Adiabatically frequency modulated source
View Patent ↗A Distributed Feed-Back (DFB) laser integrated with an Electroabsorption (EA) modulator whose facet at the end of EA modulator section has finite reflectively to create adiabatic chirp by optical feedback to the DFB laser.
1. A method for generating optical signals comprising:
modulating an optical source to generate digital frequency modulated optical signals, the frequency modulated optical source comprising an integrated multi-section laser comprising a gain section comprising a distributed feedback portion and a non-distributed feedback portion, an electro-absorption section, and a phase section disposed between the non-distributed feedback portion section and the electro-absorption section, wherein the electro-absorption section includes a reflecting element for reflecting light from the electro-absorption section back through the phase section and into the gain section;
selectively adjusting a bias of the phase section, whereby to increase frequency modulation of the optical source.
2. The method of claim 1 wherein the distributed feedback section is a complex coupled quarter wave shifted type in order to produce a single longitudinal mode.
3. The method of claim 1 wherein the length of the electro-absorption section and the length of the phase section are effective to produce desired frequency modulation characteristics.
4. The method of claim 1 , wherein modulating the optical source to generate digital frequency modulated optical signals further comprises modulating the electro-absorption section.
5. The method of claim 1 , wherein modulating the optical source to generate digital frequency modulated optical signals further comprises directly modulating the distributed feedback section.
6. The method of claim 1 , further comprising selectively adjusting a bias of the non-distributed feedback portion, whereby to adjust a magnitude of a frequency excursion of the frequency modulated signal.
7. The method of claim 1 , further comprising biasing the non-distributed feedback portion and modulating the distributed feedback portion.
8. The method of claim 1 , further comprising adjusting the bias of the phase section an amount effective to change the phase of light through the electro-absorption section to the distributed feedback section effective to induce a predetermined adiabatic chirp in the DFB.
9. The method of claim 1 , further comprising supplying modulation current to the distributed feedback section and electro-absorption sections in amounts effective to achieve a predetermined delay between FM and AM modulation.
10. A multi-section laser comprising:
a gain section having a distributed feedback portion having a grating formed thereon and a non-distributed feedback portion, a phase at the end of the grating adjacent the non-distributed feedback portion equal to about −30 degrees;
an electro-absorption section;
a phase section disposed between the distributed feedback gain section and the electro-absorption section; and
an antireflective coating, the electro-absorption section being between the phase section and the antireflective coating, the antireflective coating having a reflectivity about equal or greater than −20 dB.
11. The multi-section laser of claim 10 , further comprising first and second electrodes positioned over the distributed feedback portion and non-distributed feedback portion, respectively, the first and second electrodes being separated from one another by an isolation trench.
12. The multi-section laser of claim 10 , wherein the distributed feedback portion is a complex coupled quarter wave shifted type.
13. A method for generating an adiabatically chirped signal from electrical digital data, comprising:
biasing a gain section having a distributed feedback gain section having a grating formed thereon and a non-distributed feedback portion, a phase at the end of the grating adjacent the non-distributed feedback portion equal to about −30 degrees;
outputting light from the distributed feedback gain section to an electro-absorption modulator; and
modulating the electro-absorption modulator with the electrical digital data to selectively reflect light back to the distributed feedback gain section to provide an adiabatically chirped modulated output light encoding the electrical digital data.
14. The method of claim 13 , further comprising passing light reflected back to the distributed feedback gain section through an adjustable phase section prior to entering the distributed feedback gain section.
15. The method of claim 13 , wherein an anti-reflective coating having a reflectivity of about −20 dB or greater is formed on the electro-absorption modulator having the electro-absorption modulator positioned between the anti-reflective coating and the distributed feedback gain section.
16. The method of claim 1 , wherein the distributed feedback portion has a grating formed thereon, a phase of the grating adjacent the non-distributed feedback portion being equal to about −30 degrees.
17. The method of claim 1 , wherein the distributed feedback portion has a grating formed thereon, a phase of the grating adjacent the non-distributed feedback portion equal to about 150 degrees.
18. The method of claim 1 , further comprising applying different bias voltages to the distributed feedback portion and non-distributed feedback portion.
19. The method of claim 18 , further comprising a first electrode positioned over the distributed feedback section and a second electrode positioned over the non-distributed feedback section, the first and second electrodes being separated by an isolation trench; wherein applying different bias voltages to the distributed feedback portion and non-distributed feedback portions comprises applying different bias voltages to the first and second electrodes.