Tunable Ring Research Articles

A tunable open ring coupling structure and its application in fully tunable bandpass filter

AbstractThis letter presents a novel tunable coupling structure to simplify the design complexity of the miniaturized fully tunable filter by using open ring and varactors. Based on the proposed novel tunable coupling structure, a fully tunable bandpass filter is implemented with independently tunable operating frequency and bandwidth. The tunable resonator and tunable coupling structure can be easily combined to improve Out-of-band suppression performance. The design procedure of a fully tunable bandpass filter consists of five tunable cavities and tunable coupling rings is also proposed. A prototype of the proposed fully tunable filter is built to verify the design experimentally. Good agreement between simulated and measured results is obtained.

Resonant Frequency and Bandwidth Tunable Ring Resonator Using GaAs FET SPST Switches

Resonant Frequency and Bandwidth Tunable Ring Resonator Using GaAs FET SPST Switches

Pneumatically tunable microwave split ring resonators

We have investigated the operation of a coupled system of double split ring resonators (SRRs) to demonstrate the tunability by changing its physical layout. A pneumatic system is proposed to dynamically shift the structural arrangement of the coupled SRRs in response to the incident electromagnetic wave. It is executed by manipulating the lateral placement of the levitated bottom ring relative to the static ring in the top layer using various levels of pneumatic force. We reduced the electromagnetic interference by avoiding metallic components and improved the stability through the contactless operation. The proposed pneumatic system uses only the air to modulate the operational frequency of the coupled SRRs. Both the simulation and the experiment have shown the transition between the quasi-edge coupled and the broad-side coupled modes of the double SRRs shift the resonance frequency over 28% around 3.0 GHz. This pneumatic implementation brings a new method of reconfigurable SRRs.

Tunable dual-wavelength ytterbium-doped fiber ring laser based on a Sagnac interferometer

A tunable dual-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer is proposed and experimentally demonstrated. Due to a broad gain bandwidth of ytterbium-doped fiber, a tuning range of 17.9 nm for single-wavelength lasing output and 8.4 nm for dual-wavelength lasing have been achieved with side-mode suppression ratio higher than 38 dB. In addition, experimental results indicate that the lasing output has favorable wavelength and power stability with the maximum wavelength shift and the peak power fluctuation less than 0.06 nm and 0.94 dB, respectively. Such a wide tunable ytterbium-doped fiber ring laser around the wavelength of 1 µm with simple structure has potential applications in metrology, medical treatments or laser cooling, where the laser wavelength need adjusted accurately.

Highly tunable and broadband graphene ring modulator

We propose a ring modulator based on few-layer graphene with large tunability and modulation efficiency. Compared with monolayer graphene, a few-layer graphene structure can enhance the tunability linearly. In the proposed structure, the shift of resonance wavelength can be enlarged to 20.3 nm, implying the proposed modulator can achieve the bandwidth of 100 GHz. In addition, a large extinction ratio of 15.5 dB and a good temperature tolerance of 45 K can be obtained in this modulator.

FinFET CMOS logic gates with non-volatile states for reconfigurable computing systems

A series FinFET based non-volatile logic gates with multiple logic functions defined by embedded non-volatile states are proposed for the first time and demonstrated in advanced CMOS technology platform. The device channels in the proposed CMOS logic gate is controlled by a metal floating gate coupled by slot contacts uniquely available in the FinFET process employed in this study. The new logic gate with non-volatile states only enable reconfiguration ability in a Boolean computing unit at a gate level aimed for adaptive and specialized systems in the AI era. Furthermore, the extended applications in tunable ring oscillators for multi-functional IOT modules are successfully demonstrated in this study.

Wavelength tunable noise-like pulse generation from an erbium-doped fiber laser

We demonstrated a wavelength tunable mode-locked erbium-doped all-fiber ring cavity laser with the nonlinear polarization rotation technique. By adjusting the polarization states of the ring cavity, the laser can deliver noise-like pulses with wavelength tunable from 1568 nm up to 1610 nm. For a 1610 nm center wavelength, we could obtain an output with a pulse repetition rate of 1.67 MHz and pulse energy of 19.2 nJ. In addition, as we know, the 1610 nm is the reported longest wavelength for noise-like pulses operation with erbium’s gain in the L-band.

Tunable single-wavelength erbium-doped fiber ring laser using a large-core fiber

In this paper, a tunable single-wavelength erbium-doped fiber ring laser is proposed. A novel fiber filter based on a large-core fiber is developed for suppressing the mode competition in erbium-doped fiber lasers (EDFLs). Under the pump power of 250 mW, single-wavelength lasing output is implemented with a side mode suppression ratio (SMSR) higher than 55 dB. By adjusting the curvature applied on the large-core fiber, stably tunable single-wavelength lasing output within the wavelength range from 1552.4 nm to 1563.2 nm is obtained with a 3 dB linewidth of 0.2 nm. Furthermore, the wavelength shift and peak power fluctuation are controlled within 0.02 nm and 0.5 dB by monitoring the lasing output with an interval of 6 min in one hour, respectively. A contrast experiment of a laser without tapering LCF is carried out to examine the importance of the taper in LCF-based filter. Experimental results demonstrate that the side modes of the lasing output can be effectively suppressed and thus SMSR can be improved from 41 dB to 58 dB by using a taper.

Selectable and stable C-band multi-wavelength ring cavity erbium-doped fiber laser employing Sagnac loop and tunable filter

A tunable C-band multi-wavelength ring cavity erbium-doped fiber laser based on a Sagnac loop and tunable filter was developed and experimentally demonstrated. In this fiber laser, a Sagnac loop fabricated using a 3 × 3 coupler and polarization-maintaining fiber is employed as the comb filter. A 4-m-long C-band and 0.8-m-long L-band erbium-doped fiber serve as the gain medium, and a tunable filter connected to the 3 × 3 coupler is used for laser wavelength adjustment. In the experiment described herein, switchable single-wavelength lasing was realized from 1528.6 nm to 1562.5 nm in 4.9-nm intervals, and the peak power variation was less than 1.12 dB during 10 min of scanning at 26 °C. In addition, switchable double- and triple-wavelength lasing were realized, for which the tunable wavelength scope was 28.6 nm and 19.9 nm, and the power fluctuation was less than 1.14 dB and 1.39 dB, respectively.

Compound comb filter based on Sagnac interferometer and phase shifted fiber Bragg grating using for tunable and switchable fiber ring laser

A kind of stable, switchable and tunable erbium-doped fiber ring laser based on a Sagnac interferometer (SI) is presented and experimentally demonstrated. The SI is composed of a section of an elliptical-core spun fiber sandwiched between two polarization controllers (PCs) in a Sagnac loop. The proposed compound comb filter, which consists of an SI cascaded with a phase shifted fiber Bragg grating, is developed to suppress the mode competition in the laser oscillation. By adjusting the PCs, a stable and tunable single-wavelength lasing output can be achieved. The optical signal-to-noise ratio (OSNR) is better than 40 dB, and the 3 dB linewidth is less than 15 pm. Furthermore, stable dual-wavelength lasing outputs with different wavelength intervals of 0.132 nm, 0.336 nm and 0.418 nm can also be obtained by carefully adjusting the PCs. The power difference between the two lasing peaks is less than 2 dB, and the OSNR is about 50 dB.

Convertible Dark Pulse and Bright Pulse Fiber Ring Laser by Adjusting the Polarization

A wavelength tunable, dark pulse, and bright pulse-switched dual-wavelength fiber ring laser is reported. Through adding high nonlinear optical fiber as a nonlinear medium in the fiber ring cavity, the double-wavelength dark-bright pulse pair can be formed. The separation of dark-bright pulse pair can be achieved by polarization beam splitter. The dark pulse and bright pulse with orthogonal polarization correspond to different wavelengths, respectively. Then, via tunable optical filter and polarization controller to filter out the wavelength we need and adjust the polarization, we achieved the interconversion of dark pulse and bright pulse in the same wavelength and the tunableness of wavelengths of dark pulse and bright pulse in our laser.

Tunable multiwavelength fiber laser based on a θ-shaped microfiber filter

We propose and experimentally demonstrate a flexibly tunable multiwavelength fiber ring laser based on a θ-shaped microfiber filter in conjunction with an erbium-doped fiber amplifier. The stable operation of the multiwavelength lasing is successfully achieved at room temperature, with the peak power fluctuation less than 0.519 dB. By micro-adjusting the cavity length of the filter, the channel spacing can be independently tuned within the gain range of the optical amplifier. We have achieved 0.084 nm-spacing 48 channel, 0.147 nm-spacing 25 channel, 0.190 nm-spacing 20 channel and 0.302 nm-spacing 15 channel lasing wavelengths at room temperature.

“Point‐and‐Shoot” Synthesis of Metallic Ring Arrays and Surface‐Enhanced Optical Spectroscopy

AbstractThe realization of optically active structures with direct‐write printing has been challenging, particularly in spatially constrained microfluidic devices which are essential for point‐of‐care (POC) applications. The existing techniques are limited by resolution, accessibility, and multistep fabrication constraints. “Point‐and‐shoot” strategies to achieve site‐specific fabrication of optically active Ag rings and on‐demand targeted surface‐enhanced optical spectroscopy are reported. Stable microbubbles over an Au nanoisland (AuNI) substrate are generated using a continuous‐wave laser at low power (≈0.5 mW µm−2). Analytical modeling of bubble generation process substantiates the evolution of ring morphology and its power dependence. The tunable Ag rings exhibit surface plasmon resonances in the mid‐IR regime from 3.8 to 4.6 µm, while the AuNI shows visible region response. The Ag ring over the AuNI imparts intensified surface‐enhanced Raman spectroscopy (SERS) activity owing to amplified hot spots at Ag ring/AuNI interface. As an example, SERS and surface‐enhanced infrared spectroscopy of rhodamine 6G, crystal violet, and 2,4,6‐trinitrotoluene molecules, respectively, are demonstrated. The applicability of this technique to perform in situ fabrication and SERS sensing in microfluidic channels is shown. Using a simple in situ approach toward optically active structures, our technique can synergize multiple surface‐enhanced optical spectroscopies to facilitate POC applications.

Broadband terahertz modulator based on graphene metamaterials

Tunable complementary split ring resonators (CSRRs) based on monolayer graphene are presented in terahertz regime. By applying different gate voltage, the Fermi level and optical conductivity of monolayer graphene pattern can be changed. Here, we employ a numerical simulation to study the interaction of light with graphene CSRRs. The results indicate that the extinction in transmission becomes stronger, and the resonance frequency presents blue shift with higher Fermi level of the graphene pattern. Three pronounced resonant peaks appear which can be modulated dynamically in the range of 1-2THz and 3-7THz, and realizing dynamic broadband terahertz modulation, the modulation depth exceeds 85% at all three resonant peaks, the highest modulation depth reaches 98.8% at 7.47THz.

A narrow linewidth tunable single longitudinal mode Ga-EDF fiber laser

A tunable ring cavity single longitudinal mode (SLM) fiber laser incorporating Gallium-Erbium co-doped fiber (Ga-EDF) gain medium and several mode filtration techniques is demonstrated. With Ga-EDF, high emission power was accorded in short fiber length, allowing shorter overall cavity length and wider free spectral range. Tunable bandpass filter, sub-ring structure, and cascaded dissimilar fiber taper were utilized to filter multi-longitudinal modes. Each of the filter mechanism was tested individually within the laser cavity to assess its performance. Once the performance of each filter was obtained, all of them were deployed into the laser system. Ultimately, the 1561.47 nm SLM laser achieved a narrow linewidth laser, optical signal-to-noise ratio, and power fluctuation of 1.19 kHz, 61.52 dB and 0.16 dB, respectively. This work validates the feasibility of Ga-EDF to attain a stable SLM output in simple laser configuration.

Axicon-based Bessel beams for flat-field illumination in total internal reflection fluorescence microscopy.

Total internal reflection fluorescence microscopy (TIRF-M) provides low-invasive high-contrast surface imaging with optical sectioning of typically 100-200nm. Thus, TIRF-M has become an established tool for imaging surfaces, including cell membranes. For TIRF-M, a homogenous evanescent field of excitation over the whole field of view is generally desired for quantitative microscopy; however, this is not necessarily straightforward to generate with Gaussian beams. In recent years, several improvements on TIRF-M have been developed that have addressed non-uniform scattering fringes and other artifacts. Here, we introduce a cost-effective TIRF setup with a very low degree of complexity and no moving parts, which provides a flattop-like excitation profile. The setup uses a tunable laser ring zoom focus system to generate a full 360° TIRF illumination. Two axicon lenses and one focus lens allow for generation and control of the ring diameter to tune the TIRF excitation angle. We show that 360° laser illumination in combination with a radial polarizer will generate an evanescent Bessel-beam excitation field that exhibits a flattop intensity over an extended part of the field of view, and demonstrate the advantages of this axicon-based Bessel beam illumination for live-cell imaging.

Dynamic covalent chemistry enables formation of antimicrobial peptide quaternary assemblies in a completely abiotic manner.

Naturally occurring peptides and proteins often use dynamic disulfide bonds to impart defined tertiary/quaternary structures for the formation of binding pockets with uniform size and function. Although peptide synthesis and modification are well established, controlling quaternary structure formation remains a significant challenge. Here, we report the facile incorporation of aryl aldehyde and acyl hydrazide functionalities into peptide oligomers via solid-phase copper-catalysed azide-alkyne cycloaddition (SP-CuAAC) click reactions. When mixed, these complementary functional groups rapidly react in aqueous media at neutral pH to form peptide-peptide intermolecular macrocycles with highly tunable ring sizes. Moreover, sequence-specific figure-of-eight, dumbbell-shaped, zipper-like and multi-loop quaternary structures were formed selectively. Controlling the proportions of reacting peptides with mismatched numbers of complementary reactive groups results in the formation of higher-molecular-weight sequence-defined ladder polymers. This also amplified antimicrobial effectiveness in select cases. This strategy represents a general approach to the creation of complex abiotic peptide quaternary structures.

Over 70 nm broadband-tunable Yb-doped fiber pulse laser based on trilaminar graphene

An all-fiberized tunable Q-switched ring cavity laser was demonstrated to exploit a trilaminar graphene saturable absorber. Wavelength-tunable operation was achieved using a narrow-bandwidth tunable filter with a tunable range spanning from 1020.0 nm to 1090.4 nm. To the best of our knowledge, this is the widest tunable range for a Q-switched fiber laser in the 1 µm range. The linewidth of the emitting wavelength is less than 0.2 nm over the whole tunable range. This wavelength-tunable Q-switched pulse laser could provide a simple, low-cost and convenient light source for practical use.

III–V/Si Vernier-Ring Comb Lasers (VRCLs)

We present a novel reconfigurable comb laser design that enables channel sparing, and demonstrate its functionality in a III–V/Si external cavity configuration. The laser is comprised of a single shared tunable Si ring mirror Vernier-paired with an array of tunable channel ring filters each coupled to their respective reflective semiconductor optical amplifier. This comb laser is not only tunable, capable of shifting all comb lines together, but it is flexible, able to change the spacing of channels in the comb within a fixed grid defined by the ring mirror. This flexibility results in features not previously demonstrated in a comb, such as mixed channel spacing and channel sparing capability. This is a practical candidate for flexible, scalable wavelength division multiplexed links targeting the next generation of data centers for the cloud.

Design and Experimental Study of Tunable Fiber Ring Laser of C+L Band

A tunable fiber ring laser based on L band EDFA (erbium-doped fiber amplifier) was proposed. It has high signal-to-noise ratio and wide tuning range. The influence factor of the tuning range and the time delay of relaxation oscillation were studied. And the FFP-TF(Fabry-Perot tunable filter) was used as a wavelength selector to produce tunable laser. Experiments show that by using appropriate time-delay and auto-adjusting the intra-cavity loss, the signal-to-noise ratio can be increased and the tunable range can be broadened to C+L band.