Investigation of the inner ear is still subject of basic research. Due to the small structures of the inner ear every suggested measurement technique, which includes loading of moving parts, will not be able to detect the oscillations correctly. Therefore an optical approach detecting microvibrations in the cochlea will be discussed. In heterodyne interferometry as compared to classical interferometry two slightly different light frequencies for the reference and object beams are used. The vibration of the object is detected as a modulation of the phase of the detector signal. Many restrictions on the design of our new interferometer caused by the properties of the tissue of the membranes in the cochlea and by the anatomic and geometric shape of the surrounding of the cochlea, needed to be taken into account. A confocal fiber optic heterodyne interferometer with a miniaturized sensor head was built. To improve the optical properties of the sensor head the combination of a gradient index lens and a hologram is under test. The selected wavelength of 830 nm should allow an investigation of layered tissues. It is possible to detect amplitudes down to 0.3 angstroms in a frequency range of 500 Hz to 50 kHz with a simulated object reflectivity of 0.02%.