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This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all‐pass ring resonator are extracted based on the transmission characteristics using finite‐difference time‐domain method. As compared to conventional graphene‐oxide‐semiconductor straight waveguide, graphene integrated on an all‐pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 μm radiation and ring radius of 3.75 μm with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro‐optic applications. [ABSTRACT FROM AUTHOR]

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red‐shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source. [ABSTRACT FROM AUTHOR]

Silicon-on-insulator photonic microring resonators are ideal components for applications that require a high degree of multiplexing because of their small size. However, when very high numbers of microrings are used in parallel, grating couplers and waveguide routing quickly take up more chip space than the actual rings. Therefore, we suggest to combine microring resonators with local weak gratings to read out light directly from the microring while still maintaining high-quality factors of 19 000. We demonstrate simulation results and an experimental analysis of different grating parameters. The resonance spectrum is recovered from the vertical emission of the microring grating, without using a traditional output waveguide. [ABSTRACT FROM PUBLISHER]

Continuously tunable slow and fast light generation using a silicon-on-insulator microring resonator (MRR) incorporating a multimode interference (MMI) coupler is proposed and experimentally demonstrated. The MMI coupler is optimized for the transverse-magnetic mode. By changing the input polarization state, the self-coupling coefficient and the loss factor of the MRR are changed. The depth and the bandwidth of the MRR are tunable by tuning the self-coupling coefficient and the loss factor; thus, a tunable phase shift can be achieved at the resonance wavelength, which leads to the generation of a tunable slow and fast light. The proposed scheme is experimentally evaluated. A tunable slow light with a maximum time delay of 35 ps and a slow-to-fast light with a continuously tunable range of 102 ps are achieved for a 13.5-GHz Gaussian optical pulse by using a double-MMI coupler MRR and a single-MMI coupler MRR, respectively. [ABSTRACT FROM PUBLISHER]

Microresonators with a high Kerr nonlinearity show great potential to generate optical frequency combs with ultrabroad spectra, high repetition rate, and high coherence between comb lines. The compact size and possibility of chip-level integration make the Kerr combs attractive for many applications, especially including photonic radiofrequency (RF) filters. In this paper we report the first demonstration of a programmable photonic RF filter based on the Kerr comb from a silicon nitride microring. A novel scheme enabled by the large frequency spacing of the Kerr comb is introduced in order to suppress unwanted RF passbands including the image and periodic passbands. As a result, a single passband is achieved. To the best of our knowledge, this is the first demonstration of a single-bandpass photonic RF filter employing a discrete-wavelength comb source. [ABSTRACT FROM PUBLISHER]

We design and demonstrate for the first time an end-to-end binary phase-shift keying (BPSK) link based on silicon microring resonators, with an operational bit-rate at 10 Gb/s. The obtained bit-error-rate is below the forward error correction limit, validating the practical application of the demonstrated technique. Performance comparisons to conventional BPSK modulation and demodulation techniques are also made. The microring-based BPSK link promises a compact, energy efficient, and low-cost interconnect solution for high-capacity transceivers. [ABSTRACT FROM PUBLISHER]

In this paper, we numerically demonstrate the promise of silicon microdisks for Raman Stokes/anti-Stokes wavelength conversion. We design a silicon microdisk suitable for Raman wavelength conversion with “automatic” quasi-phase matching (QPM). By carefully designing the bus waveguide adjacent to the disk, we show that, for each wavelength involved in the nonlinear process, we can excite the proper light mode for which the “automatic” QPM concept is obtained in the microdisk, and find that with this design, we can achieve wavelength conversion efficiencies up to -2.4 dB at input pump powers as low as 3.4 mW. [ABSTRACT FROM PUBLISHER]

We propose a scheme to utilize a multimode microdisk resonator in silicon controlled through free-carrier injection for continuous fast-to-slow light tuning. Two nearby resonant modes are employed, i.e., undercoupling and overcoupling. The optical properties of a device are analytically investigated considering the resonance spacing, bandwidth, and density change of free carriers. Pulse propagation simulations are implemented, and the pulse delay/advance is studied for wavelengths between the two resonances. As the density of injected free carriers increases, a continuous transition from fast to slow light occurs for a range of wavelengths. Consequently, a microdisk resonator in silicon is experimentally realized with the desired two resonances, exhibiting electrooptical tuning with a fast response. The experimental results agree well with the simulation in power transmission, and the tunable time delay and advance are also predicted. [ABSTRACT FROM PUBLISHER]

We present a method for directly synthesizing coupled microring resonator filter networks of general 2-D coupling topologies. The method is based on the “energy coupling in time” formalism of systems of microring resonators and can be used to synthesize optical filter transfer functions in the s-domain. An example of a class of microring filters with equiripples in both the amplitude and group delay responses is also given to illustrate the application of the method to the design of complex microring filter architectures. [ABSTRACT FROM PUBLISHER]

Chip-embedded organic resonator is fabricated with 2,5-Bis(4-biphenylyl)thiophene (BP1T) crystals encapsulated with polydimethylsiloxane (PDMS). Whispering gallery mode lasing is demonstrated in these on-chip embedded crystalline microresonators, without decline in the spectral properties, and performance in comparison to the unencapsulated devices. The encapsulated lasers exhibit quality factor (Q) as high as 1066, and lasing threshold is about 120 nJ (1.5 mJ/cm2). Meanwhile, with protection of the PDMS, operation lifetime of the laser is increased from 2.1 × 106 to 4.6 × 106 pulses. [ABSTRACT FROM PUBLISHER]

We present a theoretical model to analyze all-optical switching by two-photon absorption induced free-carrier injection in silicon 2 × 2 add-drop microring resonators. The theoretical simulations are in good agreement with experimental results. The results have been used to design all-optical ultrafast (i) reconfigurable De-multiplexer/Multiplexer logic circuits using three microring resonator switches and (ii) universal, conservative and reversible Fredkin and Toffoli logic gates with only one and two microring resonator switches respectively. Switching has been optimized for low-power (25 mW) ultrafast (25 ps) operation with high modulation depth (85%) to enable logic operations at 40 Gb/s. The combined advantages of high Q-factor, tunability, compactness, cascadibility, reversibility and reconfigurability make the designs favorable for practical applications. The proposed designs provide a new paradigm for ultrafast CMOS-compatible all-optical reversible computing circuits in silicon. [ABSTRACT FROM PUBLISHER]

A photonic integrated architecture realizing the concept of coupled-resonator dual-mode optical filters is presented. The proposed structure consists of a chain of directly coupled microring resonators with a partial reflector embedded in the last resonator. The contradirectional coupling induced by the reflector makes the effective order of the filter double with respect to the number of coupled resonators. Since the counterpropagating modes share the same physical cavity, the resonant frequencies are intrinsically aligned, sensitivity of the filter to fabrication tolerances is reduced, and control of the structure is eased with respect to coupled resonator filters of the same order. Second- and fourth-order dual-mode filters made of microring resonators loaded with a Bragg grating are experimentally demonstrated on a silicon-on-insulator photonic platform. [ABSTRACT FROM PUBLISHER]

The direct patterning of hybrid-polymer microring resonators with minimal residual layers by UV-assisted nanoimprint lithography is reported. The proposed stamp-and-repeat technology requires no post-processing. The imprint polymer was applied by spin-coating as a 130-150 nm thin initial film for an optimized processing. The importance of the initial film thickness is discussed in detail. Aspect ratios of more than 5:1 were realized with 2 μm high ridge-waveguides and sub-400 nm coupling gaps on maximal 130 nm thin residual layers. The achieved ratio of structure height to residual layer thickness of 15.4 (2 μm versus 130 nm) was much larger than the typical values in high-resolution imprinting and superseded the removal of the residual layer completely. The resonators are thought as biosensor transducers. High quality devices with Q-factors up to 13000 were produced with a minimal set of process steps. [ABSTRACT FROM PUBLISHER]

This study proposes a dense multichannel optical waveguide switch based on micro ring resonators (MRRs). The proposed design is achieved by cascading five MRRs of the same structure and the phase difference between two bus waveguides that are evanescently coupled to every two MRRs is purposely set at either 0 or π in order to minutely adjusting the positions of the corresponding resonant wavelengths of the MRRs. Our proposed structure is capable of controlling ON/OFF signals associated with four optical channels. Our study finds that the resonant channel spacing is less than twice the full-width-at-half-maximum of an individual optical signal. Furthermore, among 16 different combinations of output spectra obtained, the ON/OFF signal contrast of each optical channel could reach up to -29.68 dB. [ABSTRACT FROM PUBLISHER]

We study the properties of finite-length all-pass side-coupled microring delay lines optimized using a genetic algorithm. The average bandwidth-group delay product is found to follow a linear growth with the number of cascaded stages N. Both the magnitude and the slope of the figure of merit vary with the specific optimization criteria but, for all the cases addressed, they are below the unit slope linear dependence with N of a theoretical upper bound. [ABSTRACT FROM PUBLISHER]

An all-optical clock recovery (CR) scheme with wide locking range is demonstrated, based on a silicon microring resonator (MRR) and a semiconductor optical amplifier (SOA). The MRR with a free spectral range of 40 GHz works as a comb filter, which removes the modulation information, whereas the SOA operating in the saturation regime performs amplitude equalization to achieve a good optical clock signal. The design of the MRR is investigated according to the tolerance of the subsequent equalizer. Based on the fabricated MRR, single and dual channels CR from 40 Gb/s input data streams can be achieved successfully with root mean square time jitter of ~ 900 fs. Because of the moderate finesse of the MRR, the CR can be achieved with a wide range of several gigahertz. [ABSTRACT FROM PUBLISHER]

In this letter, we experimentally demonstrate, by integrating plasmonic nanoantennas, that membrane-based micromechanical resonators can become infrared (IR) active. The photo-thermomechanical effect induced by nanoantennas enables actuation of mechanical structures. Using this hybrid nanoantenna coupled mechanical device as a thermal IR detector, we achieved a current responsivity of 12 mA/W corresponding to a displacement responsivity of 98.7 μm/W and a thermal time constant of 5.7 ms at a wavelength of 6 μm. This approach can be extended to any mechanical resonator for new optomechanical sensing modalities. [ABSTRACT FROM PUBLISHER]

We theoretically study the group-delay characteristics of a silicon microring resonator based on the coupled mode theory, and experimentally demonstrate error-free operations of an on-chip delay line using a silicon-on-insulator (SOI) microring resonator with a 20-mum radius. Four signals of different modulation formats are examined at 5 Gb/s, including return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ), return-to-zero duobinary (RZ-DB), and return-to-zero alternate-mark-inversion (RZ-AMI). Bit error rate (BER) measurements show that the maximal delay times with error-free operations are 80, 95, 110, and 65 ps, respectively, corresponding to a fractional group delay of ~0.4, ~0.5, ~0.55, and ~0.35. The differences in delay and signal degradations have been investigated based on the signal spectra and pattern dependences. Although the delays are demonstrated in a single ring resonator, the analysis is applicable in slow-light resonance structures such as all-pass filters (APF) and coupled resonator optical waveguides (CROW). [ABSTRACT FROM PUBLISHER]

All-pass, wavelength-selective, slowlight optical buffers using cascaded micro-ring resonator filters are theoretically and experimentally studied in the context of optical packet switching router architectures. Two optical buffers fabricated in high-index contrast silica technology are compared: an 8-ring buffer with narrow resonances for wavelength selective delay and a 32-ring buffer for distortion-free delay at 10 and 40 Gb/s. Accurate measurements and configurations of the transmission of the buffers allow for precise simulations that accurately predict pattern dependent distortions, signal integrity and performance extrapolation to higher data rates. Continuously tunable delays are demonstrated up to 8 bits with minimal distortion. [ABSTRACT FROM PUBLISHER]

Poled and unpoled chromophore-containing polymers offer some unique advantages in device functionality and fabrication. UV light and electron beam (e-beam) can bleach out the color of chromophores and reduce the index of refraction of the polymer. The photobleaching and e-beam bleaching methods form optical waveguides in a single step and do not involve solvents or wet chemicals, and can be applied to polymers that are not compatible with other waveguide fabrication techniques. A variety of microring resonator devices for fiber-optic telecommunication and sensors have been realized with chromophore-containing polymers. A novel broadband fiber-optic electric field sensor is presented as an example. The sensor uses a polymer with chromophores preferentially aligned after electric poling, and the microring resonator is directly coupled to the core of optical fiber. The feasibility of vertical integration of a poled electrooptic polymer waveguide device interfaced with silicon microelectronic circuits is also demonstrated. [ABSTRACT FROM PUBLISHER]

Excitation of biologically functional micro- and nanomechanical structures using optical fields is a recently emerging arena of research that couples the fields of optics, fluidics, electronics, and mechanics with potential of generating novel chemical and biological sensors. We present experimental and theoretical elucidation of optical excitation of resonant nanoelectromechanical systems (NEMS). The modulated optical fields were coupled directly into the NEMS device layer causing amplified mechanical vibrations. Dynamic detection of vibrational characteristics of nanomechanical resonators, fabricated from low-stress silicon nitride and mono crystalline silicon thin film layers, was accomplished using optical interferometry. We have analyzed the actuation mechanism using finite element modeling, and we found that the dominant actuation mechanism in close proximity of the clamped end was primarily thermal. In contrast, mechanical traveling waves are attributed as possible excitation mechanisms in the far-field regime [ABSTRACT FROM PUBLISHER]

A wide-range wavelength-tunable silicon microring resonator is proposed using a microelectromechanical actuator. The microring consists of two U-shaped silicon freestanding waveguides and two directional couplers. The circumference of the microring is varied by the actuator. The wavelength dependence of the couplers is compensated by adjusting the coupling length while varying the circumference. The initial circumference of the microring is 19.1 μm and the free spectral range is 21 nm. The resonant wavelength of the microring is varied by 27 nm at the applied voltage of 25 V with negligible power consumption. [ABSTRACT FROM PUBLISHER]

We propose a novel microring resonator concept that uses a polarization rotating asymmetrical directional coupler. The quasi-transverse electric polarized mode in the bus waveguide is used to excite the quasi-transverse magnetic (TM) polarized mode in the microring. This enables the realization of microrings with a high quality factor due to the lower scattering loss of the quasi-TM polarized mode. We demonstrate the operation principle with two all-pass microrings with radius 30 μm, working in the critically coupled regime with a quality factor of 31 000 and in the under-coupled regime with a quality factor of 125 000. [ABSTRACT FROM PUBLISHER]

Nickel cantilevers with integrated diffraction gratings are used as resonant mass sensors with a resolution of 500 femtograms. Their applicability to biosensing is demonstrated with human opioid receptors. The device is fabricated through a single-mask lithographic process. The microoptical readout provides a simple measurement platform with one external photodiode. Thanks to its AC operation principle, the device is immune to environmental noise and entails a high tolerance to fabrication defects. Obtained signal-to-noise ratio is comparable to that of a high-end Doppler vibrometer. The device with these aspects for systems integration and microarray technology is a candidate for low-cost portable sensors. [ABSTRACT FROM PUBLISHER]

A wavelength-tunable microring resonator with integrated microheater on lithium niobate is presented. Ridge structure on lithium niobate is formed by a wet-etching technique for enhancing the lateral index contrast of the waveguide. The resonant wavelength of the microring resonator is tuned through thermooptic effect by injecting current into the integrated microheater. The tuning characteristics of through port and drop port are measured and the tuning rates in the microring resonator with a radius of 100 mum for transverse-magnetic and transverse-electric polarizations are 2.54 x 10-2 nm/mA and 3.40 x 10-3 nm/mA. [ABSTRACT FROM PUBLISHER]

Mode characteristics of three-dimensional (3-D) microsquare resonators are investigated by finite-difference time-domain (FDTD) simulation for the transverse electric (TE)-like and the transverse magnetic (TM)-like modes. For a pillar microsquare with a side length of 2 mum in air, we have Q-factors about 5 times 103 for TM-like modes at the wavelength of 1550 nm, which are one order larger than those of TE-like modes, as vertical refractive index distribution is 3.17/3.4/3.17 and the corresponding center layer thickness is 0.2 mum. The mode field patterns show that TM-like modes have much weaker vertical radiation coupling loss than TE-like modes. TM-like modes can have high Q-factors in a microsquare with weak vertical field confinement. [ABSTRACT FROM PUBLISHER]