SOI Platform Research Articles

Broadband Polarization Rotator and Splitter Based on 70 nm-Etched Waveguides on SOI Platform

The standard silicon photonic platforms provide three-step silicon etching, i.e., 220 nm for full etching, 70 nm for shallow etching, and 130 nm (or 150 nm) for slab etching. Previously reported mode-evolution-based polarization rotators and splitters (PSRs) usually employ 130 nm-etched slab waveguides for adiabatic TM0-to-TE1 conversion, however, they are not compatible with the platforms adopting 150 nm-etching techniques. In this paper, we demonstrate a broadband PSR based on 70 nm-etched slab waveguides, which is compatible with all the platforms. The PSR consists of a bi-level taper and an inverse-tapered coupler. The length of the polarization rotator shrinks from hundreds to only thirty microns by employing the 70 nm-etched slab waveguides, while a high efficiency of >95% is achieved, covering an ultra-wide bandwidth from 1250 nm to 1650 nm. The proposed PSR shows superior performance over S, C, and L bands. Low cross-talk of <−20 dB and a loss of <1.5 dB are experimentally confirmed over a wavelength range of 75 nm.

The edge-coupler of fiber-to-chip with ultra-low coupling loss based on double-layer silicon waveguides

The edge-coupler of fiber-to-chip with ultra-low coupling loss is demonstrated on SOI platform. The edge-coupler is consisted of the cantilevered SiO2 waveguide, the amorphous silicon (α-Si) nano taper and the crystal silicon (c-Si) nano tapers. The thin α-Si layer is deposited on the c-Si layer to improve the pattern matching with fiber. The optical input signal from the optical fiber is launched into the suspended SiO2 waveguide, then coupled into the α-Si nano taper at the center of the SiO2 waveguide, and finally coupled into the c-Si nano taper. We characterized the cantilevered edge-coupler using cleaved single-mode optical fiber with a mode field diameter of 10.5 μm. The measured coupling loss is as low as -1.7 dB per facet for TE mode without index matching liquid at 1550 nm. The 1 dB bandwidth is more than 100 nm with 1 dB alignment tolerances of ±2.0 μm in both horizontal and vertical directions. Besides, potential hybrid optical integration could also be allowed with this results in the future.

Low-Loss Silicon Photonic 16 × 16 Cyclic AWGR Based on SOI Platform

We experimentally demonstrate a low-loss and low-crosstalk 16-channel 200 GHz-channel-spacing arrayed waveguide grating router (AWGR) with a size of 0.67 × 0.37 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , targeting for C-band wavelength division multiplexing (WDM) interconnect routing applications. As a result, the AWGR features a channel spacing of 200±10 GHz, a free spectral range of 25.62 nm and a 3 dB channel bandwidth of 0.9 nm. Based on comprehensive optimal design, the measured characterization revealed 5.55 dB maximum channel loss non-uniformity with 1.13 dB best-case channel insertion loss. Besides, the fabricated device exhibits good cyclic-frequency operation for all 16 × 16 port combinations with channel crosstalk of –15.11 dB.

HYPHa project: a low-cost alternative for integrated photonics

In this paper, a brief introduction to the Hybrid sensor platforms of integrated photonic systems based on ceramic and polymer materials (HYPHa) is presented. The project's goal is to establish a collaborative effort of institutes specialized in integrated optics. The newly formed group of professionals will be founded on research groups' experience, collaboration, and devotion. We intend to develop a method for combining competencies and a universal material platform for integrated photonics, based on newly validated hybrid materials as part of the project. Silica compounds with additions including TiO2, SnO2, used as structural matrices, polymer coatings with dopants (active or protective layers), organic dyes, and active two-dimensional materials such as transition metal dichalcogenides, graphene hybrids, and boron nitride will be the foundation for these materials. Full Text: PDF ReferencesK. Rola, A. Zajac, M. Czajkowski, A. Szpecht, M. Zdonczyk, M. Smiglak, J. Cybinska, K. Komorowska, "Ionic liquids for active photonics components fabrication", Opt. Mater. 89, 106-111 (2019). CrossRef D. Kowal, K. Rola, J. Cybinska, M. Skorenski, A. Zajac, A. Szpecht, M. Smiglak, S. Drobczynski, K. Ciesiolkiewicz, K. Komorowska, "Fluorescent ionic liquid micro reservoirs fabricated by dual-step E-beam patterning", Mater. Res. Bull. 142, 111434 (2021). CrossRef T. Martynkien, J. Olszewski, M. Szpulak, G. Golojuch, W. Urbanczyk, T. Nasilowski, F. Berghmans, and H. Thienpont, "Experimental investigations of bending loss oscillations in large mode area photonic crystal fibers", Opt. Express 15, 13547-13556 (2007). CrossRef E. Środa, J. Olszewski, and W. Urbańczyk, "Reducing bend-induced loss and crosstalk in a two-mode ridge waveguide by steplike thickness structuring", Appl. Opt. 61, 1164-1170 (2022). CrossRef P. Karasinski, C. Tyszkiewicz, A. Domanowska, A. Michalewicz, J. Mazur, "Low loss, long time stable sol–gel derived silica–titania waveguide films", Mater. Lett. 143, 5-7 (2015). CrossRef P. Karasinski, C. Tyszkiewicz, A. Maciaga, I.V. Kityk, E. Gondek, "Two-component waveguide SiO2:TiO2 films fabricated by sol–gel technology for optoelectronic applications", J. of Mater. Sci.: Mater. Electron. 26, 2733-2736 (2015). CrossRef M.A. Butt, A. Kazmierczak, C. Tyszkiewicz, P. Karasinski, R. Piramidowicz, "Mode Sensitivity Exploration of Silica–Titania Waveguide for Refractive Index Sensing Applications", Sensors 21, 7452 (2021). CrossRef A. Kazmierczak, M. Slowikowski, K. Pavlov, M. Filipiak, M. Vervaeke, C. Tyszkiewicz, H. Ottevaere, R. Piramidowicz, P. Karasinski, "Efficient, low-cost optical coupling mechanism for TiO2-SiO2 sol-gel derived slab waveguide surface grating coupler sensors", Opt. Appl. 50, 539 (2020). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "A highly sensitive design of subwavelength grating double-slot waveguide microring resonator", Laser Phys. Lett. 17, 076201 (2020). CrossRef N.L. Kazanskiy, M.A. Butt, S.N. Khonina, "Silicon photonic devices realized on refractive index engineered subwavelength grating waveguides-A review", Opt. Laser Technol. 138, 106863 (2021). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "Recent advances in photonic crystal optical devices: A review", Opt. Laser Technol. 142, 107265 (2021). CrossRef L. Xu, Y. Wang, E. El-Fiky, D. Mao, A. Kumar, Z. Xing, Md. G. Saber, M. Jacques, D.V. Plant, "Compact Broadband Polarization Beam Splitter Based on Multimode Interference Coupler With Internal Photonic Crystal for the SOI Platform", J. Light. Technol. 37, 1231 (2019). CrossRef R. Marchetti, C. Lacava, A. Khokhar, X. Chen, I. Cristiani, D.J. Richardson, G. T. Reed, P. Petropoulos, P. Minzioni, "High-efficiency grating-couplers: demonstration of a new design strategy", Sci. Rep. 7, 16670 (2017). CrossRef

Design of narrow bandwidth Si[formula omitted]N[formula omitted] stressor cladded cascaded IBG filter

In this paper design and performance estimation of a narrow-band optical filter operating at 1550 nm is presented. The narrowband filter consists of cascaded integrated Bragg grating (IBG) filters each having periodic Si3N4 cladding on silicon strip waveguide based on SOI platform. The filter design also includes the effect of stress, which is generated at the Si-Si3N4 interface on their optical performance. The design of the proposed filter for a set of target specifications such as centre wavelength, bandwidth (BW), extinction ratio (ER), insertion loss (IL), and side-lobe suppression ratio (SLSR) has been done using the conventional transfer matrix method (TMM) in absence of stress and also using a modified TMM (MTMM), which is suitable for filter designs in presence of stress. It has been demonstrated in this work that using cascaded IBG filters narrowband operation can be achieved along with wideband operation. The efficacy of the proposed filter structure has been demonstrated for two different 3-dB bandwidths of 15 nm and 1.6 nm. The study reveals that the filter, which is designed using conventional TMM for a set of target specifications, shows similar optical performance when estimated using finite-element method (FEM) in absence of stress. In presence of stress, conventional TMM method fails to design the cascaded IBG filter that shows dissimilar performance when analysed using FEM. Under stressed condition, the proposed MTMM is found to design the cascaded IBG filter effectively exhibiting similar performance when tested using FEM. The study reveals that in presence of stress the MTMM can design filter, which offers deviation of <5.8%, <4.97%, <0.01% and <6.3% for ER, BW, resonance wavelength and side-lobe suppression ratio, respectively; from the FEM estimated filter performance, for a given set of targeted specifications.

Temperature insensitive multi-channel light amplification systems on SOI platform

Temperature insensitive multi-channel light amplification systems on SOI platform

Low threshold lasing from silicon Mie resonators

The unique electromagnetic response of high-index dielectric resonators with Mie resonances facilitates the selective enhancement and confinement of light, holding great promise for nanoscale lasing. However, up to now, nanolasing exploiting Mie resonances of individual Si nanowires has been limited to theoretical proposals. Here, we demonstrate a strategy to realize nanolasing with Si nanowires in the SOI platform. It is found that, by carefully tailoring the sizes of the Si nanowires, the Mie resonances of Si nanowires enhance the pumping/emission fields, leading to continuous-wave lasing at room temperature with low threshold in the visible range. The lasing of a dye at the wavelength of 523 nm assisted by the Mie resonances of Si nanowire is demonstrated experimentally. It is shown that the lasing wavelength changes with the width of nanowire due to the different scattering peak from Mie theory. In addition, the quality factor Q of lasing modes can be affected by the thickness of silica shell which determines the interaction volume of the pumping light and dyes. The proposed strategy paves the way towards practical integrated nanolasers for single-photon sources and micro-display, which have potential applications of on-chip optoelectrical devices.

Simulation Study of Stress Effect on Performance and Design Methodology of Proposed Si/SiGe Integrated Bragg Grating Filter

The stress-induced due to thermal and intrinsic mismatch between different layers in silicon photonic devices critically affect the device performance. This makes the inclusion of stress while designing such devices absolutely necessary to ensure reliable and predictable operation of the eventually fabricated device. In this regard, this paper presents the design methodology of a proposed Si/SiGe integrated Bragg grating (IBG) filter that includes the influence of stress effect during filter design. Moreover, it also reports the variation in the optical performance of the device due to stress effect. The methodology utilizes both analytical and numerical approaches. IBG filters realized over SOI platform are designed using the proposed method for C-band of operation and having different 3-dB bandwidths. Refractive index variation along the length of the proposed filter has been achieved by introducing SiGe alloy filled grooves, which are corrugated in silicon strip waveguide. The efficacy of the methodology has been demonstrated for varying waveguide width and three different Ge fractions, i.e., 0.10, 0.15 and 0.20 in SiGe. The stress at Si-SiGe interface due to the lattice and thermal mismatch has been incorporated in a modified transfer matrix method (TMM), which is in its unmodified form can only be used under no-stress condition. The proposed design methodology has been tested for designing three IBG filters having 10 nm, 5 nm and 1.6 nm bandwidths along with other suitable user-defined parameters; such as maximum insertion loss (IL), minimum extinction ratio (ER), Ge fraction in SiGe alloy, and center wavelength. It has been found that our proposed methodology, which is based on modified TMM, can find possible combinations of width, length, SiGe groove depth of the IBG filters that meet user-defined specifications even in presence of stress. This paper also compares the results generated by the proposed modified TMM with the results from commercially available photonic device design tool. It has been found that the proposed method can result IBG filters having estimated optical performances with an accuracy of < 10%, <8%, and <0.01% for ER, bandwidth, and resonance wavelength, respectively.

Ultra-narrow passband-tunable filter based on a high-Q silicon racetrack resonator

An ultra-narrow narrow passband-tunable optical filter employing a high-Q silicon racetrack resonator is proposed and experimentally demonstrated on a SOI platform. The high-Q silicon racetrack resonator is realized by utilizing the multimode waveguide racetrack, and the Q factor is measured as high as 8.1×105. The structure of the device is based on a thermally tunable Mach-Zehnder interferometer coupled racetrack. The tunability of the bandwidth is realized by tuning the coupling coefficient between the racetrack resonator and the input or output ports. Finally, the bandwidth of the filter can be tuned from 1.92 to 11.00 pm (240 MHz to 1.375 GHz), and the free spectral range is about 0.28 nm (35 GHz), with the footprint of 0.21mm2.

High-Efficiency, Wide Working Bandwidth Antenna Based on SOI Platform for Optical Phased Array.

A novel structure of a subwavelength surface optical antenna for optical phased array is proposed in this paper. An asymmetric vertical grating structure is applied to achieve high emission efficiency (73% at 1550 nm). Optical antennas with large fabrication tolerances can also maintain a wide working bandwidth of 1 dB between 1350 and 1850 nm. The far-field scanning characteristics of 16-channel optical phased array are investigated in this study by employing the proposed antenna. The results show that the background suppression without considering side lobes caused by the antenna arrangement is −24.5 dB when the phase difference is 0 and when the scan range is as large as ±14.8° × 73.6°.

Room-temperature 2 μm luminescence from Tm doped silicon light emitting diodes and SOI substrates

Room temperature electroluminescence in the eye safe region of the spectrum over the range 1.7–2.1 μm is demonstrated from a thulium doped silicon diode. The same room temperature photoluminescence can be attained on a silicon-on-insulator substrate. The emission lines are from the first excited to ground state of the Tm3+ ion, 3F4→3H6. A detailed study has been made to establish the optimum implant and processing conditions for efficient room temperature luminescence. The importance of the correct placement of the thulium ions with respect to the depletion region edge and dislocation loops formed upon boron implantation has been established. Tm3+ has been demonstrated to lase in other systems and is the basis of widely applied, commercial, optically pumped 2 μm lasers. The demonstration of electroluminescence in silicon and luminescence on an SOI platform are necessary prerequisites for the potential development of Tm injection lasers and optical amplifiers.

Millimeter-long metamaterial surface-emitting antenna in the silicon photonics platform.

Integrated optical antennas are key components for on-chip light detection and ranging technology (LIDAR). In order to achieve a highly collimated far field with reduced beam divergence, antenna lengths on the order of several millimeters are required. In the high-index contrast silicon photonics platform, achieving such long antennas typically demands weakly modulated gratings with lithographic minimum feature sizes below 10 nm. Here, we experimentally demonstrate a new, to the best of our knowledge, strategy to make long antennas in silicon waveguides using a metamaterial subwavelength grating (SWG) waveguide core loaded with a lateral periodic array of radiative elements. The mode field confinement is controlled by the SWG duty cycle, and the delocalized propagating mode overlaps with the periodic perturbations. With this arrangement, weak antenna radiation strength can be achieved while maintaining a minimum feature size as large as 80 nm. Using this strategy, we experimentally demonstrate a 2-millimeter-long, single-etched subwavelength-engineered optical antenna on a conventional 220 nm SOI platform, presenting a measured far-field beam divergence of 0.1° and a wavelength scanning sensitivity of 0.13°/nm.

Grating double-slot micro-ring resonator for sensing

A compact grating double-slot micro-ring resonator (GDSMRR) based on an SOI platform with a footprint of less than 11 μm ×11μm is analyzed and proposed in order to achieve a refractive index sensor with high sensitivity (S) and large measurement range. And EIT-like effects of high Q factor are achieved by combining structure of the double-slot micro-ring and Bragg grating. In the absence of a free spectral range (FSR) limitation, the measurement range of the sensor is significantly improved. In the refractive index sensing applications, Q value is 4325, S value is 433.33 nm/RIU, and DL 8.26 × 10−4 RIU. Thus, the proposed compact GDSMRR with excellent performance has great value for exploration in sensing applications.

Efficient Brillouin Optomechanical Interaction Assisted by Piezomechanics on the SOI Platform

A hybrid silicon/aluminum nitride waveguide on the silicon-on-insulator platform is proposed to achieve an efficient Brillouin optomechanical interaction. Both intra-optical-mode and inter-optical-mode Brillouin scattering can be achieved. The novel arrangement of symmetric electrodes provides out-of-plane electric fields for piezoelectric materials and the possibility of suspended waveguides and cavities. The piezomechanical interaction coupling strength and the Brillouin optomechanical interaction coupling strength are numerically calculated. The simulation results show that near-unity internal conversion efficiency from the microwave domain to the optical domain can be achieved. Relatively low microwave power can be used to produced up to 5 order sidebands acousto-optical modulation. The proposed scheme paves the way for efficient classical and quantum application in integrated silicon photonics.

Demonstration of a silicon polarization splitter and rotator based on a bow-tie structure

We propose and demonstrate a polarization splitter and rotator (PSR) operating in the range of 1530–1590 nm, built on the SOI platform and based on a new bow tie converter TM0-to-TE1. Comparing with other compact (<100 µm length) state-of-the-art photonic integrated devices, the proposed device exhibits simultaneously the lowest crosstalk and penalty to fabrication errors, paving the way for high-volume photonic integration.

On-Chip Photonic Synapses Based on Slot-Ridge Waveguides With PCMs For In-Memory Computing

Because of the von Neumann bottleneck, neuromorphic networks aimed at in-memory computing, such as brains, are extensively studied. As artificial synapses are essential in neuromorphic networks, a photonic synapse based on slot-ridge waveguides with nonvolatile phase-change materials (PCMs) was proposed and demonstrated in an SOI platform with standard complementary metal-oxide-semiconductor (CMOS) process for a larger weight dynamic range. The change of the optical transmission spectrum of our photonic synapses was about 3.5dB higher than that of primitive synapses, which meant large weight dynamic range and more weight values. A 90.7% recognition accuracy based on our photonic synapses, which was 2.6% higher than that of primitive synapses, was realized for the MNIST handwritten digits recognition task performed by a three-layer perceptron. Besides, because of the nonvolatile nature of PCMs, the weights achieved by our photonic synapses can be stored in situ ensuring a lower consumption in in-memory computing. This framework can potentially achieve a more efficient in-memory computing neuromorphic network in silicon photonics.

High-Overtone Thin Film Ferroelectric AlScN-on-Silicon Composite Resonators

This letter presents the first demonstration of thin-film ferroelectric Aluminum Scandium Nitride (AlScN)-on-silicon composite resonators, targeting high-overtone resonance modes in the sub-6GHz band with a high figure of merit (FoM). The resonators are based on sputtered ferroelectric AlScN films with Sc/(Al+Sc) ratio of ~30% and thickness of $\sim 1 {\mu }\text{m}$ . Two types of AlScN thickness-extensional (TE) resonators are co-fabricated on the same SOI platform; with and without a $3.55~\mu \text{m}$ -thick Si layer in the resonant stack. We show that although the passive Si device layer underneath the thin piezo-stack results in degradation of the electromechanical coupling coefficient $({k}_{t}^{2})$ , it boosts the quality factor $({Q})$ , provides structural robustness, and improves the overall ${Q} \times {k}_{t}^{2}$ FoM. The resonant frequency spectrum of the high-overtone TE modes of AlScN-on-Si composite resonator is analyzed and the dependency of ${k}_{t}^{2}$ on the Si device layer properties is studied. A high ${k}_{t}^{2}$ value of 11.7% at the 3rd-order TE resonant frequency of 2.4 GHz is reported, yielding a high ${k}_{t}^{2}\times {Q}_{\textit {max}}$ FoM of 84. The reported FoM shows $2\,\, {\times }$ improvement compared to the co-fabricated AlScN-only FBARs.

Design of a hybrid mode and wavelength division (de)multiplexer based on contra-directional grating assisted couplers on the SOI platform

This paper presents a hybrid mode and wavelength division (de)multiplexer (MDM-WDM), based on the silicon-on-insulator platform using the grating assisted contra-directional coupling principle. The proposed hybrid MDM-WDM is able to (de)multiplex six channels with two wavelengths and three modes. The proposed device is designed by cascading three grating assisted coupler sections. Each coupler section is dedicated to reflecting a specific mode at two wavelengths. The operation of the proposed design is simulated by the 2.5D finite-difference time-domain technique. The analysis shows that the proposed device structure exhibits an insertion loss of &lt; 0.55 d B , return loss of &gt; --> 12.81 d B , extinction ratio of &gt; --> 15.49 d B , and crosstalk of &lt; − 12.74 d B . A fabrication tolerance study for the MDM-WDM device is also performed by changing the inter waveguide distance between the respective multimode bus waveguide and the single-mode waveguide.

Novel Wavelength Multiplexer Using (N + 1) × (N + 1) Arrayed Waveguide Grating and Polarization-Combiner-Rotator on SOI Platform

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 2 N 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 2 N × 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.

Experimental demonstration of an optical quantizer with ENOB of 3.31 bit by using a cascaded step-size MMI.

We experimentally demonstrated an optical phase shifted quantizer using a cascade step-size MMI (CS-MMI), which was fabricated on a commercially available 220-nm SOI platform via multi-project wafer (MPW) process. An experimental setup was built to test the ability of the CS-MMI acting as a quantizer. The experimental results show that the proposed CS-MMI-based quantizer has an effective number of bit (ENOB) of 3.31bit, which is a little slighter than the ideal ENOB of 3.32bit. The operation range is 12 nm for ENOB≥3 bit. Moreover, the insertion loss of the CS-MMI is -1.26 dB at 1560 nm, the performance of the fabricated device agrees well with simulation results.