A simple, compact, low-cost, highly efficient thermometer based on green fluorescence of Er3+/Yb3+-codoped NaYF4 microcrystals.

We developed a highly efficient optical thermometer based on intensity ratio of upconversion green fluorescence of Er3+/Yb3+-codoped NaYF4 microcrystals. The sensor consists simply of a 980nm laser diode, one narrow-band interference filter, two lenses, one Si-photocell and one multimeter, while being without use of spectrometer and additional electronics. The device not only has a simple, compact structure (hence a low cost), but also displays highly efficient sensing performance, characterized by large signal-to-noise ratio due to strong fluorescence intensity, high thermal resolution and sensitivity, which have the values 1.3K and 1.24×10-2K-1, respectively, at the physiological temperature 310K. The excellent sensing performance of the device was further confirmed by the results of the measurements repeated using a spectrometer. The thermometer is highly generalized that can be applied to other luminescent materials, and shows great potential for the physiological temperature sensing in biological tissues and cells.

Optical damage resistant Ti-diffused Zr/Er-codoped lithium niobate strip waveguide for high-power 980 nm pumping.

Ti4+-diffused Zr4+/Er3+-codoped LiNbO3 strip waveguide was fabricated on an X-cut LiNbO3 substrate by thermal diffusion in sequence of Er3+, Zr4+ and Ti4+. Secondary ion mass spectrometry study shows that the Ti4+ ions follow a sum of two error functions in the width direction and a Gauss function in the depth direction of the waveguide. Both Er3+ and Zr4+ profiles follow the desired Gauss function, and entirely cover the Ti4+ profile. Optical study shows that the waveguide is TE or TM single mode at 1.5 µm wavelength, and has a loss of 0.3 (0.5) dB/cm for the TM (TE) mode. In the case of 980 nm pumping, the waveguide shows stable 1547 nm signal output under high-power pumping without optical damage observed, and a net gain of 1.1 dB/cm is obtained for the available pump power of 120 mW.

Note: Electro-optic coefficients of Li-deficient MgO-doped LiNbO3 crystal.

A number of Li-deficient MgO-doped LiNbO3 (LN) crystals with different Li2O contents ranging from 43.4 mol. % to 44.5 mol. % were prepared by carrying out the Li-poor vapor transport equilibration treatment on 5 mol. % (in growth melt) MgO-doped LN crystals. Unclamped electro-optic (EO) coefficients γ13 and γ33 of these crystals were measured by Mach-Zehnder interferometry. The results show that γ13 (γ33) increases linearly by ∼14% (11%) as the Li2O content decreases from 44.5 mol. % of the as-grown state to 43.4 mol. % of the Li-deficient state. This feature is desired for the EO application of the Li-deficient MgO:LN crystal.

Eigenspace-Based Generalized Sidelobe Canceler Beamforming Applied to Medical Ultrasound Imaging.

The use of a generalized sidelobe canceler (GSC) can significantly improve the lateral resolution of medical ultrasound systems, but the contrast improvement isn't satisfactory. Thus a new Eigenspace-based generalized sidelobe canceler (EBGSC) approach is proposed for medical ultrasound imaging, which can improve both the lateral resolution and contrast of the system. The weight vector of the EBGSC is obtained by projecting the GSC weight vector onto a vector subspace constructed from the eigenstructure of the covariance matrix, and using the new weight vector instead of the GSC ones leads to reduced sidelobe level and improved contrast. Simulated and experimental data are used to evaluate the performance of the proposed method. The Field II software is applied to obtain the simulated echo data of scattering points and circular cysts. Imaging of scattering points show that EBGSC has the same full width at half maximum (FWHM) as GSC, while the lateral resolution improves by 35.3% and 52.7% compared with synthetic aperture (SA) and delay-and-sum (DS), respectively. Compared with GSC, SA and DS, EBGSC improves the peak sidelobe level (PSL) by 23.55, 33.11 and 50.38 dB, respectively. Also the cyst contrast increase by EBGSC was calculated as 16.77, 12.43 and 26.73 dB, when compared with GSC, SA and DS, respectively. Finally, an experiment is conducted on the basis of the complete echo data collected by a medical ultrasonic imaging system. Results show that the proposed method can produce better lateral resolution and contrast than non-adaptive beamformers.

Polarization-insensitive, shallow Ti-diffused near-stoichiometric LiTaO3 strip waveguide for integrated optics.

We report on a Ti-diffused near-stoichiometric (NS) LiTaO3 strip waveguide fabricated by diffusion of an 8 µm wide, 160 nm thick Ti-strip followed by Li-rich vapor transport equilibration. It is found that the waveguide surface caves in ∼60 nm below the crystal surface. X-ray single-crystal diffraction shows that the indentation is due to Ti-induced lattice contraction. Optical studies show that the waveguide is in an NS composition environment, supports TE and TM single-mode propagation at 1.5 µm wavelength, is polarization insensitive, and has a shallow mode field profile and a loss of 0.2/0.3 dB/cm for the TE/TM mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. With the optimized fabrication condition, the waveguide is promising for developing an optical-damage-resistant device that requires a shallow mode field profile.

Near-stoichiometric Ti-diffused LiNbO(3) strip waveguide doped with Zr(4+).

We report a near-stoichiometric Ti:Zr:LiNbO(3) strip waveguide fabricated from a congruent substrate with a technological process in the following sequence: Zr4+-diffusion-doping, diffusion of 8-µm-wide, 100-nm-thick Ti strips, and post-Li-rich vapor transport equilibration. We show that Zr(4+)-doping has little effect on the LiNbO(3) refractive index, and the waveguide is in a near-stoichiometric environment. The waveguide well supports both the TE and TM modes, shows weak polarization dependence, is in single mode at the 1.5 µm wavelength, and has a loss of ≤0.6/0.8 dB/cm for the TE/TM modes. A secondary ion mass spectrometry analysis shows that the Zr(4+)-profile part with a concentration above the threshold of photorefractive damage entirely covers the waveguide, implying that the waveguide would be optical-damage resistant.

Electro-optically tunable super-broadband filter based on long period grating in Ti:LiNbO3 waveguide.

We report an electro-optically tunable optical filter based on a parallel structure of two long period gratings in the two same Ti:LiNbO3 strip waveguides: one 675-µm-pitch grating in one waveguide and another 880-µm-pitch grating in the other waveguide. The stop-band is observed in the 1.1-1.3 (1.4-1.6) µm spectral region for the grating pitch 675 (880) µm. Its contrast increases linearly to ∼30 dB as the voltage is increased to 300 V, and the linearity is similar for the two cases of 675 and 880 µm pitches. Higher than 300 V, the contrast decreases due to photorefractive (PR) effect and/or over-coupling. Accompanying the contrast modulation, the resonant wavelength is simultaneously linearly tuned by making use of the PR effect. For the 675 (880) µm pitch, the tuning range is 160 (200) nm for the 400 (300) V voltage change range. With the two gratings, one can realize >360 nm super-broadband filtering.

Dispersion compensation for FD-OCT using spectrum reconstruction.

BACKGROUND: In OCT system, the chromatic dispersion of sample decreases the resolution and increases the depth misplacement. The developed numerical dispersion compensation techniques usually do not consider the higher order dispersion and time-consuming. OBJECTIVE: We proposed a numerical compensation technique for correcting depth error and resolution deterioration in Fourier domain optical coherence tomography (FD-OCT). METHODS: Firstly, the rough depth of each scatter in multilayer sample is estimated through magnification curve. Then the depth of a scatter is iterated to minimum the residual of this scatter in the time domain. At last, the spectrum of the scatter is reconstructed and dispersion can be compensated with the tracked depth. RESULTS: The results show that the depth error is corrected to less than resolution level and the resolution is corrected to nearly ideal. CONCLUSIONS: The technique proposed can provide precise sample tomography, thus enhancing the understanding of sample character.

Diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals.

Diffusion-doping is an effective, practical method to improve material properties and widen material application. Here, we demonstrate a new physical phenomenon: diffusion control of an ion by another in LiNbO3 and LiTaO3 crystals. We exemplify Ti(4+)/X(n+) (X(n+) = Sc(3+), Zr(4+), Er(3+)) co-diffusion in the widely studied LiNbO3 and LiTaO3 crystals. Some Ti(4+)/X(n+)-co-doped LiNbO3 and LiTaO3 plates were prepared by co-diffusion of stacked Ti-metal and Er-metal (Sc2O3 or ZrO2) films coated onto LiNbO3 or LiTaO3 substrates. The Ti(4+)/X(n+)-co-diffusion characteristics were studied by secondary ion mass spectrometry. In the X(n+)-only diffusion case, the X(n+) diffuses considerably slower than the Ti(4+). In the Ti(4+)/X(n+) co-diffusion case, the faster Ti(4+) controls the diffusion of the slower X(n+). The X(n+) diffusivity increases linearly with the initial Ti-metal thickness and the increase depends on the X(n+) species. The phenomenon is ascribed to the generation of additional defects induced by the diffusion of faster Ti(4+) ions, which favors and assists the subsequent diffusion of slower X(n+) ion. For the diffusion system studied here, it can be utilized to substantially shorten device fabrication period, improve device performance and produce new materials.

A time delay correction technique for SS-OCT.

BACKGROUND: K-trigger signals from light source or external Mach-Zehnder interferometer are commonly used in swept source optical coherence tomography (SS-OCT) to achieve interference signal sampling and resolution enhancement. But extra signal transmission time is required due to the increased complexity of interference system using k-trigger signals, resulting in a misalignment (a.k.a., time delay) between the k-trigger and the interference signals. OBJECTIVE: The objective of this paper is to propose a numerical technique to correct the time delay between these two signals. METHODS: The time delay is iterated in this technique and each iterated correction result is evaluated through calculating the full width at half maximum (FWHM) of peaks in time-domain. The precise alignment between the k-trigger and interference signals coincides with the minimum value of FWHM. RESULTS: The experimental results show that the FWHM can be improved by up to 50% using this time delay correction technique. CONCLUSIONS: The proposed technique assists to provide precise sample tomography, thus enhancing the way of understanding sample characteristic.

Sparse CT reconstruction based on multi-direction anisotropic total variation (MDATV).

BACKGROUND: The sparse CT (Computed Tomography), inspired by compressed sensing, means to introduce a prior information of image sparsity into CT reconstruction to reduce the input projections so as to reduce the potential threat of incremental X-ray dose to patients' health. Recently, many remarkable works were concentrated on the sparse CT reconstruction from sparse (limited-angle or few-view style) projections. In this paper we would like to incorporate more prior information into the sparse CT reconstruction for improvement of performance. It is known decades ago that the given projection directions can provide information about the directions of edges in the restored CT image. ATV (Anisotropic Total Variation), a TV (Total Variation) norm based regularization, could use the prior information of image sparsity and edge direction simultaneously. But ATV can only represent the edge information in few directions and lose much prior information of image edges in other directions. METHODS: To sufficiently use the prior information of edge directions, a novel MDATV (Multi-Direction Anisotropic Total Variation) is proposed. In this paper we introduce the 2D-IGS (Two Dimensional Image Gradient Space), and combined the coordinate rotation transform with 2D-IGS to represent edge information in multiple directions. Then by incorporating this multi-direction representation into ATV norm we get the MDATV regularization. To solve the optimization problem based on the MDATV regularization, a novel ART (algebraic reconstruction technique) + MDATV scheme is outlined. And NESTA (NESTerov's Algorithm) is proposed to replace GD (Gradient Descent) for minimizing the TV-based regularization. RESULTS: The numerical and real data experiments demonstrate that MDATV based iterative reconstruction improved the quality of restored image. NESTA is more suitable than GD for minimization of TV-based regularization. CONCLUSIONS: MDATV regularization can sufficiently use the prior information of image sparsity and edge information simultaneously. By incorporating more prior information, MDATV based approach could reconstruct the image more exactly.

An adaptive 6-DOF tracking method by hybrid sensing for ultrasonic endoscopes.

In this paper, a novel hybrid sensing method for tracking an ultrasonic endoscope within the gastrointestinal (GI) track is presented, and the prototype of the tracking system is also developed. We implement 6-DOF localization by sensing integration and information fusion. On the hardware level, a tri-axis gyroscope and accelerometer, and a magnetic angular rate and gravity (MARG) sensor array are attached at the end of endoscopes, and three symmetric cylindrical coils are placed around patients' abdomens. On the algorithm level, an adaptive fast quaternion convergence (AFQC) algorithm is introduced to determine the orientation by fusing inertial/magnetic measurements, in which the effects of magnetic disturbance and acceleration are estimated to gain an adaptive convergence output. A simplified electro-magnetic tracking (SEMT) algorithm for dimensional position is also implemented, which can easily integrate the AFQC's results and magnetic measurements. Subsequently, the average position error is under 0.3 cm by reasonable setting, and the average orientation error is 1° without noise. If magnetic disturbance or acceleration exists, the average orientation error can be controlled to less than 3.5°.

A new algorithm for calculating optimal viewing angles in coronary angiography based on 4-D cardiac computed tomography.

BACKGROUND: Coronary stenosis is the main cause of the coronary heart disease (CHD). However, coronary arteriography (CAG), which is considered as the 'gold standard' of determining the location and severity of CHD, hardly acquires a satisfactory image for some lesions by traditional viewing angles. OBJECTIVE: We proposed a new approach to calculate the optimal viewing angles of CAG system to observe vessel segment of interest. METHODS: Firstly, the 4-D coronary arteries are segmented to obtain a dynamic vessel model. Then, a "rendering" method in computer graphics is used to calculate the optimal viewing angles of the vessel segment in the entire cardiac cycle. At last, an intersection of these angles can be regarded as the optimal ones in the whole cardiac cycle. RESULTS: Within the constraint of 2% foreshortening, the single phase data show 1% foreshortening without overlapping at the optimal angles proposed by our method, compared with 1.8% foreshortening at working angles set by clinical experts. And the multi-phase experiments also have good results. CONCLUSIONS: The new approach can provide doctors optimal viewing angles of interested vessel segment in the whole cardiac cycle.

Appropriate solvent NaVO3 for composition analysis of LiNbO3 crystal using chemical method.

It is crucial to find an appropriate solvent for composition analysis of LiNbO(3) crystal by a chemical method, such as inductively coupled plasma atomic emission spectroscopy. We have comparatively studied several solvents for LiNbO(3) crystal, including HF acid, KHSO(4), B(2)O(3), LiBO(2), and NaVO(3). The results show that as the NaVO(3) is used as the solvent, the solubility of LiNbO(3) is as high as 1 g/g at 1000 °C. The dissolving is quite fast. Neither solute nor solvent is lost from the melting during the dissolving procedure. A clear high-concentration solution is obtained. Moreover, it is verified experimentally that such a solution is valid for composition analysis of LiNbO(3) crystal by a chemical method. In contrast, the other solvents suffer from one problem or another. We conclude that NaVO(3) is an appropriate solvent for chemical analysis of LiNbO(3).

Synthetic aperture focusing for medical endoscopic ultrasonography.

A new approach for synthetic aperture focusing (SAF) to enhance both signal to noise ratio (SNR) and resolution in endoscopic ultrasonography is presented in this paper. The technique uses the rotation feature of single element transducer probe, and transmits and receives the echoes at different time and locations during the rotary scanning. Based on theoretical simulation, axial and lateral matched-filters are developed according to the coded and linear frequency modulated characteristics of the echoes to implement axial and lateral compression. The effects of SNR and resolution enhancements by the new SAF approach are demonstrated by both Field II simulation and sample experiment. Data for 6 point targets are simulated and the performance of SAF is compared with those from conventional imaging method and Delay-and-Sum (DS) method. Pigskin samples are examined by a single element transducer at 8 MHz. The effects of sound speed errors and rotary scanning speed errors on both SNR and resolution are calculated to show the robustness of SAF algorithm. Both simulation and experimental results indicated that new SAF can improve SNR and resolution of ultrasound images by 9.38 dB and 51% respectively as compared with the conventional method. It therefore has potential for future clinical and research applications.

[Coded excitation circuit on medical ultrasonic endoscope imaging system].

In this paper, we introduce a coded excitation circuit for medical ultrasonic endoscope imaging system. This circuit is composed of TC6320 and its drive chip. The experiment demonstrates that this circuit can export frequency-adjustable, duration-controllable coded signals, and its voltage reaches +/-60 V. It still works well when excitant frequency reaches 30 MHz. Compared with the conventional medical ultrasonic pulse-echo imaging system, this coded excitation system has the potential of higher SNR and deeper penetration depth, especially for the small emission power system. This method has a bright future.

[Digital scanning converter for medical endoscopic ultrasound imaging].

This paper mainly introduces the design of digital scanning converter (DSC) for medical endoscopic ultrasound imaging. Fast modified vector totational CORDIC (FMVR-CORDIC) arithmetic complete coordinate conversion is used to increase the speed of ultrasonic scanning imaging. FPGA is used as the kernel module to control data transferring, related circuits and relevant chips' working, and to accomplish data preprocessing. With the advantages of simple structure, nice flexibility and convenience, it satisfies the demand for real-time displaying in this system. Finally, the original polar coordinate image is transformed to rectangular coordinate grey image through coordinate transformation. The system performances have been validated by the experimental result.

[RovoIving ultrasonic probe for medical endoscope imaging system based on USB2.0].

This paper mainly introduces the design and implementation of rotary scanning imaging for Endoscopic Ultrasonography System based on USB2.0. The ultrasonic pulse-echo imaging technique has been used. In the paper, we simply introduce the emission circuit, receiving circuit and isolation circuit. According to the character of rotary scanning, we design the synchronous control circuit based on FPGA and data transmission circuit based on USB2.0. Finally the original polar coordinate image is transformed to rectangular coordinate grey image through coordinate transformation. The system performances have been validated by the experimental result gotten by scanning a specific object with continuous rotary motor.

Observation of quantum interference between a single-photon state and a thermal state generated in optical fibers.

We experimentally demonstrate a Hong-Ou-Mandel type of two-photon interference effect with a heralded single-photon state and a thermal state. The light sources in the 1550 nm telecom band are generated from two independent dispersion-shifted fibers via four-wave mixing process. The observed visibility is (82+/- 11)%. This type of interference between independent sources is crucial in quantum information process with independent qubits.

Spectral study of photon pairs generated in dispersion shifted fiber with a pulsed pump.

Spectral correlation of photon pairs generated in dispersion shifted fiber by a pulsed pump is theoretically analyzed and experimentally investigated. We first calculate the spectral function of photon pairs according to the deduced two-photon state generated by spontaneous four wave mixing under the assumptions close to the real experimental conditions. We then experimentally study the spectral property of the signal and idler photon pairs generated in optical fiber by photon correlation measurements, and the experimental results agree with the calculation. The investigation is useful for developing fiber-based sources of entangled photon pairs and for studying multi-photon quantum interference with multiple photon pairs.