Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
1998-12-30
2001-02-20
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Particular coupling function
C385S031000, C385S033000, C385S034000, C385S036000, C385S042000, C385S039000, C385S024000, C359S199200
Reexamination Certificate
active
06192175
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical technology, and more particularly to a method and system for filtering an optical signal.
BACKGROUND OF THE INVENTION
Optical technology utilizes optical signals in order to carry information. Optical technology also utilizes filters for a variety of applications. Filters transmit light in a pass band. The pass band of the filter is a range of wavelengths centered around a central wavelength. For example, one application for filters is in multiplexing and demultiplexing optical signals. It is possible to transmit a plurality of signals on a single fiber. As the use of optical technology increases, the number of signals transmitted on a single fiber also increases. Currently, composite signals include twenty, forty, or more channels.
In order to transmit a large number of signals on a given cable, channels for a plurality of wavelengths are multiplexed together for transmission. After the multiplexed, multi-channel signal reaches the destination, the channels are demultiplexed to access the information carried by a single channel. Conventional wavelength division multiplexers (“WDMs”) are used to combine individual signals as well as to separate a composite signal into individual channels.
In order to function, some conventional WDMs utilize filtering. To separate a composite signal into its component channels, conventional filtering WDMs use a plurality filters cascaded in series to isolate each channel. Each filter passes light centered around a single wavelength. A filter is typically provided for each of the component wavelength. The output of each filter is the signal centered around a single wavelength. As each component wavelength is separated from the composite signal, the remaining portion of the composite signal is passed on to the next filter in the series. Thus, the signal is separated into its components. Note that other applications may also use filters. In general, filters are useful in applications where it is desired to remove a portion of the signal outside of the filter's pass band. Thus, in addition to WDMs, filters may be used in noise removal or other applications.
Typically, a signal is input to a conventional filtering system via an optical fiber. The fiber is typically held by a capillary. The signal is then provided to a graduated index of refraction (GRIN) lens for collimating. The signal is then transmitted to a filter. The filter transmits light centered around a particular wavelength. In a conventional WDM, a separate filtering system is used for each channel.
Although conventional systems for filtering signals are capable of transmitting light in the pass band, a conventional filter is used with a fixed angle of incidence. Thus, the central wavelength for the pass band is also fixed. As a result, the filter itself will be subject to tighter specifications in order to ensure that the appropriate portion of the signal is transmitted. The tighter specifications make the filter more expensive. In addition, one filter is typically used for each channel. As a result, the cost of providing filters for a composite signal is high. This is true because the cost of producing filters with different specifications is higher than the cost of producing filters having the same specifications. In addition, the filters will occupy a relatively large space.
Accordingly, what is needed is a system and method for providing a filter which is low cost, efficient, and compact. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for filtering. The system and method comprise providing first, second, third and fourth fibers for carrying a first, second, third, and fourth optical signal, respectively. The method and system also comprise providing a holder, a filter, and a first wedge assembly. The holder is for receiving the first fiber, the second fiber, the third fiber, and the fourth fiber therein. The filter is for filtering the first optical signal, the second optical signal, the third optical signal, and the fourth optical signal to provide a first filtered optical signal, a second filtered optical signal, a third filtered optical signal, and a fourth filtered optical signal. The first wedge assembly is disposed between the holder and the filter. The first wedge assembly directs the first optical signal towards the filter in a first path, directs the second optical signal toward the filter in a second path, directs the third optical signal towards the filter in a third path, and directs the fourth optical signal toward the filter in a fourth path.
According to the system and method disclosed herein, the present invention is capable of filtering a plurality of optical signals using one filter, thereby decreasing overall system size and cost.
REFERENCES:
patent: 4472797 (1984-09-01), Nicia
patent: 5956441 (1999-09-01), Fairchild
patent: 6078710 (2000-06-01), Li
Li Wei Zhong
Liu Feng
Wang Wenhui
Boutsikaris Leo
Oplink Communications Inc.
Sawyer Law Group LLP
Spyrou Cassandra
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