Optical waveguides – Integrated optical circuit
Reexamination Certificate
2002-02-28
2004-10-26
Bovernick, Rodney (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S129000, C385S033000, C385S050000
Reexamination Certificate
active
06810160
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of Japanese Patent Applications No.2001-56009, filed in Feb. 28, 2001, the Contents being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical wiring substrate utilized in information and communication systems that require high-speed and high-volume signal transmission, a method of manufacturing the optical wiring substrate and multilayer optical wiring.
2. Description of the Prior Art
In information and communication systems, optical signals suitable for high-speed and high-volume signal transmission are utilized. As for optical transmission between optical devices, optical fibers are utilized when the number of wires as optical wiring is small; meanwhile, when the number of wires is increased into several hundreds or thousands, an optical wiring substrate is utilized in which optical waveguides are provided on a substrate. Usually, a plurality of optical wiring substrates are laid, in which a plurality of optical waveguides are optically connected with each other for performing transmission of optical signals.
In this case, since light has high rectilinearity, alignment precision becomes an issue when optical fibers or optical waveguides on the substrate are coupled with each other. For example, a predetermined tolerance for misalignment between single mode optical fibers is about 5 &mgr;m.
As for multimode optical fibers, a tolerance for misalignment between the optical fibers, each having a core diameter of several tens of micrometers, used for optical waveguides is within several tens percent of the core diameter.
There is also a case of coupling optical wiring substrates having optical waveguides formed thereon by use of a connector as another member. However, such a case may incur misalignment of 100 &mgr;m or greater. Optical signals are not propagated when such misalignment greater than the applied core diameter occurs.
Moreover, in the case when light emitted from an optical waveguide of one optical wiring substrate is made incident on an optical waveguide of the other optical wiring substrate, it is desirable that the light is rendered parallel in optical path. There is a conventional constitution in which an end face of a core
1
is formed into a hemispherical shape as shown in
FIG. 1
, which is intended for rendering parallel light rays passes through the end face. Nevertheless, completely parallel light rays could not be obtained since the light reflected intricately within the optical waveguide.
Furthermore, coupling of hundreds or thousands of optical waveguides on optical wiring substrates may be contemplated by use of optical fiber connectors each fabricated with precision as a connector. However, the number of optical fibers allowable for such a connector is limited to a range from one to about twelve. Accordingly, an enormous number of optical fiber connectors are required for such use, which is unrealistic.
Since high-speed data transmission is enabled with optical signals, optical communications play a major role in long-distance transmission such as a backbone communication system. In particular, a technology of transmitting different kinds of information simultaneously with different wavelengths in one optical fiber is developed, which is called wavelength division multiplexing (WDM). High-volume information is thereby transmitted in a high speed.
At a relay station of a backbone communication system, the information sent by WDM is separated into light rays, each having a single wavelength. Then destinations of the individual light rays are switched, and the light rays are again coupled in one optical fiber.
In this case, a destination of the light ray of any wavelength needs to be switched arbitrarily. That is, a cross-connect function of changing inputs of N channels into outputs of N channels is required.
As the multiplexing of the WDM develops, it is estimated that 100 or more waves will be sent in one optical fiber. For this reason, the cross-connect function is required for a capability of processing 1,000 channels or more.
However, an optical switch capable of processing several thousands of channels does not yet exist. Accordingly, practically used are small switches arranged in a multistage combination, as shown in FIG.
2
.
FIG. 2
illustrates a state that optical transmission between input optical fibers
410
and output optical fibers
460
is performed by channel processing of 64 channels of inputs and outputs with two sets of cross-connect wiring
430
using a three-staged configuration of a first switch
420
, a second switch
440
and a third switch
450
, wherein each switch has 8×8 channels.
Each of the switches in respective stages includes a plurality of optical switches
470
, each of which takes charge of a specific number of input optical fibers
410
. In this case, the cross-connect optical wiring
430
must have an optical wiring structure in which wires between the switches of the respective stages are connected while intersecting one another.
Heretofore, Japanese Patent Laid-Open Hei 6 (1994)-331910 discloses a switching device for coated optical fibers that performs connection switching in arbitrary combinations.
However, a problem has been pointed out that the switching device requires a huge space for accommodating optical fibers in a case of 1,000 channels or more.
Accordingly, materialization of an optical wiring substrate that has a cross-connect structure capable of processing transmission of high-speed and high-volume data signals with 1,000 channels or more is anticipated.
Meanwhile, Japanese Patent Laid-Open Hei 11 (1999)-178018 discloses an optical connecting device of a structure in which a former stage substrate mounted with switches and a latter stage substrate are orthogonalized.
The optical connecting device simplifies wiring of the optical fibers therein. However, modes of mounting substrates are limited.
Moreover, in an optical cross-connect system in Japanese Patent Laid-Open Hei 10 (1998)-243424, a technology is disclosed for constituting a cross-connect structure in which a two-dimensional fiber array composed by laminating N fibers each of which has M cores and another two-dimensional fiber array having M fibers×N cores are orthogonally jointed.
Although a compact cross-connect structure is realized, the optical cross-connect system bore a manufacturing problem of an increase of coupling loss unless the lamination was exercisable in a cross-core pitch of optical fibers.
Moreover, there is also a method of using a fiber sheet technology, in which optical fiber strands are laid into arbitrary wiring and fixed in a sheet form with resin or the like. In this case, compact arrangement is feasible because the optical fibers do not have protection coating.
However, as previously shown in
FIG. 2
, the optical fibers are accumulated at the central portion of the intersection structure. Whereas a minimum bend radius is defined for the optical fiber, control of the bend radius in a vertical direction generated by lamination of the optical fibers becomes difficult. For this reason, there has been a problem that characteristics of the optical transmission may not be ensured by this method.
Recently, in the field of communications, the optical transmission is becoming a main stream not only for a long-distance signal transmission but also for a short-distance signal transmission. In conventional technologies of electrical signal transmission, clock frequencies and data transmission speeds are increased owing to progress in CPUs. Therefore, signal transmission speeds are improved day by day.
However, cross-connect devices that take charge of switching signals in the electrical signal transmission technologies are hardly applicable to signal switching for the optical communications without modification. Accordingly, optical via holes are particularly composed between layers of multilayer wiring, thus forming interlayer transfer portion of
Aoki Tsuyoshi
Ishii Masatoshi
Kato Masayuki
Sasaki Shinya
Sugama Akio
Bovernick Rodney
Fujitsu Limited
Sheppard Mullin Richter & Hampton LLP
Song Sarah
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