High-performance and scalable polarization splitter-rotator based on photonic crystal nanobeam reflection.

The polarization splitter-rotator (PSR) is a key device for polarization processing in polarization diversity systems, which has wide applications in achieving polarization independence and mixed multiplexing. However, it remains a significant challenge to simultaneously achieve a better balance in bandwidth, crosstalk (CT), polarization extinction ratio (PER), and compact footprint of the PSR. In this article, a photonic crystal nanobeam (PCN) structure is introduced to PSR for large bandwidth and compact size, with a device length of only 104 µm.

Flexible and reconfigurable integrated optical filter based on tunable optical coupler cascaded with coupled resonator optical waveguide.

Reconfigurable optical filter can satisfy diverse filtering requirements in different application scenarios and shorten development cycle. However, it is still challenging to achieve multi-functional filtering richness with high performance. Here, based on a tunable optical coupler cascaded with a coupled resonator optical waveguide (CROW), a highly flexible and reconfigurable integrated optical filter is proposed and demonstrated on the low-loss silicon nitride platform.

Continuously tunable silicon waveguide optical switched delay line based on grating-assisted contradirectional coupler.

The integrated optical delay line plays a crucial role in microwave photonic chips. Continuous tunability is a growing trend in filtering and beamforming techniques of microwave photonics. Based on the silicon platform, we present and experimentally demonstrate an integrated continuously optical tunable delay line (OTDL) chip, which contains a 4-bit optical switched delay line (OSDL) and a thermally tunable delay line based on grating-assisted Contradirectional coupler (CDC).

Low loss, wideband, and high extinction ratio TM polarizer based on subwavelength gratings.

We propose a low loss, wideband silicon transverse magnetic (TM) polarizer with high polarization extinction ratio and low reflection based on subwavelength grating. By arranging and optimizing a mutually perpendicular subwavelength grating with different duty cycles as the core and cladding, efficient waveguiding and radiation can be achieved for the TM and transverse electric (TE) injection, respectively. In simulation, the proposed TM polarizer has a footprint of 40µ×16.

Ultrahigh extinction ratio and a low power silicon thermo-optic switch.

The silicon thermo-optic switch (TOS) is one of the most fundamental and crucial blocks in large-scale silicon photonic integrated circuits (PICs). An energy-efficient silicon TOS with ultrahigh extinction ratio can effectively mitigate cross talk and reduce power consumption in optical systems. In this Letter, we demonstrate a silicon TOS based on cascading Mach-Zehnder interferometers (MZIs) with spiral thermo-optic phase shifters.

Tunable bandpass microwave photonic filter with largely reconfigurable bandwidth and steep shape factor based on cascaded silicon nitride micro-ring resonators.

Bandpass microwave photonic filter (MPF) can be achieved based on the well-known phase to intensity conversion method by using phase modulation and single micro-ring resonator (MRR) notch filter. Since MRR could introduce residual phase in handling one optical sideband, the out-of-band radio frequency (RF) rejection ratio and the shape factor of the bandpass MPF are very limited. Here, by introducing another MRR to handle the other optical sideband, the residual phase can be greatly suppressed, thus the filter's performance can be greatly improved.

Spectra reconfiguration of a silicon microring resonator via double injection with different angles.

A reconfigurable silicon microring filter, which is constructed by cascading a tunable Mach-Zehnder interferometer and a double injected silicon microring resonator with a variable input angle, is proposed and investigated. The spectra reconfigurations of the optical filter were simulated and analyzed using the transmission matrix method. The results show that when keeping the perimeter of the microring constant, the free spectral range (FSR) of the filter can be multiplied by adjusting the angle between the two injections.

Frequency-selectable microwave generation based on on-chip switchable spectral shaping and wavelength-to-time mapping.

We propose and experimentally demonstrate a scheme for the photonic generation of pulsed microwave signals with selectable frequency based on spectral shaping and wavelength-to-time mapping (WTTM) technique. The frequency selectivity is realized by channel switching on an integrated silicon-on-insulator (SOI) spectral shaping chip. The incident signal is spectrally shaped by the asymmetric Mach-Zehnder interferometer (MZI) in the selected channel, and an optical spectrum with uniform free spectral range (FSR) can be generated in a broad bandwidth up to dozens of nanometers, implying large microwave signal duration after WTTM if a pulse light source with matched bandwidth is available.

Achieving Fano resonance with an ultra-high slope rate by silicon nitride CROW embedded in a Mach-Zehnder interferometer.

Fano resonance with asymmetric line shape is very promising in many applications such as optical switching, sensing, slow light, laser. Fano resonances based on some integrated structures have been demonstrated on the silicon on insulator platform. However, the extinction ratios and slope rates of the most proposed integrated Fano resonances are relatively low, which limits their applications.

Low loss silicon nitride 1×4 microwave photonic beamforming chip.

In this paper, based on the low loss double strip silicon nitride platform, we designed and fabricated an ultra-low loss 1×4 microwave photonic beamforming chip, which contains a 1×4 beam splitter and four 5-bit optical delay lines. Each optical delay line can achieve 32 delay states varying from 0 ps to about 130 ps, which can support 21 different beamforming angles covers from -56.42° to 56.

Tunable microwave frequency comb generation using a SiN-MDR based actively mode-locked OEO.

Microwave frequency combs (MFCs) have important applications in communication and sensing owing to their characteristics of large number of comb lines, wide frequency range, and high precision of comb spacing. In many applications, MFCs are required to emit signals with tunable center frequency and variable comb spacing to accommodate different operating frequency bands and accuracies. Here, we demonstrate a tunable MFC by injecting a low-frequency electrical signal into a tunable optoelectronic oscillator (OEO).

Compact and broadband silicon mode-order converter using bricked subwavelength gratings.

A compact and broadband silicon mode-order converter (MOC) scheme by employing reciprocal mode evolution between asymmetric input/output taper and bricked subwavelength gratings (BSWG) is proposed. In the proposed MOC, a quasi-TE mode is generated in the BSWG region, which can be regarded as an effective bridge between the two TE modes to be converted. Flexible mode conversion can be realized by only choosing appropriate structure parameters for specific mode transitions between input/output modes and the quasi-TE mode.

Electrical Switching of the Off-Resonance Room-Temperature Valley Polarization in Monolayer MoS by a Double-Resonance Chiral Microstructure.

Enhancing and expanding the manipulated range of room-temperature valley polarization at off-resonance wavelength is extremely crucial to developing various functional valleytronic devices. Although these have been realized through the double-resonance strategy or twist-angle engineering, the demand for electrical control over the concepts remains elusive. Here, we fabricate a gate-tunable double-resonance chiral microstructure using a molybdenum disulfides (MoS) monolayer.

Photonic generation of broadband linearly chirped microwave waveform based on a low-loss silicon on-chip spectral shaper.

A silicon on-chip spectral shaper based on a Sagnac loop incorporating a chirped multi-mode waveguide Bragg grating (WBG) for linearly chirped microwave waveform generation is fabricated and demonstrated. The transmission spectrum of the spectral shaper displays low insertion loss characteristic due to the application of edge coupling taper and multi-mode waveguide based grating. An up-chirped microwave waveform with bandwidth as large as 44 GHz is generated by mapping the spectrum profile of the spectral shaper to the temporal domain through a dispersion fiber.

Parity-time symmetric tunable OEO based on dual-wavelength and cascaded PS-FBGs in a single-loop.

The ability to achieve low phase noise single-mode oscillation within an optoelectronic oscillator (OEO) is of fundamental importance. In the frequency-tunable OEO, the wide microwave photonic filter (MPF) bandwidth is detrimental to select single-mode among the large number of cavity modes, thus leading to low signal quality and spectral purity. Stable single-mode oscillation can be achieved in a large time delay OEO system by harnessing the mechanism from parity-time (PT) symmetry.

Broadband and compact polarization beam splitter in LNOI hetero-anisotropic metamaterials.

In this paper, theoretical modeling and numerical simulations of a high-performance polarization beam splitter (PBS) based on hetero-anisotropic metamaterials are proposed on the lithium-niobate-on-insulator (LNOI) platform. The hetero-anisotropic metamaterials constructed by sub-wavelength gratings (SWGs) can be regarded as effective anisotropy medium, which exhibits strong birefringence without breaking the geometrical symmetry, contributing to the formation of PBS. Rather than the principle of PBS based on beat-length difference of transverse electric (TE) polarization and transverse magnetic (TM) polarization, the device can realize polarization beam splitting in single beat length, and the footprint of the proposed PBS can be reduced to 8 µm × 160 µm (with S-bend).

Parity-time symmetric frequency-tunable optoelectronic oscillator based on a SiN microdisk resonator.

The optoelectronic oscillator (OEO) generates low-phase noise and high-frequency microwave signals thanks to a high Q-factor cavity with long and low-loss fiber delay. Traditionally, for the desired mode selection from the ultradense cavity modes, a narrowband electrical filter is needed, whose frequency tuning is very limited. On the other hand, for a tunable OEO offered by a microwave photonic filter (MPF), a paradox existed between the large number of cavity modes and the wide MPF bandwidth.

Silicon-assisted surface enhanced fluorescence toward improved assay performances.

A novel scheme of silicon-assisted surface enhanced fluorescence (SEF) is presented for SEF-based assays, where the blank signal suppression and the fluorescence signal enhancement is combined. The P-doped, (100) oriented silicon substrate is used to quench the fluorescence of Rose Bengal (RB) molecules attached to it, resulting in an effectively suppressed background signal, which is useful for a lower limit of detection (LOD). When a proper quantity of silver nanoparticles (AgNPs) is deposited on the RB-attached silicon substrate, a significant fluorescence enhancement of up to around 290 fold is obtained, which helps to improve the sensitivity in fluorescence-based assays.

Highly efficient and controllable photoluminescence emission on a suspended MoS-based plasmonic grating.

Being a new class of materials, transition metal dichalcogenides are paving the way for applications in atomically thin optoelectronics. However, the intrinsically weak light-matter interaction and the lack of manipulation ability has lead to poor light emission and tunable behavior. Here, we investigate the fluorescence characteristic of monolayer molybdenum disulfide on a metal narrow-slit grating, where a highly efficient, 471 times photoluminescence enhancement are realized, based on the hybrid surface plasmon polaritons resonances and the decreased influence of substrate.

Performance improvements of a tunable bandpass microwave photonic filter based on a notch ring resonator using phase modulation with dual optical carriers.

A tunable bandpass microwave photonic filter can be achieved by using a notch ring resonator with optical phase modulation. However, the filter's out of band rejection ratio and shape factor are limited due to the ring resonator's residual phase, which can seriously degrade the filter's performance. By using dual optical carriers and setting their wavelengths oppositely detuned from two resonant frequencies of a notch ring resonator, the residual phase induced by the ring resonator at radio frequencies falling outside the region of the notch stopband is reduced, thus the out-of-band rejection ratio and shape factor of the microwave photonic filter are greatly improved.

Realization of mid-infrared broadband absorption in monolayer graphene based on strong coupling between graphene nanoribbons and metal tapered grooves.

In this paper, we theoretically propose an effective broadband absorption architecture in mid-infrared region based on strong coupling between the plasmonic resonance of graphene nanoribbons and the waveguide mode of a metal tapered groove. The special architecture facilitates two new hybrid modes splitting with very strong energy distribution on graphene ribbon, which results in the broadband absorption effect. To well explain these numerical results, an analytical dispersion relation of waveguide mode is obtained based on the classical LC circuit model.

Combining Multiplex SERS Nanovectors and Multivariate Analysis for In Situ Profiling of Circulating Tumor Cell Phenotype Using a Microfluidic Chip.

Isolating and in situ profiling the heterogeneous molecular phenotype of circulating tumor cells are of great significance for clinical cancer diagnosis and personalized therapy. Herein, an on-chip strategy is proposed that combines size-based microfluidic cell isolation with multiple spectrally orthogonal surface-enhanced Raman spectroscopy (SERS) analysis for in situ profiling of cell membrane proteins and identification of cancer subpopulations. With the developed microfluidic chip, tumor cells are sieved from blood on the basis of size discrepancy.

Investigating the Intracellular Behaviors of Liposomal Nanohybrids SERS: Insights into the Influence of Metal Nanoparticles.

The recent proposition to combine liposomes with nanoparticles presents great opportunities to develop multifunctional drug delivery platforms. Although impressive progress has been made, attempts to elucidate the role nanoparticles play in the integral nanohybrids are still rather limited. Here, using surface-enhanced Raman scattering (SERS) technique, we investigate the influence of metal nanoparticles on the liposomal properties, ranging from drug release to intracellular movement.

Multilayer graphene electro-absorption optical modulator based on double-stripe silicon nitride waveguide.

A graphene electro-absorption optical modulator based on double-stripe silicon nitride waveguide is proposed and analyzed. By embedding four graphene layers in the double-stripe silicon nitride waveguide and the graphene layers co-electrode design, the total metal-graphene contact resistance can be reduced 50% and as high as 30.6GHz modulation bandwidth can be achieved theoretically.

Microfluidic chip based micro RNA detection through the combination of fluorescence and surface enhanced Raman scattering techniques.

We present a novel microfluidic chip based method for the detection of micro RNA (miRNA) via the combination of fluorescence and surface enhanced Raman scattering (SERS) spectroscopies. First, silver nanoparticles (Ag NPs) are immobilized onto a glass slide, forming a SERS enhancing substrate. Then a specificially designed molecular beacon (MB) is attached to the SERS substrate.