as e g the laser active medium or the bragg reflector waveguide a similar curve can be obtained e g when the independent variable is a voltage which influences the refractive index of a liquid crystal material in contact with the bragg reflector grating or possibly of an electro optic material the operating point of a laser can be affected also by the distance between the laser active portion and the bragg reflector portion further of interest in this respect is a bragg reflector element including a semiconductor material whose refractive index depends on carrier density as influenced by current injection as shown in fig1 control of a laser operating parameter may involve temperature control of an auxiliary medium in contact with the bragg reflector grating the cross sectional structure shown in fig1 is similar to that of fig2 except that the material of layer 24 is chosen to exhibit strong changes in refractive index as a function of temperature chromium heater strips 26 are included to control the temperature of medium 24 thereby affecting the operating point of the laser transparent silicone rubber such as e g dow corning 684 represents a particularly effective material choice for layer 24 as an alternative to the arrangement shown in fig1 a heater can be mounted on a separate substrate and placed separate from layer 23 with the space.