All-Optical Switches - Background & Technologies
In this Blog Post Rohit Kunjappa, Head of the Commercial Business Unit at HUBER+SUHNER Polatis, explains the
technology options available for all-optical switching and weighs up the merits of each.
“Switch when you can, route when you must.”
This is well understood in the telecom industry since circuit switching is cheaper and simpler than packet
routing. With data rates increasing, all-optical switching is more relevant now than ever before. All-optical switches (OOO) function by selectively switching the entire optical signal on one optical fiber to
another optical fiber.
All-optical switches have a unique value proposition over traditional OEO (optical-electrical-optical)
switches since they transmit the original input light signal through a transparent all-optical switch core,
without converting it into electrical format. The transparent nature of all-optical switches makes them
protocol, format and data rate agnostic.
Any place that is a fiber-rich environment is a potential application for all-optical switching - in data
centers for aggregation, protection and interconnection; in the government and defense space for cyber
security, Lawful Intercept, RFoF (Radio Frequency over Fiber) distribution in satellite ground stations;
automation in DevOps and test laboratories; and in the service provider space for fiber layer
virtualization and protection.
The applications mentioned above require high-radix non-blocking matrix switching rather than simple
1x2 or 2x2 optical switches. There are many technologies that can enable this. The three that have had
commercial success are:
- Robotic switching
- Beam-steering using piezoelectric actuators
take the humans out of manually patching new crossconnections but it is still a
physical, albeit automated, process of moving fibers from one port to another. They do have the
advantage that the crossconnections inherently latch and the insertion loss is lower than other types of
all-optical switches. Robotic switches also have a slight price advantage over the other two technologies.
However they do come with some features that make them less suitable for applications where
switching time and frequency is paramount:
- They can only make one connection at a time and multiple cross connections cannot be made in
parallel or simultaneously
- It can take 30 seconds to 2 minutes to make a single crossconnection and potentially hours to
reconfigure the entire switch
- In some types of robotic switches, after a certain number of crossconnections, the fibers tend to
get tangled. This requires the switch to be recalibrated – this is a very disruptive process that
impacts service uptime
- Robotic switches are not able to provide value-add features required in many applications like
variable optical attenuation, optical power meters and automatic protection switching
Though 3D-MEMS and beam-steering are very different optical switching technologies, both result in
crossconnections being made in free-space with no manual intervention. 3D-MEMS uses micro-mirrors
to deflect the optical beam from an incoming fiber to an outgoing fiber. Beam-steering uses
piezoelectric actuators to align or point the optical fibers so signals can be switched between the fibers.
For a 3D-MEMS switch
to be operational, it has some unique requirements which may be seen as
drawbacks in certain applications:
- 3D-MEMS requires light to be present in the fiber to make and maintain a connection. This issue
creates lag in circuit availability in some applications
- 3D-MEMS requires continuous feedback to keep the mirrors in their optimal alignment for
maximum signal strength. This feedback is provided by power meters – so power meters are a
prerequisite for 3D-MEMS all-optical switches.
- The mirrors require dithering based on the power meter feedback to keep them in their optimal
position. In certain applications like RFoF (Radio Frequency over Fiber), dithering degrades the
- Current 3D-MEMs systems are typically marketed in one matrix style (symmetrical i.e. an equal
number of input and output fibers) with limited port count options
creates high-radix, non-blocking all-optical switches, providing the highest overall optical
performance over a wide portfolio of matrix sizes. The largest size currently available is a symmetrical
384x384 matrix but further innovations in the pipeline will enable even larger switch sizes to be offered
in the very near future.
At the core of HUBER+SUHNER Polatis all-optical switches is the patented DirectLight™ beam-steering
technology that makes connections using compact piezoelectric actuators to align collimated beams of
light from opposing arrays of input and output fibers with minimal loss of the optical signals.
is maintained using feedback from integrated position sensors to ensure connection stability over time,
temperature and external disturbances. Switching occurs completely independently of the power level,
color or direction of light on the path, enabling pre-provisioning of dark fiber and avoiding
concatenation of switching delays across mesh or multi-stage switched optical networks.
The HUBER+SUHNER Polatis Advantage – all optical switches are not created equal
- Industry's lowest optical loss and superior performance, critical to the success of so many
applications, such as ensuring the most accurate test data in a test lab
- The broadest range of symmetric, asymmetric and custom-configurable matrix configurations
required to meet the evolving needs of customers’ applications
- Core component of a system architecture that can scale to support any size network - to tens of
thousands of fibers
- True dark fiber switching, requiring no light to make and hold connections, is critical when
wanting to pre-provision for new services or testing with low power, bi-directional (on a single
fiber) or intermittent signals
- Accurate Optical Power Meters (OPMs) precisely monitor signal strength with programmable
degrade and loss of service alarms
- Integrated Variable Optical Attenuation (VOA) enables rapid simulation of multiple link and span
Programmable shutter feature allows introduction of intermittent and repetitive fiber breaks to
test system response to unusual fault conditions.
- Optical Switch Partitioning enables different user groups to share the same switch without
- Integrated with leading test orchestration and DevOps software to replicate and schedule tests
across multiple organizations and coordinate with higher layer equipment and devices
- Easy to control, with support for the most popular network management interfaces including
NETCONF and RESTCONF Software Defined Network (SDN) protocols
If you would like to know more about HUBER+SUHNER Polatis all-optical switches and how the
technology would benefit your application, you can contact us by email or phone:
+1 781 275 5080
EMEA/Rest of World:
+44 (0)1223 424200
Further information can also be found at www.polatis.com