Abstract:
A laser apparatus includes: a laser light source; an output member for receiving and transmitting a laser light flux generated by the laser light flux, and outputting a laser light flux; an optical aligning member for positioning the laser light flux generated by the laser light source to the output member; a drive for driving the optical aligning member; a drive controller; an output detector for outputting a detected output representing an intensity of a laser light flux outputted from the output member; and an output controller. The drive controller controls the drive to drive the optical aligning member and the output controller changes a power of the laser light flux generated by the light source, based on the detected output.

Description:
[0001]    This application is a continuation of prior U.S. application Ser. No. 12/079,042, filed Mar. 24, 2009, which is based on Japanese Patent Application No. 2007-091779, filed on Mar. 30, 2007, in the Japanese Patent Office, the entire contents of which are herein incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a laser apparatus and an output control method of a laser apparatus. 
       BACKGROUND 
       [0003]    For example, U.S. Pat. No. 7,043,118 discloses a laser apparatus in which a projecting section of a laser oscillator emits a laser light flux and an optical member such as a lens aligns and guides the emitted laser light flux to a light-receiving member such as an optical fiber. It is known that an output of the laser apparatus of this kind results in Gaussian distribution for a misalignment of the laser light flux. 
         [0004]    In the U.S. Pat. No. 7,043,118, the laser light flux is positioned on the optical fiber by the method that is called wobbling. According to the method, an optical member is oscillated minutely at a certain cycle and at certain amplitude, and a change of intensity of a laser light flux in optical fiber is measured. Thereby, a direction and an amount of movement of the optical member to maximize an intensity of the received laser light flux are calculated. 
         [0005]    There is also known a control method called mountain-climbing control. According to the method, an optical member is moved by a prescribed amount in the laser apparatus of this kind, then, laser output is checked whether it increases or not. The optical member is moved repeatedly by a prescribed amount in the direction that output of the laser increases until the moment when the intensity of the received laser light flux starts decreasing. 
         [0006]    In the aligning control of the laser apparatus described above, the laser output becomes a significant value which is not zero when the alignment is operated in a range of a diameter of, for example, about 1 μm. While, positioning resolution (minimum movement amount) of the optical member is about 100 nm, for example, with an actuator of a friction drive type employing a piezoelectric element. 
         [0007]    In a conventional laser apparatus, therefore, it is difficult to position an optical member accurately at the location where the intensity of the received laser light flux becomes the maximum as shown in  FIG. 7 , for example. It causes aligning errors that a power of an actual outputted laser light flux becomes smaller than the maximum value, which has been a problem. 
         [0008]    A laser apparatus used for optical communication is requested to keep a laser output to be constant. To comply with this, it is considered that the laser output is fed back to adjust an output of a laser oscillator. However, it cannot be used together with the alignment control based on the same laser output. Therefore, in the laser apparatus in which an output of the laser oscillator is controlled, even when the laser apparatus causes a misalignment due to manufacturing errors and secular changes, or to rise of temperatures in use, the laser apparatus is controlled so as to increase the laser output. Therefore, the energy efficiency of the laser apparatus decreases, which has been a problem. 
       SUMMARY 
       [0009]    A laser apparatus relating to the present invention comprises: a laser light source for generating a laser light flux; an output member for receiving and transmitting the laser light flux generated by the laser light source, and outputting a laser light flux; and an optical aligning member for positioning the laser light flux generated by the laser light source to the output member. The laser apparatus further comprises: a drive for driving the optical aligning member; a drive controller for controlling the drive; an output detector for outputting a detected output representing an intensity of a laser light flux outputted from the output member; and an output controller for changing a power of the laser light flux generated by the light source. When the detected output is not larger than a predetermined threshold, the output controller sets the power of the laser light flux generated by the light source at a predetermined standard output, and the drive controller controls the drive to drive the optical aligning member so as to increase the detected output. When the detected output is larger than the predetermined threshold, the drive controller is stopped to statically position the optical aligning member, and the output controller controls the power of the laser light flux generated by the light source so that the detected output reaches to a predetermined target output. 
         [0010]    A method relating to the present invention is a method of controlling an output of a laser apparatus in which a laser light flux emitted by a laser light source enters into an output member and a light flux outputted from the output member is emitted to an outside of the laser apparatus. The method comprises: detecting an intensity of the laser light flux outputted from the output member; changing relative positions of the output member and a laser light flux entering into the output member; and changing a power of the laser light flux emitted by the laser light source by changing an input signal to the laser light source. The method further comprises selecting one of the followings based on the intensity of the laser light flux outputted from the output member: the step of changing the relative positions of the output member and the laser light flux entering into the output member; and the step of changing the power of the laser light flux emitted by the laser light source. 
         [0011]    A laser apparatus relating to the present invention comprises: a laser light source for generating a laser light flux with a different intensity corresponding to an input signal; an output member for receiving and transmitting the laser light flux generated by the laser light source, and outputting a laser light flux; and an optical aligning member for positioning the laser light flux generated by the laser light source to the output member. The laser apparatus further comprises: a drive for driving the optical aligning member; an output detector for outputting a detected output representing an intensity of a laser light flux outputted from the output member; and a controller for switching a drive control of the drive for driving the optical aligning member and an output control of the laser light source for changing the power of the laser light flux emitted from the laser light source, based on a signal from the output detector. 
         [0012]    These and other objects, features and advantages according to the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements numbered alike in several Figures, in which: 
           [0014]      FIG. 1  is a schematic diagram of a laser apparatus in the first embodiment of the invention; 
           [0015]      FIG. 2  is a schematic diagram of a drive apparatus of the laser apparatus in  FIG. 1 ; 
           [0016]      FIG. 3  is a block diagram showing the structure of the control unit in  FIG. 1 ; 
           [0017]      FIG. 4  is a flow chart of a control of the control unit in  FIG. 3 ; 
           [0018]      FIG. 5  is a diagram showing changes in detected output in positioning of the laser apparatus in  FIG. 1 ; 
           [0019]      FIG. 6  is a schematic diagram of a laser apparatus in the second embodiment of the invention; and 
           [0020]      FIG. 7  is a diagram showing changes in detected output in a conventional laser apparatus. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Embodiments of the invention will be explained as follows, referring to the drawings. 
         [0022]      FIG. 1  shows laser apparatus  1  in the first embodiment of the invention. The laser apparatus  1  includes therein laser diode (laser light source)  3 , projecting lens  4  positioned statically, aligning lens (optical aligning member)  7 , second harmonic generating element (output member)  8  and output lens  9 . The laser diode  3  converts electric power inputted from power circuit  2  and generates a laser light flux. The aligning lens  7  can be moved in two directions of X and Y perpendicular to the laser light flux by a drive apparatus (drive) to which the drive voltage is impressed from drive circuit  5 . The laser light flux passing through the projecting lens  4  and the aligning lens  7  enters into the second harmonic generating element  8 . The output lens  9  emits an outputted light flux of the second harmonic generating element  8 . Further, the laser apparatus  1  includes therein beam splitter  10 , power monitor (output detector)  11  and control unit  12 . The beam splitter  10  branches a portion of the outputted light flux of the second harmonic generating element  8 . The power monitor  11  converts intensity of the branched portion of the outputted light flux of the second harmonic generating element  8  into voltage signals (detected output). The control unit  12  controls operations of power circuit  2  and drive circuit  5  in accordance with detected output of power monitor  11 . 
         [0023]    The outputted light flux which has passed through the beam splitter  10  can be utilized for, for example, a scanning projector. An infrared laser light flux emitted from laser diode  3  is converted into a green light flux through the second harmonic generating element  8 , and an optical path of the green light flux is merged with those of a red laser light flux and a blue laser light flux. Thereby, a color projected image is obtained with using a mirror deflecting the light fluxes in two dimensional direction and a projecting optical system. 
         [0024]    The second harmonic generating element  8  has a light-receiving section with an aperture of about 1-3 μm. The aligning lens  7  converges a laser light flux so that it may become the same as the light-receiving section in terms of a diameter, and aligns an optical axis of the laser light flux to the center of the light-receiving section of the second harmonic generating element  8 . 
         [0025]    When the optical axis of the laser light flux is aligned to the center of the second harmonic generating element  8  by the aligning lens  7 , all energy of the laser light flux is inputted in the second harmonic generating element  8 . Therefore, an output of a second harmonic generating by the second harmonic generating element  8  becomes the maximum and the detected output of the power monitor  11  also becomes the maximum. 
         [0026]    In the laser apparatus relating to the present invention, the drive apparatus  6  can be composed of a general linear actuator which positions the aligning lens  7  in directions perpendicular to the optical axis of the laser light flux. 
         [0027]      FIG. 2  shows a structure of drive apparatus  6  that moves the aligning lens  7 . The drive apparatus  6  is composed of X-axis actuator  14  and Y-axis actuator  15 . The X-axis actuator  14  is fixed on case  13 . The Y-axis actuator  15  is moved by the X-axis actuator  14  in the X-axis direction and moves the aligning lens  7  in the Y-axis direction. 
         [0028]    The X-axis actuator  14  is fixed on case  13  at its one end, and is composed of X-axis piezoelectric element  16 , X-axis drive shaft  17 , X-axis friction-engaging member  18  and X-axis stopper  19 . The X-axis piezoelectric element  16  expands and contracts in the X-axis direction when it is impressed by voltage. The X-axis drive shaft  17  reciprocates in the X-axis direction when the X-axis piezoelectric element  16  expands and contracts. The X-axis friction-engaging member  18  engages with the X-axis drive shaft  17  through friction. The X-axis stopper  19  is provided on a tip of the X-axis drive shaft  17 . 
         [0029]    The Y-axis actuator  15  is fixed on the X-axis friction-engaging member  18  at its one end, and is composed of Y-axis piezoelectric element  20 , Y-axis drive shaft  21 , Y-axis friction-engaging member  22  and Y-axis stopper  23 . The Y-axis piezoelectric element  20  expands and contracts in the Y-axis direction when it is impressed by voltage. The Y-axis drive shaft  21  reciprocates in the Y-axis direction when the Y-axis piezoelectric element  20  expands and contracts. The Y-axis friction-engaging member  22  engages with the Y-axis drive shaft  21  through friction. The Y-axis stopper  23  is provided on a tip of the Y-axis drive shaft  21 , and the Y-axis friction-engaging member  22  supports the aligning lens  7 . The X-axis friction-engaging member  18  can move within a range from the X-axis piezoelectric element  16  and the X-axis stopper  19 , and the Y-axis friction-engaging member  22  can move within a range from the Y-axis piezoelectric element  20  and the Y-axis stopper  23 . 
         [0030]      FIG. 3  shows a structure of control unit  12 . The control unit  12  includes therein threshold value distinguishing section (distinguishing section)  24 , and aligning control section (drive controller)  27  and output control section (output controller)  28 . A detected output of the power monitor  11  is inputted to the threshold value distinguishing section  24 . The detected output of the power monitor  11  is inputted to each of the aligning control section  27  and output control section  28  respectively through switch  25  and switch  26  controlled by threshold value distinguishing section  24 . As a result of an action of switch  25  and an action of switch  26  which are opposite to each other, any one of the aligning control section  27  and output control section  28  outputs signal corresponding to detected output of power monitor  11 . 
         [0031]    For example, drive circuit  5  is a bridge circuit composed of a transistor impressing prescribed voltage respectively to X-axis piezoelectric element  16  and Y-axis piezoelectric element  20  of drive apparatus  6 . Aligning control section  27  outputs signals for turning on or turning off of a transistor of drive circuit  5  in accordance with detected output of power monitor  11 . 
         [0032]    Power circuit  2  is, for example, a fixed voltage circuit that applies current with a predetermined current value to laser diode  3 , and it normally outputs predetermined standard current. However, when output control section  28  applies voltage signals to the power circuit  2 , the power circuit provides an output current which is offset from the standard current in proportion to the voltage signals. 
         [0033]      FIG. 4  shows a flow chart of a control in the control unit  12  relating to the present invention. First, when laser apparatus  1  starts output, threshold distinguishing section  24  turns switch  25  on and turns switch  26  off in step S 1 . Thereby, output of the output control section  28  disappears, and power circuit  2  outputs predetermined standard current to cause the laser diode  3  to generate a laser light flux with a predetermined power. 
         [0034]    A laser light flux emitted from laser diode  3  is inputted in second harmonic generating element  8  through aligning lens  7 , and the second harmonic generating element  8  emits an outputted light flux that is proportional to intensity of the inputted laser light flux. Power monitor  11  detects the intensity of the outputted light flux of the second harmonic generating element  8 , and inputs it in threshold distinguishing section  24  and aligning control section  27  as detected output representing a voltage signal. 
         [0035]    The aligning control section  27  conducts aligning control called wobbling to bring an optical axis of a laser light flux guided by aligning lens  7  close to the center of the second harmonic generating element  8  as followings (step S 2 ). The aligning control section  27  detects changes of detected output by switching the drive circuit  5  so as to move the aligning lens  7  by a predetermined minute amount back and forth. Then, the aligning control section  27  switches drive circuit  5  so as to drive the aligning lens  7  by an amount obtained by multiplying a change of detected output by a predetermined coefficient. 
         [0036]    For example, as shown in  FIG. 5 , the detected output is gradually enhanced by bringing the laser light flux close to the center of the second harmonic generating element  8  in order of points P 1 , P 2 , P 3 , and P 4 . 
         [0037]    Threshold value distinguishing section  24  confirms detected output of power monitor  11  in step S 3  each time the aligning control section  27  conducts wobbling in step S 2 , in  FIG. 4 . When the detected output is not higher than a predetermined adjustment threshold value, the threshold value distinguishing section  24  keeps switch  25  turned on and switch  26  turned off. Thereby, aligning control by the aligning control section  27  in step S 2  is repeated. 
         [0038]    When the detected output exceeds a predetermined adjustment threshold value in step S 3 , the threshold value distinguishing section  24  turns switch  25  off to statically position the aligning lens  7  by stopping operations of the aligning control section  27 , and turns switch  26  on to increase and reduce output of the power circuit  2  (from point P 4  to P 5  in  FIG. 5 ) with output control section  28  so that the detected output may agree with a predetermined target output (step S 4 ). 
         [0039]    As described above, an optical aligning member aligns a laser light flux to reduce a loss of the laser light flux caused by misalignment, and output control adjusts just a slight error in output remaining within a range close to the limitation of positioning accuracy of the optical aligning member, whereby a constant amount of output is obtained. Therefore, it exhibits a high energy-efficiency. Further it can cope with both of misalignment of a laser light flux in the laser apparatus and property change of a laser light source, which further exhibits a high reliability. 
         [0040]    In step S 5 , the threshold value distinguishing section  24  monitors an output of the output control section  28 , namely, a predetermined value of output current (electric power) of power circuit  2  to be inputted in laser diode  3 . If an output of the output control section  28  does not apply input current (input signal) with a current value that is the predetermined upper limit value or higher to laser diode  3 , the threshold value distinguishing section  24  makes the output control section  28  continue the output control with keeping the switch  25  turned off and keeping the switch  26  turned on as they are. 
         [0041]    However, when an output of the output control section  28  reaches to apply an input current with the current value that is the predetermined upper limit value or higher to laser diode  3 , the threshold value distinguishing section  24  turns switch  25  on and turns switch  26  off again. Owing to this, the flow returns to step S 1 . The output of power circuit  2  returns to the standard current, then, the aligning control section  27  controls drive circuit  5 , and a laser light flux is aligned by a movement of the aligning lens  7  due to drive apparatus  6 . 
         [0042]    When elongations of respective members caused by temperature rise in use, relative position between members or optical properties changes. It causes a situation such as misalignment of the laser light flux from second harmonic generating element  8 . Thereby, the rise of an output of the output control section  28  as described above can be caused. Namely, the threshold value distinguishing section  24  monitors the positional misalignment of a laser light flux by monitoring input electric power of laser diode  3 . 
         [0043]    When the output of power circuit  2  returns to the standard current, power of the light flux emitted from the laser diode  3  decreases. However, it does not cause substantial problem in actual use when the aligning lens  7  re-aligns a light flux within a range such that, in a example of a scanning projector, the outputted light flux which returns from the end position to the start position of the scanning of the projected image does not enters into a projecting optical system. 
         [0044]    Further, the threshold value distinguishing section  24  of the above embodiment monitors an input signal from output control unit  28  to power circuit  2 . Alternatively, the threshold value distinguishing section  24  can detect and monitor an input current (input signal) from power circuit  2  to laser diode  3 , or a power (intensity) of an outputted light flux of the laser diode  3 . 
         [0045]    According to the structure, misalignment caused by a rise of temperature in use is detected by a rise of electric power inputted to a laser light source, and the optical aligning member is driven again for the alignment, whereby, high energy efficiency can be assured constantly. 
         [0046]    Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein. 
         [0047]    As in the second embodiment shown in  FIG. 6 , the laser apparatus alternatively can provide projecting lens  4  capable of being driven to move in the Y-axis direction as a first moving member and to provide aligning lens  7  capable of moving in the X-axis direction as a second moving member. 
         [0048]    Further, the laser apparatus relating to the present invention can also be applied to a laser apparatus movable on only one axis and to a laser apparatus that can be positioned on three axes or more, without being limited to the aforesaid embodiment. 
         [0049]    Further, the laser apparatus relating to the present invention can also employ a known control process which drives an optical aligning member so as to make the detected output maximum, for example, mountain-climbing control, in place of the wobbling.