Thermally insensitive optical multiplexer
In an optical multiplexer, a first Mach-Zehnder interferometer (MZI) generates a first intermediate optical signal based on i) a first input optical signal at a first wavelength, and ii) a second input optical signal at a second wavelength. A second MZI generates a second intermediate optical signal based on i) a third input optical signal at a third wavelength, and ii) a fourth input optical signal at a fourth wavelength. A polarization combiner rotator (PCR) is coupled to the first MZI and the second MZI. The PCR generates an output optical signal based on i) the first intermediate optical signal received at a first input of the PCR, and ii) the second intermediate optical signal received at a second input of the PCR. The output optical signal includes the first input optical signal, the second input optical signal, the third input optical signal, and the fourth input optical signal.
1 . An optical multiplexer, comprising:
a first Mach-Zehnder interferometer (MZI) configured to generate a first intermediate optical signal based on i) a first input optical signal at a first wavelength received at a first input of the first MZI, and ii) a second input optical signal at a second wavelength received at a second input of the first MZI;
a second MZI configured to generate a second intermediate optical signal based on i) a third input optical signal at a third wavelength received at a first input of the second MZI, and ii) a fourth input optical signal at a fourth wavelength received at a second input of the second MZI; and
a polarization combiner rotator (PCR) coupled to the first MZI and the second MZI, the PCR configured to generate an output optical signal based on i) the first intermediate optical signal received at a first input of the PCR, and ii) the second intermediate optical signal received at a second input of the PCR, the output optical signal including the first input optical signal, the second input optical signal, the third input optical signal, and the fourth input optical signal, the PCR comprising an adiabatic mode multiplexer configured to generate a third intermediate optical signal based on the first intermediate optical signal and the second intermediate optical signal, the adiabatic mode multiplexer including an adiabatic coupler having:
a first waveguide configured to receive the first optical signal, the first waveguide including a first tapered portion having a first wide end and a first narrow end, and
a second waveguide configured to receive the second intermediate optical signal, the adiabatic mode multiplexer configured to transfer the second intermediate optical signal to the first waveguide, the second waveguide including a second tapered portion proximate to the first tapered portion of the first waveguide, the second tapered portion having i) a second narrow end proximate to the first wide end of the first waveguide, and ii) a second wide end proximate to the first narrow end of the first waveguide.
2 . The optical multiplexer of claim 1 , wherein the PCR further comprises:
a polarization rotator configured to generate the output optical signal based on the third intermediate optical signal.
3 . The optical multiplexer of claim 2 , wherein the polarization rotator comprises a bi-level taper.
4 . The optical multiplexer of claim 1 , wherein:
a width of the first tapered portion changes non-linearly between the first wide end and the first narrow end; and
a width of the second tapered portion changes non-linearly between the second wide end and the second narrow end.
5 . The optical multiplexer of claim 1 , wherein the first MZI comprises:
a first optical coupler fabricated using silicon (Si);
a second optical coupler fabricated using Si;
a first arm to optically couple the first optical coupler to the second optical coupler, the second arm fabricated using silicon nitride (SiN) and having a first length; and
a second arm to optically couple the first optical coupler to the second optical coupler, the second arm fabricated using SiN and having a second length different than the first length.
6 . An optical transmitter, comprising the optical multiplexer of claim 1 , the optical transmitter further comprising:
a plurality of lasers;
a plurality of optical modulators coupled to the plurality of lasers;
a baseband processor configured to:
receive data that is to be transmitted, and
generate, based on the data that is to be transmitted, modulation signals for controlling the plurality of optical modulators; and
wherein i) the first input of the first MZI is coupled to a first optical modulator among the plurality of optical modulators, and ii) the second input of the first MZI is coupled to a second optical modulator among the plurality of optical modulators; and
wherein i) the first input of the second MZI is coupled to a third optical modulator among the plurality of optical modulators, and ii) the second input of the second MZI is coupled to a fourth optical modulator among the plurality of optical modulators.
7 . The optical transmitter of claim 6 , wherein the baseband processor comprises digital signal processing (DSP) circuitry configured to perform one or more of i) forward error correction (FEC) encoding, ii) signal pre-compensation, and iii) mapping data that is to be transmitted to transmission symbols.
8 . The optical transmitter of claim 7 , wherein the DSP circuitry is further configured to generate digital modulation signals based on the transmissions symbols.
9 . The optical transmitter of claim 8 , further comprising:
analog front end (AFE) circuitry that is configured to generate analog modulation signals based on the digital modulation signals; and
wherein the plurality of optical modulators are configured to use the analog modulation signals to modulate respective light output by the plurality of lasers.