We review the research progress of strictly nonblocking optical switches based on silicon photonics. We have developed a switch chip fabrication process based on a complementary ...metal-oxide-semiconductor pilot line and optical and electrical packaging technologies. We demonstrated all-paths transmission and switching of up to 32 input ports × 32 output ports with an average fiber-to-fiber insertion loss of 10.8 dB. Furthermore, we demonstrated an operating bandwidth wider than 100 nm for -30 dB crosstalk with double-Mach-Zehnder element switches in an 8 × 8 switch. For polarization-insensitive operation, we adopted a polarization diversity scheme and fabricated an 8 × 8 switch with fiber-based polarization-beam-splitters and two switch chips. The 8 × 8 switch exhibited a polarization-dependent loss of less than 0.5 dB. Moreover, an on-chip polarization diversity 8 × 8 switch integrated with polarization splitter rotators and two switch matrices on a single chip demonstrated a differential group delay less than 1 ps. Based on current technologies, we discuss the prospects for further port count expansion and remaining challenges for commercial deployment.
A precise flip-chip bonding (FCB) technology for indium phosphide semiconductor optical amplifiers (InP-SOAs) on a silicon photonics platform within less than ±1- μ m alignment accuracy was ...developed. For efficient optical coupling and a relaxed alignment tolerance, the mode field on both the InP-SOAs and the Si waveguides was expanded by spot-size converters (SSCs). On the InP-SOAs, width-tapered SSCs were used to obtain an isotropic mode-field having an approximately a 3- μ m diameter. On the silicon photonics platform, dual-core SSCs were used to expand the same mode-field size of 3 μ m as for the SSCs on SOAs. Using the FCB technology and the SSCs, an in-line optical amplification of 15 dB was achieved by in-line integrated SOAs with angled waveguides. The optical coupling losses were 7.7 dB, which included 5.1-dB excess losses by misalignment and a gap between InP-SOA and Si waveguides. A 4 × 4 Si switch with a hybrid-integrated 4-ch SOA array was fabricated, and achieved the first demonstration of a lossless Si switch.
Indoor free space optical (FSO) communication technology that provides high-speed connectivity to edge users is expected to be introduced in the near future mobile communication system, where the ...silicon photonics solid-state beam scanning device is a promising tool because of its low cost, long-term reliability, and other beneficial properties. However, the current two-dimensional beam scanning devices using grating coupler arrays have difficulty in increasing the transmission capacity because of bandwidth regulation. To solve the problem, we have introduced a broadband surface optical coupler, “elephant coupler,” which has great potential for combining wavelength and spatial division multiplexing technologies into the beam scanning device, as an alternative to grating couplers. The prototype port-selective silicon beam scanning device fabricated using a 300 mm CMOS pilot line achieved broadband optical beam emission with a 1 dB-loss bandwidth of 40 nm and demonstrated beam scanning using an imaging lens. The device has also exhibited free-space signal transmission of non-return-to-zero on-off-keying signals at 10 Gbps over a wide wavelength range of 60 nm. In this paper, we present an overview of the developed beam scanning device. Furthermore, the theoretical design guidelines for indoor mobile FSO communication are discussed.
We fabricate and characterize a polarization-diversity 32 × 32 silicon photonics switch by newly introducing SiN overpass waveguides onto our nonduplicate polarization-diversity path-independent ...insertion-loss switch. The SiN overpass waveguides are used to simplify the optical paths with a uniform path length between the edge couplers and the switch matrix and significantly reduce the number of waveguide intersections. The switch chip is fabricated using a 300-mm silicon-on-insulator wafer pilot line. The fabricated switch comprises more than 7,600 components, making this the largest ever complementary-metal-oxide-semiconductor-based silicon photonics circuit. The switch chip is electrically and optically packaged and evaluated for a sampled port connection with 32 paths, with an average on-chip loss of ~35 dB and an average polarization-dependent loss of 3.2 dB where 75% of the measured paths exhibit a loss of less than 3 dB. The differential group delay is measured to be 1.7 ps. The performance can be further improved by optimizing the device design.
We review our research progress of multi-port optical switches based on the silicon photonics platform. Up to now, the maximum port-count is 32 input ports×32 output ports, in which transmissions of ...all paths were demonstrated. The switch topology is path-independent insertion-loss (PILOSS) which consists of an array of 2×2 element switches and intersections. The switch presented an average fiber-to-fiber insertion loss of 10.8 dB. Moreover, -20-dB crosstalk bandwidth of 14.2 nm was achieved with output-port-exchanged element switches, and an average polarization-dependent loss (PDL) of 3.2 dB was achieved with a non-duplicated polarization-diversity structure enabled by SiN overpass waveguides. In the 8×8 switch, we demonstrated wider than 100-nm bandwidth for less than -30-dB crosstalk with double Mach-Zehnder element switches, and less than 0.5 dB PDL with polarization diversity scheme which consisted of two switch matrices and fiber-type polarization beam splitters. Based on the switch performances described above, we discuss further improvement of switching performances.
The recent advancement of cloud computing including AI applications requires a large networking capacity in datacenters resulting in a large power consumption at the same time. Optical switches ...significantly improve energy efficiency in datacenter networks, and silicon photonics enables the optical switch to operate faster than microseconds and be highly integrable for co-integration with GPUs. To support such high-capacity interconnect and switching, flexible use of multiple lanes and wavelength division multiplexing is essential, which can be implemented by a wavelength selective switch or wavelength cross-connect (WXC) switch. We proposed a novel silicon photonics WXC switch with free-spectral-range (FSR)-free grating-assisted contra-directional couplers (C-DCs) and Mach-Zehnder interferometers (MZIs), where extremely broadband operation is expected because of the unlimited FSR. In this paper, we demonstrate a largest ever port- and channel-count, 16 × 16 ports and 16 wavelength channels over the C+L-band, monolithically integrated WXC switch with 256 FSR-free grating-assisted C-DCs and 1,024 thermo-optic MZIs. Further extended multiband operation from the O-band to U-band will be potentially available by implementing two additional design considerations.
Silicon photonic switches with integrated p-i-n junctions can exhibit fast switching on the order of nanoseconds, enabling prospective optical networks with very fast reconfiguration times. However, ...carriers injected through the p-i-n junction cause extra loss, which can increase insertion loss, degrade uniformity and cause crosstalk. In this paper, we show that a path-independent insertion loss (PILOSS) switch with integrated p-i-n junctions can achieve uniform and very low on-chip insertion loss (3.8 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.19 dB) with strictly non-blocking characteristics. The switching time of our switch is <inline-formula><tex-math notation="LaTeX">< </tex-math></inline-formula>12.5 ns and <inline-formula><tex-math notation="LaTeX">< </tex-math></inline-formula>6.1 ns for 10%-90% and 10%-80% rise/fall times, respectively, and the optical crosstalk can be suppressed by more than 20 dB for a bandwidth of <inline-formula><tex-math notation="LaTeX">></tex-math></inline-formula>31 nm for the worst case.
We fabricate a 32 × 32 silicon photonics switch on a 300-mm silicon-on-insulator wafer by using our complementary metal-oxide-semiconductor pilot line equipped with an immersion ArF scanner and ...demonstrate an average fiber-to-fiber insertion loss of 10.8 dB with a standard deviation of 0.54 dB, and on-chip electric power consumption of 1.9 W. The insertion loss and the power consumption are approximately 1/60, and less than 1/4 of our previous results, respectively. These significant improvements are achieved by design and fabrication optimization of waveguides and intersections on the chip, and by employing a novel optical fiber connector based on extremely-high-Δ silica planar-lightwave-circuit (PLC) technology. The minimum crosstalk was -26.6 dB at a wavelength of 1547 nm, and -20-dB crosstalk bandwidth was 3.5 nm. Furthermore, we demonstrate low-crosstalk bandwidth expansion by using output port exchanged element switches. We achieve a -20 dB crosstalk bandwidth of 14.2 nm, which is four-times wider than that of the conventional element switch based 32 × 32 switch.
Miniaturization of silicon photonics switches is essential for both dense integration and low-loss operation. However, it has remained unclear how small the switches can be made while using ...thermo-optic (TO) element switches. In this paper, the minimum possible distance between adjacent TO phase shifter arms was first examined. Next, the architecture for a switch matrix for the high-density arrangement of TO switches that includes multi-layer electrical wirings for compact electrical wire-out was proposed and demonstrated. As a result, we achieved 1/23 miniaturization of an 8 × 8 silicon photonics switch for the PIC part when compared with our previous design.
In optical networks for telecom and datacom, an unprecedented energy efficient system is demanded since the amount of data traffic is rapidly increasing while a significant improvement of the energy ...efficiency in electronics devices such as switch ASICs is no longer expected. To overcome the energy constraints, introduction of energy-efficient optical circuit switching (OCS) to the conventional electrical packet switching network is considered. The energy consumption of the OCS is almost independent of the bandwidth because the transparent optical path with no optical-to-electrical/electrical-to-optical signal conversion supports an ultrawide bandwidth of highly multiplexed optical signals. In the OCS, high-speed and large-port-count optical switches are essential. We have been working on optical switches based on CMOS-compatible silicon photonics that offer fast switching, compactness, low power consumption, and low cost. By using our 45-nm CMOS process, we have recently demonstrated a low loss 32 × 32 silicon photonics switch and its performance improvements of wide operation bandwidth, polarization-independent operation, and so forth. In this paper, we review the recent progress of our silicon photonics switches. We discuss the importance of the silicon photonics switches for a sustainable optical network with a comparison of other switching technologies and explain comprehensively how our numerous achievements are advanced and related to each other.
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