US 12,126,386 B2
Optical transmitter that transmits multi-level optical signal
Shinsuke Tanaka, Hiratsuka (JP); and Tomoyuki Akiyama, Yokohama (JP)
Assigned to FUJITSU LIMITED, Kawasaki (JP)
Filed by Fujitsu Limited, Kawasaki (JP)
Filed on Sep. 27, 2022, as Appl. No. 17/953,375.
Claims priority of application No. 2021-203720 (JP), filed on Dec. 15, 2021.
Prior Publication US 2023/0188219 A1, Jun. 15, 2023
Int. Cl. H04B 10/50 (2013.01); H04B 10/548 (2013.01)
CPC H04B 10/548 (2013.01) [H04B 10/501 (2013.01)] 6 Claims
OG exemplary drawing
 
1. An optical transmitter comprising:
a signal processing circuit configured to generate N drive signals;
an optical modulator configured to include a Mach-Zehnder interferometer and N phase-shift segments each of which shifts a phase of light propagating through an optical path of the Mach-Zehnder interferometer according to the N drive signals, and generate a modulated optical signal according to the N drive signals, a symbol rate of the modulated optical signal being fs and each symbol of the modulated optical signal transmitting N bits, N being an integer equal to or larger than 2;
an optical filter configured to remove, from output light of the optical modulator, a frequency component in a range of #fs/2 with respect to a center frequency of the modulated optical signal to generate a filtered modulated optical signal, and extract at least a part of frequency components of the filtered modulated optical signal; and
a delay circuit configured to control timings of the N drive signals in such a manner as to reduce optical power of the frequency component extracted by the optical filter.