A free space linear cavity tunable laser source comprising: a gain medium; two lenses (512, 513); an end reflector; and a tunable Micro-electro-mechanical-system Fabry-Perot, MEMS-FP, filter (530, 210), the tunable MEMS-FP filter (530, 210) comprising: a semiconductor or dielectric substrate having an upper and a lower face; a fixed reflector attached to the surface of a cut-out on the lower face of the substrate, a bottom electrode disposed on the upper face of the substrate, and an anti-reflection, AR, layer disposed on the upper face of the substrate; a moveable reflector having an upper and a lower face, supported by one or more suspension beams, and comprising a MEMS and one or more multilayer dielectric Distributed Bragg Reflector, DBR, mirrors and a top electrode disposed on the upper face of the moveable reflector, wherein an air gap is formed between the lower face of the moveable reflector and the upper face of the substrate; wherein an optical cavity is formed between the fixed reflector and the moveable reflector, and the optical cavity includes a portion of the substrate between the fixed reflector and the moveable reflector; and a voltage source to supply voltage between the top electrode and the bottom electrode to change the cavity length of the optical cavity. a gain medium; two lenses (512, 513); an end reflector; and a tunable Micro-electro-mechanical-system Fabry-Perot, MEMS-FP, filter (530, 210), the tunable MEMS-FP filter (530, 210) comprising: a semiconductor or dielectric substrate having an upper and a lower face; a fixed reflector attached to the surface of a cut-out on the lower face of the substrate, a bottom electrode disposed on the upper face of the substrate, and an anti-reflection, AR, layer disposed on the upper face of the substrate; a moveable reflector having an upper and a lower face, supported by one or more suspension beams, and comprising a MEMS and one or more multilayer dielectric Distributed Bragg Reflector, DBR, mirrors and a top electrode disposed on the upper face of the moveable reflector, wherein an air gap is formed between the lower face of the moveable reflector and the upper face of the substrate; wherein an optical cavity is formed between the fixed reflector and the moveable reflector, and the optical cavity includes a portion of the substrate between the fixed reflector and the moveable reflector; and a voltage source to supply voltage between the top electrode and the bottom electrode to change the cavity length of the optical cavity. a semiconductor or dielectric substrate having an upper and a lower face; a fixed reflector attached to the surface of a cut-out on the lower face of the substrate, a bottom electrode disposed on the upper face of the substrate, and an anti-reflection, AR, layer disposed on the upper face of the substrate; a moveable reflector having an upper and a lower face, supported by one or more suspension beams, and comprising a MEMS and one or more multilayer dielectric Distributed Bragg Reflector, DBR, mirrors and a top electrode disposed on the upper face of the moveable reflector, wherein an air gap is formed between the lower face of the moveable reflector and the upper face of the substrate; wherein an optical cavity is formed between the fixed reflector and the moveable reflector, and the optical cavity includes a portion of the substrate between the fixed reflector and the moveable reflector; and a voltage source to supply voltage between the top electrode and the bottom electrode to change the cavity length of the optical cavity.