A real-time reflection imaging employing a terahertz (THz) camera as the imager and a 3.9 THz quantum-cascade laser (QCL) as the light source is demonstrated. The imaging light is collected and guided by only one off-axis parabolic mirror. The imaging distance is about 1 m. THz images of a coin and a knife are acquired and analyzed. An actual spatial resolution with a value of about 0.33 mm is achieved.

The low divergent Dammann grating is researched for the potential applications in aerospace. A laser-beam writing system is developed for writing the low divergent Dammann grating. The uniformity and efficiency of the Dammann grating are presented in this letter. The novelty of this letter is to demonstrate a low-cost and effective method to fabricate low divergent Dammann grating.

Compared to the traditional wavelength division multiplexing (WDM) optical networks with rigid and coarse granularities, flexible spectrum optical networks have high spectrum efficiency, which can support the service with various bandwidth requirements, such as sub and super channel. Among all network performance parameters, blocking probability is an important parameter for the performance evaluation and network planning in circuit-based optical networks including flexible spectrum optical networks. We propose an analytical method of blocking probability computation for flexible spectrum optical networks in this letter through mathematical analysis and theoretical derivation. Two blocking probability models are built respectively based on whether considering spectrum consecutiveness or not. Numerical results validate our proposed blocking probability models under different link capacity and traffic loads.

This study proposes a new hybrid Mach-Zehnder interferometric (MZI) sensor based on two core-offset attenuators and an abrupt taper in a single-mode fiber fabricated by a fiber-taper machine and electric arc discharge. When the distance between the two core-offset attenuators is stretched to 4500 mm, significant interference signals are detected with a prominent attenuation peak of ~28 dB. The proposed MZI can be used to measure temperature due to its low refractive index (RI) and strain cross-sensitivity. The temperature sensitivity is 34.95+(-)0.04 and 106.70+(-)0.04 pm/oC in the temperature ranges of 14-250 and 250-1000 oC, respectively.

We introduce a mathematical model based on a concept of intrinsic mode in order to analyse and synthesise optical wave propagation and radiation occurring in a non-uniform optical waveguide used in integrated optics as optical coupler. The model is based on numerical evaluation of electromagnetic wave by applying an intrinsic field integral to evaluate the field behaviour inside the optical waveguide. To analyse the field distribution inside the non-uniform waveguide and predict the beam propagation of optical energy involved in the propagation process, it is necessary to track the motion of any observation point along the tapered waveguide itself. Physically, the rays of the spectrum undergo reflections on the waveguide boundaries until the cut-off occurs and the phenomena of radiation begin. The numerical results show good agreement with those obtained by classical methods of evaluation used by other works.

We experimentally demonstrate a three-dimensional (3D) ghost imaging method based on period diffraction correlation imaging. Compared with conventional ghost imaging, our method can easily retrieve the images of different focal planes. Due to the correlation between the disturbed object beam and the reference beams which do not pass through any scattering, the clear images can be periodically obtained in the uncovered zones even through a scattering medium. The analysis of the 3D imaging resolution reveals that the proper resolution for actual demand can be achieved by designing our devices. The implementation of this experiment is quite simple and low-cost. It facilitates the practical applications of ghost imaging.

The fabrication deviation of prisms and the error crosstalk are two major factors that produce serious systematic errors in dual-beam roll measurement based on a rhombic prism, and an error compensation method is put forward in this letter to reduce these systematic errors. The rotation matrix, reflection matrix, and refraction matrix are used to calculate and obtain the mathematical relationship model of the roll angle as well as the fabrication deviation of prism and error crosstalk. The fabrication deviation can be obtained through comparison experiments and using the least square method. In this way, the systematic error of the roll measurement caused by fabrication deviation of prism and error crosstalk can be eliminated theoretically. The experimental results show that the maximum error of the roll angle measurement reduces evidently to 3.5′′ from the previous 347.2′′ after compensation.

A novel one dimensional periodic dielectric ring waveguide (PDRWG) is proposed and its dispersion properties are studied in details. Based on the proposed waveguide structure, a compact dual wavelength demultiplexer is designed. By a finite-difference time-domain (FDTD) simulation method, the performance of the designed device is calculated and analyzed. The dual wavelength demultiplexer can split the communication wavelengths of 1.31 and 1.55 mm into different waveguides and output from different ports with relative high transmittances of about 98% and 92%, respectively. The PDRWG may find applications in multi-wavelength demultiplexers or other novel integrated photonic devices.

The non-local optical interaction of two semiconductor microdisks with a waveguide bridged at radial direction is proposed and studied by three dimensional finite-difference time-domain (FDTD) electromagnetic simulations. The strong and weak optical interactions between two microdisks are observed and ascribed to the internal coupled modes with different coupling ratios. The vertical radiation losses and the related mode quality factors are modulated by waveguide length and present oscillation characteristics for the resonant modes. In addition, the optical leakage of coupling system is affected by the etching depth of disks due to the emission of minor components of electric field.

A new silica antireflective coating with improved hydrophobicity and optical stability in a vacuum is obtained by a two-step route. Firstly, silica sols are prepared with a sol-gel process, in which tetraethyl orthosilicate is utilized as a precursor. And by introduction of fluorine containing glycol into the sols, the porosity of silica particles and surface polarity of the coatings are decreased. Afterward, coatings are constructed with low surface roughness by modification of PMBA-PMMA. The coatings retain transmission of up to 99.6%, and laser damage threshold of about 50 J/cm2 at a wavelength of 532 nm (1-on-1, 10 ns).

A tunable luminescence from red to blue in Eu-doped mesoporous AlPO4 glass is achieved by adjusting the annealing temperature. With increasing annealing temperature, the increased Eu3+ ions reduction changes the luminescence of the obtained glass. The abnormal reduction of Eu3+ to Eu2+ occurs in AlPO4 mesoporous glass at relative low annealed temperatures from 600 to 800 oC in air. The presence of Eu2+ ions, which are reduced from Eu3+ by hole-electron pairs, is revealed by XPS spectra. Our results indicate the mesoporous AlPO4 glass is a suitable matrix to incorporate Eu ions as the tunable luminescent light sources or LEDs.

The focused ultrasound plays a role in localization and modulating the scattering light in ultrasound-modulated optical tomography (UOT). Both the modulation efficiency of the scattering light and the spatial resolution of UOT are determined by ultrasound. The effects of repetition frequency and pulse energy of impulse ultrasound on the modulated scattering light are derived through experiment in this letter. Furthermore, we compare the imaging sensitivity with 1, 2.25, 5, and 10 MHz center frequencies of impulse ultrasound. Experimental results demonstrate that better signal-to-noise ratios and higher sensitivities can be gained by use of more intense ultrasound and lower ultrasound frequencies.

Quantitative interferometric microscopy is an important method for observing biological samples such as cells and tissues. As a key step in phase recovery, a fast phase unwrapping algorithm is proposed. By shifting mod 2\pi wrapped phase map for one pixel, then multiplying the original phase map and the shifted one, the phase discontinuities could be easily determined with high speed and efficiency. The method aims at enhancing phase retrieving efficiency without any background knowledge. We test our algorithm with both numerical simulation and experiments, by focusing our attentions on wrapped quantitative phase maps of cells. The results indicate that this algorithm features fast, precise and reliable.

In conventional pulsed laser deposition (PLD) technique, plume deflection and composition distribution change with the laser incident direction and pulse energy, then causing uneven film thickness and composition distribution for a multicomponent film and eventually leading to low device quality and low rate of final products. We present a novel method based on PLD for depositing large CIGS films with uniform thickness and stoichiometry. By oscillating a mirror placed coaxially with the incident laser beam, the laser's focus is scanned across the rotating target surface. This arrangement maintains a constant reflectance and optical distance, ensuring that a consistent energy density is delivered to the target surface by each laser pulse. Scanning the laser spot across the target suppresses the formation of micro-columns, and thus the plume deflection effect that reduces film uniformity in conventional PLD technique is eliminated. This coaxial scanning PLD method is used to deposit a CIGS film, 500 nm thick, with thickness uniformity exceeding ±3% within a 5 cm diameter, and exhibiting a highly homogeneous elemental distribution.

We demonstrate an InP/InGaAs PIN photodetector with enhanced quantum efficiency by assembling silicon resonant waveguide gratings for the application of polarization sensitive systems. The measured results show that quantum efficiency of the photodetector with silicon resonant waveguide gratings can be increased by 31.6% compared with that without silicon resonant waveguide gratings at the wavelength range of 1500 to 1600 nm for TE-polarization.

Spin (polarization) is widely used in free-space optics, while in photonic integrated circuits (PICs), information is usually encoded in optical route. So a practical way to connect these two encoding methods is necessary for information communication. In this letter, an encoding convertor is designed to connect spin encoding and route encoding. Finite element method is used to calculate the conversion efficiency and extinction ratio of the encoding convertor and the theoretical analyses are also given. Our protocol shows a friendly way to convert optical spin information to route information, which will promote the compatibility of free-space optics and PICs.

In this letter, we analyze the effects of light intensity on reflective ghost imaging with thermal source. We find that the brightness of reflective ghost image can be changed by modulating the light intensity of the source and the splitting ratio of the beam splitter. The signal-to-noise ratio will be improved by increasing the light intensity of the source. More important, we can obtain the reflective ghost image with high image quality by adopting a low light intensity signal beam and a high light intensity reference beam, which is better than the classical optical imaging, because it can reduce the effects of light on the object.

High-speed light source is realized for decoy-state quantum key distribution (QKD) at telecom wavelength of 1.55 μm. By implementing two different electrical pulses together and triggering with 100 MHz pseudorandom number to drive the laser diode, the signal-state and the decoy-state pulses are prepared with identical pulse duration of 25 ps and similar spectral characteristics, avoiding the eavesdropper's attack by temporal and spectral analysis. The intensity fluctuation of the light source is quantified to satisfy the practical decoy-state QKD with random intensity error. The characteristics of the light source are analyzed with a high-speed single-photon detector.

An all fiber pulsed coherent Doppler lidar (CDL) system at 1.54 μm wavelength is developed for wind profiles measurements. This lidar affords 43.0-μJ pulse energy at 10-kHz pulse repetition frequency with 500-ns pulse width. The lidar is operated in monostatic mode with 50-mm diameter telescope. The heterodyne mixing signals are acquired with 500 M/s analog to digital converter and 2048 points fast Fourier transform (FFT) is implemented. Line of sight wind speeds are measured with more than 3.0-km range in a horizontal direction and about 1.9 km in the vertical direction with 75-m range resolution. Systematic error of speed measurement of 0.2 m/s is validated.

The stray radiation suppression in Cassegrain family optical system is presented. The design method for ultra-short outer baffle with honeycomb structure is proposed. Meanwhile the constraint formulas for designing the geometries of primary baffle and secondary baffle are deduced when basing the characteristic and taking vignette into account. According to the ray trace simulated data, the point source transmittance values of the baffle are less than 10-10 when incident angles are larger than the rejection angle. The honeycomb-look front baffle guarantees a comparable performance of stray light suppression with traditional tube baffle, while reducing the size greatly.

A novel method for preparing a luminescent solar concentrator (LSC) with fluorescent aqueous layer sandwiched between two pieces of flat glass is developed. By this method, an aqueous layer concentrator with a size of 78×78×7 (mm) is fabricated. After coupled with silicon solar cell, the concentrator shows a power conversion efficiency of 3.9%, about 30% higher than that of the same sized laminated glass concentrator employing the same dyes. Furthermore, the measured efficiency almost reaches the calculated limit of the aqueous layer LSC. This kind of aqueous layer LSC offers a potential application in the building-integrated photovoltaics.