An optical module is configured with a combination of a single-mode
oscillating light source and an optical filter. In this optical module,
the single-mode oscillating light source outputs a single-mode,
frequency-modulated signal. Further, the optical filter converts the
frequency modulation to an amplitude modulation. And, the single-mode
oscillating light source and the optical filter are packaged without
active alignment on the same substrate. Accordingly, it is possible to
realize an optical module in a simple and low-cost configuration by
packaging the single-mode oscillating light source and the optical filter
by passive alignment, without active alignment, on the same substrate,
and by using a simple optical filter such as a waveguide ring resonator,
which converts a frequency modulation to an amplitude modulation.