Showing papers on "Optical filter published in 2006"

Photonic signal processing of microwave signals

Abstract: Photonic signal processing offers the prospect of realizing extremely high multigigahertz sampling frequencies, overcoming inherent electronic limitations. This stems from the intrinsic excellent delay properties of optical delay lines. These processors provide new capabilities for realizing high time-bandwidth operation and high-resolution performance. In-fiber signal processors are inherently compatible with fiber-optic microwave systems and can provide connectivity with built-in signal conditioning. Fundamental principles of photonic signal processing, including sampling, tuning, and noise, are discussed. Structures that can extend the performance of photonic signal processors are presented, including methods for improving the filter shape characteristics of interference mitigation filters, techniques to increase the stopband attenuation of bandpass filters, and methods to achieve large free spectral range. Several photonic signal processors, including high-resolution microwave filters, widely tunable filters, arbitrary waveform generators, and fast signal correlators, are discussed. Techniques to solve the fundamental noise problem in photonic signal processors are described, and coherence-free structures for few-tap notch filters are discussed. Finally, a new concept for realizing multiple-tap coherence-free processor filters, based on a new frequency-shifting technique, is presented. The structure not only eliminates the phase-induced intensity noise limitation, but can also generate a large number of taps to enable the achievement of processors with high performance and high resolution.

A review of metal mesh filters

Abstract: The Astronomical Instrumentation Group at Cardiff University has been developing metal mesh optical filters for more than 30 years, which are currently in use in many ground-, balloon- and space-based instruments. Here we review the current state of the art with respect to these quasi-optical components (low-pass, high-pass and band-pass filters, dichroics and beam-dividers) as developed for the FIR and sub-millimetre wavelength region. We compare performance data with various modelling tools (HFSS, transmission line theory or Floquet mode analysis). These models assist with our understanding of the behaviour of these filters when used at non-normal incidence or in the diffraction region of the grid structures. Interesting artefacts, such as the Wood anomalies and behaviour with S and P polarisations, which dictate the usage of these components in polarisation sensitive instruments, will be discussed.

Photonic microwave tunable single-bandpass filter based on a Mach-Zehnder interferometer

Abstract: The authors present the theoretical analysis and experimental demonstration of a novel single-bandpass tunable microwave filter. The filter is based on a broadband optical source and a fiber Mach-Zehnder interferometer and shows a high Q factor over a tuning range of 5-17 GHz. A generalized analysis considering that the optical signal propagates along optical delay lines with a dispersion slope different from zero is presented.

Error-free all-optical wavelength conversion at 160 gb/s using a semiconductor optical amplifier and an optical bandpass filter

Abstract: Error-free and pattern-independent wavelength conversion at 160 Gb/s is demonstrated. The wavelength converter utilizes a semiconductor optical amplifier (SOA) with a recovery time greater than 90 ps and an optical bandpass filter (OBF) placed at the amplifier output. This paper shows that an OBF with a central wavelength that is blue shifted compared to the central wavelength of the converted signal shortens the recovery time of the wavelength converter to 3 ps. The wavelength converter is constructed by using commercially available fiber-pigtailed components. It has a simple configuration and allows photonic integration.

Fabrication of Transmission Color Filters Using Silicon Subwavelength Gratings on Quartz Substrates

Abstract: We investigate theoretically and experimentally transmission color filters using silicon subwavelength gratings on quartz substrates. Each grating area is 120 mum-square, which is suitable pixel size for displays and multichannel detectors. In the fabrication, electron beam lithography and fast atom beam etching are used. The grating periods are 400, 350, and 440 nm for the red, green, and blue filters, respectively. The transmission spectrum obtained from a coupling between an incident light and the submicrometer periodic grating matches with human color perception. The transmittances of 71.1%, 58.1%, and 59.3% are obtained for the red, green, and blue filters, respectively

Chirp-managed directly modulated laser (CML)

Abstract: We demonstrate a new highly dispersion tolerant modulation format using a chirp-managed directly modulated laser (CML) for uncompensated 10-Gb/s transmission over >200 km at 1.55 /spl mu/m. The CML consists of a distributed feedback (DFB) laser followed by an optical filter. We show that the combination of adiabatic chirp from the DFB and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are /spl pi/ out of phase. This results in carrier suppression, 1/2 the bandwidth of standard nonreturn-to-zero, and high tolerance to positive and negative dispersion.

Liquid-crystal-based terahertz tunable Lyot filter

Abstract: A two-element tunable Lyot filter operating in the terahertz (THz) frequency range is demonstrated. The central bandpass frequency of the filter can be continuously tuned from 0.388to0.564THz (a fractional tuning range of 40%) using magnetically controlled birefringence in nematic liquid crystals. The transmission bandwidth is 0.1THz and the insertion loss of the present device is 8dB due to the scattering of LC molecules in the thick LC cells. This filter can be operated at room temperature.

Optical properties of deep lamellar Gratings: A coupled Bloch-mode insight

Abstract: A coupled-Bloch-mode model for explaining various optical properties of strongly modulated subwavelength lamellar gratings is proposed. The model evidences the key role played by propagative Bloch modes, which bounce inside the grating and couple at the grating interfaces. Many optical properties of these gratings, such as their broadband reflectance, their polarization effect, and the presence of sharp anomalies, are understood as resulting from vertical resonances of the coupled-resonator modes. The approach provides a new insight on the physical mechanisms or optical behaviors observed, which is different from the classical study of the poles and zeros of the scattering operator.

Monolithically integrated dye-doped PDMS long-pass filters for disposable on-chip fluorescence detection

Abstract: We report the fabrication of high quality monolithically integrated optical long-pass filters, for use in disposable diagnostic microchips. The filters were prepared by incorporating dye molecules directly into the microfluidic chip substrate, thereby providing a fully integrated solution that removes the usual need for discrete optical filters. In brief, lysochrome dyes were added to a poly(dimethylsiloxane) (PDMS) monomer prior to moulding of the microchip from a structured SU-8 master. Optimum results were obtained using 1 mm layers of PDMS doped with 1200 µg mL−1 Sudan II, which resulted in less than 0.01% transmittance below 500 nm (OD 4), >80% above 570 nm, and negligible autofluorescence. These spectral characteristics compare favourably with commercially available Schott-glass long-pass filters, indicating that high quality optical filters can be straightforwardly integrated into the form of PDMS microfluidic chips. The filters were found to be robust in use, showing only slight degradation after extended illumination and negligible dye leaching after prolonged exposure to aqueous solutions. The provision of low cost high quality integrated filters represents a key step towards the development of high-sensitivity disposable microfluidic devices for point-of-care diagnostics.

An approach to ultrawideband pulse generation and distribution over optical fiber

Abstract: We propose a novel approach to generating and distributing ultrawideband (UWB) pulse signals over optical fiber. The proposed system consists of a single-wavelength laser source, an electrooptic phase modulator (EOPM), a length of single-mode fiber (SMF), and a photodetector (PD). The combination of the EOPM, the SMF link, and the PD forms an all-optical microwave bandpass filter, which is used to generate a UWB signal with a spectrum meeting the regulation of the Federal Communication Commission. Gaussian doublet pulses are obtained at the receiver front-end, which can provide several gigahertz bandwidths for applications in high-bit-rate UWB wireless communications. Experimental results measured in both temporal and frequency domains are presented.

Fabrication of add-drop filters based on frequency-matched microring resonators

Abstract: Frequency mismatches between resonators significantly impact the spectral responses of coupled resonator filters, such as high-order microring filters. In this paper, techniques allowing fabrication of frequency-matched high-index-contrast resonators are proposed, demonstrated, and analyzed. The main approach consists of inducing small dimensional changes in the resonators through alteration of the electron-beam dose used to expose either the actual resonator on a wafer or its image on a lithographic mask to be later used in filter fabrication. Third-order microring filters fabricated in silicon-rich silicon nitride, with optical resonator frequencies matched to better than 1 GHz, are reported. To achieve this, the average ring-waveguide widths of the microrings are matched to within less than 26 pm of a desired relative width offset. Furthermore, optimization and calibration procedures allowing strict dimensional control and smooth sidewalls are presented. A 5-nm dimensional control is demonstrated, and the standard deviation of sidewall roughness is reduced to below 1.6 nm.

On-chip microfluidic tuning of an optical microring resonator

Abstract: We describe the design, fabrication, and operation of a tunable optical filter based on a bus waveguide coupled to a microring waveguide resonator located inside a microchannel in a microfluidic chip. Liquid flowing in the microchannel constitutes the upper cladding of the waveguides. The refractive index of the liquid controls the resonance wavelengths and strength of coupling between the bus waveguide and the resonator. The refractive index is varied by on-chip mixing of two source liquids with different refractive indices. We demonstrate adjustment of the resonance by 2nm and tuning the filter to an extinction ratio of 37dB.

Coupled resonator optical waveguides based on silicon-on-insulator photonic wires

Abstract: Coupled resonator optical waveguides (CROWs) comprised of up to 16 racetrack resonators based on silicon-on-insulator (SOI) photonic wires were fabricated and characterized. The optical properties of the CROWs were simulated using measured single resonator parameters based on a matrix approach. The group delay property of CROWs was also analyzed. The SOI based CROWs consisting of multiple resonators have extremely small footprints and can find applications in optical filtering, dispersion compensation, and optical buffering. Moreover, such CROW structure is a promising candidate for exploration of low light level nonlinear optics due to its resonant nature and compact mode size (∼0.1μm2) in photonic wire.

Self-phase modulation-based integrated optical regeneration in chalcogenide waveguides

Abstract: We demonstrate integrated all-optical 2R regenerators based on Kerr optical nonlinearities (subpicosecond response) in chalcogenide glass waveguides with integrated Bragg grating filters. By combining a low loss As/sub 2/S/sub 3/ rib waveguide with an in-waveguide photo-written Bragg grating filter, we realize an integrated all-optical 2R signal regenerator with the potential to process bit rates in excess of 1 Tb/s. The device operates using a combination of self phase modulation induced spectral broadening followed by a linear filter offset from the input center wavelength. A nonlinear power transfer curve is demonstrated using 1.4 ps pulses, sufficient for suppressing noise in an amplified transmission link. We investigate the role of dispersion on the device transfer characteristics, and discuss future avenues to realizing a device capable of operation at subwatt peak power levels.

Wavelength Filters in Fibre Optics

Abstract: Optical Filters in Wavelength-Division Multiplex Systems.- Phase Characteristics of Optical Filters.- Diffraction Gratings WDM Components.- Arrayed Waveguide Gratings.- Fibre Bragg Gratings.- Fabry-Perot Interferometer Filters.- Dielectric Multilayer Filters.- Ring-Resonator-Based Wavelength Filters.- Interleavers.

Demonstration of incoherent microwave photonic filters with all-optical complex coefficients

Abstract: We propose and demonstrate for the first time to our knowledge an incoherent microwave photonic filter with complex coefficients implemented in the optical domain. The system is based on a tunable optically induced RF phase-shift that is obtained by means of a novel optical signal processing technique that makes combined use of optical single-sideband modulation and stimulated Brillouin scattering. A two-tap filter is built demonstrating full tunability of its frequency response by dynamically changing the phase shift of a complex coefficient

Free-Space Tunable and Drop Optical Filters Using Vertical Bragg Mirrors on Silicon

Abstract: Vertical Bragg grating mirrors are realized by the anisotropic etching of Si using deep reactive ion etching (DRIE), thus producing multiple vertical interfaces between Si and air. The Bragg mirrors are used to realize two optical filter configurations. The first is a tunable Fabry-Peacuterot cavity composed of two mirrors, where tuning is achieved by moving one of the mirrors using silicon-on-insulator (SOI) electrostatic microelectromechanical system (MEMS) actuation. The second is a drop filter, where a tilted Bragg mirror acts as a wavelength selective reflector. The enhanced etching process involving a mix of cryogenic and Bosch DRIE processes is presented. The realized structures, fabrication process, as well as measured performance are also presented

Experimental and theoretical investigation of the impact of ultra-fast carrier dynamics on high-speed SOA-based all-optical switches.

Abstract: The impact of ultra-fast carrier dynamics in semiconductor optical amplifiers (SOAs) on switches based on cross-gain and cross-phase modulation is analyzed theoretically and experimentally. We find that ultra-fast effects lead to additional spectral broadening, which improves the optical signal-to-noise ratio for switches based on an SOA and an optical filter. For such switches, the influence of ultra-fast effects on the so-called nonlinear patterning effect is analyzed for three filter configurations: the asymmetric Mach-Zehnder interferometer (AMZI), a band-pass filter (BPF), and a cascade of an AMZI and a BPF. We conclude that fast carrier dynamics dramatically reduces nonlinear patterning and that the successful high-speed (>100 Gb/s) demonstrations in the literature rely on these effects.

2R optical regeneration: an all-optical solution for BER improvement

Abstract: We show both theoretically and experimentally that signal re-amplifying and reshaping (2R) optical regenerator based on self-phase-modulation (SPM)-induced spectral broadening followed by optical filtering has significant advantages over conventional 2R regenerators. By discriminating amplified spontaneous emission noise from a pulsed signal, the SPM-based regenerator is able to selectively attenuate noise more than the pulsed signal. This unique feature results in a direct improvement in bit-error ratio (BER) of a noisy pulsed signal, whereas conventional 2R regenerators can only prevent BER degradation-not actually improve it. We compare the two classes of regenerator and highlight their fundamental differences. We also demonstrate the BER improvement of a noisy signal filtered with an SPM-based regenerator that utilizes a highly nonlinear silica fiber, and present a compact version by exploiting a short length of As2Se3 chalcogenide glass fiber

Optical analysis system and methods for operating multivariate optical elements in a normal incidence orientation

Abstract: A method of arranging and utilizing a multivariate optical computing and analysis system includes transmitting a first light from a light source; generating a second light by reflecting the first light from the sample; directing a portion of the second light with a beamsplitter; and arranging an optical filter mechanism in a normal incidence orientation to receive the portion of the second light, the optical filter mechanism being configured to optically filter data carried by the portion of the second light.

Optical analysis system and optical train

Abstract: A multivariate optical computing and analysis system includes a light source configured to radiate a first light along a first ray path; a modulator disposed in the first ray path, the modulator configured to modulate the first light to a desired frequency; a spectral element disposed proximate the modulator, the spectral element configured to filter the first light for a spectral range of interest of a sample; a cavity disposed in communication with the spectral element, the cavity configured to direct the first light in a direction of the sample; a tube disposed proximate the cavity, the tube configured to receive and direct a second light generated by a reflection of the first light from the sample, the tube being further configured to separate the first and second lights; a beamsplitter configured to split the second light into a first beam and a second beam; an optical filter mechanism disposed to receive the first beam, the optical filter mechanism configured to optically filter data carried by the first beam into at least one orthogonal component of the first beam; and a detector mechanism in communication with the optical filter mechanism to measure a property of the orthogonal component to measure the data.

Performance of coherent optical square-16-QAM-systems based on IQ-transmitters and homodyne receivers with digital phase estimation

Abstract: The potential for higher spectral efficiency and recent activities in the area of coherent optical systems raise the interest in new multi-level modulation formats for optical transmission. In this paper square-16-QAM is introduced as a novel candidate for future high-capacity and high spectrally efficient optical systems. Different possible transmitters as well as the homodyne IQ-receiver are illustrated. At the transmitter side the implementation of an electrical level-generator is shown experimentally. At the receiver side options for the realization of the optical 2/spl times/4 90 /spl deg/-hybrid are discussed. Furthermore, an algorithm for square-16-QAM digital phase estimation is developed, whose performance and limitations are investigated in simulations.

Optical coherence imaging systems having a reduced effective linewidth and methods of using the same

Abstract: Frequency domain optical coherence imaging systems have an optical source, an optical detector and an optical transmission path between the optical source and the optical detector The optical transmission path between the optical source and the optical detector reduces an effective linewidth of the imaging system The optical source may be a broadband source and the optical transmission path may include a periodic optical filter

Optical image measuring instrument

Abstract: An optical image measuring instrument capable of shorting the measurement time. A flash is outputted from a xenon lamp (2) and converted into a wide-band light by means of an optical filter (2A). The flash is converted into a linearly polarized light by means of a polarizing plate (3). The linearly polarized light is divided into a signal light (S) and a reference light (R) by means of a semitransparent mirror (6). The reference light (R) is converted into a circularly polarized light by means of a wavelength plate (7). The signal light (S) and the reference light (R) are combined by means of a semitransparent mirror (6) to produce an interference light (L). A CCD (23) detects the interference light having the same characteristic as the interference light (L). The interference light (L) is separated into an S-polarized component (L1) and a P-polarized component (L2) by means of a polarized beam splitter (11). These components are detected by means of CCDs (21, 22). A computer (30) creates an image of an object (O) to be measured from the detection signals from the CCDs (21, 22, 23). With such an optical image measuring instrument (1), since two polarized components (L1, L2) of the interference light (L) can be simultaneously obtained, the measurement time can be shortened.

Constraining Disk Parameters of Be Stars using Narrowband Hα Interferometry with the Navy Prototype Optical Interferometer

Abstract: : Interferometric observations of two well-known Be stars, gamma Cas and phi Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H(alpha) emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H(alpha)-emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H(alpha) channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H -emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ringlike structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations.

Tunable radio-frequency photonic filter based on an actively mode-locked fiber laser.

Abstract: We propose the use of an actively mode-locked fiber laser as a multitap optical source for a microwave photonic filter. The fiber laser provides multiple optical taps with an optical frequency separation equal to the external driving radio-frequency signal of the laser that governs its repetition rate. All the optical taps show equal polarization and an overall Gaussian apodization, which reduces the sidelobes. We demonstrate continuous tunability of the filter by changing the external driving radio-frequency signal of the laser, which shows good fine tunability in the operating range of the laser from 5 to 10 GHz.

Power spectrum analysis for optical tweezers. II: Laser wavelength dependence of parasitic filtering, and how to achieve high bandwidth

Abstract: In a typical optical tweezers detection system, the position of a trapped object is determined from laser light impinging on a quadrant photodiode. When the laser is infrared and the photodiode is of silicon, they can act together as an unintended low-pass filter. This parasitic effect is due to the high transparency of silicon to near-infrared light. A simple model that accounts for this phenomenon [Berg-Sorensen et al., J. Appl. Phys. 93, 3167 (2003)] is here solved for frequencies up to 100kHz and for laser wavelengths between 750 and 1064nm. The solution is applied to experimental data in the same range, and is demonstrated to give this detection system of optical tweezers a bandwidth, accuracy, and precision that are limited only by the data acquisition board’s bandwidth and bandpass ripples, here 96.7kHz and 0.005dB, respectively.