Fiber optical circulator

Details Fiber optical circulator Fiber optical circulator

1999-01-26

2001-10-30

Lee, John D. (Department: 2874)

Optical waveguides

Polarization without modulation

C385S036000, C385S047000, C359S490020

Reexamination Certificate

active

06310989

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to the field of fiber optical circulators. More particularly, the present invention relates to the field of compact, low cost and high performance optical circulators with at least three ports, which can expanded to more ports.
2. Description of the Prior Art
In general, the fiber optical circulator transfers light from a port to another sequentially. It has at least three ports. The light enters the circulator through a first port and exits through a second port. Another light that enters the second port exits through a third port and so on. Since the optical circulator is an inherently non-reciprocal device, the light never goes to other ports.
Such an optical device has a broad range of applications in the field of fiber optic communication systems, such as in bi-directional communication, dense Wavelength Division Multiplexing (WDM) and Dispersion Compensation.
Many types of optical circulators have been developed and manufactured. However, the high cost and bulky size of the circulator have limited the popular acceptance for system applications.
SUMMARY OF THE INVENTION
The present invention is a novel and unique compact fiber optical circulator that consists of three optical fibers contained in one capillary sharing one collimate lens and one walk-off crystal. Its unique structure reduces both the costs of material and the overall size of the circulator. A folding configuration is used to further reduce the size by reducing the number of crystals used.
In summary, a light beam is fed from a fiber in the first port of a capillary, then collimated before being bent to be parallel to the optical axis of the collimate lens by the angled part of a combined prism. The light beam then passes to a birefringent crystal where it is divided into two orthogonal components, o and e light component with displacement. Then the light components pass through a device group consisting of a Faraday rotator and a pair of Half Wave Plate set in different orientation that changes the State of Polarization (SOP) of two components into the same. The light components then passed a second crystal which optical axis being set in the way that allows passage of the components with that SOP without displacement.
The second Faraday rotator following the crystal then rotates both light components 45°, and the light components are reflected off a mirror, passing back through the second Faraday rotator, which rotates the SOP of the light components an additional 45°, thereby putting the SOP of both components perpendicular to that of ongoing beam. The light components then pass back through the second crystal and receive displacement due to their SOP. Then the light components pass back through the device group of half wave plates and first Faraday rotator, transferring both SOP of light components into orthogonal, are combined into one light beam by the first crystal, thereafter the beam passes through a flat portion of the combined prism and is focused into a second fiber of the capillary by the collimate lens.
The optical path of port
2
to port
3
is similar to above. The SOP in each optical part are the same as that in process of port
1
to
2
. The light from the fiber in port
2
is collimated to be parallel to the optical axis. It passes through the central flat part of prism and other parts, and is reflected by the mirror. The return beams from the mirror receive a displacement from the second crystal. The displacement shifts the light beam to the angled part of the combined prism that provides angle correction for beam to meet requirement for the fiber to receive the light. The beam is finally focused into the fiber in port
3
.
The invention may be expanded to five or more ports by the use of an n-phase prism with n surfaces set in different angles in place of the combined prism.
Further novel features and other objects of the present invention will become apparent from the following detailed description, discussion and the appended claims, taken in conjunction with the drawings.


REFERENCES:
patent: 5471340 (1995-11-01), Cheng et al.
patent: 5878176 (1999-03-01), Cheng
patent: 5930039 (1999-07-01), Li et al.
patent: 6052228 (2000-04-01), Xie et al.
patent: 6154581 (2000-11-01), Lu et al.
patent: 6192175 (2001-02-01), Li et al.

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