A free space linear cavity tunable laser source comprising: a gain medium ; two lenses ; an end reflector ; and a tunable Micro-electro-mechanical-system Fabry-Perot, MEMS-FP, filter , the tunable MEMS-FP filter 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 ; an end reflector ; and a tunable Micro-electro-mechanical-system Fabry-Perot, MEMS-FP, filter , the tunable MEMS-FP filter 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. <EOS>