. 17, 2011, and issued on Jun. 25, 2013.
9,293,889 – Seeded Raman amplifier in a nested configuration for generating a 1240 nm laser, filed on Jun. 6, 2015.
US patent 9,647,418 – Laser generation using dual seeded nested and/or in-series Raman resonators, for telecommunications applications issued on May 9, 2017.
US patent 9,502,855 – Seeded Raman amplifier in a linear configuration for generating a 1240 nm laser issued on November 22, 2016.
US patent 9,054,499 – Seeded Raman amplifier in linear configuration for laser applications in the 1100-1500 nm spectral range, filed on Jun. 23, 2014 and issued on Jun. 9, 2015.
US patent 8,761,210 – Generating narrow linewidth 1178 NM laser output using a seeded Raman amplifier, filed on Jun. 13, 2013 and issued on Jun. 24, 2014.
1 IEEE Journal of Selected Topics in Quantum Electronics, V0l. 20, N0. 5, September/October 2014.
- High power
- More efficient (high Raman conversion efficiencies)
- Controllable laser line width
- Linewidth can be broad enough to prevent SRS as limiting factor
- Raman resonator system can be nested or un-nested
- US patents: 8,472,486; 9,293,889; 9,647,418; 9,502,855; 9,054,499; and 8,761,210 available for license
- Potential for collaboration with Air Force researchers