Perfect absorption of light critically affects light-matter interaction for various applications. Coherent perfect absorbers (CPAs) gain the unique capability of controlling light with light in a linear fashion. Multicolor CPAs [S. Longhi, Time-reversed optical parametric oscillation, Phys. Rev. Lett. 107, 033901 (2011)PRLTAO0031-900710.1103/PhysRevLett.107.033901] are highly desirable for broadband and nonlinear light-to-light coherent control but the experimental demonstration has still remained elusive. Here, for the first time, we experimentally observe a dual-color version of a CPA (DC-CPA) through a second harmonic generation in a single whispering-gallery-mode microcavity. The DC-CPA enables simultaneous perfect absorption of both the incoming fundamental wave and its second harmonic. Similar to its linear counterpart, coherent control in the DC-CPA can also be realized by tuning the relative phase and intensity between the two-colored waves through nonlinear interference instead of the linear one. This scheme breaks the linear boundary of the traditional CPA into a multifrequency domain and paves the way toward all-optical signal processing and quantum information.
Perfect absorption of light critically affects light-matter interaction for various applications. Coherent perfect absorbers (CPAs) gain the unique capability of controlling light with light in a linear fashion. Multicolor CPAs [S. Longhi, Time-reversed optical parametric oscillation, Phys. Rev. Lett. 107, 033901 (2011)PRLTAO0031-900710.1103/PhysRevLett.107.033901] are highly desirable for broadband and nonlinear light-to-light coherent control but the experimental demonstration has still remained elusive. Here, for the first time, we experimentally observe a dual-color version of a CPA (DC-CPA) through a second harmonic generation in a single whispering-gallery-mode microcavity. The DC-CPA enables simultaneous perfect absorption of both the incoming fundamental wave and its second harmonic. Similar to its linear counterpart, coherent control in the DC-CPA can also be realized by tuning the relative phase and intensity between the two-colored waves through nonlinear interference instead of the linear one. This scheme breaks the linear boundary of the traditional CPA into a multifrequency domain and paves the way toward all-optical signal processing and quantum information.
Perfect absorption of light critically affects light-matter interaction for various applications. Coherent perfect absorbers (CPA) gain the unique capability of controlling light with light in a linear fashion. Multi-color CPAs [Phys. Rev. Lett. 107, 033901] are highly desirable for broadband and nonlinear light-to-light coherent control, however, the experimental demonstration has still remained elusive. Here we experimentally observe a dual-color version of CPA (DC-CPA) through a second harmonic generation in a single whispering-gallery-mode microcavity. The DC-CPA enables simultaneous perfect absorption of both the incoming fundamental wave and its second harmonic. Similar to its linear counterpart, coherent control in the DC-CPA can be also realized by tuning the relative phase and intensity between the two-colored waves through nonlinear interference instead of the linear one. This scheme breaks the linear boundary of the traditional CPA into a multi-frequency domain and paves the way toward all-optically signal processing and quantum information.
Recently, a concept of time reversed lasing or coherent perfect absorber (CPA) has been proposed by A. D. Stone and co-workers, and was shortly experimentally demonstrated by them. The CPA system is illuminated coherently and monochromatically by the time reverse of the output of a lasing mode and the incident radiation is perfectly absorbed. Shortly afterwards, Stefano Longhi extended the idea to realize a CPA for colored incident light, and have theoretically shown that the time reversal of optical parametric oscillation (OPO) in a nonlinear medium could also realize a colored CPA for incident signal and idler fields which can be seemed as a kind of nonlinear CPA. Here we present the realization of such time-reversed processes in nonlinear optics regime, including time-reversed second harmonic generation (SHG) for coherent absorption at harmonic frequency of the pump and time-reversed optical parametric amplification (OPA) for coherent attenuation of colored travelling optical fields. Time reversed SHG is carried out at both phase matching and mismatching conditions, which shows parametric near perfect absorption at the harmonic frequency of the pump. The time reversal of OPA is demonstrated experimentally in a nonlinear medium to form a coherent absorber for perpendicularly polarized signal and idler travelling waves, realizing in the condition of OPA by a type II phase matching scheme. The absorption of signal/idler pair occurs at some specific phase difference. This is the first experimental demonstration of coherent absorption processes in nonlinear optics regime.
Recent works [Chong et al., Phys. Rev. Lett. 105, 053901 (2010); Wan et al., Science 331, 889 (2011)] have shown that the time-reversed process of lasing at threshold realizes a coherent perfect absorber (CPA). In a CPA, a lossy medium in an optical cavity with a specific degree of dissipation, equal in modulus to the gain of the lasing medium, can perfectly absorb coherent optical waves at discrete frequencies that are the time-reversed counterpart of the lasing modes. Here the concepts of time reversal of lasing and CPA are extended for optical radiation emitted by a laser operated in an arbitrary regime, i.e., for transient, chaotic, or periodic coherent optical fields. We prove that any electromagnetic signal E(t) generated by a laser system S operated in an arbitrary regime can be perfectly absorbed by a CPA device ${S}^{\ensuremath{'}}$ which is simply realized by placing inside S a broadband linear absorber (attenuator) of appropriate transmittance. As examples, we discuss CPA devices that perfectly absorb a chaotic laser signal and a frequency-modulated optical wave.
Abstract Transparency and perfect absorption are two contradictory terms; a perfect absorber never permits waves to transmit through. However, this statement only remains true in the linear regime, where the nonlinearity has been omitted and the physical system like the perfect absorber is not affected by the incoming waves. Here we experimentally demonstrate an intriguing self-induced transparency effect in a perfectly absorbing optical microcavity, which perfectly absorbs any incoming waves at the low power level, but allows a portion of waves to be transmitted at the higher power due to the nonlinear coupling between the fundamental and its second harmonic modes. Moreover, the asymmetric scattering nature of the microcavity enables a chiral and unidirectional reflection in one of the input ports, this leads to asymmetric and chiral coherent control of the perfect absorption states through phase varying. More importantly, such chiral behaviors also empower the chiral emission of second-harmonic generation with a high distinct ratio in the transparency state. These results pave the way for controllable transparency in a wide range of fields in optics, microwaves, acoustics, mechanics, and matter waves.
In the past few years, a new phenomenon of absorption, called “coherent perfect absorption (CPA)”, has attracted significant attentions [1, 2]. CPA relies on the coherent interference of light. In a typical CPA system, two coherent beams are incident on the absorber from opposite sides and the reflected light of one beam interfere with the transmitted light of the other and vice versa. CPA was first realized using a silicon slab cavity, and has then been reported in composite absorptive films, planar metamaterials, graphene, waveguides and so on.
In recent works, it has been shown, rather generally, that the time-reversed process of lasing at threshold realizes a coherent perfect absorber (CPA). In a CPA, a lossy medium in an optical cavity with a specific degree of dissipation, equal in modulus to the gain of the lasing medium, can perfectly absorb coherent optical waves that are the time-reversed counterpart of the lasing field. Here, the time-reversed process of lasing is considered in detail for a homogeneously broadened two-level medium in an optical cavity and the conditions for CPA are derived. It is shown that, owing to the dispersive properties of the two-level medium, exact time-reversal symmetry is broken and the frequency of the field at which CPA occurs is generally different than the one of the lasing mode. Moreover, at a large cooperation parameter, the observation of CPA in the presence of bistability requires one to operate in the upper branch of the hysteresis cycle.