N231-059 TITLE: Orbital Angular Momentum (OAM) Laser Transformer

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): General Warfighting Requirements (GWR)

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop an Orbital Angular Momentum (OAM) mode transformer that spatially tailors light beams for high-power laser applications.

DESCRIPTION: Fiber lasers are well suited to a variety of Navy needs because they can create compact high-power sources through active gain regions kilometers long, have a large surface area for cooling, and exhibit high temperature and vibrational stability for extended lifetimes on moving platforms. These lasers have been primarily limited to infrared wavelengths between 1-2 microns, but recent advancements that selectively excite Orbital Angular Momentum (OAM) modes of light in multimode optical fibers have demonstrated power-scalable methods to efficiently extend fiber lasers across the visible band [Refs 1, 2]. Current multimode fiber methods lack a robust spatial mode conversion device both for use at the input of the fiber as well as to mode-convert the output back into a high beam-quality Gaussian-shaped beam.

This SBIR topic seeks the development of a small Size, Weight, Power and Cost (SWAP-C) mode transformation device that can receive multiple inputs from Gaussian-shaped beams of large-mode area (LMA) or conventional single-mode fibers (SMF) and convert them into desired OAM modes of a custom fiber [such as in reference 2 and 3]. The mode transformer must be fully pigtailed with at least two, preferably three, LMA/SMF input fibers carrying light at 1 micron, 1.5 microns and 2 microns wavelengths respectively, and the fiber at the output in which each input wavelength should be converted to a specified OAM mode of first radial order and angular order L, respectively. While any specific device would yield outputs at two specific OAM values of L (three preferred), the range of desired OAM values L may vary between �5 and �40, based on the application. Output mode purities in the output fiber (as measured by standard interferometric techniques such as [Refs 4, 5, or others] should exceed 10 dB (15 dB preferable) and overall device losses should be < 1 dB. The proposed device should be capable of producing on-demand pairs (triplets) of L states within the desired range, either as a dynamically tunable/reconfigurable device, or as a static device that can be designed and manufactured on-demand. Crucially, the device must be capable of handling at least 500 kW peak-power optical pulses and 15 W average power at the 1 micron wavelength range with pulse widths no more than 50 ns for inclusion in airborne fiber lasers.

An intermediate step towards device development may involve demonstrating OAM mode outputs in free space rather than in the output fiber, and for such proposals, it is important for the performer to provide quantitative metrics that connect the attributes of the free space mode with the one that would eventually be obtained in the output fiber. For instance, a proposed free-space demonstration would have to be much lower loss than 1 dB to account for subsequent coupling losses into the desired OAM mode of the output fiber. Performers are free to explore one or a combination of several promising small SWaP-C mode transformation technologies such as metasurfaces [Ref 6] multi-plane lightwave converters,[Ref 7] free-form optical setups, fiber-based [Ref 8] or 3D-written[Ref 9] photonic lanterns, or other suitable technology approaches not listed here. (Approaches relying on bulky devices such as spatial light modulators will not be considered competitive.)

PHASE I: Develop detailed simulations that could result in a fully designed optical system. The design should be capable of achieving the highest output OAM values within the loss, purity, and power-handling specifications mentioned above. Experimentally demonstrate low loss, high mode purity, and high power handling attribute of at least one (preferably all) component(s) within the designed system. It would suffice to demonstrate free-space modes at this juncture, though fiber would be available to further test performance if sufficient progress is made in program goals.

PHASE II: Deliver a compact device with two (three preferred) LMA/SMF pigtails, each carrying a different wavelength (1 micron, 1.5 microns, and 2 microns) at the input yielding three desired OAM modes in the output fiber (each wavelength input mapped to one specific OAM mode at the output). Demonstrate all performance metrics in the performers� facilities and delivery of one prototype device to the Government for testing. The specific OAM values L and the kind of fiber to be supplied will be subject to Government requirements during the execution of this phase.

PHASE III DUAL USE APPLICATIONS: Incorporate the mode transformer into a laser for use in a planned ONR Innovative Naval Prototype. Mode transformation technologies are already playing a critical role in several commercial applications such as super-resolution biological fluorescence microscopy, space-division multiplexed optical communications systems for a tremendous increase in optical fiber bandwidth, modalities for imaging, and all-optical machine learning and image processing. The technology developed in Phase II is expected to impact several such applications in addition to the Government�s interests in developing high-power lasers at non-standard wavelengths.

REFERENCES:

1.       Demas, J.; Prabhakar, G.; He, T. and Ramachandran, S. "Wavelength-agile high-power sources via four-wave mixing in higher-order fiber modes." Opt. Exp. 25, 7455, (2017).

2.       Liu, X.; Christensen, E.N.; Rottwitt, K. and Ramachandran, S. "Nonlinear four-wave mixing with enhanced diversity and selectivity via spin and orbital angular momentum conservation." APL Photonics 5, 010802, (2020).

3.       Liu, X.; Ma, Z.; Antikainen, A. and Ramachandran, S. "Systematic control of Raman scattering with topologically induced chirality of light." arXiv 2108.03330.

4.       Bozinovic, N.; Golowich, S.; Kristensen, P. and. Ramachandran, S. "Control of orbital angular momentum of light, with optical fibers." Optics Letters, vol. 37, p. 2451, 2012. /

5.       D�Errico, A.; D�Amelio, R.; Piccirillo, B.; Cardano, F. and Marrucci, L. "Measuring the complex orbital angular momentum spectrum and spatial mode decomposition of structured light beams." Optica 4, 1350-1357, 2017. https://opg.optica.org/optica/fulltext.cfm?uri=optica-4-11-1350&id=375926

6.       Devlin, R.C.; Ambrosio, A.; Rubin, A.N.; Mueller, J.P.B. and Capasso, F. "Arbitrary spin-to-orbital angular momentum conversion of light." Science 358, 896�901.

7.       Labroille, G.; Denolle, B.; Jian, P.; Genevaux, P.; Treps, N. and Morizur, J-F. "Efficient and mode selective spatial mode multiplexer based on multi-plane light conversion." Opt. Express 22, 15599-15607 (2014).

8.       Eznaveh, Z.S.; Zacarias, J.C.A.; Lopez, J.E.A.;. Shi, K.; Milione, G.; Jung, Y.; Thomsen, B.C.; Richardson, D.J.; Fontaine, N.; Leon-Saval, S.G. and Correa, R.A. "Photonic lantern broadband orbital angular momentum mode multiplexer." Opt. Express 26, 30042-30051 (2018).

9.       Thomson, R.R.; Birks, T.A.; Leon-Saval, S.G.; Kar, A.K. and Bland-Hawthorn, J. "Ultrafast laser inscription of an integrated photonic lantern." Opt. Express 19, 5698-5705 (2011).

 

KEYWORDS: High power lasers; Orbital Angular Momentum; Mode transformations; Spatial beam shaping; Multimode fibers; metasurfaces; multiplane lightwave converters; 3D-written photonic lanterns

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