A tunable coupled-cavity laser comprising: a two port phase dependent reflective multi-mode interferometer, MMI, having two opposed sides, a width W and a maximum length L along the centre axis of the MMI, the MMI comprising: a first port for input of a first beam, the first port located at a first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, a second port for input of a second beam, the second port located at said first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, the centre axis of the MMI between the first port and the second port, and a corner mirror disposed at a second side of the MMI, the corner mirror comprising a pair of reflective surfaces disposed on opposite sides of the centre axis of the MMI, the apex of the corner mirror disposed at the length L, along the centre axis of said MMI, wherein L= Lπ /4, L=Lπ/2, L =3Lπ/4, L=Lπ, L =5Lπ/4, or L =3Lπ/2; a first laser cavity coupled to the first port and comprising: an optical amplifier, and a phase tuning element; and a second laser cavity coupled to the second port and comprising: an optical amplifier, and a phase tuning element. a two port phase dependent reflective multi-mode interferometer, MMI, having two opposed sides, a width W and a maximum length L along the centre axis of the MMI, the MMI comprising: a first port for input of a first beam, the first port located at a first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, a second port for input of a second beam, the second port located at said first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, the centre axis of the MMI between the first port and the second port, and a corner mirror disposed at a second side of the MMI, the corner mirror comprising a pair of reflective surfaces disposed on opposite sides of the centre axis of the MMI, the apex of the corner mirror disposed at the length L, along the centre axis of said MMI, wherein L= Lπ /4, L=Lπ/2, L =3Lπ/4, L=Lπ, L =5Lπ/4, or L =3Lπ/2; a first port for input of a first beam, the first port located at a first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, a second port for input of a second beam, the second port located at said first side of the MMI and with its centre axis at a distance of W/3 from the centre axis of the MMI, the centre axis of the MMI between the first port and the second port, and a corner mirror disposed at a second side of the MMI, the corner mirror comprising a pair of reflective surfaces disposed on opposite sides of the centre axis of the MMI, the apex of the corner mirror disposed at the length L, along the centre axis of said MMI, wherein L= Lπ /4, L=Lπ/2, L =3Lπ/4, L=Lπ, L =5Lπ/4, or L =3Lπ/2; a first laser cavity coupled to the first port and comprising: an optical amplifier, and a phase tuning element; and an optical amplifier, and a phase tuning element; and a second laser cavity coupled to the second port and comprising: an optical amplifier, and a phase tuning element. an optical amplifier, and a phase tuning element. <EOS>