Search

In this paper, we propose an N -bit optical digital-to-analog converter (DAC) by integrating N pairs of 2 × 2 phase change based on-chip photonic switches and 2 × 2 multimode interference (MMI) splitters. An on-chip photonic switch is constructed by integrating a wavelength-selectable racetrack micro-ring resonator with the phase change chalcogenide Ge2Sb2Se4Te (GSST). The GSST-integrated switch utilizes a racetrack resonator configuration for performing the accurate modulation of the resonant wavelength to prevent intercoupling between adjacent units. In order for electrothermal heating of the GSST film to trigger its phase transition for switchable control, an indium tin oxide heater with a bowtie-shaped structure is integrated into the racetrack resonator. Using numerical calculations, we demonstrate that an 8 V voltage pulse at a duration of 300 ns, with an energy consumption of 18.45 nJ, could change the optical state from an OFF state to an ON state. Another 6 V voltage pulse of 250 ns duration, followed by a 4 V pulse of varying duration, with a total energy consumption of 34.78 nJ, can switch the optical state from an ON state to an OFF state. The asymmetric structure of the 2 × 2 MMI shows ultra-high transmittance approaching 50% in the through port (connected to the next order of MMI), enabling the creation of multistage cascaded MMI splitters with an output light power ratio close to 50%. Our results show that this configuration potentially offers a feasible solution for applications of optical DACs. [ABSTRACT FROM AUTHOR]

SU-8 is an emerging polymer material for integrated optical circuits that has demonstrated good structural properties in a cryogenic environment. In this article, we investigate the thermo-optical properties of SU-8 for a wavelength λ = 850   n m , from room temperature to cryogenic temperature down to 14 K. To measure the material properties, we designed and fabricated SU-8 racetrack resonators via electron beam lithography. While cooling the device in a closed-cycle cryostat, we measured the resonance spectrum as a function of the temperature from which we determined the temperature-induced variations of the group and effective indices of the waveguide. With the aid of waveguide eigenmode simulations, we used these data to derive the temperature dependence of the SU-8 refractive index n S U − 8 T . At room temperature (T~295 K), the thermo-optic coefficient d n S U − 8 / d T = − 5.3 ± 0.2 × 10 − 5   K − 1 . At low temperature (T~14 K), d n S U − 8 / d T = − 1.27 ± 0.05 × 10 − 4   K − 1 . Our research shows the potential of SU-8 photonics in a cryogenic environment, suitable for the integration with quantum light sources emitting in the near infrared (NIR). [ABSTRACT FROM AUTHOR]

The evolution to 5G millimeter wave (mmWave) is opening doors to many novel applications and services by leveraging the higher carrier frequency of 24 GHz and beyond. 5G mmWave promises to deliver extreme bandwidth, ultra-low latency, faster data speeds and responsiveness – thereby facilitating broadband connectivity to densely populated areas. Nevertheless, millimeter waves suffer from significant path loss, imposing severe range constraints. Beamforming is a promising technique to alleviate this impediment. Integrated photonics is sophisticated technology to realize cost-effective, compact, and power-efficient beamformers. In this paper, we propose photonically controlled continuously tunable single side coupled racetrack resonator based 1 × 8 broadband beamformer on CMOS-compatible silicon-on-insulator platform. A beam steering angle of 31.001˚ is achieved for 28 GHz mmWave wave signal. The proposed beamformer can provide maximum continuously tunable true time delay of 125 ps for delay bandwidth of 32.46 GHz. Therefore, the beam scanning range of 0–90° can be attained by properly tuning the coupling coefficient and resonance frequency of the racetrack resonator based delay element. [ABSTRACT FROM AUTHOR]

SU-8 is an emerging polymer material for integrated optical circuits that has demonstrated good structural properties in a cryogenic environment. In this article, we investigate the thermo-optical properties of SU-8 for a wavelength λ=850 nm, from room temperature to cryogenic temperature down to 14 K. To measure the material properties, we designed and fabricated SU-8 racetrack resonators via electron beam lithography. While cooling the device in a closed-cycle cryostat, we measured the resonance spectrum as a function of the temperature from which we determined the temperature-induced variations of the group and effective indices of the waveguide. With the aid of waveguide eigenmode simulations, we used these data to derive the temperature dependence of the SU-8 refractive index nSU−8T. At room temperature (T~295 K), the thermo-optic coefficient dnSU−8/dT=−5.3±0.2×10−5 K−1. At low temperature (T~14 K), dnSU−8/dT=−1.27±0.05×10−4 K−1. Our research shows the potential of SU-8 photonics in a cryogenic environment, suitable for the integration with quantum light sources emitting in the near infrared (NIR).

We present a theoretical investigation, based on the tight-binding Hamiltonian, of efficient electric-field-induced three-waves mixing (EFIM) in an undoped lattice-matched short-period superlattice (SL) that integrates quasi-phase-matched (QPM) SL straight waveguides and SL racetrack resonators on an opto-electronic chip. Periodically reversed DC voltage is applied to electrode segments on each side of the strip waveguide. The spectra of χxxxx(3) and of the linear susceptibility have been simulated as a function of the number of the atomic monolayers for “non-relaxed” heterointerfaces, and by considering all the transitions between valence and conduction bands. The large obtained values ofχxxxx(3) make the (ZnS)3/(Si2)3 short-period SL a good candidate for realizing large effective second-order nonlinearity, enabling future high-performance of the SLOI PICs and OEICs in the 1000-nm and 2000-nm wavelengths ranges. We have made detailed calculations of the efficiency of second-harmonic generation and of the performances of the optical parametric oscillator (OPO). The results indicate that the (ZnS)N/(Si2)M QPM is competitive with present PPLN technologies and is practical for classical and quantum applications.

Micro-ring resonator (MRR) is a key element in integrated optics. The mutual-coupling in dual-concentric MRR has great influence on the resonance output. In this work, high-Q silicon dual-concentric MRR and racetrack resonator have been investigated by the coupled mode theory. The theoretical model is built to explain and alleviate the phenomenon of resonance splitting. CMOS fabrication is adopted for the preparation of dual-concentric MRR and racetrack resonators. The highest Q-factors of dual-concentric MRR and racetrack resonator are measured to be ∼9.00 × 104 at 1530.783 nm and ∼7.32 × 104 at 1536.596 nm, respectively. The notch depth improvement over 20 dB has been demonstrated on the 5-μm-radius double-ring structure. The experimental results prove that the asymmetry of resonance splitting can be tuned by adjusting the distance between the inner-ring and outer-ring, as well as the waveguide width. The proposed work has potentials in the design and optimization of dual-concentric ring resonators.

• In order to satisfy the prerequisite of low-loss transmission in the optical field, we prepared silicon nitride racetrack microcavities with waveguide thicknesses up to 0.766 μm in a CMOS-compatible process. • We demonstrate a thermotropic phase shifter for hybrid 5CB liquid crystals. • With an external bias of 2 V, we achieve a phase modulation efficiency close to 329.7 pm/V at 1550.3 nm, and the corresponding V π L is calculated as 0.23 V∙cm. The 4-cyano-4′-pentylbiphenyl liquid crystals (5CB-LC) are thermotropic liquid crystals whose refractive index changes with increasing temperature. We demonstrate a silicon nitride phase shifter combining 5CB-LC with a racetrack resonator. By altering the molecular arrangement of the 5CB-LC with a heater, we find that this approach provides excellent phase modulation for the track resonator. The microelectrodes were prepared on a microcavity by a lift-off process in order to heat the 5CB-LC. By varying the voltage across the microelectrode, a 659.4 pm broadband phase shift was achieved at a central wavelength of 1550.29 nm using a voltage of 2 V, and the corresponding V π L is calculated as 0.23 V•cm. This research provides a solution for broadband wavelength phase modulation in silicon nitride heterogeneous integrated. [ABSTRACT FROM AUTHOR]

A highly compact optical modulator is proposed and analyzed. The modulator is based on the hybrid plasmonic waveguide platform. The structure of the modulator is built from silicon, silver, and electro-optical polymer layers. Hybrid plasmonic modes of symmetric and asymmetric natures excited in the structure were investigated. The symmetric mode is characterized by its lower propagation loss, so it was selected for the excitation of the device. The modulator's operation mechanism is based on the racetrack resonator configuration. Full three-dimensional electromagnetic analysis was performed around the 1.55-μm telecommunication wavelength. Different parameters such as the power coupling to the bus waveguide, the bend loss, the propagation loss, and the Q-factor of the resonances were studied in order to optimize the racetrack resonator design. The modulator is characterized by its extremely low energy consumption of 0.5 fJ/bit, high modulation depth of 10.5 dB, while the insertion losses were limited to 0.5 dB.

Featured Application: Tunable Optical Delay Line for Optical Sensing. For optical sensing or biomedical sensing where the light source usually has a stable and narrow linewidth, the design rule of the tunable optical delay line (ODL) can be different from the ODLs for optical communications and buffering. We present here a novel way to tune a racetrack resonator-based ODL by push–pull operation to stabilize the resonant wavelength. Full device simulation that accounts for the thermal tuning effect and the photonic characteristics of the whole integrated device is conducted to verify the characteristics of the tunable ODLs. With the simple racetrack resonator, the group delay can simply be tuned by changing the coupling coefficient of the resonator while the wavelength is stabilized by tuning the racetrack loop. A tuning of hundreds of picoseconds is achievable with a very compact device and small power consumption. [ABSTRACT FROM AUTHOR]

A refractive index sensor based on all-grating racetrack resonators is proposed and demonstrated in this paper. The structure consists of two subwavelength grating (SWG) waveguide-based racetrack resonators, a straight SWG bus waveguide and a SWG waveguide-based open racetrack. A sharp Fano resonance can be obtained by the mutual coupling of the two SWG racetrack resonators. Theoretical analysis and numerical simulations show that the introduction of grating can enhance the interaction between the sensor and the measured liquid analyte, thus increasing the sensitivity of the device. Calculated sensitivity of 500 nm/RIU around wavelength 1550 nm is achieved, and the figure of merit is 2000 RIU−1. The extinction ratio of this device can reach 21.53 dB. [ABSTRACT FROM AUTHOR]

A highly compact optical modulator is proposed and analyzed. The modulator is based on the hybrid plasmonic waveguide platform. The structure of the modulator is built from silicon, silver, and electro-optical polymer layers. Hybrid plasmonic modes of symmetric and asymmetric natures excited in the structure were investigated. The symmetric mode is characterized by its lower propagation loss, so it was selected for the excitation of the device. The modulator's operation mechanism is based on the racetrack resonator configuration. Full three-dimensional electromagnetic analysis was performed around the 1.55-μm telecommunication wavelength. Different parameters such as the power coupling to the bus waveguide, the bend loss, the propagation loss, and the Q-factor of the resonances were studied in order to optimize the racetrack resonator design. The modulator is characterized by its extremely low energy consumption of 0.5 fJ/bit, high modulation depth of 10.5 dB, while the insertion losses were limited to 0.5 dB. [ABSTRACT FROM AUTHOR]

Highlights • An integrated plasmonic sensor, using an MIM racetrack resonator structure, is designed and analyzed. • Refractive index and temperature sensitivity can be obtained as high as 4650 nm/RIU and 0.69 nm/°C, respectively. • The sensing performances are investigated numerically by the FDTD method. • It can potentially be applicable for biosensing applications such as hemoglobin concentration detection. Abstract In this paper, we designed a high-sensitivity plasmonic sensor using three-dimensional plasmonic metal–insulator–metal (MIM) waveguides and a racetrack resonator. By detecting the resonance wavelength, changes in the refractive index of the resonator can be sensed, on the basis of the linear relationship between these two parameters. The structure was numerically simulated by the finite-difference time-domain method (FDTD), and the results show that the refractive index and temperature sensitivity values can be obtained as high as 4650 nm per refractive index unit (RIU) and 0.33 nm /° C , respectively. We show that such improved sensitivity can be obtained by using a long lateral interaction length along the entire flat resonator sidewalls. The effects of radius and refractive index of racetrack resonator are studied from the sensing spectra to evaluate the sensitivity performance, as well. The proposed structure with such high sensitivity will be useful in bio-sensing that can provide a new possibility for the detection of biological parameters such as hemoglobin concentration. Furthermore, the applicability of our structure in the detection of hemoglobin concentration in three different blood groups is presented. [ABSTRACT FROM AUTHOR]

Optical biosensors are frontrunners for the rapid and real-time detection of analytes, particularly for low concentrations. Among them, whispering gallery mode (WGM) resonators have recently attracted a growing focus due to their robust optomechanical features and high sensitivity, measuring down to single binding events in small volumes. In this review, we provide a broad overview of WGM sensors along with critical advice and additional "tips and tricks" to make them more accessible to both biochemical and optical communities. Their structures, fabrication methods, materials, and surface functionalization chemistries are discussed. We propose this reflection under a pedagogical approach to describe and explain these biochemical sensors with a particular focus on the most recent achievements in the field. In addition to highlighting the advantages of WGM sensors, we also discuss and suggest strategies to overcome their current limitations, leaving room for further development as practical tools in various applications. We aim to provide new insights and combine different knowledge and perspectives to advance the development of the next generation of WGM biosensors. With their unique advantages and compatibility with different sensing modalities, these biosensors have the potential to become major game changers for biomedical and environmental monitoring, among many other relevant target applications.

In the last few years, strained silicon has been proposed as a potential electro-optic material, paving the way to the realization of ultrafast modulators which are compatible with the CMOS fabrication technology. The linear Pockels effect has been used for measuring the magnitude of the induced \chi ^(2) components, with values reaching hundreds of \textpm/V. Recently, it has been shown that these values could have been overestimated due to the contribution of free carriers to the electro-optic modulation. In this work, this hypothesis is validated by a series of experimental observations, which are performed on strained silicon racetrack resonators. These are fabricated with different waveguide widths and orientations. We use a low frequency (KHz) homodyne detection technique to monitor the electro-optic response of the devices. The results indicate that the modulation strength is not dependent on the waveguide geometry or direction. A lot of anomalies are encountered in the device response, which are not compatible with a modulation mechanism of \chi ^(2) origin. To this purporse, a theory based on the nonlinear injection of free carriers inside the waveguide is presented. This is able to account for all the observed anomalies. [ABSTRACT FROM PUBLISHER]

We present a theoretical sensitivity analysis of silicon-on-insulator quadruple Vernier racetrack resonators based on varying, one at a time, various fabrication-dependent parameters. These parameters include the waveguide widths, heights, and propagation losses. We show that it should be possible to design a device that meets typical commercial specifications while being tolerant to changes in these parameters. [ABSTRACT FROM AUTHOR]

In this paper, we present a new design of optical Finite Impulse Response (FIR) filter based on combination of multi-racetrack resonators realized with Silicon waveguides. Numerical investigations were carried out on the spectral response of the proposed filters design, in order to obtain FIR band-pass filter around the photonic carrier wavelength of 1.55 μm. The proposed FIR filter was fabricated using electron beam lithography (EBL). The device was preliminary experimentally examined by a combination of scanning electron microscopy (SEM) and atomic force microscopy (AFM). [ABSTRACT FROM AUTHOR]

We have numerically evaluated wavelength characteristics at telecommunication wavelengths by means of a doubleplasmonic-racetrack resonator using the finite-difference time domain method. We investigated the effect of the space between the two plasmonic racetracks of the resonator on the quality factor. The quality factor of the proposed structure is 57 when the space between two racetracks is 600 nm. The quality factor of a double-plasmonic-racetrack resonator of a dielectric-filled trench is 1.5 times greater than that of a single-plasmonic-racetrack resonator of an air-filled trench. The phase mismatch of the trench channel plasmon polaritons contributes to the quality factor of the double-plasmonicracetrack resonator. [ABSTRACT FROM AUTHOR]

A racetrack resonator, several hundred nanometers in size and composed of plasmonic waveguides is presented. The wavelength spectrum of the plasmonic racetrack resonator has been numerically evaluated by using finite-difference time-domain method. As compared to the conventional plasmonic ring resonator, the output light intensity of the proposed plasmonic racetrack resonator is greater by almost one order of magnitude. The cavity mode of the plasmonic racetrack resonator has also been investigated. [ABSTRACT FROM AUTHOR]

We present the design of a novel high-temperature superconductor double-sided racetrack resonator for a 13 C optimized nuclear magnetic resonance (NMR) transmitter/receiver coil. The coils operate in a 21.1 T magnet and accommodate a 3 mm × 6.2 mm cross-section rectangular sample tube. The design includes the incorporation of revised finger lengths to improve the homogeneity of current density across the fingers, a new laser trimming approach for adjusting the resonance frequency, and improved ability to shift higher-order modes for suitability in 1 H/ 13 C NMR probes. Resonator design methodology, simulations and experimental results are presented.

Optical Racetrack resonator waveguide which is based on silicon material possesses a good ability in sensing different materials, and urea is one of them has been simulated using a Finite different time-domain (FDTD) method. The drop port of racetrack possessed a higher spectrum shift of 7 × 10−3 nm. Urea was considered as the upper cladding in the throughput, resulting in the generation of the Q factor and full width at half maximum (FWHM) with the highest frequency. Power changes posed a significant effect on the upper cladding material. In the time domain, throughput showed the maximum time delay, resulting in 4.9 fs, which was a unit for time difference generated by urea and H 2 O materials as cladding. [ABSTRACT FROM AUTHOR]

A wavelength selective optical switch is developed based on a high-Q racetrack resonator making use of the large thermooptic coefficient of silicon. The racetrack resonator was fabricated using a silicon-on-insulator (SOI) single-mode rib waveguide. The resonator shows a high Q factor of 38 000 with spectral sidelobes of 11 dB down and can be thermooptically scanned over its full free-spectral range applying only 57 mW of electrical power. A low power of 17 mW is enough to tune the device from resonance to off-resonance state. The device functions as a wavelength selective optical switch with a 3-dB cutoff frequency of 210 kHz. [ABSTRACT FROM PUBLISHER]

In this paper, a new type of resonant cavity sensor based on diamond is proposed. Using the single straight-racetrack structure, the effective refractive index of the core layer is changed by the external factors, which can change the optical signal intensity of the output spectrum. According to the variation of the output spectrum with the different effective refractive index, the COMSOL and MATLAB software are used to simulate the amplitude attenuation factor and the transmission coefficient of the resonator. When the attenuation factor is 0.981 and the transmission coefficient is 0.99, the simulation results reveal that the effective refractive index change is Δ n eff ≈ 1.1 × 10−4, the normalized output light intensity change is Δ I 0 ≈0.87 and the sensitivity of the optimized racetrack resonant cavity sensor is 7909.09dB/RIU. In the detection system with the signal-to-noise ratio of 30 dB, the detection limit of the sensor is 3.79 × 10−7 RIU, and the quality factor Q can reach 105, improving the characteristics of the single straight-racetrack resonant cavity sensor. Finally, the interface bonding and preparation method of the diamond core layer and substrate are described. • The diamond-silica waveguide can reduce the transmission loss. • The diamond has special characteristics of biochemical sensing. • The diamond can improve the sensitivity of the sensor. • The racetrack resonator enhances the coupling efficiency by the ring - straight structure. • The single straight waveguide increases the detection limit of the sensor. [ABSTRACT FROM AUTHOR]