Fano resonance control in a photonic crystal structure and its application to ultrafast switching

Abstract

Fano resonances appear in quantum mechanical as well as classical systems as a result of the interference between two paths: one involving a discrete resonance and the other a continuum. Compared to a conventional resonance, characterized by a Lorentzian spectral response, the characteristic asymmetric and "sharp" spectral response of a Fano resonance is suggested to enable photonic switches and sensors with superior characteristics. While experimental demonstrations of the appearance of Fano resonances have been made in both plasmonic and photonic-crystal structures, the control of these resonances is experimentally challenging, often involving the coupling of near-resonant cavities. Here, we experimentally demonstrate two simple structures that allow surprisingly robust control of the Fano spectrum. One structure relies on controlling the amplitude of one of the paths and the other uses symmetry breaking. Short-pulse dynamic measurements show that besides drastically increasing the switching contrast, the transmission dynamics itself is strongly affected by the nature of the resonance. The influence of slow-recovery tails implied by a long carrier lifetime can thus be reduced using a Fano resonance due to a hitherto unrecognized reshaping effect of the nonlinear Fano transfer function. For the first time, we present a system application of a Fano structure, demonstrating its advantages by the experimental realization of 10 Gbit/s all-optical modulation with bit-error-ratios on the order of 10 -7 for input powers less than 1 mW. These results represent a significant improvement compared to the use of a conventional Lorentzian resonance.Ultra-compact photonic structures that perform optical signal processing such as modulation and switching at high-speed with low-energy consumption are essential for enabling integrated photonic chips that can meet the growing demand for information capacity . It remains, however, an important task to identify and demonstrate PhC structures that can meet the low-energy and high-bandwidth requirement. In cavity-based switches an applied control signal changes the refractive index of the cavity, thereby shifting the cavity resonance and modulating the transmission of the data signal. The shape of the transmission spectrum is then very important, since it determines the refractive

Tunable dynamic Fano resonances in coupled-resonator optical waveguides

“…asymmetric and sharp lineshapes that result from the interference of discrete resonance states with broadband continuum states, are ubiquitous in several areas of physics [2]. In optics, they are observed in systems ranging from waveguide-cavity structures to plasmonics and metamaterials [2][3][4][5], promising applications for a wide range of photonic devices such as optical filters, switches, modulators and sensors [6][7][8][9][10] . To this regard, line shape engineering, i.e.…”

Ultrafast low-energy all-optical switching using a photonic-crystal asymmetric Fano structure

“…The BER decreases as the pump energy increases due to an enhanced switching contrast. Error-free (BER<10 -9 ) operation is achieved with a coupled pump energy of only 60 fJ/bit, which is several times lower than the result obtained using an H1-type cavity with a symmetric configuration [8]. This low energy consumption is mainly ascribed to the asymmetric configuration of the device.…”

“…In contrast, a Fano resonance [6], [7] has an asymmetric spectrum, featuring a large transmission change within a narrow wavelength range, determined by the transition from constructive to destructive interference between the discrete resonance and the continuum, thus enabling low-energy switching. The advantage of a Fano resonance was recently demonstrated using a symmetric photonic-crystal (PhC) structure employing an H1-type cavity [8]. It was also found that the non-monotonous frequency-dependence of the Fano transmission spectrum implies an inherent reduction of patterning effects.…”

“…For comparison, we also characterized another Fano structure where by shifting the BH by 2 lattice constants toward port 1 one can achieve a similar Fano line shape with γ 1 ∕γ 2 ≈ 1. Noting that we cannot compare it with a structurally symmetric Fano structure, where the PTE is centered right at the middle of the waveguide, because such a structure gives a Fano resonance with its transmission minimum red shift relative to its maximum, i.e., the Fano resonance has red parity [8], which is not suitable for optical switching based on carrier effects. This structure gives the lowest BER of the order of 10 −3 at 20 Gbit/s operation, thus demonstrating the advantage of Fano structures employing broken symmetry.…”

Ultrafast all-optical modulation using a photonic-crystal Fano structure with broken symmetry

“…In contrast, a Fano resonance [5] has an asymmetric spectrum, featuring a large transmission change within a narrow wavelength range, determined by the transition from constructive to destructive interference between the discrete resonance and the continuum, thus enabling low-energy switching. The advantage of a Fano resonance was recently demonstrated using a symmetric photonic-crystal (PhC) structure employing an H1-type cavity [6]. In that work it was also found that the nonmonotonous frequency dependence of the Fano transmission spectrum implies an inherent reduction of patterning effects.…”