External cavity laser array system and WDM optical system including same
An external cavity laser array system may be used in a WDM optical system, such as a WDM-PON, for transmitting optical signals at multiple channel wavelengths. The system generally includes a plurality of laser emitters (e.g., gain chips) optically coupled to and separated from respective exit reflectors (e.g., tunable narrow-band reflectors), thereby forming an array of external cavity lasers with extended lasing cavities. The exit reflectors may be distributed Bragg reflectors (DBRs) located in the waveguides in an arrayed waveguide grating (AWG). The laser emitters emit a range of wavelengths including multiple channel wavelengths and the DBRs reflect a subset of channel wavelengths including at least a channel wavelength associated with the laser emitter such that lasing occurs at the subset of channel wavelengths. The AWG then filters the emitted laser light at the associated channel wavelengths.
1. An external cavity laser array system comprising: a plurality of laser emitters, each of the laser emitters including a gain region for emitting light across a range of wavelengths and a back reflector located at one end thereof; and an arrayed waveguide grating (AWG) including a plurality of input ports optically coupled to the laser emitters, respectively, an output port, and a plurality of optical waveguides extending from the input ports, respectively, to the output port, wherein the optical waveguides include distributed Bragg reflector (DBR) gratings, respectively, such that extended lasing cavities are formed between the back reflectors of the laser emitters and the DBR gratings, respectively, acting as exit reflectors integrated into the AWG, and wherein each of the optical waveguides of the AWG filters the light at an associated channel wavelength such that the AWG provides both channel selection and optical multiplexing; wherein each of the extended lasing cavities has a length such that a mode spacing of the laser light emitted from each of the lasing cavities is less than about 0.8 nm such that multiple lasing modes fit within respective passbands of the optical waveguides in the AWG.
2. The external cavity laser array system of claim 1 wherein the laser emitters include reflective-semiconductor-optical-amplifiers (R-SOAs).
3. The external cavity laser array system of claim 1 further comprising an optical assembly for optically coupling the emitted light into the respective waveguides of the AWG.
4. The external cavity laser array system of claim 1 wherein each of the DBR gratings has a reflection band overlapping with a respective AWG channel wavelength band of each of the optical waveguides of the AWG.
5. The external cavity laser array system of claim 1 wherein positions of at least some of the laser emitters are adjustable such that distances between the laser emitters and the DBR gratings are adjustable to adjust effective external cavity lengths.
6. The external cavity laser array system of claim 1 wherein a gain region cavity of each of the laser emitters has a length of less than about 1000 μm.
7. The external cavity laser array system of claim 1 wherein at least one of the extended lasing cavities has a length of at least about 9 mm.
8. The external cavity laser array system of claim 1 wherein at least one of the extended lasing cavities has a length such that the mode spacing of the laser light emitted from each of the extended lasing cavities is less than about 0.4 nm such that multiple lasing modes fit within respective passbands of the optical waveguides in the AWG.
9. The external cavity laser array system of claim 1 wherein at least one of the extended lasing cavities has a length such that the mode spacing of the laser light emitted from each of the extended lasing cavities is about 0.1 nm or less such that multiple lasing modes fit within respective passbands of the optical waveguides in the AWG.
10. The external cavity laser array system of claim 1 further comprising a temperature controller thermally coupled to the AWG for tuning the DBR gratings in the AWG.