Synthesized soliton crystals.

Dissipative Kerr soliton (DKS) featuring broadband coherent frequency comb with compact size and low power consumption, provides an unparalleled tool for nonlinear physics investigation and precise measurement applications. However, the complex nonlinear dynamics generally leads to stochastic soliton formation process and makes it highly challenging to manipulate soliton number and temporal distribution in the microcavity. Here, synthesized and reconfigurable soliton crystals (SCs) are demonstrated by constructing a periodic intra-cavity potential field, which allows deterministic SCs synthesis with soliton numbers from 1 to 32 in a monolithic integrated microcavity. The ordered temporal distribution coherently enhanced the soliton crystal comb lines power up to 3 orders of magnitude in comparison to the single-soliton state. The interaction between the traveling potential field and the soliton crystals creates periodic forces on soliton and results in forced soliton oscillation. Our work paves the way to effectively manipulate cavity solitons. The demonstrated synthesized SCs offer reconfigurable temporal and spectral profiles, which provide compelling advantages for practical applications such as photonic radar, satellite communication and radio-frequency filter.

Demonstration of a stable ultrafast laser based on a nonlinear microcavity.

Ultrashort pulsed lasers, operating through the phenomenon of mode-locking, have had a significant role in many facets of our society for 50 years, for example, in the way we exchange information, measure and diagnose diseases, process materials, and in many other applications. Recently, high-quality resonators have been exploited to demonstrate optical combs. The ability to phase-lock their modes would allow mode-locked lasers to benefit from their high optical spectral quality, helping to realize novel sources such as precision optical clocks for applications in metrology, telecommunication, microchip-computing, and many other areas. Here we demonstrate the first mode-locked laser based on a microcavity resonator. It operates via a new mode-locking method, which we term filter-driven four-wave mixing, and is based on a CMOS-compatible high quality factor microring resonator. It achieves stable self-starting oscillation with negligible amplitude noise at ultrahigh repetition rates, and spectral linewidths well below 130 kHz.

On-chip CMOS-compatible all-optical integrator.

All-optical circuits for computing and information processing could overcome the speed limitations intrinsic to electronics. However, in photonics, very few fundamental 'building blocks' equivalent to those used in multi-functional electronic circuits exist. In this study, we report the first all-optical temporal integrator in a monolithic, integrated platform. Our device--a lightwave 'capacitor-like' element based on a passive micro-ring resonator--performs the time integral of the complex field of an arbitrary optical waveform with a time resolution of a few picoseconds, corresponding to a processing speed of ∼200 GHz, and a 'hold' time approaching a nanosecond. This device, compatible with electronic technology (complementary metal-oxide semiconductor), will be one of the building blocks of next-generation ultrafast data-processing technology, enabling optical memories and real-time differential equation computing units.

Low power four wave mixing in an integrated, micro-ring resonator with Q = 1.2 million.

We demonstrate efficient, low power, continuous-wave four-wave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20 nm. We show theoretically that the characteristic low dispersion enables phase-matching over a tuning range > 160 nm.

A universal biosensing platform based on optical micro-ring resonators.

The use of optical micro-ring resonators as a platform for quantitative and qualitative biosensing applications was explored. Vertically coupled, high refractive index micro-ring resonators, used as sensing elements, were fabricated on silicon chips by photolithographic techniques. An optical reader system consisting of a near-infrared broad band light source and an optical spectrum analyzer were employed for data acquisition. Micro-ring resonator surfaces were modified with specific target receptors, including antibodies and single-stranded DNA oligonucleotides. The system was successfully used for label-free, specific, and rapid detection of whole bacterial cells, proteins and nucleic acids.

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.

Pedestal antiresonant reflecting waveguides for robust coupling to microsphere resonators and for microphotonic circuits.

Strip-line pedestal antiresonant reflecting waveguides are high-confinement, silica integrated optical waveguides in which the optical modes are completely isolated from the substrate by thin high-index layers. These waveguides are particularly well suited for whispering-gallery mode excitation in high-Q microspheres. They can also be used in microphotonic circuits, such as for microring resonators. The theory and design of these structures are highlighted. Experiments that show high coupling efficiency to microspheres are also demonstrated.

Filter synthesis for periodically coupled microring resonators.

The theory of filter synthesis using periodically coupled microring resonators is developed as a means to overcome the fabrication sensitivities inherent in conventional higher-order filters, while still achieving desirable spectral characteristics. Each resonator in the array can compensate for deficiencies in any of the others. These filters exhibit a boxlike shape and very high extinction ratios.

Wavelength conversion in GaAs micro-ring resonators.

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.

Planar integrated wavelength-drop device based on pedestal antiresonant reflecting waveguides and high-Q silica microspheres.

Whispering-gallery modes in silica microspheres can be accessed very efficiently with the recently introduced stripline pedestal antiresonant reflecting optical waveguide (SPARROW) structure. This integrated-optics coupling technique creates novel application opportunities for the high-Q spherical cavities. We report the demonstration of a narrow-band wavelength-drop configuration utilizing SPARROW waveguides and a silica microsphere.

Track changing by use of the phase response of microspheres and resonators.

A microsphere or resonator that is side coupled to an incident optical beam induces a phase response in the beam. In the so-called overcoupled regime, the amplitude of the incident beam remains unmodulated, whereas the phase goes through a shift of p at resonance. This shift is insensitive to the details of the coupling geometry or the resonant mode. In conjunction with an interferometer, the phase response can be used to switch the beam between two well-defined outputs, thus offering a robust means of deploying microspheres and other microresonators in practical photonic devices.

Second-order filtering and sensing with partially coupled traveling waves in a single resonator.

The counterpropagating waves in a single traveling-wave cavity can be partially coupled by means of a small perturbation such as a notch. When it is side coupled to a waveguide, this single cavity yields a general second-order (Chebyshev) reflection response in the waveguide, which is useful for narrow-bandwidth reflecting applications. In a different application, the cavity amplifies small reflections induced by external perturbations, thus finding use in ultrafine sensing. Amplification factors as great as 10(12) are predicted for the highest-Q microsphere resonators. The analytic theory of these devices is presented.

Surface-roughness-induced contradirectional coupling in ring and disk resonators.

Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes. Small reflections are thus considerably enhanced and may impair the performance of traveling-wave resonators. In addition, such contradirectional coupling leads to a splitting of the resonant peak. These effects are studied analytically.

Synthesis of ideal window filter response in grating-assisted couplers.

Synthesizing ideal windowlike spectral response in codirectional grating-assisted couplers is considered. The method of variational optimization is used to design couplers theoretically with near 100% power transfer efficiency over the passband width and with sidelobes suppressed to -40 dB. The physical role of the pi-phase-reversal sections for passband f lattening is explained.

Junction problem and loading effects in grating-assisted couplers.

Power transfer in grating-assisted couplers is governed by the excitation of the Floquet modes. This excitation not only is determined by the grating period but is also related to the amplitudes and phases of the uniform normal modes incident upon the grating as well as to the initial phase angle of the corrugation. The details of the junction are thus essential to the description of power flow. Under many practical circumstances it will be necessary to detune the grating period away the from the conventional phase-matching value to maximize coupled power. Higher-order effects that modify the uniform propagation constants, known as loading, are also considered. Coupled-mode theory is used to predict these features, including a simple expression for the detuning that maximizes power transfer.

Estimating surface-roughness loss and output coupling in microdisk resonators.

The volume current method is used to estimate analytically the scattering losses that are due to boundary corrugations and surface roughness in microdisk and ring resonators. The harmonic components of boundary imperfections either phase match the unguided continuum or lead to tunneling radiation. Phase-matched radiation can contribute significant loss and is only weakly dependent on disk radius. In high-index contrast devices the longitudinal electric field component is thus responsible for most of the radiation.

Ideal wavelength filters using semiadiabatic coupling.

Ideal wavelength-selective filters with a f lat transmission passband, large out-of-band rejection, and reduced sensitivity to fabrication can be realized by use of adiabatic coupling. The physical construction of the filter limits adiabatic power exchange to a specific range of wavelengths, thus yielding a boxlike response. Such robust response, however, requires an increased device length compared with that of optimized filters that achieve the same filter characteristics. No sophisticated synthesis method is required here, and an accurate description of filter response follows from simple physics.

Synthesis of codirectional couplers with ultralow sidelobes and minimum bandwidth.

A general variational optimization procedure is used to synthesize codirectional couplers with arbitrary sidelobe suppression down to -125 dB. Apodization shapes yielding sidelobe levels over the range of -40 dB to -75 dB are given by a single design formula. The limiting performance in terms of sidelobe suppression versus the bandwidth of passive evanescent-type couplers is found.