Optical Add-drop Filter Research Articles

3D design and analysis of an electro-optically tunable athermal and polarization-insensitive ring resonator-based add-drop filter for DWDM systems

Dense Wavelength Division Multiplexing system-based optical networks are currently the most appropriate solutions for all-optical networks that efficiently utilize the large bandwidth offered by optical fiber networks. Tunable ring resonator-based filters are highly attractive owing to their bandwidth and channel tunability, high spectral selectivity, low losses, low power consumption, and compactness; thus they are very good candidates for optical integrated circuits at a very large scale. We used titanium oxide and silicon oxide as the upper-cladding and under-cladding materials, respectively, around a silicon-rich nitride core to design an electro-optically tunable, polarization-insensitive, and thermally resilient sixth-order add-drop optical filter in the L-band (1565 nm-1625 nm). A thin film of lithium niobate added on the top of silicon oxide was used to enhance the tunability of the filter. A 3D multiphysics approach considering thermo-optic, and stress-optical effects while minimizing the polarization rotation has been adopted to solve the electromagnetic problem in a filter that can accommodate arbitrary Transverse Electric and Transverse Magnetic polarized optical signals. The device has a bandwidth of 50 GHz (linewidth of 0.4 nm) at a resonant wavelength of 1575.4 nm, an extended FSR of 2.512 THz, and losses of 0.82 dB in the bandpass. The filter is ultra-compact with a footprint of 15μm×160μm. We achieved a high-quality factor of 3250, a tunability efficiency of 8.95 pm/V, and a finesse of 31. To the best of our knowledge, it is the first time a complementary metal-oxide-semiconductor-compatible, electro-optically tunable, athermal, polarization-insensitive high order add-drop filter in the L-band with a top-flat response in the passband, and with an extended FSR has been designed for Dense Wavelength Division Multiplexing systems.

2D photonic crystal based all-optical add-drop filter consisting of square ring resonator

In this paper, using Plane Wave Expansion (PWE) and Finite Difference Time Domain (FDTD) methods, an all optical add-drop filter (ADF) is designed and simulated. It has two defect waveguides (BUS and DROP) and a square ring resonator in-between. The structure consists of a square lattice of infinitely long dielectric circular rods of refractive index 3.59 embedded in air. The total footprint of the proposed structure is merely 323μm2. The backward dropping efficiency of the designed ADF is 97% at wavelength 1554nm, with transmission efficiency and quality factor equal to 100% and 444 respectively. The effect of variation of lattice constant (a), Radius of the rods (r), and Refractive index (n) on the performance of the ADF are also investigated. As the resonant wavelength of the ring resonator can be manipulated by manipulating the parameters of the circular rods, the proposed ADF can be set to function at desired frequencies.

Broadband, silicon photonic, optical add-drop filters with 3 dB bandwidths up to 11 THz: publisher's note.

This publisher's note contains corrections to Opt. Lett.46, 2738 (2021)OPLEDP0146-959210.1364/OL.423745.

Broadband, silicon photonic, optical add-drop filters with 3 dB bandwidths up to 11 THz.

We present the designs, theory, and experimental demonstrations of ultra-broadband, optical add-drop filters on the silicon-on-insulator platform, realized using period-chirped contra-directional couplers. Our fabricated devices have ultra-broad 3 dB bandwidths of up to 11 THz (88.1 nm), with flat-top responses at their drop ports. All of our devices were fabricated using a commercial, CMOS-compatible, 193 nm deep-ultraviolet lithography process. By using lithography-prediction models, the measured bandwidths, insertion losses, central wavelengths, and extinction ratios of our devices are all in good agreement with our predicted, simulated results. Such filters are necessary for photonic integrated circuits to operate over multiple optical bands.

Designing of Optical Filter Based on Modelling Procedure of Multilayer Quadruple Combined Micro Ring Resonator (MQCMRR) Structure with 2 × 3 I/O Bus Waveguides

A new and advanced ring resonator model with its performance analysis as an optical filter is presented in this paper. The recommended model composites of four asymmetrical micro rings with two input and three output bus waveguides. This multilayer quadruple combined micro ring resonator (MQCMRR) structure is modelled in Z-domain by the application of delay lines and Masons gain principle. This model is confined in three layers by adopting series coupling as well as vertical coupling. Various performance parameters are evaluated like free spectral range (FSR), group delay (GD), dispersion (DP), full-width-half-maxima (FWHM), and Q-factor, by the analysis of spectral response in MATLAB environment. Design of optical couplers, as well as the study of field transmission through the rings and waveguides, are carried out by the finite-difference-time-domain (FDTD) method. Performance in optical communication system of this recommended ring resonator-based optical filter is investigated through a simulation program which is done by OptiSystem16.0 software. Data transmission performance is graphically shown by an eye diagram. For this proposed model high FSR and zero crosstalk is achieved at all output port. All the important consequences like large FSR, zero crosstalk, high data handling capability, perfect field transmission and exact open eye diagram certify the smashing performance of this architecture in the optical communication system as an optical add-drop filter.

Dual Ring Resonator Based 3D-Photonic Crystal For Add Drop Filter Using FDTD-Least Square Technique

The structure of an optical add-drop filter (ADF) which depends on a very-compact ring resonator made from a photonic crystal has been presented in the paper. An adequate structure of a three channel wavelength de-multiplexer along with a finite difference time domain is demonstrated in the visibility area. A 3D triangular lattice photonic crystal with 1.735 nm air pores in a silicon nitride planar waveguide provides a constraint for the light which can be detected. The double resonator has been simulated on a three-dimension photonic crystal and for the simulation of results, MATLAB has been used. The resultant structure consisting of three drops wavelengths at λ1 = 1555 nm, λ2 = 1579 nm, and λ3 = 1595 nm approximately. The average spacing between the adjacent channels is around 20 nm and the FSR obtained from numerical simulation is about 179 GHz. The output wavelength carries normalized transmissions of 0.97 having an inner rod radius for inner core 800. In addition to this, the Alternating Least Square—Add-Drop Filter (ADF)—Finite Difference Time Domain method has been used to achieve three various outputs such as transmitted intensity, reflectivity fineness, and constant factor. In future aspects, the simulation results can be further used in the fields of networks to design more accurate and efficient photonic crystals based on de-multiplexing devices.

Hitless and gridless reconfigurable optical add drop (de)multiplexer based on looped waveguide sidewall Bragg gratings on silicon.

Reconfigurable optical add-drop filters in future intelligent and software controllable wavelength division multiplexing networks should support hitless wavelength switching and gridless bandwidth tuning. The hitless switching implies that the central wavelength of one channel can be shifted without disturbing data transmissions of other channels, while the gridless tuning means that the filter bandwidth can be adjusted continuously. Despite a lot of efforts, very few integrated optical filters simultaneously support the hitless switching of central wavelength and the gridless tuning of bandwidth. In this work, we demonstrate a hitless add-drop filter with gridless bandwidth tunability on the silicon-on-insulator (SOI) platform. The filter comprises the two identical multimode anti-symmetric waveguide Bragg gratings (MASWBG) which are connected to a loop. The phase apodization technique is utilized to weaken the intrinsic sidelobe interference of grating-based devices. By sequentially manipulating central wavelengths of the two MASWBGs with the thermo-optical effect, we can reconfigure the spectral response of the filter gridlessly and hitlessly. Specifically, the central wavelength of the device is shifted by 14.5 nm, while its 3 dB bandwidth is tuned from 0.2 nm to 2.4 nm. The dropping loss and the sidelobe suppression ratio (SLSR) are dependent on the bandwidth selected. Measured variation ranges of dropping loss and SLSR are from -1.2 dB to -2.5 dB and from 12.8 dB to 21.4 dB, respectively. The hitless wavelength switching is verified by a data transmission measurement at a bit rate of 25 Gbps.

Highly Efficient Optical Add-Drop Filter With an Angle-Polished Fiber Coupler

Microbubble whispering-gallery resonators have shown great promise in fiber-optic communications because of their low confinement loss and hollow cores, which allow for facile stress-based tunability. Usually, the transmission spectrum of taper-coupled microbubbles contains closely spaced modes due to the relatively large radii and oblate geometry of microbubbles. In this letter, we develop an optical add-drop filter using a microbubble coupled to fiber taper and angle-polished fiber waveguides. Because of the extra degree of freedom in the angle of its polish surface, the angle-polished fiber can be used for the discriminatory excitation of certain radial-order modes in the optical microcavity, reducing the high modal density and enhancing add-drop selectivity. Our robust and tunable add-drop filter demonstrated a drop efficiency of 85.9% and quality factor of 2 x 10^7, corresponding to a linewidth of 9.68 MHz. As a proof of concept, the drop frequency was tuned using internal aerostatic pressure at a rate of 7.3 +/- 0.2 GHz/bar with no diminishing effects on the add-drop filter performance.

A silicon-based compact triplexer using Bragg grating assisted non-reciprocal single microring resonator

An ultra-compact silicon triplexer based on waveguide Bragg grating assisted non-reciprocal optical ring add-drop filter has been proposed. This novel scheme consists of two straight strip waveguides laterally coupled to a microring resonator. A magneto-optically active material deposited inside the microcavity is etched to induce strong non-reciprocity, which can cause resonance wavelength splitting ΔλMO of two counter propagating modes. Uniform Bragg grating reflector is fabricated in proximity to one of the input/output (I/O) ports. As a result, two downstream WDM channels (1490 nm/1550 nm) can be separated into the output ports of strip waveguide below the ring resonator, while the third channel considered as upstream signal is transmitted through the waveguide above the microring without any interaction with either the microring resonator or the waveguide Bragg grating reflector. Results show that a total length of 13.5 μm with the highest isolation ratio (IR) of 35 dB is obtained at the adjacent ports of the same strip waveguide; the lowest crosstalk (XT) of −38 dB for 1310 nm channel has also been obtained.

Special relativity-on-a-photonic-chip: Applying circuits’ analysis to characterize Einstein Velocity Addition Law

We demonstrate, for the first time to best of our knowledge, the usefulness of the analytical toolbox developed from a disparate field like Photonic Integrated Circuits (PICs) and now applied in the study of the Einstein Velocity Addition (EVA) in Special Relativity (SR). EVA is a central concept in SR that underlies many relativistic effects. The recently established analogy between the EVA and the PICs-based Optical Add-drop Filter (OADF) [J. Modern Optics 66, 679, (2019)] allows us to apply the “Critical Coupling, Over-Coupling and Under-Coupling” (or CC-OC-UC) analytical toolbox to systematically categorize, analyze, and visualize the different behaviors of EVA. We focus on the (i) relative magnitude and (ii) relative direction of the two non-collinear velocities of EVA. This analysis uncovers “not-too-obvious” features that are overlooked or would not have been discussed, otherwise, in the normal treatment of EVA in SR. Other important consequences are briefly discussed.

Coupled microstrip-cavities under oblique incidence of semi-guided waves: a lossless integrated optical add-drop filter

We investigate optical microresonators consisting of either one or two coupled rectangular strips between upper and lower slab waveguides. The cavities are evanescently excited under oblique angles by thin-film guided, in-plane unguided waves supported by one of the slab waveguides. Beyond a specific incidence angle, losses are fully suppressed. The interaction between the guided mode of the cavity-strip and the incoming slab modes leads to resonant behavior for specific incidence angles and gaps. For a single cavity, at resonance, the input power is equally split among each of the four output ports, while for two cavities an add-drop filter can be realized that, at resonance, routes the incoming power completely to the forward drop waveguide via the cavity. For both applications, the strength of the interaction is controlled by the gaps between cavities and waveguides.

Broadband flat-top SOI add-drop filters using apodized sub-wavelength grating contradirectional couplers.

We report on broadband, flat-top, optical add-drop filters using apodized, sub-wavelength grating contradirectional couplers (SWG CDCs) on a silicon-on-insulator platform. In our device, two asymmetric SWG waveguides, having corrugation-apodized Bragg gratings, are used to couple light contradirectionally between the fundamental and next higher-order transverse electric modes of a two-waveguide system. We demonstrate an apodized, SWG CDC that has a flat-top, drop-port response with a 3dB bandwidth of 32.6nm, a sidelobe suppression ratio of 19dB, and a low excess loss of 0.26dB. We also demonstrate series-cascaded, apodized, SWG CDCs that have square-shaped, drop-port responses with 3dB bandwidths >30 nm, sidelobe suppressions >50 dB, and low excess losses <0.85 dB.

Z-domain modeling approach of a multilayer sextuple-coupled micro-ring resonator with 1 × 5 input-output bus waveguides as optical filters.

This paper introduces the modeling approach of a new micro-ring resonator configuration composite of six asymmetrical rings with one input and five output bus waveguides. This multilayer sextuple-coupled micro-ring resonator (MSCMRR) is modelled in the z domain by practicing the delay line signal approach and Mason's gain formula. Both lateral coupling and vertical coupling are used to design this MSCMRR structure to confine it up to four layers. Performance analysis is carried out in a MATLAB platform with the graphical representation of performance parameters like free spectral range (FSR), group delay, dispersion, full width at half-maximum, etc. The optical couplers of the proposed model are also designed by the finite-difference time-domain (FDTD) method. Electric field propagation through the rings and the waveguides are also studied by FDTD. The proposed structure offers different values of high FSR with zero crosstalk at every output port that ensures the quality application of this proposed model as an optical add-drop filter in an optical communication network.

Hibernation Model Based on Polariton Successive Filtering

A negative entropic system formed by a close successive polariton filtering within a modified optical add–drop filter is proposed. The device ends are embedded by the gold gratings and TiO2 materials, in which the close successive polariton filtering can be formed. The selected light source is input into the system via the input port. There is no light energy injected and left into and from the system after the initial input, which can be configured as the adiabatic-like system. Polariton forms by the coupling between the intense optical field and the optical dipole generated by the gold grating. The suitable reflector (TiO2 material) lengths are applied to all device ends, from which only a small amount of the polariton output energy can be transmitted and measured at the add port output. By using the Optiwave and MATLAB programs, the polariton outputs regarding wavelength, time and frequency of the stopping states can be found and plotted. The relative polariton negentropic values of the red- and blueshifted signals are also calculated. The maximum relative negentropic value of 6.8 × 1015 m2 s−2 is obtained. The possible hibernation and quantum consciousness interpretation using the proposed system are also discussed.

Silicon Multimode Waveguide Grating Filter at 2 μm

A silicon-based on-chip add-drop optical filter is realized for the wavelength-band of 2 μ m by integrating a multimode waveguide grating (MWG) and a pair of two-channel mode (de)multiplexers. The realized add-drop optical filter has low loss and high sidelobe suppression ratio in a broad band, achieved by optimizing the corrugation depth, the apodization strength, as well as the grating length. The measurement results agree very well with the theoretical simulation results. The demonstrated ∼100 μ m-long MWG has a large 0.5 dB bandwidth of 6∼26 nm and a sidelobe suppression ratio of 22∼27 dB. The thermal-tunability of the present optical filter is also demonstrated experimentally, and the measured tuning efficiency is about 0.16 nm/mW.

Toward Special-Relativity-on-a-Chip: analogue of Einstein velocity addition using optical add-drop filter (OADF)

ABSTRACTWe present an optical analogue of a central concept (not a specific relativistic effect) in Special Relativity (SR) that underlies many relativistic effects. This concept is the Einstein Velocity Addition (EVA) which plays a fundamental role in the development of SR. The photonic circuit analogue is between the EVA, and the complex electric field, through the output signal of the optical add-drop filter (OADF). The OADF is one of the key building blocks for wavelength filtering in photonic integrated circuits (PICs or photonic chip). This analogue strengthens the vision toward a Special-Relativity-on-a-Chip. The analogy is established by equating the two relativistic normalized velocities in EVA with the two transmission coupling coefficients of the two directional couplers in the OADF. Furthermore, the generating angle in the EVA is associated with the single-pass phase shift of the OADF. We analyze its magnitude and directional angle in detail. Lastly, other important consequences are also briefly discussed.

Submicron-resonator-based add-drop optical filter with an ultra-large free spectral range.

A low-loss add-drop microring resonator (MRR) with an ultra-large free spectral range (FSR) is demonstrated by introducing an ultra-sharp multimode waveguide bend and bent asymmetrical directional couplers (ADCs). The multimode microring waveguide is introduced to achieve a low bent loss, even with a small radius (e.g., R = 0.8 μm). The bent ADCs are used to suppress the resonance of higher-order modes. For the fabricated device, the transmission at the drop port has a narrow 3 dB-bandwidth of 0.8 nm and a low excess loss of 1.8 dB. A record large FSR of 93 nm is achieved to the best of our knowledge.

Performance analysis of vertically cascaded pentacle micro-optical ring resonator as optical filters with four output bus waveguides

Modeling and performance analysis of vertically cascaded pentacle micro-optical ring resonator (VCPMORR) with single input and four output bus waveguides is presented. Overall transmittance of the proposed VCPMORR is determined in Z-domain for each output bus waveguide by practicing delay line signal processing approach and Mason’s gain formula. Frequency response analysis of the proposed model is carried out using MATLAB software. Free spectral range (FSR), group delay, and dispersion are enumerated as performance parameters of the proposed model. The detailed design of its waveguide is carried out by employing finite-difference time-domain (FDTD) method. Electric field propagation through the rings and the waveguides is also studied by FDTD. This method proposes an approach to design the numerous coupled ring resonator structures. This configuration provides more communication channels due to its wide FSR with zero crosstalk at four output buses. Hence, this coupled ring resonator structure will be very useful in optical communication systems as an optical add-drop filter.

One-Way Rotating Photonic Crystal Ring Resonator With High Quality Factor

We propose a planar photonic crystal ring resonator consists of a looped single interface between a regular and a magneto-optical photonic crystal structure. The cavity modes are shown to possess the unidirectional rotation characteristics, and the rotating direction is determined by the direction of an externally applied magnetic field normal to the rotation plane. This unique unidirectional feature results in the realization of cavity with extremely high Q factor of 3.2 × 106, more than one order of magnitude higher than the previous report for cavity with the same ring size [Z. Qiang, W. Zhou, and R. A. Soref, “Optical add-drop filters based on photonic crystal ring resonators,” Opt. Exp ress , vol. 15, no. 4, pp. 1823–1831, Feb. 2007]. As an example of its applications, we present a unidirectional channel-drop filter design based on the one-way rotating photonic crystal ring resonator. Our simulation result shows that a 96.7% backward dropping efficiency can be achieved by this filter.

Raman-Assisted Phase-Sensitive Amplification Enabled Optical Add-Drop Filter

We present a novel reconfigurable optical add-drop filter based on phase-sensitive amplifiers (PSAs). By manipulating the relative phase among an optical pump, signals, and idlers, spectral selectivity can be achieved along with low noise amplification. The use of backward Raman amplification enhances the phase-sensitive operation of the parametric process, enabling higher stopband isolation and lower intra-band crosstalk. A Raman-assisted phase-sensitive amplifier (RA-PSA) is characterized in detail, showing a 7.8-dB combined gain extinction ratio enhancement and 10.85-dB gain improvement. For the first time, we demonstrate an RA-PSA enabled optical add-drop filter with less than 0.4-dB penalty using three-channel QPSK signals. The novel scheme provides a simple way to enhance the extinction ratio of the PSA enabled add-drop filter, which can be an essential subsystem in optical links based on phase-sensitive amplification.