High-order microring resonators having from 1 to 11 coupled cavities are demonstrated. These filters exhibit low loss, flat tops, and out-of-band rejection ratios that can exceed 80 dB. They achieve performance that is suitable for commercial applications.Index Terms-Cavity resonators, filters, integrated optics, resonator filters, resonators, wavelength-division multiplexing (WDM).T IGHT CHANNEL spacing in wavelength-division-multiplexed (WDM) systems calls for filters that exhibit boxlike response. As channels are packed more closely together, filter specs become more demanding and tax available technologies to produce the required spectral performance. Thin-film filters (TFFs) have played a critical role in WDM systems due in part to the fidelity of their response which is achieved by the use higher order or coupled cavities. The ability to go to higher and higher orders has made resonators invaluable not only at optical frequencies but at all frequencies from kilohertz to microwaves. Significant fabrication challenges remain in TFFs as either the channel spacing decreases or the number of cavities increases. For instance, a four-cavity TFF for 25-GHz channel spacing applications requires from 200 to 400 sequentially deposited layers. In addition, as channel count increases, stack up losses in discrete TFFs mount.Microring resonators fabricated in planar technology offer significant advantages over discrete TFFs. In terms of fabrication, almost arbitrarily high orders can be produced with microring resonators, as all cavities reside in a single dielectric layer, as opposed to requiring hundreds of layers. Rings support traveling wave modes. This allows them to have four spatially separated ports which gives them unique advantages in optical circuit architectures. In this letter, we demonstrate very high-order microring cavities having commercial grade performance for 50-and 25-GHz applications.Coupled microrings have been suggested for add-drop filter applications [1]. Fig. 1 shows the schematic of such a filter having three cavities. Multiring cavities have been analyzed by matrix methods [2] as well as in the time domain [3]. The timedomain formulation yields a simple continued fraction representation of the filter response which may be written down by inspection for any th-order filter as (1a) Manuscript Fig. 1. Third-order microring resonator filter comprised of three coupled rings. The input and output bus waveguides are vertically coupled to the rings while the rings are laterally coupled to their neighbors. (1b)where all rings are identical and lossless. The frequency offset is denoted by , where is the resonant frequency. The term is related to the bus-to-ring coupling, while the terms are related to the coupling between adjacent rings [3]. The structure in Fig. 1 takes advantage of vertical coupling between the bus and outer rings for precise control of the coupling strength [4]- [8]. The rings are all mutually coupled laterally. During fabrication, all cavities are printed in the same step, unlike TF...

These authors contributed equally to this work.Fully exploiting the silicon photonics platform requires a fundamentally new approach to realize high-performance laser sources that can be integrated directly using wafer-scale fabrication methods. Direct band gap III-V semiconductors allow efficient light generation but the large mismatch in lattice constant, thermal expansion and crystal polarity makes their epitaxial growth directly on silicon extremely complex. Here, using a selective area growth technique in confined regions, we surpass this fundamental limit and demonstrate an optically pumped InP-based distributed feedback (DFB) laser array grown on (001)-Silicon operating at room temperature and suitable for wavelength-division-multiplexing applications. The novel epitaxial technology suppresses threading dislocations and anti-phase boundaries to a less than 20nm thick layer not affecting the device performance. Using an in-plane laser cavity defined by standard top-down lithographic patterning together with a high yield and high uniformity provides scalability and a straightforward path towards cost-effective cointegration with photonic circuits and III-V FINFET logic.The potential of leveraging well-established and high yield manufacturing processes developed initially by the electronics industry has been the main driver fueling the massive research in silicon photonics over 2 the last decade [1][2][3][4][5][6] . From the start of its development though the lack of efficient optical amplifiers and laser sources monolithically integrated with the silicon platform inhibited the widespread adoption in high-volume applications. Solutions relying on flip-chipping prefabricated laser diodes 7,8 or bonding III-V epitaxial material [9][10][11] are now being deployed in commercially available optical interconnects but are less compatible with standard high-volume and low cost manufacturing processes. Approaches focusing on the engineering of group IV materials have achieved optical gain but still require extensive work to reach room temperature lasing at reasonable efficiency [12][13][14] . Therefore, the monolithic integration of direct bandgap III-V semiconductors, well known to be efficient light emitters, with the silicon photonics platform is heavily investigated. However, considerable hurdles need to be overcome. When directly growing III-V semiconductors on silicon substrates, the large lattice mismatch (εInP/Si = 8.06 %), the difference in thermal expansion and the different polarity of the materials result in large densities of crystalline defects including misfit and threading dislocations, twins, stacking faults and anti-phase boundaries, strongly degrading the performance and reducing the lifetime of any device fabricated in the as-grown layers 15 . Several routes to overcome these issues have been proposed. GaP-related materials can be grown on exact (001) silicon substrates with a small lattice mismatch and pulsed laser oscillation around 980 nm up to 120 K 16 has been achieved but shifting the laser...

A new generation of Silicon-on-Insulator fiber-to-chip grating couplers which use a silicon overlay to enhance the directionality and thereby the coupling efficiency is presented. Devices are realized on a 200 mm wafer in a CMOS pilot line. The fabricated fiber couplers show a coupling efficiency of −1.6 dB and a 3 dB bandwidth of 80 nm.

Tightly confined, low-loss waveguides in highly nonlinear materials permit nonlinear optical interactions to occur over much shorter distances than do fibers. The nonlinear interactions are further enhanced in resonators. Both theory and experiment of enhanced four-wave mixing in micro-ring resonators are presented that can be used for many applications. A conversion efficiency of 14% achievable with only 10-mW peak pump power is predicted under realizable conditions. The experiment, the first one to the authors' knowledge in nonlinear optics performed in micro-rings, shows, even in a lossy GaAs/AlGaAs ring, a 26-dB improvement in the conversion efficiency compared with that of an equivalent straight waveguide, in agreement with theory.

High performance integrated optical modulators are highly desired for future optical interconnects. The ultra-high bandwidth and broadband operation potentially offered by graphene based electro-absorption modulators has attracted a lot of attention in the photonics community recently. In this work, we theoretically evaluate the true potential of such modulators and illustrate this with experimental results for a silicon integrated graphene optical electro-absorption modulator capable of broadband 10 Gb/s modulation speed. The measured results agree very well with theoretical predictions. A low insertion loss of 3.8 dB at 1580 nm and a low drive voltage of 2.5 V combined with broadband and athermal operation were obtained for a 50 µm-length hybrid graphene-Si device. The peak modulation efficiency of the device is 1.5 dB/V. This robust device is challenging best-in-class Si (Ge) modulators for future chip-level optical interconnects.

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Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.