Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-06-15
2001-04-10
Ngo, Hung N. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S034000, C385S036000, C385S022000
Reexamination Certificate
active
06215919
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical switches and in particular to mechanical optical switches using movable light guiding elements for altering optical beam paths to effectuate switching.
BACKGROUND OF THE INVENTION
Optical switches play a fundamental role in optical systems and in optical communications systems in particular. The function of optical switches in optical communications is to connect and disconnect transmission paths to rout light beams modulated with information. In other systems optical switches can be used to pulse a light source, e.g., a laser or to perform other functions with modulated or unmodulated light beams. Because optical signals propagate at the speed of light it is important that the optical switches have high switching rates such that they not impede the intrinsically high speed operation of optical systems.
Mechanical optical switches are known. For example, an electro-optically switched directional coupler is proposed by M. Papuchon et al. in “Electrically Switched Directional Coupler: Cobra”,
Applied Physics Letters
, Vol. 27, No. 5, Sep. 1, 1975, pp. 289-291. Further modifications to this switch and similar devices are found in numerous subsequent publications. Although these types of mechanical optical switches are capable of relatively high switching rates, they suffer from many limitations. These limitations include high insertion losses, high susceptibility to temperature variations and other detrimental effects due to external factors. Prior art solutions to the high insertion loss have resulted in devices which are low speed.
In optical communications systems optical switches have to be able to switch the light path of a light beam between optical fibers. Hence, fast switching rates have to be supplemented by high switching precision and low insertion losses to achieve efficient in-coupling into the fibers. Because of these additional requirements the early mechanical optical switches are not suitable for optical communications systems.
Mechanical optical switches adapted to optical communications systems are known. For example, in U.S. Pat. No. 4,239,330 Ashkin et al. teach a multiple optical switch built of two quarter-period graded refractive index lenses sharing a common lens axis. An input fiber delivers a light beam to one of the lenses at a radial offset from common lens axis. A number of output fibers are positioned at the same radial offset and at certain angular displacements on the second lens about the common lens axis. Rotating the lenses relative to each other results in in-coupling of light from the input fiber to different output fibers. The disadvantages of this approach are high insertion loss, low switching speed, low level of reliability and difficulties in making this type of switch.
Another mechanical optical switching device for use with optical fibers is taught by Aoyama in U.S. Pat. No. 4,239,331. This switch utilizes at least one movable transparent dielectric plate positioned between an input fiber and output fibers. The output fibers have associated lenses for in-coupling the light into them. The plate, when placed in the optical path of the light changes its optical transmission path by shifting or offsetting the optical axis of the light from one output fiber to another. U.S. Pat. No. 4,322,126 to Minowa et al. presents a similar mechanical optical switching device which can take advantage of additional prism elements to alter the light path. In a similar vein, U.S. Pat. No. 4,303,303 to Aoyama discloses a variation of the mechanical optical switching device using a parallelogram prism and additional triangular prisms. Unfortunately, the use of additional optical prism elements increases the size of the switching device and introduces a number of additional reflective surfaces in the light path which lead to alignment problems and increased insertion losses.
In U.S. Pat. No. 4,634,239 Buhrer teach a multiple optical fiber electromechanical switch utilizing a rhombic prism. The prism exchanges the optical paths of two parallel beams by means of four refractions and at least two internal reflections. This exchange operation is performed by shifting the beams. The prism's rhombic geometry minimizes the size of the prism and the shift distance to the prism's activated position.
In U.S. Pat. No. 5,361,315 Lewis et al. teach a refractive element optical transmission switch with a fixed position concave reflector and an array of optical input and output waveguides. Rotation of the refractive element is used to couple light from one of the input waveguides to one of the output waveguides.
In fact, none of the prior art mechanical switches are suitable for fast and precise switching between optical fibers. The solutions relying on reflectors are very sensitive to angular variations, while the prism-based solutions are sensitive to variations in shift or offset. Thus, small mis-alignments, thermal effects, mechanical vibration as well as other typical perturbations make it very difficult for those devices to couple light between fibers rapidly while maintaining low insertion losses. The light emitted from the core of the input fiber or waveguide has to be redirected and in-coupled into the core of the output fiber or waveguide. In optical fibers, and especially in single-mode optical fibers, the acceptance cone and the area on which the in-coupling beam has to be focused are small. The low tolerances of in-coupling angle or offset found in the prior art devices limits their usefulness in these applications. What is desired is a device which is relatively insensitive to variations in beam shift and beam angle. Such device should be capable of fast switching rates and use few optical elements in the path between the input fiber and the output fibers.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide a mechanical optical switch for switching a light beam between an input fiber and output fibers utilizing the fewest optical elements and achieving precise control over the shift and angle of the light beam.
It is a further object of the invention to provide a mechanical optical switch which has a low insertion loss and is capable of fast switching rates. Specifically, it is an object of the invention to provide the switch with a light guiding element which is small and light weight.
It is also an object of the invention to provide a mechanical optical switch which is significantly less sensitive to beam shifts and angular variations, thus rendering the switch useful for practical high-speed applications.
The above objects and advantages, as well as numerous improvements attained by the apparatus and method of the invention are pointed out below.
SUMMARY
These objects and advantages are secured by a mechanical optical switch with a first port for holding a first optical fiber and a second port for holding a second optical fiber. A first lensing element, e.g., a graded index (GRIN) lens, is positioned in front of the first and second ports. The switch has a signal port holding a signal or input fiber which emits a light beam to be switched between the first and second fibers. The light beam propagates along a free beam path to the first lensing element and is in-coupled into the first optical fiber. The switch is equipped with a beam guiding element which can be moved in and out of the free beam path by a suitable mechanism such as a mechanical actuator, electromechanical actuator, magnetic actuator, piezoelectric actuator or any other suitable device. The beam guiding element is designed such that it shifts the light beam by an offset and rotates the light beam by an angle. Thus, the light beam propagates along a guided beam path to the first lensing element and is in-coupled into the second optical fiber.
The beam guiding element is a wedge prism designed such that the light beam enters the wedge prism through a first facet and exits the wedge through a second facet without undergoing any internal reflections. Furthermo
Li Wei-Zhong
Shao Qing
Lumen Intellectual Property Services
Ngo Hung N.
Oplink Communications Inc.
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