Optical waveguides – Polarization without modulation
Reexamination Certificate
2003-01-17
2004-07-06
Lee, John D. (Department: 2874)
Optical waveguides
Polarization without modulation
C385S129000, C385S131000
Reexamination Certificate
active
06760496
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to the field of semiconductor lasers and optical isolators and more particularly to an inline ferromagnetic-composite isolator and method.
BACKGROUND OF THE INVENTION
Optical isolators are used in optical communications systems and optical networks to eliminate or reduce reflected light waves. The presence of reflected light waves in such systems and networks may result in significant problems, disadvantages and instabilities, especially when reflected light waves reach or reenter a laser source or optical amplifier.
Conventional optical isolators were developed to eliminate or minimize the presence of reflected light waves. Unfortunately, the manufacture and implementation of conventional optical isolators is complicated, unreliable, expensive and fraught with difficulties and disadvantages.
The implementation of conventional optical isolators is often cumbersome and expensive. For example, conventional optical isolators may use non-reciprocal Transverse Electric (“TE”) like mode converters and non-reciprocal Transverse Magnetic (“TM”) like mode converters, reciprocal TE like mode converters and reciprocal TM like mode converters, an absorption element to absorb modes of light of a particular polarization, and a space periodic magnetic field for quasi-phase match between TE and TM like modes. This phase match requirement of conventional optical isolators is particularly difficult and problematic, and imposes severe fabrication tolerances. For example, the fabrication tolerances on such variables as composition, layer thickness, and interaction length are extremely difficult to consistently achieve and replicate. This causes reliability and performance concerns, along with significantly increased overall costs.
The increased use of semiconductor optical elements and devices, such as semiconductor lasers, laser arrays, and optical amplifiers, have resulted in the need to integrate or interface conventional optical isolators with such semiconductor elements and devices. The different fabrication techniques and materials used in each has made such a solution either impossible or impractical. This has provided additional challenges in integrating and interfacing conventional optical isolators with semiconductor elements and devices.
SUMMARY OF THE INVENTION
From the foregoing it may be appreciated that a need has arisen for an inline ferromagnetic-composite isolator and method for use in an optical system or network. In accordance with the present invention, an inline ferromagnetic-composite isolator and method are provided that substantially eliminate one or more of the disadvantages and problems outlined above.
According to an aspect of the present invention, an optical isolator, and method for making the same, is provided that includes a waveguide, with a core and a cladding, and a magnetic-composite material. The waveguide core may include a first end, a second end, and a boundary surface, is operable to allow a light wave incident the first end of the core to propagate from the first end of the core to the second end of the core, which defines a positive propagation direction, and is operable to allow a light wave incident the second end of the core to propagate from the second end of the core to the first end of the core, which defines a negative propagation direction. The waveguide cladding is positioned relative the boundary surface of the core and includes a thinned segment of the cladding with a cladding thickness operable to allow an optical field penetration through the thinned segment of the cladding by a light wave that propagates in the positive propagation direction of the core and that propagates in the negative direction of the core. The thinned segment of the cladding having a length that extends relative to a portion of the core. The magnetic-composite material is provided in the presence of a magnetic field, which is preferably a static magnetic field, with at least a component of the magnetic field oriented in a direction perpendicular to the positive propagation direction of the core parallel to the magnetic vector of the optical field, and is positioned relative the thinned segment of the cladding of the waveguide to receive the optical field penetration through the thinned segment of the cladding. The magnetic-composite material having a thickness and an index of refraction to attenuate a light wave that propagates in the portion of the core in the negative propagation direction by an amount greater than the attenuation of a light wave that propagates in the portion of the core in the positive propagation direction.
According to an aspect of the present invention, an optical isolator, and method for making the same, is provided that includes a waveguide with a guide layer, a first clad layer, a second clad layer, and a magnetic-composite material. The waveguide guide layer may include a first end, a second end, a top and a bottom, is operable to allow a light wave incident the first end of the guide layer to propagate from the first end of the guide layer to the second end of the guide layer, which defines a positive propagation direction, and is operable to allow a light wave incident the second end of the guide layer to propagate from the second end of the guide layer to the first end of the guide layer, which defines a negative propagation direction. The first clad layer of the waveguide is provided relative the bottom of the guide layer, and the second clad layer of the waveguide is provided relative the top of the guide layer. The second clad layer includes a thinned segment with a thickness operable to allow an optical field penetration through the thinned segment of the second clad layer by a light wave that propagates in the positive propagation direction of the guide layer and that propagates in the negative direction of the guide layer. The thinned segment of the second clad layer having a length that extends relative to a portion of the guide layer. The magnetic-composite material is provided in the presence of a magnetic field with at least a component of the magnetic field oriented in a direction perpendicular to the positive propagation direction of the guide layer parallel to the magnetic vector of the optical field, and is positioned relative the thinned segment of the second clad layer of the waveguide to receive the optical field penetration through the thinned segment of the second clad layer. The magnetic-composite material having a thickness and an index of refraction to attenuate a light wave that propagates in the portion of the guide layer in the negative propagation direction by an amount greater than the attenuation of a light wave that propagates in the portion of the guide layer in the positive propagation direction.
Related aspects of the optical isolator of the present invention may include providing the thickness of the magnetic-composite material at an optimal thickness defined by such variables as (i) the thickness where maximum attenuation occurs of a light wave of a known frequency that propagates in the portion of the core in the negative propagation direction, (ii) the thickness where minimum attenuation occurs of a light wave of a known frequency that propagates in the portion of the core in the positive propagation direction, and/or (iii) the thickness where the maximum isolation-to-loss ratio occurs, where the isolation is defined as the attenuation of a light wave of a known frequency that propagates in the portion of the core or guide layer in the negative propagation direction, and the loss is defined as the attenuation of a light wave of a known frequency that propagates in the portion of the core or guide layer in the positive propagation direction. Additional related aspects of the optical isolator of the present invention may include providing the thickness of the magnetic-composite material at a thickness defined by such variables as (i) the thickness that results in a larger optical intensity of the optical field of the light wave of a known
Holmes Patrick C. R.
Lee John D.
Lin Tina M
Photodigm Inc.
Yee Duke W.
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