Thermal compensation and alignment for optical devices

A planar waveguide device having

• one or more optical paths passing through a star coupler, and a set of waveguides having differing optical path lengths extending from the star coupler,
• the device also having a movable part for adjusting a position of one or more of the optical paths at the star coupler, by thermal expansion, to adjust a wavelength response of the device,
• the device having a bearing surface parallel to a plane of the waveguides at the star coupler, to prevent movement of the movable part out of the plane and allow movement of the moveable part along the bearing surface parallel to the plane, and a bias arrangement for applying a force to bias the moveable part against the bearing surface.

The device of clam 10, the movement being lateral movement in the plane and perpendicular to the respective optical path, to alter the position of interface of the optical path with the star coupler.

A planar waveguide device having:

• one or more optical paths passing through a star coupler, and a set of waveguides having differing optical path lengths extending from the star coupler,
• the device also having a movable part for adjusting a position of one or more of the optical paths at the first or second star coupler, by thermal expansion, to adjust a wavelength response of the device,
• the device having a reference surface for the thermal expansion to act against, to cause the relative movement, and an axial bias arrangement for applying a force along an axis of the movement to bias the moveable part against the reference surface, to overcome mechanical hysteresis associated with frictional resistance to the movement.

An optical flat-topped filter arrangement having:

• an arrayed waveguide chip for multiplexing or demultiplexing a wavelength division multiplexed (WDM) signal, and having a star coupler,
• a second chip incorporating a multimode (MMI) section coupled in series with the arrayed waveguide, and providing a spatial power distribution that convolves with that of the arrayed waveguide to give a flat-topped overall response for each of a number of WDM channels, and
• a passive mechanical thermal compensation arrangement for providing a thermal expansion-driven relative movement between the arrayed waveguide chip and the MMI chip, to shift a location of an input or output to the star coupler of the waveguide, so as to shift its frequency response.

An optical waveguide assembly having an arrayed waveguide, and a transitional waveguide coupled optically to the arrayed waveguide and mounted on separate chips on a substrate and having a passive athermalisation arrangement for the arrayed waveguide.

A method of assembling an optical component assembly having a substrate, and first and second chips each having waveguides, the first of the chips having one or more first mating profiles, for mating with one or more second mating profiles on the substrate or on a spacer or movable part attached to the substrate the method having the steps of:

• attaching the second chip to the substrate, with a coarse alignment process, to align the second chip with the second profiles and
• making a coarse alignment of the first chip with the second chip by mating the first and second mating profiles.