Showing papers on "Optical filter published in 2007"

Ultra-compact high order ring resonator filters using submicron silicon photonic wires for on-chip optical interconnects

Abstract: Ultra-compact 5(th) order ring resonator optical filters based on submicron silicon photonic wires are demonstrated. Out-of-band rejection ratio of 40dB, 1dB flat-top pass band of 310GHz with ripples smaller than 0.4dB, and insertion loss of only (1.8+/-0.5)dB at the center of the pass band are realized simultaneously, all within a footprint of 0.0007mm(2) on a silicon chip.

Error-Free 320-Gb/s All-Optical Wavelength Conversion Using a Single Semiconductor Optical Amplifier

Abstract: We demonstrate error-free wavelength conversion at 320 Gb/s by employing a semiconductor optical amplifier that fully recovers in 56 ps. Error-free operation is achieved without using forward error correction technology. We employ optical filtering to select the blue sideband of the spectrum of the probe light, to utilize fast chirp dynamics introduced by the amplifier, and to overcome the slow gain recovery. This leads to an effective recovery time of less than 1.8 ps for the wavelength converter. The wavelength converter has a simple configuration and is implemented by using fiber-pigtailed components. The concept allows photonic integration

Particle swarm optimization and its application to the design of diffraction grating filters

Abstract: Particle swarm optimization (PSO) is an evolutionary, easy-to-implement technique to design optical diffraction gratings. Design of reflection and transmission guided-mode resonance (GMR) grating filters using PSO is reported. The spectra of the designed filters are in good agreement with the design targets in a reasonable computation time. Also, filters are designed with a genetic algorithm (GA) and the results obtained by the GA and PSO are compared.

Compound eye camera module and method of producing the same

Abstract: A compound eye camera module where an optical filter array (2) and a light shielding block (6) are arranged between a lens module (7) and imaging regions (4a-4d). The optical filter array (2) has optical filters (2a-2d). The light shielding block (6) has light shielding walls (61a-61d) forming openings (6a-6d) independent from each other. The lens module (7) integrally has lenses (1a-1d) arranged on a single plane. First sliding surfaces (66-69) are provided on the light shielding block. The lens module is provided with second sliding surfaces (56-59) sliding on the first sliding surface, and the lens module is provided so that it can rotate relative to the light shielding block with an axis normal to the imaging regions as the center axis of the rotation. The compound eye camera module is small sized, thin, and low cost.

A Photonic Microwave Frequency Quadrupler Using Two Cascaded Intensity Modulators With Repetitious Optical Carrier Suppression

Abstract: We theoretically analyzed and experimentally demonstrated a novel 4- to 40-GHz frequency quadrupler for radio-over- fiber systems. By using an optical carrier suppression modulation scheme in two cascaded intensity modulators, four-fold microwave or millimeter wave signals are optically generated without the need for an optical and electrical notch filter to remove the residual carrier components. Moreover, the limitation of high drive voltage is greatly reduced through tandem intensity modulation with pi/2 phase shift between two driving signals.

Centralized Lightwave Radio-Over-Fiber System With Photonic Frequency Quadrupling for High-Frequency Millimeter-Wave Generation

Abstract: We have proposed a novel radio-over-fiber architecture to reduce the system cost at both central office (CO) and base station (BS). In this architecture, by incorporating the proper dc bias and optical filtering techniques in CO, the optical millimeter- wave (mm-wave) carriers are generated with four times frequency of the local oscillator signal. The BS is simplified by using the separated optical carrier along with downlink mm-wave signals to carry the upstream data. We have experimentally demonstrated optical mm-wave carrier generation up to 64-GHz, and both down- and upstream signal delivery over 20 km fiber with 1-dB power penalty.

Recent Advances in High-Birefringence Fiber Loop Mirror Sensors

Abstract: Recent advances in devices and applications of high-birefringence fiber loopmirror sensors are addressed. In optical sensing, these devices may be used as strain andtemperature sensors, in a separate or in a simultaneous measurement. Other describedapplications include: refractive index measurement, optical filters for interrogate gratingsstructures and chemical etching control. The paper analyses and compares different types ofhigh-birefringence fiber loop mirror sensors using conventional and microstructured opticalfibers. Some configurations are presented for simultaneous measurement of physicalparameters when combined with others optical devices, for example with a long periodgrating.

Nonlinear Vector Filtering for Impulsive Noise Removal from Color Images

Abstract: A comprehensive survey of 48 filters for impulsive noise removal from color images is presented. The filters are formulated using a uniform notation and categorized into 8 families. The performance of these filters is compared on a large set of images that cover a variety of domains using three effectiveness and one efficiency criteria. In order to ensure a fair efficiency comparison, a fast and accurate approximation for the inverse cosine function is introduced. In addition, commonly used distance measures (Minkowski, angular, and directional-distance) are analyzed and evaluated. Finally, suggestions are provided on how to choose a filter given certain requirements.

90% Extraordinary optical transmission in the visible range through annular aperture metallic arrays

Abstract: We demonstrate what we believe to be the first experimental extraordinary optical transmission (EOT) of up to 90%, thanks to a well-identified guided mode that propagates through annular apertures engraved into an optically thick silver layer. In spite of the metal losses, high transmission can be obtained by adjusting the geometrical parameters of the fabricated structure, as was already theoretically demonstrated. To our knowledge, this is the first study showing such a large transmission in the visible range.

Experimental demonstration of a narrowband, angular tolerant, polarization independent, doubly periodic resonant grating filter.

Abstract: Resonant grating filters are promising components for free-space narrowband filtering. Unfortunately, due to their weak angular tolerance, their performances are strongly deteriorated when they are illuminated with a standard collimated beam. Yet this problem can be overcome by resorting to a complex periodic pattern known as the doubly periodic grating [Lemarchand et al., Opt. Lett.23, 1149 (1998)]. We report what we believe to be the first experimental fabrication and characterization of a bidimensional doubly periodic grating filter. We obtained a 0.5 nm bandpass polarization independent reflection filter for telecom wavelengths (1520-1570 nm) that presents a transmittivity minimum of 18% with a standard incident collimated beam.

High-speed all-optical differentiator based on a semiconductor optical amplifier and an optical filter.

Abstract: We demonstrate a novel all-optical differentiator that carries out the first-order temporal derivation of optical intensity variation at high speed. It consists of a semiconductor optical amplifier (SOA) and an optical filter (OF) serving as an optical phase modulator and a frequency discriminator, respectively. A polarity-reversed derivative pair with a certain bias can be obtained by locating the probe wavelength at the positive or negative slope of the OF. Differentiations of super-Gaussian and Gaussian signals are obtained at various data rates. Defined as the mean absolute deviation of the measured result from the ideal result, total average errors of less than 0.12 are observed in all cases. Input power dynamics as well as control wavelength dependence are investigated and show that the cross-gain modulation in the SOA is detrimental to the differentiation performance.

Control of guided resonance in a photonic crystal slab using microelectromechanical actuators

Abstract: A wavelength-selective variable-reflection filter is proposed, in which a guided resonance in a photonic crystal (PC) slab is controlled by microelectronic mechanical actuators. A narrow wavelength response is generated by the guided resonance of PC slab, and the variable optical response at the wavelength is caused by evanescent-wave coupling to a substrate. The coupling is controlled by microelectromechanical actuators. The proposed filter has been fabricated by silicon micromachining and the mechanism has been confirmed.

Binary-phase spatial filter for real-time swept-source optical coherence microscopy.

Abstract: We report a novel scheme to optimize the focusing condition for real-time, swept-source optical coherence microscopy. The axial and lateral behaviors of four-zone binary-phase spatial filters are presented numerically. A nearly constant axial intensity distribution along an extended depth of focus of 1.5 mm and a lateral resolution of 5 μm are experimentally verified. The A-line scan rate is up to 16 kHz, yielding a frame rate of 25 Hz and 640 lines per image.

Gigahertz-Wide Optically Reconfigurable Filters Using Stimulated Brillouin Scattering

Abstract: Flat-top sharp optical filters of gigahertz bandwidth are realized using stimulated Brillouin scattering (SBS). Pump chirp control of the SBS process enables versatile programming of the filter shape and bandwidth. The operating wavelength of the filters is tunable, and their frequency response is inherently aperiodic. Full widths at half maximum of 1.3-2.5 GHz are demonstrated, with a filtering selectivity up to 30 dB and an rms ripple of 0.5-1 dB. The filters are used to convert double sideband to single sideband (SSB) modulations for 1-GHz-wide linear-frequency-modulated (LFM) signals of arbitrary radio-frequency carrier. Such SSB modulation is highly instrumental for photonic implementations of true time delay, for example, in antenna beam-forming. The peak-side-lobe ratio of the processed LFM signal was -32 dB; its main lobe was broadened by only 4%. The integrated side-lobe ratio, which is limited by noise from spontaneous Brillouin scattering, was better than 21 dB, which is a sufficient value for most systems. The technique results in a large modulation index and does not lead to harmonic distortions.

Noise Figure Reduction in Externally Modulated Analog Fiber-Optic Links

Abstract: An octave-bandwidth microwave photonic link with a third-order limited spurious-free dynamic range of 121 dB in a 1-Hz bandwidth has been demonstrated. The link noise figure of 9 dB at a modulation frequency of 2 GHz was achieved by using a bias-shifted Mach-Zehnder modulator with an optical input power of 500 mW. This level of performance was realized without electronic or optical linearization

Rayleigh Noise Reduction in 10-Gb/s DWDM-PONs by Wavelength Detuning and Phase-Modulation-Induced Spectral Broadening

Abstract: A novel scheme for reducing Rayleigh beat noise in centralized light source dense wavelength-division-multiplexed passive optical networks is demonstrated using an optimized channel-detuned optical filtering of 30 GHz and phase-modulation-induced spectral broadening of a 10-Gb/s upstream nonreturn-to-zero (PM-NRZ) signal. The required optical-signal-to-Rayleigh-noise-ratio (OSRNR), characterized experimentally, can be reduced by up to 16 dB while retaining negligible transmission penalty over 20-km single-mode fiber without dispersion compensation. Numerical analysis is performed to study the tradeoff between OSRNR improvement and attenuation of the PM-NRZ signal as a function of different channel detuning and center wavelength suppressions

Optical design of a compact imaging spectrometer for planetary mineralogy

Abstract: We present the design of a compact, wide-angle pushbroom imaging spectrometer suitable for exploration of solar system bodies from low orbit. The spectrometer is based on a single detector array with a broadband response that covers the range 400 to 3000 nm and pro- vides a spectral sampling of 10 nm. The telescope has a 24-deg field of view with 600 spatially resolved elements detector pixels. A specially designed convex diffraction grating permits optimization of the signal-to- noise ratio through the entire spectral band. Tolerances and design pa- rameters permit the achievement of high uniformity of response through field and wavelength. The spectrometer performance is evaluated in terms of predicted spectral and spatial response functions and from the point of view of minimizing their variation through field and wavelength. The design serves as an example for illustrating the design principles specific to this type of system. © 2007 Society of Photo-Optical Instrumentation

Realization of Four-Pass $I_{2}$ Absorption Cell in 532-nm Optical Frequency Standard

Abstract: Several innovations have been adopted in our portable 532-nm optical frequency standard. Particularly, the authors realized a four-pass scheme equivalent to 1.8-m J2 absorption length, which gives adequate signal-to-noise ratio (~170 in a 10-kHz bandwidth). In addition, an active feedback control has been designed and implemented. The fluctuations of the residual-amplitude modulation in the electrooptic modulator have been successfully suppressed. As a result, the laser-frequency stability is greatly improved. When both lasers are locked on the same molecular iodine transition line of R (56) 32-0: alpha10, the Allan deviation is lower than 2.3 10-14 at 1-s averaging time, reaching the flicker floor at about 4 10-15 after 200 s. The maximum frequency excursion at 532 nm is about 175 Hz during a continuous measuring time of 150 000 s

Photonic Generation of Microwave Signals Based on Pulse Shaping

Abstract: A novel approach to generating microwave signals based on optical pulse shaping is proposed and experimentally demonstrated. The proposed system consists of a femtosecond pulse laser source, a Sagnac-loop filter (SLF), a dispersive element, and a photodetector. The spectrum of the femtosecond pulse is shaped by the SLF that has a sinusoidal spectral response. Thanks to the frequency-to-time conversion in the dispersive element, time-domain pulse exhibiting the shape of the optical power spectrum is obtained. Depending on the free-spectral range of the SLF and the total dispersion of the dispersive element, signals with frequencies up to terahertz can be generated. A model to describe the signal generation is developed. Experimental results agree well with the theoretical analysis

A Tunable Photonic Microwave Filter With a Complex Coefficient Using an Optical RF Phase Shifter

Abstract: A novel tunable photonic microwave filter with complex coefficients is proposed and experimentally demonstrated. The complex coefficient is generated using a wideband tunable optical RF phase shifter that consists of two electrooptic intensity modulators. The phase of the RF signal is shifted by simply adjusting the bias voltages applied to the two electrooptic intensity modulators, and the phase shift remains constant over the microwave spectral region of interest. A two-tap photonic microwave filter with one tunable complex coefficient, with a wide and continuous tuning range, is experimentally demonstrated.

Photonic Microwave Bandpass Filter With Negative Coefficients Using a Polarization Modulator

Abstract: A novel photonic microwave bandpass filter with negative coefficients implemented using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed filter, a lightwave from a tunable laser source (TLS) is sent to a PolM, with the incident lightwave adjusted to have its polarization direction aligned at an angle of plusmn45deg to the principal axes of the PolM. A microwave signal is applied to the PolM through its RF port. Thanks to the polarization modulation in the PolM, two complementary microwave signals with identical amplitudes carried by two optical carriers with orthogonal polarizations are generated. The two complementary optical microwave signals are then sent to an optical delay line consisting of one section or two sections of polarization-maintaining fiber (PMF), with the polarization directions aligned with the fast and slow axes of the PMF. A photonic microwave bandpass filter with two or four taps is obtained

Reconfigurable Microwave Photonic Filter Using Multiwavelength Erbium-Doped Fiber Laser

Abstract: A microwave photonic filter using a simple and novel multiwavelength erbium-doped fiber laser (EDFL) is proposed. The filter was experimentally demonstrated featuring tunability and reconfigurability by adjustment of the output from the EDFL. The experimental results show excellent agreement with the numerical simulations.

Tunable infrared detector with integrated micromachined Fabry-Perot filter

Abstract: This paper reports design, fabrication and test results of a tunable pyroelectric detector with an integrated micromachined Fabry-Perot (FP) filter for gas analysis in the Mid-Wave Infrared (MWIR). The new approach is based on a bulk micromachined Fabry-Perot interferometer with an air cavity, which is electrostatically tuned. Various types of moveable reflectors and spring configurations have been fabricated to determine the optimum solution with respect to maximum tuning range, low gravity influence on center wavelength and suitable filter bandwidth. Short and long cavity filters were designed for the spectral ranges of 3...4.3 μm and 3.7...5.0 μm respectively. The tunable filter is arranged on top of a current mode pyroelectric detector with a flat spectral response. It could be shown that the main challenge is to achieve a high finesse in spite of non-perfect parallelism, mirror curvature and additional phase shift caused by the Bragg reflectors.

Wideband microwave and millimeter wave filters using photonic spectral filtering

Abstract: An apparatus and method is disclosed for producing and filtering optical and electrical waveforms. The apparatus includes an electro-optical modulator, an optical filter capable of modulating at least two spectral regions within the bandwidth of the electrical waveform, and an optical-to-electrical converter. The optical filter includes a spatial dispersion means, a spatial modulating means having the capability to substantially independently modulate a characteristic of each of a pair of optical spatial elements.

Terahertz frequency bandpass filters.

Abstract: The design, measurement, and analysis of a range of artificial materials for use at terahertz frequencies are described. The chosen structures consist of arrays of cylindrical gold-plated pillars with period comparable to the wavelength of incident radiation. An ultraviolet (UV) micromachining approach to the fabrication of these high aspect-ratio pillars is described using the negative epoxy-based resin SU8. Lattice fence structures are also realized using the same method. Terahertz (THz) frequency time domain spectroscopy is performed on these structures in the range 200 GHz to 3.0 THz and the relative transmission of the structures is determined. The pass and stop bands are observed with peak transmission of up to 97%. Finite difference time domain simulations and complex photonic band structure calculations are shown to provide good descriptions of the electromagnetic properties of the structures and are used to interpret the observed transmission spectra.

Mechano-optical octave-tunable elastic colloidal crystals made from core-shell polymer beads with self-assembly techniques.

Abstract: Elastic colloidal crystals, even without a full photonic band gap, hold promise for fascinating applications and for easy large-scale fabrication by self-assembly. However, high mechanical robustness is required for optical, decorative, or security applications, such as tunable optical modulators/filters or optical tension indicators. Here, we present brilliantly colored filled-pore colloidal crystals that withstand elongation by 100%, i.e., one optical octave. We employ a variety of vertical deposition techniques to self-assemble monodisperse core-shell polymer beads with a film-forming shell and flexible core. We find a good theoretical description of crystal thickness for all techniques. The crystals have centimeter-sized macroscopic order, and their orientation is fully controlled by the substrate plane and meniscus line.

Design and Application of Compact and Highly Tolerant Polarization-Independent Waveguides

Abstract: In this paper, the design, fabrication, and application of a highly tolerant polarization-independent optical-waveguide structure suited for operation in the third communication window is presented. The waveguide structure has been optimized toward minimized sensitivity to technological tolerances and low fabrication complexity. The tolerance analysis has been based on the typical processing tolerances of the widely applied silicon-oxynitride technology, being plusmn3times10 -4 in refractive index, plusmn1% in thickness, and plusmn0.1 mum in channel width. The optimized waveguide design fulfills the criterion of a channel birefringence within 5times10-5, including processing tolerance. It also enables a fiber-to-chip coupling loss below 1 dB/facet and is suited for the realization of low-loss bends with a radius down to 600 mum. Based on this waveguide design, a passband-flattened optical wavelength filter with 50-GHz free spectral range has been realized and tested. The measured TE-TM shift of 0.03 nm confirms the polarization dependence of the optical waveguides being as low as 3times10-5

Tunable Transmission Resonant Filter and Modulator With Vertical Gratings

Abstract: Resonant filters in waveguides with vertical gratings have been realized on a silicon-on-insulator wafer. Two identical uniformly distributed Bragg reflectors with vertical gratings are separated by a quarter wavelength phase offset. Experimental studies show a broad stopband and a narrow transmission band which shifts with changing substrate temperature that is also illuminated by an external laser pump beam at 514-nm wavelength. Experimental results on a low-frequency thermal modulation using an external light source are also presented

A method and apparatus for a downhole spectrometer based on tunable optical filters

Abstract: Thermally tunable optical sensors are used in sampling tools for analysis of samples from a wellbore. The thermally tunable optical sensors generate a series passbands of wavelength emissions and detect attenuation in a signal thereof. The attenuation detected is processed and used to determine aspects of the samples. Analysis may be completed remotely (outside of the wellbore), within the wellbore (during drilling or otherwise), or as a part of another process such as fluid management, transport and refinement.