From a classical dynamic simulation, we find the kinetic energy of the electrons generated during laser plasma generation depends on the laser polarization and intensity. The electron kinetic energy reaches its maximum with a fixed laser intensity for circularly polarized laser pulse. The fluorescence spectra at 380.4 nm from N2 and 391.3 nm from N2+ are measured; these are generated by both the direct excitation and electron collision excitation. The electron collision excitation is determined by the electron energy and reaches the maximal with a circularly polarized pulse.

We present both numerical and experimental results to study the diffraction of twisted light beams based on orbital angular momentum (OAM) eigenmode decomposition, where the total initial field, including light and aperture, is represented by a two-dimensional spectrum of Laguerre–Gaussian modes. We use a phase-only spatial light modulator to display a holographic grating for both generating the twisted light and mimicking the finite aperture. We take a triangular aperture as an example to describe the diffraction behavior of a twisted light beam carrying an OAM number of =3 from the near-field to far-field regions, where the interesting gradual formation of triangular bright lattices are observed. An excellent agreement between the numerical simulations and experimental observations is clearly seen. It is noted that this method is particularly useful for the study of the diffraction of twisted light fields incident on any apertures of rotational symmetry.

We propose and experimentally demonstrate a universal and blind polarization-state tracking scheme for M-quadrature amplitude modulation (QAM) signals based on a decision-free radius-directed linear Kalman filter (RD-LKF). The polarization tracking performance is investigated through simulation and experiments for both quadrature phase-shift keying (QPSK) and 16-QAM signals. The influence of the filter parameters on the static polarization demultiplexing performance and dynamic tracking capability are discussed via simulation. The optimization strategy of the filter parameters in modulation-format-independent scenarios is proposed and simulations are carried out to evaluate the polarization demultiplexing penalty for QPSK, 16QAM, and hybrid QPSK/16QAM signals. Finally, the proposed decision-free RD-LKF is experimentally compared to the respective algorithms of constant modulus algorithm and multimodulus algorithm for QPSK and 16-QAM and the advantage of ultrafast polarization tracking ability is confirmed.

We propose a method of modulation format identification based on compressed sensing using a high-order cyclic cumulant combined with a binary tree classifier. Through computing the fourth-order cyclic cumulant of the pretreated band signal, which is obtained by compressed sensing with the sampling rate much less than the Nyquist sampling value, the feature vector for classification is extracted. Simulations are carried out in the optical coherent fiber communication system with different modulation formats of multiple phase-shift keying and multiple quadrature amplitude modulation. The results indicate that this method can identify these modulation formats correctly and efficiently. Meanwhile, the proposed method is insensitive to laser phase noise and signal noise.

A high sensitivity magnetic fluid (MF) filled side-hole fiber magnetic field sensor based on surface plasmon resonance (SPR) is designed and investigated. Within the side-hole fiber, the water-based MF is injected into the two side holes, and both of the holes are coated with gold to realize the measurement of the magnetic field by using the SPR effect. The refractive index of the MF changes with different external magnetic fields, resulting in the resonant wavelength moving to other wavelengths. Furthermore, when the external magnetic field increases from 30 to 210.9 Oe, the magnetic field sensitivity can reach to 1.063 nm/Oe.

We propose and experimentally demonstrate a simple visible light communication system by combining an adaptive transmission technique with orthogonal frequency division multiplexing. In the adaptive transmission scheme, power allocation is performed in such a way as to maximize the channel capacity under electric power constraints, and adaptive modulation is then introduced to achieve the maximum data rate given a target bit error rate. Experimental results show that spectrum efficiency can be greatly improved through this adaptive transmission technique.

A simple wavelength-independent scale factor model is established for a closed-loop interferometer fiber optic gyroscope (IFOG) and a method to keep the scale factor radiation tolerant and temperature stable in a high performance IFOG for space application is proposed. The half-wave voltage (Vπ) of the multifunction gyro chip at different wavelengths and temperatures is measured and the radiation-independent inherent parameter of the modulator is picked out and found be proportional to the temperature and slightly wavelength dependent. An experimental IFOG is developed and the scale factor is measured at different temperatures and under Co60 irradiation, respectively. Less than a 10 ppm scale factor instability is achieved within the 40°C to +60°C temperature range and more than 100 krad(Si) total radiation dose.

A fiber structure with a circularly polarizing property is proposed. The fiber consists of a round core and a triple-lobe stress region in the cladding, which is compatible with single-mode fibers, and it can be fabricated using conventional metal chemical vapor deposition processes. By coating a layer with a high-refractive index, the twist pitch required for resonant coupling is increased to hundreds of micrometers, and the mature pit-in-jacket drawing technique can be used. The polarization filtering properties of the fabricated circularly polarizing fibers are measured experimentally, showing high distinction ratios in a broad frequency region.

In this Letter, free-space optical (FSO) communication using patterned modulation and bucket detection is introduced to improve the bit error rate (BER) performance in complex and noisy environments. The scattered light is averaged in this communication structure. Second-order correlation, wavelet normalization, and compressed sensing are combined in the reconstruction algorithm. A signal with N bits is reconstructed well from much less than N measurements. Numerical simulations and experiments are performed without the narrowband optical filters used in traditional FSO communication. It can also be employed in real networks where secure communication is required. This provides the great opportunity to pave the way for real applications of FSO communication.

As microsatellite technology develops, precise inter-satellite measurement shows its significance in distributed satellite systems. In this Letter, a novel technique is proposed for measuring the inter-satellite distance, which adopts optoelectronic resonance and has a function of self-referencing. Resonance cavities have a high spectral purity and a high oscillation frequency. By utilizing the accumulative amplification principle to convert the measurement of distance to that of the frequency, high accuracy is achieved. In the experiment, this measuring scheme has a large measuring range between 1 and 6 km (can be potentially larger), and the accuracy is better than 1.5 μm. The relative accuracy reaches the level of 10 10.

A novel compact optoelectronic oscillator (OEO) employing a Fabry–Perot (FP) resonant electro-optic (EO) modulator is proposed and experimentally demonstrated. The resonant modulator is used as the optical storage element as well as the mode selection element, which can greatly reduce the system complexity and make the system more portable. Moreover, the optical resonance and electrical transmission response for the FP resonant EO modulator are theoretically and experimentally studied. The proposed OEO oscillates at 10 and 20 GHz in the proof-of-concept experiment, and the corresponding single-sideband phase noise can reach below 118 and 108 dBc/Hz at 1 MHz offset frequency, respectively.

High speed pseudorandom modulation and photon counting techniques are applied to a three-dimensional imaging lidar system. The specific structure and working principle of the lidar system is described. The actual detector efficiency of a single-photon detector in an imaging system is discussed, and the result shows that a variety of reasons lead to the decrease in detection efficiency. A series of ranging and imaging experiments are conducted, and a series of high-resolution three-dimensional images and a distance value of 1200 m of noncooperative targets are acquired.

3D imaging techniques such as computed tomography, ultrasonography, and magnetic resonance imaging usually combine many scans computationally. Here, we report a 3D imaging approach using an optical-laser diffraction microscope with two different wavelength lasers in the same orientation. A double-layered sample constructed of silica spheres is used for coherent diffraction imaging with two lasers at 543 and 432 nm. The diffraction patterns obtained using a planar detector at a high numerical aperture are projected onto the Ewald spheres. 3D images of the double-layered sample are successfully reconstructed from the two-color spherical diffraction patterns.

Correlation imaging is attracting more and more attention as a novel imaging technique taking advantage of the high-order coherence of light fields. To reconstruct an image of the object, many frames of different speckle patterns are required. Therefore, the speed of imaging is strongly limited by the speed of the refreshing rate of the light field. We propose a coprime-frequencied sinusoidal modulation method for speckle pattern creation using a spatial light modulator in a computational ghost imaging system to increase the speed of imaging. The performance of the proposed method is discussed as well.

Four tomography algorithms, including the algebraic reconstruction technique, simultaneous iterative reconstruction technique, the multiplicative algebraic reconstruction technique, and the adaptive algebraic reconstruction technique (AART), are compared with each other based on the tunable diode laser absorption spectroscopy technique; the determination of the relaxation parameter is discussed to improve reconstruction quality and shorten computational time as much as possible. The calculated results demonstrate that the AART algorithm can produce the reconstruction results with better quality and less computational time. In the experimental measurement, the AART algorithm with a two-line thermometry scheme is adopted to measure the spatial distribution of H2O temperature and concentration, two H2O absorption lines near 1397.8 nm are selected, the temperature and H2O concentration in the McKenna plat premixed flames are experimentally reconstructed and analyzed, and the results of integrated tomography reconstruction are consistent with the thermocouple traverse measurement.

A 1.88 μm Ba(NO3)2-based stimulated Raman scattering (SRS) laser pumped by a potassium-titanyl-phosphate-based optical parametric oscillator (OPO) laser is presented. Under the pumping energy of a 130 mJ 1064 nm Q-switched Nd:YAG laser, a 40 mJ 1.57 μm laser is achieved; the maximum output energy of the 1.88 μm Raman laser reaches 7.5 mJ with a pulse duration of 5.3 ns at repetition rates of 10 Hz, and the corresponding total optical conversion efficiency is about 5.8%. The combination of the SRS and OPO techniques significantly extends the wavelength from 1.064 to 1.57 μm (OPO) and then demonstrates Stokes-shifting to 1.88 μm (SRS).

A stable passively mode-locked laser of Nd3+:Gd0.5Y2.5Al5O12 (Nd:GYAG) disordered crystal is experimentally investigated both using Z-type and W-type cavities with a semiconductor saturable absorbed mirror. The continuous-wave mode-locked threshold of the absorbed pump power is just 1.8 W. The maximum average output power is 210 mW, which is obtained at the absorbed pump power of 2.3 W. The pulse width is measured to be 11.1 ps assuming a Gaussian shape.

In order to solve the problem of low measurement accuracy caused by uneven imaging resolutions, we develop a three-dimensional catadioptric vision sensor using 20 to 100 lasers arranged in a circular array called omnidirectional dot maxtric projection (ODMP). Based on the imaging characteristic of the sensor, the ODMP can image the area with a high image resolution. The proposed sensor with ODMP can minimize the loss of the detail information by adjusting the projection density. In evaluating the performance of the sensor, real experiments show the designed sensor has high efficiency and high precision for the measurement of the inner surfaces of pipelines.

Wavelength-dependent birefringence and dielectric anisotropy, two major optical properties of the nematic liquid crystal materials used in phase-only liquid crystal on silicon (LCOS) devices, are measured as a function of operating temperatures. The dynamic phase modulation depth and threshold voltage of these phase-only LCOS devices are also measured in the corresponding temperature range and compared with theoretical predictions. The results show that the dynamic response time can be reduced significantly by an appropriate increase of device operative temperature, while the necessary device elements, such as phase modulation depth and threshold voltage, can be maintained at the same time.

Research on white light-emitting diodes (LEDs) based on multi-color-emitting quantum dots (QDs) is carried out in this Letter. The equations of luminous efficiency (LE), color rendering index (CRI), chromaticity coordinates (x,y), and color temperature (Tc) of white LEDs are obtained, according to the spectral-LE function Φ of LED chips and QDs. The calculated results indicate that the values of the performance parameters of QD-based white LEDs are closely related and proportional to the QDs’ fluorescence spectra, and white LEDs with a high LE and a high CRI may be fabricated based on QDs. We have provided theoretical guidance for preparing such white LEDs.

We demonstrate an ultra-narrow-band optical filter based on a hybrid-microsphere consisting of a coated SiO2 microsphere. As compared to the SiO2 microsphere, the hybrid-microsphere produces a quality factor of >108, a transmission spectrum bandwidth of <1 pm, and an increased side-mode suppression ratio. The microsphere surface roughness and whispering gallery mode (WGM) transmission spectra are measured experimentally. A 0.01 nm bandwidth, single-wavelength fiber laser output is achieved with a tunable wavelength, using the SiO2 microsphere as the mode selector. The optical field distribution and WGM transmission spectrum of the hybrid-microsphere with different coating parameters are theoretically investigated by the finite-difference time-domain method.

A slim optical fingerprint recognition sensor (OFRS) based on a grating input coupler and a microprism sensing surface is proposed. By using a subwavelength grating coupler, input light is coupled into the planar waveguide and the propagation angle is well engineered to avoid image overlap, thus an undistorted fingerprint is captured. For maintaining a thin structure, a microprism array is utilized to facilitate the breaking of total internal reflection under a large diffraction angle from the grating. The feasibility, efficiency, and image quality of the proposed structure are verified and discussed. The device has the advantages of a slim structure, a high image contrast, and a compact architecture, suitable for mobile devices.

In order to improve the inversion precision of aerosol mass concentrations based on the particle group light scattering method, the concept that particles through a laser beam are equivalent to an aggregate is proposed. A fractal model for aerosol mass concentration using the signal amplitude distribution of aggregates is presented, and then the subsection calibration method is given. The experimental results show that the mass concentrations inversed by this model agree well with those measured by the norm-referenced instrument. The average relative errors of the two experiments are 5.6% and 6.0%, respectively, which are less than those obtained by the conventional inversion model.

The mechanism of ferromagnetic ordering in ZrOx film is investigated by both experimental observation and theoretical calculation. Magnetic measurements reveal that the magnetic properties can be adjusted from diamagnetism to ferromagnetism by varying the oxygen stoichiometry. We find that oxygen-rich defects can be responsible for the observed magnetic properties by taking the measurements of x-ray photoelectron spectroscopy and room temperature photoluminescence spectra. Density functional theory calculations further confirm that the ferromagnetic order is mainly driven by the exchange interaction between the oxygen antisites and the neighboring anion atoms.