US 12,149,291 B2
Coherent receiver having low VOA-induced phase changes
Michel Poulin, Québec (CA); Antoine Bois, Québec (CA); Tom Luk, Ottawa (CA); François Pelletier, Québec (CA); and Sean Sebastian O'Keefe, Dunrobin (CA)
Assigned to Ciena Corporation, Hanover, MD (US)
Filed by Ciena Corporation, Hanover, MD (US)
Filed on Mar. 17, 2022, as Appl. No. 17/696,948.
Prior Publication US 2023/0299855 A1, Sep. 21, 2023
Int. Cl. H04B 10/60 (2013.01); H04B 10/61 (2013.01); H04B 10/07 (2013.01); H04B 10/079 (2013.01)
CPC H04B 10/6164 (2013.01) [H04B 10/6163 (2013.01); H04B 10/6165 (2013.01); H04B 10/65 (2020.05); H04B 10/07 (2013.01); H04B 10/079 (2013.01); H04B 10/07955 (2013.01); H04B 10/60 (2013.01); H04B 10/61 (2013.01); H04B 10/615 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A coherent receiver comprising:
a receive signal (SIG) path including i) an input configured to connect a receive signal, ii) one or more signal paths connected to the input and to one or more optical hybrids, and iii) at least one first variable optical attenuator (VOA); and
a local oscillator (LO) signal path including an input configured to connect to an LO and the one or more optical hybrids;
wherein the optical receiver includes a VOA-induced phase change compensation mechanism that reduces any VOA-induced phase change in a SIG-LO beat signal due to the at least one first VOA being in the signal path, wherein the VOA-induced phase change compensation mechanism includes one or more of (i) an at least one tandem second VOA in the LO path before the one or more optical hybrids, the at least one second VOA configured to add a LO phase change to the LO path to at least partially compensate for the VOA-induced phase change in the signal path due to the at least one first VOA, and (ii) the at least one first VOA being a chirp-free Mach-Zehnder interferometer forming the at least one first VOA in the signal path.