Reducing flicker noise in free space optical communications

Abstract

In some embodiments, an optical communication system may include a light source, a modulator, and a light receiver. The light source may be configured to generate a beam comprising a series of light pulses. The light receiver may have a detection window duration of 1 nanosecond or less. As a first pulse travels through a variable refractive medium, photons in the first pulse may be refracted to travel along different ray paths to reach the light receiver according to a time profile. A full width at half maximum (FWHM) value of the time profile may be greater than a coherence time value of the first pulse, and a detection window of the light receiver may be greater than the FWHM value of the time profile.

Description

[0001] Cross - Reference to Related Applications

[0002] This patent application is a PCT international application and claims the benefit of U.S. Non - Provisional Serial No. 17 / 932,364, filed on September 15, 2022. The above - mentioned application is incorporated herein by reference. Field of the Invention

[0003] The subject matter described herein relates to free - space optical (FSO) wireless transmission, including optical communication, remote sensing, lidar, power - beam transmission, etc., and more particularly to enhanced optical transmission efficiency enabled by beam propagation through a variable refractive medium (e.g., the earth's atmosphere) using an ultrashort - pulse laser (USPL) source for wavelength propagation. Background of the Invention

[0004] FSO communication has the potential to greatly increase data throughput, reduce costs, and increase access to high - speed Internet and other communication technologies. However, to date, due to atmospheric interference, FSO communication systems have had limited operational success rates. Atmospheric interference shortens the distance over which data can be optically transmitted and introduces error codes. At the same time, alternative communication technologies such as radio - frequency communication and microwave communication face severe spectrum limitations and cannot be used to transmit sufficient data to meet demand. Currently available optical systems cannot produce data transmission results that are accurate, reliable, and available enough to reliably share the burden of communication demand for these radio - frequency and microwave systems and improve data transmission and access, and currently available optical systems also cannot transmit data over long distances.

[0005] Accordingly, there is a need for optical communication systems that can provide highly reliable and highly available data transmission over long distances. In addition, there is a need for optical communication that can reliably transmit data over long distances (e.g., half a mile or more). Summary of the Invention

[0006] A simplified overview is presented below to provide a basic understanding of some aspects described herein. This overview is not an exhaustive review of the claimed subject matter. It is neither intended to identify key or critical elements of the claimed subject matter nor to delineate the scope of the claimed subject matter.

[0007] In some embodiments, an optical communication system for optically transmitting data through a variable refractive medium may include a light source, a modulator, and a photoreceiver. The light source may be configured to generate a beam including a series of optical pulses, each optical pulse having a duration of less than 100 picoseconds. The modulator may be configured to modulate the series of optical pulses in response to a data transmission signal, thereby encoding transmission data into the series of optical pulses. The photoreceiver may have a detection window duration of less than 1 nanosecond and a detection threshold. The photoreceiver may be configured to indicate whether the optical energy received during a given detection window is greater than the detection threshold. The series of optical pulses may include a first optical pulse having a coherence length of less than 400 micrometers. As the first pulse travels through the variable refractive medium, photons in the first pulse may be refracted, thereby traveling along different ray paths having different lengths toward the photoreceiver, and photons of the first pulse may reach the photoreceiver according to a time distribution curve that depends at least in part on the duration of the first pulse and the lengths of the different ray paths taken by the photons of the first pulse to reach the photoreceiver. The full width at half maximum (FWHM) value of the time distribution curve may be at least three times a coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium, and the detection window of the photoreceiver may be at least six times the FWHM value of the time distribution curve.

[0008] In some embodiments, a laser ranging system may include a light source and a photoreceiver. The light source may be configured to generate a beam including a series of optical pulses, each optical pulse having a duration of less than 100 picoseconds. The photoreceiver may have a detection window duration of less than 1 nanosecond and a detection threshold. The photoreceiver may be configured to indicate whether the optical energy received during a given detection window is greater than the detection threshold. The series of optical pulses may include a first optical pulse having a coherence length of less than 400 micrometers. As the first pulse travels through the variable refractive medium, photons in the first pulse may be refracted, thereby traveling along different ray paths having different lengths toward the photoreceiver. Photons of the first pulse may reach the photoreceiver according to a time distribution curve that depends at least in part on the duration of the first pulse and the lengths of the different ray paths taken by the photons of the first pulse to reach the photoreceiver. The full width at half maximum (FWHM) value of the time distribution curve may be at least three times a coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium, and the detection window of the photoreceiver may be at least six times the FWHM value of the time distribution curve. The laser ranging system may be configured to send the series of optical pulses toward a surface, receive at least a portion of the series of optical pulses that has been reflected by the surface, and determine a distance of at least a portion of the surface relative to the laser ranging system based on a time of flight of the received portion of the series of optical pulses.

[0009] Other variations encompassed within these systems and methods are described in the detailed description of the invention below. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings, which are incorporated in and constitute a part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the written description, serve to explain certain principles associated with the disclosed embodiments.

[0011] Figure 1 Examples of optical communication platforms are depicted that include free - space coupling of a USPL source as a light source for transmission to a remote optical receiving terminal.

[0012] Figure 2 Examples of optical communication platforms are depicted that include fiber - optic coupling of a USPL source as a light source for transmission to a remote optical receiving terminal.

[0013] Figure 3 Examples of optical communication platforms are depicted that include fiber - optic coupling of a USPL source with an external modulator for transmission to a remote optical receiving terminal.

[0014] Figure 4 Examples of optical communication platforms are depicted that include fiber - optic coupling of a USPL source through a fiber - optic medium with an external modulator for transmission to a remote optical receiving terminal.

[0015] Figure 5 Examples of transmitting and receiving elements are depicted that can be of types derived from hyperbolic mirror fabrication techniques or conventional Newtonian designs.

[0016] Figure 6 Examples of fiber - optic amplifier elements are depicted that are identified and used to increase the enhanced optical transmission power for transmission to a remote optical receiving terminal.

[0017] Figure 7 Examples of USPL laser devices are depicted that are fiber - optically coupled to an external modulator for transmission in a point - to - point configuration for transmission to a remote optical receiving terminal.

[0018] Figure 8 Examples of USPL laser devices are depicted that are fiber - optically coupled to an external modulator in a point - to - multi - point configuration.

[0019] Figure 9 Examples of the use of a USPL source as a tracking and alignment (pointing) beacon source are depicted.

[0020] Figure 10Depicts an example of the polarization of a USPL laser source that is reused on an optical signal being transmitted to provide polarization multiplexed USP-FSO (PM-USP-FSO) functionality.

[0021] Figure 11A and Figure 11B Depicts examples of USPL-FSO transceivers for use in line-of-sight laser communication applications and non-line-of-sight laser communication applications, respectively.

[0022] Figure 12 Depicts an example where light including light from a data signal propagating forward is backscattered due to interaction with airborne particles under investigation.

[0023] Figure 13 Depicts a USPL laser source as an optical receiving technique for improving detection sensitivity; examples of a USPL laser source and an optical receiving technique for improving detection sensitivity.

[0024] Figure 14 Depicts an example of a USPL-FSO transceiver that is used and operated as a rangefinder and a point determination device across an infrared wavelength range that optionally includes light from a data signal for target recognition purposes.

[0025] Figure 15 Depicts an example of a USPL pulse multiplier device consistent with an embodiment of the current subject matter.

[0026] Figure 16 Depicts another example of a device for generating a high pulse rate USPL optical stream consistent with an embodiment of the current subject matter.

[0027] Figure 17 Depicts another example of an optical device for generating a USPL RZ data stream from a conventional transmission networking element.

[0028] Figure 18 Depicts an example of a USPL pulse multiplier device that implements a system for generating a 10× TDM type signal to give a 100 Gbps output.

[0029] Figure 19 Depicts an example of implementing another type of USPL pulse multiplier device to extend the pulse repetition rate for high-capacity networks.

[0030] Figure 20 Depicts an example of implementing another type of USPL pulse multiplier device to extend the pulse repetition rate for high-capacity networks.

[0031] Figure 21Depicts an example of an actively mode-locked linear fiber laser with a feedback regeneration system: fiber reflector (FR), wavelength division multiplexer (WDM), erbium-doped fiber (EDF), optical coupler (OC), photodetector (PD), phase-locked loop (PLL), and Mach-Zehnder modulator (MZM).

[0032] Figure 22 and Figure 23 Depicts an example of a passively mode-locked linear fiber laser using a carbon nanotube saturable absorber: fiber reflector (FR), wavelength division multiplexer (WDM), erbium-doped fiber (EDF), optical coupler (OC), and saturable absorber (SA).

[0033] Figure 24 Depicts an example of a time-delay stabilization mechanism: optical couplers (OCin, OCout), photodetectors (PDin, PDout), high-pass filter (HPF), low-pass filter (LPF), phase-locked loop (PLL), phase comparator (PC), frequency divider (1 / N), clock data recovery system (CDR), piezoelectric actuators (PZ1...PZN), summing operational amplifier, for stabilizing the pulse-to-pulse relationship of optical pulses generated from a USPL source.

[0034] Figure 25A and Figure 25B Respectively include a schematic diagram and a graph related to an example of a control mechanism for stabilizing the output frequency of a TDM source using an idealized PZ actuator.

[0035] Figure 26 Depicts an example of time-division multiplexing (TDM), where TDM multiplexes pulse trains using parallel time-delay channels, so that the delay channels are "aligned" with respect to each other (since the frequency of the output multiplexed pulse train is ideally as insensitive as possible to environmental variations, the feedback loop control system can correct the delay units for any fluctuations that compromise the stability of the output repetition rate, and feedback can be provided through interconnection with a neural network).

[0036] Figure 27 Depicts an example of using a fiber-based collimator together with a piezoelectric transducer to control individual MFC circuits.

[0037] Figure 28 Depicts an example of the timing of a TDM chip from a USPL modulation source to provide terabits per second (or faster) using a multiplier photonic chip.

[0038] Figure 29 Depicts an example of the timing of a TDM chip from a USPL modulation source to provide terabits per second (or faster) using a multiplier photonic chip operating in a WDM configuration.

[0039] Figure 30 Illustrates an example of the configuration of a computer-aided system that can use recursive linear polarization adjustment to control the pulse width of an all-fiber mode-locked laser, while using a synchronous self-regenerative mechanism to stabilize the cavity repetition rate, and can also provide tunability of the repetition rate and pulse width.

[0040] Figure 31 Illustrates an example of a modified pulse interleaving scheme by pulse multiplication techniques, where a lower repetition rate pulse train from a well-characterized, well-mode-locked laser can be coupled to an integrated optical directional coupler, where a well-defined portion of the pulses is tapped off and "recirculated" in an optical loop with an optical delay equal to the expected inter-pulse interval in the output pulse train, and is recoupled to the output of the directional coupler.

[0041] Figure 32 Is a process flow diagram illustrating the features of a method consistent with an embodiment of the present subject matter.

[0042] Figure 33 Is another process flow diagram illustrating the features of a method consistent with an embodiment of the present subject matter.

[0043] Figure 34 Is another process flow diagram illustrating the features of a method consistent with an embodiment of the present subject matter.

[0044] Figure 35A and Figure 35B Illustrates an exemplary node that can be used to send and / or receive information.

[0045] Figure 36 Illustrates an exemplary arrangement where data is transmitted from a first communication network 3542 to a second communication network 3544 across an optical communication distance D using a transmitting node 3510 and a receiving node 3530.

[0046] Figure 37 Illustrates an exemplary beam traveling across an optical communication distance D (such as 1 mile) through a constant refractive medium.

[0047] Figure 38 Provides a schematic representation of photons in a beam traveling through a variable refractive medium.

[0048] Figure 39 Illustrates a schematic representation of the broadening of a pulse as it travels across an optical communication distance.

[0049] Figure 40 Illustrates an exemplary time distribution curve of a short-duration pulse 4010 that has traveled a significant distance through a variable refractive medium and has been broadened in time.

[0050] Figure 41 A schematic representation of an optical pulse arriving within a detection window of an optical receiver is shown.

[0051] Figure 42 An example of test data received over an optical communication distance of one mile is shown.

[0052] Figure 43 An exemplary ranging node is shown that can be used to detect objects or surfaces and determine the position of these objects relative to the node. Detailed Description

[0053] While aspects of the subject matter of this disclosure may be embodied in many forms, the following description and the drawings are only intended to disclose some of these forms as specific examples of the subject matter. Accordingly, the subject matter of this disclosure is not intended to be limited to the forms or embodiments so described and illustrated.

[0054] Figure 1 An example of an optical communication platform 100 configured to transmit using a USPL source as a light source is shown. As Figure 1 shown, the USPL source 102 can be directly modulated by an external source element 104. The optical power from the USPL source 102 can be optionally coupled to a transmitting element 106 across free space 110 through an optical telescope. The transmitting element 106 can optionally include optical components formed by hyperbolic mirror fabrication techniques or conventional Newtonian designs, etc. A reciprocal receiving telescope located at the receiver system can provide optical reception. Consistent with embodiments of the present subject matter, each optical transmission platform can be designed to operate as a two-way unit. In other words, the transmitting element 106 of the optical communication platform 100 can also act as a receiving element. Generally speaking, unless otherwise explicitly stated, the described transmitting element 106 can also be considered to be able to act as a receiving element, and vice versa. An optical element that performs both the transmitting function and the receiving function can be referred to herein as an optical transceiver.

[0055] Figure 2 An example of an optical communication system 200 of an optical communication platform 100 including Figure 1 is shown. Figure 2 A second complementary receiving element 204 is also shown therein, which can be a receiving telescope located at a long distance relative to the transmitting element 106. As described above, both the transmitting element 106 and the receiving element 204 can be two-way, and each element can act as both the transmitting element 106 and the receiving element 204, depending on the instantaneous direction of data transmission in the optical communication system 200. Unless otherwise explicitly stated, this feature applies to the transmitting element and the receiving element throughout this disclosure. Either or both of the transmitting element 106 and the receiving element 204 can be an optical telescope or other devices for transmitting and receiving optical information.

[0056] Figure 3 Shows an example of an optical communication platform 300 for using a USPL source 102 that is fiber-coupled to an external modulator 302 through an optical fiber medium 304 and connected to a transmitting element 106 through an additional transmission medium 306, which can optionally be an optical fiber medium, a free space connection, etc. The USPL source 102 can be externally modulated by the external modulator 302 such that the optical power from the USPL source 102 is fiber-coupled to the transmitting element 106 or processed through an equivalent optical telescope.

[0057] Figure 4 Shows an optical communication system 400 including Figure 3 of the optical communication platform 300. Also shown in Figure 4 is a second complementary receiving telescope 204, as pointed out above in connection with Figure 2 , which can be a receiving telescope located at a long distance relative to the transmitting element 106.

[0058] Figure 5 Shows an example of an optical communication architecture 500. Figure 5 The architecture 500 of can include Figure 4 elements of and can further include a first communication network 502 connected to the first optical communication platform 300. The receiving element 204 is part of a second optical communication platform 504, which can optionally include components similar to those of the first optical communication platform 300. A second communication network 506 can be connected to the second optical communication platform 504 such that data is optically transmitted between the transmitting element 106 and the receiving element 204 or passed between the first communication network 502 and the second communication network 506, and each of the first communication network and the second communication network can include one or more of optical networking features and electrical networking features.

[0059] Figure 6 Shows an example of an optical communication system 600. As part of the optical communication platform 602, the USPL source 102 is fiber-coupled to the external modulator 302, for example, through an optical fiber 202 or other transmission medium. The light from the USPL source 102 propagates via the transmitting element 106 in a manner similar to that discussed above. An optical amplifier element 604 (which can optionally be a fiber amplifier element) can be used to increase the optical transmission launch power and can optionally be disposed between the external modulator 302 and the transmitting element 106 and connected to one or both of the external modulator and the transmitting element through an additional transmission medium 306, which can optionally be an optical fiber medium, a free space connection, etc. Figure 6Also shown is a second complementary receiving element 204 located at a distance relative to the optical communication platform 602. It is readily understood that the second optical communication platform 504 including the receiving element 204 may also include an optical amplifier element 604. The first communication network 502 and the second communication network 506 may be connected to the two optical communication platforms 602, 504 respectively.

[0060] Figure 7 An example of an optical communication system 700 is shown. Figure 6 The optical communication platform 602 shown in may communicate with a second optical communication platform 702, which may include a receiving element 204 and an optical preamplifier 704 in this embodiment. Other components similar to those shown in the optical communication platform 602 may also be included in the second optical communication platform 702, although they are not Figure 7 shown in. It should be understood that a bidirectional optical communication platform may include both an optical preamplifier 704 for amplifying received optical signals and an optical amplifier element 604 for enhancing transmitted optical signals.

[0061] In accordance with Figure 7 the embodiment shown in and other embodiments of the present subject matter, optical amplification (e.g., for either or both of the optical amplifier element 604 or the optical preamplifier 704) may be included to enhance the optical budget of the data link between the transmitting element 106 and the receiving element 204 (and vice versa), e.g., using one or more of an erbium-doped fiber amplifier (EDFA), a high-power erbium-ytterbium-doped fiber amplifier (Er / Yb-DFA), or equivalent devices, which may include but are not limited to semiconductor optical amplifiers (SOA).

[0062] Figure 8 An example of an optical communication system 800 is shown. Figure 6 The optical communication platform 602 shown in may communicate with a second optical communication platform 802, which may include a receiving element 204 and an optical preamplifier 704 similar to those shown in Figure 7 . As Figure 8 shown, the second optical communication platform 802 may further include an optical receiver circuit 804, which may receive the amplified and electrically recovered data received at the receiving element 204 and amplified by the optical preamplifier. A plurality of clock sources 806 may be docked as needed to a plurality of remote multipoint network connections with a plurality of communication networks 810. In a similar manner, a complementary set of clock sources and a plurality of communication networks may operate in conjunction with the optical communication platform 602 (e.g., instead of Figure 8 the single shown communication network 502 in ).

[0063] Figure 9 An example of an optical communication system 900 is shown. The optical communication platform 902 (which may be characterized by elements similar to those in the optical communication platform 602 discussed herein first with reference to Figure 6 the elements discussed) may also include additional USPL sources 904 that act as tracking and alignment (pointing) beacon sources. The second optical communication platform 906 may also include additional USPL sources 910 that act as tracking and alignment (pointing) beacon sources. The tracking and alignment (pointing) beacon sources 904, 910 may optionally be sourced from available communication sources used in data transfer transmissions or may be provided by separate dedicated USPL sources. Additionally, each USPL beacon source 904, 910 may include in-band or out-of-band sources (thereby realizing the advantages of available optical amplification sources) or from dedicated optical amplification resources.

[0064] Figure 10 An example of an FSO communication system 1000 including a dual-polarization USPL-FSO optical data link platform 1001 is shown, in which USPL sources are polarization multiplexed onto the transmitted optical signals, thereby providing polarization multiplexed USP-FSO (PM-USP-FSO) functionality. Two USPL sources 102 and 1002 are fiber-coupled to a directly modulated modulation component 1004 or an externally modulated modulation component 1006, respectively. Each corresponding modulation signal is optically amplified by optical amplifier components 1010, 1012 and then the optical polarization state is adjusted using polarization components 1014, 1016. The polarization state signals are fiber-coupled to a polarization-dependent multiplexer (PDM) component 1020, which is then docked to an optical transmission platform component 1022, which may be similar to the transmitting element 106 discussed above. The PDM 1020 multiplexes the optical signals with different polarization states into a single pulse train for transmission via the optical transmission platform component 1022. A USPL optical beacon 904 may be included to provide capabilities similar to those discussed above with reference to Figure 9 those discussed, and thus operate, for example, together with or in combination with a second USPL optical beacon 906 at the receiving platform 1024, which may include receiving elements 204 similar to those described above. As pointed out above, the receiving element 204 and other features and components of the receiving platform 1024 are generally capable of supporting the transmitting function, thereby establishing a two-way link. The received signal recovered by the receiving element 204 may provide an optical signal that is docked to an appropriate polarization-dependent demultiplexer 1026, which is capable of providing two signals for further optical amplification using amplification elements 1030, 1032. Each optical amplification signal provided by the amplification elements 1030, 1032 may be docked to an appropriate optical network 1034, 1036 for network use.

[0065] Figure 11AAn example of system 1100 is shown, in which a USPL-FSO transceiver can be used in a line-of-sight optical communication (e.g., "laser communication") application, and Figure 11B An example of system 1150 is shown, in which a USPL-FSO transceiver can be used in a non-line-of-sight laser communication application. As the transmitted light passes through the atmosphere, due to the scattering of the optical signal transmitted from the transmitting element, advantages for some embodiments of the current subject matter can be achieved. This scattering can allow for the use of non-line-of-sight communication. In addition, the radio components used in such communication systems can operate in the solar-blind portion of the UV-C band, in which light is emitted at wavelengths from 200 nm to 280 nm. In this band, as solar radiation propagates through the environment, the Earth's atmosphere strongly attenuates the solar radiation. This means that as the solar radiation gets closer to the ground, the amount of background noise radiation drops sharply, and low-power communication link operation becomes possible. On the other hand, environmental elements such as oxygen, ozone, and water may attenuate or interrupt the communication broadcast, thus limiting the use to short-distance applications.

[0066] When UV waves are scattered throughout the atmosphere, they are typically strongly scattered into a variety of signal paths. Signal scattering is crucial for UV systems operating under non-line-of-sight conditions, and the communication performance can highly depend on the transmitted beam pointing and the field of view of the receiver. As Figure 11A the line-of-sight arrangement 1100 shown in Figure 11B can differ from the non-line-of-sight arrangement 1150 shown in

[0067] Figure 12 An example of a remote sensing system 1200 is shown, in which a USPL source 102 is fiber-coupled through a fiber optic component 202 to an optical transmitting element 1202 capable of transmitting and receiving optical signals. Some of the forward-propagating light (including the light from the data signal passing through the optical transmitting element 1202) is backscattered by interacting with airborne particles that are the subject of the investigation. The optical backscattered signal is detected by the optical transmitting element 1202 or a similar receiving aperture and is passed for Figure 12Detection circuits 1204, etc. in it are used for detection and spectral analysis. The identification characteristics of the particles in the target atmospheric region 1206 where the investigation and research are carried out can be calibrated by known schemes. For example, predetermined spectral calibration measurements based on one or more of ultraviolet spectra, infrared spectra, Raman spectra, etc. are used. Consistent with this embodiment, using a USPL laser source operating in the spectral range of interest, the optical system can be operated as a lidar instrument providing enhanced resolution and detection sensitivity performance. The adjustable ability of the spectral range can contribute to the evaluation and analysis of the chemical composition in the atmosphere.

[0068] Using an optical transmission terminal manufactured by a hyperbolic mirror fabrication technique that focuses the received signal on an ideal point or a conventional Newtonian design, the USPL-FSO transceiver can be used for remote sensing and detection of the identification characteristics of airborne elements using ionization or non-ionization detection techniques. Moreover, certain adaptations can be related to ionization detection in remote areas, including controllable ionization that has been shown to occur at these frequencies and an ionization process that can be focused at a distance to adjust the atmospheric penetration depth (especially in weather and clouds).

[0069] Figure 13 An example of using a USPL source and optical reception technology to improve detection sensitivity is shown. Researchers at the National Institute of Standards and Technology (NIST) have established a laser ranging system that can accurately locate multiple objects with nanometer precision over a distance of up to 100 km. Lidar (light detection and ranging) systems can have applications ranging from precision manufacturing on Earth to maintaining a satellite network with perfect formation (Nature Photonics DOI: 10.1038 / NPHOTON.2009.94). The NIST device uses two coherent broadband fiber laser frequency combs. The frequency comb outputs a series of stable short pulses that also contain highly coherent carriers extending across the pulse train. This means that frequency combs can be used for both interferometric and time-of-flight measurements simultaneously, thereby enhancing the analysis ability for specific application scenarios.

[0070] In Figure 13In the arrangement shown, two phase-locked frequency combs 1301 and 1302 are used in a coherent linear optical sampling configuration, also known as multi-heterodyne, where one frequency comb measures two distance paths and the other frequency comb provides the distance information encoded in the light of the first comb. Pulses from one frequency comb 1301 can be launched from an optical fiber and directed towards two glass plates, namely a reference 1303 and a target 1304. Plates 1303 and 1304 can reflect a portion (e.g., approximately 4%) of the pulses back along the optical fiber, effectively creating two new pulses. The time interval between these two pulses 1301 can give the distance between the movable target plate and the reference plate. The second frequency comb 1302 is tightly phase-locked to the first frequency comb but has a slightly different repetition rate. Due to the different delays between consecutive pulses during source interference, the second frequency comb can sample slightly different portions of the light of the electric field from the first comb.

[0071] Using the techniques Figure 13 described, it is possible to employ two suitable USPL sources in place of these two coherent broadband fiber laser sources, with the two suitable USPL sources being used within the scope of the configuration outlined, which fiber couples each USPL source to a dedicated free-space optical telescope design. By doing so, the overall efficiency, optical ranging, and accuracy can be significantly improved.

[0072] In some embodiments, the native pulse repetition rate of the USPL laser source can be 50 MHz or lower, which may be an undesirably low frequency for optical data transmission, thus limiting the system to low data rate applications of 50 Mbps or lower. Therefore, a system is needed that increases the operating rate of the USPL to provide a data transmission solution that exceeds 50 Mbps.

[0073] Figure 14 An example of a remote sensing system 1400 is shown, in which a USPL source 102 is fiber-coupled through a fiber component 202 to an optical transmitting element 1202 capable of transmitting and receiving optical signals. Light (including light from data signals) propagating forward through the optical transmitting element 1202 is backscattered by interaction with known and unknown targets that are the objects of investigation within an atmospheric region 1206. The optical backscattered signal, including light from data signals, is detected by the optical transmitting element 1202 or a similar receiving aperture and is passed for Figure 14 detection and analysis by the detection circuit and spectral analysis component 1402 within. The identification characteristics of the particles within the region 1206 under investigation can be calibrated, for example, where ranging analysis can be performed. As Figure 14The system 1400 therein may include a USPL-FSO transceiver that operates and functions as a rangefinder and a point-determining device across the infrared wavelength range for the purposes of target recognition and interrogation applications. As used herein, the term "optical" includes at least visible light wavelengths, infrared wavelengths, and near-infrared wavelengths.

[0074] Figure 15 The optical pulse multiplier module 1500 is shown that can increase the repetition rate of the output from the USPL source 102. Exemplary USPL may have a pulse width of 10 - 100 femtoseconds and a repetition rate of, for example, 50 MHz. The output from the USPL 102 can be fed as input 1502 into the USPL photon chip pulse multiplier module 1504. In this example, the photon chip may contain a 20,000:1 beam splitter element 1506 that divides the input into discrete optical units. Each optical unit on the opposite sides of the beam splitter element 1506 contains a 50 MHz pulse train. Then each optical unit passes through a delay controller (fiber optic loop or lens array) 1510 that causes a time delay of the pulse train of that unit, for example, a delay of several picoseconds. Thus, successive optical units are delayed by incrementing picoseconds. All of these pulse trains with their unique time delays are combined into a single pulse train using a 20,000:1 optical combiner element 1512 in a manner similar to time division multiplexing. The required ratios of the beam splitter and the combiner can be controlled to provide the necessary optical design for the desired application. The final output 1514 is a pulse train of 10 - 100 femtosecond pulses with a repetition rate of 1 THz. Then this THz pulse train can be modulated by a 10 GigE signal or a 100 GigE signal, for example, as Figure 28 shown, such that 100 femtosecond pulses are generated per bit for a 10 GigE system and 10 femtosecond pulses are generated per bit for a 100 GigE system. The cited applications are not limited to the specific data rates of 10 Gbps and 100 Gbps, but can operate according to the requirements of the application under consideration. These quantities are for illustrative purposes only. Embodiments of the present subject matter can use any multiplier factor to increase the repetition rate of the USPL to any arbitrary repetition rate via the photon chip pulse multiplier module 1504. Other examples for generating an enhanced USPL repetition rate are illustrated in this submission.

[0075] Figure 16 The system 1600 for the generation, transmission, and reception of a high pulse rate USPL optical stream is depicted. The optical chip multiplexing module 1610 (e.g., similar to that discussed with reference to Figure 15 can be used in this application. In this scheme for implementing USPL pulse multiplication, the signals 1601, 1602, 1603, 1604 ( Figure 16Four signals are shown, but it should be understood that any number is within the scope of the current subject matter) A series of 10 GigE router connections (10 GigE is not intended to be a limiting feature) as described are interfaced to an optical chip multiplexing module 1610. In operation, the optical chip multiplexing module 1610 can support full duplex (Tx and Rx) to connect to 10 GigE routers 1601, 1602, 1603, 1604. The optical chip multiplexing module 1610 can provide high-efficiency modulation for incoming optical signals 1601, 1602, 1603, 1604 through the USPL signal 1685 output from the USPL source 1690. The optical chip multiplexing module 1610 can provide the ability to modulate and multiplex these incoming optical signals.

[0076] At the remote receiving site where the receiving device is located, appropriate receiver elements 1665 can be used to recover all signals transmitted via the transmitting elements 1660 at the transmitting device. A complementary set of optical chip multiplexing modules 1675 can provide the necessary capabilities for demultiplexing the received data stream shown through the unit for transmission to a series of routers 1601', 1602', 1603', 1604' (depicting four such routers is also not intended to be limiting). End-to-end network connectivity can be demonstrated through network endpoint elements.

[0077] Figure 17 An exemplary system 1700 is depicted, where an optical chip is interconnected to a wavelength division multiplexing (WDM) system. The WDM system has the advantage of not requiring timing or synchronization (such as that required between a 10 GigE (or other speed) router 1701), because each 10 GigE signal operates on its own wavelength independently of other such signals. Timing or synchronization of the TDM optical chip with the 10 GigE router may be very important in the TDM optical chip. The GbE switch 1701 can provide the necessary electrical RF signal 1705 directly or by using the USPL pulse multiplier module detailed previously herein. The electrical RF signal is from the switch 1701 for modulating the USPL source 1702. A typical RZ output 1710 can be coupled into an external modulator 1720 (which can be modulated using an NRZ clock source for the switch 1701), thereby generating an RZ modulation spectrum 1730. A conversion process using readily available equipment can provide the ability to introduce the USPL source and its benefits into the terrestrial backhaul network spectrum.

[0078] For the optical chip system to successfully bridge between two remote 10GigE switches, the chip can operate like a simple optical fiber. Thus, the timing of the TDM chip can be driven by the 10GigE switch 1701. Both actively mode-locked USPL (i.e., 40 GHz, 1 picosecond pulse width) and passively mode-locked USPL (i.e., 50 MHz, 100 femtosecond pulse width) can be driven by RF timing signals.

[0079] Figure 18 Device 1800 is shown that can support another scheme for progress towards high pulse repetition data rate operation, e.g., for extremely high data rate operation, where fiber or free space optics can be used to perform the optical chip design. A 50 MHz USPL source 1801 can be interfaced to a series of optical delay controller elements 1802 (which can be designed with fiber loops or offset lenses) to result in the exact generation of a 10.313 Gbps RZ output stream, which is the 10GigE line rate (greater than 10 Gbps due to 64B / 66B encoding). A beam splitter element 1803 together with a variable optical delay line 1804 provides the function of splitting an incoming optical signal train 1801 into (in this example) 206 paths. After introducing sufficient delay through the design, all signals are multiplexed together by a combiner element 1805. In doing so, a series of optical signals that are identical for each and equally spaced between adjacent pulses form a continuous group of pulses for modulation. Before entering the E-O modulator element 1806, all optical incoming signals can be conditioned by pre-emphasis techniques (e.g., using typical optical amplification techniques) to result in a uniform power spectrum for each outgoing signal from the combiner element 1805. Then, the conditioned outgoing signals can be coupled into the E-O modulator element 1806 and modulated using the available NRZ signal from the 10GigE signal source element 1807. The modulated output 1809 of 10GigE can be interfaced to an EDFA and then into the TX of an FSO system (or fiber system). The Rx side (after the detector) can be fed directly into a 10GigE switch as the modulated and amplified output 1810.

[0080] Figure 19 Another example of a device 1900 that can be used for USPL pulse multiplication is shown that is consistent with an embodiment of the current subject matter. Consistent with this scheme, a 10× TDM system is configured to give a 100 Gbps output. The TDM demultiplexing chip can be located on the receiving side of the communication link to break down the individual 10GigE signals and can include a reciprocal scheme for the Figure 19 design shown.

[0081] As Figure 18As shown, a 50 MHz USPL source 1801 can be interfaced to a series of optical delay controller elements 1802 (which can be designed with fiber optic loops or offset lenses) to result in the exact generation of a 10.313 Gbps RZ output stream, which is the 10 GigE line rate (greater than 10 Gbps due to 64B / 66B encoding). A beam splitter element 1803 together with a variable optical delay line 1804 provides the function of splitting the incoming optical signal train 1801 into (in this example) 206 paths. After introducing sufficient delay through the design, all signals are multiplexed together by a combiner element 1805. However, as an alternative to a single modulator element 1806 as shown in Figure 18 the 10.313 GHz RZ output 1901 from the combiner element 1805 can be fed into a second beam splitter element 1910, in which case the second beam splitter element can be a 10× beam splitter that separates the optical signal into ten parallel paths. Other embodiments of this design can support various beam splitting ratios according to design requirements. The optical paths emerging from the second beam splitter element 1910 are individually connected to designated optical delay lines 1920. Each individual delay path is connected to a dedicated optical modulator in a set of optical modulators 1930 that are modulated with the available NRZ signals from a 10×10 GigE signal source element 1931, thereby generating a series of modulated optical signals 1935. An optical combiner identified as 1940 provides a single optical pulse train 1950. A series of optical pulses in the single optical pulse train 1950 can be interfaced to a suitable optical amplifier for the desired optical conditioning for network use.

[0082] Figure 20 Another example of a device 2000 that can be used for USPL pulse multiplication in accordance with an embodiment of the present subject matter is shown. The depicted device 2000 can provide the ability to achieve a high USPL pulse repetition data rate for network applications through the modulation of pulses within a low repetition rate channel. By applying direct modulation to each channel on the delay controller, the creation of modulation schemes that are not limited by the current speed limitations from electronic technology can be advantageously achieved. Embodiments of the present subject matter can provide a mechanism for enhancing the data transmission capacity of a system, in a manner that is at the current standard electronic modulation speed (at Figure 20In the example of [[ID=]], each channel is separately modulated at a rate of 100 × 10 GigE signal input 2001 and the channels are multiplexed into a single high-frequency high-repetition-rate pulse stream. In this scheme, the current standard limited by the speed of the electro-optic modulator (40 Gbps) can be enhanced by approximately N orders of magnitude, where N is the number of channels of the time multiplexer. For example, a 100-channel TDM (where each channel is amplitude-modulated at the current standard data rate) can provide a data rate of up to 4 Tbs. N may be limited by the width of the optical pulse itself. Under the limitation of carrying information at 1 bit / pulse, the time slot occupied by 1 bit is the width of the pulse itself (in this sense, the RZ system converges to NRZ). For example, in this scheme, a laser with a 40 fs pulse width and a 40 GHz repetition rate can carry information at a maximum rate of 25 Tbps. This scheme can be used for a 40 Gbps channel modulation scheme (i.e., 1 bit per 25 ps) and can correspond to the capacity of N~625 channels in a single transmission, which can be the number of 40 fs time intervals matched to the 25 ps time interval. A significant advantage of this scheme is the ability to "optically enhance" a limited data capacity modulation scheme while still interfacing with existing modulators with limited data rates. For example, a Mach-Zehnder interferometer-based amplitude modulator can be easily integrated into a TDM IC package because of the need to split the channel into two separate paths, add a small phase modulator (nonlinear crystal) in one of these paths, and combine these paths for interference.

[0083] Figure 20Including a USPL source 2010 coupled to a multi-port optical beam splitter element 2020. The number of identified optical ports need not be limited to those described or shown herein. A series of optical delay lines 2030 provide the required optical delay between each parallel path from the multi-port beam splitter element 2020 and can be customized for a particular application. The optical delay paths from the optical delay lines 2030 are added together using an optical combiner element 2035. The resulting combined optical data stream emerging through element 2040 represents a multiplicative enhancement of the pulse repetition rate of the original USPL source identified by element 2010. Further enhancement of the pulse repetition rate is accomplished by using element 2041 (described by an optical beam splitter where the incoming signal 2040 is split into a series of paths not limited to those identified by element 2041). Through a second delay controller 2045, an optical delay can be introduced into each path within the device, as identified by a second set of optical delay paths 2042. Then, using an available RF signal source identified by signal input 2001, each parallel path 2042 is modulated by a modulation element 2044. An optical combiner element 2050 integrates all incoming signals onto a single data stream 2060.

[0084] Optical pre-emphasis and de-emphasis techniques can be introduced within each of the described segments of elements to customize the spectrum, thereby achieving a uniform or asymmetric optical power distribution. Pre-emphasis and de-emphasis can be accomplished using common optical amplifiers, such as erbium-doped optical fiber amplifiers (EDFAs) for example.

[0085] Figure 21 An example of a system 2100 is depicted that includes a mode-locked USPL source 2101 that can be used to appropriately generate the required clock and data streams for an application. A mode-locked laser can represent an option for a high-performance, high-finesse clock source in a digital communication system. In this regard, mode-locked fiber lasers (in linear or ring configurations) can be attractive preferred candidates because they can achieve pulse widths in the USPL source region as well as repetition rates up to GHz. In addition to this, the fiber also offers compactness, low cost, low sensitivity to thermal noise, low jitter, and the absence of problems associated with diffraction or air dust contamination, to name just a few examples. In a communication scenario, the pulse width can determine the available bandwidth of the system, and the repetition rate limits the data rate. The pulse width can be determined by the inherent characteristics of the laser cavity (i.e., the balance of the total group velocity dispersion (GVD) and the choice of saturable absorber (in the case of passive systems)) or the bandwidth of the active element (in the case of active mode-locked systems). The repetition rate of the pulse train is limited by the fiber length. For example, in a linear laser, the fundamental mode vos of the laser can be expressed as:

[0086]

[0087] where c is the speed of light in a vacuum, n g is the average group refractive index, and L is the length of the cavity. Thus, a 10 cm long fiber laser cavity element 2110 with an average group refractive index of 1.47 will have a repetition rate of 1 GHz. In a strictly passive system, mode locking can be achieved by using a saturable absorber. In an active laser, an amplitude modulator element 2150 can be inserted into the cavity to increase the repetition rate of the laser (harmonic mode locking). To achieve a high repetition rate clock using a mode-locked USPL source, one or more of (i) an intracavity amplitude Mach-Zehnder modulator (MZM) 2150 as shown in Figure 21 and (ii) a low-threshold saturable absorber can be used. For terrestrial, submarine, or FSO systems in air, space, or undersea applications, these techniques, referred to as "harmonic mode locking", can be used within a fiber-based power distribution system or within an FSO system.

[0088] In Figure 21 is detailed a 980 nm pump element 2102 coupled to an optical WDM device 2105. An erbium-doped optical amplifier 2110 or equivalent can be used to create a nonlinear environment to obtain mode-locked pulse train emission within a closed cavity established between two Faraday reflectors 2101 and 2160 located at the two ends of the optical USPL cavity. The operation of this device can establish a self-contained series of optical pulses with a rate exceeding 100 Gbps and highly synchronized essentially at the output port 2170 of the module. To achieve a high-gain nonlinear medium, the EDFA 2110 can be specifically designed. A phase-locked loop 2130 can maintain a synchronized clock source by modulating the signals passing through the components 2120, 2130, 2150 of a self-contained high repetition rate pulse generator, thereby providing favorable operational stability. To achieve a high repetition rate in a laser limited by its size (length for a linear laser and perimeter for a ring laser), intracavity generation of the fundamental mode multiple may be required. In the active case, the amplitude modulator inserted into the cavity modulates the loss of a system operating as a "threshold gating" device. For this scheme to succeed, the control signal for the modulator may have to reference the oscillation of the laser itself to avoid driving signals that "force" the oscillation of an external frequency on the laser. This can be achieved by introducing a phase-locked loop element 2130 or a synchronous oscillator circuit to track and lock to the repetition rate of the laser and regenerate the signal. In terms of the PLL, the RF output can be set to a multiple of the input signal (very much like this device is used in cellular phone technology), and the repetition rate of the laser is increased. Then, this signal can be used to trigger a pulse generator or be used in combination with a low-pass filter. An MZ amplitude modulator 2150 outside the laser cavity can be used to create on-off keying (OOK) modulation of the pulse train emerging from the mode-locked laser.

[0089] Figure 22 Illustrates graphical depiction 2200, which exemplifies the effect of loss modulation introduced into input pulse train 2201 due to the presence of amplitude modulator 2205 along with control signal NRZ signal 2210 composed of a bit sequence as illustrated. The signal obtained at the output of device 2220 represents an NRZ-to-RZ converter device for telecommunication and scientific applications, where such applications can benefit from an RZ data stream. A clock signal 2201 (optical input) at a given pulse repetition rate will pass through modulator 2205. At the same time, a control signal composed of a sequence of 1s and 0s can be applied to the RF port of modulator element 2215. When modulator element 2215 is biased at minimum transmission, in the absence of a control signal, the loss experienced by the optical signal may be at its maximum. In the presence of an RF signal (1), the loss will be minimized (OPEN GATE), thus acting as an on-off keying modulation device. The pulse width of the output optical signal is typically much smaller than the time slot occupied by the information of a single bit (even less than half of a clock cycle in the NRZ scheme), making the system truly RZ, as identified by element 2220.

[0090] Figure 23 Illustrates an exemplary system 2300 for generating a high optical harmonic USPL pulse train with a high pulse repetition rate using a saturable absorber (SA) device 2330. In some examples, SA device 2330 can include carbon nanotubes. Passively mode-locked fiber lasers using carbon nanotube SA (CNT-SA) have become another attractive option for high repetition rate sources due to their ability to generate high harmonics of the fundamental repetition rate. In the described scheme, a closed, self-contained optical cavity is established, where two Faraday reflectors 2301 and 2350 form the optical cavity. Although Figure 23 a high-power erbium-doped fiber amplifier (EDFA) 2310 is shown, any inverse medium that generates a nonlinear optical cavity can also be used. A seed laser 2315, such as a 980 nm pump laser as shown in Figure 23 can be used to generate a high repetition rate optical train. In particular, any suitable pump laser can be considered depending on the desired optical wavelength and pulse repetition rate. SA element 2330 can be placed inside the cavity to establish the desired optical pulse characteristics 2350 as required according to the design requirements.

[0091] Figure 23 Illustrates a schematic diagram of an example of a laser that can be used in one or more embodiments of the current subject matter. And Figure 22Unlike the active lasers shown, here the MZ modulator can be replaced by the SA element 2330. For terrestrial, submarine, or FSO systems in air, space, or undersea applications, techniques similar to those described herein can be used within a fiber-based power plant distribution system or within an FSO system.

[0092] Figure 24 A scheme for providing time-division multiplexing (TDM) is shown, where TDM uses parallel time-delay channels to multiplex pulse trains. In some cases, it may become important to manipulate the delay channels so that they are "aligned" relative to each other. Ideally, the frequency of the output multiplexed pulse train can be as insensitive as possible to environmental variations. To this end, a feedback-loop control system is proposed that is designed to correct the delay units for any fluctuations that impair the stability of the output repetition rate.

[0093] Figure 24 A diagram showing an example of the delay control system 2400 is shown. The control loop can be implemented in one of several ways consistent with the current subject matter. Figure 24 One possibility is described for illustrative purposes. An input pulse train enters the TDM and is multiplexed onto N paths, each path having its own delay line. If the paths are made of low "bend loss" fiber waveguides, each path can be wound around a cylindrical piezoelectric actuator (PZ) with a radius R. The actuator generally expands radially due to the control voltage (Vc). This expansion ΔR, which is linearly proportional to Vc, results in a fiber length change ΔL = 2πNΔR, where N is the number of turns of fiber around the PZ. For terahertz multiplexing, the delay between pulses (and thus the resulting PZ1) must be 1 picosecond. This may require a length change equal to 200 microns, which corresponds to ΔR = 32.5 microns for one turn of the PZ actuator. Most commercially available piezoelectric actuators are highly linear and operate well within this range. Thus, the control mechanism can be based on several PZ actuators (each with a number of turns corresponding to a multiple of the first delay, i.e., (32 microns, 64 microns, 96 microns, etc.)) and controlled by a single voltage Vc. The control voltage is determined by a feedback system that uses a phase comparator (PC) to compare the frequency of the output signal using a 1 / N divider with the frequency of the input signal. The frequency of the "slow" input optical signal (by Figure 24The waveform representation with τRT (in ) is converted into an RF signal using the photodetector PDin. To reduce the effect of electronic jitter, a "differentiator" (or high-pass filter) can be applied to this RF signal to steepen the leading edge of the pulse. A phase-locked loop is used to track and lock the signal and regenerate it into a 50% duty cycle waveform. Similarly, on the output side, the optical signal is picked up by the photodetector PDout, high-pass filtered, and regenerated using the clock output port of the clock and data recovery system. The clock of the output signal having a frequency N times that of the input signal is sent to an N-divider before entering the phase comparator. From the phase comparator, the DC voltage level representing the mismatch between the input signal and the output signal (very much like that used in the architecture of a PLL circuit) indicates the correction direction of the actuator. The low-pass filter adds a time constant to the system to enhance its insensitivity to parasitic noise.

[0094] In contrast to the PLL, the CDR can be advantageously used in the output such that the output signal can be either modulated or not. This system can be designed to operate in an unmodulated scheme and a "modulation within TDM" (i.e., one modulator per delay path) scheme. However, this is a completely deterministic method of compensating for variations in the delay line length. Ideally, from a practical perspective, the delay paths should all refer to the same "thermal level", i.e., be sensitive to the same thermal variations simultaneously. If each line senses different variations, this system will not be able to correct for this in real time.

[0095] Alternatively, a completely statistical scheme can include the summation of operational amplifier circuits (S1...SN) to convey a control voltage to the actuator. Using this method, the input voltages (V1 to VN) can be used to compensate for the length differences between the lines in a completely static sense, or else they can be used for an initial fine-tuning of the system. This scheme usually also has to compensate for or at least take into account any bending loss requirements of the optical fibers used. Some newly available optical fibers can have a critical radius of only a few millimeters.

[0096] In the case where each path delay line senses different temperature variations or experiences uncorrelated length variations due to parasitic local noise, the previously described methods may encounter difficulties in performing real-time correction as they are. A more robust scheme operating in a completely statistical sense, consistent with some embodiments of the current subject matter, can be used. In such a scheme, the summation of operational amplifier circuits (S1...SN) can be used to convey a control voltage to the actuator. In this case, the input voltages (V1 to VN) can be used to compensate for the length differences between the delay lines in a completely statistical sense, or else they may only be available for an initial fine-tuning (calibration) of the system.

[0097] Refer again to Figure 24, the input USPL source identified as element 2401 is optically coupled to an optical coupler element 2403 such that one leg of the coupler is connected to an optical photodiode selected to operate at the operating data rate of 2401. Using standard electronic filtering techniques described by elements 2404, 2405, and 2406, the electrical square-wave representation of the incoming USPL signal is extracted and identified by element 2407. The second optical leg of coupler 2403 is butt-coupled to an appropriate optical beam splitter element identified as 2410, where the incoming signal into 2410 is split into 206 parallel optical paths. Also shown are variable-rate optical delay lines established in parallel for each of the parallel branches of beam splitter element 2410. The parallel piezoelectric elements are identified by element 242N and electronically controlled by the feedback circuit in the figure. The control voltage identified as Vc is generated by photodiode 2485 together with electronic circuit elements 2480 and 2475. The clock and data recovery (CDR) element 2475 generates a clock source for controlling each of the PZ elements. After an appropriate delay is introduced into each leg of element 2410, the optical paths identified as 244N are combined. Thereby generating a pulse-multiplied USPL signal 2490.

[0098] Figure 25A A schematic diagram of a fiber optic PZ actuator 2500 is shown, and Figure 25B a graph 2590 of the radius of such an actuator versus voltage is shown. These appended Figure 1 illustrate the operation of the PZ actuator, which is used to increase the pulse repetition rate of an incoming USPL pulse train through the induced optical delay. Although shown as an element for generating an enhanced pulse repetition rate of the USPL signal, the same technique can be used for other optical devices that require or benefit from optical delay. The basic structure of the device is a fiber-based PZ actuator 2501. When a voltage 2550 is applied to the electrode 2520, a voltage-induced stress is generated within the fiber, resulting in a time delay of the optical signal traveling through the fiber. By varying the applied voltage, a performance curve of the optical delay versus the applied voltage is obtained, as Figure 25B shown in graph 2590.

[0099] Figure 26 An illustration exemplifying the features of an exemplary statistical corrector 2600 is shown. Figure 26The coarse correction controller 2640 shown corresponds to the system described in the previous section, which can correct for length variations picked up by all delay lines simultaneously. As previously mentioned, it is desirable for these variations to occur on a time scale much slower than the "in-delay-line" parasitic variations. This latter effect can manifest as cycle-to-cycle jitter introduced in the system. This type of jitter can be monitored using a RF spectrum analyzer (RFA), which causes the repetition rate line of the system to show "skirts" (or sidebands), which are the result of the analyzer mixing together the noise frequencies originating from the non-uniform time intervals between consecutive pulses. One such pattern can be processed using an analog-to-digital converter (ADC) and saved as an array of values, which is then fed into a neural network (NN) machine. Neural network machines are known to have excellent adaptation characteristics, which allow them to essentially learn patterns from external events by adapting to a new set of inputs and outputs. In this case, a set of inputs can be generated from a set of "imperfect observations", i.e., the "noisy" output of the TDM system detected by the RFA and converted into a digital array by the ADC ({f1,f2,...,fN}, where fi is the frequency component picked up by the RFA). A set of outputs can be generated from the corrections ({V1,V2,...,VN}, where Vt is the compensation input voltage of the summing operational amplifier), which are needed to eliminate the output frequency group from the unwanted excess frequency noise, which is attributed to external perturbations of the system. With a sufficiently large number of {f,V} pairs, where f, V are the frequency array, voltage array, a statistical ensemble can be constructed to train the NN machine to learn the underlying pattern associated with the presence of in-channel noise. These machines can be purchased off the shelf in the form of ICs from several manufacturers, or implemented as software and used in conjunction with a computer feedback control mechanism. A single-layer perceptron neural network or ADALINE (Adaptive Linear Neuron or later Adaptive Linear Element) should be sufficient to accomplish this task.

[0100] In connection with the foregoing Figure 24 As described in connection with the Figure 24 electronic circuit elements 2480 and 2475 and the photodiode 2485, the statistical corrector element 2670 can include electronic circuitry similar to or providing similar functionality to Figure 26 For the example scenario shown, the RF spectrum analyzer 2695, together with the neural network 2670 and the coarse correction controller element 2640, is used to perform the required optical delays introduced into a series of parallel PZ elements 262N.

[0101] Figure 27Illustrates the concepts and capabilities of a solution consistent with embodiments of the present subject matter, where performance, accuracy, and resolution can be improved by replacing the piezoelectric disk (PZ) modules identified by elements 2795 and 272N, where a compact microfiber-based collimator (MFC) 2795 surrounded by a ceramic disk is used to obtain an optical delay line. Although a technique for increasing the native pulse repetition rate of a USPL pulse train is shown, the illustrated design is not limited to such applications, but can be applied or extended to other requirements in the optical field as long as they require optical delay. By doing so, a more controllable amount of time delay can be introduced within each MFC element of the circuit. The use of improvements leveraging MFC elements can improve response, resolution, and the realization of voltage response reproducibility needed for rapid prototyping in mass production devices. Figure 27 The concepts identified in can be incorporated into precisely manufactured elements that can act as complementary pairing units for the purpose of reducing USPL pulse-to-pulse jitter and meeting data encryption requirements.

[0102] Further reference Figure 27 , a USPL source 2701 having a certain pulse repetition rate is split into a preselected number of optical paths 271N (which can be a number other than 206), as identified by a beam splitter element 2705. Using the elements described by 2795 and 272N, a suitably controlled delay 273N is introduced into each parallel branch of the split optical paths 271N. The resulting delayed paths 274N are added together by an optical combiner element 2760. A pulse-multiplied USPL signal 2780 is produced.

[0103] One potential drawback of some previously available TDM designs where fiber "wraps" a piezoelectric actuator is that the mechanism must comply with the bending loss requirements of the fiber used. Some newly available fibers have a critical radius of only a few millimeters. To correct this problem, embodiments of the present subject matter can use a microfabricated air-gap U-bracket instead of a fiber-wrapped cylindrical piezoelectric element. Figure 27This principle is illustrated. In this scheme, the piezoelectric actuators (PZ1,...PZN) can be replaced by an air-gap U-shaped bracket structure constructed of microfiber collimators (MFC) and micro-rings made of piezoelectric material. However, in this case, the piezoelectric actuators expand longitudinally in response to the control voltages (V1, V2,...VN), thereby increasing (or decreasing) the air-gap distance between the collimators. As in the case of cylindrical piezoelectrics, a single voltage Vc can be used to drive all the piezoelectric devices, provided that the gain (G1, G2,...GN) of each channel is adjusted accordingly to provide the correct expansion for each line. Ideally, apart from the inherent deviations of the system (i.e., the intrinsic differences between operational amplifiers), the gain adjustments should be G1, 2G1, 3G1, etc., thereby providing an expansion that is a multiple of τRT / N. Another way to implement such a scheme could be to use multiple piezoelectric rings at the channels. In this way, channels with 1, 2, 3, N piezoelectric rings can be driven by the same voltage, with all amplifiers at the same gain.

[0104] Figure 28 A conceptual representation of an optical chip system 2800 is provided that is used to successfully bridge between two remote 10 GigE switches. Ideally, such a connection can operate similar to a simple single optical fiber. The timing of the TDM chip can be driven by the 10 GigE switches.

[0105] Reference Figure 28 , a USPL source 2805 having a predetermined native pulse repetition rate identified by 2806 is connected to an optical pulse multiplier chip 2807. Element 2807 is designed to convert the incoming pulse repetition rate signal 2806 to an appropriate level for combined operation with a high-speed network Ethernet switch identified by 2801. The switch 2801 provides a reference signal 2802 for modulating the signal 2809 at the data rate of interest through a standard electro-optic modulator 2820. The resulting RZ optical signal as shown in element 2840 is generated.

[0106] An alternative for timing from a 10 GigE switch lies in building the USPL to terabits per second (or faster) with a multiplier photon chip and then modulating this terabit per second signal directly from the 10 GigE switch. Each bit will have around 100 pulses. One advantage of this scheme could be the elimination of the need to run a separate timing signal from the switch to the USPL. The USPL only has to pump out terabit per second pulses via the multiplier chip. Another advantage is that the output of the multiplier chip does not have to be exactly 10.313 Gbps or 103.12 Gbps. It only has to be at a rate of around 1 terabit per second. This limitation is not a problem in the case where each 10 GigE bit has 100 or 101 or 99 pulses. Another advantage is that each bit will have many 10 USPLs, so the 10 GigE signal will have an advantage in atmospheric propagation (fog and scintillation). Another advantage can be achieved at the receiver end. If a bit has around 100 USPL pulses within that single bit, the detector will more easily detect the bit. This can result in improved receiver sensitivity and thus an improved range for the FSO system. Another advantage can be achieved because upgrading to 100 GigE can be as simple as replacing the 10 GigE switch with a 100 GigE switch. In this case, each bit will have around 10 pulses.

[0107] From a pure signal processing perspective, this scheme presents an efficient way to send data and clock combined in a single transmission stream. Very similar to using an optical pulse stream to "sample" bits, this scheme has the advantage that the bit "size" is determined by the maximum number of pulses it carries, thus establishing a basis for counting bits when they reach the receiving end. In other words, if the bit unit has a time slot capable of matching N pulses, the system clock can be established to have "a new information bit" after every 5th bit.

[0108] For terrestrial, submarine, or FSO systems in air, space, or submarine applications, techniques similar to those described herein can be used within a fiber-based power plant distribution system or within an FSO system, and for the first time illustrate how to achieve the interconnection from a USPL source to optical network elements for networking applications.

[0109] Figure 29 System 2900 is shown, which illustrates a conceptual network expansion of the design concept reflected in Figure 28 Each of multiple USPL sources 2901, 2902, 2903 (it should be noted that although three are shown, any number is within the scope of the current subject matter), configured in a WDM arrangement, is modulated via a dedicated optical switch and USPL laser multiplier chip circuitry. As referenced Figure 28As described, the electrical signals from each Ethernet switch can be used to modulate dedicated optical modulators 2911, 2922, 2928 for each optical path. The optical power for each section of the system can be provided by optical amplification elements 2931, 2932, 2933 for amplification purposes. Then, each amplified USPL path can be docked to an appropriate optical combiner 2940 for transmission to network 2950, and can be free space or fiber-based as required. The output from the WDM module can then be configured to the transmitting element 102 for FSO transmission or be configured into the fiber power plant equipment.

[0110] For terrestrial, submarine, or FSO systems in air, space, or submarine applications, techniques similar to those described herein can be used within a fiber-based power plant distribution system or within an FSO system, and for the first time illustrate how to achieve the interconnection from a USPL source to optical network elements for networking applications.

[0111] Figure 30 A schematic diagram of an experimental setup for an embodiment of the current subject matter is shown, which includes constructing a computer-aided system to control the pulse width of an all-fiber mode-locked laser using recursive linear polarization adjustment while stabilizing the repetition rate of the cavity using a synchronous self-regenerative mechanism. The design can also provide tuning capabilities for the repetition rate and pulse width.

[0112] The fiber ring laser is represented by the internal blue loop, where all intracavity fiber branches are coded in blue, except for the positive high-dispersion fiber outside the loop, which is part of the fiber grating compressor (coded in dark brown). The external loop represents the feedback active system.

[0113] Figure 30 A diagram of system 3000 is shown, which illustrates the features of a USPL module that provides pulse width control and pulse repetition rate control through all the mirrors (M1, M2), gratings (G1, G2), lengths (L1, L2), second harmonic generator (SHG), photomultiplier tube (PMT), lock-in amplifier (LIA), data acquisition system (DAC), detector (DET), clock extraction mechanism (CLK), frequency-to-voltage controller (FVC), high-voltage driver (HVD), reference signal (REF), pulse generator (PGEN), amplitude modulator (AM), isolator (ISO), piezoelectric actuator (PZT), optical coupler (OC), polarizer (POL), and polarization controller (PC) that all play a role in providing pulse repetition rate control and pulse width control.

[0114] The passive mode-locking mechanism can be based on Nonlinear Polarization Rotation (NPR), which can be used to mode-lock fiber lasers. In this mechanism, a weakly birefringent single-mode fiber (SMF) can be used to create elliptically polarized light in the forward-propagating pulse. As the pulse travels along the fiber, it experiences a nonlinear effect where intensity-dependent polarization rotation occurs. By the time the pulse reaches the polarization controller (PC) 3001, the polarization state of the high-intensity part of the pulse undergoes more rotation than the low-intensity part. The controller can perform the function of rotating the high-intensity polarization component of the pulse so that its orientation is as close as possible to align with the axis of the polarizer (POL). Thus, when the pulse passes through the polarizer, its low-intensity component experiences more attenuation than the high-intensity component. As a result, the pulse emerging from the polarizer narrows, and the whole process acts as a fast saturable absorber (FSA). This nonlinear effect acts in combination with the group velocity dispersion (GVD) of the loop, and after several round trips, a stable situation emerges and passive mode-locking is achieved. By using different types of fibers (such as single-mode, dispersion-shifted, polarization-maintaining, etc...) and adding up their contributions to the average GVD of the laser, the total GVD of the optical loop can be customized to produce a specific desired pulse width within the error margin.

[0115] Actively controlling the linear polarization rotation from the PC can greatly improve the performance of the laser. This can be achieved using a feedback system that tracks the evolution of the pulse width. By Figure 1The outer loop represented in [the figure] can be used to maximize compression and thus the average power of the pulse. Pulses emerging from the fiber ring laser via the OC are expected to have a width on the order of a few picoseconds. An external pulse compression scheme using a fiber grating compressor is used to narrow the pulse to a range below 100 fsec. This technique has been widely used in many reported experiments to generate high-energy, high-power USPL pulses. Here, the narrowed pulse is focused on a second harmonic generator (SHG) crystal and detected using a photomultiplier tube (PMT). A lock-in amplifier (LIA) provides an output DC signal to a data acquisition card (DAC). This signal follows the change in pulse width by tracking the increase or decrease in the peak power of the pulse. A similar technique has been successfully used in the past, except that a spatial light modulator (SLM) was used as an alternative. Here, a programmable servo mechanism directly controls the linear polarization rotation using actuators on a PC. Using the DC signal data provided by the DAC, decision-making software (such as but not limited to LABVIEW or MATLAB SIMULINK) can be developed to control the servo mechanism, which in turn adjusts the rotation angle of the input pulse relative to the polarizer axis. These adjustments performed by the actuators are achieved using stress-induced birefringence. For example, if the pulse width decreases, the mechanism will prompt the actuator to follow a linear angular rotation in a certain direction to compensate for it, and if the pulse width increases, it will act in the opposite direction, both aiming to maximize the average output power.

[0116] A self-regenerative feedback system that is synchronized with the repetition rate of the optical oscillation and serves as the drive signal for an amplitude modulator (AM) can regulate the laser round-trip time. In an active system, the amplitude modulator acts as a threshold gating device by modulating the loss synchronously with the round-trip time. In recent reports, this technique has been successfully used to stabilize mode-locked lasers. The signal picked up by a photodetector (DET) from an optical coupler (OC) can be electronically locked and regenerated by a clock extraction mechanism (CLK) such as a phase-locked loop or a synchronous oscillator. The regenerated signal triggers a pulse generator (PGen), which is then used to drive the modulator. In a fully synchronized scenario, at each round-trip time (TRT), the AM will "turn on" each time the pulse passes through it. Since the CLK follows the changes on the TRT, the drive signal for the AM will also change accordingly.

[0117] An external reference signal (REF) can be used to tune the repetition rate of the cavity. It can be compared with the signal recovered from the CLK using a mixer, and the output is used to drive a piezoelectric (PZT) system that can adjust the length of the cavity. Adjusting the length of the cavity using such a PZT system is a well-known concept, and similar designs have been successfully demonstrated in experiments. Here, a linear frequency-to-voltage converter (FVC) can be calibrated to provide an input signal to the high-voltage driver (HVD) of the PZT. The PZT will adjust the length of the cavity to match the repetition rate of the REF signal. For example, if the REF signal increases its frequency, the output of the FVC will decrease, and the HV drive level to the piezoelectric stack will also decrease, forcing it to contract, thus increasing the repetition rate of the laser. The opposite occurs when the repetition rate of the reference decreases.

[0118] A pair of negative dispersion gratings can be used to tune the width of the pulse to the "transform-limited" value. This chirped pulse compression technique is well established, and it has been reported that pulses can be compressed as narrow as 6 fs. The idea is to mount the grating pair pulse compressor on a moving stage that translates along the line setting the spacing between the gratings. As the distance changes, the compression factor also changes.

[0119] In an example of a data modulation scheme consistent with embodiments of the present subject matter, a passively mode-locked laser can be used as an ultrafast pulse source, which limits our flexibility in changing the data modulation rate. To scale up the data rate of our system, we need to increase the fundamental repetition rate of our pulse source. Traditionally, the repetition rate of a passively mode-locked laser has been increased by shortening the laser cavity length or by harmonic mode-locking of the laser. Both of these techniques result in a reduction in the peak power of the pulses inside the cavity, leading to longer pulse widths and more unstable mode-locking.

[0120] One solution to this problem involves using an improved pulse interleaving scheme through a technique we call pulse multiplication. Figure 31This concept is illustrated. The lower repetition rate pulse train of a well-characterized, well mode-locked laser 3101 is coupled to an integrated optical directional coupler 3180, where a well-defined portion of the pulses is tapped off and "recirculated" in an optical loop with an optical delay 3150 equal to the expected inter-pulse interval in the output pulse train, and re-coupled to the output of the directional coupler. For example, to generate a 1 GHz pulse train from a 10 MHz pulse train, an optical delay of Ins is required, and in order for the 100th pulse in the train to coincide with the input pulse from the 10 MHz source, the optical delay may have to be precisely controlled. The optical delay loop includes an optical gain 3120 to compensate for signal attenuation, a dispersion compensation 3160 to restore the pulse width, and an active optical delay control 3150. Once pulse multiplication has occurred, the output pulse train is OOK modulated 3175 using a data stream 3182 to generate an RZ signal 3190, and amplified in an erbium-doped fiber amplifier 3185 to bring the pulse energy to the same level as the pulse train (or to the expected output pulse energy level).

[0121] One or more of the features described herein, whether considered alone or in combination, can be included in various aspects or embodiments of the present subject matter. For example, in some aspects, an optical wireless communication system can include at least one USPL laser source, which can optionally include one or more of picosecond, nanosecond, femtosecond, and attosecond type laser sources. An optical wireless communication system can include a USPL source that can be fiber-coupled or free-space coupled to an optical transmission system, can be modulated using one or more modulation techniques for a point-to-multipoint communication system architecture, and / or can utilize an optical transmission terminal or telescope fabricated using one or more of a hyperbolic mirror fabrication technique, a conventional Newtonian mirror fabrication technique, or other techniques that are functionally equivalent or similar. Also or alternatively, an aspherical optical design can be used to minimize, reduce, etc. the obstruction of received optical signals.

[0122] A free-space optical transmission system consistent with embodiments of the current subject matter can utilize a USPL laser design that focuses the received signal at an ideal point. In some embodiments, a telescope or other optical element for focusing and transmitting light can be considered the transmitting element, and a second telescope or other optical element for focusing and receiving light located at a remote location relative to the first telescope or other optical element can function as the receiving element to create an optical data link. Both optical communication platforms can optionally include components required to provide both transmitting and receiving functions and can be referred to as USPL optical transceivers. Either or both of the telescopes or other optical elements for focusing and transmitting light can be coupled to the transmitting USPL source by either via an optical fiber or by free-space coupling to the transmitting element. Either or both of the telescopes or other optical elements for focusing and receiving light can be coupled to the receiving endpoint by an optical fiber or by free-space coupling to the optical receiver. A free-space optical (FSO) wireless communication system including one or more USPL sources can be used as follows: within the framework of an optical communication network, in combination with an optical fiber backhaul network (and can be used transparently within the optical communication network, within the optical communication network (and can be used within the optical communication band of 1550 nm and modulated using on-off keying (OOK) non-return-to-zero (NRZ) and return-to-zero (RZ) modulation techniques), within the optical communication network (and can be modulated using differential phase shift keying (DPSK) modulation techniques), within the optical communication network (and can be modulated using common modulation techniques for a point-to-point communication system architecture using common free-space optical transceiver terminals), within an optical communication network utilizing D-TEK detection technology, within a communication network used in combination with an erbium-doped fiber amplifier (EDFA) and a high-power erbium-ytterbium-doped fiber amplifier (Er / Yb-DFA), within the optical communication network (and can be modulated using common modulation techniques for a point-to-multipoint communication system architecture), and so on.

[0123] In some aspects, the USPL technology can be used as a beacon source to provide optical tracking and beam steering for use in automatic tracking capabilities and for maintaining terminal co-alignment during operation. The recovered clock and data extracted at the receiving terminal can be used for multi-hop spans for extending the network reach. In a WDM configuration, similar benefits can be provided for the optical network, thereby increasing the size of the effective optical bandwidth of the carrier data link. Also or alternatively, the USP laser source can be polarization multiplexed onto the transmitted optical signal to provide polarization multiplexed USP-FSO (PM-USP-FSO) functionality. The recovered clock and data extracted at the receiving terminal can be used for multi-hop spans for extending the network reach and can include a common large bandwidth operating range for providing constant data rate operation. An optical preamplifier or semiconductor optical amplifier (SOA) can be used before the optical receiver element and, alternatively or in combination with the recovered clock and data extracted at the receiving terminal, can be used for multi-hop spans for extending the network reach, thereby having a common large bandwidth operating range for providing constant data rate operation. Terminal co-alignment can be maintained during operation such that significant improvements in performance and terminal co-alignment can be achieved by using the USPL technology, by using the USPL data source, and by providing an improved scheme for maintaining transceiver alignment by using the USPL laser beacon.

[0124] In some aspects, the USPL-FSO transceiver can be used for remote sensing and detection of the identification characteristics of airborne elements using ionization or non-ionization detection techniques with an optical transmission terminal fabricated using hyperbolic mirror fabrication techniques or conventional Newtonian designs that focus the received signal on an ideal point. The USPL-FSO transceiver consistent with embodiments of the present subject matter can be used for non-line-of-sight laser communication applications. The USPL-FSO transceiver consistent with embodiments of the present subject matter can allow for: adjustment of the distance at which the occurrence of scattering effects (enabling NLOS technology), a receiving technique for improving detection sensitivity using the DTech detection scheme, and an increased bandwidth via a broadband detector including a frequency comb. The USPL-FSO transceiver consistent with embodiments of the present subject matter can be used in combination with adaptive optics (AO) techniques for performing incoming optical wavefront correction (AO-USPL-FSO). The USPL-FSO transceiver consistent with embodiments of the present subject matter can be used and operated across the infrared wavelength range. The USPL-FSO transceiver consistent with embodiments of the present subject matter can be used in combination with optical add-drop techniques and optical multiplexing techniques in both single-mode fiber configurations and multi-mode fiber configurations. The USPL-FSO transceiver consistent with embodiments of the present subject matter can be used and operated as a rangefinder and a position determination device across the infrared wavelength range for the purposes of target identification and interrogation applications.

[0125] In other aspects of the present subject matter, a series of switched network connections, such as 10 GigE or 100 GigE connections, can be connected from one point to another, for example, via time division multiplexing (TDM) over optical fiber or free space optics.

[0126] A mode-locked USPL source consistent with embodiments of the present subject matter can be used to generate both clock and data streams. A mode-locked laser can represent an option for a high-performance, high-finesse clock source in a digital communication system. In this regard, mode-locked fiber lasers (in linear or ring configurations) can be attractive preferred candidates because they can achieve pulse widths in the USPL source region and repetition rates up to GHz.

[0127] The use of carbon nanotube saturable absorbers can enable the generation of high harmonics. Passively mode-locked fiber lasers using carbon nanotube saturable absorbers (CNT-SAs) are an option for high repetition rate sources due to their ability to easily generate high harmonics of the fundamental repetition rate.

[0128] FSO can be used for terrestrial, space, and undersea applications.

[0129] Conditional path length control from a beam splitter to a diaphragm can be an important parameter. TDM multiplexing consistent with embodiments of the present subject matter can be employed to control the relative time domain time delay between the diaphragm and the source path. Each pulse train can be controlled using parallel time delay channels. This technique can be used to control conventional multi-transmit FSO diaphragm systems employing WDM systems as well as TDM systems. For both TDM systems and WDM systems, the pulse-to-pulse interval of the USPL laser can be maintained and controlled for precise time domain requirements. The techniques described can be used for systems based on TDM fiber and WDM fiber. The use of the TDM multiplexer as described herein can be used to implement unique encryption means on the transmitted optical signal. Complementary TDM multiplexers can be used to reverse incoming received signals and thereby recover the unique identification characteristics of the pulse signal. The TDM multiplexers described herein can be used to control WDM pulse characters for the purpose of WDM encryption. TDM multiplexers can be used in conventional FSO systems where multiple diaphragms connected to a common source signal can enable control of the time delay between pulses to maintain a constant path length. TDM multiplexers can be used for systems based on TDM fiber and systems based on FSO. TDM multiplexers can be an enabling technology for controlling the optical pulse train relationship of a USPL source. By measuring a neural correction factor to obtain the same pulse relationship, TDM multiplexers can be used for atmospheric link characterization functions across an optical link.

[0130] Any combination of PZ disks can be used in the transmitter and can provide an unlimited number of encryption combinations for USPL-based systems (both fiber-based and FSO). The timing can run from a 10 GigE switch or equivalent, and the USPL can be built to terabits per second (or faster) with a multiplier photonic chip, and this terabit per second signal can be directly modulated from a 10 GigE switch. When operating in a WDM configuration, an interface with a fiber-based system or with FSO network elements can be included.

[0131] The system can accept an ultrafast optical pulse train and can generate an optical pulse train having the same pulse width, spectral content, and chirp characteristics as the input optical pulse, and whose pulse repetition rate is an integer multiple of the pulse repetition rate of the input pulse. This can be accomplished by tapping a portion of the input pulse power in a 2×2 optical coupler with an actively controllable optical coupling coefficient, recycling the tapped pulse in an optical delay line with optical amplification, optical isolation, optical delay (path length) control, optical phase and amplitude modulation, and compensation for the temporal and spectral evolution of the optical pulse as it travels through the optical delay line for one round trip to minimize the temporal pulse width at the output of the device, and recombining this power with the 2×2 optical coupler.

[0132] Passive or active optical delay control can be used, and optical gain using rare-earth-doped fiber and / or rare-earth-doped integrated optical devices and / or electrically or optically pumped semiconductor optical amplification can also be used. Fiber Bragg gratings and / or volume Bragg gratings can be used to provide dispersion compensation. Wavelength-division multiplexing data modulation of the pulses traversing the delay line can be used, or pulse-coded data modulation of the pulses traversing the delay line can be used.

[0133] For FSO applications, the synthesis of a conventional USPL source can be customized by the synthesis of USPL square-wave pulses using microlithography amplitude and phase mask techniques. The ability to adjust the pulse width using control techniques and similar schemes and to actively control the pulses using this technique can improve the propagation efficiency through the FSO transmission link, thereby improving system availability and the received optical power level.

[0134] An actively programmable pulse shaper can be used to actively control the USPL pulse width, which can include matching real-time atmospheric conditions to maximize propagation through a changing environment. One or more of the following techniques can be used in FSO applications to adapt the optical time spectrum using techniques: Fourier transform pulse shaping, liquid crystal on silicon (LCOS) arrays, liquid crystal on silicon (LCOS) technology, programmable pulse shaping using an acousto-optic modulator (AOM), acousto-optic programmable dispersion filter (AOPDF), and polarization pulse shaping.

[0135] Figure 32 A process flow diagram 3200 illustrates features of an exemplary method, one or more of which may be present in embodiments of the current subject matter. At 3202, a beam of optical pulses each having a duration of about 1 nanosecond or less is generated. At 3204, a modulation signal is applied to the beam to generate a modulated optical signal. The modulation signal carries data for transmission to a remote receiving device. At 3206, the modulated optical signal is received at an optical transceiver within an optical communication platform, and at 3210, the modulated optical signal is transmitted using the optical transceiver for reception by a second optical communication device.

[0136] Figure 33 Another process flow diagram 3300 illustrates features of an exemplary method, one or more of which may be present in embodiments of the current subject matter. At 3302, a beam of optical pulses each having a duration of about 1 nanosecond or less is generated, for example, using a USPL source. The beam of optical pulses is transmitted in 3304 via an optical transceiver towards a target atmospheric region. At 3306, the optical information received at the optical transceiver is analyzed, which is the result of optical scattering of the beam of optical pulses from one or more objects in the target atmospheric region.

[0137] Figure 34 Another process flow diagram 3400 illustrates features of an exemplary method, one or more of which may be present in embodiments of the current subject matter. At 3402, a first beam and a second beam including optical pulses are generated, for example, by a USPL source. At 3404, a first modulation signal is applied to the first beam to generate a first modulated optical signal, and a second modulation signal is applied to the second beam to generate a second modulated optical signal. The first polarization state of the first modulated optical signal is adjusted at 3406. Optionally, the second polarization state of the second modulated optical signal may also be adjusted. At 3410, the first modulated optical signal having the adjusted first polarization state is multiplexed with the second modulated signal. At 3412, the first modulated optical signal having the adjusted first polarization state multiplexed with the second modulated signal is transmitted by an optical transceiver for reception by a second optical communication device.

[0138] Figure 35A and Figure 35B illustrates an exemplary node that can be used to transmit and / or receive information. The transmitting node 3510 and the receiving node 3530 can be communication platforms as described above, including reference Figures 1 to 9Additionally, while the transmitting node 3510 is shown as having components for generating and transmitting data-bearing optical signals and while the receiving node 3530 is shown as having components for receiving optical signals and extracting data from the optical signals, these components may be combined in a single node configured to both transmit and receive optical signals. In some embodiments, for example, the telescope 3522 may act as a diaphragm for both transmitting and receiving optical signals.

[0139] Figure 35A An exemplary transmitting node 3510 is shown. In some embodiments, the transmitting node 3510 may include a source 3512. In some embodiments, the source 3512 may be a USPL source, a superluminescent diode, or other source. In other embodiments, the source 3512 may be a continuous wave source. Preferably, the source 3512 may be configured to generate a beam of optical pulses, where each pulse has a coherence length of less than 400 microns. The coherence length of the source is determined as: where C is a shaping constant equal to 1 / 2, λ is the center wavelength of the pulse, and Δλ is the full width at half maximum (FWHM) spectral width of the pulse. In some embodiments, the coherence length may be less than 1 mm, less than 600 microns, less than 400 microns, less than 200 microns, less than 100 microns, less than 50 microns, or less than 1 micron. In embodiments using a continuous wave source, these values may refer to the coherence length of the continuous wave beam rather than the coherence length of the pulses.

[0140] In some embodiments, the source 3512 may have a center wavelength in the infrared range. In other instances, the center wavelength of the source 3512 may be between 1400 nm and 1700 nm. In some embodiments, the source 3512 may be configured to output pulses at a repetition rate of at least 50 MHz, 100 MHz, 200 MHz, 500 MHz, 800 MHz, 1 GHz, 1.25 GHz, 1.5 GHz, 2 GHz, 5 GHz, or 10 GHz. The source 3512 may include (internally or externally) a pulse multiplier, as generally described above, including references Figure 15 and Figures 18 to 20 . In some embodiments, the pulse width may be less than 10 ns, less than 1 ns, less than 500 ps, less than 300 ps, less than 100 ps, less than 50 ps, less than 10 ps, less than 1 ps, less than 700 fs, less than 500 fs, less than 300 fs, less than 200 fs, or less than 100 fs.

[0141] The transmitting node 3510 may optionally include a beam splitter 3514. The beam splitter 3514 may be configured to split a pulse from the source 3512 into a plurality of separate pulses having different wavelength segments. For example, a pulse having an original spectral width from 1500 nm to 1600 nm may be split into twenty-five pulses, each pulse having a corresponding spectral width of 4 nm from 1500 nm to 1600 nm (e.g., 1500 nm to 1504 nm, 1504 nm to 1508 nm, 1508 nm to 1512 nm, etc.). The beam splitter 3514 may use any known beam splitting mechanism. Each of the plurality of separate pulses may have a coherence length of less than 1 mm, less than 600 microns, less than 400 microns, less than 200 microns, less than 100 microns, less than 50 microns, or less than 1 micron.

[0142] The transmitting node 3510 may include one or more modulators 3516. In some embodiments, each of the modulators 3516 may be a Mach-Zehnder modulator (MZM). The modulator 3516 may receive a data signal indicating the data to be transmitted in the light beam, and based on this data signal, may encode the data into the pulses of the beam using on-off keying or other modulation techniques. In some embodiments, the modulator 3516 may allow a pulse to pass through to indicate a "1" in the bit stream, and may block the pulse or reduce the amplitude of the pulse to indicate a "0" in the bit stream. In embodiments where the beam is split, each of the plurality of separate pulses may be directed to a corresponding one of the plurality of modulators 3516. In other embodiments, each of the plurality of separate pulses may be modulated by a single modulator 3516. For example, the separate pulses may be delayed and interleaved relative to each other in time, and the modulator 3516 may encode data into each pulse at a repetition rate higher than the pulse generation repetition rate of the source. In the case where the source 3512 generates pulses at a rate of at least 1 GHz, for example, the beam splitter may split each pulse into twenty-five or more separate pulses, which may be modulated by one or more modulators 3516 to encode data at a rate of at least 25 Gbps. In some embodiments, the source may generate pulses at a rate of at least 1 GHz, and the beam splitter may split each pulse into at least ten, at least twenty, at least thirty, at least forty, or at least fifty separate pulses to produce a data rate of at least 10 Gbps, at least 20 Gbps, at least 30 Gpbs, at least 40 Gpbs, or at least 50 Gbps. In some embodiments, the FWHM bandwidth of the source may be at least 100 nm, at least 150 nm, or at least 200 nm, which may allow the pulses to be split into more separate pulses without reducing the coherence length of those pulses to below the value described below in connection with Figure 40 and Figure 41 the values described.

[0143] After being modulated, the pulses (optionally, separate pulses in the case of using a beam splitter) can be passed to an optional threshold filter 3518. In some embodiments, the threshold filter can be a saturable absorber (or a different non-linear device) that attenuates weak pulses and transmits strong pulses. The threshold filter 3518 can be configured to eliminate or sufficiently reduce pulses below a defined threshold while allowing pulses above that threshold to pass through. In some embodiments, the modulator 3516 can significantly attenuate the pulses intended to send a "0", but the modulator may be imperfect and a certain amount of optical energy can pass through. When this optical energy is amplified by the amplifier 3520, it may generate a signal strong enough to generate an error code. By using the threshold filter 3518, the pulses intended to be eliminated can be more fully eliminated, thereby improving the data transmission accuracy of the system.

[0144] The modulated pulses can be passed to an amplifier 3520, which can increase the amplitude of the pulses for transmission by a telescope 3522 (which can be, for example, a diaphragm and / or a lens). In the case of using a beam splitter, the separate pulses can be recombined using a combiner (not shown) before or after being passed to the amplifier 3520.

[0145] Figure 35B An exemplary embodiment of a receiving node 3530 is shown, which can be configured to receive a light beam transmitted by, for example, a transmitting node 3510 and extract data from the light beam. The receiving node 3530 can include a diaphragm 3532, an optional beam splitter 3534, and one or more optical receivers 3536, which can have specific characteristics related to the source, as described in detail below. The optical receiver 3536 can include a photodiode and processing circuitry. In some embodiments, the optical receiver 3536 can be, for example, an avalanche photodiode. In some embodiments, the processing circuitry of the optical receiver can determine whether the received light in the detection window exceeds a detection threshold and output the bit data (e.g., "0" or "1") of the window based on the result of the determination. The receiving node 3530 can be an optical communication platform as described above. In some embodiments, the components of the transmitting node 3510 and the receiving node 3530 can be included in a single transceiver node.

[0146] The diaphragm 3532 can be configured to receive an optical signal, such as by Figure 35AThe light beam transmitted by the transmitting node 3510 described in. In some embodiments, the light received at the aperture 3532 may pass through a filter that screens out light of wavelengths not close to the center wavelength of the source. For example, the source in the transmitting node may have a center wavelength between 1500 nm and 1700 nm, and the filter at the receiving node 3530 may block or reduce light outside the source frequency band. For example, the filter may reduce the amplitude of light below 1500 nm. Optionally, the filter may additionally block light of longer wavelengths, or may set a threshold at a lower wavelength, such as 1480 nm or 1460 nm. Optionally, the receiving node 3530 may include a beam splitter 3534 that may split the pulses in the received beam into multiple separate pulses of different wavelength segments. When the pulses are split and individually modulated at the transmitting node 3510, the pulses may be split by the beam splitter 3534 in the receiving node into the same wavelength segments. Then, the pulses (merged pulses or separate pulses in the case of using a beam splitter) may be processed by one or more optical receivers 3536. In embodiments where the pulse is split into multiple separate pulses, each pulse may be directed to a corresponding optical receiver that may be configured to determine whether an "on" signal or an "off" signal was transmitted within a given detection window. In some embodiments, coding schemes other than on-off keying may be used, such as frequency modulation. Details will be provided below with reference to Figure 41 Provide additional details regarding the optical receiver 3536.

[0147] Figure 36 An exemplary arrangement is shown in which data is transmitted from a first communication network 3542 to a second communication network 3544 across an optical communication distance D using a transmitting node 3510 and a receiving node 3530 (such as those described above in connection with Figures 35A to 35B Those). The data may be received from the optical communication network 3542, encoded into the light beam, and transmitted across the optical communication distance D using the transmitting node 3510. The receiving node 3530 may receive the light beam, extract the transmitted data, and pass the data to the communication network 3544. In some embodiments, data from the communication 3544 may also be transmitted from the node 3530 back to the node 3510, which may pass the data to the communication network 3542 for two-way communication. In some embodiments, the optical communication distance may be at least 0.5 miles, at least 1 mile, at least 2 miles, at least 3 miles, at least 5 miles, at least 7 miles, at least 10 miles, or at least 20 miles.

[0148] Figure 37An exemplary beam is shown traveling across an optical communication distance D, such as 1 mile, through a medium with a perfectly uniform refractive index. Even in a medium with a perfectly constant refractive index, the beam will naturally spread due to diffraction. However, the beam maintains the same shape and only expands by an amount proportional to the propagation distance, and there is no beam flash effect in a medium with a uniform refractive index.

[0149] Figure 38 A schematic representation of photons in a beam traveling through a variable refractive medium is provided. The atmosphere has fluctuations in temperature, density, pressure, humidity, aerosols, wind, convection, and other parameters, which cause the refractive index of the atmosphere to change. When a light beam travels through the atmosphere or other variable refractive media, such as water, the photons within the beam can be refracted slightly differently from other photons. As Figure 38 shown, due to the variation of the refractive index in the variable refractive medium, different ray paths within the beam may be refracted differently. As a result, in a system that transmits over a sufficiently large optical communication distance D and receives a free-space light beam at a receiving node (such as the system shown in FIG. 35), different photons within a single pulse can take different lengths of paths to reach the receiving node and can arrive at different times. If the time delay is less than the coherence length of the source, these differences in path lengths and the time required for the photons to travel these distances may create coherent interference and degrade the signal quality in a free-space optical communication system. Solutions to this problem are described herein, including reference Figure 40 and Figure 41 , and as applied in systems such as those shown in Figure 35A , Figure 35B and Figure 36 .

[0150] In addition to the variation in path lengths, due to changes in atmospheric conditions including humidity, temperature, and density, the photons in a pulse can travel at variable speeds. Since different photons in a pulse travel through slightly different atmospheric conditions, the photons may travel at different speeds and arrive at different times. Additionally, light of different wavelengths within a pulse can travel at different speeds, which can further broaden the pulse as it passes through the variable refractive medium.

[0151] Figure 39 A schematic representation of a pulse transmitted by a transmitter and received by an optical receiver is shown. As Figure 39 shown, when the pulse is transmitted by the transmitting node, the pulse can have a pulse width of 90 femtoseconds. The pulse can then travel an optional transmission distance, where the pulse can be received by an optical receiver with a detection window 4020 having a predetermined duration, e.g., 500 picoseconds. When the pulse is received by the optical receiver, its received pulse width may be broadened due to passing through the variable refractive medium, as described above in connection withFigures 37 to 38 As described. Due to variations in the path length traveled by the beam and variations in the atmospheric conditions through which the beam travels, different photons may reach the detector at different times according to a distribution curve that can have a duration longer than the pulse duration at emission. The amount of broadening may vary, depending on the length of the optical communication distance and the atmospheric conditions, which include humidity, temperature, density, and the presence of aerosols such as fog. Under some conditions, this broadening can be on the order of picoseconds or greater.

[0152] The pulse can have a temporal distribution curve as shown. While a normal temporal distribution curve is shown, other pulse shapes are possible. By making the width of curve 4010 longer than the coherence length of the emitted pulse (e.g., 3 times its length), coherent beam interference and coherent beam scintillation can be reduced.

[0153] Figure 40 An exemplary temporal distribution curve of a short-duration (e.g., approximately 100 femtoseconds) pulse 4010 is shown, which travels a significant distance (e.g., one mile) through a variable refractive medium and is broadened in time. The pulse can have a FWHM duration 4030 and a coherence time 4040 when it reaches the optical receiver, and the coherence time can be equal to the coherence length of the pulse divided by the speed of light through the variable refractive medium. In some embodiments, the FWHM duration 4030 can be greater than the coherence time 4040 of the pulse. Preferably, the FWHM duration 4030 can be at least 2 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 8 times, at least 10 times, or at least 12 times the coherence time 4040 of the pulse. By ensuring that the FWHM duration 4030 of the pulse received at the optical receiver is relatively large compared to the coherence time 4040 of pulse 4010, interference between different ray paths of the pulse when the pulse reaches the optical receiver at different times can be reduced, and a signal with reduced noise and higher quality can reach the optical receiver.

[0154] The optical receiver can have a detection window 4020 that has a specified duration. A shorter detection window generally allows for higher data throughput. For example, in a system using on-off keying for data modulation, an optical receiver with a 1 nanosecond detection window can extract up to 1 Gbps, while an optical receiver with a 100 picosecond detection window can extract up to 10 Gbps. The optical receiver can have a repetitive detection window that is less than 100 ns, less than 10 ns, less than 1 ns, less than 100 ps, or less than 10 ps.

[0155] However, the pulse length and temporal broadening may cause photons from a pulse intended to be received within one detection window to fall into an adjacent detection window. This phenomenon may create an error code in cases where photons of the transmitted signal should not be received in the adjacent detection window (e.g., because a "0" is transmitted at that bit position). Thus, to maximize data transmission accuracy, it is important that the FWHM duration 4030 of the pulse received at the optical receiver is greater than the coherence length 4040 of the pulse (and preferably at least three times thereof), while at the same time the FWHM duration 4030 of the pulse received at the optical receiver should also be significantly less than the detection window 4020 of the optical receiver.

[0156] For example, the detection window 4020 may be at least 2 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 10 times, or at least 20 times the FWHM duration 4030 of the pulse received at the optical receiver. Preferably, at least 95%, at least 99%, or at least 99.99% of the photons in the pulse arriving at the optical receiver may arrive at corresponding arrival times separated from the center 4040 of the temporal distribution curve of the pulse by a corresponding time difference that is less than half of the detection window duration of the optical receiver. Note that while the center 4040 of the temporal distribution curve of the pulse is shown as being located at the center of the detection window 4020, this need not be the case, and the pulse may arrive earlier or later than the midpoint of the detection window. The center 4040 of the temporal distribution curve may preferably be located at or near the center of the detection window 4020 to reduce the likelihood of photons in the pulse spilling over into an adjacent detection window. In some embodiments, the center 4040 of the temporal distribution curve may be separated from the center of the detection window 4020 by less than 100 picoseconds, 50 picoseconds, 20 picoseconds, 10 picoseconds, 5 picoseconds, 1 picosecond, 800 femtoseconds, or 500 femtoseconds.

[0157] By specifying the relationship between the coherence time 4040 of the pulse, the FWHM duration 4030 of the pulse when it arrives at the optical receiver, and the detection window 4020 of the optical receiver in the manner described herein, the data transmission accuracy and the effective transmission range can be greatly improved (see below in connection with Figure 42Discussion of the test results). The FWHM duration 4030 of the pulse when it reaches the optical receiver can vary depending on the pulse length when sent from the source, the medium through which the pulse travels (e.g., atmospheric pressure, temperature, sunlight intensity, aerosols), and the distance the pulse travels to reach the optical receiver. Thus, it may be necessary to reduce the coherence time 4040 of the pulse and / or it may be necessary to increase the detection window 4020 of one or more optical receivers, depending on the conditions of the optical communication system. Thus, reducing the coherence time 4040 and increasing the detection window 4020 can improve the data transmission quality while having a negative impact on the data throughput. In some embodiments, the system can be configured to determine the data transmission quality of the system (e.g., bit error rate or signal value measurement results above or below a detection threshold), and in response to the determined data transmission quality, modify either or both of the coherence time 4040 of the pulse or the detection window duration 4020 of the optical receiver.

[0158] Similarly, when using a source that can continuously emit light, such as a continuous wave source or a superluminescent diode, the emitted light can be gated into pulses (or otherwise converted into pulses using data modulation or other known techniques), and these pulses only occupy a relatively small fraction of the detection window duration, and these pulses can be timed to arrive at or near the center of the detection window of the optical receiver. Gating and timing the pulses in this way can reduce the risk that photons in the "on" window (where light is intended to be transmitted) may spill over into the "off" window (where light is not intended to be transmitted) and cause bit errors. Thus, the pulse durations and positions relative to the detection window described above can also apply to pulses generated using a source that can continuously emit light. In such cases, although these sources can continuously emit light, even during the "on" transmission window where light is intended to be transmitted, the effective output can be "off" most of the time, leaving enough of a gap between the center of the pulse and the end of the detection window to avoid spillover. For example, during the "on" bit window where light is intended to be transmitted, the effective output from a continuously emitting source can be "on" for less than 50%, less than 30%, less than 20%, or less than 10% of the corresponding transmission bit window.

[0159] Figure 41 A schematic representation of optical pulses arriving within the detection windows 4020a, 4020b, 4020c of an optical receiver is shown. The optical pulses can have any shape and generally may broaden to some extent due to traveling across an optical communication distance through a variable refractive medium. In the first detection window 4020a, the optical pulse can arrive at or near the center of the window and can cause the total received light in the window to exceed the detection threshold V th, which can be processed by the circuitry of the optical receiver to indicate that a pulse has been received in that window. In some embodiments, this can cause the optical receiver to output a “1” for this detection window. At the end of detection window 4020a and before detection window 4020b, the optical receiver circuitry can be reset and returned to zero. In detection window 4020b, no pulse is transmitted (e.g., because a “0” is intended to be transmitted and the modulator at the sending node blocks the pulse), and the total light received in window 4020b can be below the detection threshold V th . This can cause the optical receiver to output a “0” for this detection window. The optical receiver circuitry can be reset again and returned to zero, and the cycle can repeat with a third window 4020c, and so on.

[0160] Detection threshold V th can be configured such that it is high enough so that ambient light will not trigger a false alarm, but low enough so that a true pulse will reliably exceed the detection threshold V th . Importantly, the pulse sufficiently exceeds the background noise so that there is sufficient signal difference between the “on” bit window and the “off” bit window such that the detection threshold V th can be both high enough to ignore ambient noise and low enough to capture each transmitted pulse. This is particularly challenging at long distances (e.g., one mile or more) and under sub-optimal environmental conditions (e.g., partially sunny, large amounts of aerosols). The relationship between the pulse length, coherence time, and detection window at the optical receiver described herein significantly improves the signal quality transmission and allows for an effective detection threshold V even for free-space optical systems that transmit data over optical transmission distances spanning more than 1 mile, 2 miles, 3 miles, 5 miles, or 7 miles Figures 39 to 41 . th .

[0161] In the case of having a beam splitter and multiple optical receivers, each of the multiple optical receivers can generate a bit stream based on the separate pulses directed to that optical receiver, and the bit streams from the respective optical receivers can be interleaved to produce a combined bit stream with a higher data rate. The combined bit stream can be output to a communication network as described above (including reference Figure 36 ).

[0162] Figure 42 shows an example of test data received over an optical communication distance of one mile. The test data compares an optical signal generated by the sending node described above in reference Figure 35A with an optical signal generated using a continuous wave source having the same average power as the USPL source. Specifically, to generate the data shown in the top row of the graph shown in Figure 42 , incorporated into the above reference Figure 35AThe USPL source in the described transmitting node is used to transmit data across an optical communication distance of one mile. The received signal is directed to a sheet of white paper and an infrared camera is placed behind the paper to record the light passing through the paper. To generate the data shown in the bottom row of the graph shown in Figure 42 , the same experimental setup is used with a continuous wave source having the same average power and the same optical communication distance as the USPL source. The light from both the USPL source and the CW source is directed to the same sheet of white paper, and the two signal spots in the same frame are captured using the infrared camera. The spot size has a diameter of approximately 12 inches. The background ambient light is subtracted from each pixel, and each pixel is subjected to threshold logic processing such that pixels in which the received optical signal is above the threshold are set to "white", and pixels in which the received optical signal is below the threshold are set to "black". The four images shown for each source are taken from the same frame in the video feed, and the frames are equally spaced at 10-second intervals. Frame A shows the signals received from the USPL source and the CW source at 10 seconds, Frame B shows the signals received from the USPL source and the CW source at 20 seconds, Frame C shows the signals received from the USPL source and the CW source at 30 seconds, and Frame D shows the signals received from the USPL source and the CW source at 40 seconds.

[0163] This data shows that the transmitting node described herein generates ultrashort pulses that are significantly more clustered and reliably exceed the detection threshold much more in the detection field. When applied to a communication system using an optical receiver having the features described above (including reference Figures 35B to 41 ), this results in a greatly improved data transmission accuracy. Tests of the system by the applicant according to this description have shown free space optical communication distances of more than 1 mile, 2 miles, 3 miles, 5 miles, and up to 7.4 miles with a zero bit error rate, which were measured over time intervals of at least 10 seconds, at least 30 seconds, at least 60 seconds, at least 10 minutes, at least 30 minutes, and at least 1 hour. In some embodiments, the system described herein can transmit data across an optical communication distance of at least one mile and have a measured bit error rate of less than one in a million, less than one in a billion, less than one in a trillion, or less than one in a quadrillion over a measurement period of at least sixty seconds. To the applicant's knowledge, no other free space optical system can achieve similarly low over even a half-mile optical communication distance.

[0164] Accordingly, the systems described herein allow for significantly improved data transmission accuracy, communication link distances, and they also allow for the use of free-space optical communication in adverse environmental conditions (e.g., rain, fog, atmospheric scintillation), which render free-space optical communication ineffective in existing systems. In some embodiments, the improved data transmission quality and range may also allow for the application of free-space optical communication to systems where it was not previously possible to use effectively. For example, a transmitting node and / or a receiving node according to the present disclosure may be provided in an Earth-orbiting satellite to provide ground-to-air and / or air-to-ground free-space optical communication. Due to the amount of atmosphere traversed in traveling between the Earth's surface and space, prior art before the present disclosure has not been used to demonstrate effective optical data transmission, but the techniques described herein can achieve effective optical communication across this distance.

[0165] Figure 43 An exemplary ranging node 4400 is shown, which can be used to detect objects or surfaces and determine the position of these objects relative to the node. The ranging node 4400 generally may include components of the transmitting node 3510 and the receiving node 3530 described above in connection with Figure 35A and Figure 35B described. For example, the ranging node 4400 may include a source 3512, a beam splitter, one or more modulators, an amplifier, and a telescope. These elements may be configured together to emit light pulses that travel towards the surface S through a variable refractive medium. In the case of a laser ranging node, data modulation is optional but may be included to encode information related to the pulse, the node, or other information. Photons from the light pulse may be reflected by the surface S and returned to the node 4400. The total travel distance of the light pulse from transmission by the ranging node to reception of the reflected pulse may be twice the distance from the node to the surface S. Upon returning to the node, the pulse may be received by the diaphragm 3532, optionally split by the beam splitter 3534, and analyzed using one or more optical receivers 3536. Each of these components may have the same properties and parameters as the corresponding components described above in connection with Figures 35A to 41 described. The ranging node 4400 may additionally include a time-of-flight (TOF) circuit 4410, which may be configured to determine the time of flight of the pulse to reach the surface S and return to the node 4400, and thereby determine the distance of the surface S relative to the ranging node 4400.

[0166] One or more aspects or features of the subject matter described herein can be implemented in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), computer hardware, firmware, software, and / or combinations thereof. These various aspects or features can be embodied in one or more computer programs that are executable and / or interpretable on a programmable system including at least one programmable processor, which may be coupled, for a special or general purpose, to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

[0167] These computer programs, which may also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented using high-level procedural and / or object-oriented programming languages, and / or by assembly / machine languages. As used herein, the term "machine-readable medium" refers to any computer program product, apparatus, and / or device, such as a magnetic disk, optical disk, memory, and programmable logic device (PLD), that provides machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal that provides machine instructions and / or data to a programmable processor. A machine-readable medium may store such machine instructions non-transitorily, such as in non-transitory solid state memory or a magnetic hard disk drive or any equivalent storage medium. A machine-readable medium may alternatively or additionally store such machine instructions in a transient manner, such as in a processor cache or other random access memory associated with one or more physical processor cores.

[0168] To provide for interaction with a user, one or more aspects or features of the subject matter described in this document may be implemented on a computer having a display device (such as, for example, a cathode ray tube (CRT), a liquid crystal display (LCD), or a light emitting diode (LED) monitor) for displaying information to the user and a keyboard and a pointing device (such as, for example, a mouse or a trackball) by which the user may provide input to the computer. Other kinds of devices may also be used to provide for interaction with the user. For example, feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including but not limited to acoustic, speech, or tactile input. Other possible input devices include, but are not limited to, touch screens or other touch-sensitive devices, such as single-point or multi-point resistive or capacitive touchpads, speech recognition hardware and software, optical scanners, optical pointers, digital image capture devices, and associated interpretation software, among others. A computer located remotely from the analyzer may be linked to the analyzer via a wired or wireless network to effect data exchange between the analyzer and the remote computer (such as, for example, receiving data from the analyzer at the remote computer and transmitting information such as calibration data, operating parameters, and software upgrades or updates) and for remote control, diagnostics, etc., of the analyzer.

[0169] Although the subject matter of this disclosure has been described and shown in considerable detail with reference to certain illustrative embodiments, including various combinations and sub-combinations of features, those skilled in the art will readily appreciate other embodiments and variations and modifications within the scope of this disclosure. Additionally, the description of such embodiments, combinations, and sub-combinations is not intended to convey that the claimed subject matter requires features or combinations of features other than those expressly recited in the claims. Accordingly, the scope of this disclosure is intended to cover all modifications and variations that fall within the spirit and scope of the following appended claims.

Claims

1. An optical communication system for optically transmitting data through a variable refractive medium, the system comprising: a light source configured to generate a beam including a series of optical pulses; a modulator configured to modulate the series of optical pulses in response to a data transmission signal, thereby encoding transmission data into the series of optical pulses; an optical receiver having: a detection window duration of 1 nanosecond or less; and a detection threshold, wherein the optical receiver is configured to indicate whether the optical energy received during a given detection window is greater than the detection threshold; wherein: the series of optical pulses includes a first pulse having a coherence length of less than 400 micrometers; when the first pulse travels through the variable refractive medium, photons in the first pulse are refracted and thus travel along different ray paths of different lengths toward the optical receiver; the photons of the first pulse arrive at the optical receiver according to a time distribution curve that depends at least in part on the duration of the first pulse and the lengths of the different ray paths taken by the photons in the first pulse to reach the optical receiver; the full width at half maximum value (FWHM value) of the time distribution curve is greater than the coherence time value, the coherence time value being equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium; and the detection window duration of the optical receiver is greater than the FWHM value of the time distribution curve.

2. The optical communication system according to claim 1, wherein the light source and the optical receiver are separated by a free space optical communication distance of at least one mile, and the optical communication system has a measured bit error rate of less than one in a billion within the free space optical communication distance of at least one mile during a measurement period of at least sixty seconds.

3. The optical communication system according to claim 1, wherein the FWHM value of the time distribution curve is at least three times the coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium.

4. The optical communication system according to claim 3, wherein the light source is a continuous wave source and the beam is gated into a series of optical pulses, each of the series of optical pulses generating a corresponding time distribution curve as it travels toward the optical receiver, the corresponding time distribution curve having a corresponding full width at half maximum (FWHM) value that is 50% or less of the detection window duration.

5. The optical communication system according to claim 3, wherein the light source is a continuous wave source and the beam is gated into the series of optical pulses, each of the series of optical pulses generating a corresponding time distribution curve as it travels toward the optical receiver, the corresponding time distribution curve having a corresponding full width at half maximum (FWHM) value that is 30% or less of the detection window duration.

6. The optical communication system according to claim 1, wherein the FWHM value of the time distribution curve is at least six times the coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium.

7. The optical communication system according to claim 1, wherein at least 95% of the photons of the first pulse arriving at the optical receiver arrive at corresponding arrival times, the corresponding arrival times being spaced from the center of the time distribution curve by a corresponding time difference, the corresponding time difference being less than half of the detection window duration of the optical receiver.

8. The optical communication system according to claim 1, wherein the light source is located on a ground station and the optical receiver is disposed on an Earth-orbiting satellite, and the optical communication system has a measured bit error rate of less than one in a billion within the free space optical communication distance between the ground station and the Earth-orbiting satellite during a measurement period of at least sixty seconds.

9. The optical communication system according to claim 1, wherein the series of optical pulses generated by the light source has a center wavelength between 1500 nm and 1700 nm, and the optical receiver is disposed at a detection node, the detection node including a filter configured to reduce the amount of light having a wavelength below 1500 nm arriving at the optical receiver.

10. The optical communication system according to claim 1, wherein: the light source is disposed in a transmitting node; the transmitting node includes a beam splitter configured to split a combined pulse generated by the light source into a plurality of separate pulses having different wavelength segments, the first pulse being among the plurality of separate pulses; the transmitting node is configured to individually modulate each of the plurality of separate pulses in response to the data transmission signal, thereby encoding the transmission data among the plurality of separate pulses; each of the plurality of separate pulses has a corresponding coherence length of less than 400 microns; the optical receiver is disposed in a receiving node; the receiving node includes a beam splitter configured to direct the plurality of separate pulses to a corresponding optical receiver among a plurality of optical receivers, the optical receiver being among the plurality of optical receivers; each of the plurality of separate pulses includes a corresponding ray path arriving at the corresponding optical receiver among the plurality of optical receivers according to a corresponding time distribution curve; and each of the plurality of separate pulses has a corresponding FWHM value of its time distribution curve, the corresponding FWHM value being at least three times the coherence time value equal to the corresponding coherence length of the corresponding separate pulse divided by the speed of light through the variable refractive medium.

11. The optical communication system according to claim 1, the optical communication system further comprising: an amplifier configured to amplify the amplitude of the series of optical pulses; and a threshold filter configured to receive the series of optical pulses after the transmission data has been encoded by the modulator and before the series of optical pulses arrives at the amplifier, wherein The threshold filter is configured to selectively attenuate pulses having an amplitude less than the threshold of the threshold filter.

12. A laser ranging system, the laser ranging system comprising: A light source configured to generate a beam including a series of optical pulses; A light receiver having: A detection window duration of 1 nanosecond or less; And A detection threshold, wherein the light receiver is configured to indicate whether the optical energy received during a given detection window duration is greater than the detection threshold; Wherein: The series of optical pulses includes a first pulse having a coherence length less than 400 micrometers; When the first pulse travels through the variable refractive medium, photons in the first pulse are refracted so as to travel to the light receiver along different ray paths having different lengths; The photons of the first pulse reach the light receiver according to a time distribution curve that depends at least in part on the duration of the first pulse and the lengths of the different ray paths taken by the photons in the first pulse to reach the light receiver; The full width at half maximum (FWHM value) of the time distribution curve is greater than the coherence time value, the coherence time value being equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium; The detection window duration of the light receiver is greater than the FWHM value of the time distribution curve; and The laser ranging system is configured to send the series of optical pulses towards a surface, receive at least a portion of the series of optical pulses that has been reflected by the surface, and determine the distance of at least a portion of the surface relative to the laser ranging system based on the time of flight of the received portion of the series of optical pulses.

13. The laser ranging system according to claim 12, wherein the FWHM value of the time distribution curve is at least three times the coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium.

14. The laser ranging system according to claim 13, wherein the light source is a continuous wave source and the beam is gated into a series of light pulses, each of the series of light pulses generating a corresponding time distribution curve as it travels towards the light receiver, the corresponding time distribution curve having a corresponding full width at half maximum (FWHM) value that is 50% or less of the detection window duration.

15. The laser ranging system according to claim 13, wherein the light source is a continuous wave source and the beam is gated into the series of light pulses, each of the series of light pulses generating a corresponding time distribution curve as it travels towards the light receiver, the corresponding time distribution curve having a corresponding full width at half maximum (FWHM) value that is 30% or less of the detection window duration.

16. The laser ranging system according to claim 12, wherein the FWHM value of the time distribution curve is at least six times the coherence time value equal to the coherence length of the first pulse divided by the speed of light through the variable refractive medium.

17. The laser ranging system according to claim 12, wherein at least 95% of the photons of the first pulse arriving at the optical receiver arrive at corresponding arrival times that are spaced from the center of the time distribution curve by a corresponding time difference that is less than half of the detection window duration of the optical receiver.

18. The laser ranging system according to claim 12, wherein the light source and the optical receiver are located on a ground station and the surface is disposed on an Earth-orbiting satellite, and the laser ranging system has a measured bit error rate of less than one in a billion over a distance of at least one mile during a measurement period of at least sixty seconds.

19. The laser ranging system according to claim 12, wherein the series of optical pulses generated by the light source has a center wavelength between 1500 nm and 1700 nm, and the optical receiver is disposed after a filter configured to reduce the amount of light having a wavelength below 1500 nm that arrives at the optical receiver.

20. The laser ranging system according to claim 12, wherein: the laser ranging system includes a first beam splitter configured to split a combined pulse generated by the light source into a plurality of separate pulses having different wavelength segments, the first pulse being among the plurality of separate pulses; the laser ranging system is configured to individually modulate each of the plurality of separate pulses in response to a signal, thereby encoding signal data into the plurality of separate pulses; each of the plurality of separate pulses has a corresponding coherence length of less than 400 microns; the laser ranging system includes a second beam splitter configured to direct the plurality of separate pulses to corresponding optical receivers among a plurality of optical receivers; each of the plurality of separate pulses includes a corresponding ray path that arrives at the corresponding optical receiver among the plurality of optical receivers according to a corresponding time distribution curve; and each of the plurality of separate pulses has a corresponding FWHM value of its time distribution curve, the corresponding FWHM value being at least three times the coherence time value equal to the coherence length of the corresponding separate pulse divided by the speed of light through the variable refractive medium.

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