DBR active optical filters: transfer function and noisecharacteristics

A theoretical model of distributed Bragg reflector (DBR) active filters is presented and verified experimentally through measurements of the transfer function and the noise spectra. The theory allows simple yet accurate evaluation of the transmission transfer function and of the noise properties of this class of filters. A conventional DBR laser device used as a filter is shown, experimentally and theoretically, to have two drawbacks: a multilobe transfer function and small gain (less than 10 dB facet-to-facet). It is shown how both problems can be overcome via reduction of two key device parameters: the grating coupling coefficient and the physical length of the active and/or phase control sections. This technique can lead to devices with attractive properties, having a gain of 35 dB, sidelobe suppression of 32 dB, and bandwidth as narrow as 1 GHz     

High Modulation Efficiency Gigabit/s Modulation of Twin-Contact High-Brightness Tapered DBR Laser

We report a compact single-chip optical transmitter with 0.4-W output optical modulation amplitude at 1 Gb/s using a twin-contact directly modulated laser with an applied ${sim}$ 100-mA current swing. Bit-error-ratio measurements confirm high signal quality for optical wireless communications.      

Rashba effect resonant tunneling spin filters

We propose an InAs/GaSb/AlSb-based asymmetric resonant interband tunneling diode (a-RITD) as a spin filter. The device exploits the Rashba effect to achieve spin polarization under zero magnetic field using nonmagnetic III-V semiconductor heterostructures. We discuss the basic principles of the interband tunneling spin filter, and present modeling results that demonstrate its advantage. We also propose an implementation procedure for realizing device structure.     

Bandpass resonant filters in photonic-crystal waveguides

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.     

Concept of multiorder multimode resonant optical filters

The idea of implementing optical filters by coupling evanescent waves from several diffracted orders into multiple leaky waveguide modes is studied theoretically. Using a dielectric thin-film structure consisting of a coupling grating placed between adjacent waveguides, guided-mode resonance filters exhibiting multiple reflection peaks within a specified wavelength range can be obtained. These peaks originate in the resonant waveguide modes that are excited by the diffracted waves dispersed by the grating. It is shown that this device can be used to realize multiwavelength as well as wide-band spectral filters.     

Optimal data transmission filters

In the letter new closed-form formulas (in terms of the poles) for a class of optimal data transmission filters are derived. These formulas always put the main sample point at the peak value of the impulse response.     

Tapered transmission lines with a controlled ripple response

A synthesis procedure is presented which generalizes Klopfenstein's Dolph-Chebyshev design of a tapered transmission line to give a response with all lobe heights in the passband individually specified. This iterative technique permits the design of tapered transmission line sections with frequency responses of a wide variety. A rippled response can also be produced, with the peak and trough of each ripple cycle separately prescribed. A mixed response, part lobelike and part rippled, is also feasible. The computer program used in this technique is simple to write and economical to run. Experience has shown that the convergence is rapid, and that practical specifications lead to physically realizable tapers     

Tapered transmission line computer program using Collin's derivation

Collin's synthesis of the equal ripple transmission line is shown to be computationally identical with Klopfenstein's synthesis. A simple computer program for computing impedance versus length of a tapered line is given, based on Collin's work.     

Practical design of side-coupled quarter-wave shifteddistributed-Bragg resonant filters

This paper presents equations that the together the spectral response, physical dimensions, and optical properties of side-coupled quarter-wave shifted distributed-Bragg resonant filters. Four constraints on the available design space are presented to show that side-coupled resonant filters, as designed herein, must, remain narrow-band to achieve acceptable performance. The global design space and the available design subspace for the InGaAsP/InP and Ge-doped SiO ₂ material systems are presented, as well as a discussion of modifications that can be made to improve the scope of possible filter designs     

Active DBR filters for 2.5 Gb/s operation: linewidth, crosstalk,noise, and saturation properties

The design of four-section distributed Bragg reflector (DBR) laser filters, for application in wavelength multiplexed systems with a 2.5 Gb/s bit rate on each wavelength channel, has been analyzed. The results of the analysis indicate that optimized filters will support at least 10 channels and will have a dynamic range exceeding 10 dB. Bit error rate (BER) measurements on three-section DBR filters in a 2.4 Gb/s system experiment support this conclusion     

Narrow-bandwidth optical waveguide transmission filters

A general method for fabricating narrowband transmission filters at optical frequencies is proposed. For fibre- or integrated-optic applications the method consists of forming a waveguide loop by connecting the output ports of a 3dB coupler to each other. A Bragg reflection grating in the loop determines the filters frequency response.     

Complex coefficient data transmission filters

The author shows how to design filters with asymmetric amplitude and group delay properties, while maintaining low intersymbol interference. The asymmetry gives independent control of the lower and upper stopband rolloff rates. Examples are given to illustrate the method, and its results     

Design of multireflector resonant bandpass filters for guided waveoptics

A design algorithm for ripple-free flat-top bandpass filters in optical waveguides containing N equally spaced, lossless mirrors is described. The algorithm assumes that the propagation phase shift φ between centers of adjacent mirrors equals (m+1/2)π radians at resonance frequencies ν_m, with m an integer. The mirror reflectances R_j, j=1,…,N, are chosen such that the transmittance T(ν) of the filter is 1 at the resonance frequencies, and terms in the power series expansion of T(ν) of order less than (ν-ν_m)^2(N-1) are eliminated. This ensures that T(ν) approaches an ideal rectangular profile with increasing N, as illustrated by calculated transmittance spectra for N=2, 4 and 6. The dispersion of these multimirror etalons has also been explored. For the higher N values, it is found that the group refractive index is a minimum at the resonance frequencies, in contrast to the case N=2 for which the group index is a maximum at the resonances     

Coupling of modes analysis of resonant channel add-drop filters

The operation principle of resonant channel add-drop filters based on degenerate symmetric and antisymmetric standing-wave modes has been described elsewhere using group theoretical arguments. In this paper, the analysis is carried out using coupling of modes in time. A possible implementation of such a filter is a four-port system utilizing a pair of identical single-mode standing wave resonators. The analysis allows a simple derivation of the constraints imposed on the design parameters in order to establish degeneracy. Numerical simulations of wave propagation through such a filter are also shown, as idealized by a two-dimensional geometry     

Design method for optimal data transmission filters

A data transmission filter design method is introduced. The method yields filters that are optimal in the sense that for given pole locations the intersymbol interference error is minimum. The prescribed loss requirements in the stopband are met and the eye diagrams are wide open.<>     

Wide-band equal-ripple filters in nonuniform transmission lines

In this paper, a novel method to realize equal-ripple filters over microwave frequencies is presented. All networks are implemented by using cascade serial and shunt transmission-line sections having the same electrical length. The transfer functions of such networks are formulated in the Z domain. In particular, it can be shown that some shunt components are able to contribute zeros locating on the unit circle if the components are open circuited. Due to the feature of transfer-function zeros locating on the unit circle, we may use an optimization procedure to implement equal-ripple filters. Both low-pass and bandpass filters are realized in the form of microstrip lines and their frequency responses are measured to validate this novel method     

Wide-stopband chirped fibre moire grating transmission filters

Efficient, wide-stopband fibre transmission filters with single narrow transmission bands produced using multiply exposed chirped fibre grating resonators are reported. Tailored combinations of these structures with additional chirped gratings have achieved single passband transmission with an effective finesse of 48. This demonstrates the feasibility of fabricating all-fibre transmission filters with arbitrary passband/stopband combinations     

Digital transmission performance of standard analog filters

This work analyzes the performances of Bessel, Gaussian, Butterworth, and Chebyshev (0.1-dB ripple) filters for synchronous baseband digital transmission. Numerical results showing the effects of system parameters such as signal rate, filter bandwidth, filter order, and pulse duty-cycle are presented. For rectangular inputs, linear phase filters perform better than those with nonlinear phase, from the viewpoint of the Nyquist 1 criterion. In terms of the Nyquist 2 criterion, linear phase filters perform better when the input duty-cycle is unity. For lower duty-cycles, there are symbol rate ranges over which nonlinear phase filters perform better. From the viewpoint of symbol time synchronization, the performances of the two types of filter are essentially the same. Linear phase filters are more robust to sampling clock jitter than nonlinear ones when the symbol rate is higher than the bandwidth. Furthermore, it is shown that for linear phase filters it is possible to increase the transmitting rate while keeping the filter bandwidth constant and with only a minor increase in degradation, by using low duty-cycle inputs     

Design tables for partial-response data transmission filters

Practical design tables are presented for partial-response class 1 data transmission filters. These tables give the pole and zero locations and the main sample point of several filters. This information can be used to analyse the performance of the filters, both in the time domain and frequency domain, thus assisting the user in the choice of a filter to meet the requirements. The filters given in the tables can be syntheised in either active or passive form.