Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-01-31
2002-12-03
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S011000, C385S036000, C385S033000, C359S199200, C359S341430
Reexamination Certificate
active
06490386
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical amplifiers within wavelength division multiplexed optical communications systems. More particularly, the present invention relates to an optical amplifier system and a method for optical amplification within a wavelength division multiplexed optical communications system wherein a first plurality of optical signal channels propagate in a first direction and a second plurality of optical signal channels that are interleaved with the first plurality propagate in a second direction opposite to the first direction.
BACKGROUND OF THE INVENTION
Fiber optic communication systems are becoming increasingly popular for data transmission due to their high speed and high data capacity capabilities. Wavelength division multiplexing (WDM) is used in such fiber optic communication systems to transfer a relatively large amount of data at a high speed. In wavelength division multiplexing, multiple information-carrying signals, each signal comprising light of a specific restricted wavelength range, may be transmitted along the same optical fiber.
In this document, the individual information-carrying lights of a WDM system are referred to as either “signals” or “channels.” The totality of multiple combined signals in a wavelength-division multiplexed optical fiber, optical line or optical system, wherein each signal is of a different wavelength range, is herein referred to as either a “composite optical signal” or simply as a “plurality of optical channels”. Each information-carrying channel actually comprises light of a certain range of physical wavelengths within a band. However, for simplicity, an individual channel is often referenced to a single wavelength, &lgr;, at the nominal center of the band. A plurality of such channels (i.e., a composite optical signal) are often denoted by a set of indexed wavelengths, such as “&lgr;
1
-&lgr;
n
”, or “&lgr;
1
, &lgr;
2
, &lgr;
3
, . . . ”, etc.
Strictly speaking, a multiplexer is an apparatus which combines separate channels into a single wavelength division multiplexed composite optical signal and a de-multiplexer is an apparatus that separates a composite optical signal into one or more subsets of component channels. However, since many multiplexers and de-multiplexers ordinarily operate in either sense, the single term “multiplexer” is usually utilized to described either type of apparatus. Because of the nature of the present invention, however, the precise usage of the terms multiplexer and de-multiplexer is adhered to in this document—that is, as used in this document, a “multiplexer” (MUX) combines channels but does not operate in the reverse sense so as to separate channels and a “de-multiplexer” (DEMUX) separates channels but does not operate in the reverse sense so as to combine channels. An apparatus which can perform either channel separation or channel combining is referred to in this document as a “channel separator”.
As the terms are used in this document, either a multiplexer or a channel separator may perform an interleaving function and either a de-multiplexer or a channel separator may perform a de-interleaving operation. An interleaving operation occurs when a first composite optical signal comprising a first plurality of optical channels is multiplexed together with a second composite optical signal comprising a second plurality of optical channels, wherein the first plurality of channels and the second plurality of channels are interleaved with one another. It is to be understood that the above stipulation that “the first plurality of channels and the second plurality of channels are interleaved with one another” means that the wavelengths (or frequencies) of the first plurality of optical channels are interleaved with the wavelengths (or frequencies) of the second plurality of optical channels. A de-interleaving operation is the opposite of an interleaving operation. Multiplexers, de-multiplexers and channel separators that perform interleaving or de-interleaving operations are herein referred to as interleaved channel multiplexers, interleaved channel de-multiplexers and interleaved channel separators.
An apparatus that performs a de-multiplexing operation is referred to herein as an “m×n de-multiplexer” where m is an integer representing the number of input ports, n is an integer representing the number of output ports and n≧m. An apparatus that performs a multiplexing operation is referred to herein as an “j×k multiplexer” where j is an integer representing the number of input ports, k is an integer representing the number of output ports and j≧k. Channel separator apparatuses are referred to herein as an “i×j channel separator” apparatuses where i is an integer representing the number of a first logical or physical group of ports, and j is an integer representing the number of a second logical or physical group of ports, wherein optical signals may propagate between the first and second groups but not between one port and another within an individual group.
It is desirable, within many fiber optic wavelength division multiplexed optical communications systems, for optical signals to be transmitted bi-directionally—that is, such that one or more first optical signals comprising a first wavelength or a first plurality of wavelengths are propagated in one direction whilst one or more second optical signals comprising either a second wavelength or a second plurality of wavelenghs are propagated in the opposite direction. Where optical signals propagate within a long transmission line, it is frequently necessary to amplify the bidirectional signals at intermediate points. Since the construction of most optical amplifiers only permits unidirectional optical transmission through the amplifier, it is thus necessary to interrupt the transmission path, route the two counter-propagating signals unidirectionally through the optical amplifier, and then return them to the transmission path to continue in their original, opposite directions of propagation. The temporary conversion of the counter-propagating signals into a combined unidirectional signal through the optical amplifier enables a single amplifier to be used, thereby saving expense and avoiding differences of amplification.
A prior-art bi-directional amplifier apparatus of this type is illustrated in FIG.
1
. The prior-art apparatus
100
shown in
FIG. 1
comprises a series of wavelength-selective devices
10
,
12
,
14
and
16
, each having four ports designated P
1
, P
2
, P
3
and P
4
, respectively. Each device comprises two graded-index one quarter pitch lenses disposed end-to-end with an optical bandpass filter sandwiched between their juxtaposed ends. Reference numbers utilized in
FIG. 1
have the suffix “L” or “R” to identify whether it is at the right hand side or the left hand side, as shown. Thus, the left hand lenses of devices
10
,
12
,
14
and
16
are designated
10
L,
12
L,
14
L and
16
L, respectively, and the right hand lenses are designated
10
R,
12
R,
14
R and
16
R, respectively. The lenses are arranged so that light beams from each first port P
1
will be collimated by the left-hand lens to illuminate substantially the whole of the corresponding bandpass filter and refocussed by the right-hand lens to couple into the opposite port P
4
—and vice versa. Likewise, light beams from the second port P
2
will be collimated as they pass through the filter and refocussed to couple into the opposite third port P
3
—and vice versa. Where the collimated light beams from one port are reflected by the filter, they will be refocussed by the same lens but couple to the adjacent port.
Whereas the lenses are identical, each of the bandpass filters, designated
10
F,
12
F,
14
F and
16
F, respectively, will transmit a different band of wavelengths. The passbands of the bandpass filters
10
F,
12
F,
14
F and
16
F are designated &Lgr;
2
, &Lgr;
4
, &Lgr;
6
and &Lgr;
N
, respectively. Each bandpass filter will pass light beams having a wavelength within its passband to
Cao Xiaofan
Cooney Thomas F.
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