Integration Of Optical Waveguides Research Articles

Mode thermo-optic coefficient engineering of sub-wavelength gratings and its application for a mode-insensitive switch.

It is shown that the thermo-optic (TO) coefficients of various waveguide modes of a sub-wavelength grating (SWG)-assisted strip waveguide is closely dependent on the various waveguide parameters with different dependencies, including the SWG width, strip waveguide width, duty cycle, and pitch. This offers what we believe to be new degrees of freedom in the design of TO coefficients for integrated-optic waveguides, opening the door to engineering the TO coefficients of individual spatial modes or polarization states using sub-wavelength structures. Such a capability is expected to offer new design possibilities for a variety of integrated photonic, thermo-optic devices. To demonstrate the application of the concept, a mode-insensitive switch on silicon-on-insulator using a TO coefficient-engineered SWG as a mode-independent, thermo-optic phase shifter is designed and experimentally demonstrated. The experimental results show that the switching powers of the TE0-TE2 modes are only ∼29 mW, and the maximum extinction ratios for the cross (bar) states are 38.2 dB (31 dB), 37.9 dB (37 dB), and 31.9 dB (20.5 dB) for the TE0-TE2 modes, respectively, at the wavelength of 1550 nm.

On-Chip Ultralow-Threshold Tunable CdSSe Nanobelt Lasers Excited by the Emission of Linked ZnO Nanowire.

The integration of optical waveguide and on-chip nanolasers source has been one of the trends in photonic devices. For on-chip nanolasers, the integration of nanowires and high antidamage ability are imperative. Herein, we realized the on-chip ultralow-threshold and wavelength-tunable lasing from alloyed CdSSe nanobelt chip that is excited by the emission from linked ZnO nanowires. ZnO nanowire arrays are integrated into CdSSe nanobelt chips by the dry transfer method. A one-dimensional (1D) ZnO nanowire forms high-quality optical resonators and serves as an indirect pumping light to stimulate CdSSe nanobelt chips, and then wavelength-tunable lasing is generated with the ultralow threshold of 3.88 μW. The lasing mechanism is quite different than direct excitation by nanosecond laser pulse and indirect pumping by ZnO emission. The ZnO-CdSSe blocks provide a new solution to realize nanowire lasing from linked nanowires rather than direct laser pumping and thus avoid the light direct damage under general nanosecond laser excitation.

Immersive Tuning the Guided Waves for Multifunctional On‐Chip Metaoptics

AbstractWith the great promise to reshape the landscape of photonic integrated circuits (PIC), the introduction of metasurface onto optical waveguide integration gives rise to tremendous potential functionalities via converting the guided waves to free‐space, including directional beam‐steering, mode‐conversion, optical on‐chip router, etc. Despite these endeavors, on‐chip metaoptics still faces critical challenges to achieve multifunctionalities with dynamic switchable ability between arbitrary‐encoding channels. Here, a series of novel on‐chip metaoptics functionalities are originally proposed and experimentally demonstrated. Through utilizing a serial optimization algorithm of computer‐generated hologram (CGH), a 3D hologram with multiple sliced information channels is successfully enabled to project above the on‐chip space. Moreover, by strategically exploring water immersive tuning scheme, on‐chip dynamic tuning in real‐time is realized for dual‐channel arbitrary‐encoded hologram, practically verified as a large‐scale easy‐accessible switch method. Eventually, the encoding freedom is further expanded by breaking the degeneracy of forward/backward guided propagations, beyond the state‐of‐art of multiplexing and information storage capacity. This study can easily find paths to numerous practical applications in the next generation of AR display, 3D vision, optical storage, and photonics integrated devices.

Erratum to “Computational analysis of the effect of SOI vertical slot optical waveguide specifications on integrated-optic biochemical waveguide wensitivity”

Erratum to “Computational analysis of the effect of SOI vertical slot optical waveguide specifications on integrated-optic biochemical waveguide wensitivity”

Toward optical coherence tomography on a chip: in vivo three-dimensional human retinal imaging using photonic integrated circuit-based arrayed waveguide gratings

In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system.

Thermoforming of planar polymer optical waveguides for integrated optics in smart packaging materials

Abstract The innovations in smart packaging will open up a wide range of opportunities in the future. This work describes the processing of additive manufactured and planar integrated polymer optical waveguides for use in smart packaging products. The previously published combination of flexographic and Aerosol Jet printing is complemented by thermoforming and thus creates three-dimensional integrated multimode waveguides with optical attenuation of 1.9 dB/cm ± 0.1 dB/cm @ 638 nm. These properties will be the basis to develop smart applications in packaging materials.

Minimized two- and four-step varifocal lens based on silicon photonic integrated nanoapertures.

Integration of optical waveguide and subwavelength structure may help address the problems of large footprint, low robustness, and small operation bandwidth, those of that are typically inborn in traditional integrated optical devices. Here, a design method of an ultra-compact small footprint lens is proposed. Combing particle swarm optimization (PSO) algorithm with spatial multiplexing technology, we successfully integrated two- and four-step varifocal lenses on SOIs chips with small footprint of 35×35 µm2, non-mechanically leading to 2.5× and 3.4× zoom capacity, respectively. The proposed designed method may shed a new light on compact on-chip display devices and offer an alternative approach to design integrated optical communication with high information storage capacity.

Low loss CMOS-compatible silicon nitride photonics utilizing reactive sputtered thin films.

Low temperature deposition of low loss silicon nitride (SiN) thin-films is very attractive as it opens opportunities for realization of multi-layer photonic chips and hybrid integration of optical waveguides with temperature sensitive platforms such as processed CMOS silicon electronics or lithium niobate on insulator. So far, the most common low-temperature deposition technique for SiN is plasma enhanced chemical vapor deposition (PECVD), however such SiN thin-films can suffer from significant losses at C-band wavelengths due to unwanted hydrogen bonds. In this contribution we present a back end of line (< 400°C), low loss SiN platform based on reactive sputtering for telecommunication applications. Waveguide losses of 0.8 dB/cm at 1550 nm and as low as 0.6 dB/cm at 1580 nm have been achieved for moderate confined waveguides which appear to be limited by patterning rather than material. These findings show that reactive sputtered SiN thin-films can have lower optical losses compared to PECVD SiN thin-films, and thus show promise for future hybrid integration platforms for applications such as high Q resonators, optical filters and delay lines for optical signal processing.

Sensing Infrared Photons at Room Temperature: From Bulk Materials to Atomic Layers.

Room-temperature operating means a profound reduction of volume, power consumption, and cost for infrared (IR) photodetectors, which promise a wide range of applications in both military and civilian areas, including individual soldier equipment, automatic driving, etc. Inspired by this fact, since the beginning of 1990s, great efforts have been made in the development of uncooled thermal detectors. During the last two decades, similar efforts have been devoted using IR photon detectors, especially based on photovoltaic effects. Herein, the proven technologies, which have been commercialized with a large format, like InGaAs/InP pin diodes, InAsSb barrier detectors, and high-operating-temperature HgCdTe devices, are reviewed. The newly developed technology is emphasized, which has shown unique superiority in detecting mid-wavelength and long-wavelength IR signals, such as quantum cascade photodetectors. Finally, brand-new concept devices based on 2D materials are introduced, which are demonstrated to provide additional degrees of freedom in designing and fabricating room-temperature IR devices, for example, the construction of multi-heterojunctions without introducing lattice strain, the convenient integration of optical waveguides and electronic gratings. All information provided here aims to supply a full view of the progress and challenges of room-temperature IR detectors.

Study and Analysis of Light Scattering Loss in Irregular Integrated Optical Waveguides

Results are presented that have been obtained in numerical and experimental investigations of three-layer single-mode and multimode polystyrene, liquid, and liquid-crystal integrated optical waveguides. Numerical simulation results are presented and compared to the experimental data. The form of the scatter diagram from both the coordinates of the observation points and the waveguide phase slow-down factor is investigated. Characteristic experimental scatter diagrams in the plane transverse to the plane of incidence are given for TE- and TM-polarization. Calculated and experimental scatter diagrams are found to be in satisfactory agreement. Measurement of optical loss in the waveguides has allowed determining, in particular, the root-mean-square roughness height of the substrates of the polystyrene and liquid waveguides, which fairly corresponds to the known surface finish. In the liquid-crystal waveguide, the investigations have been focused on the features of the TE- and TM-mode scattering in a wide range of the phase slow-down factor variation. Complicated nonlinear processes of radiation field transformation beyond the waveguide are observed experimentally and through numerical simulation. Statistical parameters obtained for the irregularities of the investigated waveguides are presented. In addition, the root-mean-square estimates are given for spatial fluctuations of the director and compared to the average correlation radius for fluctuations of local orientation of nematic liquid crystal molecules.

Модель многослойного плавно-нерегулярного интегрально-оптического волновода в нулевом векторном приближении: теория и численный анализ.

Модель многослойного плавно-нерегулярного интегрально-оптического волновода в нулевом векторном приближении: теория и численный анализ.

Oblique angle deposited silver islands on Ge20Se70Te10 film substrate for surface-enhanced infrared spectroscopy

Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful tool for characterizing and identifying chemical/biological species. Though SEIRA technique has enabled detection up to few molecule levels with sophisticated device structures, there is still room for improvement (can extend to detect down to a single molecule). Superior sensor platforms can be developed by incorporating advanced substrate material, so as to be actively employed in trace analysis, forensic sciences etc. In this work, chalcogenide glass of composition Ge20Se70Te10 is characterized to probe its usability as a SEIRA substrate. Silver island structures were developed on Ge20Se70Te10 film via oblique angle deposition and its SEIRA response was recorded using FTIR spectrometer with Hexa Decane Thiol (HDT) as the analyte. Investigations reveal an optimum silver thickness at which maximum absorption enhancement is obtained. The response of the system to variations in the analyte concentration is also explored. Studies prove them to be a promising candidate as an IR substrate which can be used to develop integrated optical waveguide for highly sensitive SEIRA spectroscopy.

Cascaded Integration of Optical Waveguides With Third-Order Nonlinearity With Lithium Niobate Waveguides on Silicon Substrates

The cascaded integration of optical waveguides with third-order optical nonlinearity ( $\chi ^{(3)}$ susceptibilitiy) with lithium niobate (LiNbO $_{3}$ ) waveguides is demonstrated on the same chip. Thin-film (LiNbO $_{3}$ ) and chalcogenide (ChG) glass (Ge $_{23}$ Sb $_{7}$ S $_{70}$ ) waveguides are integrated on silicon (Si) substrates. An optical mode transition between the two waveguides is achieved through low-loss mode-converting tapers, with a measured loss of $\sim$ 1.5 dB for transverse-electric and $\sim$ 1.75 dB for transverse-magnetic input polarizations. For nonlinear characterization, wavelength conversion via four-wave mixing is demonstrated on the ChG-LN waveguides. This platform provides an efficient method for the utilization of second- and third-order optical nonlinearities on the same chip, rendering it ideal for nonlinear applications such as stabilized octave-spanning optical frequency comb generation.

Study of the Effect of Pulsed-Periodic Electric Field and Linearly Polarized Laser Radiation on the Properties of Liquid-Crystal Waveguide

Integrated-optical waveguides with a nematic liquid-crystal 4-cyano-4’-pentylbiphenyl (5CB) waveguiding layer have been investigated for different polarizations of incident laser radiation and under a pulsed-periodic electric field. A dependence of the damping coefficient of waveguide modes and the sizes of quasi-steady-state irregularities of nematic liquid-crystal layer on the linear polarization of laser radiation and the strength of pulsed-periodic field has been found experimentally. The correlation length is estimated for waveguiding layer irregularities. The waveguide scattering method has provided a resolution in correlation length exceeding the classical resolution limit by approximately an order of magnitude. The observed decrease in the damping coefficient of waveguide modes and irregularity sizes under external field is explained by the decrease in the correlation length of director fluctuations.

TE modes of UV-laser generated waveguides in a planar polymer chip of parabolic refractive index profile

The UV-laser lithographic method is used for the preparation of Polymeric integrated-optical waveguides in a planar polymer chip. The waveguide samples are irradiated by an excimer laser of wavelength 248 nm with different doses and with the same fluencies. The refractive index depth profile for the waveguides, in the first zone is found to have a parabolic shape and Gaussian shape in the second one that can be determined by Mach–Zehnder interferometer. Both the mode field distribution and the effective mode indices for the first zone only are determined by making use of the theoretical mode and the experimental data. It is found that the model field distribution is strongly dependent on the refractive indices for each zone.

Independently controllable multiple Fano resonances in side-coupled MDM structure and its applications for sensing and wavelength demultiplexing

Tunable single and multiple Fano resonances are investigated theoretically and numerically in a plasmonic structure, which consists of a cavity (or cavities) side-coupled with a defective metal–dielectric–metal (MDM) waveguide. The results show the Fano resonances originate from the interference between discrete states and a continuum state. These Fano resonances can be independently tuned by adjusting the corresponding cavity parameters. This structure can be utilized to achieve ultrasensitive plasmonic sensor yields with a sensitivity of 1400 nm/RIU. The highest figure of merit (FOM) ~1.75 × 104 is obtained by optimizing structure. Furthermore, compact and high wavelength resolution plasmonic 1 × 2 and 1 × 3 wavelength demultiplexers based on Fano resonances are designed and investigated. This compact and flexible structure has significant applications for sensing, switching, wavelength selecting, as well as constructing highly integrated optical circuits and complex waveguide networks.

Theoretical Investigation of a Plasmonic Demultiplexer in MIM Waveguide Crossing with Multiple Side-Coupled Hexagonal Resonators

A novel plasmonic demultiplexer in metal–insulator–metal (MIM) waveguide crossing with multiple side-coupled hexagonal resonators is proposed and numerically investigated. The operating principle of the structure is analyzed by using the temporal coupled-mode theory. It is found that wavelength demultiplexing can be realized by modulating locations of resonators, which is validated by finite-difference time-domain (FDTD) simulations. In addition, the influences of structural parameters on transmission characteristics are studied by simulations. Simulation results reveal that the demultiplexed wavelength, transmission efficiency, and bandwidth of each channel can be manipulated by adjusting structural parameters of the demultiplexer. The proposed demultiplexer will provide an alternative for the design of highly integrated optical circuits and complex waveguide networks.

Integration of optical waveguide on pneumatic balloon actuator for flexible scanner in endoscopic imaging diagnosis applications

This paper reports a flexible scanner consisting of a scanning actuator and optical waveguides for medical imaging applications such as endoscopic fluorescence imaging diagnosis. The 0.3-mm-thick and 5-mm-wide functional scanner was designed to be smaller enough than the 10 mm-diameter of channel of endoscope. The proposed device can be used to introduce an excitation light into the abdominal cavity or digestive tract. A pneumatic balloon actuator (PBA) consisting of polydimethylsiloxane (PDMS) is used as the scanning actuator for the scanner in consideration of its small, soft, and safe features. The SU-8 optical waveguides with high refractive index (nSU-8 = 1.575) are integrated onto the PBA structure made of PDMS with a lower refractive index (nPDMS = 1.405). Excitation light at a wavelength of 405 nm is transmitted through an optical fiber to the SU-8 waveguides. The outgoing light from the waveguide can be scanned by the bending motion of the PBA. The waveguide functions as a detector as well. Our developed device has successfully scanned, excited, and detected light from fluorescence beads at a wavelength of 540 nm distributed in a pseudo-tissue.

Evanescent Field Biosensor Using Polymer Slab Waveguide-Based Cartridges for the Optical Detection of Nanoparticles

We present a polymer optical waveguide integration technology for the detection of nanoparticles in an evanescent field (EF)-based biosensor. Polymer waveguides together with their light coupling structures are designed to be integrated in a novel cartridge concept which will eventually lead to cost-effective, rapid, and easy-to-use point-of-care testing (POCT). The selected slab waveguides generate a homogeneous and well-defined EF, illuminating magnetic nanoparticles that are used as optical contrast labels and are measured using dark-field microscopy. The nanoparticles quantitatively bind to the sensor surface in the presence of target molecules, mediated by antibodies. Compatibility of the waveguide materials with these biomolecules is therefore a strong requirement. When designing a biosensor for POCT, it is also necessary to consider fabrication and manipulation tolerances, targeting the compatibility with mass-production technologies. In this context, polymer optics offer unique advantages, and in combination with the optical contrast labels a very high sensitivity can be achieved. The sensing concept was assessed by comparing various commercially available polymer materials (LightLink, Ormocer, Epocore/Epoclad) in terms of waveguide design and fabrication, optical performance (detection of nanoparticles), and biological compatibility and performance as a sensor surface in an immuno-assay for cardiac troponin I.

Si nanowire phototransistors at telecommunication wavelengths by plasmon-enhanced two-photon absorption.

The on-chip integration of optical waveguides with complementary metal-oxide-semiconductor (CMOS) transistors is the next generation technology for high-speed communications. The advance of such a technology requires a high-performance photodetector operating at communication wavelengths. However, silicon does not absorb photons at communication wavelengths because of its relatively large bandgap. Growing high quality small bandgap semiconductors on top of silicon is challenging due to lattice mismatch. An all silicon photonic CMOS technology is an attractive option. Here, we demonstrate a high-performance silicon phototransistor that operates at the communication wavelengths by two-photon absorption effect. To turn silicon into a light absorptive material at communication wavelengths, we have designed a sophisticated plasmonic antenna structure to increases the intensity of light in the silicon nanowire by 5 orders of magnitude. At the high light intensity, the light absorption in silicon is dominated by the two-photon absorption effect. The generated photocurrent is further amplified by the Si nanowire phototransistor, a section of which is doped to be a core-shell pn junction. Simulation results indicate that the device can achieve a responsivity of 2.4×104 A/W and a 3-dB bandwidth over 300 GHz. Successful development of such a device is important for the next generation high-speed communication technology.