Showing papers on "Optical filter published in 2003"

Image pickup lens unit and image pickup device

Abstract: Lenses 1, 2, and 4 as an optical element having a power are cemented together in an optical axis direction. An optical filter 3 is sandwiched between the lenses 2 and 4. Optical elements neighboring each other are cemented together such that a positioning section which is disposed on a side surface of the optical element disposes an appropriate space in an optical axis direction and optical axes of optical elements align in a direction orthogonal to the optical axis. The cemented optical element arrays are cemented together and cut at a line for cutting operation. By doing this, it is possible to manufacture a small image pickup lens unit which can be used for an image pickup device in mass-production and in a low cost.

Terahertz plasmonic high pass filter

Abstract: Metamaterials, which contain engineered subwavelength microstructures, can be designed to have positive or negative e and μ at desired frequencies. In this letter, we demonstrate a metamaterial which has a “plasmonic” response to electromagnetic waves in the terahertz (THz) range. The sharp change of reflection and transmission at this plasma frequency makes the structure a high pass filter. The reflection response is characterized by Fourier transform infrared spectroscopy, and a plasma frequency at 0.7 THz is observed, which agrees with the theoretical calculation. The metamaterial is a two-dimensional cubic lattice consisting of thin metal wires, having wire diameter of 30 μm, lattice constant of 120 μm, and wire length of 1 mm. The microstereolithography technique is employed to fabricate the high-aspect-ratio lattice.

Optical Elements with Subwavelength Structured Surfaces

Abstract: Various optical elements with subwavelength structured surfaces have been developed. The periods of the subwavelength structures are too short to generate diffracted light waves. But the structures are equivalent to refractive index materials with form birefringence. Many new optical elements are realized using the artificial refractive indices of these subwavelength structures. Some typical elements are described here in the passive element regime, and fabrication methods of the elements are explained.

Distributed Feedback Laser Diodes and Optical Tunable Filters

Abstract: Preface.Acknowledgements.Glossary of Abbreviations.Glossary of Symbols.1. An Introduction to Optical Communication Systems.2. Principles of Distributed Feedback Semiconductor Laser Diodes: Coupled Wave Theory.3. Structural Impacts on the Solutions of Coupled Wave Equations: An Overview.4. Transfer Matrix Modelling in DFB Semiconductor Lasers.5. Threshold Analysis and Optimization of Various DFB LDs Using the Transfer Matrix Method.6. Above-Threshold Characteristics of DFB Laser Diodes: A TMM Approach.7. Above-Threshold Analysis of Various DFB Lase r Structures Using the TMM.8. Circuit and Transmission-Line Laser Modelling (TLLM) Techniques.9. Analysis of DFB Laser Diode Characteristics Based on the Transmission-Line Modelling (TLLM).10. Wavelength Tunable Optical Filters Based on DFB Laser Structures.11. Other Wavelenght Tunable Optical Filters Based on the DFB Laser Structure.12. Conclusion, Summary and Suggestions.Index.

Bandpass resonant filters in photonic-crystal waveguides

Abstract: A precise and effective technique for the design of bandpass resonant filters realized in a one-missing-row photonic-crystal waveguide by inserting proper defects along the waveguide is proposed. The main characteristics of photonic-crystal-based resonant filters are discussed and an application as channel-dropping filter is presented.

Integrated color pixels in 0.18-microm complementary metal oxide semiconductor technology.

Abstract: Following the trend of increased integration in complementary metal oxide semiconductor (CMOS) image sensors, we have explored the potential of implementing light filters by using patterned metal layers placed on top of each pixel’s photodetector. To demonstrate wavelength selectivity, we designed and prototyped integrated color pixels in a standard 0.18-µm CMOS technology. Transmittance of several one-dimensional (1D) and two-dimensional (2D) patterned metal layers was measured under various illumination conditions and found to exhibit wavelength selectivity in the visible range. We performed (a) wave optics simulations to predict the spectral responsivity of an uncovered reference pixel and (b) numerical electromagnetic simulations with a 2D finite-difference time-domain method to predict transmittances through 1D patterned metal layers. We found good agreement in both cases. Finally, we used simulations to predict the transmittance for more elaborate designs.

Fabrication and characterization of high-quality waveguide-mode resonant optical filters

Abstract: Optical filters containing resonant waveguide gratings are designed and fabricated using low-loss, robust materials. The double-layer filters contain a silicon dioxide diffractive element on a hafnium dioxide waveguide deposited on a fused silica substrate. Noise-pattern formation is minimized by use of an antireflective absorption layer during holographic grating recording in photoresist. Subsequent fabrication steps include metallization, lift-off, and oxygen plasma etch to create a metal etch mask for final CF4 plasma etching of a surface-relief grating. Spectral characterization with a tunable laser shows that the resulting filter exhibits 90% efficiency, 1.2 nm linewidth, and low sidebands.

Selectable Color Adjustment for Image Display

Abstract: A display system is configured to produce a color image formed of a plurality of differently colored images and may include at least one light source that directs light along an optical path, and at least one filter having a given optical filter characteristic. The display system may be selectively operable in a first state in which the optical path does not pass through a first filter during production of the plurality of differently colored images to form a color image having a first optical characteristic, and in a second state in which the optical path passes through the first filter during production of the plurality of differently colored images to form a color image having a second optical characteristic different than the first optical characteristic.

Ring-resonator filters in silicon oxynitride technology for dense wavelength-division multiplexing systems.

Abstract: The design and characterization of ring-resonator-based filters with free spectral ranges of 100 and 50 GHz by use of SiO(x)N(y) technology is presented. Fiber-to-fiber insertion losses of 4.4 dB on the drop port and 2.1 dB on the through port have been achieved for a single-ring filter. An interleaver filter for a 25-GHz spaced dense wavelength-division multiplexing system with two cascaded rings is demonstrated. The filter has a 7.4-GHz bandwidth at -1 dB and an extinction ratio of 15 dB and is polarization independent.

Optoelectronic millimeter-wave synthesis using an optical frequency comb Generator, optically injection locked lasers, and a unitraveling-carrier photodiode

Abstract: This paper demonstrates multi-octave, milliwatt-class millimeter-wave synthesis using three key components: an optical frequency comb generator, an optical injection-locking filter, and a unitraveling-carrier photodiode. The experimental system synthesizes 10-110-GHz millimeter-wave signals with 3-dBm output at 60 GHz. Phase noise results are also presented.

Design of superresolving continuous phase filters.

Abstract: We present a procedure for designing rotationally symmetric pupil-plane masks to control the three-dimensional light-intensity distribution near focus. Our method is based on the use of a series of figures of merit that are properly defined to describe the effect of general complex pupil functions. As a practical implementation, we have applied our method to obtain superresolving continuous smoothly varying phase-only filters. The advantages of these kinds of filters are that they do not produce energy absorption and they are easy to build with a phase-controlling device such as a deformable mirror. Results of comparisons between the performance of our method and that of other phase-filter designs are provided.

A tunable optical filter

Abstract: We present the details of a new tunable optical filter, suitable for selecting different bands of wavelength in the UV, visible and IR regions. The filter comprises a ferrofluid-based emulsion cell (emulsion sandwiched between two transparent sheets), a miniature solenoid and a variable direct current source for changing the magnetic field inside the solenoid. By varying the magnetic field, one can tune the filter and select the desired wavelength. We discuss the working principle of the new tunable optical filter with a few examples.

Method and apparatus for generating structural pattern illumination

Abstract: A three-dimensional imaging method and system illuminates an object to be imaged with a light pattern that is formed from two or more light sub-patterns. The sub-patterns can each encompass the visible light spectrum or can be spatially varying intensity sub-patterns that each correspond to a red, green, or blue component. The light pattern is generated by a slotted planar member or an optical filter.

SiON high-refractive-index waveguide and planar lightwave circuits

Abstract: The rapidly growing optical communication market requires photonic components with ever-increasing functionality and complexity that can be fabricated reliably at low cost. Of the various approaches used to fabricate photonic components, those based on planar waveguides have achieved high performance and represent a promising path toward compact integration of optical functions. We present an overview of an approach used to produce an optical single-mode waveguide. Through its strong mode confinement, the approach makes it possible to integrate optical filter functions with higher functionality, as required for high-data-rate communication networks. The waveguide is based on the use of a silicon oxynitride (SiON) core and silicon oxide cladding layers, and can be fabricated using conventional chip fabrication techniques. Using the new approach, conventional passive optical components such as arrayed waveguide gratings for wavelength-division-multiplexed transmission systems can be fabricated in a more compact way than using standard silica-on-silicon waveguide methods. Moreover, the realization of more enhanced, adaptive optical functions such as finite- impulse-response as well as infinite-impulse-response filters is possible. Reconfiguration is achieved through the thermo-optic effect. A reconfigurable gain-flattening filter and an adaptive dispersion compensator are presented as examples.

Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges

Abstract: Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for 1.5-microm infrared systems. The waveguide's low-loss bends with 2.5-microm radius reduce the total length of the filter to less than 100 microm and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.

Vacuum evaporated porous silicon photonic interference filters.

Abstract: Porous materials with nanometer-scale structure are important in a wide variety of applications including electronics, photonics, biomedicine, and chemistry. Recent interest focuses on understanding and controlling the properties of these materials. Here we demonstrate porous silicon interference filters, deposited in vacuum with a technique that enables continuous variation of the refractive index between that of bulk silicon and that of the ambient (n ∼ 3.5 to 1). Nanometer-scale oscillations in porosity were introduced with glancing angle deposition, a technique that combines oblique deposition onto a flat substrate of glass or silicon in a high vacuum with computer control of substrate tilt and rotation. Complex refractive index profiles were achieved including apodized filters, with Gaussian amplitude modulations of a sinusoidal index variation, as well as filters with index matching antireflection regions. A novel quintic antireflection coating is demonstrated where the refractive index is smoothly decreased to that of the ambient, reducing reflection over a broad range of the infrared spectrum. Optical transmission characteristics of the filters were accurately predicted with effective medium modeling coupled with a calibration performed with spectroscopic ellipsometry.

Optical polymer nanocomposites

Abstract: A composite material that includes a host matrix and a plurality of dispersed nanoparticles within the host matrix. Each of the plurality of nanoparticles may include a halogenated outer coating layer that seals the nanoparticle and prevents agglomeration of the nanoparticles within the host matrix. The invention also includes a process of forming the composite material. Depending on the nanoparticle material, the composite material may have various applications including, but not limited to, optical devices, windowpanes, mirrors, mirror panels, optical lenses, optical lens arrays, optical displays, liquid crystal displays, cathode ray tubes, optical filters, optical components, all these more generally referred to as components.

One-chip micro-integrated optoelectronic sensor

Abstract: This disclosure describes one-chip micro-integrated optoelectronic sensors and methods for fabricating and using the same. The sensors may include an optical emission source, optical filter and a photodetector fabricated on the same transparent substrate using the same technological processes. Optical emission may occur when a bias voltage is applied across a metal-insulator-semiconductor Schottky contact or a p-n junction. The photodetector may be a Schottky contact or a p-n junction in a semiconductor. Some sensors can be fabricated on optically transparent substrate and employ back-side illumination. In the other sensors provided, the substrate is not transparent and emission occurs from the edge of a p-n junction or through a transparent electrode. The sensors may be used to measure optical absorption, optical reflection, scattering or fluorescence. The sensors may be fabricated and operated to provide a selected spectrum of light emitted and a multi-quantum well heterostructure may be fabricated to filter light reaching the photodetector.

Impact of filtering on RZ-DPSK reception

Abstract: We discuss the influence of optical and electrical filtering on the performance of beat-noise limited balanced and single-ended direct detection of return-to-zero differential phase-shift keying (DPSK). Our simulations, supported by 40-Gb/s measurements, show that balanced DPSK detection outperforms both its single-ended equivalent and ON-OFF keying by /spl sim/2.7 dB, with higher gains at narrower optical filter bandwidths.

Photonic crystal optical filter based on contra-directional waveguide coupling

Abstract: Wavelength-selective operation of an optical filter (add/drop) based on a contra-directional photonic crystal waveguide coupler is demonstrated. The waveguides are defined as line defects in a two-dimensional triangular photonic crystal fabricated in an InP/GaInAsP heterostructure. The device is characterized using the end-fire method for the drop functionality. The experimental data are in good agreement with the theoretical results predicted by finite-difference time-domain simulations.

Tunable optical filter

Abstract: A tunable optical filter is provided that includes an array of independently tunable filter elements. Each of the elements is located along a different optical path that extends between an input and an output port. Optical assemblies for receiving an incident optical signal for providing a filtered optical signal are also provided. In one embodiment, polarization independent spectral filtering can be achieved. Wavelength selectable add/drop multiplexers and demultiplexers, dynamic gain equalizers and attenuators, optical channel blockers and branch filters, switches, and modulators are also provided. Furthermore, methods for constructing and operating filters consistent with this invention are also provided.

Ultralow biased widely continuously tunable fabry-Perot filter

Abstract: Optical filters capable of single control parameter-based wide tuning are implemented and studied. The surface micromachined Fabry-Perot filter consists of two InP-air-gap distributed Bragg reflectors and shows a wavelength tuning of more than 140 nm using only a single voltage of up to 3.2 V at currents below 0.2 mA. The membrane-based filter is designed to block all wavelengths in the whole range of 1250-1800 nm apart from its transmission wavelength.

Distance measuring device

Abstract: A distance-measuring device, comprising a light source unit for emitting a distance-measuring light, a photodetection optical system, a projecting optical system for projecting the distance-measuring light from the light source unit to an object to be measured and for guiding the distance-measuring light reflected by the object to be measured to the photodetection optical system, and an internal reference optical system for guiding the distance-measuring light from the light source unit toward the photodetection optical system, wherein the light source unit can emit two distance-measuring lights having different spreading angles and having the same or almost the same wavelengths, and the photodetection optical system has an optical filter which transmits light components of narrower wavelength range of the distance-measuring light.

Analysis of corrugated long-period gratings in slab waveguides and their polarization dependence

Abstract: We analyze theoretically the light transmission characteristics of corrugated long-period gratings formed in slab waveguides. The transmission spectra of the gratings show distinct rejection bands at specific wavelengths, known as the resonance wavelengths. We investigate in detail the phase-matching curves of the gratings, which govern the relationship between the resonance wavelength and the grating period. Thanks to the flexibility in the choice of the waveguide parameters, the phase-matching curves of a long-period waveguide grating can be different characteristically from those of a long-period fiber grating (LPFG), which implies that the former can exhibit much richer characteristics than the latter. Unlike an LPFG, the transmission spectrum of a long-period waveguide grating is in general sensitive to the polarization of light. Nevertheless, a proper choice of the waveguide and grating parameters can result in a polarization-independent rejection band. Long-period waveguide gratings should find potential applications in a wide range of integrated-optic waveguide devices and sensors.

Mechanically switchable photonic crystal filter with either all-pass transmission or flat-top reflection characteristics.

Abstract: We theoretically introduce a new type of optical all-pass filter based on guided resonance in coupled photonic crystal slabs. The filter exhibits near-complete transmission for both on- and off-resonant frequencies and yet generates large resonant group delay. We further show that such a filter can be mechanically switched into a flat-top band rejection filter.

Novel tunable photonic microwave filter based on laser arrays and N/spl times/N AWG-based delay lines

Abstract: In this letter, a novel tunable and flexible photonic microwave filter architecture based on the use of laser arrays and the periodicity of N/spl times/N arrayed-waveguide-gratings optical response is proposed. Filter coarse and fine-tuning capabilities are experimentally demonstrated showing an excellent agreement with theory.

Holographic edge-illuminated polymer bragg gratings for dense wavelength division optical filters at 1550 nm

Abstract: We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100–200-μm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard’s method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (<0.2 nm) and high side-lobe suppression (<-30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (<0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.

A micromachined in-plane tunable optical filter using the thermo-optic effect of crystalline silicon

Abstract: This paper presents a micromachined in-plane tunable optical filter using the thermo-optic effect of crystalline silicon. The device was fabricated by a silicon deep reactive ion etching process with a silicon-on-insulator wafer and thermal oxide removal to improve the sidewall smoothness. Optical fibers could be horizontally aligned on the fabricated TOF device by exploiting in-plane device structures, which enable TOFs to easily connect with other optical components. Tunability of the TOFs was experimentally achieved through thermal modulation of optical path length by heating the silicon etalon. As the input voltage increases, a notch in the reflectance spectrum shifts to a longer wavelength with an average tuning sensitivity of 0.9 nm K−1 and a best bandwidth of 1.1 nm. The proposed device can be utilized for spectroscopy or optical communication.

Optical microwave filter based on spectral slicing by use of arrayed waveguide gratings

Abstract: We have experimentally demonstrated a new optical signal processor based on the use of arrayed waveguide gratings. The structure exploits the concept of spectral slicing combined with the use of an optical dispersive medium. The approach presents increased flexibility from previous slicing-based structures in terms of tunability, reconfiguration, and apodization of the samples or coefficients of the transversal optical filter.

Ohmic loss in frequency-selective surfaces

Abstract: The present study was undertaken in order to quantify absorption effects due to ohmic loss in frequency-selective surfaces (FSS) at infrared frequencies. The structures considered in this work act as electromagnetic filters, and as such, are of interest for use as thermophotovoltaic spectral control devices. For this application, absorption is of primary concern since it leads to reduced filter efficiency. This work focuses on the behavior of single-layer, free-standing FSS arrays comprised of circular apertures (holes) and circular loop apertures (rings). Numerical calculations of the transmission, reflection, and absorption characteristics of various arrays were carried out for wavelengths between 1 and 15 μm using a commercial finite-element software package. Absorption effects were included using measured optical properties as input parameters to a surface impedance boundary condition. Analytical techniques were then employed to determine the absorption behavior in the static limit. An interesting result of this analysis is the fact that absorption at 15 μm is predicted by the finite-element calculations to increase versus aperture radius (for fixed aperture separation), while in the static limit absorption was found (through the use of analytical techniques) to decrease. The results of the finite-element calculations were confirmed using another numerical method based on the periodic moment method. We are thus led to the conclusion that the qualitative relationship for absorption versus aperture radius must reverse for some frequency regime yet to be investigated.