Photonic integrated device

1. A photonic integrated device having a substrate layer, epitaxial layers formed on said substrate layer and a guiding layer formed by one of the epitaxial layers, wherein an optical waveguide is formed within the guiding layer, the device further comprising, in the waveguide, a splitter having at least two outputs, each output being transmitted to a Mach-Zehnder modulator, the phase of the output of at least one modulator being shiftable, the signals being recombined to provide an optical phase shift key (PSK) output, wherein a trench is etched into the substrate layer between each pair of modulators to isolate the modulators from one another.

2. The photonic integrated device according to claim 1 , wherein the waveguide between the splitter and the modulator comprises an S-curve.

3. The photonic integrated device according to claim 1 , wherein the splitter comprises a 1×2 MMI and the recombiner comprises a 2×2 MMI, which co-operate to provide a substantially π/2 phase shift in the output of one of the modulators.

4. The photonic integrated device according to claim 3 , further comprising a control electrode adapted to provide fine control of the phase shift.

5. The photonic integrated device according to claim 1 , further comprising a laser that generates an output that is fed to the splitter.

6. The photonic integrated device according to claim 1 , wherein an output power of the signal is monitored with a two photon absorption detector.

7. The photonic integrated device according to claim 1 , wherein a bias is applied to n-doped epitaxial layers via a forward biased Schottky contact.

8. The photonic integrated device according to claim 1 , further comprising a capacitor disposed at an output of each modulator for decoupling RF.

9. The photonic integrated device according to claim 8 , wherein the capacitor comprises an area of metal deposited on the surface of the device.