A laser, said laser comprising: a resonant laser cavity; said resonant laser cavity comprising a Bragg grating the pitch of the Bragg grating providing the wavelength selection for the laser, at least one active section comprising a material configured to amplify an optical signal in response to a driving current and a controllable optical loss section, said controllable optical loss section being controllable to transition between a high optical loss mode and a lower optical loss mode; a control signal input configured to supply a control signal to said controllable optical loss section to control said optical loss section to transition between said high optical loss mode and said lower optical loss mode, a lasing effect of said resonant cavity being suppressed by optical losses when said optical loss section is in said high optical loss mode such that said transitioning of modes of said optical loss section causes said laser to transition between outputting said optical signal and outputting no optical signal; and control circuitry configured to control said control signal supplied to said optical loss section, said control circuitry being configured to generate a periodically varying control signal to periodically switch said optical loss section from said lower loss mode to said high loss mode such that said laser operates in a burst mode, said control circuitry comprising driving current control circuitry configured to control said driving current supplied to said at least one active section such that an average electrical power supplied to said at least one active section is substantially the same during a period when said laser is not emitting said output signal and during a period when said laser is emitting said output signal; wherein said laser comprises a directly modulated laser, said driving current control circuitry being configured to modulate said driving current such that said active section generates a modulated optical signal. a resonant laser cavity; said resonant laser cavity comprising a Bragg grating the pitch of the Bragg grating providing the wavelength selection for the laser, at least one active section comprising a material configured to amplify an optical signal in response to a driving current and a controllable optical loss section, said controllable optical loss section being controllable to transition between a high optical loss mode and a lower optical loss mode; a control signal input configured to supply a control signal to said controllable optical loss section to control said optical loss section to transition between said high optical loss mode and said lower optical loss mode, a lasing effect of said resonant cavity being suppressed by optical losses when said optical loss section is in said high optical loss mode such that said transitioning of modes of said optical loss section causes said laser to transition between outputting said optical signal and outputting no optical signal; and control circuitry configured to control said control signal supplied to said optical loss section, said control circuitry being configured to generate a periodically varying control signal to periodically switch said optical loss section from said lower loss mode to said high loss mode such that said laser operates in a burst mode, said control circuitry comprising driving current control circuitry configured to control said driving current supplied to said at least one active section such that an average electrical power supplied to said at least one active section is substantially the same during a period when said laser is not emitting said output signal and during a period when said laser is emitting said output signal; wherein said laser comprises a directly modulated laser, said driving current control circuitry being configured to modulate said driving current such that said active section generates a modulated optical signal.