The adoption of optical technologies by high-volume consumer markets is severely limited by the cost and complexity of
manufacturing complete optical transceiver systems. This is in large part because "boutique" semiconductor fabrication
processes are required for III-V lasers, modulators, and photodetectors; furthermore, precision bonding and painstaking
assembly are needed to integrate or assemble such dissimilar devices and materials together. On the other hand, 200mm
and 300mm silicon process technology has been bringing ever-increasing computing power to the masses by relentless
cost reduction for several decades. Intel's silicon photonics program aims to marry this CMOS infrastructure and recent
developments in MEMS manufacturing with the burgeoning field of microphotonics to make low cost, high-speed
optical links ubiquitous. In this paper, we will provide an overview of several aspects of silicon photonics technology
development in a CMOS fabrication line. First, we will describe fabrication strategies from the MEMS industry for
micromachining silicon to create passive optical devices such as mirrors, waveguides, and facets, as well as alignment
features. Second, we will discuss some of the challenges of fabricating hybrid III-V lasers on silicon, including such
aspects as hybrid integration of InP-based materials with silicon using various bonding methods, etching of InP films,
and contact formation using CMOS-compatible metals.
Silicon photonics shows tremendous potential for the development of the next generation of ultra fast telecommunication,
tera-scale computing, and integrated sensing applications.
One of the challenges that must be addressed when integrating a "photonic layer" onto a silicon microelectronic circuit is
the development of a wafer scale optical testing technique, similar to that employed today in integrated electronics
industrial manufacturing. This represents a critical step for the advancement of silicon photonics to large scale
production technology with reduced costs.
In this work we propose the fabrication and testing of ion implanted gratings in sub micrometer SOI waveguides, which
could be applied to the implementation of optical wafer scale testing strategies.
An extinction ratio of over 25dB has been demonstrated for ion implanted Bragg gratings fabricated by low energy
implants in submicron SOI rib waveguides with lengths up to 1mm. Furthermore, the possibility of employing the
proposed implanted gratings for an optical wafer scale testing scheme is discussed in this work.
Integrated Bragg gratings are an interesting candidate for waveguide coupling, telecommunication applications,
and for the fabrication of integrated photonic sensors. These devices have a high potential for optical integration
and are compatible with CMOS processing techniques if compared to their optical fibre counterpart.
In this work we present design, fabrication, and testing of Germanium ion implanted Bragg gratings in silicon
on insulator (SOI). A periodic refractive index modulation is produced in a 1μm wide SOI rib waveguide by
implanting Germanium ions through an SiO2 hardmask.
The implantation conditions have been analysed by 3D ion implantation modelling and the induced refractive
index change has been investigated on implanted samples by Rutherford Backscattering Spectroscopy (RBS)
and ellipsometry analysis.
An extinction ratio of up to 30dB in transmission, around the 1.55μm wavelength, has been demonstrated for
Germanium implanted gratings on SOI waveguides.
Single wavelength hybrid silicon evanescent lasers are described based on wafer bonding III-V multiple quantum wells
to gratings patterned on a silicon waveguide. Distributed Bragg feedback and distributed Bragg reflector lasers are
demonstrated integrated with passive silicon waveguides showing thresholds as low as 25mA and output powers as high
as 11mW around 1600nm wavelength.
Recently, AlGaInAs-silicon evanescent lasers have been demonstrated as a method of integrating active photonic devices on a silicon based platform. This hybrid waveguide architecture consists of III-V quantum wells bonded to silicon waveguides. The self aligned optical mode leads to a bonding process that is manufacturable in high volumes. Here give an overview of a racetrack resonator laser integrated with two photo-detectors on the hybrid AlGaInAs-silicon evanescent device platform. Unlike previous demonstrations of hybrid AlGaInAs-silicon evanescent lasers, we demonstrate an on-chip racetrack resonator laser that does not rely on facet polishing and dicing in order to define the laser cavity. The laser runs continuous-wave (c.w.) at 1590 nm with a threshold of 175 mA, has a maximum total output power of 29 mW and a maximum operating temperature of 60 C. The output of this laser light is directly coupled into a pair of on chip hybrid AlGaInAs-silicon evanescent photodetectors used to measure the laser output.
Photonic integration is one of the important ways to realize low cost and small form factor optical transceivers for future high-speed high capacity I/O applications in computing systems. The photonic integration on silicon platform is particularly attractive because of the CMOS photonics and electronics process compatibility. In this paper, we present design and fabrication of a silicon photonic integrated circuit that is capable of transmitting data at hundreds gigabits per second. In such an integrated chip, 8 high-speed silicon optical modulators with a 1:8 wavelength demultiplexer and an 8:1 wavelength multiplexer are fabricated on a single silicon-on-insulator (SOI) substrate. We review the recent results of individual silicon modulator based on electric-field-induced carrier depletion in a SOI waveguide containing a reverse biased pn junction. We characterize the individual multiplexer/demultiplexer as well as the integrated chip. The basic functionality of the photonic integration is demonstrated.
Recently, AlGaInAs-silicon evanescent lasers have been demonstrated as a method of integrating active
photonic devices on a silicon based platform. This hybrid waveguide architecture consists of III-V quantum wells
bonded to silicon waveguides. The self aligned optical mode leads to a bonding process that is manufacturable in high
volumes. Here give an overview of a racetrack resonator laser integrated with two photo-detectors on the hybrid
AlGaInAs-silicon evanescent device platform. Unlike previous demonstrations of hybrid AlGaInAs-silicon evanescent
lasers, we demonstrate an on-chip racetrack resonator laser that does not rely on facet polishing and dicing in order to
define the laser cavity. The laser runs continuous-wave (c.w.) at 1590 nm with a threshold of 175 mA, has a maximum
total output power of 29 mW and a maximum operating temperature of 60 C. The output of this laser light is directly
coupled into a pair of on chip hybrid AlGaInAs-silicon evanescent photodetectors used to measure the laser output.
We present an electrically pumped silicon evanescent laser that utilizes a silicon waveguide and offset AlGaInAs
quantum wells. The silicon waveguide is fabricated on a Silicon-On-Insulator (SOI) wafer and is bonded with the
AlGaInAs quantum well structure using low temperature O2 plasma-assisted wafer bonding. The optical mode in the
hybrid waveguide is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V
active region providing optical gain via electrical current injection. The device lases continuous wave at 1577 nm with a
threshold of 65 mA at 15 °C. The maximum single-sided fiber-coupled cw output power is 1.8 mW. The maximum operating temperature is 40 °C mainly limited by a high series resistance of the device. Operation up to 60 °C should be achievable by lowering the series resistance and thermal impedance.
The transfer function of a photonic filter is significantly influenced by the profile of the waveguides forming the device. In this work we discuss requirements for devices based on two geometries, rib and wire shaped waveguides in Silicon-on-Insulator, from both the modal and polarisation standpoints. General guidelines and recommendations for the design of single-mode and polarisation-independent ring resonator filters with large Free Spectral Range (>30nm) are given, together with supportive experimental results.
In recent years there has been a growing interest in using Silicon on Insulator (SOI) as a platform for integrated planar optical circuits, this is mainly due to the high quality yield volume processes demonstrated by the CMOS manufacturing industry and recent MEMS technology progress. In this work we present monolithic integration of Silicon and SiON planar lightwave circuits on a single SOI chip processed in a CMOS fabrication environment. The demonstration of a processing scheme that yields low loss waveguides for both silicon and SiON as well as efficient transition of light between the two materials is the goal of this present work. The patterning of waveguides in both silicon and SiON regions is done in a self aligned process using one lithography mask and two separate dry etch steps each highly selective to one of the two materials. The effect of a high temperature anneal on the IR absorption of SiON related N-H bond was measured using FTIR and waveguide optical loss. Up to 98% reduction in absorption is demonstrated which allows acceptable loss across the C-band. We have achieved low propagation loss, single mode, and rib waveguides for both Silicon and SiON core regions as well as low loss silicon-SiON waveguides junction. The silicon-SiON junction loss has been measured to be 0.9+/-0.1dB, only 0.3dB greater than the theoretical value determined by Fresnel's facet reflection.
With a reverse biased p-i-n structure embedded in a silicon waveguide, we efficiently reduced the nonlinear loss due to two photon absorption induced free carrier absorption and achieved continuous-wave net Raman amplification and lasing in a silicon waveguide on a single chip. The low-loss p-i-n waveguides also enabled efficient wavelength conversion in the 1550 nm band via four-wave mixing in silicon. Here we report the performance characteristics of the silicon based laser, amplifier as well as wavelength converter for different device configurations. With a pump wavelength at 1550 nm, the laser output at 1686 nm is single mode with over 55 dB side mode suppression and has less than 80 MHz linewidth. At 25V reverse bias, the threshold pump power is ~180 mW. The slope efficiency is ~4.3% for a single side output and a total output power of >10 mW can be reached at a pump power of 500 mW. The laser wavelength can be tuned by adjusting the wavelength of the pump laser. A 3 dB on-chip amplification and -8.5 dB wavelength conversion efficiency is achieved in an 8-cm long waveguide at a pump powers of < 640 mW. We demonstrate that a high-speed pseudo-random bit sequence optical data at 10 Gb/s rate can be amplified or converted to a new wavelength channel with clear open eye diagram and no waveform distortion.
We report a novel laser architecture, the silicon evanescent laser (SEL), that utilizes a silicon waveguide and offset AlGaInAs quantum wells. The silicon waveguide is fabricated on a Silicon-On-Insulator (SOI) wafer using a CMOS-compatible process, and is bonded with the AlGaInAs quantum well structure using low temperature O2 plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. This approach combines the advantages of high gain III-V materials and the integration capability of silicon technology. Moreover, the difficulty of coupling an external laser source is overcome as the hybrid waveguide can be self-aligned to silicon-based passive optical devices. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum single-sided fiber-coupled CW output power is 4.5 mW. The SEL characteristics are dependent on the silicon waveguide dimensions resulting in different confinement factors in the III-V gain region.
With a reverse biased p-i-n structure embedded in a silicon waveguide, we efficiently reduced the nonlinear loss due to two photon absorption induced free carrier absorption and achieved continuous-wave net gain and lasing in a silicon waveguide cavity on a single chip. We report here the laser characterization for different cavity lengths from 1.6 to 8 cm. With a pump wavelength at 1550 nm, the laser output at 1686 nm is single mode with over 55 dB side mode suppression and has less than 80 MHz linewidth. The lasing threshold depends on the p-i-n reverse bias voltage. With 25V bias, the threshold pump power is ~180 mW. The slope efficiency is ~4.3% for a single side output and a total output power of >10 mW can be reached at a pump power of 500 mW. The laser wavelength can be tuned by adjusting the wavelength of the pump laser. In addition to the laser line at Stokes wavelength, a narrow linewidth anti-Stokes line at 1434.3 nm is also generated in the laser cavity through parametric conversion process.
Due to the mature silicon fabrication technology and vast existing infrastructures, silicon photonics has a chance to offer low cost solutions to telecommunications and data communications. It could also enable a chip-scale platform for monolithic integration of optics and microelectronics circuits for applications of optical interconnects for which high data streams are required in a very small footprint. Two key building blocks needed for any silicon based optoelectronics are silicon based light source and high-speed optical modulator. This paper gives an overview of recent results for a fast (>1GHz) silicon modulator and a silicon Raman laser. We present optical characterization of a high speed metal-oxide-semiconductor (MOS) capacitor-based silicon optical modulator. We show that a Mach-Zehnder interferometer (MZI) structure with a custom-designed driver circuit results in the realization of a silicon modulator transmitting data at 2.5 Gb/s with an extinction ratio of up to 2.8 dB. In addition we show that by reducing the waveguide dimensions one can improve the phase efficiency. In addition, as single crystal silicon possesses higher (four orders of magnitude) Raman gain coefficient as compared to silica, it is possible to achieve sizeable gain in chip-scale silicon waveguide for optical amplification and lasing. With a 4.8 cm long waveguide containing a reverse biased p-i-n diode, we demonstrate lasing operation using a pulsed pump laser. We achieve ~10% slope efficiency. We in addition model a continuous-wave silicon Raman laser and show that higher conversion efficiency and lower threshold power can be realized with optimised cavity device design.
In this paper the optical characterization of a novel, metal-oxide-silicon (MOS) capacitor-based, high speed, silicon optical modulator is presented. By using a capacitor based rather than the conventional p-i-n junction based architecture to modulate the free carrier density inside the waveguide, we show the realization of a fast, 2.5-GHz, optical modulator.
We present design, fabrication, and testing of a high-speed all-silicon optical phase modulator in silicon-on-insulator (SOI). The optical modulator is based on a novel silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. We show that, under the accumulation condition, the drive voltage induced charge density change in the silicon waveguide having a MOS capacitor can be used to modulate the phase of the optical mode due to the free-carrier plasma dispersion effect. We experimentally determined the phase modulation efficiency of the individual phase shifter and compared measurements with simulations. A good agreement between theory and experiment was obtained for various phase shifter lengths. We also characterized both the low- and high-frequency performance of the integrated Mach-Zehnder interferometer (MZI) modulator. For a MZI device containing two identical phase shifters of 10 mm, we obtained a DC extinction ratio above 16 dB. For a MZI modulator containing a single-phase shifter of 2.5 mm in one of the two arms, the frequency dependence of the optical response was obtained by a small signal measurement. A 3-dB bandwidth exceeding 1 GHz was demonstrated. This modulation frequency is two orders of magnitude higher than has been demonstrated in any silicon modulators based on current injection in SOI.