CWDM transmit module for wavelength tuning and tracking

A photonic integrated circuit comprising:

• a semiconductor substrate, comprising a first surface and a second surface;
• an optical bus waveguide disposed through the semiconductor substrate;
• at least four ring laser cavities disposed within the semiconductor substrate, the ring cavities optically coupled to the optical bus waveguide, each ring laser cavity comprising a portion of a respective laser and having a local wavelength control mechanism;
• a wavelength selective filter optically coupled to the bus waveguide, the filter having a first photodetector;
• and
• a control circuit electronically coupled to each wavelength control mechanism, and the first photodetector, wherein, in operation, the control circuit is configured to:
• determine whether a respective laser's wavelength aligns with a channel spacing grid;
• and
• control the wavelength control mechanisms to adjust the wavelength of the first ring laser, and the second ring laser, to align the wavelengths to the channel spacing grid.

A method for tuning a photonic integrated circuit, the method comprising:

• transmitting a first wavelength emission through a bus waveguide using a first ring laser;
• receiving a portion of the wavelength emission using a wavelength selective filter;
• determining a first photocurrent value for the first wavelength emission;
• transmitting a second wavelength emission through the bus waveguide using a second ring laser;
• receiving a portion of the second wavelength emission using the wavelength selective filter;
• determining a second photo current value for the second wavelength emission;
• generating a map of each laser's wavelength of resonance as a function of the bias on the wavelength selective filter and the determined photocurrent values;
• determining whether each laser's wavelength aligns with a channel spacing grid;
• and
• adjusting the wavelength of the first ring laser, and the second ring laser, to align the wavelengths to the channel spacing grid.