A photonic integrated circuit device comprising: - a planar detector comprising a first photodetector and a second photodetector - a waveguide layer arranged substantially parallel to said planar detector, the waveguide layer comprising a first integrated waveguide for guiding a first light signal, wherein a cavity is formed in said waveguide layer in a region spaced away from the edges of said waveguide layer such as to terminate the first integrated waveguide in said region, wherein a first reflective surface is provided in said cavity to reflect the first light signal guided by the first integrated waveguide toward the first photodetector of said planar detector, wherein said waveguide layer comprises a second integrated waveguide for guiding a second light signal, said second integrated waveguide being arranged such that said cavity also terminates the second integrated waveguide in said region spaced away from the edges of the waveguide layer, and wherein a second reflective surface is provided in the cavity to reflect the second light signal when guided by the second integrated waveguide toward the second photodetector of said planar detector, wherein the first and second waveguides are arranged in line with each other, and wherein the cavity is arranged for coupling light out of the respective waveguide (11, 12) to the respective photodetector (7, 17). - a planar detector comprising a first photodetector and a second photodetector - a waveguide layer arranged substantially parallel to said planar detector, the waveguide layer comprising a first integrated waveguide for guiding a first light signal, wherein a cavity is formed in said waveguide layer in a region spaced away from the edges of said waveguide layer such as to terminate the first integrated waveguide in said region, wherein a first reflective surface is provided in said cavity to reflect the first light signal guided by the first integrated waveguide toward the first photodetector of said planar detector, wherein said waveguide layer comprises a second integrated waveguide for guiding a second light signal, said second integrated waveguide being arranged such that said cavity also terminates the second integrated waveguide in said region spaced away from the edges of the waveguide layer, and wherein a second reflective surface is provided in the cavity to reflect the second light signal when guided by the second integrated waveguide toward the second photodetector of said planar detector, wherein the first and second waveguides are arranged in line with each other, and wherein the cavity is arranged for coupling light out of the respective waveguide (11, 12) to the respective photodetector (7, 17). wherein a first reflective surface is provided in said cavity to reflect the first light signal guided by the first integrated waveguide toward the first photodetector of said planar detector, wherein said waveguide layer comprises a second integrated waveguide for guiding a second light signal, said second integrated waveguide being arranged such that said cavity also terminates the second integrated waveguide in said region spaced away from the edges of the waveguide layer, and wherein a second reflective surface is provided in the cavity to reflect the second light signal when guided by the second integrated waveguide toward the second photodetector of said planar detector, wherein the first and second waveguides are arranged in line with each other, and wherein the cavity is arranged for coupling light out of the respective waveguide (11, 12) to the respective photodetector (7, 17).