Laser light generator

• US 5,771,255 A
• Filed: 02/11/1997
• Issued: 06/23/1998
• Est. Priority Date: 02/22/1996
• Status: Expired due to Fees

• Current Assignee: KDDI Corporation
• Original Assignee: Kokusai Denshin Denwa KK (KDDI Corporation)
• Inventors: Yamamoto, Shu, Horiuchi, Yukio, Akiba, Shigeyuki
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US08/799,119
• Time in Patent Office: 497 Days
• Field of Search: 372/26, 372/31, 372/32, 372/29, 372/19, 372/38
• US Class Current: 372/31
• CPC Class Codes: H04B 10/504 using direct modulation
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/5051 using a series, i.e. cascade, combination of modulators
• CPC Class Codes: H04B 10/50593 to control the modulating signal amplitude including amplitude distortion
• CPC Class Codes: H04B 10/50597 to control the phase of the modulating signal
• CPC Class Codes: H04B 10/564 Power control

Abstract

A laser light generator includes an adder 12 which adds an optical frequency modulation signal Sm onto a d.c. voltage for driving a laser diode 10 for continuous laser oscillation, and applies the sum signal to the laser diode 10 to drive it. An light output from the laser diode 10 is introduced to an optical intensity controller 14 that is controlled by a control signal prepared by adjusting the optical frequency modulation signal Sm both in phase and in amplitude by a phase adjusting circuit 16 and an amplitude adjusting circuit 18. The optical intensity controller 14 may be an electroabsorption modulator that changes its transmissivity in response to an output voltage of the circuit 18. Quantities of adjustment by the circuits 16 and 18 are determined so that fluctuation in transmissivity of the optical intensity controller 14 suppresses intensity fluctuation of the light output of the laser diode 10.

Claims

1. A laser light generator comprising:

a laser source driven for continuous laser oscillation by a drive signal superposed with an optical frequency modulation signal Sm; and

optical intensity fluctuation suppressing means substantially responsive to said optical frequency modulation signal Sm for suppressing optical intensity fluctuation contained in an light output from said laser source.

2. The laser light generator according to claim 1 wherein said optical intensity fluctuation suppressing means includes:

phase/amplitude adjusting means for adjusting at least one of the phase and the amplitude of said optical frequency odulation signal Sm; and

optical intensity control means responsive to an output signal from said phase/amplitude adjusting means for controlling the intensity of the light output of said laser source to thereby suppress optical intensity fluctuation contained in the light output of said laser source.

3. The laser light generator according to claim 2 wherein said optical intensity fluctuation suppressing means further includes:

residual fluctuation detecting means for detecting residual of optical intensity fluctuation components caused by said optical frequency modulation signal Sm from the light output of said optical intensity control means;

correlation detecting means for detecting correlation between an output signal from said residual fluctuation detecting means and said optical frequency modulation signal Sm; and

amplitude control means responsive to a correlation rate detected by said correlation detecting means for controlling the quantity of amplitude adjustment by said phase/amplitude adjusting means.

4. The laser light generator according to claim 2 or 3 wherein said optical intensity control means comprises optical amplifier means controllable in amplification gain by an external control signal.

5. The laser light generator according to claim 2 or 3 wherein said optical intensity control means comprises light transmission means controllable in accordance with a attenuation factor by an external control signal.

6. The laser light generator according to claim 2 or 3 wherein said optical intensity control means comprises one selected from the group of a Mach-Zehnder interferometer-type modulator, optical filter, optical attenuator, semiconductor laser amplifier or optical fiber amplifier.

7. The laser light generator according to claim 1 further comprising optical modulator means for modulating the light output of said optical intensity fluctuation suppressing means with a data signal Sd.

8. A laser light generator comprising:

a laser source driven for continuous laser oscillation by a drive signal superposed with an optical frequency modulation signal Sm;

phase/amplitude adjusting means for adjusting at least one of the phase and the amplitude of said optical frequency modulation signal Sm;

composite means for compounding said optical frequency modulation signal Sm adjusted at least phase or amplitude by said phase/amplitude adjusting means with a data signal Sd;

optical modulating means for modulating the light output of said laser source in response to an output of said composite means, for thereby suppressing optical intensity fluctuation contained in the light output of said laser source, and for outputting an optical signal intensity-modulated by said data signal Sd.

9. The laser light generator according to claim 8, further comprising:

residual fluctuation detecting means for detecting residual of the optical intensity fluctuation components caused by said optical frequency modulation signal Sm from the light output of said optical modulator means;

correlation detecting means for detecting correlation between an output signal from said residual fluctuation detector means and said optical frequency modulation signal Sm; and

amplitude control means responsive to a correlation rate detected by said correlation detecting means for controlling the quantity of amplitude adjustment by said phase/amplitude adjuster means.

10. The laser light generator according to claim 8 or 9 wherein said optical modulator means comprises optical amplifier means controllable in amplification gain by an external control signal.

11. The laser light generator according to claim 8 or 9 wherein said optical modulator means comprises light transmission means controllable in attenuation factor by an external control signal.

12. The laser light generator according to claim 8 or 9 wherein said optical modulator means comprises one selected from the group of a Mach-Zehnder interferometer-type modulator, optical filter, optical attenuator, semiconductor laser amplifier 11 or optical fiber amplifier.

13. The laser light generator according to claim 8 wherein said composite means includes:

multiplying means for multiplying the output signal from said phase/amplitude adjusting means by said data signal Sd; and

adding means for adding to an output from said multiplying means a bias that determines the operative point of said optical modulating means.

14. The laser light generator according to one of claim 8 or 9, wherein said composite means comprises adding means for adding to an output signal from said phase/amplitude adjusting means a bias that determines the operative point of said optical modulating means and said data signal Sd.