A thin film magnetic read/write head for use in magnetic data storage systems to enable writing of data to a magnetic data storage medium with the assistance of laser heating. The read/write head allows magnetic reading of data from the storage medium, and thermally assisted magnetic writing of data on the storage medium. A waveguide is provided in a write gap in the form of an optical circuit having a plurality of inputs and a single output at the air bearing surface (ABS) for concentrating laser light used for heating the storage medium during the write operation. The thermally assisted magnetic writing improves the thermal stability of the recorded data and usefulness thereof throughout a wide temperature range.