Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2000-02-14
2002-04-16
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S088000
Reexamination Certificate
active
06374021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light transmitting/receiving module, eg., to an LD/PD (Laser Diode/Photodiode) module, an LD/APD (Laser Diode/Avalanche Photodiode) module, an LED/PD (Light Emitting Diode/Photodiode) module or an LED/APD (Light Emitting Diode/Avalanche Photodiode) module unifying a light transmitting device and a light receiving device which are used at base ports (broadcasting station) and subscribers in a unidirectional or bidirectional optical communication system capable of transmitting optical signals with different wavelengths in a unidirectional or bidirectional manner, and more particularly, relates to an LD/PD or an LED/PD module enjoying a simple structure, easy production method, high reliability, and low cost.
2. Description of Related Art
This application claims the priority of Japanese Patent Application No. 11-38672 (38672/1999) filed Feb. 17, 1999 which is incorporated herein by reference.
[Explanation of Bidirectional Optical Communication]
Recent development of technology has been striving to reduce the transmission loss of optical fibers and has been enhancing the properties of semiconductor laser diodes (indicated as LDs hereafter) and semiconductor photodiodes (indicated as PDs hereafter).
The light emitting devices used in the optical communication system include LDs and LEDs, but in this invention an LD (laser diode) is picked as a light emitting device. Further, the light receiving devices includes PDs and APDs, but this invention picks a PD (photodiode) as a light receiving device. This invention can include both the LD and the PD. There exist telephones, facsimiles, televisions and so on as means for transmitting information. Particularly, people have rigorously tried optical communication utilizing long wavelength light, for example, the light with a 1.3 &mgr;m wavelength or the light with a 1.55 &mgr;m wavelength. Recently, there develops a bidirectional transmission system capable of transmitting and receiving signals in forward and backward directions at the same time by only a single optical fiber. Such a communication system is called a “bidirectional communication system”. Single optical fiber is one of the most beneficial advantages.
FIG. 1
schematically shows a multiwavelength bidirectional optical communication system which adopts a plurality of wavelengths for transmitting signals simultaneously both in a forward direction and in a backward direction. One station is connected to a plurality of subscribers (ONUs) by optical fibers. Although
FIG. 1
shows only a single subscriber for simplicity, many subscriber ports are connected to the central station. The fiber from the station branches through many bisecting points into a plurality of fibers linking with individual subscribers.
The central station amplifies the signals of telephones or televisions as digital signals or analog signals, and drives a semiconductor laser (LD
1
) which produces &lgr;
1
light responsive to the amplified signals. The light of &lgr;
1
emitted from the LD
1
enters an optical fiber
1
as light signal of &lgr;
1
. A wavelength division multiplexer (WDM)
2
introduces the &lgr;
1
light into an intermediate optical fiber
3
. Another wavelength multiplexer (WDM)
4
allocated to the subscriber side leads the &lgr;
1
light to an optical fiber
5
, and the &lgr;
1
light is received by a photodiode (PD
2
) capable of converting the optical signals to electric signals. A receiver apparatus on the subscriber side amplifies and processes the electric signals for reproducing the voice of telephone or the image of television. The signals flowing from the station to the subscribers are called “downward signals”, and the direction is called a “downward direction”.
On the contrary, the subscriber converts electric signals of facsimile or telephone into &lgr;
2
light signals by a semiconductor laser diode (LD
2
). The &lgr;
2
light enters an optical fiber
6
, is introduced to an intermediate optical fiber
3
by the WDM
4
, and enters the PD
1
capable of converting the &lgr;
2
signals to electric signals, passing through the WDM
2
. These electric signals are dealt with by converters or signal processing circuits on the station side. The signals flowing from the subscribers to the station are called “upward signals”, and the direction of the signals is called an “upward direction”.
The above system appropriates &lgr;
1
to the downward signals, and &lgr;
2
to the upward signals exclusively. In practice, light with the same wavelength may be used for both the upward and downward signals. Another system allocates two wavelengths &lgr;
1
and &lgr;
2
to both the upward signals and the downward signals. In this case, the separation of two wavelengths is an extremely important problem in the optical communication system capable of carrying two different wavelength signals in an optical fiber. [Explanation of Wavelength Division Multiplexer]
When the bidirectional communication (two-way communication) using two sorts of light with different wavelengths is carried out by only one optical fiber, both the station and the subscribers require a device for discriminating and separating the wavelengths. The WDMs
2
and
4
play the role of distinguishing and separating different wavelengths. The WDMs has the function of connecting the &lgr;
1
light to the &lgr;
2
light for leading both lights into a fiber, and the function of extracting only one wavelength light from two sorts of wavelength light propagating in the fiber. Therefore, the WDMs perform an important part in the multiwavelength bidirectional communication systems.
Various types of wavelength division multiplexers have been proposed, which will be explained by FIG.
2
and FIG.
3
.
FIG. 2
indicates a WDM consisting of optical fibers or optical waveguides. Two optical paths
8
and
9
are close to each other at a part
10
for exchanging the energy of light therebetween. Various coupling modes are realized by determining the distance D and the length L of the close part
10
. For example, when &lgr;
1
enters the optical path
8
, the light with &lgr;
1
wavelength appears in a path
11
. When &lgr;
2
enters an optical path
12
, the light with &lgr;
2
wavelength appears in the optical path
9
instead of the path
8
.
FIG. 3
shows another WDM that uses a multilayered mirror. This WDM consists of two rectangular isosceles triangle columns (glass blocks)
13
and
14
and a dielectric multilayer mirror
15
formed on the slanting plate of the columns. It is possible to make the whole of &lgr;
1
light pass through the dielectric multilayer mirror and to make the whole of &lgr;
2
light reflect from the dielectric multilayer mirror by an appropriate combination of the refractive index and the thickness. The dielectric multilayer allows the incident light at 45 degrees to pass through or reflect. This dielectric layer type WDM can be utilized for the WDMs
2
and
4
in the optical communication system of FIG.
1
. The WDM is sometimes called a “wave-division-integration device” or “wavelength division multiplexer”. Fiber-type WDMs and glass block type WDMs have already been on sale.
An example of an LD/PD module on the subscriber side is explained by referring to
FIG. 4. A
single mode optical fiber
16
leading from the center station to the subscriber side is connected to an optical fiber
18
of a subscriber (ONU) module by an optical connector
17
. The ONU module has a fiber-type WDM
21
which couples the fiber
18
to a fiber
19
with wavelength-selectivity An optical connector
22
couples the optical fiber
18
to an LD module
25
in the ONU. Another optical connector
23
joins the fiber
19
to a PD module
27
.
The light signals transmitted from the LD
25
via the optical fibers
24
and
18
are upward system. 1.3 &mgr;m light carries signals from the subscriber side to the station through the upward system. The signals transmitted from the fibers
19
and
26
to the PD module
27
are downward system.
Kuhara Yoshiki
Nakanishi Hiromi
Bovernick Rodney
Smith , Gambrell & Russell, LLP
Stahl Michael J.
Sumitomo Electric Industries Ltd.
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