Optical: systems and elements – Polarization without modulation – Depolarization
Reexamination Certificate
1999-07-23
2001-06-19
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Polarization without modulation
Depolarization
C359S506000, C359S490020
Reexamination Certificate
active
06249379
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical beam power controllers and, in particular, to power controllers using a tiltable birefringent plate for fast, continuous control.
BACKGROUND OF THE INVENTION
Optical beam power controllers are useful in a wide variety of practical and experimental applications such as optical communications, optical instrumentation and optical inspection systems. Typically the beam is a linearly polarized laser beam.
A wide variety of techniques have been used to control beam power, but none provide fast, continuous control with low loss, small beam displacement and minimal group-velocity dispersion. Traditional methods include translation of neutral density filters with spatially varying optical density. They also include acousto-optical, electro-optical, and liquid-crystal modulation as well as variation of Fresnel reflections and the rotation of half-wave plates. The methods vary widely in their speed, dynamic range, effects on beam-pointing, wavelength sensitivity, dispersion, and cost.
Electro-optical and acousto-optical methods are by far the fastest (sub-&mgr;s). They are widely employed where speed is essential such as in pulse-pickers or in fluorescence lifetime instrumentation. Unfortunately they are expensive.
Acousto-optical modulators (Bragg cells) have a large dynamic range but high insertion losses (10-20%). They also have angular wavelength dispersion in the diffracted beam which complicates use with very short laser pulses. The fundamental (undiffracted) beam affords, at best, a 10:1 intensity modulation.
Electro-optical modulators (Pockels-cells) require high voltages or small apertures, which complicates alignment, in conjunction with a long optical pathlength, which causes group-velocity dispersion.
Methods that involve the mechanical movement of optical elements are slower than acousto-optical and electro-optical techniques but are generally more cost effective. Variable neutral density (ND) filters suffer from intensity variations across the beam, laser power dependent thermal-lensing effects, and beam pointing variations. Rotation of half-wave plates suffers from pointing variations if the plate surfaces are not perfectly parallel. Both variable ND filters and rotating half-wave plates require typically tens of milliseconds to change the intensity. Accordingly there is a need for an inexpensive beam power controller providing fast, continuous control.
SUMMARY OF THE INVENTION
The present invention is an inexpensive optical beam power controller for providing fast, continuous control of a linearly polarized optical beam, such as a beam from a laser. In essence, the controller comprises a birefringent plate tiltable in relation to the beam and a polarization analyzer. Alternative double pass embodiments reduce beam displacement and the required tilt angle.
REFERENCES:
patent: 5033828 (1991-07-01), Haruta
Agere Systems Guardian
Assaf Fayez
Lowenstein & Sandler PC
Schuberg Darren
LandOfFree
Optical beam power controller using a tiltable birefringent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical beam power controller using a tiltable birefringent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical beam power controller using a tiltable birefringent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2540590