Photonic RF phase shifter and tunable photonic RF notch filter

A new photonic RF phase shifter structure for phased array antennas is presented. It is based on a single dual-output modulator and two optical switches and optical attenuators. This can realize continuous phase shifting of 0/spl deg/-360/spl deg/ without altering the signal amplitude. It has the advantages of wide bandwidth, fast response time, and fine tuning resolution. Experimental results demonstrate phase shifts over a 360/spl deg/ phase range, with RF signal power changes of less than 0.2 dB, which is in close agreement with predictions. A tunable photonic RF notch filter, which is based on the new phase shifter, is also presented. Experimental results demonstrate continuous tuning of the photonic notch filter over a wide tuning range, which covers the full free spectral range, which is in good agreement with predictions.     

Blindness limitations in optical coherence domain reflectometry

The theoretical and measured limitations on dynamic range near strong reflections in optical coherence domain reflectometry are examined. A model and data are presented that show that such blindness limitations can be caused by broad spectral tails from the superluminescent diodes typically used in such measurements.<>     

An analog notch filter for piezoelectric optical scanner

The optical scanner is one of the most important components in free-space optical communications,airborne and space-based lidars,adaptive optics,and so on.The performance of an optical scanner is frequently limited by the presence of mechanical resonances.This paper presents an analog notch filter with adjustable function to reject the mechanical resonances of the optical scanner.First of all,the structure and work principle of the piezoelectric optical scanner are introduced.Furthermore,the frequency sweep method based on virtual instruments is used to gain the natural frequency of the piezoelectric optical scanner.Then,the notch filters in series are used to reduce the oscillation of the scanner at the resonance frequencies.A variety of scanning experiments were carried out.After the introduction of the notch filter,the non-linearity was reduced to±1.1% from ±2.1%.The linearity performance was greatly improved.     

Photonic crystal-based optical filter: a brief investigation

Ring resonator-based channel drop filters are investigated conceptually and analytically with different ring (square and hexagonal) structures. In the proposed architecture, silicon rods (\(n=3.4641\)) are contrived over an air substrate of refractive index \(n=1\) in the equilateral triangular lattice which has the lattice constant \(a=900\,\hbox {nm}\). The characteristics of the design are examined for various types of pillars (circular and elliptical) and are reported in the analysis. The band gap for each structure is calculated and observed by plane-wave expansion method. The normalized transmission spectra and resonance wavelengths for different photonic crystal ring resonators are obtained using 2D finite-difference time-domain method. From the investigation, the resonance of circular pillar falls over the region of the third window at C-band (1530–1565 nm) which has the lowest attenuation losses and most widely used. Full width at half maximum and quality factor of the desired layout are also being calculated. The size of the device is about \(20 \times 14\,{\upmu }\hbox {m}\) which is highly compact and useful for the integration of photonic circuits.     

Four-channel tunable optical notch filter using InGaAsP/InPreflection gratings

A new tunable optical notch filter for use in wavelength division multiplexing (WDM) transmission system has been fabricated in the InGaAsP/InP material system for use at 1.55 μm. The device uses tunable reflection gratings in a waveguide to control the channels (4 in this case). Crosstalk levels between 9 dB and 20 dB have been measured, depending on the channel. System experiments at 150 Mb/s show less than 1 dB crosstalk penalty at 10^-9 bit-error rate     

Demonstration of tunable optical notch filter using 1-D opto-VLSI processor

An opto-very-large-scale-integrated (opto-VLSI)-based tunable optical filter structure is demonstrated. Filter tunability is achieved by reconfiguring the holographic diffraction grating of an opto-VLSI processor, allowing virtually any type of filter response to be synthesized. A proof-of-concept tunable notch filter with wavelength span of 7 nm is experimentally verified.     

Photonic switch size limitations imposed by phase noise fromsemiconductor optical amplifier gates

A possible way to design photonic switch matrices is by interconnecting multiple 2×2 switches based on semiconductor optical amplifier gates. The size of these matrices is limited by many phenomena including phase noise from the gates. The authors examine the limitations imposed by this noise in a system using DPSK direct detection     

Complex notch filter design using allpass filter

Complex coefficient IIR notch filter design problems are investigated. The specification of a notch filter is first transformed into that of an allpass filter. An effective approach to the design of this desired allpass filter is developed. The realisation of the proposed notch filter is equivalent to the realisation of an allpass filter. Owing to the mirror-image symmetry relation between the numerator and denominator polynomials of allpass filters, the notch filter can be realised by a computationally efficient lattice structure with very low sensitivity     

A piloted adaptive notch filter

In the implementation of an adaptive notch filter using the least mean squares (LMS) algorithm, the zero of the filter is steered toward the input sinusoid based on the gradient information. The convergent may be speeded up if a larger step size is used when the zero of the notch filter is far away from the frequency of the input sinusoid. The gradient provides information on the direction where the zero should be steered but does not provide information on the distance between the zero and the frequency of the sinusoid. Conventional variable step-size algorithms determine the step size based on a (linear/nonlinear) weighted average of the gradient estimate at several sampling instances (time domain averaging). In this paper, we propose a new method for extracting information on the distance between the frequency of the input sinusoid and the zero of the notch. We use three (or more) notches, namely, a main notch and two (or more) pilot notches implemented with minimal additional cost. The pilot notches are used to analyze the gradient estimates at the same sampling instance but at several frequency points as the main notch. Simulation results show that our new piloted notch technique is significantly superior to step-size determination based on a time-averaging technique. Novel theoretical analysis is presented. Our method can be used in conjunction with most existing algorithms to determine the step size.     

MMIC tunable active notch filter

A novel microwave notch filter is reported which has a single-stage reflection topology. The identical RLC reflection terminations employ independent voltage controlled elements. As a result, the Q-factor and notch frequency can be varied. An experimental notch filter, tunable from 2 to 3.5 GHz, has been successfully realised using monolithic technology     

Continuously tunable photonic radio-frequency notch filter

We present a continuously tunable nonrecursive radio-frequency (RF) photonic filter. The filter provides fine tuning through the use of a novel RF phase shifter and coarse tuning using an an optical variable time delay. This architecture permits wide-band continuous tuning of the filter null frequency and is useful in applications such as moving target indication (MTI) in an airborne radar.     

2D multiple notch filter design

The authors propose a decomposition method to reduce the 2D multiple notch filter design problem to two pairs of 1D filter design problems. They develop a simple algebraic method for the design of two pairs of 1D IIR filter design. This approach not only has closed form transfer function but also satisfies the bounded input/output (BIBO) stability condition     

70 MHz surface-acoustic-wave resonator notch filter

A 70 MHz notch filter employing a surface-acoustic-wave resonator in a hybrid-coil circuit to produce a notch depth of 50 dB has been developed. The notch frequency is tunable over a 40 kHz range and the passband attenuation is approximately 7 dB.     

A tunable microwave notch absorber filter

A magnetized plasma column is found to be a notch absorber of microwave radiation propagating in the extraordinary mode. Based on this fact, a compact tunable microwave filter is designed and tested successfully. The center frequency of the absorbed band can be varied by adjusting the background magnetic field stength. The 3dB bandwidth and amount of attenuation are functions of the plasma current. These characteristics offer a great tunability, often sought after in microwave devices. This filter can find applications in microwave measurement systems where filtering of unwanted harmonics and spurious signals can directly affect the accuracy and resolution of the measurements.     

Design of a high-frequency notch filter

Design equations for a high-frequency notch filter are presented. The filter makes use of a hybrid coil for decoupling input from output. The notch is obtained from a bridge-type balance, and can be made quite narrow.     

Photonic bandgap dielectric waveguide filter

The application of photonic bandgap (PBG) structures as the sidewall of the printed circuit board (PCB) dielectric waveguide filter is investigated. The effect of different PBG parameters on the Q-value of PBG dielectric waveguide resonator is evaluated. A PBG dielectric waveguide three-pole Chebyshev bandpass filter is realized. The measured performance matched well with the calculated results. The newly proposed I/O coupling structure makes the filter much easier for mass production     

Evaluation of the adaptive speckle suppression filter for coronary optical coherence tomography imaging

During the last few years, optical coherence tomography (OCT) has demonstrated considerable promise as a method of high-resolution intravascular imaging. The goal of this study was to apply and to test the applicability of the rotating kernel transformation (RKT) technique to the speckle reduction and enhancement of OCT images. The technique is locally adaptive. It is based on sequential application of directional masks and selection of the maximum of all outputs. This method enhances the image features by emphasizing thin edges while suppressing a noisy background. Qualitatively, the RKT algorithm provides noticeable improvement over the original image. All processed images are smoother and have better-defined borders of media, intima, and plaque. The quantitative evaluation of RKT performance showed that in terms of average contrast-to-noise ratio, there is a significant improvement in image quality between original and enhanced images. The RKT image enhancement technique shows great promise in improving OCT images for superior boundary identification.     

All-optical filter for simultaneous implementation of microwave bandpass and notch responses based on semiconductor optical amplifier

An all-optical filter structure to simultaneously implement microwave bandpass and notch filter is proposed and experimentally demonstrated. The structure is based on a recirculating delay line (RDL) loop consisting of a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter and a 10:90 coupler. The converted signal is generated in a wavelength conversion process based on cross-gain modulation of amplified spontaneous emission in the SOA. The converted signal circulating in RDL loop realizes a negative bandpass response. The negative bandpass filter and a broadband allpass filter are synthesized to achieve a notch filter with flat passband which can excise interference with minimal impact on the wanted signal.