Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-10-27
2001-12-25
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C359S199200, C385S024000, C385S031000, C385S049000
Reexamination Certificate
active
06334014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber apparatus provided with a demultiplexing/multiplexing unit on its fiber's end surface, such as an optical fiber provided with an optical detector array having a demultiplexing function for separating wavelength multiplexed signals of a wavelength division multiplexing (WDM) optical transmission and for receiving separated optical signals by respective optical detectors, an optical detecting apparatus provided with a demultiplexing-multiplexing unit on its light receiving surface, and an optical transmission system using the same.
2. Related Background Art
Conventionally, the following combination structures were proposed as an optical detector having a demultiplexing function for demultiplexing wavelength multiplexed signals and for receiving respective demultiplexed optical signals, as disclosed in Japanese Laid-Open Patent Nos. 8(1996)-82711 and 8(1996)-211237. In one structure, a device having a combination of a branching function and an optical filter (band-pass) function is used. In another structure, so-called array-waveguide diffraction gratings are used as a demultiplexer and an optical detector (or an optical detector array) is combined with the diffraction gratings. In the array-waveguide diffraction gratings, a plurality waveguides having different optical lengths are combined, and different wavelengths are coupled to different output waveguides due to an interference effect.
The prior art device of Japanese Laid-Open Patent No. 8(1996)-82711, however, has the following technical disadvantages since optical separation is effected using multiple reflections:
1. External light must be collimated and then input;
2. The angle of input light must be set to a given angle; and
3. Performance of the optical filter must be varied according to its location.
Further, the prior art device of Japanese Laid-Open Patent No. 8(1996)-211237 has the following technical disadvantages since demultiplexing is effected using interference between different optical lengths:
1. An optical fiber must be optically coupled to the waveguide;
2. A possibility exists that variation in a waveguide width of the array-waveguide gratings adversely affects characteristics;
3. A thin waveguide device must be fixed to a fiber end; and
4. A slab waveguide portion must be precisely processed to uniformly distribute light.
In addition to those disadvantages, in both prior art devices, an optical coupling system is needed between the optical fiber and the demultiplexer, and a portion having a separating function (spatial separation) and a size larger than the optical fiber is needed.
Furthermore, there is not yet provided an optical fiber (typically, a plastic optical fiber having a relatively large core diameter) which has a demultiplexing/multiplexing unit provided directly on its end portion to solve the above disadvantages.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical fiber apparatus including a demultiplexing/multiplexing unit on an end face of the optical fiber, such as an optical fiber provided with an optical detector having a demultiplexing function for separating wavelength multiplexed signals of a wavelength division multiplexing (WDM) optical transmission and for receiving respective separated optical signals, an optical detecting apparatus provided with a demultiplexing/multiplexing unit on its light receiving surface, and an optical transmission system using the same.
An optical fiber apparatus for achieving the object of the present invention includes an optical fiber and a demultiplexing/multiplexing unit for demultiplexing or multiplexing a light wave of at least a wavelength with a sufficiently narrow wavelength spectrum that is determined by a resolving power of the demultiplexing/multiplexing unit. The demultiplexing/multiplexing unit is provided or formed directly on at least an end face of the optical fiber.
Typically, the demultiplexing/multiplexing unit is provided on the end face of the optical fiber, so that needed demultiplexing and receiving are performed within an area of a size of a core of the optical fiber. For example, transmission wavelengths of the demultiplexing/multiplexing unit vary depending on its light emergence places, and optical detectors are respectively arranged at those places. Thus, where wavelength multiplexed optical signals transmitted through the optical fiber are received by a receiver per wavelength, precision needed for optical couplings and the number of positional alignment processes can be reduced.
In the structure of the present invention, a plurality of optical filters with different transmission wavelengths need not be finely provided in a small area, in contrast with the conventional apparatus. For example, when an etalon with predetermined opposite end surfaces is used, a demultiplexing/multiplexing unit whose transmission wavelengths vary depending on its light emergence places can be readily fabricated. Such a structure can be effectively built especially where the optical fiber has a relatively large core diameter or size.
Based on the above fundamental structure, the following specific structures are possible with the following technical advantages.
Typically, the demultiplexing/multiplexing unit demultiplexes or multiplexes a plurality of light waves at different wavelengths with sufficiently narrow wavelength spectra that are determined by the resolving power of the demultiplexing/multiplexing unit.
The demultiplexing/multiplexing unit is a Fabry-Perot etalon whose optical length varies along a direction approximately perpendicular to an optical-axial direction of the optical fiber. For example, the unit may be a wedge-shaped Fabry-Perot etalon including reflective mirrors wherein spacings between the reflective mirrors gradually vary along the direction approximately perpendicular to the optical-axial direction of the optical fiber. In these etalons, transmission wavelengths vary depending on places along the direction approximately perpendicular to the optical-axial direction of the optical fiber.
The demultiplexing/multiplexing unit may include a unit for preventing multiple reflection bridging paths of demultiplexed light waves such that crosstalk between adjacent demultiplexed light waves can be prevented. In such a structure, channels in the etalon can be separated from each other, and unwanted leaks of light between channels can be lowered. Thus, demultiplexing performance can be effectively improved.
The wedge-shaped Fabry-Perot etalon may be composed of an optical material having non-parallel opposite end surfaces, and a uniform refractive index and reflective films provided on the non-parallel opposite end surfaces.
The optical fiber apparatus may further include an optical detector array including a plurality of optical detectors for detecting demultiplexed light waves, and the demultiplexing/multiplexing unit may be a wedge-shaped Fabry-Perot etalon including a reflective film provided on the end face of the optical fiber and a reflective film provided on an end surface of the optical detector array. The reflective films are set in a predetermined non-parallel relationship with a spacing between the reflective films. In such a structure, no special material for the etalon is needed, so that the structure can be simplified.
The wedge-shaped Fabry-Perot etalon may further include a jig for placing the optical fiber and the optical detector array along a common axis, or a spacer for placing the optical fiber and the optical detector array with a spacing between the optical fiber and the optical detector array, to achieve the predetermined non-parallel relationship. In this case, a control unit for varying the predetermined non-parallel relationship, such as a piezoelectric element, may be further provided.
The demultiplexing/multiplexing unit may include parallel reflective films and an optical material which are sandwiched between the reflective films and have a predetermined refrac
Handa Yuichi
Nitta Jun
Numai Takahiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee John D.
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