Quantum digital signature (QDS) has been proved to be secure in theory, but will inevitably be interfered by channel noise during the practice transmission of qubits. We propose two practical fault tolerant quantum digital signature protocols for the collective noises. For resisting the collective noises, a decoherence-free subspace (DFS) containing four logical qubits has been constructed, which improves the performance of QDS protocols in terms of communication fidelity. Moreover, we prove that the protocols are secure against forging and repudiation attacks, and further discuss the influence of different verification thresholds on the security and give a quantitative analysis.

Pulse compression by second harmonic generation in a type II nonlinear optical crystal controlled by a time predelay of the faster input pulse is not simple to achieve high-average-power Yb:YAG lasers with wavelength of 1030 nm. The reason is that the borate nonlinear crystals with their excellent thermal properties do not have the optimal ratio of group velocities of the interacting pulses to achieve efficient pulse compression. We have changed the effective group velocities by tilting the pulse fronts at a diffraction grating and imaging the tilted 1.7 ps pulses into the 6 and 8.5 mm thick BBO crystals. As a result, we have measured significant spectral broadening to 4.5 nm, supporting pulses as short as 100 fs, with an energy conversion efficiency in excess of 20 %. The measured data correspond well with numerical simulations. This research opens a way to extend the range of possible applications of Yb:YAG high-average-power thin-disk lasers into the fs regime.

Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system; however, this simplified model does not capture all the physics of EIT experiments with real systems. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. In addition to the expected broadening of the EIT resonance and reduction in EIT transparency due to multiple excited states, we find some unexpected and interesting results. A comparison with a model that does not allow for coupling of the excited states shows that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transparency under some conditions and can enhance and shift the resonance frequency of off-resonance Raman absorption. Furthermore, through a dressed state analysis of the full four-level system, we find that the underlying mechanism for the reduction in EIT transparency is a shift in the two-photon resonance due to unequal dipole moments of the transitions coupled by the control field. Complete transparency can only be recovered for systems with equal dipole moments or when the separation between the two excited states is at least of the order of the Doppler width. To support our theoretical study, we present experimental EIT measurements in the D1 lines of 85Rb and 87Rb that agree with our predictions of an enhancement or reduction of EIT transparency under specific conditions. The experimental results also verify the roles that the dipole moments and the separation between the two excited states have on recovering the EIT transparency.

This paper proposes a method for a scheme of spectral phase encoding with resolution of up to 10 MHz and addressability of 40GHz, for a typical wide-band optical data carrying signal, by means of optical instruments and prior knowledge about the signal. The setup includes an array of Fabri-Perot Interferometers (FPI) which bypass the grating limitations, and a phase-only spatial light modulator (SLM) to properly encode the diffracted light. Their arrangement along with the method of Optical Code Division Multiple Access (OCDMA) was simulated, and promised fine results for various encoding schemes.

We show that narrow trenches in a high-contrast silicon-photonics slab can act as lossless power dividers for semi-guided waves. Reflectance and transmittance can be easily configured by selecting the trench width. At sufficiently high angles of incidence, the devices are lossless, apart from material attenuation and scattering due to surface roughness. We numerically simulate a series of devices within the full 0-to-1-range of splitting ratios, for semi-guided plane wave incidence as well as for excitation by focused Gaussian wave bundles. Straightforward cascading of the trenches leads to concepts for 1×M-power dividers and a polarization beam splitter.

In this paper, we propose a non-invasive method for measuring pulse waves corresponding to heart rate (HR) by capturing the color change on the soles of rats’ feet using a high-speed RGB camera. Remote photoplethysmography (rPPG) with a camera has been used as a non-invasive biometric method. However, the rPPG method has been challenging to apply to rats with body hair. We applied the rPPG method using a high frame rate to the sole where the skin was directly visible and successfully and accurately detected pulse waves under non-invasive, non-restraint, and non-anesthetized conditions.

We propose a plasmonic device, based on the combination of a Yagi-Uda nanoantenna and a bowtie nanoantenna, that can enable on-chip implementation of plasmon-enhanced light-matter interaction processes such as surface-enhanced Raman scattering (SERS), surface-enhanced infrared absorption spectroscopy, and plasmon-enhanced fluorescence. In this device, a localized source is employed to excite the Yagi-Uda nanoantenna, which in turn drives the bowtie nanoantenna. We employ finite difference time domain (FDTD) method to perform numerical simulations to obtain radiation characteristics of the Yagi-Uda nanoantenna as well as the electric field enhancements in the vicinity of the bowtie nanoantenna excited by the Yagi-Uda nanoantenna. We find that for a wavelength of 785 nm, an electric field enhancement of ∼ 196 can be achieved in between the arms of the bow-tie nanoantenna even when the minimum gap between nanostructures is as large as 10 nm. It is found that this electric field enhancement is significantly large when compared with the maximum electric field enhancement (∼ 11) obtained for direct excitation of the bowtie nanoantenna by a point source or with the maximum electric field enhancement (∼ 34) obtained for plane wave excitation of the bowtie nanoantenna. As the electromagnetic enhancement of SERS can be approximated to be the fourth power of the electric field enhancement, SERS electromagnetic enhancement of ∼ 1.5 × 109 is achieved for the bow-tie nanoantennas excited by the Yagi-Uda nanoantennas, even when the minimum gap between the arms of the bow-tie nanoantenna is as large as 10 nm. We also analyze the effect of various geometrical parameters of the nanoantennas and show that the maximum electric field enhancement at a given wavelength can only be obtained when both the Yagi-Uda nanoantenna and the bowtie nanoantenna are resonant at that wavelength. Moreover, we calculate the electric field enhancements at different near-infrared wavelengths. Employing the proposed device, an electric field enhancement of ∼ 945 is obtained at a wavelength of 1500 nm resulting in a SERS electromagnetic enhancement factor as high as ∼ 8 × 1011, even when the minimum gap between nanostructures is as large as 10 nm.

We propose a quantitative phase imaging technique with single-path phase-shifting digital holography using a light-emitting diode (LED). A reference wave is generated from an object wave in the Fourier plane using a single-path interferometer, based on self-reference digital holography. The object wave interferes with the reference wave, and the quantitative phase information of the object wave is recorded as a digital hologram. Quantitative phase images of objects are obtained by applying a phase-shifting interferometry technique. All the light diffracted from the objects can be utilized to generate a digital hologram. Its validity is experimentally demonstrated by constructing an optical system with a wide-field optical microscope.

Illumination estimation is a fundamental prerequisite for many computer vision applications. Various statistics and deep learning-based estimation methods have been proposed, and further studies are ongoing. In this study, we first perform a comparative analysis of representative statistics and deep learning-based methods and subsequently investigate combining them to improve the illumination estimation accuracy. We use hyperspectral images as the training data and support vector regression to combine the methods. Based on the results, we confirm that their combination enhances their accuracy.

In this paper, we propose a ring-type grating in which grating vectors formed by periodic molecular alignments are superimposed radially. Depending on incident polarization states, the anisotropic gratings generate polarization dependencies for the ring-like first order diffraction. To determine the polarization states of incident light for both single and multi-wavelengths, we attempted to extract the optical intensity distribution on the ring-like diffraction from each single-shot diffraction image. In addition, a system that enables the detection of spatial modulation of optical birefringence is proposed. Finally, we concluded that the optical intensity distribution on the circumference of the ring-like diffraction has sufficient potential to be available.