Optical Network Unit (ONU) Wavelength Self-Tuning

Abstract

A remote node (RN) comprises a downstream port, a wavelength multiplexer (WM) coupled to the downstream port and comprising ports for passing optical waves, an optical rotator coupled to the WM, and a mirror coupled to the optical rotator, wherein the WM, the optical rotator, and the mirror are part of a wavelength tuning scheme. An apparatus comprises a tunable transmitter, a polarization beam splitter (PBS) coupled to the tunable transmitter, a filter coupled to the PBS, a receiver coupled to the filter, a photodiode (PD) coupled to the PBS, and a processor coupled to the tunable transmitter and the PD. An apparatus comprises a tunable transmitter configured to transmit a first optical wave, a filter configured to receive a first reflected optical wave associated with the first optical wave, and a processor configured to tune the tunable transmitter based on the first reflected optical wave.

What is claimed is: 
     
         1 . A remote node (RN) comprising:
 a downstream port;   a wavelength multiplexer (WM) coupled to the downstream port and comprising ports for passing optical waves;   an optical rotator coupled to the WM; and   a mirror coupled to the optical rotator, wherein the WM, the optical rotator, and the mirror are part of a wavelength tuning scheme.   
     
     
         2 . The RN of  claim 1 , further comprising an upstream port coupled to the mirror, wherein the WM is an arrayed waveguide grating (AWG), wherein the optical rotator is a  45 -degree)(° Faraday rotator (FR), wherein the mirror is a partial-reflection mirror (PRM), and wherein the FR and the PRM form a Faraday rotator mirror (FRM). 
     
     
         3 . The RN of  claim 1 , further comprising:
 a coupler positioned between the WM and the optical rotator; and   an upstream port coupled to the coupler,   wherein the WM is an arrayed waveguide grating (AWG),   wherein the optical rotator is a 45-degree (°) Faraday rotator (FR),   wherein the mirror is a high-reflection mirror (HRM), and   wherein the FR and the PRM form a Faraday rotator mirror (FRM).   
     
     
         4 . The RN of  claim 3 , wherein the coupler is a tap coupler configured to forward at least part of an optical wave upstream. 
     
     
         5 . The RN of  claim 1 , wherein the WM is configured to multiplex a first optical wave with second optical waves, wherein the optical rotator is configured to rotate the first optical wave, and wherein the mirror is configured to reflect at least part of the first optical wave to create a reflected optical wave. 
     
     
         6 . The RN of claim of  claim 5 , wherein the WM is configured to forward the reflected optical wave downstream. 
     
     
         7 . The RN on  claim 5 , wherein the first optical wave and the reflected optical wave are orthogonal to each other.