Laser systems for combined power beaming and free-space optical communication

Abstract

Laser systems and methods for combined power beaming (PB) and free-space optical communication (FSOC) are disclosed. The system includes a fiber laser with a gain fiber forming an optical cavity, the cavity containing a fiber gain medium; a pump source unit configured to inject pump light into the cavity to excite the gain medium and thereby generate a PB beam at a PB wavelength; and an output fiber coupled to the cavity. The system also includes a seed assembly with a seed laser, the seed assembly configured to generate an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength and direct the FSOC beam into the cavity, where the FSOC beam is combined with and amplified alongside the PB beam to generate an output beam, which is coupled into the output fiber and may then be launched into free space toward an optical receiver.

Description

LASER SYSTEMS FOR COMBINED POWER BEAMING AND FREE-SPACE OPTICAL COMMUNICATIONRELATED PATENT APPLICATION

[0001] The present application claims priority to U.S. Provisional Patent Application No. 63 / 560,446 filed on March 1, 2024, the disclosure of which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The technical field generally relates to laser systems and methods, and more particularly to laser systems and methods designed for combined power beaming and free-space optical communication (FSOC).BACKGROUND

[0003] Power beaming, a form of point-to-point wireless power transfer, employs directed beams of electromagnetic radiation, such as laser and microwave beams, to transmit electrical energy from a transmitter to a receiver, often over considerable distances (e.g., hundreds or even thousands of kilometers). Laser power beaming, in particular, offers the potential for high-intensity, low-divergence, and long-range transmission, with applications spanning various fields and industries, both on Earth and in space. In these systems, a laser transmitter emits laser radiation toward a photovoltaic (PV) receiver, which captures the laser radiation and converts it into electricity. Despite ongoing advancements, numerous challenges remain in the field of power beaming.SUMMARY

[0004] The present disclosure relates to laser systems configured for combined power beaming (PB) and free- space optical communication (FSOC) within a single beam.

[0005] In accordance with an aspect, there is provided a laser system for combined power beaming (PB) and free-space optical communication (FSOC), the laser system including: a fiber laser including: a gain fiber forming an optical cavity, the optical cavity containing a fiber gain medium; a pump source unit configured to inject pump light into the optical cavity to excite the fiber gain medium and thereby generate a PB beam at a PB wavelength through laser amplification; and an output fiber coupled to the optical cavity; and a seed assembly including a seed laser, the seed assembly configured to generate an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength and direct the FSOC beam into the optical cavity, where the FSOC beam is combined with and amplified alongsidethe PB beam to generate an output beam, wherein the output beam is coupled out of the optical cavity and into the output fiber.

[0006] In some embodiments, the optical cavity includes a first optical reflector and a second optical reflector positioned alongside the gain fiber, respectively upstream and downstream of the fiber gain medium. In some cases, the first and second optical reflectors include fiber Bragg gratings inscribed in the gain fiber.

[0007] In some embodiments, the gain fiber is a double-clad optical fiber.

[0008] In some embodiments, the fiber gain medium is doped with rare-earth ions. In some cases, the rare- earth ions include ytterbium, erbium, or neodymium.

[0009] In some embodiments, the seed laser is a laser diode.

[0010] In some embodiments, the seed assembly further includes an amplifier followed by an isolator disposed along the path of the FSOC beam between the seed laser and the fiber laser.

[0011] In some embodiments, the seed assembly includes multiple seed lasers, each generating a respective FSOC beam. In some cases, the seed assembly further includes a seed signal combiner unit configured to combine the multiple FSOC beams into a combined FSOC beam prior for injection into the optical cavity.

[0012] In some embodiments, the laser system further includes a pump and signal combiner unit configured to combine the pump light from the pump source unit with the FSOC beam from the seed assembly into a combined pump-FSOC beam prior for injection into the optical cavity.

[0013] In some embodiments, the PB wavelength and the FSOC wavelength are in the visible or near-infrared spectrum. In some cases, the PB wavelength and the FSOC wavelength are between 1000 nm and 1200 nm.

[0014] In some embodiments, the FSOC wavelength is shorter than the PB wavelength, while in other embodiments, the FSOC wavelength is longer than the PB wavelength.

[0015] In some embodiments, the FSOC wavelength is positioned in a higher-gain spectral region of the optical cavity compared to the PB wavelength.

[0016] In some embodiments, the laser system further includes a beamsplitter assembly configured to extract at least one back-propagating signal exiting from the upstream side of the optical cavity. In some cases, the laser system further includes at least one photodetector configured to detect the at least one extracted back- propagating signal. In some cases, the at least one back-propagating signal includes a portion of the PB beam. In some cases, the at least one back -propagating signal includes an external FSOC signal received through the output fiber.

[0017] In some embodiments, the encoded communication data carried by the FSOC beam includes network data, video data, voice data, pointing, acquisition, and tracking (PAT) signals, telemetry data, navigation data, sensor reading data, or any combination thereof.

[0018] In some embodiments, the output fiber terminates at an emission end from which the output beam is launched into free space.

[0019] In some embodiments, the laser system is configured for spacebome operation.

[0020] In accordance with another aspect, there is provided an optical wireless transmission system for combined power beaming (PB) and free-space optical communication (FSOC), the optical wireless transmission system including: a laser system as described herein, which is configured to emit an output beam containing both a PB component and an FSOC component, with the FSOC component carrying encoded communication data; and an optical receiver configured to capture the output beam, harvest power from the PB component, and process the communication data from the FSOC component.

[0021] In accordance with another aspect, there is provided a method for combined power beaming (PB) and free-space optical communication (FSOC), the method including: providing a fiber laser including a gain fiber forming an optical cavity, with the optical cavity containing a fiber gain medium; injecting pump light into the optical cavity to excite the fiber gain medium and thereby generate a PB beam at a PB wavelength through laser amplification; generating an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength; coupling the FSOC beam into the optical cavity for the FSOC beam to be combined with and amplified alongside the PB beam to generate an output beam; and allowing the output beam to exit the optical cavity.

[0022] In some embodiments, the method further includes: launching the output beam into free space toward an optical receiver, with the output beam containing a PB component and an FSOC component; capturing the output beam with the optical receiver; harvesting power from the PB component; and processing the communication data from the FSOC component.

[0023] In some embodiments, the gain fiber is a double-clad optical fiber.

[0024] In some embodiments, the fiber gain medium is doped with rare-earth ions. In some cases, the rare- earth ions include ytterbium, erbium, or neodymium.

[0025] In some embodiments, generating the FSOC beam includes generating multiple FSOC beams at distinct FSOC wavelengths.

[0026] In some embodiments, the method further includes combining the multiple FSOC beams into a combined FSOC beam, and injecting the combined FSOC beam into the optical cavity.

[0027] In some embodiments, the method further includes combining the pump light and the FSOC beam into a combined pump-FSOC beam, and injecting the combined pump-FSOC beam into the optical cavity.

[0028] In some embodiments, the PB wavelength and the FSOC wavelength are in the visible or near-infrared spectrum. In some cases, the PB wavelength and the FSOC wavelength are between 1000 nm and 1200 nm.

[0029] In some embodiments, the FSOC wavelength is shorter than the PB wavelength, while in other embodiments, the FSOC wavelength is longer than the PB wavelength.

[0030] In some embodiments, the FSOC wavelength is positioned in a higher-gain spectral region of the optical cavity compared to the PB wavelength.

[0031] In some embodiments, the method further includes extracting at least one back-propagating signal exiting from the upstream side of the optical cavity, and detecting the at least one back-propagating signal. In some cases, the at least one back-propagating signal includes a portion of the PB beam, and the method further includes monitoring the PB wavelength based on the detected portion. In some instances, the at least one back- propagating signal includes an external FSOC signal received through the output fiber, and the method further includes processing communication data carried by the detected external FSOC signal.

[0032] In some embodiments, the encoded communication data carried by the FSOC beam includes network data, video data, voice data, pointing, acquisition, and tracking (PAT) signal data, telemetry data, navigation data, sensor reading data, or any combination thereof.

[0033] In accordance with another aspect, there is provided a laser system including: a fiber laser including: an optical cavity containing a fiber gain medium and configured to generate a PB beam at a PB wavelength; and an output fiber coupled to the optical cavity; and a seed laser configured to generate an FSOC beam encoding communication data at an FSOC wavelength distinct from the PB wavelength and inject the FSOC beam within the optical cavity for the FSOC beam to be combined with the PB beam to generate an output beam, wherein the output beam is coupled out of the optical cavity and into the output fiber.

[0034] In some embodiments, the laser system includes an amplifier followed by an isolator (e.g., a Faradaytype isolator) interposed in the beam path of the FSOC beam between the seed laser and the fiber laser.

[0035] In some embodiments, the fiber laser is a diode-pumped fiber laser. In some embodiments, the fiber gain medium is a rare-earth-doped gain medium, for example, an ytterbium-doped gain medium. In some embodiments, the optical cavity of the fiber laser is formed by a first optical reflector coupled to the seed laser and a second optical reflector coupled to the output fiber. Both optical reflectors can be embodied by fiber Bragg gratings (FBGs), for example, a high-reflectivity (HR) FBG for the first optical reflector and output coupler (OC) FBG for the second optical reflector.

[0036] In some embodiments, the laser system is linked with an optical receiver to enable combined PB and FSOC within the output beam.

[0037] In some embodiments, the seed laser is a wavelength-tunable laser. In some embodiments, the seed laser is a semiconductor laser, such as a laser diode. In some embodiments, the seed laser is a modulated laser source configured to encode the communication data into the FSOC beam.

[0038] In some embodiments, the FSOC beam is utilized for pointing, acquisition, and tracking (PAT) to establish and maintain a stable and reliable communication link between the laser system and an optical receiver, which can facilitate optical power transfer by the PB beam.

[0039] In some embodiments, both the PB wavelength and the FSOC wavelength are encompassed within a waveband ranging from about 1000 nm to about 1200 nm. In some embodiments, the PB wavelength is longer than the FSOC wavelength. In other embodiments, the PB wavelength is shorter than the FSOC wavelength. In some embodiments, the FSOC wavelength lies in a higher-gain spectral region of the optical cavity than the PB wavelength. In other embodiments, it is the PB that lies in a higher-gain spectral region of the optical cavity.

[0040] In some embodiments, the seed laser is one of a plurality of seed lasers, wherein each seed laser is configured to generate its own FSOC beam at its own specific FSOC wavelength and to encode its own communication data. The FSOC wavelengths are distinct both from one another and from the PB wavelength.

[0041] In some embodiments, the laser system is spacebome. In other embodiments, the laser system is landbome, waterborne, or airborne.

[0042] In accordance with another aspect, there is provided a method for providing combined power beaming (PB) and free-space optical communication (FSOC) within a single laser beam. The method can include steps of: providing a laser system as disclosed herein; generating a PB beam at a PB wavelength within the optical cavity of the fiber laser; generating an FSOC beam with encoded communication data at an FSOC wavelength, distinct from the PB wavelength, using the seed laser; injecting the FSOC beam into the optical cavity; allowingthe FSOC beam to combine with the PB beam within the optical cavity to generate an output beam; coupling the output beam out of the cavity and into the output fiber; and launching the output beam from the output fiber into free space toward an optical receiver.

[0043] It should be noted that other steps may be performed prior, during, or after the steps described herein. The order of certain steps may also differ, with some steps potentially omitted, repeated, or combined, as appropriate. Additionally, some steps may be performed using various analysis and processing techniques, implemented in hardware, software, firmware, or any combination thereof.

[0044] Other objects, features, and advantages of the present disclosure will become more apparent from the following description of specific embodiments, provided by way of example only, with reference to the accompanying figures. While certain features presented in the foregoing summary or the following description may be described with reference to specific embodiments, they may also be combined unless otherwise specified.BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Fig. 1 is a schematic representation of a laser system configured for combined power beaming (PB) and free-space optical communication (FSOC), in accordance with one embodiment. Fig. 1A shows the absorption and emission cross-section spectra of the fiber gain medium, specifically for an ytterbium-doped core, with the PB wavelength and FSOC wavelength indicated.

[0046] Fig. 2 is a schematic representation of a laser system configured for combined PB and FSOC, in accordance with another embodiment. Fig. 2A shows the absorption and emission cross-section spectra of the fiber gain medium, specifically for an ytterbium-doped core, with the PB wavelength and multiple FSOC wavelengths indicated.

[0047] Fig. 3 is a schematic representation of a laser system configured for combined PB and FSOC, in accordance with another embodiment. Fig. 3 A shows the absorption and emission cross-section spectra of the fiber gain medium, specifically for an ytterbium-doped core, with the PB wavelength, multiple FSOC wavelengths, and external communication wavelength indicated.

[0048] Fig. 4 is a flow diagram of a method for combined PB and FSOC, in accordance with another embodiment.DETAILED DESCRIPTION

[0049] The present disclosure pertains to laser systems and methods capable of combining power beaming (PB) and free-space optical communication within the same beam.

[0050] In certain embodiments, the laser system includes a fiber laser and a seed assembly. The fiber laser features a gain fiber forming an optical cavity that contains a fiber gain medium and generates a PB beam at a PB wavelength. The fiber laser also includes an output fiber optically coupled to the cavity. The seed assembly, which incorporates a seed laser, is configured to generate an FSOC beam at an FSOC wavelength distinct from the PB wavelength and to direct or couple — whether directly or indirectly through an intervening component — the FSOC beam into the optical cavity. Within the cavity, the FSOC beam is combined with the PB beam, forming an output beam that is coupled into the output fiber.

[0051] In these embodiments, the fiber laser serves a dual role, acting both as a laser source (for the PB beam) and as an optical amplifier (for the externally generated FSOC beam). This approach enables the fiber laser to support efficient power and data transmission without significantly increasing system complexity. As a result, certain embodiments facilitate the generation of a high-power PB signal while simultaneously amplifying a lower-power FSOC signal carrying communication data. The combined PB and FSOC beam propagate through the output fiber and may be launched into free space toward an optical receiver.

[0052] The disclosed techniques are applicable across a wide range of fields and industries where enhanced optical wireless transmission is desired or necessary. Examples include space-based solar power; space and astronomical body exploration and mining; Earth-orbit applications; telecommunications; land, sea, and aerial transportation; climate and environmental monitoring; remote area power supply; post-disaster aid and recovery; and energy decarbonization. The present techniques can be implemented across various environments, including on Earth or within Earth’s atmosphere (encompassing ground, marine, and aerial settings), in space, as well as or on another astronomical body such as the Moon or another planet.

[0053] Various power beaming configurations can be employed depending on the application. Examples include Earth-to-Earth, space-to-Earth, Earth-to-space, space-to-space, Moon-to-Moon, space-to-Moon, and Moon-to-space transmission. In some embodiments, the laser system operates as a beam transmitter that, together with an optical receiver, forms an optical wireless transmission system. The transmitter and receiver may be separated from each other by a beam transmission distance ranging from about one or a few hundred meters to about one or a few hundred kilometers (e.g., from about 40 km to about 200 km), although distances outside these ranges may be used in other embodiments. Additionally, either or both of the transmitter and receiver may be configured for spacebome operation or, alternatively, for landbome, waterborne, or airborne operation on the Earth, the Moon, another planet (e.g., Mars), or another astronomical body. For example, in solar-based solar power applications, the laser transmitter may be positioned in space (e.g., on a satellite), while the optical receiver may be located on Earth (at a ground-based site).

[0054] In some embodiments, the laser system and the optical receiver are mounted on respective platforms, which may be stationary or mobile. The term “platform” broadly refers to landbome, waterborne, airborne, orspacebome device, vehicle, infrastructure, or equipment, whether manned or unmanned, on which the laser system and the optical receiver can be installed. Examples of platforms for space-based applications include launchers, landers, rovers, satellites, space probes, spaceplanes, space capsules, and space stations.

[0055] The optical receiver may be implemented as a photovoltaic (PV) receiver composed of an array of PV cells. The PV cells may be based on various PV cell technologies and may vary in size, shape, composition, configuration (e.g., fill factor, cell packing density, array geometry), electrical and thermal characteristics, and circuitry. Some PV cells may be designed for terrestrial use, while others may be configured for space or other extraterrestrial environments. Certain embodiments may use single -junction PV cells, while others may rely on multi-junction designs, such as vertical multi-junction (VMJ) cells. Multi-junction cells stack multiple layers of PV materials, each with distinct bandgap energies tailored for optoelectronic photon conversion across different spectral ranges.

[0056] Various PV materials may be used, including both direct-bandgap and indirect-bandgap semiconductor materials capable of absorbing light and converting it into electrical power. Examples include silicon (e.g., monocry stalline, polycrystalline, or amorphous), germanium, III-V semiconductors and related alloys (e.g., GaAs, InP, InGaAs, InGaP, GalnP, InAlGaAs, InGaAsP, GaAlInAsSb), thin-fdm PV materials (e.g., CdTe, CIGS), and organic PV materials. The principles and operation of PV cells in optical wireless transmission applications are well established and are described only as necessary to understand the present techniques.

[0057] Various aspects and implementations of the disclosed techniques are described below with reference to the accompanying figures. These figures are schematic and intended to illustrate certain components and features of the disclosed techniques, such that additional components and features that may enhance practical operation are not necessarily depicted.

[0058] Fig. 1 illustrates an embodiment of a laser system 100 designed for combined PB and FSOC. In this configuration, the laser system 100 functions as a beam transmitter that operates in conjunction with an optical receiver 102 to form an optical wireless transmission system 104. The optical receiver 102 may be implemented as a PV cell array.

[0059] The laser system 100 includes a fiber laser 106 and a seed assembly 108. The fiber laser 106 generates a PB beam 110 at a PB wavelength, while the seed assembly 108 generates an FSOC beam 112 carrying communication data at an FSOC wavelength distinct from the PB wavelength. The FSOC beam 112 is coupled into the fiber laser 106, where it is combined with and amplified alongside the PB beam 110, forming an output beam 114. This output beam 114 is then launched into free space toward the optical receiver 102, enabling simultaneous power transfer and data communication within the optical wireless transmission system 104.

[0060] The fiber laser 106 may be a high-power, rare-earth-doped, continuous-wave, laser-diode-pumped, double-clad fiber laser, though other configurations are possible. The principles, instrumentation, and operation of fiber lasers, including their use in high-power applications such as PB, are well established and are described only as necessary to understand the present techniques. In the illustrated embodiment, the fiber laser 106 includes a pump source unit 116, a pump and signal combiner unit 118, a gain fiber 120 forming an optical cavity 122 that contains a fiber gain medium 124, and an output fiber 126 with an emission end 128. The fiber gain medium 124 is the active (e.g., rare-earth doped) segment of the gain fiber 120 that provides laser amplification within the optical cavity 122. The gain fiber 120 may have various configurations. In some embodiments, the gain fiber 120 is a double-clad fiber, where pump light is injected into the inner cladding while the laser signal is guided through the core, with the fiber gain medium 124 consisting of doped core segment. The configuration of the fiber laser 106 depicted in Fig. 1 is presented for illustrative purposes only, and various other configurations are possible.

[0061] The pump source unit 116 may include one or more individual pump sources, depending on power and application requirements. Some embodiments use a single pump source, while others employ multiple pump sources in an array. Various types of pump lasers may be used, including diode lasers and fiber lasers. The pump wavelength depends on the fiber gain medium 124. For example, ytterbium-doped fibers often use 980- nm pump sources to generate laser light in the 1000-1100 nm range.

[0062] The pump and signal combiner unit 118 is configured to combine the pump signals 130 from the pump source unit 116 with the FSOC beam 112 from the seed assembly 108 into a combined pump-FSOC beam 132 and inject it into the optical cavity 122. Depending on system requirements, various fiber-based configurations of the pump and signal combiner unit 118 may be employed, such as wavelength-division multiplexers based on fused fiber bundles. In some embodiments, the laser system 100 may omit the pump and signal combiner unit 118, with the FSOC beam 112 instead being delivered into the optical cavity 122 separately from the pump signals 130.

[0063] The optical cavity 122 is defined by a first optical reflector 134 and a second optical reflector 136. The first optical reflector 134, coupled to the pump and signal combiner unit 118, may be a high-reflectivity (HR) fiber Bragg grating (FBG) that reflects laser light back into the fiber gain medium 124. The second optical reflector 136, coupled to the output fiber 126, may be an output coupler (OC) FBG partially reflecting light to sustain laser operation while allowing a portion to exit the optical cavity 122 as the output beam 114. FBGs may be directly inscribed in the core of the gain fiber 120 to function as reflective elements, though non-FBG- based optical reflectors may also be used in alternative designs.

[0064] Depending on the fiber gain medium 124, the fiber laser 106 can operate across a broad spectral range, including the visible region (400-700 nm) and the near-infrared region (700-2500 nm) of the electromagneticspectrum. Common fiber gain media include glasses or crystals doped with laser-active ions, including ions of rare-earth elements such as ytterbium, erbium, and neodymium, with ytterbium-doped fibers operating in the 1000-1100 nm range being particularly well suited for high-power PB applications.

[0065] In some embodiments, the laser system 100 may include a cladding light stripper 138 positioned between the optical cavity 122 and the output fiber 126. The cladding light stripper 138 is configured to remove unwanted cladding light from the output beam 114, such as residual pump power, to enhance beam quality, improve efficiency, and protect downstream optical components.

[0066] The seed assembly 108 includes a seed laser 140, which can be any laser source or combination of sources capable of generating the FSOC beam 112 at an FSOC wavelength distinct from the PB wavelength while remaining within the operational range of the fiber laser 106 for efficient coupling into the optical cavity 122. Examples for the seed laser 140 include semiconductor lasers (e.g., laser diodes), distributed- feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers, external cavity lasers (ECLs), and verticalcavity surface-emitting lasers (VCSELs). In some embodiments, the seed laser 140 may be wavelength tunable. Depending on the application, the seed assembly 108 may encode communication data into the FSOC beam 112 by direct modulation of the seed laser 140 or through a separate modulator downstream of the seed laser 140.

[0067] To manage signal strength and prevent back-reflections that could interfere with the seed laser 140, the seed assembly 108 may include an optical amplifier 142 followed by an optical isolator 144, such as a Faraday isolator, positioned along the path of the FSOC beam 112 between the seed laser 140 and the fiber laser 106.

[0068] Depending on system configuration, the output fiber 126 may be a downstream continuation or extension of the gain fiber 120, or it may be a separate fiber segment, such as a passive fiber connected downstream. The emission end 128 of the output fiber 126 may be provided with a fiber endcap or another type of termination designed to control characteristics of the output beam 114 emitted by the laser system 100. This termination can perform various functions, including collimation, beam steering, mode filtering, mode matching, beam quality enhancement, and damage prevention.

[0069] The FSOC beam 112 may carry various types of communication data, including network data, voice data, video data, or any digital information that can be converted into an optical signal. In some embodiments, the communication data may include pointing, acquisition, and tracking (PAT) signals, which help stabilize the optical communication link between the laser system 100 and the optical receiver 102, thereby improving optical power transfer by the PB beam 110. Additional communication data may include telemetry data, navigation data, or sensor reading data from devices such as high-resolution cameras or spectrometers.

[0070] The optical receiver 102 is configured to capture the output beam 114 emitted from the laser system 100 and process it to handle both power harvesting and communication functions. Specifically, theoptical receiver 102 is designed to collect power from the PB component of the output beam 114 while decoding communication data from its FSOC component. The optical receiver 102 can be implemented in various configurations to enable simultaneous power harvesting and data processing, depending on system requirements.

[0071] In the illustrated embodiment, both the PB wavelength zm and the FSOC wavelength AFSOC are between 1000 nm and 1200 nm, corresponding to the operational range of the fiber laser 106, as shown in Fig. 1A. In this case, the FSOC wavelength is shorter than the PB wavelength and positioned in a higher-gain spectral region of the optical cavity 122. However, other configurations are possible, including scenarios where the FSOC wavelength is longer than the PB wavelength, positioned in a lower-gain spectral region, or both.

[0072] Fig. 2 illustrates another embodiment of a laser system 100, designed for combined PB and FSOC within the same beam. This embodiment shares several features with the system depicted in Fig. 1, which will not be described again. In the configuration shown in Fig. 2, the seed assembly 108 includes multiple seed lasers 140, each configured to generate a separate FSOC beam 112 carrying respective communication data at a distinct FSOC wavelength. In some embodiments, the number of seed lasers may range from two to ten, though a greater number is possible in other designs. Additionally, the laser system 100 may include a seed signal combiner unit 146, such as a wavelength-division multiplexer or another type of optical coupler, configured to combine the multiple FSOC beams 112 into a combined FSOC beam 148 before amplification. In the illustrated embodiment, the multiple FSOC wavelengths are distinct from both one another and the PB wavelength. As depicted in Fig. 2A, the FSOC wavelengths AFSOC may be closely spaced compared to their spectral separation from the PB wavelength ZI>I;. though this is not a requirement. Depending on the application, the FSOC wavelengths may be positioned entirely on either side of the PB wavelength or distributed on both sides.

[0073] Fig. 3 illustrates another embodiment of a laser system 100, designed for combined PB and FSOC within the same beam. This embodiment shares several features with the systems depicted in Figs. 1 and 2, which will not be described again. In this configuration, the laser system 100 includes components for extracting and detecting back-propagating signals exiting from the upstream side of the optical cavity 122. For example, these signals may include a first back-propagating signal 150, representing a portion of the PB beam 110 that inadvertently escapes through the first optical reflector 134 of the optical cavity 122, and a second back-propagating signal 152, corresponding to an external FSOC signal captured by the laser system 100 and then propagating upstream through the output fiber 126 and the optical cavity 122. The external FSOC signal, which carries encoded communication data, may originate from the optical receiver 102 or another source.

[0074] To extract these signals 150, 152, the laser system 100 in Fig. 3 incorporates a beamsplitter assembly 154 positioned upstream of the pump and signal combiner unit 118, along the path of the combined FSOC beam 148. The beamsplitter assembly 154 includes a first beamsplitter 156 and a second beamsplitter 158. The first beamsplitter 156 is configured to extract the first back-propagating signal 150 and direct it onto a first photodetector 160 for internal monitoring of the PB wavelength. The second beamsplitter 158 is configured to extract the second back-propagating signal 152 and direct it onto a second photodetector 162 for optoelectronic conversion and subsequent processing of the external communication data.

[0075] Various types of spectral beamsplitters, such as demultiplexers or optical taps, can be used depending on system requirements. While the illustrated embodiment uses two distinct beamsplitters 156, 158, the extraction of both back-propagating signals 150, 152 could be performed in a single step. Additionally, the laser system 100 shown in Fig. 3 extracts two back-propagating signals 150, 152, but other configurations could extract more, depending on application requirements. In the illustrated embodiment, the first extracted signal 150 is internal, while the other 152 is external. However, the system 100 can be adapted to extract any number of internal and external back-propagating signals as needed. The external communication wavelength of the second extracted signal 152 is positioned between the FSOC wavelengths and the PB wavelength, as shown in Fig. 3A. However, this specific placement is not a requirement, and the external communication wavelength 2EXT could be located anywhere relative to the FSOC and PB wavelengths AFSOC, 2PB, depending on system designs and operational constraints.

[0076] Fig. 4 depicts a flow diagram of a method 200 for combined PB and FSOC. The method 200 may be implemented in a laser system 100 or optical wireless transmission system 104 as described above, or in another suitable system. The method 200 includes a step 202 of providing a fiber laser including a gain fiber forming an optical cavity, with the optical cavity containing a fiber gain medium, and a step 204 of injecting pump light into the optical cavity to excite the fiber gain medium and thereby generate a PB beam at a PB wavelength through laser amplification. The method 200 also includes a step 206 of generating an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength, followed by a step 208 of coupling the FSOC beam into the optical cavity for the FSOC beam to be combined with and amplified alongside the PB beam to generate an output beam, and a step 210 of allowing the output beam to exit the optical cavity.

[0077] In certain embodiments, the method 200 further include steps of launching the output beam into free space toward an optical receiver, with the output beam containing a PB component and an FSOC component; capturing the output beam with the optical receiver; harvesting power from the PB component; and processing the communication data from the FSOC component.

[0078] In certain embodiments, the method 200 may include a step of extracting at least one back-propagating signal exiting from the upstream side of the optical cavity, followed by a step of detecting the at least one back- propagating signal. In some instances, the at least one back-propagating signal may include a portion of the PB beam and / or an external FSOC signal received through the output fiber. In such cases, method 200 may further include monitoring the PB wavelength based on the detected portion and / or processing communication data carried by the detected external FSOC signal.

[0079] It is noted that various aspects and features described above with reference to system embodiments are also applicable to method embodiments.

[0080] Throughout the present description, similar features in the drawings have been given similar reference numerals. To avoid cluttering certain figures, some elements may not be indicated if previously identified in a preceding figure. Elements in drawings are not necessarily depicted to scale, with emphasis placed on clearly illustrating elements and structures of the disclosed embodiments. Positional descriptors indicating the location or orientation of one element relative to another are used for ease and clarity of description. Unless indicated otherwise, these descriptors should be understood in the context of the figures and should not be considered limiting. Such spatially relative terms are intended to encompass different orientations in use or operation of the disclosed embodiments, in addition to orientations exemplified in the figures. Furthermore, when a first element is referred to as “on”, “above”, “below”, “over”, or “under” a second element, the first element can be directly or indirectly on, above, below, over, or under the second element, such that one or multiple intervening elements may be disposed between the first element and the second element.

[0081] The terms “a”, “an”, and “one” are defined herein to mean “at least one”, and do not exclude a plural number of elements unless stated otherwise.

[0082] The term “or” is defined herein to mean “and / or” unless stated otherwise.

[0083] Terms such as “substantially”, “generally”, and “about”, when modifying a value, condition, or characteristic of a feature of an exemplary embodiment, should be understood to mean that the value, condition, or characteristic is defined within tolerances acceptable for the proper operation of the exemplary embodiment for its intended application or that fall within an acceptable range of experimental error. In particular, the term “about” generally refers to a range of numbers that one skilled in the art would consider equivalent to the stated value (e.g., having the same or nearly the same function or result). In some instances, the term “about” means a variation of ±10% of the stated value. It is noted that all numerical values used herein are assumed to be modified by the term “about” unless stated otherwise.

[0084] The term “based on” as used herein is intended to mean “based at least in part on”, whether directly or indirectly, and to encompass both “based solely on” and “based partly on”. In particular, the term “based on”may also be understood to mean “depending on”, “representative of’, “indicative of’, “associated with”, “relating to”, and the like.

[0085] The terms “match”, “matching”, and “matched” refer herein to a condition in which two or more elements are either the same or within some predetermined tolerance of one another. These terms are meant to encompass not only “exactly” or “identically” matching the two or more elements, but also “substantially”, “approximately”, or “subjectively” matching the elements, as well as providing a higher or best match among multiple matching possibilities.

[0086] The terms “connected” and “coupled”, along with their variants and derivatives, refer herein to any connection or coupling, either direct or indirect, between two or more elements, unless stated otherwise. For example, the connection or coupling between the elements may be mechanical, optical, electrical, magnetic, thermal, chemical, logical, fluidic, operational, or any combination thereof.

[0087] The term “concurrently” refers herein to the simultaneous or overlapping occurrence of two or more processes. The term “concurrently” does not necessarily imply complete synchronicity but encompasses various scenarios. These scenarios include the simultaneous occurrence of two processes; a first process that both begins and ends during the duration of a second process; and a first process that starts during the duration of a second process but ends after the second process is completed.

[0088] The term “measured” when referring to a quantity or parameter is intended to mean that the quantity or parameter can be measured either directly or indirectly. In the case of indirect measurement, the quantity or parameter can be derived, retrieved, inferred, or otherwise determined from directly measured data.

[0089] The terms “light” and “optical”, along with their variants and derivatives, encompass radiation across any appropriate region of the electromagnetic spectrum. This includes not only visible light, but also extends to invisible regions such as the microwave (MW), terahertz (THz), infrared (IR), and ultraviolet (UV) spectral bands. For example, in some embodiments, the present techniques may be implemented with optical signals with a bandwidth lying within a wavelength band ranging from about 400 nm to about 2500 nm. However, this wavelength range is provided for illustrative purposes only, and the present techniques may operate beyond this range. It is noted that all the references to wavelength herein may be adapted to be expressed in terms as a function of frequency, wave number, energy, or the like.

[0090] The various laser sources described herein can be any suitable device or combination of devices capable of generating laser beams with suitable beam characteristics for implementing the present techniques. Examples of laser sources that can be used for optical wireless transmission applications include solid-state lasers, including bulk crystal lasers and fiber lasers; semiconductor lasers, including laser diodes; gas lasers, including carbon dioxide lasers and chemical oxygen-iodine lasers; and dye lasers. Depending on the specific application,the laser sources may be operated in a continuous-wave or pulsed regime and may or may not be modulated. The selection of the laser sources may be based on various factors, including the operation wavelength; the beam irradiance; the spatial, temporal, and spectral beam profiles; the beam quality and divergence; the degree of coherence; the compactness, reliability, and ruggedness; and for pulsed light sources, pulse characteristics such as peak power, repetition rate, duration, and temporal shape. The principles, instrumentation, and operation of laser sources used in conventional optical wireless transmission applications, including power beaming, are well established and are described only as necessary to understand the present techniques.

[0091] Numerous modifications could be made to the embodiments described above without departing from the scope of the appended claims.

Claims

CLAIMS1. A laser system for combined power beaming (PB) and free-space optical communication (FSOC), the laser system comprising: a fiber laser comprising: a gain fiber forming an optical cavity, the optical cavity containing a fiber gain medium; a pump source unit configured to inject pump light into the optical cavity to excite the fiber gain medium and thereby generate a PB beam at a PB wavelength through laser amplification; and an output fiber coupled to the optical cavity; and a seed assembly comprising a seed laser, the seed assembly configured to generate an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength and direct the FSOC beam into the optical cavity, where the FSOC beam is combined with and amplified alongside the PB beam to generate an output beam, wherein the output beam is coupled out of the optical cavity and into the output fiber.

2. The laser system of claim 1, wherein the optical cavity comprises a first optical reflector and a second optical reflector positioned alongside the gain fiber, respectively upstream and downstream of the fiber gain medium.

3. The laser system of claim 2, wherein the first and second optical reflectors comprise fiber Bragg gratings inscribed in the gain fiber.

4. The laser system of any one of claims 1 to 3, wherein the gain fiber is a double-clad optical fiber.

5. The laser system of any one of claims 1 to 4, wherein the fiber gain medium is doped with rare-earth ions.

6. The laser system of claim 5, wherein the rare-earth ions comprise ytterbium, erbium, or neodymium.

7. The laser system of any one of claims 1 to 6, wherein the seed laser is a laser diode.

8. The laser system of any one of claims 1 to 7, wherein the seed assembly further comprises an amplifier followed by an isolator disposed along the path of the FSOC beam between the seed laser and the fiber laser.

9. The laser system of any one of claims 1 to 8, wherein the seed assembly comprises multiple seed lasers, each generating a respective FSOC beam.

10. The laser system claim 9, wherein the seed assembly further comprises a seed signal combiner unit configured to combine the multiple FSOC beams into a combined FSOC beam prior for injection into the optical cavity.11 . The laser system any one of claims 1 to 10, further comprising a pump and signal combiner unit configured to combine the pump light from the pump source unit with the FSOC beam from the seed assembly into a combined pump-FSOC beam prior for injection into the optical cavity.

12. The laser system of any one of claims 1 to 11, wherein the PB wavelength and the FSOC wavelength are in the visible or near-infrared spectrum.

13. The laser system of claim 12, wherein the PB wavelength and the FSOC wavelength are between 1000 nm and 1200 nm.

14. The laser system of any one of claims 1 to 13, wherein the FSOC wavelength is shorter than the PB wavelength.

15. The laser system of any one of claims 1 to 13, wherein the FSOC wavelength is longer than the PB wavelength.

16. The laser system of any one of claims 1 to 15, wherein the FSOC wavelength is positioned in a higher-gain spectral region of the optical cavity compared to the PB wavelength.

17. The laser system of any one of claims 1 to 16, further comprising a beamsplitter assembly configured to extract at least one back -propagating signal exiting from the upstream side of the optical cavity.

18. The laser system of claim 17, further comprising at least one photodetector configured to detect the at least one extracted back-propagating signal.

19. The laser system of claim 17 or 18, wherein the at least one back-propagating signal comprises a portion of the PB beam.

20. The laser system of any one of claims 17 to 19, wherein the at least one back-propagating signal comprises an external FSOC signal received through the output fiber.21 . The laser system of any one of claims 1 to 20, wherein the encoded communication data carried by the FSOC beam comprises network data, video data, voice data, pointing, acquisition, and tracking (PAT) signals, telemetry data, navigation data, sensor reading data, or any combination thereof.

22. The laser system of any one of claims 1 to 21, wherein the output fiber terminates at an emission end from which the output beam is launched into free space.

23. The laser system of any one of claims 1 to 22, wherein the laser system is configured for spacebome operation.

24. An optical wireless transmission system for combined power beaming (PB) and free-space optical communication (FSOC), the optical wireless transmission system comprising: a laser system configured to emit an output beam containing both a PB component and an FSOC component, with the FSOC component carrying encoded communication data, wherein the laser system is in accordance with any one of claims 1 to 23; and an optical receiver configured to capture the output beam, harvest power from the PB component, and process the communication data from the FSOC component.

25. A method for combined power beaming (PB) and free-space optical communication (FSOC), the method comprising: providing a fiber laser comprising a gain fiber forming an optical cavity, with the optical cavity containing a fiber gain medium; injecting pump light into the optical cavity to excite the fiber gain medium and thereby generate a PB beam at a PB wavelength through laser amplification; generating an FSOC beam with encoded communication data at an FSOC wavelength distinct from the PB wavelength; coupling the FSOC beam into the optical cavity for the FSOC beam to be combined with and amplified alongside the PB beam to generate an output beam; and allowing the output beam to exit the optical cavity.

26. The method of claim 25, further comprising: launching the output beam into free space toward an optical receiver, with the output beam containing a PB component and an FSOC component; capturing the output beam with the optical receiver; harvesting power from the PB component; and processing the communication data from the FSOC component.

27. The method of claim 25 or 26, wherein the gain fiber is a double-clad optical fiber.

28. The method of any one of claims 25 to 27, wherein the fiber gain medium is doped with rare-earth ions.

29. The method of claim 28, wherein the rare-earth ions comprise ytterbium, erbium, or neodymium.

30. The method of any one of claims 25 to 29, wherein generating the FSOC beam comprises generating multiple FSOC beams at distinct FSOC wavelengths.31 . The method of claim 30, further comprising: combining the multiple FSOC beams into a combined FSOC beam; andinjecting the combined FSOC beam into the optical cavity.

32. The method of any one of claims 25 to 31, further comprising: combining the pump light and the FSOC beam into a combined pump-FSOC beam; and injecting the combined pump-FSOC beam into the optical cavity.

33. The method of any one of claims 25 to 32, wherein the PB wavelength and the FSOC wavelength are in the visible or near-infrared spectrum.

34. The method of claim 33, wherein the PB wavelength and the FSOC wavelength are between 1000 nm and 1200 nm.

35. The method of any one of claims 25 to 34, wherein the FSOC wavelength is shorter than the PB wavelength.

36. The method of any one of claims 25 to 34, wherein the FSOC wavelength is longer than the PB wavelength.

37. The method of any one of claims 25 to 36, wherein the FSOC wavelength is positioned in a higher-gain spectral region of the optical cavity compared to the PB wavelength.

38. The method of any one of claims 25 to 37, further comprising: extracting at least one back-propagating signal exiting from the upstream side of the optical cavity; and detecting the at least one back-propagating signal.

39. The method of claim 38, wherein the at least one back-propagating signal comprises a portion of the PB beam, the method further comprising monitoring the PB wavelength based on the detected portion.

40. The method of claim 38 or 39, wherein the at least one back-propagating signal comprises an external FSOC signal received through the output fiber, the method further comprising processing communication data carried by the detected external FSOC signal.41 . The method of any one of claims 25 to 40, wherein the encoded communication data carried by the FSOC beam comprises network data, video data, voice data, pointing, acquisition, and tracking (PAT) signal data, telemetry data, navigation data, sensor reading data, or any combination thereof.

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