Fabrication of a mono-crystalline emitter using a combination of selective and differential growth modes. The optical amplifier comprises a first measuring device for measuring a property of an input signal of the optical amplifier, a second measuring device for measuring a property of an output signal of the optical amplifier, and a control circuit for controlling a gain characteristic of the optical amplifier in dependence of said input and output signal properties. In certain embodiments the cannulated implants are expandable within an intraosseous space to introduce scaffold-like structures such that subsequent introduction of a bone cement forms a composite in situ.