Methods, systems, and apparatus, for optical communication. One optical assembly includes a Fabry-Perot (FP) laser diode; a first polarization controller (PC) coupled to the FP laser diode; a circulator having four ports, a first port coupled to the first PC; an optical fiber coupled at a first end to a second port of the circulator; a second PC coupled to a third port of the circulator; an optical amplifier coupled to the second PC and a fourth port of the circulator; a wavelength division multiplexer (WDM) filter coupled to the second end of the optical fiber; a splitter having at least three ends coupled at a first end to the WDM; and a Faraday rotator mirror (FRM) coupled directly or indirectly to a second end of the splitter.