  We report an optical detector with tunable positive operator-valued measures
(POVMs). The device is based on a combination of weak-field homodyne techniques
and photon-number-resolving detection. The resulting POVMs can be continuously
tuned from Fock-state projectors to a variety of phase-dependent quantum-state
measurements by adjusting different system parameters such as local oscillator
coupling, amplitude and phase, allowing thus not only detection but also
preparation of exotic quantum states. Experimental tomographic reconstructions
of classical benchmark states are presented as a demonstration of the detector
capabilities.
