Abstract
Most present-day resonant systems, throughout physics and engineering, are characterized by a strict time-reversal symmetry between the rates of energy coupled in and out of the system, which leads to a trade-off between how long a wave can be stored in the system and the system’s bandwidth. Any attempt to reduce the losses of the resonant system, and hence store a (mechanical, acoustic, electronic, optical, or of any other nature) wave for more time, will inevitably also reduce the bandwidth of the system. Until recently, this time-bandwidth limit has been considered fundamental, arising from basic Fourier reciprocity. In this work, using a simple macroscopic, fiber-optic resonator where the nonreciprocity is induced by breaking its time-invariance, we report, in full agreement with accompanying numerical simulations, a time-bandwidth product (TBP) exceeding the ‘fundamental’ limit of ordinary resonant systems by a factor of 30. We show that, although in practice experimental constraints limit our scheme, the TBP can be arbitrarily large, simply dictated by the finesse of the cavity. Our results open the path for designing resonant systems, ubiquitous in physics and engineering, that can simultaneously be broadband and possessing long storage times, thereby offering a potential for new functionalities in wave-matter interactions.
Highlights
Most present-day resonant systems, throughout physics and engineering, are characterized by a strict time-reversal symmetry between the rates of energy coupled in and out of the system, which leads to a trade-off between how long a wave can be stored in the system and the system’s bandwidth
Fiber-optic resonator, in which Lorentz reciprocity is broken by suitable time modulation, we report a time-bandwidth product (TBP) above the fundamental limit of ordinary reciprocal cavities by a factor of 30, solely limited by current experimental constraints of our setup
This corresponds to a closed cavity decay-time of about 1.37 times longer than the cavity round trips (RT) time, leading to a TBP of 2.37
Summary
Most present-day resonant systems, throughout physics and engineering, are characterized by a strict time-reversal symmetry between the rates of energy coupled in and out of the system, which leads to a trade-off between how long a wave can be stored in the system and the system’s bandwidth. In a reciprocal resonant system, ∆ωacc coincides with the cavity linewidth, and, its TBP is always limited to unity by Fourier relation stating ∆ωcav = 1/τout, a value commonly referred to as the ‘time-bandwidth limit’[1,2,3] This inherent limitation dictates that long storage times unavoidably imply narrow input bandwidths, while large bandwidths are retained only for short periods of time. The trade-off arises from pulse temporal broadening owing to various dispersion phenomena (2nd and 3rd order dispersion, dispersion of gain/absorption), preventing significant slowing-down of broadband s ignals[4,7,13,14] Another attempt to overcome the time-bandwidth limit was reported some time ago[15]. The simultaneous storage of multiple pulses in the system cannot be achieved with that scheme: while the bandwidth of the first pulse is adiabatically compressed, a second pulse cannot be injected into the device
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