Shift in how we build computers: Photonics

Date:
June 17, 2020
Source:
University of California - Santa Barbara
Summary:
Information technology continues to progress at a rapid
pace. However, the growing demands of data centers have pushed
electrical input-output systems to their physical limit, which
has created a bottleneck.

Maintaining this growth will require a shift in how we built
computers.

The future is optical.



FULL STORY ========================================================================== Information technology continues to progress at a rapid pace. However,
the growing demands of data centers have pushed electrical
input-output systems to their physical limit, which has created a
bottleneck. Maintaining this growth will require a shift in how we built computers. The future is optical.


==========================================================================
Over the last decade, photonics has provided a solution to the
chip-to-chip bandwidth problem in the electronic world by increasing
the link distance between servers with higher bandwidth, far less energy
and lower latency compared to electrical interconnects.

One element of this revolution, silicon photonics, was advanced 15
years ago by the demonstration from UC Santa Barbara and Intel of a
silicon laser technology. This has since triggered an explosion of this
field. Intel is now delivering millions of silicon photonic transceivers
for data centers all around the world.

A new discovery in silicon photonics by a collaboration of UC Santa
Barbara, Caltech and the Swiss Federal Institute of Technology Lausanne
(EPFL) reveals another revolution in this field. The group managed to
simplify and condense a complex optical system onto a single silicon
photonic chip. The achievement, featured in Nature, significantly lowers
the cost of production and allows for easy integration with traditional, silicon chip production.

"The entire internet is driven by photonics now," said John Bowers, who
holds the Fred Kavli Chair in Nanotechnology at UC Santa Barbara, directs
the campus's Institute for Energy Efficiency and led the collaborative
research effort.

Despite the great success of photonics in the Internet backbone,
challenges still exist. The explosion of data traffic puts a growing requirement on the data rate each individual silicon photonic chip can
handle. Using multicolor laser light to transmit information is the most efficient way to address this demand. The more laser colors, the more information that can be carried.



========================================================================== However, this poses a problem for integrated lasers, which can generate
only one color of laser light at a time. "You might literally need 50
or more lasers in that chip for that purpose" said Bowers. And using 50
lasers has a number of drawbacks. It's expensive, and rather inefficient
in terms of power. What's more, the frequency of light each laser produces
can fluctuate slightly due to noise and heat. With multiple lasers,
the frequencies can even drift into each other, much like early radio
stations did.

A technology called "optical frequency combs" provide a promising solution
to address this problem. It refers to a collection of equally spaced frequencies of laser light. Plotting the frequencies reveals spikes and
dips that resemble a hair comb -- hence the name. However, generating
combs required bulky, expensive equipment. Using an integrated photonics approach, Bowers' team has demonstrated the smallest comb generator in
the world, which resolves all of these problems.

The configuration of the system is rather simple, consisting of a
commercially distributed feedback laser and a silicon nitride photonic
chip. "What we have is a source that generates all these colors out of
one laser and one chip.

That's what's significant about this," Bowers said.

The simple structure leads to a significant reduction of scale, power
and cost.

The whole setup now fits in a package smaller than a match box, whose
overall price and power consumption are smaller than previous systems.

What's more, the new technology is also much more convenient to operate.

Previously, generating a stable comb had been a tricky
endeavor. Researchers had to modulate the frequency and adjust power
just right to produce a coherent comb state, called soliton. That process
was not guaranteed to generate such state every time. "The new approach
makes the process as easy as switching on a room light," said coauthor
Kerry Vahala, a professor of applied physics and information science
and technology at Caltech.



========================================================================== "What is remarkable about the result is the reproducibility with which frequency combs can be generated on demand," added Tobias J. Kippenberg, professor of physics at EPFL who provided the low loss silicon nitride photonics chips, a technology already commercialized via LIGENTEC. "This process used to require elaborate control in the past." The magic behind
all these improvements lies in an interesting physical phenomenon. When
the pump laser and resonator are integrated, the interaction between
them forms a highly coupled system that is self-injection locking and simultaneously generates "solitons," pulses that circulate indefinitely
inside the resonator and give rise to optical frequency combs. "Such interaction is the key to directly generating the comb and operating
it in the soliton state" explained coauthor Lin Chang, a postdoctoral researcher in Bowers' lab.

This new technology will have a big impact on photonics. In addition
to addressing the demands of multicolor light sources in communication
related products, it also opens up a lot of new opportunities in many applications. One example is optical clocks, which provide the most
accurate time standard in the world and have many uses -- from navigation
in daily life to measurements of physical constants.

"Optical clocks used to be large, heavy and expensive," Bowers noted,
"and there are only a few in the world. With integrated photonics, we
can make something that could fit in a wristwatch, and you could afford
it. Low noise integrated optical microcombs will enable a new generation
of optical clocks, communications and sensors. We should see more compact,
more sensitive GPS receivers coming out of this approach." All in all,
the future looks bright for photonics. "It is the key step to transfer
the frequency comb technology from the laboratory to the real world."
Bowers said. "It will change photonics and our daily lives."

========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Barbara. Original written by Harrison
Tasoff. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Boqiang Shen, Lin Chang, Junqiu Liu, Heming Wang, Qi-Fan Yang, Chao
Xiang, Rui Ning Wang, Jijun He, Tianyi Liu, Weiqiang Xie,
Joel Guo, David Kinghorn, Lue Wu, Qing-Xin Ji, Tobias
J. Kippenberg, Kerry Vahala, John E. Bowers. Integrated
turnkey soliton microcombs. Nature, 2020; 582 (7812): 365 DOI:
10.1038/s41586-020-2358-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617150031.htm

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