Optical spectrometer comprising an adjustably strained photodiode

An optical spectrometer 1 comprises a photodiode 2 and a straining mechanism 4 for imposing adjustable strain on the photodiode. The spectrometer l includes measurement apparatus 7 for measuring variation of photocurrent with strain at different values of the adjustable strain imposed by the straining mechanism 4. Adjusting the strain allows adjustment of the band gap Eg of the photosensitive region of the photodiode 1, and this determines the cut-off energy for absorption of photons. Measuring variation of photocurrent with strain at different values of the adjustable strain imposed by the straining mechanism allows study of photons within a desired energy range of the band gap energy corresponding to each strain value. The photodiode 2 may comprise a PIN photodiode formed in a nanowire as a radial or axial heterostructure. A polarizer 6 may be adapted to transmit a predetermined polarized component of incident light to the photodiode. The polarizer 6 may comprise a coating on the photodiode.