We previously proposed a photonics-electronics convergence system to solve bandwidth bottlenecks among large scale integrations (LSIs) and demonstrated a high bandwidth density with silicon optical interposers at room temperature. For practical applications, interposers should be usable under high temperature conditions and rapid temperature changes so that they can cope with the heat generated by mounted LSIs. We designed and fabricated athermal silicon optical interposers integrated with temperature-insensitive components on a silicon substrate. An arrayed laser diode (LD) chip was flip-chip bonded to the substrate. Each LD had multiple quantum dot layers with a 1.3-µm lasing wavelength. The output power was higher than 10 mW per channel up to 100º C. Silicon optical modulator and germanium photo detector (PD) arrays were monolithically integrated on the substrate. The modulators were structured as symmetric Mach- Zehnder interferometers, which were inherently temperature insensitive. The phase shifters composed of p-i-n diodes were stable against temperature with constant bias currents. The PD photo current was also temperature insensitive and the photo-to-dark current ratio was higher than 30 dB up to 100º C. We achieved error-free data links at 20 Gbps and high bandwidth density of 19 Tbps/cm2 operating from 25 to 125º C with the interposers without adjusting of the LDs, modulators, or PDs. The interposers are tolerant of the heat generated by the mounted LSIs and usable over the extended industrial temperature range without complex monitoring or feedback controls. The bandwidth density is sufficient for the needs of the late 2010s.
We developed a design technique for a photonics-electronics convergence system by using an equivalent circuit of optical devices in an electrical circuit simulator. We used the transfer matrix method to calculate the response of an optical device. This method used physical parameters and dimensions of optical devices as calculation parameters to design a device in the electrical circuit simulator. It also used an intermediate frequency to express the wavelength dependence of optical devices. By using both techniques, we simulated bit error rates and eye diagrams of optical and electrical integrated circuits and calculated influences of device structure change and wavelength shift penalty.
One of the most serious challenges facing the exponential performance growth in the information industry is a bandwidth bottleneck in inter-chip interconnects. Optical interconnects with silicon photonics have been expected to solve the problem because of the intrinsic properties of optical signals and the industrial advantages of silicon for use in the electronics industry. We therefore propose an optical interconnect system by using silicon photonics to solve the problem. We examined integration between photonics and electronics and integration between light sources and silicon substrates, and we propose a photonics-electronics convergence system based on these examinations. We also investigated the configurations and characteristics of optical components for the system, including silicon spot-size converters, silicon optical waveguides, silicon optical splitters, silicon optical modulators, germanium photodetectors, and arrayed laser diodes. We then demonstrated the feasibility of the system by fabricating a high-density silicon optical interposer by using silicon photonics hybridly integrated with arrayed laser diodes and monolithically integrated with the other optical components on a single silicon substrate. The pad pitches of optical modulators and photodetectors were designed to be 100 μm so that LSI bare chips were able to contact to them electrically by flip-chip bonding. Since this system was optically complete and closed and no temperature sensitive component was used, we did not need to align the fibers, control the polarization, or control the temperature throughout the experiments. As a result, we achieved errorfree data links at 20 Gbps and high bandwidth density of 30 Tbps/cm2 with the silicon optical interposer.
Silicon (Si) photonic wire waveguides provide a compact photonic platform on which passive, dynamic, and active photonic devices can be integrated. This paper describe the demonstrations of several kinds of integrated photonic circuits. The platform consists of Si wire, silicon-rich Si dioxide (SiOx) and Si oxinitride (SiON) waveguides for passive devices and a Si rib waveguide with a p-i-n structure and a germanium (Ge) device formed on Si slab for active devices. One of the key technologies for the photonic integration platform is low temperature fabrication because a back-end process with high temperature may damage active and electronic devices. To overcome this problem, we have developed electron cyclotron resonance chemical vapor deposition as a low-temperature deposition technique. Another key technology is polarization manipulation for reducing polarization dependence. A polarization diversity circuit is fabricated by applying Si wire and SiON integration. The polarization-dependent loss of the diversity circuit is less than 1 dB. Moreover we have developed several kinds of integrated circuit including passive, dynamic and active devices. Ge photodiodes are monolithically integrated with an SiOx-arrayed waveguide grating (AWG). We have confirmed that the operation speed of the integrated Ge photodiode is over 22 Gbps for all 16 channels. Variable optical attenuators (VOAs) fabricated on the Si p-i-n rib waveguides and an AWG based on the SiOx waveguide are integrated successfully. The total size of 16-ch-AWG-VOAs is 15 8 mm2. The device has already been made polarization independent. Furthermore electronic circuits are successfully mounted on the integrated photonic device by using flip-chip bonding.
Silicon photonic wire waveguides, featuring very strong optical confinement and compatibility with silicon electronics,
provide a compact photonic platform on which passive, dynamic, and active photonic devices can be integrated. We have
already developed a low-loss waveguide platform and integrated various photonic devices. For passive devices, we have
developed polarization-independent wavelength filters using a monolithically integrated polarization diversity circuit, in
which waveguide-based polarization manipulation devices are implemented. The polarization-dependent loss of a ring
resonator wavelength filter with polarization diversity is less than 1 dB. For dynamic devices, we have developed
compact carrier-injection-type variable optical attenuators (VOAs). The length of the device is less than one millimeter,
and the response time is nanosecond order. The device has already been made polarization independent. We have
recently monolithically integrated these fast VOAs with low-dark-current germanium photodiodes and achieved
synchronized operation of these devices. For nonlinear devices, a free-carrier extraction structure using a PIN junction
implemented in the waveguide can increase the efficiency of nonlinear functions. For example, in a wavelength
conversion based on the Four-wave-mixing effect, the conversion efficiency can be increased by 6 dB.
We devised a silicon photonic circuit with polarization diversity. The circuit consists of polarization splitters and
rotators. The splitter is based on simple 10-micrometer-long directional couplers. The polarization extinction ratio is 23
dB and excess loss is less than 0.5 dB. The rotator consists of a silicon waveguide embedded in an off-axis siliconoxynitride
waveguide. A 35-micrometer-long rotator gives a rotation angle of more than 72 degrees and excess loss of
about 1 dB. Both devices can be made by using planar fabrication technology and do not require a complex structure
such as three-dimensional forming. Using these devices, we developed a polarization diversity circuit for a ringresonator
wavelength filter. The polarization dependent loss of the filter with polarization diversity is about 1 dB. A 10-
Gbps data transmission with scrambled polarization is demonstrated.
We demonstrate efficient nonlinear functions using silicon nanophotonic structures. In the ultrasmall core of the
waveguides and cavities, nonlinear phenomena are significantly enhanced. Applying the two-photon absorption effect,
we have confirmed all optical modulation, in which the modulation speed is improved to around 50 ps by eliminating
free carriers. Applying the four-wave-mixing effect, we have achieved high-efficiency wavelength conversion. The
conversion efficiency is -11 dB, and the efficiency will be further improved by eliminating free carriers. Using the four-wave-
mixing effect, we have also realized a low-noise entangled photon pair source. The source does not need a
refrigeration system for noise reduction, which is a great advantage for practical application.
This paper presents our recent progress in the development of a Si wire waveguiding system for microphotonics devices. We have developed function devices that integrate several fundamental components and confirmed that they exhibited excellent characteristics due to the accuracy of the Si microfabrication. The propagation loss of the waveguide is less than 1.2dB/cm, and branching devices and basic filters show good characteristics. Using the fundamental microfabrication technique, we have developed other passive and dynamic functional devices. As an example of our recent advances using passive devices, we present a polarization diversity system consisting of a separator and a rotator. As a component of a dynamic functional device, we show a low-loss rib-type silicon wire waveguide with low-impedance p-i-n structure and its optical attenuation characteristics.
We investigate waveguide resonators, and a coupled system based on two-dimensional silicon-on-insulator photonic crystal (PhC) slabs. First, we show a way of designing PhC waveguides and PhC resonators to overcome the radiation loss that occurs in the thickness direction in a two-dimensional system and how to couple a PhC waveguide to an optical fiber. Next, we effectively couple PhC waveguides to PhC resonators, devise a three-port-resonant-tunneling filter, and develop an ultrasmall multi-port channel-drop filter. Finally, we describe a two-beam optical switch operating with very low power that employs a PhC coupled resonator-waveguide system.
We study various types of two-dimensional photonic crystal (PhC) waveguides (WG) on silicon-on-insulator (SOI) substrates for future photonic integrated circuit (PIC) applications. One of our goals is to realize a low-loss single-mode PhC WG. Off-plane diffractive leakage above the cladding layer light line is a serious problem in SOI-based PhC-WGs. We overcame this problem in width-varied line defect waveguides whose core-widths are changed by sliding PhC domains or deforming holes beside the waveguides. Narrow-core WGs have a wide transmission band below the cladding layer light line, and wide-core WGs can greatly suppress the diffractive leakage even above the cladding layer light line, and both types have a very low propagation loss. Another goal is to achieve a highly efficient coupling between SOI-based PhC WGs and single-mode fibers (SMFs). Normally, the loss of such a coupling system is very large, i.e. over 20 dB, because of the quite different mode profiles of the WGs and SMFs, and this loss is an obstacle to the development of PhC-based devices. Our system achieves a very small mode-profile-conversion loss of about 3-4 dB/connection from 1500 to 1600 nm wavelength.
We have experimentally demonstrated single-mode light-wave transmission and tunable waveguiding characteristics in photonic crystal (PC) waveguides constructed on a silicon-on-insulator (SOI) substrate as is most likely to be used for the a large scale integration of photonic circuits. Although off-plane diffractive leakage has been a serious problem in SOI-PC waveguides, we have overcome this problem in our narrow line-defect and phase-shifted-hole line-defect waveguide structures. These devices were developed through intensive theoretical studies on PC line-defect waveguieds. We have also demonstrated low-loss mode profile converter that will enable efficient connection between conventional silica-based waveguides and PC line-defect waveguides. The converter features an inversely-tapered silicon wire waveguide with an ultra-thin tip constructed on an SOI substrate. In our experiments, this converter proved capable of coupling loss as low as 0.5dB per conversion. These SOI-based devices represent an important step towards practical large-scale integrated photonic crystal circuits.
We experimentally demonstrate the structural tuning of the waveguiding modes of line defects in photonic crystal slabs. By tuning the defect widths, we realized efficient single-mode waveguides that operate within photonic band gap frequencies in SOI photonic crystal slabs. The observed waveguiding characteristics agree very well with 3D finite- difference time-domain calculations. The propagation loss of the line defect waveguides is experimentally determined to be 6 dB/mm. In addition, we measure group velocity dispersion of line defects by using Fabry-Perot resonance of the sample. Extremely large group dispersion is observed, and the traveling speed of light is reduced down to 1/100 of the light velocity in air.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.