Hybrid Waveguide Research Articles

High‐Resolution Optical Convolutional Neural Networks Using Phase‐Change Material‐Based Microring Hybrid Waveguides

In the More‐than‐Moore era, the explosive growth of data and information has driven the exploration of alternative non‐von Neumann computational paradigms. Photonic neuromorphic computing has emerged as a promising approach, offering high speed, wide bandwidth, and massive parallelism. Herein, a high‐resolution optical convolutional neural network (OCNN) is introduced using phase‐change material Ge2Sb2Te5 (GST)‐based microring hybrid waveguides. This on‐chip optical computing platform integrates GST into photonic devices, enabling versatile programming and in‐memory computing capabilities. Central to this platform is a photonic convolutional computational kernel, constructed from photonic switching cells embedded with GST on a microring resonator. This programmable photonic switch leverages the refractive index modulation during the GST phase transition to achieve up to 64 discrete levels of transmission contrast, suitable for representing matrix elements in neural network algorithms with 6‐bit resolution. Using these matrix elements, an OCNN capable of performing parallelized image edge detection and digital recognition tasks with high accuracy is demonstrated. The architecture is scalable for large‐scale photonic neural networks, offering ultrahigh computational throughput, a compact design, complementary metal‐oxide‐semiconductor‐compatible fabrication, and broad bandwidth.

Electro-optical intensity and phase modulations of racetrack micro-resonator base on LiNbO3-silicon hybrid waveguide covered by electro-optical polymers

Electro-optical intensity and phase modulations of racetrack micro-resonator base on LiNbO3-silicon hybrid waveguide covered by electro-optical polymers

Four-wave mixing temperature sensor based on graphene oxide-coated microfiber hybrid waveguide

Utilizing a hybrid waveguide comprising microfiber and graphene oxide (GO), this study introduced an innovative temperature sensor based on four-wave mixing (FWM) effect. The methodology involved a tunable continuous wave (TCW) laser and a self-engineered all-fiber mode-locked laser operating at 1560 nm. The microfiber, featuring a minimum diameter of 10 μm, was fabricated through the flame fusion tapering technique, and the microfiber surface was coated with a GO film through the spontaneous evaporation of a GO solution. To improve the stability and robustness of the sensor, a layer of polydimethylsiloxane (PDMS) was applied to the surface as a protective coating. The GO film compensated for dispersion in conjunction with microfiber, enhanced nonlinearity and facilitated low-power FWM phenomena. Furthermore, it increased temperature sensing sensitivity. By measuring the center wavelength shift of the idler and signal light, we achieved a temperature sensing sensitivity of −2.08 nm/℃ from −15 ℃ to 20 ℃ using the CW laser at 1540 nm. This sensor also had a resolution of 0.024 ℃, a response time of 0.12 s and a maximum temporal resolution of 0.08 s. Our study marks the initial investigation of a temperature sensing mechanism employing the FWM phenomenon within this unique hybrid waveguide. It serves as a proof of concept for using a microfiber combined with the two-dimensional material GO film to generate nonlinear FWM for temperature sensing. Continuous optimization of experimental conditions and waveguide dimensions is expected to enhance sensing performance. This opens up new avenues for future research in novel optical sensing technology, particularly in the exploration of high-performance sensors through the integration of nonlinear phenomena with different two-dimensional materials, showcasing substantial research potential.

Dispersion-Engineered SiN-Coated TeO2 Hybrid Waveguide for Nonlinear Applications

Dispersion-Engineered SiN-Coated TeO2 Hybrid Waveguide for Nonlinear Applications

Low-Power-Consumption and Broadband 16-Channel Variable Optical Attenuator Array Based on Polymer/Silica Hybrid Waveguide

A variable optical attenuator (VOA) is a crucial component for optical communication, especially for a variable multiplexer (VMUX) and reconfigurable optical add-drop multiplexer (ROADM). With the capacity increasing dramatically, a large-port-count and low-power-consumption VOA array is urgent for an on-chip system. In this paper, we experimentally demonstrate a 16-channel VOA array based on a polymer/silica hybrid waveguide. The proposed array is able to work over C and L bands. The VOA array shows an average attenuation larger than 14.38 dB with a low power consumption of 15.53 mW. The low power consumption makes it possible to integrate silica-based passive devices with a large port count on-chip.

High-quality on-chip entangled photon source with broad tunable range based on coupling compensation

This paper introduces a tunable and high-quality photon source that utilizes evanescent-wave coupling phase matching. By adjusting the coupling gap, the signal light can be tuned from 1307 nm to 1493.9 nm, and the idler light can be tuned from 1612.8 nm to 1907 nm. Throughout the entire tuning range, the purity of the photon pairs remains above 92%. In specific tuning ranges (signal photons from 1307 nm to 1421.7 nm and idler photons from 1706.4 nm to 1907 nm), the purity exceeds 99% and the full width at half-maximum of the generated photon spectra is less than 1.85 nm. The photon source is designed using a silicon–organic hybrid waveguide, which effectively minimizes the impact of two-photon absorption and achieves a 15 dB enhancement in four-wave mixing conversion efficiency compared to a strip waveguide. This design may promote efficient and precise generation of high-quality photons at desired frequencies, offering promising potential for various applications in quantum technologies.

Optical to terahertz frequency conversion using near zero-index nonlinear hybrid waveguides

Terahertz communications has emerged as an excellent candidate for the next generation of wireless communication networks. Despite of significant advances, one still looks for a high-efficiency terahertz source using nonlinear optics, such as optical refraction and difference-frequency generation. Concurrently, recent years have witnessed significant progress in metamaterials-assisted nonlinear optical processes. In this study, we propose a theoretical approach using near zero-index nonlinear hybrid waveguides to realize a high generation efficiency of terahertz waves via on-chip difference-frequency generation. Remarkably, thanks to the simultaneous realization of near zero-index both at terahertz and telecom frequencies, such a nonlinear hybrid waveguide can overcome two major bottlenecks in the conversion from optical wave to terahertz waves: phase mismatch and weak nonlinear optical-terahertz waves interactions, resulting in a high conversion as 2.2 × 10−3W−1 just within the propagation length of several terahertz wavelengths. Our results demonstrate the feasibility of an on-chip terahertz source, offering unique properties such as high integration and ultra-low power consumption for terahertz communication systems.

Passive wavelength selective polarization rotator in a hybrid waveguide platform

Polarization rotation and wavelength filtering are key functionalities used to build complex photonic integrated circuits. Both these functionalities have been demonstrated in various material and device platforms. We propose, for the first time, a fully passive wavelength selective polarization rotation in silicon nitride/amorphous silicon hybrid waveguide. We demonstrate TE0 → TM0 and TM0 → TE0 wavelength selective polarization rotator-cum-filter with a measured 3dB bandwidth of 14.8 nm. Further, we experimentally demonstrate a proof of concept for simultaneous coarse wavelength division multiplexing and polarization rotation for the first time in a passive configuration. We also show the feasibility of bandwidth engineering from 0.59 nm to 81 nm, enabled by the unique flexibility of the proposed hybrid waveguide.

Ultrasensitive Silicon Photonic Refractive Index Sensor Based on Hybrid Double Slot Subwavelength Grating Microring Resonator.

Silicon photonic-based refractive index sensors are of great value in the detection of gases, biological and chemical substances. Among them, microring resonators are the most promising due to their compact size and narrow Lorentzian-shaped spectrum. The electric field in a subwavelength grating waveguide (SWG) is essentially confined in the low-refractive index dielectric, favoring enhanced analyte-photon interactions, which represents higher sensitivity. However, it is very challenging to further significantly improve the sensitivity of SWG ring resonator refractive index sensors. Here, a hybrid waveguide blocks double slot subwavelength grating microring resonator (HDSSWG-MRR) refractive index sensor operating in a water refractive index environment is proposed. By designing a new waveguide structure, a sensitivity of up to 1005 nm/RIU has been achieved, which is 182 nm/RIU higher than the currently highest sensitivity silicon photonic micro ring refractive index sensor. Meanwhile, utilizing a unique waveguide structure, a Q of 22,429 was achieved and a low limit of detection of 6.86 × 10-5 RIU was calculated.

225 Gb/s PAM4 2 km and 10 km Transmission of Electro-Absorption Modulator Integrated Laser With Hybrid Waveguide Structure for 800 Gb/s and 1.6 Tb/s Transceivers

225 Gb/s PAM4 2 km and 10 km Transmission of Electro-Absorption Modulator Integrated Laser With Hybrid Waveguide Structure for 800 Gb/s and 1.6 Tb/s Transceivers

Achieving Multiwavelength Optical Amplification Based on Polymer Waveguides Doped with NaYF4:Er3+, Yb3+ Nanoparticles under Commercial and Convenient Led Pumping

AbstractRelying on a reverse energy transfer mechanism between erbium (Er3+) and ytterbium (Yb3+) ions, optical gains at wavelengths of 1550, 980, and 1067 nm are achieved in NaYF4: Er3+, and Yb3+ nanoparticles‐doped polymer waveguides under excitation of low‐power light‐emitting diodes (LEDs) instead of 976 or 1480 nm semiconductor laser as pump sources. The optical gains at 1550, 980, and 1067 nm are demonstrated in five waveguide structures: active‐rectangular, evanescent‐field with and without an aluminium (Al) reflector, and dual‐active hybrid with and without an Al reflector. The maximum relative optical gains of 6.6, 4.0, and 3.8 dBcm−1 are realized at 1550, 1067, and 980 nm, respectively, in a 5 mm long dual‐active hybrid waveguide with cross‐section of 4 × 10 µm, and a ≈100 nm‐thick Al reflector grown under the lower cladding layer under excitation of a 395 nm LED. This work proves the feasibility of using a low‐cost LED to realize multi‐wavelength amplification in a dense wavelength‐division multiplexing system and is thus valuable for the development of complex multi‐functional photonic‐integrated‐module mixed‐band optical communication systems.

A new SOI sensor design for detecting cancer using hybrid waveguide with higher sensitivity than both strip and slot waveguides

A new highly accurate optical biomedical sensor is proposed for cancer detection characterized by high sensitivity, small footprint, low cost, and low limit of detection. The sensor is based on double-ring resonators made of silicon on insulator. The type of the waveguide is critical in determining the sensor performance. To compromise the advantages and disadvantages of strip and slot waveguides, a mixed design of both has been introduced in literature at the expense of increased footprint compared to traditional sensors. Indeed, almost 27-fold footprint increase is required to improve the sensitivity by only one third of that of slot waveguide’s sensitivity. In this paper, we introduce a new design that keeps the same footprint of traditional sensors, while achieving high sensitivity. This sensitivity depends on the resonance wavelength shift due to different refractive indices of the biosample. It has the value 109.8 nm/RIU compared to 55.57 nm/RIU and 129.621 nm/RIU for strip and slot waveguides, respectively. The hybrid waveguide quality factor is 537.7 while the quality factors of the strip and the slot waveguides are 627.99 and 380.76, respectively. In addition, the new design achieves the minimum limit of detection (0.0255) when compared to that of traditional designs. Furthermore, a new method of detection is proposed with the same design, providing a higher sensitivity over both traditional waveguide types with a value of 15.3, compared to 13.2 and 11.5 for strip and slot waveguides, respectively. In this method, the sensitivity relies on various values of output transmitted light at the same wavelength due to altering the biocell refractive index. The biosensor output equation is developed. In addition, the relationship between the supermodes and the sensitivity is determined at variance conditions. It is found that there is an inverse relation between them.

Efficient Parametric Frequency Conversions in Chalcogenide‐Loaded Etchless Thin‐Film Lithium Niobate Waveguides

AbstractParametric frequency conversion based on second‐order nonlinearity (χ(2)) is critical in many applications. The implementation of second‐order nonlinearity on integrated photonic platforms, in particular on the lithium niobate‐on‐insulator platform, has attracted considerable interest due to its low power consumption and small footprint. However, high‐efficiency on‐chip parametric frequency conversion remains challenging due to fabrication complexity. Here, efficient parametric frequency conversions via modal phase matching (MPM) in etchless thin‐film lithium niobate (TFLN)‐chalcogenide glass (ChG) hybrid waveguides fabricated by a simplified process free from domain engineering and etching of TFLN are proposed and demonstrated. An overall conversion efficiency of 25.55% W−1 for second‐harmonic generation is experimentally achieved in a 1‐cm‐long waveguide, significantly over the reach of the etchless counterparts and in the same order of magnitude as those of the etched cases based on MPM. Broadband frequency conversion with a 3‐dB bandwidth of 57 nm is achieved based on cascaded second‐harmonic generation and difference‐frequency generation via MPM in a nanophotonic waveguide using a continuous‐wave pump. This device shows great promise for efficient on‐chip parametric frequency conversion, enabling a wide range of photonic applications, and paving the way for further integration with various advanced ChG photonic devices toward on‐chip multifunctional microsystems.

Ge-polymer bridge waveguide for mode-locked laser pulse generation.

A Ge-polymer hybrid waveguide is sandwiched between an indium phosphide (InP) reflective gain chip and a fiber Bragg grating (FBG) to construct a laser system. The hybrid waveguide serves as a bridge between the gain chip and the fiber with tailored mode-field matching at both facets. The 50-nm amorphous Ge (α-Ge) layer shows a nonlinear absorption effect at 1550 nm. The hybrid waveguide is further verified by a femtosecond laser transmission experiment to show the pulse width compression effect. Such waveguide is then integrated inside the laser cavity as a passive saturable absorber to modulate the longitudinal modes for a pulsed output. This polymer-bridged mode-locked laser adopts an InP gain chip for compact assembly and also a FBG with a flexible length to adjust the pulse repetition rate. The mode-locked laser output around the designed 50 MHz repetition rate is demonstrated. The pulse width is measured as 147 ps, and the signal-to-noise ratio is larger than 50 dB. This work introduces a "ternary" mode-locked laser system, taking advantage of discrete photonic components bridged by a polymer-based waveguide. It also proves the feasibility of applying α-Ge films as practical and low-cost saturable absorbers in photonic devices.

Characterization of hybrid waveguide for Terahertz guidance

Characterization of hybrid waveguide for Terahertz guidance

Molecularly imprinted polymer-coated hybrid optical waveguides for sub-aM fluorescence sensing.

The sensitivity of fluorescent sensors is crucial for their applications. In this study, we propose a molecularly imprinted polymer (MIP)-coated optical fibre-hybrid waveguide-fibre sensing structure for ultrasensitive fluorescence detection. In such a structure, the MIP coated-hybrid waveguide acts as a sensing probe, and the two co-axially connected optical fibres act as a highly efficient probing light launcher and a fluorescence signal collector, respectively. For the dual-layered waveguide sensing probe, the inner hybrid waveguide core was fabricated using a hollow quartz nanoparticle-hybridized polymer composite with a low refractive index, and the outer MIP coating layer possesses a high refractive index. Simulations showed that this dual-layer configuration can cause light propagation from the waveguide core to the MIP sensing layer with an efficiency of 98%, which is essential for detection. To validate this concept, we adopted a popular fluorescent dye, rhodamine B, to evaluate the sensing characteristics of the proposed system. We achieved an extremely low limit of detection of approximately 1.3 × 10-19 g ml-1 (approximately 0.27 aM).

Mode-Independent Optical Switch Based on Graphene-Polymer Hybrid Waveguides

Mode-division multiplexing (MDM) is a promising multiplexing technique to further improve the transmission capacity of optical communication and on-chip optical interconnection systems. Furthermore, the multimode optical switch is of great importance in the MDM system, since it makes the MDM system more flexible by directly switching multiple spatial signals simultaneously. In this paper, we proposed a mode-independent optical switch based on the graphene–polymer hybrid waveguide platform that could process the TE11, TE12, TE21 and TE22 modes in a few-mode waveguide. The presented switch is independent of the four guided modes, optimizing the buried position of graphene capacitors in the polymer waveguide to regulate the coplanar interaction between the graphene capacitors and spatial modes. The TE11, TE12, TE21 and TE22 modes can be regulated simultaneously by changing the chemical potential of graphene capacitors in a straight waveguide. Our presented switch can enable the independent management of the spatial modes to be more flexible and efficient and has wide application in the MDM transmission systems.

Dual Coupled Long-Range Hybrid Surface Plasmon Polariton Waveguide for Sub-Wavelength Confinement.

In this paper, a long-range hybrid waveguide for subwavelength confinement based on double SPP coupling is proposed. The hybrid waveguide consists of a metal-based cylindrical hybrid waveguide and a silver nanowire. There are two coupling regions in the waveguide structure that enhance mode coupling. Strong mode coupling enables the waveguide to exhibit both a small effective mode area (0.01) and an extremely long transmission length (700 μm). The figure of merit (FOM) of the waveguide can be as high as 4000. In addition, the cross-sectional area of the waveguide is only 500 nm × 500 nm, allowing optical operation in the subwavelength range, which helps enhance the miniaturization of optoelectronic devices. The excellent characteristics of the hybrid waveguide make it have potential applications in photoelectric integrated systems.

III–V gain region/Si waveguide hybrid lasers by chip-on-wafer hydrophilic bonding process using UV-ozone treatment

The direct bonding process of InP chips on a silicon-on-insulator (SOI) wafer is investigated using surface hydrophilization by UV-ozone treatment. The influence of the treatment on surface roughness is observed by atomic force microscopy, and found to be negligibly small. A high-quality III–V/Si bonding interface without crystal defects is verified in a scanning transmission electron microscope observation. The III–V layers remaining on the SOI wafer after the removal process of the InP substrate show uniform photoluminescence intensity over the whole region of the chip, indicating a bonding interface without the influence of lateral etching and peeling-off. From this bonding process, Fabry–Perot lasers with III–V gain and Si waveguide regions are fabricated, and cw operation is successfully achieved at a stage temperature from 20 °C to 85 °C. Stable operation is also confirmed from the changes of threshold current in the aging test (200 mA at 85 °C) after 2000 h.

Filtering couplers based on multi-layer self-packaged suspended coplanar waveguide hybrid and coupled techniques

In this paper, new 3 dB/10 dB filtering couplers using branch line loading, multi-line hybrid coupling, and electromagnetic coupling, which are based on self-packaged suspended coplanar waveguide-microstrip (SCPW-MS) hybrid and broadside coupled suspended coplanar waveguide (BC SCPW) techniques, have been proposed. The filtering function is achieved by the branch line loaded resonator, multi-line hybrid coupling and electromagnetic coupling of the SCPW resonator. All of the proposed filtering couplers have been fabricated and measured, and the experimental results approach to the predictions. The advantages of the new designs with low insertion loss of no more than 0.82 dB, favorable isolation of more than 18 dB, phase imbalance of no more than ± 5°, and multiple transmission zeros in some works to introduce high frequency selectivity, and self-packaging have been demonstrated. The dual-layer routing of the core circuit not only retains the advantages of SCPW, but also improves the design flexibility.