Optical upconverter with integrated heterojunction phototransistor and light-emitting diode

We report an optical upconversion device that converts input $1.5\mu \mathrm{m}$ light to output $0.87\mu \mathrm{m}$ light with a built-in gain mechanism. The device consists of an $\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{In}\mathrm{P}$ heterojunction phototransistor (HPT) integrated with a $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ light-emitting diode (LED) by wafer fusion process. Incoming $1.5\mu \mathrm{m}$ optical radiation is absorbed by the HPT, generating an amplified photocurrent. The resultant photocurrent drives the LED that emits at $0.87\mu \mathrm{m}$ , which could be detected by a conventional silicon charge-coupled device. Upconversion is demonstrated at room temperature with a gain of 20 from the HPT and an overall external upconversion efficiency of $0.07\mathrm{W}∕\mathrm{W}$ .