First Sensor is expanding its range of optical sensors with innovative silicon photomultipliers (SiPM) for measuring the smallest amounts of light through to the detection of single photons. Compared to conventional photomultipliers that use an electron tube, the semiconductor-based SiPMs offer key advantages such as low supply voltage, excellent temperature stability, insensitivity to magnetic fields, and a much smaller size for easy integration into end devices. The optical sensors are suitable for measurement in the near UV range (SiPM-NUV series) or in the visible red, green and blue wavelength range (SiPM-RGB series) with highest sensitivities at 420 or 550 nm. First Sensor's silicon photomultipliers are constructed as matrix arrays of a large number of very small avalanche photodiodes operated above their breakdown voltage (Geiger mode). The high accuracy NUV and RGB SiPMs are very temperature stable in terms of breakdown voltage and gain. Improved materials and state-of-the-art semiconductor technology allow very low noise sensors with reduced dark count rate, lower crosstalk and very small post-pulse with a probability of typically <4%. The silicon photomultipliers offer very large gain factors of >106 as well as very high photon detection efficiency. Typical applications of First Sensor's silicon photomultipliers are in high-energy physics, medical diagnostics, nuclear medicine, analytical instruments, and radiation hazard detection. Their insensitivity to magnetic fields makes SiPMs ideal for medical imaging applications. Examples include hybrid devices that combine positron emission tomography (PET) or single photon emission computed tomography (SPECT) with magnetic resonance imaging (MRI).