Waveguide Resonator Research Articles

Superconducting Quantum Circuits Based on 2D Materials

Transmon-type superconducting qubits have become a popular platform for quantum computing due to their robust qubit coherence properties. In recent years, different types of materials have been searched to replace the Al2O3 tunnel barrier in conventional Al-based Josephson junctions, in order to explore new functions of qubits utilizing the distinct nature of the chosen materials. In this report, we introduce our works involving using Weyl semimetals and graphene as a component in Josephson junctions for qubit designs and coupling to coplanar waveguide (CPW) resonators. We fabricate a MoTe2 transmon and investigate whether it exhibits topological properties by tuning the resonator frequency with magnetic flux. Next, we introduce a graphene gatemon, in which the gate-tunability of resonator frequency has been demonstrated and the two-tone spectroscopy has shown a qubit state transition.

Active Differential Fiber Coupled Plasmon Waveguide Resonance Sensor Based on the Mode Competition Effect

We proposed an active differential intensity (DI) fiber coupled plasmon waveguide resonance (CPWR) sensor based on the mode competition effect in the C-band, aiming to enhance the sensitivity. The sensing head is a fiber probe with a sensing layer of ITO/Au/ITO/TiO2 film, enabling the excitation of CPWR in the C-band. The narrow CPWR spectrum allows DI interrogation by tracking the intensity of light at two wavelengths. The fiber probe is inserted into a dual-wavelength fiber laser to adjust the intra-cavity loss at the two lasing wavelengths. By using the differential modulation of the reflectivity from the refractive index variations, the mode competition effect is triggered. The powers at two lasing wavelengths change oppositely, enlarging the power difference and then resulting in enhanced sensitivity. The average sensitivity is up to 5702 dB/RIUs, which is 10 times higher than that of conventional DI interrogation. The sensitivity enhancement mechanism based on the mode competition effect provides a new technical approach for enhancing the sensitivity of DI SPR sensors.

Hybrid laser diode with ultrawide wavelength-tunable range using curved directional couplers.

Wavelength-tunable laser diode with a wide tuning range is required for optical communication systems and optical sensing. External cavity laser diodes with silicon-photonic wire waveguides and ring resonators have small footprint because of high refractive index contrast between Si. However, power coupling efficiency κ of conventional straight directional coupler between ring and bus waveguides have large wavelength dependence, which lowers tunable range. In this study, we demonstrate a hybrid wavelength-tunable laser diode using curved directional couplers, whose wavelength dependence on κ is low. The wavelength-tunable range record of 120.9 nm has been achieved. In addition, curved directional couplers are tolerant of waveguide width fabrication error.

Lithium niobate waveguide squeezer with integrated cavity length stabilisation for network applications.

We report a titanium indiffused waveguide resonator featuring an integrated electro-optic modulator for cavity length stabilisation that produces close to 5 dB of squeezed light at 1550 nm (2.4 dB directly measured). The resonator is locked on resonance for tens of minutes with 70 mW of SH light incident on the cavity, demonstrating that photorefraction can be mitigated. Squeezed light production concurrent with cavity length stabilisation utilising the integrated EOM is demonstrated. The device demonstrates the suitability of this platform for squeezed light generation in network applications, where stabilisation to the reference field is typically necessary.

Design of Nonreciprocal Filtering Antenna Using Spatio-Temporal Modulated SIW Resonators

This article reports on, for the first time, the design of nonreciprocal filtering antennas using spatio-temporal modulated substrate integrated waveguide (SIW) resonators. It consists of two SIW cavities and a half-mode SIW (HMSIW) cavity, which is designed as the last-stage resonator and the radiator. By integrating time-modulated capacitors on the surface gaps of the three cavities, the nonreciprocal radiation patterns in transmission and reception modes are achieved at the same operating frequency. Three radiation nulls are generated due to the cross-coupling in the time-modulated network and source-load coupling. The theoretical analysis of the co-designed nonreciprocal SIW filtering antenna is detailed, along with methods for its co-simulations and measurements. For the proof-of-concept demonstration, a nonreciprocal SIW filtering antenna operating at 2.4 GHz is designed and fabricated. The measured 10-dB bandwidth and peak gain are 1.7% and 2.6 dBi, respectively. The measured realized gains at transmission and reception show that the reverse isolation is greater than 11 dB within a bandwidth of 30 MHz. The frequency selectivity values are 756 and 368 dB/GHz at the left and right sides of the passband, respectively.

Alternative Approach to Design and Optimization of High-Q Ring Resonators for Membrane-Free Acoustic Sensors.

Membrane-free acoustic sensors based on new principle and structure are becoming a research hotspot, because of many advantages, e.g., their wide bandwidth and high sensitivity. It is proposed that a membrane-free acoustic sensor employs a semi-buried optical waveguide ring resonator (SOWRR) as a sensing element. Using air as the upper cladding medium, the excited evanescent field in the air cladding medium would be modulated by acoustic wave. On this basis, the acoustic sensing model is established. Taking high Q factor and resonance depth as design criteria, the optimal design parameters are given. The optimal values of the air/SiO2: Ge/SiO2 waveguide resonator length and coupling spacing are obtained as 50 mm and 5.6 μm, respectively. The Q factor of the waveguide resonator of this size is as high as 8.33 × 106. The theoretical simulation indicates that the frequency response ranges from 1 Hz to 1.58 MHz and that the minimum detectable sound pressure is 7.48 µPa using a laser with linewidth of 1 kHz. Because of its advantages of wide bandwidth and high sensitivity, the membrane-free sensor is expected to become one of the most promising candidates for the next-generation acoustic sensor.

Ridge resonators with compact guided mode coupling.

Ridge resonators are a recently introduced integrated photonic circuit element based on bound states in the continuum (BICs) which can produce a single, sharp resonance over a broad wavelength range with high extinction ratio. However, to excite these resonators, a broad beam of laterally unbound slab mode is required, resulting in a large device footprint, which is not attractive for integrated photonic circuits. In this contribution, we propose and numerically validate a guided-mode waveguide structure that can be analogue to the BIC-based ridge resonators. Our simulations show that the proposed guided-mode waveguide structure can produce resonances with similar characteristics, yet with a significantly reduced footprint. Furthermore, we investigate the influence of the resonator's dimensions on the bandwidth of the resonance, demonstrating that resonances with Q-factors from low to very high (> 10000) are feasible. We believe that the reduced footprint and ability to design filters systematically make the guided-mode waveguide resonators an attractive photonic circuit component with particular value for foundry fabricated silicon photonic circuits.

Resonant Waveguide Grating Biosensors Based on Label-free Optical Principle

Label-free optical biosensors are powerful tools for the real-time monitoring of both molecular and cellular-scale interactions. Resonant waveguide grating biosensors are based on the detection of refractive index changes induced by molecular interactions and/or cell mass redistributions. The Epic BenchTop and Epic Cardio are two biosensors with high sensitivity and throughput that offer excellent potential for life science research. Both instruments are suitable for cell-based and biochemical assays. In this paper, I describe the principles of operation and performance of the Epic BenchTop and Epic Cardio label-free waveguide grating biosensors and discuss their applications in various research areas.

Plasmon waveguide resonance for tag-free selective Raman detection of biochemical composition in single-cell

Highly selective and non-radioactive Raman detection of the biochemical composition of living single-cell is a key method of evaluating complex biological reaction processes. Conventional selective Raman detection relies on tagging technology to separate the Raman signals from the different cell structures, which involves both a complex synthesis process and a long incubation time. To address this, we present a tag-free Raman selective detection with plasmon waveguide resonance (PWR). PWR biochemical composition detection exhibits a high longitudinal spatial resolution based on the surface and bulk response of low- and high-order modes. Hence, compared with conventional selective Raman detection with tagging technology, it can distinguish Raman signals from cell structures more effectively, without an antibody and label, providing effective tag-free selective detection with high spatial resolution. In addition, rapid selective detection can be achieved using the PWR Raman scattering biochemical composition detection, thereby improving the stability of a living single cell without a long incubation time. Moreover, the electromagnetic field of the evanescent field can be significantly amplified by the proposed PWR biochemical composition detection, which also enhances the Raman signal with high sensitivity without requiring a complicated fabrication process. The proposed PWR has potential applications in drug release and living-cell analysis.

Investigation of the deposition of α-tantalum (110) films on a-plane sapphire substrate by molecular beam epitaxy for superconducting circuit

Polycrystalline α-tantalum (110) films deposited on the c-plane sapphire substrate by sputtering are used in superconducting qubits nowadays. However, these films always occasionally form other structures, such as α-tantalum (111) grains and β-tantalum grains. To improve the film quality, we investigate the growth of α-tantalum (110) films on the a-plane sapphire substrate under varying conditions by molecular beam epitaxy technology. The optimized α-tantalum (110) film is a single crystal, with a smooth surface and atomically flat metal–substrate interface. The film with thickness of 30 nm shows a Tc of 4.12 K and a high residual resistance ratio of 9.53. The quarter wavelength coplanar waveguide resonators fabricated with the 150 nm optimized α-tantalum (110) film exhibit intrinsic quality factor of over one million under single photon excitation at millikelvin temperature.

Hybrid quantum systems with high-T_c superconducting resonators

Superconducting microwave resonators are crucial elements of microwave circuits, offering a wide range of potential applications in modern science and technology. While conventional low-T_c superconductors are mainly employed, high-T_c cuprates could offer enhanced temperature and magnetic field operating ranges. Here, we report the realization of textrm{YBa}_2textrm{Cu}_3textrm{O}_{7-delta } superconducting coplanar waveguide resonators, and demonstrate a continuous evolution from a lossy undercoupled regime, to a lossless overcoupled regime by adjusting the device geometry, in good agreement with circuit model theory. A high-quality factor resonator was then used to perform electron spin resonance measurements on a molecular spin ensemble across a temperature range spanning two decades. We observe spin-cavity hybridization indicating coherent coupling between the microwave field and the spins in a highly cooperative regime. The temperature dependence of the Rabi splitting and the spin relaxation time point toward an antiferromagnetic coupling of the spins below 2 K. Our findings indicate that high-Tc superconducting resonators hold great promise for the development of functional circuits. Additionally, they suggest novel approaches for achieving hybrid quantum systems based on high-T_c superconductors and for conducting electron spin resonance measurements over a wide range of magnetic fields and temperatures.

Real-time free spectral range measurement based on a correlated resonance-tracking technology.

In this paper, we present a real-time measurement technology for the free spectral range (FSR) of an ultrahigh-aspect-ratio silicon nitride (Si3N4) waveguide ring resonator (WRR). Two different correlated resonant modes were tracked by two optical single-sideband frequency-shifted lights to eliminate interference noise in the Pound-Drever-Hall error signals. A relative precision of 0.1474 ppm was achieved for a 35 mm WRR with FSR = 1,844,944.5 kHz and finesse (F) = 13.2. Furthermore, a cross-correlation of 0.913 between FSR-calculated and thermistor-measured temperatures indicated a high correlation between the real-time FSR and room temperature. We believe this technology is currently the best way to realize low-finesse (F < 50) real-time FSR measurements in the GHz range.

Fano Resonance Based on Coupling Between Nanoring Resonator and MIM Waveguide for Refractive Index Sensor

Fano Resonance Based on Coupling Between Nanoring Resonator and MIM Waveguide for Refractive Index Sensor

Selective Gain in a Periodic Array of Nano-organic Light-Emitting Diodes.

We report nanoscale organic light-emitting diodes (OLEDs) arranged periodically into a large-area array, which produces an amplified emission with a selected spectrum in a narrow band. These nano-OLEDs share a common active layer of super yellow light-emitting PPV copolymer (SY-PPV), which acts both as a waveguide and as a gain channel for the light-emitting signals. The periodic structure supplies Bragg-like diffraction of the emission from SY-PPV under electrical excitation so that the electroluminescence signal is coupled into and confined in the SY-PPV waveguide. During propagation, the waveguide resonance mode interacts with the nano-OLED region and gains amplification. Both the waveguide resonance mode and the output coupling process have strong spectral selectivity, so that the amplification is observed within a spectrum as narrow as 32 nm at FWHM. Such a nano-OLED design not only defines a new scheme of nano-OLEDs, but also proposes potential approaches for electrically pumped organic lasers.

Flexible dispersion engineering using polymer patterning in nanophotonic waveguides

We demonstrate the engineering of waveguide dispersion by lithographically patterning the polymer cladding on silicon nitride waveguide resonators. Both normal and anomalous dispersion, ranging from − 462 to 409 ps/nm/km, can be achieved for the same waveguide dimension within an integrated photonic chip. In the meantime, this simple process shows no impact on the waveguide loss and the quality factor of the waveguide resonators, offering flexibility in tailoring designable dispersion for a universal photonic platform. In addition, by adjusting the coverage ratio of cladding, relatively low dispersion (≈ − 130 ps/nm/km) is also demonstrated in the same waveguide resonator, yielding the potentials for zero-dispersive waveguide resonators by a proper coverage ratio of the polymer cladding.

Two-photon 3D printing diaphragm-integrated ring waveguide coupler for ultrasound detection.

We demonstrate a diaphragm-integrated ring waveguide coupler fabricated by the two-photon direct laser wring technique as an ultrasonic sensor, which is integrated on an optical fiber tip. The device consists of a micro-ring waveguide with a diameter of 5 µm functionalized as an optical fiber tip light reflection mirror and a straight waveguide connecting a diaphragm. The evanescent field coupling can be realized between the two waveguides, and the coupling efficiency can be changed due to the variation of the coupling gap induced by ultrasound. Accordingly, the light reflection can be changed. Based on the plate vibration theory, the vibration frequency can be changed through optimizing the diaphragm size. The experiments show that the device exhibits a high sensitivity and low noise equivalent acoustic signal level of 1.07 mPa/Hz1/2 at 100 kHz, which has great potential in various acoustic wave sensing applications.

Single- and two-photon absorption induced all-optical control of gallium selenide integrated silicon nitride photonic devices in the 700–800 nm wavelength range

In this work, we report single- and two-photon absorption (TPA) induced transmission and resonance modulation in a multilayer gallium selenide (GaSe) integrated silicon nitride (Si3N4) waveguide and ring resonator operating in the 700–800 nm wavelength range. Intensity dependent saturable absorption at low optical powers followed by TPA at higher power levels in GaSe integrated Si3N4 waveguides is observed at 785 nm pulsed laser excitation. A TPA coefficient of 0.117 cm/GW for the GaSe–Si3N4 composite waveguide and a three-photon absorption coefficient of 7.876 × 10−6 cm3/GW2 for the bare Si3N4 waveguide are extracted from intensity dependent transmission measurements. The single-photon absorption process induced by a blue laser incident on the multilayer GaSe transferred on top of the Si3N4 ring resonator is used for all-optical resonance tuning through the free-carrier refraction effect. A strong blue shift of the resonance by ∼12.3 pm/mW combined with resonance broadening is observed due to the free-carrier induced refractive index and absorption modulation. The TPA in the GaSe integrated Si3N4 ring resonator is also shown to result in a blue shift of the resonances excited using a 785 nm pulsed laser. This work demonstrates the all-optical control of 2D material integrated Si3N4 guided-wave structures operating in the shorter near-infrared wavelength range with potential applications in integrated quantum photonics, miniaturized sensing devices, and biomedical imaging.

Detection of underwater low frequency sound wave based on SiO2 optical waveguide resonator

Detection of underwater low frequency sound wave based on SiO2 optical waveguide resonator

Detecting acoustic chirality with matched metamaterial vortex wave antennas.

Acoustic communications often have limited data rates because of the intrinsically low frequencies. Exploring new spatial modes to increase data bandwidth at fixed frequency is a possible solution to this problem. Here, we demonstrate acoustic wave chirality transmission between two reciprocal metamaterial vortex wave antennas, generating and sensing transmitted acoustic wave chirality through the sub-wavelength geometry of the system. By adding an acoustic leaky wave surface to a ring resonator waveguide, acoustic vortex waves with positive or negative integer mode chirality are independently radiated and detected using a small number of microphones. Through computational simulation and experimental verification, using three-dimensional printed waveguides, we show that the vortex mode chirality can be transferred between two opposing acoustic vortex wave antennas across a small unguided air gap. We also show that emission into an external waveguide can provide long distance data transmission. This demonstrates the first use of metamaterial vortex wave antennas as chiral, mode multi-channel data transceivers.

Tunable nanolaser based on quasi-BIC in a slanted resonant waveguide grating.

Nanolasers based on quasi-bound states in the continuum (quasi-BIC) have attracted much attention owing to their unique optical properties providing strong light-matter interaction. Although various quasi-BIC lasers have been designed, so far, few efforts have been devoted to their tunability in wavelength. Here we propose an approach to employ quasi-BIC and guided mode in a slanted resonant waveguide grating. The proposed structure supports a specially designed eigenmode localized both in the grating and in the 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) layer, which allows it to obtain lasing emission as well as the ability to tune the wavelength. Numerical simulation results show that the threshold is approximately 7.75 μJ/cm2 with the tuning range being 28 nm. In addition, we show that the distribution of the lasing intensity between the transmission and reflection directions can be controlled by changing the parameters of the structure. This work shows good potential of combining quasi-BIC with guided mode to design tunable nanolaser.