Optical waveguides – Polarization without modulation
Reexamination Certificate
1999-04-06
2001-06-12
Ngo, Hung N. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S034000, C359S484010, C359S490020
Reexamination Certificate
active
06246807
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fiber optic devices. In particular, the invention relates to a compact optical circulator.
BACKGROUND OF THE INVENTION
Non-reciprocal devices are used in microwave and optical communications for selectively directing signals from one port to another. With the growth in fiber optic communications, there is an increasing demand for non-reciprocal components that are suitable for use with fiber optic systems. For example, isolators are used for increasing the stability of the frequency and power produced by single mode semiconductor lasers by reducing the power of light feeding back into the laser. As fiber optic systems become more sophisticated, for example with the advent of wavelength division multiplexing (WDM), there is an increased need for advanced components such as optical circulators for use in, for example, multiplexing/demultiplexing and bidirectional transmission.
A variety of circulators can be made. Many circulators have three ports. In these circulators, light incident at the first port is transmitted through the circulator to the second port. This light may then be transmitted to another optical device. Upon returning to the second port, the light is transmitted through the circulator to a third port. Often this third port is close to the first port and, in some cases, the first and third ports include optical fibers held together in contact by a common holder.
Present approaches to circulator design often rely on the use of individual collimating lenses for each fiber. This increases the complexity of aligning the device and necessitates the use of many elements.
SUMMARY OF THE INVENTION
The present invention is directed to reducing the number of elements in the circulator and also reducing the complexity of aligning the components. Generally, the present invention relates to optical circulators having a single focusing element to couple light between the circulator components and two optical fibers forming the first and third ports. The input face of the first birefringent element of the circulator is adapted for the non-parallel light paths resulting from the single focusing element, while maintaining an essentially in-line circulator geometry.
In particular, an optical circulator includes a first birefringent splitting and combining element configured to split an input beam of light propagating from a first port into orthogonally polarized first and second light paths, a first surface of the first birefringent splitting and combining element has input and output portions optically coupled respectively to the first port and a third port, the input and output portions being non-parallel. A first non-reciprocal polarization rotator is configured to rotate polarization directions of light propagating along the first and second light paths from the first splitting and combining element by approximately 45° in respectively opposing directions. A birefringent translating element is disposed along the first and second light paths and configured to laterally displace a light beam having a first polarization direction propagating therethrough and to transmit without lateral displacement a light beam having a second polarization direction orthogonal to the first polarization direction. A second non-reciprocal polarization rotator is configured to rotate electric field vectors of light propagating along the first and second light paths from the translating element by approximately 45° in opposite directions. A second birefringent splitting and combining element is configured to combine light beams propagating along the first and second light paths into an output light beam path directed to a second port.
In another embodiment, a first focusing element optically couples light from first and third ports to a first birefringent splitting and combining element along non-parallel input and output paths respectively. The first birefringent splitting and combining element is configured to split an input beam of light propagating along the input path into orthogonally polarized first and second light paths. A first non-reciprocal polarization rotator is configured to rotate polarization directions of light propagating along the first and second light paths from the first splitting and combining element by approximately 45° in respectively opposing directions. A birefringent translating element is disposed along the first and second light paths and is configured to laterally displace a light beam having a first polarization direction propagating therethrough and to transmit without lateral displacement a light beam having a second polarization direction orthogonal to the first polarization direction. A second non-reciprocal polarization rotator is configured to rotate electric field vectors of light propagating along the first and second light paths from the translating element by approximately 45° in opposite directions. A second birefringent splitting and combining element configured to combine light beams propagating along the first and second light paths into an third light path directed to a second port.
In another embodiment, an optical circulator includes a first birefringent splitting and combining means for splitting an input beam of light propagating along an input path into orthogonally polarized first and second light paths. Input and output beam directing means on a surface of the first birefringent splitting and combining means direct input and output beams passing through the surface. First non-reciprocal polarization rotation means rotate polarization directions of light propagating along the first and second light paths from the first splitting and combining means. Birefringent translating means laterally displaces a light beam having a first polarization direction propagating therethrough and for transmitting without lateral displacement a light beam having a second polarization direction orthogonal to the first polarization direction. Second non-reciprocal polarization rotation means for rotates polarization directions of light propagating along the first and second light paths from the translating means. Second birefringent splitting and combining element means combine light beams propagating along the first and second light paths into an third light path.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.
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Lu Liang-Ju
Zhang B. Barry
ADC Telecommunications Inc.
Altera Law Group
Ngo Hung N.
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