An optical apparatus comprising: a silicon [claim 14] semiconductor substrate ; a germanium-silicon layer coupled to the semiconductor substrate, the germanium-silicon layer including an optical sensor [p. 8, 1. 28-29] region [claim 1] configured to absorb photons and to generate photo-carriers from the absorbed photons, wherein a composition of the germanium-silicon layer differs from a composition of the semiconductor substrate; one or more first switches controlled by a first control signal , the one or more first switches configured to collect at least a portion of the photo-carriers based on the first control signal; and one or more second switches controlled by a second control signal , the one or more second switches configured to collect at least a portion of the photo-carriers based on the second control signal, wherein the second control signal is different from the first control signal, wherein the one or more first switches comprise: a first p-doped region in the germanium-silicon layer, wherein the first p-doped region is controlled by the first control signal; and a first n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the first n-doped region is coupled to a first readout integrated circuit ; wherein the one or more second switches comprise: a second p-doped region in the germanium-silicon layer, wherein the second p-doped region is controlled by the second control signal; and a second n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the second n-doped region is coupled to a second readout integrated circuit . a silicon [claim 14] semiconductor substrate ; a germanium-silicon layer coupled to the semiconductor substrate, the germanium-silicon layer including an optical sensor [p. 8, 1. 28-29] region [claim 1] configured to absorb photons and to generate photo-carriers from the absorbed photons, wherein a composition of the germanium-silicon layer differs from a composition of the semiconductor substrate; one or more first switches controlled by a first control signal , the one or more first switches configured to collect at least a portion of the photo-carriers based on the first control signal; and one or more second switches controlled by a second control signal , the one or more second switches configured to collect at least a portion of the photo-carriers based on the second control signal, wherein the second control signal is different from the first control signal, wherein the one or more first switches comprise: a first p-doped region in the germanium-silicon layer, wherein the first p-doped region is controlled by the first control signal; and a first n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the first n-doped region is coupled to a first readout integrated circuit ; a first p-doped region in the germanium-silicon layer, wherein the first p-doped region is controlled by the first control signal; and a first n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the first n-doped region is coupled to a first readout integrated circuit ; wherein the one or more second switches comprise: a second p-doped region in the germanium-silicon layer, wherein the second p-doped region is controlled by the second control signal; and a second n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the second n-doped region is coupled to a second readout integrated circuit . a second p-doped region in the germanium-silicon layer, wherein the second p-doped region is controlled by the second control signal; and a second n-doped region in either the germanium-silicon layer or the semiconductor substrate, wherein the second n-doped region is coupled to a second readout integrated circuit . <EOS>