Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-30
2001-10-16
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C372S034000, C372S023000, C385S024000, C385S027000
Reexamination Certificate
active
06304350
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a multi-channel, wavelength-division-multiplexed (WDM) passive optical network (PON) communication system and, more particularly, to a method and apparatus for the temperature compensating of such networks using a waveguide grating router (WGR) for detecting the power received at the routing networks of such a system.
BACKGROUND OF THE INVENTION
Passive optical networks (PON) have gained much interest in the past years because of their fiber gain, broadband capability, and unpowered outside plant which reduces maintenance cost [1]. (Note that in the above and following description, a reference's identification [e.g., 1] refers to that reference's location in the Appendix) Generally, PONs can be either time division multiplex (TDM), wavelength division multiplex (WDM) or both. In a TDM PON, the signals, which are electronically multiplexed at the Central Office (CO), are equally split at the remote node (RN) by a passive power splitter among all the optical network units (ONU) where they are electronically demultiplexed. The receivers at each ONU have to process the information at the aggregate bit-rate. Furthermore, the optical signal power coming from the CO is attenuated at the RN because of the splitting loss. In WDM PONs, each ONU is assigned a different wavelength, which is passively demultiplexed at the RN by a router. This provides a virtual point-to-point connectivity which also means that the receiver and the transmitter do not operate at the aggregate bit-rate. Such a system allows high flexibility in bandwidth allocation and upgradability for individual ONUs or for the whole system. However, one of the prices to pay for this flexibility is wavelength management. Each wavelength must be precisely spaced and aligned with the router. The multifrequency laser (MFL) provides a precise channel spacing due to its internal waveguide grating router (WGR) which acts as an intra cavity filter [2]. The WGR also provides single-knob wavelength comb tunability by changing the device temperature alone, simplifying the locking of the MFL source wavelengths to the passive WGR demultiplexer at the RN, which drifts due to temperature changes of the uncontrolled outside plant. What is needed is a practical and reliable way to lock the MFL wavelength frequencies to the WGR demultiplexer with temperature changes in the outside plant (i.e., WGR).
SUMMARY OF THE INVENTION
The present invention solves the prior art problems using a novel method and apparatus for temperature compensation of a multi-channel, wavelength-division-multiplexed (WDM) passive optical network (PON) communication system. In accordance with the present invention, changes in the power level at each remote node (RN) caused by frequency drift of its waveguide grating router (WGR), due to changes in its temperature, can be determined by monitoring the power level received at RN and corrected by appropriate changes in the temperature of the multifrequency laser (MFL). Our invention, uses a WGR where one output port (e.g., channel
1
) is looped-back through the WGR a second time to increase the temperature sensitivity of the received power measurements.
More particularly, in accordance with the present invention, a WDM communication system comprises a transmitter unit a receiver unit and a controller. The transmitter includes (1) a temperature sensitive multifrequency laser MFL for transmitting a multifrequency laser signal over an optical facility, and (2) a controller for controlling the temperature of the multifrequency laser in response to a power level signal received over a facility from a WDM receiver unit. The receiver unit includes a WGR apparatus comprising (1) a first input port of the WGR for receiving a wavelength division multiplexed (WDM) signal having a plurality of wavelengths signals, each wavelength being demultiplexed by the WGR and outputted at a separate first type output port of a plurality of first type output ports, (2) a second input port of the WGR arranged to communicate a preselected wavelength signal to a second type output port and (3) wherein a preselected one of the plurality of first type output ports is connected to the second type output port, so that a preselected wavelength signal received at the selected first type output port is outputted from the second input port. The controller receives the preselected wavelength signal, detects its power level and sends the received power level signal to the WDM transmitter unit.
In a single receiver WDM system, the controller may be located at the receiver and in a multiple receiver system the controller may be located at a separate location or at one of the receiver locations. According to one aspect of the invention, the temperature controller includes a temperature control algorithm for controlling the temperature of the MFL as a function of the received power at the WGR of the WDM receiver unit. According to another aspect, the MFL includes a WGR which is the same type as the WGR of the WDM receiver unit.
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Doerr Christopher Richard
Joyner Charles H.
Monnard Rene Henri
Stulz Lawrence Warren
Zirngibl Martin
Caccuro John A.
Lucent Technologies Inc
Nguyen Chau M.
Pascal Leslie
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