Thermally insensitive optical multiplexer

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.