AN146

The Photonics Pioneer

Analyzing dynamic Fiber Optic Components using the OP740: Optical Switches

Overview
The OP740 can be used to capture dynamic optical signals. In this example the OP740 will be used to monitor the switching
behavior of two types of optical switches: mechanical and MEMs based.

Detector

SourceNE W

RefdBm1310nm1550nm

OP715
Stabilized Light Source

Optical Switch

Figure 1: high-speed multichannel Optical Power Meter and two optical switches

Test Setup
To analyze an optical switch, the setup requires an optical source to be routed to the input of the optical switch and all outputsof the switch are routed to the OP740. The OP740 will be used to monitor the switching behavior.

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Test Process and Results

Figure 2 shows what occurs when switching channels.
When switching from one channel to the next channel,
the first channel goes dark and then the channel
that is being switched to becomes active for a shorttime,
N E W followed by periods of intermittent light on thedestination channel. The switching takes roughly 90
to 100ms to complete.

Figure 2: Channel Switch Transitions

1OptoTest Corp.

SANTEC
4750
CalleCORPORATION
Quetzal5823
Ohkusa-Nenjozaka,
Komaki,
Camarillo,
CA 93012
Aichi 485-0802,
UnitedStates Japan+81-568-79-3536

Doc: AN-146 Rev. A 2/12/21

Advancing the World of Fiber Optics®
www.optotest.com
www.santec.com
The Photonics Pioneer

SANTEC USA CORPORATION
1.805.987.170 0
USA Toll Free+1-800-726-8321
sales@optotest.com
suppor t@optotes t.com
SANTEC
LIMITED
MTP® is EUROPE
a registered trademarkof US Connec
Tel. +44-20-3176-1550

AN146

The Photonics Pioneer

Analyzing dynamic Fiber Optic Components using the OP740: Optical Switches

Analysis of Results
To understand what is happening, it is important to look at how mechanical switches are constructed and controlled. Typically,
the common port is aligned with the active port. When the switch changes channels, the common port is moved into alignment
with the destination channel. The motor driving the switch needs to move quickly to get to the channel. This speed causes thecommon to overshoot its position, then return to alignment.
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Channel 1

CommonChannel 1

Channel 1

Channel 2

Channel 2

Channel 2CommonCommon

Figure 3: example of common overshooting the correct position and then coming back into alignment.

The overshoot and alignment are shown in the optical signalby the intermittent light on the port. The OP740 captures
and accurately represents this dynamic optical signal.

Figure 4: switch transition channel 1 to channel 2

Full Channel Step-ThroughNow we look at a “worst case” scenario where the 16-channel
switch is switched from channel 1 directly to channel 16.
Channels 1, 7, and 16 are monitored. The data shows thatit takes about 300ms to fully transition from channel 1 toNE W

channel 16, but it is also seen that channel 7 briefly lights up.
As channel count of the switch increases, the time to get tochannels that are far away gradually increases.

Figure 5: Switch Transition Channel 1 to Channel 16

2

OptoTest Corp.

SANTEC
4750
CalleCORPORATION
Quetzal5823
Ohkusa-Nenjozaka,
Komaki,
Camarillo,
CA 93012
Aichi 485-0802,
UnitedStates Japan+81-568-79-3536

Doc: AN-146 Rev. A 2/12/21

Advancing the World of Fiber Optics®
www.optotest.com
www.santec.com
The Photonics Pioneer

SANTEC USA CORPORATION
1.805.987.170 0
USA Toll Free
+1-800-726-8321
sales@optotest.com
suppor t@optotes t.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

AN146

The Photonics Pioneer

Analyzing dynamic Fiber Optic Components using the OP740: Optical Switches

Full Channel Step-Through1.

Channel 1

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Common2.

Channel 1

CommonChannel 7

ChannelChannel 77

CommonChannel 16

Channel 16

3.

Channel 1

ChannelChannel 77

CommonChannel 16

CommonCommonFigure 6: Switch Transition Channel 7 briefly lights up as it is passed going to Channel 16

As the channel changes from 1 to 16, the common port briefly passes
by channel 7 on its path to channel 16. This “pass by” causes a brief
power spike on channel 7 The high-speed data capture of the OP740
allows the signal to be seen, where sampling at a lower data ratewould likely miss this event.

Figure 7: “pass by” power spike on channel 7

High Speed MEMs Switch Analysis
MEMs Switch Structure
To understand the optical behavior ofMEMs switches, it helps to understandNE W

their internal structure. Not all MEMs
switches have the same internalstructure but figure 8 shows a commonstructure. The switch has a bundle

Ch 6Ch 5Ch 4

Ch 1Ch 6Ch 2Ch 5Ch 3Ch 1Ch 2Ch 4Ch 3Input(Common)Figure 8: Common MEMs Switch Structure. Mirror steers the input beam to output fibers.

of fibers that are incident on a small
mechanical mirror. In the center of the bundle is the common fiber known as the input fiber. Situated around the common
fiber are the fibers for the switch channels. The switch steers the input beam to the fibers depending on which channel isselected. When incrementing through channels, the mirror steers the beam to each channel.
Unlike with mechanical switches, the mirror does not need to travel on a fixed path. This means that the switch can change
channels and the mirror can move the beam directly to the appropriate output channel without needing to pass the intermediatechannels.

3

OptoTest Corp.

SANTEC
4750
CalleCORPORATION
Quetzal5823
Ohkusa-Nenjozaka,
Komaki,
Camarillo,
CA 93012
Aichi 485-0802,
UnitedStates Japan+81-568-79-3536

Doc: AN-146 Rev. A 2/12/21

Advancing the World of Fiber Optics®
www.optotest.com
www.santec.com
The Photonics Pioneer

SANTEC USA CORPORATION
1.805.987.170 0
USA Toll Free
+1-800-726-8321
sales@optotest.com
suppor t@optotes t.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

AN146

The Photonics Pioneer

Analyzing dynamic Fiber Optic Components using the OP740: Optical Switches

Test Process and Results
Now we look at the performance of a MEMs switch thatis switching from one channel to another and skipping
intermediate channels. In this case, when the switch ison channel one and channel three is selected the switch
N E Wdirectly to channel three. The MEMs mirror does notgoesneed to travel on a fixed path like the mechanical switch.
The total transition time from channel one to three isabout 10ms.

Figure 9: brief low power detected on channel
two while switching Ch 1 to Ch 3

Ch 6

Ch 1

Ch 5

Ch 6

Ch 2

Ch 4

Ch 5

Ch 3

Ch 4

Ch 1
Ch 2
Ch 3

Ch 6
Ch 5

Ch 1
Ch 2

Ch 4
Ch 3

Input
(Common)

Input(Common)Figure 10: Common MEMs Switch Structure. Mirror steers the input beam to output fibers.

With the system switching from channel one to channel three, there is brief low power detected on channel two. The beam
passes by channel two only partially on its way to channel three, resulting in the small power blip on channel two that isobserved. This blip is much smaller than what is seen with mechanical switches. The OP740 can capture the fine details of thispower blip as well as the transition between the active channel and the destination channel. Even the damped transition to thedestination channel is captured by the OP740. The result of this MEMs structure is a much more uniform response time whennavigating across channels.

Conclusion
Optical switches are dynamic systems that re-direct an optical signal from on channel to another. To analyze such behavior
in a switch the OP740 is uniquely qualified. It has a wide dynamic range to accommodate the large shift in optical power froma dark signal to a bright signal and it has a fast response and fast sampling rate to yield highly resolved traces of the opticalsignal during its transient behavior.
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4

OptoTest Corp.

SANTEC
4750
CalleCORPORATION
Quetzal5823
Ohkusa-Nenjozaka,
Komaki,
Camarillo,CA 93012
Aichi 485-0802,
UnitedStates Japan+81-568-79-3536

Doc: AN-146 Rev. A 2/12/21

Advancing the World of Fiber Optics®
www.optotest.com
www.santec.com
The Photonics Pioneer

SANTEC USA CORPORATION
1.805.987.170 0
USA Toll Free+1-800-726-8321
sales@optotes
t.com
suppor t@optotes t.com
SANTEC
LIMITED
MTP® is EUROPE
a registered trademarkof US Connec
Tel. +44-20-3176-1550