Tunable laser diode

An oscillation wavelength adjustment type tunable laser diode comprising:

• an optical gain waveguide configured to generate and amplify light;
• a multi-mode interference waveguide configured to include M input ports and N output ports (where M is a natural integer and N is a positive integer equal to or greater than 2);
• and
• a reflective delay line array including N reflective delay lines connected to a side of the N output ports of the multi-mode interference waveguide, each of N reflective delay lines being terminated by a reflector configured to reflect the light,
• the optical gain waveguide, the multi-mode interference waveguide, and the reflective delay line array being integrated on a top surface of an identical substrate,
• wherein each of the N reflective delay lines is provided with an electro-absorption modulator, and when ti (i=0, 1, 2, . . . , N−1) denotes an electric field transmittance of reciprocating light in each of the N reflective delay lines, each of the electro-absorption modulator is configured to control an intensity of the reciprocating light so that a total value of the electric field transmittance
• (
• ∑
• i
• =
• 0
• N
• -
• 1
• ⁢
• t
• i
• )
• is constant, and
• wherein the N reflective delay lines are configured to adjust the intensity of the reciprocating light in accordance with a wavelength of the light transmitted through the N reflective delay lines.