Query: Dramatic size reduction of waveguide bends on a micron-scale silicon photonic platform

Candidate papers:

abstract: We demonstrate theoretically and experimentally how highly multimodal high index contrast waveguides with micron scale cores can be bent, on an ultra broad band of operation, with bending radii below 10 um and losses for the fundamental mode below 0.02 dB/90deg. The bends have been designed based on the Euler spiral and fabricated on 4 um thick SOI. The proposed approach enabled also the realization of 180deg bends with 1.27 um effective radii and 0.09 dB loss, which are the smallest low loss bends ever reported for an optical waveguide. These results pave the way for unprecedented integration density in most semiconductor platforms.
author_names: Matteo Cherchi

Sami Ylinen

Mikko Harjanne

Markku Kapulainen

Timo Aalto
title: Dramatic size reduction of waveguide bends on a micron scale silicon photonic platform.
venue: Optics express
year: 2013

abstract: Even though submicron silicon waveguides have been proposed for dense integration of photonic devices, to date the lightwave circuits on the market mainly rely on waveguides with micron scale core dimensions. These larger waveguides feature easier fabrication, higher reliability and better interfacing to optical fibres. Single mode operation with large core dimensions is obtained with low lateral refractive index contrast. Hence, the main limitation in increasing the level of integration and in reducing the cost of micron scale waveguide circuits is their mm to cm scale minimum bending radius. Fortunately, single mode rib waveguides with a micron scale silicon core can be locally transformed into multi mode strip waveguides that have very high lateral index contrast. Here we show how Euler spiral bends realized with these waveguides can have bending radii below 10 \mu}m and losses below 0.02 dB/90{\deg} for the fundamental mode, paving way for a novel densely integrated platform based on micron scale waveguides.
author_names: Matteo Cherchi

Sami Ylinen

Mikko Harjanne

Markku Kapulainen

Timo Aalto
title: New silicon photonics integration platform enabled by novel micron scale bends
year: 2013

abstract: In this letter, a reflection type arrayed waveguide grating (AWG) (de)multiplexer using high reflection photonic crystal reflector (PCR) in the Indium phosphide Membrane on Silicon (IMOS) platform is proposed and experimentally demonstrated for the first time. This reflection type AWG enables a 35% size reduced footprint compared with the traditional transmission type AWG having the same spectral parameters. Considering the realized performance of silicon nanowire R AWGs, an acceptable performance <inline formula> <tex math notation="LaTeX"$680\\times ,190\\mu \text {m}{2} /tex math>/inline formula> size, 6.7 dB loss, and 10 dB crosstalk) is obtained. By using the ultra small <inline formula> <tex math notation="LaTeX"$5.4\\times ,0.7\\mu \text {m}{2} /tex math>/inline formula> PCR, merely 1.1 dB power loss higher than the corresponding transmission type AWG is implemented. The PCR is a standard building block with a reflectivity of >90% Besides, the length reduction of the arrayed waveguide will contribute to minimize the accumulated phase error in fabrication.
author_names: Xuebing Zhang

Jorn P van Engelen

Sander F G Reniers

Zizheng Cao

Yuqing Jiao

Antonius M J Koonen
title: Reflecting AWG by Using Photonic Crystal Reflector on Indium Phosphide Membrane on Silicon Platform
venue: IEEE Photonics Technology Letters
year: 2019

abstract: The minimum bending radius of optical waveguides is typically the most important parameter that defines the footprint and cost of a photonic integrated circuit. In optical fibers and in planar waveguides with equally large mode fields ~10 mm) the bending radii are typically in the cm scale. The main advantage of using a high index waveguide core with a thickness below 1 mm is the ability to realise single mode bends with bending radii of just a few micrometers. In this paper we review the dependence of the minimum bending radius on the size and shape of waveguides with the main emphasis on silicon on insulator (SOI) waveguides. Then we present simulation and measurement results from advanced waveguide bends and mirrors that have been integrated with 4 10 mm thick single mode SOI waveguides. We show that multi step patterning and novel designs allow the reduction of the bending radius by up to three orders of magnitude while also reducing the bending losses by approximately one order of magnitude when compared to traditional rib waveguide bends on 4 mm SOI. This allows to use the mm scale SOI waveguides for making almost as compact photonic integrated circuits as those based on sub mm SOI waveguides.
author_names: Timo Aalto

Matteo Cherchi

Mikko Harjanne

Sami Ylinen

Markku Kapulainen
title: Bend size reduction on the SOI rib waveguide platform
venue: Photonics West Optoelectronic Materials and Devices
year: 2013

abstract: Silicon photonics is a very promising solution to achieve high speed and energy efficient optical interconnects at reduced cost of production. For several years now, Silicon photonic platforms have offered high performance passive and active compact components, with first 100 Gb/s silicon photonics commercial transceivers on the market. However, interferometric devices still remain sensitive to temperature changes. Silicon nitride appears as an appealing material for CMOS compatible, energy efficient and cost effective photonics. Its low optical index contrast with the SiO2 cladding provides low loss waveguide and a better tolerance to fabrication imperfections while its optical index is much less sensitive to temperature variations. In particular, the monolithic integration of multiple Si and SiN layers on the same platform provides a promising solution for Coarse Wavelength Division Multiplexing (CWDM) transceiver applications for which thermal stability is essential. We report here on a 200mm CMOS compatible platform where SiN is co integrated with Si to benefit from the advantages of both materials. We present the fabrication flow of this enhanced platform and we show the wafer scale characterization of its passive Si, SiN and hybrid components, assessing their performances in term of 4 wavelength CWDM application in the O band. Building on the CEA LETI silicon photonics fabrication line, we present the monolithic integration of a low stress PECVD SiN deposited at 300degC, which make it compatible with the standard SOI platform with doped active devices. The success of the integration is confirmed by the preserved performances of Si components (waveguide, bend and fiber grating coupler losses) as well as propagation losses as low as 0.8dB/cm for a single mode SiN waveguide. Furthermore, characterizing micro ring resonators, the resonance shift with temperature allows us to extract a 10 fold reduction of the SiN thermo optic coefficient compared to Si. An essential building block of the Si SiN platform is the Si SiN interlayer transition. We present a complete study of such transitions with both simulation and experimental data of various geometries, and we demonstrate state of the art insertion losses of 0.09 0.01 dB over the O band for the TE mode at the wafer scale. We show as well the realization of hybrid Si SiN grating couplers, compatible with a standard packaging fiber angle of 8deg. In such couplers, the main SiN grating is combined with a Si grating placed underneath and a longitudinal shift between gratings allows the tuning of the coupler's directionality. Consequently, we achieve a dramatic improvement in terms of bandwidth with respect to the standard all Si fiber couplers, going from a 23nm 1dB bandwidth for Si couplers to more than 50nm for hybrid couplers. These wideband hybrid couplers are key for CWDM where a flat transmission spectrum is needed over the O band. Finally, to complete the CWDM components review, we present SiN Echelles grating (de)multiplexer for 4 channels CWDM in the O band showing quasi absolute thermal insensitiveness and low insertion losses.
author_names: Quentin Wilmart

Daivid Fowler

Corrado Sciancalepore

Karim Hassan

Laetitia Adelmini

Stephanie Garcia

Daniel Robin-Brosse

Stephane Malhouitre

Segolene Olivier
title: Enhanced hybrid Si SiN photonic platform and performances of passive components for CWDM applications (Conference Presentation)
year: 2018

abstract: Sinusoidal anti coupling (AC) symmetric waveguides provide a means to design dense waveguide arrays that have minimal inter waveguide crosstalk for high density integration of photonic circuits. Also, the polarization sensitivity of sinusoidal AC symmetric waveguides and the reduction of wavelength dependence that is achieved by the sinusoidal waveguides can be used to design broadband polarization beam splitters (PBSs) for polarization diversity systems. In this thesis, I demonstrate the use of sinusoidal bends to suppress the optical power exchange between pairs of symmetric strip waveguides for both transverse electric (TE) and transverse magnetic (TM) modes as well as to separate the TE and TM modes into two output symmetric strip waveguides on a silicon on insulator platform. I design, model, simulate, and analyze sinusoidal AC symmetric waveguide pairs for both the TE and TM modes. Then, based on the TE sinusoidal AC waveguide structure, I design, simulate, and analyze a PBS using a symmetric directional coupler (DC) with sinusoidal bends. I also compare the modal dispersions of the sinusoidally bent symmetric DC, which is used in the PBS, with the modal dispersions of an equivalent straight symmetric DC. I measure the fabricated test devices and evaluate their performances. The TE sinusoidal AC device, which has a gap width of 200 nm, has an average crosstalk suppression ratio (SR) of 38.2 dB, and the TM sinusoidal
author_names: Fan Zhang
title: Sinusoidal anti coupling symmetric strip waveguides on a silicon on insulator platform
year: 2017

abstract: 1. Background To solve the metal electronic interconnect problem by optical interconnect, silicon photonics is promising and is the main stream due to the natural compatibility with micro electronics CMOS process lines [1] but laser problem still remains for silicon photonics. Though the III V/Si hybrid platform [2] can solve the laser problem, it seems difficult to integrate monolithically III V/Si hybrid photonics and Si CMOS electronics due to the thermal budget difference between III V and Si. To realize the real monolithic integration for electronics and photonics, we develop a unique platform called 'III V CMOS photonics platform' which uses III V OI wafers by direct wafer bonding to fabricate high performance electronics and photonics devices [3] On this platform, sharp bends [4] AWGs [4] grating couplers [5] modulators/switches [6] MOSFETs [7] have been demonstrated so far. In addition, we have demonstrated the waveguide InGaAs MSM PDs [8] However the demonstrated PD exhibited relatively large dark current. Thereby, in this paper, we introduce an InP/InAlAs layer as Schottky barrier enhancement (SBE) layer between the InGaAs absorption layer and metal electrode to reduce the dark current. 2. Fabrication For device fabrication, we prepare III V OI wafers by direct wafer bonding. At first, i InP/i InGaAs/i InAlAs/i InP are grown on an InP wafer. A 2.3mm thick SiO2 BOX layer is also thermally grown on a Si wafer. After depositing Al2O3 on both wafers by atomic layer deposition (ALD) the two wafers are bonded together. Finally, the InP/InAlAs/InGaAs/InP on SiO2/Si wafer is obtained by etching the InP substrate. By the III V OI wafers, we fabricate the waveguide InGaAs MSM PD as shown in Fig. 1. At first, we form InP photonic wire waveguides and InGaAs mesas by deep ultra violet (DUV) lithography and reactive ion etching (RIE) Then, we etch the InP/InAlAs/InGaAs on top of the InP waveguides. We deposit Al2O3 for passivation by ALD and open a contact window on InGaAs mesa. Finally, we form the interdigitated electrodes by Ni deposition and lift off. 3. Experimental results As the Fig. 2 shows, the dark current of the PD can be decreased to 7 nA at 1V bias after the SBE layer insertion onto the InGaAs layer, which has a 2 order reduction in comparison with the first demonstration. When 2 V bias is applied, we obtain the photocurrent of 32 mA. By taking into account of 8 dB coupling loss, the intrinsic responsivity is estimated to approximately 0.2 A/W. The SBE layer may also block some photo generated carriers, resulting in relatively low responsivity, which can be improved by the gradually changed SBE layer. Acknowledgements This work was supported by Grant in Aid for Young Scientists (A) from MEXT. The authors would like to thank O. Ichikawa, T. Osada, M. Hata, Sumitomo Chemical Company Ltd. Tsukuba, Japan, for their technical support. Reference
author_names: Yongpeng Cheng
title: Dark current reduction of waveguide InGaAs MSM photodetector on III V CMOS photonics platform by InAlAs cap layer
year: 2014

abstract: A hybrid integrated light source was developed with a configuration in which a laser diode (LD) array was mounted on a silicon optical waveguide platform for interchip optical interconnection. This integrated light source is composed of 13 channel stripes with a pitch of 20 or 30 mm. The output power of each LD in the 400 or 600 mm long LD array was over 40 mW at room temperature without cooling. An output power uniformity was 1.3 dB including an LD array power uniformity. The use of a SiON waveguide with a spot size converter resulted in an optical coupling loss of 1 dB between an LD and SiON waveguide. The integrated light source including 52 output ports demonstrated a reduction in the footprint per channel. We also demonstrated a light source with over 100 output ports in which the number of output ports is increased by using a waveguide splitter and multichip bonding. These integrated light sources are practical candidates for use with photonic integrated circuits for high density optical interconnection.
author_names: Takanori Shimizu

Nobuaki Hatori

Makoto Okano

Masashige Ishizaka

Yutaka Urino

Tsuyoshi Yamamoto

Masahiko Mori

Takahiro Nakamura

Yashuhiko Arakawa
title: Multichannel and high density hybrid integrated light source with a laser diode array on a silicon optical waveguide platform for interchip optical interconnection
year: 2014

abstract: All optical signal processing implemented in silicon photonics is considered as a promising route to solve several bottlenecks for the realization of future dense and mixed integrated electronic and photonic chips including ultrahigh data bit rate issues and power consumption constraints. In the context of the planar silicon photonics technology, a dramatic reduction of the needed power to reach optical nonlinear effects is obtained due to the sub micrometer size of silicon wires ~450nmX260nm) in the telecommunication wavelength window, although silicon does not exhibit second order response (kh^(2) due to the centrosymmetry of its lattice. Moreover, third order effects (kh^(3) are partially spoiled in this material due to the strength of the two photon absorption (TPA) effect, which in turn generates free carriers inducing additional absorption and refractive index changes. One way to overcome this limitation is the hybrid integration on silicon of low index soft materials with luminescence or nonlinear optical properties lacking to silicon. In this context, the present work is devoted to the study of third order nonlinearities in silicon based integrated structures exploiting enhanced electromagnetic field effects (e.g. in Si resonators and slow light waveguides) First, we have developed a dedicated single beam non destructive method to characterize the instantaneous third order effects though the quantification of complex effective waveguide susceptibility. The method is named "Bi directional top hat D Scan" and consists on a temporal analogous of the top hat Z Scan. We have established an analytical and numerical model and we report the first measurement of a silicon waveguide by using a pulse shaping set up and a bi directional procedure. The originality of our methods stands in the capability to measure in two steps the 3rd order nonlinear Figure Of Merit (FOM) independently of the injection losses, and the effective nonlinear waveguide parameters (Kerr and TPA) taking into account measured coupling losses at each facet. Furthermore, we apply the method to other integrated novel materials including Ge rich GeSi alloys, carbon nanotube doped thin films, and chalcogenide waveguides. Additionally, two further enhancements of light matter nonlinear interactions have been explored within this work: optical microcavities and slow light waveguides. In the first picture, index variations caused by non linearities shift the resonance frequencies precluding the coincidence with the excitation signal frequency, thereby decreasing the injection efficiency. In order to maintain the benefit of light localization throughout the pulsed excitation, we have experimentally and numerically studied the behavior of a designed and fabricated silicon nanobeam cavity excited by a high power tailored chirped pulse whose spectral phase relation compensates for the nonlinear frequency drift of the cavity resonance. We report a numerical study of this first experimental demonstration of the coherent excitation of a nonlinear micro cavity, leading to an enhanced intra cavity nonlinear interaction. Finally, we have dedicated efforts to engineer, fabricate and characterize silicon slot photonic crystal waveguides (SPhCW) in order to compensate their strong dispersion present in the slow light regime while taking benefit from large group index light propagation. We showed that their frequency dispersion properties can be engineered from anomalous to normal dispersion, along with zero group velocity dispersion (ZGVD) crossing points exhibiting a Normalized Delay Bandwidth Product (NDBP) as high as 0.156. The reported results provide the first experimental evidence for an accurate control of the dispersion properties of fillable periodical slotted structures in silicon photonics, which is of direct interest for on chip all optical data treatment using nonlinear optical effects in hybrid on silicon technologies.
author_names: Serna Otalvaro

Samuel Felipe
title: Design and characterization of Silicon Photonic structures for third order nonlinear effects
year: 2016

abstract: Mid infrared (mid IR) spectroscopy is a nearly universal way to identify chemical and biological substances, as most of the molecules have their vibrational and rotational resonances in the mid IR wavelength range. Commercially available mid IR systems are based on bulky and expensive equipment, while lots of efforts are now devoted to the reduction of their size down to chip scale dimensions. The use of silicon photonics for the demonstration of mid IR photonic circuits will benefit from reliable and high volume fabrication to offer high performance, low cost, compact, lightweight and power consumption photonic circuits, which is particularly interesting for mid IR spectroscopic sensing systems that need to be portable and low cost. Among the different materials available in silicon photonics, Germanium (Ge) and Silicon Germanium (SiGe) alloys with a high Ge concentration are particularly interesting because of the wide transparency window of Ge up to 15 um. In this context, the objective of this thesis is to investigate a new Ge rich graded SiGe platform for mid IR photonic circuits. Such new plateform was expected to benefit from a wide transparency wavelength range and a high versatility in terms of optical engineering (effective index, dispersion, During this thesis, different waveguides platforms based on different graded profiles have been investigated. First it has been shown that waveguides with low optical losses of less than 3 dB/cm can be obtained in a wide wavelength range, from 5.5 to 8.5 um. A proof of concept of sensing based on the absorption of the evanescent component of the optical mode has then been demonstrated. Finally, elementary building blocs have been investigated. The first Bragg mirror based Fabry Perot cavities and racetrack resonators have been demonstrated around 8 um wavelength. A broadband dual polarization MIR integrated spatial heterodyne Fourier Transform spectrometer has also been obtained. All these results rely on material and device design, clean room fabrication and experimental characterization. This work was done in the Framework of EU project INsPIRE in collaboration with Pr. Giovanni Isella from Politecnico Di Milano.
author_names: Qiankun Liu
title: SiGe photonic integrated circuits for mid infrared sensing applications
year: 2019