Tunable Wavelength Filter Research Articles

Tunable Šolc-type filter in periodically poled LiNbO3by UV-light illumination

We demonstrate a tunable Solc-type filter in periodically poled lithium niobate by UV-light illumination in this paper. Due to the photovoltaic effect, a Solc-type filter in PPLN can be formed without applying an external electric field. Through this mechanism, a tunable wavelength filter by UV-light illumination is realized. A wavelength shift as large as 15nm is observed under 778mW/cm(2) uniform UV illumination. The dependence of wavelength shift on illumination intensity shows a nearly linear relationship and the tuning rate is about 52 mW/cm(2) per nm at 20 degrees C.

Field trial of data-granularity-flexible reconfigurable OADM with wavelength-packet-selective switch

Reconfigurable optical add/drop multiplexers (ROADMs), which enable dynamic and flexible node-to-node connection via wavelength paths, are key components in metro ring network nodes. A data-granularity-flexible ROADM node that combines a wavelength-tunable filter, and an optical packet ADM (PADM) has been proposed and demonstrated. In this paper, the first field trial of the data-granularity-flexible ROADM network with wavelength- and packet-selective switch is demonstrated using a novel concurrent generation technique of address-reconfigurable optical-code (OC) labels and payload data. Bit error rates (BERs) of less than 10/sup -12/ for all 16-wavelength channels are obtained over 90 km of transmission at 10 Gb/s.

Transmittance Characteristics of Buckled Fabry--Perot Tunable Filter with Membrane Structure

A wavelength tunable thermo-optic filter has been designed and fabricated for 1550 nm transmission. It has a Fabry--Perot resonator at the center with two sets of distributed Bragg reflector mirrors at both ends. The filter is fabricated as a free-standing membrane of alternating poly-Si and SiO2 films surrounded by a thick silicon frame. The membrane is buckled due to the residual stress. Because of the buckling effect, high tuning efficiency of more than 0.17 nm/°C is observed. When the filter has a buckled surface, the incident light normal to the filter should have a range of non-zero angle of incidence to the membrane, which is dependent on the degree of buckling that depends again on the temperature. The transmittance calculations which integrate each incoming ray from a different incident angle show good qualitative agreement with the temperature dependence of the center wavelength and bandwidth.

Microring resonators on side-polished optical fiber

A novel fiber optical device based on microring resonators fabricated on side-polished fiber is proposed. The compact size and light weight device structure can be useful for various fiber-optic sensors, fixed and tunable wavelength filters, and intensity modulators. Since the device is directly fabricated on the optical fiber, many issues associated with fiber-to-chip coupling and attachment can be avoided. A preliminary experiment using polymer microring resonators made by two-photon polymerization has proved this new device concept.

Design of a fast tunable wavelength filter based on an arrayed waveguide grating

We present the design of a tunable wavelength filter based on an active arrayed waveguide grating (AWG). We show a novel layout and simulated performance of a tandem filter configuration that covers 43 nm in C band with 0.2-nm (25-GHz) channel spacing at –35-dB crosstalk level. Design of the device is based on Fourier-Fresnel formalism with special emphasis on tuning mechanisms. The Gerchberg-Saxton phase retrieval method is used to estimate phase errors and generate phase patterns required for device tuning. A polarization insensitive filter is presented with its main parameters and simulation results. The technological considerations of achieving nanoseconds-scale tunability by exploiting the electro-optical effect in LiNbO3 crystals are discussed in detail. Such a filter may find various applications in packet-switched coarse and dense multiwavelength dynamic networks.

Spectrum Tuning of Fiber Bragg Gratings by Strain Distributions and Its Applications

We report tunable optical devices based on fiber Bragg gratings (FBGs), whose filtering characteristics are controlled by strain distributions. These devices include a widely wavelength tunable filter, a tunable group-velocity dispersion (GVD) compensator, a tunable dispersion slope (DS) compensator, and a variable-bandwidth optical add/drop multiplexer (OADM), which will play important roles for next-generation reconfigurable optical networks.

Monolithic Fabry–Perot Wavelength Tunable Filter with Electrothermal Actuation

We report on a micromachined monolithic Fabry–Perot wavelength tunable filter with a thick moving structure operated by an electrothermal actuation. The monolithic structure simplifies the fabrication process and the electrothermal actuation mechanism reduces the required operation voltage. For the wet etching of the AlGaAs sacrificial layer, an HCl-based solution rather than a HF-based one was used because it results in a larger selectivity between the AlxGa1-xAs layers and less damage to the suspended structure. The wavelength tuning range of the 7.64-µm-thick structure was 47 nm for the power consumption of 5 mW, which results in the high tuning efficiency of ∼9.9 nm/mW. The wide tuning range of 81.2 nm for the 5.2-µm-thick structure, that is not possible with an electrostatic actuation mechanism due to the occurrence of breakdown, is achieved at the driving voltage below 5.7 V. Due to the simplicity of fabrication and the ease of integration, this structure is advantageous for use in wavelength tunable light sources and photodetectors.

Temperature-compensated, highly accurate wavelength-tunable filters for photonic networks

A temperature compensation technique is proposed and demonstrated for highly accurate control of the transmission wavelength of wavelength-tunable optical bandpass filters. The technique calculates wavelength error, which is caused by transient variations of the operating temperature of filter modules, by use of the theory of thermal conduction and controls the filter with an appropriate offset according to the calculated value to maintain a constant transmission wavelength. A disk-shaped wavelength-tunable filter based on a mechanical tuning mechanism is demonstrated to confirm the validity of the technique. For the filter, the transmission wavelength is controlled to an accuracy of 0.01 nm against drastic temperature variations whose maximal change rate reaches 2.5 °C∕min in the range of 20-50 °C. A filter controlled with this technique has the potential to provide high-performance channel selectors for wavelength-division-multiplex-based photonic networks, and its feasibility is confirmed by transmission experiments at 2.5 Gbit/s.

P-180L: Late-News Poster: Tunable Liquid Crystal Color Filter for Image Analysis

The wavelength tunable liquid crystal color filter is developed for the image analysis. The control of the transmitted spectrum is realized by introducing the new design concept. It was clarified that the compensation of the dispersion property in liquid crystal is possible by usual retardation film.

Optical-carrier-frequency detection using a synchroscan disk-shaped optical filter embedded in bidirectional fiber delay line for superdense WDM network systems

We propose and demonstrate a method of detecting the optical carrier frequency of an optical data stream using a disk-shaped wavelength-tunable optical bandpass filter operated in the synchroscan mode. The method is based on a differential technique that uses an S-shaped curve obtained from divided data streams. A bidirectional configuration with a delay line enables the data streams not only to pass through the filter at a different time but also to enter each photodiode at the same time. Consequently, pattern-oriented noise, which degrades the accuracy, can be eliminated by an optimized low-pass filter. An experimental demonstration carried out for optical signals with a non-return-to-zero format 2^7 - 1 pattern at 150 Mbit/s verifies the method. A high resolution of 100 MHz is achieved with a filter having a transmission bandwidth of 0.06 nm. This performance is promising for photonic networks that manage a large number of optical channels multiplexed in the frequency domain.

Widely tunable filter based on side-polished polarisation-maintaining fibre coupled with thermo-optic polymer overlay

A wide wavelength tunable filter based on a side-polished polarisation-maintaining fibre in contact with a polymer planar waveguide overlay is proposed and demonstrated. The good thermo-optic effect of the polymer waveguide induced by a micro-strip heater leads to a wide tunable wavelength range of 230 nm with an applied electrical power of 0.76 W.

Wavelength tunable thermo-optic filter using buckling effect of etalon composed poly-Si/SiO2 multi-layers

Wavelength tunable thermo-optic filter has been designed and fabricated for 1550 nm transmission. Its basic structure has a Fabry–Perot resonator with a poly-Si cavity layer at the center and two sets of distributed Bragg reflector (DBR) mirrors consisting of four poly-Si/SiO2 multi-layers. The device uses free-standing membrane surrounded by thick silicon frame and thus its surface is buckled due to the residual stress. Its transmitted wavelength can be tuned from 1554.4 nm at 25.3 � C to 1565.7 nm at 100 � C, and thus tuning efficiency of 0.15 nm/K for the temperature range of 74.7 � C is obtained. It is believed that the buckling effect of the filter results in wider tuning range and higher tuning efficiency than that of plane filters without buckling effect. It is also found that the buckled membrane increases the tolerance limit of tilting errors of the filter. � 2004 Elsevier B.V. All rights reserved.

Micromechanical Digital-to-Analog Converter for Out-of-Plane Motion

This paper describes a novel micromechanical digital-to-analog converter (MDAC) for out-of-plane motion using electrostatic parallel-plate actuators. The proposed mechanism converts an N-bit digital signal to a mechanical out-of-plane displacement that is proportional to the analog value represented by the N-bit binary word. The mechanism is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a movable platform, an array of parallel-plate microactuators each operating in an ON/OFF mode and a set of connection springs that connect the actuators to the platform. The spring constants of the connection springs are weighted so that the stiffness of successive springs is related by a factor of 2. A 4-bit mechanism has been fabricated using the Poly-MUMPS process, achieving a total stroke of 675 nm (full-scale output) and step size (LSB) of 45 nm in a highly repeatable and stable manner. The linearity error (LE) of the device is within /spl plusmn/0.28 LSB, and the differential linearity error (DLE) is within /spl plusmn/0.25 LSB. This mechanism can be configured for many promising applications, particularly in optical devices and systems such as tunable external cavity diode laser, tunable VCSELs, adaptive micromirror array and tunable wavelength filter.

Electrothermally Actuated Fabry–PÉrot Tunable Filter With a High Tuning Efficiency

We report on a electrothermally actuated Fabry-Pe/spl acute/rot wavelength tunable filter with a high tuning efficiency by using surface micromachining. To prevent a current flowing through the mirror, a Wheatstone bridge structure is introduced. Because the full wafer is monolithically grown and the electrodes are formed in a single step, the fabrication processes is simple and reproducible. As the current flows through the two parallel thermal actuators, the top mirror moves away from the bottom mirror so that a sticking problem does not occur. The maximum voltage for the 69-nm wavelength tuning by using a 5.2-/spl mu/m-thick filter structure is only 1.7 V and the high tuning efficiency of /spl sim/75 nm/mW is achieved.

Thermo-optically Tunable Wavelength Filter with Permanent Refractive Index Grating into Azo-Polymer Waveguide

Refractive index gratings into an azo-polymer waveguide were fabricated by irreversible photo-induced bleaching (photodecomposition) of the polymer. The waveguide grating was formed by exposure of an interference pattern from two laser beams. Coupling characteristics of the waveguide grating were investigated around the infrared wavelength region. The coupling efficiency of the grating was dependent on the polarization direction of the guiding beam. This phenomenon seems to result from the anisotropic refractive index change due to the photobleaching at the vertical plane of the film. Furthermore, we demonstrated a tunable wavelength filter with the refractive index gratings into the azo-polymer waveguide. This filter has a spatial tunability, i.e., wavelength tuning can be attained due to thermooptic refractive index change of the polymer. In the fabricated wavelength filter, the diffraction pass wavelength is tuned over 19 nm at around the 1.3 µm from 5°C to 65°C.

Analysis of a distributed coupling coefficient phase-controlled distributed feedback optical filter

We have proposed a new phase-controlled distributed feedback wavelength tunable optical filter with distributed coupling coefficient. The analysis, which is based on the transfer matrix method, reveals that an almost constant peak transmissivity (gain) of more than 37dB, tuning range of better than 21.7A and side-mode suppression ratio (SMSR) of more than 17dB can be achieved using this structure.

Accurate high-speed spectrum measurement with disk-shaped wavelength-tunable filter for DWDM networks

A novel spectrum measurement with a motor-driven disk-shaped scanning wavelength-tunable filter can measure the spectra of dense wavelength division multiplexing (DWDM) signals precisely owing to the stability of the filter's optical properties against mechanical influence. Fast spectrum measurement with a sweep frequency of 10 Hz was successfully demonstrated with standard deviation of 0.4 pm.

Wide-range tunable wavelength filter in periodically poled lithium niobate

In this paper, a tunable narrowband spectral filter in periodically poled lithium niobate (PPLN) by temperature is experimentally demonstrated. We observe a shift of transmission spectrum of PPLN Šolc-type filter when the temperature is modified. The tuning rate is measured to be −0.422 nm/°C, which is in agreement with calculation results of the coupled-mode theory.

Theory of quarter-wave-stack dielectric mirrors used in a thin Fabry-Perot filter

I present a new derivation of the analytic form for the phase shift near resonance and the optical penetration length upon reflection from a distributed dielectric mirror consisting of a quarter-wave stack. The requirement of proper termination to achieve high reflectivity is suspended to investigate large optical penetration depths. Separate equations, derived for N and N + 1/2 layer pairs, are convenient for the design of tunable Fabry-Perot filters with a specified tuning range. The analysis is also applicable to distributed Bragg reflectors, vertical-cavity surface-emitting lasers, and resonant photodiodes. I show that the penetration length can sharply reduce the overly broad free spectral range of an ultrathin Fabry-Perot filter that might be useful in applications such as tunable wavelength filters for wavelength division multiplexing applications. The results also demonstrate regimes of zero dispersion and of superluminal reflection in the dielectric mirrors, which are of particular interest in photonic bandgap structures.

Wavelength-tunable spectral filters based on the optical rotatory dispersion effect.

An optical arrangement for constructing wavelength-tunable spectral filters is presented that makes use of a set of dispersive polarization rotations to select wavelengths. A filter in the arrangement is initially mechanically tunable, requires no achromatic retarder, and can be further electrically tunable, switchable, or both, depending on the elements selected. Test measurements and results are presented and described. Modified arrangements with additional retarder(s) or liquid-crystal polarization rotator(s) are suggested and discussed.