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Silicon photonics (SiPh) switches are key devices for meeting data traffic growth in optical networks and data centres

Global data traffic has been exploding in recent years, putting increased pressure on data centre communication systems. To meet the rapid growth of data traffic, data switching technologies require larger switching capacity and higher interconnect bandwidth. To overcome the energy and capacity constraints in telecom and datacom networks, introduction of energy-efficient optical circuit switching (OCS) to the conventional electrical packet switching network is widely considered. Photonic switches have potential applications as packet switches in data centers and high performance Silicon photonics (SiPh) can create complex photonic circuits, including photonic packet switches and photonic circuit switches. Fast optical-circuit-switches (OCS) having a large number of ports can significantly enhance the performance and the efficiency of modern data centers by actively rearranging network patterns.

 

Commercially available optical switches typically operate with the use of moving mirror arrays. It made use of Micro-Electro-Mechanical-System (MEMS) actuators to move the mirrors and thereby to deflect free-space optical beams between optical fibers for switching. These switches can have port counts exceeding 100×100 and insertion losses lower than a few dBs. However, their switching speeds are typically tens-of-milliseconds which limits their applications in highly dynamic traffic patterns. Moreover, the moving-mirror-based optical switches make use of free-space optics that requires manual assembly and, as a result, the costs are high.

 

Recently, optical switches based on silicon photonics technology have been designed and built. Silicon photonics technology provides an attractive platform for optical switches. In them, light is tightly confined in silicon waveguides due to its high refractive index. The tight confinement allows dense integrations of switch components.

 

By leveraging complementary-metal-oxide semiconductor (CMOS) fabrication processes, large scale integrated optical circuits can be made at relatively low cost in high volume. Silicon-on-insulator (SOI) is a low-cost platform to develop high-performance optical switching technologies for data centre communication applications. For such applications, switches that are high-speed, broadband, and have low crosstalk are highly desired. Silicon photonic switches with microsecond or nanosecond response times have been demonstrated using thermo-optic effects or electro-optic effects, and silicon photonic switches with integrated CMOS driving circuits have been demonstrated.

Japan’s AIST touts polarization-diverse silicon photonics optical switch

Japan’s National Institute of Advanced Industrial Science and Technology (AIST)  describe the creation of an integrated optical switch realized via silicon photonics that will accommodate light that is carrying signals in both vertical and horizontal polarizations. To accommodate dual-polarized modulated transmission, a separate switch circuit must be used for each polarization. An optical switch for such transmission therefore must be twice the size of a similar device that only has to accommodate one polarization.

 

The device which the group calls a “fully integrated non-duplicate polarization-diversity silicon-photonic switch,” comprises a single 8×8 grid of 2×2 element switches. The researchers say that such a grid with unique port assignments could take the place of two synchronized grids, and thus be used to simultaneously manage both polarizations of light and achieve polarization diversity.

 

“In this way, the switch chip achieves polarization ‘insensitivity’ without doubling the size and cost of the chip, which is important for broadening the practical application of such photonics integrated devices,” said lead author Ken Tanizawa of AIST. “We strongly believe that a silicon-photonic switch is a key device for achieving sustainable growth of traffic bandwidth in optical networks, including both telecommunications and data communications, and eventually computer communications.”

 

 

Aeponyx: Optical Chips For Telecom

Aeponyx, a fabless chip company based in Montreal is developing  optical switches that can be tuned dynamically to handle huge amounts of data by combining MEMS and silicon photonics. “With a micro-optical switch, you can take the cost down 10 times, speed up data by 100 times, and it can all be done in a package that is 7 times smaller than existing switches,” said Philippe Babin, president of Aeponyx. “To make this possible we had to build a platform so that we could build a micro-optical switch. The way we solved that was to use planar MEMS with silicon photonics. We start with an industrial process on MEMS and create waveguides and filters. They we build a switch, which can be added as a standalone device or be used inside a transceiver.”

 

Babin believes this technology will become critical as 5G begins to roll out over the next few years. There is widespread agreement that 5G will be required to move huge quantities of data around for the IoT, high-definition video and imaging, and autonomous driving. But the infrastructure for 5G will be expensive because the technology operates at a much higher frequency than 4G LTE, so signals will be absorbed by buildings, people, trees, and just about anything standing in the way. The solution, at least at this point, is a much denser infrastructure, and that has set off a scramble among startups to develop a low cost solution that could be sold in huge volumes.

 

Aeponyx’s approach is to make these switches tunable, both for receiving signals and transmitting them, based on a silicon on insulator substrate with a hybrid integration scheme for packaging photonics with a MEMS chip. The technology supports the next-generation passive optical 2 standard (NG-PON2) and wavelength division multiplexing PON, or WDM-PON. WDM-PON uses one wavelength for downstream traffic and another for upstream traffic over single-mode fiber.

 

Russian scientists developed the world’s fastest nanoscale photonics switch

International team of researchers from Lomonosov Moscow State University and the Australian National University in Canberra created an ultrafast all-optical switch on silicon nanostructures. Researchers developed a “device”: a disc 250 nm in diameter that is capable of switching optical pulses at femtosecond rates (femtosecond is a one millionth of one billionth of a second). Switching speeds that fast will allow creating data transmission and processing devices that will work at tens and hundreds terabits per second. This can make possible downloading thousands of HD-movies in less than a second.

 

The operation of the all-optical switch created by MSU researchers is based on the interaction between two femtosecond pulses. The interaction becomes possible due to the magnetic resonance of the silicon nanostructures. This type of resonance is characterized by strong localization of light waves on subwavelength scales, inside the nanoparticles. If the pulses arrive at the nanostructure simultaneously, one of them interacts with the other and dampers it due to the effect of two-photon absorption. If there is a 100-fs delay between the two pulses, the interaction does not occur, and the second pulse goes through the nanostructure without changing.

 

“We were able to develop a structure with the undesirable free-carrier effects are suppressed, — says Maxim Shcherbakov. — Free carriers (electrons and electron holes) place serious restrictions on the speed of signal conversion in the traditional integrated photonics. Our work represents an important step towards novel and efficient active photonic devices– transistors, logic units, and others. Features of the technology implemented in our work will allow its use in silicon photonics. In the nearest future, we are going to test such nanoparticles in integrated circuits”.

 

Server networks could instead be connected by optical fibers, with photonic switches acting as the traffic cops, Wu says. Photonic switches require little power and don’t generate any heat, so they don’t face the same limitations as electrical switches. However, today’s photonic switches cannot accommodate as many connections and also are plagued by signal loss, which means the light beam gets dimmer as it passes through the switch, which makes it hard to read the encoded data once it reaches its destination.

 

In the new switch from Berkley, beams of light travel through a crisscrossing array of nanometer-thin channels until they reach individual light switches, each of which is built like a microscopic freeway overpass. When the switch is off, the light travels straight through the channel. Applying a voltage turns the switch on, lowering a ramp that directs the light into a higher channel, which turns it 90 deg. Another ramp lowers the light back into a perpendicular channel. “It’s literally like a freeway ramp,” Wu says. “All the light goes up, makes a 90-deg. turn, and then goes back down. This is an efficient process—more efficient than what everybody else is doing on silicon photonics. It is this mechanism that lets us make low-loss switches.”

 

Large Array of Fast Photonic Switches Will Serve as “Traffic Cop” for Fiber-Based Data Centers

Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light beams passing through optical fibers faster and more efficiently than ever. This optical “traffic cop” could one day revolutionize how information travels through data centers and high-performance supercomputers used for AI and other data-intensive applications.

 

The photonic switch consists of more than 50,000 microscopic light switches, each of which directs one of 240 tiny beams of light to either make a right turn when the switch is on, or to pass straight through when the switch is off. The 240-×-240 array of switches is etched into a silicon wafer and covers an area only slightly larger than a postage stamp. “For the first time in a silicon switch, we are approaching the large switches people can only build using bulk optics,” says UC professor Ming Wu. “This switch is not only not only large, but it is 10,000 times faster, so it can switch data networks in ways not many people have thought about.”

 

The photonic switch is made using photolithography, in which each “light switch” structure is etched into a silicon wafer. Each light gray square on the wafer contains 6,400 of these switches. Currently, the only photonic switches that can control hundreds of light beams at once are built with mirrors or lenses that must be physically turned to switch the direction of light. Each turn takes about one-tenth of a second to complete, which is eons compared to electronic data transfer rates. The new photonic switch is built using tiny silicon structures that can switch on and off in a fraction of a microsecond, approaching the speed necessary for use in high-speed data networks.

 

Data centers—where photos, videos, and documents are stored in the cloud—are composed of hundreds of thousands of servers that constantly send information back and forth. Electrical switches act as traffic cops, making sure that information sent from one server reaches the target server and doesn’t get lost along the way. But as data transfer rates continue to grow, we are reaching the limits of what electrical switches can handle, says Wu.

 

“Electrical switches generate so much heat that even if we could cram more transistors onto a switch, the heat they generate would pose certain limits,” he says. “Industry expects to continue the trend for maybe two more generations and, after that, something more fundamental has to change. Some people are thinking optics can help.”

 

Configurable circuit technology poised to expand silicon photonic applications

Researchers have developed a new way to build power efficient and programmable integrated switching units on a silicon photonics chip. The new technology is poised to reduce production costs by allowing a generic optical circuit to be fabricated in bulk and then later programmed for specific applications such as communications systems, LIDAR circuits or computing applications. “Silicon photonics is capable of integrating optical devices and advanced microelectronic circuits all on a single chip,” said research team member Xia Chen from the University of Southampton. “We expect configurable silicon photonics circuits to greatly expand the scope of applications for silicon photonics while also reducing costs, making this technology more useful for consumer applications.”

 

In The Optical Society (OSA) journal Optics Express, researchers led by Graham Reed demonstrate the new approach in switching units that can be used as building blocks to create larger chip-based, programmable photonic circuits. “The technology we developed will have a wide range of applications,” said Chen. “For example, it could be used to make integrated sensing devices to detect biochemical and medical substances as well as optical transceivers for connections used in high-performance computing systems and data centers.”

 

Erasable components

The new work builds on earlier research in which the investigators developed an erasable version of an optical component known as a grating coupler by implanting germanium ions into silicon. These ions induce damage that changes silicon’s refractive index in that area. Heating the local area using a laser annealing process can then be used to reverse the refractive index and erase the grating coupler. In the Optics Express paper, the researchers describe how they applied the same germanium ion implantation technique to create erasable waveguides and directional couplers, components that can be used to make reconfigurable circuits and switches. This represents the first time that sub-micron erasable waveguides have been created in silicon.

 

“We normally think about ion implantation as something that will induce large optical losses in a photonic integrated circuit,” said Chen. “However, we found that a carefully designed structure and using the right ion implantation recipe can create a waveguide that carries optical signals with reasonable optical loss.”

 

Building programmable circuits

They demonstrated the new approach by designing and fabricating waveguides, directional couplers and 1 X 4 and 2 X 2 switching circuits, using the University of Southampton’s Cornerstone fabrication foundry. Photonic devices from different chips tested both before and after programming with laser annealing showed consistent performance.

 

Because the technique involves physically changing the routing of the photonic waveguide via a one-time operation, no additional power is needed to retain the configuration when programmed. The researchers have also discovered that electrical annealing, using a local integrated heater, as well as laser annealing can be used to program the circuits.

 

The researchers are working with a company called ficonTEC to make this technology practical outside the laboratory by developing a way to apply the laser and/or electrical annealing process at wafer scale, using a conventional wafer prober (wafer testing machine), so that hundreds or thousands of chips could be programmed automatically. They are currently working on integrating the laser and electrical annealing processes into such a wafer-scale prober — an instrument found in most electronic-photonic foundries — being testing at the University of Southampton.

 

Global Photonic Switch Market

Research firm ReportsnReports finds that as networks add more bandwidth, the number of optical fibre connections is growing significantly. To keep up with increased demands for fibre optic switching technology, CommScope and its consortium of industrial, research, and academic partners launched SwIFT (optical Switch combining Integrated photonics and Fluidics Technologies), a project of the EU’s 7th Framework Programme for Information and Communications Technology ICT (FP7). The aim is to develop a low-cost solution for automatic and remote fibre management. The EU granted 1.85 million euros to fund this project. Recent research commissioned by the European Union (EU) highlights the importance of micro fluidics and silicon photonics for remote fibre management. Unique fibre optic switching technologies could potentially automate manual processes and reduce energy costs across telecommunications.

 

The key product type of Photonic Switch market are: Mechanical Optical Switch, Liquid Crystal Optical Switch, Waveguide Optical Switch
Thermal Optical Switch,  and Magneto-Optical Switch.

 

The Major market players are: Agilent Technologies, Cisco, Infinera, HP, Agiltron Corp, Coriant, Alcatel-Lucent, Ericsson, EmcoreOptical Switches, Luna Innovations, TE Connectivity, ZTE, Huawei, NEC and Fujitsu

 

References and Resources also include:

https://semiengineering.com/aeponyx-optical-chips-for-telecom/

http://www.lightwaveonline.com/articles/2017/02/japan-s-aist-touts-polarization-diverse-silicon-photonics-optical-switch.html

https://www.machinedesign.com/3d-printing-cad/article/21837782/large-array-of-fast-photonic-switches-will-serve-as-traffic-cop-for-fiberbased-data-centers

About Rajesh Uppal

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