Bandwidth-Enhanced coherent perfect absorption based on tunable coupling of borophene nanoribbons

Broadband optical absorbers are critical for photonics and optoelectronics applications like photodetection and energy harvesting. Achieving high-efficiency broadband absorption, however, remains challenging. To enhance the bandwidth of coherent perfect absorption (CPA), this study proposes an absorber architecture using periodically arranged borophene nanoribbon arrays, designed via temporal coupled-mode theory and operating in the telecom C-band (centred at 1530 nm). The findings demonstrate that meticulous optimization of the nanostructure's geometric parameters enables the system to satisfy the critical coupling condition. When irradiated by two phase-controlled, counter-propagating coherent beams, the system achieves near-unity CPA efficiency. Significantly, increasing the number of nanoribbons per period from one to three broadens the absorption bandwidth from ~30 nm to ~54 nm and ~80 nm respectively, representing a >160% increase. The underlying mechanism involves the manipulation of resonant modes and their coupling efficiency via the geometry of the nanostructure. This work establishes a viable design paradigm for efficient, broadband, near-infrared optoelectronic devices that can be applied directly to next-generation optical communications, sensing and integrated photonics.