Mode converter and quadrant photodiode for sensing optical cavity mode mismatch

Patent metadata

Field	Value
Publication number	US-10453971-B2
Application number	US-201816019889-A
Country	US
Kind code	B2
Filing date	Jun 27, 2018
Priority date	Jun 27, 2017
Publication date	Oct 22, 2019
Grant date	Oct 22, 2019

Abstract

A new technique for sensing optical cavity mode mismatch using a mode converter formed from a cylindrical lens mode converting telescope, radio frequency quadrant photodiodes (RFQPDs), and a heterodyne detection scheme. The telescope allows the conversion of the Laguerre-Gauss basis to the Hermite-Gauss (HG) basis, which can be measured with quadrant photodiodes. Conversion to the HG basis is performed optically, measurement of mode mismatched signals is performed with the RFQPDs, and a feedback error signal is obtained with heterodyne detection.

First claim

What is claimed is:

1. A system for sensing optical cavity mode mismatch, comprising:
a mode converter having a pair of cylindrical lenses with a focal length, wherein the pair of lenses are spaced apart by the focal length multiplied by the square root of two; and
a photodiode having quadrants aligned with the mode converter for sensing optical cavity mode mismatch.

2. The system of claim 1 , wherein the focal length of the pair of lenses is a function of a waist size of an incoming beam.

3. The system of claim 2 , further comprising a Gouy phase telescope positioned between the mode converter and the incoming beam.

4. The system of claim 3 , wherein the incoming beam comprises an optical cavity reflection containing mismatched signals.

5. The system of claim 4 , further comprising a mixer coupled to the photodiode for demodulating a signal output from the photodiode.

6. The system of claim 5 , further comprising a set of feedback electronics coupled to an output of the mixer and controlling a mode matching actuator positioned between an electro-optic modulator and an optical cavity that will produce the optical cavity reflection.

7. The system of claim 6 , further comprising an oscillator coupled between the electro-optic modulator and the mixer.

8. The system of claim 7 , wherein the feedback electronics is configured to compare the quadrants of the photodiode to produce a mode mismatching error signal.

9. The system of claim 8 , wherein the focal length of the pair of lenses is determined by f (w o )=(πw o 2 )/λ(1+1/√2).

10. A method of sensing optical cavity mode mismatch, comprising the steps of:
passing an incoming beam through a mode converter having a pair of cylindrical lenses with a focal length, wherein the pair of lenses are spaced apart by the focal length multiplied by the square root of two; and
detecting the incoming beam after the mode converter with a photodiode having quadrants to sense optical cavity mode mismatch.

11. The method of claim 10 , wherein the focal length of the pair of lenses is a function of a waist size of an incoming beam.

12. The method of claim 11 , further comprising the step of passing the incoming beam through a Gouy phase telescope before the mode converter.

13. The method of claim 12 , wherein the incoming beam comprises an optical cavity reflection containing mismatched signals.

14. The method of claim 13 , further comprising the step of using a mixer coupled to the photodiode for demodulating the signal output from the photodiode.

15. The method of claim 14 , further comprising the step of using a set of feedback electronics coupled to an output of the mixer to control a mode matching actuator positioned between an electro-optic modulator and an optical cavity that will produce the optical cavity reflection.

16. The method of claim 15 , further comprising an oscillator coupled between the electro-optic modulator and the mixer.

17. The method of claim 16 , wherein the feedback electronics compares the quadrants of the photodiode to produce a mode mismatching error signal.

18. The method of claim 17 , wherein the focal length of the pair of lenses is determined by f (w o )=(πw o 2 )/λ(1+1/√2).

Assignees

• Magana Sandoval Fabian
• Ballmer Stefan
• Vo Thomas
• Vander Hyde Daniel
• Sanders Jax
• Univ Syracuse

Inventors

• Magaña-Sandoval Fabian
• Ballmer Stefan
• Vo Thomas
• Vander-Hyde Daniel
• Sanders Jax

Classifications

• G01J1/00

  Photometry, e.g. photographic exposure meter (spectrophotometry G01J3/00; specially adapted for radiation pyrometry G01J5/00 {; exposure meters built in cameras G03B17/06}) · CPC title

• G02B23/2407

  Optical details · CPC title

• G02B27/0955

  Lenses (lenses per se G02B3/00) · CPC title

• H01S3/005

  Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B) · CPC title

• G02F1/0136

  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 title