Circuit And Method For Lessening Noise In A Laser System Having A Frequency Converting Element

• US 20080144678A1
• Filed: 12/05/2007
• Published: 06/19/2008
• Est. Priority Date: 12/14/2006
• Status: Active Grant

• Current Assignee: Lumentum Operations, LLC (Lumentum Holdings Inc.)
• Original Assignee: JDS Uniphase Corporation (Lumentum Holdings Inc.)
• Inventors: Issier, Vincent, Miller, Andy, Simons, David, Lu, Haiping
• Granted Patent: US 7,826,502 B2
• Time in Patent Office: Days
• US Class Current: 372/22
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence

Abstract

A method and circuit is disclosed for a laser system wherein the power of the laser signal is kept at a constant near optimum value and a portion of an frequency doubled output signal is monitored and detected so that noise within the frequency doubled output signal can be minimized. A feedback signal is used to dither the temperature of a frequency doubled crystal so as to minimize the noise in the frequency doubled output signal.

Claims

1. A method of controlling the output signal generated by a frequency converting crystal comprising the steps of:

a) providing a frequency converting crystal with light of a first wavelength at an input end thereof;

b) detecting a portion of frequency converted light exiting an output end of the frequency converting crystal and converting the portion of frequency converted light to an electrical signal;

c) determining from the electrical signal, a level of noise present in the detected portion of the frequency converted light; and

d) repeatedly varying the temperature of the frequency converting crystal upward and downward, while continuing to perform steps (b) and (c) so as to minimize the RMS noise present in the frequency converted light.

2. A method as defined in claim 1, wherein the power of the frequency converted light exiting an output end of the crystal is maintained at a constant value during steps (b) through (d), and wherein the step of repeatedly varying the temperature upward and downward is performed by varying the temperature in predetermined increments.

3. A method as defined in claim 2 wherein the step of repeatedly varying the temperature of the frequency converting crystal upward and downward includes the step of varying the temperature upward or downward numerous times prior to varying the temperature in an opposite direction.

4. A method as defined in claim 3, wherein the temperature is varied in a same direction, upward, or downward in dependence upon the relative level of noise detected.

5. A method as defined in claim 3 wherein the temperature is varied in an opposition direction from upward to downward, or from downward to upward if the noise level detected is determined to be increasing from a last recorded value.

6. A method as defined in claim 3 wherein the converting crystal is a frequency doubling crystal.

7. A circuit for generating a low noise short wavelength signal comprising:

a laser for providing a first optical signal having a first wavelength;

a frequency converting element positioned to receive the first optical signal from the laser and for converting the first optical signal into a second optical signal having a shorter wavelength than the first wavelength;

a detector for detecting a portion of the second optical signal and for providing a first electrical signal having characteristics dependent upon the second optical signal;

a first control circuit responsive to the first electrical signal and for determining an optical power value and a noise value corresponding to power and noise present in the second optical signal in dependence upon characteristics of the first electrical signal;

a second control responsive to input from the first control circuit in communication with the laser for maintaining the power of the laser at a constant value;

a third control circuit responsive to input from the first control circuit for varying the temperature in a continuous manner so as to lessen noise present in the second optical signal.

8. A circuit for generating a low noise short wavelength signal as defined in claim 7, wherein the laser is a DPSS laser.

9. A circuit for generating a noise short wavelength signal as defined in claim 8, further including a Bragg grating for providing a narrow width optical signal, wherein the Bragg grating is disposed between the DPSS laser and the frequency converting element.

10. A circuit for generating a noise short wavelength signal as defined in claim 9 wherein the frequency converting element is a frequency doubling crystal.

11. A circuit for generating a noise short wavelength signal as defined in claim 7, wherein the frequency converting element is a frequency doubling crystal.

12. A circuit for generating a low noise short wavelength optical signal comprising:

a laser for providing a first optical signal having a first wavelength longer than the short wavelength signal;

a frequency converting element positioned to receive the first optical signal from the laser and for converting the first optical signal into the short wavelength signal;

a feedback circuit for detecting a portion of the second optical signal and for adjusting the temperature of the frequency converting element upward one or more temperature increments and downward one or more temperature increments continuously so as to lessen noise present in the short wavelength signal, wherein said increases upward and downward in temperature are based on an amount of detected noise in the short wavelength signal; and

,

a control circuit for maintaining the power level of the short wavelength signal to be at a constant value while the feedback circuit lessens noise present in the short wavelength signal.