In this work, the simplified modeling of silicon phase modulators is presented along with a comparison among different options of modulators. The proposed simplified model enables a substantial reduction in computational effort while maintaining a good accuracy. The presented model is validated against complete 3D-simulations by means of the design of four different modulators. Furthermore, with the help of the model a deep insight on the performances tradeoffs in the choose and design of silicon modulators is provided.
We present two novel capacitive modulator phase shifter architectures using a vertical oxide. The first structure consists of a vertical oxide slot embedded in a silicon waveguide along the propagation direction. The second structure is based on a sub-wavelength approach, with several periodic vertical oxide layers along the propagation direction. This paper focuses on the design of the modulator devices and the simulation of their performances.
Modulators based on free-carrier plasma dispersion effect has attracted a lot of attention in the recent years. Particularly, a lot of effort is dedicated nowadays into optimizing carrier accumulation silicon modulators. In this work a novel structure of carrier accumulation modulator is proposed and analyzed. The structure is based on interleaved capacitors in a periodic segmented waveguide such as SubWavelength Gratings (SWG) waveguides. This new structure overcomes the major limitation of carrier accumulation structures, which is the limited overlap of the optical mode with the region where the carrier accumulation takes place. The analysis of this novel structure is presented in detail from the optical and the electrical point of view. Furthermore, the procedure to analyze and extract the modulator performance is also presented. Values of modulation efficiency and loss below 0.5Vcm and 5 dB respectively were obtained for the proposed modulator.
Silicon photonics technology is an enabler for the integration of complex circuits on a single chip, for various optical link applications such as routing, optical networks on chip, short range links and long haul transmitters. Quadrature Phase Shift Keying (QPSK) transmitters is one of the typical circuits that can be achieved using silicon photonics integrated circuits. The achievement of 25GBd QPSK transmitter modules requires several building blocks to be optimized: the pn junction used to build a BPSK (Binary Shift Phase Keying) modulator, the RF access and the optical interconnect at the package level. In this paper, we describe the various design steps of a BPSK module and the related tests that are needed at every stage of the fabrication process.
The ever growing demands of bandwidth in optical communication systems are making traditional Wavelength Division Multiplexing (WDM) based systems to reach its limit. In order to cope with future bandwidth demand is necessary to use new levels of orthogonality, such as the waveguide mode or the polarization state. Mode Division Multiplexing (MDM) has recently attracted attention as a possible solution to increase aggregate bandwidth. In this work we discuss the proposition a of mode converter that can cover the whole C-Band of optical communications. The Mode Converter is based on two Multimode Interference (MMI) couplers and a phase shifter. Insertion loss (IL) below 0.2 dB and Extinction ratio (ER) higher than 20 dB in a broad bandwidth range of 1.5 μm to 1.6 μm have been estimated. The total length of the device is less than 30 μm.
A new technological platform aimed at making prototypes and feasibility studies has been setup at STMicroelectronics using 300mm wafer foundry facilities. The technology, called DAPHNE (Datacom Advanced PHotonic Nanoscale Environment), is devoted at developing and evaluating new devices and sub-systems in particular for wavelength division multiplexing (WDM) applications and ring resonator based applications. Developed in the course of PLAT4MFP7 European project, DAPHNE is a flexible platform that fits perfectly R&D needs. The fabrication flow enables the processing of photonic integrated circuits using a silicon-on-insulator (SOI) of 300nm, partial etches of 150nm and 50nm and a total silicon etching. Consequently, two varieties of rib waveguides and one strip waveguide can be fabricated simultaneously with auto-alignment properties. The process variability on the 150nm partially etched silicon and the thin 50nm slab region are both less than 6 nm. Using a variety of different implantation configurations and a back-end of line of 5 metal layers, active devices are fabricated both in germanium and silicon. An available far back-end of line process consists of making 20 μm diameter copper posts on top of the electrical pads so that an electronic integrated circuit can be bonded on top the photonic die by 3D integration. Besides having those fabrication process options, DAPHNE is equipped with a library of standard cells for optical routing and multiplexing. Moreover, typical Mach-Zehnder modulators based on silicon pn junctions are also available for optical signal modulation. To achieve signal detection, germanium photodetectors also exist as standard cells. The measured single-mode propagation losses are 3.5 dB/cm for strip, 3.7 dB/cm for deep-rib (50nm slab) and 1.4 dB/cm for standard rib (150nm slab) waveguides. Transition tapers between different waveguide structures are as low as 0.006 dB.
In this work, the modeling of phase shifters based in PN interleaved junctions is analyzed. Three different models based on different approximations are presented in details. Comparisons with previous published experimental data are presented, as well as a comparison and a discussion on the different models.
High contrast structures with a sub-wavelength pitch, small enough to suppress diffraction, exhibit extraordinary optical properties: depending on the design they may behave as perfect mirrors, anti-reflective interfaces, homogenous materials with controllable refractive index, or strongly dispersive materials. Here we discuss on the design possibilities such structures offer in planar waveguide devices in silicon-on-insulator. We briefly review the application of sub-wavelength structures in a variety of waveguide devices. We then focus on some of the latest advances in the design ultra-compact and ultra-wideband multimode interference couplers based on dispersion engineered sub-wavelength structures.
In most integrated optics platforms device design is restricted to variations in the lateral dimensions, and a small set of etch depths. Sub-wavelength gratings (SWGs) in silicon-on-insulator enable engineering of refractive index in a wide range. SWGs exhibit a pitch smaller than the wavelength of light propagating through them, thereby suppressing diffraction and acting as a homogenous medium with an equivalent refractive index controlled by the duty-cycle. Here, we propose to not only engineer refractive index, but to control SWG dispersion. We use this concept to design ultra-broadband directional couplers (DCs) and multimode interference couplers (MMIs) with a fivefold bandwidth enhancement compared to conventional devices.
Subwavelength gratings (SWG) are periodically segmented waveguides with a pitch small enough to suppress
diffraction. These waveguides can be engineered to implement almost any refractive between the refractive indices of
the material that compose the waveguide, thereby opening novel design possibilities. In this communication we explore
the use of SWGs in the design and optimization of a variety of integrated optical devices in the silicon-on-insulator
platform: fiber-to-chip grating couplers, polarization splitters and high performance multimode interference couplers.
We furthermore show that the dispersion properties of SWGs enable the design of novel filters, and discuss the design of
low transitions between SWG waveguides of different characteristics.