Sandwiched photonic crystal fiber for dispersion compensation over the S + C + L + U wavelength bands.

We numerically investigated a sandwiched photonic crystal fiber (S-PCF) based on triangular lattice air holes that can be used for broadband dispersion compensation. By adjusting two layers of air holes diameter in the cladding, the S-PCF performs a large negative dispersion curve that can compensate for the dispersion of a standard single-mode fiber (SMF). The kappa value of the proposed PCF is also consistent with that of the SMF at the wavelength of 1.55 µm. In addition, the dispersion compensation multiple reaches up to 25.37. We have successfully obtained an effective compensated dispersion with the value of -0.5 to +0.1ps/nm/km in the wavelength of 1.46-1.67 µm, which covers the S+C+L+U wavelength bands. Moreover, we considered the manufacturing tolerance of the dispersion and effective compensated dispersion with ±2% and ±5% variation.

A Photonic crystal fiber with large effective refractive index separation and low dispersion.

A photonic crystal fiber (PCF) structure with a ring-core and 5 well-ordered semiellipse air-holes has been creatively proposed. Through a comparison between the structures with a high refractive index (RI) ring-core and the structure without, it conclude that a PCF with a high RI ring-core can work better. Schott SF57 was elected as the substrate material of ring-core. This paper compares the effects of long-axis and short-axis changes on the PCF and selects the optimal solution. Especially TE0,1 mode's dispersion is maintained between 0 and 3 ps / (nm · km) ranging from 1.45 µm to 1.65 µm. This property can be used to generate a supercontinuum with 200 µm long zero dispersion wavelength (ZDM). In addition, Δneff reaches up to 10-3, which enables the near -degeneracy of the eigenmodes to be almost neglected. The proposed PCF structure will have great application value in the field of optical communications.

Simultaneous measurement of optical rotation dispersion and absorption spectra for chiral substances.

We present a new method based on optical null methods for simultaneously measuring the optical rotatory dispersion (ORD) and absorption spectra of chiral substances. The optical rotation angle at a specific wavelength can be obtained from the optical nulls of the Malus curves with and without the sample. We use the optical nulls of the two curves as benchmark points and the readings to the right of the benchmark points by a certain angular offset to eliminate the influence of the analyzer on the light intensity and obtain the absorbance of the chiral substance at a specific wavelength. The 4096 pixels of the line scan CCD can measure multiple wavelengths simultaneously so that continuous ORD and absorption spectra can be obtained. The experimental results show that the standard deviation of the specific optical rotation is 0.11 deg mL g-1 dm-1 , the standard deviation of the maximum absorption wavelength is 0.45 nm, and that absorbance of the sample varies linearly with the concentration. This method is helpful for simplifying the experiment and has a profound influence on the analysis of the contents and molecular configurations of chiral substances in the future.

Theoretical proposal of a low-loss wide-bandwidth silicon photonic crystal fiber for supporting 30 orbital angular momentum modes.

We propose a novel four-ring hollow-core silicon photonic crystal fiber (PCF), and we systematically and theoretically investigate the properties of their vector modes. Our PCF can stably support 30 OAM states from the wavelength of 1.5 µm to 2.4 µm, with a large effective refractive index separation of above 1×10-4. The confinement loss is less than 1×10-9 dB/m at the wavelength of 1.55 µm, and the average confinement loss is less than 1×10-8 dB/m from the wavelength of 1.2 µm to 2.4 µm. Moreover, the curve of the dispersion tends to flatten as the wavelength increases. In addition, we comparably investigate PCFs with different hole spacing. This kind of fiber structure will be a potential candidate for high-capacity optical fiber communications and OAM sensing applications using fibers.

Equivalent model optimization with cyclic correction approximation method considering parasitic effect for thermoelectric coolers.

As thermoelectric coolers (TECs) have become highly integrated in high-heat-flux chips and high-power devices, the parasitic effect between component layers has become increasingly obvious. In this paper, a cyclic correction method for the TEC model is proposed using the equivalent parameters of the proposed simplified model, which were refined from the intrinsic parameters and parasitic thermal conductance. The results show that the simplified model agrees well with the data of a commercial TEC under different heat loads. Furthermore, the temperature difference of the simplified model is closer to the experimental data than the conventional model and the model containing parasitic thermal conductance at large heat loads. The average errors in the temperature difference between the proposed simplified model and the experimental data are no more than 1.6 K, and the error is only 0.13 K when the absorbed heat power Q c is equal to 80% of the maximum achievable absorbed heat power Q max . The proposed method and model provide a more accurate solution for integrated TECs that are small in size.

Novel method for determination of optical rotatory dispersion spectrum by using line scan CCD.

A novel method is presented for rapid measurement of optical rotatory dispersion (ORD). Light passes through a polarizer, sample and analyzer, to a transmission grating that disperses the collimated light beam. A step-motor rotating stage controlled by a digital signal processor changes the analyzer orientation. The light power is measured by a charge-coupled device (CCD) after each rotating-stage step. The optical rotation angle for each wavelength is determined from the shift between two Malus curves obtained from each CCD pixel. The ORD spectrum is obtained by transforming the optical rotation angle into specific rotation. The ORD spectrum for a standard quartz tube demonstrates good continuity and agreement with reference data.

Research of optical rotation measurement system based on centroid algorithm.

An optical rotation measurement system based on digital signal processor, modulated laser, and step motor rotating stage is established. Centroid algorithm featured fast and simple calculation is introduced to process light signals with or without sample to obtain the optical rotating angle through the step difference between two centroids. The system performance is proved experimentally with standard quartz tubes and glucose solutions. After various measurements, the relative error and precision of the system are determined to 0.4% and 0.004°, which demonstrates the reliable repeatability and high accuracy of whole measurement system.

Three-parameter error analysis method based on rotating coordinates in rotating birefringent polarizer system.

We propose error analysis using a rotating coordinate system with three parameters of linearly polarized light--incidence angle, azimuth angle on the front surface, and angle between the incidence and vibration planes--and demonstrate the method on a rotating birefringent prism system. The transmittance and angles are calculated plane-by-plane using a birefringence ellipsoid model and the final transmitted intensity equation is deduced. The effects of oblique incidence, light interference, beam convergence, and misalignment of the rotation and prism axes are discussed. We simulate the entire error model using MATLAB and conduct experiments based on a built polarimeter. The simulation and experimental results are consistent and demonstrate the rationality and validity of this method.

Generation of cylindrically symmetric modes and orbital-angular-momentum modes with tilted optical gratings inscribed in high-numerical-aperture fibers.

Optical fiber with high numerical aperture (NA) can efficiently relieve the degeneracy of higher-order linearly polarized modes. The degeneracy relief is investigated in two types of high-NA fibers, i.e., low-index-cladding fiber and high-index-core fiber. A naked-core fiber, as with low-index cladding, can be used theoretically to generate the orbital-angular-momentum mode (OAMM) HE21 and the cylindrically symmetric modes (CSMs) TM01 and TE01. A high-index-core fiber incorporated with high-contrast-index structure can be used similarly to obtain OAMM HE31. The generation of both CSMs and OAMMs required tilted optical gratings to couple the fundamental core mode HE11 into these modes. The tilt angle and modulation period of the grating fringes can be calculated simply and visually with the method proposed in this article.

Mode add/drop multiplexers of LP02 and LP03 modes with two parallel combinative long-period fiber gratings.

Two parallel combinative long-period fiber gratings (LPFGs) can convert the fundamental core mode LP(01) in a single-mode fiber (SMF) into one desired higher order core mode LP(0m) in a few-mode fiber (FMF), in the process of which one specific cladding mode acts as a medium coupled from one fiber to another. Different LP(0m) modes can be obtained by controlling the grating period of LPFG in FMF to meet the phase matching condition. In this article we focus on the design and analyses of LP(02) and LP(03) mode add / drop multiplexers (MADMs). This device has some advantages of facile and good scalability, and particularly, of eliminating coupling interferences for the ahead multiplexed modes by the posterior MADMs or couplers. Furthermore, the conversion rate of mode power theoretically can approach as much as 98%and the 3dB bandwidth can reach 10nm or more.

Correction of image distortions in endoscopic optical coherence tomography based on two-axis scanning MEMS mirrors.

A two-axis scanning microelectromechanical (MEMS) mirror enables an optical coherence tomography (OCT) system to perform three-dimensional endoscopic imaging due to its fast scan speed and small size. However, the radial scan from the MEMS mirror causes various distortions in OCT images, namely spherical, fan-shaped and keystone distortions. In this paper, a new method is proposed to correct all of three distortions presented in OCT systems based on two-axis MEMS scanning mirrors. The spherical distortion is corrected first by directly manipulating the original spectral interferograms in the phase domain, followed by Fourier transform and three-dimensional geometrical transformation for correcting the other two types of distortions. OCT imaging experiments on a paper with square ink printed arrays and a glass tube filled with milk have been used to validate the proposed method. Distortions in OCT images of flat or curved surfaces can all be effectively removed.

Endoscopic swept-source optical coherence tomography based on a two-axis microelectromechanical system mirror.

A microelectromechanical system (MEMS) mirror based endoscopic swept-source optical coherence tomography (SS-OCT) system that can perform three-dimensional (3-D) imaging at high speed is reported. The key component enabling 3-D endoscopic imaging is a two-axis MEMS scanning mirror which has a 0.8×0.8 mm2 mirror plate and a 1.6×1.4 mm2 device footprint. The diameter of the endoscopic probe is only 3.5 mm. The imaging rate of the SS-OCT system is 50 frames/s. OCT images of both human suspicious oral leukoplakia tissue and normal buccal mucosa were taken in vivo and compared. The OCT imaging result agrees well with the histopathological analysis.

Improving the accuracy of optical rotation measurement based on optical null methods by curve-fitting.

An optical rotation measuring system using optical null methods is set up. The system is based on a step-motor rotating stage structure and a modulated laser, which both are controlled by digital signal processor. By introducing a curve-fitting method, the optical rotation angle is obtained from the step difference between the crossed positions in light signal curves with or without sample. The principle of this method is studied, and the system performance is investigated experimentally. We achieved an accuracy of the order of 10(-3) degree in at least ±45° range, which is an improvement compared with the resolution of 0.01° for step-motor rotation stage.

[Determination of optical parameters in thin films by transmittance spectra].

The high tin-doped SiO2 films prepared by CVD will bring some crystals, but sol gel can control the accurate chemical component of the films. So it can produce high tin-doped materials. In the present paper, the tin-doped SiO2 films were prepared by a sol gel dip-coating process on glass substrates at concentrations of 66 mol% and 75 mol%. Then dipping was performed several times to enhance the thickness of the films. The transmittance spectrum was obtained by spectrophotometer. Compared with the films prepared in a thin film on a thick substrate previously, the model here has been modified to describe the transmittance of a thick film (substrate) sandwiched between two thin films (coating method). The authors used the curves method to calculate the film's parameters. The result showed that uhe refractive index of different samples was increased with the wave-length. And the film thickness was about 900 nm.

[Structure changes of lead silicate glasses induced by UV laser irradiation].

The structure changes of lead silicate glasses induced by UV laser irradiation were studied by UV-visible spectra and electron spin resonance (ESR). The Urbach energies of lead silicate glasses exposed to the 266 nm UV laser increased. This implied that the disorder of the lead silicate glasses was increased. The electron spin resonance experiments showed that the oxygen deficiency centers in lead silicate glass did not change to paramagnetic defects after exposure to 266 nm laser beam, and the absorption peak near 235 nm for lead silicate glass film did not change either. But this absorption peak was bleached after exposure to the 248 nm UV laser.