An optical system includes a first optical source, a second optical source, a first optical modulator, and a second optical modulator. The first optical modulator includes a first input and a first output. The second optical modulator includes a second input, a third input, a second output, and a third output. During a first mode, the first optical source emits a first optical signal to the first input and the second input, the first optical modulator produces a first modulated optical signal at the first output, and the second optical modulator produces a second modulated optical signal at the second output. During a second mode, the second optical source emits a second optical signal to the third input and the second optical modulator produces a third modulated optical signal at the third output.