Coupled Microring Resonator Research Articles

Wavelength-Selective Reflector Based on a Circular Array of Coupled Microring Resonators

We propose and analyze a novel type of wavelength-selective reflector for planar lightwave technology based on a circular array of coupled microring resonators. Narrow-band reflection peaks can be achieved without the need for additional complex lithography and processing steps. The ring resonators also allow for simple and wide-range tuning of the reflection peak.

High-Finesse Laterally Coupled Single-Mode Benzocyclobutene Microring Resonators

We demonstrate benzocyclobutene microring resonators. These devices, made of a readily available polymer and fabricated with a simple process, are among the smallest radius (10 /spl mu/m) of polymer microrings. They feature the widest free-spectral range (23.7 nm) as well as highest finesse (192) in any single-ring polymer devices reported to date.

Loss-Less Multilevel Crossing of Busline Waveguide in Vertically Coupled Microring Resonator Filter

To eliminate the scattering loss at the crossing points of cross grid busline waveguides, a multilevel crossing structure of busline waveguide was introduced into the vertically coupled microring resonator filter. The top surface of each buried waveguide was perfectly planarized by a new fabrication process and clear filter responses were observed for a single ring and a series coupled double ring resonator with multilevel crossing busline waveguides.

Wide Range Center Wavelength Trimming of Vertically Coupled Microring Resonator Filter by Direct UV Irradiation to SiN Ring Core

We developed a precise and wide range ultraviolet (UV) trimming of the center wavelength of vertically coupled microring resonator, by using the direct UV irradiation to the SiN ring core. We discovered that the UV-induced refractive index change of SiN was -1.3/spl times/10/sup -2/ and there was no aging of refractive index after the UV irradiation. Utilizing this phenomenon, -12.1 nm of center wavelength shift was demonstrated without the aging effect for 1200 h.

Characterization of Vertically Waveguide Coupled Microring Resonators by Means of Quantitative Image Analysis

The standard method of measuring the response of a micro resonator with in- and output waveguides consists of detecting the output power as a function of wavelength. In this paper a complementary method by means of quantitative image analysis is proposed. A vertically coupled waveguide microring resonator has been characterized with this method by projecting the scattered power of the device to an IR camera and analyzing the image as a function of wavelength. The reliability of this method has been confirmed by comparison with the standard measurement.

All-optical switching in a laterally coupled microring resonator by carrier injection

We demonstrate all-optical switching in a laterally coupled GaAs-AlGaAs microring resonator by carriers injections. The ring waveguide is optically pumped just above its bandgap energy, which results in a temporal tuning of the microring resonant wavelengths by the refractive index change due to the induced carriers. A switching window of 20 ps could be obtained and is only limited by the carrier recombination time. A switching energy of a few tens of picojoules per pulse is used and has resulted in a 1.2-nm wavelength shift of the microring resonance.

Wavelength tunable polymer microring resonator filter with 9.4 nm tuning range

Wide range (9.4 nm) tuning of a vertically coupled microring resonator filter was demonstrated utilising a large TO coefficient of the polymer core. The power consumption was about 60 mW and no degradation of filter response was observed after a heat cycle.

Dense Integration of Optical Filter Circuit by Vertically Coupled Microring Resonator with Cross Grid Geometry

We have proposed and demonstrated a vertically coupled microring resonator (VCMRR) filter. This configuration has many features, such as the independent optimum design of lower waveguide and upper ring, and the possibility of dense integration resulting from the cross-grid configuration. In addition, the coupling strength between the ring and bus waveguides can be controlled more precisely than the lateral coupling, because the vertical separation is obtained by the well controlled deposition rather than etching fine gaps. In this review, the recent progress in the development of compact integrated photonic functional devices using micro-ring resonator is reported. The key features of the vertically coupled micro-ring resonator filters are summarized and the potential applications of the filters leading to the development of ultra-dense integrated photonic circuits are described.

Box-like filter response and expansion of FSR by a vertically triple coupled microring resonator filter

The Lorentzian-shape filter response of a microring resonator filter is not suitable for practical use in wavelength division multiplexing (WDM) systems because of the lack of passband flatness, high crosstalk, and the large wing in the rejection band. Therefore, the tailoring of filter response shape is required to improve the performance. The series coupled microring resonator is one of the solutions. We designed and fabricated vertically triple coupled microring resonator add/drop filters with a stacked configuration. A box-like filter response with a flat passband was successfully obtained, and the free spectral range (FSR) was expanded to 25.8 nm owing to the Vernier effect.

Coupling-loss reduction of a vertically coupled microring resonator filter by spot-size-matched busline waveguides.

To improve the input-output coupling loss of a vertically coupled microring resonator filter, we fabricated microring resonators on an antiresonant reflecting optical waveguide (ARROW) with a large spot size and on the rectangular busline waveguide with a spot-size transformer. The spot size and the tapered structure were optimally designed from the viewpoint of spot-size matching to single-mode fibers and the reduction of radiation loss. Clear dropping responses were demonstrated for the ARROW-based microring resonator filters, and the coupling loss was successfully reduced by 22 dB.

Precise control of wavelength channel spacing of microring resonator add-drop filter array

The vertically coupled microring resonator filter is an attractive add-drop wavelength filter due to its functionality and compactness and the possibility of dense integration resulting from the cross-grid configuration. However, in the concatenated 1 /spl times/ 8 filter array in which the ring radii are changed with the increments of 50 nm, the wavelength channel spacing was limited to 5.7 nm due to the resolution limit of photomask (50 nm). Therefore, we developed a new technique to control precisely the channel spacing by an ultraviolet (UV)-trimming technique using polysilane as the over-cladding layer. As a result, we successfully decreased the channel spacing to 0.5 nm, and also controlled the channel spacing precisely to 1.0 nm using the same trimming technique.

Vertically coupled GaInAsP–InP microring resonators

Vertically coupled microring resonator channel-dropping filters are demonstrated in the GaInAsP-InP material system. These devices were fabricated without regrowth. In this method, low-loss single-mode waveguides are removed from the growth substrate and bonded to a GaAs transfer substrate with benzocyclobutene. This permits fabrication of vertically coupled waveguides on both sides of the epilayer. Optical quality facets are obtained by cleaving through the transfer substrate. Operation of single-mode, single-ring optical channel-dropping filters is demonstrated.

Ultrashort optical pulse transmission characteristics of vertically coupled microring resonator add/drop filter

The ultrashort optical pulse transmission characteristics of a vertically coupled microring resonator (VCMRR) filter were measured at 1.55 /spl mu/m wavelength, and the transmission capacity per channel was evaluated. The pulsewidth at the output was measured to be 3.4 ps, when 1.2 ps input pulse with a sech pulse shape from a fiber laser was incident on the microring resonator filter with a fullwidth at half-maximum (FWHM) of 0.75 nm (94 GHz). From this result, the maximum transmission capacity of the filter was estimated to be approximately 50 Gb/s. The pulse broadening through the filter was theoretically analyzed, and it was confirmed that the pulse broadening evaluated from the bandwidth of the filter spectrum response were in good agreement with the measured results.

Higher order filter response in coupled microring resonators

Second- and third-order filter response is experimentally shown in filters constructed using mutually coupled microring resonators. The higher order filters have passbands with sharper rolloff and flatter tops, and greater out-of-band rejection than previously demonstrated microring filters, which were first order. The effect of varying interesonator coupling on filter passband shape was studied.

Temperature insensitive vertically coupled microring resonator add/drop filters by means of a polymer overlay

The temperature dependence of vertically coupled glass microring resonator add/drop filters is investigated. Measurements show that the passband of the air-clad microring resonator filter increases with temperature at a rate of 0.0137 mm//spl deg/C. Using a PMMA-TFMA polymer that has an opposite refractive index temperature gradient than glass as the overlay of the microring resonator, the temperature dependence of the filter is compensated to -0.0025 nm//spl deg/C in the operation range of 25/spl deg/C to 55/spl deg/C.

An eight-channel add-drop filter using vertically coupled microring resonators over a cross grid

An eight-channel add-drop cross-grid vertically coupled microring resonator (VCMRR) filter is proposed and demonstrated. The cross grid comprises a grid-like array of buried channel waveguides which perpendicularly cross through each other, VCMRRs at each of the cross-grid nodes serve as the wavelength selective add-drop filters. Measured crosstalk levels at the crossings are typically less than -30 dB. Rings with a nominal radius of 10 μm are used to achieve a free-spectral range of 20 nm and optical bandwidths of 1 nm, while changes of the radii in increments of 50 nm lead to a nominal channel spacing of 5.7 nm.

Design and modeling of waveguide-coupled single-mode microring resonators

We discuss a first-order design tool for waveguide-coupled microring resonators based on an approximate solution of the wave propagation in a microring waveguide with micron-size radius of curvature and a large lateral index contrast. The model makes use of the conformal transformation method and a linear approximation of the refractive index profile, and takes into account the effect of waveguide thickness, dispersion, and diffraction. Based on this model, we develop general design rules for the major physical characteristics of a waveguide-coupled microring resonator, including the resonance wavelength, the free spectral range, the coupling ratio, the bending radiation loss and the substrate leakage loss. In addition, the physical model provides leads to alternative coupling designs. We present two examples, one using a phase-matching parallel waveguide with a smaller width than the ring waveguide, and the other using a vertical coupling structure. Both these designs significantly increase the coupling length and reduce or eliminate the dependence on a narrow air gap in a waveguide coupled microring resonator.