Channel Add-drop Filters Research Articles

Reconfigurable add-drop filter based on an antisymmetric multimode photonic crystal nanobeam cavity in a silicon waveguide.

We have designed and demonstrated a reconfigurable channel add-drop filter (ADF) based on an antisymmetric multimode photonic crystal nanobeam cavity (AM-PCNC) in a silicon waveguide. The proposed AM-PCNC can realize channel add-drop filtering by selectively filtering and reflecting the fundamental mode (TE0) and 1st-order mode (TE1) in the multimode waveguide. A high-performance add-drop filter has been demonstrated with a high extinction ratio of 28.2 dB and an insertion loss of 0.18 dB. Meanwhile, the reconfigurable add-dropping has been realized by heating the nanobeam cavity to tune the filtering wavelength. A tuning efficiency of 0.464 nm/mW was measured. The rising and falling time are ∼6.5 µs and ∼0.6 µs, respectively, which are at microsecond time scale. The footprint of the involved nanobeam cavity is only 16.5 µm2. The device can potentially provide an integrated component for optical switch array, routers, and wavelength-division multiplexing in the optical networks.

Ultracompact Channel Add-Drop Filter Based on Single Multimode Nanobeam Photonic Crystal Cavity

Ultracompact channel add-drop filter utilizing a single nanobeam photonic crystal cavity is analyzed, designed, and demonstrated. Anti-symmetric multimode periodic waveguide structure is employed to implement mode conversion and thus produce degenerate resonant states in the involved nanobeam cavity. Theoretical analysis results indicate that the inter-modal conversion coefficient and the waveguide-cavity coupling coefficient have significant effects on the lineshape of the filter. By carefully engineering the structure of the multimode nanobeam cavity and its side-coupled configuration, we successfully achieve an ultracompact add-drop filter with device area around 20 μm2. The experimental results on silicon-on-insulator (SOI) platform show that the insertion losses of drop port, the crosstalk of add port of the fabricated filter are -1.1 dB and -14.7 dB, respectively. The modal volume of the involved nanobeam cavity are small as 1.2(λ/n) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , indicating huge potentials in developing low-power consumption tunable devices for future very large scale integration (VLSI) photonic applications.

Design of silicon-wire waveguide ultracompact racetrack resonators: geometrical parameters for optimal coupling.

In this paper, it is shown that a suitable choice of the geometrical parameters of a silicon-wire waveguide microracetrack resonator structure can lead to a substantial improvement in the control of coupling coefficients and, hence, the design of ultracompact devices for high-performance channel add-drop filters and all-optical switching applications. On the one hand, some simple theoretical arguments and simulation results indicate that the reduction of the silicon-wire rectangular waveguide cross-section area (width×height) is possible, from standard (450 nm×220 nm) to (380 nm×200 nm) on both the bus and the resonator waveguides; this action, apart from still guaranteeing a quasi-TE single-mode operation, would provide an effective improvement into scale-of-integration by a 1.30 factor per device volume. On the other hand, it will be shown by a semianalytical method (analytical calculation + numerical simulation) that achieving the waveguide-racetrack optimal coupling condition for a particular application can be reduced to a prime calculation of the main resonator geometrical parameters (bend radius, straight length, air gap and overall coupling length). In particular, the design of high-performance ultracompact waveguide-racetrack resonator structures, with pre-established Q factor (Q≥2000), free spectral range (FSR≥15 nm), full width at half-maximum (FWHM≤5 nm), finesse (F≥40) or extinction ratio signals (ER≥20 dB) can be systematically obtained with this procedure.

Electrically reconfigurable terahertz signal processing devices using liquid metal components

Many applications of terahertz (THz) technology require the ability to actively manipulate a free space THz beam. Yet, although there have been many reports on the development of devices for THz signal processing, few of these include the possibility of electrical control of the functionality, and novel ideas are needed for active and reconfigurable THz devices. Here, we introduce a new approach, based on the integration of electrically actuated liquid metal components in THz waveguides. This versatile platform offers many possibilities for control of THz spectral content, wave fron"ts, polarization, and power flow. We demonstrate two illustrative examples: the first active power-splitting switch, and the first channel add–drop filter. We show that both of these devices can be used to electrically switch THz communication signals while preserving the information in a high bit-rate-modulated data stream.

Traveling wave-like Fabry–Perot resonator-based add-drop filters

We have proposed and studied a novel channel add-drop filter (ADF) based on a single Fabry-Perot resonator. The resonator consists of two mode-conversion Bragg grating reflectors separated by a wide waveguide that laterally coupled to two narrow waveguides. It behaves like a traveling-wave resonator where fields are coupled to the buses in one direction. Compact and narrowband ADFs are achieved with dropping efficiencies higher than 95%, as shown by the three-dimensional finite-difference time-domain simulations. In addition, the proposed device is applied to realize an eight-channel add-drop multiplexer in the C-band by cascading the ADFs with adjusted channel wavelengths.

Channel add-drop filter based on dual photonic crystal cavities in push-pull mode.

We demonstrate an add-drop filter based on a dual photonic crystal nanobeam cavity system that emulates the operation of a traveling wave resonator, and, thus, provides separation of the through and drop port transmission from the input port. The device is on a 3×3 mm chip fabricated in an advanced microelectronics silicon-on-insulator complementary metal-oxide semiconductor (SOI CMOS) process (IBM 45 nm SOI) without any foundry process modifications. The filter shows 1 dB of insertion loss in the drop port with a 3 dB bandwidth of 64 GHz, and 16 dB extinction in the through port. To the best of our knowledge, this is the first implementation of a port-separating, add-drop filter based on standing wave cavities coupled to conventional waveguides, and demonstrates a performance that suggests potential for photonic crystal devices within optical immersion lithography-based advanced CMOS electronics-photonics integration.

Performance evaluation of photonic crystal ring resonators based optical channel add-drop filters with the aid of whispering gallery modes and their Q-factor

As a basic type of linear defects, the PhC ring resonators are considered the most fascinating elements to be used in photonics integrated circuits for applications such as dense wavelength division multiplexing and Optical filtering that are among the most important components of the telecommunication systems. This article proposes two different optical channel add-drop filters (CDFs) based on rod-type two-dimensional square-lattice all-circular photonic crystal ring resonator. In the studied ring-type PhC cavity, there are some modes that are analogous to whispering gallery (WG) modes. For the proposed all-circular PhC ring resonator, the WG-like mode with the azimuthal mode number $$m=10$$ , couples out from cavity to the drop waveguide. Although because of the absence of perfectly circular symmetry, these WG-like modes are not exactly degenerate but they form a close doublet. The normalized frequencies ( $$a/\lambda $$ ) of the doublets of $$m=10$$ are $$a/\lambda =0.3684$$ , and 0.3645 and their $$Q$$ -factors are 1050, 866 respectively. By selecting appropriate coupling distance between the PhC ring resonator and side-coupled $$W_{1}$$ waveguide, the CDFs are formed. For a TM polarized Gaussian source, the drop efficiency of both filters is more than 99.8 % in the 1.535–1.625 $$\upmu \hbox {m}$$ wavelength interval. The photonic bandgap and the WG-like modes of the PhC ring resonator are calculated using the PWE method, and the $$Q$$ -factor of modes and the transmission spectra of CDFs are calculated using 2D-FDTD method.

Efficient wavelength multiplexers based on asymmetric response filters

We propose integrated photonic wavelength multiplexers based on serially cascaded channel add-drop filters with an asymmetric frequency response. By utilizing the through-port rejection of the previous channel to advantage, the asymmetric response provides optimal rejection of the adjacent channels at each wavelength channel. We show theoretically the basic requirements to realize an asymmetric filter response, and propose and evaluate the possible implementations using coupled resonators. For one implementation, we provide detailed design formulas based on a coupled-mode theory model, and more generally we provide broad guidelines that enumerate all structures that can provide asymmetric passbands in the context of a pole-zero design approach to engineering the device response. Using second-order microring resonator filter stages as an example, we show that the asymmetric multiplexer can provide 2.4 times higher channel packing (bandwidth) density than a multiplexer using the same order stages (number of resonators) using conventional all-pole maximally-flat designs. We also address the sensitivities and constraints of various implementations of our proposed approach, as it affects their applicability to CMOS photonic interconnects.

Analysis of a channel-drop filter based on dispersive waveguides and two resonant cavities

By use of coupled-mode theory we analyze a channel add–drop filter based on two dispersive waveguides symmetrically coupled with two resonant optical cavities. We show new solutions for the channel-drop filter processes compared to the solutions found by Manolatou et al (1999 IEEE J. Quantum Electron. 35 1322). For a special choice of the dispersion of the waveguides, we reveal a frequency region with sufficient total reflection.

Waveguide-coupled octagonal microdisk channel add-drop filters.

We report planar waveguide-coupled octagonal microdisk channel add-drop filters on silicon nitride-on-silica substrates. Using ray optics, we show that discrete octagonal cavities have wave-front-matched four- and eight-bounce ray orbits. From a planar waveguide-coupled 50-microm-sized octagonal microdisk filter, our experiment demonstrates TM-polarized eight-bounce modes with a coupling efficiency of approximately 56%, Q approximately equal to 1150, and a finesse of approximately 5. Using the two-dimensional finite-difference time-domain method, we obtain qualitative agreement between measurement and simulation of a smaller-sized waveguide-coupled octagonal microdisk filter.

Photonics Filters, Switches and Subsystems for Next-generation Optical Networks

This article reviews a host of photonics devices and subsystems research that are of increasing interest for next-generation wavelength division multiplexing optical networks. On the device front, we report our initial results on silicon-based planar optical micro-resonator channel add-drop filters, and on liquid-crystal-based optical switches and tunable devices. On the subsystem work, we report an effective and scalable protection switching for large-capacity MEMS-based optical crossconnect systems.

Loss-induced on/off switching in a channel add/drop filter

We introduce a mechanism that provides an on/off switching capability in channel add-drop filter structures. These filters consist of two waveguides, a bus and a drop, coupled through a frequency-selective element. The switching functionality is achieved by incorporating materials with variable absorbing characteristics into the coupling element. When the variable material displays minimum absorption, the frequency channel of interest is transferred completely from the bus waveguide to the drop waveguide. When the variable material displays maximum absorption, the frequency channel is not transferred and remains essentially undisturbed in the bus waveguide. We also discuss the practical feasibility of realizing this approach using either electrical or mechanical means.

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.

Large-capacity local access network

A large-capacity local access network providing users with a dedicated two-way link to a central office is presented. The network is built along a single optical fiber ring. Connection to the fiber is obtained by combining time-division-multiplexing (TDM) and frequency-division-multiplexing (FDM) techniques and by using a novel optical channel add-drop filter. Optical signals are generated at the central office. The users have a simple device integrated with the channel dropping filter to receive and transmit data without the use of an optical source. Such a system can support 210 users transmitting at 100 Mb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>