+44 (0)24 7671 8970
More publications     •     Advertise with us     •     Contact us
Technical Insight

Big step forward in silicon integration

The hybrid III-V/silicon laser manufactured by Intel and its collaborators may not represent true silicon photonics, but it is a significant development in optical interconnects for chip and board communications, discovers Michael Hatcher.

Until the last couple of years, research into silicon photonics had been moving at snail s pace. Now things seem to be happening at breakneck speed. "Silicon photonics is on fire!" is how Graham Reed, head of electronic engineering at the University of Surrey, UK, puts it.

"Just look at the number of Nature papers in the past two years," he said. "There is a daily increase in the number of groups and companies in this field."

One of those companies is Intel, the biggest player in silicon electronics bar none. But it is also at the forefront of the emerging silicon photonics research field. In September, it revealed details of an electrically pumped hybrid III-V/silicon laser, developed in collaboration with researchers at the University of California, Santa Barbara (UCSB). While many key optical functions have been demonstrated on a silicon platform, finding a suitable light-emitting source has posed the biggest problem – until now, it appears.

According to Intel, the breakthrough addresses one of the last major barriers to producing silicon photonics for use inside and around future computers and data center architectures. In essence, that means using components compatible with volume silicon manufacturing methods to generate, amplify, route, modulate and detect light in very high speed terabit optical interconnects of a suitable size for a high-performance computer.

Reed, whose credentials include initiating the field of silicon optical integrated circuits in the UK, concurs: "This device has a lot of potential" he said. "There s no doubt that it s certainly a very significant piece of the puzzle. While it s not truly a silicon laser, it s probably the next best thing".

The flurry of silicon photonics papers appearing in the leading science journals over the past couple of years suggests that with the fundamental building blocks in place, integration of these various components in an optical system has now become the major challenge.

For example, electro-optic modulators are one of these key building blocks. Earlier this year a Danish team published details in Nature of just such a device. Using a silicon nitride layer to compressively strain the active layer of silicon, Rune Jacobsen from the Technical University of Denmark and colleagues discovered that this strain induces a linear electro-optic effect that can modulate light at high speeds. In theory, it could be used instead of an electronic "bus" to transport data in computer architectures.

Unlike some other approaches to optical modulators based on silicon, the device proposed by the Jacobsen team is not limited by any charge mobility or carrier recombination effects. They argue that this could be a critical advantage when it comes to commercial deployment of silicon-based photonics because these effects could limit modulation speeds.

Despite the apparently different material platforms that the Danish team s modulator and Intel s hybrid silicon laser are based upon, Reed believes that these two devices could, in theory, function together as part of an optical system. "Most of the parts that are emerging are compatible at a high level because they are almost all based on a silicon-on-insulator (SOI) platform," he said.

Intel s hybrid laser is made by fusing together a AlGaInAs/InP quantum well structure and a silicon strip waveguide. That waveguide is first formed on the surface of an undoped SOI substrate. The "special sauce" that allows the laser to function is the way that the silicon waveguide and the active AlGaInAs layers bond.

Both surfaces are treated in an oxygen plasma reactive ion etch chamber, pressed together and annealed. The materials couple so well that the III-V and silicon elements each form a critical part of the laser structure, with the silicon waveguide fundamental to the lasing action. The degree of alignment between the two types of material does not require a particularly high level of precision. John Bowers from UCSB has been leading the research: "All of the optical mode confinement – in the laser, in subsequent modulators, in output waveguides and in a fiber holder – is determined by the same CMOS lithography step," he explained.

According to Graham Reed, the complexities of integrating lasers, modulators and detectors will always throw up issues of compatibility, particularly when it comes to processing optical and electronic parts in the same layer of material. For high-end applications capable of 40 Gbit/s communications, it will also be necessary to develop another part – a silicon-based optical isolator – that can be easily integrated into a circuit.

These high modulation frequencies will have to be achieved in Intel s vision for commercialization of "silicon" photonics, however. Although it is funding a big effort into the development of the hybrid laser, the chip giant s overall photonics strategy is difficult to understand given recent events. In September, Intel sold its optical networking components business (which makes control electronics, rather than optical communications modules) to venture-backed newcomer Cortina Systems.

So why the push to develop the hybrid laser? Intel knows that its commercialization at any level is at least five years away, but it is already talking about using integrated photonic chips as part of its terascale computing research program. This program is based on the idea of multi-core processing and Intel s plan is to house tens or even hundreds of these cores onto a single chip.

The problem arises when you try to move this amount of data around using conventional copper interconnects. While copper can support very fast interconnection speeds, it can only do this over a very short distance. To deliver terabit communications, it seems more than likely that photonic interconnections will be needed.

But what exactly would such a system look like? Intel has already proposed its idea of a terabit optical transceiver. It consists of a row of hybrid silicon lasers, all of which are tuned to operate at a slightly different wavelength. The individual wavelengths can be defined by altering the width of each silicon waveguide and its grating pitch, and can be tightly controlled thanks to the precision that state-of-the-art photolithography allows.

If 25 lasers are used and each of these individual data streams is modulated at 40 Gbit/s, the result would be terabit per second data transmission from a single chip. Even Intel s prototype hybrid die featured as many as 36 lasers, although only 26 actually lased.

With the hybrid laser and the other building blocks required for silicon photonics on the road to commercial development, the long-awaited marriage between optoelectronics and computing suddenly appears to be within reach. And not, as some had predicted, to the exclusion of compound semiconductors.

PIC International to return to Brussels – bigger and better than ever!

The leading global integrated photonics conference and exhibition will once again bring together key players from across the value chain for two-days of strategic technical sessions, dynamic talks and unrivalled networking opportunities.

Join us face-to-face on 18-19 April 2023

  • View the agenda.
  • 3 for the price of 1. Register your place and gain complementary access to TWO FURTHER industry leading conferences: CS International and Power Electronics International.
  • Email info@picinternational.net  or call +44 (0)24 7671 8970 for more details.


Picocom and Antevia collaborate on 5G in-building solutions
Fast, narrow-linewidth tunable laser is a first
Luceda Photonics and Spark Photonics announce partnership
Imec demonstrates co-integration of high-quality SiN waveguide technology with silicon photonics platform
Toptica acquires Azurlight Systems
CEA-Leti Will Highlight Progress on Key Augmented Reality Building Blocks
Trumpf Venture invests in quantum startup
Trumpf to show latest lasers at Photonics West 2023
OpenLight appoints Adam Carter as CEO
Dutch consortium invests €3.5M in LioniX
POET releases optical engines for 100G, 200G and 400G
Thorlabs to acquire JML Optical
Vector appoints factory applications engineer
Trumpf expands VCSEL portfolio
Needle-free blood glucose monitoring
Vector Photonics appoints Peter Linton to drive PCSEL design
Closing the 'terahertz gap'
LioniX International Secures €3.5M Investment
Novel laser can transmit 200Gbps over 10km
III-V Lab counts on Riber MBE
US centre to tackle processor energy efficiency
High-performance Visible-light Lasers that Fit on a Fingertip
ANELLO Photonics Announce Silicon Photonics Optical Gyroscope
FBH presents latest light sources at Photonics West 2023
NIST and AIM team up on photonics chips
OpenLight unveils 800G DR8 PIC design to advance datacenter Interconnect industry
Characterisation of VCSELs, µLEDs and AR/VR displays
Vector Photonics fast-tracks PCSEL commercialisation
Changing the color of quantum light on an integrated chip
Jenoptik receives Thuringia Innovation Award 2022 for opto-electronic UFO Probe®Card
Silicon photonics is driven by data center applications
Scantinel lands €10M for next gen LiDAR

Search the news archive

To close this popup you can press escape or click the close icon.
Register - Step 1

You may choose to subscribe to the PIC Magazine, the PIC Newsletter, or both. You may also request additional information if required, before submitting your application.

Please subscribe me to:


You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in: