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In this paper, solid immersion lenses (SILs) in silicon-based planar waveguides are designed and fabricated. The lenses are designed by the ray-tracing method to optimize the lens profiles. Experimental results show that a minimum spot size of 0.77 μm can be obtained as the calculation prediction. Hence, the SILs combined with other optical components in planar waveguides can alleviate the alignment, tilt, and packaging problems in free-space optical systems. [ABSTRACT FROM PUBLISHER]

On-chip 1-D photonic crystal nanocavities were designed and fabricated in a 300 mm silicon-on-insulator wafer using a CMOS-compatible process with 193 nm immersion lithography and silicon oxide planarization. High quality factors up to 105 were achieved. By changing geometrical parameters of the cavities, we also demonstrated a wide range of wavelength tunability for the cavity mode, a low insertion loss and excellent agreement with simulation results. These on-chip nanocavities with high quality factors and low modal volume, fabricated through a high-resolution and high-volume CMOS compatible platform open up new opportunities for the photonic integration community. [ABSTRACT FROM PUBLISHER]

A new integration technique of a 45-degree micromirror providing a vertical coupling between a free-space wave and a guided wave in a dielectric-glass waveguide for high-density intra-board optical interconnection was described. A planar waveguide consisting of a 4-μm-thickness GeO :SiO guiding core layer and a 2-μm-thickness SiO cladding layer on an SiO substrate was used for characterization of the micromirror. A trench with 8-μm depth and 8-μm width was formed in the waveguide by using a dry etching technique. A photoresist filling the trench was exposed at an angle of 45 degrees in the water to give a 45-degree taper in the trench. Au was evaporated on the taper to give high-reflection micromirror. An excess loss due to the micromirror insertion was estimated to be about 2 dB by comparing insertion losses of waveguides with and without the micromirror. [ABSTRACT FROM PUBLISHER]

In this article, we have theoretically and experimentally investigated the unique vector refractive index (RI) sensing property of tilted fiber grating (TFG). Due to the orthogonal symmetric grating structure, TFGs would mainly achieve the coupling between the fiber core mode and the two orthogonal polarization LP1m of cladding mode. And the numerical simulation results showed that the coupling coefficient between fundamental core mode to the LP1m cladding mode is higher than the others. In the experiment, we have furthermore observed the cladding mode field distribution of excessively TFG (Ex-TFG) and long period fiber grating (LPFG), which indicated that the evanescent field distribution of cladding mode of TFG shows an asymmetric near field distribution with two lobes oriented along the fast axis of TFG, and the one of LPFG has a circularly symmetric cladding mode field distribution. In addition, by employing side-immersion method, we have measured the azimuth RI sensitivities of Ex-TFG, tilted fiber Bragg grating (TFBG) and LPFG, which exhibited that both Ex-TFG and TFBG have shown a direction-dependency RI sensitivity, and the RI sensitivity with side-immersion along fast axis is almost half of the one along slow axis, and the RI sensitivity of LPFG is azimuth independent. Overall, the experiment results show that the TFGs inherently show unique directional RI sensing property, which could be potentially applied in vector sensing area. [ABSTRACT FROM AUTHOR]

We report on the first step-index biodegradable polymer optical fiber (bioPOF) fabricated using commercially available polyesters, with a core made from poly(D,L-lactic-co-glycolic acid) and a cladding made from poly(D,L-lactic acid). We prepared the preforms with a rod-in-tube technique and the fibers with a standard heat drawing process. We discuss the chemical and optical properties of the polyesters along the fabrication process from polymer granulates to optical fiber. More specifically, we address the influence of the processing steps on the molecular weight and thermal properties of the polymers. Cutback measurements return an attenuation of 0.26 dB/cm at 950 nm for fibers with an outer diameter of 1000 ± 50 μm, a core of 570 ± 30 μm, and a numerical aperture of 0.163. When immersed in phosphate-buffered saline (PBS), bioPOFs degrade over a period of 3 months, concurrent with a 91% molecular weight loss. The core decomposes already after three weeks and features 85% molecular weight loss. There is no any additional optical loss caused by immersion in PBS during the first 30–40 min for a bioPOFs with a diameter of about 500 μm. Our result demonstrates that bioPOF can be suitable for applications requiring light delivery, deep into living tissue, such as photodynamic therapy. [ABSTRACT FROM AUTHOR]

Long-period gratings (LPGs) induced in optical fibers show exceptional refractive index (RI) sensitivity and thus they are often applied for label-free biosensing. However, during measurements at changing environmental conditions, the surface of the fiber made of fused silica is subjected to stresses that can cause alterations in its structure. The problem is particularly important when long-term or biosensing measurements are considered and when sensor surface may be exposed to subsequent drying and immersion in aqueous solutions. The aim of this paper was to investigate the influence of sequential drying in air and soaking in water of the fused silica fiber cladding surface on the optical response of LPGs. We demonstrated that transmission spectrum of LPG measured in water before and after drying in air differed significantly and further changed with subsequent drying steps indicating increase of the local RI. All these changes correspond to the alterations in the cladding surface, i.e., its fracturing and pores rearrangement, caused by the stress induced during drying and then immersing in water, as well as possible corrosion and formation of nanosized objects on the cladding surface. The effect can be additionally influenced by washing the samples in organic solvents. We confirmed that measurements done in a flow-cell system, where the sensor was kept wet during the sensing experiment may eliminate the water-induced fiber surface alteration effect and thus minimize the amount of false results. Described findings are highly important for biosensing applications of any optical-fiber-based devices. [ABSTRACT FROM AUTHOR]

We fabricate a 32 × 32 silicon photonics switch on a 300-mm silicon-on-insulator wafer by using our complementary metal-oxide-semiconductor pilot line equipped with an immersion ArF scanner and demonstrate an average fiber-to-fiber insertion loss of 10.8 dB with a standard deviation of 0.54 dB, and on-chip electric power consumption of 1.9 W. The insertion loss and the power consumption are approximately 1/60, and less than 1/4 of our previous results, respectively. These significant improvements are achieved by design and fabrication optimization of waveguides and intersections on the chip, and by employing a novel optical fiber connector based on extremely-high-Δ silica planar-lightwave-circuit (PLC) technology. The minimum crosstalk was −26.6 dB at a wavelength of 1547 nm, and −20-dB crosstalk bandwidth was 3.5 nm. Furthermore, we demonstrate low-crosstalk bandwidth expansion by using output port exchanged element switches. We achieve a −20 dB crosstalk bandwidth of 14.2 nm, which is four-times wider than that of the conventional element switch based 32 × 32 switch. [ABSTRACT FROM AUTHOR]

Electron-beam lithography allows precise photonic crystal (PC) fabrication, but is not suitable for mass production. Therefore, the development and optimization of CMOS-compatible processes is necessary to implement unique nanocavity technologies in optoelectronic circuits. We investigated the quality factors (Q) and the resonant wavelengths (λ) of PC heterostructure nanocavities fabricated by the 193-nm argon fluoride immersion lithography on a 300-mm-wide silicon-on-insulator wafer. We measured 30 cavities distributed over nine chips at various positions of the wafer. An average Q of 1.9 million was obtained for the 30 cavities, and the highest value was 2.5 million, which is the highest Q reported so far for a nanocavity fabricated by photolithography. Such high Q were realized by the improvements of the nanocavity design and the fabrication process. All nanocavities exhibited a Q of larger than 1 million and the fluctuation of the chip-averaged Q was independent of the chip location. On the other hand, the measured λ tended to shift to shorter wavelengths as the distance between the nanocavity and the substrate center increased. Among the nine chips, the difference of the chip-averaged λ was as large as 8.0 nm. We consider that a systematic shift of the average air-hole radius by several nanometers is responsible for the large fluctuation of the chip-averaged λ. These statistical studies provide important hints to accelerate the application study of PC high-Q nanocavities. [ABSTRACT FROM AUTHOR]

Plane-by-plane fabrication of fiber Bragg gratings in optical fibers using a short-pulse femtosecond IR laser is proposed and demonstrated. By incorporating a cylindrical lens in the fabrication setup, a plane of indexmodification can be directly inscribed in the fiber core by a single laser pulse. The planes of index modification are produced in the core of a free-standing fiber without an oil immersion objective. This plane-by-plane method simplifies the direct grating inscription process and allows for the fabrication of complicated grating structures. [ABSTRACT FROM AUTHOR]

We report the development and characterization of a low loss polymer waveguide material with a polysiloxane backbone for enabling the new generation electrooptical printed circuit boards (PCBs). The polymer was designed to have low optical loss of <0.05 dB/cm at 850 nm and low residual stress to withstand the harsh reliability requirements during PCB integration. The thermomechanical properties of the polymer were tuned to exhibit a residual stress of ∼1 MPa over a temperature range of 25 °C to 200 °C in ambient air. Multimode polymer waveguides were fabricated using the polysiloxane polymer and embedded in a six-layer PCB architecture that was subjected to lamination, through-hole via drilling, plating, and IPC shock test (immersion) in solder bath at 288 °C. Eight channels of multimode polymer waveguide spirals of length 1.2 m were fabricated and the insertion loss measured after wave guide fabrication, lamination, and solder reflow. The deviation in insertion loss as a function of the PCB fabrication process was less than 3% with final insertion loss after solder reflow being 0.052 +/- 0.002 dB/cm. This finding presents an optical waveguide material which when embedded in a PCB fabricated using an industry standard process meets reliability requirements while maintaining optical performance. [ABSTRACT FROM AUTHOR]

The temperature dependence of refractive indices for nematic liquid crystal (NLC) is characterized in the near-infrared region by employing an all-fiber ultrasensitive microfiber-assisted Mach–Zehnder interferometer (MAMZI). Owing to the unique thermal-optic properties of NLC, the proposed MZI shows inverse temperature sensitivities of –7.311 and 77 nm/K right above and below the clearing temperature of liquid crystal E7, respectively. Furthermore, the temperature dependences of ordinary and extraordinary refractive indices could be acquired by performing curve fitting on the experimentally measured interference dip wavelength as functions of environmental temperature based on the four-parameter model derived from Vuks equation. [ABSTRACT FROM PUBLISHER]

We propose and experimentally demonstrate a slit beam shaping method for femtosecond laser Point-by-Point (PbP) inscription of highly localized Fiber Bragg Gratings (FBGs). The influence of slit width on the shape and area of Refractive Index Modulation Region (RIMR) induced by a single femtosecond laser pulse was investigated. The shape of RIMR can be changed from a spot to a line with an enlarged RIMR, and hence enhances the coupling strength of core mode and cladding modes. The RIMRs were precisely assembled along the fiber core, producing highly localized FBGs with a spectral comb of pronounced Cladding Mode Resonances (CMRs) intensity of more than 30 dB, a wide wavelength span of 240 nm and a low insertion loss of 0.3 dB. Note that the total processing time for fabricating such a highly localized FBG only requires ∼3.7 s. Subsequently, by including tilted angle on the slit, highly localized tilted FBGs were fabricated and these FBGs show adjustable envelope on the CMRs. Moreover, we investigated the surrounding Refractive Index (RI) response and thermal characteristics of the fabricated highly localized FBGs, which exhibit a sensitivity of 510.87 nm/RIU in a wide RI measurement range and excellent high temperature resistance at 1000°C. Therefore, such highly localized FBGs could potentially be used for multi-parameter sensing in many extreme environments. [ABSTRACT FROM AUTHOR]

A miniaturepolymer Bragg grating (PBG) sensor is fabricated and employed for ultrasonic imaging of seismic physical models (SPMs). The sensing Bragg grating is inscribed into an ultraviolet (UV) glue polymer waveguide with a femtosecond laser. The uniform polymer waveguide is fabricated by sealing the UV glue into a capillary fibre through capillary effect. By using line-by-line inscription technique, the laser beam is scanned transversely to periodically modulate the refractive index of the polymer waveguide, leading to the formation of the PBGs with various grating lengths. The sensor response to ultrasonic waves are investigated experimentally. When compared to single-mode fiber Bragg grating and phase-shifted fiber Bragg grating, the PBG with the same reflectivity presents a higher response amplitude due to its lower Young’s modulus. Besides, the sensor has a good spectral stability when transferred from air to water due to the waterproof coating on the sensor end. Finally, the sensor is used to scan a large-scale 3D SPM and the structural features, such as fault, fluctuation, and depositional termination, can be distinctly reconstructed. The proposed PBG sensor provides a new technique with easy fabrication, high sensitivity, and good stability for high-fidelity ultrasonic imaging of seismicphysical models. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novelsingle-frequency erbium-doped random distributed Bragg reflector fiber laser (RDBR-FL) constructed by a random fiber grating (RFG) and a high-reflection fiber Bragg grating (HR-FBG). Since it is not necessary to precisely control the axial position of the sub-gratings constituting the RFG, the inscription of long RFGs is easy and low-cost. The RFG manufactured by femtosecond laser point-by-point inscription technique has a length of up to 76 mm. The reflection spectrum of the RFG is designed to ensure the stable single-peak emission of the RDBR-FL under the HR-FBG spectral filtering. The bandwidth of the selected reflection peak of the RFG is only 13 pm, which ensures the single frequency operation of the RDBR-FL. The measured linewidth of the RDBR-FL is 3.9 kHz. Experimental measurement shows that the effective cavity length of the RDBR-FL is as long as 109 mm, which is consistent with the theoretical calculation. [ABSTRACT FROM AUTHOR]

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material. [ABSTRACT FROM AUTHOR]

We demonstrate room temperature mid-wave infrared detectors with high peak detectivity. Our detector structures consist of type-II superlattice nBn detectors with ultra-thin ($\sim $ 250 nm) absorbers, integrated into an all-epitaxial guided-mode resonance architecture. The resulting devices show strong spectral selectivity, controlled by grating period, and low dark currents. We achieve room temperature $\vphantom {_{\int }}$ TE-polarized peak specific detectivity ($D^{*}$) of $\approx {1.2\times 10^{10}} \, {\text {cm}\sqrt {\text {Hz}}/\text {W}}$ at $\lambda = {4.4} \,{\mu }\text {m}$ and $\approx {1\times 10^{10}} \, {\text {cm}\sqrt {\text {Hz}}/W}$ at $\lambda = {4.7} \,{\mu }\text{m}$ , for grating periods of $\Lambda = {1.6} \, {\mu }\text{m}$ and $\Lambda ={1.8}\, {\mu }\text{m}$ , respectively. The presented all-epitaxial devices offer a unique approach to efficient room temperature mid-wave infrared detection with strong spectral and polarization selectivity. [ABSTRACT FROM AUTHOR]

An opticalfiber vector magnetometer based on a thin-cladding polarization-maintaining fiber (TPMF) long-period fiber grating (LPFG) and magnetic fluid (MF) is proposed and experimentally demonstrated. The non-circular symmetric fiber structure and asymmetric evanescence field distribution of the LPFG induce a vector surrounding refractive index (SRI) response. Based on the magneto-optical properties of the MF nanoparticles and the directional SRI characteristics of the TPMF-LPFG, the resonance dip wavelength shift of the grating is dependent on the angle between the principal axis of TPMF and the external magnetic field direction when being applied to an external magnetic field. The achieved maximum sensitivity of the wavelength shift was −618 pm/mT when the magnetic intensity changes in the range of 0–10.5 mT. The achieved maximum orientation sensitivity of the sensor was 72 pm/degree, but the magnetic orientation can be detected only within the range of 0–90 degree. The minimum magnetic field intensity that can be detected is about 32.3 μT due to the 0.02 nm wavelength resolution of the optical spectrum analyzer. Our study proves that the high birefringence fiber based LPFG combined with MF can be developed as a high-performance vector magnetometer and such type of sensor is anticipated to find potential applications in magnetic or electric field systems. [ABSTRACT FROM AUTHOR]

The digitization of smart catheters will dramatically increase the demand for reliable and high data transmission in the distal tips. Optical fiber is a good candidate to provide high-speed data transmission. However, the extremely small size of the smart catheter tip, with less than a few millimeters in diameter, hampers the integration of optical fiber connections in the catheter tip. Our work presents a stand-alone optical data link module (ODLM) with a dimension of 240 µm × 280 µm × 420 µm for use in a 1 mm diameter intravascular ultrasound (IVUS) smart catheter. The fabrication of the ODLM is based on the Flex-to-Rigid (F2R) integration technology. In the ODLM, the flexible interconnects reroute the electrical contacts of the flip-chipped vertical-cavity sur-face-emitting laser (VCSEL) to the side of the device. This design enables the ODLM to be mounted on a flex-PCB and fit into a 200–300 µm gap in the IVUS catheter tip. An optical fiber that runs parallel to the catheter shaft is self-aligned to a commercially available VCSEL by inserting it into the through-silicon hole (TSH) of the ODLM. Clear eye diagrams prove the stand-alone ODLM can transmit 25.8 Gb/s, 231−1 Pseudo-Random Binary Sequence (PRBS) when driven through a high-speed bias-tee. The BER test indicates that error-free operation can be achieved at an optical output of around −4 dBm. [ABSTRACT FROM AUTHOR]

Trapping nanoscale particles in a stable and non-destructive way is of great importance to life sciences. Near-field optical tweezers are a common way to trap nanoparticles. Here we propose and demonstrate an all-fiber near-field optical tweezer for trapping nanoparticles using a laser beam that has been totally reflected three times on a fiber tip with a double frustum structure. The light totally internally reflects on the optical fiber end-face and generates an evanescent field that traps the nanoparticles in water. Simulated results show that the evanescent field with high gradient distribution generating on the optical fiber end face leads to an insignificant temperature rise (0.0765 K). The experimental results demonstrate that all-fiber near-field optical tweezer allows us to trap fluorescent particles as small as 100 nanometers in diameter. The max temperature rise is 0.091 K. Compared with the plasmonic optical tweezers, the all-fiber optical tweezer reduces the thermal effect. The proposed all-fiber near-field optical tweezer plays an essential role in nanoscale optical trapping. [ABSTRACT FROM AUTHOR]

Fiber–optic sensors have been widely deployed in various applications, and their use has gradually increased since the 1980 s. Distributed fiber–optic sensors, which enable continuous and real–time measurements along the entire length of an optical fiber cable, have undergone significant improvements in underlying industries. In the oil and gas industry, distributed fiber–optic sensors can provide significantly valuable information throughout the life cycle of a well and can monitor pipelines transporting hydrocarbons over great distances. Here, we review the deployment of fiber–optic Rayleigh–based distributed acoustic sensing (DAS), Raman–based distributed temperature sensing (DTS), and Brillouin–based distributed temperature and strain sensing (DTSS) in the oil and gas industry. In particular, we describe the operation principle and basic experimental setups of the DAS, DTS, and DTSS, highlighting their applications in the upstream, midstream, and downstream sectors of the oil and gas industry. We further developed a prototype of a fiber–optic hybrid DAS–DTS system that simultaneously measures vibration and temperature along a multimode fiber (MMF). The reported hybrid sensing system was tested in an operational oil well. This work also discusses the challenges that might hinder the growth of the distributed fiber–optic sensing market in the petroleum industry, and we further point out the future directions of related research. [ABSTRACT FROM AUTHOR]

We report on an extrinsic surface plasmon-enhanced refractometer based on cladding mode resonance excitation in a photonic crystal fiber (PCF) equipped with a straight fiber Bragg grating (FBG). First, we show that the lattice pitch and the air hole diameter of the PCF microstructure define the spectral location of the excited cladding mode resonances. Second, we demonstrate that if the PCF parameters are properly selected, those resonances are sensitive to increases in steps of 1 × 10−4 refractive index units (RIU) of the refractive index value close to that of water. To the best of our knowledge, this is the first time that the sensitivity of PCF cladding mode resonances to refractive index changes in water-based solutions is reported. We achieved experimental values of 40.3 nm/RIU in terms of wavelength sensitivity and −801 dB/RIU in terms of amplitude sensitivity. The performance of our sensor is therefore comparable to that of tilted FBGs in step-index fibers used for water refractometry, which indicates the potential of our PCF sensor for biosensing. In addition, the sensor fabrication does not require any post-processing such as etching or polishing, which allows preserving the integrity of the fiber probe. Finally, the narrow spectrum within which the PCF operates, allows envisaging multi-target detection with a single fiber probe by using cascaded wavelength-multiplexed gratings. [ABSTRACT FROM AUTHOR]

We propose an efficient analytical method to evaluate the robustness of integrated photonic devices and circuits in the presence of independently-distributed random variations in the device parameters. By approximating the output of a photonic system in terms of a first or second-order Taylor series, we derive closed-form expressions for the mean and variance of the system output, which allow us to compute the one-standard-deviation (1-sigma) bounds on the expected system performance. Compared to other approaches for evaluating robustness, our method does not require computationally-intensive numerical simulations of the system output and can apply to any statistical distribution of parameter variations, including uniform and normal distributions. We demonstrate the method by analyzing the robustness of two coupled resonator systems: a fifth-order microring filter, and optical delay lines based on 1D Coupled Resonator Optical Waveguides and 2D Floquet topological microring lattice. Our method could provide a useful tool in the design and analysis of robust optical devices and circuits. [ABSTRACT FROM AUTHOR]

This paper aims to give an outlook of future advanced antenna systems for 5G and 6G wireless networks. The trend to increase the peak data rate and to reduce latency and power consumption will continue in the future. This will be made possible by the exploitation of millimeter wave frequency bands and by the introduction of massive multiple-input multiple-output antenna technology which requires a transformation of the antenna hardware architectures and technologies. Advanced antenna systems based on arrays of several hundreds of antenna elements are under development and to keep the fronthaul throughput manageable, some digital signal processing functions have been moved inside the antenna, creating the need to distribute very big volumes of data at high bit rate across the antenna. The characteristics and hardware architecture of future advanced antenna systems are discussed and the relevant interconnect requirements are presented. A new type of monolithically integrated optical transceiver is presented, integrating electronic and photonic circuits on the same chip with high bandwidth density, high energy efficiency and low latency. The transceiver technology is discussed and results of experimental demonstrations are given. [ABSTRACT FROM AUTHOR]

As implantable optical systems recently enabled new approaches to study the brain with optical radiations, tapered optical fibers emerged as promising implantable waveguides to deliver and collect light from sub-cortical structures of the mouse brain.They rely on a specific feature of multimodal fiber optics: as the waveguide narrows, the number of guided modes decreases and the radiation can gradually couple with the environment. This happens along a taper segment whose length can be tailored to match with the depth of functional structures of the mouse brain, and can extend for a few millimeters. This anatomical requirement results in optical systems which have an active area that is very long compared to the wavelength of the light they guide and their behavior is typically estimated by ray tracing simulations, because finite element methods are too computationally demanding. Here we present a computational technique that exploits the beam-envelope method and the cylindrical symmetry of the fibers to provide an efficient and exact calculation of the electric field along the fibers, which may enable the design of neural interfaces optimized to meet different goals. [ABSTRACT FROM AUTHOR]

A three-parameter sensor based on a point-by-point fiber Bragg grating (PBP-FBG) is proposed. The fabricated sensor is 40 mm long. The spectrum loss at 1336.15 nm is selected to measure the surrounding liquid level. The sensitivity for liquid level sensing is −0.046 dB/mm. The temperature is measured using the Bragg dip shifts with sensitivity of 10.06 pm/ °C. The cut-off mode shift is used to measure the surrounding refractive index with sensitivity of 535.14 nm/RIU. As a benefit of femtosecond laser direct inscription fabrication, the grating length is controllable and the liquid level sensing range is expandable. This sensor provides a simple, reliable method for accurate liquid level, temperature and refractive index measurements in hazardous environments. [ABSTRACT FROM AUTHOR]

An optical fiber in-line Mach-Zehnder interferometer based on an inner air-cavity with long cavity length is demonstrated. The device is fabricated by using femtosecond laser to inscribe a waveguide structure in the optical fiber core, followed by discharging the waveguide area with a fusion splicer. The inner air-cavity structure is highly robust, and the relatively long cavity length corresponds to a small free spectral range, which makes it possible to implement accurate measurement. Such an inner air-cavity device fabricated in single mode fiber has good high temperature sustainability. The device is also “open” to the external environment when being fabricated in multimode fiber, thus supporting refractive index measurement. The proposed device is attractive in many optical fiber sensing applications. [ABSTRACT FROM AUTHOR]

Fiber Bragg gratings (FBGs) inscribed by using femtosecond laser point-by-point (PbP) technology typically have high birefringence due to the elliptical cross-sectional pattern of refractive index modulations (RIMs) created in the fiber core. Additionally, a highly reflective type II PbP FBG, which has a large coupling coefficient, also exhibits large insertion loss due to the limited RIM area induced by a single femtosecond laser pulse. Here we demonstrate a slit beam shaping method for femtosecond laser PbP inscription of high-quality FBGs, featuring by high reflectivity, low insertion loss, and low birefringence. The slit beam shaping method could reduce the ellipticity in the cross-sectional pattern of RIMs without reducing the cross-sectional area, leading to low birefringence and low insertion loss. The experimental results agree well with numerical calculations. Hence, a high-quality type II PbP FBG, which has high reflectivity of 99.12% (i.e., Bragg resonance attenuation of 20.52 dB), low insertion loss of 0.30 dB, and low birefringence of 1.86 × 10−6, was successfully created by use of a slit width of 0.8 mm. Moreover, an enlarged cross-sectional area was created by use of a slit width of 0.2 mm, resulting in a high ratio of 172.46 of the coupling strength coefficient to the scattering loss coefficient in the fabricated PbP FBG, which exhibits very high reflectivity of 99.99% (i.e., a strong Bragg resonance attenuation of 46.65 dB) and low insertion loss of 0.27 dB. Such high-quality FBGs will be promising in many applications, such as optical fiber communications, sensors, and lasers. [ABSTRACT FROM AUTHOR]

Many breakthroughs in the laboratories often do not bridge the gap between research and commercialization. However, silicon photonics bucked the trend, with industry observers estimating the commercial market to close in on a billion dollars in 2020. Silicon photonics leverages the billions of dollars and decades of research poured into silicon semiconductor device processing to enable high yield, robust processing, and most of all, low cost. Silicon is also a good optical material, with transparency in the commercially important infrared wavelength bands, and is a suitable platform for large-scale photonic integrated circuits. Silicon photonics is therefore slated to address the world's ever-increasing needs for bandwidth. It is part of an emerging ecosystem which includes designers, foundries, and integrators. In this paper, we review most of the foundries that presently enable silicon photonics integrated circuits fabrication. Some of these are pilot lines of major research institutes, and others are fully commercial pure-play foundries. Since silicon photonics has been commercially active for some years, foundries have released process design kits (PDK) that contain a standard device library. These libraries represent optimized and well-tested photonic elements, whose performance reflects the stability and maturity of the integration platforms. We will document the early works in silicon photonics, as well as its commercial status. We will provide a comprehensive review of the development of silicon photonics and the foundry services which enable the productization, including various efforts to develop and release PDK devices. In this context, we will report the long-standing efforts and contributions that previously IME/A*STAR and now AMF has dedicated to accelerating this journey. [ABSTRACT FROM AUTHOR]

Ultra-high-definition (UHD) technologies have recently received attention on account of their practical applications in consumer electronics. UHD devices require uncompressed video transmission at a data rate exceeding 100 Gb/s; thus, an optical fiber connection is essential. In consumer applications, optical fibers are very short. Moreover, their connections must permit variations in the fiber alignment, which accommodates rough handling by consumers. Under this condition, the transmitted signal quality is significantly degraded owing to noise and instabilities that strongly depend on the fiber alignment conditions in optical modules and connectors. Therefore, graded-index plastic optical fibers (GI POFs) are promising optical cables for consumer applications because of their flexibility, safety, and high bandwidth. Recently, the authors experimentally demonstrated that GI POFs can reduce interferometric noise, such as modal noise and multipath interference noise, in a multimode fiber link based on a vertical-cavity surface-emitting laser (VCSEL). This noise reduction effect results from strong mode coupling of GI POFs, which is closely related to microscopic heterogeneous structures of a core polymer matrix. In this paper, a control method of mode coupling using the copolymerization process for fiber core materials is proposed. The formation of composition fluctuations by copolymerization increases the mode coupling in the GI POF core. It thereby enables highly stable and robust data transmission with a large fiber misalignment tolerance in a VCSEL-based multimode fiber link. The proposed method for mode coupling control is expected to contribute to household optical communication systems in the upcoming UHD era. [ABSTRACT FROM AUTHOR]

By filling the liquid crystal (LC) in the air holes of a photonic crystal fiber (PCF) with 8 mm length, a compact multi-band thermal optical switch is proposed here including two important telecommunication band, i.e., 1265 to 1317 nm and 1508 to 1568 nm. Within the bandwidth, the extinction ratio can be as high as 30 dB. Under the combined action of the bandgap-guiding mechanism and the interference effect, a temperature change of only 1 °C after clearing temperature (Tc) of the LC induces multi-band thermal optical switch of the LC-filled PCF. It is also noted that the transmission spectrum of the LC-filled PCF is quite sensitive to the ambient temperature. The consequent thermal sensitive is 3.9 nm/°C, making it a very good candidate for monitoring the temperature herein. [ABSTRACT FROM AUTHOR]

We propose an ultra-compact novel wavelength multiplexer employing a (N + 1) × (N + 1) arrayed waveguide grating (AWG) and a polarization-combiner-rotator (PCR) on the SOI platform, to realize a multiplexing for 2N wavelengths with a spacing of Δλ. The (N + 1) × (N + 1) AWG works at a bidirectional way to provide two groups of N × 1 wavelength multiplexing with each group having a channel spacing of 2×Δλ, and the central wavelengths of all input channels in one group have a wavelength shift of Δλ with respect to those in the other group. The double channel spacing results in a significant decrease on the footprint of the (N + 1) × (N + 1) AWG-based multiplexer compared with a conventional 2N × 1 AWG multiplexer with the same wavelength spacing Δλ. Due to the fact that a single mode fiber is insensitive to the polarization of input light, if we consider short reach datacom applications such as 100/400 GbE, the two separate multiplexing outputs of the (N + 1) × (N + 1) AWG can be combined as one output with one half wavelengths working at TE polarization and the other at TM polarization by employing a low loss and broadband PCR. In the experiment, we demonstrate a 16 × 200 GHz multiplexer based on a 9 × 9 AWG. The experimental results show that the on-chip loss of the fabricated multiplexer is 2.7 dB and the loss uniformity is 0.5 dB. The 1-dB and 3-dB bandwidths are >0.56 nm (i.e., 35% of the wavelength spacing) and >1.1 nm (i.e., 69% of the wavelength spacing), respectively. They can also be further increased by decreasing the gap between adjacent input waveguides at the interfaces of star couplers of the designed AWG without inducing an excess loss. The proposed multiplexer has great potential for application to future super large capacity (> Tb/s) data transmission systems. [ABSTRACT FROM AUTHOR]

An optical fiber in-line Fabry--Perot interferometric device is presented for ultrasensitive strain sensing by use of vernier effect. The device consists of two parallel structured Fabry--Perot cavities in cascaded connection, formed by two pairs of femtosecond laser inscribed in-fiber reflection mirrors. The cavity lengths and their difference can be accurately controlled, which enables an extremely large amplification factor when vernier effect is used and the strain sensitivity achieved is ∼236.32 pm/μϵ. Moreover, the temperature cross sensitivity realized is as low as ∼29.2 nϵ/°C. The device is featured with ultra-compact size, robust structure, easy fabrication, convenient operation and good reproducibility, which makes it highly attractive in many sensing applications where extremely large strain sensitivity is critically required. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a port-alternated switch-and-select architecture for planar waveguide-based optical switches. The proposed architecture reduces the number of intersections on a path, which leads to both small insertion loss and small path dependence. We demonstrate an 8 × 8 optical switch based on the proposed architecture using a silicon photonic platform, which exhibits a fiber-to-fiber insertion loss of 5.7 dB with a crosstalk below −30 dB. We discuss the scalability of the switch, including the propagation and bend losses of the waveguides. [ABSTRACT FROM AUTHOR]

In this article, we report the development of a strictly non-blocking 8 × 8 silicon photonics switch designed to operate in the O-band. This 8 × 8 switch is based on path-independent insertion-loss topology and is composed of 2 × 2 thermo-optic double Mach–Zehnder switches and adiabatic intersections. The fabricated 8 × 8 switch chip is electrically packaged with a ceramic chip carrier and inserted into a socket on a printed circuit board. As for the optical connection, an optical fiber array and edge couplers are used. The fabricated 8 × 8 switch exhibits an average fiber-to-fiber insertion loss of 16.6 dB, including a fiber to chip coupling loss of 11.2 dB and crosstalk of less than −30 dB over a bandwidth of 70 nm. Moreover, we investigate the nonlinear characteristics of Si devices in the O-band. The cw input/output response and degradation free 28-Gb/s OOK signal transmission demonstrate that two-photon absorption and four-wave mixing are not significant when the input power is less than approximately 4 mW. These results indicate that it is possible to produce low-loss and low-crosstalk silicon photonics switches that operate in the O-band. [ABSTRACT FROM AUTHOR]

We report ultra-low propagation losses in silicon sub-micrometric waveguides on a 200 mm CMOS compatible photonics platform. We show median losses in C-band (O-band) as low as 0.1 dB/cm and 0.7 dB/cm (0.14 dB/cm and 1.1 dB/cm) in monomode rib and strip waveguides, respectively, thanks to a H2 smoothing annealing. In addition to the significant loss reduction, we show that the performance characteristic of the main passive and active components of the photonics platform are preserved or even improved by the smoothing process. [ABSTRACT FROM AUTHOR]

We proposed and fabricated a microwave-frequency photonic fiber grating (MPFG) by femtosecond laser micromachining on optical fibers. Illuminated by low coherent light source, the MPFG can be interrogated using proposed microwave photonic system to show the resonant peaks in microwave frequency domain. We studied the working principle and characteristics of this device. After that, we discussed the influence of fiber type, apodization and light source coherence lengths on this device. The device can also respond to ambient temperature change like fiber optic sensors. [ABSTRACT FROM AUTHOR]

On-chip waveguide-integrated suspended microcavity resonator as a good sensing element is constantly pursued combining with the advantages of an optical material to enhance device performance. In this work, low-loss waveguide-integrated suspended Ge11.5As24Se64.5 microdisk resonators have been successfully demonstrated using an optimized etching recipe. The realization of propagation loss down to 0.48 dB/cm verifies the low-loss characteristic of chalcogenide glass rectangular waveguide. An optical loaded quality factor of 1.1 × 106 for the no suspended microdisk resonator, approaching to the highest figure (1.2 × 106) so far reported in planar chalcogenide optical devices, is obtained experimentally to reveal the natural evolution of high quality chalcogenide glass membrane during the engineering of shallow suspension configuration. By comparing with the scattering loss of mode in no suspended case, the contributions of bottom roughness scattering to the optical losses increase exceeding 50% in the shallowly suspended counterparts. The optimization and optical losses analysis of the waveguide-integrated suspended chalcogenide microdisk resonators are helpful to further estimate its potentials in the emerging stress or strain sensors. [ABSTRACT FROM AUTHOR]

The construction of fiber Bragg grating (FBG) unit is of great technological importance for various distributed remote sensing applications. A major challenge is the effective suppression of its temperature sensitivity without the additional complex structure or back-end calculation. Here we present a topological engineering strategy for notably reducing the temperature sensitivity of FBG in multicomponent glass system. The theoretical analysis indicates that the temperature insensitive FBG unit can be realized via introduction of self-compensation mechanism, based on combination of the positive thermal expansion and negative thermal-optic effect. Guided by the theory analysis, two typical multicomponent glass fibers are constructed and FBG is inscribed by femtosecond laser into the fiber core. Sensing tests show that the lowest temperature sensitivity of the fiber reaches to ∼8.3 pm/ °C, which is low than that of the standard commercial device (∼13.7 pm/ °C). The findings described here suggest an attractive opportunity to constructing new class of fiber probe with controllable optical response by topological engineering in multicomponent glass. [ABSTRACT FROM AUTHOR]

To mimic extreme downhole application conditions, a series of optical fibers was aged in crude oil at a pressure of 2000 psi and temperatures of 100–300 °C. The fibers under investigation used various coatings, including dual and single acrylate, silicone/acrylate, carbon/acrylate, silsesquioxane-type hybrid, polyimide, carbon/polyimide, acrylate/PFA and polyimide/PFA. Interactions with crude oil led to swelling, delamination, and dissolution of some of the coatings, which ultimately resulted in reduction of mechanical strength of the fibers. For different coating types, the temperatures were determined above which a significant strength degradation was observed. Carbon/polyimide, acrylate/PFA, and polyimide/PFA coatings were found to be the most oil-resistant. The amount of hydrogen generated by crude oil was evaluated from the attenuation spectra collected from the immersed fibers. For this analysis, two fibers (one doped with germanium and the other with germanium and phosphorus) were utilized as sensors. Using this approach, it was possible to estimate the amount of hydrogen generated by crude oil at different temperatures. [ABSTRACT FROM AUTHOR]

Data communication in silicon photonic interconnects requires efficient and broadband on/off-chip coupling components. Recently, perfectly vertically-emitting grating couplers have been proposed to increase spatial I/O density of the optical link and potentially improve manufacturing costs and ease of optical beam characterization. In this article, adjoint optimization was leveraged in the design of low-loss single (silicon) and dual layer (silicon + silicon nitride) perfectly-vertical grating couplers that are compatible with a scalable silicon-on-insulator (SOI) platform for the 65 nm CMOS technology node. In simulation, the best design peaks at −0.52 dB insertion loss with a 1 dB-bandwidth of 24 nm at the 1310 nm datacom wavelength. [ABSTRACT FROM AUTHOR]

The electrical interconnects in high performance computing (HPC) systems are reaching their bandwidth capacities in supporting data-intensive applications. Currently, communication between compute nodes through these interconnects is the main bottleneck for overall HPC system performance. Optical interconnects based on the emerging silicon photonics (SiP) platform are considered to be a promising replacement to boost the speed of the data transfer with reduced cost and energy consumption compared to electrical interconnects. In this paper, we present a comprehensive analysis of a comb source microring-based SiP link architecture with p-i-n photodetectors. In particular, we direct our focus on improved grating coupler and bus waveguide designs to reduce the link power penalties. Additionally, we map the required performance from the comb laser to provide an aggregated data rate of 1 Tbps under the constraints of free spectral range (FSR) and nonlinearities of the microring resonators (MRRs). We show that a select few comb configurations satisfy these requirements, and energy consumption as low as $3\,\frac{\text{pJ}}{\text{bit}}$ is achievable. [ABSTRACT FROM AUTHOR]

We propose a novel silicon photonics wavelength selective switch (WSS) with sidewall-corrugated contra-directional couplers (C-DCs), which has an unlimited free spectral range and is suitable for broadband operation. Fabricated 2 × 2 1-ch and 2-ch WSSs demonstrate the expected operation with channel wavelengths of 1532 and 1553 nm, a 3-dB bandwidth of ∼3 nm, a flattop spectral shape, and an outband extinction ratio larger than 30 dB over a wavelength range wider than C-band. We discuss a limiting factor for the lower inband extinction of ∼15 dB, which is a leakage to the bar port in the Mach–Zehnder (MZ) switch. Matching the center wavelength of each MZ switch to the Bragg wavelength of the corresponding C-DCs will improve the inband extinction ratio to be larger than 30 dB. [ABSTRACT FROM AUTHOR]

In order to support continuous growth of global IP traffic, highly energy-efficient networks are demanded. One of the key components is an optical multicast switch which has large bandwidth with small power consumption. When using multicast switches, however, intrinsic losses will be an issue especially for large port count switches. Erbium doped fiber amplifiers (EDFAs) are typically used for the loss compensation, although it would much increase the number of components and footprint of the system. One of the options to solve this problem would be an integration technology of semiconductor optical amplifiers (SOAs) on the silicon photonics switches which we have recently developed. In the previous work, we have demonstrated a gain-integrated 4 × 4 silicon matrix switch. For the practical use of our technology, it is very important to show further scalability of the platform. Moreover, it is also important to show applicability to other switch topologies, such as multicast switches. In this article, we demonstrate an 8 × 8 silicon photonics multicast switch with on-chip integrated 2 × 4-ch. SOAs. The on-chip SOAs exhibit a net gain of ∼9 dB, which almost compensates for the intrinsic loss. We observe the crosstalk of less than −35 dB. Loss/crosstalk reduction and chip power consumption are also discussed. [ABSTRACT FROM AUTHOR]