Engineers improve signal processing for small fiber optic cables

Date:
September 16, 2020
Source:
Michigan Technological University
Summary:
Tiny circuits can go the distance. Researchers have mapped a noise-
reducing magneto-optical response that occurs in fiber-optic
communications, opening the door for new materials technologies.



FULL STORY ========================================================================== Optical signals produced by laser sources are extensively used in
fiber-optic communications, which work by pulsing information packaged
as light through cables, even at great distances, from a transmitter to
a receiver. Through this technology it is possible to transmit telephone conversations, internet messages and cable television images. The great advantage of this technology over electrical signal transmission is its bandwidth -- namely, the amount of information that can be broadcast.


==========================================================================
New research from a collaboration between Michigan Technological
University and Argonne National Laboratory further improves optical
signal processing, which could lead to the fabrication of even smaller fiber-optic devices.

The article, unveiling an unexpected mechanism in optical nonreciprocity
- - developed by the research group of Miguel Levy, professor of physics
at Michigan Tech -- has been published in the journal Optica. "Boosting
Optical Nonreciprocity: Surface Reconstruction in Iron Garnets" explains
the quantum and crystallographic origins of a novel surface effect in nonreciprocal optics that improves the processing of optical signals.

An optical component called the magneto-optic isolator appears
ubiquitously in these optical circuits. Its function is to protect the
laser source -- the place where light is generated before transmission --
from unwanted light that might be reflected back from downstream. Any
such light entering the laser cavity endangers the transmitted signal
because it creates the optical equivalent of noise.

"Optical isolators work on a very simple principle: light going in
the forward direction is allowed through; light going in the backwards direction is stopped," Levy said. "This appears to violate a physical
principle called time- reversal symmetry. The laws of physics say that if
you reverse the direction of time -- if you travel backwards in time --
you end up exactly where you started. Therefore, the light going back
should end up inside the laser." But the light doesn't. Isolators
achieve this feat by being magnetized. North and south magnetic poles
in the device do not switch places for light coming back.

"So forward and backward directions actually look different to the
traveling light. This phenomenon is called optical nonreciprocity,"
Levy said.

Optical isolators need to be miniaturized for on-chip integration into
optical circuits, a process similar to the integration of transistors
into computer chips. But that integration requires the development of
materials technologies that can produce more efficient optical isolators
than presently available.

Recent work by Levy's research group has demonstrated an
order-of-magnitude improvement in the physical effect responsible for
isolator operation. This finding, observable in nanoscale iron garnet
films, opens up the possibility of much tinier devices. New materials technology development of this effect hinges on understanding its
quantum basis.

The research group's findings provide precisely this type of
understanding.

This work was done in collaboration with physics graduate student
Sushree Dash, Applied Chemical and Morphological Analysis Laboratory
staff engineer Pinaki Mukherjee and Argonne National Laboratory staff scientists Daniel Haskel and Richard Rosenberg.

The Optica article explains the role of the surface in the electronic transitions responsible for the observed enhanced magneto-optic
response. These were observed with the help of Argonne's Advanced Photon Source. Mapping the surface reconstruction underlying these effects was
made possible through the state-of-the-art scanning transmission electron microscope acquired by Michigan Tech two years ago.

The new understanding of magneto-optic response provides a powerful
tool for the further development of improved materials technologies to
advance the integration of nonreciprocal devices in optical circuits.


========================================================================== Story Source: Materials provided by
Michigan_Technological_University. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Sushree S. Dash, Pinaki Mukherjee, Daniel Haskel, Richard
A. Rosenberg,
Miguel Levy. Boosting optical nonreciprocity: surface
reconstruction in iron garnets. Optica, 2020; 7 (9): 1038 DOI:
10.1364/OPTICA.398732 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916113414.htm

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