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...

Abstract-A biosensor application of vertically coupled glass microring resonators with Q ∼ 12 000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensitivity to refractive index changes (limit of detection of 1.8 × 10

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Electro-optic phase modulators are critical components in modern communication, microwave photonic, and quantum photonic systems. Important for these applications is to achieve modulators with low half-wave voltage at high frequencies.Here we demonstrate an integrated phase modulator, based on a thin-film lithium niobate platform, that simultaneously features small on-chip loss (∼ 1 dB) and low half-wave voltage over a large spectral range (3.5 -4.5 V at 5 -40 GHz). By driving the modulator with a strong 30-GHz microwave signal corresponding to around four half-wave voltages, we generate an optical frequency comb consisting of over 40 sidebands spanning 10 nm in the telecom L-band. The high electro-optic performance combined with the high RF power-handling ability (3.1 W) of our integrated phase modulator are crucial for future photonics and microwave systems.

A surface-emitting semiconductor laser that utilizes a concentric-circle grating defined by electron-beam lithography is observed to oscillate in a circularly symmetric fashion. The laser emits a circularly symmetric beam with a total beam divergence of less than 1°. Despite its broad-area geometry, the laser shows no evidence of filamentation. The laser maintains a relatively narrow wavelength spectrum approximately 1 Å in width.

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.

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We report results for photoluminescence studies of an impurity-related defect system in 450 C annealed Czochralski-grown silicon resulting in optical emission with a wavelength near 1.7 pm. The photoluminescence emission is found to have a significant intensity that persists to room temperature. The external quantum efBciency at 300 K is measured to be approximately 2.5 X 10 '. Photoluminescence (PL) arising from impurity defects in silicon has been extensively studied for many years. ' Recent interest has been largely prompted by the desire to identify eIcient mechanisms by which indirect-bandgap group-IV materials can be made to emit photons with energies smaller than that of the band gap, with a view to integrating photonic devices with Si and Si/Ge electronics. Much of the work in this field has drawn its inspiration from the success achieved with impurityrelated luminescence from GaP, another indirect-gap semiconductor.The chalcogen impurities sulfur ' and selenium have each been shown to be involved in defect centers which can produce strong emission in the near-infrared region of the spectrum. These complex centers are distinguished by their high external PL quantum ef6ciency, which can be as high as 5&o. Relatively efficient electroluminescence has also been reported.The measured radiative lifetimes suggest that the emission is caused by the radiative decay of excitons bound to isoelectronic impurity complexes. The spectra associated with these impurity centers are similar in nature. They both exhibit a narrow-band component which dominates the spectrum at low temperatures ( T-35 K) and a distinctly different broad component which peaks in intensity at considerably higher temperatures (T-60 K). This component can persist to temperatures up to T-150 K.We present here the results for what appears to be another chalcogen-related system in Czochralski-(CZ)grown silicon. The PL signal from this system also exhibits two distinct bands whose relative intensities vary with temperature. This systein is remarkable, however, in that the high-temperature band has a signi6cant PL signal strength which persists to room temperature. Reports in the literature of room-temperature luminescence in silicon are rare. While phonon-assisted free-carrier combination is observed in Si, the efficiency of this process is understandably low, with a measured ' internal quantum efficiency (QE) of 10 -10 . Recently, bandedge recombination at room temperature in a Sioe/Si quantum-well structure has also been reported to have an electroluminescent internal QE of 2X10 . Spectra have been shown for room-temperature luminescence from Er-doped silicon, ' but we know of no literature reports of the QE to date. Ge detector and a Stanford Research Systems lock-in amplifier.As in the case of the other chalcogen impurity centers described above, the spectrum contains two distinct components. The peak near wavelength A, =1.6 jum (energy = 0.767 eV) in the T =30 K spectrum is the well-known P line. " As the sample temperature is raised, we find