Device for driving a semiconductor laser by a plurality of driving elements

Abstract

A semiconductor laser apparatus comprises a semiconductor laser, a photodetector, first and second variable gain units, a controllable amplifying unit a driving unit, and a compensation unit. A control signal is supplied to one of input terminals of each of the first and second variable gain units and an output signal of the photodetector is negative-fed back to the other of the input terminals of each of the first and second variable gain units. A varied gain of an error between the control signal and the output signal is output independently of each of the first and second variable gain units. The controllable amplifying unit amplifies the error signal from the first variable gain unit with desired frequency characteristics. The driving unit includes a plurality of driving elements connected in parallel and supplies a driving current to the semiconductor laser in accordance with a drive control signal from the controllable amplifying unit. The compensation unit negatively feeds back a compensation current to the negative feedback terminals to compensate a phase delay on the basis of the error signal output from the second variable gain unit.

What is claimed is:  
     
       1. A semiconductor laser apparatus comprising: 
       a semiconductor laser;  
       a photodetector for detecting an output beam of said semiconductors laser;  
       a driving unit having a plurality of driving elements connected in parallel, for driving said semiconductor laser;  
       a controllable amplifying unit for receiving an externally supplied control signal and a monitor signal of said photodetector and supplying a drive signal determined by said control signal and said monitor signal of said photodetector to said driving unit, thereby feedback-controlling the output beam of the semiconductor laser; and  
       a compensation unit for actively controlling a phase of a feedback control loop constituted by said photodetector, said driving unit and said controllable amplifying unit in accordance with temporal and electrical behaviors of the feedback control loop.  
     
     
       2. The semiconductor laser apparatus according to  claim 1 , wherein said compensation unit comprises a variable gain amplifier and a CR circuit including a capacitance and a resistor, 
       the control signal and the output beam of said photodetector are delivered to input terminals of said variable gain amplifier,  
       an output terminal of said variable gain amplifier is connected to one terminal of said CR circuit, and  
       the other terminal of the CR circuit is connected to an input of said controllable amplifying unit.  
     
     
       3. The semiconductor laser apparatus according to  claim 2 , wherein said variable gain amplifier has flat frequency characteristics up to a frequency band of at least 1.5 times the control band of said variable gain amplifier. 
     
     
       4. The semiconductor laser apparatus according to  claim 1 , wherein said controllable amplifying unit includes at least a variable gain differential amplifier functioning as a first-stage amplifier, and a rear-stage amplifier having a higher gain than said first-stage amplifier. 
     
     
       5. The semiconductor laser apparatus according to  claim 4 , wherein said controllable amplifying unit includes a high-frequency addition unit provided between said first-stage amplifier and said rear-stage amplifier, said high-frequency addition unit adding a high-frequency signal to an output of said first-stage amplifier. 
     
     
       6. The semiconductor laser apparatus according to  claim 4 , wherein said controllable amplifying unit includes a D/A conversion unit for converting an externally supplied digital signal to an analog control signal and supplying the analog control signal to said first-stage amplifier in order to control the output beam in accordance with the externally supplied digital signal. 
     
     
       7. The semiconductor laser apparatus according to  claim 1 , further comprising a transient compensation unit for preventing an overshoot from occurring in the feedback control loop. 
     
     
       8. The semiconductor laser apparatus according to  claim 1 , further comprising an equalizing compensation unit for compensating for a control signal input to the feedback control loop to prevent a sag from occurring in pulse response characteristics of the output beam of said semiconductor laser. 
     
     
       9. The semiconductor laser apparatus according to  claim 1 , wherein said semiconductor laser, said photodetector, said driving unit, said controllable amplifying unit and said compensation unit are formed on one chip. 
     
     
       10. The semiconductor laser apparatus according to  claim 1 , wherein said semiconductor laser, said photodetector, said driving unit, said controllable amplifying unit and said compensation unit are formed on one chip, and said apparatus is applied to an information recording apparatus. 
     
     
       11. The semiconductor laser apparatus according to  claim 1 , wherein said semiconductor laser, said photodetector, said driving unit, said controllable amplifying unit and said compensation unit are formed on one chip, and said apparatus is applied to an information recording/reproduction apparatus. 
     
     
       12. A semiconductor laser control device for supplying a high-frequency superimposed drive current to a semiconductor laser, comprising: 
       
         a control circuit which receives a control signal and processes the control signal to obtain a signal output corresponding to an amount of emission light from semiconductor laser;  
       
       
         a high-frequency signal generating circuit which generates a high-frequency signal for reducing noise caused by light returning to the semiconductor laser; and  
       
       
         an addition unit which adds the high-frequency signal to the signal output from the control circuit,  
       
       
         wherein the control circuit, the high-frequency signal generating circuit, and the addition unit are integrally fabricated on one chip. 
       
     
     
       13. A semiconductor laser control device according to  claim 12 , wherein the control circuit includes an amplifier having a gain control terminal. 
     
     
       14. A semiconductor laser control device according to  claim 12 , wherein the control circuit receives a detection signal, other than the control signal, obtained by detecting an output beam of the semiconductor laser. 
     
     
       15. A semiconductor laser control device according to  claim 12 , further comprising a driver transistor which outputs the high-frequency superimposed drive current to the semiconductor laser. 
     
     
       16. A semiconductor laser control device for supplying a high-frequency superimposed drive current to a semiconductor laser, comprising: 
       
         a control circuit which receives a control signal and processes the control signal;  
       
       
         a high-frequency signal generating circuit which generates a high-frequency signal for reducing noise caused by light returning to the semiconductor laser;  
       
       
         a terminal disposed to couple the high-frequency signal generating circuit with an external resistor; and  
       
       
         an addition unit which adds the high-frequency signal to an output signal from the control circuit,  
       
       
         wherein the control circuit, the high-frequency signal generating circuit, the terminal, and the addition unit are integrally fabricated on one chip. 
       
     
     
       17. A semiconductor laser control device according to  claim 16 , wherein the control circuit includes an amplifier having a gain control terminal. 
     
     
       18. A semiconductor laser control device according to  claim 16 , wherein the control circuit outputs a signal for adjusting an amount of emission light from the semiconductor laser. 
     
     
       19. A semiconductor laser control device according to  claim 16 , wherein the control circuit receives a detection signal, other than the control signal, obtained by detecting an output beam of the semiconductor laser. 
     
     
       20. A semiconductor laser control device according to  claim 16 , further comprising a driver transistor which outputs the high-frequency superimposed drive current to the semiconductor laser. 
     
     
       21. A semiconductor laser control device including an auto-power-control circuit for negatively feeding back a detection signal obtained by detecting an output beam of a semiconductor laser to control an amount of emission light from the semiconductor laser, wherein the improvement comprises: 
       
         a high-frequency signal generating circuit integrated with the auto-power control circuit within one chip, the high-frequency signal generating circuit generating a high-frequency signal for reducing noise caused by light returning to the semiconductor laser. 
       
     
     
       22. A semiconductor laser control device according to  claim 21 , wherein the auto-power-control includes an amplifier having an inverted input terminal supplied with the detection signal. 
     
     
       23. A semiconductor laser control device according to  claim 21 , further comprising a driver transistor which outputs a high-frequency superimposed drive current to the semiconductor laser.