Optical beam transmission device

Abstract

The present invention includes: a light distribution means (102) for splitting laser light into one local light and transmission light for each path; an optical frequency shift means (103) for shifting the frequency of the local light; a collimator lens (104) for converting the frequency-shifted local light into a local beam; optical phase shifters (105) for shifting the phases of the corresponding transmission light in response to control signals; optical modulators (106) for modulating the phase-shifted transmission light according to modulating electrical signals; optical amplifiers (107) for amplifying the intensities of the corresponding modulated transmission light; optical collimator arrays (108) for converting the corresponding amplified transmission light into transmission beams; light beam splitting means (109) for splitting a portion of each of the transmission beams, respectively, and combining the corresponding portions of each of the transmission beams with the local beam to obtain composite phase monitor light, respectively; photoelectric conversion means (111) for photoelectrically converting the corresponding composite phase monitor light to obtain electrical signals; modulating electrical signal output means for outputting delay time-controlled modulating electrical signals to the corresponding optical modulators (106), respectively, on the basis of each of the electrical signals; and optical phase synchronization control means (115) for detecting the phases of the corresponding electrical signals and outputting the control signals based on the phases to the corresponding optical phase shifters (105).

Description

Optical beam transmitter

[0001] The present disclosure relates to an optical beam transmitter that phase-synchronizes and combines a plurality of optical beams.

[0002] Conventionally, devices for transmitting high-power optical beams over long distances, such as in optical space communications or optical energy transmission, are known. In these devices, the transmission power per beam is limited due to the power-handling limitations of optical fiber amplifiers or the optical fibers transmitting the output light. Spatial phase combining (CBC: coherent beam combining) is a technique that overcomes this limitation. In this spatial phase combining technique, multiple optical beams are transmitted in an array, and the phases of the optical beams are aligned to combine them in space.

[0003] To phase-combine optical beams with wavelengths on the order of microns, it is necessary to align the optical path length fluctuations between the optical beams on the order of microns. However, environmental fluctuations such as temperature typically cause the phase of light waves transmitted through different optical paths, such as optical fibers or optical fiber amplifiers, to fluctuate. In conventional technology, an optical beam (local beam) that serves as a reference wavefront (phase) is spatially combined with each transmitted beam, and each transmitted beam and the local beam are photoelectrically converted into a heterodyne beat signal. Then, in conventional technology, the phase error of each transmitted signal is detected from the phase information of the heterodyne beat signal, and the phase of each transmitted signal is corrected based on the phase information, thereby transmitting a phase-synchronized array of optical beams. In this way, conventional technology performs spatial phase combining.

[0004] Furthermore, in order to transmit high-power light beams, it is necessary to increase the number of beams and the intensity of each light beam. However, when a light beam is transmitted through an optical fiber such as an optical fiber amplifier, the intensity that can be transmitted through the optical fiber is limited by stimulated Brillouin scattering (SBS) caused by the nonlinearity of the optical fiber. SBS is more likely to occur as the linewidth of the light beam becomes narrower. Therefore, in order to suppress the occurrence of SBS, it is desirable for the linewidth of the light beam to be wide, and when the linewidth of the light beam output from a laser light source is narrow, it is necessary to widen the linewidth.

[0005] In the technology disclosed in Non-Patent Document 1, the linewidth of a laser beam is expanded by phase-modulating (25 GHz Φ-mod) the laser beam output from a light source (MO) with a wideband signal. Non-Patent Document 1 also suggests the use of a pseudo random bit sequence (PRBS).

[0006] On the other hand, as the linewidth of laser light becomes wider, the actual lengths of the transmission paths between each optical transmission path must be matched to within the order of the reciprocal of the linewidth or less. When the linewidth is on the order of several tens of GHz, the actual lengths of the fibers must be matched to within the order of mm or less. Furthermore, to phase-combine optical beams, they must be stabilized to within the order of the wavelength of light (<1 μm). Therefore, the technology disclosed in Non-Patent Document 1 provides a variable delay line (VDL) in the optical path of the transmitted light. This allows the lengths of each optical path to be matched, and an optical phase modulator (φMod) is used to suppress optical phase fluctuations between the optical paths.

[0007] Angel Flores, Chunte Lu, Craig Robin, Shadi Naderi, Christopher Vergien, Iyad Dajani, "Experimental and theoretical studies of phase modulation in Yb-doped fiber amplifiers," Proc. SPIE 8381, Laser Technology for Defense and Security VIII, 83811B (21 May 2012)

[0008] In the technology disclosed in Non-Patent Document 1, the linewidth of laser light output from a light source (MO) is broadened (line broadening), then split into multiple optical paths, amplified by an optical amplifier, and spatially combined (coherent beam combining). In this case, the technology disclosed in Non-Patent Document 1 uses a variable delay line to match the actual lengths of each optical path in order to create correlation between the optical beams in a linewidth-broadened state, and compensates for phase fluctuations between each path to perform coherent beam combining. However, as the linewidth broadening range (frequency) increases, the tolerance for the actual lengths between the optical paths decreases. Therefore, it is difficult to manufacture a laser beam with a consistent optical path length from the split to the emission from the collimator into space. Furthermore, even when a variable delay line is used for adjustment to compensate for this error, there are problems, such as limitations on the control range of the variable delay line and the possibility of loss fluctuations due to control of the delay amount.

[0009] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an optical beam transmitting device that can ease manufacturing requirements compared to conventional devices.

[0010] A high-brightness optical beam transmission device according to the present disclosure includes an optical distribution means for branching laser light into one local light and transmission lights for each path, an optical frequency shifting means for shifting the frequency of the local light obtained by the optical distribution means, a collimating lens for converting the local light after frequency shifting by the optical frequency shifting means into a local beam that is a parallel beam, an optical phase shifter provided for each path for changing the phase of the corresponding transmission light obtained by the optical distribution means in response to a control signal, an optical modulator provided for each path for modulating the transmission light after phase change by the corresponding optical phase shifter in response to a modulated electrical signal, an optical amplifier provided for each path for amplifying the intensity of the transmission light after modulating by the corresponding optical modulator, and a collimating lens provided for each path for converting the transmission light after amplified by the corresponding optical amplifier into a transmission beam that is a parallel beam. the optical phase synchronization control means for each path, which detects the phase of the electrical signal obtained by the corresponding optical converter and outputs a control signal based on the detected phase to the corresponding optical phase shifter.

[0011] According to the present disclosure, the above-described configuration makes it possible to ease manufacturing requirements compared to the prior art.

[0012] FIG. 1 is a diagram illustrating an example of the configuration of an optical beam transmission device according to embodiment 1. FIG. 2A to FIG. 2E are schematic diagrams illustrating an example of the frequency allocation of light and electrical signals in each section of the optical beam transmission device according to embodiment 1. FIG. 1 is a diagram illustrating an example of the configuration of an optical beam transmission device according to embodiment 2. FIG. 2A is a diagram illustrating an example of the configuration of an optical frequency synchronization control means in embodiment 2. FIG. 5A to FIG. 5E are schematic diagrams illustrating an example of the frequency allocation of light and electrical signals in each section of the optical beam transmission device according to embodiment 2. FIG. 1 is a diagram illustrating an example of the configuration of an optical beam transmission device according to embodiment 3. FIG. 1 is a diagram illustrating an example of the configuration of an optical beam transmission device according to embodiment 4. FIG. 8A and FIG. 8B are diagrams illustrating examples of the hardware configuration of the optical beam transmission devices according to embodiments 1 to 4.

[0013] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1. Fig. 1 is a diagram showing an example of the configuration of an optical beam transmitter 1 according to embodiment 1. In Fig. 1, solid arrows indicate the flow of optical signals, and dashed arrows indicate the flow of electrical signals (including high-frequency signals (microwave signals)). As shown in Fig. 1, the optical beam transmitter 1 includes a laser light source 101, an optical distribution means 102, an optical frequency shifting means 103, a collimating lens 104, a plurality of optical phase shifters 105, a plurality of optical modulators 106, a plurality of optical amplifiers 107, an optical collimator array 108, an optical beam branching means 109, a plurality of beam focusing means 110, a plurality of photoelectric conversion means 111, a signal generating means 112, a plurality of delay calculation devices 113, a plurality of RF variable delay means 114, and a plurality of optical phase synchronization control means 115.

[0014] 1, the optical beam transmitting device 1 is provided with optical phase shifters 105-1 to 105-n as the plurality of optical phase shifters 105, optical modulators 106-1 to 106-n as the plurality of optical modulators 106, optical amplifiers 107-1 to 107-n as the plurality of optical amplifiers 107, beam focusing means 110-1 to 110-n as the plurality of beam focusing means 110, photoelectric conversion means 111-1 to 111-n as the plurality of photoelectric conversion means 111, delay calculation devices 113-1 to 113-n as the plurality of delay calculation devices 113, RF variable delay means 114-1 to 114-n as the plurality of RF variable delay means 114, and optical phase synchronization control means 115-1 to 115-n as the plurality of optical phase synchronization control means 115. Note that -1 to -n represent element (path) numbers in the array, and n is the number of elements.

[0015] The laser light source 101 generates a laser beam. The laser light generated by the laser light source 101 is output to the light distribution means 102.

[0016] The optical distribution means 102 branches the laser light output by the laser light source 101 into one local light and transmission lights for each path. That is, the optical distribution means 102 branches the laser light into (n+1) beams. The local light obtained by the optical distribution means 102 is output to the optical frequency shift means 103. Furthermore, the transmission lights for each path obtained by the optical distribution means 102 are each output to the corresponding optical phase shifter 105. In FIG. 1, reference numeral 11 denotes transmission lights.

[0017] The optical frequency shifter 103 shifts the frequency of the local light obtained by the optical distributor 102. The local light after frequency shift by the optical frequency shifter 103 is output to a collimator lens 104. In FIG. 1, reference numeral 12 denotes the local light.

[0018] As the optical frequency shifting means 103, for example, an acousto-optical modulator (AOM) or a modulator using LiNbO3 is used.

[0019] The collimator lens 104 converts the local light whose frequency has been shifted by the optical frequency shifter 103 into a local beam, which is a parallel beam. The local beam obtained by the collimator lens 104 is output to the optical beam splitter 109. In FIG. 1, reference numeral 13 denotes the local beam.

[0020] An optical phase shifter 105 is provided for each path. The optical phase shifter 105 changes the phase (transmission phase) of the corresponding transmission light obtained by the optical distribution unit 102 in response to a control signal from the corresponding optical phase synchronization control unit 115. The transmission light after the phase change by the optical phase shifter 105 is output to the corresponding optical modulator 106.

[0021] In the example of FIG. 1 , the optical phase shifter 105-1 changes the phase (transmission phase) of the corresponding transmission light obtained by the optical distribution unit 102 in response to a control signal from the optical phase synchronization control unit 115-1. The transmission light after the phase change by the optical phase shifter 105-1 is output to the optical modulator 106-1. Furthermore, the optical phase shifter 105-2 changes the phase (transmission phase) of the corresponding transmission light obtained by the optical distribution unit 102 in response to a control signal from the optical phase synchronization control unit 115-2. The transmission light after the phase change by the optical phase shifter 105-2 is output to the optical modulator 106-2. Furthermore, the optical phase shifter 105-n changes the phase (transmission phase) of the corresponding transmission light obtained by the optical distribution unit 102 in response to a control signal from the optical phase synchronization control unit 115-n. The transmission light after the phase change by the optical phase shifter 105-n is output to the optical modulator 106-n.

[0022] An optical modulator 106 is provided for each path. The optical modulator 106 modulates the transmission light whose phase has been changed by the corresponding optical phase shifter 105 in response to a modulated electrical signal from the corresponding RF variable delay means 114. The transmission light modulated by this optical modulator 106 is output to the corresponding optical amplifier 107.

[0023] For example, a phase modulator or an intensity modulator is used as the optical modulator 106. Note that as the optical modulator 106, a phase modulator is preferable, in which the average intensity of the output light does not fluctuate depending on the input RF signal.

[0024] In the example of FIG. 1, the optical modulator 106-1 modulates the transmission light whose phase has been changed by the optical phase shifter 105-1 in response to the modulated electrical signal from the RF variable delay means 114-1. The transmission light modulated by the optical modulator 106-1 is output to the optical amplifier 107-1. The optical modulator 106-2 modulates the transmission light whose phase has been changed by the optical phase shifter 105-2 in response to the modulated electrical signal from the RF variable delay means 114-2. The transmission light modulated by the optical modulator 106-2 is output to the optical amplifier 107-2. The optical modulator 106-n modulates the transmission light whose phase has been changed by the optical phase shifter 105-n in response to the modulated electrical signal from the RF variable delay means 114-n. The transmission light modulated by the optical modulator 106-n is output to the optical amplifier 107-n.

[0025] An optical amplifier 107 is provided for each path. The optical amplifier 107 amplifies the intensity of the transmission light modulated by the corresponding optical modulator 106. The transmission light amplified by the optical amplifier 107 is output to the corresponding optical collimator array 108.

[0026] In the example of FIG. 1, the optical amplifier 107-1 amplifies the intensity of the transmission light modulated by the optical modulator 106-1. The transmission light amplified by this optical amplifier 107-1 is output to the optical collimator array 108-1. Furthermore, the optical amplifier 107-2 amplifies the intensity of the transmission light modulated by the optical modulator 106-2. The transmission light amplified by this optical amplifier 107-2 is output to the optical collimator array 108-2. Furthermore, the optical amplifier 107-n amplifies the intensity of the transmission light modulated by the optical modulator 106-n. The transmission light amplified by this optical amplifier 107-n is output to the optical collimator array 108-n.

[0027] An optical collimator array 108 is provided for each path. The optical collimator array 108 converts the transmission light amplified by the corresponding optical amplifier 107 into a transmission beam, which is a parallel beam. The transmission beam obtained by the optical collimator array 108 is output to an optical beam branching means 109. In FIG. 1, reference numeral 14 denotes the transmission beam input to the optical beam branching means 109.

[0028] In the example of FIG. 1 , the optical collimator array 108-1 converts the transmission light amplified by the optical amplifier 107-1 into a transmission beam that is a parallel beam. The transmission beam obtained by this optical collimator array 108-1 is output to the optical beam branching means 109. Furthermore, the optical collimator array 108-2 converts the transmission light amplified by the optical amplifier 107-2 into a transmission beam that is a parallel beam. The transmission beam obtained by this optical collimator array 108-2 is output to the optical beam branching means 109. Furthermore, the optical collimator array 108-n converts the transmission light amplified by the optical amplifier 107-n into a transmission beam that is a parallel beam. The transmission beam obtained by this optical collimator array 108-n is output to the optical beam branching means 109.

[0029] The optical beam branching means 109 branches a portion of the transmission beams obtained by each optical collimator array 108 and combines the portion of the transmission beam with the local beam obtained by the collimator lens 104 to obtain a combined phase monitor light. The remaining transmission beams that have passed through the optical beam branching means 109 are combined together at a distance to form a combined beam, which is output to the outside. The combined phase monitor light for each path obtained by the optical beam branching means 109 is output to the corresponding beam focusing means 110. In FIG. 1, reference numeral 15 denotes a combined beam, and reference numeral 16 denotes a combined phase monitor light.

[0030] A beam focusing means 110 is provided for each path. The beam focusing means 110 focuses the corresponding combined phase monitor light obtained by the light beam branching means 109. The combined phase monitor light after being focused by the beam focusing means 110 is output to the corresponding photoelectric conversion means 111.

[0031] In the example of FIG. 1, beam focusing means 110-1 focuses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after focusing by the beam focusing means 110-1 is output to the opto-electrical conversion means 111-1. Furthermore, beam focusing means 110-2 focuses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after focusing by the beam focusing means 110-2 is output to the opto-electrical conversion means 111-2. Furthermore, beam focusing means 110-n focuses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after focusing by the beam focusing means 110-n is output to the opto-electrical conversion means 111-n.

[0032] An opto-electrical conversion unit 111 is provided for each path. The opto-electrical conversion unit 111 performs opto-electrical conversion on the combined phase monitor light after being focused by the corresponding beam focusing unit 110. That is, the opto-electrical conversion unit 111 obtains an electrical signal by opto-electrically converting the local beam and the corresponding transmission beam that have been converted to the same optical path by the optical beam branching unit 109. This electrical signal is an electrical signal (heterodyne beat signal) equal to the frequency difference between the transmission beam and the local beam. The electrical signal obtained by the opto-electrical conversion unit 111 is output to the corresponding delay calculation device 113 and the corresponding optical phase synchronization control unit 115.

[0033] In the example of FIG. 1 , the photoelectric conversion unit 111-1 photoelectrically converts the combined phase monitor light after focusing by the beam focusing unit 110-1 to obtain an electrical signal. The electrical signal obtained by this photoelectric conversion unit 111-1 is output to the delay calculation unit 113-1 and the optical phase synchronization control unit 115-1. Furthermore, the photoelectric conversion unit 111-2 photoelectrically converts the combined phase monitor light after focusing by the beam focusing unit 110-2 to obtain an electrical signal. The electrical signal obtained by this photoelectric conversion unit 111-2 is output to the delay calculation unit 113-2 and the optical phase synchronization control unit 115-2. Furthermore, the photoelectric conversion unit 111-n photoelectrically converts the combined phase monitor light after focusing by the beam focusing unit 110-n to obtain an electrical signal. The electrical signal obtained by this photoelectric conversion unit 111-n is output to the delay calculation unit 113-n and the optical phase synchronization control unit 115-n.

[0034] The signal generating means 112 generates a modulated electrical signal, which is a broadband signal. This broadband signal is a signal that can widen the linewidth of the signal output from the optical modulator 106 relative to the signal input. The modulated electrical signal generated by the signal generating means 112 is output to each delay calculation device 113 and each RF variable delay means 114.

[0035] A delay calculation device 113 is provided for each path. The delay calculation device 113 calculates the delay time difference between the electrical signal obtained by the corresponding photoelectric conversion means 111 and the modulated electrical signal generated by the signal generation means 112. The electrical signal indicating the delay time difference calculated by the delay calculation device 113 is output to the corresponding RF variable delay means 114.

[0036] The delay time difference can be calculated by the delay calculation device 113 using, for example, the beat signals of the two signals, or by calculating the correlation while shifting the timing of the two signals and finding the difference that maximizes the correlation.

[0037] In the example of FIG. 1 , the delay calculation device 113-1 calculates the delay time difference between the electrical signal obtained by the photoelectric conversion means 111-1 and the modulated electrical signal generated by the signal generation means 112. The electrical signal indicating the delay time difference calculated by this delay calculation device 113-1 is output to the RF variable delay means 114-1. Furthermore, the delay calculation device 113-2 calculates the delay time difference between the electrical signal obtained by the photoelectric conversion means 111-2 and the modulated electrical signal generated by the signal generation means 112. The electrical signal indicating the delay time difference calculated by this delay calculation device 113-2 is output to the RF variable delay means 114-2. Furthermore, the delay calculation device 113-n calculates the delay time difference between the electrical signal obtained by the photoelectric conversion means 111-n and the modulated electrical signal generated by the signal generation means 112. The electrical signal indicating the delay time difference calculated by this delay calculation device 113-n is output to the RF variable delay means 114-n.

[0038] An RF variable delay unit 114 is provided for each path. The RF variable delay unit 114 controls the delay time based on the delay time difference calculated by the corresponding delay calculation device 113, and then outputs the modulated electrical signal generated by the signal generation unit 112 to the corresponding optical modulator 106.

[0039] This RF variable delay means 114 can be realized, for example, by a means for mechanically changing the length of a transmission path, or by a means for switching between a plurality of transmission paths of different lengths using a switch, etc. An example of a means for mechanically changing the length of a transmission path is a line stretcher.

[0040] 1, the RF variable delay means 114-1 controls the delay time based on the delay time difference calculated by the delay calculation device 113-1 and outputs the modulated electrical signal generated by the signal generating means 112 to the optical modulator 106-1. Also, the RF variable delay means 114-2 controls the delay time based on the delay time difference calculated by the delay calculation device 113-2 and outputs the modulated electrical signal generated by the signal generating means 112 to the optical modulator 106-2. Also, the RF variable delay means 114-n controls the delay time based on the delay time difference calculated by the delay calculation device 113-n and outputs the modulated electrical signal generated by the signal generating means 112 to the optical modulator 106-n.

[0041] The signal generating means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 constitute a "modulated electrical signal output means that outputs a modulated electrical signal with a controlled delay time to each optical modulator 106 based on the electrical signal obtained by each photoelectric conversion means 111."

[0042] An optical phase synchronization control unit 115 is provided for each path. The optical phase synchronization control unit 115 detects the phase of the electrical signal obtained by the corresponding photoelectric conversion unit 111 and outputs a control signal based on the detected phase to the corresponding optical phase shifter 105. This control signal is a signal for controlling the phase, and is, for example, an electrical signal such as a voltage. At this time, each optical phase synchronization control unit 115 generates a control signal so that the phase difference between the transmission beams is constant. For example, the optical phase synchronization control unit 115 may generate a control signal by comparing the phase difference between a reference signal source (not shown) and the electrical signal obtained by the corresponding photoelectric conversion unit 111, or may generate a control signal by comparing the phase difference between electrical signals output from adjacent photoelectric conversion units 111.

[0043] 1, the optical phase synchronization control unit 115-1 detects the phase of the electrical signal obtained by the opto-electrical conversion unit 111-1 and outputs a control signal based on that phase to the corresponding optical phase shifter 105-1. The optical phase synchronization control unit 115-2 detects the phase of the electrical signal obtained by the opto-electrical conversion unit 111-2 and outputs a control signal based on that phase to the corresponding optical phase shifter 105-2. The optical phase synchronization control unit 115-n detects the phase of the electrical signal obtained by the opto-electrical conversion unit 111-n and outputs a control signal based on that phase to the corresponding optical phase shifter 105-n.

[0044] Next, an example of the operation of the optical beam transmitter 1 according to the first embodiment configured as shown in Fig. 1 will be described. In this optical beam transmitter 1, first, a laser beam output from a laser source 101 is divided into (n+1) laser beams by an optical dividing means 102.

[0045] One of the distributed laser beams is frequency-shifted as local light by the optical frequency shifter 103. The local light output from the optical frequency shifter 103 is then collimated by the collimator lens 104 and emitted into space as a local beam.

[0046] On the other hand, the n laser beams among the distributed laser beams are controlled as transmission beams by the respective optical phase shifters 105 in terms of transmission phase in response to control signals from the respective optical phase synchronization control means 115. Then, the transmission beams output from the respective optical phase shifters 105 are modulated by the respective optical modulators 106 in response to the modulation electrical signals from the respective RF variable delay means 114 and are output.

[0047] The intensity of the transmitted light output from each optical modulator 106 is amplified by each optical amplifier 107, and then the light is converted into a parallel beam by each optical collimator array 108 and emitted into space as a transmitted beam. The transmitted beams emitted into space are then combined together at a distance to form a combined beam.

[0048] Furthermore, some of the transmission beams emitted into space, namely, the transmission beams and the local beam, are combined by the optical beam branching means 109 and focused as combined phase monitor light on the photoelectric conversion means 111 via the beam focusing means 110. Then, the combined phase monitor light is photoelectrically converted by the photoelectric conversion means 111, and an electrical signal is output, which is a heterodyne beat signal equal to the frequency difference between the transmission beams and the local beam.

[0049] Each delay calculation device 113 then compares the modulated electrical signal output from the signal generating means 112 with the corresponding electrical signal output from each photoelectric conversion means 111 to determine the delay time difference between them. Each modulated electrical signal output from the signal generating means 112 is then delayed by each RF variable delay means 114 in accordance with the delay time difference obtained by each delay calculation device 113, and becomes a modulated signal for each optical modulator 106.

[0050] In this way, the optical beam transmitter 1 according to the first embodiment performs optical modulation and delay control of the modulated electrical signal on all transmitted light, so that the transmitted beams constituting the composite beam have the same modulated waveform at the same timing.

[0051] Furthermore, in the optical beam transmitter 1 according to the first embodiment, each optical phase synchronization control means 115 receives as input the electrical signal output from each optoelectric conversion means 111, calculates a control signal for each optical phase shifter 105 from the phase information thereof, and controls the phase of the transmitted light passing through each optical phase shifter 105. In this case, the optical phase synchronization control means 115 operates so that the phase difference between the transmitted beams is constant. Then, in the optical beam transmitter 1 according to the first embodiment, the phase of the laser light is synchronized between the paths by these phase comparisons and controls.

[0052] Fig. 2 is a diagram schematically showing an example of a frequency allocation (spectral allocation) of an optical signal or an electrical signal at each point in Fig. 1. Fig. 2A schematically shows an example of a frequency allocation at part (A) in Fig. 1, Fig. 2B schematically shows an example of a frequency allocation at part (B) in Fig. 1, Fig. 2C schematically shows an example of a frequency allocation at part (C) in Fig. 1, Fig. 2D schematically shows an example of a frequency allocation at part (D) in Fig. 1, and Fig. 2E schematically shows an example of a frequency allocation at part (E) in Fig. 1.

[0053] 2A shows the frequency of the laser light output from the laser light source 101. The frequency of this laser light is fo.

[0054] 2B shows the frequency of the local light output from the optical frequency shifter 103. The frequency of this local light is fo+fref, which is shifted by fref from the frequency of the laser light output from the laser light source 101.

[0055] 2C also shows the frequency of the transmission beam output from the optical collimator array 108. The frequency of this transmission beam is modulated to a wide band (bandwidth 2 fs in FIG. 2C) by a modulated electrical signal from the RF variable delay means 114. Furthermore, a signal with a frequency fo+fp is also superimposed on the transmission beam near the frequency (fo+fref) of the local light for comparison of optical synchronization. These transmission beams are each emitted into space and coherently combined at a distance to form a combined beam. Note that, since this transmission beam is spread over a wide band relative to the frequency (fo) of the laser light shown in FIG. 2A, the occurrence of SBS is suppressed.

[0056] 2D shows the frequency of the combined phase monitor light output from the optical beam branching means 109. The frequency of this combined phase monitor light is a combination of the frequency of the local light shown in FIG. 2B and the frequency of the transmission beam shown in FIG. 2C.

[0057] FIG. 2E also shows the frequency of the electrical signal output from the photoelectric conversion means 111. The frequency of this electrical signal is the difference frequency (beat) component between the signals shown in FIG. 2D. The delay time between each beam is calculated by using a broadband signal centered on fref in FIG. 2E and performing a correlation calculation with the output from the signal generating means 112. While the center frequency of the broadband signal is fref in FIG. 2E, it goes without saying that this can be converted to any frequency (for example, the center frequency can be set to DC) using a microwave mixer or the like. The optical phase difference between the paths can be calculated using the frequency (fref - fp), which makes it possible to synchronize the optical phase between the paths.

[0058] With the above configuration, in the optical beam transmission device 1 of embodiment 1, the spectral width of the transmission beam is widened and the phases between multiple transmission beams are synchronized, making it possible to perform coherent synthesis using high-brightness beams.

[0059] As described above, according to the first embodiment, optical beam transmitter 1 comprises optical distribution means 102 for branching laser light into one local light and transmission lights for each path, optical frequency shifting means 103 for shifting the frequency of the local light obtained by optical distribution means 102, collimating lens 104 for converting the local light after frequency shifting by optical frequency shifting means 103 into a local beam that is a parallel beam, optical phase shifter 105 provided for each path for changing the phase of the corresponding transmission light obtained by optical distribution means 102 in response to a control signal, optical modulator 106 provided for each path for modulating the transmission light after phase change by corresponding optical phase shifter 105 in response to a modulating electrical signal, optical amplifier 107 provided for each path for amplifying the intensity of the transmission light after modulating by corresponding optical modulator 106, and optical amplifier 107 provided for each path for converting the transmission light after amplified by corresponding optical amplifier 107 into a parallel beam. The optical beam transmitter 1 according to the first embodiment includes an optical collimator array 108 that converts a certain transmission beam into a certain transmission beam, optical beam branching means 109 that branches a portion of the transmission beams obtained by the optical collimator array 108 for each path and combines the portion of the transmission beam with a local beam obtained by the collimator lens 104 to obtain a combined phase monitor light, optoelectric conversion means 111 provided for each path that performs optoelectric conversion on the corresponding combined phase monitor light obtained by the optical beam branching means 109 to obtain an electrical signal, modulated electrical signal output means that outputs a modulated electrical signal with a controlled delay time to the optical modulator 106 for each path based on the electrical signal obtained by the optoelectric conversion means 111 for each path, and optical phase synchronization control means 115 provided for each path that detects the phase of the electrical signal obtained by the corresponding optoelectric conversion means 111 and outputs a control signal based on the phase to the corresponding optical phase shifter 105. This enables the optical beam transmitter 1 according to the first embodiment to have relaxed manufacturing requirements compared to conventional optical beam transmitters. That is, in the optical beam transmitter 1 according to the first embodiment, the linewidth of the laser light is expanded after it is distributed to each element. As a result, in the optical beam transmitter 1 according to the first embodiment, it is no longer necessary to make the lengths of the fiber paths the same, and manufacturing requirements can be alleviated compared to the prior art.

[0060] Furthermore, in the optical beam transmitting device 1 according to embodiment 1, the optical system can be simplified by eliminating the optical system for synthesizing multiple transmitted beams and local beams, and the sub-array configuration makes it easy to expand the array size.

[0061] Embodiment 2. Figure 3 is a diagram showing an example configuration of an optical beam transmitter 1 according to embodiment 2. In optical beam transmitter 1 according to embodiment 2 shown in Figure 3, compared to optical beam transmitter 1 according to embodiment 1 shown in Figure 1, optical frequency shifting means 103 is eliminated, the plurality of optical phase shifters 105 are changed to a plurality of optical frequency conversion means 116, and the plurality of optical phase synchronization control means 115 are changed to a plurality of optical frequency synchronization control means 117. The other configuration example of optical beam transmitter 1 according to embodiment 2 shown in Figure 3 is the same as that of optical beam transmitter 1 according to embodiment 1 shown in Figure 1, so the same reference numerals are used and only the different parts will be described.

[0062] Also, although no reference numerals are shown in Figure 3, the optical beam transmitting device 1 is provided with optical frequency conversion means 116 as a plurality of optical frequency conversion means 116, and with optical frequency synchronization control means 117 as a plurality of optical frequency synchronization control means 117, namely optical frequency conversion means 116-1 to 116-n.

[0063] The local light obtained by the optical distribution unit 102 in the second embodiment is output to the collimator lens 104. Furthermore, the transmission light for each path obtained by the optical distribution unit 102 in the second embodiment is output to the corresponding optical frequency conversion unit 116.

[0064] Furthermore, the collimator lens 104 in the second embodiment converts the local light obtained by the light distribution means 102 into a local beam that is a parallel beam.

[0065] An optical frequency conversion unit 116 is provided for each path. The optical frequency conversion unit 116 shifts the frequency of the corresponding transmission light obtained by the optical distribution unit 102 in response to a control signal from the corresponding optical frequency synchronization control unit 117. The transmission light after frequency shift by the optical frequency conversion unit 116 is output to the corresponding optical modulator 106.

[0066] In the example of FIG. 3, the optical frequency conversion means 116-1 shifts the frequency of the corresponding transmission light obtained by the optical distribution means 102 in response to a control signal from the optical frequency synchronization control means 117-1. The transmission light after the frequency shift by the optical frequency conversion means 116-1 is output to the optical modulator 106-1. Furthermore, the optical frequency conversion means 116-2 shifts the frequency of the corresponding transmission light obtained by the optical distribution means 102 in response to a control signal from the optical frequency synchronization control means 117-2. The transmission light after the frequency shift by the optical frequency conversion means 116-2 is output to the optical modulator 106-2. Furthermore, the optical frequency conversion means 116-n shifts the frequency of the corresponding transmission light obtained by the optical distribution means 102 in response to a control signal from the optical frequency synchronization control means 117-n. The transmission light after the frequency shift by the optical frequency conversion means 116-n is output to the optical modulator 106-n.

[0067] Furthermore, the optical modulator 106 in the second embodiment modulates the transmission light after the frequency has been shifted by the corresponding optical frequency conversion means 116 in response to the modulating electrical signal from the corresponding RF variable delay means 114 .

[0068] Moreover, the electrical signal obtained by the photoelectric conversion means 111 in the second embodiment is output to the corresponding delay calculation device 113 and the corresponding optical frequency synchronization control means 117 .

[0069] An optical frequency synchronization control unit 117 is provided for each path. The optical frequency synchronization control unit 117 detects frequency fluctuations in the electrical signal obtained by the corresponding photoelectric conversion unit 111 and outputs a control signal based on the frequency fluctuations to the corresponding optical frequency conversion unit 116. This control signal is a signal for controlling frequency, such as a high-frequency signal. At this time, each optical frequency synchronization control unit 117 generates a control signal so that the frequency fluctuation difference between the transmission beams is constant. For example, the optical frequency synchronization control unit 117 may generate a control signal by comparing the frequency fluctuation difference between a reference signal source (not shown) and the electrical signal obtained by the corresponding photoelectric conversion unit 111, or may generate a control signal by comparing the frequency fluctuation difference between electrical signals output from adjacent photoelectric conversion units 111.

[0070] 3, the optical frequency synchronization control unit 117-1 detects frequency fluctuations in the electrical signal obtained by the photoelectric conversion unit 111-1 and outputs a control signal based on the frequency fluctuations to the optical frequency conversion unit 116-1. The optical frequency synchronization control unit 117-2 detects frequency fluctuations in the electrical signal obtained by the photoelectric conversion unit 111-2 and outputs a control signal based on the frequency fluctuations to the optical frequency conversion unit 116-2. The optical frequency synchronization control unit 117-n detects frequency fluctuations in the electrical signal obtained by the photoelectric conversion unit 111-n and outputs a control signal based on the frequency fluctuations to the optical frequency conversion unit 116-n.

[0071] As shown in Fig. 4, each optical frequency synchronization control means 117 includes a PFD (Phase Frequency Detector) 1171, a LF (Loop Filter) 1172, and a VCO (Voltage Controlled Oscillator) 1173. A reference oscillator 1174 is also provided as a component commonly used by all of the optical frequency synchronization control means 117. The configuration shown in Fig. 4 is a representative example.

[0072] In FIG. 4, PFDs 1171-1 to 1171-n are provided as the PFDs 1171, LFs 1172-1 to 1172-n are provided as the LFs 1172, and VCOs 1173-1 to 1173-n are provided as the VCOs 1173.

[0073] The PFD 1171 obtains an error signal by comparing the frequency of the electrical signal obtained by the corresponding photoelectric conversion means 111 with the frequency of the signal from the external reference oscillator 1174. The error signal obtained by the PFD 1171 is output to the corresponding LF 1172.

[0074] In the example of FIG. 4, PFD 1171-1 obtains an error signal by comparing the frequency of the electrical signal obtained by photoelectric conversion means 111-1 with the frequency of the signal from external reference oscillator 1174. The error signal obtained by PFD 1171-1 is output to LF 1172-1. PFD 1171-2 obtains an error signal by comparing the frequency of the electrical signal obtained by photoelectric conversion means 111-2 with the frequency of the signal from external reference oscillator 1174. The error signal obtained by PFD 1171-2 is output to LF 1172-2. PFD 1171-n obtains an error signal by comparing the frequency of the electrical signal obtained by photoelectric conversion means 111-n with the frequency of the signal from external reference oscillator 1174. The error signal obtained by PFD 1171-n is output to LF 1172-n.

[0075] In order to stabilize the phase locked loop, the LF 1172 obtains a DC signal by smoothing the error signal obtained by the corresponding PFD 1171. The DC signal obtained by the LF 1172 is output to the corresponding VCO 1173.

[0076] In the example of FIG. 4, LF 1172-1 smooths the error signal obtained by PFD 1171-1 to obtain a DC signal. The DC signal obtained by LF 1172-1 is output to VCO 1173-1. LF 1172-2 smooths the error signal obtained by PFD 1171-2 to obtain a DC signal. The DC signal obtained by LF 1172-2 is output to VCO 1173-2. LF 1172-n smooths the error signal obtained by PFD 1171-n to obtain a DC signal. The DC signal obtained by LF 1172-n is output to VCO 1173-n.

[0077] The VCO 1173 generates a control signal based on the DC signal obtained by the corresponding LF 1172. The control signal generated by this VCO 1173 is output to the corresponding optical frequency conversion means 116.

[0078] In the example of FIG. 4, VCO 1173-1 generates a control signal based on the DC signal obtained by LF 1172-1. The control signal generated by VCO 1173-1 is output to optical frequency conversion means 116-1. Furthermore, VCO 1173-2 generates a control signal based on the DC signal obtained by LF 1172-2. The control signal generated by VCO 1173-2 is output to optical frequency conversion means 116-2. Furthermore, VCO 1173-n generates a control signal based on the DC signal obtained by LF 1172-n. The control signal generated by VCO 1173-n is output to optical frequency conversion means 116-n.

[0079] Next, an example of the operation of the optical beam transmitter 1 according to the second embodiment configured as shown in Fig. 3 will be described. In this optical beam transmitter 1, first, a laser beam output from the laser source 101 is divided into (n+1) laser beams by the optical dividing means 102.

[0080] Then, the local light, which is one of the distributed laser beams, is converted into a parallel beam by the collimator lens 104 without passing through the optical frequency shifting means 103, and is emitted into space as a local beam.

[0081] On the other hand, the n laser beams among the distributed laser beams are frequency-controlled as transmission beams by the respective optical frequency conversion means 116 in accordance with control signals from the respective optical frequency synchronization control means 117. Then, the transmission beams output from the respective optical frequency conversion means 116 are modulated by the respective optical modulators 106 in accordance with the modulating electrical signals from the respective RF variable delay means 114 and are output.

[0082] The intensity of the transmitted light output from each optical modulator 106 is amplified by each optical amplifier 107, and then the light is converted into a parallel beam by each optical collimator array 108 and emitted into space as a transmitted beam. The transmitted beams emitted into space are then combined together at a distance to form a combined beam.

[0083] Furthermore, some of the transmission beams emitted into space, namely, the transmission beams and the local beam, are combined by the optical beam branching means 109 and focused as combined phase monitor light on the photoelectric conversion means 111 via the beam focusing means 110. Then, the combined phase monitor light is photoelectrically converted by the photoelectric conversion means 111, and an electrical signal is output, which is a heterodyne beat signal equal to the frequency difference between the transmission beams and the local beam.

[0084] Each delay calculation device 113 then compares the modulated electrical signal output from the signal generating means 112 with the corresponding electrical signal output from each photoelectric conversion means 111 to determine the delay time difference between them. Each modulated electrical signal output from the signal generating means 112 is then delayed by each RF variable delay means 114 in accordance with the delay time difference obtained by each delay calculation device 113, and becomes a modulated signal for each optical modulator 106.

[0085] In this way, the optical beam transmitter 1 according to the second embodiment performs optical modulation and delay control of the modulated electrical signal on all transmitted light beams, so that the transmitted beams constituting the composite beam have the same modulated waveform at the same timing.

[0086] Furthermore, in the optical beam transmitter 1 according to the second embodiment, each optical frequency synchronization control means 117 receives an electrical signal output from each photoelectric conversion means 111, calculates a control signal for each optical frequency conversion means 116 based on the frequency fluctuation information, and controls the frequency of the transmitted light passing through each optical frequency conversion means 116. In this case, the optical frequency synchronization control means 117 operates to maintain a constant frequency fluctuation difference between the transmitted beams. In the optical beam transmitter 1 according to the second embodiment, the phase of the laser light between the paths is synchronized by comparing and controlling these frequency fluctuations. In other words, there is generally a relationship between the phase and frequency of a wave in which the frequency is determined by differentiating the phase. Therefore, it is possible to control the phase of the transmitted light by controlling the instantaneous frequency.

[0087] The transmission signal is looped in either an optical or electrical state through the optical frequency conversion means 116, the optical modulator 106, the optical amplifier 107, the optical collimator array 108, the optical beam branching means 109, the beam focusing means 110, the photoelectric conversion means 111, the optical frequency synchronization control means 117, and the optical frequency conversion means 116, and the transmission signal transmitted within the loop is stabilized by the optical frequency synchronization control means 117.

[0088] Fig. 5 is a diagram schematically showing an example of the frequency allocation (spectral allocation) of an optical signal or an electrical signal at each point in Fig. 3. Fig. 5A schematically shows an example of the frequency allocation at portions (A) and (B) in Fig. 3, Fig. 5B schematically shows an example of the frequency allocation at portion (C) in Fig. 3, Fig. 5C schematically shows an example of the frequency allocation at portion (D) in Fig. 3, Fig. 5D schematically shows an example of the frequency allocation at portion (E) in Fig. 3, and Fig. 5E schematically shows an example of the frequency allocation at portion (F) in Fig. 3.

[0089] 5A shows the frequency of the laser light output from the laser light source 101 and the frequency of the local light input to the collimator lens 104. The frequency of this laser light is f. The frequency of the local light is also f, which is the same as the frequency of the laser light output from the laser light source 101.

[0090] 5B shows the frequency of the transmitted light output from the optical frequency conversion means 116. The frequency of this transmitted light is fo+fref, which is shifted by fref from the frequency of the laser light output from the laser light source 101.

[0091] 5C shows the frequency of the transmission beam output from the optical collimator array 108. The frequency of this transmission beam is modulated to a wide band (bandwidth 2 fs in FIG. 5C) by the modulated electrical signal from the RF variable delay means 114. In addition to the wide band signal, this transmission beam is also modulated with fref, so that a signal fo+ (frep-fp) is also superimposed. These transmission beams are each emitted into space and coherently combined at a distance to form a combined beam. Note that, since this transmission beam is spread over a wide band relative to the frequency (fo) of the laser light shown in FIG. 5A, the occurrence of SBS is suppressed.

[0092] 5D shows the frequency of the combined phase monitor light output from the optical beam branching means 109. The frequency of this combined phase monitor light is a combination of the frequency of the local light shown in FIG. 5A and the frequency of the transmission beam shown in FIG. 5C.

[0093] FIG. 5E shows the frequency of the electrical signal output from the photoelectric conversion means 111. The frequency of this electrical signal is the difference frequency (beat) component between the signals shown in FIG. 5D. The delay time between each beam is calculated by using a broadband signal centered on fref in FIG. 5E and performing a correlation calculation with the output from the signal generating means 112. While the center frequency of the broadband signal is fref in FIG. 5E, it goes without saying that this can be converted to any frequency (for example, the center frequency can be set to DC) using a microwave mixer or the like. The optical phase difference between the paths can be calculated using the frequency (fref - fp), which makes it possible to synchronize the optical phase between the paths.

[0094] With the above configuration, in the optical beam transmitter 1 according to embodiment 2, the spectral width of the transmitted beam is widened and the phases of the multiple transmitted beams are synchronized, making it possible to perform coherent combining using high-brightness beams. Furthermore, in the optical beam transmitter 1 according to embodiment 2, phase control between paths is performed by instantaneous frequency control using the optical frequency conversion means 116, making it possible to expand the range of application of phase control compared to the optical beam transmitter 1 according to embodiment 1.

[0095] As described above, according to the second embodiment, optical beam transmitter 1 comprises optical distribution means 102 that branches laser light into one local light and transmission lights for each path, collimator lens 104 that converts the local light obtained by optical distribution means 102 into a local beam that is a parallel beam, optical frequency conversion means 116 that is provided for each path and shifts the frequency of the corresponding transmission light obtained by optical distribution means 102 in response to a control signal, optical modulator 106 that is provided for each path and modulates the transmission light after the frequency shift by corresponding optical frequency conversion means 116 in response to a modulating electrical signal, optical amplifier 107 that is provided for each path and amplifies the intensity of the transmission light after modulation by corresponding optical modulator 106, and optical collimator array 108 that is provided for each path and converts the transmission light after amplified by corresponding optical amplifier 107 into a transmission beam that is a parallel beam. The optical beam transmission device 1 according to the second embodiment includes optical beam branching means 109 that branches a portion of the transmission beams obtained by the optical collimator arrays 108 for each path and combines the portion of the transmission beam with a local beam obtained by the collimator lens 104 to obtain a combined phase monitor light, optoelectric conversion means 111 that is provided for each path and performs optoelectric conversion on the corresponding combined phase monitor light obtained by the optical beam branching means 109 to obtain an electric signal, modulated electric signal output means that outputs a modulated electric signal with controlled delay time to the optical modulator 106 for each path based on the electric signal obtained by the optoelectric conversion means 111 for each path, and optical frequency synchronization control means 117 that is provided for each path and detects frequency fluctuations in the electric signal obtained by the corresponding optoelectric conversion means 111 and outputs a control signal based on the frequency fluctuation to the corresponding optical frequency conversion means 116. As a result, the optical beam transmission device 1 according to the second embodiment can achieve the effects of the optical beam transmission device 1 according to the first embodiment and can also expand the range of application of phase control.

[0096] Embodiment 3. In embodiment 3, another configuration example of the modulated electrical signal output means will be described. Figure 6 is a diagram showing a configuration example of an optical beam transmitter 1 according to embodiment 3. In the optical beam transmitter 1 according to embodiment 3 shown in Figure 6, the signal generating means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 of the optical beam transmitter 1 according to embodiment 2 shown in Figure 3 are replaced with a plurality of signal processing devices 118 and a plurality of signal generating means 119. The other configuration example of the optical beam transmitter 1 according to embodiment 3 shown in Figure 6 is the same as that of the optical beam transmitter 1 according to embodiment 2 shown in Figure 3, and the same reference numerals are used, and only the different parts will be described.

[0097] Although not shown in FIG. 6, the optical beam transmitting device 1 is provided with signal processing devices 118-1 to 118-n as the plurality of signal processing devices 118, and with signal generating means 119-1 to 119-n as the plurality of signal generating means 119.

[0098] The electrical signal obtained by the photoelectric conversion means 111 in the third embodiment is output to the corresponding signal processing device 118 and the corresponding optical frequency synchronization control means 117 .

[0099] A signal processing device 118 is provided for each path. The signal processing device 118 calculates a delay time of the electrical signal based on the electrical signal obtained by the corresponding photoelectric conversion means 111, and generates a timing signal based on the delay time. The timing signal generated by this signal processing device 118 is output to the corresponding signal generation means 119.

[0100] In the example of Figure 6, the signal processing device 118-1 calculates the delay time of the electrical signal based on the electrical signal obtained by the photoelectric conversion means 111-1, and generates a timing signal based on the delay time. The timing signal generated by this signal processing device 118-1 is output to the signal generation means 119-1. Furthermore, the signal processing device 118-2 calculates the delay time of the electrical signal based on the electrical signal obtained by the photoelectric conversion means 111-2, and generates a timing signal based on the delay time. The timing signal generated by this signal processing device 118-2 is output to the signal generation means 119-2. Furthermore, the signal processing device 118-n calculates the delay time of the electrical signal based on the electrical signal obtained by the photoelectric conversion means 111-n, and generates a timing signal based on the delay time. The timing signal generated by this signal processing device 118-n is output to the signal generation means 119-n.

[0101] A signal generating means 119 is provided for each path. The signal generating means 119 outputs a modulated electrical signal to the corresponding optical modulator 106 in accordance with a timing signal generated by the corresponding signal processing device 118. The modulated electrical signals used by each signal generating means 119 are broadband signals with a common waveform. This broadband signal is a signal that can widen the linewidth of the signal output from the optical modulator 106 relative to the signal input thereto.

[0102] The signal generating means 119 can generate a signal at any timing, for example, by outputting digital waveform data stored in an internal memory via D / A (digital-to-analog conversion) at the timing instructed by the signal processing device 118.

[0103] 6, the signal generating means 119-1 outputs a modulated electrical signal to the optical modulator 106-1 in response to a timing signal generated by the signal processing device 118-1. The signal generating means 119-2 outputs a modulated electrical signal to the optical modulator 106-2 in response to a timing signal generated by the signal processing device 118-2. The signal generating means 119-n outputs a modulated electrical signal to the optical modulator 106-n in response to the timing signal generated by the signal processing device 118-n.

[0104] Furthermore, the optical modulator 106 in the third embodiment modulates the transmission light after the frequency has been shifted by the corresponding optical frequency conversion means 116 in accordance with the modulated electrical signal output by the corresponding signal generation means 119 .

[0105] The plurality of signal processing devices 118 and the plurality of signal generating means 119 constitute "modulated electrical signal output means that outputs modulated electrical signals with controlled delay times to each optical modulator 106 based on the electrical signals obtained by each photoelectric conversion means 111."

[0106] Next, an example of the operation of the light beam transmitter 1 according to the third embodiment configured as shown in Fig. 6 will be described. In this light beam transmitter 1, first, a laser beam output from the laser source 101 is distributed by the optical distribution means 102 into (n+1) laser beams.

[0107] Then, a local beam, which is one of the distributed laser beams, is collimated by a collimator lens 104 and emitted into space as a local beam.

[0108] On the other hand, the n laser beams among the distributed laser beams are frequency-controlled as transmission beams by the respective optical frequency conversion means 116 in accordance with control signals from the respective optical frequency synchronization control means 117. Then, the transmission beams output from the respective optical frequency conversion means 116 are modulated by the respective optical modulators 106 in accordance with modulating electrical signals from the respective signal generation means 119 and are output.

[0109] The intensity of the transmitted light output from each optical modulator 106 is amplified by each optical amplifier 107, and then the light is converted into a parallel beam by each optical collimator array 108 and emitted into space as a transmitted beam. The transmitted beams emitted into space are then combined together at a distance to form a combined beam.

[0110] Furthermore, some of the transmission beams emitted into space, namely, the transmission beams and the local beam, are combined by the optical beam branching means 109 and focused as combined phase monitor light on the photoelectric conversion means 111 via the beam focusing means 110. Then, the combined phase monitor light is photoelectrically converted by the photoelectric conversion means 111, and an electrical signal is output, which is a heterodyne beat signal equal to the frequency difference between the transmission beams and the local beam.

[0111] Here, in the third embodiment, instead of the signal generating means 112, the plurality of RF variable delay means 114, and the plurality of delay calculation devices 113 of the second embodiment, a plurality of signal processing devices 118 and a plurality of signal generating means 119 are provided. Each signal processing device 118 receives an electrical signal output from each photoelectric conversion means 111 and calculates a delay time for each path. Furthermore, each signal processing device 118 generates a timing signal indicating the timing at which each signal generating means 119 outputs a signal in accordance with the calculated delay time. Each signal generating means 119 then outputs a modulated electrical signal, which is a wideband signal with the same waveform, to each optical modulator 106 in accordance with the timing signal from each signal processing device 118.

[0112] In this way, in the optical beam transmitter 1 according to the third embodiment, the timing of the waveform output can be controlled by digital signal processing. As a result, the optical beam transmitter 1 according to the third embodiment does not require the RF variable delay means 114, and restrictions on the setting range and setting resolution of the delay time can be alleviated.

[0113] In FIG. 6, a signal processing device 118 and a signal generating means 119 are provided for each path, but it goes without saying that these may be included in a single device, and that the signal processing devices 118 are synchronized with each other to match the timing between them.

[0114] 6 shows a case in which the signal generating means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 in the optical beam transmitting apparatus 1 according to embodiment 2 are replaced with a plurality of signal processing devices 118 and a plurality of signal generating means 119. However, this is not limiting, and the signal generating means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 in the optical beam transmitting apparatus 1 according to embodiment 1 may be replaced with a plurality of signal processing devices 118 and a plurality of signal generating means 119, with the same effects as those described above being obtained.

[0115] As described above, according to the third embodiment, the modulated electrical signal output means comprises signal processing devices 118, which are provided for each path and which calculate a delay time for an electrical signal based on the electrical signal obtained by the corresponding photoelectric conversion device 111 and generate a timing signal based on the delay time, and signal generating devices 119, which are provided for each path and which output modulated electrical signals having a common waveform to the corresponding optical modulators 106 in accordance with the timing signals generated by the corresponding signal processing devices 118. As a result, the optical beam transmission device 1 according to the third embodiment does not require the RF variable delay device 114 compared to the optical beam transmission devices 1 according to the first and second embodiments, and restrictions on the setting range and setting resolution of the delay time can be alleviated.

[0116] Fourth Embodiment In the fourth embodiment, another example configuration of the modulated electrical signal output means will be described. Figure 7 is a diagram showing an example configuration of an optical beam transmitter 1 according to the fourth embodiment. In the optical beam transmitter 1 according to the fourth embodiment shown in Figure 7, the plurality of delay calculation devices 113 in the optical beam transmitter 1 according to the second embodiment shown in Figure 3 are replaced with a plurality of delay comparison devices 120. The other example configuration of the optical beam transmitter 1 according to the fourth embodiment shown in Figure 7 is the same as that of the optical beam transmitter 1 according to the second embodiment shown in Figure 3, and the same reference numerals are used, and only the different parts will be described.

[0117] Although not shown in FIG. 7, the optical beam transmitter 1 is provided with a plurality of delay comparators 120, namely, delay comparators 120-2 to 120-n.

[0118] The electrical signal obtained by the photoelectric conversion means 111 in the fourth embodiment is output to the corresponding delay comparison device 120 and the corresponding optical frequency synchronization control means 117 .

[0119] Moreover, the modulated electrical signal generated by the signal generating means 112 in the fourth embodiment is output to each RF variable delay means 114 .

[0120] A delay comparison device 120 is provided for each path. The delay comparison device 120 calculates the delay time difference between the electrical signals based on the electrical signals obtained by two corresponding adjacent photoelectric conversion means 111. The electrical signal indicating the delay time difference calculated by the delay comparison device 120 is output to the corresponding RF variable delay means 114.

[0121] 7, the delay comparison device 120-2 calculates the delay time difference between the electrical signals obtained by the photoelectric conversion means 111-1 and 111-2 based on the electrical signals. The electrical signal indicating the delay time difference calculated by the delay comparison device 120-2 is output to the RF variable delay means 114-2. Furthermore, the delay comparison device 120-n calculates the delay time difference between the electrical signals obtained by the photoelectric conversion means 111-n-1 and 111-n based on the electrical signals. The electrical signal indicating the delay time difference calculated by the delay comparison device 120-n is output to the RF variable delay means 114-n.

[0122] Furthermore, the RF variable delay means 114 in the fourth embodiment controls the delay time based on the delay time difference calculated by the corresponding delay comparison device 120, and then outputs the modulated electrical signal generated by the signal generating means 112 to the corresponding optical modulator 106. Note that the RF variable delay means 114 (RF variable delay means 114-1 in FIG. 7) provided on the reference path outputs the modulated electrical signal generated by the signal generating means 112 to the corresponding optical modulator 106 without controlling the delay time.

[0123] The signal generating means 112, the plurality of delay comparison devices 120, and the plurality of RF variable delay means 114 constitute a "modulated electrical signal output means that outputs a modulated electrical signal with controlled delay time to each optical modulator 106 based on the electrical signal obtained by each photoelectric conversion means 111."

[0124] Next, an example of the operation of the optical beam transmitter 1 according to the fourth embodiment configured as shown in Fig. 7 will be described. In this optical beam transmitter 1, first, a laser beam output from the laser source 101 is divided into (n+1) laser beams by the optical dividing means 102.

[0125] Then, a local beam, which is one of the distributed laser beams, is collimated by a collimator lens 104 and emitted into space as a local beam.

[0126] On the other hand, the n laser beams among the distributed laser beams are frequency-controlled as transmission beams by the respective optical frequency conversion means 116 in accordance with control signals from the respective optical frequency synchronization control means 117. Then, the transmission beams output from the respective optical frequency conversion means 116 are modulated by the respective optical modulators 106 in accordance with the modulating electrical signals from the respective RF variable delay means 114 and are output.

[0127] The intensity of the transmitted light output from each optical modulator 106 is amplified by each optical amplifier 107, and then the light is converted into a parallel beam by each optical collimator array 108 and emitted into space as a transmitted beam. The transmitted beams emitted into space are then combined together at a distance to form a combined beam.

[0128] Furthermore, some of the transmission beams emitted into space, namely, the transmission beams and the local beam, are combined by the optical beam branching means 109 and focused as combined phase monitor light on the photoelectric conversion means 111 via the beam focusing means 110. Then, the combined phase monitor light is photoelectrically converted by the photoelectric conversion means 111, and an electrical signal is output, which is a heterodyne beat signal equal to the frequency difference between the transmission beams and the local beam.

[0129] Here, in the fourth embodiment, instead of the multiple delay calculation devices 113 of the second embodiment, multiple delay comparison devices 120 are provided. Each delay comparison device 120 compares two electrical signals output from each photoelectric conversion means 111 to determine the delay time difference between the paths. For example, in FIG. 7, the delay comparison device 120-2 determines the delay time difference between the electrical signals output from the photoelectric conversion means 111-2 based on the electrical signal output from the photoelectric conversion means 111-1, and the delay comparison device 120-3 determines the delay time difference between the electrical signals output from the photoelectric conversion means 111-3 based on the electrical signal output from the photoelectric conversion means 111-2. In this way, each delay comparison device 120 determines the delay time difference in turn. The modulated electrical signals output from the signal generation means 112 are each delayed by each RF variable delay means 114 according to the delay time difference obtained by each delay comparison device 120, and become modulated signals for each optical modulator 106. For example, in FIG. 7, the RF variable delay means 114-1 outputs the modulated electrical signal directly to the optical modulator 106-1, the RF variable delay means 114-2 outputs the modulated electrical signal to the optical modulator 106-2 based on the delay time difference obtained by the delay comparison device 120-2, and the RF variable delay means 114-3 outputs the modulated electrical signal to the optical modulator 106-3 based on the delay time difference obtained by the delay comparison device 120-3.

[0130] As described above, in the optical beam transmission device 1 according to the fourth embodiment, each delay comparison device 120 compares the electrical signals of the other devices to determine the delay time difference. Here, since the paths are installed adjacent to each other, the amount of fluctuation in temperature and the like is similar. Therefore, it is expected that the delay time difference between adjacent paths will also be small. Therefore, in the optical beam transmission device 1 according to the fourth embodiment, it is possible to narrow the dynamic range of delay control.

[0131] 7 shows a case where the plurality of delay calculation devices 113 in the optical beam transmission device 1 according to embodiment 2 are replaced with a plurality of delay comparison devices 120. However, this is not limiting, and the plurality of delay calculation devices 113 in the optical beam transmission device 1 according to embodiment 1 may be replaced with a plurality of delay comparison devices 120, and the same effect as above can be obtained.

[0132] As described above, according to the fourth embodiment, the modulated electrical signal output means includes signal generating means 112 that generates a modulated electrical signal, delay comparator 120 that is provided for each path and that calculates a delay time difference between the electrical signals based on the electrical signals obtained by two corresponding adjacent photoelectric converting means 111, and RF variable delay means 114 that is provided for each path and that controls the delay time based on the delay time difference calculated by the corresponding delay comparator 120 and then outputs the modulated electrical signal generated by signal generating means 112 to the corresponding optical modulator 106. As a result, the optical beam transmitter 1 according to the fourth embodiment can have a smaller dynamic range of delay control than the optical beam transmitters 1 according to the first to third embodiments.

[0133] In the above-described first to fourth embodiments, the modulated electrical signal output from the signal generating means 112 may be, for example, a sine wave, a rectangular wave, or a triangular wave. Furthermore, in the above-described first to fourth embodiments, the modulated electrical signal output from the signal generating means 112 may be a pseudo-random signal. Even in this case, the optical beam transmitter 1 can determine the respective delay time differences by performing delay control and cross-correlation calculations between the signal source and the transmission signal. Furthermore, in the above-described first to fourth embodiments, the modulated electrical signal output from the signal generating means 112 may be a signal modulated for communication. Even in this case, the optical beam transmitter 1 can determine the respective delay time differences by performing delay control and cross-correlation calculations between the signal source and the transmission signal.

[0134] Furthermore, in the above-described first to fourth embodiments, the optical beam transmitter 1 has been shown to determine the delay time difference from the correlation between the signal source and the transmission signal. However, this is not limiting, and the optical beam transmitter 1 may, for example, superimpose a short pulse signal in a band that can be separated from any of the above frequencies, separate from the phase detection signal (frequency fp), and determine the delay time difference from the time until the relevant pulse signal is detected.

[0135] Finally, with reference to FIG. 8 , an example of the hardware configuration of the optical beam transmitter 1 according to the first to fourth embodiments will be described. Note that, while the following describes an example of the hardware configuration of the optical beam transmitter 1 according to the first embodiment, the same applies to the example of the hardware configuration of the optical beam transmitter 1 according to the second to fourth embodiments. The functions of the delay calculation device 113 and the optical phase synchronization control means 115 in the optical beam transmitter 1 are realized by a processing circuit 51. The processing circuit 51 may be dedicated hardware as shown in FIG. 8A , or may be a CPU (also referred to as a central processing unit, processing device, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) 52 that executes a program stored in a memory 53 as shown in FIG. 8B .

[0136] When the processing circuit 51 is dedicated hardware, the processing circuit 51 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The functions of each part of the delay calculation device 113 and the optical phase synchronization control means 115 may be realized by the processing circuit 51 individually, or the functions of each part may be realized collectively by the processing circuit 51.

[0137] When the processing circuit 51 is a CPU 52, the functions of the delay calculation device 113 and the optical phase synchronization control means 115 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 53. The processing circuit 51 realizes the functions of each unit by reading and executing the programs stored in the memory 53. In other words, the optical beam transmitting device 1 includes a memory for storing programs that, when executed by the processing circuit 51, result in the execution of, for example, the processing described above. It can also be said that these programs cause a computer to execute the procedures and methods of the delay calculation device 113 and the optical phase synchronization control means 115. Here, examples of the memory 53 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs (Digital Versatile Discs).

[0138] It is also possible to realize some of the functions of the delay calculation device 113 and the optical phase synchronization control means 115 with dedicated hardware and some with software or firmware. For example, the function of the delay calculation device 113 can be realized by a processing circuit 51 as dedicated hardware, and the function of the optical phase synchronization control means 115 can be realized by the processing circuit 51 reading and executing a program stored in a memory 53.

[0139] In this way, the processing circuitry 51 can realize each of the above-described functions by hardware, software, firmware, or a combination of these.

[0140] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0141] The optical beam transmission device according to the present disclosure can ease manufacturing requirements compared to conventional devices, and is suitable for use in optical beam transmission devices that phase-synchronize and combine multiple optical beams.

[0142] 1 Optical beam transmitting device, 51 Processing circuit, 52 CPU, 53 Memory, 101 Laser light source, 102 Optical distribution means, 103 Optical frequency shifting means, 104 Collimating lens, 105 Optical phase shifter, 106 Optical modulator, 107 Optical amplifier, 108 Optical collimator array, 109 Optical beam branching means, 110 Beam focusing means, 111 Photoelectric conversion means, 112 Signal generating means, 113 Delay calculation device, 114 RF variable delay means, 115 Optical phase synchronization control means, 116 Optical frequency conversion means, 117 Optical frequency synchronization control means, 118 Signal processing device, 119 Signal generating means, 120 Delay comparison device, 1171 PFD, 1172 LF, 1173 VCO, 1174 Reference oscillator.

Claims

1. Optical distribution means for branching laser light into one local light and a transmission light for each path; optical frequency shifting means for shifting the frequency of the local light obtained by the optical distribution means; collimating lenses for converting the local light after frequency shifting by the optical frequency shifting means into a local beam that is a parallel beam; optical phase shifters provided for each of the paths for changing the phase of the corresponding transmission light obtained by the optical distribution means in response to a control signal; optical modulators provided for each of the paths for modulating the transmission light after phase change by the corresponding optical phase shifter in response to a modulating electrical signal; optical amplifiers provided for each of the paths for amplifying the intensity of the transmission light after modulating by the corresponding optical modulator; optical collimator arrays provided for each of the paths for converting the transmission light after amplified by the corresponding optical amplifier into a transmission beam that is a parallel beam; optical beam branching means for branching a portion of the transmission beams obtained by the optical collimator arrays for each of the paths and combining the portion of the transmission beams with the local beams obtained by the collimating lenses to obtain a combined phase monitor light; an optical beam transmitting device comprising: an optical-electrical conversion means provided for each of the paths, which performs optical-electrical conversion on the corresponding composite phase monitor light obtained by the optical beam branching means to obtain an electrical signal; a modulated electrical signal output means for outputting a modulated electrical signal having a controlled delay time to each of the optical modulators for each of the paths based on the electrical signal obtained by the optical-electrical conversion means for each of the paths; and an optical phase synchronization control means provided for each of the paths, which detects the phase of the electrical signal obtained by the corresponding optical-electrical conversion means, and outputs a control signal based on the phase to the corresponding optical phase shifter.

2. Optical distribution means for branching laser light into one local light and a transmission light for each path; a collimating lens for converting the local light obtained by the optical distribution means into a local beam which is a parallel beam; optical frequency conversion means provided for each of the paths and shifting the frequency of the corresponding transmission light obtained by the optical distribution means in response to a control signal; an optical modulator provided for each of the paths and modulating the transmission light after frequency shifting by the corresponding optical frequency conversion means in response to a modulated electrical signal; an optical amplifier provided for each of the paths and amplifying the intensity of the transmission light after modulating by the corresponding optical modulator; an optical collimator array provided for each of the paths and converting the transmission light after amplified by the corresponding optical amplifier into a transmission beam which is a parallel beam; optical beam branching means for branching a portion of the transmission beams obtained by the optical collimator array for each of the paths and combining the portion of the transmission beam with the local beam obtained by the collimating lens to obtain a composite phase monitor light; and photoelectric conversion means provided for each of the paths and photoelectrically converting the corresponding composite phase monitor light obtained by the optical beam branching means to obtain an electrical signal. an optical beam transmitting device comprising: a modulated electrical signal output means for outputting a modulated electrical signal with a controlled delay time to the optical modulator for each of the paths based on the electrical signal obtained by the photoelectric conversion means for each of the paths; and an optical frequency synchronization control means provided for each of the paths for detecting a frequency fluctuation of the electrical signal obtained by the corresponding photoelectric conversion means, and outputting a control signal based on the frequency fluctuation to the corresponding optical frequency conversion means.

3. An optical beam transmitting device as claimed in claim 1 or 2, characterized in that the modulated electrical signal output means comprises: signal generating means for generating a modulated electrical signal; a delay calculation device provided for each of the paths for calculating the delay time difference between the electrical signal obtained by the corresponding photoelectric conversion means and the modulated electrical signal generated by the signal generating means; and RF variable delay means provided for each of the paths for controlling the delay time based on the delay time difference calculated by the corresponding delay calculation device and outputting the modulated electrical signal generated by the signal generating means to the corresponding optical modulator.

4. An optical beam transmitting device as claimed in claim 1 or claim 2, characterized in that the modulated electrical signal output means comprises: a signal processing device provided for each of the paths, which calculates a delay time of the electrical signal based on the electrical signal obtained by the corresponding photoelectric conversion means, and generates a timing signal based on the delay time; and a signal generating means provided for each of the paths, which outputs a modulated electrical signal having a common waveform to the corresponding optical modulator in response to the timing signal generated by the corresponding signal processing device.

5. An optical beam transmitting device as claimed in claim 1 or claim 2, characterized in that the modulated electrical signal output means comprises: signal generating means for generating a modulated electrical signal; a delay comparator provided for each of the paths and for calculating a delay time difference between the electrical signals based on the electrical signals obtained by two corresponding adjacent photoelectric conversion means; and RF variable delay means provided for each of the paths and for controlling the delay time based on the delay time difference calculated by the corresponding delay comparator, and outputting the modulated electrical signal generated by the signal generating means to the corresponding optical modulator.

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