This invention relates generally to optical isolators, circulators and interleavers, and more particularly to wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers with wavelength dependent bi-directionality.
Optical communications systems, as well as other optical technologies, require devices that manipulate optical signals that are in the form of light rays. One of the best known apparatus for such manipulation is the silica based optical fiber which is widely used for both short and long distance optical transmission. Additionally, other well known apparatus include couplers and multiplexers that have been developed to couple one or more optical signals into one or more optical fibers or waveguides. Some applications for transmission of optical signals also desirably use non-reciprocal apparatus or devices, where the propagation characteristics of light within the apparatus depends upon the direction of light propagation within the apparatus.
One type of such a non-reciprocal device is an optical circulator. An optical circulator has 3 or more. ports which permit light to pass from a first to a second port, for example, but not from the second port to the first port; instead light entering the second port passes to a third port. Another type of non-reciprocal device is an isolator. An isolator may be thought of as a two-port circulator. However, the term isolator is the preferred term.
Many types of optical devices, including circulators and isolators, have been developed for commercial applications. For many applications, such a device should be polarization independent to the external world; that is, device operation should not depend upon the polarization of the incoming light.
An optical isolator is a device that allows transmission of light in only one direction, but not in the opposite direction. It is widely used in optical systems to prevent unwanted optical back-reflection, which cause degradation of system performance. Optical isolators are required in particular in fiber-optic data transmission systems. The optical isolators are intended to prevent light reflected or diffracted at interfaces from impinging on optically active components, for example laser diodes or optical fiber amplifiers, and adversely affecting their operation.
The basic structure of a conventional optical isolator is composed of two polarizers and one Faraday rotator as shown in FIG. 1. The Faraday rotator rotates the polarization direction of linearly polarized input light by 45 degrees, but the rotation direction is dependant on the optical transmission direction. It is clockwise and counterclockwise for the light propagating to right and left, respectively, and this feature is the origin of nonreciporocity of the optical isolator. The two polarizers are aligned to have the difference of 45 degrees between their polarization axes.
When the light travels from left to right, it is vertically polarized by POL1, rotated by 45 degree in polarization direction by the Faraday rotator, and then goes through POL2 without undergoing optical loss. On the other hand, when the light travels from right to left, the polarization changed by Faraday rotator is orthogonal to POL1, and it is completely blocked by POL1.
The optical isolator of FIG. 1 does not function properly when the input beam has random polarization, because the light with polarization orthogonal to the first polarizer cannot be transmitted. This produces unacceptable polarization dependent loss for optical transmission systems.
There is a need for an improved wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal interleavers. There is a further need for wavelength selective optical isolators, wavelength dependent circulators and non-reciprocal interleavers that have wavelength dependent bi-directionality.
According, an object of the present invention is to provide an improved wavelength dependent optical isolator.
Another object of the present invention is to provide an improved wavelength dependent circulator.
A further object of the present invention is to provide an improved non-reciprocal wavelength interleaver
Yet another object of the present invention is to provide wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers which allow different wavelengths to go in different directions.
Still another object of the present invention is to provide wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers that permit different wavelengths to go in opposite directions.
Another object of the present invention is to provide wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers with wavelength dependent bi-directionality.
A further object of the present invention is to provide wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers with adjustable wavelength directionality.
Yet another object of the present invention is to provide wavelength dependent optical isolators, wavelength dependent circulators and non-reciprocal wavelength interleavers with switchable wavelength directionality.
These and other objects of the present invention are achieved in an optical data apparatus with a first polarization splitter configured to receive an input and split the input into first and second orthogonal polarizations. A second polarization splitter is included and configured to combine the first and second orthogonal polarizations. A non-reciprocal phase rotator is positioned between the first and second polarization splitters. At least one birefringent crystal is positioned between the first and second polarization splitters to create wavelength dependent bi-directionality.
In another object of the present invention, an optical data apparatus includes a first isolator with a first polarization splitter configured to receive an input and split the input into first and second orthogonal polarizations, and a second polarization splitter configured to combine the first and second orthogonal polarizations. A non-reciprocal phase rotator is positioned between the first and second polarization splitters. At least one birefringent crystal is positioned between the first and second polarization splitters and creates wavelength dependent bi-directionality. An amplifier is coupled to the first isolator.
In another embodiment of the present invention, an optical data apparatus includes a first polarizing beam splitter with a first port and a second port. The first polarizing beam splitter receives an input and splits the input into first and second orthogonal polarizations. A second polarizing beam splitter has third and fourth ports. A non-reciprocal phase rotator is positioned between the first and second polarizing beam splitters. A first birefringent crystal is positioned between the first and second polarizing beam splitters.