A scheme for measuring a small variation rate of the refractive index (RI) based on orbital angular momentum (OAM) interferometry and time-frequency analysis is proposed and demonstrated in this paper. Two vortex beams carrying OAM of opposite signs are used for interference to produce a petal-like intensity distribution. The variation in RI of the sample leads to a time variable phase delay between the reference and measurement paths, and causes the rotation of the petal-like spots. The rotation angular velocity of the petal-like spots is proportional to the RI variation rate, the normalized cross correlation method is used to estimate it. Then, a time-frequency analysis method is employed to study the time evolution of the variation rate of RI. Three kinds of RI models with different variation rates are simulated and the results are consistent with expectations. The proposed measurement method is simple in structure, and extends a new approach to detect other physical coefficients of RI or the tiny velocity.
We propose and demonstrate a simple method to generate an all-fiber CVBs and LP01 mode switchable laser using a few-mode fiber Bragg grating. A few-mode circulator is used to output the excited high-order modes. By adjusting the temperature to change the laser wavelength in the cavity, switching of the fundamental mode and the radial and azimuthally polarized laser is realized and their efficiencies are 10.76% and 5.55%, respectively. The purity of the radial and the azimuthally polarized beam is higher than 98%. The working wavelength of the radial and the azimuthally polarized beam is 1549.6nm. The 30 dB bandwidth is less than 0.15 nm, and the side mode suppression ratio is more than 73dB.
We propose and demonstrate a method to generate and detect high-order Poincaré sphere beams. By adjusting the input homogeneous polarization states, arbitrary high-order Poincaré sphere beams are obtained. A one-to-one correspondence between the traditional Poincaré sphere beams and high-order Poincaré sphere beams is represented. The generation and detection of the high-order Poincaré sphere beams are realized simultaneously. Our research is helpful to deepen the understanding of the polarization states of light beams and provide useful ideas for the handling of optical experiments.
We propose and demonstrate a simple method to generate an all-fiber high-order transverse-mode switchable laser using a few-mode Bragg fiber grating (FM-FBG). The switchable output of the LP02 mode, LP11 mode, and LP01 modes is precisely realized by adjusting the operating wavelength in the cavity, which breaks through the limitation of only two low-order modes in most reports about all-fiber transverse-mode switchable lasers. The slope efficiencies for the three modes are 2.5%, 5.9%, and 9.3%, respectively. The central wavelengths of the lasers are 1530.2 nm, 1531.3 nm, and 1532.1 nm, respectively, and the corresponding side mode suppression ratios are -61 dB, -67 dB, and -65 dB, which ensures the purity of the modes. This work has huge potential applications in sensing, mode division multiplexing, optical communication, laser processing, and surface plasmon excitation.
Recently, the development of augmented reality (AR)/ virtual reality (VR) has brought new life to holographic display. Holographic Maxwellian display technology, also known as holographic retinal projection display (RPD), is considered as a promising AR near-eye display technology. It can provide consistently sharp two-dimensional images within a range of depth of field without being affected by human eye focusing. Several recent works of holographic Maxwellian near- eye display are introduced. Firstly, we have proposed a hybrid holographic Maxwellian near-eye display based on spherical wave and plane wave reconstruction to extend the depth of field. Secondly, we have proposed a lensless full- color holographic Maxwellian near-eye display with horizontal eyebox expansion using a single spatial light modulator (SLM). Thirdly, we have proposed a conjugate wavefront encoding method to efficiently expand the eyebox for the holographic Maxwellian near-eye display.
We demonstrate a random fiber laser with cylindrical vector beams (CVBs) emission. A 9-km-long fiber is applied to form one of the laser mirrors providing random distributed feedback (RDFB). Due to the RDFB provided by the ultralong fiber, mode competitions are well suppressed in the cavity leading to the laser output with modeless behavior. A mode selective coupler (MSC) inserted in the cavity is used to achieve the mode conversion from fundamental mode to cylindrical vector modes. By adjusting the mechanical polarization controllers carefully, both azimuthally and radially polarized beams are achieved with high mode purity. The designed laser retains many advantages of the random lasers, such as low cost and modeless output. The CVBs with modeless behavior may be useful in many practical applications such as biomedical imaging, laser radars and free space communication.
With the development of ultra-high definition television (UHDTV), an effective gamut mapping algorithm (GMA) from high-definition television (HDTV) to UHDTV is vital. In this paper, we propose a hue-preserved GMA in the CIELCH color space. To balance the restriction between the color difference and the utilization rate of gamut, a mapping method based on barycenter transformation is used. With this algorithm, the color signals for HDTV can be applicable to UHDTV and the image quality can be improved significantly.
In this paper, a laser speckle contrast imaging (LSCI) system using light field (LF) microscope approach is proposed. As far as we known, it is first time to combine LSCI with LF. To verify this idea, a prototype consists of a modified LF microscope imaging system and an experimental device was built. A commercially used Lytro camera was modified for microscope imaging. Hollow glass tubes with different depth fixed in glass dish were used to simulate the vessels in brain and test the performance of the system. Compared with conventional LSCI, three new functions can be realized by using our system, which include refocusing, extending the depth of field (DOF) and gathering 3D information. Experiments show that the principle is feasible and the proposed system works well.
We demonstrate a new method to detect the vortex beams carrying orbital angular momentum (OAM) by a sectorial screen. When the sectorial screen is illuminated with vortex beams, the far-field diffraction pattern can be used to define the modulus and sign of topological charges. The number of the petals denotes the number of topological charge. The direction of intensity pattern flip by 180° for a change in the sign of topological charge. The experimental results agree well with the simulated results.
Based on a few-mode fiber Bragg grating as polarization-selective output coupler and topological insulators Bi2Te3 as the saturable absorber, we propose a passively Q-switched fiber laser with cylindrical vector beam output. Both radially and azimuthally polarized beams can be readily generated, and the output polarization can be switchable through tuning the polarization controllers inside the laser cavity. The laser operates at the wavelength of 1557.5 nm with a 3 dB linewidth of less than 0.04 nm. The repetition rate of the Q-switched laser can be tuned from 31.54 kHz to 49.40 kHz when the pump power increases from 103.5 mW to 139.5 mW.
A thin and lensless two-dimensional (2D) to three-dimensional (3D) convertible display based on integral imaging using an edge-lit light guide plate (LGP) is proposed with improved optical efficiency. The proposed system is composed of a general flat backlight and an edge-lit LGP which is commonly used in the backlight of LCD and a LC panel. The edge lit LGP is a waveguide (an acrylic sheet) that is drilled by laser to form a diffuser dot array at the bottom and edge illuminated with LEDs. Light from the LEDs is channeled through the waveguide to the opposite side except where it encounters the diffuser dots, which scatter light and cause bright spots to appear. A point light source array for 3D mode is created then. A general flat backlight behind the transparent LGP is turned on for 2D mode meanwhile edge-lit light is turned off. The 2D and the 3D display modes can be simply modulated by turning on different light source. The explanation of the proposed system is provided and the experimental results are also presented.
We demonstrated an all fiber actively mode-locked laser emitting cylindrical vector beam. A few-mode fiber Bragg grating is adopted to achieve mode selecting and spectrum filtering. An offset splicing of single-mode fiber with fourmode fiber is utilized as a mode coupler in the laser cavity. A LiNbO3 Mach-Zehnder modulator is used to achieve active mode locking in the laser. The laser operates at 1547nm with 30 dB spectrum width of 0.3nm. The emitted modelocked pulses have a duration of 1ns and repetition of 12.06MHz. Both radially and azimuthally polarized beams have been obtained with very good modal symmetry by adjusting the polarization in the laser cavity.
We have proposed and demonstrated a nanosecond square-wave fiber laser working in the 1060nm band. The passively
mode-locked fiber laser based on the nonlinear optical loop mirror has a peak power clamping effect which leads to the
generation of nanosecond square-wave pulses. To investigate the spectrum width of the nanosecond square-wave pulse
laser, we added couplers with different coupling ratio to the bidirectional ring of the figure-8 fiber laser and analyzed the
laser output. The results show that a higher output coupling ratio leads to stronger peak power clamping effect, and the
peak power of the square-wave pulse gets lower and the corresponding spectrum band width is narrower.
In this paper, a new integral imaging method is proposed for depth extraction in an optical tweezer system. A mutual coherence algorithm of stereo matching are theoretically analyzed and demonstrated feasible by virtual simulation. In our design, optical tweezer technique is combined with integral imaging in a single microscopy system by inserting a lens array into the optical train. On one hand, the optical tweezer subsystem is built based on the modulated light field from a solid laser, and the strong focused beam forms a light trap to capture tiny specimens. On the other hand, through parameters optimization, the microscopic integral imaging subsystem is composed of a microscope objective, a lens array (150x150 array with 0.192mm unit size and 9mm focal length) and a single lens reflex (SLR). Pre-magnified by the microscope objective, the specimens formed multiple images through the lens array. A single photograph of a series of multiple sub-images has recorded perspective views of the specimens. The differences between adjacent sub-images have been analyzed for depth extraction with the mutual coherence algorithm. The experimental results show that the axial resolution can reach to 1μm -1 and lateral resolution can reach to 2 μm -1.
In this paper, the relationship between the spatial coherence of light field and the speckle contrast in a laser based projection display system is studied under the consideration of human visual percept. By using a varifocal liquid-crystal lens and a monochromatic CCD, a system which is used for simulating the human eye is set up to record the speckle pattern. An efficient method for controlling the spatial coherence by using a dielectric elastomer actuator (DEA) is proposed. The results show that the total efficiency for energy utilization is more than 60% during our experiment. When the distance between the observer and the screen is large enough (<3 meters), the speckle contrast can be eliminated well at last (<4%) and the observer won’t feel the speckle phenomenon.
In this paper, the laser speckle pattern on human retina for a laser projection display is simulated. By introducing a
specific eye model ‘Indiana Eye’, the statistical properties of the laser speckle are numerical investigated. The results
show that the aberrations of human eye (mostly spherical and chromatic) will decrease the speckle contrast felt by
people. When the wavelength of the laser source is 550 nm (green), people will feel the strongest speck pattern and the
weakest when the wavelength is 450 nm (blue). Myopia and hyperopia will decrease the speckle contrast by introducing
large spherical aberrations. Although aberration is good for speckle reduction, but it will degrade the imaging capability
of the eye. The results show that laser source (650 nm) will have the best image quality on the retina. At last, we
compare the human eye with an aberration-free imaging system. Both the speckle contrast and the image quality appear
different behavior in these two imaging systems. The results are useful when a standardized measurement procedure for
speckle contrast needs to be built.
A classical iterative Lucy-Richardson (LR) inversion algorithm used for recovering particle-size distributions (PSD) from light-scattering data is proposed. The convergence of iteration is validated in the numerical simulation for three different distributions: the gamma, the log-normal, and the Rosin-Rammler. The accuracy of the inversion is checked graphically against the exact distribution with good results, even for the synthesized intensity data of a signal-noise-ratio smaller than 20 dB. Finally, an experiment with linear charge coupled device as the detector is carried out, and the PSD is recovered successfully by the LR inversion method.
Based on the few-mode fiber Bragg grating’s reflection characteristics, we propose and demonstrate a transverse modes switchable fiber laser fiber laser, fundamental mode and 1st higher order modes, and the states be switched by tuning the laser’s oscillating wavelength. The radial vector beam is also obtained by splitting the degenerated 1st higher order modes.
Stacking chirped pulse has been studied on its shape ability. When it propagates in single-mode fiber, the nonlinear
effects become very significant because of high peak power. By numerical solving the nonlinear Schrodinger equation
the simulation results indicate that stacking chirped pulse has different transmission characteristic from chirped pulse
because of its special spectrogram distribution. In the paper, the dispersion length and the nonlinear length are modified
for stacking chirped pulse. Even the SPM effects dominate over GVD effects in propagation, GVD effects should not be
ignored or be treated as perturbation. More details about pulse evolution are discussed: as the stacking chirped pulse
propagating, the pulse width changes little while the detail structure becomes unorganized and peak power decreases; the
spectrum are significantly broadened because of the intense SPM effects.
Direct laser driven ICF system requires a high degree of uniformity in laser energy in order to avoid Rayleigh-Taylor
instability. In all-fiber laser driven ICF system, millions of fibers are fixed around the target chamber. We suggest the
fibers are arranged in bundles with a single lens coupling the output of a bundle. If the arrangement is optimized, top-flat
intensity profile is acquired near the focus of the lens. Least square method is used here in determining the optimum
values of relative parameters. Factors on the irradiation nonuniformity are also analyzed here by numerical simulations.
We present a numerical model for generating cylindrical vector beams (CVBs) through an ytterbium-doped few-mode
fiber laser. A practical numerical model based on propagation rate equations with consideration of propagating modes
competition between LP01 and LP11. To optimize the output power of LP11 while depress LP01, we analyze the
dependence of this competition on resonant wavelength, pump power, ytterbium doped fiber (YDF) length, doping
concentration and distribution. We also propose an effect method to completely depress the generation of LP01.
The effect of stimulated Brillouin scattering is considered and found to be important in high power
optical fibers especially when amplifier is used. Numerical simulation has been done to show how the
effect of stimulated Brillouin scattering is affects the amplified spontaneous emission and the signal.
Found the difference between just decrease the Brillouin signal and decrease the NF, and give a method
to decrease it through change the pump method.
Image restoration for constructing high-spatial-resolution images in an imaging system which realizes indirectly far-filed
imaging by integrating the microlenses array with LCD is reported. We have investigated the indirectly far-field imaging
condition where adjacent sampling points contribute the detected signal. Experimental setup with microlens of 500 μm
diameter and 8 mm focal length is built to prove this condition by studying performance of image restoration using
modified point spread function (PSF). Since any one iterative method is not optimal for all image deblurring problems,
some deblurring algorithms including direct deconvolution and iterative deconvolution are applied to our imaging system
and we compared the effectiveness of these iterative procedures to choose right one for our use.
This paper presents an improvement approach to realize tracking on smooth glass surface based on
subjective speckle. The scattering mechanism on glass surface is analyzed and the affection on tracking
precise and range for tracking with subjective speckle is researched. The speckle captured by CCD just
from the upper surface of the glass is achieved by grazing incidence of the laser beam and the noise
mixed with the signal is eliminated by a barrier above the surface. Based on the apparatus of subjective
speckle tracking, the speckle contrast is improved from 0.25 to 1.25 by non-Gauss effect and the range
of the tracking has been increased from 200 μm to 400 μm compared with the objective speckle
method on the same condition.
We proposed and demonstrated an all-fiber laser to generate cylindrical vector beams at
1030 nm. The cylindrical vector beams were obtained by exciting high order mode operating in
the few-mode fiber inside the laser system, which was implemented through adjusting the angle
and transversal dimension of a couple of fiber collimators. The radial and azimuthal polarization
beams can be switchable conveniently just by applying twist and pressure to the few-mode fiber.
Recently, we have undertaken an experimental study of nonstandard refraction of light from one- and twodimensional
dielectric quasi-periodic surfaces. The mechanism underlying this effect is the large local slope of
the quasi-periodic surface.
Not only do meta-materials have the properties of negative refraction, the planar designer surfaces have shown some of
these properties as well.
Recently, we have undertaken an experimental study of nonstandard refraction of light from one-dimensional dielectric
quasi-periodic surfaces. The mechanism behind this is the large local slope of the quasi-periodic surface that causes the
nonstandard refraction.
In this paper, we report a recent design and experimental results of an optical feedback technique for the setup of Collett-Wolf beam, which is a partially coherent source. A large negative and positive shift for a mirror with a dielectric slab backed by a metal is tested. The Collett-Wolf beam with Goos-Haenchen effect will further reduce speckle contrast by means of an ensemble average of many feedback beams.
We have studied the inverse scattering problem as an optimization problem. Firstly, we deal with the direct scattering
problem of a one-dimensional, perfectly conducting rough surface. We discuss the complexity of the relation between
the surface profile, the incident field, and the far-field intensity. Then, we approach the inverse problem as an
optimization problem of constraint. In general we adopt a mathematical representation of the surfaces based on B-spline
curves, and describe the evolutionary strategies. Concerning the mutation operator in evolutionary algorithm, some effort
to facilitate self-adaptation of the mutation has been presented. The typical results are presented with our main
conclusions.
We present approaches to the design of two-dimensional randomly rough surfaces that produce scattered fields
with specified coherence properties, and transform an incident beam with a specified intensity profile into a
scattered beam with a different specified intensity profile. We also show how illuminating a single realization of a
randomly rough surface, drawn from an ensemble of such random surfaces, by a partially coherent polychromatic
(broadband) beam can be used to replace the average over the ensemble of realizations of the surface used to
suppress the speckle produced when the incident field is monochromatic. Finally, we describe an experimental
setup for producing a partially coherent beam by an optical feedback technique, and present experimental results
demonstrating the reduction of speckle by the use of this beam.
We have studied the inverse scattering problem as an optimization problem for a 1-D surface. As the input data for our
self-adaptation genetic algorithm for surface inversion, the scattered intensity has been measured with the laser BRDF
instruments. In addition, the transmission data are collected. The typical reconstruction of inverse scattering for a 1-D
random surface is compared with the profile measured by an atomic force microscope (AFM).
The independent control of the upper and lower cutoff frequencies of the guided modes in coupled-cavity wavguides (CCWs) is investigated numerically. The CCWs are formed in a two-dimensional photonic crystal (2D PhC) consisting of a square array of dielectric rods in the air. The dielectric constant and radius of the rods in the perfect PhC is 11.56 and 0.18α, respectively, in which α is lattice constant. By using the plane wave expansion method (PWEM), the impact of two influencing factors on cutoff frequencies in CCWs is calculated systematically. Efficient methods have been demonstrated for tuning one cutoff frequency while keeping the other unchanged. The indepent control ranges of the upper and lower cutoff can be up to 67.85% and 68.57% of photonic band gap (PBG), respectively. The results can be applied to the design of PhC-based optical devices such as band filters and optical switches.
We present a novel numerical model for an ytterbium-doped fiber ring laser. A comprehensive numerical model based on an iterative solution of propagation rate equations is used to analyze the impact of various laser variables. The dependence of laser output power on pump power, ytterbium-doped fiber (YDF) length, and emission wavelength has been investigated, with the aim to optimize laser parameters with respect to emission wavelength and output power. Close to emission wavelength, the optical signal-to-noise ratio is higher than 65 dB. We also investigate that the initial oscillation is damped oscillation, and the laser output become steady-state output one millisecond later.
Multimode interference optical pulse power splitters for 1.053μm wavelength have been designed in this paper. The guided mode propagation analysis method is used to analyze the working principle of MMI power splitter. We designed the power splitters base on the analysis. Then finite difference beam propagation method (FDBPM) was used to analyze the splitting performance of the devices. At last, we analyzed the temporal performance of the device (such as pulse broaden) working for optical pulse input with the Finite Difference Time Domain (FDTD) method. The dispersion properties for ultra short 1.053μm optical pulses input were analyzed.
A new, compact laser Doppler velocimetry is proposed, which is composed of a single-mode vertical-cavity surface-emitting laser modulated by a dynamical triangular current and a collimating lens. It can indicate the direction of velocity without ambiguity in the wide dynamic range of 5.2mm/s to 479.9mm/s when the sampling time is 0.1 second in the measurement. The accuracy of velocity measurement is better than 3.1% in the whole velocity range. What's more, this LDV works very well on different diffusing surfaces, even on a black glossy photographic paper.
This paper presents a theoretical and numerical analysis of polarization properties used as Doppler velocimetry in Vertical-Cavity Surface-Emitting lasers. A good match is found between numerical results and reported experiment results. We show that condition of generating square waves is the VCSELs must operated inside the bistable region and frequency difference between two linear polarization modes is equal to several certain values. We can select proper VCSELs which frequency difference between two linear polarization modes is multiple of ±3G to obtain asymmetric waveform of self-mixing signal.
A temperature-tunable polarization interference filter (PIF) made of YVO4 crystal has been presented and applied for wavelength monitoring of a distributed feedback (DFB) laser in a dense wavelength-division-multiplexing (DWDM) optical communication system. This novel device offers a flexible way to monitor the operating wavelength of the transmitter over a wide capture range. Monitoring resolution of 0.02 nm can be obtained by measuring the temperature variation of the filter while its transmission value is kept at a constant value.
A diode-pumped, compact, wavelength tunable, single frequency Er3+:Yb3+ codoped DBR fiber laser is reported. An output power of 2.4mW for 75mW of 980nm diode pump power and a slope efficiency of 6% at 1557.05nm were obtained. Linewidth of the laser was estimated at 1557.05nm to be less than 1MHz. Also, the laser can be tuned to wavelengths between 1557nm to 1561nm and operates single mode throughout this range.
The self-injection locking single frequency Yb-doped fiber ring laser is reported. The system shows compact, stable and tunable. In the primary experiment, the Self-injection locking single frequency fiber ring laser with wavelength 1.05325)mum, power exceeding 3.5mW,line-width less than 36 MHz was manufactured. The laser shows stability, low threshold and high power. No mode-hopping was observed within 2 hours. The single polarization output can be obtained when use single polarization fiber.
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