Integrated semiconductor laser element

An integrated semiconductor laser element, comprising and integrated of:

• a plurality of semiconductor lasers of distributed feedback type that oscillate in single mode at emission wavelengths different from each other;
• an optical coupler that has as many input ports as the plurality of semiconductor lasers, the input ports to which output light from the plurality of semiconductor lasers are input, the optical coupler guiding and outputting the output light;
• and
• a semiconductor optical amplifier that amplifies the output light from the optical coupler,
• wherein the following relation (1) holds true, where “N” is the number of the plurality of semiconductor lasers, “Ldfb” is a cavity length of each of the plurality of semiconductor lasers, “Δν0” is a spectral linewidth of laser light output therefrom, “Lsoa” is an amplifier length of the semiconductor optical amplifier, “A” is an amplification factor of the semiconductor optical amplifier, “Δν” is a spectral linewidth of amplified laser light output therefrom, and “R” is Δν/Δν0:
• Lsoa
• Ldfb
• ≤
• (
• R
• -
• 1
• )
• ·
• N
• ·
• 1.44
• ·
• A
• -
• 0.74
• .
• (
• 1
• )