Fei Qin

All-optical logic gates based on two-dimensional low-refractive-index nonlinear photonic crystal slabs

This article demonstrates theoretical design of ultracompact all-optical AND, NAND, OR, and NOR gates with two-dimensional nonlinear photonic crystal slabs. Compound Ag-polymer film with a low refractive index and large third-order nonlinearity is adopted as our nonlinear material and photonic crystal cavities with a relatively high quality factor of about 2000 is designed on this polymer slab. Numerical simulations show that all-optical logic gates with low pump-power in the order of tens of MW/cm2 can be achieved. These design results may provide very useful schemes and approaches for the realization of all-optical logic gates with low-cost, low-pump-power, high-contrast and ultrafast response-time.

10 fs ultrafast all-optical switching in polystyrene nonlinear photonic crystals

An ultrafast all-optical switching with the response time on the order of 10 fs is demonstrated in a three-dimensional opal polystyrene nonlinear photonic crystal by means of precise femtosecond pump-probe technique. The switching is realized by the shift in the photonic band gap under external optical pumping of 8 fs Ti:sapphire pulse laser with a peak pump power of 20.6u2002GW/cm2. The good performance of optical switching is attributed to the very strong and fast Kerr nonlinear optical response of the polystyrene material.

Ultrafast and low-power photonic crystal all-optical switching with resonant cavities

We theoretically investigate and discuss the response time, switching contrast, and pump power of all-optical switching in a nonlinear photonic crystal structure with high quality factor (high-Q) cavity. For the response time of all-optical switching, the drop and rise time are considered, respectively. Moreover, we find that when the duration of pump pulse is shorter than the lifetime, the response curve of all-optical switching is asymmetric, and the drop time is determined by both the lifetime of high-Q cavity and duration of pump pulse, and the rise time is mainly determined by lifetime of high-Q cavity. In contrast, when the duration of pump pulse is much longer than the lifetime, the dynamic response curve is symmetric, and both the drop and rise time are determined by the duration of pump pulse. On the other hand, the pump power can be significantly reduced by using a setup where the probe beam is located at the high-Q cavity mode with very narrow linewidth. Furthermore, if the central wavelength o...

Fabrication of semiconductor-polymer compound nonlinear photonic crystal slab with highly uniform infiltration based on nano-imprint lithography technique

We present a versatile technique based on nano-imprint lithography to fabricate high-quality semiconductor-polymer compound nonlinear photonic crystal (NPC) slabs. The approach allows one to infiltrate uniformly polystyrene materials that possess large Kerr nonlinearity and ultrafast nonlinear response into the cylindrical air holes with diameter of hundred nanometers that are perforated in silicon membranes. Both the structural characterization via the cross-sectional scanning electron microscopy images and the optical characterization via the transmission spectrum measurement undoubtedly show that the fabricated compound NPC samples have uniform and dense polymer infiltration and are of high quality in optical properties. The compound NPC samples exhibit sharp transmission band edges and nondegraded high quality factor of microcavities compared with those in the bare silicon PC. The versatile method can be expanded to make general semiconductor-polymer hybrid optical nanostructures, and thus it may pave the way for reliable and efficient fabrication of ultrafast and ultralow power all-optical tunable integrated photonic devices and circuits.

Design of Kerr-effect sensitive microcavity in nonlinear photonic crystal slabs for all-optical switching

We design a Kerr-effect sensitive microcavity in hybrid semiconductor nonlinear photonic crystal (PhC) slabs for application in all-optical switching. Our new concept cavity is made from infiltrating the air hole array and coating the surface of usual semiconductor PhC slabs with polystyrene, and let the polystyrene instead of the semiconductor occupy the center of the cavity. Optimization of the cavity design by modulating the structure parameter yields a quality factor Q=1600 and shift magnitude δf≈8.4u2002nm while pumping the cavity with a light intensity of 80u2002GW/cm2. This cavity configuration can help to realize very fast response speed and low pump intensity in all-optical switching devices, reduce the demand for rigorous precision during the high-Q PhC cavity fabrication, and allow for easy integration with other integrated optical components.

Optical switching in hybrid semiconductor nonlinear photonic crystal slabs with Kerr materials

Nonlinear photonic crystals, whose refractive index distribution can be tuned optically, have been used to demonstrate all-optical switching due to a change of the refractive index and subsequent shift of the bandgap edge or the defect state resonant frequency. Semiconductor-based all-optical switching is still limited by the weak nonlinearity and the slow response time owing to the slow dynamics of two-photon-generated free carriers. Here we introduce a concept of hybrid nonlinear photonic crystals that are made from infiltrating the air-hole array or coating the surface of the usual semiconductor photonic crystal slabs with organic polystyrene materials. The hybrid configuration can help to realize very fast response speeds and strong nonlinearity in the semiconductor-based device. We study the influence of the thickness of the polystyrene film on the gap shift scale, and also analyze its physical mechanism. The switching effect on this structure was discussed, and shows that the nonlinear hybrid structure can achieve relatively larger transmission contrast. Our result may be helpful in designing integrated optical circuits.

Broadband large-angle self-collimation in two-dimensional silicon photonic crystal

We report a two-dimensional silicon photonic crystal structure that supports the self-collimation effect with large incident angles over a broad wavelength range. We theoretically and experimentally show the propagation light in the designed and fabricated structure without diffraction. Broadband large-angle self-collimation is observed in infrared wavelength.

Ultrafast all-optical switching in one-dimensional semiconductor–polymer hybrid nonlinear photonic crystals with relaxing Kerr nonlinearity

The achievement of ultrafast all-optical switching on chip is a fundamental issue of all-optical integration. A feasible and promising method for this is to combine semiconductor photonic crystals with highly nonlinear polymer materials to form the hybrid nonlinear photonic crystal. In this paper we numerically investigate the femtosecond dynamic response of all-optical switching based on the effect of band gap edge shift in one-dimensional (1D) semiconductor–polymer hybrid nonlinear photonic crystal (NPC) structures. Taking into account the Kerr relaxation time of the polymer and semiconductor materials simultaneously, the introduction of highly nonlinear polymer materials with femtosecond relaxation time can realize all-optical switching in the femtosecond range in spite of the low response speed of the semiconductor materials. The physical origin is the large and ultrafast response Kerr nonlinearity of the polymer materials and this is proved by examining the dependence of switching time on the relaxation speed of the polymer materials. The results can be extended to 2D and 3D NPC structures.

High-Q microcavities in low-index one-dimensional photonic crystal slabs based on modal gap confinement

Recently, various high quality factor photonic crystal microcavities have been demonstrated theoretically and experimentally with only one-dimensional periodicity. However, in most cases high-index materials such as silicon were chosen for easily achievable large photonic bandgap and elaborate refractive index modulation or taper structure is required for reducing radiation loss. Here, we present a design of high-Q microcavities in one-dimensional multilayer polystyrene photonic crystal slab structures with a low-index contrast of 1.59:1. Microcavities are introduced by simply decreasing the thickness of layers at the center region to form a double-heterostructure. A resonant mode with a quality factor up to 20 000 is obtained and found to originate from the modal gap confinement by comparing with a Fabry–Perot cavity. The dependence of the maximal quality factor on the cavity length further reveals that the small group velocity of light within the heterostructure cavity contributes significantly to the h...

Design of all-optical switching component based on pillar-array hybrid nonlinear photonic crystal cavity

A Kerr-effect sensitive microcavity device based on the two-dimensional pillar-array hybrid nonlinear photonic crystal slab has been designed for all-optical switching. The cavity is made from infiltrating the void space of the pillar-array semiconductor photonic crystal slab with polystyrene. The structure parameters have been optimized by numerical simulations based on the three-dimensioanl finite-difference time-domain method. It is found that the resonant wavelength can shift 15xa0nm under the pump light with an intensity of 80u2009u2009GW/cm2, which is far larger than the shift magnitude of the holes-array nonlinear photonic crystal slab.