This PDF file contains the editorial “Globalization” for OE Vol. 54 Issue 09

There is an increasing demand for high-intensity subnanosecond lasers for emerging industrial applications. While femtosecond and picosecond laser sources are considered promising, they suffer from the significant drawbacks of increased complexity and cost. In this regard, we demonstrate a unique edge-pumped passively Q-switched Nd∶YAG/Cr⁴⁺∶YAG microchip laser. The microchip is made of a Nd∶YAG/Sm∶YAG composite ceramic, and a Sm∶YAG cladding is utilized as both the pump beam waveguide and amplified spontaneous emission absorber. With the use of a flat-concave laser cavity, we obtain single-pulse energy of 1.66 mJ for an absorbed pump energy of 24 mJ. Further, the resulting pulse width is 683 ps, and the repetition rate is 10 Hz.

Higher capacity and larger scales have always been the top targets for the evolution of optical access networks, driven by the ever-increasing demand from the end users. One thing that started to attract wide attention not long ago, but with at least equal importance as capacity and scale, is energy efficiency, a metric essential nowadays as human beings are confronted with severe environmental issues like global warming, air pollution, and so on. Here, different from the conventional energy consumption analysis of tree-topology networks, we propose an effective energy consumption calculation method to compare the energy efficiency of the tree-topology 10 gigabit ethernet passive optical network (10G-EPON) and ring-topology time- and wavelength-division-multiplexed passive optical network (TWDM-PON), two experimental networks deployed in China. Numerical results show that the ring-topology TWDM-PON networks with 2, 4, 8, and 16 wavelengths are more energy efficient than the tree-topology 10G-EPON, although 10G-EPON consumes less energy. Also, TWDM-PON with four wavelengths is the most energy-efficient network candidate and saves 58.7% more energy than 10G-EPON when fully loaded.

The representation of a three-dimensional (3-D) scene is essential in multiview imaging technologies. We present a unified geometry and texture representation based on global resampling of the scene. A layered data map representation with a distance-dependent nonuniform sampling strategy is proposed. It is capable of increasing the details of the 3-D structure locally and is compact in size. The 3-D point cloud obtained from the multilayered data map is used for view rendering. For any given viewpoint, image synthesis with different levels of detail is carried out using the quadtree-based nonuniformly sampled 3-D data points. Experimental results are presented using the 3-D models of reconstructed real objects.

Hyperspectral image data suffer from pixel-to-pixel response nonuniformity that degrades the imagery in the form of columnated striping noise. This nonuniformity, or fixed pattern noise (FPN), is typically compensated for through flat-field calibration procedures. FPN is a particularly challenging problem because the detector responsivities drift relative to one another in time, requiring that the sensor be periodically recalibrated. Both the rate and severity of the drift depend on a host of factors that result in varying levels of residual calibration error being present within the data at all times. Scene-based nonuniformity correction (SBNUC) algorithms estimate and remove FPN by exploiting content within the scene data and are often necessary to acceptably remove sensor artifacts for subpixel target detection applications. We present results from two SBNUC techniques that reduce residual FPN and improve target signal-to-clutter ratio. We make the observation that temporally reordering the data in conjunction with the use of spatial ratios or differentials results in algorithms that require a low number of temporal data samples to reliably correct for FPN with minimal introduction of image artifacts. Additionally, application of the algorithms within the principal components domain can further improve their correction ability.

Optical flow (OF) methods are used to estimate dense motion information between consecutive frames in image sequences. In addition to the specific OF estimation method itself, the quality of the input image sequence is of crucial importance to the quality of the resulting flow estimates. For instance, lack of texture in image frames caused by saturation of the camera sensor during exposure can significantly deteriorate the performance. An approach to avoid this negative effect is to use different camera settings when capturing the individual frames. We provide a framework for OF estimation on such sequences that contain differently exposed frames. Information from multiple frames are combined into a total cost functional such that the lack of an active data term for saturated image areas is avoided. Experimental results demonstrate that using alternate camera settings to capture the full dynamic range of an underlying scene can clearly improve the quality of flow estimates. When saturation of image data is significant, the proposed methods show superior performance in terms of lower endpoint errors of the flow vectors compared to a set of baseline methods. Furthermore, we provide some qualitative examples of how and when our method should be used.

This paper proposes a temperature-dependent behavioral circuit model to predict the optical characteristics of an active-matrix liquid crystal display with a fringe-field switching (FFS) mode. The optical responses of liquid crystal displays (LCDs) are strongly affected by their ambient temperature. We optimized the time-constant parameters that describe the movement of liquid crystal molecules so that simulated optical responses of FFS LCD provide the best fit to the measured responses over the temperature range of 0 to 50°C. It is found that these time-constant parameters have a linear relationship with the ambient temperature, which enables the prediction of optical responses at any given temperature. The simulation results of the transient responses show an excellent match with the measured results regardless of the ambient temperature.

A fast and effective algorithm for designing the diffraction optical element (DOE) with a wide-diffraction angle is presented. DOE had been widely used in many fields in recent years, but there are finite methods which can design DOE with wide-diffraction angle quickly occupying a small quantity of computing resource. By the use of a nonparaxial scalar diffraction equation as the light transmission operator, a modified iterative algorithm is proposed. To verify our algorithm, the checkerboard image, binary image, and gray-scale image are numerically simulated, respectively. The simulation results show that the final variance between the preset image and final pattern is very small, the value is generally lower than 10⁻⁵, and the natural images even have a final variance less than 10⁻¹². At the same time, the diffraction efficiency has been significantly increased to be larger than 90%, which indicates that the design method is effective and practical.

The unprecedented amount and multiple applications of remote sensing image data have created a strong need for efficient data transmission. Commonly used in the transmission of various types of data, peer-to-peer (P2P) opens up new possibilities for the transmission of remote sensing image data. A considerable amount of work has been done toward the transmission of remote sensing data by using map tiles for fast online browsing. However, issues concerning the transmission of original image data require more volume and flexibility, which is indispensable in the application of remote sensing images. According to the spatial and band characteristics of remote sensing images, an approach using image subset blocks (ISBs) is proposed for P2P transmission of remote sensing image data. The method improves efficiency in two ways: transmitting ISBs on demand to reduce unnecessary transmission and using a P2P method to break the bandwidth bottleneck of the central server. The results of the performance evaluation reveal that compared with the traditional transmission method that uses the central server, the proposed method considerably enhances the efficiency to approach the level of general P2P file transmission.

This study proposes an alternative and simple method for measuring full-field refractive index. This method is based on the phase-shifting technique with a modulated electro-optical (EO) modulator and the phenomenon of total internal reflection. To this purpose, a linear polarized light is expanded and incident on the interface between the prism and the tested specimen, and the reflected light passes through an analyzer for interference. The phase difference between the s- and p-polarized light is sensitive to the refractive index of the tested specimen when the total internal reflection appears on this interface. Based on this effect, the resulting phase differences make it possible to analyze the refractive index of the tested specimen through a phase-shifting technique with a modulated EO modulator. The feasibility of this method was verified by experiment, and the measurement resolution can reach a value of refractive index unit of at least 3.552×10⁻⁴. This method has advantages of simple installation, ease of operation, and fast measurement.

This paper describes the use of a hybrid evolutionary optimization algorithm (HEOA) for computing the wavefront aberration from real interferometric data. By finding the near-optimal solution to an optimization problem, this algorithm calculates the Zernike polynomial expansion coefficients from a Fizeau interferogram, showing the validity for the reconstruction of the wavefront aberration. The proposed HEOA incorporates the advantages of both a multimember evolution strategy and locally weighted linear regression in order to minimize an objective function while avoiding premature convergence to a local minimum. The numerical results demonstrate that our HEOA is robust for analyzing real interferograms degraded by noise.

Soil reflectance signatures were modeled using the digital imaging and remote sensing image generation model and Blender three-dimensional (3-D) graphic design software. Using these tools, the geometry, radiometry, and chemistry of quartz and magnetite were exploited to model the presence of particle size and porosity effects in the visible and the shortwave infrared spectrum. Using the physics engines within the Blender 3-D graphic design software, physical representations of granular soil scenes were created. Each scene characterized a specific particle distribution and density. Chemical and optical properties of pure quartz and magnetite were assigned to particles in the scene based on particle size. This work presents a model to describe an observed phase-angle dependence of beach sand density. Bidirectional reflectance signatures were simulated for targets of varying size distribution and density. This model provides validation for a phenomenological trade space between density and particle size distribution in complex, heterogeneous soil mixtures. It also confirms the suggestion that directional reflectance signatures can be defined by intimate mixtures that depend on pore spacing. The study demonstrated that by combining realistic target geometry and spectral measurements of pure quartz and magnetite, effects of soil particle size and density could be modeled without functional data fitting or rigorous analysis of material dynamics. This research does not use traditional function-based models for simulation. The combination of realistic geometry, physically viable particle structure, and first-principles ray-tracing enables the ability to represent signature changes that have been observed in experimental observations.

We present the application of a laser ultrasonic technique in nondestructive characterization of the bonding layer (BL) in a thermal barrier coating (TBC). A physical mode of a multilayered medium is established to describe the propagation of a longitudinal wave generated by a laser in a TBC system. Furthermore, the theoretical analysis on the ultrasonic transmission in TBC is carried out in order to derive the expression of the BL transmission coefficient spectrum (TCS) which is used to determine the velocity of the longitudinal wave in the BL. We employ the inversion method combined with TCS to ascertain the attenuation coefficient of the BL. The experimental validations are performed with TBC specimens produced by an electron-beam physical vapor deposition method. In those experiments, a pulsed laser with a width of 10 ns is used to generate an ultrasonic signal while a two-wave mixing interferometer is created to receive the ultrasonic signals. By introducing the wavelet soft-threshold method that improves the signal-to-noise ratio, the laser ultrasonic testing results of TBC with an oxidation of 1 cycle, 10 cycles, and 100 cycles show that the attenuation coefficients of the BL become larger with an increase in the oxidation time, which is evident for the scanning electron microscopy observations, in which the thickness of the thermally grown oxide increases with oxidation time.

The thermal optical properties of a holographic material were measured using total internal reflection heterodyne interferometry. The effective thermal expansion coefficients (ETECs) of the holographic material were determined at various exposure times. Our results showed that the holographic material exhibited a smaller thermal expansion coefficient (TEC) with a longer exposure time than those materials with short exposure times. Thus the diffraction power increased as the exposure time of the holographic material increased. Furthermore, the proposed method provides a highly accurate means of measurement for determination of the TEC. The theoretical ETEC error of the proposed method is better than 1.1×10⁻⁷ and the practical ETEC error under the precision measurement conditions can reach to 2.3×10−⁶.

Hardware architecture of parallel computation is proposed for generating Fraunhofer computer-generated holograms (CGHs). A pipeline-based integrated circuit architecture is realized by employing the modified Fraunhofer analytical formulism, which is large scale and enables all components to be concurrently operated. The architecture of the CGH contains five modules to calculate initial parameters of amplitude, amplitude compensation, phases, and phase compensation, respectively. The precalculator of amplitude is fully adopted considering the “reusable design” concept. Each complex operation type (such as square arithmetic) is reused only once by means of a multichannel selector. The implemented hardware calculates an 800×600  pixels hologram in parallel using 39,319 logic elements, 21,074 registers, and 12,651 memory bits in an Altera field-programmable gate array environment with stable operation at 50 MHz. Experimental results demonstrate that the quality of the images reconstructed from the hardware-generated hologram can be comparable to that of a software implementation. Moreover, the calculation speed is approximately 100 times faster than that of a personal computer with an Intel i5-3230M 2.6 GHz CPU for a triangular object.

A freeform lens design method based on energy mapping and complementary optimization approaches is proposed to achieve uniform illumination with extended light-emitting diode (LED) sources. This method is primarily derived from a simple source–a target energy mapping approach, while a complementary illuminance on the target plane is introduced to optimize the primary axisymmetric lens so that the profile of the lens can be reformed to produce uniform illumination when applying an extended LED source. By using this optimization method, the illuminance uniformity and optical efficiency of the lens can be improved, respectively, from 0.56 to 0.85 and from 92.4% to 94.3% for an LED light source with chip diameter of 8.9 mm, while the aspect ratio of the lens clear aperture to the source diameter is only 3.8.

Projection objectives for deep-ultraviolet lithography typically have a dual-telecentric design, and the telecentricity in object space (mask) is idealized as zero. However, for combined illumination and objective lens systems, telecentricity matching on mask can result in a dramatic change in the pupil intensity distribution. Here, we propose a method of identifying the impact of the mismatch on the pupil fill and decoupling the pupil intensity balance from the telecentricity modulation. The technique is implemented in a user-defined program, and a series of simulations for a hypernumerical aperture immersion objective under off-axis illumination conditions verifies the method.

A modified spectrometer with tandem gratings that exhibits high spectral resolution and imaging quality for solar observation, monitoring, and understanding of coastal ocean processes is presented in this study. Spectral broadband anastigmatic imaging condition, spectral resolution, and initial optical structure are obtained based on geometric aberration theory. Compared with conventional tandem gratings spectrometers, this modified design permits flexibility in selecting gratings. A detailed discussion of the optical design and optical performance of an ultraviolet spectrometer with tandem gratings is also included to explain the advantage of oblique incidence for spectral broadband.

An optical code division multiple access (OCDMA) secure communications system scheme with rapid reconfigurable polarization shift key (Pol-SK) bipolar user code is proposed and demonstrated. Compared to fix code OCDMA, by constantly changing the user code, the performance of anti-eavesdropping is greatly improved. The Pol-SK OCDMA experiment with a 10  Gchip/s user code and a 1.25  Gb/s user data of payload has been realized, which means this scheme has better tolerance and could be easily realized.

A compact continuous-wave and actively Q-switched Ho : LuVO₄ laser pumped by a 1.94  μm Tm:YAP laser is demonstrated. The maximum output power of 6.7 W at 2058.13 nm in continuous-wave regime is obtained at an absorbed pump power of 17.8 W, corresponding to a slope efficiency of 48.4%. For Q-switched operation, average output power of 6.65 W and pulse width of 22.3 ns are obtained with a repetition frequency of 20 kHz, corresponding to a central wavelength of 2058.13 nm. In addition, different Q-switched pulses at repetition frequencies of 20, 30, 40, 50, and 60 kHz are investigated comparatively.

Design and experimental realization of C-band superfluorescent fiber sources using a well-designed high reflector/filter of fiber Bragg grating (FBG) in three configurations, namely double-pass forward (DPF), double-pass backward (DPB), and DPF+DPB, is realized. Using a numerical method, the optimum length and peak absorption coefficient of erbium-doped fiber as well as the optimum specifications of FBG, i.e., its 3-dB bandwidth and central wavelength, are calculated. Our numerical calculations illustrate that an appropriate design may result in a flattened amplified spontaneous emission (ASE) output spectrum with a 3-dB bandwidth of about 22 nm and a central wavelength of 1550 nm. Furthermore, the peak power of the flattened ASE spectrum is 16 dBm larger than the power at a wavelength of 1530 nm that is beneficial for increasing the 3-dB bandwidth. The experimental results show that using an optimum design, there are negligible differences between ASE output spectra acquired by different double-pass configurations. However, the DPB configuration has a higher efficiency as compared with other configurations and can provide a C-band superfluorescent fiber source with a simultaneously good spectral flatness, <0.73  dB, high output power of 12 dBm, and maximum 3-dB bandwidth of about 22 nm.

This paper reports a simple technique for hydraulic pressure measurement with enhanced resolution using a fiber Bragg grating (FBG) and a metal spring which acts as transducer. The sensor works by means of measuring the Bragg wavelength shift of FBG caused by the longitudinal elongation of optical fiber due to applied pressure. Experimental results show that the sensor possesses good linearity and repeatability in pressure measurement ranging over 0 to 55 bar, with a sensitivity of 57.7  pm/bar. A wavelength-intensity interrogation scheme using single-multiple-single-mode fiber structure is designed for FBG sensor, which enabled the system to be compact, lightweight, inexpensive, and high resolution.

_{The spectral response of long-period fiber gratings can be tailored by the cladding index perturbation (C-LPFGs) induced by written methods. Here, we investigate theoretically the effects of radial dependence and the magnitude of the cladding index modulation on the transmission spectra of C-LPFGs. Simple analytical expressions that describe the dispersion characteristics of the guided core mode and cladding modes are derived from a multilayer cylindrical waveguide. As the radial depth increases, we demonstrate that transition points exist for the resonances of lower cladding modes, i.e., LP06 and LP15 modes, by comparing the mode-coupling phase to the value π/2. In addition, we show that resonant wavelength shifts of all cladding modes follow the same trend. For the LPνj (ν≠0) modes with two polarizations, the cross talk weakens the power exchanges between core mode LP01 and LPνj(ν≠0) modes. Moreover, the coupling mechanism relating to cladding index modulation is explained by the presence of the interaction between the evanescent field of the core mode and cladding modes. This work is promising in terms of providing sufficient guidelines to understand and explore design and application of LPFGs.}

We report a compact, 130-W single-stage master oscillator power amplifier with a high peak power of 51.3 kW and a narrow spectral linewidth of 0.1 nm. The seed source is a single-mode, passively mode-locked solid-state laser at 1064 nm with an average power of 2 W. At a repetition rate of 73.5 MHz, the pulse duration is 30 ps. After amplification, it stretches to 34.5 ps. The experiment enables the optical-to-optical conversion efficiency to reach 75%. To the best of our knowledge, this is the first report of such a high-power, narrow spectral linewidth, high peak power picosecond-pulse fiber amplifier based on a continuous-wave, mode-locked solid-state seeding laser. No amplified spontaneous emission and stimulated Raman scattering were observed when the pump was increased.

We describe a layer-1-based intrusion detection system for fiber-optic–based networks. Layer-1-based intrusion detection represents a significant elevation in security as it prohibits an adversary from obtaining information in the first place (no cryptanalysis is possible). We describe the experimental setup of the intrusion detection system, which is based on monitoring the behavior of certain attributes of light both in unperturbed and perturbed optical fiber links. The system was tested with optical fiber links of various lengths and types, under different environmental conditions, and under changes in fiber geometry similar to what is experienced during tapping activity. Comparison of the results for perturbed and unperturbed links has shown that the state of polarization is more sensitive to intrusion activity than the degree of polarization or power of the received light. The testing was conducted in a simulated telecommunication network environment that included both underground and aerial links. The links were monitored for intrusion activity. Attempts to tap the link were easily detected with no apparent degradation in the visual quality of the real-time surveillance video.

A hybrid bidirectional orthogonal frequency division multiple access-passive optical network (OFDMA-PON) based on offset quadrate phase shift keying (OQPSK) to support 60- and 120-GHz radio-over-fiber system is proposed. The system can support wired/wireless applications and enable the dynamic bandwidth allocation according to a subscriber’s application. It is successfully achieved by using the millimeter waves (MMWs) generation and the carrier-reuse technique. In the proposed scheme, the MMW bands used for downlink (DL) and uplink transmissions are generated at the optical line terminal by the dual-arm Mach–Zehnder modulators. Both 60- and 120-GHz MMWs are obtained for the transmission of the high bit-rate services in source-free optical network units (ONUs), only using a single 15-GHz sinusoidal wave source. The Rayleigh backscattering effect is considered in the proposed OQPSK-based OFDMA-PON. For DL transmission over a 30-km single-mode fiber, the power penalties are less than 0.8 and 1 dB for the OQPSK-OFDM wired data at 10  Gb/s and the OQPSK-OFDM wireless data at 5  Gb/s, respectively.

A red-emitting external cavity diode laser (ECDL) module was designed to increase the slope efficiency and reduce the bandwidth by tilting the solitary laser diode (LD) 90 deg. This tilt resulted in parallel polarization, which yielded high-slope efficiency and also produced a favorable geometry that minimized the area of the back-focused beam, thereby facilitating selection of a specific wavelength. A ray-tracing simulator was used to optimize optical parameters such as the back focal length of the collimating lens, the cavity length, and the grating’s groove density. Based on the optimized structure, an ECDL module package was designed for thermal control by using autodisk computer-aided design tool. The resulting module obtained high-slope efficiency and narrow-bandwidth emission of red light, making it suitable for potential application as a light source for a commercial three-dimensional holographic system. The module achieved the narrow bandwidth of 80 pm and the slope efficiency of 0.81  W/A, which compared favorably with the output power of 0.8 to 0.9  W/A of commercial solitary LDs.

The process of ablation in obsidianus lapis is mainly governed by pulse energy from the laser source and scanning speed. The rate of material ablation is influenced by chemical and physical properties. In this work, laser energy at 1064 nm has been used for ablation behavior in a Q-switch regime. A <40  W average power Nd:YAG source with pulse energies ranging from 3 mJ to nearly 7 mJ, achieved surface damages up to 160  μm of depth. Photomechanical ablation in terms of scan speed showed a maximum depth of nearly 500  μm at 130  mm/s. The maximum pulse energy of 12 mJ resulted in the ablation of 170-μm depth. Highly efficient ablation in obsidianus lapis for artistic work is an interesting field of application.

An electromagnetic (EM) energy harvesting application based on metamaterials is introduced. This application is operating at the the industrial, scientific, and medical band (2.40 GHz), which is especially chosen because of its wide usage area. A square ring resonator (SRR) which has two gaps and two resistors across the gaps on it is used. Chip resistors are used to deliver the power to any active component that requires power. Transmission and reflection characteristics of the metamaterial absorber for energy harvesting application are theoretically investigated and 83.6% efficient energy harvesting application is realized. To prove that this study can be used for different sensor applications other than harvesting, a temperature sensor configuration is developed that can be applied to other sensing applications.

We demonstrated that achieving suitable adjustable and tunable magneto-optical (MO) responses is possible by offering an appropriate approach for the design of magnetophotonic crystal (MPC) structures. The introduced MPCs are thin and high performance (with Kerr rotations around or even more than 90 deg accompanied by reflections near 100%). Our designs also offer multifunctional operations that can lead to devices which possess multioperation modes such as polarization mode converting, MO sensing, and isolation. To attain different modes of operation, we use an adjustment parameter.

A Fabry–Perot (F-P) fiber acoustic sensor, which can work under high-temperature harsh environment with temperature self-compensation, is designed and prepared. A condenser was used to maintain the sensor to work in a stable temperature environment. Because of the special structure of the sensor and the function of the condenser, the cavity variation of the sensor caused by changes of external temperature from −10°C to 500°C would not exceed 8 nm. The experimental results show that the sensor has a good frequency response in a range of 1 to 5 kHz and the field experiment results show that it could be used for hydraulic decoking online monitoring by judging the acoustic frequency spectrum.

This paper presents a large negative flattened dispersion with high birefringence for a very wide wavelength range by designing a new high index lead silicate (SF57) soft glass equiangular decagonal spiral microstructured optical fiber (DS-MOF). The bandwidth supports the second and third windows covering the O+E+S+C+L+U bands in the infrared region. The guiding properties of the DS-MOF are investigated by the finite-element method with a perfectly matched layer boundary. The proposed design is a suitable candidate for the application of residual dispersion compensation with maintaining polarization characteristics since it offers a high negative flattened dispersion of −(453 ± 7)  ps⋅nm⁻¹ km⁻¹ with a high birefringence of the order 10⁻² for the wide wavelength range of 1.15 to 1.75  μm. The DS-MOF has some circular air holes that make the fabrication process simple. In addition, the effects of changing the structural parameters by up to ±4% are also analyzed to ensure the accuracy during the fabrication process.

We report on dual-line waveguides fabricated by direct femtosecond laser writing in Cu:KNSBN crystal. Two different sizes have been designed with the separation between lines of 20 and 30  μm, respectively. The detailed structure of the dual-line waveguide has been imaged by means of micro-Raman analysis, indicating that the microstructure of the Cu:KNSBN crystal has no significant change after direct femtosecond laser writing. The dual-line waveguides support single-mode guidance along both transverse electric and transverse magnetic polarization at the wavelengths of 632.8 and 1064 nm, and show insensitivity to polarization of light. We suggest the potential application of the laser-written Cu:KNSBN waveguides as new integrated optical devices.

Long-range surface plasmon polariton (LRSPP) interference in a dielectric supported bimetal layer configuration is analyzed for nanoscale periodic feature fabrication. The single metal layer in a conventional configuration has been split into a bimetal layer configuration supported by a dielectric layer to enable LRSPP interference in different layers. It is shown that the configuration can be implemented in two different ways to record the interference pattern with high exposure depth and high contrast. Subwavelength periodic pattern having a half-pitch resolution of 65 nm at 446-nm wavelength is illustrated with the proposed two-beam and four-beam LRSPP interference configurations.

We investigate macroscopic polymer lenses (0.5- to 2.5-cm diameter) fabricated by dropping hydrophobic photocurable resin onto the surface of various hydrophilic liquid surfaces. Due to the intermolecular forces along the interface between the two liquids, a lens shape is formed. We find that we can vary the lens geometry by changing the region over which the resin is allowed to spread and the surface tension of the substrate to produce lenses with theoretically determined focal lengths ranging from 5 to 25 mm. These effects are varied by changing the container width, substrate composition, and substrate temperature. We present data for five different variants, demonstrating that we can control the lens dimensions for polymer lens applications that require high surface quality.

We present an analytical model to investigate power detection-based interrogation methods for optical fiber Bragg grating (FBG) sensors. This model is used to facilitate the optimization of interrogation systems in terms of sensitivity and dynamic range. In general, power detection methods are passive intensity-based interrogation schemes, where the spectral shift in the FBG due to the applied measurand is converted into a change in optical power due to the spectral properties of the light source. The analytical model developed herein assumes that the FBG and light source are Gaussian shaped. As such, the filtering of the light source by the FBG results in the reflection of a Gaussian spectrum governed by the properties of both the light source and FBG. The further investigation of the model has enabled analytical expressions to be developed for the sensitivity and dynamic range of the different power detection methods considered. The different power detection methods investigated include linear edge source and narrow bandwidth source (utilizing the reflected component, transmitted components, and both the transmitted and reflected components). Results show how the dynamic range and sensitivity of the power detection methods vary for different FBG sensor widths and different light source properties, specifically the width and optical power. This facilitates a direct comparison between the interrogation methods and also enables system optimization based on either a given light source or FBG.