Optical Subsystems Research Articles

Spatial Registration for a Three-Arm Robot Assisted Mandible Reconstruction Surgery

The three-arm surgical robot system assisted mandible reconstruction surgery (TMR-MRS) is developed to repair the mandible defects caused by congenital defect, trauma, or acquired disease. The surgical robot system is divided into four parts, including 3D reconstructed image subsystem, robotic subsystem, optical measurement subsystem, and patient subsystem. The spatial registration based on quaternion is proposed to obtain the transformation relationship between four surgical subsystems. A method of hand-eye coordination is presented to control the end-effector of the robot arm to target position according to surgical planning. A least square error criterion is developed to optimize and compensate the hand-eye coordination method. In addition, the position of fibular implant in the robot space is calculated when it is grasped by end-effector of robot middle arm. Finally, the positioning accuracy tests and skull model experiments were conducted to evaluate the function of the surgical robot system. The results validate its feasibility and are consistent with the preoperative surgical planning.

Holographic diffraction-through-aperture spectrum splitting for increased hybrid solar energy conversion efficiency

A holographic module is designed to split light into two spectral bands for hybrid solar energy conversion. Incoming light is either transmitted to a large subsystem receiver or diffracted through an aperture in this receiver toward a second subsystem receiver. The holographic element is simulated using rigorous diffraction and ray-tracing methods. Two applications of the design are described and simulated. A photovoltaic/thermal system with 93% optical efficiency and adjustable subsystem power output ratio is designed to address solar intermittency and provide energy storage. A photovoltaic system added to an alga biofuel operation significantly increases energy output while maintaining 92% of the original algae yield. The energy return on investment of this photovoltaic/biofuel system is 2.4× greater than that of the biofuel system alone, leading to economically viable operation. Modifications to the standard holographic lens provide additional increases in spectrum-splitting capability, optical efficiency, and energy conversion efficiency. The diffraction-through-aperture concept is demonstrated as a successful approach to spectrum splitting for hybrid solar applications. Copyright © 2014 John Wiley & Sons, Ltd.

Analysis of adaptive optics-based telescope arrays in a deep-space inter-planetary optical communications link between Earth and Mars

Earth-based telescope array receivers employing optical communications have the potential to fulfill the communication needs of technologically sophisticated, deep-space exploration missions. Atmospheric turbulence is the chief restrictive factor in an optical deep-space channel (ODSC). In this paper, investigation and design of adaptive optics (AO) subsystems are presented for the compensation of the coupled effects of optical turbulence and background noise in telescope array receivers. An end-to-end simulation platform for an ODSC between Mars and Earth is implemented, which incorporates pulse-position modulation (PPM), direct-detection receivers, and detectors with the capability of detection of single photon. The extreme conditions of atmospheric turbulence and background noise are also modeled in the analysis. AO subsystems are incorporated at individual telescopes in the array receiver to mitigate the turbulence effects. The performance of array receivers is evaluated in terms of the probability of error and communication throughput. The analysis in this research depicts that in worst-case turbulence and background noise conditions, inclusion of AO systems results in 8.5dB performance improvement in communication data rates. The performance improvement of 5.6dB is achievable in moderate channel conditions. Comparison of performance of array receivers with that of a large monolithic telescope shows that incorporation of AO systems is more feasible in arrays comprising telescopes with relatively smaller diameters.

Thermal design, build, and test of the JWST Aft Optics Subsystem

Ball Aerospace and Technologies Corporation (BATC) has completed the design, construction, and qualification of the James Webb Space Telescope (JWST) Aft Optics Subsystem (AOS). This paper summarizes the evolution of the thermal design, technical challenges, and the results of thermal performance testing at temperature (30–40K) of this passively cooled subsystem.

Performance assessment of a wideband code‐division multiple access‐based radio‐over‐fibre system with near–far effect: downlink scenario

The impact of a radio-over-fibre subsystem on the total degradation (TD) performance of downlink wideband code-division multiple access with near-far effect is evaluated. The study investigates the use of pilot-aided channel estimation to compensate for the optical subsystem non-linearities for different channel conditions, estimation intervals, load factors (LFs) and near-far factors (NFFs). The results show that pilot-aided channel estimation is an effective method for compensating the composite impairments of the optical subsystem and the radio frequency channel. It is found that there is always a suitable quiescent point that optimises the system performance regardless of aforementioned conditions, however, the optimum achievable performance depends on the LF, spreading factor (SF) and NFF. Also, LF has more impact on the system performance in comparison to SF. Further, the optimum TD performance is only slightly affected by a decrease in the estimation interval over the optimum output backoff range.

Optical evaluation of heliostat mirrors using caustics

Solar thermal power generation is based on the concept of concentrating solar radiation to provide high temperature heat for electricity generation via conventional power cycles. The high relative cost of optical subsystems necessitates a careful study of their components. Solar collector fields are typically modeled by ray-tracing or convolution methods; however, no general method is available for engineering analysis. We propose the use of caustics to predict the image of the sun reflected by an arbitrary mirror of focal length F and aperture a on a target. The mirror surface is described parametrically by a quadric and placed at a distance L from the target on a heliostat. The method of caustics was validated against SolTRACE, a ray-tracing code developed by U.S. National Renewable Energy Laboratories . We show that there is a value of aF which depends on aL, for which the incident average energy flux to the target reaches a maximum. The method of caustics allows the efficient computation of the image on an arbitrary target surface and obviates many of the difficulties with ray-tracing methods.

Pilot‐aided estimation and equalisation of a Radio‐over‐Fibre system in Wideband Code Division Multiple Access

In this study, the impact of a Radio-over-Fibre (RoF) subsystem on the capacity performance of wideband code division multiple access is evaluated. This study investigates the use of pilot-aided channel estimation to compensate for the optical subsystem non-linearities for different channel conditions, estimation intervals and coding schemes. The results show that pilot-aided channel estimation is an effective method for compensating the composite impairments of the optical subsystem and the radio frequency (RF) channel. It is found that there is always a suitable pilot power level which maximises the system capacity performance regardless of coding scheme and channel condition. Also, the peak capacity is only slightly affected by a decrease in the estimation interval.

Introducing Node Architecture Flexibility for Elastic Optical Networks

A large number of factors generate uncertainty on traffic demands and requirements. In order to deal with uncertainty optical nodes and networks are equipped with flexibility. In this context, we define several types of flexibility and propose a method, based on entropy maximization, to quantitatively evaluate the flexibility provided by optical node components, subsystems, and architectures. Using this method we demonstrate the equivalence, in terms of switching flexibility, of finer spectrum granularity, and faster reconfiguration rate. We also show that switching flexibility is closely related to bandwidth granularity. The proposed method is used to derive formulae for the switching flexibility of key optical node components and the switching and architectural flexibility of four elastic optical node configurations. The elastic optical nodes presented provide various degrees of flexibility and functionality that are discussed in the paper, from flexible spectrum switching to adaptive architectures that support elastic switching of frequency, time, and spatial resources plus on-demand spectrum defragmentation. We further complement this analysis by experimentally demonstrating flexible time, spectrum, and space switching plus dynamic architecture reconfiguration. The implemented architectures support continuous and subwavelength heterogeneous signals with bitrates ranging from 190 Mb/s, for a subwavelength channel, to 555 Gb/s for a multicarrier superchannel. Results show good performance and the feasibility of implementing the architecture-on-demand concept.

Caustics as an Alternate of Ray Tracing to Evaluate Heliostat Mirrors

Solar thermal power generation is based on the concept of concentrating solar radiation to provide high temperature heat for electricity generation via conventional power cycles. The high relative cost of optical subsystems necessitates a careful study of their components. The capital cost of the heliostat field in central receiver power plants is significant, reaching up to 50% of the capital investment. Therefore, it is essential to maximize the energy yield from a heliostat with a given mirror area. Solar collector fields are typically modeled by ray-tracing or convolution methods; however, no general method is available for engineering analysis. We propose the use of caustics to predict the image of the sun reflected by an arbitrary mirror of focal length F and aperture a on a target. The method of caustics was validated against SolTRACE, a ray-tracing code developed by the US National Renewable Energy Laboratory (NREL).

Modular sub-wavelength diffractive light modulator for high-definition holographic displays

Holography is undoubtedly the ultimate 3D visualization technology, offering true 3D experience with all the natural depth cues, without the undesirable side-effects of current stereoscopic systems (uncomfortable glasses, strained eyes, fatiguing experience). Realization of a high-definition holographic display however requires a number of breakthroughs from existing prototypes. One of the main challenges lies in technology scaling, as holography is based on light diffraction and interference – to achieve wide viewing angles, the light-modulating pixels need to be spaced close to or below the wavelength of the used visible light. Furthermore, achieving high 3D image quality, hundreds of millions of such individually programmable pixels are needed. As a solution, we develop a modular sub-wavelength light modulator, consisting of three main sub-systems: the optical sub-system, comprising a 2D array of sub-wavelength pixels; the driver sub-system for individual pixel control, and the holographic computational engine. Based on conclusions from our state-of-the art studies, numerous experiments and holographic demonstrators, we have focused on reflective phase-modulating MEMS-based system and its scaling beyond 500nm pitch. We have devised a unique binary-programmable phase-modulating pixel architecture realizing vertical pixel displacement of up to 150nm at 500nm by 500nm pixel pitch, while sustaining low operating voltages compatible with CMOS driver circuitry. IMEC SiGe MEMS technology enables integration of the CMOS pixel-line drivers, scan-line drivers and I/O circuits underneath the 2D MEMS array, resulting in a compact and modular single-chip system design. Refresh rates of few hundred frames per second are achieved using our patented segmented driver-array architecture. Integrated circuits implementing parallel holographic computational engines can be added to the module using advanced 3D stacking technology. Herein we further report on our progress in realizing our first prototype system, featuring 2000×2000 pixels with 1.2μm pixel pitch, to demonstrate the first holographic video module with approximately 30 degree diffraction angle.

Optical design of low concentrator photovoltaic modules

This paper addresses the necessary procedures that need to be considered when designing an optical sub-system of low concentrator photovoltaic (LCPV) module. CPV systems make use of optical elements and solar tracking to concentrate solar flux onto a photovoltaic (PV) receiver. The performance of a concentrator module is highly dependent on the configuration and alignment of the optical elements in the system. In this study, various design considerations were taken into account to construct a LCPV module that was characterised with respect to optical design and electrical performance

A large-scale photonic node architecture that utilizes interconnected OXC subsystems

We propose a novel photonic node architecture that is composed of interconnected small-scale optical cross-connect subsystems. We also developed an efficient dynamic network control algorithm that complies with a restriction on the number of intra-node fibers used for subsystem interconnection. Numerical evaluations verify that the proposed architecture offers almost the same performance as the equivalent single large-scale cross-connect switch, while enabling substantial hardware scale reductions.

Coronagraphic phase diversity: a simple focal plane sensor for high-contrast imaging

Exoplanet direct imaging is a challenging goal of today's astronomical instrumentation. Several high-contrast imaging instruments dedicated to this task are currently being integrated; they are ultimately limited by the presence of quasi-static speckles in the imaging focal plane. These speckles originate in residual quasi-static optical aberrations, which must be measured and compensated for, typically at a nanometric level. We present a novel focal plane wavefront sensor (WFS) designed for this particular application. It is an extension of the phase diversity technique to coronagraphic imaging. This sensor requires no dedicated hardware and uses only two scientific images differing from a known aberration, which can be conveniently introduced by the adaptive optics subsystem. The aberrations are therefore calibrated all the way down to the scientific camera, without any differential aberrations between the sensor and the scientific camera. We show the potential of this WFS by means of simulations, and we perform a preliminary experimental validation.

Optical subsystems calibration and derived radiometric instrument response of the PHEBUS spectrometer on board of the BepiColombo Mission

Probing of Hermean By Ultraviolet Spectroscopy (PHEBUS) is a double spectrometer that will fly onboard of the BepiColombo mission. It will investigate the composition and dynamic of Mercury's exosphere to better understand the coupled surface - exosphere - magnetosphere system of the planet. The radiometric calibration tests are ongoing and an approach based on the Mueller Matrix formalism has been adopted to determine the pure efficiency of the instrument. To our knowledge, this is the first time that a such complete method is applied to the calibration of space instrumentation.

P1-3: Individual Differences in Chromostereopsis under Natural Viewing Conditions

Chromostereopsis is a type of visual perception where a specific color is perceived closer to or farther from the observer than other colors in the plane pattern. The mechanism is considered to be binocular stereopsis by the chromatic aberration of the eyeball optical subsystem, but there are large individual differences in natural viewing conditions. For example, in the case of a red-blue pattern with black background, about 70% of observers perceive the red pattern to be closer while 20% perceive the blue pattern to be closer. In the present research, the binocular disparity of the chromostereopsis was estimated both experimentally and numerically and the reason for the individual differences studied. First, the disparity was measured using a constant method, in which a stereo pair of red-blue stimulus patterns (random dots) was presented on a black background. The distance between the red and blue patterns for the right eye image was varied to generate a binocular disparity. It was found that the range...

Thermal effects in the Input Optics of the Enhanced Laser Interferometer Gravitational-Wave Observatory interferometers

We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO interferometers, designed to run with 30 W input power. At four times the power of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift, minimal thermal lensing, and higher optical efficiency. The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO.

Adaptive optics multispectral photoacoustic imaging

Photoacoustic imaging is an advanced medical imaging technology based on the effect of ultrasound generation by electromagnetic irradiation. However in photoacoustic imaging, because the optical property of tissue is always very complex, the aberration of light in tissue is ineluctable and the image spot is dispersed, which greatly influences the photoacoustic image resolution. For improving the lateral resolution of photoacoustic imaging, the adaptive optics multispectral photoacoustic imaging system is proposed in this paper. In this system an adaptive optics sub-system is designed to correct the wavefront errors of the illuminating light for obtaining high-resolution images of biological tissues. Moreover, the multispectral imaging is combined to obtain different wavelength photoacoustic images, which is useful for distinguishing organization accurate structure, identifying organizational components, etc. The simulation results demonstrate that when the wavefront errors are corrected by the adaptive optics system, the image resolution and quality are improved significantly. This research will be helpful for improving the ability and application of photoacoustic imaging.

Evaluation of packet scheduling in hybrid optical/electrical switch

This paper presents a hybrid optical/electrical switch for high-capacity future network development. A switch architecture to provide packet switching by solving contention in wavelength and time domains is considered relying on available optical and electrical technology. Physical and logical aspects regarding switch feasibility and management, in relation to the hybrid nature of the switch, are addressed. Scheduling algorithms to support multi-service packet forwarding are compared with optimally exploit optical and electrical subsystems according to traffic characteristics and needs. The main outcomes of the paper suggest criteria to design high-capacity packet switches, based on present-day technology constraints and quality of service requirements, to achieve a fair balance between optical transparency and loss performance.

Development of optical packet and circuit integrated ring network testbed

We developed novel integrated optical packet and circuit switch-node equipment. Compared with our previous equipment, a polarization-independent 4 × 4 semiconductor optical amplifier switch subsystem, gain-controlled optical amplifiers, and one 100 Gbps optical packet transponder and seven 10 Gbps optical path transponders with 10 Gigabit Ethernet (10GbE) client-interfaces were newly installed in the present system. The switch and amplifiers can provide more stable operation without equipment adjustments for the frequent polarization-rotations and dynamic packet-rate changes of optical packets. We constructed an optical packet and circuit integrated ring network testbed consisting of two switch nodes for accelerating network development, and we demonstrated 66 km fiber transmission and switching operation of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10GbE frames. Error-free (frame error rate < 1×10(-4)) operation was achieved with optical packets of various packet lengths and packet rates, and stable operation of the network testbed was confirmed. In addition, 4K uncompressed video streaming over OPS links was successfully demonstrated.

Micron: An Actively Stabilized Handheld Tool for Microsurgery

We describe the design and performance of a hand-held actively stabilized tool to increase accuracy in micro-surgery or other precision manipulation. It removes involuntary motion such as tremor by actuating the tip to counteract the effect of the undesired handle motion. The key components are a three-degree-of-freedom piezoelectric manipulator that has 400 μm range of motion, 1 N force capability, and bandwidth over 100 Hz, and an optical position measurement subsystem that acquires the tool pose with 4 μm resolution at 2000 samples/s. A control system using these components attenuates hand motion by at least 15 dB (a fivefold reduction). By considering the effect of the frequency response of Micron on the human visual feedback loop, we have developed a filter that reduces unintentional motion, yet preserves intuitive eye-hand coordination. We evaluated the effectiveness of Micron by measuring the accuracy of the human/machine system in three simple manipulation tasks. Handheld testing by three eye surgeons and three non-surgeons showed a reduction in position error of between 32% and 52%, depending on the error metric.