6-W Optical Power Link With Integrated Optical Data Transmission

Abstract

This work demonstrates a fiber-based power-by-light system that is capable of delivering up to 6.2 W of continuous electrical power at common voltages of 3.3 V and 5 V. This optical link includes bidirectional optical communication, for which the data stream from the base to the remote unit is realized by amplitude modulation of the laser beam over the same fiber. At the remote unit a GaAs based photovoltaic laser power converter receives and converts the light. The data is demodulated with a dedicated electric circuit, while the power is forwarded to a dc/dc boost converter. The optical data uplink is realized over a separate optical fiber. In operation a photovoltaic conversion efficiency of above 50% has been measured. For downlink data rates up to 115.2 kbit/s unperturbed signal integrities are demonstrated, at higher data rates the signal integrity deteriorates. An assessment of power budget and power losses in the overall system is presented. Finally, a smart power management concept is introduced which controls the laser output power with respect to changing electrical load, optimizes the operating point of the PV cell, and thus increases system efficiency for varying load operation. Thereby it also minimizes laser and PV cell operating temperatures, and eventually prolongs the lifetime of the system.

Full text

7904 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 35, NO. 8, AUGUST 2020
6-W Optical Power Link With Integrated
Optical Data Transmission
Henning Helmers , Cornelius Armbruster, Moritz von Ravenstein , David Derix, and Christian Schöner
Abstract—This article demonstrates a fiber-based power-by-
light system that is capable of delivering up to 6.2 W of continuous
electrical power at common voltages of 3.3 and 5 V. This optical link
includes bidirectional optical communication, for which the data
stream from the base to the remote unit is realized by amplitude
modulation of the laser beam over the same fiber. At the remote unit,
a gallium arsenide-based photovoltaic (PV) laser power converter
receives and converts the light. The data are demodulated with a
dedicated electric circuit, while the power is forwarded to a dc–dc
boost converter. The optical data uplink is realized over a separate
optical fiber. In operation, a PV conversion efficiency of above 50%
has been measured. For downlink data rates up to 115.2 kb/s, unper-
turbed signal integrities are demonstrated, at higher data rates, the
signal integrity deteriorates. An assessment of power budget and
power losses in the overall system is presented. Finally, a smart
power management concept is introduced, which controls the laser
output power with respect to changing electrical load, optimizes the
operating point of the PV cell, and, thus, increases system efficiency
for varying load operation. Thereby, it also minimizes laser and PV
cell operating temperatures, and eventually prolongs the lifetime
of the system.
Index Terms—Photovoltaic cells, lasers, power transmission,
optical communication, amplitude modulation, optical receivers,
laser applications, optical fibers, dc-dc power converters, energy
management, power transmission.
I. INTRODUCTION
OPTICAL power transmission is an elegant way to supply
power to sensors, actuators, and other electrical con-
sumers with high isolation demands. Compared with conven-
tional copper wiring, this technology provides unique benefits,
such as galvanic isolation, avoidance of electromagnetic inter-
ference, replacement of copper cables with low-weight fiber,
avoidance of electric sparks while ensuring highest reliability
and the possibility for wireless power transmission through
free space. Thereby, it enables new applications in various
domains (e.g., power supply for gate-drivers, probes, or sensors
in high-voltage environment [2]–[7], ripple-free opto-couplers
Manuscript received September 12, 2019; revised December 13, 2019; ac-
cepted January 12, 2020. Date of publication January 16, 2020; date of current
version April 22, 2020. This work was presented in part at the 1st Optical
Wireless and Fiber Power Transmission Conference (OWPT2019), Yokohama,
Japan, April 2019 [1]. Recommended for publication by Associate Editor L.
Chang. (Corresponding author: Henning Helmers.)
The authors are with the Fraunhofer Institute for Solar Energy Systems ISE,
Freiburg 79110, Germany (e-mail: henning.helmers@ise.fraunhofer.de;
cornelius.armbruster@ise.fraunhofer.de; moritz.von.ravenstein@ise.
fraunhofer.de; david.derix@ise.fraunhofer.de; christian.schoener@ise.
fraunhofer.de).
Color versions of one or more of the figures in this article are available online
at https://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TPEL.2020.2967475
Fig. 1. Visualization of the system.
[8], optically powered networks [9], [10], optical powering of
remote antenna units [11], [12], magnetic-resonance compatible
active implants [13], wireless powering of medical devices from
outside the body [14]–[16], lightning-safe power supply for wind
turbine structural health monitoring systems [17], and wireless
powering of consumer electronics [18]). An interesting exten-
sion of power-by-light technology, or power-over-fiber when
optical fiber is used as a waveguide, is the combination with
optical communication (also known as simultaneous wireless
information and power transfer). To facilitate market penetra-
tion, the integration of power and data transmission into a single
fiber and a reduction in number of required costly optoelec-
tronic components and related optical coupling are of great
interest [19].
This article demonstrates the development and evaluation of
an optical power transmission system with integrated bidirec-
tional optical data transmission. As a first step toward integration
of power and data, here, the data downlink from base transmitter
unit to remote receiver unit is realized by amplitude modulation,
i.e., the photovoltaic (PV) cell is used as a receiver for power and
data at the same time. The system configuration of this system
is reported in detail in Section II. In Section III, experimental
measurement results and a power loss analysis is discussed.
Finally, in Section IV, a smart power management scheme is
introduced, which allows for minimizing the laser output power
based on the power demand of the load at the remote unit.
II. SYSTEM CONFIGURATION
The developed optical link consists of a base transmitter unit
and a remote receiver unit connected by two optical fibers, as
shown in Fig. 1. Both units feature generic external interfaces.
An overview of the system specifications is given in Table I.
A. Base Transmitter Unit
The block diagram of the functional building blocks including
power and data stream on the base unit is shown in Fig. 2. The
This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/

HELMERS et al.: 6-W OPTICAL POWER LINK WITH INTEGRATED OPTICAL DATA TRANSMISSION 7905
Fig. 2. Block diagram of the system consisting of base transmitter unit and remote receiver unit.
TAB LE I
SYSTEM SPECIFICATIONS
base unit is driven by a 12-V external power supply. The 12 V are
down-converted on-board into 5 and 3.3 V using commercially
available integrated circuit (IC) converters. Bidirectional data
are received and transmitted in a digital form.
The base unit hosts the laser driver and is connected to a
fiber-coupled diode laser (809 nm, optical power output up to
15 W at fiber end). The laser driver is capable of analog and
digital modulation of the laser diode output up to 200 MHz.
In this article, analog modulation up to 1000 kHz controlled
by the microcontroller (µC) has been applied. A thermoelectric
cooler (TEC) with integrated thermistor and a separate control
circuit are used to maintain a constant laser diode temperature
in operation of 25 °C. A separate photodiode (data RX in Fig. 2)
receives incoming data from the remote unit, which is forwarded
through the µC to the external digital data interface.
B. Signal Amplitude Modulation
The µC uses the Infrared Data Association (IrDA) protocol
to transmit the digital data input. The IrDA protocol is chosen
due to its low power consumption and broad range of supported
data rates (kb/s to Gb/s). The conventional IrDa signal is shown
in Fig. 3(a). To increase the average output power, the IrDA
signal is modified for the amplitude modulation as follows [see
Fig. 3(b)]: 1) the signal is flipped, 2) the pulsewidth Tpulse is
shortened from 3/16 of the bit length Tbit to 100 ns, and 3) the
modulation depth is reduced from 1 to 2/3, i.e., the laser does
Fig. 3. Illustration of the IrDA signal modification. Plotted is the amplitude I
over time t.
not shut off completely with “0” bit, but instead only drops to
one-third of the power. It should be noted that the signal-to-noise
ratio at the receiver is expected to be influenced by both bit length
and modulation depth, and is data rate dependent. However, a
thorough optimization in that regard was outside the scope of
this article.
C. Remote Receiver Unit
The remote unit hosts the PV cell for power conversion
and data reception as well as downstream electronics for data
processing, power management, voltage conversion, and data
transmission. In order to enable generic application, the remote
unit provides constant power supply at two external terminals
at common voltage levels of 3.3 and 5 V. The block diagram of
the remote receiver unit and its functional elements is shown in
Fig. 2.
A10×10 mm² gallium arsenide (GaAs)-based PV cell,
which has been developed and fabricated at Fraunhofer ISE,
is used for laser power conversion. The front grid structure
features parallel grid lines (comb design) designed for operation
under high intensity to extract currents up to 10 A. The nominal
designated area is Ades =0.978 cm². The PV cell is mounted
on a 29 ×29 mm² metalized ceramic submount guaranteeing
electrical isolation while providing good thermal contact to

7906 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 35, NO. 8, AUGUST 2020
Fig. 4. Schematic representation of the separation circuit at the remote receiver
which divides the PV cell output into an ac data branch and a dc power branch.
the aluminum housing for effective passive heat dissipation.
The backside contact of the PV cell is established by vacuum
soldering of the chip onto a contact pad on the submount, the
front side of the cell is contacted by thin Au wire bonding on
two opposite sides of the PV. A picture of the mounted PV cell
contacted on a measurement chuck is shown in Fig. 2. It should
be noted that the PV cell has not been designed to operate
as a data receiver, but has been selected to be able to receive
and convert the optical power of up to 15 W. Especially, since
the junction capacitance scales with area, a smaller PV cell is
advantageous from data reception point of view [20]. However,
then increasing current density and associated resistive losses as
well as proper optical coupling to a smaller receiver would need
to be carefully taken into consideration.
The PV cell output couples into a separation circuit, which
separates the modulated data signal from the constant power
response. A schematic representation of the circuit and the
respective current and voltage signals are illustrated in Fig. 4.
An inductor is used to achieve sufficiently high impedance so
that alternating signals cannot propagate into the power path.
When a “0” bit interrupts the otherwise constant PV current
IPV, the inductor maintains the current flow to the power path
for this short period. At the same time, a negative voltage spike
VPV occurs at the PV cell, which carries the bit information.
The data path is ac coupled using a high-pass filter. Behind the
filter, the negative edge of the voltage spike is detected by a
comparator and translated into a clear pulse signal. This pulse
is, then, stretched by a monostable multivibrator to meet the
specification of the IrDA to enable processing by the µC. Finally,
the µC forwards the data to the digital external interface. For
the uplink of remote data back to the base, the digital external
data are forwarded by the µC to a conventional vertical-cavity
surface-emitting laser transmitter, shown as data TX in Fig. 2.
The power branch behind the separation circuit consists of a
boost converter, which provides 3.3 V, as shown in “discrete
boost” in Figs. 2 and 4, a supercapacitor for energy storage
(100 Ws to maintain at least 20 s of operation in case of a
link breakdown) and related charge controller, and a second
boost converter to provide the additional 5 V output, as shown
in “IC boost” in Fig. 2. For the first stage conversion from
the PV output voltage to 3.3 V, a compact boost converter
based on gallium nitride (GaN) transistors has been developed
Fig. 5. Current-voltage (top) and power-voltage (bottom) characteristics of
the GaAs-based PV cell under continuous illumination with 809 nm laser light
at different optical power levels Pin between 3 and 15 W. The short-circuit
current ISC, open-circuit voltage VOC , maximum power Pmp, and fill factor
FF are stated with each curve.
and realized with discrete components. It is based on an inter-
leaved boost topology with a switching frequency of 250 kHz,
details on the design and layout of GaN based dc–dc con-
verters have been published elsewhere [21], [22]. For input
currents up to 8 A, it boosts from start-up voltages between
Vin =0.85 V and Vin =1 V to a constant output voltage of
Vout =3.3 V. As the name suggests, for the second stage boost
from 3.3 to 5 V a commercial IC [23] has been used.
III. PERFORMANCE MEASUREMENTS
To investigate the performance of the system, the subunits
have been characterized both individually and as a complete
system. The laser power at the end of the 1.5-m long opti-
cal fiber has been measured with an optical power meter for
various driving currents. The PV cell’s current- and power-
voltage characteristics, as plotted in Fig. 5, have been measured
separately at different optical input power under illumination
with the 809 nm laser light coupled from the fiber to the PV
cell (approximately Gaussian profile). The output power of the
PV cell in operation, which corresponds to the input power of
the electronics of the remote unit, has been measured using
an oscilloscope and a clamp-on ammeter. Thereby, additional
impedances between PV cell and electronics caused by the mea-
surement itself have been avoided. The dc–dc boost converter as
a subunit has been characterized with a precision power analyzer
for different input voltages. The electrical input power at the
base unit’s external interface and the electrical output power at
the remote unit’s external interface have been measured with a
precision power analyzer, results are presented in the following
sections.
A. Discrete DC–DC Boost Converter
The measured conversion efficiency of the discrete dc–dc
boost converter as single stage (i.e., without the additional down-
stream “IC boost” converter) at the remote unit is shown in Fig. 6.
At Vin =1 V and an electrical power output of 2.45 W, a peak
efficiency of 86.2% is reached. At lower power, the efficiency
drops due to relatively higher auxiliary power demand mainly

HELMERS et al.: 6-W OPTICAL POWER LINK WITH INTEGRATED OPTICAL DATA TRANSMISSION 7907
Fig. 6. Measured efficiency curves of the discrete boost converter for different
input voltage levels Vin and a constant output voltage Vout =3.3 V.
Fig. 7. Measured delivered output power at 3.3 V constant output voltage as a
function of data rate for a modulation depth of 2/3. The relative power at 100%
here amounts to 6.2 W (the measured power at 1 kb/s). The insets show the
eye diagrams of Vhp at different data rates. All eye diagrams represent a time
interval of 2.4 µs.
for gate drive circuit supply, at higher power, the efficiency
drops due to increasing Joule heating. For lower input voltages,
the drop at high power operation is more pronounced because
of the related higher currents at the same power levels. For
Vin =0.85 V, the efficiency peak is shifted toward lower power,
which is a result of the reduction of gate driving losses at these
low voltage and low power operating conditions.
B. Power and Data Performance
At transmission of random data at a low data rate of 1.2 kb/s, a
constant electrical power output of 6.2 W at 3.3 V stable voltage
output is measured. Beyond this, data transmission with data
rates up to 1000 kb/s has been tested. With increasing data rate,
a drop in the delivered output power at the external terminal
is observed. The measured dependence of the output power on
the transmitted data rate is shown in Fig. 7. The observed drop
may be attributed to the increasing power budget required for
demodulation and processing of the data stream. The insets in
Fig. 7 show eye diagrams of Vhp, i.e., the voltage signal that
enters the ac branch behind the high-pass filter (see Fig. 4), for
four example data rates. At low data rate of 1.2 kb/s, the eye is
clearly open, each “0” bit is well detected by the distinguished
negative flank at the beginning of the pulse. The same still holds
true for an elevated data rate of 115.2 kb/s. At 230.4 kb/s,
the eye begins to close, i.e., not all “0” bits lead to the same
Fig. 8. Sankey diagram of the optical power link, starting with electrical power
input, power budget on base transmitter unit, optoelectrical conversion, power
budget on remote receiver unit, to final delivered electrical output power. The
shown data represents the case of 5.5 W delivered power at output voltage of
3.3 V with simultaneous data transmission over the same optical link at a data
rate of 1 kb/s.
voltage pulse, which indicates that signal integrity deteriorates.
At 1000 kb/s, the overshoot of one pulse clearly extends into
the next pulse. Hence, proper pulse detection poses a challenge.
Still, advanced flank detection, signal processing schemes, and
data transmission protocols may be sufficient to operate properly
with these pulses.
C. Power Budget and Loss Analysis
To understand the power budget of the optical link as a
whole and its subunits, a respective loss analysis for continuous
operation at a delivered output power of 5.5 W and data rate of
1 kb/s has been performed. The results of this analysis for the
case of 14 W optical laser power on the PV cell are visualized
in form of a Sankey diagram, as shown in Fig. 8.
The electrical power consumption at the 12 V input of the
base transmitter unit is 49.2 W. The largest fraction of this power
is consumed at the transmitter side of the optical link, namely for
the laser driver circuit including the amplitude modulation for
integrated data transmission (9.8 W), thermoelectric cooling of
the diode laser (10.2 W), and the laser electrical-to-optical power
conversion and losses in the fiber (15.2 W). Consequently, the PV
cell is irradiated with 14.0 W of optical power. The measured PV
conversion efficiency in continuous operation varied between
51% and 54%. A comparatively small amount of the remaining
fraction relates to optical losses at the PV cell, namely metal
grid shading of the irradiated area (approximately 10%) and
reflection of the laser light at the front surface of the active PV

7908 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 35, NO. 8, AUGUST 2020
cell area (<1%). The majority of the power loss is related to
heat generated inside the PV cell. It is remarked that this heat
generation is affecting the performance of the optical power
link in two ways. First, as it relates back to nonunity efficiency
of the optical-to-electrical conversion by the PV cell, it limits
the delivered electrical output of the link. Second, in continuous
operation, the heat must be effectively dissipated. The effective
thermal resistance between PV cell and heat sink (i.e., in the
usual case of passive cooling given by the environment) defines
the temperature rise of the PV cell in operation. And with
increasing operating temperature, the conversion efficiency
drops and results in an even further increased heat generation.
IV. SMART POWER MANAGEMENT
In many applications, for optical power transmission, the load
profile is not constant and, thus, the externally requested power
for the presented system will often be below the maximum
delivered power. Therefore, here we introduce a smart power
management procedure as follows.
The system starts with full laser power, so that also the PV
cell photocurrent (or more precisely the light-induced shift of its
current-voltage characteristics) is maximal. If the requested load
power is below the power provided by the PV cell, the charge
controller on the remote unit charges the on-board storage. The
proposed power management is based on a feedback control
between the charge controller on the remote unit and the laser
driver on the base unit only (and the respective µCs involved for
data processing and communication), i.e., no external controller
is required. As long as the charge controller measures sufficient
voltage at the supercapacitor, the laser power is incrementally
reduced. This continues until the power provided by the PV cell
drops below the requested power at the external terminal. To
maintain constant power output, the remaining power is provided
by the storage. As soon as the charge controller detects the
related voltage drop there, the laser driver receives the command
to increase the power again. Hence, with a respective control al-
gorithm, which should be adapted to suit typical load variations,
this procedure maintains continuous operation without affecting
the security of delivering power to the load when it is needed.
Yet, at the same time, the laser power is reduced to the minimum
with respect to the load demand only.
This smart power management has several advantages for
the overall system performance: Since the laser is driven at
minimal power, the heat that needs to be dissipated by the
TEC is minimized. Consequently, the power budget for laser
cooling drops. Also, the laser diode junction temperature is re-
duced, which is beneficial for its electrical-to-optical conversion
efficiency. Similarly, as only a minimum of optical power is
transmitted, the generated heat at the PV cell is minimized as
well. This results in a lower PV cell operating temperature,
which, in turn, increases the optical-to-electrical conversion
efficiency and output voltage since both these properties feature a
negative temperature coefficient [24]. Finally, besides improved
efficiencies, due to lower operating temperatures, the presented
smart power management scheme leads to prolonged lifetimes
of the components, especially the laser.
V. C ONCLUSION
A purely optical system for combined power and bidirectional
data transmission has been presented. The system is capable of
continuous delivery of up to 6.2 W of electrical power at a voltage
output of 3.3 and 5 V.
The link is based on a 809-nm fiber-coupled laser diode that
is directed onto a GaAs-based PV laser power converter, with
an efficiency in operation of above 50%. The downlink data
stream (i.e., from base transmitter unit to remote receiver unit)
is realized by amplitude modulation of the laser beam over
the same fiber using a modified IrDA protocol. At the remote
receiver unit, the data are demodulated with a separation circuit.
The power is passed to a discrete dc–dc converter that boosts the
comparatively low PV cell voltage of about 1–3.3 V to supply
the external load as well as a small on-board energy storage.
Thereby, a peak efficiency of 86.2% was reached. In addition,
a second off-the-shelf boost converter provides additional 5 V
external voltage output.
A maximum delivered power of 6.2 W has been realized at a
downlink data rate of 1.2 kb/s. Beyond higher data rates up to
1000 kb/s have been tested, whereas this comes at the cost of
delivered output power and deteriorating signal integrity. Unper-
turbed signals and clear pulses were measured for data rates up to
115.2 kb/s; at 230.4 kb/s, the signal integrity starts to deteriorate.
For the uplink data stream from remote receiver unit to the base
transmitter unit, a conventional optical communication link is
implemented over a separate fiber. Hence, this article can be
understood as a first step toward a fully integrated optical power
and data transmission system over only one optical fiber [19].
It should be remarked that a significant boost in electrical
performance is expected when the PV cell is replaced with
more advanced structures with front lateral conduction layer
[25] and a back mirror for photon recycling [26], [27]. Still,
the low-loss extraction of high currents from cm²-sized PV cells
remains a challenge. Regarding voltage conversion, the use of
PV cells with integrated series connection, such as multijunction
[28]–[35] or multisegment [32], [34], [36]–[38] cells, is an inter-
esting option because of their elevated output voltages. Yet, the
respective downsides, namely increased sensitivity against tem-
perature variation [31], [34] and misalignment [39]–[41] need
to be considered in light of the actual application. In addition,
series-connected receivers are beneficial for data transmission,
as the reciprocal capacitance of a string of subcells is given by
the sum of the reciprocals of the subcells’ capacitances. Further
performance improvements of the system can be expected from
optimization of laser driving circuit and thermal management
on both base and remote units.
In addition to the presented hardware and its capabilities, a
smart power management concept has been introduced, which
is based on a simple feedback control loop between the charge
controller of the storage and the laser driver. With respect to
a varying external load, the procedure controls the laser power
to a minimum value that meets the demand. In other words,
contrary to a solar energy conversion system, not a fluctuating
resource is managed by proper control of the load (maximum
power point tracking), but rather a fluctuating load is managed
by proper control of the laser. Thereby, it maximizes the overall

HELMERS et al.: 6-W OPTICAL POWER LINK WITH INTEGRATED OPTICAL DATA TRANSMISSION 7909
system efficiency, keeps temperatures of laser, and PV cell low
resulting in prolonged lifetimes (mean time to failure) of the
components. The latter is of special significance since current
system lifetimes are typically limited by that of the laser diode.
ACKNOWLEDGMENT
The authors gratefully acknowledge the contributions of
O. Kalmbach and M. Haid to the dc–dc boost converter de-
velopment, system integration, and electrical performance mea-
surements. Furthermore, they thank L. Probst and F. Dimroth for
valuable discussions. Also, they would like to thank M. Grave
for epitaxial growth, R. Koch for semiconductor processing,
T. Dörsam and A. Dilger for packaging support, and M. Schacht-
ner, K. Reichmuth, and G. Siefer for support with electrical
measurements.
REFERENCES
[1] M. Haid, C. Armbruster, D. Derix, C. Schöner, and H. Helmers, “5 W
optical power link with generic voltage output and modulated data signal,”
in Proc. 1st Opt. Wireless FiberPower Transmiss.Conf., Yokohama, Japan,
2019, pp. 31–32.
[2] M. Ishigaki, S. Fafard, D. P. Masson, M. M. Wilkins, C. E. Valdivia, and
K. Hinzer, “A new optically-isolated power converter for 12 V gate drive
power supplies applied to high voltage and high speed switching devices,”
in Proc. 32nd Ann. IEEE Appl. Power Electron. Conf. Expo.,Tampa,FL,
USA, 2017, pp. 2312–2316.
[3] X. Zhang et al., “A gate drive with power over fiber-based isolated power
supply and comprehensive protection functions for 15-kV SiC MOSFET,”
IEEE J. Emerg. Sel. Topics Power Electron., vol. 4, no. 3, pp. 946–955,
Sep. 2016.
[4] F. V. B. de Nazare and M. M. Werneck, “Hybrid optoelectronic sensor for
current and temperature monitoring in overhead transmission lines,” IEEE
Sensors J., vol. 12, no. 5, pp. 1193–1194, May 2012.
[5] J.B.Rosolemet al., “Quantitative and qualitative monitoring system
for switchgear with full electrical isolation using fiber-optic technology,”
IEEE Trans. Power Delivery, vol. 30, no. 3, pp. 1449–1457, Jun. 2015.
[6] P. Antonini et al., “Realization of a high voltage generator by series
connection of floating modules,” Rev. Sci. Instrum., vol. 88, no. 2, 2017,
Art. no. 25113.
[7] R. Peña and C. Algora, “One-watt fiber-based power-by-light system
for satellite applications,” Prog. Photovolt: Res. Appl., vol. 20, no. 1,
pp. 117–123, 2012.
[8] M. M. Wilkins et al., “Ripple-free boost-mode power supply using pho-
tonic power conversion,” IEEE Trans. Power Electron., vol. 34, no. 2,
pp. 1054–1064, Feb. 2019.
[9] M. Röger et al., “Optically powered fiber networks,” Opt. Express, vol. 16,
no. 26, pp. 21821–21834, 2008.
[10] H. Miyakawa, Y. Tanaka, and T. Kurokawa, “Design approaches to
power-over-opticallocal-area-network systems,” Appl. Opt., vol. 43, no. 6,
pp. 1379–1389, 2004.
[11] M. Matsuura and J. Sato, “Bidirectional radio-over-fiber systems using
double-clad fibers for optically powered remote antenna units,” IEEE
Photon. J., vol. 7, no. 1, pp. 1–9, Feb. 2015.
[12] T. Umezawa, P. T. Dat, K. Kashima, A. Kanno, N. Yamamoto, and
T. Kawanishi, “100-GHz radio and power over fiber transmission through
multicore fiber using optical-to-radio converter,” J. Lightw. Technol.,
vol. 36, no. 2, pp. 617–623, Jan. 15, 2018.
[13] A. Stett, S. Rudorf, R. Rudorf, and H. Helmers, “Implant device having
an optical interface,” WO 2018/146032 A1, Aug. 16, 2018.
[14] K. Goto, T. Nakagawa, O. Nakamura, and S. Kawata, “An implantable
power supply with an optically rechargeable lithium battery,” IEEE Trans.
Biomed. Eng., vol. 48, no. 7, pp. 830–833, Jul. 2001.
[15] C. Algora and R. Peña, “Recharging the battery of implantable biomedical
devices by light,” Artif. Organs, vol. 33, no. 10, pp. 855–860, 2009.
[16] A. Ahnood et al., “Diamond encapsulated photovoltaics for transdermal
power delivery,” Biosensors Bioelectron., vol. 77, pp. 589–597, 2016.
[17] K. Worms et al., “Reliable and lightning-safe monitoring of wind turbine
rotor blades using optically powered sensors,” Win d Energ., vol. 20, no. 2,
pp. 345–360, 2017.
[18] Q. Zhang, W. Fang, Q. Liu, J. Wu, P. Xia, and L. Yang, “Distributed laser
charging: A wireless power transfer approach,” IEEE Internet Things J.,
vol. 5, no. 5, pp. 3853–3864, Oct. 2018.
[19] H. Helmers, D. Lackner, G. Siefer, E. Oliva, F. Dimroth, and A. W. Bett,
“Integrated power and data transceiver devices for power-by-light systems
– a concept study,” in Proc. 32nd Eur. Photovolt. Solar Energy Conf.
Exhib., Munich, Germany, 2016, pp. 218–222.
[20] J. Fakidis, S. Videv, H. Helmers, and H. Haas, “0.5-Gb/s OFDM-based
laser data and power transfer using a GaAs photovoltaic cell,” IEEE
Photon. Technol. Lett., vol. 30, no. 9, pp. 841–844, May 2018.
[21] D. Derix, R. Freiche, C. Schoner, and A. Hensel, “Comparison of con-
tinuous and transition mode in a PV-booster with GaN-transistors and
switching frequencies up to 250 kHz,” in Proc. 17th Eur. Conf. Power
Electron. Appl., Geneva, Switzerland, 2015, pp. 1–7.
[22] C. Armbruster, C. Schoener, T. Schoenbett, A. Kloenne, and R. Merz,
“Development of a high efficient MPPT for space applications using
GaN power transistors,” in Proc. Int. Exhib. Conf. Power Electron., Intell.
Motion, Renewable Energy Energy Manage., Nuremberg, Germany, 2017,
pp. 451–456.
[23] Analog Devices, “LTC3425: 5A, 8MHz, 4-Phase synchronous step-
up DC/DC converter,” [Online] Available: https://www.analog.com/en/
products/ltc3425.html. Accessed on: Jan. 24, 2020.
[24] G. Siefer and A. W. Bett, “Analysis of temperature coefficients for III–V
multi-junction concentrator cells,” Prog. Photovolt., Res. Appl., vol. 22,
no. 5, pp. 515–524, 2014.
[25] E. Oliva, F. Dimroth, and A. W. Bett, “GaAs converters for high power
densities of laser illumination,” Prog. Photovolt., Res. Appl., vol. 4, no. 16,
pp. 289–295, 2008.
[26] C. L. Schilling et al., “Combining photon recycling and concentrated
illumination in a GaaS heterojunction solar cell,”IEEE J. Photovolt.,vol.8,
no. 1, pp. 348–354, Jan. 2018.
[27] H. Helmers et al., “Highly efficient III-V based photovoltaic laser power
converter,” in Proc. 1st Opt. Wireless Fiber Power Transmiss. Conf.,
Yokohama, Japan, 2019, pp. 5–6.
[28] S. Fafard et al., “High-photovoltage GaAs vertical epitaxial monolithic
heterostructures with 20 thin p/n junctions and a conversion efficiency of
60%,” Appl. Phys. Lett., vol. 109, no. 13, 2016, Art. no. 131107.
[29] S. Fafard et al., “Ultrahigh efficiencies in vertical epitaxial heterostructure
architectures,” Appl. Phys. Lett., vol. 108, no. 7, 2016, Art. no. 71101.
[30] C. Guan et al., “Fabrication and characterization of a high-power assembly
with a 20-junction monolithically stacked laser power converter,” IEEE J.
Photovolt., vol. 8, no. 5, pp. 1355–1362, Sep. 2018.
[31] S. K. Reichmuth, H. Helmers, S. P. Philipps, M. Schachtner, G. Siefer, and
A. W. Bett, “On the temperature dependence of dual-junction laser power
converters,” Prog. Photovolt: Res. Appl., vol. 25, no. 1, pp. 67–75, 2017.
[32] J. Schubert, E. Oliva, F. Dimroth, W. Guter, R. Löckenhoff, and A. W. Bett,
“High-voltage GaAs photovoltaic laser power converters,” IEEE Trans.
Electron Devices, vol. 56, no. 2, pp. 170–175, Feb. 2009.
[33] Y. Zhao, Y. Sun, Y. He, S. Yu, and J. Dong, “Design and fabrication of
six-volt vertically-stacked GaAs photovoltaic power converter,” Sci. Rep.,
vol. 6, 2016, Art. no. 38044.
[34] H. Helmers et al., “Photovoltaic Cells with increased voltage output for
optical power supply of sensor electronics,” in Proc. 17th Int. Conf. Sensors
Meas. Technol., 2015, pp. 519–524.
[35] G. Keller et al., “GaAs multi-junction laser power converters at AZUR
SPACE: Current status and development activities,” in Proc. 1st Opt. Wire-
less Fiber Power Transmiss. Conf., Yokohama, Japan, 2019, pp. 11–12.
[36] R. Kimovec, H. Helmers, A. W. Bett, and M. Topic, “On the Influence
of the Photo-Induced Leakage Current in Monolithically Interconnected
Modules,” IEEE J. Photovolt., vol. 8, no. 2, pp. 541–546, Mar. 2018.
[37] R. Kimovec, H. Helmers, A. W. Bett, and M. Topiˇc, “Comprehensive
electrical loss analysis of monolithic interconnected multi-segment laser
power converters,” Prog. Photovolt. Res. Appl., vol. 27, pp. 199–209, 2019.
[38] R. Pena and C. Algora, “The influence of monolithic series connection
on the efficiency of GaAs photovoltaic converters for monochromatic
illumination,” IEEE Trans. Electron Devices, vol. 48, no. 2, pp. 196–203,
Feb. 2001.
[39] R. Kimovec, H. Helmers, A. W. Bett, and M. Topiˇc, “Power loss mech-
anisms in small area monolithic-interconnected photovoltaic modules,”
Opto-Electron. Rev., vol. 26, no. 2, pp. 158–164, 2018.
[40] R. Peña and C. Algora, “Mismatch losses in GaAs monolithically series
connected photovoltaic converters for monochromatic illumination,” in
Proc. 16th Eur. Photovolt. Solar Energy Conf., Glasgow, U.K., 2000,
pp. 1038–1041.
[41] L. Wagner, A. W. Bett, and H. Helmers, “On the alignment tolerance of
photovoltaic laser power converters,” Optik—Int. J. Light Electron Opt.,
vol. 131, pp. 287–291, 2017.