Broadband Optical Systems Research Articles

35‐2: Multispectral Pancharatnam‐Berry Phase Liquid Crystal Lens and Its Aplication in AR Displays

Pancharatnam‐Berry (PB) phase liquid crystal (LC) lenses show attractive benefits in optical systems because of their high efficiency, compact size and polarization‐dependent behavior. However, as a kind of diffraction‐based devices, PB LC lenses suffer from chromatic dispersion, which limits their applications in multi‐wavelength imaging systems. In this paper, we demonstrate a multispectral PB LC lens design to overcome this issue. An active multispectral PB LC lens has been fabricated and characterized. It can focus different wavelengths at the same distance so they are expected to solve the chromatic dispersion problem in the multi‐wavelength display system and other broadband optical systems.

Infrared color-sorting metasurfaces.

The process of sorting light based on colors (photon energy) is a prerequisite in broadband optical systems, typically achieved in the form of guiding incoming signals through a sequence of spectral filters. The assembly of filters often leads to lengthy optical trains and consequently, large system footprints. In this work, we address this issue by proposing a flat color-sorting device comprising a diffraction grating and a dielectric Huygens' metasurface. Upon the incidence of a broadband beam, the grating disperses wavelengths to a continuous range of angles in accordance with the law of diffraction. The following metasurface with multiple paired Huygens' resonances corrects the dispersion and binds wavelengths to the corresponding waveband with a designated output angle. We demonstrate the sorting efficacy by designing a device with a color-sorting metasurface with two discrete dispersion-compensated outputs (10.8 ± 0.3 μm and 11.9 ± 0.3 μm), based on the proposed approach. The optimized metasurface possesses an overall transmittance exceeding 57% and reduces lateral dispersion by 90% at the output. The proposed color-sorting mechanism provides a solution that benefits the designing of metasurfaces for miniature multi-band systems.

High-sensitivity weighing sensor based on broadband optical coherence displacement measurement of a dual-beam elastic element

A novel weight sensor based on the Michelson interferometer is proposed in this study to meet the demands of complex environments. The sensor uses a dual-beam type elastic element, optimized to enhance its sensitivity. Its deformation under load is sensed by a broadband optical coherence displacement measurement system, which, in combination with the spectrum correction method, enables displacement sensing down to sub-nanometer resolution. An optical interferometric weight sensor with a rated load of 6 kg is fabricated under laboratory conditions, and its performance is verified experimentally. The proposed weight sensor demonstrates good stability and achieves a sensitivity of 146.814 μm/kg, theoretical resolution of 0.004 g, nonlinearity error of 0.034%, maximum repeatability error of 0.036%, and maximum hysteresis error of 0.055%, with the relative error of the identification threshold not exceeding 0.1%. The proposed weighing method and sensor represent a significant improvement over other reported interferometer-type weight sensors.

Dispersion-engineered broadband diffractive optical elements with multilayer subwavelength structures.

Diffractive optical elements (DOEs) play an important role in modern optical applications such as spectral and imaging systems, but it is challenging to balance the diffraction efficiency with the working bandwidth. The core issue is controlling the broadband dispersion of all phase units to achieve achromatic 2π-phase modulation in the broadband domain. Here, we demonstrate broadband DOEs utilizing multilayer subwavelength structures with different materials, making it possible to freely control the phase and phase dispersion of the structural units on a much larger scale than monolayer structures. The desired dispersion-control abilities arose due to a dispersion-cooperation mechanism and vertical mode-coupling effects between the top and bottom layers. An infrared design comprised of two vertically concatenated T i O 2 and Si nanoantennas separated by a S i O 2 dielectric spacer layer was demonstrated. It showed an average efficiency of over 70% in the three-octave bandwidth. This work shows enormous value for broadband optical systems with DOEs such as spectral imaging and augmented reality.

Mid-infrared biomimetic moth-eye-shaped polarization-maintaining and angle-insensitive metalens.

Metalenses can potentially reduce the size and complexity of existing cameras, displays, and other optical devices, owing to their capability of flexible manipulation of the polarization, amplitude, and phase of light. However, metalenses capable of maintaining polarization and broadband wavefront shaping under arbitrarily polarized excitation have not been studied. In this study, we present the first demonstration of a biomimetic moth-eye-shaped metalens for polarization-maintaining, broadband and angle-insensitive focusing under an arbitrarily polarized excitation in the mid-infrared waveband (3.1-8.0 µm). Modulation and focusing efficiencies of 92% and 90%, respectively, were achieved. Moreover, a bifocal moth-eye-shaped metalens operating at normal and oblique incidences was realized. Compared to previously reported metalenses, the one proposed in this study exhibited a better focusing under oblique incidence, ensuring light transmission as effectively as a traditional lens. This study paves the way for the development of polarization-maintaining, broadband, and angle-insensitive microscale optical devices and imaging systems.

Tunable Broadband Mode Converter Based on Long-Period Fiber Gratings at 2-μm Waveband

We demonstrate the fabrication of a broadband mode converter (MC) operating at 2 μm waveband based on long-period fiber gratings (LPFGs) written in the two-mode fiber (TMF) by CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. The proposed MC offers a 10-dB bandwidth of 58 nm, making it suitable for high-speed broad-band optical communication system at 2 μm waveband. The maximum conversion efficiency reaches 98.89% at wavelength of 2 μm. The torsion, strain, bending, and polarization characteristics of the broadband MC were measured experimentally. The torsion sensitivity of the LPFGs was measured to be 1.32 nm/(rad/m) at 2 μm waveband, which was almost three times higher than that of the grating with the same order mode coupling at 1.55 μm waveband. The proposed broadband MC can function as not only a promotion in fiber communication system but also a high sensitivity torsion sensor in fiber sensing system.

Bio-inspired multimodal 3D endoscope for image-guided and robotic surgery.

Image-guided and robotic surgery based on endoscopic imaging technologies can enhance cancer treatment by ideally removing all cancerous tissue and avoiding iatrogenic damage to healthy tissue. Surgeons evaluate the tumor margins at the cost of impeding surgical workflow or working with dimmed surgical illumination, since current endoscopic imaging systems cannot simultaneous and real-time color and near-infrared (NIR) fluorescence imaging under normal surgical illumination. To overcome this problem, a bio-inspired multimodal 3D endoscope combining the excellent characteristics of human eyes and compound eyes of mantis shrimp is proposed. This 3D endoscope, which achieves simultaneous and real-time imaging of three-dimensional stereoscopic, color, and NIR fluorescence, consists of three parts: a broad-band binocular optical system like as human eye, an optical relay system, and a multiband sensor inspired by the mantis shrimp's compound eye. By introducing an optical relay system, the two sub-images after the broad-band binocular optical system can be projected onto one and the same multiband sensor. A series of experiments demonstrate that this bio-inspired multimodal 3D endoscope not only provides surgeons with real-time feedback on the location of tumor tissue and lymph nodes but also creates an immersive experience for surgeons without impeding surgical workflow. Its excellent characteristics and good scalability can promote the further development and application of image-guided and robotic surgery.

Dielectric metalenses at long-wave infrared wavelengths: Multiplexing and spectroscope

Metalenses, being composed of subwavelength phase-control nanostructures, can achieve peculiar manipulations of incident rays. Dispersion is one of the key optical characteristics to be eliminated or exploited in designing broadband optical systems. In the study, the silicon metalenses made of nanobricks are investigated to achieve multiwavelength multiplexing or spectroscope in the long-wave infrared regime. Firstly, the geometrical dependencies of silicon nanobricks’ transmittance, phase difference, and structural dispersion are investigated to obtain the fundament of constructing the metalenses. Then, the metalenses are constructed, of which the chromatic aberration is analyzed. Via spatial multiplexing, two multiwavelength-metalens configurations are proposed to realize achromatism and multifocal features respectively. Furthermore, via exploiting the nanobricks’ structural dispersion, a compact spectrometer based on an off-axis metalens is demonstrated. This study gives out an insight into exploiting the structural dispersion of silicon nanobricks in constructing metalenses, which paves an efficient way for the development of integrated imaging and spectroscopy systems in the long-wave infrared range.

Flat optics in high numerical aperture broadband imaging systems

Diffractive optical elements (DOEs) remain highly underutilized in broadband optical systems even though different technologies for DOEs including échelette-type gratings (EGs), multilevel DOEs, and metagratings have been introduced. Specifically, nanocomposite-enabled EGs can achieve efficiencies of close to throughout the visible spectrum, but only for relatively small diffraction angles. Therefore, the question remains if they are suitable for high-numerical-aperture (NA) systems. Here we show that this is indeed the case. To this end, we first demonstrate that macroscopic nanocomposite-enabled diffractive lenses (DLs) can achieve perfect broadband focusing up to a NA of 0.03. We then derive analytic relationships and investigate prototypical optical designs to show that this threshold fully covers the requirements of high-end imaging systems with This holistic all-system analysis demonstrates that the individual NA of a DL in a broadband imaging system is one to two orders of magnitude lower than the overall system’s NA. This shows that high-NA flat optical elements are not required for high-NA broadband systems. Therefore, nanocomposite-enabled EGs can unlock the full potential of DOEs for broadband optical systems, whereas other technologies cannot fulfill their high efficiency requirements.

General design formalism for highly efficient flat optics for broadband applications.

The use of flat diffractive optical elements (DOEs) for broadband applications, e.g. conventional optical systems, requires DOEs that maintain high efficiencies across the required range of wavelengths, angles of incidence, and grating periods. Here we introduce a general framework for how dispersion engineering can be used to design DOEs that fulfill these requirements and use our approach to determine design rules for broadband DOEs. Our analysis shows that the key to making échelette-type gratings (EGs) suitable for broadband optical systems is the development of new optical materials with specific uncommon dispersion properties. Subsequently, we use our framework to design a representative range of prototype EGs, which allows us to link the specifications of an optical system to the requirements on the EGs' materials. Finally, we show that our design rules apply to all DOEs based on propagation delays including GRIN DOEs and metagratings. Our design rules therefore guide the way towards unlocking the full potential of DOEs for different kinds of broadband applications.

Dispersion-engineered nanocomposites enable achromatic diffractive optical elements

The use of diffractive optical elements (DOEs) in broadband optical systems can often significantly reduce their size or enhance their performance but is mostly prevented by stray light in unwanted diffraction orders. This is because dispersion causes the diffraction efficiency to decrease as a function of the wavelength. Here we introduce nanocomposites as a material platform that allows for the design of dispersion-engineered materials. We show that these materials enable the design of almost dispersion-free, i.e., achromatic, echelette-type gratings with diffraction efficiencies of close to 100% in the entire visible spectral range. Using numerical simulations, we demonstrate that such high efficiencies are maintained across the range of incidence angles and grating periods required for most optical systems. This concept of dispersion-engineered nanocomposites can also be applied to other applications, and nanocomposite-enabled DOEs have the potential to be an enabling technology for a new generation of better and more compact optical systems.

Link dimensioning of hybrid FSO/fiber networks resilient to adverse weather conditions

The presented paper deals with wireless networks composed of FSO (free space optics) links supported by terrestrial optical fiber connections in order to increase resilience to adverse weather conditions. An FSO link realizes, at low cost, a broadband optical transmission system established by means of two parallel light beams connecting a pair of (remote) transceivers placed in the line of sight. However, a major disadvantage of FSO links (with respect to fiber links) is their sensitivity to weather conditions: bad weather affects optical channel, resulting in substantial degradation of the transmission power at the receivers, which in general leads to capacity degradation on multiple FSO links. When the transmission power received at the end node of an FSO link is decreased, the signal modulation and coding scheme (MCS) at the transmitter should be adjusted accordingly; in effect, an FSO link can be kept operational, but with decreased capacity, even if the channel is affected. Yet, since in severe weather conditions some FSO links may not be able to realize any reliable transmission at all (whichever MSC is used), the network may become disconnected and a portion of traffic lost. Therefore, it is reasonable to consider using fibers instead of free space light beams since weather insensitive (and high capacity) fibers installed on the key links will ensure network connectivity in all weather states. Certainly, the so obtained connectivity does not come for free because of the high cost of the optical fiber connections as compared to the FSO systems and hence the number of fibers should be kept at minimum. Thus, for designing hybrid FSO/fiber networks we need an optimization model for finding cheapest configurations of links (and their capacities) that will be able to carry the demanded traffic on acceptable level in all weather states foreseen in network operation. This is not a simple task as it requires not only robust network optimization methods but also a tractable way of characterizing possible weather states (which are not known in advance) and their influence on FSO link capacity. In the paper we present an approach to the so described task and illustrate its effectiveness by means of a numerical study.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

Effects of fixture rotation on coating uniformity for high-performance optical filter fabrication

Abstract Coating uniformity is critical in fabricating high-performance optical filters by various vacuum deposition methods. Simple and planetary rotation systems with shadow masks are used to achieve the required uniformity [J. B. Oliver and D. Talbot, Appl. Optics 45, 13, 3097 (2006); O. Lyngnes, K. Kraus, A. Ode and T. Erguder, in ‘Method for Designing Coating Thickness Uniformity Shadow Masks for Deposition Systems with a Planetary Fixture’, 2014 Technical Conference Proceedings, Optical Coatings, August 13, 2014, DOI: http://dx.doi.org/10.14332/svc14.proc.1817.]. In this work, we discuss the effect of rotation pattern and speed on thickness uniformity in an ion beam sputter deposition system. Numerical modeling is used to determine statistical distribution of random thickness errors in coating layers. The relationship between thickness tolerance and production yield are simulated theoretically and demonstrated experimentally. Production yields for different optical filters produced in an ion beam deposition system with planetary rotation are presented. Single-wavelength and broadband optical monitoring systems were used for endpoint monitoring during filter deposition. Limitations of thickness tolerances that can be achieved in systems with planetary rotation are shown. Paths for improving production yield in an ion beam deposition system are described.

宽波段光学系统三级光谱的校正方法

宽波段光学系统三级光谱的校正方法

Determination of internal temperatures within nitric oxide inductively coupled plasmas

Determination of molecular temperatures within inductively coupled plasmas is critical to understanding the reactions that drive the chemistry of these systems and the mechanisms involved in surface processing. To investigate such interactions, a dual, in situ broadband absorption and optical emission spectroscopy system was designed; providing insight into neutral and excited state species energetics, specifically rotational (TR) and vibrational (TV) temperatures across a broad spectral range (&gt;800 nm). Nitric oxide plasmas have been investigated, where measured TV values were higher than TR values, indicating rotational degrees of freedom are more easily thermalized. Using the imaging of radicals interacting with surfaces technique, surface scatter coefficients were measured for NO radicals, which are discussed in relation to energy partitioning in these systems.

High-speed and broadband optical transmission system special issue based on selected IEEE ICOCN 2015 papers

High-speed and broadband optical transmission system special issue based on selected IEEE ICOCN 2015 papers

Design and Deployment of a Multichroic Polarimeter Array on the Atacama Cosmology Telescope

We present the design and the preliminary on sky performance with respect to beams and pass-bands of a multichroic polarimeter array covering the 90 and 146 GHz Cosmic Microwave Background (CMB) bands and its enabling broadband optical system recently deployed on the Atacama Cosmology Telescope (ACT). The constituent pixels are feedhorn-coupled multichroic polarimeters fabricated at NIST. This array is coupled to the ACT telescope via a set of three silicon lenses incorporating novel broad-band metamaterial anti-reflection coatings. This receiver represents the first multichroic detector array deployed for a CMB experiment and paves the way for the extensive use of multichroic detectors and broadband optical systems in the next generation of CMB experiments.

Low profile Flip-Type or Embedded Silicon Capacitors for decoupling

The very high capacitance platform of the 3D Silicon capacitors technology presents lots of interest in different domains. In this paper we'll focus on Optical networking, Signal and Power integrity .The intrinsic IPDiA Silicon capacitors group delay, a key parameter in the phase sensitive broadband applications, will be compared with the multilayer ceramic capacitor (MLCC) one. All the components involved in the main signal line have indeed to manage properly their phase behavior to minimize their group delay impact on final performances. First ,the intrinsic construction and the simplified equivalent electrical models will be compared .Secondly, it will be demonstrated how the Silicon Capacitors are better candidates for performances ,miniaturization and integration thanks to their low profile whereas the high thickness is a limiting factor for Ceramic capacitors. On top of the competitive overview of performances specific to the Ultra Wide Broadband Capacitors, signal integrity, frequency response, linearity, dielectric absorption, the silicon capacitor technology benefits will be detailed .Design recommendations will be given to those who want to optimize performances in the overall broadband optical system. The perspectives and roadmap for the future will be disclosed.

PAPR Influence Analysis in 8QAM-OFDM Optical Access Systems

In this article, the peak to average power ratio (PAPR) performance of 8 quadrature amplitude modulation-orthogonal frequency division multiplexing (8QAM-OFDM) optical signals has been researched in broadband optical access system. The complementary cumulative distribution functions (CCDFs) are analyzed of two different 8QAM-OFDMsignals with 16, 32, 64, 128, 256, 512 sub- carriers by simulation. The simulation results show that, with the increase of the number of subcarrier, the PAPR value becomes higher. When the numbers of subcarrier are16 and 512, the PAPR of 8QAM-OFDM optical signals are smaller than 5.2 dB and 5.3 dB respectively. Hence, the number of sub-carriers should be chosen according to practical application.