Integrated optical, acoustically tunable wavelength filter

A TM/TE convertor is combined with a TE-pass polariser on a common LiNbO/sub 3/ chip to obtain an integrated optical, acoustically tunable wavelength filter. Its tuning range is 1.45-1.57 mu m wavelength with a filter half-width of 2.8 nm. Due to the combined acoustical/optical strip guide structure used in the mode convertor, a very low acoustic drive power of only 9 mW is required.<>     

1.5 μm two-section Fabry-Perot wavelength tunable optical filter

A 1.5 μm two-section Fabry-Perot wavelength tunable optical filter is studied. As opposed to DFB filters, this wavelength tunable optical filter has the advantage that the wavelength tuning range and the transmission bandwidth can be designed independently. This two-section Fabry-Perot filter also controls the transmissivity (gain) and the transmission wavelength independently by current injection and the constant-gain and constant-bandwidth wavelength tuning is achieved. The wavelength tuning range is as wide as 188 GHz (15 Å), the constant-gain is as high as 23 dB and the constant-bandwidth is as narrow as 5 GHz during wavelength tuning. A 25-channel wavelength selection with less than -10 dB crosstalk is expected with this filter     

Widely (132 nm) wavelength tunable laser using a semiconductor optical amplifier and an acousto-optic tunable filter

A widely wavelength tunable laser combining a semiconductor optical amplifier, an acousto-optic tunable filter and a Fabry-Perot etalon has been developed. It exhibited good characteristics over a 132 nm (1480-1612 nm) tuning range.     

Digitally tunable wavelength filter and laser

A novel nonmechanical, digitally tunable, polarization insensitive and optically transparent wavelength filter using holograms electro-optically written on a ferroelectric liquid crystal (FLC) spatial light modulator (SLM) has been constructed and operated to tune to discrete wavelengths spaced by 1.3 nm. The filter has been incorporated in a ring laser which is tunable over a range of 38.5 nm across the erbium window, giving output powers of 10 mW. Both wavelength filter and tunable laser are suitable for wavelength division multiplexing (WDM) applications.     

An active interference filter as an optical maser amplifier

Approximate theoretical expressions for gain, bandwidth, and root gain-bandwidth are derived by introducing negative absorption into equations for a Fabry-Perot interference filter. Resuits of gain vs frequency calculations are given for a 10-cm maser with high single-pass gain and a 100-cm maser with low single-pass gain. Root gain-bandwidth is shown to be a constant for a given cavity as long as the cavity bandwidth is much smaller than the Doppler or fluorescent linewidth of the maser transition. Frequency drift due to temperature variations and the necessity for precise control of single-pass gain are two practical problems. These must be solved in order to make a stable amplifier with high gain.     

Optically transparent digitally tunable wavelength filter

A new digital architecture combining a spatial light modulator written dynamic hologram and a fixed diffractive grating has been demonstrated to produce a tunable wavelength filter with a tuning resolution of 2.5 nm over a 160 nm range. Three modes of a broadband 1.45 μm laser diode have been isolated using the filter and selectively coupled into singlemode communications fibre     

High-speed wavelength tunable liquid crystal filter

We describe the first high-speed, continuously tunable liquid crystal optical filter suitable for wavelength division multiaccess (WDMA) optical networks. The filter utilizes chiral smectic A* electroclinic liquid crystal as the active cavity material in a Fabry-Perot etalon to obtain microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter with a switching speed of less than 10 μs and a tuning range of approximately 30 nm, when the filter passband is centered at 1.55 μm     

Acoustically tunable wavelength filter with gain

The first integrated optical amplifying acoustically tunable wavelength filter in Er-doped LiNbO₃ is reported. At the signal wavelength of λ_s=1531 nm a maximum gain of 4.8 dB has been obtained with a coupled pump power of 160 mW (λ_p =1484 nm). Lossless signal transmittance has been achieved with a pump power as low as 13.5 mW for λ_s>1561 nm     

An ARROW optical wavelength filter: design and analysis

A novel ARROW (antiresonant reflecting optical waveguide)-based optical wavelength filter is proposed. The modal characteristics of the coupled ARROW structures is analyzed rigorously by the transverse resonance method. As an alternative configuration to the conventional directional coupler filter, the proposed device features large core size compatible with fiber and nearly periodic dependence of the coupling-length on the waveguide separation, which provides more flexibility for fabrication of the device. A design procedure for this type of coupled ARROW structure used for wavelength filtering is presented. The devices designed are simulated and verified by the beam propagation method. An ARROW wavelength filter based on SiO₂/TiO₂ has a FWHM bandwidth narrower than 7 Å     

Polarization state rotation filter for optical generation of continuously tunable millimeter-wave signal employing an external intensity modulator

A method to generate a continuously tunable millimeter-wave signal employing an optical external intensity modulator and polarization state rotation filter (PSRF) is proposed. The technique is based on the optical heterodyne, the Mach–Zehnder modulator (MZM) is biased to suppress odd-order sidebands, and the polarization-dependent PSRF is used to filter the optical carrier. A concept-proof experiment system is built to demonstrate the generation of microwave signal by beating the generated two second-order optical components. The results show that a high purity tunable microwave signal with very narrow linewidth at four times the frequency of microwave drive signal can be obtained. Moreover, the generated signal does not suffer obvious phase-noise degradation after transmission through a 25-km SSMF link. The operation principle of PSRF and the effect of its performance on the generated electrical signal are also analyzed. The proposed technique based on PSRF is very easy to implement, flexible and cost-effective to generate continuously tunable millimeter-wave signals.     

An efficient digital sliding controller for adaptive power-supplyregulation

Proposes a digital controller for adaptive power-supply regulation that uses sliding control, which is a widely used technique in switching power supplies for its fast transient response and robust stability. A novel reformulation of the sliding control law enables a simple and power-efficient digital implementation. The reference circuit can be either a delay line or a ring oscillator, and the sensor circuits for both cases are discussed. The prototype chip fabricated in 0.25-μm CMOS technology demonstrates a power efficiency of 89% - 95 % over the regulated voltage range of 1.1 - 2.3 V     

Flexibly tunable microwave photonic FIR filter incorporating wavelength spacing programmable, arrayed micro-mirror based optical filter

A novel tunable microwave photonic FIR filter incorporating a wavelength spacing tunable multiwavelength filter based on a programmable arrayed micro-mirror device (AMMD) is demonstrated. Owing to the unique characteristic of the AMMD, that an arbitrary optical filter shape can be produced by defining a desired spatial pattern on an array of /spl sim/800 000 micro-mirrors, a wavelength spacing tunable multiwavelength optical filtering pattern is readily obtainable. By controlling the optical filter wavelength spacing, flexible resonance RF frequency tuning is achieved over a range of 2.3 GHz.     

Electrically tunable narrowband optical filter

A narrowband optical filter of the Sole type is made from a twisted stack of birefringent plates between polarisers. If the plates are replaced by homogeneously aligned liquid-crystal cells whose retardation is controllable, the transmitted wavelength of the filter can be varied over the visible spectrum. The characteristics of a rudimentary device of this type agree with predictions.     

一种基于MEMS技术的可调谐光滤波器

文章介绍了一种基于微电子机械系统(MEMS)技术的可调谐光滤波器(TOF),分析了其基本原理和光学结构,给出了合理的设计方案及所进行的实验验证.实验结果表明,该滤波器性能优良,20 dB带宽<0.65 nm,3 dB带宽<0.24 nm,整个光路的插损控制在2 dB以内.根据该方案设计的滤波器具有体积小、成本低和波长调...     

FSK demodulation using an adaptive recursive digital filter

A second-order adaptive recursive digital filter is used for frequency-shift keying (FSK) demodulation. Explicit formulas are derived for the noise variance in the frequency detector, and optimum transmitter carrier frequencies and detector threshold frequencies are calculated. A formula for the adaptation time is derived and the error probability is found. Computer simulations verify the derived results     

Bragg grating fast tunable filter for wavelength divisionmultiplexing

A Bragg grating fast tunable filter prototype working over a linear tuning range of 45 nm with a maximum tuning speed of 21 nm/ms has been realized. The tunable filter system is based on two piezoelectric stack actuators moving a mechanical device thus compressing an apodized fiber Bragg grating. The filter allows both traction and compression and can work in transmission and in reflection. It is designed to work with a channel spacing of 100 GHz according to the ITU specifications for wavelength division multiplexing systems     

Increasing input power dynamic range of SOA by shifting thetransparent wavelength of tunable optical filter

Gain-saturation-induced self-phase modulation (SPM) leading to pulse distortion in a semiconductor optical amplifier (SOA) is overcome by shifting a tunable optical filter (TOF). A recovered or broadened pulse can be obtained after filtering the amplified pulse in the SOA even if the short pulse is only 2-3 ps long. The input power dynamic range (IPDR) can be strongly increased by shifting the TOF and the direction of the shifted transparent wavelength is different for 10 Gb/s return-to-zero (RZ) or nonreturn-to-zero (NRZ) signals. The transparent wavelength of the TOF should be shifted to a longer wavelength for RZ signals and to a shorter for NRZ signals. 80-Gb/s optical time division multiplexing (OTDM) signal amplification in the SOA is demonstrated for the first time. We also demonstrate that a large IPDR for the 80-Gb/s OTDM signal can be obtained by shifting the TOF     

Inline tunable etalon filter for optical channel selection in highdensity wavelength division multiplexed fibre systems

Reports an inline angle-tuned Fabry-Perot etalon for optical channel selection in a high-density wavelength division multiplexed (WDM) direct-detection experiment. Feasibility is demonstrated in experiments with two different etalons: one for 5 distributed feedback (DFB) lasers in the 1550 nm region (1527-1559 nm), each spaced by 8 nm, and the other for 12 lasers (1527-1549 nm), each spaced by 2 nm     

A combined tunable optical filter and tunable MQW ring laser

A dual-purpose, grating-based tunable optical filter/ring laser is described for accurate wavelength selection and generation at customer terminals. The device selects a single-wavelength channel from a HDWDM multiplex with 1 nm channel spacing, and simultaneously generates an identical wavelength as part of a tunable ring laser. The device is tunable over a 125 nm wavelength range, centered in the 1.5 μm low-loss fiber window