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Abstract: Holographic filters are used as optical sensors and in wavelength division multiplexing (WDM) filtering applications. Temperature dependence is a critical concern for telecommunications. Researcher realize the design of an athermal holographic filter employing a thermally actuated MEMS mirror to compensate for the drift of Bragg wavelength due to changes of temperature. The center wavelength of our holographic filter is shown to remain constant from 21°C to 60°C. Summary : A grating holographically imprinted inside a recording material can be operated as a WDM filter in the reflection geometry. The wavelength satisfying the grating equation will be strongly reflected, whereas the other wavelengths pass through the filter unaffected. where n(T0) is the refractive index of the material at lB at temperature T0 and L(T0) is the period of the index grating at T0. By inspecting (1), we notice that we can Bragg match the grating to a shorter wavelength if we tilt the incident beam away from the normal. Temperature changes affect holographic filters mainly through two mechanisms: (Other possible effects will be neglected here, e.g. the thermal dependence of the piezoelectric tensor will manifest itself when stress is being applied.) 1. Thermal expansion or contraction of the bulk material (in our experiments, LiNbO3:Fe). 2. Thermal dependence of the dielectric constant of the bulk material. Assume the Bragg wavelength of the filter is corresponding to an incident angle ( is the angle measured inside the crystal, whereas ’ is measured outside the crystal) at temperature T0. When the temperature changes to T0+, the Bragg wavelength of the filter will have a corresponding shift and move to +. To specify the MEMS mirror parameters, researcher first figure out the Bragg wave-lengths for a series of incident angles at three different temperatures (21.79°C, 45.68°C, 58.46°C). Temperature monitoring is made possible by reading the resistance off a thermistor in close contact with the LiNbO3 crystal when the whole system is in thermal equilibrium. A thermoelectric (TE) cooler is used to control the temperature of the system. Researcher suggest that for operation around an incident angle=5°, an angular correction of 1.18 degrees will be required for a temperature change of 100°C. The aluminum-silicon composite beam was designed to deflect about 0.59 degrees for a temperature change of 100°C. Researcher mount the holographic filter and the MEMS mirror on two separate TE coolers. Two identical thermistors are used to monitor the temperatures of the filter and the mirror. The output from a tunable laser is reflected off the mirror toward the filter at an (outside) incident angle of 5 degrees. At this point both the filter and the mirror are at room temperature. The filter response is measured and the Bragg wavelength is determined. Then the TE coolers are turned on and raise the temperatures of both. The readings of the two thermistors are kept the same throughout the measurements of filter response. The filter shapes at =5° for three different temperatures are plotted in Fig. 4. Compared with Fig. 3, the drift of the Bragg wavelength is indeed compensated for by the deflection of the mirror. Researcher have shown that the temperature dependence of the Bragg wavelength of a holographic filter can be compensated by incorporating a passive, thermally actuated MEMS mirror into the system. To improve the performance of the athermal filter design, it’s vital to gain a deeper understanding of the evolution of filter shapes away from normal incidence. Other topics such as beam walk-off, polarization dependent loss (PDL) and the elimination of mirror hysteresis are also important considerations in practical applications. MEMS mirror into the system. To improve the performance of the athermal filter design, it’s vital to gain a deeper understanding of the evolution of filter shapes away from normal incidence. Other topics such as beam walk-off, polarization dependent loss (PDL) and the elimination of mirror hysteresis are also important considerations in practical applications.