a fractional bandwidth of 6.51%, and a pair of transmission zeros are located at 2.322 and 2.522 GHz separately, which are close to the passband, providing a better cutoff rate in the stopband, thus giving much improved selectivity. It is interesting to note that there is an additional transmission zero at 3.429 GHz, which is mainly caused by the high-order modes and should be useful for the rejection of the interference in the passband. The measured results are slightly shifted up to about 30 MHz in contrast to the simulated results. The measured minimum insertion loss is about 2.17 dB in the passband, which is mainly due to the conductor and dielectric losses of the substrate. Both the simulated and measured results are in good agreement. CONCLUSIONSA novel modified hexagonal loop resonator has been designed and discussed in this article. In contrast to the typical hexagonal loop resonator, the proposed modified resonator can support three fundamental modes, and three modes resonant frequencies can be easily adjusted, whereas the others are nearly not affected. It provides a convenient method to design a triplemode filter using this novel modified hexagonal resonator with a pair of transmission zeros close to the passband. A triple-mode bandpass filter based on the proposed resonator with a center frequency at 2.42 GHz has been fabricated and measured. Both the simulated and measured results are presented and discussed. The superior features of designing this kind of filters indicate that it has the potential to be utilized in microwave planar circuits. ACKNOWLEDGMENTThis work is supported by the National Science Foundation of China (NSFC) under grant 60871058. A low-cost tunable laser has been considered to be an inevitable ingredient for wavelength-division-multiplexing passive optical network and reconfigurable optical add/drop multiplexing networks [1]. One of the ways to realize a low-cost tunable laser is a hybrid integration of a broadband source such as a superluminescent laser diode (SLD) or a reflective semiconductor optical amplifier (R-SOA) with a passive wavelength-selective reflector based on planar waveguides. A grating patterned on a waveguide has been usually used to implement the wavelength-selective reflector for the hybrid integration [2, 3]. The fabrication of a first-order grating structure needs an additional process of holographic patterning after waveguide formation, which might increase the cost of the hybrid-integrated laser. Recently, higher order gratings, which can be realized with a grating pattern on a mask, have also been used for waveguide formation. However, the tuning range of the higher order grating is still limited by the refractive index change of the materials. In this article, for the grating structures to be substituted, we propose an add/ drop reflection filter (ADRF) based on a double-ring resonator. The radii of two rings are designed to be slightly different from each other so that a few tens of nanometers of tuning range with a small amount of current is obtained...
A hybrid‐integrated tunable optical source composed of a wavelength‐selective reflector, which is based on a polymer double‐ring‐resonator followed by a loop‐back mirror, and a reflective semiconductor optical amplifier is proposed and fabricated.Hybrid‐integration is realized using an active alignment method. The tuning range is about 40 nm with a maximum tuning current of 42 mA. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:924–927, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25871
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