Optical: systems and elements – Optical amplifier
Reexamination Certificate
1999-11-10
2001-11-06
Tarcza, Thomas H. (Department: 3662)
Optical: systems and elements
Optical amplifier
Reexamination Certificate
active
06313938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a planar lightwave circuit module for an optical fiber amplifying device suitable for use in optical fiber communications, and to the aforementioned optical fiber amplifying device.
2. Description of Related Art
An optical fiber amplifier is described in “Optical Fiber Amplifiers and Their Use” (Chapter 5: Erbium-doped Fiber Amplifier (EDFA); by Hideki Ishio, Ohm Publishing House, pp. 110-111) (Reference 1).
The structure of this conventional optical fiber amplifier (or amplifying device) is shown in
FIG. 1. A
brief description of the conventional optical fiber amplifying device will be given with reference to FIG.
1
.
In
FIG. 1
, part of a signal light input is separated by an optical coupler
131
and provided to a photodetector (hereinafter abbreviated as “PD”)
132
. The remaining signal light is provided to a wavelength division multiplexer (hereinafter abbreviated as “WDM”)
134
.
In WDM
134
, multiplexing is performed between signal light provided by the optical coupler
131
and forward pumping light provided by a laser diode (hereinafter abbreviated as “LD”)
135
serving as an a pumping source, and the resultant multiplexed signal is provided to an amplifying optical fiber
136
through an optical isolator
133
. In WDM
137
, backward pumping light provided by LD
138
is multiplexed with signal light and the resultant multiplexed signal is provided to the amplifying optical fiber
136
.
The amplifying optical fiber
136
is provided with the signal light and forward pumping light from WDM
134
through the optical isolator
133
and with the backward pumping light from WDM
137
, and the signal light is amplified. Pumping light is removed from the amplified signal light by WDM
137
, and the resultant amplified signal light is provided to an optical coupler
140
through an optical isolator
139
.
Most of the signal light provided to the optical coupler
140
is outputted to an output terminal, and the remaining signal light is provided to PD
142
. Part of the reflected light input from the output terminal is separated by the optical coupler
140
and provided to PD
141
.
As noted above, various optical components (for example, optical couplers, WDM, optical isolators, PD, and LD) are used for conventional optical fiber amplifying devices, and optical fibers (hereinafter referred to as “pigtails”) are generally used to transmit light to and from the input/output units of such optical components.
With conventional optical fiber amplifying devices, however, pigtails are used for the input/output units of the optical components constituting these devices, and connections among the components are formed using these pigtails, thereby creating a need to accommodate such optical components, connections among them, and pigtail fibers. This arrangement is disadvantageous in that it yields a bulky device. Another drawback is the need to perform work involved in the mounting of the optical components, connections among them, and pigtail fibers, thereby increasing the number of manufacturing steps.
An alternative to using such pigtails is to directly connect the exit surface of an optical component and the incident surface of another optical component, and to use a composite optical component obtained by the partial or complete integration of these components. Using such composite optical components is preferred as a way of overcoming the aforementioned shortcomings.
Because of the absence of light-transmitting pigtails in such composite optical components, however, a plurality of optical components must be fixed at appropriate positions in relation to a single optical collimator (parallel beam) system. Specifically, the optical axes of optical components must be aligned with each other. As a result, fine adjustment or the use of high-precision components is required, making this approach disadvantageous because of an increase in the number of manufacturing steps and a higher cost.
Furthermore, constructing erbium-doped fibers (light-amplifying fibers) in the form of optical waveguides was studied by T. Kitagawa (“Rare-earth Doped Planar Waveguide Amplifiers,”
Proc. of Topical Meeting Optical Amplifiers and Their Applications
, MC1, pp. 136-139 (1993) (Reference 2)). This construction is suitable for miniaturization. This construction is still disadvantageous, however, in that a phenomenon called concentration extinction occurs because of increased erbium density, and optical amplification characteristics are adversely affected by this phenomenon.
Another feature of optical fiber amplifying devices is that a large number of optical components other than light amplification fibers are mounted in a narrow space. Configuring these optical components as planar lightwave circuit modules would make them interchangeable independent of the type of optical fiber amplifying device.
SUMMARY OF THE INVENTION
Consequently, an object of the present invention is to provide a planar lightwave circuit module in which the desired optical components of the optical fiber amplifier are integrated together.
Another object of the present invention is to provide an optical fiber amplifying device constructed using the aforementioned planar lightwave circuit module.
Aimed at attaining the stated objects, the planar lightwave circuit module of the present invention comprises signal light input ports, signal light output ports, a first connection port connected to the signal light input ports and to one end of an amplifying optical fiber, a second connection port connected to the signal light output ports and to the other end of the amplifying optical fiber, and optical coupling means for feeding pumping light from a pumping source (or an excitation light source) to the amplifying optical fiber.
In addition, the planar lightwave circuit module of the present invention should preferably comprise a third connection port connected to the pumping source, and a fourth connection port connected to a monitoring element for monitoring the operating state of the amplifying optical fiber.
Furthermore, in the preferred embodiment of the planar lightwave circuit module of the present invention, the ports should be spaced at regular intervals and it is sometimes possible to adopt a structure in which dummy ports are provided to the aforementioned module, and the ports are spaced at regular intervals.
The optical fiber amplifying device of the present invention may also be configured such that an amplifying optical fiber is connected to the aforementioned planar lightwave circuit module.
Of the optical components constituting an optical fiber amplifying device based on the planar lightwave circuit module described above, required optical components other than the amplifying optical fiber are configured as a single module. To achieve such modularization, light propagation paths are substantially configured as optical waveguides. Consequently, optical components that can be configured as waveguides are incorporated as such waveguides into a single substrate. Optical components that cannot be configured as waveguides are formed by integration at and/or mounted on the substrate. Optical couplers and WDMs can be configured as waveguides. Optical isolators, monitoring photodetectors (PD), and pumping sources (LD) cannot be configured as waveguides and are thus formed by integration at and/or mounted on a substrate provided with waveguides. When they are in the form of multilayer dielectric films, WDMs cannot be configured as waveguides and are therefore integrated at and/or mounted on the substrate.
According to the above-described planar lightwave circuit module of the present invention, all the optical components or only the required portion thereof can be incorporated into a common substrate.
According to the planar lightwave circuit module of the present invention, incorporation of the required optical components of an optical fiber amplifying device into a single substrate allows the required connections between the incorpo
Sasaki Akira
Shikii Shigeru
Burdett James R.
Frank Robert J.
Hughes Deandra M.
OKI Electric Industry Co., Ltd.
Tarcza Thomas H.
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