CA2339911A1 - Accurate agile wavelength optical source and use thereof - Google Patents

Abstract

This disclosure applies to an improvement on conventional optical transmitter architecture which allows the production of bursts of data signals with accurate selectable optical frequency within the target optical band.
The invention overcomes the limitation caused when the monitor and feedback circuits do not provide sufficient control within the required time. A key aspect of this invention is the ability to ensure the output frequency is well controlled, even for rapid changes in output frequency, as in packet on wavelength systems. Two approaches are discussed: one for cases when the laser cannot be tuned within an allowed switching time, and one which applies when the laser can be tuned sufficiently quickly but requires on-going stabilization. The second approach may be used to improve the performance of the first approach.
The first approach, in which a single laser cannot tune accurately within the required time, makes use of multiple lasers implemented with an appropriately fast optical switch to select the desired laser, each laser being tuned and locked on the frequency required for the packet it will address while an other is (or others are) transmitting. In the second approach, in which a single laser can be tuned to the nominal frequency during the transition time, the implementation improves the initial spectral quality and frequency accuracy on switching to a new frequency through: -setting the initial frequency as determined by a set of parameters in a table, -improving the output quality during the data transmission, -updating the table parameters based on the changes necessary to improve the signal. The second approach is particularly appropriate for rapid cyclical requirements for a particular wavelength, as the conditions for any wavelength may be nominally unchanged from cycle to cycle.
If the tunable lasers cover only a fraction of the desired optical band, multiple lasers may be operated in paralleled to provide full coverage of the wavelength band, and combined with a fast optical switch, while being controlled with either of the two control approaches. This disclosure also applies to the use of such rapidly tuned optical sources to provide data units, frames or packets where each data unit can be of arbitrary frequency within a set of operational frequencies.

Claims

We claim:

1) An optical transmitter consisting of a) a wavelength agile optical source which can provide an optical signal at any of the desired wavelengths and which can generate the optical signal to the required wavelength accuracy, within the required time, through the use of feedback signals. The agile source consisting of sufficient number and disposition of tunable sources to cover the wavelengths of interest and provide sufficient redundant wavelength coverage for stabilization operations. The various tunable sources being operated nominally sequentially to provide more time for adjusting the output wavelength to the desired accuracy; the alternative source or sources being set up while one of the sources is transmitting data.
b) A set of parameters and an algorithm, used for determining the open loop settings for a tunable laser, where the parameters may be variable over time; determination based on the modifications required to maintain accurate output during the operation of the source.
c) a fast optical switch to select between the optical sources, the speed of the optical switch being sufficient for the intended use.
d) modulation means, by which data is impressed on the optical signal.
e) wavelength locking means for ensuring each source output either being set prior to sending data or transmitting data is controlled to the desired accuracy.
f) control means which selects the desired output signal to set the output wavelength of the transmitter, and which sets the output wavelength of the additional sources to the desired wavelength within the required frequency accuracy and within the required time based on feedback signals from wavelength referencing units and in response to system level management.
And used to send data units of various wavelengths