Patent ID: 6980578

Claim:
A laser comprising: (a) a resonant cavity, (b) a tuning element in the resonant cavity, the tuning element comprising: i. an optical waveguide having a first portion and a second portion, the first and second portions being serially connected, the first portion having optical transmission characteristics that are different than those of the second portion; ii. a first long period grating for converting signal light propagating in mode LP 01 into signal light propagating in mode LP m,n , iii. an optical coupler configured to transmit signal light propagating in mode LP m,n in the first portion to LP r,s mode light in the second portion, wherein m =r and n =s, iv. a second long period grating for converting a selected band Δλ 2 of signal light propagating in mode LP r,s in the second portion to light propagating in mode LP 01 .