Optical waveguides – Polarization without modulation
Reexamination Certificate
2000-09-30
2002-11-12
Healy, Brian (Department: 2874)
Optical waveguides
Polarization without modulation
C385S001000, C385S002000, C385S014000, C385S024000, C385S123000, C385S136000, C385S137000
Reexamination Certificate
active
06480637
ABSTRACT:
BACKGROUND OF THE INVENTION
Fiber optic network equipment and test equipment often require careful control of the polarization of light propagating in a fiber optic cable. One method of obtaining such polarization control is to insert a series of wave plates in the light path of the propagating light. However, utilizing wave plates typically involves directing light out of the fiber and redirecting the polarization corrected light back into an optical fiber. Such techniques are complicated and require careful alignment. Redirecting the polarization corrected light back into the optical fiber also results in back reflections and insertion losses.
In order to control the polarization of light in a fiber without the losses and alignment problems associated with wave plate systems, several patents describe a technique to control the polarization of light propagating in a fiber by applying pressure to an optical fiber. These references include U.S. Pat. No. 4,988,169 entitled “Optical Signal Control Method and Apparatus” issued to Neigle G. Walker; U.S. Pat. No. 4,753,507 entitled “Piezoelectric Loading Housing and Method” issued to Ramon P. DePaula et al; and U.S. Pat. No. 5,903,684 entitled “Independent Control of Normally Interdependent Light Transmission Characteristics of Optical Fiber” issued to Robert M. Payton. All three patents are hereby incorporated by reference.
Each of the three references describes a polarization compensation system that utilizes a plurality of fiber squeezers. Each fiber squeezer squeezes a different segment of the optical fiber. It is known that applying a transverse compressive force to a length of optical fiber changes the refractive index of the fiber via a photoelastic effect and introduces a stress induced birefringence. By applying transverse pressure along different directions, each fiber squeezer rotates the polarization of light propagating in the optical fiber about orthogonal axes on a Poincare sphere.
Although the principles of using pressure on a fiber to control polarization are well documented, one problem with building such systems is high signal losses caused by fiber squeezing. Typical activation induced losses in such systems are in the 0.5 dB range. The activation-induced loss measures the addition insertion loss caused by the activation of the device and is defined as the difference of the maximum and minimum insertion loss of the device at all activation conditions. This specification is particularly important because all polarization-impairment compensation schemes involve a feedback signal to activate the polarization controller. The activation-induced loss causes errors in the feedback signal and directly degrades the performance of the compensation apparatus. When a polarization controller is used in an instrument for measuring the polarization dependent loss (PDL) of optical components, the activation-induced loss limits the resolution and accuracy of the measurement. Controller PDL also contributes to error in the feedback system for PDL measurements and complicates the design of compensation hardware and software.
Another problem with prior art fiber squeezing systems is that high voltages are needed to drive the piezoelectric actuators that move the squeezers. Thus the driver circuits of the piezoelectric actuators require large power supplies and transformers to “step up” the voltages. These additional components increase the size and cost of the polarization controllers.
Thus an improved system for minimizing activation losses, minimizing fiber breakage and reducing the power needed to drive the piezoelectric is needed.
BRIEF SUMMARY
The present invention describes an improved polarization control system for controlling the polarization of light in an optical fiber. The systems uses various mechanisms such as piezoelectric drivers to control a fiber squeezing surface that applies a transverse compressive force to a segment of optical fiber. In one embodiment of the invention, the piezoelectric driver is driven at a resonance frequency to minimize the voltages needed to operate the piezoelectrics. The fiber-squeezing surfaces are preferably super polished to reduce irregularities below 100 microns.
REFERENCES:
patent: 3625589 (1971-12-01), Snitzer
patent: 4341442 (1982-07-01), Johnson
patent: 4389090 (1983-06-01), LeFevre
patent: 4729622 (1988-03-01), Pavlath
patent: 4753507 (1988-06-01), DePaula et al.
patent: 4793678 (1988-12-01), Matsumoto et al.
patent: 4898441 (1990-02-01), Shimizu
patent: 4923290 (1990-05-01), Brinkmeyer et al.
patent: 4960319 (1990-10-01), Dankowych
patent: 4966431 (1990-10-01), Heismann
patent: 4979235 (1990-12-01), Rumaugh et al.
patent: 4988169 (1991-01-01), Walker
patent: 5004312 (1991-04-01), Shimizu
patent: 5212743 (1993-05-01), Heismann
patent: 5903684 (1999-05-01), Payton
“Active Stabilization of Polarisation on a Single-Mode Fibre”, Electronics Letters, Apr. 26th, 1984, vol. 20, No. 9, pp. 365-366.
Mark Johnson, “In-Line Fiber-Optical Polarization transformer”, Applied Optics, May 1st, 1979, vol. 18, No. 9 pp. 1288-1289.
H. Shimizu, S. Yamazaki, T. Ono, and K. Emura, “Highly Practical Fiber Squeezer Polarization Controller” Journal of Lightwave Technology, Oct. 1991, vol. 9, No. 10, pp. 1217-1224.
“Endless Polarisation Conrtrol in Coherent Optical Communications” Electronics Letters, Jul. 17th, 1986, vol. 22, No. 15, pp. 772-773 and 1207.
R. Noe, H. Heidrich, and D. Hoffmann, “Endless Polarization Control Systems for Coherent Optics”, Journal of Lightwave Technology, Jul. 1988, vol. 6, No. 7, pp. 1199-1206.
Fish & Richardson P.C.
General Photonics Corporation
Healy Brian
LandOfFree
Fiber squeezer polarization controller with low activation loss does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fiber squeezer polarization controller with low activation loss, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fiber squeezer polarization controller with low activation loss will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2914652