Power over Fiber
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Technical Note
Power over Fiber
This technical note provides guidelines to ensure the proper operation and optimum
performance of the Lumentum power over fiber (PoF) product family, which consists of a
photovoltaic power converter (PPC) and a photonic power module (PPM).
The combination of the PPC and the PPM, hereafter referred to
as the PPM-K, can drive electronics in remote locations that are
hazardous, electrically noisy, remote, inaccessible, or exposed to
extreme weather. The PPM-K consists of a local laser module
with drive electronics connected to a remote PPC using
multimode fiber. Electrical power from an external source is
provided at the PPM-K input to drive the diode laser. The PPC
converts the optical power to electrical power at the remote
location. Fiber lengths up to 1000 meters can be supported.
The fiber pigtail provided with the PPM-K is not intended for use
directly with the PPC. Instead, a fiber patch cord, or jumper,
should be inserted between the fiber pigtail and the PPC for
optimum performance. It should have a minimum length of
10 meters (30 feet), preferably 50 meters (150 feet).
Operational configurations and reliability requirements depend
on customer-specific applications and operating environments.
Therefore, Lumentum does not guarantee the reliability of the
module attachment or control method within customer-specific
applications and can only recommend good engineering practices.
The end-user must confirm the final reliability and quality of any
system in field applications.
Topics addressed in this application note include:
• Photonic Power Module
• Photovoltaic Power Converter
• Fiber Contamination and Cleaning
• Power Supply and Control
• Precautions in Dealing with Laser Light
• Mounting Procedures
Photonic Power Module
The PPM includes one diode laser and a driver control board
with one 6-pin connector. The PPM provides up to 2 W of
optical power output, which is launched into multimode fiber
(60/125 µm, NA 0.22) at nominally 830 nm wavelength. An extra
heat sink for the module is required as described in the Mounting
section of this note. Figure 2 shows the locations of the 4 screw
holes with threads on the bottom of PPM to attach the PPM to
a heat sink.
Assembly Drawing
Figure 1. PPM-K with a selection of PPCs
The PPM-K is ideal for the following applications:
• Electronic circuits operating in:
−− High RF, EMI, and magnetic fields
−− High-voltage environments
−− Extreme environmental conditions
• Sensors, gauges, and actuators
• Data communication transceivers
Figure 2. PPM mechanical drawing
• GPS and wireless receivers
• Current transducers in high-voltage environments
• IGBTs in high-voltage environments
• Communication and sensor operational systems
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Power over Fiber
The manufacturer of the 6-pin connector is Samtec® p/n: IPL1-10601-L-S-RA-K, and the recommended cable is MMSS-06-26-XX.
XX-D-K-LUS, where XX.XX denotes the length of the cable. Refer
to http://www.samtec.com/ for detailed schematics and drawings.
Module Operation
External power must be applied to the module in accordance with
the following table for proper operation of PPM. The module
accepts a supply voltage in the range of 6 V to 12 V and the
overall power consumption for the module is no higher than 6.5
W. The power supply should comply with the Power Supply and
Control section in this note.
Photovoltaic Power Converter
The photovoltaic power converter (PPC) is a multi-segmented
gallium-arsenide (GaAs) device. The output voltage is determined
by the number of segments with each segment contributing
roughly one volt. Output (open-circuit) voltages of 4 V, 6 V and
12 V are available in the PPC product family. The maximum
electrical power output from a PPC is 500mW, depending on the
input optical power, selected PPC, and load resistance. Two
connector versions are available, FC and ST, with the FC being the
most recommended by Lumentum.
Pinout
Pin
Description
In/Out
1
Ground
—
2
Power (+6V ~ +12V)
Input
3
Laser Current Monitor
Output
4
Module Enable
Input
5
Laser Current Setting
Input
6
Ground
—
The PPC is typically characterized by the I-V curve shown in
Figure 5. The open circuit voltage (VOC) and short circuit current
(ISC ) denote the maximum voltage and current that can be
extracted from PPC, while VMP and IMP correspond to the voltage
and current where the maximum electrical power (V×I) is
obtained. The maximum output voltage is limited by the opencircuit voltage, and the maximum current output is limited by the
short circuit current. However, the maximum power output is
neither at the open-circuit voltage point nor at the short-circuit
current point. In fact, at both of those points, the electrical power
output is zero.
Figure 3 PPM pin configuration and connector socket
A voltage applied on pin #4 enables the module when the voltage
is higher than 1.74 V and disables this module when the voltage
is lower than 0.5 V. The output optical power can be adjusted
through pin #5 with a voltage ranging from 0 to 1.25 V. The drive
current increases linearly with the voltage applied on pin #5 until
the voltage reaches 1.25 V, as shown in Figure 4. The drive
current of the laser diode (ILD) can be monitored by the voltage
measured on Pin #3:
Each point on the I-V curve corresponds to an operational point
and a proper load resistance is required in order to maximize the
power output. The slope of the load line in the figure determines
the load resistance.
ILD = VPin3/(20×R SNS)
3
3
2.5
2.5
Driving Current (A)
Optical Power (W)
where R SNS is 50 mΩ.
2
1.5
1
0.5
PMAX 2
1.5
1
0.5
0
0
0
0.25
0.5
0.75
1
1.25
1.5
Setting Voltage (V)
0
0.25
0.5
0.75
1
Setting Voltage (V)
Voltage
3
Driving Current (A)
Load line
Op point
ISC
IMP
1.25
VMP 1.5
VOC
Figure 5. PPC characteristic curves
2.5
2
1.5
1
0.5
0
0
0.25
0.5
0.75
1
1.25
1.5
Setting Voltage (V)
Figure 4. Optical power and driving current
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Power over Fiber
Figure 6 shows how the I-V curve evolves with different optical
power input. Generally ISC is linearly proportional to the optical
power whereas VOC varies logarithmically with input power.
However, due to voltage losses stemming from resistance, VMP
decreases for optical power levels higher than 500 mW whereas
IMP linearly increases, as shown in Figure 7.
0.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Application Examples
Overview
A typical PoF application using the PPM-K is shown in Figure 8.
The PPM is at one end of the fiber and the PPC at the other.
Fiber adaptor
PPM 7.00
Extension MMF
PPC + Customer – electronics
-20.00
50 mW
Current (mA)
-40.00
100 mW
500 mW
-80.00
750 mW
-100.00
1.0 W
1.5 W
-120.00
2.0 W
-140.00
-160.00
Voltage (V)
Figure 6. Typical PPC-6E I-V curve with different optical power
140.00
6.50
6.30
120.00
6.10
Vmp (V)
5.70
80.00
5.50
60.00
5.30
5.10
Imp (mA)
100.00
5.90
Vmp
Imp
40.00
4.90
20.00
4.70
4.50
0
0.5
1
1.5
2
0.00
2.5
Optical Power (W)
Figure 8. Typical PoF use of the PPM-K
250 mW
-60.00
In system design, the loss induced by the fiber adapter and MMF
should be taken into account, especially when the PPC is located
far from the PPM. The pigtail fiber from the PPM has a core/
cladding diameter of 60 µm/125 µm and an NA of 0.22. The
extension fiber should be chosen to be compatible with the
pigtail fiber, such as 62.5 µm/125 µm and an 0.22 NA, to achieve
the lowest connection loss. Other MMFs with larger core diameter
and the same NA are also applicable. However, the PPC should be
optimized (in terms of optical alignment) to the type of fiber to
which it will be connected. Hence, to ensure the best alignment
when the PPC is mounted in the receptacle the fiber type must
be specified.
Parallel Connection
In case a single PPM-K cannot provide enough electrical power,
two or more can be connected in parallel to increase the
electrical power output. Each output from the PPC should be
serially connected to a diode before feeding into a customer’s
electronics. The diode prevents reverse current into the PPC.
The diode should have a low forward voltage to reduce the
power losses induced by it. Figure 9 shows an example where
two PPM-K units are configured to supply the customer’s
electronics with almost double the electrical power.
Figure 7. Typical PPC-6E VMP and IMP at different optical power
Depending on the application, there are usually two ways of
extracting power from the PPC. If constant output power delivery
is preferred, one can design the load line to be around the value
of Vmp/Imp to extract the most power from the PPC with the input
laser power to the PPC remaining constant. Another common
mode of operation is to regulate the output voltage at a voltage
level such as 5 VDC or 3.3 VDC. While this approach may sacrifice
some conversion efficiency, it ensures no power variation with
load resistance.
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Fiber adapter
PPM PPM PPC + –
+ Extension MMF
Customer
Customer
electronics
electronics
–
Figure 9. Parallel connection example of two PPM-K units
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Power over Fiber
PPM Redundancy
PPM redundancy is recommended when a customer application
requires a higher level of reliability. By using an optical power
combiner, the optical output from the PPM can be switched when a
failure occurs. A power combiner is a fused optical fiber device which
can combine multiple input optical power into a single fiber output.
PPC + Customer
– electronics
Fiber adapter
PPM PPM Power
combiner
2x1 Extension MMF
Figure 10. PPM redundancy configuration example
Optical Power Sharing
It is possible to share the optical power from a single PPM and
feed it into multiple PPCs. This is especially cost effective when
the electrical power requirement for each PPC is low. A power
splitter (a fused optical fiber device which can split the input
optical power evenly into multiple outputs) is used so that each
of the PPCs can get a fraction of the optical power from the PPM.
Fiber adapter
PPM 1x2 MMF
Power splitter
Extension
PPC + –
+ – Customer
Customer
electronics
electronics
Figure 11. Optical power sharing example
Precautions
Safety
The PPM provides an output optical power of up to 2 W in the
infrared region. Be sure to follow standard safety protocol for
eye and skin for Class IV IR lasers.
Electrostatic Discharge (ESD)
ESD damage to a laser diode is induced from the rapid flow of
electrical charge between two bodies at different potentials,
either through direct contact or through an induced electrical
field. ESD can cause catastrophic or latent damage and is of
particular concern for the module’s laser diode.
Latent ESD damage, which occurs when the energy of an ESD
event is below the critical level required to produce a
catastrophic failure, can result in defects which propagate during
module deployment resulting in catastrophic failure over time.
A human body model (HBM) ESD test is used to determine the
damage threshold of both PPM and PPC, which are tested in
accordance with GR-468-CORE section 5.22 (MIL-STD-883,
method 3015.7). A number of industry specifications are
available to make the work area ESD safe (for example, EIA-625,
JEDEC 108-A).
Below are common recommended guidelines for preventing
ESD damages:
• Refer to PPM and PPC specification sheets for ESD voltage
ratings (2000 V max)
• Use shorting clips or foam on the PPC pins when the modules
are disconnected from the operational circuit
• Ground operators, equipment, WIP transport carts/trays,
modules or systems, and work surface to eliminate
static electricity
• Only use confirmed ESD dissipative coatings/surface finishes
on fixtures/tooling used to assemble the modules
• When manipulating lasers or modules, use ESD protective
smocks, gloves and shoes/covers, dissipative bench-top mats
and ESD protective flooring or matting
• Remove or control static generating sources to voltages below
the specified maximum for safe ESD handling
• Install air ionizers as necessary for additional
environmental control
• Use electrically grounded soldering irons for soldering the
pump module to the mounting surface
• Use electrostatic shielding containers and antistatic or
dissipative carriers
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Power over Fiber
Fiber Contamination and Cleaning
Fiber contamination is a key consideration for high-power laser
modules. Fiber contamination, especially contamination with dark
color, will cause a local temperature increase as it absorbs the
dissipated cladding modes.
• Wear gloves when handling fiber
• Avoid any contamination of fiber
• No dark color contamination with an area larger than 100 µm
x 100 µm is allowed within the first ~2΄ of buffer and should be
avoided along the entire length of fiber
Fiber cleaning materials and procedures shown here are for
informational purposes only and are not meant to recommend,
endorse, or discredit any existing procedures. It is recommended
that users evaluate any procedure or product before using it in
applications where damage or failure could result. As always,
safety precautions must be exercised at all times when using
glass, chemicals, and lasers.
There are many materials commercially available for fiber optic
cleaning. Some are marketed specifically for the fiber optic
industry, while others are considered “raw materials” or generic
in nature but can be used for the same purpose.
Mounting
Mounting topics include:
• Heat Sinks
• Thermal Interface Materials
• Fiber Handling
Heat Sinks
The design of the receiving heat sink is crucial to PPM and PPC
performance and reliability. The PPM requires a heat sink and will
fail catastrophically if operated without one. It is not compulsory,
but it will benefit conversion efficiency if the PPC is mounted on
a heat sink.
The goal of the heat sink is to dissipate the heat from the package
base with minimized thermal resistance. Heat sink performance is
usually specified in terms of thermal resistance (Q):
Θs = (Ts –Ta)/Q
where:
Θs = Thermal resistance in °C per watt
Ts = Heat sink temperature in °C
Ta = Ambient or coolant temperature in °C
Q = Heat input to heat sink in watts
Each thermal cooling application will have a unique heat sink
requirement and frequently there will be various mechanical
constraints that may complicate the overall design. Because each
case is different, there is no single heat sink configuration
suitable for all situations.
A well-designed heat sink in combination with a high-performance
thermal interface material and package mounting technique should
guarantee that the module case temperature does not exceed the
maximum temperature specified for each series (refer again to the
absolute maximum characteristics). Failure to keep a package base
below the specified maximum temperature will lead to the pump
module overheating and result in module damage.
The following general heat sink guidelines are recommended:
• Mount the module on a heat sink with a surface finish of
0.8 microns or less
• The heat sink should be designed to handle at least maximum
module heat dissipation through the life of the product. For
total module power dissipation, refer to PPM specifications.
Maximum module heat dissipation is approximately equal to
the ex-fiber optical power.
• Design a heat sink that is capable of keeping the module case
temperature below the maximum rated temperature for all
operating conditions. For maximum package base temperature,
refer to the PPM specification.
• The operation of a PPC generally does not require a heat sink,
but we strongly recommend it, especially when the PPC is
operated at a high input optical power level (>500 mW)
Thermal Interface Materials
Ideally, thermally conductive materials are used as an interface
between PoF products and the heat sink to account for any
flatness/smoothness discrepancies between the two parts.
Suitable thermally-conductive materials include phase-change
materials, greases, thermal compounds, elastomers, and adhesive
films. All are designed to conform to surface irregularities,
thereby eliminating air voids to improve heat flow between
thermal interfaces.
Use thermal grease to minimize thermal resistance. If semi-rigid
thermal-interface materials (for example, phase-change material
or thermal pads) are used, the thermal-interface material must
cover the entire base plate including the bolt-hole area to avoid
bending the base during bolt down.
The specific choice and implementation of a thermal interface
material depends on the customer’s specific application and
reliability considerations.
Failure to follow proper pump module mounting procedures to a
properly prepared heat sink can result in high thermal resistances
and module warpage, both of which can impact performance and
may lead to catastrophic failure.
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Power over Fiber
Fiber Handling
Both the fiber buffer and external furcation cable are heat
sensitive as well as being susceptible to buffer damage. Care
must be taken during the setup and qualification of any process
used in the handling and assembly of pump modules as the
buffer is readily susceptible to damage—even, for example, by
coiling the fiber during product assembly and securing the coil
with sections of solder or wire. This practice is commonly seen
and is known to cause compression and delamination damage to
the optical buffer.
Maximum storage and exposure temperatures for the optical
buffer are 85°C as recommended by fiber manufacturers.
Exposure of the buffer to temperatures above 85°C will likely
cause permanent damage to the pigtail. If temperature exposure
beyond 85°C is required, it is critical to understand the risk
associated to optical fiber reliability.
Follow proper fiber-handling procedures to avoid catastrophic
damage in high-power lasers:
• Do not expose fiber to temperatures higher than 85°C
• Always wear finger cots or gloves when handling fiber to avoid
fiber contamination
• Whenever possible, handle fiber in loops to prevent fiber
damage
• Do not drag fiber over equipment
• Avoid a fiber contact with any sharp object
• Never use the fiber to pick up or support the weight of the
module. Always handle modules with two hands, one holding a
package and the other handling fiber coil to avoid fiber damage
or breakage.
• Do not allow kinks or knots to develop in the fiber. Carefully
work out any tangles; pulling on the fiber will cause any kinks
or curls to tighten and exceed the minimum bend radius.
• Do not bend a fiber with a radius smaller than specified as
minimum bending radius (30 mm for PPM)
Bending the fiber to a smaller than specified minimum radius can
result in an increased fiber temperature due to a bend loss and
subsequent optical absorption by the fiber and its buffer.
Catastrophic damage of the fiber can occur due to a crack growth
induced by a temperature increase. In less severe bend
situations, a temperature increase can lead to degradation of the
coating and long-term reliability issues.
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Power Supply and Control
General laser diode power supply requirements are applicable to
high-power modules. Failure to follow these requirements may
result in module degradation or failure. When designing or
utilizing an LD power supply, designers should refer to the
specified absolute maximum ratings specified for each series of
high-power lasers.
Power supplies and test equipment can induce EOS. Recommended
guidelines for preventing EOS of pump modules include:
Electrical overstress (EOS) damage occurs when a module is
subjected to voltage or current levels beyond its surge-absorbing
capacity. The location and degree of damage depends on the
magnitude and duration of the voltage, current, total energy,
polarity, and waveform of the electrical overstress.
• Use transient suppression for power supplies
• Transient electrical stress to the module should be avoided or
minimized through operational life. The maximum specified
transient current time for a module should never be exceeded
while operating a LD; refer to the absolute maximum ratings
(AMR) in the pump module specifications.
• Use over-voltage protection for power supplies and fuses at
critical locations
• Confirm modules are mounted with the correct electrical pin
configurations as specified
• Ensure that all operational and assembly equipment is properly
grounded with no loose connections (which can lead to
intermittent connections)
North America
Toll Free: 844 810 LITE (5483)
Outside North America
Toll Free: 800 000 LITE (5483)
China
Toll Free: 400 120 LITE (5483)
© 2015 Lumentum Operations LLC
Product specifications and descriptions in this
document are subject to change without notice.
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