Near-field effect in the infrared range through periodic Germanium subwavelength arrays.

Using finite-difference-time-domain simulation, we have studied the near-field effect of Germanium (Ge) subwavelength arrays designed in-plane with a normal incidence. Spectra of vertical electric field component normal to the surface show pronounced resonance peaks in an infrared range, which can be applied in a quantum well infrared photodetector. Unlike the near-field optics in metallic systems that are commonly related to surface plasmons, the intense vertical field along the surface of the Ge film can be interpreted as a combination of diffraction and waveguide theory. The existence of the enhanced field is confirmed by measuring the Fourier transform infrared spectra of fabricated samples. The positions of the resonant peaks obtained in experiment are in good agreement with our simulations.

Enhanced and suppressed infrared transmission through germanium subwavelength arrays.

We have studied the zero-order transmission of periodic germanium (Ge) subwavelength arrays in an infrared range by using finite-difference time-domain simulations. A special wavelength-selective peak in a triangular hole array of Ge film is observed with an enhanced transmission accompanied by a drastic suppression nearby, which cannot be found in a one-dimensional Ge subwavelength array and is different from the extraordinary transmission related to surface plasmons in a metal film. The electromagnetic field is found to be concentrated on both surfaces of the Ge film at this peak. The unique transmission is verified through measurements on fabricated samples and is interpreted using the photonic band structure.

Noncollinear parametric fluorescence by chirped quasi-phase matching for monocycle temporal entanglement.

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Opt. Express 98, 063602 (2007)] suggested using ultrabroad parametric fluorescenc generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In the Harris's original proposal, it is assumed that the photons are collinearly generated and then spatially separated by frequency filtering Here, we alternatively propose using noncollinearly generated SPDC. In our numerical calculation, to achieve 1.2 cycle temporal correlation for a 532 nm pump laser, only 10% -chirped device is sufficien when noncollinear condition is applied, while a largely chirped (50%) device is required in collinear condition. We also experimentally demonstrate an octave-spanning (790-1610 nm) noncollinear parametric fluorescenc from a 10% chirped MgSLT crystal using both a superconducting nanowire single-photon detector and photomultiplier tube as photon detectors. The observed SPDC bandwidth is 194 THz, which is the largest width achieved to date for a chirped QPM device. From this experimental result, our numerical analysis predicts that the bi-photon can be compressed to 1.2 cycles with appropriate phase compensation.

A narrow band-rejection filter based on block copolymers.

We demonstrate filtering characteristics of a polymer band-rejection filter (PBRF) with highly-ordered microphase-separated structure of block copolymers (BCPs). This PBRF is characterized by an Optical Density > 5 blocking at the center wavelength and narrow blocking full bandwidth of 8 nm. Moreover, the wavelength is easily tuned by blending two BCPs with different molecular-weight. A low frequency Raman shift of 200 cm(-1) are, in fact, detected with a sufficient resolution by using this filter in Raman spectroscopy.