We characterize the performance of a quantum well infrared photodetector (QWIP), which is fabricated as a photonic crystal slab (PCS) resonator. The strongest resonance of the PCS is designed to coincide with the absorption peak frequency at 7.6 µm of the QWIP. To accurately characterize the detector performance, it is illuminated by using single mode mid-infrared lasers. The strong resonant absorption enhancement yields a detectivity increase of up to 20 times. This enhancement is a combined effect of increased responsivity and noise current reduction. With increasing temperature, we observe a red shift of the PCS-QWIP resonance peak of -0.055 cm(-1)/K. We attribute this effect to a refractive index change and present a model based on the revised plane wave method.
In passive UHF RFID systems backscattering is used for tag to reader communication. This technique relies on a continuous wave signal being transmitted by the reader during the tag's data transfer. In order to separate transmission and reception paths circulators, directional couplers or disjoint transmit and receive antennas can be used. Perfect isolation is not achievable with any of those approaches. So a leaking carrier is present at the receiver in any case. It is possible to reduce the interference from this signal by some kind of leaking carrier cancellation. Such a cancellation prevents receiver blocking and reduces the baseband hardware's requirements, depending on the receiver concept. Usually, the narrowband properties of carrier cancellers are studied. This is only sufficient for conventional RFID systems, if the transmitter noise can be neglected. Broadband RFID systems, as recently discussed in literature, also require broadband leaking carrier cancellers. In this paper the broadband suppression properties of carrier cancellers are first investigated theoretically. Further a hardware implementation is presented and characterized. Finally, measurement results are compared to the theoretical findings.
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