Brillouin fiber laser spectrometer

An apparatus comprising:

• a spectrometer receiving an optical input signal, the optical input signal comprising an input optical spectrum, said input optical spectrum comprising at least one input frequency, said spectrometer being free of a pump generator generating the optical input signal, said spectrometer outputting a measurement of the input optical spectrum, said spectrometer comprising:
• a fiber laser cavity pumped by a first optical replica of the optical input signal, the first optical replica of the optical input signal generating stimulated Brillouin scattering traveling in a direction opposite to a direction of the optical input signal, the first optical replica of the optical input signal exciting at least one lasing mode in the fiber laser cavity, the at least one lasing mode respectively comprising at least one lasing mode frequency, the at least one lasing mode frequency being offset by a respective Brillouin frequency shift from the respective at least one input frequency, said fiber laser cavity outputting a portion of the at least one lasing mode;
• an optical heterodyne receiver receiving a second optical replica of the optical input signal and, from said fiber laser cavity, the portion of at least one lasing mode, said optical heterodyne receiver generating an electrical output signal, the electrical output signal comprising an output electrical spectrum that includes a compressed, electrical replica of the input optical spectrum;
• and
• a processor receiving the electrical output signal and outputting the measurement of the input optical spectrum based on a monotonic relationship between the respective Brillouin frequency shift and the at least one input frequency.