Advanced optical modulation generation by combining orthogonal polarized optical signals
View Patent ↗Disclosed are adaptive structures and methods for generating advanced modulation formats using multiple levels such as PAM-4, PAM-8 as well as regular OOK or PM OOK formats. Structures and methods disclosed include an unequal power splitter that may exhibit a fixed or tunable splitting ratio such that adaptive format(s) may be generated.
1. An optical modulator comprising:
a Mach-Zehnder interferometer (MZI) structure including a tunable splitter arranged to split input light into two modulator arms of the MZI;
a polarization combiner arranged to combine light from the two modulator arms into an output signal, wherein the two modulator arms connect the tunable splitter to the polarization combiner;
an on-off keying (OOK) modulator positioned in a first arm of the two modulator arms; and
a single-polarization, four-level, pulse-amplitude (PAM-4) modulator and a polarization rotator positioned in a second arm of the two modulator arms, wherein the tunable splitter is configured such that 4/7 of the input light is directed into the first arm and 3/7 of the input light is directed into the second arm for modulating the input light according to eight-level pulse-amplitude modulation (PAM-8) format.
2. The MZI optical modulator of claim 1 , wherein the OOK modulator comprises a Mach Zehnder interferometer.
3. The MZI optical modulator of claim 1 , wherein the OOK modulator comprises a electro-absorption modulator or ring modulator.