Semiconductor optical devices and methods of making them

摘要

An optical monomode guided-wave device, especially an electroabsorption modulator, having an active region (18) with a mode size small compared with that of an optical fibre is integrated with at least one passive spot size adjuster (tapered region (14)) which has an optical core that tapers simultaneously from a width and height substantially equal to those of the active region adjacent to that region to a width large compared with the width of the active region and a thickness substantially smaller than the thickness of the active region. Usually - unless the device includes its own light source (35)- there will be two spot size adjusters. <??>The device is a buried hetero-structure device; its optical core tapers smoothly in both width and height; the dimensions of the core are such that there is an optical transmission mode for which the effective refractive index difference between the mode and any other mode (including the radiation field) is large enough to ensure that no more than 20% (preferably 5%) of light entering one end of the guided wave device in that mode will (or would) be lost (or gained) by radiation. <??>The simultaneous smooth tapers can be obtained by taking advantage of the characteristics of the mass-transport limited MOVPE technique, depositing in a narrow channel defined between two deposit-resist bands, the thickness deposited, at least in the centre of the channel, varying in a direct sense with the widths of the adjacent bands and in an inverse sense with the width of the channel. <IMAGE>