Branched waveguide multisection dbr semiconductor laser

A tunable semiconductor laser, comprising:

• a branched optical waveguide comprising a stem waveguide section with a stem optical reflector therein and optically coupled to at least two branch waveguide sections having tunable branch optical reflectors therein;
• and
• a gain section bounded by the stem optical reflector and at least one of the tunable branch optical reflectors;
• wherein the stem optical reflector is a distributed Bragg reflector “DBR”,
• wherein one of the tunable branch optical reflectors has a reflection spectrum tunable within a first wavelength range, and another of the tunable branch optical reflectors has a reflection spectrum tunable within a second wavelength range, different to the first wavelength range,
• such that in operation a lasing cavity is formed between the stem optical reflector and at least one of the tunable branch optical reflectors, causing the laser to emit light at a wavelength within either the first or the second wavelength range.