Patent Publication Number: US-2020303576-A1

Title: Optical Communication and Power Generation Device and Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of and claims priority to non-provisional U.S. patent application Ser. No. 16/438,393, filed on Jun. 11, 2019, which claims priority to provisional U.S. Patent Application No. 62/683,861, filed on Jun. 12, 2018. The entirety of U.S. patent application Ser. No. 16/4738,393 and U.S. Patent Application No. 62/683,861 are incorporated herein by reference 
    
    
     FIELD OF THE TECHNOLOGY 
     Aspects described herein are generally related to the fields of optical communication and optical energy conversion. More specifically, aspects described herein provide a thin film communication and power generation device using a photovoltaic element, a retroreflector element, and an optical modulator element. 
     BACKGROUND 
     Autonomously operating systems are used in many fields of the modern economy. Their usage usually comprises the collection of environmental data, and subsequent data processing and aggregation, as well as data communication to and from a data transmitting, receiving and control system. To power autonomously operating systems, a reliable and standalone energy source is needed, such as solar power, batteries or similar. Radio frequency (RF) based systems are often used for communication to and between autonomous systems due to their simplicity of integration. However, radio frequency systems can be limited due to their short range of operation, high power requirements, signal interference, limited beam steering capabilities, and health risks. In particular, for military operations which require large standoff distances, radio frequency communication links are susceptible to detectability, spamming or spoofing. Optical communication systems, on the other hand, allow for high data rates and are less susceptible to signal interference. However, optical communication systems often require precise pointing control of both receiver and sender unit and often require large, heavy, and expensive optics. Therefore, the integration of optical communication systems can be complicated in a variety of autonomous and unmanned sensor, communication and transport systems, including but not limited to satellites, ground vehicles, unpiloted air vehicles, as well as consumer products. 
     SUMMARY 
     The following summary presents a simplified summary of certain features. The summary is not an extensive overview and is not intended to identify key or critical elements. 
     Aspects described herein provide a solution that allows both the generation of electrical energy and optical communication in one integrated device which is lightweight, mechanically flexible, and scalable for various energy generation and optical free-space (FSO) communication needs. 
     Aspects described herein may include a photovoltaic element, a retroreflector element, an optical modulator element, electrical contacts, and electrical conductors. An interrogating light beam can be pointed at the device, and a modulated light beam is reflected back by the device in the direction substantially parallel to the interrogating light beam with the reflected light beam containing information/data being modulated by the device onto the reflected light beam. 
     Described herein is an integrated optical communication and electrical energy generation device with at least one photovoltaic element, at least one light modulating element, a one or more first electrical contacts and/or conductors coupled to the at least one light modulating element, and at least one light reflecting element. The integrated optical communication and electrical energy generation device may also comprise one or more second electrical contacts and/or conductors coupled to the photovoltaic element. In some embodiments, power harvesting and storage circuitry may be connected to said second electrical contacts and/or conductors to convert and store the electrical energy generated by the photovoltaic element. A signal generating circuitry, which may be powered by the power harvesting and storage circuitry, may generate the electric signals for the light modulating element. 
     In some embodiments, the photovoltaic element may be adjacent to the light reflecting element. The photovoltaic element may receive a first light beam from a first direction, and may generate electrical energy from at least a portion of energy associated with the first light beam. The light modulating element may receive a second light beam from a second direction, and may modulate the second light beam in response to electric signals from the one or more first electrical contacts and/or conductors. The light reflecting element may redirect a substantial portion of the modulated second light beam in a third direction parallel to the second direction. 
     In some embodiments, the photovoltaic element may be adjacent to the light modulating element. The photovoltaic element may receive a first light beam from a first direction, and convert at least a portion of energy associated with the first light beam into electrical energy. The light modulating element may modulate a second light beam from a second direction in response to electric signals from the one or more first electrical contacts and/or conductors. The light reflecting element may redirect a substantial portion of the modulated second light beam in a third direction parallel to the second direction. In some embodiments, one or more first doped semiconducting elements may be disposed between the at least one modulator element and the light reflecting element, and one more second doped semiconducting elements may be disposed between the at least one light modulator element and the photovoltaic element. 
     In some embodiments, the integrated optical communication and electrical energy generation device may further comprise a transparent element or a display adjacent to the photovoltaic element. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise a first light reflecting element and a second light reflecting element. The first light reflecting element may have a first internal surface adjacent to the photovoltaic element and a first external textured surface. The first light reflecting element may receive a first light beam from a first direction through the first external textured surface. The second light reflecting element may have a second internal surface adjacent to the light modulating element and a second external textured surface. The second light reflecting element may receive a second light beam from a second direction through the second external textured surface. The photovoltaic element may receive a third light beam from a third direction. The photovoltaic element may convert at least a portion of energy associated with the third light beam into electrical energy. The light modulating element may modulate at least one of the first light beam and the second light beam in response to electric signals from the one or more first conductors. The first light reflecting element may redirect a substantial portion of the second light beam in a fourth direction parallel to the second direction, and the second light reflecting element redirects a substantial portion of the first light beam in a fifth direction substantially parallel to the first direction. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise a plurality of light modulating elements separated by one or more insulating layers and coupled to the one or more first conductors. The plurality of light modulating elements may comprise a first light modulating element adjacent to the photovoltaic element and a second light modulating element adjacent to the light reflecting element. The photovoltaic element receives a first light beam from a first direction, and converts at least a portion of energy associated with the first light beam into electrical energy. Each of the light modulating elements, from the plurality of light modulating elements, may modulate one or more second light beams within a light wavelength range specific to said light modulating element in response to electric signals from the one or more first conductors. The light reflecting element redirects a substantial portion of the modulated one or more second light beams in one or more third directions substantially parallel to the one or more second directions. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise a plurality of photovoltaic elements and a plurality of light modulating elements disposed over the light reflecting element. An element from the plurality of photovoltaic elements and the plurality of light modulating elements receives a first light beam from a first direction. Each light modulating element from the plurality of light modulating elements, modulates the first light beam, within a light wavelength range specific to said light modulating element in response to electric signals from the one or more first conductors. Each photovoltaic element from the plurality of photovoltaic elements, converts at least a portion of energy associated with a second light beam from a second direction into electrical energy. The light reflecting element redirects a substantial portion of the modulated first light beam in a third direction parallel to the first direction. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise a light reflecting substrate, a plurality of light modulating elements disposed over the light reflecting substrate, one or more first conductors coupled to the plurality of light modulating elements, a plurality of photovoltaic elements disposed over the plurality of light modulating elements, and one or more second conductors coupled to the plurality of photovoltaic elements. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise a plurality of photovoltaic elements, a light modulating element, and a light reflecting element. Each photovoltaic element of the plurality of photovoltaic elements may have a bandgap different than bandgaps of other photovoltaic elements of the plurality of photovoltaic elements. Each photovoltaic element may be configured to generate power from a portion of the received light beam associated with its bandgap. The plurality of photovoltaic elements may comprise diodes. The plurality of photovoltaic elements may be connected in series, or electrically isolated. 
     In some embodiments of the integrated optical communication and electrical energy generation device, a light modulating element may be disposed between a first photovoltaic element and a second photovoltaic element. The first photovoltaic element may comprise a n-type doped semiconductor material and the second photovoltaic element may comprise a p-type doped semiconductor material, and the arrangement of the first photovoltaic element, the light modulating element, and the second photovoltaic element may form a p-i-n diode. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise an electrical switching element comprising a first surface in contact with one of the plurality of photovoltaic elements and a second surface in contact with the light modulating element. The electrical switching element, in response to electrical signals, may be configured to send a signal to the light modulating element. The electrical switching element may comprise a bi-polar junction transistor or a field-effect transistor. The signal may comprise a voltage across the plurality of photovoltaic elements. 
     Some embodiments of the integrated optical communication and electrical energy generation device may comprise temperature stabilizing circuitry, which may be powered by the power harvesting and storage circuitry, wherein the temperature stabilizing circuitry maintains an operating temperature of the integrated device. 
     Applications include but are not limited to systems which require an autonomous electrical energy supply as well as a data communication interface and link, such as satellites, unmanned airplanes, ground, marine and underwater vehicles, friend-or-foe detection devices, identification tags for consumer products and shipping containers; handheld mobile devices capable of optical communication; as well as road traffic signs. 
     Some advantages of the integrated optical communication and electrical energy generation device include: (a) self-powered, autonomous operation using ambient light including but not limited to the sun, or directed light sources such as lasers, (b) high data rates for optical communication, (c) suitability for short-range, medium-range and long-range communication links ranging from less than 1 m to more than 100 km, (d) suitability for multi-user/link operation, (e) lightweight and mechanically flexible/bendable structure with a thickness of less than 1 mm, and (f) scalability of the surface area of the device over several orders of magnitude from less than 1 square mm to more than 1 square m. 
     Other advantages comprise a design of the integrated optical communication and electrical energy generation device that is transparent at wavelengths visible to the human eye. 
     Some aspects, e.g., may be used to create an identification tag that cannot be spammed by radio frequency based systems. Some embodiments are particularly useful for space applications. For example, satellite attitude control requirements can be largely reduced, which complicated the integration of FSO links into smaller satellites in the past. The combined optical communication and power generation device can be integrated into existing satellite solar arrays at virtually no additional weight and no additional surface area requirements. The combined optical communication and power generation device can replace and/or complement otherwise power consuming and heavy RF communication equipment and overcome already challenging RF bandwidth limitations, in particular for large CubeS at constellations. The combined optical communication and power generation device can also enable FSO communications between Earth and a lunar lander or a deep space platform. 
     Furthermore, the “Internet of Things” movement has produced an increasing number of autonomously operating sensor and data transmission systems which leads to an increasing number of autonomously operating sensor and data transmission systems for which energy efficient operation, secure communication, and high data transmission rates are crucial. This trend is supported by autonomously operated vehicles and their increasing need for secure, high-speed data exchange for which optical data links can be attractive in dense traffic conditions. The combined optical communication and power generation device can add a power and data exchange capability to such an autonomously operating sensor and data transmission systems. 
     These and other features and advantages are described in greater detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some features are shown by way of example, and not by limitation, in the accompanying drawings. In the drawings, like numerals reference similar elements. 
         FIG. 1A  illustrates a cross-sectional view of a first embodiment of an integrated optical communication and electrical energy generation device comprising a photovoltaic element, an optical modulator element, a retroreflector element, and electrical contacts. 
         FIG. 1B  illustrates a schematic view of the integrated optical communication and electrical energy generation device. 
         FIG. 2  illustrates a cross-sectional view of a second embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 3  illustrates a cross-sectional view of a third embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 4  illustrates a cross-sectional view of a fourth embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 5  illustrates a cross-sectional view of a fifth embodiment of an integrated optical communication and electrical energy generation device capable of dual wavelength data communication. 
         FIG. 6  illustrates a cross-sectional view of a sixth embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 7  illustrates a method for using the integrated optical communication and electrical energy generation device for data retrieval from a satellite to a ground station. 
         FIG. 8  illustrates a method for using the integrated optical communication and electrical energy generation device for road safety applications, vehicle communication applications, and determination of vehicle location and speed. 
         FIG. 9  illustrates a method for using the integrated optical communication and electrical energy generation device for parcel tracking, collection of parcel information/data, and determination of parcel distance and parcel location. 
         FIG. 10  illustrates a schematic view of a first embodiment of an integrated optical communication and electrical energy generation device with arrays of sub-devices. 
         FIG. 11  illustrates a schematic view of a second embodiment of an integrated optical communication and electrical energy generation device with arrays of sub-devices. 
         FIG. 12  illustrates a cross-sectional view of a seventh embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 13  illustrates a cross-sectional view of an eighth embodiment of an integrated optical communication and electrical energy generation device. 
         FIG. 14  illustrates the wavelength-dependent absorbance of the integrated optical communication and electrical energy generation device in  FIG. 13  at different operating temperatures. 
         FIG. 15  illustrates a cross-sectional view of a ninth embodiment of an integrated optical communication and electrical energy generation device. 
     
    
    
     DETAILED DESCRIPTION 
     Example and illustrative methods and systems are described herein. Any illustrative embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The illustrative embodiments and aspects described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. 
     Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments and/or aspects may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined, split into multiple components/steps, or omitted. Yet further, one or more illustrative embodiments may include elements that are not explicitly illustrated in the Figures. 
     Aspects described herein contribute to an apparatus, method of manufacturing, and system for an integrated optical communication and electrical energy generation device. The apparatus or system may be used in diverse commercial, consumer, defense, aerospace, environmental, road safety, transportation, and telecommunication related applications. Aspects and features described in the following combine the electrical energy generation capability of a photovoltaic device with the optical data communication capability of an electrically modulated retroreflector in one device. 
       FIG. 1A  shows an illustrative embodiment of the integrated optical communication and electrical energy generation device  100 . The device may include a photovoltaic element  110  for light to electrical energy conversion, an electrically controlled light modulator element  120  which is able to change its transparency for light of a defined wavelength range as a function of an externally applied electrical signal, a retroreflector element  130 , such as a cat-eye reflector or a corner cube reflector, which is able to reflect the modulated light  320  back in the direction of the incoming light beam  310 . 
     The photovoltaic element  110  may absorb incoming light  330 , such as light from the sun  340 , ambient room light or otherwise suited light sources and convert the incoming light to electrical energy which can be made available to a power harvesting and storage circuitry  168  through electrical contacts and/or conductors  210  and  220 . The photovoltaic element may comprise a planar semiconductor p-n diode made of Silicon, GaAs, InGaAs or other semiconductors, such as III-V semiconductors like GaInP, InP, AlGaAs or similar, or other materials suited for photovoltaic energy conversion, like CdTe, CIGS, or similar. The photovoltaic element  110  may absorb a portion of the incoming light within a certain wavelength range as defined by the photovoltaic element&#39;s bandgap energy or light absorption characteristics. The photovoltaic element  110  may be transparent in a certain wavelength range or semi-transparent in a certain wavelength range, such that incoming light of a certain wavelength range can reach the optical modulator  120 . For example, the photovoltaic element may not include any metal backing, and may be constructed on a transparent wafer or handling substrate which may be polished on one or both sides. 
     The optical modulator  120  may change its transparency for light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts and/or conductors  220  and  230  by the signal generating circuitry  166 . The signal generating circuitry  166  may be powered by the power harvesting and storage circuitry  168 . Incoming light  310  of a certain wavelength range and incident angle can pass through the photovoltaic element  110  towards the optical modulator  120  where depending on the externally applied electrical signal, the modulator can impose a digital or analog or otherwise suited modulation onto the light, including but not limited to states of the modulator during which the modulator is transparent, semi-transparent or opaque or during which the modulator affects, changes, modulates, transmits, or absorbs light of a defined polarization. The modulation allows encoding information/data onto the incoming light  310 . The optical modulator may comprise one or a multitude of the following elements, including but not limited to a liquid crystal modulator, an acousto-optic modulator, a Fabry-Perot based modulator, a multi-quantum well (MQW) based modulator, a distributed Bragg-reflection modulator, an optically tunable filter modulator, a polarization modulator, or similar. Modulation frequencies may be in the range of 10 Hz or less to 1 GHz or more. 
     A retroreflector element  130  reflects the modulated light  315  back in the direction  320  substantially parallel to the direction of the incoming light  310 . The retroreflector may comprise a corner cube reflector, a spherical reflector, a phase-conjugate mirror, moth-eye like gratings, gratings, dispensed spheres, etched structures, holographic structures or otherwise suited mirror or reflector materials including but not limited to commercially available reflective tape such as 3M flexible prismatic reflective sheeting, or a combination thereof. A corner cube reflector may be fabricated by use of a Nickel shim from a master polymer via two-photon absorption for sharp corners and defined angles. The retroreflector element  130  may also be designed to reflect the modulated light  315  back in a desired direction which is not parallel to the direction of the incoming light  310 . 
     Once the reflected and modulated light  320  exits the integrated optical communication and electrical energy generation device, it contains data/information which can be detected and recorded by a communication and control system  400 . Control system  400  may comprise a telescope and/or a photodiode. 
     The integrated optical communication and electrical energy generation device  100  may have a height of less than 200 μm. Due to its relatively thin thickness, the integrated optical communication and electrical energy generation device  100  may be mechanically flexible and may be attached to certain objects like a regular sticker. The device and elements of the integrated optical communication and electrical energy generation device  100  can be manufactured by epitaxial growth, epitaxial lift-off, bonding, transfer printing, mechanical stacking, gluing, similar methods, or a combination of said methods. A device  100  that is manufactured using epitaxial processes may be comprised of a single or double-sided polished (DSP) wafer or a substrate made of GaAs, InP, Si, Ge or similar to achieve desired properties of optical reflection, diffraction, transmission, surface smoothness, and device flatness. 
     The electrical energy generated by the photovoltaic element  110  may be used to power and control the optical modulator  120  as well as the signal generating circuitry  166 . This makes the integrated optical communication and electrical energy generation device  100  suitable for applications that require (a) standalone operation without an external electrical energy source, (b) long operational lifetime, (c) a high speed optical data communication interface, (d) data readout capability from a long standoff distance, as well as resilience against radio frequency spamming or spoofing. 
     The wavelength range of the incoming light  310  to be modulated by device  100  may be in the range of 500 nm or less to 2500 nm or more, whereas the wavelength may be chosen to be larger than the respective wavelength of the bandgap energy of the photovoltaic element  110  to minimize absorption losses within device  100 . In an illustrative embodiment of device  100  with a photovoltaic element  110  comprised of GaAs having a bandgap energy at room temperature corresponding to the absorption of photons with a wavelength of less than approximately 900 nm a suitable operating wavelength range of the modulator element  120  may be within 950 nm or less and 1100 nm or more including wavelengths of up to approximately 1550 nm to best couple to commercially available laser systems. Multi-quantum-well modulators operating in such a wavelength range can be fabricated via epitaxial growth including but not limited to the usage of III-V semiconductors such as InGaAs, InGaAsP, InP, InAsP, AlGaAs, InAlGaAs, GaAsP, or similar. The applied electrical signal to the electrical contacts of the modulator  220  and  230  may be a voltage of less than 5V or a voltage of more than 15V. 
     Standard solar cells often have a metalized electrically conductive rear side which absorbs light and which generally yields very low optical transmission properties. The photovoltaic element  110  for usage in device  100  may be comprised of an electrically conductive rear side which may be located at the interface between photovoltaic element  110  and modulator  120 , and which may be optically transparent in a defined wavelength range. Said electrically conductive rear side of the photovoltaic element  110  may contain or may be made of a highly doped semiconductor lateral conduction layer, an Indium-Tin-Oxide (ITO) layer, a fluorine doped tin oxide (FTO) layer, a carbon nanotube network layer, a graphene layer, a doped zinc oxide layer, a combination of such layers, or an otherwise suited optically transparent and electrically conductive layer. The electrically conductive rear side of photovoltaic element  110  may be electrically connected to the electrical contact  220 . The electrical contact  220  may serve as a common ground for both the photovoltaic element  110  and the modulator  120  such that device  100  may be a three-terminal device. Metal interconnects, contacting schemes and technologies, as described in U.S. Pat. No. 5,0190,177 for usage in an III-V semiconductor three-terminal device, may be used to as electrical contacts. 
     In another illustrative embodiment, the photovoltaic element  110  and the light modulating element  120  may have no common electrical contact or contacts. The photovoltaic element  110  and the light modulating element  120  may have individual electrical contacts and may be separated by an electrically insulating and for the modulated light optically transparent layer located between photovoltaic element  110  and the light modulating element  120  such that the device  100  may have four or more electrical terminals. 
     In another illustrative embodiment, the device  100  may have two electrical contacts, also referred to as a two terminal device, such that the photovoltaic element  110  and the light modulating element  120  may be electrically connected and said electrical connection may not be available as an external electrical contact. 
     If device  100  is operated in an environment in which large fluctuations of temperature occur, such as in space, the wavelength dependent absorption, transmission, polarization and modulation properties of the photovoltaic element  110 , the light modulating element  120 , and the light reflecting element  130  may change with temperature. This may be accounted for by a change of the emitting and/or receiving light wavelength and/or light polarization properties of the communication and control system  400 . That is, the wavelength range of multi-quantum-well modulators may shift with temperature. Existing laser systems allow for the changing of the emitted wavelength and thus could be used to account for the potential change of the temperature dependent characteristics of multi-quantum-well modulators or other light modulating elements. Similarly, temperature-induced changes of the polarization properties of device  100  may be accounted for by changing the emitting and receiving light polarization properties of the communication and control system  400 . The temperature of device  100  may also be stabilized by a heater or a cooler which may be controlled and powered fully or in part by electrical energy generated by the photovoltaic element  110  and stored in the power harvesting and storage circuitry  168 . 
     The angle of incidence of the incoming light  310  may be within 0 degrees from normal to about 70 degrees or more from normal. 
     Multiple communication and control units  400  may be used simultaneously and/or sequentially from similar and/or different directions and incoming angles to read data from device  100 . 
     The incoming light  310  may already be modulated. Said modulation of the incoming light may be by modulation of the light intensity, the light wavelength, the modulation frequency, the light polarization, or a combination of said modulation methods. A sensor, such as a photodiode or a filtered photodiode, can be attached to or be integrated into device  100  to measure and record this modulation. The modulated signal may comprise instructions for device  100 , such as instructions on which information/data shall be modulated onto the light beam by device  100  prior to the light being reflected back to control unit  400 . Said instructions may also contain information on the desired modulation data rate, method, duty cycle, electrical energy usage, or similar. 
     The photovoltaic element  110  may be operated in reverse, e.g., as a light emitting diode, to emit light with modulated data/information into a multitude of directions. 
     The order in which optically relevant elements and/or electrically relevant elements, such as electrical contacts, are stacked or arranged within device  100  may be changed in part or as a whole, including but not limited to the placement of the light modulating element  120  at the or near the surface of device  100  and/or on top of the photovoltaic element  110 . 
     In some cases, the modulating frequency may be increased by segmenting the device  100  into smaller sub-devices which may be arranged in a mosaic or array pattern and which may be driven with the same or different modulation signals. A reduced area size often correlates with a reduced RC switching time and reduced power consumption. Segmentation may be achieved via localized etching, localized ion bombardment, transfer printing, cutting, or similar methods. Electrical contacts to the sub-devices may comprise wires, backside contacts, metal-wrap-through technology, or other contact technology that may be realized from the rear side of the device. Segmentation size and shape of the modulating element and the photovoltaic element may be similar or different. Only the modulating element may be segmented whereas the photovoltaic element may be unsegmented. Sub-devices may be smaller than 1 square mm or larger than 100 square mm. 
     Several devices  100  may also be arranged in pairs or in an array whereas the respective electrical contacts of each photovoltaic element  110  may be connected in parallel or series, individually connected or a combination thereof and whereas the electrical contacts of each optical modulator element  120  may be connected in parallel, series, individually or a combination thereof. In such a paired or array configuration of serval devices  100  the overall area suitable for light to electrical energy conversion via the photovoltaic element may be increased by the factor of the amount of paired devices  100  whereas the effective area determining the RC switching time of the light modulating element may remain unchanged which may be favorable for overall fast data rates and increased energy generation of device  100 . 
       FIG. 1B  illustrates a schematic view of the integrated optical communication and electrical energy generation device  100  in  FIG. 1A . The device may include a photovoltaic element  110 , an electrically controlled light modulator element  120 , a retroreflector element  130  and electrical contacts and conductors, such as the conductive strips  210   a ,  210   b ,  210   c ,  220 , and  230 . The conductive strips  210   a ,  210   b ,  210   c ,  220 , and  230 , may be made of polysilicon, metal or other suitable conductive material, such as a plurality of metal layers made of tungsten (W), titanium nitride (TiN), tantalum nitride (TaN) or the arbitrary combinations thereof. 
     The retroreflector element  130  may be separated from the conductive strip  230  by a first doped semiconducting element  135 . Even though only one conductive strip is shown between the retroreflector element  130  and the first doped semiconducting element  135 , multiple conducting strips may be disposed on top of the first doped semiconducting element  135 . The electrically controlled light modulator element  120  is disposed on top of the first doped semiconducting element  135  and is electrically coupled to the conductive strip  230 , and any other conductive strips disposed on top of the first doped semiconducting element  135 . Electrical signals can be applied through the conductive strip  230 , and any other conductive strips disposed on top of the doped semiconducting element  135  to the optical modulator element  120 . A second doped semiconducting element  125  may be disposed on top of the electrically controlled light modulator element  120 . A second plurality of conductive strips, such as the conductive strip  220 , is disposed on top of the second doped semiconducting element  125 . The second plurality of conductive strips, such as the conductive strip  220 , may act as a ground contact for the integrated optical communication and electrical energy generation device  100 . The photovoltaic element  110  is disposed on top of the second doped semiconducting element  125  and is electrically coupled to the conductive strip  220 , and any other conductive strips disposed on top of the second doped semiconducting element  125 . A third doped semiconducting element  115  may be disposed on top of the photovoltaic element  110 . A third plurality of conductive strips, such as the conductive strips  210   a ,  210   b , and  210   c , is disposed on top of the third doped semiconducting element  115 . Converted electrical energy from the photovoltaic element  110  can be made available through the third plurality of conductive strips, such as the conductive strips  210   a ,  210   b , and  210   c . The first doped semiconducting element  135 , the second doped semiconducting element  125  and the third doped semiconducting element  115  may comprise high and/or low doped semiconductor layers or an otherwise suited optically transparent material such as glass or similar or a combination thereof. 
       FIG. 2  shows another illustrative aspect of the integrated optical communication and electrical energy generation device, comprising two retroreflector elements  131  and  132  with textured surfaces. As described here, a textured surface is a surface that is not smooth, such as the front surface of the retroreflector element  132  and the back surface of the retroreflector element  131  with convex and/or concave shapes, lenses and/or mirrors to direct the exiting light  320  back in the direction of the incoming light  310 . The back surface of the retroreflector element  131  and/or the front surface of the retroreflector element  132  may partially or fully comprise a reflective surface and/or a reflective coating functioning as an optical mirror. 
     The back surface of the retroreflector element  131  and/or front surface of the retroreflector element  132  may also be shaped such that an incoming light beam  380  towards the rear side of device  100  is reflected within device  100  and exits device  100  at the rear side in a direction  390  parallel to the incoming light beam or at a desired angle relative to the incoming light. 
     The photovoltaic element  110  of device  100  may absorb and convert ambient light into electricity which impinges onto the front side  132  and/or onto the rear side  131  of device  100 . 
       FIG. 3  shows another illustrative aspect of the integrated optical communication and electrical energy generation device (e.g., used with, on, and/or in a mobile phone), comprising a display  500  or a transparent element with electrical contacts  250 . The display or the transparent element  500  may be transparent or semi-transparent for incoming light  310  and exiting light  320 . The display  500  may emit light  350  in a multitude of directions. 
     In some illustrative embodiments, the display  500  may itself be transparent or semitransparent, or alternatively may be permanently transparent to light within a predefined wavelength range. In some embodiments, a transparent OLED may be used, or the display may be made of glass (e.g., a window) or other transparent or semitransparent material. In such an embodiment, ambient light  330  and the photovoltaic element  110  may power the modulator  120 . The modulator  120  provides information and/or data in accordance with aspects described herein such that the data would become available inside a room, predefined area, or within a line of sight from the display, for instance where a receiver device  400  can receive the modulated signal  320  using a photodiode. In such an embodiment, the display may remain transparent to the human eye, and infrared wavelengths may be modulated to provide information to a receiving device without significantly altering the transparency and/or legibility of the display and without the display significantly altering and/or absorbing the modulated light  320 . If no energy generation is required for device  100 , the photovoltaic element  110  may be omitted. 
       FIG. 4  shows another illustrative aspect of the integrated optical communication and electrical energy generation device, comprising a first optical modulator  121  and a second optical modulator  122 . The first optical modulator  121  may modulate incoming light  310  within a defined wavelength range. The second optical modulator  122  may modulate incoming light  360  within a defined wavelength range that may be different from the wavelength range of the first optical modulator  121 . This allows simultaneous and independent data modulation for different light sources and receivers as indicated by incoming light beams  310 ,  360  and exiting light beams  320 ,  370 , respectively. 
     At the interface between the optical modulator  121  and optical modulator  122 , an electrically isolating layer  123  may be located to allow for electrical isolation and independent operation of both optical modulators. An electrical signal may be applied to the first optical modulator  121  via electrical contacts  222  and  211 / 210 . An electrical signal may be applied to the second optical modulator  122  via electrical contacts  230  and  233 . For the synchronous operation of both optical modulators  121  and  122 , the electrically insulating layer  123  may be omitted, and an electrical signal may be applied to both modulators via electrical contacts  230  and  211 / 210 . In another embodiment, the layer  123  may alter the polarization of the incoming and/or modulated light. In another embodiment, device  100  may contain one, two, or more optical modulators. The electrically insulating layer  123  may be a low doped semiconductor layer, a low doped semiconductor wafer, or an otherwise suited optically transparent material such as glass or similar, or a combination thereof. 
       FIG. 5  shows another illustrative aspect of the integrated optical communication and electrical energy generation device, comprising a first photovoltaic device  111 , a first optical modulator  121 , a second photovoltaic device  112 , and a second optical modulator  122 . The second optical modulator  122  may modulate incoming light  360  within a defined wavelength range that may be different from the wavelength range of the first optical modulator  121 . The first optical modulator  121  may be designed for light modulation within a wavelength range of approximately 900 nm or less to 1100 nm or more. The second optical modulator  122  may be designed for light modulation within a wavelength range of approximately 1400 nm or less to 1600 nm or more. This allows simultaneous and independent data modulation for different light sources and receivers as indicated by incoming light beams  310 ,  320  and exiting light beams  360 ,  370 , respectively. The second photovoltaic element  112  may have a lower bandgap energy than the first photovoltaic element  111  and may convert light within a defined wavelength range into electricity and/or may operate as an optical detector, such as a photodiode, whereas the first photovoltaic may also function as an optical filter for light with wavelengths lower than its respective bandgap energy. In some embodiments, more than two, and even six or more photovoltaic elements may be grown or stacked on top of each other, each with a different bandgap. In some embodiments, more than two optical modulators may be grown or stacked on top of each other. In some embodiments, the optical modulators may alter the light polarization. 
       FIG. 6  shows another illustrative aspect and method of the integrated optical communication and electrical energy generation device  100  in which the optically relevant elements and/or electrically relevant elements, such as electrical contacts, may be stacked or arranged within device  100  such that an incoming and interrogating light beam  310  may be modulated and reflected back in direction  320  with said light beams reaching and exiting device  100  on its front side and such that ambient light  330  may be converted to electrical energy by the photovoltaic element when reaching the device  100  on its rear side. Additional layers, such as glass, a semiconductor wafer, Kapton, Mylar, a polymer layer, a similarly suited layer, or a combination of said layers may be incorporated into device  100  for purposes of electrical insulation, mechanical stability, handling, electrical conduction, electrical contacts, or similar. 
       FIG. 7  shows another illustrative aspect and method of the integrated optical communication and electrical energy generation device for usage as an optical communication and electrical energy generation device on a satellite. The satellite  800  is shown with two arrays which may be fully or partly comprised of the integrated optical communication and electrical energy generation device  100  or arrays of the integrated optical communication and electrical energy generation devices. Electrical energy can be generated by light to electricity conversion of the photovoltaic element inside the integrated optical communication and electrical energy generation device  100 . A source for incoming light  330  for light to electricity conversion may be the sun  340 . A transmitter and receiver unit  400  may be located on the surface of the Earth  900  or may also be located on another satellite. The transmitter and receiver unit  400  may use a laser beam  310  directed towards the satellite  800  and receive modulated light  320  which contains information/data of the satellite  800 . Aspects described herein overcome current system integration limitations since both the photovoltaic element and the free space optical communication system are combined in one device. Further, the large surface area typically used for photovoltaic arrays can now be used by the integrated optical communication and electrical energy generation device as a large area optical communication interface. The energy-intensive part of sending a laser beam to the satellite relies solely upon the ground station  400  and saves energy on the satellite platform  800 . 
       FIG. 8  shows another illustrative aspect and method of the integrated optical communication and electrical energy generation device for usage in road safety and vehicle guidance and communication systems. The integrated optical communication and electrical energy generation device  100  may be integrated into a road sign  710 . A lamp  730  of a vehicle  720 , including but not limited to an incandescent bulb, an LED, a laser or a combination thereof, may be directed towards the road sign  710 , indicated by light beam  310 . Information/data contained within the road sign  710 , including but not limited to location, outside temperature, traffic information, or similar can be sent to a receiver contained in the vehicle  720  via a modulated light beam  320 . Further, the reflective nature of road sign  710  allows for measurement of the time-of-flight between vehicle  720  and road sign  710  to determine the distance and velocity of vehicle  720 . Since the road sign  710  reflects the light back in the same direction of the incoming light, one or more vehicles  740  can simultaneously receive information/data from the road sign  710 , as indicated by light beams  360  and  370  and lamp  750 . The integrated photovoltaic element allows for self-powered operation of the road sign. Light beams  310  and  360  may already contain modulated data which may be recorded by the road sign for re-transmission to other vehicles. 
       FIG. 9  shows another illustrative aspect and method of the integrated optical communication and electrical energy generation device  100  for usage in transport, logistics, and inventory systems. Parcels  610  and  620  may be stored in a warehouse at different locations. A transmitter and receiver unit  400  may use a directed light beam  310  and  360 , including but not limited to a laser beam, to direct light towards a tag  601  and  602  which are attached to the parcel  610  and  620  and which contain said device  100  to obtain information/data on the properties of the parcel via a modulated and reflected light beam  320  and  370  containing these information/data. Further, through the time of flight measurements, the distance between the transmitter and receiver unit and one or a multitude of parcels  610  and  620  can be measured. In addition, since a directed and narrow light beam  310  and  360  is used, the angular orientation of the parcel  610  and  620  and their attached tags  601  and  602  with respect to the transmitter and receiver unit  400  may be obtained via a measurement of the orientation of the light source located within the transmitter and receiver unit  400 . The combination of the measurement of the time-of-flight, i.e., distance, and angular orientation allows the determination of the location of the parcel within 3-dimensional space. The reflected and modulated light beam may contain information on the properties of the parcel or otherwise relevant information. 
       FIG. 10  shows another illustrative aspect of the integrated optical communication and electrical energy generation device  100  with smaller sub-devices, such as the sub-devices  101 ,  102 ,  103 ,  104 . The sub-devices may be arranged in a mosaic or array pattern. The sub-devices may share a common retroreflector element  130  and have its individual photovoltaic element  110  and electrically controlled light modulator element  120 . In some embodiments, the arrays of sub-devices may share common electrical contacts, such as the electrical contacts  210 ,  220 , and  230 . In some embodiments, rows or columns of sub-devices in the array may share common electrical contacts. In other embodiments, each sub-device may have its own electrical contacts  210 ,  220 , and  230 . 
     The photovoltaic element  110  of each sub-device may absorb incoming light  330 , such as light from the sun  340 , ambient room light or otherwise suited light sources and convert the incoming light to electrical energy which can be made available to an external circuit through electrical contacts  210  and  220  and stored in the power harvesting and storage circuitry  168 . The optical modulator  120  of each sub-device may change its transparency for a light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts  220  and  230 . The common retroreflector element  130  reflects the modulated light  315  back in the direction  320  substantially parallel to the direction of the incoming light  310 . 
     The electrically controlled light modulator element  120  may change its transparency for a light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts  220  and  230  by the signal generating circuitry  166 . The signal generating circuitry  166  can be powered by the power harvesting and storage circuitry  168 . 
     The temperature of device  100  may also be stabilized by a heater or a cooler which may be controlled and powered fully or in part by electrical energy generated by the photovoltaic element  110  and stored in the power harvesting and storage circuitry  168 . 
       FIG. 11  shows another illustrative aspect of the integrated optical communication and electrical energy generation device  100  with smaller sub-devices, such as the sub-devices  105  and  106 . The sub-devices may be arranged in a mosaic or array pattern. The sub-devices may share a common photovoltaic element  110  and have its individual electrically controlled light modulator element  120  and retroreflector element  130 . In some embodiments, the arrays of sub-devices may share common electrical contacts, such as the electrical contacts  210 ,  220 ,  230 , and  231 . In some embodiments, rows or columns of sub-devices in the array may share common electrical contacts. In other embodiments, each sub-device may have its own electrical contacts  230  and  231  with common electrical contacts  210  and  220  for the photovoltaic element  110 . 
     The photovoltaic element  110  of each sub-device may absorb incoming light  330 ,  331   331 , such as light from the sun  340 , ambient room light or otherwise suited light sources and convert the incoming light to electrical energy which can be made available to an external circuit through electrical contacts  210  and  220  and stored in the power harvesting and storage circuitry  168 . The optical modulator  120  of each sub-device may change its transparency for a light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts  230  and  231 . The retroreflector element  130  reflects the modulated light back in the direction  320  substantially parallel to the direction of the incoming light  310 . 
       FIG. 12  shows an illustrative embodiment of an integrated optical communication and electrical energy generation device with multiple photovoltaic elements (e.g., a first photovoltaic element  111  and a second photovoltaic element  112 ) for converting incoming light to electrical energy. The device in  FIG. 12  further comprises an electrically controlled optical modulator element  120  which is able to change its transparency for a light of a defined wavelength range as a function of an externally applied electrical signal, a retroreflector element  130 , such as a cat-eye reflector or a corner cube reflector, which is able to reflect the modulated light  320  back in the direction substantially parallel to the incoming light beam  310 . 
     The integrated optical communication and electrical energy generation device in  FIG. 12  may comprise multiple photovoltaic elements. Each photovoltaic element in the device may comprise a planar semiconductor p-n diode made of Silicon, GaAs, InGaAs, or other semiconductors, such as III-V semiconductors like GaInP, InP, AlGaAs or similar, or other materials suited for photovoltaic energy conversion, like CdTe, CIGS, or similar. Each photovoltaic element may absorb a portion of the incoming light within a certain wavelength range as defined by the photovoltaic elements&#39; bandgap energies or light absorption characteristics. The photovoltaic elements may be transparent in a certain wavelength range or semi-transparent in a certain wavelength range, such that incoming light of a certain wavelength range can reach the optical modulator  120 . For example, the photovoltaic elements may not include any metal backing, and may be constructed on a transparent wafer or handling substrate which may be polished on one or both sides. Each photovoltaic element may have similar or different bandgap energy or light absorption properties and may be electrically connected in series by one or more electrically conductive layers or elements, such as a highly doped semiconductor conduction layer, an Indium-Tin-Oxide (ITO) layer, a fluorine doped tin oxide (FTO) layer, a carbon nanotube network layer, a graphene layer, a doped zinc oxide layer, a tunnel diode layer, a combination of such layers, or an otherwise suited electrically conductive layer which is optically transparent in a defined wavelength range. 
     The plurality of photovoltaic elements may absorb incoming light  330 , such as light from the sun  340 , ambient room light or otherwise suited light sources and convert the incoming light to electrical energy which can be made available to a power harvesting and storage circuitry  168  through electrical contacts and/or conductors  210  and  220 . For applications with high variability of the spectral distribution of the incoming light  330 , which may result in increased mismatch of the photocurrent generated in each photovoltaic element, the photovoltaic elements may have individual electrical contacts and/or conductors and may be electrically isolated from each other. 
     The second photovoltaic element  112  may have lower bandgap energy than the first photovoltaic element  111 . The second photovoltaic element  112  may convert light within a defined wavelength range into electricity and/or may operate as an optical detector, such as a photodiode, whereas the first photovoltaic element may also function as an optical filter for light with wavelengths lower than its bandgap energy. In some embodiments, more than two and even six or more photovoltaic elements may be grown or stacked on top of each other, each with different or similar bandgap energy. In some embodiments, more than two optical modulators may be grown or stacked on top of each other. In some embodiments, the optical modulators may alter the light polarization. 
     The optical modulator element  120  may change its transparency for light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts and/or conductors  220  and  230  by the signal generating circuitry  166 . The signal generating circuitry  166  may be powered by the power harvesting and storage circuitry  168 . Incoming light  310  of a certain wavelength range and incident angle can pass through the plurality of photovoltaic elements towards the optical modulator element  120  where depending on the externally applied electrical signal through contacts and/or conductors  220  and  230 , the optical modulator element can impose a digital or analog or otherwise suited modulation onto the light, including but not limited to states of the optical modulator element during which the optical modulator element is transparent, semi-transparent or opaque or during which the optical modulator element affects, changes, modulates, transmits, or absorbs light of a defined polarization. The modulation allows encoding information/data onto the incoming light  310 . The optical modulator element may comprise one or a multitude of the following elements, including but not limited to a liquid crystal modulator, an acousto-optic modulator, a Fabry-Perot based modulator, a multi-quantum well (MQW) based modulator, a distributed Bragg-reflection modulator, an optically tunable filter modulator, a polarization modulator, or similar. Modulation frequencies may be in the range of 10 Hz or less to 1 GHz or more. 
     A retroreflector element  130  reflects the modulated light  315  back in the direction  320  substantially parallel to the direction of the incoming light  310 . The retroreflector may comprise a corner cube reflector, a spherical reflector, a phase-conjugate mirror, moth-eye like gratings, gratings, dispensed spheres, etched structures, holographic structures or otherwise suited mirror or reflector materials including but not limited to commercially available reflective tape such as 3M flexible prismatic reflective sheeting, or a combination thereof. A corner cube reflector may be fabricated by the use of a Nickel shim from a master polymer via two-photon absorption for sharp corners and defined angles. The retroreflector element  130  may also be designed to reflect the modulated light  315  back in a desired direction which is not parallel to the direction of the incoming light  310 . The retroreflector element may comprise glass, such as BK7, or may comprise polymers, such as PMMA, PC, PEI, or otherwise suited materials. 
     Once the reflected and modulated light  320  exits the integrated optical communication and electrical energy generation device, it contains data/information which can be detected and recorded by a communication and control system  400 . Control system  400  may comprise a telescope and/or a photodiode. 
     The integrated optical communication and electrical energy generation device in  FIG. 12  may have a height of less than 200 μm. Due to its relatively thin thickness, the integrated device may be mechanically flexible and may be attached to certain objects like a regular sticker. The device and elements of the integrated optical communication and electrical energy generation device can be manufactured by epitaxial growth, epitaxial lift-off, bonding, transfer printing, mechanical stacking, gluing, similar methods, or a combination of said methods. The device can be manufactured using epitaxial processes that may be comprised of a single or double-sided polished (DSP) wafer or a substrate made of GaAs, InP, Si, Ge or similar to achieve desired properties of optical reflection, diffraction, transmission, surface smoothness, and device flatness. 
     The electrical energy generated by the plurality of photovoltaic elements may be used to power and control the optical modulator  120 , as well as the signal generating circuitry  166 . This makes the integrated optical communication and electrical energy generation device  100  suitable for applications that require (a) standalone operation without an external electrical energy source, (b) long operational lifetime, (c) a high speed optical data communication interface, (d) data readout capability from a long standoff distance, as well as resilience against radio frequency spamming or spoofing. 
     The wavelength range of the incoming light  310  to be modulated by the device in  FIG. 12  may be in the range of 500 nm or less to 2500 nm or more, whereas the wavelength may be chosen to be larger than the respective wavelengths of the bandgap energies of the plurality of photovoltaic elements to minimize absorption losses within the device. In an illustrative embodiment, the device may comprise a photovoltaic element  112  comprised of GaAs having a bandgap energy at room temperature corresponding to the absorption of photons with a wavelength of less than approximately 900 nm a suitable operating wavelength range of the modulator element  120  may be within 950 nm or less and 1100 nm or more including wavelengths of up to approximately 1550 nm to best couple to commercially available laser systems. Multi-quantum-well modulators operating in such a wavelength range can be fabricated via epitaxial growth including but not limited to the usage of III-V semiconductors such as InGaAs, InGaAsP, InP, InAsP, AlGaAs, InAlGaAs, GaAsP, or similar. The applied electrical signal to the electrical contacts of the modulator  220  and  230  may be a voltage of less than 5V or a voltage of more than 15V. 
     Standard solar cells often have a metalized electrically conductive rear side, which absorbs light and which generally yields very low optical transmission properties. The plurality of photovoltaic elements in the device in  FIG. 12  may be comprised of an electrically conductive rear and/or front side which may be located at the interface between adjacent photovoltaic elements and/or the optical modulator element  120 , and which may be optically transparent in a defined wavelength range. The electrically conductive rear and/or front side of a photovoltaic element may contain or may be made of a highly doped semiconductor lateral conduction layer, an Indium-Tin-Oxide (ITO) layer, a fluorine doped tin oxide (FTO) layer, a carbon nanotube network layer, a graphene layer, a doped zinc oxide layer, a combination of such layers, or an otherwise suited optically transparent and electrically conductive layer. The electrically conductive rear side of the second photovoltaic element  112  may be electrically connected to the electrical contact  220 . The electrical contact  220  may serve as a common ground for both the plurality of photovoltaic elements and the optical modulator element  120  such that device  100  may be a three-terminal device. Metal interconnects, contacting schemes and technologies, as described in U.S. Pat. No. 5,0190,177 for usage in an III-V semiconductor three-terminal device, may be used to as electrical contacts. 
     In another illustrative embodiment, the plurality of photovoltaic elements and the light modulating element  120  may have no common electrical contact or contacts. The plurality of photovoltaic elements and the optical modulator element  120  may have individual electrical contacts and may be separated by an electrically insulating and for the modulated light optically transparent layer located between the second photovoltaic element  112  and the optical modulator element  120  such that the device  100  may have four or more electrical terminals. 
     In another illustrative embodiment, the device in  FIG. 12  may have two electrical contacts, also referred to as a two terminal device, such that the plurality of photovoltaic elements and the optical modulator element  120  may be electrically connected and said electrical connection may not be available as an external electrical contact. If the device is operated in an environment in which large fluctuations of temperature occur, such as in space, the wavelength dependent absorption, transmission, polarization and modulation properties of the plurality of photovoltaic elements, the optical modulator element  120 , and the light reflecting element  130  may change with temperature. This may be accounted for by a change of the emitting and/or receiving light wavelength and/or light polarization properties of the communication and control system  400 . That is, the wavelength range of multi-quantum-well modulators may shift with temperature. Existing laser systems allow for the changing of the emitted wavelength and thus could be used to account for the potential change of the temperature dependent characteristics of multi-quantum-well modulators or other light modulating elements. Similarly, temperature-induced changes of the polarization properties of the device may be accounted for by changing the emitting and receiving light polarization properties of the communication and control system  400 . The temperature of the device may also be stabilized by a heater or a cooler, which may be controlled and powered fully or in part by electrical energy generated by the plurality of photovoltaic elements and stored in the power harvesting and storage circuitry  168 . 
     Multiple communication and control units  400  may be used simultaneously and/or sequentially from similar and/or different directions and incoming angles to read data from the device in  FIG. 12 . The angle of incidence of the incoming light  310  may be within 0 degrees from normal to about 70 degrees or more from normal. The incoming light  310  may already be modulated. The modulation of the incoming light may be by modulation of the light intensity, the light wavelength, the modulation frequency, the light polarization, or a combination of said modulation methods. A sensor, such as a photodiode, a filtered photodiode, or an optical modulator element, can be attached to or be integrated into the device to measure and record this modulation. The modulated signal may comprise instructions for the device, such as instructions for reflecting light back to control unit  400 . The instructions may also contain information on the desired modulation data rate, method, duty cycle, electrical energy usage, or similar. 
     The plurality of photovoltaic elements may be operated in reverse (e.g., as a light emitting diode) to emit light with modulated data/information into multiple directions. The order in which optically relevant elements and/or electrically relevant elements, such as electrical contacts, are stacked or arranged within the device in  FIG. 12  may be changed in part or as a whole, including but not limited to the placement of the light modulating element  120  at the or near the surface of device  100  and/or on top or inside of a photovoltaic element. 
     In some cases, the modulating frequency may be increased by segmenting the device into smaller sub-devices, which may be arranged in a mosaic or array pattern and which may be driven with the same or different modulation signals. A reduced area size often correlates with a reduced RC switching time and reduced power consumption. 
     Segmentation may be achieved via localized etching, localized ion bombardment, transfer printing, cutting, or similar methods. Electrical contacts to the sub-devices may comprise wires, backside contacts, metal-wrap-through technology, or other contact technology that may be realized from the rear side of the device. The segmentation size and shape of the modulating element and the photovoltaic elements may be similar or different. Only the light modulating element may be segmented whereas the photovoltaic elements may be unsegmented. Sub-devices may be smaller than 1 square mm or larger than 100 square mm. Several devices may also be arranged in pairs or in an array whereas the respective electrical contacts of each photovoltaic element  110  may be connected in parallel or series, individually connected or a combination thereof and whereas the electrical contacts of each optical modulator element  120  may be connected in parallel, series, individually or a combination thereof. In such a paired or array configuration of serval devices, the overall area suitable for light to electrical energy conversion via the photovoltaic element may be increased by the factor of the amount of paired devices whereas the effective area determining the RC switching time of the light modulating element may remain unchanged which may be favorable for overall fast data rates and increased energy generation of the device. 
       FIG. 13  shows another illustrative aspect of an integrated optical communication and electrical energy generation device, comprising an optical modulator element  120 , a retroreflector element  130 , and a photovoltaic element comprising one or more sub-photovoltaic elements (e.g., the sub-photovoltaic elements  110   n  and  110   p ). The sub-photovoltaic elements  110   n  and  110   p  may be arranged around the optical modulator element  120 . The optical modulator element  120  may be disposed between the sub-photovoltaic elements  110   n  and  110   p . The sub-photovoltaic elements  110   n  and  110   p  may comprise semiconductor layers. The effective doping concentration of the sub-photovoltaic element  110   n  may be n-type, while the effective doping concentration of the sub photovoltaic element  110   p  may be p-type. The effective doping concentration of the optical modulator element  120  may be quasi-intrinsic, i.e. low p-type or low n-type. Therefore, the arrangement of the sub-photovoltaic element  110   n , the optical modulator element  120 , and the sub-photovoltaic element  110   p  may form a p-i-n junction or diode. The effective doping polarity of the sub-photovoltaic elements may also be reversed, thereby forming an n-i-p junction or diode. 
     The device in  FIG. 13  may have two electrical contacts  210  and  230 , and the device may be referred to as a two terminal device. The optical modulator  120  may change its transparency for light of a certain wavelength range as a function of an electrical signal which can be applied through electrical contacts and/or conductors  210  and  230 . The photovoltaic element may absorb the incoming light  330  and convert the incoming light  330  to electrical energy. The electrical energy can be made available to a power harvesting and storage circuitry through electrical contacts and/or conductors  210  and  230 . 
     The device in  FIG. 13  may also be used for applications related to directed energy or power beaming. Under the exposure of a directed light beam  310  with an elevated intensity and wavelength λ L , the temperature of the device may increase. As illustrated in  FIG. 14 , at an increased temperature T Beam , or after crossing a threshold temperature, the effective bandgap energy and/or absorption properties of the device in  FIG. 13  may be shifted to longer wavelengths  520 ,  521 ,  522  in comparison to the operation of the device at a lower device temperature T Data  with device absorption properties  510 ,  511 ,  512 . The lower device temperature T Data  may occur during operation under ambient light and exposure to directed light beams with lower intensities as sufficient for data communication. The absorption properties of the photovoltaic element may shift from  510  at lower temperatures to  520  at elevated temperatures above the threshold temperature. The absorption properties of the optical modulator element may shift from  511  and  512  at lower temperatures to  521  and  522  at elevated temperatures. The optical modulator may change its transparency for light of a certain wavelength range as a function of an electrical signal which can be applied through the electrical contacts and/or conductors  210  and  230 . The state in which the optical modulator element has increased transparency and lower absorption may be denoted by  512  and  522 .  511  and  521  may denote the state in which the optical modulator element has lower transparency and increased absorption. 
     At lower intensities of the directed light beam  310 , as it may occur during data communication and ambient light harvesting applications, the wavelength λ L    501  of the directed light beam  310  is within the range of wavelengths, which are modulated by the optical modulator element  120 . As such, the device may operate as a data communication and electrical energy generation device for ambient light. 
     With an increase of the intensity of the directed light beam  310  or after the operating temperature of the device crosses a threshold temperature, such as it may occur during short or prolonged periods of power beaming, the temperature of the device may increase, and the temperature-induced shift of the absorption properties shifts the absorption of light with wavelength λ L    501  from within the modulator at temperature T Data  to within the photovoltaic element at temperature T Beam . This means that when conditions of elevated intensities of a directed light beam  310  occur, the device may then harvest, in addition to ambient light  330 , also the directed light beam  310  of wavelength λ L    501 . 
     The temperature of the device in  FIG. 13  may also be stabilized by a heater or a cooler, which may be controlled and powered fully or in part by electrical energy generated by the photovoltaic element  110  and stored in the power harvesting and storage circuitry. The device in  FIG. 13  may comprise one, two, or more than two photovoltaic elements and/or multiple optical modulator elements. 
       FIG. 15  shows another illustrative aspect of the integrated optical communication and electrical energy generation device, comprising a retroreflector element  130 , an optical modulator element  120 , a first photovoltaic element  111 , a second photovoltaic element  112 , and an electrical switching element  160 . The electrical switching element may be adapted to allow a small signal at the electrical contact  260  to control the resistivity between its upper interface, which is connected to the photovoltaic element  112 , and its lower interface, which is connected to the optical modulator element  120 . Depending on the signal at the electrical contact  260 , the electrical switching element  160  may have a high resistance (i.e., electrically isolating) or a low resistance (i.e., electrically conductive). The electrical switching element  160  may comprise a bipolar junction transistor, a field-effect transistor, or otherwise suited semiconductor layers. An internal electrical connection  261  may connect the lower interface of the optical modulator element  120  and the upper interface of the first photovoltaic element  111 . Upon a signal at the electrical contact  260 , the electrical switching element  160  may be in a low resistance state or a high resistance state. Then, the combined voltage across the first photovoltaic element  111  and the second photovoltaic element  112  may be applied as an input signal to the optical modulator element  120  which may thereby change the transparency or the polarization of the optical modulator element  120 . 
     The voltage of the input signal to the optical modulator element  120  may be increased by adding more photovoltaic elements, such as three, four, or more photovoltaic elements, to the device structure in  FIG. 15  and by adapting the internal electrical connection  216  such that the combined voltage of said photovoltaic elements may be applied across the optical modulator element  120  when the electrical switching element  160  may be in a low resistance state. As such, the necessary input signal for the optical modulator element which may often require a voltage of more than 3V may be generated internally within the device, and only a small trigger signal may be needed and applied to the electrical contact  260  to change the transparency or polarization of the optical modulator element  120 . This may reduce external wiring and simplify circuitry for operation of the device. When a small signal at the electrical contact  260  leads the electrical switching element  160  to be in a high resistance state, the electrical energy generated by the photovoltaic elements  111  and  112  may be made available to a power harvesting and storage circuitry through the electrical contacts and/or conductors  210  and  224 . 
     The plurality of photovoltaic elements may be semi-transparent and may have optical absorption properties with similar bandgap energies or different bandgap energies. The device may be comprised by at least one, two, three or four photovoltaic elements. The order in which optically relevant elements and/or electrically relevant elements, such as electrical contacts or switching elements, are stacked, omitted, or arranged within the device may be changed in part or as a whole, including but not limited to, the placement of the electrical switching element  160  which may be incorporated into the internal electrical connection  261 . Optically relevant elements and/or electrically relevant elements may be mechanically and/or electrically connected through suited interface semiconductor layers, including but not limited to high or low doped semiconductor layers, tunnel diodes, Indium-Tin-Oxide (ITO) layers, fluorine doped tin oxide (FTO) layers, carbon nanotube layers, graphene layers, zinc oxide layers, a combination of such layers or otherwise suited electrically conductive or electrically insulating layers which are optically transparent in a defined wavelength range. 
     Although examples are described above, features and/or steps of those examples may be combined, divided, omitted, rearranged, revised, and/or augmented in any desired manner. Various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this description, though not expressly stated herein, and are intended to be within the spirit and scope of the disclosure. Accordingly, the foregoing description is by way of example only and is not limiting.