Yulan Fu

Ultralow-power and ultrafast all-optical tunable plasmon-induced transparency in metamaterials at optical communication range

Actively all-optical tunable plasmon-induced transparency in metamaterials paves the way for achieving ultrahigh-speed quantum information processing chips. Unfortunately, up to now, very small experimental progress has been made for all-optical tunable plasmon-induced transparency in metamaterials in the visible and near-infrared range because of small third-order optical nonlinearity of conventional materials. The achieved operating pump intensity was as high as several GW/cm2 order. Here, we report an ultralow-power and ultrafast all-optical tunable plasmon-induced transparency in metamaterials coated on polycrystalline indium-tin oxide layer at the optical communication range. Compared with previous reports, the threshold pump intensity is reduced by four orders of magnitude, while an ultrafast response time of picoseconds order is maintained. This work not only offers a way to constructing photonic materials with large nonlinearity and ultrafast response, but also opens up the possibility for realizing quantum solid chips and ultrafast integrated photonic devices based on metamaterials.

Ferroelectric Hybrid Plasmonic Waveguide for All-Optical Logic Gate Applications

A ferroelectric hybrid plasmonic waveguide, made of a polycrystal lithium niobate waveguide separated from a gold film by a silicon dioxide isolation layer, is fabricated by use of laser molecular beam epitaxy growth, electron beam evaporation, and focused ion beam etching. Strong subwavelength mode confinement and excellent long-range propagation are achieved simultaneously for the hybrid plasmonic mode. An all-optical logic OR gate is also realized based on the ferroelectric hybrid plasmonic waveguide. This may provide a way for the study of all-optical logic gates and integrated photonic circuits.

Low‐Power and Ultrafast All‐Optical Tunable Nanometer‐Scale Photonic Metamaterials

IO N Recently, photonic metamaterials, a kind of artifi cial microstructure material constructed by resonant sub-wavelength electromagnetic units arranged periodically in space, have attracted great attention because of their important applications in fi elds of nanophotonics, near-fi eld optics, and optical cloaking. The optical properties of photonic metamaterials strongly depend on the geometry of the sub-wavelength electromagnetic units rather than the component materials. [ 1 ] Tunable photonic metamaterials, the effective dielectric constant of which can be controlled through external parameters, can fi nd more fl exible applications. Two methods have been used to realize tunable photonic metamaterials: one is to directly reconfi gure the sub-wavelength electromagnetic units, [ 2 , 3 ] and the other is to vary the constituent materials or change the surrounding medium. [ 4 , 5 ] Thermally tuning liquid crystal or ferroelectric materials, [ 6 , 7 ] electrically tuning liquid crystal or semiconductor materials, [ 8 , 9 ] and magnetically tuning ferromagnetic materials [ 10 ] have been adopted to realize tunable photonic metamaterials. The tuning process controlled by temperature, electric fi eld, and magnetic fi eld typically respond on time scales ranging from microseconds to seconds. [ 11 ] It is promising to obtain a faster response time by use of alloptical tuning based on a third-order non-linear optical Kerr effect. [ 12 , 13 ] However, owing to the relatively small third-order non-linear susceptibility of conventional materials, the pump intensity is very high, usually of the order of several gigawatts per square centimetre. [ 14 ] Moreover, for conventional materials, the larger the non-linear susceptibility, the slower the response time. [ 15 ] This has restricted the practical applications of all-optical tunable photonic metamaterials. Recently, Dani et al. reported nanosecond tuning of a 2D fi shnet-structured photonic metamaterial made of silver and amorphous silicon with an operating pump intensity of 1.8 GW cm − 2 . [ 16 ] Shen et al. achieved a large tuning range, from 0.76 to 0.96 THz, for the magnetic resonance frequency of a 2D photonic metamaterial made of silicon and gold with an operating pump intensity of 8.5 GW cm − 2 . [ 17 ] However, to date, it is still a great challenge to realize a low operating pump power, an ultrafast response, and large tunability for all-optical tunable photonic metamaterials.

Ultrafast all-optical tunable Fano resonance in nonlinear ferroelectric photonic crystals

We report an ultrafast all-optical tunable Fano resonance in a nonlinear ferroelectric photonic crystal made of polycrystal lithium niobate, which provides a large nonlinear susceptibility because of strong quantum size effect of nanoscale crystal grains. The femtosecond pump and probe method is adopted to measure the tunability of the Fano resonance based on the nonlinear optical Kerr effect. A 37-nm shift in the Fano resonance wavelength is obtained under excitation of a 30 MW/cm2 pump laser. An ultrafast response time of 43 ps is achieved due to fast relaxation dynamics of bound electrons in polycrystal lithium niobate.

Ultrafast all-optical tunable Fano resonance in nonlinear metamaterials

An ultrafast all-optical tunable Fano resonance is realized in a nonlinear metamaterial composed of arrays of asymmetrically split rings etched in a gold film, coated with a polycrystalline lithium niobate layer. The metamaterial has a large optical nonlinearity because of strong nonlinearity enhancement associated with field reinforcement provided by plasmonic resonance, and quantum confinement effect provided by nanoscale crystal grains. A large shift of 23 nm in the Fano resonance wavelength is achieved under excitation of a weak pump light with an intensity of 15 MW/cm2. While an ultrafast response time of 48 ps is also maintained.

Electro-optic tunable multi-channel filter in two-dimensional ferroelectric photonic crystals

An electro-optic tunable multi-channel filter is presented, which is based on a two-dimensional ferroelectric photonic crystal made of barium titanate. The filtering properties of the photonic crystal filter can be tuned by an applied voltage or by adjusting the structural parameters. The channel shifts about 30 nm under excitation of an applied voltage of 54.8 V. The influences of the structural disorders caused by the perturbations in the radius or the position of air holes on the filtering properties are also analyzed.

All-optical switching via tunable coupling of nanocomposite photonic crystal microcavities

We report a low-power all-optical switching in a two-dimensional nanocomposite photonic crystal microcavity made of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] doped with gold nanoparticles, realized based on surface plasmon resonance enhancing nonlinearity and dynamically tunable coupling of two asymmetric defect modes. Under excitation around the surface plasmon resonance peak, the value of the nonlinear susceptibility of the nanocomposite material reaches the order of 10−6 esu. A threshold photon energy as low as 700 fJ and an ultrahigh switching efficiency of 90% are realized simultaneously.

Ultrawide-band photon routing based on chirped plasmonic gratings

We report an ultrawide-band photon routing based on a chirped plasmonic grating, which consists of a gold film coated with a chirped dielectric grating made of organic polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]. The photon routing is realized based on rainbow-trapping like effect. An ultrawide operating bandwidth of 200 nm is reached through scanning near-field optical microscopy measurement. The tunable photon routing is reached through adjusting structural parameters of chirped plasmonic grating or using a pump light. A shift of 0.5 μm in the terminal channel is achieved for the 850-nm incident laser when the groove width changes from 150 to 180 nm.