Narrow Results

One-dimensional defective binary photonic crystal is considered with the structure (AB)${}^N$D(AB)${}^N$, where A (TiO${}_2)$ and B (SiO${}_2)$ are the layers constituting the photonic crystal and D is the defect layer. The temperature dependence of the defect mode is investigated by considering both thermo-optic and thermal expansion effects. As the refractive indices and thicknesses of the photonic crystal layers are varied by temperature, the properties of the photonic crystal, such as bandgap and defect mode, are modified. Thus, we propose a tunable transmission filter operating in the visible region of the spectrum. It is found that the transmittance peak shift of the defect mode can be enhanced with the increase of both thermo-optic and the thermal expansion coefficients of the defect mode. As an example, we consider a photonic crystal with the structure (TiO₂–SiO${}_2{)}^6$/SiOC/(TiO₂–SiO${}_2{)}^6$ and a transmittance peak shift of the defect mode of 1.51 nm is obtained for a temperature increase of $100^{\circ }$C.

This paper presents the design of tunable heterodyne filter that can be used very effectively in the elimination of narrowband interference in wide-band communications. The filter makes use of the heterodyne process to create a tunable notch filter from a fixed coefficient high-pass filter. It has been shown that it is possible to generate a signal that can be used to set the heterodyne frequency to match the tunable heterodyne notch filter to the center of the detected interference through the use of a simple second order IIR band-pass filter to detect the narrowband interference. Moreover various options have been illustrated for the implementation of heterodyne filters using Xilinx Virtex field programable gate arrays (FPGAs).

In this paper, a new realization of a current-mode first-order all-pass filter (APF) using a single active building block (ABB) and one grounded capacitor is presented. As the ABB, the current backward transconductance amplifier (CBTA) is used, which is one of the most recently reported active elements in the literature. The theoretical results are in detail verified by numerous SPICE simulations using a new low-voltage implementation of CBTA. In the design, the PTM 90nm level-7 CMOS process BSIM3v3 parameters with $\pm$0.45V supply voltages were used. The proposed resistorless CBTA-C APF provides easy electronic tuning of the pole frequency in the frequency range from 763kHz to 17.6MHz, which is more than one decade. Maximum power dissipation of the circuit is 828$\mu$W at bias current 233$\mu$A. Nonideal, parasitic effects, sensitivity analyses, temperature and noise variation, current swing capability, and Monte Carlo analysis results are also provided. Compared to prior state-of-the-art works, the proposed CBTA-C APF has achieved the highest figure of Merit value, which proves its superior performance.

A novel broad tunable bandwidth and narrow instantaneous line-width linear swept laser source using combined tunable filters working at 1,300 nm center wavelength is proposed. The combined filters consist of a fiber Fabry–Perot tunable filter and a tunable filter based on diffractive grating with scanning polygon mirror. In contrast to traditional method using single tunable filter, the trade-off between bandwidth and instantaneous line-width is alleviated. Parallel implementation of two semiconductor optical amplifiers with different wavelength range is adopted in the laser resonator for broadband light amplification. The Fourier domain mode locking swept laser source with combined tunable filters offers broadband tunable range with narrow instantaneous line-width, which is especially benefiting for high-quality optical frequency domain imaging. The proposed Fourier domain mode locking swept laser source provides a tuning range of 160 nm with instantaneous line-width of about 0.01 nm at sweeping rate of 15 kHz, a finesse of 16,000 is thus achieved.

We demonstrate a new electrically tunable dispersion compensator by electrically tuning the chirp of a uniform fiber Bragg grating (FBG) without center wavelength shift. A distributed on-fiber thin film heater was deposited on the surface of a taper FBG by means of controllable electrical plating to adjust the chirp and hence dispersion of the FBG. A negative thermal-expansion coefficient (NTEC) ceramic was used to fix the central wavelength in the tuning. With an applied electrical power smaller than 0.68 W, the dispersion tuning range from−178 ps/nm to −302 ps/nm with a dispersion ripple of less than 30 ps was achieved. The corresponding central wavelength shift was as small as 0.173 nm.