Optical beam transmission device

Abstract

An optical distribution means (102) that branches laser light into one local light and transmission light for each path, an optical frequency shift means (103) that shifts the frequency of the local light, a collimating lens (104) that converts the frequency-shifted local light into a local beam, an optical phase shifter (105) that changes the phase of the corresponding transmission light according to a control signal, an optical modulator (106) that modulates the corresponding transmission light after the phase change according to a modulation electrical signal, an optical amplifier (107) that amplifies the intensity of the corresponding modulated transmission light, an optical collimator array (108) that converts the corresponding amplified transmission light into a transmission beam, an optical beam branching means (109) that branches a part of each transmission beam and synthesizes each of the branched transmission beams with the local beam to obtain a synthesized phase monitor light, a photoelectric conversion means (111) that photoelectrically converts the corresponding synthesized phase monitor light to obtain an electrical signal, a modulation electrical signal output means that outputs a modulation electrical signal with a controlled delay time to the corresponding optical modulator (106) based on each electrical signal, and an optical phase synchronization control means (115) that detects the phase of the corresponding electrical signal and outputs a control signal based on the phase to the corresponding optical phase shifter (105).

Description

Technical Field

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

Background Art

[0002] Conventionally, devices for transmitting high-power optical beams over long distances, such as in free-space optical communication or optical energy transmission, are known. In such devices, there is a limit to the transmission power per beam due to the power resistance limit in an optical fiber amplifier or an optical fiber that transmits its output light. As a means to overcome such limitations, there is a spatial phase synthesis (CBC: Coherent Beam Combining) technique. In this spatial phase synthesis technique, a plurality of optical beams are transmitted in an array, and the phases between the optical beams are aligned to synthesize the optical beams in space.

[0003] Here, in order to phase-synthesize optical beams with a wavelength on the order of μm, it is necessary to align the optical path length fluctuations between the optical beams on the order of μm. However, usually, due to environmental fluctuations such as temperature, the phases of light waves transmitted through different optical paths, such as optical fibers or optical fiber amplifiers, fluctuate. In the prior art, an optical beam (local beam) serving as a reference wavefront (phase) is spatially combined with each transmission beam, and the each transmission beam and the local beam are photoelectrically converted to convert them into a heterodyne beat signal. Then, in the prior art, the phase error of each transmission signal is detected from the phase information of the heterodyne beat signal, and the phases of the respective transmission signals are corrected based on the phase information to transmit an array of phase-synchronized optical beams. In this way, in the prior art, phase synthesis was performed in space.

[0004] Furthermore, in order to transmit a high-power optical beam, it is necessary to increase the number of beams and also increase the intensity of each optical beam. However, when an optical 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) due to the non-linearity of the optical fiber. SBS is more likely to occur when the linewidth of the optical beam is narrower. Therefore, in order to suppress the occurrence of SBS, it is desirable that the linewidth of the optical beam be wide, and when the linewidth of the optical beam output from the laser light source is narrow, it is necessary to expand the linewidth.

[0005] In the technique disclosed in Non-Patent Document 1, the linewidth of the laser light output from the light source (MO) is expanded by phase-modulating (25 GHz Φ-mod) the laser light with a broadband signal. Also, Non-Patent Document 1 suggests using a pseudo-random variable (PRBS: Psuedo Radndom Bit Sequence).

[0006] On the other hand, when the linewidth of the laser light becomes wide, it is necessary to match the actual lengths of the transmission paths among the respective transmission optical paths on the order of not more than the reciprocal of the linewidth. When the linewidth is on the order of several 10 GHz, the actual length of the fiber must be matched on the order of mm or less. Furthermore, in order to phase-combine the optical beams, it must be stabilized on the order of less than the wavelength of light (<1 μm). Therefore, in the technique disclosed in Non-Patent Document 1, a variable delay line (VDL: Variable Delay Line) is provided in the optical path of the transmitted light. Thus, in the technique disclosed in Non-Patent Document 1, the lengths of the respective optical paths are made to match, and the optical phase fluctuations between the optical paths are suppressed by an optical phase shifter (φMod).

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

[0008] In the technology disclosed in Non-Patent Document 1, after expanding the line width (Line Broadening) of the laser light output from the light source (MO), it is divided into a plurality of optical paths, amplified by an optical amplifier, and then spatially combined (coherent beam combination). At this time, in the technology disclosed in Non-Patent Document 1, in order to make the optical beams have a correlation in the state where the line width is expanded, the actual lengths of each optical path are adjusted by a variable delay line, and in order to perform coherent synthesis of light, phase fluctuations are compensated between each path. However, when the broadening range (frequency) of the line width becomes wider, the allowable error with respect to the actual length between the optical paths becomes smaller. Therefore, it is difficult to manufacture with the optical path lengths being made to match from after the distribution of the laser light until it is radiated into space from the collimator. Also, when adjusting using a variable delay line to compensate for this error, there are problems such as being limited by the control range of the variable delay line and the loss being able to vary due to the control of the delay amount.

[0009] The present disclosure has been made to solve the above problems, and an object thereof is to provide an optical beam transmission device that can relax the manufacturing requirements compared to the prior art. Means for Solving the Problems

[0010] The high-brightness light beam transmission device according to the present disclosure includes: an optical distribution means for branching laser light into one local light and transmission light for each path; an optical frequency shift means for shifting the frequency of the local light obtained by the optical distribution means; a collimating lens for converting the local light after the frequency shift by the optical frequency shift means into a local beam which is a parallel beam; an optical phase shifter provided for each path, which changes the phase of the corresponding transmission light obtained by the optical distribution means according to a control signal; an optical modulator provided for each path, which modulates the transmission light after the phase change by the corresponding optical phase shifter according to a modulation electrical signal; an optical amplifier provided for each path, which amplifies the intensity of the transmission light after modulation by the corresponding optical modulator; an optical collimator array provided for each path, which converts the transmission light after amplification by the corresponding optical amplifier into a transmission beam which is a parallel beam; an optical beam branching means for branching a part of the transmission beams among the transmission beams obtained by the optical collimator array for each path, and respectively combining the part of the transmission beams with the local beam obtained by the collimating lens to obtain a combined phase monitor light; a photoelectric conversion means provided for each path, which photoelectrically converts the corresponding combined phase monitor light obtained by the optical beam branching means to obtain an electrical signal; a modulation electrical signal output means for outputting a modulation electrical signal with a controlled delay time to the optical modulators for each path based on the electrical signal obtained by the photoelectric conversion means for each path; and an optical phase synchronization control means provided for each path, which detects the phase of the electrical signal obtained by the corresponding photoelectric conversion means and outputs a control signal based on the phase to the corresponding optical phase shifter.

Advantages of the Invention

[0011] According to the present disclosure, since it is configured as described above, the manufacturing requirements can be relaxed compared to the prior art.

Brief Description of the Drawings

[0012]

Figure 1

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Embodiments for Carrying Out the Invention

[0013] Hereinafter, the embodiments will be described in detail with reference to the drawings. Embodiment 1. Fig. 1 is a diagram showing a configuration example of the optical beam transmission device 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 transmission device 1 includes a laser light source 101, an optical distribution means 102, an optical frequency shift 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 condensing means 110, a plurality of optoelectronic conversion means 111, a signal generation means 112, a plurality of delay arithmetic devices 113, a plurality of RF variable delay means 114, and a plurality of optical phase synchronization control means 115.

[0014] Also, although not shown in Fig. 1, in the optical beam transmission device 1, optical phase shifters 105-1 to 105-n are provided as a plurality of optical phase shifters 105, optical modulators 106-1 to 106-n are provided as a plurality of optical modulators 106, optical amplifiers 107-1 to 107-n are provided as a plurality of optical amplifiers 107, beam condensing means 110-1 to 110-n are provided as a plurality of beam condensing means 110, photoelectric conversion means 111-1 to 111-n are provided as a plurality of photoelectric conversion means 111, delay arithmetic devices 113-1 to 113-n are provided as a plurality of delay arithmetic devices 113, RF variable delay means 114-1 to 114-n are provided as a plurality of RF variable delay means 114, and optical phase synchronization control means 115-1 to 115-n are provided as a plurality of optical phase synchronization control means 115. Here, -1 to -n represent the element (path) numbers of the array, and the number of elements is n.

[0015] The laser light source 101 generates laser light. The laser light generated by this laser light source 101 is output to the optical 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 light for each path. That is, the optical distribution means 102 branches the laser light into (n + 1) parts. The local light obtained by this optical distribution means 102 is output to the optical frequency shift means 103. Also, the transmission light for each path obtained by the optical distribution means 102 is output to the corresponding optical phase shifter 105. In Fig. 1, the reference numeral 11 indicates the transmission light.

[0017] The optical frequency shift means 103 shifts the frequency of the local light obtained by the optical distribution means 102. The local light after the frequency shift by this optical frequency shift means 103 is output to the collimating lens 104. In Fig. 1, the reference numeral 12 indicates the local light.

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

[0019] The collimating lens 104 converts the local light after the frequency shift by the optical frequency shift means 103 into a local beam which is a parallel beam. The local beam obtained by this collimating lens 104 is output to the optical beam branching means 109. In FIG. 1, reference numeral 13 indicates the local beam.

[0020] The optical phase shifter 105 is provided for each path. The optical phase shifter 105 changes the phase (transmission phase) of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the corresponding optical phase synchronization control means 115. The transmitted light after the phase change by this 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 transmitted light obtained by the optical distribution means 102 according to the control signal from the optical phase synchronization control means 115-1. The transmitted light after the phase change by this optical phase shifter 105-1 is output to the optical modulator 106-1. Also, the optical phase shifter 105-2 changes the phase (transmission phase) of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the optical phase synchronization control means 115-2. The transmitted light after the phase change by this optical phase shifter 105-2 is output to the optical modulator 106-2. Also, the optical phase shifter 105-n changes the phase (transmission phase) of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the optical phase synchronization control means 115-n. The transmitted light after the phase change by this optical phase shifter 105-n is output to the optical modulator 106-n.

[0022] The optical modulator 106 is provided for each path. The optical modulator 106 modulates the transmitted light after the phase change by the corresponding optical phase shifter 105 in response to the modulation electrical signal from the corresponding RF variable delay means 114. The transmitted light modulated by this optical modulator 106 is output to the corresponding optical amplifier 107.

[0023] As this optical modulator 106, for example, a phase modulator or an intensity modulator is used. Note that as the optical modulator 106, a phase modulator whose average intensity of the output light does not fluctuate with the input RF signal is desirable.

[0024] In the example of FIG. 1, the optical modulator 106-1 modulates the transmitted light after the phase change by the optical phase shifter 105-1 in response to the modulation electrical signal from the RF variable delay means 114-1. The transmitted light modulated by this optical modulator 106-1 is output to the optical amplifier 107-1. Also, the optical modulator 106-2 modulates the transmitted light after the phase change by the optical phase shifter 105-2 in response to the modulation electrical signal from the RF variable delay means 114-2. The transmitted light modulated by this optical modulator 106-2 is output to the optical amplifier 107-2. Also, the optical modulator 106-n modulates the transmitted light after the phase change by the optical phase shifter 105-n in response to the modulation electrical signal from the RF variable delay means 114-n. The transmitted light modulated by this optical modulator 106-n is output to the optical amplifier 107-n.

[0025] The optical amplifier 107 is provided for each path. The optical amplifier 107 amplifies the intensity of the transmitted light modulated by the corresponding optical modulator 106. The transmitted light amplified by this 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 transmitted light modulated by the optical modulator 106-1. The transmitted light amplified by this optical amplifier 107-1 is output to the optical collimator array 108-1. Also, the optical amplifier 107-2 amplifies the intensity of the transmitted light after modulation by the optical modulator 106-2. The transmitted light amplified by this optical amplifier 107-2 is output to the optical collimator array 108-2. Also, the optical amplifier 107-n amplifies the intensity of the transmitted light after modulation by the optical modulator 106-n. The transmitted light amplified by this optical amplifier 107-n is output to the optical collimator array 108-n.

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

[0028] In the example of FIG. 1, the optical collimator array 108-1 converts the transmitted light amplified by the optical amplifier 107-1 into a transmitted beam that is a parallel beam. The transmitted beam obtained by this optical collimator array 108-1 is output to the optical beam branching means 109. Also, the optical collimator array 108-2 converts the transmitted light amplified by the optical amplifier 107-2 into a transmitted beam that is a parallel beam. The transmitted beam obtained by this optical collimator array 108-2 is output to the optical beam branching means 109. Also, the optical collimator array 108-n converts the transmitted light amplified by the optical amplifier 107-n into a transmitted beam that is a parallel beam. The transmitted 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 part of the transmitted beams obtained by each optical collimator array 108, and combines each of the part of the transmitted beams with the local beam obtained by the collimating lens 104 to obtain a combined phase monitor light. Each of the remaining transmitted beams that have passed through the optical beam branching means 109 is combined with each other at a distance to form a combined beam and output to the outside. Further, the combined phase monitor light for each path obtained by the optical beam branching means 109 is output to the corresponding beam condensing means 110. In FIG. 1, reference numeral 15 indicates the combined beam, and reference numeral 16 indicates the combined phase monitor light.

[0030] The beam condensing means 110 is provided for each path. The beam condensing means 110 condenses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after being condensed by the beam condensing means 110 is output to the corresponding photoelectric conversion means 111.

[0031] In the example of FIG. 1, the beam condensing means 110-1 condenses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after being condensed by the beam condensing means 110-1 is output to the photoelectric conversion means 111-1. Further, the beam condensing means 110-2 condenses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after being condensed by the beam condensing means 110-2 is output to the photoelectric conversion means 111-2. Further, the beam condensing means 110-n condenses the corresponding combined phase monitor light obtained by the optical beam branching means 109. The combined phase monitor light after being condensed by the beam condensing means 110-n is output to the photoelectric conversion means 111-n.

[0032] The photoelectric conversion means 111 is provided for each path. The photoelectric conversion means 111 photoelectrically converts the combined phase monitor light after being condensed by the corresponding beam condensing means 110. That is, the photoelectric conversion means 111 obtains an electrical signal by photoelectrically converting the local beam and the corresponding transmitted beam that have been converted to the same optical path by the optical beam branching means 109. This electrical signal is an electrical signal (heterodyne beat signal) equal to the frequency difference between the transmitted beam and the local beam. The electrical signal obtained by this photoelectric conversion means 111 is output to the corresponding delay arithmetic unit 113 and the corresponding optical phase synchronization control means 115.

[0033] In the example of FIG. 1, the photoelectric conversion means 111-1 obtains an electrical signal by photoelectrically converting the combined phase monitor light after being condensed by the beam condensing means 110-1. The electrical signal obtained by this photoelectric conversion means 111-1 is output to the delay arithmetic unit 113-1 and the optical phase synchronization control means 115-1. Also, the photoelectric conversion means 111-2 obtains an electrical signal by photoelectrically converting the combined phase monitor light after being condensed by the beam condensing means 110-2. The electrical signal obtained by this photoelectric conversion means 111-2 is output to the delay arithmetic unit 113-2 and the optical phase synchronization control means 115-2. Also, the photoelectric conversion means 111-n obtains an electrical signal by photoelectrically converting the combined phase monitor light after being condensed by the beam condensing means 110-n. The electrical signal obtained by this photoelectric conversion means 111-n is output to the delay arithmetic unit 113-n and the optical phase synchronization control means 115-n.

[0034] The signal generation means 112 generates a modulation electrical signal which is a broadband signal. This broadband signal is a signal capable of broadening the line width of the signal output with respect to the input signal in the optical modulator 106. The modulation electrical signal generated by this signal generation means 112 is output to each delay arithmetic unit 113 and each RF variable delay means 114.

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

[0036] As a method for calculating the delay time difference by this delay calculation device 113, for example, there are a method of obtaining it using each other's beat signals, or a method of taking correlation while shifting each other's timings and obtaining it from the shift at which the correlation becomes maximum.

[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. Also, 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. Also, 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] The RF variable delay means 114 is provided for each path. The RF variable delay means 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 means 112 to the corresponding optical modulator 106.

[0039] This RF variable delay means 114 can be realized, for example, by means of mechanically changing the length of the transmission line, or means of switching a plurality of transmission paths with different lengths by a switch. As means of mechanically changing the length of the transmission line, for example, a line stretcher can be mentioned.

[0040] In the example of FIG. 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 then outputs the modulated electrical signal generated by the signal generation means 112 to the optical modulator 106-1 after controlling the delay time. 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 then outputs the modulated electrical signal generated by the signal generation means 112 to the optical modulator 106-2 after controlling the delay time. 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 then outputs the modulated electrical signal generated by the signal generation means 112 to the optical modulator 106-n after controlling the delay time.

[0041] Note that the signal generation means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 constitute "modulated electrical signal output means for respectively outputting 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] The optical phase synchronization control means 115 is provided for each path. The optical phase synchronization control means 115 detects the phase of the electrical signal obtained by the corresponding photoelectric conversion means 111, and outputs a control signal based on the phase to the corresponding optical phase shifter 105. This control signal is a signal for controlling the phase, and is an electrical signal such as a voltage, for example. At this time, each optical phase synchronization control means 115 generates a control signal so that the phase difference between the transmission beams becomes constant. For example, the optical phase synchronization control means 115 may compare the phase difference between a reference signal source (not shown) and the electrical signal obtained by the corresponding photoelectric conversion means 111 to generate a control signal, or may compare the phase difference between the electrical signals output from adjacent photoelectric conversion means 111 to generate a control signal.

[0043] In the example of FIG. 1, the optical phase synchronization control means 115-1 detects the phase of the electrical signal obtained by the photoelectric conversion means 111-1, and outputs a control signal based on the phase to the corresponding optical phase shifter 105-1. Further, the optical phase synchronization control means 115-2 detects the phase of the electrical signal obtained by the photoelectric conversion means 111-2, and outputs a control signal based on the phase to the corresponding optical phase shifter 105-2. Also, the optical phase synchronization control means 115-n detects the phase of the electrical signal obtained by the photoelectric conversion means 111-n, and outputs a control signal based on the phase to the corresponding optical phase shifter 105-n.

[0044] Next, an operation example of the optical beam transmission device 1 according to Embodiment 1 configured as shown in FIG. 1 will be described. In this optical beam transmission device 1, first, the laser light output from the laser light source 101 is split into (n + 1) laser lights by the optical distribution means 102.

[0045] Then, one of the split laser lights is frequency-shifted by the optical frequency shift means 103 as local light. Then, the local light output from the optical frequency shift means 103 is made into a parallel beam by the collimating lens 104 and radiated into space as a local beam.

[0046] On the other hand, n of the split laser lights are used as transmission lights, and the transmission phases are controlled by the respective optical phase shifters 105 according to the control signals from the respective optical phase synchronization control means 115. Then, the transmission light output from each optical phase shifter 105 is modulated by each optical modulator 106 according to the modulation electrical signal from each RF variable delay means 114 and output.

[0047] Then, the transmission light output from each optical modulator 106 is amplified in intensity by each optical amplifier 107, and then made into a parallel beam by each optical collimator array 108 and radiated into space as a transmission beam. After that, the transmission beams radiated into space are combined with each other at a distance to form a combined beam.

[0048] Also, among the respective transmission beams radiated into space, a part of each transmission beam and the local beam are each combined by the optical beam branching means 109, and are condensed onto each photoelectric conversion means 111 via each beam condensing means 110 as combined phase monitor light. Then, this combined phase monitor light is photoelectrically converted by each photoelectric conversion means 111, and an electric signal which is a heterodyne beat signal equal to the frequency difference between the transmission beam and the local beam is output.

[0049] And in each delay arithmetic unit 113, the modulated electric signal output from the signal generation means 112 and the corresponding electric signal output from each photoelectric conversion means 111 are compared to obtain their delay time difference. Then, the modulated electric signals output from the signal generation means 112 are each given a delay by each RF variable delay means 114 according to the delay time difference obtained by each delay arithmetic unit 113, and become modulation signals to each optical modulator 106.

[0050] In this way, in the optical beam transmission device 1 according to Embodiment 1, optical modulation and delay control of the modulated electric signal are performed on all the transmission lights. Thereby, in the optical beam transmission device 1 according to Embodiment 1, each transmission beam constituting the combined beam has the same modulation waveform at the same timing.

[0051] Furthermore, in the optical beam transmission device 1 according to Embodiment 1, each optical phase synchronization control means 115 takes the electric signal output from each photoelectric conversion means 111 as an input, obtains a control signal to each optical phase shifter 105 from the phase information thereof, and controls the phase of the transmission light passing through each optical phase shifter 105. At this time, the optical phase synchronization control means 115 operates so that the phase difference between the transmission beams becomes constant. And in the optical beam transmission device 1 according to Embodiment 1, the phases of the laser lights are synchronized between the paths by these phase comparisons and controls.

[0052] FIG. 2 schematically shows an example of the frequency arrangement (spectrum arrangement) of the optical signal or electrical signal at each point in FIG. 1. FIG. 2A schematically represents an example of the frequency arrangement in the part (A) in FIG. 1, FIG. 2B schematically represents an example of the frequency arrangement in the part (B) in FIG. 1, FIG. 2C schematically represents an example of the frequency arrangement in the part (C) in FIG. 1, FIG. 2D schematically represents an example of the frequency arrangement in the part (D) in FIG. 1, and FIG. 2E schematically represents an example of the frequency arrangement in the part (E) in FIG. 1.

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

[0054] Also, FIG. 2B shows the frequency of the local light output from the optical frequency shift means 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] Also, FIG. 2C shows the frequency of the transmission beam output from the optical collimator array 108. The frequency of this transmission beam is modulated over a wide band (bandwidth 2fs in FIG. 2C) by the modulation electrical signal from the RF variable delay means 114. Also, in the transmission beam, a signal with a frequency of fo + fp is superimposed in the vicinity of the frequency of the local light (fo + fref) for optical synchronization comparison. This transmission beam is radiated into space respectively and becomes a combined beam coherently combined at a distance. Note that in this transmission beam, since it spreads over a wide band with respect to the frequency (fo) of the laser light shown in FIG. 2A, the occurrence of SBS is suppressed.

[0056] Also, FIG. 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 the combination of the frequency of the local light shown in FIG. 2B and the frequency of the transmission beam shown in FIG. 2C.

[0057] Further, FIG. 2E 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 appearing in FIG. 2D. The calculation of the delay time between the beams is obtained by using a broadband signal centered on fref in FIG. 2E and performing a correlation calculation with the output from the signal generation means 112 or the like. In FIG. 2E, the center frequency of the broadband signal is fref. Needless to say, this can be converted to an arbitrary frequency (for example, the center frequency can be set to DC) by using a microwave mixer or the like. Also, the optical phase difference between the paths can be obtained by using the frequency (fref - fp), and thereby the optical phases between the paths can be synchronized.

[0058] With the above configuration, in the optical beam transmission device 1 according to the first embodiment, the spectral width of the transmission beam spreads, and the phases between the plurality of transmission beams are synchronized, so that coherent combination using a high-intensity beam becomes possible.

[0059] As described above, according to the first embodiment, the optical beam transmission device 1 includes an optical distribution unit 102 that branches laser light into one local light and transmission light for each path, an optical frequency shift unit 103 that shifts the frequency of the local light obtained by the optical distribution unit 102, a collimating lens 104 that converts the local light after the frequency shift by the optical frequency shift unit 103 into a local beam that is a parallel beam, an optical phase shifter 105 provided for each path that changes the phase of the corresponding transmission light obtained by the optical distribution unit 102 according to a control signal, an optical modulator 106 provided for each path that modulates the transmission light after the phase change by the corresponding optical phase shifter 105 according to a modulation electrical signal, an optical amplifier 107 provided for each path that amplifies the intensity of the transmission light after modulation by the corresponding optical modulator 106, an optical collimator array 108 provided for each path that converts the transmission light after amplification by the corresponding optical amplifier 107 into a transmission beam that is a parallel beam, an optical beam branching unit 109 that branches some of the transmission beams among the transmission beams obtained by the optical collimator array 108 for each path and synthesizes each of the some transmission beams with the local beam obtained by the collimating lens 104 to obtain a synthesized phase monitor light, a photoelectric conversion unit 111 provided for each path that photoelectrically converts the corresponding synthesized phase monitor light obtained by the optical beam branching unit 109 to obtain an electrical signal, a modulation electrical signal output unit that outputs a modulation electrical signal with a controlled delay time to the optical modulators 106 for each path based on the electrical signal obtained by the photoelectric conversion unit 111 for each path, and an optical phase synchronization control unit 115 provided for each path that detects the phase of the electrical signal obtained by the corresponding photoelectric conversion unit 111 and outputs a control signal based on the phase to the corresponding optical phase shifter 105. Thereby, the optical beam transmission device 1 according to the first embodiment can relax the manufacturing requirements compared to the prior art. That is, in the optical beam transmission device 1 according to the first embodiment, the linewidth broadening of the laser light is performed after being distributed to each element. Thereby, in the optical beam transmission device 1 according to the first embodiment, it is not necessary to match the lengths of the respective fiber paths, and the requirements for manufacturing can be relaxed compared to the prior art.

[0060] In addition, in the optical beam transmission device 1 according to Embodiment 1, the optical system can be simplified by eliminating the combining optical system for a plurality of transmission beams and the local beam, and the expansion of the array scale can be facilitated by the sub-array configuration.

[0061] Embodiment 2. FIG. 3 is a diagram showing a configuration example of the optical beam transmission device 1 according to Embodiment 2. In the optical beam transmission device 1 according to Embodiment 2 shown in this FIG. 3, with respect to the optical beam transmission device 1 according to Embodiment 1 shown in FIG. 1, the optical frequency shift means 103 is deleted, a plurality of optical phase shifters 105 are changed to a plurality of optical frequency conversion means 116, and a plurality of optical phase synchronization control means 115 are changed to a plurality of optical frequency synchronization control means 117. Regarding other configuration examples in the optical beam transmission device 1 according to Embodiment 2 shown in FIG. 3, they are the same as those in the optical beam transmission device 1 according to Embodiment 1 shown in FIG. 1, and only the different parts will be described with the same reference numerals.

[0062] Also, although not shown by reference numerals in FIG. 3, in the optical beam transmission device 1, optical frequency conversion means 116-1 to 116-n are provided as a plurality of optical frequency conversion means 116, and optical frequency synchronization control means 117-1 to 117-n are provided as a plurality of optical frequency synchronization control means 117.

[0063] Note that the local light obtained by the optical distribution means 102 in Embodiment 2 is output to the collimating lens 104. Also, the transmission light for each path obtained by the optical distribution means 102 in Embodiment 2 is output to the corresponding optical frequency conversion means 116, respectively.

[0064] Also, the collimating lens 104 in Embodiment 2 converts the local light obtained by the optical distribution means 102 into a local beam that is a parallel beam.

[0065] The optical frequency conversion means 116 is provided for each path. The optical frequency conversion means 116 changes the frequency of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the corresponding optical frequency synchronization control means 117. The transmitted light after the frequency transition by this optical frequency conversion means 116 is output to the corresponding optical modulator 106.

[0066] In the example of FIG. 3, the optical frequency conversion means 116-1 changes the frequency of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the optical frequency synchronization control means 117-1. The transmitted light after the frequency transition by this optical frequency conversion means 116-1 is output to the optical modulator 106-1. Also, the optical frequency conversion means 116-2 changes the frequency of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the optical frequency synchronization control means 117-2. The transmitted light after the frequency transition by this optical frequency conversion means 116-2 is output to the optical modulator 106-2. Also, the optical frequency conversion means 116-n changes the frequency of the corresponding transmitted light obtained by the optical distribution means 102 according to the control signal from the optical frequency synchronization control means 117-n. The transmitted light after the frequency transition by this optical frequency conversion means 116-n is output to the optical modulator 106-n.

[0067] Also, the optical modulator 106 in Embodiment 2 modulates the transmitted light after the frequency transition by the corresponding optical frequency conversion means 116 according to the modulation electrical signal from the corresponding RF variable delay means 114.

[0068] Also, the electrical signal obtained by the optoelectronic conversion means 111 in Embodiment 2 is output to the corresponding delay arithmetic device 113 and the corresponding optical frequency synchronization control means 117.

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

[0070] In the example of FIG. 3, the optical frequency synchronization control means 117-1 detects the frequency variation of the electrical signal obtained by the photoelectric conversion means 111-1, and outputs a control signal based on the frequency variation to the optical frequency conversion means 116-1. Further, the optical frequency synchronization control means 117-2 detects the frequency variation of the electrical signal obtained by the photoelectric conversion means 111-2, and outputs a control signal based on the frequency variation to the optical frequency conversion means 116-2. Further, the optical frequency synchronization control means 117-n detects the frequency variation of the electrical signal obtained by the photoelectric conversion means 111-n, and outputs a control signal based on the frequency variation to the optical frequency conversion means 116-n.

[0071] Each optical frequency synchronization control means 117 includes, for example, as shown in FIG. 4, a PFD (Phase Frequency Detector) 1171, an LF (Loop Filter) 1172, and a VCO (Voltage controlled Oscillator) 1173. Further, a reference oscillator 1174 is provided as a configuration commonly used for the entire optical frequency synchronization control means 117. Note that the configuration shown in FIG. 4 shows a typical one.

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

[0073] The PFD 1171 compares 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 to obtain an error signal. The error signal obtained by this PFD 1171 is output to the corresponding LF 1172.

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

[0075] The LF 1172 smoothes the error signal obtained by the corresponding PFD 1171 to obtain a DC signal in order to stabilize the phase-locked loop. The DC signal obtained by this LF 1172 is output to the corresponding VCO 1173.

[0076] In the example of FIG. 4, the LF 1172-1 smoothes the error signal obtained by the PFD 1171-1 to obtain a DC signal. The DC signal obtained by this LF 1172-1 is output to the VCO 1173-1. Also, LF1172-2 smoothes the error signal obtained by PFD1171-2 to obtain a DC signal. The DC signal obtained by this LF1172-2 is output to VCO1173-2. Also, LF1172-n smoothes the error signal obtained by PFD1171-n to obtain a DC signal. The DC signal obtained by this LF1172-n is output to VCO1173-n.

[0077] VCO1173 generates a control signal based on the DC signal obtained by the corresponding LF1172. The control signal generated by this VCO1173 is output to the corresponding optical frequency conversion means 116.

[0078] In the example of FIG. 4, VCO1173-1 generates a control signal based on the DC signal obtained by LF1172-1. The control signal generated by this VCO1173-1 is output to optical frequency conversion means 116-1. Also, VCO1173-2 generates a control signal based on the DC signal obtained by LF1172-2. The control signal generated by this VCO1173-2 is output to optical frequency conversion means 116-2. Also, VCO1173-n generates a control signal based on the DC signal obtained by LF1172-n. The control signal generated by this VCO1173-n is output to optical frequency conversion means 116-n.

[0079] Next, an operation example of the optical beam transmission device 1 according to Embodiment 2 configured as shown in FIG. 3 will be described. In this optical beam transmission device 1, first, the laser light output from the laser light source 101 is split into (n + 1) laser lights by the optical distribution means 102.

[0080] Then, one of the distributed laser lights, i.e., the local light, is made into a parallel beam by the collimating lens 104 without passing through the optical frequency shift means 103 and is radiated into space as a local beam.

[0081] On the other hand, among the allocated laser beams, n laser beams are each used as transmission light, and their frequencies are controlled by each optical frequency conversion means 116 according to a control signal from each optical frequency synchronization control means 117. Then, the transmission light output from each optical frequency conversion means 116 is modulated and output by each optical modulator 106 according to a modulation electrical signal from each RF variable delay means 114.

[0082] Then, the transmission light output from each optical modulator 106 is amplified in intensity by each optical amplifier 107, and then made into a parallel beam by each optical collimator array 108 and radiated into space as a transmission beam. Thereafter, the transmission beams radiated into space are combined with each other at a distance to form a combined beam.

[0083] Also, a part of each of the transmission beams radiated into space and the local beam are each combined by the optical beam branching means 109 and condensed onto each photoelectric conversion means 111 via each beam condensing means 110 as combined phase monitor light. Then, this combined phase monitor light is photoelectrically converted by each photoelectric conversion means 111, and an electrical signal which is a heterodyne beat signal equal to the frequency difference between the transmission beam and the local beam is output.

[0084] Then, in each delay arithmetic device 113, the modulation electrical signal output from the signal generation means 112 is compared with the corresponding electrical signal output from each photoelectric conversion means 111, and their delay time difference is obtained. Then, the modulation electrical signals output from the signal generation means 112 are each given a delay by each RF variable delay means 114 according to the delay time difference obtained by each delay arithmetic device 113, and become modulation signals to each optical modulator 106.

[0085] Thus, in the optical beam transmission device 1 according to Embodiment 2, optical modulation and delay control of the modulation electrical signal are performed on all transmitted light. As a result, in the optical beam transmission device 1 according to Embodiment 2, each transmitted beam constituting the combined beam has the same modulation waveform at the same timing.

[0086] Furthermore, in the optical beam transmission device 1 according to Embodiment 2, each optical frequency synchronization control means 117 takes the electrical signal output from each photoelectric conversion means 111 as an input, obtains a control signal for each optical frequency conversion means 116 from the frequency fluctuation information thereof, and controls the frequency of the transmitted light passing through each optical frequency conversion means 116. At this time, the optical frequency synchronization control means 117 operates so that the frequency fluctuation difference between the transmitted beams becomes constant. Then, in the optical beam transmission device 1 according to Embodiment 2, the phases of the laser lights are synchronized between the paths by these frequency fluctuation comparisons and controls. That is, generally, there is a relationship between the phase and frequency of a wave such that the derivative of the phase is the frequency. Therefore, it is possible to control the phase of the transmitted light by controlling the instantaneous frequency.

[0087] Note that the transmission signal loops through the optical frequency conversion means 116, optical modulator 106, optical amplifier 107, optical collimator array 108, optical beam branching means 109, beam condensing means 110, photoelectric conversion means 111, optical frequency synchronization control means 117, and optical frequency conversion means 116 in either an optical or electrical state, 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 arrangement (spectrum arrangement) of the optical signal or electrical signal at each point in FIG. 3. FIG. 5A schematically represents an example of the frequency arrangement in the parts (A) and (B) in FIG. 3, FIG. 5B schematically represents an example of the frequency arrangement in the part (C) in FIG. 3, FIG. 5C schematically represents an example of the frequency arrangement in the part (D) in FIG. 3, FIG. 5D schematically represents an example of the frequency arrangement in the part (E) in FIG. 3, and FIG. 5E schematically represents an example of the frequency arrangement in the part (F) in FIG. 3.

[0089] FIG. 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 collimating lens 104. The frequency of this laser light is fo. Also, the frequency of the local light is the same as the frequency of the laser light output from the laser light source 101 and is fo.

[0090] Also, FIG. 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] Also, FIG. 5C shows the frequency of the transmitted beam output from the optical collimator array 108. The frequency of this transmitted beam is modulated over a wide band (bandwidth 2fs in FIG. 5C) by the modulation electrical signal from the RF variable delay means 114. Also, in this transmitted beam, in addition to the above wide-band signal, fref is also superimposed and modulated, so that a signal of fo + (frep - fp) is also superimposed. This transmitted beam is radiated into space respectively and becomes a combined beam that is coherently combined at a distance. Note that in this transmitted beam, since it spreads over a wide band with respect to the frequency (fo) of the laser light shown in FIG. 5A, the occurrence of SBS is suppressed.

[0092] Also, FIG. 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 the combination of the frequency of the local light shown in FIG. 5A and the frequency of the transmitted beam shown in FIG. 5C.

[0093] Also, 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 appearing in FIG. 5D. The calculation of the delay time between each beam is obtained by using a wide-band signal centered on fref in FIG. 5E and performing a correlation operation with the output from the signal generation means 112 and the like. In addition, although the center frequency of the broadband signal is fref in Fig. 5E, it goes without saying that this can be converted to an arbitrary frequency (for example, the center frequency can be set to DC) by using a microwave mixer or the like. Also, the optical phase difference between the paths can be obtained by using the frequency (fref - fp), and thereby the optical phases between the paths can be synchronized.

[0094] With the above configuration, in the optical beam transmission device 1 according to Embodiment 2, the spectral width of the transmission beam spreads, and the phases between the plurality of transmission beams are synchronized, so that coherent combination using a high-intensity beam becomes possible. Furthermore, in the optical beam transmission device 1 according to Embodiment 2, since the inter-path phase control is performed by instantaneous frequency control using the optical frequency conversion means 116, it is possible to expand the applicable range of the phase control with respect to the optical beam transmission device 1 according to Embodiment 1.

[0095] As described above, according to the second embodiment, the optical beam transmission device 1 includes an optical distribution unit 102 that branches the laser beam into one local light beam and transmission light for each path, a collimating lens 104 that converts the local light beam obtained by the optical distribution unit 102 into a local beam that is a parallel beam, an optical frequency conversion unit 116 provided for each path that transitions the frequency of the corresponding transmission light obtained by the optical distribution unit 102 according to a control signal, an optical modulator 106 provided for each path that modulates the transmission light after the frequency transition by the corresponding optical frequency conversion unit 116 according to a modulation electrical signal, an optical amplifier 107 provided for each path that amplifies the intensity of the transmission light after modulation by the corresponding optical modulator 106, an optical collimator array 108 provided for each path that converts the transmission light after amplification by the corresponding optical amplifier 107 into a transmission beam that is a parallel beam, an optical beam branching unit 109 that branches a part of the transmission beams among the transmission beams obtained by the optical collimator array 108 for each path and synthesizes each of the part of the transmission beams with the local beam obtained by the collimating lens 104 to obtain a synthesized phase monitor light, a photoelectric conversion unit 111 provided for each path that photoelectrically converts the corresponding synthesized phase monitor light obtained by the optical beam branching unit 109 to obtain an electrical signal, a modulation electrical signal output unit that outputs a modulation electrical signal with a controlled delay time to the optical modulators 106 for each path based on the electrical signal obtained by the photoelectric conversion units 111 for each path, and an optical frequency synchronization control unit 117 provided for each path that detects the frequency fluctuation of the electrical signal obtained by the corresponding photoelectric conversion unit 111 and outputs a control signal based on the frequency fluctuation to the corresponding optical frequency conversion unit 116. Thereby, in addition to the effects of the optical beam transmission device 1 according to the first embodiment, the optical beam transmission device 1 according to the second embodiment can expand the application range of phase control.

[0096] Embodiment 3. In Embodiment 3, another configuration example of the modulation electrical signal output unit will be described. FIG. 6 is a diagram showing a configuration example of the optical beam transmission device 1 according to Embodiment 3. In the optical beam transmission device 1 according to Embodiment 3 shown in this FIG. 6, with respect to the optical beam transmission device 1 according to Embodiment 2 shown in FIG. 3, the signal generation means 112, the plurality of delay arithmetic units 113, and the plurality of RF variable delay means 114 are changed to a plurality of signal processing devices 118 and a plurality of signal generation means 119. Regarding other configuration examples in the optical beam transmission device 1 according to Embodiment 3 shown in FIG. 6, they are the same as those in the optical beam transmission device 1 according to Embodiment 2 shown in FIG. 3, and only the different parts will be described with the same reference numerals.

[0097] Also, although not shown by reference numerals in FIG. 6, in the optical beam transmission device 1, signal processing devices 118-1 to 118-n are provided as the plurality of signal processing devices 118, and signal generation means 119-1 to 119-n are provided as the plurality of signal generation means 119.

[0098] Note that the electrical signal obtained by the photoelectric conversion means 111 in Embodiment 3 is output to the corresponding signal processing device 118 and the corresponding optical frequency synchronization control means 117.

[0099] The signal processing device 118 is provided for each path. The signal processing device 118 calculates the 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 FIG. 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. Further, 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. Also, 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] The signal generation means 119 is provided for each path. The signal generation means 119 outputs the modulated electrical signal to the corresponding optical modulator 106 according to the timing signal generated by the corresponding signal processing device 118. The modulated electrical signals used by each signal generation means 119 are broadband signals with waveforms common to each other. This broadband signal is a signal capable of broadening the line width of the output signal with respect to the input signal in the optical modulator 106.

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

[0103] In the example of FIG. 6, the signal generation means 119-1 outputs the modulated electrical signal to the optical modulator 106-1 according to the timing signal generated by the signal processing device 118-1. Also, the signal generation means 119-2 outputs the modulated electrical signal to the optical modulator 106-2 according to the timing signal generated by the signal processing device 118-2. Also, the signal generation means 119-n outputs the modulated electrical signal to the optical modulator 106-n according to the timing signal generated by the signal processing device 118-n.

[0104] Further, the optical modulator 106 in Embodiment 3 modulates the transmitted light after the frequency transition by the corresponding optical frequency conversion means 116 in accordance with the modulation electrical signal output by the corresponding signal generation means 119.

[0105] Note that the plurality of signal processing devices 118 and the plurality of signal generation means 119 constitute "modulation electrical signal output means" that respectively output modulation electrical signals with controlled delay times to the respective optical modulators 106 based on the electrical signals obtained by the respective optoelectronic conversion means 111.

[0106] Next, an operation example of the optical beam transmission device 1 according to Embodiment 3 configured as shown in FIG. 6 will be described. In this optical beam transmission device 1, first, the laser light output from the laser light source 101 is distributed by the optical distribution means 102 into (n + 1) laser lights.

[0107] Then, one of the distributed laser lights, the local light, is made into a parallel beam by the collimating lens 104 and radiated into space as a local beam.

[0108] On the other hand, n of the distributed laser lights are each used as transmitted light, and their frequencies are controlled by the respective optical frequency conversion means 116 according to the control signals from the respective optical frequency synchronization control means 117. Then, the transmitted light output from each optical frequency conversion means 116 is modulated and output by each optical modulator 106 according to the modulation electrical signal from each signal generation means 119.

[0109] Then, the transmitted light output from each optical modulator 106 is amplified in intensity by each optical amplifier 107, and then made into a parallel beam by each optical collimator array 108 and radiated into space as a transmission beam. After that, the transmission beams radiated into space are combined with each other at a distance to form a combined beam.

[0110] Also, among the transmitted beams radiated into space, each of the transmitted beams and the local beam, a part of them, are respectively combined by the optical beam branching means 109, and condensed onto each photoelectric conversion means 111 through each beam condensing means 110 as combined phase monitor light. Then, this combined phase monitor light is photoelectrically converted by each photoelectric conversion means 111, and an electrical signal, which is a heterodyne beat signal equal to the frequency difference between the transmitted beam and the local beam, is output.

[0111] Here, in the third embodiment, in contrast to the second embodiment, instead of the signal generation means 112, the plurality of RF variable delay means 114, and the plurality of delay arithmetic devices 113, a plurality of signal processing devices 118 and a plurality of signal generation means 119 are provided. Then, each signal processing device 118 takes the electrical signal output from each photoelectric conversion means 111 as an input, and calculates the delay time for each path. Further, each signal processing device 118 generates a timing signal indicating the timing at which a signal is output in each signal generation means 119 according to the calculated delay time. Then, each signal generation means 119 outputs a modulated electrical signal, which is a broadband signal of 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 transmission device 1 according to the third embodiment, the timing of waveform output can be controlled by digital signal processing. Thereby, in the optical beam transmission device 1 according to the third embodiment, the RF variable delay means 114 becomes unnecessary, and limitations such as the setting range of the delay time and the setting resolution can be relaxed.

[0113] Note that in FIG. 6, each signal processing device 118 and each signal generation means 119 are provided for each path, but needless to say, these may be in a single device, and it goes without saying that they are synchronized with each other in order to synchronize the timing between the signal processing devices 118.

[0114] Further, in FIG. 6, a case is shown where, with respect to the optical beam transmission device 1 according to the second embodiment, the signal generation means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 are changed to the plurality of signal processing devices 118 and the plurality of signal generation means 119. However, the present invention is not limited to this. With respect to the optical beam transmission device 1 according to the first embodiment, the signal generation means 112, the plurality of delay calculation devices 113, and the plurality of RF variable delay means 114 may be changed to the plurality of signal processing devices 118 and the plurality of signal generation means 119, and the same effects as described above can be obtained.

[0115] As described above, according to the third embodiment, the modulation electrical signal output means is provided for each path, calculates the 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 signal processing device 118 and the signal generation means 119 are provided for each path and output a modulation electrical signal having waveforms common to each other to the corresponding optical modulator 106 according to the timing signal generated by the corresponding signal processing device 118. Thereby, in the optical beam transmission device 1 according to the third embodiment, the RF variable delay means 114 becomes unnecessary with respect to the optical beam transmission devices 1 according to the first and second embodiments, and restrictions such as the setting range of the delay time and the setting resolution can be relaxed.

[0116] Embodiment 4. In Embodiment 4, another configuration example of the modulation electrical signal output means will be described. FIG. 7 is a diagram showing a configuration example of the optical beam transmission device 1 according to the fourth embodiment. In the optical beam transmission device 1 according to the fourth embodiment shown in FIG. 7, with respect to the optical beam transmission device 1 according to the second embodiment shown in FIG. 3, the plurality of delay calculation devices 113 are changed to the plurality of delay comparison devices 120. Other configuration examples of the optical beam transmission device 1 according to the fourth embodiment shown in FIG. 7 are the same as those of the optical beam transmission device 1 according to the second embodiment shown in FIG. 3, and only the different parts will be described with the same reference numerals.

[0117] Also, although not shown in FIG. 7, in the optical beam transmission device 1, delay comparison devices 120-2 to 120-n are provided as a plurality of delay comparison devices 120.

[0118] Note that 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] Also, the modulation electrical signal generated by the signal generation means 112 in the fourth embodiment is output to each RF variable delay means 114.

[0120] The 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 the corresponding two adjacent photoelectric conversion means 111. The electrical signal indicating the delay time difference calculated by this delay comparison device 120 is output to the corresponding RF variable delay means 114.

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

[0122] Also, 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 modulation electrical signal generated by the signal generation means 112 to the corresponding optical modulator 106. Regarding the RF variable delay means 114 (RF variable delay means 114-1 in FIG. 7) provided in the reference path, the modulated electrical signal generated by the signal generation means 112 is output to the corresponding optical modulator 106 without controlling the delay time.

[0123] Note that the signal generation means 112, the plurality of delay comparison devices 120, and the plurality of RF variable delay means 114 constitute "modulated electrical signal output means that respectively output modulated electrical signals with controlled delay times to the respective optical modulators 106 based on the electrical signals obtained by the respective optoelectronic conversion means 111".

[0124] Next, an operation example of the optical beam transmission device 1 according to Embodiment 4 configured as shown in FIG. 7 will be described. In this optical beam transmission device 1, first, the laser light output from the laser light source 101 is distributed by the optical distribution means 102 into (n + 1) laser lights.

[0125] And one of the distributed laser lights, the local light, is made into a parallel beam by the collimating lens 104 and radiated into space as a local beam.

[0126] On the other hand, n of the distributed laser lights are used as transmission lights, and their frequencies are controlled by the respective optical frequency conversion means 116 according to the control signals from the respective optical frequency synchronization control means 117. And the transmission light output from each optical frequency conversion means 116 is modulated and output by each optical modulator 106 according to the modulated electrical signal from each RF variable delay means 114.

[0127] And the transmission light output from each optical modulator 106 is amplified in intensity by each optical amplifier 107, and then made into a parallel beam by each optical collimator array 108 and radiated into space as a transmission beam. After that, the transmission beams radiated into space are combined with each other at a distance to form a combined beam.

[0128] Also, among the transmitted beams radiated into space, each of a part of the transmitted beams and the local beam are combined by the optical beam branching means 109, and condensed onto each photoelectric conversion means 111 via each beam condensing means 110 as combined phase monitor light. Then, this combined phase monitor light is photoelectrically converted by each photoelectric conversion means 111, and an electrical signal which is a heterodyne beat signal equal to the frequency difference between the transmitted beam and the local beam is output.

[0129] Here, in Embodiment 4, in contrast to Embodiment 2, a plurality of delay comparison devices 120 are provided instead of the plurality of delay operation devices 113. Then, in each delay comparison device 120, two electrical signals output from each photoelectric conversion means 111 are compared to obtain the delay time difference between the paths. For example, in FIG. 7, the delay comparison device 120-2 obtains the delay time difference of the electrical signal output from the photoelectric conversion means 111-2 with reference to the electrical signal output from the photoelectric conversion means 111-1, and the delay comparison device 120-3 obtains the delay time difference of the electrical signal output from the photoelectric conversion means 111-3 with reference to the electrical signal output from the photoelectric conversion means 111-2. Each delay comparison device 120 obtains the delay time difference in order. Then, the modulation electrical signals output from the signal generation means 112 are each given a delay by each RF variable delay means 114 according to the delay time difference obtained by each delay comparison device 120, and become modulation signals to each optical modulator 106. For example, in FIG. 7, the RF variable delay means 114-1 outputs the modulation electrical signal as it is to the optical modulator 106-1, the RF variable delay means 114-2 outputs the modulation 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 modulation electrical signal to the optical modulator 106-3 based on the delay time difference obtained by the delay comparison device 120-3.

[0130] Thus, in the optical beam transmission device 1 according to the fourth embodiment, each delay comparison device 120 compares the electrical signals with each other to obtain the delay time difference. Here, since the paths are installed adjacent to each other, the amount of variation such as temperature becomes close. Therefore, it is expected that the delay time difference between adjacent paths will also become small. Thus, in the optical beam transmission device 1 according to the fourth embodiment, it is possible to reduce the dynamic range of delay control.

[0131] Also, in FIG. 7, the case where a plurality of delay calculation devices 113 are changed to a plurality of delay comparison devices 120 with respect to the optical beam transmission device 1 according to the second embodiment is shown. However, not limited to this, a plurality of delay calculation devices 113 may be changed to a plurality of delay comparison devices 120 with respect to the optical beam transmission device 1 according to the first embodiment, and the same effect as described above can be obtained.

[0132] As described above, according to the fourth embodiment, the modulation electrical signal output means includes a signal generation means 112 that generates a modulation electrical signal, and is provided for each path, and is based on the electrical signals obtained by two adjacent photoelectric conversion means 111 corresponding to each other. A delay comparison device 120 that calculates the delay time difference between the electrical signals, and is provided for each path, and based on the delay time difference calculated by the corresponding delay comparison device 120, after controlling the delay time, the modulation electrical signal generated by the signal generation means 112 is output to the corresponding optical modulator 106. And an RF variable delay means 114. Thereby, in the optical beam transmission device 1 according to the fourth embodiment, it is possible to reduce the dynamic range of delay control with respect to the optical beam transmission device 1 according to the first to third embodiments.

[0133] In the above-described first to fourth embodiments, the modulation electrical signal output from the signal generation means 112 may be, for example, any of a sine wave, a rectangular wave, or a triangular wave. Also, in the above-described Embodiments 1 to 4, the modulated electrical signal output from the signal generation means 112 may be a pseudo-random signal. Even in this case, the optical beam transmission device 1 can obtain the respective delay time differences by performing delay control and cross-correlation calculation between the signal source and the transmission signal. Also, in the above-described Embodiments 1 to 4, the modulated electrical signal output from the signal generation means 112 may be a signal modulated for communication. Also in this case, the optical beam transmission device 1 can obtain the respective delay time differences by performing delay control and cross-correlation calculation between the signal source and the transmission signal.

[0134] Also, in the above-described Embodiments 1 to 4, the case where the optical beam transmission device 1 obtains the delay time difference from the correlation between the signal source and the transmission signal is shown. However, not limited to this, the optical beam transmission device 1 may, for example, superimpose a short pulse signal on a band separable from any of the above frequencies separately from the signal (frequency fp) for phase detection, and obtain the delay time difference from the time until the corresponding pulse signal is detected.

[0135] Finally, with reference to FIG. 8, a hardware configuration example of the optical beam transmission device 1 according to Embodiments 1 to 4 will be described. In the following, a hardware configuration example of the optical beam transmission device 1 according to Embodiment 1 will be shown, but the same applies to the hardware configuration examples of the optical beam transmission devices 1 according to Embodiments 2 to 4. Each function of the delay calculation device 113 and the optical phase synchronization control means 115 in the optical beam transmission device 1 is realized by the processing circuit 51. As shown in FIG. 8A, the processing circuit 51 may be dedicated hardware, or as shown in FIG. 8B, it may be a CPU (Central Processing Unit, central processing unit, processing device, arithmetic device, microprocessor, microcomputer, processor, or also referred to as DSP (Digital Signal Processor)) 52 that executes a program stored in the memory 53.

[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. Each function of the delay operation device 113 and the optical phase synchronization control means 115 may be realized by the processing circuit 51, or the functions of each part may be realized together by the processing circuit 51.

[0137] When the processing circuit 51 is a CPU 52, the functions of the delay operation 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 described as programs and stored in the memory 53. The processing circuit 51 realizes the functions of each part by reading and executing the programs stored in the memory 53. That is, the optical beam transmitter 1 includes a memory for storing a program that, when executed by the processing circuit 51, will result in the execution of, for example, the processing shown above. Also, these programs can be said to cause a computer to execute the procedures and methods of the delay operation 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), EEPROM (Electrically EPROM), magnetic disks, flexible disks, optical disks, compact disks, mini disks, or DVDs (Digital Versatile Discs).

[0138] Regarding the functions of the delay operation device 113 and the optical phase synchronization control means 115, part of them may be realized by dedicated hardware and part by software or firmware. For example, regarding the delay operation device 113, its function can be realized by the processing circuit 51 as dedicated hardware, and regarding the optical phase synchronization control means 115, its function can be realized by the processing circuit 51 reading and executing the program stored in the memory 53.

[0139] In this way, the processing circuit 51 can realize the above-mentioned various functions by hardware, software, firmware, or a combination thereof.

[0140] Note that free combinations of each embodiment, or modifications of any components of each embodiment, or omissions of any components in each embodiment are possible.

Industrial Applicability

[0141] The optical beam transmission device according to the present disclosure can relax the manufacturing requirements compared to the prior art and is suitable for use in an optical beam transmission device that synthesizes a plurality of optical beams with phase synchronization.

Description of Reference Numerals

[0142] 1 Optical beam transmission device, 51 Processing circuit, 52 CPU, 53 Memory, 101 Laser light source, 102 Optical distribution means, 103 Optical frequency shift 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 condensing means, 111 Photoelectric conversion means, 112 Signal generation means, 113 Delay operation 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 generation 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 transmission light for each path; Optical frequency shift 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 shift by the optical frequency shift means into a local beam which is a parallel beam; Optical phase shifters provided for each path, which change the phase of the corresponding transmission light obtained by the optical distribution means according to a control signal; Optical modulators provided for each path, which modulate the transmission light after the phase change by the corresponding optical phase shifters according to a modulation electrical signal; Optical amplifiers provided for each path, which amplify the intensity of the transmission light after modulation by the corresponding optical modulators; An optical collimator array provided for each path, which converts the transmission light amplified by the corresponding optical amplifier into a transmission beam which is a parallel beam; Optical beam branching means for branching some of the transmission beams among the transmission beams obtained by the optical collimator array for each path, and respectively combining the some of the transmission beams with the local beam obtained by the collimating lens to obtain a combined phase monitor light; Photoelectric conversion means provided for each path, which photoelectrically converts the corresponding combined phase monitor light obtained by the optical beam branching means to obtain an electrical signal; Modulation electrical signal output means for outputting a modulation electrical signal with a controlled delay time to the optical modulators for each path respectively based on the electrical signals obtained by the photoelectric conversion means for each path; Optical phase synchronization control means provided for each path, which detects the phase of the electrical signal obtained by the corresponding photoelectric conversion means and outputs a control signal based on the phase to the corresponding optical phase shifter; An optical beam transmission device comprising the above.

2. Optical distribution means for branching laser light into one local light and transmission light for each path; A collimating lens that converts the local light obtained by the light distribution means into a local beam that is a parallel beam, Optical frequency conversion means provided for each path, which transitions the frequency of the corresponding transmitted light obtained by the light distribution means according to a control signal, An optical modulator provided for each path, which modulates the transmitted light after the frequency transition by the corresponding optical frequency conversion means according to a modulation electrical signal, An optical amplifier provided for each path, which amplifies the intensity of the transmitted light after modulation by the corresponding optical modulator, An optical collimator array provided for each path, which converts the transmitted light after amplification by the corresponding optical amplifier into a transmitted beam that is a parallel beam, Optical beam branching means that branches some of the transmitted beams among the transmitted beams obtained by the optical collimator array for each path, and synthesizes each of the part of the transmitted beams with the local beam obtained by the collimating lens to obtain a synthesized phase monitor light, Photoelectric conversion means provided for each path, which photoelectrically converts the corresponding synthesized phase monitor light obtained by the optical beam branching means to obtain an electrical signal, Modulation electrical signal output means that outputs a modulation electrical signal with a controlled delay time to the optical modulators for each path based on the electrical signals obtained by the photoelectric conversion means for each path, Optical frequency synchronization control means provided for each path, which detects the frequency fluctuation of the electrical signal obtained by the corresponding photoelectric conversion means and outputs a control signal based on the frequency fluctuation to the corresponding optical frequency conversion means An optical beam transmission device comprising the above.

3. The modulation electrical signal output means includes: Signal generation means for generating a modulation electrical signal, A delay calculation device provided for each path, which calculates the delay time difference between the electrical signal obtained by the corresponding photoelectric conversion means and the modulation electrical signal generated by the signal generation means, RF variable delay means provided for each of the paths, which outputs the modulated electrical signal generated by the signal generation means to the corresponding optical modulator after controlling the delay time based on the delay time difference calculated by the corresponding delay calculation device. The optical beam transmission device according to claim 1 or claim 2, characterized in that.

4. The modulated electrical signal output means includes a signal processing device provided for each of the paths, which calculates the 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 signal generation means provided for each of the paths, which outputs the modulated electrical signals having the same waveform to the corresponding optical modulator according to the timing signal generated by the corresponding signal processing device. The optical beam transmission device according to claim 1 or claim 2, characterized in that.

5. The modulated electrical signal output means includes signal generation means for generating a modulated electrical signal; delay comparison devices provided between each pair of adjacent paths, which calculate the delay time difference between the electrical signals based on the electrical signals obtained by the corresponding adjacent two photoelectric conversion means; and RF variable delay means provided for each of the paths, which outputs the modulated electrical signal generated by the signal generation means to the corresponding optical modulator after controlling the delay time based on the delay time difference calculated by the corresponding delay comparison device. The optical beam transmission device according to claim 1 or claim 2, characterized in that.

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