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With the advantages of high speed, small size, and easy integration, the silicon photonic resonant ring modulator has gradually become a critical device for emerging integrated optical platforms. Ring modulators are primarily used in optical communications, optical computing, artificial intelligence, and other fields. In this work, the proposed ring modulator can operate in both the O- and C-bands. The 3 dB electro-optical (EO) bandwidth of the ring modulator is 39 GHz and 34 GHz at −4 V in the O-band and C-band, respectively. The modulation efficiency of the device is 0.92 V·cm and 0.95 V·cm in the O-band and C-band, respectively. The eye diagram of an optical output signal from the device is tested using a 100 Gbit/s non-return-to-zero (NRZ) input signal with a 2.5 Vpp in both the O-band and C-band. The modulation speed can reach 140 Gb/s and 120 Gb/s in the O-band and C-band with four-level pulse amplitude modulation (PAM-4) formats at a voltage swing of 2.5 Vpp, respectively. [ABSTRACT FROM AUTHOR]

Fixed-length segment (FLS) optimization method offers a way to realize the high-efficiency analog inverse design of nanophotonic devices. However, due to the limitation of the variable dimensions and restricted search space, this method can hard to simultaneously achieve large bandwidth, compact size, and efficient performance when dealing with high-dimension design. Here, we propose a highly efficient variable-length segment (VLS) based inverse design method, aiming to solve complex analog inverse design and fully demonstrate the targeted performance. It divides the optimized region into several tapered segments of unequal length and inserts a subwavelength transition waveguide between each tapered segment, which can expand the search space of the algorithm, thus making it easier to obtain a better locally optimal solution. As typical complex proof-of-concept examples, a 1 × 4 power splitter on a silicon-on-insulator (SOI) platform is chosen to demonstrate the validity of our design paradigm. The simulation results show that, compared with the conventional FLS, VLS has about 4–5 times higher efficiency and obtains better optimization performance. In our experiment, the fabricated device has a compact footprint of 9.8 μm × 4.9 μm and is complementary metal oxide semiconductor (CMOS) compatible. The measured insertion loss and the uniformity are less than 0.58 dB and 0.8 dB, respectively. In addition, the tolerances to fabrication errors are also investigated. Our work may find important applications in the advanced design of future nanoscale high-quality optical devices.

A novel single-layer graphene-based structure is designed in this article. This structure consists of two graphene strips and two graphene blocks. The components of this structure generate two bright modes and one dark mode in the terahertz region, and these three modes undergo destructive interference, leading to the phenomenon of double plasmonic induced transparency. The graphene of this structure has continuity, and the Fermi level can be adjusted by adjusting the bias voltage applied to the structure. Compared with those discontinuous structures, it is easier to achieve tuning function. The structure uses the finite-difference time-domain for data simulation, uses the coupled mode theory for theoretic calculation, and compares the transmission spectra obtained by the two methods. Through observation, it can be found that the frequency positions of the peaks and dips of the simulated transmission spectrum increase with the increase of the Fermi level, showing a perfect linear relationship, which indicates that this structure has great prospects in the modulator. In addition, the structure has achieved good results in the slow light effect, and after measurement, the peak values of group index and group delay can reach up to 380 and 0.241 ps, respectively. By utilizing these advantages, this structure can provide more possibilities for the development and research of slow light fields. [ABSTRACT FROM AUTHOR]

Microspectrometers have numerous applications in mobile optical sensing due to their dramatic advantages of compact size, light weight, and low power consumption. Reconstructive spectrometers, based on computational algorithms, have garnered considerable interest as they exhibit superior resolution or spectral bandwidth. However, existing reconstructive spectrometer designs face challenges in spectral applicability, algorithm robustness, and the resolution‐bandwidth limit. Here, a reconstructive spectrometer that utilizes a microring resonator (MRR) is proposed to achieve compressed sensing in hardware by decomposing an arbitrary continuous spectrum into a series of simple comb spectra. Owing to the presparse operation of the MRR, one needs to construct the comb spectra with a known line shape, only leaving the amplitude to be solved. Consequent random gratings measure the comb spectra, which are reconstructed with high robustness. Thanks to the independent engineering of spectral resolution and bandwidth, the approach breaks the traditional resolution‐bandwidth limit. A narrowband signal of a dual peak at 0.2 nm and a broadband spectrum with a large spectral bandwidth of 60 nm and 300 spectral channels using only eight physical channels is retrieved, achieving an ultrahigh reconstructive compression ratio of 37.5. This work opens up the possibility of on‐site spectral spectroscopy applications for the lab‐on‐a‐chip system. [ABSTRACT FROM AUTHOR]

Germanium-on-silicon (Ge-on-Si) single photon avalanche diodes (SPADs) have received wide attention in recent years due to their potential to be integrated with Si photonics. In this work, we propose and demonstrate a high-performance waveguide coupled Ge-on-Si separate-absorption-charge-multiplication SPAD with three electric terminals. By providing two separate voltage drops on the light absorption and multiplication regions, the drift and multiplication of carriers can be optimized separately. This indeed improves the freedom of voltage regulation for both areas. Moreover, thanks to the separate controlling, doping profile of the charge layer is greatly released compared to that of the conventional device because of the flexible carrier injection. In this scenario, the dark counts of the detector can be largely reduced through decreasing the electric field on the sidewalls of the Ge absorption region without affecting the detection efficiency. The proposed SPAD exhibits a high on-chip single photon detection efficiency of 34.62% and low dark count rates of 279 kHz at 1310 nm with the temperature of 78 K. The noise equivalent power is as low as 3.27 × 10−16 WHz−1/2, which is, to the best of our knowledge, the lowest of that of the reported waveguide coupled Ge-on-Si SPADs. This three-terminal SPAD enables high-yield fabrication and provides robust performance in operation, showing a wide application prospect in applications such as on-chip quantum communication and lidar.

Mach-Zehnder interferometers (MZIs) are vital in optical biosensor applications and high-density integrated photonic circuits. In this research work, we theoretically investigate the design steps of MZIs, consisting of 3-dB plasmonic splitters sandwiched between two dielectric waveguides with an air-gap coupler at the interface from each side. The proposed MZI designs feature a compact size, ensuring high transmission coupling efficiency without introducing additional radiation or reflection losses, as observed in tapered, T- and Y-shaped splitters. The analytical results and simulations prove that the proposed MZI designs offer a broad spectrum range with a high fabrication tolerance and the ability to use them in all-optical plasmonic circuits.

We present a straightforward metamaterial structure based on a graphene monolayer, which comprises a single graphene block and two graphene strips. This innovative design enables plasma-induced transparency (PIT) phenomenal generation by harnessing the interplay between bright and dark modes. To elucidate this phenomenon, we conduct comprehensive theoretical calculations that corroborate the findings of simulate results from finite difference time domain (FDTD). Furthermore, we explore the PIT phenomenon across various Fermi energy levels while also investigating the associated slow light effect in relation to the structural parameter, Fermi energy level, and carrier mobility. By increasing the carrier mobility from 0.4 to 3.4 m2/(V⋅s), the group index can be elevated from 80 to 430. Consequently, this graphene-based metamaterial holds promise for inspiring novel approaches to the design of modulators, optical switches, and devices for manipulating slow light.

Efficient fiber‐chip couplers operating at distinct wavelength bands are key components to combine or split different optical bands for emerging data transmission and nonlinear applications. Herein, a dual‐band silicon‐integrated grating coupler (GC) operated at 1.55 and 2 μm wavebands is designed and demonstrated. The proposed device can simultaneously couple 1.55 and 2 μm wavebands light into the in‐plane waveguides at the same incident angle. Numerical simulations indicate that coupling efficiencies (CEs) are −2.5 and −3.9 dB for center wavelengths at 1561 and 1979 nm, respectively. The dual‐band GC is experimentally demonstrated on a commercially available 340 nm silicon‐on‐insulator wafer. The fabricated dual‐band GC with center wavelengths of 1559 and 1968 nm obtains CEs of −4.9 and −6.4 dB, with 3 dB bandwidths of 81 and 80.4 nm, respectively. Also, the first proof‐of‐concept demonstration of 10 Gb s−1 wavelength division multiplexing transmission at 1.55 and 2 μm waveband is presented based on the fabricated dual‐band GC.

On‐chip micro‐spectrometers are sought after with great effort owing to extensive potential applications in mobile optical sensing and imaging. By multiplexing more physical channels, the reconstructive spectrometers based on the spectral‐to‐spatial mapping technique can improve the spectral range. However, this method is challenging to implement and sustain due to the increase in system complexity and the decrease of dynamic range or spectral resolution. Here, a micro‐spectrometer utilizing a single tunable microdisk resonator (MDR) is demonstrated. Such a single MDR spectrometer has only one physical channel to receive all spectral components with a compact size, overcoming the trade‐off among spectral resolution, spectral range, and dynamic range. Leveraging the wavelength and temperature‐dependent response matrix, unknown spectra are reconstructed from their corresponding output light intensity vector. The fabricated device illustrates a high resolution of 0.01 nm for a dual peak and a medium resolution of 0.2 nm in the 20 nm spectral range. A wide variety of complex input spectra, including narrowband and broadband spectral signals, can be well recovered, exhibiting the robustness of the spectral reconstruction approach. Moreover, this proposed spectrometer exhibits ease of scalability and flexible configuration to a spectrometer array covering a set of desired and even discrete spectral ranges. [ABSTRACT FROM AUTHOR]

Recently, polymer nanocomposites have attracted great interest due to their remarkable characteristics of high performance and enabling production of low-cost devices. This article explores the reflective index sensing application of the polymer nanocomposite IOC-133, which is a TiOx/polymer nanocomposite with a reflective index between 1.8 and 1.9. Considering the material properties of high reflective index, low absorption loss, and compatibility with nanoimprint lithography, a microring-based reflective index sensor with a suspended slot waveguide structure is proposed. We combined the sensing mechanism of slot waveguides with high reflective index polymer nanocomposites and designed the suspended structure to address the problem of decreasing sensitivity caused by residual layers. The sensing device was adopted as a microring resonator, which is conducive to large-scale integration. The finite-difference time-domain (FDTD) method was employed to analyze the effects of several key parameters. The results showed that the racetrack microring sensor we propose can achieve a high sensitivity of 436 nm/RIU (Refractive Index Units), about six times higher than the microring sensor with a ridge waveguide. The Q factor of the microring reaches 1.42 × 104, and the detection limit is 1.38 × 10−4 RIU. The proposed suspended slot microring sensor has potential value in the field of nanoprinted photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Mode converters is a key component in mode-division multiplexing (MDM) systems, which plays a key role in signal processing and multi-mode conversion. In this paper, we propose an MMI-based mode converter on 2%-Δ silica PLC platform. The converter transfers E00 mode to E20 mode with high fabrication tolerance and large bandwidth. The experimental results show that the conversion efficiency can exceed −1.741 dB with the wavelength range of 1500 nm to 1600 nm. The measured conversion efficiency of the mode converter can reach −0.614 dB at 1550 nm. Moreover, the degradation of conversion efficiency is less than 0.713 dB under the deviation of multimode waveguide length and phase shifter width at 1550 nm. The proposed broadband mode converter with high fabrication tolerance is promising for on-chip optical network and commercial applications. [ABSTRACT FROM AUTHOR]

Optical vortices carrying orbital angular momentum (OAM) have recently attracted increasing interest for providing an additional degree of freedom for capacity scaling in optical communications. The optical vortex generator is an essential component to facilitate OAM-enabled optical communications. Traditional devices face challenges of limited compactness, narrow bandwidth, and first-order OAM modes. Here, using the direct-binary search (DBS) optimization algorithm, we design, fabricate, and demonstrate a digitized subwavelength surface structure on silicon platform for the generation of wavelength-/polarization-/charge-diverse optical vortices. It features an ultra-compact footprint (∼3.6 × 3.6 μm2) and ultra-wide bandwidth (1480–1630 nm), supporting two polarizations (x-pol., y-pol.) and high-order OAM modes (OAM+1, OAM−1, OAM+2, OAM−2) with high purity of larger than 84%. The mode crosstalk matrix is measured in the experiment with favorable performance. When generating x-pol. OAM+1, x-pol. OAM−1, y-pol. OAM+1, and y-pol. OAM−1 mode, the crosstalk of the worst case is less than −14 dB. When generating OAM+1, OAM−1, OAM+2, and OAM−2 mode, the crosstalk between any two OAM modes is less than −10 dB, and the lowest crosstalk is about −17 dB. In addition, we also show the possibility for generating much higher-order OAM modes (e.g. OAM+3, OAM−3, OAM+4, and OAM−4) with the digitized subwavelength surface structure. The wavelength-/polarization-/charge-diverse optical vortex generator enables the full access of multiple physical dimensions (wavelength, polarization, space) of lightwaves. The demonstrations may open up new perspectives for chip-scale solutions to multi-dimensional multiplexing optical communications.

We propose a mode switch based on hybrid-core vertical directional couplers with an embedded graphene electrode to realize the switching function with low power consumption. We designed the device with Norland Optical Adhesive (NOA) material as the guide wave cores and epoxy polymer material as cladding to achieve a thermo-optic switching for the E11, E21 and E12 modes, where monolayer graphene served as electrode heaters. The device, with a length of 21 mm, had extinction ratios (ERs) of 20.5 dB, 10.4 dB and 15.7 dB for the E21, E12 and E11 modes, respectively, over the C-band. The power consumptions of three electric heaters were reduced to only 3.19 mW, 3.09 mW and 2.97 mW, respectively, and the response times were less than 495 µs, 486 µs and 498 µs. Additionally, we applied such a device into a mode division multiplexing (MDM) transmission system to achieve an application of gain equalization of few-mode amplification among guided modes. The differential modal gain (DMG) could be optimized from 5.39 dB to 0.92 dB over the C-band, together with the characteristic of polarization insensitivity. The proposed mode switch can be further developed to switch or manipulate the attenuation of the arbitrary guided mode arising in the few-mode waveguide. [ABSTRACT FROM AUTHOR]

We propose a novel continuously tunable delay line in X-cut lithium niobate thin film driven by graphene electrodes, featuring low power consumption and low half-wave voltage-length product. The use of the graphene electrodes combined with the air slots makes the device quite low power consumption. Our designed device, which has a footprint of 8.9 mm × 1.9 mm, is capable of providing a continuously tunable delay range from 0 to 100 ps with minimum 3 dB bandwidth of >20 GHz. By optimizing the width of the waveguide core and the distance between the graphene and the waveguide core, we can obtain the low power consumption and low voltage - length product VπL = 1.12 V·cm at 1550 nm when w = 2 μm and d = 0.3 μm. In addition, the graphene electrode has negligible light absorption with w = 2 μm and d = 0.3 μm, the switching power is 151 mW without air slots, and the switching power is 95.36 mW with air slots etching depth of 5.3 μm formed on both sides of the waveguides. And further, the air slots formed on both sides and at the bottom of the waveguides make a low switching power of 2.85 mW.

In this paper, a novel inline optical fiber sensor for curvature and temperature measurement simultaneously has been proposed and demonstrated, which can measure two parameters with very little crosstalk. Two combinational mechanisms of anti-resonant reflecting optical waveguide and inline Mach–Zehnder interference structure are integrated into a 3 mm-long single hole twin suspended core fiber (SHTSCF). The 85 μm hole core gives periodic several dominant resonant wavelengths in the optical transmission spectrum, acting as the anti-resonant reflecting optical waveguide (ARROW). The modes in two suspended cores and the cladding form the comb pattern. Reliable sensor sensitivity can be obtained by effective experiments and demodulation. Through intensity demodulation of the selected dip of Gaussian fitting, the curvature sensitivity can be up to −7.23 dB/m−1. Through tracking the MZI dip for wavelength demodulation, the temperature sensitivity can be up to 28.8 pm/°C. The sensor is simple in structure, compact, and has good response, which can have a bright application in a complex environment. [ABSTRACT FROM AUTHOR]

Integrated terahertz (THz) technology is of great significance for driving high‐speed communication, sensing, and imaging with its advantages of miniaturization, low cost, and high efficiency. Recent research has focused on highly‐efficient transmitters and ultrafast detectors, as well as exploring new devices for coupling, transmission, and polarization control. However, multidimensional on‐chip multiplexing and demultiplexing techniques in the THz region still remains unexplored, due to the lack of multifunctional integrated components and systems. Here, a novel silicon‐based integrated multidimensional THz (de)multiplexer for high‐capacity communication is proposed and demonstrated based on ring resonators and polarization beam splitter‐rotators, which simultaneously enable the manipulation of THz polarization and frequency. Furthermore, a THz communication system operating in the 380 GHz band is experimentally demonstrated. By using on‐chip polarization‐ and frequency‐division multiplexing techniques, an aggregate data rate of 8 Gbit s−1 is successfully achieved with quadrature phase‐shift keying modulation scheme. This work provides a spectrally efficient way for accelerating the development of on‐chip THz technologies and the application in future large‐volume communications. [ABSTRACT FROM AUTHOR]

We propose a novel continuously tunable delay line in X-cut lithium niobate thin film driven by graphene electrodes, featuring low power consumption and low half-wave voltage-length product. The use of the graphene electrodes combined with the air slots makes the device quite low power consumption. Our designed device, which has a footprint of 8.9 mm × 1.9 mm, is capable of providing a continuously tunable delay range from 0 to 100 ps with minimum 3 dB bandwidth of >20 GHz. By optimizing the width of the waveguide core and the distance between the graphene and the waveguide core, we can obtain the low power consumption and low voltage - length product VπL = 1.12 V·cm at 1550 nm when w = 2 μm and d = 0.3 μm. In addition, the graphene electrode has negligible light absorption with w = 2 μm and d = 0.3 μm, the switching power is 151 mW without air slots, and the switching power is 95.36 mW with air slots etching depth of 5.3 μm formed on both sides of the waveguides. And further, the air slots formed on both sides and at the bottom of the waveguides make a low switching power of 2.85 mW. [ABSTRACT FROM AUTHOR]

The phase modulator is a key component in optical communications for its phase modulation functions. In this paper, we numerically demonstrate a variety of ultra-compact high-efficiency graphene phase modulators (GPMs) based on metal–nanoribbon integrated hybrid plasmonic waveguides in the near-infrared region. Benefiting from the good in-plane mode polarization matching and strong hybrid surface plasmon polariton and graphene interaction, the 20 μm-length GPM can achieve excellent phase modulation performance with a good phase and amplitude decoupling effect, a low insertion loss around 0.3 dB/μm, a high modulation efficiency with VπLπ of 118.67 V μm at 1.55 μm, which is 1–3 orders improvement compared to the state-of-the-art graphene modulators. Furthermore, it has a wide modulation bandwidth of 67.96 GHz, a low energy consumption of 157.49 fJ/bit, and a wide operating wavelength ranging from 1.3 to 1.8 μm. By reducing the overlap width of the graphene–Al2O3–graphene capacitor, the modulation bandwidth and energy consumption of the modulator can be further improved to 370.36 GHz and 30.22 fJ/bit, respectively. These compact and energy-efficient GPMs may hold a key to various high-speed telecommunications, interconnects, and other graphene-based integrated photonics applications.

The optimum femtosecond laser direct writing of Bragg gratings on silica optical waveguides has been investigated. The silica waveguide has a 6.5 × 6.5 µm2 cross-sectional profile with a 20-µm-thick silicon dioxide cladding layer. Compared with conventional grating inscribed on fiber platforms, the silica planar waveguide circuit can realize a stable performance as well as a high-efficiency coupling with the fiber. A thin waveguide cladding layer also facilitates laser focusing with an improved spherical aberration. Different from the circular fiber core matching with the Gaussian beam profile, a 1030-nm, 400-fs, and 190-nJ laser is optimized to focus on the top surface of the square silica waveguide, and the 3rd-order Bragg gratings are inscribed successfully. A 1.5-mm long uniform Bragg gratings structure with a reflectivity of 90% at a 1548.36-nm wavelength can be obtained. Cascaded Bragg gratings with different periods are also inscribed in the planar waveguide. Different reflection wavelengths can be realized, which shows great potential for wavelength multiplexing-related applications such as optical communications or sensing. [ABSTRACT FROM AUTHOR]

A novel all-pass slot microring resonator (SMRR), intended for label-free optical biosensing based on silicon-on-insulator platforms, is proposed. The sensor consists of a bent asymmetric directional coupler and an asymmetric-slot microring waveguide. The appropriate slot width of 140 nm is identified by the three-dimensional finite-difference time-domain (3D-FDTD) method for better light–matter interaction in applications. According to numerical calculations, the SMRR sensor with a footprint of 10 µm × 10 µm has a concentration sensitivity of 725.71 pm/% for sodium chloride (NaCl) solutions. The corresponding refractive index sensitivity is 403 nm/RIU (refractive index unit), which is approximately six times greater than that of traditional microring resonator sensors. A low detection limit of 0.129% is also achieved. This SMRR is an excellent candidate for label-free optical biosensors due to its compact structure and excellent sensing capability. [ABSTRACT FROM AUTHOR]

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A high-accuracy unsupervised classification model is developed in a multimode self-interference microring resonator (SIMRR). For the SIMRR, there are many whispering gallery modes (WGMs) present. Each of these resonance modes supported by the SIMRR has a different response to different target parameters, so that the SIMRR-based sensor has the super capability to distinguish between multiple components. In the classification model, principal component analysis (PCA) is firstly used to reduce the dimensionality of this multimode sensing information from the SIMRR-based sensor. When the original higher-dimensional data points are projected onto the lower-dimensional data with only the first few principal components, they can be easily categorized into several different types by using density-based spatial clustering of application with noise (DBSCAN) algorithm. As an example, the unsupervised classification method is numerically validated based on a designed three-gas SIMRR-based sensor. The numerical results prove that the classification model can achieve an ultra high classification accuracy for the designed three-gas sensor with more than 60 dB in signal-to-noise ratio.

We propose a coupled-tolerant subwavelength photonic racetrack resonator (PRR) on the silicon-on-insulator (SOI) platform, in which a subwavelength grating (SWG) PRR is coupled to a symmetrical SWG bus waveguide. The material equivalent refractive index can be manipulated by the SWG characteristic and thus an additional fabrication degree of freedom can be achieved. The resonant characteristics can be improved significantly by controlling the pillar size and increasing the interaction length between SWG racetrack and bus waveguide (RBW). The simulation results show that the PRR has a high-quality factor and large extinction ratio around 1550nm. Two groups of SWG and strip waveguide (SW) PRRs are fabricated. The fabrication tolerance is tested when fabrication error is changed from 0 to 20 nm and the quality factor is more than 7000 in de-ionized water. The testing results show that the tolerance in SWG-PRR has a 2.0-fold improvement than that in the SW-PRR. Then a fabricated SWG-PRR is employed to monitor different concentration glycerol injected on the chip. An optimal quality factor of 9500 around 1550 nm and bulk sensitivity of 412± 0.5 nm/RIU are achieved. Therefore, the structure is a potential candidate for label-free sensing in medical diagnosis and environmental monitoring.

Ring resonator is an essential element in silicon integrated circuit, it is widely used as filter, wavelength multiplexer and switch in single-mode operation regime. As the rapid development of mode division multiplexing (MDM) technique, ring resonator that can process multi-mode signals simultaneously and uniformly is highly desired. However, the severe modal dispersion makes identical transmission for different modes very hard. In this paper, by breaking through the limitation of conventional multi-mode manipulation design with evanescent coupling or mode interference, we propose and demonstrate a multi-mode ring resonator (MMRR) inspired by the free space geometric optics. Arbitrary number of supporting modes can be achieved by simply widening the waveguide width. For proof-of-concept demonstration, an MMRR supporting four modes is fabricated with uniform transmittance. Furthermore, architecture of cascaded four MMRRs are also demonstrated experimentally.

Spoof surface plasmon polaritons (SPPs) with strong subwavelength field confinement and enhancement offer a promising way for realizing integrated on‐chip terahertz (THz) devices. How to find a simple way to control the dispersion of spoof SPPs and then achieve functional on‐chip devices is thus highly desired. Here, the authors theoretically and experimentally demonstrate that such a method can provide sufficient design degrees of freedom to enable versatile THz spoof SPP metadevices. As a proof‐of‐concept demonstration, a series of on‐chip meta‐devices including the switch, the wavelength demultiplexer, and the splitters are presented. The proposed strategy paves a simple way toward the integrated on‐chip THz devices with various functionalities. [ABSTRACT FROM AUTHOR]

The rapid development of optofluidic technologies in recent years has seen the need for sensing platforms with ease-of-use, simple sample manipulation, and high performance and sensitivity. Herein, an integrated optofluidic sensor consisting of a pillar array-based open microfluidic chip and caged dye-doped whispering gallery mode microspheres is demonstrated and shown to have potential for simple real-time monitoring of liquids. The open microfluidic chip allows for the wicking of a thin film of liquid across an open surface with subsequent evaporation-driven flow enabling continuous passive flow for sampling. The active dye-doped whispering gallery mode microspheres placed between pillars, avoid the use of cumbersome fibre tapers to couple light to the resonators as is required for passive microspheres. The performance of this integrated sensor is demonstrated using glucose solutions (0.05–0.3 g/mL) and the sensor response is shown to be dynamic and reversible. The sensor achieves a refractive index sensitivity of ~40 nm/RIU, with Q-factors of ~5 × 103 indicating a detection limit of ~3 × 10−3 RIU (~20 mg/mL glucose). Further enhancement of the detection limit is expected by increasing the microsphere Q-factor using high-index materials for the resonators, or alternatively, inducing lasing. The integrated sensors are expected to have significant potential for a host of downstream applications, particularly relating to point-of-care diagnostics. [ABSTRACT FROM AUTHOR]

We realized integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy of particles in a fluid. In these devices, multiple beams directed towards the device center lead to a local field enhancement around this center and thus counteract the effect of light concentration near the facets, which is a disadvantage of dual-waveguide traps. Thus, a trapping region is created around the center, where a single particle of a size in a wide range can be trapped and studied spectroscopically, free from the influence of surfaces. We report the design (including simulations), fabrication and performance demonstration for multi-waveguide devices, using our Si3N4 waveguiding platform as the basis. The designed ridge waveguides, optimized for trapping and Raman spectroscopy, emit narrow beams. Multiple waveguides arranged around the central microbath result from fanning out of a single input waveguide using Y-splitters. A second waveguiding layer is implemented for detection of light scattered by the trapped particle. For reliable filling of the device with sample fluid, microfluidic considerations lead to side channels of the microbath, to exploit capillary forces. The interference of the multiple beams produces an array of hot spots around the bath center, each forming a local trap. This property is clearly confirmed in the experiments and is registered in videos. We demonstrate the performance of a 2-waveguide and a 16-waveguide device, using 1 and 3 μm polystyrene beads. Study of the confined Brownian motion of the trapped beads yields experimental values of the normalized trap stiffness for the in-plane directions. The stiffness values for the 16-waveguide device are comparable to those of tightly focused Gaussian beam traps and are confirmed by our own simulations. The Raman spectra of the beads (in this work measured via an objective) show clear peaks that are characteristic of polystyrene. In the low-wavenumber range, the spectra have a background that most likely originates from the Si3N4 waveguides.

Mode converters is a key component in mode-division multiplexing (MDM) systems, which plays a key role in signal processing and multi-mode conversion. In this paper, we propose an MMI-based mode converter on 2%-Δ silica PLC platform. The converter transfers E00 mode to E20 mode with high fabrication tolerance and large bandwidth. The experimental results show that the conversion efficiency can exceed −1.741 dB with the wavelength range of 1500 nm to 1600 nm. The measured conversion efficiency of the mode converter can reach −0.614 dB at 1550 nm. Moreover, the degradation of conversion efficiency is less than 0.713 dB under the deviation of multimode waveguide length and phase shifter width at 1550 nm. The proposed broadband mode converter with high fabrication tolerance is promising for on-chip optical network and commercial applications.

The phase modulator is a key component in optical communications for its phase modulation functions. In this paper, we numerically demonstrate a variety of ultra-compact high-efficiency graphene phase modulators (GPMs) based on metal–nanoribbon integrated hybrid plasmonic waveguides in the near-infrared region. Benefiting from the good in-plane mode polarization matching and strong hybrid surface plasmon polariton and graphene interaction, the 20 μm-length GPM can achieve excellent phase modulation performance with a good phase and amplitude decoupling effect, a low insertion loss around 0.3 dB/μm, a high modulation efficiency with VπLπ of 118.67 V μm at 1.55 μm, which is 1–3 orders improvement compared to the state-of-the-art graphene modulators. Furthermore, it has a wide modulation bandwidth of 67.96 GHz, a low energy consumption of 157.49 fJ/bit, and a wide operating wavelength ranging from 1.3 to 1.8 μm. By reducing the overlap width of the graphene–Al2O3–graphene capacitor, the modulation bandwidth and energy consumption of the modulator can be further improved to 370.36 GHz and 30.22 fJ/bit, respectively. These compact and energy-efficient GPMs may hold a key to various high-speed telecommunications, interconnects, and other graphene-based integrated photonics applications. [ABSTRACT FROM AUTHOR]

We demonstrate a four-line selective optical phased array (FLS-OPA) with improved uniformity of radiated beam patterns. The FLS-OPA contains four basic OPA units, which are divided into two symmetric groups with the opposite incident directions of lights. In each group, the grating periods of the OPA units are set to 630 nm and 650 nm, respectively. Besides, a $1\times 4$ thermo-optical switch is used to select an OPA unit out of four as the beam emitting unit. Therefore, four different emitting angles in the vertical direction can be realized by only two grating periods with a fixed wavelength. By tuning the wavelength from 1530 nm to 1635 nm and switching the OPA units, the FLS-OPA achieves a scanning range of 34.2° in the vertical direction, and the corresponding tuning efficiency is 0.33°/nm. In addition, the beam steering range in the horizontal direction is 21.4°. Thus, the overall field of view is $21.4^{\circ } \times 34.2^{\circ }$. Moreover, the symmetrical arrangement of the OPA units can improve the uniformity of the radiated beam patterns in the vertical direction. [ABSTRACT FROM AUTHOR]

Femtosecond laser point-by-point (PbP) technology can be used as a direct writing method to inscribe fiber Bragg gratings (FBGs) into the cladding of optical fibers. When the refractive index modulated area of cladding FBGs (CLFBGs) is close to the core–cladding interface, the CLFBGs exhibit characteristics similar to conventional core-based FBGs. When bending was applied, the reflected power of the CLFBGs changed significantly and showed an orientation dependence on the fiber bending direction. The CLFBG inscription method provides a new opportunity to fabricate vector sensing devices, which can be realized by parallelly inscribed multiple CLFBGs. Compact CLFBGS with a low insertion loss (less than 0.05 dB) have application value in the fields of optical fiber sensors, communications, and lasers. [ABSTRACT FROM AUTHOR]

A converter that manipulates the energy exchange between two arbitrary guided modes having different mode orders and polarization states is proposed. This objective is achieved through engraving a periodic grating on a strip waveguide. Theoretical analysis, based on the coupled-mode theory, is developed to match the proposed structure. In addition, coupling analysis is addressed to provide a comprehensive view regarding the various couplings that can be achieved, including acceptable margins for perturbation designing parameters and their optimum values for each coupling. Moreover, our converter is implemented via both 3D-FDTD simulation and computational solution to examine the validity of the proposed approach and verify the coupling analysis through performing two conversions, namely TM $_{\boldsymbol{1}}$ -to-TE $_{\boldsymbol{0}}$ and TM $_{\boldsymbol{1}}$ -to-TE $_{\boldsymbol{3}}$. The first conversion is obtained with an insertion loss of $\boldsymbol{-1}\,$ dB and a crosstalk lower than $\boldsymbol{-17.5}\,$ dB at a conversion length of $\boldsymbol{9.15\,\mu }$ m. The second is executed with an insertion loss of $\boldsymbol{-1.5}\,$ dB and a crosstalk lower than $\boldsymbol{-15}\,$ dB at a conversion length of $\boldsymbol{16.937\,\mu }$ m. Furthermore, tolerance fabrication analysis is implemented to confirm the degree of stability that the proposed structure can achieve. Finally, the findings reveal that the proposed design achieved its function at a compact length and without being restricted by the hybridization approach. [ABSTRACT FROM AUTHOR]

In this paper, a novel design of a 1×N multimode-interference power splitter is proposed and investigated. By using the finite difference time domain method and particle swarm optimization algorithm, our proposed 1×N optical power splitter can be optimized to realize compact size, good uniformity, low insertion loss, and broad bandwidth. To verify the effectiveness of this design, the designed 1×4 and 1×8 multimode-interference power splitters are experimentally demonstrated on an silicon-on-insulator platform. The lengths of the designed 1×4 and 1×8 power splitters are 36 μm and 47.8 μm, respectively. Experimental results show that, for the fabricated 1×4 power splitter, the uniformity ranges from 0.07 to 0.89 dB and the corresponding maximum insertion loss is 0.62 dB within a bandwidth from 1520 to 1624 nm. For the fabricated 1×8 power splitter, within a bandwidth from 1519 to 1623 nm, the uniformity varies from 0.19 to 0.83 dB and a maximum insertion loss of 0.64 dB are obtained. [ABSTRACT FROM AUTHOR]

Abstract The efficiency of optical power transferred between two bidimensional waveguides, continuous waveguide and periodic subwavelength waveguide has been designed and optimized by using a taper composed by variable length segments (0.03 − 0.27 µm). Waveguides with variable width (270 − 330 nm) have been considered and the number of segments on the taper region has been varied from 10 to 15. The optimized taper was efficiently designed using bio-inspired algorithms based on the genetic algorithms and the artificial immune system. The power coupled has been computed using the frequency domain finite element method. The best solution is 20% shorter than previously existent tapers with coupling light efficiency above 90% over a broadband interval of frequencies and it exhibits high fabrication error tolerances.

All-optical modulators avoid the conversion from external electronic signals to optical signals and thus have the potential to achieve an energy-efficient high-speed photonic system. Phosphorene recently debuted as an attractive material that exhibits outstanding high electron mobility, strong light-matter interaction and modifiable bandgap, making it ideal for all-optical modulators. In this paper, by incorporating a phosphorene and silicon-based micro-ring resonator (MRR), we first propose and experimentally demonstrate a unique phosphorene-integrated all-optical modulator in telecommunications. By utilizing a phosphorene thin film with an average thickness of 22 nm as the absorption material, the rise time of only 479 ns and decay time of 113 ns are achieved, which is the fastest reported response time in the family of phosphorene modulators. The corresponding 3 dB bandwidth is larger than 2.5 MHz, and it exhibits a low-loss performance benefited from its finite bandgap. The proposed phosphorene/MRR hybrid modulator may have potential in the applications of all-optical interconnections.

We demonstrate an integrated photonic platform comprising a refractive index (RI) sensor based on Photonic Molecule (PM) that effectively mitigates the influence of environmental perturbations using a differential measurement scheme while providing high quality-factor (Q) resonances. The RI sensor consists of a partially unclad microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. We report a RI sensitivity of 24 nm/RIU, achieving a limit of detection (LOD) of 1.7 × 10-3 refractive index units (RIU) with improved stability for an operation range of 0.15 RIU in a compact footprint of 40 × 40 μm2, representing an important solution for real-life applications in which measurement conditions are not easily controllable.

Terahertz quantum cascade laser sources with intra-cavity non-linear frequency mixing are the first room-temperature electrically pumped monolithic semiconductor sources that operate in the 1.2–5.9 THz spectral range. However, high performance in low-frequency range is difficult because converted terahertz waves suffer from significantly high absorption in waveguides. Here, we report a sub-terahertz electrically pumped monolithic semiconductor laser. This sub-terahertz source is based on a high-performance, long-wavelength (λ ≈ 13.7 μm) quantum cascade laser in which high-efficiency terahertz generation occurs. The device produces peak output power of 11 μW within the 615–788 GHz frequency range at room temperature. Additionally, a source emitting at 1.5 THz provides peak output power of 287 μW at 110 K. The generated terahertz radiation of

Abstract We analyze and explore the potential of using a polymer horizontal slot waveguide as light-analyte interactive region to implement a low-cost and highly sensitive liquid refractive index sensor. Numerical analysis shows that the optimized polymer horizontal slot waveguide is able to realize high waveguide sensitivity. With the optimized horizontal slot waveguide, polymer liquid refractive index sensors based on Mach-Zehnder interferometer (MZI) and microring resonator (MRR) are then investigated numerically, and the results show that the MZI-based sensor can achieve high sensitivity of 17024nm/RIU and low limit of detection (LOD) of 1.76×10−6 RIU while the MRR-based sensor can achieve the sensitivity of 177nm/RIU and the LOD of 1.69×10−4 RIU with a very small footprint. Compared with the sensors employing conventional silicon or silicon nitride vertical slot waveguide, the sensors employing polymer horizontal slot waveguide exhibit comparable performances but simpler and lower fabrication costs.

Graphene is a material with exceptional optical, electrical and physicochemical properties that can be combined with dielectric waveguides. To date, several optical devices based on graphene have been modeled and fabricated operating in the near-infrared range and showing excellent performance and broad application prospects. This paper covers the main aspects of the optical behaviour of graphene and its exploitation as electrodes in several device configurations. The work compares the reported optical devices focusing on the wavelength tuning, showing how it can vary from a few hundred up to a few thousand picometers in the wavelength range of interest. This work could help and lead the design of tunable optical devices with integrated graphene layers that operate in the NIR. [ABSTRACT FROM AUTHOR]

We report on the design, growth, fabrication, and performance of InAs/InP quantum dash (QD) multi-wavelength lasers (MWLs) developed by the National Research Council (NRC) Canada. The key technical specifications investigated include optical and RF beating spectra, relative intensity noise (RIN), and optical phase noise of each individual wavelength channel. Data bandwidth transmission capacity of 5.376 Tbit/s and 10.8 Tbit/s respectively in the PAM-4 and 16-QAM modulation formats are demonstrated using only a single C-band QD 34.2-GHz MWL chip. We have also developed a monolithic InAs/InP QD dual-wavelength (DW) DFB laser as a compact optical beat source to generate millimeter-wave (MMW) signals. Due to the common cavity, highly coherent and correlated optical modes with optical linewidth as low as 15.83 kHz, spectrally pure MMW signals around 46.8 GHz with a linewidth down to 26.1 kHz were experimentally demonstrated. By using this QD DW-DFB laser, a one GBaud (2 Gbps) MMW over-fiber transmission link is demonstrated with PAM-4 signals. The results show that the demonstrated device is suitable for high speed high capacity MMW fiber-wireless integrated fronthaul of 5G networks. [ABSTRACT FROM AUTHOR]

A high-accuracy unsupervised classification model is developed in a multimode self-interference microring resonator (SIMRR). For the SIMRR, there are many whispering gallery modes (WGMs) present. Each of these resonance modes supported by the SIMRR has a different response to different target parameters, so that the SIMRR-based sensor has the super capability to distinguish between multiple components. In the classification model, principal component analysis (PCA) is firstly used to reduce the dimensionality of this multimode sensing information from the SIMRR-based sensor. When the original higher-dimensional data points are projected onto the lower-dimensional data with only the first few principal components, they can be easily categorized into several different types by using density-based spatial clustering of application with noise (DBSCAN) algorithm. As an example, the unsupervised classification method is numerically validated based on a designed three-gas SIMRR-based sensor. The numerical results prove that the classification model can achieve an ultra high classification accuracy for the designed three-gas sensor with more than 60 dB in signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate on-chip modal crosstalk mitigation over two mode-division multiplexing (MDM) integrated circuits supporting four and eleven waveguide modes employing low-coherence matched detection. 30-Gbaud 8-PSK mode-multiplexed signal is successfully transmitted over the circuits without using multiple-in-multiple-output (MIMO) processing under a maximum modal crosstalk of 10 dB. Ten-mode-multiplexed on-chip transmission achieves a total capacity of 900 Gbit/s. This work shows the feasibility of using high-order modes in on-chip MDM transmission for future high-capacity optical interconnects. [ABSTRACT FROM AUTHOR]

Nonlinear integrated optics leveraging platforms with high nonlinear figure of merit offer energy efficient optical signal processing capabilities. Over the last five years, CMOS-compatible ultra-silico-rich nitride (USRN) has emerged as a promising platform on which to implement various nonlinear optics functions. Bandgap engineered to maximize the Kerr nonlinearity while maintaining two-photon absorption free behavior at telecommunications wavelengths, USRN possesses a nonlinear refractive index that is 100× larger than that in stoichiometric silicon nitride. In this article, we review the recent progress made in USRN-based nonlinear integrated optics devices. The impacts it has made spanning from high gain optical parametric amplification and observations of soliton effects in photonic waveguides and photonic crystal waveguide structures will be discussed. Finally, we assess the future outlook of CMOS-compatible USRN-based nonlinear optics.