JP2011254028A - Phased array laser apparatus - Google Patents

Abstract

Provided is a phased array laser apparatus that corrects a phase difference in each subarray, corrects a directivity angle of each subarray, and adjusts a focal point to a desired position using the same apparatus.
In a phased array laser apparatus that branches output light of a reference laser light source into sub-arrays, amplifies each sub-array, and performs coherent addition, reference light generated based on one of the sub-arrays for each sub-array And a quadrant optical detector 9 that converts the combined light of the subarray output light into an electrical signal for each quadrant, a translational drive mechanism 11 for an optical system that collimates the subarray output light, and a signal from the four quadrant optical detector Feedback control for detecting the optical phase difference between the reference light and the sub-array output light and performing feedback control to the optical phase modulator for the sub-array, and detecting the directivity direction error of the sub-array output light and performing feedback control to the translation drive mechanism And means 10.
[Selection] Figure 1

Description

  The present invention relates to a phased array laser apparatus that branches a single-frequency reference light into subarrays, optically amplifies each subarray, detects and feeds back an optical phase error between the subarrays, and coherently adds output light.

  In a phased array laser device that splits single-frequency reference light into subarrays, optically amplifies each subarray, detects and feeds back the optical phase error between the subarrays, and coherently adds the output light, directs the beam output from each subarray It is necessary to align the angle error to the order of μrad. In order to obtain a combined beam at an arbitrary distance, it is necessary to give a wavefront curvature between the subarrays. For this reason, conventionally, the optical axis is statically adjusted in the light source, the array directivity angles are made parallel to perform coherent addition, and the condensing position is changed using a telescope (see, for example, Patent Document 1 below).

JP 2000-323774 A

  However, in the conventional configuration, there is a problem that the directivity angle shifts with the input of the thermal load accompanying the optical amplification in each subarray. Another problem is that it takes time to mechanically adjust the distance between the primary mirror and the secondary mirror of the telescope to change the focusing position.

  The present invention has been made in order to solve the above-mentioned problems. The correction of the phase difference in each subarray, the correction of the directivity angle of each subarray, and the focus adjustment to a desired position are performed by the same device. An object of the present invention is to provide a phased array laser device to be performed.

  The present invention provides a phased array laser apparatus that branches the output light of a reference laser light source into subarrays, amplifies each subarray, and performs coherent addition, for each subarray, the reference light generated based on one of the subarrays And a quadrant optical detector that converts the combined light of the subarray output light into an electric signal for each quadrant, a translational drive mechanism for an optical system that collimates the subarray output light, and a signal from the quadrant optical detector. Feedback control means for detecting an optical phase difference between the reference light and the sub-array output light and performing feedback control to the optical phase modulator for the sub-array, and detecting a directivity direction error of the sub-array output light and performing feedback control to the translational drive mechanism; The phased array laser apparatus is characterized by comprising:

  According to the present invention, it is possible to provide a phased array laser apparatus that corrects the phase difference in each subarray, corrects the directivity angle of each subarray, and further adjusts the focus to a desired position using the same apparatus.

It is a schematic diagram which shows the structure of the phased array laser apparatus by Embodiment 1 of this invention. It is a schematic diagram which shows the structure of the phased array laser apparatus by Embodiment 2 of this invention. It is a schematic diagram which shows the structure of the phased array laser apparatus by Embodiment 3 of this invention.

  According to the present invention, in a phased array laser device that branches a single frequency reference light into subarrays, optically amplifies each array, and detects and feeds back the optical phase error of the subarray and coherently adds the output light. Simultaneously, the directivity angle error of each subarray is detected, and feedback control is performed to the output light collimating lens driving mechanism for each subarray, thereby correcting the directivity angle of each subarray and adjusting the focus to a desired position with the same device. Is.

  Hereinafter, a phased array laser apparatus according to the present invention will be described with reference to the drawings according to each embodiment. In each embodiment, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing the configuration of a phased array laser apparatus according to Embodiment 1 of the present invention. In FIG. 1, 1 is a reference laser light source, 2 is an optical frequency shifter, 3a to 3c are optical phase modulators, 4a to 4c are optical amplifiers, 5a to 5c are sub-array output light collimating lenses, and 6 is a reference light collimating lens. , 7 is a beam reference flat plate, 8a to 8c are condensing lenses, 9a to 9c are 4-quadrant photodetectors, 10a to 10c are arithmetic circuits constituting feedback control means, and 11a to 11c are collimating lenses for sub-array output light. 5a to 5c translational drive mechanisms, 12 denotes an optical demultiplexer. In FIG. 1, the optical paths from the optical phase modulators 3 a to 3 c to the optical amplifiers 4 a to 4 c are referred to as subarray optical paths 13 a to 13 c, respectively, and the optical path including the optical frequency shifter 2 is referred to as a reference optical path 14. The sub-array light paths 13a to 13c are not limited to three, and a plurality of sub-array light paths 13a to 13c are provided, and the sub-array output light collimating lenses 5a to 5c, the condensing lenses 8a to 8c, and the four-quadrant light detectors 9a to 9c according to the number. Arithmetic circuits 10a to 10c and translation drive mechanisms 11a to 11c are provided.

  In FIG. 1, a reference laser light source 1, an optical frequency shifter 2, optical phase modulators 3a to 3c, optical amplifiers 4a to 4c, and an optical demultiplexer 12 are light in which laser light is input and output through an optical fiber. It is a fiber type device, and the above devices are connected by an optical fiber indicated by a relatively thick broken line. Furthermore, these optical fibers are assumed to be polarization-maintaining optical fibers.

  These devices may be spatial devices that input and output laser light via a spatial optical system. In this case, however, a reflecting mirror is required to change the optical path of the laser light. It is necessary to adjust the optical axis. By using an optical fiber type device, it is not necessary to adjust the optical axis between devices, and it is difficult to be affected by disturbances such as vibration. Furthermore, since the polarization direction in the fiber is maintained by using the polarization maintaining optical fiber, the detection device and the adjustment device for the polarization direction for each sub-array become unnecessary.

  Next, the operation will be described. The reference laser light source 1 generates a continuous wave laser beam with a predetermined oscillation wavelength and output power. A reference laser light source 1 that can obtain a desired oscillation wavelength is used. In addition, in order to perform coherent addition, a narrow line width is suitable. The output power of the reference laser light source 1 is sufficiently large so that the input power to the optical amplifiers 4a to 4c is not problematic for the amplification operation of each amplifier, and sufficient power can be branched to the reference optical path 14. Use one that can output more than the required predetermined power.

  The laser light output from the reference laser light source 1 is split into a plurality of subarrays by the optical demultiplexer 12 at a predetermined ratio to the respective optical paths. One of the optical paths branched by the optical demultiplexer 12 is input to the reference optical path 14 as reference light. The other branched optical paths are input to the subarray optical paths 13a to 13c as input light for the subarray. In FIG. 1, only the subarray optical paths 13a to 13c are shown, but all the optical paths other than those used for the reference light among the optical paths branched by the optical demultiplexer 12 can be used as the subarray optical paths.

  As the optical demultiplexer 12, an optical fiber type two-branch coupler connected in a plurality of stages, an optical waveguide type branch coupler, or the like can be used. Also, the number of branches can be increased by combining these and multistage connection.

  The reference frequency branched by the optical demultiplexer 12 and input to the reference optical path 14 is given a predetermined frequency change by the optical frequency shifter 2. The frequency change given by the optical frequency shifter 2 needs to be a band that can be detected by the four-quadrant photodetectors 9a to 9c. An acousto-optic modulator (AOM) or the like can be used for the optical frequency shifter 2. When AOM is used, the frequency change amount is usually about several tens to several hundreds MHz.

  The reference light to which the frequency change is given by the optical frequency shifter 2 is output from the optical fiber to the space, and is converted into a collimated beam by the reference light collimating lens 6. The reference light collimating lens 6 can be a various lens such as a spherical lens or an aspherical lens, or a beam diameter converting optical system such as a beam expander, but the focal length is set so that the beam diameter of the collimated beam becomes a predetermined value or more. Use the appropriate one. The beam diameter of the reference light collimated beam needs to be increased so that all of the output beams from the respective subarrays can be accommodated in the reference light collimated beam.

  The laser beams branched to the subarray optical paths 13a to 13c are subjected to a phase state change by the optical phase modulators 3a to 3c in the subarrays, respectively, and then amplified by the optical amplifiers 4a to 4c.

  As the optical phase modulators 3a to 3c, an LN phase modulator using a LiNbO3 crystal or a Mach-Zehnder optical phase modulator can be used as long as it is a fiber type. As the spatial phase modulator, a spatial phase modulator using a liquid crystal element or the like can be used. In any of these, the amount of phase modulation can be controlled by the voltage applied to the element.

  The optical amplifiers 4a to 4c amplify the inputted laser light and increase it to a predetermined power. As the optical amplifiers 4a to 4c, an optical fiber amplifier, an optical amplifier using a rod type or waveguide type amplification medium, a semiconductor type amplifier, or the like can be used. The wavelength of the reference laser light source 1 and a desired amplification are used. Select a suitable one in consideration of the rate.

  The output lights of the optical amplifiers 4a to 4c are collimated into beams by the sub-array output light collimating lenses 5a to 5c and output to the space. The collimating lenses 5a to 5c have focal lengths such that the beam diameter after collimation has a predetermined value. As described above, considering the spatial arrangement of the subarray output light beam and the reference light collimated beam from each subarray, the beam diameter of the subarray output light collimated beam and the arrangement of the subarray output light (arrangement of the subarray optical paths 13a to 13c). To decide.

  The sub-array output light collimating lenses 5a to 5c have translation drive mechanisms 11a to 11c that can adjust the positions in the vertical and horizontal directions in a plane perpendicular to the output light, respectively. By changing the positions of the subarray output light collimating lenses 5a to 5c with respect to the subarray output light by the translation drive mechanisms 11a to 11c, the emission direction of the subarray output light collimated beam can be adjusted. As the translation drive mechanisms 11a to 11c, those having a position adjusting function in a direction parallel to the output light may be used. In this case, the distance from the subarray output light (the output ends of the subarray optical paths 13a to 13c) to the subarray output light collimating lenses 5a to 5c can also be adjusted, and the collimated state of the subarray output light collimated beam can be adjusted.

  The output light collimated beam from each subarray is partially reflected by the beam reference flat plate 7. At this time, the subarray output light reflected by the beam reference flat plate 7 is combined with the reference light collimated beam. The beam reference flat plate 7 is installed at an angle of approximately 45 degrees with respect to the emission direction of the subarray output light. The beam reference flat plate 7 can be a mirror with a low reflection coating on the reflection surface or an optically polished glass surface, and preferably has a non-reflection coating on the back surface. The reflectivity of the beam reference flat plate 7 is considered together with the power of the reference collimated beam so that the four-quadrant light detectors 9a to 9c can obtain the light input power necessary for obtaining sufficient detection sensitivity. Since the loss of the output optical power that is transmitted increases as the ratio increases, an appropriate reflectance is selected and used.

  The combined light of the subarray output light reflected by the beam reference flat plate 7 and the reference light collimated beam is condensed by the condensing lenses 8a to 8c, respectively, and forms beam spots on the four-quadrant light detectors 9a to 9c, respectively. To do. The condensing lenses 8a to 8c are selected with a focal length so that the diameter of the condensed beam becomes an appropriate size in consideration of the detection accuracy of the beam spot center position in the four-quadrant light detectors 9a to 9c. Use.

  In the four-quadrant light detectors 9a to 9c, the combined light of the reference light and the sub-array output light is converted into an electric signal for each quadrant and input to the arithmetic circuits 10a to 10c, respectively.

The arithmetic circuits 10a to 10c detect the optical phase difference of the sub-array output light from the beat signals of the reference light and the sub-array output light among the input electric signals. Further, the center position of the beam spot is detected by calculating the center of gravity of the combined light power of the reference light and the subarray output light input to each quadrant.
The arithmetic circuits 10a to 10c perform feedback control using the detected optical phase difference as a phase modulation amount to be input to the optical phase modulators 3a to 3c. Thereby, the phase difference of each subarray output light can be correct | amended and it can align with the same phase.
The arithmetic circuits 10a to 10c calculate the amount of deviation of the detected beam spot center position from the reference position, which is the beam spot center position when the sub array output lights are parallel, thereby directing each sub array output light. Detect direction error. Feedback control is performed using this as a position adjustment amount to be input to the translation drive mechanisms 11a to 11c. Thereby, each subarray output light can be kept parallel.

  In the above configuration, the phase error and the pointing direction error of the subarray output light can be detected at the same time by using the four-quadrant light detector, and the phase and the pointing direction can be corrected at the same time by feedback control. As a result, changes in the position of the collimating lens for subarray output light due to heat generated by the optical amplifier, ambient temperature, vibration, and the like can be corrected in real time, and the operation stability of the apparatus can be improved.

Embodiment 2. FIG.
In the first embodiment, the configuration in which each sub-array output light is made parallel (horizontal) has been described. However, the output direction of each sub-array output light is set to a desired direction by the translation drive mechanism provided in the sub-array output collimating lens. It is possible to adjust the output direction of the output light of the entire plurality of subarrays to a desired direction.

  FIG. 2 is a schematic diagram showing the configuration of a phased array laser apparatus according to Embodiment 2 of the present invention. In the sub-array output light collimating lenses 5a to 5c, the emission direction of the collimated light can be changed by the relative position of the input light and the central axis of the lens. In the configuration of FIG. 2, the arithmetic circuits 10 a to 10 c calculate the deviation amount of the detected beam spot center position from a predetermined position different from the reference position that is the beam spot center position when the subarray output lights are parallel. Thus, an error from a desired directivity direction of each subarray output light is detected. This (that is, offset pointing direction error) is used as a position adjustment amount to be input to the translation drive mechanisms 11a to 11c to perform feedback control.

  Thereby, the directivity direction of each subarray output light can be controlled to a desired directivity direction. Furthermore, by controlling all the subarray output light in a desired directivity direction, it is possible to control the directivity direction of the output light of the entire plurality of subarrays. Accordingly, the output light beam can be adjusted in an arbitrary direction without using an optical element such as a mirror. Further, it is possible to eliminate variations in the directivity direction of individual subarray output light, and to operate the apparatus stably and efficiently.

Embodiment 3 FIG.
In the second embodiment, the device for controlling the output direction of the output light of the entire plurality of subarrays while maintaining the output light of each subarray in parallel has been shown. However, the phase state and the output direction for each beam of the subarray output light are shown. By adjusting, the output light of the entire plurality of subarrays can be collected.

  FIG. 3 is a schematic diagram showing the configuration of a phased array laser apparatus according to Embodiment 3 of the present invention. In the configuration of FIG. 3, the arithmetic circuits 10a to 10c detect the beam spot center position shift amount so that the directivity directions of the sub-array output light are respectively desired directions, and input them to the translation drive mechanisms 11a to 11c. Feedback control is performed as a position adjustment amount. Thereby, as shown in FIG. 3, the directivity direction of each subarray output light is adjusted so that the output light of each subarray overlaps at one point. At the same time, feedback control is performed by adjusting the amount of phase modulation input to the optical phase modulators 3a to 3c so that the phases of the subarrays coincide at the point where the output light beams of the subarray output light intersect. Due to this (that is, the offset optical phase difference), the beams of the subarray output lights overlap at one point, and the phases coincide with each other. Therefore, the output light from each subarray is added coherently at this one point.

  With this configuration, it is possible to create a state in which the sub-array output light is condensed without using a condensing optical element such as a lens or a telescope outside. Furthermore, by simply operating the position adjustment amount of the sub-array output light collimating lens, it is possible to adjust the condensing position of the plurality of sub-array output lights as a whole and to automate the focus position adjustment.

  DESCRIPTION OF SYMBOLS 1 Standard laser light source, 2 Optical frequency shifter, 3a-3c Optical phase modulator, 4a-4c Optical amplifier, 5a-5c Collimating lens for subarray output light, 6 Reference light collimating lens, 7 Beam reference flat plate, 8a-8c Condensing lens, 9a-9c 4-quadrant light detector, 10a-10c arithmetic circuit (feedback control means), 11a-11c translational drive mechanism, 12 optical demultiplexer, 13a-13c subarray optical path, 14 reference optical path.

Claims (3)

In the phased array laser device that branches the output light of the reference laser light source into subarrays, amplifies each subarray, and performs coherent addition,
For each subarray,
A four-quadrant photodetector that converts the combined light of the reference light generated based on one of the sub-arrays and the sub-array output light into an electrical signal for each quadrant;
A translation drive mechanism for an optical system that collimates the sub-array output light;
Based on the signal from the four-quadrant optical detector, the optical phase difference between the reference light and the subarray output light is detected and feedback controlled to the optical phase modulator for the subarray, and the pointing direction error of the subarray output light is detected and Feedback control means for feedback control to the translation drive mechanism;
A phased array laser device comprising:   The feedback control means gives a desired offset to the directivity error of the subarray output light detected from the electric signal of the four-quadrant light detector and feeds back to the translation drive mechanism to control the directivity of the subarray output light in the desired direction. The phased array laser apparatus according to claim 1.   The feedback control means gives a desired offset to the optical phase difference of the sub-array output light detected from the electric signal of the four-quadrant photodetector and feeds back to the optical phase modulator to collect the sub-array output light at a desired position. The phased array laser device according to claim 2.

Images