Optical test circuit

1. An optical test circuit comprising:

an optical circuit including a first optical waveguide on a substrate and having a core made of silicon;

a second optical waveguide having a core made of silicon and being optically connected to the optical circuit;

a first silicon layer on the substrate and continuous with the core of the second optical waveguide;

a third optical waveguide having a core made of silicon and being optically connected to the optical circuit;

a light emitting diode optically connected to the second optical waveguide and having an active layer comprising germanium, wherein the active layer is on the first silicon layer, and wherein the light emitting diode further comprises:

a first region of a first conductivity type in the first silicon layer; and

a first semiconductor layer comprising germanium of a second conductivity type on the active layer, wherein the active layer is on the first region; and

a photodiode optically connected to the third optical waveguide and having an optical absorption layer comprising germanium.

2. The optical test circuit according to claim 1 , further comprising a second silicon layer on the substrate and continuous with the core of the third optical waveguide, wherein the optical absorption layer is on the second silicon layer.

3. The optical test circuit according to claim 2 , wherein the photodiode further comprises:

a second region of the first conductivity type in the second silicon layer; and

a second semiconductor layer of the second conductivity type on the optical absorption layer, wherein the optical absorption layer is on the second region.

4. The optical test circuit according to claim 3 , wherein the second semiconductor layer comprises germanium of the second conductivity type.

5. A method of providing an optical test circuit, the method comprising:

providing an optical circuit including a first optical waveguide on a substrate, the first optical waveguide having a core made of silicon;

optically connecting a second optical waveguide having a core made of silicon to the optical circuit;

forming a first silicon layer on the substrate continuous with the core of the second optical waveguide;

optically connecting a third optical waveguide having a core made of silicon to the optical circuit;

optically connecting a light emitting diode to the second optical waveguide, the light emitting diode having an active layer comprising germanium, wherein the active layer is formed on the first silicon layer, and wherein the light emitting diode further comprises:

a first region of a first conductivity type formed in the first silicon layer; and

a first semiconductor layer comprising germanium of a second conductivity type formed on the active layer, wherein the active layer is formed on the first region; and

optically connecting a photodiode to the third optical waveguide, the photodiode having an optical absorption layer comprising germanium.

6. The method according to claim 5 , further comprising forming a second silicon layer on the substrate continuous with the core of the third optical waveguide, wherein the optical absorption layer is formed on the second silicon layer.

7. The method according to claim 6 , wherein the photodiode further comprises:

a second region of the first conductivity type formed in the second silicon layer; and

a second semiconductor layer of the second conductivity type formed on the optical absorption layer, wherein the optical absorption layer is formed on the second region.

8. The method according to claim 7 , wherein the second semiconductor layer comprises germanium of the second conductivity type.