Silicon Photonics

Silicon photonics is a new technology that should at least enable electronics and optics to be integrated on the same optoelectronic circuit chip, leading to the production of low-cost devices on silicon wafers by using standard processes from the microelectronics industry. In order to achieve real-low-cost devices, some challenges need to be taken up concerning the integration technological process of optics with electronics and the packaging of the chip. In this paper, we review recent progress in the packaging of silicon photonic circuits from on-CMOS wafer-level integration to the single-chip package and input/output interconnects. We focus on optical fiber-coupling structures comparing edge and surface couplers. In the following, we detail optical alignment tolerances for both coupling architecture, discussing advantages and drawbacks from the packaging process point of view. Finally, we describe some achievements involving advanced-packaging techniques.

— Realizing small-footprint and energy-efficient
optical switching fabrics is of crucial importance to solve the data
movement challenges faced by optical interconnection networks.
This letter demonstrates silicon photonic 2 × 2 full crossbar
switching functionality based on a single microring. The ultracompact
device is shown to successfully switch data channels
from two input ports simultaneously. Data channels in both the
multiple and the same wavelength switching experiments are
measured to be error-free. Simulation shows that by optimizing
some of the microring parameters crosstalk could be reduced.
This letter confirms the applicability of a single microring as
a 2 × 2 switch element for on-chip optical interconnects.

Magnetoresistive memory (MRAM) is one of the
forerunners of the nanotechnology enabled memories lined to
replace the traditional memories like Flash, DRAM and SRAM.
MRAMs are based on the phenomenon of spin dependent
tunneling in magnetic tunnel junctions (MTJs). It stores data in
the magnetization of a magnetic layer as opposed to electrical
charge in conventional RAMs. Yet the read-out of MRAM is
electrical. It is claimed to offer something close to the speed of
SRAM, with a density approaching that of single-transistor
DRAM and the ability to store information when power is
removed, like flash memory or EEPROM. This paper works out
the microstructure processing steps in the fabrication of an MTJ
based MRAM cell in two distinct versions. The technicalities of
the two MTJ based MRAM cell configurations have been
discussed in this paper. The I-V characteristics and TMR ratios
of the widely investigated Fe/MgO/Fe magnetic tunnel junction
have also been evaluated using first principle LSDA bandstructure
calculations. Micro magnetic simulations of the MTJ
demonstrate the magnetic switching in the two ferromagnetic
layers. The resulting hysteresis loop has been presented at the
end of the paper.

A novel wavelength routing device for optical on-chip network applications is presented. It is based on the constructive and destructive interferences that occur when two side-coupled integrated spaced sequences of resonators (SCISSORs) are coupled in parallel to a single common waveguide. Its potential application for coarse wavelength division multiplexing, i.e., band routing functionalities, and its robustness against fabrication tolerances and signal imbalances are analyzed. Design, simulation, fabrication, and experimental characterizations are described. We compare measurements of the fabricated device with simulations for the ideal and the actual device, where random variations in the geometrical parameters inherent in the fabrication process are considered. This allows demonstrating the concept of interferometric SCISSOR routing and to discuss the limits and advantages of coupled resonator-based design for routing.

A s the field of integrated optics has expanded 1 , small-scale silicon-based modulators and filters have been studied and demonstrated, consequently motivating exploration at both the transmitter and receiver sides 2,3. In many applications, specific frequencies or electrical responses are desired 4-6 : in radio-frequency (RF) applications, linear transmission is typically required to provide a large spurious-free dynamic range (SFDR) 7. Detecting digitally modulated optical signals requires an optical comparator that can be realized by a device having a square-wave shape 8. A square-like behaviour, this time in the frequency domain, is also encountered when considering a bandpass 'box-like' filter in high-capacity optical links such as wavelength-division multiplexing (WDM) 9. WDM-based devices can be used in dense WDM (DWDM) systems through multiplexing/de-multiplexing odd and even channels by employing a so-called interleaver filter 10,11. The separation of channels , obtained by the interleaved shaped waveform, is also needed to facilitate traffic routing within a relay station. The above-mentioned response shapes are commonly realized by complex optical circuits, often comprising several optical elements. In the case of analog RF applications, a chain of Mach-Zehnder interferometers (MZIs) was required to obtain a high SFDR 12 ; ring-assisted MZIs (RAMZIs) with multiple electrodes have also been widely explored 13-15. Several complex designs were suggested 8,16,17 for detecting digitally modulated optical signals using an optical comparator. These designs require multiple electrodes and a large footprint. To obtain a sharp box-like filter response, five cascaded rings were devised 9 while several rings coupled to a MZI have also been reported 5,6,18. For an interleaver, a flat-top spectral response is required, otherwise the transmission efficiency will be sensitive to a slight shift in wavelength (for example, laser quality or temperature). Consequently, the sinusoidal response of a single crossbar MZI is not adequate. This motivated analysis of circuits comprising MZIs in a serial configuration made of directional couplers (DC) or multimode interferometer (MMI) elements to obtain a flat-top response 10,19. An interleaver for Nyquist-WDM (super-channel) based on RAMZI circuits with additional coupled rings has recently been demonstrated 20. The above-mentioned solutions exhibit similar characteristics, such as large footprint, fabrication sensitivity and a multiplicity of electrodes. A large free spectral range (FSR) is required in a variety of applications. These include some sensing applications, tunable filters, and WDM architectures where a large FSR is required to avoid cross-talk among channels. The increase in FSR is typically achieved by reducing the resonator length; however, this also reduces the electrode length, consequently increasing the required operating voltage. Small-scale optical structures, such as photonic crystals 21 and rather complex ring resonator-based designs 22-24 , have been suggested to increase the FSR and may, in theory, be able to operate under low voltage. However, these are more complicated to fabricate and harder to integrate with an electrical control. Optical circuits based on ring resonators are very sensitive to fabrication deviations. A small variation in the coupling or loss coefficients may drastically decrease the extinction ratio (ER) of the transmission. A three-dimensional finite difference (FDTD) sensi-Modern systems often provide complex functionality that can be realized by tailoring together elements of simpler functional-ity. Multiplicity of simple optical functions (response shapes), when densely fabricated on a chip, can promote the concept of a field-programmable optical array. Shaping of the frequency response, or otherwise an electrical-to-optical response, is studied and demonstrated by means of a racetrack-shaped ring resonator designed and fabricated in the so-called double injection configuration. This configuration possesses a unique property that allows two free spectral range states (regular, 2 × regular) to exist for a single ring length. Shaping is realized by properly selecting different coupling coefficients that provide a variety of interesting responses. Here, we demonstrate various shapes including: sinusoidal, triangular (linear), square (bandpass), dips and peaks (two states), spikes (tangent-like), interleaver and a so-called 20dB-min parameters-insensitive-response modula-tor. The transmission responses were experimentally realized, fabricated in a silicon-on-insulator platform and characterized at wavelengths around 1,550 nm. Su bs tra te E il E i2 E in E t2

We present here research work on two optical biosensors which have been developed within two separate European projects (6 th and 7 th EU Framework Programmes). The biosensors are based on the idea of a disposable biochip, integrating photonics and microfluidics, optically interrogated by a multichannel interrogation platform. The objective is to develop versatile tools, suitable for performing screening tests at Point of Care or for example, at schools or in the field.

The described work is study and design of Multimode Interference based Thermo-Optic switch using Silicon on Insulator (SOI) technology. The main focus of this work is to analysis of thermo-optical switches. First, the physical principle of Thermo-Optics effect is briefly introduced. A comparative analysis of commonly used technology for fabrication of Thermo-Optic switches along with the materials is done.

A digital radiography delivers a radiation dose to patients; therefore it poses potential risk to the patients. One effort to reduce dose is carried out using a radiation filter, e.g. Silicone Rubber (SR) sheet. The purpose of this research was to determine the impact of the SR sheet on the high contrast objects (HCO) and the low contrast objects (LCO). The dose reduction was determined from attenuation x-rays before and after using the SR sheet. Assessment of HCO and LCO was observed from CDR TOR phantom at tube voltage of 48 kVp and tube current of 8 mAs. The physical parameter to assess image quality was the Signal to Noise Ratio (SNR) value in LCO. The maximum x-ray attenuation using the SR sheet is 48.82%. The visibility of the HCO remains the same, namely 16 objects; however the LCO slighly decreases from 14 objects to 13 objects after using the SR sheet. The SNR value decreases with an average value of 15.17%.Therefore, the SR sheet as a alternative filter has no effect on the HCO and has realtively little effect on the LCO. Thus, the SR sheet potentially is used for radiation protection in patients, especially on examinations that do not require low contrast resolution.