Optical waveguide router with controlled transmission characteristics

A router for optical waves including a planar member for support of the optical waveguides forming the router, an input free space slab on the planar member including input and output ports, an output free space slab on the planar member having input and output ports, and a grating on the planar member connected between the output ports of the input free space slab and the input ports of the output free space slab including a succession of optical waveguide arms, the optical lengths of successive optical waveguide arms differing by an essentially constant amount, and a control arrangement bonded to the planar member including an active element whose length is variable and whose changes in length are used to provide primarily longitudinal strain in the waveguide arms of the grating to affect their optical length without causing significant birefringence in the grating.