Apparatus and method for controlling optical gain profiles in a temperature independent manner

• US 6,614,572 B2
• Filed: 05/17/2002
• Issued: 09/02/2003
• Est. Priority Date: 07/19/2001
• Status: Expired due to Term

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Coadna Photonics Incorporated (Coherent Corp.)
• Inventors: Washburn, Hudson, Kelly, Jack R., Yuan, Haiji J.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Thompson, Tim
• Application Number:
  US10/150,206
• Publication Number:
  US 20030016431A1
• Time in Patent Office: 473 Days
• Field of Search: 359/238, 359/245, 359/246, 359/248, 359/251, 359/259, 359/337.1, 359/341.4, 349/1, 349/74, 349/76
• US Class Current: 359/238
• CPC Class Codes: G02F 1/0136 for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation G02F1/0353 takes precedence
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation

Abstract

An apparatus for processing an optical beam has at least one variable optical element to dynamically alter the polarization state of a polarized optical beam to form a polarization-altered optical beam. The polarization-altered optical beam includes elliptical polarization. The at least one variable optical element is a compound birefringent crystal with a designed retardation response to temperature variations. In one embodiment, the compound birefringent crystal has a designed retardation response that is substantially invariant with operating temperature variations. At least one wave plate processes the polarized optical beam. Each wave plate has a selected retardation, order of retardation, and orientation. A polarization analyzer is operative in conjunction with the at least one variable optical element and wave plate to alter the transmitted amplitude of the polarization-altered optical beam as a function of wavelength, and thereby produce an output optical beam with transmitted amplitude adjusted as a function of wavelength.

Claims

1. An apparatus for processing an optical beam, comprising:

at least one variable optical element to dynamically alter the polarization state of a polarized optical beam to form a polarization-altered optical beam, wherein said polarization-altered optical beam includes elliptical polarization, wherein said at least one variable optical element is a compound birefringent crystal with a designed retardation response to temperature variations;

at least one wave plate to process said polarized optical beam, each wave plate having a selected retardation, order of retardation, and orientation; and

a polarization analyzer operative in conjunction with said at least one variable optical element and wave plate to alter the transmitted amplitude of said polarization-altered optical beam as a function of wavelength, and thereby produce an output optical beam with transmitted amplitude adjusted as a function of wavelength.

2. The apparatus of claim 1 wherein said compound birefringent crystal has a designed retardation response that is substantially invariant with operating temperature variations.

3. The apparatus of claim 1 wherein said compound birefringent crystal is configured to form a transmission versus wavelength slope from approximately +0.057 dB/nm at approximately −

20°

C. to approximately −

0.057 dB/nm at approximately 70°

C. with zero slope at a central temperature of approximately 25°

C. centered around a wavelength of approximately 1550 nm.

4. The apparatus of claim 3 wherein said compound birefringent crystal has nominally zero retardation at approximately 25°

C.

5. The apparatus of claim 4 wherein said compound birefringent crystal includes one or more crystals selected from the group of Rutile, YVO4, alpha-BBO, Quartz, Calcite, and Lithium Niobate.

6. The apparatus of claim 5 wherein said Rutile crystal has a 135°

optic axis orientation.

7. The apparatus of claim 5 wherein said YVO₄ crystal has a 45°

optic axis orientation.

8. The apparatus of claim 1 wherein said compound birefringent crystal is configured such that the retardation difference between a first crystal and a second crystal is positive above 25°

C.

9. The apparatus of claim 8 wherein said compound birefringent crystal has an optic axis along the optic axis of a first crystal above room temperature and along the optic axis of a second crystal below room temperature.

10. The apparatus of claim 1 wherein said at least one waveplate includes a compound birefringent crystal with a designed retardation response that is substantially invariant with operating temperature variations.

11. The apparatus of claim 1 wherein said at least one waveplate includes a half wave plate with an approximately −

63.5°

optical axis orientation.

12. The apparatus of claim 10 wherein said compound birefringent crystal includes a Rutile crystal and a YVO₄ crystal.

13. The apparatus of claim 12 wherein said Rutile crystal has a 90°

optical axis orientation.

14. The apparatus of claim 12 wherein said YVO₄ crystal has a 0°

optical axis orientation.

15. The apparatus of claim 13 wherein said Rutile crystal is combined with a supplemental crystal.

16. The apparatus of claim 15 wherein said Rutile crystal is combined with a quartz crystal.