System and method for laser wavelength control
Disclosed are systems and methods for improving wavelength control in tunable laser sources. Embodiments of the systems and methods include delivering a fraction of the light output from the laser to an optical filter subsystem. The optical filter subsystem is capable of outputting at least one filter response signal, and comprises 2 complementary optical etalon filters with nominally identical free spectral ranges but offset by nominally one third of the free spectral range. The filter response signal is processed in a control unit which executes a control algorithm to generate a tuning signal that is used to control the wavelength of the laser.
1. A wavelength-controlled laser system comprising:
a laser with an output wavelength responsive to at least one tuning signal,
an optical sampling device configured to deliver a fraction of light output from the laser to an optical filter subsystem, said optical filter subsystem capable of outputting at least one filter response signal,
a control unit configured to receive said at least one filter response signal and execute a control algorithm to generate a tuning signal that is used to control the wavelength of the laser, wherein said control algorithm, in determining the tuning signal, uses a weighted combination of the at least one filter response signals such that response signals with higher signal-to-noise ratio are weighted more heavily; and
wherein the optical filter subsystem comprises at least one periodic optical frequency discriminator that is configured to provide at least first and second complementary optical filter outputs associated with discriminator transfer functions that are spectrally offset.
2. The system of claim 1 , wherein said control algorithm also uses previously determined state information about the wavelength dependence on temperature, bias current or output power in generating the tuning signal.
3. The system of claim 1 , wherein
said optical filter subsystem further comprises a coarse wavelength filter with the transmission slope or period that extends over many times the wavelength range of said at least one periodic optical frequency discriminator.
4. The system of claim 1 , wherein
the at least one periodic optical frequency discriminator is configured to provide the at least first and second complementary optical filter outputs by directing associated optical beams through a single optical etalon at different angles.
5. A method for controlling the wavelength of a tunable laser source, in which the laser source is responsive to at least one tuning signal, the method comprising
delivering a fraction of the light output from the laser to an optical filter subsystem, said optical filter subsystem capable of outputting at least one filter response signal, and wherein the optical filter subsystem comprises at least one optical etalon filter configured to provide at least first and second wavelength responses that are offset,
receiving said at least one filter response signal in a control unit, and
executing a control algorithm to generate a tuning signal that is used to control the wavelength of the laser, wherein said control algorithm, in determining the tuning signal, uses a weighted combination of the at least one filter response signal such that response signals with higher signal-to-noise ratio are weighted more heavily.
6. The method of claim 5 , wherein
said control algorithm also uses previously determined state information about the wavelength dependence on temperature, bias current or output power in generating the tuning signal.
7. The method of claim 5 , wherein
said optical filter subsystem further comprises a coarse wavelength filter with the transmission slope or period that extends over many times the wavelength range of said etalon filter.
8. The method of claim 5 , wherein
the first and second wavelength responses are obtained by passing associated optical beams through the at least one optical etalon filter at different angles.
9. The wavelength-controlled laser system of claim 1 , wherein the spectral offset is about one third of a period of the at least one periodic optical frequency discriminator.
10. The wavelength-controlled laser system of claim 9 , wherein the optical filter subsystem further comprises a coarse wavelength filter with the transmission slope or period that extends over many times the wavelength range of the at least one periodic optical frequency discriminator.
11. The wavelength-controlled laser system of claim 1 , wherein the optical filter subsystem comprises at least 2 periodic optical frequency discriminators with nominally identical periods configured to produce the first and second complementary optical filter outputs, respectively, and wherein the wavelength responses of the at least 2 periodic optical frequency discriminators are offset by nominally one third of the period.
12. The wavelength-controlled laser system of claim 11 , wherein the periodic optical frequency discriminators are etalon filters and the identical period corresponds to a free spectral range.
13. The method of claim 5 , wherein the at least first and second wavelength responses are offset by nominally one third of the free spectral range.
14. The method of claim 5 , wherein the optical filter subsystem comprises first and second complementary optical etalon filters with nominally identical free spectral ranges offset by nominally one third of the free spectral range, wherein the first and second wavelength responses are obtained from the first and second complementary optical filters, respectively.