The winners of the Rudolf Kingslake Medal and Prize are recognized in this editorial. The Kingslake Medal is awarded annually to the most noteworthy original paper to appear in Optical Engineering on theoretical or experimental aspects of optical engineering.

A linearization scheme based on two cascaded intensity modulators is proposed and experimentally demonstrated. By optimizing the biases, the power ratio and the phase difference between the drive signals applied to the two Mach–Zehnder modulators (MZMs), the third-order intermodulation distortion (IMD3) can be effectively eliminated over a wide operating bandwidth of 1 to 12 GHz without the same RF phase at two modulators, which is required in previous works. The ratio of the fundamental output to the IMD3 reaches 50.21 to 63.28 dB, which has an improvement of 18.35 to 31.42 dB compared to that of a single MZM link.

Streak tube imaging lidar has been widely applied in target recognition and imaging because of its high accuracy and frame rate. Compressed ultrafast photography technique employs a digital micromirror device (DMD) and a streak camera. It is developed to satisfy the requirements of imaging of ultrafast processes. The concept of structure provides a new direction for three-dimensional (3-D) imaging. This paper studies the streak tube 3-D imaging system based on compressive sensing (CS) from the perspective of imaging system construction and image reconstruction algorithms. The system model is built, and mainly structures are introduced such as the fiber array and DMD. Two simulation experiments are organized. First, the stripe images of a simple target are obtained. In the process of reconstructing the intensity image and range image, the extraction methods of the measurement matrix required by the CS algorithm are given, respectively. The resulting images and variance curve show that the image quality increases with the number of measurements. The second experiment with a complex target is carried out. Two levels of distance interval are used to analyze the imaging effect in the simulation. It is found that the image resolution is directly related to the distance interval selection.

To remove noise from infrared thermal images captured in underground mining working face under low luminance and dusty environment, a nonreference infrared thermal image denoising method based on heuristic dual-tree wavelet thresholding is proposed. The threshold is optimized through estimating noise variance in wavelet domain using an improved chaotic drosophila algorithm (CDOA), which is promoted by a spatial–spectral entropy based metric. The basic DOA, genetic algorithm, particle swarm optimization algorithm, and virus colony search algorithm are implemented to compare the convergence rate and optimization ability of improved CDOA. Moreover, other representative denoising methods, such as BM3D, BLS-GSM, fast translation invariant, and nonlocal Bayes, are also applied for comparison. Comparison result proves effectiveness and superiority of the proposed method. Finally, the proposed method is applied in infrared thermograph-based visual surveillance system, and the denoising results also prove the state-of-art performance.

We propose a security-enhanced optical interference-based multiple-image encryption (IBMIE) using a modified multiplane phase retrieval algorithm (MPPRA) in the Fresnel transform domain. In this IBMIE scheme, while a phase-only mask (POM) distributing randomly between   [  0  ,  2π  ]   is fixed, the other POM is iteratively extracted based on a modified mMPPRA, and thus, multiple plaintexts are simultaneously encrypted into two POMs with different distances to the image planes. At last, the retrieved POM is pixel scrambled by chaotic pixel scrambling (CPS). During image decryption, the decrypted images can be obtained at their preset positions by an intensity detector directly. The silhouette of the original images cannot be obtained using either of the two POMs. The parameters of both CPS and Fresnel transform can serve as security keys to enhance the security. Numerical simulation is presented to demonstrate the validity of the proposed mMPPRA-based IBMIE.

Bioluminescence tomography (BLT) is a promising optical molecular imaging technique in preclinical research. One key problem for BLT is how to deal with the severe ill-posedness and obtain accurate and stable reconstruction. We propose a penalty method for recovering bioluminescence sources, in which we transform reconstruction of BLT into an L1/2-norm penalty problem and solve it via a nonmonotone proximal gradient method with a suitable penalty parameter update scheme. Simulations and phantom experiments based on multispectral measurements were designed to evaluate the proposed reconstruction method. The encouraging results show that the proposed method has better reconstruction accuracy and image quality than the comparative methods.

We present a method for designing spectral interference filters optimized for different kinds of projectors for three-dimensional (3-D) projection systems. Among the parameters considered, the color balance, the transmission efficiency, and the filter isolation are critical and should be optimized in such a way that color correction is no longer necessary. We compare filter design optimizations according to the previous criteria for ultrahigh-performance lamp and light-emitting diode projectors. Finally, we discuss the impact of technical manufacturing constraints on the considered filters with respect to crosstalk and viewing angle tolerance.

We present a hierarchical extraction algorithm to extract pole-like objects (PLOs) from scene point clouds. First, the point clouds are divided into a set of data blocks along the x- and y-axes after computing the dimensionality structure of each point. An effective height constrained voxel-based segmentation algorithm is proposed to segment the scene point clouds. The adjacent voxels with similar heights are grouped into an individual object based on the spatial proximity and height information. The objects consisting of a smaller number of voxels and most of the linear points are extracted and regarded as the pole-like candidates (PLCs). Then a Euclidean distance clustering algorithm is adopted to segment the PLCs and remove the floating and short segments. Next, each PLC is divided along the z-axis to extract the vertical structure. The straightness of the vertical structure is computed to remove the false PLOs. Finally, a collection of characteristics, such as point distribution and size, are applied to classify the PLOs into a street light pole, high-mast light, beacon light, and single pole. The experimental results demonstrate that our method can extract PLOs quickly and effectively.

A photonic-assisted radio-frequency (RF) self-interference cancellation (SIC) scheme for in-band full-duplex radio-over-fiber system is proposed based on a dual-drive Mach–Zehnder modulator (DD-MZM) and a fiber Bragg grating (FBG). The received signal with an interference from the transmitter is applied to one arm of the DD-MZM, and the reference signal tapped from the transmitter is injected into another arm of the DD-MZM. By properly controlling the amplitude and phase of the reference signal, and adjusting the bias point of the DD-MZM, the RF interference can be cancelled in the optical domain. An FBG is used to convert the phase-modulated received signal to an intensity-modulated signal for information recovery. Since the self-interference is cancelled directly in the optical domain, the proposed SIC scheme is suitable for long-distance fiber transmission. A simulation is performed, where a cancellation depth of more than 50 dB is achieved. The proposed SIC system features good transmission capability and frequency tunability, which is only limited by the bandwidths of the DD-MZM and the FBG.

The resolution of an optical imaging system is often limited by various phase aberrations. To get the joint estimation of an object and aberrations of an imaging system with perturbations, a defocused spatial diversity technology with aperture scanning was proposed and evaluated. This technology creates spatial diversity images by scanning an aperture in the defocused plane of the aberrated imaging system. Based on these diversity images, the stochastic parallel gradient descent algorithm was used to recover the phase aberration of the imaging system by adaptively optimizing the coefficients of Zernike polynomials. Then the near-diffraction-limited image of the object can be restored using a multiframe Winner–Helstrom filter. Numerical simulations performed with different phase distributions validated the technology. The technology proposed may be widely used in aberrated imaging systems for aberration detection and image restoration.

Aircraft coatings are critical for protecting the substrate material from corrosion, and in some cases, serve to reduce the aircraft’s RADAR cross section. A coating system is generally formed from three layers: a topcoat, primer, and substrate. Exposed substrate or primer, from defects in the topcoat, poses an operational hazard to the aircraft and can shorten a component’s lifetime. Conventional computer vision techniques require intensive image processing algorithms to detect such defects across a wide range of observation angles, variations in incident illumination, and nondefect markings. We introduce a polarimetric imaging technique that can classify topcoat defects that penetrate to the primer or substrate versus superficial surface markings. Results demonstrate that circular and linear polarization can discriminate metallic and carbon fiber substrates from the dielectric paint and low observable topcoats. To this end, we demonstrate that the technique of using polarimetric imaging may be viable for in-situ robotic inspection of aircraft topcoats. This is followed by our experimental results, which demonstrate material identification on the single-pixel level.

Changes in the position and alignment of cylindrical objects (shafts, pipes, etc.) in heavy machines from a particular coordinate system or from its aligning counterpart need to be measured accurately to prolong the life of machinery and to avoid large-scale accidents. A method for online measurement of the position of cylindrical objects in a two-dimensional (2-D) plane using linear optical fiber array-based laser triangulation sensors is proposed. A mathematical model was first developed to deduce the 2-D change in position of the target axis using two perpendicularly placed sensors and considering the effect of the curvature of the target surface on measurements. Then, using the formula derived and our recorded experimental data, we have demonstrated the measurement of the 2-D position of a cylindrical object with two developed sensors placed remotely at a 100-mm standoff distance.

Determination of intrusion location in a phase-sensitive optical time-domain reflectometer is important and fundamental. In general, the spatial resolution of event location is limited by the temporal width of the probe pulse. We found that the location of a single intrusion event could be precisely determined with high spatial resolution regardless of the pulse width. First, the concept of “response section” was proposed and then it was proved that its left edge indicated the exact location of the intrusion event. Then, the spatial frequency energy distribution was used to achieve explicit edge determination. Three experiments were conducted to demonstrate the superiority of the proposed method in terms of locating the events compared with the traditional trace differential method.

To improve optical measurements, which are degraded by optical distortions, wavefront correction systems can be used. Generally, these systems evaluate a guide star in transmission. The guide star emits well-known wavefronts, which sample the distortion by propagating through it. The system is able to directly measure the distortion and correct it. There are setups, where it is not possible to generate a guide star behind the distortion. Here, we consider a liquid jet with a radially open surface. A Mach–Zehnder interferometer is presented where both beams are stabilized through a fluctuating liquid jet surface with the Fresnel guide star (FGS) technique. The wavefront correction system estimates the beam path behind the surface by evaluating the incident beam angle and reflected beam angle of the Fresnel reflex with an observer to control the incident angle for the desired beam path. With this approach, only one optical access through the phase boundary is needed for the measurement, which can be traversed over a range of 250  μm with a significantly increased rate of valid signals. The experiment demonstrates the potential of the FGS technique for measurements through fluctuating phase boundaries, such as film flows or jets.

A compact stand-off chemical detector using a Michelson interferometer has been developed and is presented. Its size is only 104  ×  183  ×  108  mm³ and its weight is 2.5 kg, which makes it suitable for hand-held operation. This compact detector is a minimized version of the conventional Michelson interferometer. The housing for the interferometer was designed to be divided into two parts for minimization and convenient assembly. All the optics composing the interferometer were directly fastened to the housing. The moving mirror module in the Michelson interferometer was specially designed for the small size detector. Using a symmetrically positioned linear elastic plate, the tip and tilt angle of reflected light from the moving mirror were smaller than 8 arc sec during linear back-and-fourth motion without any active alignment feedback system, which results in low noise in the interference signal. The spectra of SF₆ and NH₃ were measured with changing concentration and the detection limit was determined to be 46.7 and 65.2  mg  /  m², respectively. Additionally, outdoor measurement was demonstrated with a distance of about 1 km.

Ptychography is a diffraction imaging method that allows one to solve inverse problems in microscopy with the ability to retrieve information about and correct for systematic errors. Here, we propose techniques to correct for axial position uncertainty, detector point spread, and inhomogeneous detector response using ptychography’s inherent self-calibration capabilities. The proposed methods are tested with visible light and x-ray experimental data. We believe that the results are important for precise calibration of ptychographic experimental setups and rigorous quantification of partially coherent beams by means of ptychography.

In the fast three-dimensional (3-D) shape measurement, it is an important factor to use the least number of the fringe pattern to get 3-D shape measurement of arbitrary objects. Although one-shot technologies can use one-frame deformed fringe pattern to get the wrapped phase, they are easily affected by the surface property and suffer from poor spatial resolution. In addition to the process, phase unwrapping may affect the quality of absolute phase. This paper proposes a fast measurement method based on a phase measurement profilometry and stereo vision system. This method can reconstruct 3-D surface without phase unwrapping. Using original image matching constraint, a rough parallax is used in the phase matching. To resist the false matching, subpixel parallax optimization is used to reduce the matching errors. To detect the edge point of wrapped phase, the average phase is calculated. Experimental results verify the feasibility of the proposed method and it can measure complex objects without phase unwrapping.

The excitation and emission obtained from an Er^3  +-doped tellurite glass with embedded silver nanoparticles (SNPs) through nanostructured surfaces consisting of a square lattice of nanoholes (squares or circles) in a silver thin film are addressed. The periodic nanostructures were fabricated with a focused gallium ion beam on a silver thin film deposited onto an Er^3  +-doped tellurite glass with embedded SNPs. The Er^3  + microluminescence spectra were measured in the far field (510- to 590-nm wavelength range). The emission observed through the plasmonic nanoholes is caused by the excitation of the Er^3  + ions via extraordinary optical transmission from the periodic nanostructures. Two coupling types are proposed: (i) one between the SNPs and the Er^3  + ions (electric dipole type) and (ii) a resonant coupling between the SNPs (localized surface plasmon resonance) and a silver thin film (surface plasmon polariton). These two couplings modify the local field, which improves the emission intensity of Er^3  +. A dependence of the intensity emission with the geometrical shape of the nanoholes and the number of elements of the square lattice was observed. These findings can be very useful for nanophotonic device applications employing a transparent medium with optical gain.

Many infrared systems operate in extreme environments (such as space or military), which require stable optical performance over an extended temperature range. We present a model for the first-order optical design of athermal, radial gradient-index (GRIN) systems, based on a form of the thermo-optic glass coefficient adapted to inhomogeneous material combinations. We find that radial GRIN components can significantly reduce the optical power balance of athermal, achromatic systems, thus reducing aberration contributions from individual lens elements and improving overall performance. This introduces the scope for a class of GRIN multispectral infrared imaging solutions. We apply this enhanced first-order modeling technique to generate starting points for optimization of a short wave to long wave infrared (SWIR/LWIR) multispectral optical design. An example of SWIR/LWIR optical design for a weapon sight application is generated and shown to have significantly reduced mass and improved performance compared with a conventional non-GRIN solution.

Coded masks (CM) often lack a self-supporting structure that is difficult to manufacture without recourse to drilled holes in place of ideal square apertures, degrading imaging properties. An alternative approach is presented with three-dimensional (3-D) printed CM molds cast with a radio-opaque material that allows square elements to be retained. Two methods are presented; hot casting a bismuth alloy (density 8.6  g cm  −  3) and cold casting with tungsten powder/epoxy resin (densities 9.6 and 10.6  g cm  −  3). A critical review of 3-D printed-CM fabrication along with some typical x-ray backscatter images is presented. A signal-to-noise ratio from both the machined tungsten and cold cast 3-D printed mask were comparable, with the former having a slight advantage. Also, 3-D printed cold cast masks were found to be more economical and easier to rapid prototype over traditional drilled tungsten masks.

We propose an algorithm for absolute phase retrieval from multiwavelength noisy phase coded diffraction patterns. A lensless optical system is considered with a set of successive single wavelength experiments (wavelength-division setup). The phase masks are applied for modulation of the multiwavelength object wavefronts. The algorithm uses the forward/backward propagation for coherent light beams and sparsely encoding wavefronts, which leads to the complex-domain block-matching three-dimensional filtering. The key-element of the algorithm is an original aggregation of the multiwavelength object wavefronts for high-dynamic-range absolute phase reconstruction. Simulation tests demonstrate that the developed approach leads to the effective solutions explicitly using the sparsity for noise suppression and high-accuracy object absolute phase reconstruction from noisy data.

Scale factor, as an important indicator for evaluating the dynamic performance of high-precision fiber optic gyroscopes (FOG), shows high sensitivity to the environmental temperature. Research on the temperature dependency of scale factor is meaningful to improve the robust performance and reliability of high-precision FOG. We theoretically analyze the sensitive factors, which could cause the scale factor error, and propose an effective method to compensate the scale factor via the temperature dependency of Er-doped superfluorescent fiber source. The experimental results show that, with our method, scale factor error can be reduced from 1185 to 640 ppm over 100°C temperature range (−40°C to 60°C).

A scheme to realize the flexible photonic frequency multiplication at millimeter-wave (mm-wave) and radio over fiber (RoF) transmission has been proposed and demonstrated. To enable the generated multiple-frequency signal to have a better performance of phase preserving, we theoretically investigated the phase change during the generation and transmission and proposed an adaptive coding algorithm to reduce the impact of phase fluctuation. The coding algorithm brings the frequency multiplication and fiber transmission distance together into consideration and adjusts the phase of the signal consequently. Due to the proposed coding algorithm, the system not only realizes the flexible frequency multiplication but also eliminates the phase deviation induced by the modulation and fiber dispersion, which effectively increases the transmission distance of fiber link. In addition, it also reduces the complexity of phase retrieval at receiver side. A 50-GHz to 100-GHz RoF system with 1  Gbit  /  s radio signal has been implemented by numerical simulation, and the result shows that the adaptive mm-wave RoF system could realize arbitrary multiple-frequency of quadrature phase shift-keying signal from double to decuple and reliable transmission of the tenfold signal at least 50 km.

A simple, frequency-multiplied optoelectronic oscillator (OEO) based on a dual-parallel Mach–Zehnder modulator (DPMZM) is proposed and demonstrated. The generated high-frequency microwave signals have improved performance in their phase noise (PN) and signal-to-noise ratio. Two loops (master and slave) are contained in this OEO, each linked to a separate port of the DPMZM. By tuning the voltages of the modulator, a frequency-doubled radio frequency signal is generated in the slave loop and a frequency-quadrupled signal is generated in the master loop. In these experiments, the microwave signals have good performance in purity and PN. The PN of the generated frequency-doubled and frequency-quadrupled signals is −113.3  dBc  /  Hz@10  kHz and −106.1  dBc  /  Hz@10  kHz, respectively.

We present stable dispersion-managed soliton (DMS) molecules in a passively mode-locked Yb-doped polarization-maintaining fiber laser based on chirped fiber Bragg grating in the anomalous dispersion regime. The generation of DMSs are characterized by their sech2-like spectral profile with no steep spectral edges, which is distinct from those of dissipative solitons generated in Yb-doped fiber lasers with a large net positive cavity group velocity dispersion regime. The pulse width is 4.8 ps if the sech2 profile is assumed. The corresponding pulses width could be compressed to 278 fs with grating pair compressor. Furthermore, DMS molecules exhibit multiple discrete equilibrium distances and a regular spectral modulation pattern. All these DMS molecules are stable in the sense that after being obtained they can remain several days. The proposed laser proves its great potential to future practical use in high-resolution optics for coding and optical communication.

A dual stream asymmetrically clipped optical (DSACO)-orthogonal frequency division multiplexing (OFDM) with intensity modulation/direct detection receiver is proposed that combines the ACO-OFDM, which is generated from individual streams of odd and even frequencies in a single frame without loss of information. The clipping noise, which is its absolute value, is subtracted from even subcarriers of DSACO-OFDM signal and further delayed in time domain to recover the ACO-OFDM data of the odd stream. The proposed DSACO has the same spectral efficiency of DC-biased optical OFDM (DCO-OFDM). It performs better in terms of optical signal-to-noise ratio (OSNR) and peak-to-average power ratio (PAPR) when compared to ASCO-OFDM and Lowery’s layered/enhanced ACO-OFDM (L/E ACO-OFDM). For a bit error rate of 10^−  3, DSACO shows around 1.9, 3.4, and 7.6 dB improvements of OSNR over two-layered L/E ACO-OFDM, three-layered L/E ACO-OFDM, and ASCO-OFDM for 1024-quadrature amplitude modulation constellations, respectively. The complimentary cumulative distributive function of PAPR for DSACO achieves 0.27 dB lower PAPR than three-layered L/E ACO-OFDM system and 1.17 dB lower PAPR than two-layered L/E ACO-OFDM and ASCO-OFDM.

Flexible optical networks (FONs) are used to handle the enormous bandwidth demands and significantly improve the flexibility and efficiency of spectrum resources. This flexibility opens the door to strategies that can optimize the allocation of spectrum resources. The dynamic setup and teardown of traffic will inevitably fragment these resources and increase the network blocking probability. Different modulation formats can be configured to guarantee efficient spectrum resource allocation by taking the transmission distance into account. We investigated routing and fragmentation-avoiding spectrum allocation for the unicast service over FONs with the constraints of spectrum resource and transmission distance. To alleviate spectrum fragmentation, the available spectrum adjacency (ASA) is used to estimate the adjacency among available spectrum block resources on routing paths or links. A distance-adaptive fragmentation-avoiding spectrum resource allocation (DA-FASA) algorithm based on ASA and genetic operators is proposed to resolve the spectrum fragmentation problem in FONs. The DA-FASA algorithm defines an ASA value for the free spectrum blocks on each routing path and each modulation format to maximize spectrum availability, which effectively reduces the spectrum fragmentation and network congestion. Simulation results indicate that DA-FASA exhibits highly efficient performance with regard to the bandwidth blocking probability and the spectrum utilization ratio under different network scenarios, compared to the benchmark algorithms.

In the field of intersatellite laser communication, there are two high-sensitivity demodulation methods: binary phase-shift keying (BPSK) coherent detection and differential phase-shift keying (DPSK) coherent detection. After taking into account the advantages and disadvantages of BPSK and DPSK, a DPSK heterodyne coherent detection scheme with local oscillation enhancement is proposed. The structure and the principles of this detection system are described, and the theoretical deduction is presented. Moreover, an experimental setup was constructed to test the proposed detection scheme. The offline processing procedure and results are presented. This scheme has potential applications in high-speed intersatellite laser communication.

A comprehensive study of an optical voltage-controlled oscillator (OVCO) is presented. With the help of analyzing the coherent receiving process for the binary phase-shift keying signal in a Costas subcarrier optical phase-locked loops system, the method to evaluate the OVCO performance based on calculating the transfer function of the modulator inside the OVCO is proposed, including the power efficiency and the requirement for received signal bandwidth. In addition, three possible OVCO configurations realized by Mach–Zehnder modulator, IQ modulator, and phase modulator are presented. The means to achieve the optimal performance of the OVCO configurations in practical implementations are theoretically explained, respectively, and their properties and the complexity are summarized. This work provides useful theoretical guides for the OVCO design in a lab experiment or for the production of a commercially integrated OVCO component.

An intracavity optical parametric oscillator (IOPO) pumped by a continuous-wave (CW) mode-locked laser is experimentally realized. The fundamental cavity and optical parametric oscillator cavity are designed to satisfy synchronous pumping. The output characteristics of signal and idle light are measured. Because of higher fundamental photon intensity in IOPO, the threshold of IOPO is lower than that of an extra-cavity optical parametric oscillator. The spectroscopy of signal light is obtained and the wavelength of idle light can be estimated to be 3.298  μm from noncritical phase matching. Based on the intensity fluctuation mechanism of fundamental locking, the dynamical model for IOPO pumped by a CW mode-locked laser is developed. The simulated results for the temporal shape of three lights are calculated from the derived rate equations. Because of dispersion, the signal pulse width of the theory is smaller than that of the experiment with the same pump energy.

Optical wireless power transfer (OWPT) can be a suitable candidate for long-distance wireless power transfer. We experimentally demonstrate the OWPT using a laser diode (LD) as the optical power transmitter and two candidates for the optical power receiver: a photodiode (PD) and a solar cell. Our results show a maximum electric-to-optic conversion efficiency of 72.7% for the LD at an optimum operating voltage. The maximum optic-to-electric conversion efficiencies of the solar cell and PD are 16.7% and 6.0% (including the receiving lens loss), respectively, with optimization of load resistance. Therefore, the total back-to-back transfer efficiency is 12.1% (DC-to-DC) with the solar cell receiver. Our results show a potential attenuation of 0.006 dB/m, implying a 3-dB distance of 500 m, if the laser beam divergence challenge can be addressed.

A microwave photonic phase shifter that can realize a full 360-deg phase shift is presented. In the scheme, an optical polarization modulator is used to generate a single-sideband optical microwave signal with two orthogonally polarized tones, then a polarization sensitive electro-optical phase modulator is used to introduce the relative phase shifts between the two orthogonally polarized tones to realize the desired phase shift for the microwave signal in the photocurrent, and the phase shift of the microwave signal increases linearly with the DC driving voltage while it keeps a constant amplitude. The simulation results show that continuous phase shift with tuning range from −180  deg to +180  deg is realized for the microwave with the frequency from 4 to 38 GHz and the amplitude variation of the phase-shifted microwave signal is <1  dB.

In underwater direct current-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) system, high peak-to-average power ratio (PAPR) brings in-band distortion and out-of-band power. It also decreases the signal-to-quantization noise ratio of the analog-to-digital converter and the digital-to-analog converter. A time–frequency-domain interleaved subbanding scheme is proposed to reduce the PAPR of underwater DCO-OFDM system with low computation complexity and bit error rate (BER). The system BER is evaluated by the distances of the underwater optical wireless communication (UOWC), as well as by the signal attenuation of the UOWC channel. A least-square channel estimation method is adopted for adaptive power amplification at the receiver side, to further decrease the system BER.

We demonstrate influences of the power splitting ratio of the quadrature-arm to the input signal on both receiver sensitivity and residual phase error for a 10-Gb/s binary phase-shift keying coherent receiver based on an optical homodyne Costas loop. Fine adjustment of the signal power splitting ratio (Ks) is realized by tuning the polarization state of the input signal light of a dual-polarization optical 90-deg hybrid, leading to the precise control of the power distribution on two orthogonal states of polarization that are used for in-phase and quadrature arm, respectively. When the phase error is negligible (<10  deg) under different Ks, the sensitivity is improved by 2.65 dB and the Ks is optimized around 0.05. Based on loop bandwidth maintaining, the requirement on laser linewidth is also relaxed, i.e., 5.26 times larger linewidth is permitted at Ks  =  0  .  05 than that without loop bandwidth maintaining. To fully utilize the signal light power and to avoid excess losses of the dual-polarization hybrid, homodyne Costas coherent receiver with a free-space optics-based 90-deg hybrid is also proposed. All experimental and theoretical results demonstrate the potential of approaching shot noise limited sensitivity for a Costas coherent receiver with an optimum Ks. It is significant to increase power budget and transmission span for satellite optical communication and free-space optical communication.

A relatively simple design of a terahertz (THz) polarization splitter based on an asymmetric dual-suspended-core fiber is proposed. One core is formed by two intersecting rectangular dielectric strips with dissimilar thickness, whereas the other is a round solid core suspended by crossed dielectric strips with the same thickness. The distance between the cores can be adjusted to ensure a short splitting length and low transmission loss. A THz polarization splitter with a length of 1.27 cm is realized with a low transmission loss of 0.53 and 0.67 dB for the x- and y-polarization modes, respectively. An extinction ratio of about −20  dB and a broad bandwidth of 0.046 THz are demonstrated.

We simulated and investigated the performance of optical overlay of two multicast and a unicast data on a wavelength division multiplexed passive optical network using intensity and minimum shift keying modulation. In an optical line terminal (OLT), three optical subcarriers are generated from a single sinusoidal clock to carry two independent 10-Gbps multicast data and one 10-Gbps unicast data through dispersion-shifted fiber. At the same time, another 10-Gbps data are remodulated and transmitted back to the OLT. Error-free transmission is achieved and almost the same power penalty is observed for the downstream unicast as well as the remodulated upstream data irrespective of whether either one or both of the multicast data are enabled or disabled.

The properties of coatings deposited by electron-beam (e-beam) technique can be easily influenced by environmental humidity, causing spectrum shift, residual stress evolution, and wave front errors. HfO2  /  SiO2 multilayer coatings with different overcoat layer deposition parameters have been prepared. The optical spectrum shifts induced by atmosphere-vacuum effect are investigated by a spectrometer. The laser resistance is studied and their damage morphologies are characterized by a scanning electron microscope. The surface morphologies and the global mechanical stresses of the films are analyzed by an atomic force microscope and zygo interferometer, respectively. The experimental results demonstrate that by introducing a dense capping SiO2 layer employed with plasma ion assisted deposition, considerable environmental stability of e-beam coatings can be improved due to retarded water vapor transport. A relatively smaller grain size can be obtained as well. Moreover, the laser-induced damage threshold shows no significant difference.

We propose a scheme for a large scalable and compact antenna array with subwavelength antenna spacing. In this scheme, the array consists of a series of hybrid plasmonic nanoantennas, which operate at 1550 nm and have a subwavelength footprint. In a wide bandwidth, the nanoantenna is highly compatible with a low-loss silicon waveguide, which feeds light from the bottom of the nanoantenna. Based on the proposed nanoantenna, two silicon photonic antenna arrays (1  ×  8 and 8  ×  8) are designed and investigated in detail. Both the one- and two-dimensional arrays can realize wide steering without grating lobes. For the 8  ×  8 array, a high gain of 24.2 dB and wide steering range of 88.0 deg  ×   90.0 deg are achieved.

We propose an optical switch with a circular tunable aperture based on electrowetting effect. The device is composed of two immiscible liquids. One liquid is dye-doped and conductive, while the other is transparent and insulating. The dye-doped water droplet is placed in the center of the bottom substrate, surrounded by transparent oil. In our experiment, in the voltage-off state, the light beam cannot pass through the aperture. When the voltage is applied, the black liquid expands in the radial direction because of the effect of electric field force and a circular aperture appears in the center of the device. Therefore, the device can achieve the function of light-on and light-off. Our device can provide a reasonable attenuation (∼582  ∶  1). The aperture can be tuned from ∼0 to ∼5.8  mm. It requires ∼260  ms and ∼2.4  s for the device to switch on and off, respectively. Potential applications of this tunable optical switch are wide, for example, in adaptive irises, light shutters, and optical beam controls.

An integrated optical displacement sensor based on a reflective Mach–Zehnder interferometer (MZI) was developed. The sensor features a low-loss autocollimation measurement head fabricated using a 62.5-μm gradient index fiber as lens, which separates the incoming and reflected light. The mounting of the lenses and the fiber coupling were performed using a passive alignment assembly technology. Using a 3  ×  3 directional coupler (DC), the direction of the phase shift can be resolved. The measurement head exhibits low losses compared to a conventional DC to separate the reflected light. A measurement range of 225  μm could be achieved in good agreement with the expected 230  μm. The results show a good agreement between simulation and measurements. Using basic measurement electronics, movements of 2 nm can be resolved, while a resolution of &lt;1  nm is expected using optimized measurement equipment.

The integrated optical chip (IOC) is one of the most critical parts of the interferometric fiber optic gyroscope (IFOG). Unfortunately, the integral implementation of the IOC has a number of undesirable effects, which includes the modulation phase error. The inflexible influence of the modulation phase error on the bias error is analyzed in theory. For demonstrating, a method is found to measure the modulation phase error quantitatively. By experiment, the quantized parameter and its effect on bias error are presented. In addition, we offer a practical method to compensate the mentioned effect in IFOG, which is proved by the quantitative measurement. This study proposes a direction for IOC manufacturing inspection and evaluation.

This paper focuses on designing and analyzing a visible light-based communication and positioning system for indoor wireless communication under light-emitting diodes (LEDs) lighting environments. The indoor positioning system uses trichromatic white LEDs, both for illumination purposes and as transmitters, and an optical processor, based on a-SiC:H technology, as a mobile receiver. An on–off keying modulation scheme is used, proving a good trade-off between system performance and implementation complexity. The relationship between the transmitted data and the received output levels is decoded. LED bulbs work as transmitters, sending information together with different identifiers, IDs, related to their physical locations. Square and diamond topologies for the unit cell are analyzed, and a two-dimensional localization design, demonstrated by a prototype implementation, is presented. Fine-grained indoor localization is tested. The received signal is used in coded multiplexing techniques for supporting communications and navigation concomitantly on the same channel. The location and motion information are found by mapping the position and estimating the location areas.

Fresnel reflection losses have been reduced by the fabrication of random nanostructures on optical component surfaces, acting as an antireflective treatment. These structures have shown a broadband enhancement over a wide range of angle-of-incidence and polarization insensitivity. The random nanostructures were fabricated on pre-existing, near-wavelength period, fused silica binary gratings, with periods of 1.595 and 1.166  μm, respectively. The diffractive properties and the efficiency were measured and compared prior and postimplementation of the random nanostructures. The postprocessed gratings retained the diffractive properties of the original gratings, such as the propagating diffraction order angles, period, and the fill factor. A selectable multiwavelength He–Ne laser working at 594, 612, and 633 nm was used to test the gratings for both incident polarizations, S (TE) and P (TM). The data were collected at normal and Bragg incidence. The Fresnel reflection was suppressed by a factor of 10 postprocessing, resulting in a reflected intensity of 0.5% to 1.0% for 1.595-μm period grating and around 0.5% to 4% for 1.166-μm period grating. A 10% enhancement was observed for the combined transmission diffraction efficiency at S polarization for the 1.166-μm grating. Beam profiles of the diffracted light show no adverse changes due to the random nanostructuring on both the gratings. The results indicate that random nanostructures can be an antireflective treatment for pre-existing binary gratings, without adverse effects on the grating diffractive properties and beam profiles.

A micro all-glass fiber-optic accelerometer based on the extrinsic Fabry–Perot interferometer (EFPI) is developed. A microcantilever beam is fabricated using a femtosecond laser and assembled with a silica tube and a silica inertial mass. Two mirrors, the end face of the leading single-mode fiber and the inner glass/air interface of the cantilever beam, form an EFPI. When the accelerometer is subjected to the vibration along the fiber axis, the vibration is detected by interrogating the variation in the cavity length of the EFPI. The proposed accelerometer has a compact structure and high signal-to-noise ratio. Experimental results show that the sensitivity of 2.9 nm/g@500 Hz within the acceleration range of 0 to 3 g is achieved. The accelerometer can work within the frequency range of 100 to 1500 Hz.

When the peak positions of propagating surface plasmon polaritons (SPPs) and localized surface plasmon resonances (LSPRs) become very close to each other in a single nanoparticle array structure, an anticrossing behavior of the surface plasmon resonances (SPRs) peak positions usually occurs, which can considerably enhance the near-field intensity. We first report on the interaction of two types of SPRs in a dimer nanodisk–SiO2 spacer–gold film hybrid sandwich structure. The anticrossing behavior does not appear always due to various modes of LSPRs in such structures. Moreover, a crossing behavior also appears based on the interaction of SPPs and a longitudinal bonding mode of LSPRs. When the anticrossing behavior occurs, a bandgap that changes only with the array period also appears. This bandgap influences the electric field intensity enhancement not only in the anticrossing behavior but also in the crossing behavior. The electric field intensity distribution properties both in the anticrossing behavior and crossing behavior are discussed with reference to the hybrid properties of the SPPs and LSPRs modes. Furthermore, we report on the occurrence mechanisms of these different behaviors.

Metamaterial band-selective perfect absorbers are attractive for constructing surfaces with specified infrared emissivity. The difficulty in realizing such surfaces arises from the complexity in the manufacturing of multilayered (usually trilayered) and micro or nanostructures with high fidelity over large areas. Here, we develop and experimentally realize a simplified design for large-area metamaterials with specified infrared emissivity by utilizing the resonant excitations in a bilayered microstructure. The design is validated using computational models, and the origin of absorption in the metamaterial structure is identified. The design of the metamaterial allows for a simplification in the fabrication processes, and it is fabricated in sequential steps of fabrication of a master pattern by laser interference lithography, microstructuring on arbitrary surfaces by soft imprint lithography, and vacuum deposition of two layers of thin films. The methods are suitable for fabricating the metamaterial over flexible and extremely rough surfaces also and can be adopted easily for rapid prototyping and roll-to-roll manufacturing.

A metamaterial-based energy harvesting structure has been designed and experimentally tested in this study. The proposed structure has square and split ring resonators placed in different angles on the back and front sides for compatible multiband operation in energy harvesting. Resonance points have been defined at 900 MHz, 1.37 GHz, 1.61 GHz, 1.80 GHz, and 2.55 GHz, by simulation and experimental methods. These points correspond to Global System for Communication (GSM) 900, GSM 1800, Universal Mobile Telecommunication System (UMTS), satellite navigation, and Industrial Scientific and Medical (ISM) band frequencies. Supporting multiband application in a single structure without changing dimensions or design is one of the properties of this study. To harvest captived electromagnetic energy, an HSMS 2860 Schottky diode has been used. For wireless power transmission efficiency, voltage across the Schottky diode has been measured by a spectrum analyzer in different points experimentally. The maximum obtained voltage across the Schottky diode is 90 mV at 1800 MHz when a 500 mV signal is applied from a 5 cm distance. Simulated and experimental results prove that the proposed structure can effectively be used in GSM, satellite communication, and UMTS electromagnetic bands for energy harvesting and filtering applications.

Erratum to correct Fig. 6.