Examples herein relate to optical systems. In particular, implementations herein relate to an optical system including an optical transmitter configured to transmit optical signals. The optical transmitter includes a first optical source coupled to an input waveguide and configured to emit light having different wavelengths through the input waveguide. The optical transmitter includes a Mach-Zehnder interferometer that includes a first arm and a second arm. The MZI further includes a first optical coupler configured to couple the emitted light from the input waveguide to the first and second arms and an array of two or more second optical sources coupled to the first arm. Each of the two or more second optical sources are configured to be injection locked to a different respective wavelength of the emitted light transmitted from the first optical source. The MZI further includes a second optical coupler configured to combine the emitted light from the first and second arms after propagating therethrough.