The present invention provides an integrated device and a method of its fabrication and use. Two parts of the device each having an electronic circuit are aligned adjacent to each other with an accuracy of at least 1 micron. An alignment system includes two parts: a first part integrated with the first electronic circuit of the integrated device on the first substrate and a second part integrated with the second electronic circuit of the integrated device on the second substrate. The second part of alignment system includes at least one photodiode. The maximal value of the photodiode current indicates the best alignment of two parts of the integrated device. In one embodiment the integrated device is a coherent optical detector for high speed optical communications and chemical sensing. In another embodiment the integrated optical device is a coherent optical detector operating in two polarization states of light.