An infrared sensor comprises a first film configuration (103), a second film configuration (104), and a gap formed between the first film configuration (103) and the second film configuration (104). Reference light is incident on one of the film configurations (103,104). When the gap is changed, reference light intensity transmitted through one film configuration changes, and reflected reference light intensity changes. When infrared light is incident, at least one film configuration absorbs the infrared light and the temperature thereof changes accordingly, thereby resulting in the change of the gap. The infrared light is detected by detecting the change of the transmitted light intensity or the change of the reflected light intensity.
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