Control of center wavelength in reflective-arrayed waveguide-grating multiplexers

A new approach to compensate for the channel-wavelength shift due to fabrication errors and thermal effects in arrayed waveguide-grating multiplexers is described. The method combines a silica-based reflective multiplexer with a composite mirror made of materials with different coefficients of thermal expansion. Differential thermal expansion of the mirror assembly rotates its reflecting surface at a constant rate with temperature, compensating for the temperature-induced changes in the effective index of refraction of the waveguide material. The use of external mirror also allows for wavelength trimming that centers the channel wavelength at the standard grid. The channel wavelength can be tuned by up to 2 nm without increased insertion loss or changes in channel-to-channel separation. The channel wavelength shifts linearly with the external mirror angle at a rate of ∼66 nm/deg in excellent agreement with simulation. A finite element analysis of the composite mirror shows negligible deformation of the reflecting surface over a wide range of temperatures, in good agreement with experimental results.