Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2000-01-13
2003-12-09
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S031000, C385S033000, C385S034000, C398S083000, C398S085000, C398S088000
Reexamination Certificate
active
06661944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical add/drop multiplexer. More particularly, the present invention relates to an optical add/drop multiplexer that comprises an optical filter plate and a plane reflector.
2. Description of the Related Art
FIG. 1
is a sketch of a conventional optical add/drop module. As shown in
FIG. 1
, the module includes a drop multiplexer
10
and an add multiplexer
20
. The drop multiplexer
10
includes an input graded-index lens
12
, a dropout filter plate
14
and a dropout graded-index lens
16
. The add multiplexer
20
includes an output graded-index lens
22
, an add filter plate
24
, and an add graded-index lens
26
. Both the dropout filter plate
14
and the add filter plate
24
are involved in filtering electromagnetic waves of the same wavelength.
A group of incoming optical signals containing signals of various wavelengths is first coupled to the input graded-index lens
12
so that the signals are delivered to the dropout filter plate
14
. The filter plate
14
block out all signals except signals at a specified waveband so that the signals at the specified waveband are permitted to pass through the filter
14
and couple with the dropout graded-index lens
16
. Signals of the specified waveband or the so-called dropout signals can be read at the other side of the dropout graded-index
16
. Meanwhile, blocked signals outside the specified wavelength are reflected back by the dropout filter plate
14
.
However, only a portion of signals having the specified wavelength penetrate through the dropout filter plate
14
. Hence, a small portion of the signals within the specified waveband will be reflected back by the filter plate
14
together with the rest of the group of signals. Thus, the signal within the specified waveband together with the rest of the group of signals needs to be further deliver to the add filter plate
24
. When the group of signals reaches the add filter plate
24
, the remaining signals within the specified waveband are able to penetrate through. Consequently, strength of the signals within the specified waveband after reflection from the add filter plate
24
is further reduced to an acceptable low-level. In addition, add-in signals can be added by shining a beam with add-in signals onto the graded-index lens
26
. The add-in signals are also within the specified waveband so that the add-in signals can penetrate through the add filter plate
24
and mix with the original group of signals reflected from the add filter plate
24
. The add-in signals and the original group of signals emerge from the graded-index lens
22
as a group of output signals. Since the original signals within the specified waveband have been reduced to acceptable low-level, the newly added signals, also within the specified waveband, are unaffected and does not increase the bit error rate.
FIGS. 2
a
and
2
b
are patented optical add/drop multiplexers (U.S. Pat. No. 5,712,727). In
FIG. 2
a
, the add/drop multiplexer has two optical filter plates
110
and
120
and four graded-index lenses
112
,
114
,
122
, and
124
. Functions of the filter plates
110
and
120
and the graded-index lenses
112
,
114
,
122
, and
124
are similar to the filter plates
14
and
24
and the graded-index lenses
12
,
16
,
22
, and
26
of FIG.
1
. When an incoming light beam containing a group of signals at various wavelengths reaches at the first filter plate
110
, only the signals within a specified waveband can penetrate through the filter plate
110
and a optical fiber grating
116
to become dropout signals for reading. Meanwhile, signals having wavelengths outside the specified range are reflected by the filter plate
110
. In addition, the optical fiber grating
116
further intercept the signals having wavelengths outside the specified range. An optical fiber grating
130
is installed to intercept the reflected light from the filter plate
110
so that residual signals within the specified waveband after first reflection are further reduced. Finally, any remaining signals within the specified waveband are removed on reflection from the second filter plate
120
so that strength of signals within the specified waveband is reduced to an acceptable level. Additional signals can also be added to the reflected signals from the second filter
120
by shining a beam of light containing the add-in signals through filter plate
120
. Ultimately, a group of output signals emerges from the second filter
120
.
The major disadvantage of this type of optical add/drop multiplexer is that two filter plates
110
and
120
must be used. Furthermore, the group of input optical signals, the group of output optical signals, the add-in signals and the dropout signals must couple with graded-index lenses
112
,
114
,
122
, and
124
. Hence, cost of implementation will be high.
The alternative arrangement as shown in
FIG. 2
b
has a filter plate
210
, two graded-index lenses
212
and
214
, and a 2×1 optical fiber coupler
220
. Function of the filter plate
210
is similar to the filter plate
14
as shown in FIG.
1
. Signals within a specified waveband in a group of input optical signals are able to penetrate through the filter plate
210
to become dropout signals for reading. The optical fiber grating
216
further filter our undesired signals after the input signals penetrate through the filter plate
210
. Other signals contained within the group are reflected by the filter plate
210
. An optical fiber grating
230
is installed to intercept the reflected light from the filter plate
210
so that residual signals within the specified waveband are further reduced. Finally, light signals from the optical fiber grating
230
and any additional add-in signals are integrated inside a 2×1 optical fiber coupler
220
so that a group of output optical signals emerges from the coupler
220
.
The major disadvantage for this type of optical add/drop multiplexer is the use of a 2×1 optical coupler
220
. This is because strength of the group of output optical signals will be reduced by half (representing a 3 dB coupling loss).
SUMMARY OF THE INVENTION
The invention provides a type of optical add/drop multiplexer. The multiplexer comprises a first lens
310
, a second lens
330
and a third lens
320
, a reflector
350
, and an optical filtering device
340
. The first lens is used for receiving and transmitting a group of optical signals. The group of optical signals contains a spectrum of wavelengths. The optical filtering device includes an optical filter plate and a reflector. The optical filter plate receives the entire group of optical signals, but permits only a specified waveband within the spectrum of wavelengths to penetrate through. Signals from other part of the spectrum are reflected back and forth a number of times between the filter plate and the reflector. On the last reflection from the filter plate, the rest of the group signals with the acceptable low-level signals within the specified waveband emerge as a group of output signals. The second lens picks up the signals within the specified waveband from the filter plate to become dropout signals for reading. The second lens also receives add-in signals having wavelengths within the specified waveband and passes them through the optical filter plate. The third lens integrates the rest of the group signals, the acceptable low-level signals within the specified waveband and the add-in signals from the filter plate, and then transmits the mixed signals out as a group of optical output signals.
This invention also provides a type of optical add/drop multiplexer that includes a glass substrate. An anti-reflection coating is plated over a first planar surface of the substrate while an optical filtering film is coated over a second planar surface of the substrate. The first planar surface and the second planar surface are parallel to each other. The anti-reflection coating receives a group of incoming optical signals and th
Chiang Hsin-Chien
Chou Wei-Jen
Lin Shih-Chiang
Wu Jiun-Shyong
Healy Brian
Industrial Technology Research Institute
J.C. Patents
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