Mode-selective detection of optical guided waves by integrated metal-oxide-metal structures

We show that a metal-oxide-metal (Al-AlO(x)-Al) tunnel junction fabricated directly upon a planar ion-exchange glass waveguide can be used to detect the guided radiation through evanescent coupling. Carriers photogenerated in the electrode next to the guide can be internally photoemitted over the oxide barrier to generate a photocurrent. Because of the greater metallic absorption of TM-polarized modes, the process is polarization sensitive. 32-dB TM selectivity is achieved in a simple device.