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Using the ADFs, two multi-channel drop filters have been designed in order to be used as optical MUX/DeMUX with a channel spacing of 4 nm which are suitable for wavelength division multiplexing systems. The results obtained from these structures indicate the high flexibility of the proposed PhCRR and ADFs and their applicability in optical communication systems. At a central wavelength of 1550.5 nm, the four proposed ADFs have an average transmission coefficient, a bandwidth, and a quality factor of 100%, 1.2 nm and 1330, respectively. The resulting filter is the equivalent of a box attenuator formed from the R 1's and R 2's connected in cascade with an ideal lattice filter as shown in the diagram.In this research, using photonic crystal dielectric rods with a triangular lattice constant, a photonic crystal ring resonator (PhCRR) has been designed in order to be used in optical add/drop filters (ADF).Query Using the proposed hexagonal PhCRR with four different dropping waveguides, new ADFs have been designed and simulated. The purpose of the shunt resistors, R 2, is to bring the image impedance of the filter back to the original design R 0.
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This ensures that the attenuation at high frequency is the same as the attenuation at low frequency and brings the filter back to a flat response.
#Ful lattice crystal filter design series
In the example diagram, the resistors placed in series with the capacitors, R 1, are made equal to the unwanted stray resistance present in the inductors. This results in significant resistance being in the inductive branches of the filter, which in turn causes attenuation at low frequencies. Sections designed to equalise low audio frequencies will have larger inductors with a high number of turns. However, practical considerations of properties of real components leads to resistors being incorporated. With ideal components there is no need to use resistors in the design of lattice filters. This is not required in the case of lattice filters.ĭesign Parts of this article or section rely on the reader's knowledge of the complex impedance representation of capacitors and inductors and on knowledge of the frequency domain representation of signals.Ī lattice filter with compensation for the resistance of its inductors and its equivalent circuit Many other types of filter section are intrinsically unbalanced and have to be transformed into a balanced implementation in these applications which increases the component count. This is useful when used with landlines which invariably use a balanced format. Consequently, landlines used by broadcasters for stereo transmissions are equalised to very tight differential phase specifications.Īnother property of the lattice filter is that it is an intrinsically balanced topology. A phase difference translates to a delay, which in turn can be interpreted as a direction the sound came from. This is because the formation of the stereo image in the brain relies on the phase difference information from the two ears. However, the differential phase between legs has a very dramatic effect on the stereo image. The same is true of the absolute phase distortion on each leg (left and right channels) of a stereo pair of lines. Phase distortion on a monophonic line does not have a serious effect on the quality of the sound unless it is very large. The lattice filter has an important application on lines used by broadcasters for stereo audio feeds. The characteristic impedance of this structure is given by