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Minimizing the material usage in thin‐film solar cells can reduce manufacturing costs and enable mechanically flexible implementations, but concomitantly diminishes optical absorption. Coherent optical effects can help alleviate this inevitable drawback at discrete frequencies. For example, coherent perfect absorption guarantees that light is fully absorbed in a thin layer regardless of material or thickness—but only on resonance. Here, it is shown that "omni‐resonance" delivers such coherent enhancement over a broad bandwidth by structuring the optical field to nullify the angular dispersion intrinsic to resonant structures. After embedding an amorphous‐silicon thin‐film photovoltaic cell in a planar cavity, pre‐conditioning the incident light using an alignment‐free optical arrangement severs the link between the resonant bandwidth and the cavity‐photon lifetime, thereby rendering the cavity omni‐resonant. Coherently enhanced near‐infrared absorption doubles the photocurrent over the targeted spectral range 660–740 nm where every wavelength resonates. These results may pave the way to transparent solar cells that optimally harvest near‐infrared light. [ABSTRACT FROM AUTHOR]

Coherent perfect absorption (CPA) is an interferometric effect that guarantees full absorption in a lossy layer independently of its intrinsic losses. To date, it has been observed only at a single wavelength or over narrow bandwidths, whereupon wavelength-dependent absorption can be ignored. Here we produce CPA over a bandwidth of ∼60 nm in a 2 µm thick polymer film with a low-doping concentration of an organic laser dye. A planar cavity is designed with a spectral 'dip' to accommodate the dye resonant linewidth, and CPA is thus achieved even at its absorption edges. This approach allows realizing strong absorption in laser dyes—and resonant materials in general—independently of the intrinsic absorption levels, with a flat spectral profile and without suffering absorption quenching due to high doping levels. [ABSTRACT FROM AUTHOR]

Coherent perfect absorption refers to the interferometric enhancement of absorption in a partially lossy medium upto 100%. This can be achieved without modifying the absorbing medium itself, instead of engineering its photonic environment. Ion-doped fibers are one of the most technologically relevant absorbing materials in optics, which are widely employed in fiber amplifiers and lasers. Realizing complete optical absorption of an incident field in short-length moderately-doped fibers remains a challenge for the cost-effective design of compact fiber lasers. Here, we exploit the concept of coherent perfect absorption to overcome this challenge, whereby two appropriately designed fiber Bragg gratings define a short-length erbium-doped-fiber cavity that enforces complete absorption of an incident field on resonance—-independently of the doped-fiber intrinsic absorption. This approach applies to any spectral window and guarantees the efficient utilization of the fiber dopants along its length, thus, suggesting the possibility of next-generation efficient single-longitudinal-mode fiber lasers for applications in optical communication, sensing, and metrology. [ABSTRACT FROM AUTHOR]