A fluid density sensor configured to optically receive operating power and to optically communicate a measured fluid density, the fluid density sensor comprising: a fluid tight housing separating an interior cavity from an exterior environment, the fluid tight housing configured to prevent a fluid from the exterior environment from entering the interior cavity; a fiber optic connection port (34A-C) configured to connect to an optical fiber in the exterior environment while providing an optical path for light energy to traverse the fluid tight housing, the light energy communicated between the optical fiber and the interior cavity; a fluid density transducer in the housing configured to be immersed in the fluid, the fluid density transducer generating an electrical output signal indicative of a density of the fluid; and sensor electronics located entirely within the interior cavity, the sensor electronics comprising: an optical power converter configured to convert the light energy communicated from the optical fiber via the fiber optic connection port (34A-C) into DC electrical energy; an energy storage device configured to store the converted DC electrical energy; a signal generator configured to generate, using at least a portion of the stored DC electrical energy, an electrical input signal for use by the fluid density transducer; a transducer interface configured to supply the generated electrical input signal to the fluid density transducer and to receive the electrical output signal of the fluid density transducer; and an optical signal generator configured to generate a light signal, based on the received electrical output signal, the light signal indicative of the density of the fluid; characterised in that the optical signal generator is configured to generate the light signal indicative of the density of the fluid by modulating a reflection of the light energy delivered by the optical fiber, and the reflected light signal is communicated by the optical fiber in a direction antiparallel to the direction of the unreflected light energy carried by the optical fiber, and wherein the reflected light signal has an amplitude between 1% and 10% of an amplitude of the light energy delivered by optical fiber such that a majority of the light energy delivered by the optical fiber can be converted into DC electrical energy by the optical energy converter. a fluid tight housing separating an interior cavity from an exterior environment, the fluid tight housing configured to prevent a fluid from the exterior environment from entering the interior cavity; a fiber optic connection port (34A-C) configured to connect to an optical fiber in the exterior environment while providing an optical path for light energy to traverse the fluid tight housing, the light energy communicated between the optical fiber and the interior cavity; a fluid density transducer in the housing configured to be immersed in the fluid, the fluid density transducer generating an electrical output signal indicative of a density of the fluid; and sensor electronics located entirely within the interior cavity, the sensor electronics comprising: an optical power converter configured to convert the light energy communicated from the optical fiber via the fiber optic connection port (34A-C) into DC electrical energy; an energy storage device configured to store the converted DC electrical energy; a signal generator configured to generate, using at least a portion of the stored DC electrical energy, an electrical input signal for use by the fluid density transducer; a transducer interface configured to supply the generated electrical input signal to the fluid density transducer and to receive the electrical output signal of the fluid density transducer; and an optical signal generator configured to generate a light signal, based on the received electrical output signal, the light signal indicative of the density of the fluid; an optical power converter configured to convert the light energy communicated from the optical fiber via the fiber optic connection port (34A-C) into DC electrical energy; an energy storage device configured to store the converted DC electrical energy; a signal generator configured to generate, using at least a portion of the stored DC electrical energy, an electrical input signal for use by the fluid density transducer; a transducer interface configured to supply the generated electrical input signal to the fluid density transducer and to receive the electrical output signal of the fluid density transducer; and an optical signal generator configured to generate a light signal, based on the received electrical output signal, the light signal indicative of the density of the fluid; characterised in that the optical signal generator is configured to generate the light signal indicative of the density of the fluid by modulating a reflection of the light energy delivered by the optical fiber, and the reflected light signal is communicated by the optical fiber in a direction antiparallel to the direction of the unreflected light energy carried by the optical fiber, and wherein the reflected light signal has an amplitude between 1% and 10% of an amplitude of the light energy delivered by optical fiber such that a majority of the light energy delivered by the optical fiber can be converted into DC electrical energy by the optical energy converter.