Communicating information using photonic crystal transceivers

Abstract

In a general aspect, a communication system comprises a first station and a second station. Each station includes a transceiver and a control subsystem. The transceiver includes having one or more photonic crystal masers and one or more photonic crystal receivers. The control subsystem includes one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers. The control subsystem also includes modulation electronics in communication with the one or more lasers and configured to control one or more characteristics of a first input optical signal received by each photonic crystal maser. The control subsystem additionally includes demodulation electronics in communication with the one or more lasers and configured to control one or more characteristics of a second input optical signal received by each photonic crystal receiver.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 667,244, filed February 8, 2022, the disclosure of which is incorporated herein by reference.

[0002] The following description relates to communicating information using photonic crystal transceivers. [Background technology]

[0003] A communication system may include stations that transmit and receive wireless signals to move information between the stations. During propagation, the wireless signals may be emitted outward or, alternatively, may be focused into a beam along a path. The beam may enable two or more stations of the communication system to communicate in a point-to-point mode. Because beams are less prone to interception, such point-to-point communication may enable secure transmission of information. A beam may also require less power for its propagation between two stations than a broad, spherical emission. Lasers have traditionally been utilized for point-to-point communication due to their beam-like emission. However, laser beams are susceptible to scattering by common atmospheric phenomena such as clouds, rain, fog, snow, dust, etc. This scattering can attenuate the intensity of the laser beam and reduce its ability to deliver a signal between two stations. [Brief explanation of the drawings]

[0004] [Figure 1A] 1 is a schematic diagram of an exemplary communication system including a satellite and a submarine partially submerged in a body of water. [Figure 1B] 1 is a schematic diagram of an exemplary communication system including a satellite and multiple vessels deployed on a body of water. [Figure 1C] 1 is a schematic diagram of an exemplary communication system including a pair of satellites. [Figure 2A]1 is a schematic diagram of an exemplary communication system including a first station and a second station. [Figure 2B] 2B is a schematic diagram of the exemplary communication system of FIG. 2A, but in which satellites serve as relay stations for the exemplary communication system. [Figure 3A] 1 is a schematic perspective view of an exemplary photonic crystal maser including a dielectric body bonded to two optical windows. [Figure 3B] 1 is a schematic perspective view of an exemplary photonic crystal receiver for detecting a beam of radio frequency (RF) electromagnetic radiation. [Figure 4] 1 is a block diagram of an exemplary station in a point-to-point communication system. [Figure 5] 5 is a schematic diagram of an exemplary application layer utilized by a data processing subsystem to handle Rx data flow to and Tx data flow from the exemplary station of FIG. 4. [Figure 6] 1 is a schematic diagram of an exemplary message format including exemplary synchronization, signaling, and traffic packets. [Figure 7] FIG. 1 is a schematic diagram of an exemplary process for converting an input beam of RF electromagnetic radiation into time series data. DETAILED DESCRIPTION OF THE INVENTION

[0005] In a general aspect, a communication system includes a first station and a second station. The first station includes a photonic crystal maser, a laser subsystem, and a tracking subsystem. The photonic crystal maser includes a photonic crystal structure formed from a dielectric material. The photonic crystal structure has an array of cavities and an elongated slot disposed within a defect region of the array of cavities. The photonic crystal maser also includes a vapor disposed within the elongated slot and operable to emit targeted RF electromagnetic radiation in response to receiving an optical signal. The array of cavities and the elongated slot define a waveguide configured to shape the targeted RF electromagnetic radiation into a beam upon emission. The beam of targeted RF electromagnetic radiation represents information to be transmitted to a second station of the communication system. The laser subsystem includes a pump laser optically coupled to the elongated slot and configured to generate an optical signal. The laser subsystem also includes signal processing electronics in communication with the pump laser and configured to control one or more characteristics of the optical signal. The one or more characteristics of the optical signal include at least one of the intensity, phase, or frequency of the optical signal. The tracking subsystem is configured to control the orientation of the photonic crystal maser to direct the beam of targeted RF electromagnetic radiation toward a targeted location.

[0006] The second station of the communication system includes a receiver configured to couple to the beam of target RF electromagnetic radiation. In some variations, the receiver is a photonic crystal receiver including a second photonic crystal structure formed from a dielectric material. The second photonic crystal structure has a second array of cavities and a second elongated slot disposed within a defect region of the second array of cavities. The photonic crystal receiver includes an antenna structure configured to couple the beam of target RF electromagnetic radiation to a second waveguide defined by the second array of cavities and the second elongated slot. The second waveguide is configured to concentrate the combined beam within the second elongated slot. The photonic crystal receiver additionally includes a second vapor disposed within the second elongated slot. In these variations, the second station includes a second laser subsystem having one or more input lasers optically coupled to the second elongated slot and configured to provide an input optical signal thereto. The input optical signal is adapted to interact with one or more electronic transitions of the second vapor. The second station also includes an optical subsystem configured to generate spectroscopic data based on the output optical signal from the second vapor. The spectroscopic data represents one or more characteristics of the beam of target RF electromagnetic radiation. The second station additionally includes a data processing subsystem configured to generate time series data based on the spectroscopic data over time. The time series data represents information transmitted from the first station.

[0007] In some embodiments, the communication system is a point-to-point communication system. In these embodiments, the communication system may use a beam of RF electromagnetic radiation as a directional means to communicate information from a first station to a second station (or vice versa). Point-to-point communication using a narrow bandwidth may be useful for several reasons. For example, point-to-point directional communication may enable jamming-resistant communication. Point-to-point communication may also be secure because an adversary would need to intercept the beam to listen for a message. Moreover, point-to-point communication may allow for better utilization of the frequency spectrum because directional beams do not generate as much interference as traditional radio frequency (RF) systems.

[0008] In certain cases, beams of RF electromagnetic radiation used by communication systems can offer advantages over systems that use light beams emitted by lasers. Lasers in the visible and near-infrared frequency ranges have been the primary workhorse of point-to-point communications because lasers produce highly directional emissions and can be relatively small when compared to standard RF systems. However, a major drawback of laser-based systems is that they do not perform well in common atmospheric conditions such as rain, snow, dust, smoke, fog, and cloud cover (when transmission through clouds is required). In particular, atmospheric particles (e.g., raindrops) are larger than the laser wavelength and can therefore scatter beams of visible and near-infrared light.

[0009] On the other hand, radio frequency (RF) electromagnetic radiation can penetrate rain, snow, dust, fog, and cloud cover. RF electromagnetic radiation is not commonly used for point-to-point communications because the corresponding RF transmitters have poor directionality. For example, RF antennas typically emit beams with angular spreads of more than a few degrees. In contrast, RF masers can emit with high directionality. However, these masers are bulky and operate only at a few frequencies, such as those associated with molecular transitions that are conductive for maser operation (e.g., ammonia). To create an RF point-to-point directional communications system, a compact maser operating at the relevant frequencies is required. A photonic crystal maser in a communications system is such a device. A photonic crystal maser, which may be a Rydberg atomic maser, can be paired with a photonic crystal receiver (or, for example, a Rydberg atomic receiver) to form a transceiver based on the same technology. The photonic crystal maser can serve as the transmitting component (Tx) of a transceiver, while the photonic crystal receiver can serve as the receiving component (Rx). In many embodiments, both the photonic crystal maser and the photonic crystal receiver are all-dielectric devices coupled to signal processing and laser systems for control. However, in some embodiments, the receiver component (Rx) may be a conventional receiver (e.g., an antenna).

[0010] Directing the photonic crystal maser from the transceiver to the receiver on the second station can be facilitated by a tracking system on one or both of the first station and the second station. For example, the first station may be a satellite station and the second station may be a ground station. The tracking system on the first station may operate to direct the photonic crystal maser to the ground station. As another example, the first station may be a lunar station and the second station may be an earth station. In this example, the first station and the second station may each include one or more photonic crystal masers and one or more photonic crystal receivers that define a transceiver. The tracking systems of the first station and the second station may be operable to direct the transceiver of the first station to the second station, and vice versa.

[0011] Many different systems are possible for encoding communications between a first station and a second station. For example, the intensity of a beam of RF electromagnetic radiation can be modulated at the first station, the second station, or both. On-off keying and pulse-position modulation are two possible forms of intensity modulation that can be used. Phase-shift keying, differential phase-shift keying, frequency-shift keying, or polarization-shift keying can also be used. These latter forms can be implemented when the photonic crystal maser is injection-seeded with a stable RF signal, such as from a reference RF oscillator. The injection seeding (or locking) fixes the phase and frequency of the maser output and, in some variations, links it to a stable clock signal. To use polarization-shift keying, two orthogonal photonic crystal masers with different polarizations can be used along with two polarization-sensitive receivers (e.g., two orthogonal photonic crystal receivers). The phase and frequency (or, more generally, the phase or angle) can be determined by heterodyne measurements using synchronized photonic crystal masers in each transceiver.

[0012] The first station and the second station may be part of or define a point-to-point communication system. Point-to-point communication may be inherently more secure and may cause less interference than conventional communication systems. Spoofing is also more difficult in point-to-point communication systems because it is more difficult to direct radiation from a spoofing transmitter to a receiver aimed at the target transmitter. Point-to-point communication may also enable stealth applications. For stealth applications, the power level of the beam of RF electromagnetic radiation may be lower than the power level required for omnidirectional radiation (e.g., spherical broadcast radiation). Size, weight, and power (SWaP) may also be reduced compared to conventional RF systems. Antennas in point-to-point communication systems may be relatively small, and communication channels may be located over a wide range of frequencies. Moreover, point-to-point communication systems may operate at multiple frequencies.

[0013] Lasers have traditionally been utilized in satellite communications and other point-to-point systems due to their availability. Lasers are highly directional and can be relatively small. However, compared to light, radio frequency radiation (e.g., 1 MHz to 300 GHz) offers advantages for communications. This is because radio frequency radiation can better penetrate rain, snow, dust, cloud cover, and fog, especially in some radio frequency bands. However, radio frequency systems tend to be poorly directional, and therefore are not typically used for point-to-point communications. In many cases, radio frequency antennas emit over a spread of several degrees or more. Radio frequency masers, due to the highly directional nature of their emissions, can be used to reduce this spread. However, today, radio frequency masers are bulky and can only function at an extremely limited number of frequencies. Therefore, to create a practical radio frequency point-to-point communications system with laser-like directionality, a directional radio frequency transceiver can be constructed by pairing a small maser operating at the relevant frequency with a receiver.

[0014] In many embodiments, the photonic crystal masers described herein are configured to emit directional RF electromagnetic radiation, such as a beam of RF electromagnetic radiation. Such masers can be used in stations of point-to-point communication systems. Photonic crystal masers can operate using Rydberg atom-based sensing technology, which detects electromagnetic radiation using quantum interference of internal energy states, including the Rydberg state of an atom. This operating process is self-calibrating, sensitive, electromagnetically transparent, and subwavelength. Other advantages are possible. Rydberg atom-based sensing technology can operate over a frequency range from MHz to THz and can also be used to create masers that function for virtually any Rydberg atomic transition. To do so, the maser can use a photonic crystal cavity to facilitate masing for the transition. Photonic crystal cavities can also be used to create ultrasensitive receivers (or photonic crystal receivers). This receiver can be ultrasensitive to both polarization and RF electric fields. Photonic crystal receivers can also be self-calibrating and all-dielectric.

[0015] A photonic crystal maser can be combined with a receiver (e.g., a conventional receiver or a photonic crystal receiver) to create a Rydberg atom-based transceiver. The transceiver can be used for point-to-point communication between stations in a communication system. Multiple transceivers, or multiple receivers and multiple photonic crystal masers, can be grouped together to form a multi-frequency and / or multi-polarization and / or multi-channel communication system. The photonic crystal maser in the transceiver can be injection-seeded with a phase- and frequency-stable RF wave to lock the phase and frequency of the photonic crystal maser. The injection seed can be phase- or frequency-modulated to frequency- or phase-modulate the output of the photonic crystal maser to encode the signal. Phase and frequency encoding can enable schemes such as differential phase-shift keying, phase-shift keying, or frequency-shift keying. One or more pump lasers can be used to modulate the intensity of the photonic crystal maser. Modulating the pump laser can be one method for implementing intensity modulation encoding schemes, such as on-off key shifting and pulse-position modulation. An injection-locked photonic crystal maser or a second injection-locked photonic crystal maser can be used with a receiver for heterodyne or homodyne detection techniques. Such techniques can enable frequency or phase encoding of communication systems. RF fields referenced to a clock can also be used for heterodyne and homodyne measurements.

[0016] In some embodiments, the communication system can be configured for defense or military applications. Because the communication system uses a very narrow, coherent beam from the photonic crystal maser to transmit information, such transmission can enable point-to-point communication between stations (e.g., a first station and a second station) of the communication system. The high directionality of the transmit and receive functions can make such communication jam-resistant and secure. The directionality of the communication link also reduces interference. Moreover, the use of radio frequencies allows for better penetration of fog, cloud cover, and other forms of precipitation than light generated by lasers. Laser light systems have been demonstrated for both ground-based and spaceborne systems. However, photonic crystal maser amplification may enable the creation of Rydberg technology spaceborne communication systems.

[0017] The communications system's directional transceiver can also be used to securely transmit or relay positioning, navigation, and timing (PNT)+ information between GPS-open and GPS-denied areas, and can also serve as the backbone of a beacon system for GPS-denied PNT. Another example of the transceiver's use is ship-to-ship communications in adverse weather conditions, particularly for military applications where transmitter security and reduced detection are essential. For example, the communications system can be used to create covert, secure communications between ships forming a carrier group. The inner patrol area is approximately 19 km, which is within the horizon (e.g., approximately 22 km) of a Zumwalt-class destroyer. The outer patrol area, 22 to 45 km, is within the point-to-point capacity of the inner patrol area. As a result, the inner and outer patrol areas can establish a secure communications system with the majority of the carrier group. The outer patrol area is located approximately 370 km away, thus outside point-to-point range.

[0018] In some variations, satellite communications can be used to relay communications to defensive screens, particularly patrol lines. FIGS. 1A-1C present schematic diagrams of exemplary communications systems deployed in various environments. It is easy to see in FIGS. 1A-1B that radio frequency has many advantages over light, for example, in situations where the consequences of losing a communications channel due to bad weather are unacceptable. Note that signal lights are still used by the Navy. Communications systems could certainly replace signal lights with ones that penetrate bad weather better and have much greater data rates.

[0019] FIG. 1A presents a schematic diagram of an exemplary communication system including a satellite and a submarine partially submerged in a body of water. The satellite and the submarine can serve as a first station and a second station, respectively, in the exemplary communication system. However, the satellite may also be a relay station in the exemplary communication system. The ambient environment of the exemplary communication system includes clouds, precipitation (e.g., rain), and the body of water in which the submarine is partially submerged. Moreover, the satellite and the submarine may participate in bidirectional point-to-point communication. FIG. 1B presents a schematic diagram of an exemplary communication system including a satellite and multiple ships deployed on the body of water. The satellite and the ships can serve as respective stations in the exemplary communication system. Similar to FIG. 1A, the ambient environment of the communication system of FIG. 1B includes clouds and precipitation (e.g., rain). The satellite and the ships of the fleet may participate in bidirectional point-to-point communication with each other. FIG. 1C presents a schematic diagram of an exemplary communication system including a pair of satellites. A satellite pair can serve as a first station and a second station in an exemplary communications system, which may include being part of a relay chain in the exemplary communications system (e.g., the first station and the second station are each relay stations). However, other types of airborne stations are possible. For example, drones are another area where point-to-point communication between satellites in a communications system may be useful. In some cases, the communications system may find use in drone control, naval communications, satellite communications, and military communications in general, among other security communications applications.

[0020] Point-to-point communication systems can offer several advantages. As mentioned above, point-to-point communication is inherently more secure because it is more difficult to intercept than conventional communications. When point-to-point communication can be used, such communication can be covert and stealthy. Point-to-point communication can also reduce interference and enable more efficient use of the available electromagnetic spectrum (e.g., RF spectrum). However, a major hurdle to using point-to-point communication in the RF domain is the lack of highly directional RF transmitters. Antennas, and even most multi-element antennas, have wide spatial emissions. Moreover, while conventional masers can be used to generate highly directional RF beams, this only exists for limited frequencies. In addition, known maser systems are limited in the frequencies they can generate. On the other hand, light has been used extensively for point-to-point communication due to the availability of lasers. Widespread adoption of point-to-point communication for secure and covert applications using light has been hindered by the fact that precipitation, dust, and clouds efficiently scatter light, making operation under these conditions impractical. However, RF electromagnetic radiation can penetrate precipitation, dust, and clouds better than light, and the reliability of RF electromagnetic radiation for point-to-point communications can be superior to light if a directional laser source can be used.

[0021] In clear skies, the atmospheric transmittance for wavelengths less than about 1 cm is roughly equal to the near-infrared atmospheric transmittance band. For point-to-point communications, there is little difference in the choice of radiation at these wavelengths. However, at a rainfall of about 0.25 mm / hour, the attenuation of infrared frequencies exceeds that of radio frequency wavelengths by an order of magnitude. For attenuation measured in decibels per kilometer, radio frequency wavelengths suffer a loss of about 0.02 dB / km, while infrared suffers a loss of about 0.7 dB / km. 3For fog, this effect can be even more dramatic. For radio frequency wavelengths, fog has no effect on attenuation, but infrared attenuation increases by four orders of magnitude to about 200 dB / km. For heavy rain at 25 mm / hour, radio frequency wavelengths may be attenuated by about 1 dB / km, but infrared is attenuated much more significantly by about 10 dB / km. These dramatic differences in attenuation in common weather conditions indicate that point-to-point communication systems built around Rydberg atomic masers are useful when high-fidelity communications are desired.

[0022] FIG. 2A presents a schematic diagram of an exemplary communication system 200 including a first station 202 and a second station 204. The first station 202 includes a photonic crystal maser 202a and, in some variations as shown in FIG. 2A, also includes a photonic crystal receiver 202b. The photonic crystal maser 202a and the photonic crystal receiver 202b may be part of or may define a transceiver for the first station 202. The second station 204 may include a receiver configured to couple to a beam of target RF electromagnetic radiation. The receiver may be a conventional receiver or, as shown in FIG. 2A, may be a photonic crystal receiver 204b. In some variations, the second station 204 also includes a photonic crystal maser 204a. In these variations, the photonic crystal maser 204a and the photonic crystal receiver 204b may be part of or may define a transceiver for the second station 204. In some variations, photonic crystal masers 202 a, 204 a and receivers 202 b, 204 b are Rydberg atom masers and receivers, respectively, and in these variations, photonic crystal masers 202 a, 204 a and receivers 202 b, 204 b may each comprise a vapor defined by gaseous Rydberg atoms (e.g., Group 1 atoms such as Rb and Cs).

[0023] In these embodiments, photonic crystal masers 202a, 204a each include a photonic crystal structure formed from a dielectric material. The photonic crystal structure has an array of cavities and an elongated slot disposed within a defect region of the array of cavities. Photonic crystal masers 202a, 204a also each include vapor disposed within the elongated slot and operable to emit targeted RF electromagnetic radiation in response to receiving an optical signal. The array of cavities and the elongated slot define a waveguide configured to shape the targeted RF electromagnetic radiation into a beam upon emission. The beam of targeted RF electromagnetic radiation represents information to be transmitted to another station in a communications system (e.g., second station 204 in the case of photonic crystal maser 202a, first station in the case of photonic crystal maser 204a, etc.). Features of photonic crystal masers 202a, 204a are further described in connection with FIG. 3A.

[0024] In an embodiment having a photonic crystal receiver (e.g., photonic crystal receiver 202b or 204b), the photonic crystal receiver includes a second photonic crystal structure formed from a dielectric material and having a second array of cavities and a second elongated slot. The second elongated slot is disposed within a defect region of the second array of cavities. The photonic crystal receiver also includes an antenna structure configured to couple the beam of target RF electromagnetic radiation to a second waveguide defined by the second array of cavities and the second elongated slot. The antenna structure may be an integral part of the second photonic crystal structure. The second waveguide is configured to concentrate the coupled beam within the second elongated slot. The photonic crystal receiver additionally includes a second vapor disposed within the second elongated slot. In some variations, the antenna structure includes a polarizer configured to filter the polarization of the beam of target RF electromagnetic radiation. Features of the photonic crystal receiver are further described in connection with FIG. 3B.

[0025] In some embodiments, photonic crystal maser 202a can serve as a transmitter (or Tx component) of a transceiver of first station 202. Similarly, photonic crystal maser 204a can serve as a transmitter (or Tx component) of a transceiver of second station 204. In some embodiments, photonic crystal receiver 202b can serve as a receiver (or Rx component) of a transceiver of first station 202. Similarly, photonic crystal receiver 204b can serve as a receiver (or Rx component) of a transceiver of second station 204. In operation, photonic crystal masers 202a, 204a and photonic crystal receivers 202b, 204b can enable first station 202 and second station 204 to operate in a point-to-point communication mode using beams of RF electromagnetic radiation. For example, photonic crystal maser 202a at first station 202 can transmit a beam of RF electromagnetic radiation to second station 204. Photonic crystal receiver 204b at second station 204 can receive the beam of RF electromagnetic radiation by coupling its antenna structure to the beam of RF electromagnetic radiation.

[0026] In many embodiments, photonic crystal masers 202a, 204a are Rydberg atomic masers. Rydberg atomic masers can operate at virtually any frequency, ranging from MHz to THz. For example, the Rydberg atomic maser can resonate with a waveguide mode of a waveguide defined by the photonic crystal structure of the Rydberg atomic maser. This resonance can allow the Rydberg atomic maser to function at a specific selected frequency, and the vapor cell structure within the dielectric body can be varied to allow the Rydberg atomic maser to operate at nearly any frequency within this range. In some embodiments, photonic crystal receivers 202b, 204b are Rydberg atomic receivers. In these embodiments, a single laser system may be used to operate the Tx and Rx components of the transceiver. For example, an agile laser system capable of switching to or operating at multiple frequencies can be used to support multiple transceivers within a station in a communications system. Multiple lasers can also be used to operate multiple transceivers. Rydberg atom receivers can benefit from properties such as being dielectric (so that receivers can be grouped with minimal interference), being highly sensitive, and being driven by the same laser, control, and signal processing package as the Rydberg atomic maser in the transceiver. In some variations, the Rydberg atomic maser can be amplified in a photonic crystal waveguide vapor cell or vapor cell, such as a structure similar to the Rydberg atom receiver.

[0027] In some embodiments, the first station 202 includes a laser subsystem 202c having a pump laser and signal processing electronics. The pump laser is optically coupled (e.g., via an optical fiber) to the elongated slot of the photonic crystal maser 204a and configured to generate an optical signal. In some cases, there may be multiple pump lasers. The signal processing electronics is in communication with the pump laser and configured to control one or more characteristics of the optical signal. The one or more characteristics of the optical signal include at least one of the intensity, phase, or frequency of the optical signal. In further cases, the one or more characteristics of the optical signal include the polarization of the optical signal.

[0028] In some embodiments, laser subsystem 202c includes one or more input lasers optically coupled to the second elongated slot of photonic crystal receiver 202b and configured to provide an input optical signal thereto. In some cases, the one or more input lasers include a pump laser. The input optical signal is adapted to interact with one or more electronic transitions of the second vapor of photonic crystal receiver 202b. Laser subsystem 202c also includes an optical subsystem configured to generate spectroscopic data based on the output optical signal from the second vapor. The spectroscopic data represents one or more characteristics of a beam of target RF electromagnetic radiation from another station (e.g., second station 204) of communication system 200. In some variations, the one or more characteristics of the beam of target RF electromagnetic radiation include at least one of the intensity, phase, or frequency of the beam. For variations in which the antenna structure of the photonic crystal receiver includes a polarizer (e.g., photonic crystal receiver 202b or 204b), the one or more characteristics may include polarization of the beam. In many variations, such as that shown in FIG. 2A, the second station 204 includes a laser subsystem 204 c similar to that described in connection with the first station 202 .

[0029] In some embodiments, the first station 202 additionally includes a data processing subsystem 202d (or application subsystem) configured to generate time-series data based on the time-lapse spectroscopic data. The time-series data represents information transmitted from another station (e.g., the second station 204) of the communication system 200. In some cases, the data processing subsystem 202d may be part of the laser subsystem 202c. In many variations, such as that shown in FIG. 2A, the second station 204 includes a data processing subsystem 204d similar to that described in connection with the first station 202.

[0030] In some embodiments, one or both of the first station 202 and the second station 204 includes a respective tracking subsystem 202e, 204e. The tracking subsystems 202e, 204e may include an inertial navigation unit (INU). Each tracking subsystem 202e, 204e is configured to control the orientation of a transceiver associated with the first station 202 or the second station 204. For example, the tracking subsystem 202e can control the orientation of the transceiver of the first station 202, thereby controlling the orientation of the photonic crystal maser 202a to point a beam of target RF electromagnetic radiation emitted therefrom toward a target location. In some variations, the target location is a first target location, and the tracking subsystem 204e of the second station 204 points its transceiver toward a second target location. In these variations, the first station 202 and the second station 204 may be located at a second location and a first location, respectively. Thus, the transceiver of the first station 202 faces the second station and vice versa, although other orientations are possible.

[0031] For example, the communication system 200 may include a relay station (e.g., a satellite, a drone, an aircraft, a ship, a tower, etc.) disposed at a relay location and configured to receive and transmit a beam of target RF electromagnetic radiation. One or both of the first target location and the second target location may correspond to the relay location. FIG. 2B presents a schematic diagram of the example communication system 200 of FIG. 2A , but with a satellite 206 serving as a relay station in the example communication system. The transceivers of the first station 202 and the second station 204 are oriented to point toward the satellite 206. Moreover, the first station 202 and the second station 204 participate in bidirectional point-to-point communication with the satellite 206. Thus, the satellite 206 may be configured similarly to the first station 202 and the second station 204 (e.g., serving as a third station in the communication system 200). While FIG. 2B illustrates a relay station, the satellite 206 may be part of a chain of relay stations, such as a terminal end. In this case, the first station 202 may point to a satellite 206 and the second station 204 may point to another relay station in the chain.

[0032] The tracking subsystems 202e, 204e can be configured to actively lock the orientation of the first station 202 and the second station 204 to secure the communication channel, which may involve moving a target location (e.g., an airplane, a drone, etc.). The tracking subsystems 202e, 204e may include gimbal mounts for independently orienting the receiver and transmitter as well as movable optical elements (e.g., a mirror on a three-axis tilt stage) to fine-tune the orientation. An inertial navigation unit can assist in orienting the transceiver. However, in some variations, a beacon, or a series of beacons, can be used to improve the orientation until a communication link can be established. Once the link is established, the orientation and tracking can be actively locked to maintain the channel.

[0033] The photonic crystal masers 202a, 204a can be frequency-, phase-, or amplitude-modulated to encode the signal. The receiver signal can be demodulated using local maser radiation using techniques such as homodyne or heterodyne detection. The photonic crystal masers at different stations can be made coherent with each other by using clock signals from inertial navigation units, which may be atomic clocks or GPS timing signals. Figure 2A shows an example in which a satellite is operable to provide a GPS signal containing timing and position information.

[0034] In some embodiments, one or both of the first station 202 and the second station 204 includes a reference RF subsystem configured to generate reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase. In some variations, the reference RF subsystem includes a reference RF oscillator (e.g., an atomic clock) and may be part of the clock and timing subsystem (e.g., clock and timing subsystem 202f, 204f) of the first station 202 or the second station 204. The clock and timing subsystem is configured to synchronize communication signals between the station and other stations in the communication system 200. The clock and timing subsystem is also configured to serve as a stable reference for the station's photonic crystal maser (e.g., through injection locking). The clock and timing subsystem may also be configured to assist the station's tracking subsystem, such as to establish communication channels between the station and other stations in the communication system 200.

[0035] In cases where first station 202 includes a reference RF subsystem, photonic crystal maser 202a may include an input coupler configured to couple reference RF electromagnetic radiation into its waveguide. Similarly, in cases where second station 204 includes a reference RF subsystem, photonic crystal maser 204a may include a similar input coupler. The input couplers of photonic crystal masers 202a, 204a may be integral parts of their respective photonic crystal structures. The reference RF subsystem, if present, may enable photonic crystal masers 202a, 204a to be injection locked. For example, the masers may be injection locked by a small RF oscillator signal referenced to a clock signal from a clock and timing subsystem. In some variations, the reference RF subsystem may be approximately 1 part in 10 11 ) timing accuracy is possible. However, in a further variation, timing accuracy of about 1 part in 10 13 ) timing accuracy is possible (e.g., for portable systems).

[0036] Polarization modulation is also possible, for example, by using two orthogonally polarized photonic crystal masers and two photonic crystal receivers oriented to receive orthogonal polarizations. In addition to redundancy, multiple transceivers can be used within the first station 202 and the second station 204 to increase the bandwidth of the communication system 200. For example, the bandwidth of a single photonic crystal maser and receiver pair can be approximately 20 MB / s. Such a system can be driven by a single laser system, such as one based on a frequency comb.

[0037] In some embodiments, one or both of the first station 202 and the second station 204 includes a reference antenna configured to generate second reference RF electromagnetic radiation. The second reference RF electromagnetic radiation has one or more controlled characteristics, including at least one of a controlled amplitude, a controlled frequency, or a controlled phase. The reference antenna is electromagnetically coupled to a receiver (e.g., a conventional receiver, the antenna structure of the photonic crystal receivers 202b, 204b, etc.). During operation, the reference antenna can superimpose the second reference RF electromagnetic radiation onto an input beam of RF electromagnetic radiation received by the receiver. Such superposition can cause interference between the second reference RF electromagnetic radiation and the input beam of RF electromagnetic radiation, thus allowing the phase and frequency of the input beam of RF electromagnetic radiation to be determined relative to a reference field.

[0038] In some embodiments, the first station 202 and the second station 204 each include a communications interface (e.g., communications interface 202g, 204g). In these embodiments, the data processing subsystems 202d, 204d take signals (audio, video, codec, etc.) from the respective communications interfaces 202g, 204g, format them for transmission, and send them to the signal processing electronics of the laser subsystem. To assist in such operations, the signal processing electronics may include modulation electronics. The data processing subsystems 202d, 204d control synchronization and maintain connections, including handling signaling packets. Similarly, the data processing subsystems 202d, 204d may take raw data from the photonic crystal receivers, signal process the raw data, and format the signals for the respective communications interfaces 202g, 204g. Some forms of demodulation may occur, in part, in the photonic crystal receivers 202b, 204b, such as heterodyne or homodyne detection of signals. Once processed, the received signals are formatted for output to respective communication interfaces 202g, 204g.

[0039] Referring now to FIG. 3A, a schematic diagram of an exemplary photonic crystal maser 300 is presented in perspective, including a dielectric body 302 bonded to two optical windows 304, 306. The exemplary photonic crystal maser 300 may be similar to the photonic crystal masers 202a, 204a described in connection with FIGS. 2A and 2B. The dielectric body 302 includes an array of cavities 308 periodically ordered to define a photonic crystal structure 310 within the dielectric body 302. For example, the cavities 308 of the array may be arranged at respective sites of a two-dimensional lattice, such as an orthorhombic lattice, a square lattice, a rectangular lattice, a hexagonal lattice, a rhombic lattice, or the like. In FIG. 3A, each cavity 308 is defined by a through-hole. However, other shapes of the cavities 308 (e.g., blind holes, internal voids, etc.) are possible, including combinations of multiple shapes. The dielectric body 302 also includes regions 312 (or defect regions) within the array of cavities 308 that define defects within the photonic crystal structure 310. The regions may be defined by the absence of cavities 308 in two or more contiguous locations of a two-dimensional lattice. In Figure 3A, the regions 312 are linear regions lacking a single row of cavities 308. However, other geometric shapes are possible, including curved, circular, elliptical, serpentine, square, rectangular, hexagonal, etc.

[0040] The dielectric body 302 may be formed from a material that is substantially transparent to RF electromagnetic radiation. The material may be an insulating material with a high resistivity, for example, ρ>10 Ω·cm, and may correspond to a single crystalline material, a polycrystalline material, or an amorphous (or glass) material. For example, the dielectric body 302 may be formed from silicon. In another example, the dielectric body 302 may be formed from silicon dioxide (e.g., SiO , SiO ), such as quartz glass, borosilicate glass, or aluminosilicate glass. xIn some cases, the material of the dielectric body 302 is an oxide material such as magnesium oxide (e.g., MgO), aluminum oxide (e.g., Al2O3), silicon dioxide (e.g., SiO2), titanium dioxide (e.g., TiO2), zirconium dioxide (e.g., ZrO2), yttrium oxide (e.g., YO3), lanthanum oxide (e.g., La2O3), etc. The oxide material may be non-stoichiometric (e.g., SiO2). x ), or a combination of one or more binary oxides (e.g., Y:ZrO2, LaAlO3, etc.). In certain variations, the combination is BaLn2Ti4O 12 where Ln refers to one or more elements from the lanthanide group of the periodic table of elements. In other cases, the material of the dielectric body 302 is a non-oxide material such as silicon (Si), diamond (C), gallium nitride (GaN), calcium fluoride (CaF), etc.

[0041] The dielectric body 302 additionally includes an elongated slot 314 through the region 312, extending from a slot opening in the surface of the dielectric body 302 at least partially through the dielectric body. In FIG. 3A , the elongated slot 314 extends completely through the dielectric body 302 to a second slot opening. The array of cavities 308 and the elongated slot 314 define a waveguide having a waveguide mode. In operation, the waveguide can guide radio frequency (RF) electromagnetic radiation (or waves thereof) along the axis of the region 312, such as toward an end of the dielectric body 302.

[0042] The exemplary photonic crystal maser 300 also includes a vapor (or vapor source) within the elongated slot 314. The vapor may include components such as an alkali metal atomic gas, a noble gas, a diatomic halogen molecular gas, or an organic molecular gas. For example, the vapor may include an alkali metal atomic gas (e.g., K, Rb, Cs, etc.), a noble gas (e.g., He, Ne, Ar, Kr, etc.), or both. In another example, the vapor may include a diatomic halogen molecular gas (e.g., F2, Cl2, Br2, etc.), a noble gas, or both. In yet another example, the vapor may include an organic molecular gas (e.g., acetylene), a noble gas, or both. Other combinations of vapors, including other components, are possible. The vapor source can generate the vapor in response to an energy stimulus, such as heat, exposure to ultraviolet radiation, irradiation with laser light, etc. For example, the vapor may correspond to an alkali metal atomic gas, and the vapor source may be disposed within the elongated slot 314. 314 The alkali metal mass may correspond to a mass of alkali metal that has been cooled sufficiently to be in a solid or liquid phase when placed within the alkali metal mass.

[0043] In many embodiments, the vapor has electronic transitions (e.g., Rydberg transitions, atomic transitions, molecular transitions, etc.) defined between pairs of electronic energy levels. In particular, the vapor includes one or more input electronic transitions and one or more output electronic transitions coupled to the input electronic transitions. The output electronic transitions are operable to emit targeted RF electromagnetic radiation and are resonant with one or more waveguide modes of the waveguide. In some embodiments, the exemplary photonic crystal maser 300 includes a laser (e.g., a pump laser of the laser subsystem) configured to generate an optical signal capable of exciting one or more input electronic transitions of the vapor. In some embodiments, the output electronic transitions are operable to emit targeted RF electromagnetic radiation having a frequency in the range of 100 MHz to 1 THz.

[0044] Photonic crystal structure 310 may define a photonic bandgap for the target RF electromagnetic radiation within the waveguide. The photonic bandgap may relate to a transverse magnetic (TM) mode, a transverse electric (TE) mode, or both of the target RF electromagnetic radiation within the waveguide. The photonic bandgap may enable photonic crystal structure 310 to affect the properties of the target RF electromagnetic radiation. For example, photonic crystal structure 310 may be configured to concentrate the target RF electromagnetic radiation within elongated slot 314. Photonic crystal structure 310 may also be configured to reduce the group velocity of the target RF electromagnetic radiation (or waves thereof) along the direction of elongated slot 314 (e.g., along the axis of elongated slot 314). Such an effect may allow photonic crystal structure 310 to control the absorption and emission of photons by the vapor.

[0045] In some embodiments, elongated slot 314 extends partially through dielectric body 302, and dielectric body 302 includes a surface that defines a slot opening of elongated slot 314. In these embodiments, exemplary photonic crystal maser 300 includes an optical window (e.g., optical window 304) covering elongated slot 314 and having a window surface bonded to the surface to form a seal around the slot opening. Such a seal can help the optical window and dielectric body 302 seal out the vapor (or vapor source) within elongated slot 314, thereby defining a vapor cell within region 312. The optical window can be bonded to dielectric body 302 using compression bonding, anodic bonding, glass frit bonding, or the like. Such bonding may be formed using techniques described in U.S. Pat. No. 10,859,981, entitled "Vapor Cells Having One or More Optical Windows Bonded to a Dielectric Body," the disclosure of which is incorporated herein by reference in its entirety.

[0046] The optical window may be formed from a material that is transparent to the electromagnetic radiation (e.g., laser light) used to stimulate the vapor to emit the target RF electromagnetic radiation. For example, the optical window may be transparent to infrared wavelengths of electromagnetic radiation (e.g., 700-5000 nm), visible wavelengths of electromagnetic radiation (e.g., 400-700 nm), or ultraviolet wavelengths of electromagnetic radiation (e.g., 10-400 nm). Furthermore, the optical window material may be an insulating material with a high resistivity, e.g., ρ>10 Ω·cm, and may correspond to a single-crystal material, a polycrystalline material, or an amorphous (or glass) material. For example, the optical window material may be silicon dioxide (e.g., SiO , SiO ), such as that found in quartz, fused silica, or borosilicate glass. x In another example, the optical window material may include aluminum oxide (e.g., Al2O3, Al), such as that found in sapphire or aluminosilicate glasses. x O y In some cases, the optical window material is an oxide material such as magnesium oxide (e.g., MgO), aluminum oxide (e.g., Al2O3), silicon dioxide (e.g., SiO2), titanium dioxide (e.g., TiO2), zirconium dioxide (e.g., ZrO2), yttrium oxide (e.g., YO3), lanthanum oxide (e.g., La2O3), etc. The oxide material may be non-stoichiometric (e.g., SiO x ), or a combination of one or more binary oxides (e.g., Y:ZrO2, LaAlO3, BaLn2Ti4O 12 In other cases, the material of the optical window is a non-oxide material, such as diamond (C), calcium fluoride (CaF), etc.

[0047] In some embodiments, the dielectric body 302 The surface of the cavity 308The optical window may or may not cover each of the cavity openings. In embodiments in which the optical window covers each of the cavity openings, the window surface of the optical window may form a seal around each of the cavity openings.

[0048] In some embodiments, elongated slot 314 extends completely through dielectric body 302. For example, as shown in FIG. 3A , dielectric body 302 can include a first surface 316 opposite a second surface 318, with elongated slot 314 extending from first surface 316 through dielectric body 302 to second surface 318. First surface 316 can define a first slot opening 320 of elongated slot 314, and second surface 318 can define a second slot opening (not shown) of elongated slot 314. In these embodiments, exemplary photonic crystal maser 300 includes first and second optical windows 304, 306 covering first and second slot openings of elongated slot 314, respectively. First and second optical windows 304, 306 are optically transparent to dielectric body 302. 302 Each optical window 304 may have a window surface bonded to a surface of the dielectric body 302 to seal the vapor (or vapor source) within the elongated slot 314 and define a vapor cell. In such a case, the first optical window 304 may cover the first slot opening 320 and may be bonded to the first surface 316 of the dielectric body 302 to seal the vapor (or vapor source) within the elongated slot 314 and define a vapor cell. 320 The second optical window 306 may have a first window surface 322 that forms a seal around the second slot opening. Similarly, the second optical window 306 may cover the second slot opening and may have a second window surface 324 that is bonded to the second surface 318 of the dielectric body 302 to form a seal around the second slot opening.

[0049] In embodiments in which exemplary photonic crystal maser 300 includes first and second optical windows 304 and 306, first and second surfaces 316 and 318 of dielectric body 302 can define first and second cavity openings, respectively, of each of array of cavities 308. In these embodiments, first and second optical windows 304 and 306 can cover or not cover each of the first and second cavity openings, respectively. In embodiments in which an optical window covers each of the cavity openings, first optical window 322 can form a seal around each of the first cavity openings, and second optical window 324 can form a seal around each of the second cavity openings.

[0050] In some embodiments, exemplary photonic crystal maser 300 includes output coupler 326 configured to impedance match the target RF electromagnetic radiation to the surrounding environment of photonic crystal maser 300. Output coupler 326 can assist the waveguide in shaping the target RF electromagnetic radiation into a beam upon emission. In these embodiments, region 312 within array of cavities 308 can extend along axis 328, and elongated slot 314 can be aligned parallel to (e.g., coincident with) axis 328. Dielectric body 302 then includes output coupler 326, which can extend from end 330 of dielectric body 302 and be aligned with axis 328. Output coupler 326 can be an integral part of dielectric body 302 (or photonic crystal structure 310), or can be a separate body. If separate, output coupler 326 can be formed from a dielectric material. However, output coupler 326 can also be a conventional coupler formed from metal. 3A shows output coupler 326 as a protrusion from dielectric body 302 that terminates in a taper. However, other geometries for output coupler 326 are possible.

[0051] In some embodiments, output coupler 326 is electromagnetically coupled to an output mirror, such as photonic crystal mirror 332, for impedance matching the output beam to the medium (e.g., air) through which the output beam is intended to propagate. Photonic crystal mirror 332 can be defined by one or more offset cavities that are spatially offset from an ideal periodic position within the array. The one or more offset cavities can be located proximate an end (e.g., end 330) of elongated slot 314 and can have respective spatial offsets outward from the end of elongated slot 314. The one or more offset cavities can also be located proximate a side of elongated slot 314 and can have respective spatial offsets outward from the side of elongated slot 314. Other locations are possible. A lens can also be added to collimate the output beam. In some variations, the elongated slot 314 may be tapered (eg, in width along its axis). Such tapering can aid in the formation of photonic crystal mirror 332.

[0052] In some embodiments, a polarizer can be added to output coupler 326 to filter the polarization of the output beam. For example, 326 The coplanar segment array may terminate in a tapered end and may include a constricted portion aligned with the tapered end. The coplanar segment array may extend outward from the constricted portion and may be periodically spaced therealong. The coplanar segment array is configured to filter polarization of the target RF electromagnetic radiation.

[0053] In some embodiments, photonic crystal mirror 332 is positioned at one or both ends of elongated slot 314. Figure 3A shows the case where photonic crystal mirror 332 is present at both ends of elongated slot 314. Photonic Crystal Mirror 332The presence of region 312 can increase the output power, lower the gain threshold of the maser, or both. For example, photonic crystal mirror 332 can reflect electromagnetic radiation that traverses region 312 during operation (e.g., targeted RF electromagnetic radiation emitted by the vapor during operation of exemplary photonic crystal maser 300). In this capacity, region 312 can serve as part of the maser cavity, such as the interior of the maser cavity. Moreover, photonic crystal mirror 332 can assist the array of cavities 308 and elongated slots 314 in defining a cavity structure (e.g., a slot waveguide) for the electromagnetic radiation emitted by the vapor. If present, the taper of elongated slots 314 can also assist photonic crystal mirror 332 in defining a cavity structure for the electromagnetic radiation emitted by the vapor.

[0054] In many variations, photonic crystal mirror 332 corresponds to modifying dimensional characteristics of photonic crystal structure 310 near the ends of elongated slot 314. For example, transmission of target RF electromagnetic radiation through photonic crystal structure 310 at the ends of elongated slot 314 can be modified by changing the spacing of cavities 308 within the array, the thickness of dielectric body 302, the diameter of cavities 308 within the array, etc. A perfect photonic crystal geometry for the target RF electromagnetic radiation (or resonant wave) within dielectric body 302 can act as a perfect reflector, while the absence of a photonic crystal can act as a perfect transmitter.

[0055] In some embodiments, photonic crystal mirror 332 is tuned to the cavity resonant frequency ω of photonic crystal structure 310. cThe photonic crystal structure 310 may be configured to have a reflectivity of greater than 80% for frequencies of electromagnetic radiation at or near the photonic crystal structure 310. This reflectivity may increase the cavity quality factor Q associated with the photonic crystal structure 310 (or region 312 therein), thereby lowering the threshold condition for maging. In some variations, the reflectivity is greater than 85%. In some variations, the reflectivity is greater than 90%. In some variations, the reflectivity is greater than 92%. In some variations, the reflectivity is greater than 94%. In some variations, the reflectivity is greater than 96%.

[0056] In some embodiments, an optical mirror 334 is disposed at one or both ends of the elongated slot 314. The optical mirror 334 may be angled with respect to the optical path defined by the elongated slot 314, or may be angled perpendicular to the optical path. The optical mirror 334 may serve to guide an optical signal along a longitudinal axis of the elongated slot, such as axis 328. To do so, the optical mirror 334 may include a surface configured to reflect such an optical signal. The optical signal may include light received into the elongated slot 314 from a laser (e.g., a pump laser).

[0057] In some embodiments, the vapor is a vapor of atoms (e.g., Rydberg atoms), with each atom capable of functioning as an emitter. In operation, the photonic crystal structure 310 surrounding the elongated slot 314 can slow down and focus electromagnetic waves at the atomic transition frequencies of the atoms. The atoms are pumped by a laser, resulting in the establishment of a population inversion at the atomic transition, which is resonant with the resonant mode (or waveguide mode) of the waveguide. Emission of radiation into the resonant mode of the waveguide can be enhanced because the electric field is stronger, favoring emission. Stimulated emission dominates, creating a coherent, directional maser beam along the waveguide that can be impedance-matched and shaped for free-space propagation. Photonic crystal mirrors can be implemented at the ends of the elongated slot 314, allowing radiation to propagate back and forth within the elongated slot 314 and further amplified. The elongated slots 314 capture the energy stored in the population inversion and allow it to be released into the waveguide modes of the waveguide, resulting in a coherent, directional beam of radiation. Similar operation is possible for embodiments of exemplary photonic crystal maser 300 in which the vapor is a molecular vapor.

[0058] The exemplary photonic crystal maser 300 can be constructed to be suitable for mass production. The amount of power output by the exemplary photonic crystal maser 300 can be controlled down to very low levels by varying the intensity of the optical signal provided by the laser. Furthermore, switching times can be on the order of nanoseconds because of the cavity lifetimes that can be on the order of nanoseconds. Because the lifetime is in nanoseconds and the laser can be modulated over GHz bandwidths, the laser can imprint baseband modulation onto a carrier frequency on the same frequency scale (e.g., GHz).

[0059] The exemplary photonic crystal maser 300 may also be combined with a Rydberg atomic receiver, a Rydberg atomic vapor cell sensor, or a Rydberg atomic vapor cell sensor to create a device capable of receiving and transmitting RF electromagnetic radiation. For example, as shown in Figures 2A and 2B, a photonic crystal maser may be paired with a photonic crystal receiver to define part or all of a transceiver.

[0060] Referring now to FIG. 3B , a schematic diagram of an exemplary photonic crystal receiver 350 for detecting a beam of radio frequency (RF) electromagnetic radiation is presented in perspective. The exemplary photonic crystal receiver 350 may be similar to the photonic crystal receivers 202b, 204b described in connection with FIGS. 2A and 2B . The exemplary photonic crystal receiver 350 includes a dielectric body 352, which may be formed from a material that is substantially transparent to the RF electric field (or RF electromagnetic radiation) measured by the exemplary photonic crystal receiver 350. The material may be an insulating material with a high resistivity, for example, ρ>10 Ω·cm, and may correspond to a single-crystal material, a polycrystalline material, or an amorphous (or glass) material. For example, the dielectric body 352 may be formed from silicon. In another example, the dielectric body 352 may be formed from a silicon dioxide (e.g., SiO , SiO ), such as quartz glass, borosilicate glass, or aluminosilicate glass. x In some cases, the material of the dielectric body 352 is an oxide material such as magnesium oxide (e.g., MgO), aluminum oxide (e.g., Al2O3), silicon dioxide (e.g., SiO2), titanium dioxide (e.g., TiO2), zirconium dioxide (e.g., ZrO2), yttrium oxide (e.g., YO3), lanthanum oxide (e.g., La2O3), etc. The oxide material may be non-stoichiometric (e.g., SiO2). x ), or may be a combination of one or more binary oxides (e.g., Y:ZrO2, LaAlO3, etc.). In certain variations, the combination is BaLn2Ti4O 12where Ln refers to one or more elements from the lanthanide group of the periodic table of elements. In other cases, the material of the dielectric body 352 is a non-oxide material such as silicon (Si), diamond (C), gallium nitride (GaN), calcium fluoride (CaF), etc.

[0061] The dielectric body 352 includes an array of cavities 354 that are periodically ordered to define a photonic crystal structure 356 within the dielectric body 352 (e.g., the photonic crystal structure 356 is formed from a dielectric material and includes the array of cavities 354). The array of cavities 354 may extend partially or completely through the dielectric body 352. For example, the array of cavities 354 may be an array of blind holes or, as shown in FIG. 3B, an array of through-holes. The array of cavities 354 may also be divided into portions that extend partially or completely through the dielectric body 352. For example, the array of cavities 354 may include a first portion (e.g., blind holes) that extends partially through the dielectric body 352 and a second portion (e.g., through-holes) that extends completely through the dielectric body 352. Although FIG. 3B depicts the array of cavities 354 as being an array of circular through-holes, other shapes of the array of cavities 354 are possible (e.g., hexagonal, oval, etc.). In some variations, each of the array of cavities 354 has a maximum dimension in the range of 0.5 millimeters to 10 millimeters. The maximum dimension may be the same for each cavity. In some variations, the array of cavities 354 has a periodic spacing in the range of 0.9 millimeters to 15 millimeters. In some variations, the dielectric body 352 is a plate having a thickness in the range of 0.5 millimeters to 10 millimeters.

[0062] The dielectric body 352 also includes regions 358 within the array of cavities 354 that define defects within the photonic crystal structure 356. In many variations, the regions 358 are solid regions within the array of cavities 354 defined by the absence of cavities. The absence of cavities may correspond to defects within the photonic crystal structure 356. For example, the defects may be rows or columns of “filled” cavities. However, other patterns of “filled” cavities are possible. In some variations, the region 358 may be located in the center of the dielectric body 352, as shown in FIG. 3B . The dielectric body 352 additionally includes an elongated slot 360 through the region 358 that extends at least partially through the dielectric body 352 from a slot opening 362 in a surface 364 of the dielectric body 352. The elongated slot 360 may be part of the photonic crystal structure 356. 3B, elongated slot 360 is located in the center of this region and aligned along the longitudinal axis of dielectric body 352. It will be appreciated that during operation of exemplary photonic crystal receiver 350, the array of cavities and elongated slot 360 can cooperate to function as a waveguide for RF electromagnetic radiation.

[0063] In some embodiments, photonic crystal structure 356 may define a photonic bandgap for exemplary photonic crystal receiver 350. For example, photonic crystal structure 356 may define a photonic bandgap associated with a transverse magnetic (TM) mode of RF electromagnetic radiation. In another example, photonic crystal structure 356 may define a photonic bandgap associated with a transverse electric (TE) mode of RF electromagnetic radiation. A combination of the TM and TE modes of RF electromagnetic radiation is also possible.

[0064] In some embodiments, photonic crystal structure 356 is configured to reduce the group velocity of target RF electromagnetic radiation (e.g., target RF electromagnetic radiation having a frequency in the range of 100 MHz to 1 THz). Such configuration may involve selecting the size of one or more cavities in the array of cavities 354, selecting the spacing of one or more cavities in the array of cavities 354, selecting the ordering of the array of cavities 354, and / or selecting the thickness of dielectric body 352. Other characteristics are possible (e.g., selecting the material of dielectric body 352). In some cases, the configuration of photonic crystal structure 356 may be determined through numerical modeling.

[0065] In some embodiments, photonic crystal structure 356 is configured to concentrate targeted RF electromagnetic radiation within elongated slot 360. The targeted RF electromagnetic radiation may have a frequency in the range of 100 MHz to 1 THz. Such configuration may involve selecting the size of one or more cavities in the array of cavities 354, selecting the spacing of one or more cavities in the array of cavities 354, selecting the ordering of the array of cavities 354, and / or selecting the thickness of dielectric body 352. Other characteristics are possible (e.g., selecting the material of dielectric body 352). In some cases, the configuration of photonic crystal structure 356 may be determined through numerical modeling.

[0066] In some embodiments, the photonic crystal structure 356 may include a photonic crystal mirror configured to redirect (e.g., reflect) target RF electromagnetic radiation. For example, the array of cavities 354 may include one or more offset cavities that are spatially offset from an ideal periodic position within the array 354. The one or more offset cavities may define a photonic crystal mirror. In some variations, the one or more offset cavities may be nearest to an end of the elongated slot 360 and have respective spatial offsets outward from the end of the elongated slot 360. In some variations, the one or more offset cavities are nearest to a side of the elongated slot 360 and have respective spatial offsets outward from the side of the elongated slot 360.

[0067] The exemplary photonic crystal receiver 350 can also include a vapor or vapor source within the elongated slot 360. The vapor may include components such as a gas of alkali metal atoms, a noble gas, a gas of diatomic halogen molecules, or a gas of organic molecules. For example, the vapor may include a gas of alkali metal atoms (e.g., K, Rb, Cs, etc.), a noble gas (e.g., He, Ne, Ar, Kr, etc.), or both. In another example, the vapor may include a gas of diatomic halogen molecules (e.g., F2, Cl2, Br2, etc.), a noble gas, or both. In yet another example, the vapor may include a gas of organic molecules (e.g., acetylene), a noble gas, or both. Other combinations of vapors, including other components, are possible. The vapor source can generate the vapor in response to an energy stimulus such as heat, exposure to ultraviolet radiation, irradiation with laser light, etc. For example, the vapor may correspond to a gas of alkali metal atoms, or the vapor source may correspond to an alkali metal mass that has been cooled sufficiently to be in a solid or liquid phase when placed within the elongated slot 360.

[0068] The exemplary photonic crystal receiver 350 can additionally include an optical window 366 having a window surface that covers the elongated slot 360 and is bonded to the surface 364 of the dielectric body 352 to form a seal around the slot opening 362. The optical window 366 can be bonded to the dielectric body 352 using compression bonding, anodic bonding, glass frit bonding, or the like. Such bonding may be formed using techniques described in previously referenced U.S. Pat. No. 10,859,981, entitled "Vapor Cells Having One or More Optical Windows Bonded to a Dielectric Body." The optical window 366 may be formed from a material that is transparent to the electromagnetic radiation (e.g., laser light) used to probe the vapor. For example, the optical window 366 may be transparent to infrared wavelengths of electromagnetic radiation (e.g., 700-5000 nm), visible wavelengths of electromagnetic radiation (e.g., 400-700 nm), or ultraviolet wavelengths of electromagnetic radiation (e.g., 10-400 nm). Moreover, the material of the optical window 366 may be an insulating material with a high resistivity, e.g., ρ>10 Ω·cm, and may correspond to a single-crystalline material, a polycrystalline material, or an amorphous (or glass) material. For example, the material of the optical window 366 may be silicon dioxide (e.g., SiO , SiO ), such as that found in quartz, fused silica, or borosilicate glass. x In another example, the material of the optical window 366 may include aluminum oxide (e.g., Al2O3, Al), such as that found in sapphire or aluminosilicate glasses. x O y In some cases, the material of the optical window 366 is an oxide material such as magnesium oxide (e.g., MgO), aluminum oxide (e.g., Al2O3), silicon dioxide (e.g., SiO2), titanium dioxide (e.g., TiO2), zirconium dioxide (e.g., ZrO2), yttrium oxide (e.g., YO3), lanthanum oxide (e.g., La2O3), etc. The oxide material may be non-stoichiometric (e.g., SiO x), or a combination of one or more binary oxides (e.g., Y:ZrO2, LaAlO3, BaLn2Ti4O 12 In other cases, the material of the optical window 366 is a non-oxide material, such as diamond (C), calcium fluoride (CaF), or the like.

[0069] In some embodiments, the optical window 366 covers only the elongated slot 360 and the surface 364 of the dielectric body 352 immediately adjacent to the elongated slot 360 (e.g., region 358 or a portion thereof). However, in some embodiments, the optical window 366 also covers the surface 364 of the dielectric body 352 associated with the photonic crystal structure 356. In these embodiments, as shown in FIG. 3B , the surface 364 of the dielectric body 352 defines a cavity opening for each of the array of cavities 354. The optical window 366 may cover each of the cavity openings. Moreover, the window surface of the optical window 366 may form a seal around each of the cavity openings.

[0070] In embodiments in which the elongated slot 360 extends only partially through the dielectric body 352, a single optical window may be bonded to the dielectric body 352 to seal the vapor or vapor source within the elongated slot 360. However, in some embodiments, the elongated slot 360 may extend through the dielectric body 352. In these embodiments, two optical windows may be bonded to the dielectric body 352 to seal the vapor or vapor source within the elongated slot 360. For example, the surface 364 of the dielectric body 352 may be a first surface, and the dielectric body 352 may include a second surface opposite the first surface. The elongated slot 360 may then extend from the first surface through the dielectric body 352 to the second surface. In this case, the slot opening 362 may be a first slot opening, and the second surface of the dielectric body 352 may define a second slot opening of the elongated slot 360. 3B, the exemplary photonic crystal receiver 350 can include a second optical window 368 covering the second slot opening, with the second optical window 368 having a second window surface bonded to a second surface of the dielectric body 352 to form a seal around the second slot opening.

[0071] In some embodiments, the second optical window 368 covers only the elongated slot 360 and the second surface of the dielectric body 352 immediately adjacent to the elongated slot 360 (e.g., region 358 or a portion thereof). However, in some embodiments, the second optical window 368 also covers the second surface of the dielectric body 352 associated with the photonic crystal structure 356. For example, the first and second surfaces of the dielectric body 352 can define first and second cavity openings, respectively, of each of the array of cavities 354. In this case, the array of cavities 354 extends from the first surface through the dielectric body 352 to the second surface. The second optical window 368 can then cover each of the second slot openings, as shown in FIG. 3B . Additionally, the second window surface can form a seal around each of the second cavity openings.

[0072] In some embodiments, the dielectric body 352 includes an antenna structure 370 extending from an end 372 of the dielectric body 352 and aligned with the elongated slot 360. For example, the antenna structure 370 may be a protrusion extending from the end 372 of the dielectric body 352 and terminating in a taper. The antenna structure 370 can be configured to couple to a beam of targeted RF electromagnetic radiation (e.g., a beam of targeted RF electromagnetic radiation having a frequency in the range of 100 MHz to 1 THz). Such configuration can involve selecting a length of the antenna structure 370, which can be determined by numerical simulation of the targeted RF electromagnetic radiation. Other dimensions can also be involved, including, for example, ratios of dimensions such as thickness and width, length-to-width ratio, length-to-thickness ratio, etc. Configuring the antenna structure 370 to couple to a beam of targeted RF electromagnetic radiation can also involve selecting a shape of the antenna structure 370 or a degree of curvature of the antenna structure 370. The shape, the degree of curvature, or both can also be determined by numerical simulation.

[0073] In some variations, the antenna structure 370 includes a polarizer, which may be integral with the antenna structure 370. For example, the antenna structure 370 may include a constricted portion aligned with the elongated slot 360. The antenna structure 370 may also include an array of periodically spaced coplanar segments extending outward from the constricted portion. The array of coplanar segments is configured to filter (or select) the polarization of the target RF electromagnetic radiation.

[0074] In some variations, the antenna structure 370 includes one or more channels 374 defining a taper 376 therein. The taper 376 is configured to couple electromagnetic radiation received by the antenna structure 370, such as a beam of target RF electromagnetic radiation, to a waveguide (e.g., the elongated slot 360) of the exemplary photonic crystal receiver 350. To do so, the taper 376 can have an apex 378 aligned with the elongated slot 360. For example, the antenna structure 370 can be a protrusion extending from the end 372 of the dielectric body 352. In this case, the antenna structure 370 can include a V-shaped channel defining a taper therein. The taper can have a tip (or apex) offset from the end of the elongated slot 360 aligned therewith. In an alternative case, as shown in FIG. 3B , the antenna structure 370 can include a Y-shaped channel within the protrusion, including a base 374 a and two branch portions 374 b. Base 374a is aligned with elongated slot 360 and terminates at an end that is offset from the end of elongated slot 360. Two branched portions 374b diverge from base 374a to define a taper (e.g., taper 376) within the protrusion. Other configurations of taper 376 are possible.

[0075] In operation, the exemplary photonic crystal receiver 350 receives RF electromagnetic radiation at the antenna structure 370 of the dielectric body 352. In some cases, the exemplary receiver 350 couples the received RF electromagnetic radiation into the elongated slot 360 using a taper 376 inside the antenna structure. The exemplary photonic crystal receiver 350 also interacts with the received RF electromagnetic radiation with the photonic crystal structure 356. In such interaction, the photonic crystal structure 356 can be configured to reduce the group velocity of the received RF electromagnetic radiation along a direction parallel to the elongated slot 360 (e.g., the axis of the elongated slot 360). The photonic crystal structure 356 can also concentrate the received RF electromagnetic radiation within the elongated slot 360. The exemplary photonic crystal receiver 350 additionally passes an input optical signal through the vapor within the elongated slot 360 to generate one or more output optical signals. The input optical signals can be generated by one or more input lasers (e.g., a probe laser, a coupling laser, etc.). In some variations, the exemplary photonic crystal receiver 350 acts as an exemplary receiver for RF electromagnetic radiation. 350 It can be used with a parabolic antenna to improve sensitivity.

[0076] In some embodiments, passing the input optical signal includes propagating the input optical signal along an optical path defined by elongated slot 360. In some embodiments, passing the input optical signal includes reflecting the input optical signal off a mirror disposed at an end of the elongated slot. For example, exemplary receiver 350 may include a mirror 380 disposed at the end of elongated slot 360. Mirror 380 may be angled with respect to the optical path (e.g., angled at 45°) or may be perpendicular to the optical path, as shown in FIG. 3B . Such an orientation may allow mirror 380 to direct light into elongated slot 360, direct light along elongated slot 360 through the vapor, and / or direct light outward from elongated slot 360.

[0077] In some embodiments, the exemplary photonic crystal receiver 350 functions as a Rydberg atom-based radar receiver with electric field sensitivity that is enhanced by a significant factor (e.g., a factor of about 1000, or another factor) compared to a bare vapor cell. The exemplary photonic crystal receiver 350 can have sensitivity at least comparable to conventional receivers and can be capable of reaching the thermal noise floor. A method for fabricating a photonic crystal receiver involves laser machining of silicon and glass, which allows for the formation of microstructures in these materials with μm precision and feature sizes of less than 10 μm. Such precision and feature scale are well suited for photonic crystal frames that interact with radio frequency fields, since the wavelength of radio frequency fields is much larger than 10 μm. The high accuracy of the machining process relative to the wavelength of the target radiation can also reduce losses in the device.

[0078] 2A and 2B, the communication system 200 may be configured to include a unidirectional communication channel. For example, the first station 202 may include a photonic crystal maser (e.g., photonic crystal maser 202a), and the second station 204 may include a receiver (e.g., a metal antenna or photonic crystal receiver 204b). However, one or both of the first station 202 and the second station 204 may include a transceiver having two main components. In these variations, the first component is a receiving device (Rx component), and the second component is a transmitting device (Tx component) based on the photonic crystal maser. For example, the transceiver may include one or more photonic crystal masers and one or more photonic crystal receivers. The transceiver may enable the first station 202 and the second station 204 of the communication system 200 to establish a bidirectional communication channel.

[0079] In communication systems, and sometimes in radar systems, it can be advantageous to separate the receiving and transmitting components. This separation can mitigate signal crosstalk between the receiving and transmitting components, which are typically formed from metal, and thus enable higher data rates than could otherwise be achieved. The separation can allow each component to be optimized for its specific operation. However, due to the all-dielectric construction, communication system 200 can combine a photonic crystal maser and a photonic crystal receiver in close proximity while simultaneously enabling higher performance than achieved with conventional metal receiving transmitting components. Moreover, the photonic crystal maser generates a laser-like directional output, which can enable communication system 200 to operate as a point-to-point communication system. In variations in which a station transceiver includes a photonic crystal maser and a photonic crystal receiver, these components can use the same laser system to generate or receive radio frequency signals using atoms partially in the Rydberg state. By sharing a laser subsystem, the station can be more compact. Other advantages are possible.

[0080] The photonic receiver is based on the idea of increasing the interaction time and local electric field strength in the region where the vapor is present. The photonic crystal receiver includes a photonic crystal structure that couples incident RF electromagnetic radiation into a waveguide. The waveguide includes slots for concentrating the incident RF electromagnetic radiation, which is configured to decelerate the incident RF electromagnetic radiation and increase its interaction time with the vapor. In some cases, the field of the incident RF electromagnetic radiation can be enhanced by approximately a thousand times. This enhancement can increase the sensitivity of the photonic crystal receiver to the thermal noise floor. Two-photon or three-photon preparation and reading methods can be performed in a collinear configuration. However, higher-order photon processes are possible. In some variations, a three-photon process is used. A three-photon process can increase the number of atoms or molecules in the vapor that interact with the laser field, but requires three lasers instead of two. For this reason, some variations may rely on photonic crystal receivers that use two-photon processes, such as those used in Rydberg atom-based sensing. Multiphoton processes for photonic crystal receivers are further described in US Pat. No. 11,137,432, entitled "Photonic Crystal Receivers," the entire disclosure of which is incorporated herein by reference.

[0081] Similar to a photonic crystal receiver, a photonic crystal maser includes a photonic crystal structure and an elongated vapor cell therein. Rydberg atoms (e.g., a vapor of atoms) in a highly reflective cavity can generate phasing at an extremely low threshold, even at very low atomic vapor pressures. Furthermore, atoms or molecules in a traveling-wave waveguide can also be made to exhibit phasing. A photonic crystal maser can manipulate the field of target RF electromagnetic radiation to enhance its interaction with the vapor, such as through a waveguide defined by a photonic crystal structure (e.g., an array of cavities and elongated slots therein). Thus, the vapor experiences a modified electromagnetic environment that favors its emission into the resonant modes of the waveguide. If the enhanced emission is sufficiently large, the vapor reaches the phasing threshold, and the photonic crystal maser emits radiation coherently. If the enhancement is lower, the photonic crystal maser can reach the operating regime of a photonic crystal receiver. For example, phasing can occur when the vapor emission rate A at the phasing transition multiplied by the quality factor Q of the waveguide or cavity divided by the phasing frequency w is greater than 1 (i.e., AQ / w>1). When AQ / w is less than 1, the photonic crystal maser can operate as a photonic crystal receiver. The operating characteristics of photonic crystal masers are further described in U.S. patent application Ser. No. 17 / 514,819, entitled "Photonic Crystal Masers," the disclosure of which is incorporated herein by reference in its entirety.

[0082] To ensure operation as a maser, the photonic crystal structure of the photonic crystal maser can be configured to increase the Q, for example. In some variations, the photonic crystal structure is configured to include photonic crystal mirrors. These mirrors can enable reflectivities of up to 98%, which is sufficient to achieve masing due to their low threshold. Furthermore, output powers of over 10 nanowatts can be achieved. These powers are sufficient for terrestrial point-to-point communication systems but too low for spaceborne systems. To increase power, the photonic crystal maser can be amplified using a vapor cell or another waveguide structure with atoms pumped to the same state as the photonic crystal maser, which can be efficiently coupled by a waveguide coupler. In many cases, output powers in the milliwatt range are possible.

[0083] In some embodiments, communication system 200 is configured as a point-to-point communication system. The range of a point-to-point communication system can be affected by several factors. For example, the beam of targeted RF electromagnetic radiation may be attenuated along its path. The beam of targeted RF electromagnetic radiation may also be diverged (or less focused) along its path. However, photonic crystal receivers have sufficient sensitivity that attenuation of the beam of RF electromagnetic radiation does not disrupt communications. For example, when configured as a Rydberg atom receiver, the photonic crystal receiver can detect signals of approximately -110 dBm in a 20 MHz bandwidth. By comparison, the attenuation relative to the horizon, which is conservatively estimated at approximately 30 km for most applications, is less than 3 dBm. Furthermore, an unamplified photonic crystal maser operating at -60 dBm still has a large link margin operating with a large signal-to-noise ratio. A similar analysis applies to transmissions through the atmosphere from a satellite, since most of the atmosphere is contained within the stratosphere, which terminates at approximately 30 km.

[0084] However, beam divergence of the target RF electromagnetic radiation can have a stronger effect on the stability of the communication channel. For example, if a photonic crystal generates approximately 10 nanowatts of power at 80 GHz and the resulting beam is collimated to a diameter of 75 cm, the angular divergence of the beam is approximately 0.5 degrees. At a distance of 30 km, the beam diameter increases to approximately 100 m based solely on optical elements (e.g., a Gaussian beam assuming 86% of the power within the spot size). Assuming a similar photonic crystal receiver entrance aperture, the signal level at the photonic crystal receiver can be estimated to be approximately -93 dBm, assuming a 20 MHz bandwidth, which is 17 dBm above the receiver noise level.

[0085] In some variations, the output power of the photonic crystal maser can be increased to neutralize the adverse effects of beam divergence (e.g., to about 1 milliwatt). For example, at 1 milliwatt output power, the station aperture can be significantly reduced depending on the application. If the station is located in low Earth orbit (LEO) at about 2000 km (e.g., the station is a satellite), the spot size on Earth as transmitted by the station will be 6 km in size. To achieve the same signal margin, approximately 100 μm of power is required, significantly lower than current RF systems in orbit. However, the 2000 km distance is the outer limit of LEO. Most satellites in LEO are below 1000 km, with some as low as 160 km. At these distances, communication from the station can be reliably performed without photonic crystal maser amplification. In geosynchronous orbit (GEO) at about 35,000 km, tens of milliwatts are required, but in this case, the photonic crystal maser can be amplified. It will be appreciated that a larger beam size, when compared to laser communications, may also reduce the accuracy requirements on the tracking subsystem while still maintaining many of the advantages of point-to-point communications.

[0086] Referring now to FIG. 4, a block diagram of an exemplary station in a point-to-point communication system is presented. The exemplary station may be similar to the first station 202 and the second station 204 described in connection with FIGS. 2A and 2B. The transmitter is a photonic crystal maser, and the receiver may be a conventional receiver (e.g., a metal antenna) or a photonic crystal receiver. In variations in which the receiver is a photonic crystal receiver, the transmitter and receiver may operate from the same or different laser subsystems. Modulation of the maser signal and demodulation of the received signal may occur partly at the physical layer and partly at the application layer. For example, heterodyne detection may occur in the receiver itself by beating a portion of the maser signal with the received signal. Once the received signal is converted to an electrical signal by a detector using light transmitted through the receiver, further processing may occur digitally, such as by a data processing subsystem.

[0087] In some embodiments, the transmitter is a photonic crystal maser (e.g., a Rydberg atomic maser). The amplitude of the photonic crystal maser can be modulated by switching the pump laser on and off. Phase and frequency modulation can be achieved by injection locking the photonic crystal maser to a stable RF source (e.g., a reference RF oscillator in a reference RF subsystem). Injection locking can be performed by using an output coupler on one side of the photonic crystal maser, and in some variations involves inserting the output coupler into an antenna or waveguide. Only a small amount of power may be required to injection lock the photonic crystal. The injection lock signal need only be large enough to bias the maser to the phase and frequency of the injected wave. Phase or frequency modulation of the injection lock can be used to frequency or phase modulate the output of the photonic crystal maser. A photonic crystal maser can be made coherent with a photonic crystal maser at another station if the two are synchronized. Synchronization can be achieved by locking the injected RF waves to a synchronized clock, possibly part of the inertial navigation unit.

[0088] In some embodiments, the receiver is a photonic crystal receiver (e.g., a Rydberg atom receiver). The antenna structure of the photonic crystal receiver can implement a polarizer, making it sensitive to the polarization of the input (or incident) beam of RF electromagnetic radiation. Two photonic crystal receivers can be used to detect polarization-modulated signals. Moreover, multiple photonic crystal receivers can be grouped together to receive input beams at multiple frequencies and polarizations. The photonic crystal receiver can include a parabolic antenna to increase the intensity of the incident RF electromagnetic radiation beam. The photonic crystal receiver can be oriented using a tracking subsystem (e.g., a three-axis motorized mechanical drive and a gimbal mount). Furthermore, fine adjustments can be made through three-axis control of optical elements such as mirrors. The vapor in the vapor cell of the photonic crystal receiver can be optically prepared and read (e.g., by a probe laser, a coupling laser, etc.). The optical signal can be transported to the vapor cell via a fiber optic cable. Arrays of broadband Rydberg atom receivers and vapor cells, which have lower sensitivity, can also be used in the exemplary station. An array of vapor cells can be advantageous because it presents a larger target, thereby making it easier to point and track.

[0089] In some variations, the exemplary station can include a reference component, such as an antenna or Rydberg atomic maser, for determining phase and frequency. The reference component can generate reference RF electromagnetic radiation for superposition on an input beam of RF electromagnetic radiation (e.g., a beam incident on a photonic crystal receiver). The determined phase and frequency can be used, for example, via heterodyne measurements using a transmission maser or an injection seeding source. The Rydberg atomic maser can also be used as an amplifier for the incident beam or to provide a reference signal. The Rydberg atomic maser can also be dielectric and primed or pumped by the same laser type used to read and prime the photonic crystal receiver. Because the photonic crystal receiver can be self-calibrating, absolute amplitude information can be used by the exemplary station to improve pointing stability.

[0090] In some embodiments, an exemplary station includes a laser subsystem having an input laser for generating preparation and readout signals. The laser subsystem may also include a laser stabilization device (e.g., a laser lock and tuning reference) and electronics for switching laser frequencies (for multi-frequency systems using a single laser source). The exemplary station also includes an optical subsystem configured for signal acquisition via a photodetector or the like. The exemplary station may additionally include low-level electronics required to control the laser and optical subsystem. For an exemplary station with multiple photonic crystal receivers, this example may include multiple input lasers or switches, such that a reduced number of input lasers can drive the exemplary station. The electronics also include a laser intensity stabilization unit and necessary actuators for frequency stabilizing the input laser to a reference, such as a Fabry-Perot cavity, a reference vapor cell, or a wavemeter. The exemplary station may also include a reference RF subsystem having a reference RF oscillator (e.g., a microwave oscillator) for injection-locking the photonic crystal maser. This reference RF oscillator may be referenced to an inertial navigation clock or a timing subsystem (e.g., GPS). In some variations, the reference RF oscillator is coupled to the photonic crystal maser via a waveguide or antenna.

[0091] In some embodiments, the exemplary station includes an inertial navigation unit. The clock signal can be used to synchronize the time and phase of signal detection and can also serve as a synchronization signal for the inertial navigation unit to position the station. The clock signal can be derived from a GPS signal if satellite communications are available (operating in a non-GPS denial area). However, in some variations, the exemplary station includes a backup clock such as an atomic clock (e.g., based on Cs or Rb), a maser, or a quartz crystal oscillator. A chip-scale atomic clock can be used. These devices can be combined with GPS to resynchronize signals; for example, the clock can be GPS-steered. The maser clock can be located at another remote location, and its synchronization signal can be transmitted to the exemplary station via a communication channel. The synchronization signal can be transmitted between stations to synchronize the clocks, as shown in Figures 1 and 2A. The clock signal can also be used to synchronize a photonic crystal maser in each station by synchronizing the injection seed frequency and phase in each station.

[0092] An inertial navigation unit can be located with the exemplary station to determine its position. In some cases, the inertial navigation unit and GPS can be used for coarse orientation to establish a link between the Tx and Rx components at each station in the point-to-point communication system. The inertial navigation unit may include a clock (or several clocks and a GPS) used for timing, an accelerometer, a GPS receiver, and a gyroscope, or some combination thereof. In some variations, the exemplary station maintains communication with satellites. In these variations, GPS positioning may be used. If satellite communication is denied for a period of time, the inertial navigation unit can track position if moving. The inertial navigation unit can then reinitialize itself when GPS communication is restored. Communication with another station can be used to update the clock at the other station by transmitting timing information. Because photonic crystal receivers can self-calibrate, it is also possible to obtain position using RF ranging between stations in a point-to-point communication system. This latter point is particularly useful when one of the base stations is operating in a GPS-denied environment and the other is not (or when some stations in a point-to-point communications system are GPS-denied and others are not).

[0093] In some embodiments, an exemplary station includes a tracking subsystem. The tracking subsystem is operable to orient and track the Rx and Tx components so that the Tx on one station is aligned with the Rx on the other station. In cases involving satellite communications, the tracking subsystem can handle multiple layers of signal acquisition. The tracking subsystem can include actuators for controlling gimbal mounts that orient devices (e.g., transmitters, receivers, transceivers) or control mirror orientations. For example, the course actuators and control system can have a wide field of view, so that the incoming beam of RF electromagnetic radiation can be more easily acquired with subsequent refinements until the communications channel is locked at the Rx and Tx level. GPS positioning can be used at the coarsest level of the system, along with an inertial navigation unit. RF beacons with a wider field of view can then be used. RF antennas or expanded maser beams can be used to establish communications links. Positioning can also be refined using an inertial navigation system to predict the location of a moving target. Active locking of the communications channel can be used once the channel is established.

[0094] In some embodiments, an exemplary station includes modulation electronics. The modulation electronics can serve to control the characteristics of the beam of RF electromagnetic radiation (or Tx signal) (e.g., the output beam) generated by the photonic crystal maser. Modulation of the Tx signal can be achieved in several different ways. For example, a pump laser can be turned on and off to modulate the amplitude of the Tx signal. Communication schemes such as pulse position modulation and on-off keying can be used. Phase and frequency modulation can be achieved by injection seeding the maser with another RF wave. The injection seed biases the maser to mese in phase and at the seed's frequency. If the seed is phase-locked to clocks at two or more stations in the point-to-point communication system, a coherent detection strategy can be used. These encoding message schemes enable methods such as phase shift keying, differential phase shift keying, frequency shift keying, and polarization shift keying. Polarization shift keying is also possible, but requires two masers emitting different polarizations.

[0095] In some embodiments, the exemplary station includes demodulation electronics. The demodulation electronics can serve to determine the time-varying characteristics of an input beam (or Rx signal) of RF electromagnetic radiation (e.g., an incoming beam) received by the photonic crystal receiver. In Rydberg atom-based detection, the incoming Rx signal is optically read. The resulting optical signal can be detected, for example, on a square-law detector. While amplitude detection is simple as a result, phase and frequency detection can involve overlapping a reference RF electromagnetic radiation (e.g., generated by a reference component) with the incoming signal. Interference between the reference RF electromagnetic radiation and the input beam of RF electromagnetic radiation can be used to determine the phase and frequency of the incident field relative to the reference field. These methods can be implemented using so-called homodyne or heterodyne detection of the signal. In some variations, demodulation of the Rx signal can be achieved by using part or all of the signal from an injection-locked photonic crystal maser. The signal can provide the reference RF electromagnetic radiation, in part or in whole. It is also possible to generate a signal referenced to a system clock from the antenna and use it as a reference. If the receiver is a conventional antenna (but RF coupled to an injection-locked photonic crystal maser), then a high-speed detector and spectrum analyzer can be used to obtain the phase and frequency relative to the clock.

[0096] In some embodiments, an exemplary station includes signal processing electronics. The signal processing electronics can communicate with the laser subsystem to control the characteristics of the optical signal provided by the pump laser to the photonic crystal maser. The signal processing electronics can also control the characteristics of the input optical signal provided by the input laser to the photonic crystal maser. The signal processing electronics can cooperate with the optical subsystem to generate spectroscopic data. For example, the signal processing electronics and optical subsystem can capture the received optical signal (or the output optical signal) and remove noise from the signal before generating the spectroscopic data. The spectroscopic data can then be sent to the data processing subsystem for further processing (e.g., formatting operations as shown in FIG. 7). The signal processing subsystem and optical subsystem can extract pulses or other communication waveforms using methods such as matched filtering. They can also capture beat signals from the demodulation electronics and convert the beat signals to frequency and phase data. In some cases, the signal processing electronics includes FPGA circuitry designed for a particular signaling protocol. If the signaling protocol changes, for example, phase shift keying for amplitude modulation, the FPGA can be reprogrammed on the fly.

[0097] In some embodiments, the exemplary station includes a data processing subsystem. The data processing subsystem can operate to establish an application layer that processes the spectrum acquired by the optical subsystem to obtain intensity, phase, or frequency (or a combination thereof) and turn it into time-series data. FIG. 5 presents a schematic diagram of exemplary application layers utilized by the data processing subsystem to handle the Rx data flow to and Tx data flow from the exemplary station of FIG. 4. The time-series data can be correlated to a timing system to receive information. To transmit information, the data processing subsystem packages the information and prepares it for modulation electronics. The modulation electronics modulates the output of the photonic crystal maser (e.g., a beam of RF electromagnetic radiation) to transmit the information. The data processing subsystem also takes amplitude, frequency, and phase information from the incoming signal, packages it, and prepares it for the communications interface. Similarly, the data processing subsystem takes signals generated by the communications interface and prepares them for modulation electronics to send through the photonic crystal maser.

[0098] In some variations, the data processing subsystem consists of a system-on-chip (SoC). The SoC can be a CPU combined with a field-programmable gate array (FPGA). The data processing subsystem can manipulate the time-series data before transmitting it to the communication interface. On-off keying and pulse-position modulation are two possible intensity modulation methods that can be used. Phase-shift keying, differential phase-shift keying, frequency-shift keying, or polarization-shift keying can also all be used. These latter methods can be implemented when the photonic crystal maser is injection-seeded with a reference RF signal (or electromagnetic radiation). Injection locking locks the phase and frequency and links it to a stable clock signal. To use polarization-shift keying, two orthogonal photonic crystal masers with different polarizations can be used along with two polarization-sensitive receivers (e.g., two orthogonal photonic crystal receivers). Phase and frequency (generally, phase or angle) can be determined by heterodyne measurements using synchronized masers in each transceiver. 6 presents a schematic diagram of exemplary message formats, including exemplary synchronization, signaling, and traffic packets. The exemplary message formats may be generated by the data processing subsystem before being passed to the communication interface, or alternatively, may be received by the data processing subsystem from the communication interface.

[0099] In some embodiments, the exemplary station includes a communications interface. The communications interface exchanges data with the data processing subsystem. The data may be the result of computer processes running in the application layer. The communications interface may also be an SoC or a series of specialized SoCs. The configuration of the SoC depends on the number and nature of the communications channels. The communications interface may connect to the data processing subsystem via wired, wireless, or fiber optic communications means, or any combination thereof. The communications interface protocol may be specific to the channel, the required data rate, and the required timing. For example, codecs, voice, and video may be used. The communications interface may also be used to tune or maintain the exemplary station, as well as to input and extract data. In some cases, for example, a computer with an audio-to-digital transducer may be present. Data may be input via a keyboard, voice, or other such medium. Data storage may also be associated with the communications interface.

[0100] Referring now to FIG. 7 , a schematic diagram of an exemplary process for converting an input beam of RF electromagnetic radiation into time-series data is presented. The input beam of RF electromagnetic radiation is received by a photonic crystal receiver of the exemplary station. In particular, the schematic diagram shows how output optical signals from the photonic crystal receiver are processed and converted into time-series data that may represent voice data, codec data, video data, and the like. The application layer of the data processing subsystem can communicate with the inertial navigation unit of the tracking system to schedule and determine whether a communication channel is open. These subsystems can also cooperate to maintain the communication channel and, in doing so, can operate through the inertial navigation unit. Timing electronics of a local clock can provide a clock signal for the exemplary station. The clock signal can be used to format synchronization signals for the exemplary station and queue management.

[0101] In some embodiments, the communication system includes a first station and a second station having respective transceivers including a plurality of photonic crystal masers and receivers. The communication system may be a point-to-point communication system. Moreover, the photonic crystal masers may be similar to the photonic crystal masers 202a and 204a described in connection with FIGS. 2A and 2B and the exemplary photonic crystal maser 300 described in connection with FIG. 3A. The photonic crystal receiver may be similar to the photonic crystal receivers 202b and 204b described in connection with FIGS. 2A and 2B and the exemplary photonic crystal receiver 350 described in connection with FIG. 3B.

[0102] Each station of the communication system includes a transceiver having one or more photonic crystal masers and one or more photonic crystal receivers. In particular, each photonic crystal maser is configured to generate an output beam of RF electromagnetic radiation in response to receiving a first input optical signal. The output beam represents information to be transmitted to another station of the communication system. Moreover, each photonic crystal receiver is configured to generate an output optical signal in response to receiving an input beam of RF electromagnetic radiation and a second input optical signal. The input beam represents information received from another station of the communication system. In some variations, the one or more photonic crystal masers include a pair of photonic crystal masers configured to generate respective output beams of RF electromagnetic radiation having orthogonal polarizations. In some variations, the one or more photonic crystal receivers include a pair of photonic crystal receivers configured to process respective input RF electromagnetic beams at orthogonal polarizations.

[0103] The first station and the second station each also include a control subsystem that can function in part as a laser control subsystem. The control subsystem has one or more lasers optically coupled to one or more photonic crystal masers and one or more photonic crystal receivers. The one or more lasers are configured to generate a first input optical signal and a second input optical signal. The control subsystem also includes modulation electronics in communication with the one or more lasers. The modulation electronics are configured to control one or more characteristics of the first input optical signal. The one or more characteristics of the first input optical signal include the intensity, frequency, or phase of the first input optical signal. The control subsystem additionally includes demodulation electronics in communication with the one or more lasers. The demodulation electronics are configured to control one or more characteristics of the second input optical signal. The one or more characteristics of the second input optical signal include the intensity, frequency, or phase of the second input optical signal.

[0104] In some embodiments, the first station and the second station each additionally include a tracking subsystem configured to control the orientation of the transceiver and thereby direct the one or more photonic crystal masers and one or more photonic crystal receivers toward a target location. In some variations, the first station is disposed at the target location of the second station, and the second station is disposed at the target location of the first station. In some variations, the communication station includes a relay station disposed at a relay location and configured to receive and transmit a beam of target RF electromagnetic radiation. The relay location serves as the target location for the tracking subsystems of one or both of the first station and the second station.

[0105] In some embodiments, the first and second communication systems include navigation subsystems in communication with the control and tracking subsystems. The navigation subsystems may include positioning electronics configured to determine a position of the first or second station and timing electronics configured to set local reference parameters for the first or second station. One or both of the position and timing electronics may define part or all of the inertial navigation unit. The local reference parameters may include parameters such as a local reference time, a local reference frequency, and a local reference phase. In further embodiments, the communication system includes a global reference station configured to exchange synchronization signals with the navigation subsystems of at least the first and second stations. The synchronization signals represent global reference parameters of the communication system, including a global reference time. The global reference parameters may also include one or both of a global reference frequency and a global reference phase.

[0106] In some embodiments, the control subsystems of the first station and the second station include an optical detector optically coupled to the one or more photonic crystal receivers and configured to generate a set of spectroscopic data for each photonic crystal receiver. The set of spectroscopic data is based on output optical signals from the photonic crystal receivers and represents one or more characteristics of the input beam of RF electromagnetic radiation. The one or more characteristics of the input beam of RF electromagnetic radiation may include at least one of intensity, phase, frequency, or polarization of the input beam of RF electromagnetic radiation.

[0107] In embodiments in which the control system includes an optical subsystem, the first station and the second station may each include a data processing subsystem in communication with the control subsystem. The data processing subsystem is configured to perform operations including generating a first time series of data based on a set of spectroscopic data received from the optical detector over time. The first time series of data represents information to be transmitted from another station in the communication system. The operations also include generating a control signal for the modulation electronics based on a second time series of data received from a communication interface of the first station or the second station. The control signal represents one or more characteristics of the first input optical signal over time. The second time series of data represents information to be transmitted to another station in the communication system.

[0108] In some embodiments, the control subsystems of the first and second stations include a reference antenna electromagnetically coupled to at least one photonic crystal receiver of the transceiver. The reference antenna is configured to generate reference RF electromagnetic radiation having one or more controlled characteristics, including at least one of a controlled amplitude, a controlled frequency, or a controlled phase. During operation, the reference antenna can superimpose the reference RF electromagnetic radiation onto an input beam of RF electromagnetic radiation received by the photonic crystal receiver. Such superposition can cause interference between the reference RF electromagnetic radiation and the input beam of RF electromagnetic radiation, thereby allowing the phase and frequency of the input beam of RF electromagnetic radiation to be determined relative to a reference field of the reference RF electromagnetic radiation.

[0109] In some aspects of what has been described, the communication system can be illustrated by the following examples. Example 1. A communication system, It is the first station, Photonic crystal maser a photonic crystal structure formed from a dielectric material and having an array of cavities and elongated slots disposed within defect regions of the array of cavities; and a vapor disposed within the elongated slot and operable to emit targeted RF electromagnetic radiation in response to receiving an optical signal; the array of cavities and the elongated slots define a waveguide configured to shape the targeted RF electromagnetic radiation into a beam when emitted, the beam of targeted RF electromagnetic radiation representing information to be transmitted to a second station of the communications system; Photonic crystal maser, In the laser subsystem, a pump laser optically coupled to the elongated slot and configured to generate an optical signal; and signal processing electronics in communication with the pump laser and configured to control one or more characteristics of the optical signal, the one or more characteristics of the optical signal including at least one of an intensity, a phase, or a frequency of the optical signal; a laser subsystem comprising: a tracking subsystem configured to control the orientation of the photonic crystal maser to thereby direct the beam of targeted RF electromagnetic radiation toward a targeted location. a first station comprising: a second station comprising a receiver configured to couple to the beam of target RF electromagnetic radiation; A communication system comprising: Example 2. the target location is a first target location; 2. The communication system of example 1, wherein the second station comprises a second tracking subsystem configured to control the orientation of the receiver to direct the receiver toward a second target location. Example 3. The communication system of example 2, wherein the first station and the second station are located at the second target location and the first target location, respectively. Example 4. a relay station disposed at a relay location and configured to receive and transmit a beam of targeted RF electromagnetic radiation; 3. The communication system of example 2, wherein one or both of the first target location and the second target location correspond to a relay location. Example 5. The communication system of example 1 or any one of examples 2-4, wherein the waveguide is configured to reduce the group velocity of the target RF electromagnetic radiation along a direction parallel to the axis of the elongated slot. Example 6. The communication system of example 1 or any one of examples 2-5, wherein the photonic crystal maser comprises an output coupler configured to impedance match the beam of target RF electromagnetic radiation to an environment surrounding the photonic crystal maser. Example 7. The communication system of example 6, wherein the output coupler is an integral part of the photonic crystal structure. Example 8. The output coupler terminates in a tapered end, a constricted portion aligned with the tapered end; an array of coplanar segments extending outwardly from the constriction and periodically spaced therealong, the array of coplanar segments being configured to filter polarization of the beam of target RF electromagnetic radiation; and 8. The communication system according to claim 6 or 7, comprising: Example 9. the first station comprises a reference RF subsystem configured to generate reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase; The communication system of example 1 or any one of examples 2-8, wherein the photonic crystal maser comprises an input coupler configured to couple reference RF electromagnetic radiation into the waveguide. Example 10. The communication system of example 9, wherein the output coupler is an integral part of the photonic crystal structure. Example 11 The receiver is a photonic crystal receiver, a second photonic crystal structure formed from a dielectric material, the second photonic crystal structure having a second array of cavities and a second elongated slot, the second elongated slot being disposed within a defect region of the second array of cavities; an antenna structure configured to couple a beam of target RF electromagnetic radiation into a second waveguide defined by a second array of cavities and a second elongated slot, the second waveguide configured to concentrate the coupled beam within the second elongated slot; and a second steam turbine disposed within the second elongated slot; Equipped with The second station is a second laser subsystem, the second laser subsystem comprising: one or more input lasers optically coupled to the second elongated slot and configured to provide an input optical signal thereto, the input optical signal adapted to interact with one or more electronic transitions of the second vapor; an optical subsystem configured to generate spectroscopic data based on the output optical signal from the second vapor, the spectroscopic data representing one or more characteristics of the beam of target RF electromagnetic radiation; and a data processing subsystem configured to generate time series data based on the time-lapse spectroscopic data, the time series data representing information transmitted from the first station; and The communication system according to any one of the first embodiment and the second to tenth embodiments, comprising: Example 12. The communication system of example 11, wherein the antenna structure is an integral part of the second photonic crystal structure. Example 13. The communication system of example 11 or 12, wherein the second waveguide is configured to reduce a beam group velocity of the coupled target RF electromagnetic radiation along a direction parallel to the axis of the second elongated slot. Example 14. A communication system as described in Example 11 or any one of Examples 12-13, wherein the one or more characteristics of the beam of targeted RF electromagnetic radiation include at least one of the intensity, phase, or frequency of the beam. Example 15. the antenna structure comprises a polarizer configured to filter polarization of the beam of targeted RF electromagnetic radiation; The communication system of example 11 or any one of examples 12-14, wherein the one or more characteristics of the beam of targeted RF electromagnetic radiation include a polarization of the beam of targeted RF electromagnetic radiation. Example 16. the second station comprises a reference antenna configured to generate second reference RF electromagnetic radiation, the second RF electromagnetic radiation having one or more controlled characteristics including at least one of a controlled amplitude, a controlled frequency, or a controlled phase; The communication system according to embodiment 11 or any one of embodiments 12 to 15, wherein the reference antenna is electromagnetically coupled to the antenna structure of the photonic crystal receiver.

[0110] In some embodiments of what has been described, methods of communicating information using radio frequency (RF) electromagnetic radiation can be illustrated by the following examples. Example 17. A method of communicating information using radio frequency (RF) electromagnetic radiation, comprising: generating, at a first station, a beam of targeted RF electromagnetic radiation representing information to be transmitted to a second station, the first station comprising: The photonic crystal maser includes: a photonic crystal structure formed from a dielectric material, the photonic crystal structure having an array of cavities and an elongated slot, the elongated slot being disposed within a defect region of the array of cavities; and a vapor disposed within the elongated slot and operable to emit targeted RF electromagnetic radiation in response to receiving an optical signal; the array of cavities and the elongated slots define a waveguide that is configured to, upon emission, shape the targeted RF electromagnetic radiation into a beam of targeted RF electromagnetic radiation; and receiving the beam of targeted RF electromagnetic radiation at a second station, the second station comprising a receiver configured to couple to the beam of targeted RF electromagnetic radiation; A method comprising: Example 18. the first station comprises a laser subsystem having a pump laser optically coupled to the elongated slot; 18. The method of example 17, wherein generating the beam of targeted RF electromagnetic radiation includes generating an optical signal by operation of a pump laser. Example 19. the laser subsystem comprises signal processing electronics in communication with the pump laser; 19. The method of example 18, wherein generating the optical signal includes controlling one or more characteristics of the optical signal by operation of signal processing electronics, the one or more characteristics of the optical signal including at least one of an intensity, a phase, or a frequency of the optical signal. Example 20. The method of any one of example 17 or examples 18-19, comprising reorienting the photonic crystal maser to direct the beam of targeted RF electromagnetic radiation toward the targeted location by operation of a tracking subsystem of the first station. Example 21. the target location is a first target location; 21. The method of example 20, wherein the method includes reorienting the receiver by operation of a tracking subsystem of the second station to point the receiver toward the second target location. Example 22. The method of Example 21, wherein the first station and the second station are located at the second target location and the first target location, respectively. Example 23. the first target location and the second target location correspond to locations of the relay station; 22. The method of example embodiment 21, wherein the method includes transmitting, by operation of the relay station, a second beam of targeted RF electromagnetic radiation to the second station in response to reception at the relay station of the beam of targeted RF electromagnetic radiation from the first station. Example 24. The method of example 17 or any one of examples 18-23, wherein generating the beam of targeted RF electromagnetic radiation includes reducing the group velocity of the targeted RF electromagnetic radiation along a direction parallel to the axis of the elongated slot. Example 25. The photonic crystal maser includes an output coupler; The method of any one of Example 17 or Examples 18 to 24, wherein generating the beam of targeted RF electromagnetic radiation includes impedance matching the beam of targeted RF electromagnetic radiation to an ambient environment of the photonic crystal maser by operation of an output coupler. Example 26. The photonic crystal maser comprises an input coupler; The method is: generating reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase; By operation of the input coupler, reference RF electromagnetic radiation is coupled into the waveguide; The method of any one of Example 17 or Examples 18-25, comprising: Example 27. The receiver is a photonic crystal receiver, a second photonic crystal structure formed from a dielectric material and having a second array of cavities and a second elongated slot, the second elongated slot being disposed within a defect region of the second array of cavities; and an antenna structure aligned with the elongated slot; a second steam turbine disposed within the second elongated slot; Equipped with The method of any one of example 17 or examples 18-26, wherein receiving the beam of targeted RF electromagnetic radiation includes coupling, by operation of the antenna structure, the beam of targeted RF electromagnetic radiation into a second waveguide defined by a second array of cavities and a second elongated slot. Example 28. The method of Example 27, wherein receiving the beam of RF electromagnetic radiation includes concentrating the combined beam into the second elongated slot by operation of the second waveguide. Example 29. The second station is a second laser subsystem, the second laser subsystem comprising: one or more input lasers optically coupled to the second elongated slot; an optical subsystem optically coupled to the second elongated slot; Equipped with The method is: generating an input optical signal of the second vapor by operation of one or more pump lasers, the input optical signal adapted to interact with one or more electronic transitions of the second vapor; generating spectroscopic data based on the output optical signal from the second vapor by operating the optical subsystem, the spectroscopic data being indicative of one or more characteristics of the beam of target RF electromagnetic radiation; and The method of Example 27 or 28, comprising: Example 30. the second laser subsystem includes a data processing subsystem in communication with the optical subsystem; The method is: 30. The method of example 29, including generating, by operation of the data processing subsystem, time series data based on sets of spectroscopic data received from the optical subsystem over time, the time series data representing information transmitted from the first station.

[0111] In some aspects of what has been described, the communication system can be illustrated by the following examples. Example 31. A communication system, The system includes a first station and a second station, wherein the first station and the second station 1. A transceiver having one or more photonic crystal masers and one or more photonic crystal receivers, each photonic crystal maser configured to generate an output beam of RF electromagnetic radiation in response to receiving a first input optical signal, the output beam representing information to be transmitted to another station in the communications system; each photonic crystal receiver configured to generate an output optical signal in response to receiving an input beam of RF electromagnetic radiation and a second input optical signal, the input beam representing information received from another station in the communications system; A transceiver; In the control subsystem, one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers, the lasers configured to generate a first input optical signal and a second input optical signal; modulation electronics in communication with the one or more lasers and configured to control one or more characteristics of a first input optical signal, the one or more characteristics of the first input optical signal including an intensity, a frequency, or a phase of the first input optical signal; and demodulation electronics in communication with the one or more lasers and configured to control one or more characteristics of the second input optical signal, the one or more characteristics of the second input optical signal including an intensity, a frequency, or a phase of the second input optical signal; a control subsystem comprising: a tracking subsystem configured to control the orientation of the transceiver to thereby direct the one or more photonic crystal masers and the one or more photonic crystal receivers toward a target location; A communication system comprising: Example 32. The first station and the second station are: a navigation subsystem in communication with the control subsystem and the tracking subsystem, each of which includes: positioning electronics configured to determine a position of the first station or the second station; timing electronics configured to set local reference parameters of the first station or the second station, the local reference parameters including a local reference time; 32. The communication system of claim 31, comprising: Example 33. The communication system of Example 32, wherein the local reference parameters include one or both of a local reference frequency and a local reference phase. Example 34. 34. The communication system of embodiment 32 or 33, comprising a global reference station configured to exchange synchronization signals with navigation subsystems of at least the first station and the second station, the synchronization signals representing global reference parameters of the communication system including a global reference time. Example 35. The communication system of Example 34, wherein the global reference parameters include one or both of a global reference frequency and a global reference phase. Example 36. The control subsystem comprises: A communication system as described in Example 31 or any one of Examples 32 to 35, comprising an optical detector optically coupled to one or more photonic crystal receivers and configured to generate a set of spectroscopic data for each photonic crystal receiver, the set of spectroscopic data being based on output optical signals from the photonic crystal receivers and representing one or more characteristics of the input beam of RF electromagnetic radiation. Example 37. The communication system of Example 36, wherein the one or more characteristics of the input beam of RF electromagnetic radiation include at least one of an intensity, a phase, a frequency, or a polarization of the input beam of RF electromagnetic radiation. Example 38: The first station and the second station Each of the data processing subsystems communicates with the control subsystem, the data processing subsystems comprising: generating a first time series of data based on a set of spectroscopic data received from the optical detector over time, the first time series of data representing information transmitted from another station in the communication system; generating a control signal for the modulation electronics based on a second time series of data received from a communication interface of the first station or the second station, the control signal representing one or more characteristics of the first input optical signal over time, and the second time series of data representing information to be transmitted to another station in the communication system; 38. The communication system of claim 36 or 37, configured to perform operations including: Example 39. The control subsystem comprises: The communication system of example 31 or any one of examples 32-38, comprising a reference RF oscillator electromagnetically coupled to the at least one photonic crystal maser and configured to generate reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase. Example 40. The control subsystem comprises: A communication system described in Example 31 or any one of Examples 32 to 39, comprising a reference antenna electromagnetically coupled to at least one photonic crystal receiver of the transceiver and configured to generate reference RF electromagnetic radiation having one or more controlled characteristics including at least one of a controlled amplitude, a controlled frequency, or a controlled phase. Example 41. The communication system of example 31 or any one of examples 32-40, wherein the one or more photonic crystal masers include a pair of photonic crystal masers configured to generate respective output beams of RF electromagnetic radiation having polarizations that are orthogonal to each other. Example 42. The communication system of example 31 or any one of examples 32-41, wherein the one or more photonic crystal receivers include a pair of photonic crystal receivers configured to process respective input RF electromagnetic beams at polarizations that are orthogonal to each other. Example 43. The communication system of any one of Examples 31 or 32-42, wherein the first station is located at a target location of the second station, and the second station is located at a target location of the first station. Example 44. a relay station disposed at a relay location and configured to receive and transmit a beam of targeted RF electromagnetic radiation; 44. The communication system of example 1 or any one of examples 32-43, wherein the relay location serves as a target location for a tracking subsystem of one or both of the first station and the second station.

[0112] In some embodiments of what has been described, methods of communicating information using radio frequency (RF) electromagnetic radiation can be illustrated by the following examples. Example 45. A method of communicating information using radio frequency (RF) electromagnetic radiation, comprising: transmitting a beam of RF electromagnetic radiation between a first station and a second station of a communication system, the first station and the second station comprising: 1. A transceiver having one or more photonic crystal masers and one or more photonic crystal receivers, each photonic crystal maser configured to generate an output beam of RF electromagnetic radiation in response to receiving a first input optical signal, the output beam representing information to be transmitted to another station in the communications system; each photonic crystal receiver configured to generate an output optical signal in response to receiving an input beam of RF electromagnetic radiation and a second input optical signal, the input beam representing information received from another station in the communications system; A transceiver; a control subsystem comprising one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers, the control subsystem configured to generate a first input optical signal and a second input optical signal; a tracking subsystem configured to control the orientation of the transceiver to thereby direct the one or more photonic crystal masers and the one or more photonic crystal receivers toward a target location; Each of the methods comprises: Example 46. the first station or the second station is a source of a beam of RF electromagnetic radiation; 46. The method of example 45, wherein transmitting the beams of RF electromagnetic radiation includes generating one or more respective output beams of RF electromagnetic radiation by operation of one or more photonic crystal masers at the source station. Example 47. Transmitting a beam of RF electromagnetic radiation comprises: transmitting a first beam of RF electromagnetic radiation from a first station to a second station; transmitting a second beam of RF electromagnetic radiation from the second station to the first station, the second beam being transmitted at least in part simultaneously with the first beam; The method of Example 45 or 46, comprising: Example 48. a control subsystem of each of the first station and the second station comprising modulation electronics in communication with the one or more lasers; the first station or the second station is a source of a beam of RF electromagnetic radiation; 48. The method of any one of example 45 or example 46-47, wherein the method includes controlling, by operation of modulation electronics of the originating station, one or more characteristics of a first input optical signal generated by the one or more lasers, wherein the one or more characteristics of the first input optical signal include an intensity, a frequency, or a phase of the first input optical signal. Example 49. a control subsystem of each of the first station and the second station including demodulation electronics in communication with the one or more lasers; the first station or the second station is a destination station for the beam of RF electromagnetic radiation; 49. The method of any one of example 45 or examples 46-48, wherein the method includes controlling, by operation of demodulation electronics of the destination station, one or more characteristics of a second input optical signal generated by the one or more lasers, wherein the one or more characteristics of the second input optical signal include an intensity, a frequency, or a phase of the second input optical signal. Example 50. the control subsystem of each of the first station and the second station comprises an optical detector optically coupled to one or more photonic crystal receivers; the first station or the second station is a destination station for the beam of RF electromagnetic radiation; The method of any one of example 45 or examples 46-49, wherein the method includes generating a set of spectroscopic data for each photonic crystal receiver of the destination station by operation of an optical detector of the destination station, the set of spectroscopic data being based on output optical signals from the photonic crystal receivers and representing one or more characteristics of the input beam of RF electromagnetic radiation. Example 51. The method of Example 50, wherein the one or more characteristics of the input beam of RF electromagnetic radiation include at least one of the intensity, phase, frequency, or polarization of the input beam of RF electromagnetic radiation. Example 52. the first station and the second station each include a data processing subsystem in communication with the control subsystem; 52. The method of claim 50 or 51, wherein the method includes generating, by operation of a data processing subsystem of the destination station, a first time series of data based on a set of spectroscopic data received from the optical detector over time, the first time series of data representing information to be transmitted from another station in the communication system. Example 53. The first station and the second station a data processing subsystem in communication with the control subsystem; a communication interface, The method according to any one of Example 50 or Examples 51-52, wherein the method includes generating, by operation of a data processing subsystem of the destination station, a control signal for modulation electronics of the control subsystem based on a second time series of data received from the communication interface, the control signal representing one or more characteristics of the first input optical signal over time, and the second time series of data representing information to be transmitted to another station in the communication system. Example 54. the first station and the second station each include a navigation subsystem in communication with the control subsystem and the tracking subsystem, the navigation subsystem having positioning electronics and timing electronics; The method is: determining a position of the first station or the second station by operation of positioning electronics of the first station or the second station, respectively; setting local reference parameters of the first station or the second station by operation of timing electronics of the first station or the second station, respectively, the local reference parameters including a local reference time; The method of any one of Example 45 or Examples 46-53, comprising: Example 55. The method of Example 54, wherein the local reference parameters include one or both of a local reference frequency and a local reference phase. Example 56. 56. The method of embodiment 54 or 55, comprising exchanging synchronization signals between a global reference station and navigation subsystems of at least the first station and the second station, the synchronization signals representing global reference parameters of the communication system including a global reference time. Example 57. The method of Example 56, wherein the global reference parameters include one or both of a global reference frequency and a global reference phase. Example 58. the control subsystem of each of the first station and the second station comprises a reference RF oscillator electromagnetically coupled to at least one photonic crystal maser; The method is: generating reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase by operation of a reference RF oscillator; coupling the reference RF electromagnetic radiation into the waveguide of the at least one photonic crystal maser by operation of an input coupler of the at least one photonic crystal maser; The method of any one of Example 45 or Examples 46-57, comprising: Example 59. the control subsystem of each of the first station and the second station includes a reference antenna electromagnetically coupled to at least one photonic crystal receiver of the transceiver; The method is: generating, by operation of a reference antenna, reference RF electromagnetic radiation having one or more controlled characteristics including at least one of a controlled amplitude, a controlled frequency, or a controlled phase; coupling the reference RF electromagnetic radiation into the waveguide of the at least one photonic crystal receiver by operation of an input coupler of the at least one photonic crystal receiver; The method of any one of Example 45 or Examples 46-58, comprising: Example 60. a relay station disposed at the relay location and configured to receive and transmit the beam of targeted RF electromagnetic radiation; The method of any one of example 45 or examples 46 to 59, wherein the method includes, by operation of a tracking subsystem of the first station or the second station, altering the orientation of each transceiver to point one or more photonic crystal masers and one or more photonic crystal receivers of the respective transceiver toward the relay location.

[0113] While this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that are specific to particular examples. Certain features that are described herein or illustrated in the drawings in the context of separate embodiments may also be combined. Conversely, various features that are described or illustrated in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.

[0114] Similarly, although operations are depicted in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order or sequential order shown, or that all illustrated operations be performed to achieve desirable results. In certain environmental situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments; the described program components and systems may generally be integrated together in a single product or packaged in multiple products.

[0115] Although several embodiments have been described, it will be understood that various modifications may be made and, therefore, other embodiments are within the scope of the appended claims.

Claims

1. 1. A communication system comprising: a first station and a second station, wherein the first station and the second station 1. A transceiver having one or more photonic crystal masers and one or more photonic crystal receivers, each photonic crystal maser configured to generate an output beam of RF electromagnetic radiation in response to receiving a first input optical signal, said output beam representing information to be transmitted to another station of said communications system; each photonic crystal receiver configured to generate an output optical signal in response to receiving an input beam of RF electromagnetic radiation and a second input optical signal, said input beam representing information received from another station in the communications system; A transceiver; In the control subsystem, one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers, the lasers configured to generate the first input optical signal and the second input optical signal; modulation electronics in communication with the one or more lasers and configured to control one or more characteristics of the first input optical signal, the one or more characteristics of the first input optical signal including an intensity, a frequency, or a phase of the first input optical signal; and demodulation electronics in communication with the one or more lasers and configured to control one or more characteristics of the second input optical signal, the one or more characteristics of the second input optical signal comprising an intensity, a frequency, or a phase of the second input optical signal; a control subsystem; a tracking subsystem configured to control the orientation of the transceiver to thereby direct the one or more photonic crystal masers and the one or more photonic crystal receivers toward a target location; A communication system comprising:

2. The first station and the second station a navigation subsystem in communication with the control subsystem and the tracking subsystem, respectively, the navigation subsystem comprising: positioning electronics configured to determine a position of the first station or the second station; timing electronics configured to set local reference parameters of the first station or the second station, the local reference parameters including a local reference time; The communication system of claim 1 , comprising:

3. The communication system of claim 2 , wherein the local reference parameters include one or both of a local reference frequency and a local reference phase.

4. 3. The communication system of claim 2, comprising a global reference station configured to exchange synchronization signals with the navigation subsystems of at least the first station and the second station, the synchronization signals representing global reference parameters of the communication system including a global reference time.

5. The communication system of claim 4 , wherein the global reference parameters include one or both of a global reference frequency and a global reference phase.

6. The control subsystem is 10. The communication system of claim 1, further comprising an optical detector optically coupled to the one or more photonic crystal receivers and configured to generate a set of spectroscopic data for each photonic crystal receiver, the set of spectroscopic data being based on the output optical signal from the photonic crystal receiver and representing one or more characteristics of the input beam of RF electromagnetic radiation.

7. 7. The communication system of claim 6, wherein the one or more characteristics of the input beam of RF electromagnetic radiation include at least one of an intensity, a phase, a frequency, or a polarization of the input beam of RF electromagnetic radiation.

8. The first station and the second station each of the plurality of data processing subsystems in communication with the control subsystem, the plurality of data processing subsystems including: generating a first time series of data based on the set of spectroscopic data received from the optical detector over time, the first time series of data representing information transmitted from another station in the communication system; generating a control signal for the modulation electronics based on a second time series of data received from a communication interface of the first station or the second station, the control signal representing the one or more characteristics of the first input optical signal over time, and the second time series of data representing information to be transmitted to another station in the communication system; 7. The communication system of claim 6, configured to perform operations including:

9. The control subsystem includes:

10. The communication system of claim 1, comprising a reference RF oscillator electromagnetically coupled to the at least one photonic crystal maser and configured to generate reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase.

10. The control subsystem includes:

10. The communication system of claim 1, comprising a reference antenna electromagnetically coupled to at least one photonic crystal receiver of the transceiver and configured to generate reference RF electromagnetic radiation having one or more controlled characteristics including at least one of a controlled amplitude, a controlled frequency, or a controlled phase.

11. 10. The communication system of claim 1, wherein the one or more photonic crystal masers comprise a pair of photonic crystal masers configured to produce respective output beams of RF electromagnetic radiation having polarizations that are orthogonal to each other.

12. 10. The communication system of claim 1, wherein the one or more photonic crystal receivers include a pair of photonic crystal receivers configured to process respective input RF electromagnetic beams at orthogonal polarizations.

13. 2. The communication system of claim 1, wherein the first station is located at the target location of the second station, and the second station is located at the target location of the first station.

14. a relay station disposed at a relay location and configured to receive and transmit a beam of targeted RF electromagnetic radiation; 2. The communication system of claim 1, wherein the relay location serves as the target location for the tracking subsystem of one or both of the first station and the second station.

15. 1. A method for communicating information using radio frequency (RF) electromagnetic radiation, comprising: transmitting a beam of RF electromagnetic radiation between a first station and a second station of a communication system, the first station and the second station comprising:

1. A transceiver having one or more photonic crystal masers and one or more photonic crystal receivers, each photonic crystal maser configured to generate an output beam of RF electromagnetic radiation in response to receiving a first input optical signal, said output beam representing information to be transmitted to another station of said communications system; each photonic crystal receiver configured to generate an output optical signal in response to receiving an input beam of RF electromagnetic radiation and a second input optical signal, said input beam representing information received from another station in said communications system; A transceiver; a control subsystem comprising one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers and configured to generate the first input optical signal and the second input optical signal; a tracking subsystem configured to control the orientation of the transceiver to thereby direct the one or more photonic crystal masers and the one or more photonic crystal receivers toward a target location; Each of the methods comprises:

16. the first station or the second station is a source station of the beam of RF electromagnetic radiation; 16. The method of claim 15, wherein transmitting the beams of RF electromagnetic radiation comprises generating one or more respective output beams of RF electromagnetic radiation by operation of the one or more photonic crystal masers at the origination station.

17. Transmitting a beam of RF electromagnetic radiation transmitting a first beam of RF electromagnetic radiation from the first station to the second station; transmitting a second beam of RF electromagnetic radiation from the second station to the first station, the second beam being transmitted at least in part simultaneously with the first beam; 16. The method of claim 15, comprising:

18. the control subsystem of each of the first station and the second station comprises modulation electronics in communication with the one or more lasers; the first station or the second station is a source station of the beam of RF electromagnetic radiation; 16. The method of claim 15, wherein the method includes controlling, by operation of the modulation electronics of the origination station, one or more characteristics of the first input optical signal generated by the one or more lasers, the one or more characteristics of the first input optical signal including an intensity, a frequency, or a phase of the first input optical signal.

19. the control subsystem of each of the first station and the second station comprises demodulation electronics in communication with the one or more lasers; the first station or the second station is a destination station for the beam of RF electromagnetic radiation; 16. The method of claim 15, wherein the method includes controlling, by operation of the demodulation electronics of the destination station, one or more characteristics of the second input optical signal generated by the one or more lasers, the one or more characteristics of the second input optical signal comprising an intensity, a frequency, or a phase of the second input optical signal.

20. the control subsystem of each of the first station and the second station comprises an optical detector optically coupled to the one or more photonic crystal receivers; the first station or the second station is a destination station for the beam of RF electromagnetic radiation; 16. The method of claim 15, wherein the method includes generating a set of spectroscopic data for each photonic crystal receiver of the destination station by operation of the optical detector of the destination station, the set of spectroscopic data being based on the output optical signal from the photonic crystal receiver and representing one or more characteristics of the input beam of RF electromagnetic radiation.

21. 21. The method of claim 20, wherein the one or more characteristics of the input beam of RF electromagnetic radiation include at least one of an intensity, a phase, a frequency, or a polarization of the input beam of RF electromagnetic radiation.

22. the first station and the second station each include a data processing subsystem in communication with the control subsystem; 21. The method of claim 20, wherein the method includes generating, by operation of the data processing subsystem of the destination station, a first time series of data based on the sets of spectroscopic data received from the optical detector over time, the first time series of data representing information transmitted from another station in the communications system.

23. The first station and the second station a data processing subsystem in communication with the control subsystem; Communication interface and Each of them has 21. The method of claim 20, wherein the method includes generating, by operation of the data processing subsystem of the destination station, control signals for modulation electronics of the control subsystem based on a second time series of data received from the communications interface, the control signals representing the one or more characteristics of the first input optical signal over time, and the second time series of data representing information to be transmitted to another station in the communications system.

24. the first station and the second station each include a navigation subsystem in communication with the control subsystem and the tracking subsystem, the navigation subsystem having positioning electronics and timing electronics; The method comprises: determining a position of the first station or the second station by operation of the positioning electronics of the first station or the second station, respectively; setting local reference parameters of the first station or the second station by operation of the timing electronics of the first station or the second station, respectively, the local reference parameters including a local reference time; 16. The method of claim 15, comprising:

25. 25. The method of claim 24, wherein the local reference parameters include one or both of a local reference frequency and a local reference phase.

26. 25. The method of claim 24, comprising exchanging synchronization signals between a global reference station and the navigation subsystems of at least the first station and the second station, the synchronization signals representing global reference parameters of the communication system including a global reference time.

27. 27. The method of claim 26, wherein the global reference parameters include one or both of a global reference frequency and a global reference phase.

28. the control subsystem of each of the first station and the second station comprises a reference RF oscillator electromagnetically coupled to at least one photonic crystal maser; The method comprises: generating reference RF electromagnetic radiation having one or both of a controlled frequency and a controlled phase by operation of the reference RF oscillator; coupling the reference RF electromagnetic radiation into a waveguide of the at least one photonic crystal maser by operation of an input coupler of the at least one photonic crystal maser; 16. The method of claim 15, comprising:

29. the control subsystem of each of the first station and the second station comprises a reference antenna electromagnetically coupled to at least one photonic crystal receiver of the transceiver; The method comprises: generating, by operation of the reference antenna, reference RF electromagnetic radiation having one or more controlled characteristics including at least one of a controlled amplitude, a controlled frequency, or a controlled phase; coupling the reference RF electromagnetic radiation into a waveguide of the at least one photonic crystal receiver by operation of an input coupler of the at least one photonic crystal receiver; 16. The method of claim 15, comprising:

30. a relay station disposed at the relay location and configured to receive and transmit the beam of targeted RF electromagnetic radiation; 16. The method of claim 15, wherein the method includes, by operation of the tracking subsystem of the first station or the second station, reorienting the respective transceivers to point the one or more photonic crystal masers and the one or more photonic crystal receivers of the respective transceivers toward the relay location.

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