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In this work, the authors present their recent progress in the development of a platform for the mid-infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch-step and can be designed for strong light-matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides.

A novel technique for realization of configurable/one-time programmable (OTP) silicon photonic circuits is presented. Once the proposed photonic circuit is programmed, its signal routing is retained without the need for additional power consumption. This technology can potentially enable a multi-purpose design of photonic chips for a range of different applications and performance requirements, as it can be programmed for each specific application after chip fabrication. Therefore, the production costs per chip can be reduced because of the increase in production volume, and rapid prototyping of new photonic circuits is enabled. Essential building blocks for the configurable circuits in the form of erasable directional couplers (DCs) were designed and fabricated, using ion implanted waveguides. We demonstrate permanent switching of optical signals between the drop port and through the port of the DCs using a localized post-fabrication laser annealing process. Proof-of-principle demonstrators in the form of generic 1×4 and 2×2 programmable switching circuits were fabricated and subsequently programmed.

High performance silicon optical modulators underpin a number of current and emerging applications based upon silicon photonic technology. Here we present our recent breakthroughs in this field.

Critical coupling control is an important concept used in integrated photonics to obtain functionalities such as single and coupled resonator optical filters and wavelength multiplexers. Realization of critical coupling depends strongly on device fabrication, and reproducibility is therefore an ongoing challenge.Post-fabrication trimming offers a solution for achieving optimal performance for individual devices. Ion implantation into silicon causes crystalline lattice damage which results in an increase of the material’s refractive index and therefore creates a platform for realization of various optical devices. In recent years, we have presented results on the development of erasable gratings, optical filters and Mach-Zehnder interferometers using ion implantation of germanium into silicon. Here, we report the design, fabrication and testing of silicon-on-insulator racetrack resonators, trimmed by localised annealing of germanium ion implanted silicon using continuous and pulsed wave laser sources. The results demonstrate the ability to permanently tune the critical coupling condition of racetrack resonators. Compared to the pulsed lasers used for annealing, continuous wave lasers revealed much higher extinction ratio due to improved material quality after silicon recrystallization.

In this work, potential ways of accessing a greater spectral range at mid-infrared (MIR) wavelength ranges in silicon photonics are explored, in particular for sensing applications that use on-chip spectroscopy. To utilise the full low-loss transmission of silicon, silicon membranes are transfer printed onto MIR-transparent substrates for waveguides with no absorption from the substrate. A Y-junction splitter with low loss across a 1 µm optical bandwidth is also designed and experimentally demonstrated.

A CMOS compatible three-dimensional (3D) integrated photonics circuit for multilayer silicon photonics is reported. Slopes with angles between 10o and 15° were created in the oxide layer using single step wet etching to connect the two Si waveguide layers. Amorphous Si (a-Si) deposited using hot wire chemical vapor deposition (HWCVD) at a temperature of 230°C was used to fabricate the device. Losses of 0.5 dB/slope were measured in the slope waveguides at 1310 nm wavelength. As a demonstration, we propose a 4x4 network switch using a-Si based vertical directional coupler.

Advanced photonic probing techniques are of great importance for the development of non-contact wafer-scale testing of photonic chips. Ultrafast photomodulation has been identified as a powerful new tool capable of remotely mapping photonic devices through a scanning perturbation. Here, we develop photomodulation maps into a quantitative technique through a general and rigorous method based on Lorentz reciprocity that allows the prediction of transmittance perturbation maps for arbitrary linear photonic systems with great accuracy and minimal computational cost. Excellent agreement is obtained between predicted and experimental maps of various optical multimode-interference devices, thereby allowing direct comparison of a device under test with a physical model of an ideal design structure. In addition to constituting a promising route for optical testing in photonics manufacturing, ultrafast perturbation mapping may be used for design optimization of photonic structures with reconfigurable functionalities., Advanced photonic probes are important for the development of non-contact wafer-scale testing of photonic chips. Here, Vynck et al. develop a quantitative technique based on mapping of transmittance variations by ultrafast perturbations to analyze arbitrary linear multi-port photonic devices.

[EN] Integrated photonics changes the scaling laws of information and communication systems offering architectural choices that combine photonics with electronics to optimize performance, power, footprint, and cost. Application-specific photonic integrated circuits, where particular circuits/chips are designed to optimally perform particular functionalities, require a considerable number of design and fabrication iterations leading to long development times. A different approach inspired by electronic Field Programmable Gate Arrays is the programmable photonic processor, where a common hardware implemented by a two-dimensional photonic waveguide mesh realizes different functionalities through programming. Here, we report the demonstration of such reconfigurable waveguide mesh in silicon. We demonstrate over 20 different functionalities with a simple seven hexagonal cell structure, which can be applied to different fields including communications, chemical and biomedical sensing, signal processing, multiprocessor networks, and quantum information systems. Our work is an important step toward this paradigm., J.C. acknowledges funding from the ERC Advanced Grant ERC-ADG-2016-741415 UMWP-Chip, I.G. acknowledges the funding through the Spanish MINECO Ramon y Cajal program. D.P. acknowledges financial support from the UPV through the FPI predoctoral funding scheme. D.J.T. acknowledges funding from the Royal Society for his University Research Fellowship.

Silicon-on-insulator (SOI) is the dominant platform in near-infrared silicon photonics. However, the high absorption of SiO2 at wavelengths above 4 μm limits the range at which this material can be used in the midinfrared wavelengths (2 – 20 μm). In this paper we review our recent investigation on suspended devices, building on our previous work based on suspended silicon devices with sub-wavelength grating (SWG) lateral cladding at 3.8 μm, followed by our more recent results at 7.67 μm. This platform which uses the well-known fabrication techniques of SOI, only requires a single lithographic etch step and it allows the use of the whole transparency range of the waveguide core material. Due to this, it could be a good candidate for sensing applications since the design covers a very large wavelength range. As the bottom cladding of the waveguide is air, the waveguide can be designed so that the mode is squeezed to increase the evanescent field proportion and therefore the interaction with a surrounding analyte., 2019 21st International Conference on Transparent Optical Networks (ICTON), July 9-13, 2019, Angers, France

High-speed and low-power silicon optical modulators are key in realising low cost photonic circuits for data transmission purposes. Depending on the application, different wavelength bands are preferred and therefore designs of optical modulator, which operate in these bands, are required. Here we present our recent work on silicon optical modulators at 1310, 1550, 2000 and 3800 nm wavelengths.

In recent years, we have presented results on the development of a variety of silicon photonic devices such as erasable gratings and directional couplers, tunable resonators and Mach-Zehnder interferometers, and programmable photonic circuits using germanium ion implantation and localised laser annealing. In this paper we have carried out experiments to analyse a series of devices that can be fabricated using the same technology, particularly silicon-on-insulator racetrack resonators which are very sensitive to fabrication imperfections. Simulation and experimental results revealed the ability to permanently optimise the coupling efficiency of these structures by selective localised laser annealing.

Germanium has become a material of high interest for mid-infrared (MIR) integrated photonics due to its complementary metal-oxide-semiconductor (CMOS) compatibility and its wide transparency window covering the 2-15 μm spectral region exceeding the 4 μm and 8 μm limit of the Silicon-on-Insulator (SOI) platform and Si material respectively. Here, we present suspended germanium waveguides operating at wavelengths of 3.8 μm and 7.67 μm with propagation losses of 2.9 ± 0.2 dB/cm and 2.6 ± 0.3 dB/cm respectively.

SiN layers are typically deposited by low-pressure chemical vapour deposition (LPCVD) and plasma-enhanced chemical vapour deposition (PECVD). The issue with these deposition techniques is that they require high temperature processing (>400ºC) in order to produce waveguides with low propagation losses. As a result, they are incompatible with multilayer platforms in which the integration of active devices is intended, because the fabrication of these devices requires processes that are sensitive to high temperatures such as metallisation and doping. To address this situation, we are proposing hot wire chemical vapour deposition (HWCVD) as a means to deposit SiN layers at temperatures below 400ºC. This technique has already been used in solar cell applications [1,2] to produce amorphous SiN layers with low hydrogen content and high mass density [3]. In this study, several deposition recipes were defined with a design of experiments methodology (DoE) in which different combinations of deposition parameters were investigated to understand how they affect the material structure of the SiN layers in order to optimise the quality and the losses of the deposited materials. The physical, chemical and optical properties of the obtained SiN layers were characterised using ellipsometry, scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR) and atomic force microscopy (AFM). Also, waveguide structures were fabricated on the deposited materials to measure their propagation losses at 1310 and 1550nm using the cutback method. SiN layers with good uniformity, roughness as low as 0.61nm, H concentration as low as 10.4x1021 atoms/ cm3 and losses of 7.1dB/cm at 1310nm and 12.3dB/cm at 1550nm were obtained. [1] H. D. Goldbach, C. H. M. van der Werf, J. Löffler, A. Scarfo, A. M. C. Kylner, B. Stannowski, W. M. Arnoldbik, A. W. Weeber, H. Rieffe, W. J. Soppe, J. K. Rath, and R. E. I. Schropp,“Hot-wire chemical vapor deposition of silicon nitride for multicrystalline silicon solar cells,” in Conference Record of the Thirsy-first IEEE Photovoltaic Specialists Conference, pp. 1249–1252, IEEE, January 2005. [2] J. K. Holt, D. G. Goodwin, A. M. Gabor, F. Jiang, M. Stavola, and H. A. Atwater, “Hot-wire chemical vapor deposition of high hydrogen content silicon nitride for solar cell passivation and anti-reflection coating applications,” Thin Solid Films 430, pp. 37–40, April 2003. [3] V. Verlaan, R. Bakker, C. H. M. van der Werf, Z. S. Houweling, Y. Mai, J. K. Rath, and R. E. I. Schropp, “High-density silicon nitride deposited at low substrate temperature with high deposition rate using hot wire chemical vapour deposition,” Surface and Coating Technologies 201, pp. 9285–9288, September 2007.

The high speed conversion of signals between the optical and electrical domains is crucial for many key applications of silicon photonics. Electro-optic modulators integrated with electronic drive amplifiers are typically used to convert an electrical signal to the optical domain. Design of these individual elements is important to achieve high performance, however a true optimisation requires careful co-design of the photonic and electronic components considering the properties of each other. Here we present our recent results in this area together with a MOSCAP type modulator with the potential for high speed, high efficiency and highly linear modulation.

We reviewed our recent developments on the post-fabrication trimming techniques and programmable photonic circuits based on germanium ion implanted silicon waveguides. Annealing of ion implanted silicon can efficiently change the refractive index. This technology has been employed to fine-tune the optical phase, and therefore the operating point of photonic devices, enabling permanent correction of optical phase error induced by fabrication variations. High accuracy phase trimming was achieved with laser annealing and a real-time feedback control system. Erasable waveguides and directional couplers were also demonstrated, which can be used to implement programmable photonic circuits with low power consumption.

The growing demand for fast, reliable and low power interconnect systems requires the development of efficient and scalable CMOS compatible photonic devices, in particular optical modulators. In this paper, we demonstrate an innovative electro absorption modulator (EAM) developed on an 800 nm SOI platform; the device is integrated in a rib waveguide with dimensions of a 1.5 µm x 40 µm, etched on a selectively grown GeSi cavity. High speed measurements at 1566 nm show an eye diagram with dynamic ER of 5.2 dB at 56 Gbps with a power consumption of 44 fJ/bit.

Synergistic design of a CMOS driver and a depletion type Si MZM has been illustrated from circuit level design to real chip tape-out. The compact wire-bonded transmitter achieves 1.5pJ/bit power efficiency at 22Gb/s, provided 3.0dB extinction raio is maintained.

We demonstrate CMOS compatible photonic components such as high speed Ge/SiGe electro-absorption modulators and a flexible BEOL SiN waveguide platform for applications such as temperature insensitive CWDM and all optical signal processing through enhanced non-linear characteristics.

We discuss the latest progress on the development of all-optical signal processing devices in Si-based platform. We discuss the realization of intra- and inter-modal wavelength converters by using our internally developed Si-rich-silicon nitride platform.

Breaking the parity symmetry of a photonic crystal waveguides can lead to the bonding of guided modes with orthogonal dominant polarizations. Here we present how this coupling allows anomalous zero-group-velocity and prominent circular polarization to emerge, which can be used to enhance uni-directional photon emission.

Silicon is a low-cost material platform in which it is possible to form photonic integrated circuits serving a number of applications from optical communications to sensing. For optical communications applications, e.g. short reach data communication within data centres, the optical modulator is a key component with its capabilities having a significant bearing on the overall performance of the photonic circuit. In this paper we report our recent work on optical modulators in silicon and their integration with CMOS electronics on silicon.

This work presents an experimental demonstration of a 500μm long MZI carrier accumulation type modulator based on lateral MOS-capacitor integration on a silicon platform. A modulation efficiency (V π L π ) of 1.53V-cm, moderate modulation speed of 20Gbit-s−1 and extinction ratio of 3.65dB have been obtained.

We review our recent developments of the trimming techniques for correcting the operating point of ring resonator and Mach-Zehnder Interferometers (MZIs). This technology has been employed to fine-tune the effective index of waveguides, and therefore the operating point of photonic devices, enabling permanent correction of optical phase error induced by fabrication variations. Large resonance wavelength shift of ring resonators was demonstrated, and the shift can be tuned via changing the laser power used for annealing. A higher accuracy trimming technique with a scanning laser was also demonstrated to fine-tune the operating point of integrated MZIs. The effective index change of the optical mode is up to 0.19 in our measurements, which is approximately an order of magnitude improvement compared to previous work, whilst retaining similar excess optical loss.

We demonstrate low temperature hot-wire chemical vapor deposition of low loss a-Si:H wire waveguides. We achieved propagation loss of 0.65 dB/cm at TE polarized $1.55 \ \mu \mathrm{m}$ wavelength for waveguides deposited at 230°C.

Hybrid integration of nanoplasmonic devices with silicon photonic circuits holds promise for a range of applications in on-chip sensing, field-enhanced and nonlinear spectroscopy, and integrated nanophotonic switches. Here, we demonstrate a new regime of photon-plasmon coupling by combining a silicon photonic resonator with plasmonic nanoantennas. Using principles from coherent perfect absorption, we make use of standing-wave light fields to maximize the photon-plasmon interaction strength. Precise placement of the broadband antennas with respect to the narrowband photonic racetrack modes results in controlled hybridization of only a subset of these modes. By combining antennas into groups of radiating dipoles with opposite phase, far-field scattering is effectively suppressed. We achieve ultrafast tuning of photon-plasmon hybridization including reconfigurable routing of the standing-wave input between two output ports. Hybrid photonic-plasmonic resonators provide conceptually new approaches for on-chip integrated nanophotonic devices.

Germanium-on-silicon is a highly promising platform for planar photonics for the midinfrared, due to germanium’s wide transparency range. In this letter, we report Ge-on-Si waveguides with record low losses of only 0.6 dB/cm, which is achieved using a 2.9- $\mu \text{m}$ thick germanium layer, thus minimizing mode interaction with dislocations at the germanium/silicon interface. Using these waveguides, multimode interferometers with insertion losses of only 0.21 ± 0.02 dB are also demonstrated.

We present ring resonator (RR)-coupled Mach–Zehnder interferometers (MZIs) based on silicon-on-insulator rib waveguides, operating around the mid-IR wavelength of 3.8 μm. A number of different photonic integrated devices have been designed and fabricated experimentally to obtain the asymmetric Fano resonances in the mid-IR. We have investigated the influence of the coupling efficiency between the RR and the MZI as well as the phase shift between the two arms of the MZI on the Fano-type resonance spectral features, in agreement with theoretical predictions. Finally, wavelength-dependent Fano transmittances have been successfully measured with insertion losses up to ∼1 dB and extinction ratios of ∼20 dB. A slope of sharp Fano resonances as high as −574.6/μm has been achieved and estimated to be 35.5% higher than the slope of single RR Lorentzian-type resonances.

[EN] Universal multiport photonic interferometers that can implement any arbitrary unitary transformation between input and output optical modes are essential to support advanced optical functions. Integrated versions of these components can be implemented by means of either a fixed triangular or a fixed rectangular arrangement of the same components. We propose the implementation of a fixed rectangular universal interferometer using a reconfigurable hexagonal waveguide mesh circuit. A suitable adaptation synthesis algorithm tailored to this mesh configuration is provided and the experimental demonstration of a rectangular multiport interferometer by means of a fabricated silicon photonics chip is reported. The 7¿hexagonal cell chip can implement 2 × 2, 3 × 3 and 4 × 4 arbitrary unitary transformations. The proposed hexagonal waveguide mesh operates in a similar way as a Field Programmable Gate Array (FPGA) in electronics. We believe that this work represents an important step¿forward towards fully programmable and integrable multiport interferometers., The authors acknowledge financial support by the ERC ADG-2016 741415 UMWP-Chip, the Generalitat Valenciana PROMETEO 2013/012 research excellency award, I. G. acknowledges the funding through the Spanish MINECO Ramon y Cajal program. D.P. acknowledges financial support from the UPV through the FPI predoctoral funding scheme. D.J.T. acknowledges funding from the Royal Society for his University Research Fellowship. The chips were fabricated in the frame of the CORNERSTONE project funded by the EPSRC in the UK (EP/L021129/1)

We present the first waveguide electro-absorption modulator in germanium-on-silicon material platform at 3.8 μm wavelength, based on free-carrier injection into a straight waveguide. The fabricated 1 mm long device has modulation depth of >35 dB at 7 V.

We present an interlayer slope waveguide, designed to guide light from one level to another level in a multilayer silicon photonics platform. The waveguide is fabricated using HWCVD a-Si:H at 350oC. Measured loss of 0.5 dB/slope was obtained at a wavelength of 1550 nm and for TE mode polarization.

Slot waveguides are used for many photonic applications. However, existing fabrication techniques impose restrictions on the width of the slot region. Here, we propose and experimentally demonstrate a fabrication process to realize an arbitrarily narrow vertical dielectric slot in a silicon waveguide. Using this fabrication method, we have realized silicon slot waveguides with a 10-nm oxide slot region. The propagation loss of the fabricated slot waveguide was 1.36 ± 0.3 dB/mm.

A crucial component of any large scale manufacturing line is the development of autonomous testing at the wafer scale. This work offers a solution through the fabrication of grating couplers in the silicon-on-insulator platform via ion implantation. The grating is subsequently erased after testing using laser annealing without affecting the optical performance of the photonic circuit. Experimental results show the possibility for the realisation of low loss, compact solutions which may revolutionise photonic wafer-scale testing. The process is CMOS compatible and can be implemented in other platforms to realise more complex systems such as multilayer photonics or programmable optical circuits.

Germanium based photonic devices can play a significant role in several applications, particularly in the so-called fingerprint wavelength region. Here, we review our recent results on mid-infrared germanium photonic devices that show promising performance in the 2–7.5 μm wavelength range.

In this paper we demonstrate the implementation of optical delay lines on a programmable hexagonal waveguide mesh integrated in Silicon on Insulator (SOI). This building block enables the synthesis of reconfigurable discrete-time filters and beamforming networks.

In recent years, we have presented results on the development of erasable gratings in silicon to facilitate wafer scale testing of photonics circuits via ion implantation of germanium. Similar technology can be employed to develop a range of optical devices that are reported in this paper. Ion implantation into silicon causes radiation damage resulting in a refractive index increase, and can therefore form the basis of multiple optical devices. We demonstrate the principle of a series of devices for wafers scale testing and have also implemented the ion implantation based refractive index change in integrated photonics devices for device trimming. NRF (Natl Research Foundation, S’pore) Published version

We demonstrate a back end of line compatible SiN based material with tunable refractive index enabling low optical loss, high non-linear Kerr response, low index photonic crystals, high efficiency couplers, low loss waveguides and temperature tolerant MUX for DWDM.

A broad transparency range of its constituent materials and compatibility with standard fabrication processes make germanium-on-silicon (Ge-on-Si) an excellent platform for the realization of mid-infrared photonic circuits. However, the comparatively large Ge waveguide thickness and its moderate refractive index contrast with the Si substrate hinder the implementation of efficient fiber-chip grating couplers. We report for the first time, to the best of our knowledge, a single-etch Ge-on-Si grating coupler with an inversely tapered access stage, operating at a 3.8 μm wavelength. Optimized grating excitation yields a coupling efficiency of -11 dB (7.9%), the highest value reported for a mid-infrared Ge-on-Si grating coupler, with reflectivity below -15 dB (3.2%). The large periodicity of our higher-order grating design substantially relaxes the fabrication constraints. We also demonstrate that a focusing geometry allows a 10-fold reduction in inverse taper length, from 500 to 50 μm.

Optical modulators are central to a large number of applications in photonics particularly in the area of communication as they provide the function of writing electrical data onto an optical carrier. Silicon photonics provides a route to the realisation of low cost photonic integrated circuits through fabrication which is synonymous with CMOS electronic fabrication, i.e., high volume and high yield. The development of high performance optical modulators based on a silicon photonic platform can therefore support a number of low cost applications. Tremendous progress has been made in the realisation of high performance silicon based optical modulators over the last decade. Successful demonstrations have been made of ‘silicon only’ approaches which are based upon the plasma dispersion effect [1] as well as hybrid approaches involving the incorporation of other materials such as III–V compounds [2], SiGe [3], graphene [4], or organic materials [5]. On the component level, a large amount of research is ongoing worldwide to achieve increased levels of performance in different metrics such as speed, power consumption, modulation depth, footprint, wavelength independence, temperature insensitivity and optical loss. Furthermore, other significant research is underway in the area of silicon optical modulators including the use of more complex modulation formats, modulation at non-conventional wavelengths, the integration of the modulator into more complex photonic systems and the integration of high performance drive electronics. At the University of Southampton we are working on a number of projects across these different research focuses. Here we present an overview of our recent progress and results in these areas.

We present our recent work on fibre-chip grating couplers operating around 1310 nm. For the first time, we demonstrated the combination of dual-etch and apodization design approaches which can offer state of the art performance. Initial tests from fabricated structures show a -2.2dB loss.

This paper discusses some of the remaining challenges for silicon photonics, and how we at Southampton University have approached some of them. Despite phenomenal advances in the field of Silicon Photonics, there are a number of areas that still require development. For short to medium reach applications, there is a need to improve the power consumption of photonic circuits such that inter-chip, and perhaps intra-chip applications are viable. This means that yet smaller devices are required as well as thermally stable devices, and multiple wavelength channels. In turn this demands smaller, more efficient modulators, athermal circuits, and improved wavelength division multiplexers. The debate continues as to whether on-chip lasers are necessary for all applications, but an efficient low cost laser would benefit many applications. Multi-layer photonics offers the possibility of increasing the complexity and effectiveness of a given area of chip real estate, but it is a demanding challenge. Low cost packaging (in particular, passive alignment of fibre to waveguide), and effective wafer scale testing strategies, are also essential for mass market applications. Whilst solutions to these challenges would enhance most applications, a derivative technology is emerging, that of Mid Infra-Red (MIR) silicon photonics. This field will build on existing developments, but will require key enhancements to facilitate functionality at longer wavelengths. In common with mainstream silicon photonics, significant developments have been made, but there is still much left to do. Here we summarise some of our recent work towards wafer scale testing, passive alignment, multiplexing, and MIR silicon photonics technology.

We present Vernier-effect photonic microcavities based on a germanium-on-silicon technology platform, operating around the mid-infrared wavelength of 3.8 μm. Cascaded racetrack resonators have been designed to operate in the second regime of the Vernier effect, and typical Vernier comb-like spectra have been successfully demonstrated with insertion losses of ∼5 dB, maximum extinction ratios of ∼23 dB, and loaded quality factors higher than 5000. Furthermore, an add-drop racetrack resonator designed for a Vernier device has been characterized, exhibiting average insertion losses of 1 dB, extinction ratios of up to 18 dB, and a quality factor of ∼1700.

We present three main material platforms: SOI, suspended Si and Ge on Si. We report low loss SOI waveguides (rib, strip, slot) with losses of ~1dB/cm. We also show efficient modulators and detectors realized in SOI, as well as filters and multiplexers. To extend transparency of SOI waveguides, bottom oxide cladding can be removed. We have fabricated low loss passive devices in a suspended platform that employ subwavelength gratings. Ge on Si material can have larger transparency range than suspended Si. We have designed passive devices in this platform, demonstrated all optical modulation and carried out two photon absorption measurements. We have also investigated theoretically free carrier optical modulation in Ge.

We report methods of engineering the bandgap of SiGe and Ge compounds for the fabrication of electro absorption modulators and light emitting devices. We demonstrate uniform composition, single crystal, defect free SiGe-on-insulator formation. The composition can be tuned in different positions of the chip by modifying the structural design. We also demonstrate Ge disks with strain values of 1.1 and 0.6%.

In this paper we present a review of passive and active photonic devices in three mid-IR silicon photonics material platforms: germanium on silicon, suspended silicon and silicon on insulator (SOI).

Chirality is a crucial property to enthrone quantum computation on-chip and thereby engineer efficient deterministic photonic building blocks analogous to gates and transistors. Photonic Crystal Waveguides (PCWs) are promising for this purpose due to circular polarisation points that can unbalance the directionality of a quantum emitter (QE). In non-symmorphic waveguides, the local chirality is prominent and extends into high field intensity regions. Nevertheless, the Purcell effect at circular polarisation points saturates near the band-edge, the preferred region for Quantum ElectroDynamics (QED). Consequently, uni-directionality and ultra-strong light-matter interaction are difficult to combine. Here, we detract from the vicinity of the band-edge, and couple modes with different parities by breaking the mirror symmetry. Simulated bandstructures of the implemented Photonic Bonding States (PBS) display single-mode anomalous zero-group-velocity (ZGV) points with a non-vanishing energy flow far from the band edge, synonymous with an idealistic infinite Purcell Factor. Fabricated devices in Silicon (Si) slabs demonstrate an extremely large slow-down effect. On top of that, their simulated electric field patterns feature circular polarisation points at high field intensity regions where a QE would acquire uni-directional emission behaviour. This method to engineer PBS in PCWs paves the way for outperforming chiral light-matter experiment on-chip.

Silicon photonics has been a very buoyant research field in the last several years mainly because of its potential for telecom and datacom applications. However, prospects of using silicon photonics for sensing in the mid-IR have also attracted interest lately. In this paper, we present our recent results on waveguide-based devices for near- and mid-infrared applications. The silicon-on-insulator platform can be used for wavelengths up to 4 μm; therefore, different solutions are needed for longer wavelengths. We show results on passive Si devices such as couplers, filters, and multiplexers, particularly for extended wavelength regions and finally present integration of photonics and electronics integrated circuits for high-speed applications.

Suspended structures enable low loss propagation in silicon waveguides for mid-infrared wavelengths by removing the lossy buried oxide (BOX) layer. We previously demonstrated suspended waveguides with a silicon core and a sub-wavelength grating (SWG) lateral cladding, which allows access to the buried oxide layer for under-etching with hydrofluoric acid. Here we show that bends, multimode interference couplers (MMI) and Mach-Zehnder interferometers (MZI) can be successfully implemented in this platform. Specifically, we report waveguides with propagation losses of 1.2 dB/cm, 90° bends with 0.03 dB/bend loss, compact MMI couplers with imbalances of 0.5 dB, and MZI structures with extinction ratios in excess of 24 dB., 12th IEEE International Conference on Group IV Photonics, GFP 2015, 26 August 2015 through 28 August 2015

In this paper we present SOI, suspended Si, and Ge-on-Si photonic platforms and devices for the mid-infrared. We demonstrate low loss strip and slot waveguides in SOI and show efficient strip-slot couplers. A Vernier configuration based on racetrack resonators in SOI has been also investigated. Mid-infrared detection using defect engineered silicon waveguides is reported at the wavelength of 2-2.5 μm. In order to extend transparency of Si waveguides, the bottom oxide cladding needs to be removed. We report a novel suspended Si design based on subwavelength structures that is more robust than previously reported suspended designs. We have fabricated record low loss Ge-on-Si waveguides, as well as several other passive devices in this platform. All optical modulation in Ge is also analyzed., Silicon Photonics X, February 9-12, 2015, Series: Proceedings of SPIE; no. 9367

Germanium-on-silicon is a promising platform for planar photonics over the entire mid-infrared range. We report here grating coupled Ge-on-Si waveguides with record low losses of 0.6dB/cm, multimode interferometers and Mach-Zehnder interferometers.

Silicon and germanium are transparent up to approximately 8 m and 15 m, respectively, thus offering a range of applications in biochemical and environmental sensing, medicine, astronomy and communications [1]. Silicon-on-insulator (SOI), can be used only up to 4 m due to the high absorption loss of silicon dioxide, and therefore alternative material platforms have to be utilized for longer wavelengths. Also, to fully exploit the transparency range of SOI, 400 or 500 nm thick overlayers need to be used rather than the most popular 220 nm platform [2]. In this paper we report record low loss MIR SOI strip and slot waveguides, as well as Vernier racetrack configurations. If the buried oxide can be removed and replaced with air, such a platform would be transparent up to 8 m. We report a robust design based on single etch suspended Si waveguides. Ge-on-Si waveguides have already been demonstrated with losses of 2.5-ぬ┻ど dB【cm at ぢサの┻ぱ ヅm by Chang et. al [3] and Shen et. al [4]. We report a record low loss in Ge-on-Si and a demonstration of all optical modulation in such waveguides. Although Si is transparent beyond 1.1 m, it has been demonstrated that it can be used as a photodetector if mid-bandgap states are created by ion implantation. In this paper we show that detection in Si can be extended to up to 2.5 m by implantation of SOI waveguides with boron. Finally, we also report theoretical analysis of electroabsorption and electrorefraction in Ge., 2015 IEEE Photonics Society Summer Topical Meeting Series (SUM), July 13-15, 2015, Nassau, Bahamas