An apparatus, comprising: a laser arrangement which is configured to provide a laser radiation, and including a ring optical cavity which comprises: - a dispersive optical waveguide first arrangement including a fiber Bragg grating, FBG (1909, 2014, 2233, 2303, 2404), having first and second sides, and which is configured to (i) receive a first electro-magnetic radiation at the first side from an intensity modulator (1902, 2000, 2230, 2300, 2400) so as to provide a second electro-magnetic radiation to an optical amplifier (1904, 2003, 2234, 2305, 2408), and (ii) to receive at least one third electro-magnetic radiation at the second side from the optical amplifier so as to provide at least one fourth electro-magnetic radiation, wherein the first and second sides are different from one another, and wherein the second and third radiations are related to one another, - an active optical modulator second arrangement comprising the intensity modulator (1902, 2000, 2230, 2300, 2400), which is configured to receive and modulate the fourth radiation so as to provide the first electro-magnetic radiation to the first arrangement, and - a fixed periodic spectral filter arrangement (1903, 2002, 2235, 2304a, 2417a), wherein the laser radiation is associated with at least one of the first, second, third or fourth radiations and is output at an output coupler (1910, 2005, 2237, 2309), wherein the first arrangement comprises (i) at least one first circulator (1906, 2001, 2231, 2302a, 2402a) which receives the first radiation and transmits the second radiation, and (ii) at least one second circulator (1907, 2007, 2232, 2302b, 2402b) which receives the third radiation and transmits the fourth radiation, and wherein the second electro-magnetic radiation is received by the optical amplifier (1904, 2003, 2234, 2305, 2408) via the fixed periodic spectral filter arrangement (1903, 2002, 2235, 2304a, 2417a). a laser arrangement which is configured to provide a laser radiation, and including a ring optical cavity which comprises: - a dispersive optical waveguide first arrangement including a fiber Bragg grating, FBG (1909, 2014, 2233, 2303, 2404), having first and second sides, and which is configured to (i) receive a first electro-magnetic radiation at the first side from an intensity modulator (1902, 2000, 2230, 2300, 2400) so as to provide a second electro-magnetic radiation to an optical amplifier (1904, 2003, 2234, 2305, 2408), and (ii) to receive at least one third electro-magnetic radiation at the second side from the optical amplifier so as to provide at least one fourth electro-magnetic radiation, wherein the first and second sides are different from one another, and wherein the second and third radiations are related to one another, - an active optical modulator second arrangement comprising the intensity modulator (1902, 2000, 2230, 2300, 2400), which is configured to receive and modulate the fourth radiation so as to provide the first electro-magnetic radiation to the first arrangement, and - a fixed periodic spectral filter arrangement (1903, 2002, 2235, 2304a, 2417a), - a dispersive optical waveguide first arrangement including a fiber Bragg grating, FBG (1909, 2014, 2233, 2303, 2404), having first and second sides, and which is configured to (i) receive a first electro-magnetic radiation at the first side from an intensity modulator (1902, 2000, 2230, 2300, 2400) so as to provide a second electro-magnetic radiation to an optical amplifier (1904, 2003, 2234, 2305, 2408), and (ii) to receive at least one third electro-magnetic radiation at the second side from the optical amplifier so as to provide at least one fourth electro-magnetic radiation, wherein the first and second sides are different from one another, and wherein the second and third radiations are related to one another, - an active optical modulator second arrangement comprising the intensity modulator (1902, 2000, 2230, 2300, 2400), which is configured to receive and modulate the fourth radiation so as to provide the first electro-magnetic radiation to the first arrangement, and - a fixed periodic spectral filter arrangement (1903, 2002, 2235, 2304a, 2417a), wherein the laser radiation is associated with at least one of the first, second, third or fourth radiations and is output at an output coupler (1910, 2005, 2237, 2309), wherein the first arrangement comprises (i) at least one first circulator (1906, 2001, 2231, 2302a, 2402a) which receives the first radiation and transmits the second radiation, and (ii) at least one second circulator (1907, 2007, 2232, 2302b, 2402b) which receives the third radiation and transmits the fourth radiation, and wherein the second electro-magnetic radiation is received by the optical amplifier (1904, 2003, 2234, 2305, 2408) via the fixed periodic spectral filter arrangement (1903, 2002, 2235, 2304a, 2417a).