Tuneable laser having comb reflectors producing combs of reflective wavelength peaks

A tuneable laser, comprising a cavity having first and second reflective ends, a gain section located within the cavity, the first reflective end comprising first and second comb reflectors, the first comb reflector being adapted to produce a first comb of reflective wavelength peaks and the second comb reflector being adapted to produce a second comb of wavelength peaks, the spacings between the peaks of the first comb being substantially uniform and being different from the substantially uniform spacings of the peaks in the second comb, the gain section having an associated electrode capable, in use, of passing current selectively through the gain section, wherein the gain section has both the first comb reflector and the second comb reflector on the same side, the first comb reflector and the second comb reflector being capable of being tuned such that, in use, tuning causes movement in wavelength of the reflective peaks of the first comb relative to those of the second comb so as to cause alignment of a single reflective peak at the same wavelength in both the first and second combs to form a supermode, at which wavelength the gain section can cause the laser to lase.