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In this paper, the static optical transfer function of dielectric lithium niobate (LiNbO 3) electro-optic sensors is modeled and experimentally measured. This function represents the transmitted optical power at the output of an optical waveguide in a LiNbO 3 crystal which acts as an electric field sensor. The sensor is electrode-less and operates as a dielectric probe. Under such a condition, the electric field is present in the dielectric media surrounding the waveguide and the measured field intensity is determined by the boundary condition between the media and the LiNbO 3 crystal. The electro-optic transfer function is theoretically modeled and experimentally measured. Such a transfer function shows a sinusoidal shape, from which the half-wave electric field, the optical extinction ratio and the linear and nonlinear regions can be determined. LiNbO 3 electric field sensors are inherently wide band, and a sensing scheme is tested, showing a high-linearity sensing detection of high-intensity and wide-band electric fields.

As the measurement of wide-band (multimegahertz) electric fields is often of practical interest in industrial and commercial environments, in this paper, a methodology of design and implementation of a wide-band electric field sensing scheme, using optical delays as information carriers is described. The scheme is based on a lithium niobate (LiNbO 3 ) birefringent optical waveguide that performs simultaneously as an optical retarder and as a dielectric (electrode-less) sensor. In this scheme, the LiNbO 3 sensor introduces an optical delay and simultaneously senses an on-air electric field and imprints it around an optical delay. At the receiver, the sensed electric field is detected when the sensor and demodulator are optically matched, i.e., when both introduce identical optical delays. An important aspect, when sensing electric fields using LiNbO 3 dielectric sensors, is that the optically sensed field is weaker than the external field by a factor given by the ratio of the permittivity of the surrounding dielectric media over the LiNbO 3 permittivity (boundary condition for normal electric fields). When the surrounding media is air, the optically sensed electric field is 35 times weaker than the external field, as described in this paper. Another practical issue is that a birefringent optical waveguide is highly sensitive to optical polarization variations. Such a sensitivity implies that the output dc component of the received light changes with time (dc-drift). The dc-drift performance of the proposed electric field sensing scheme is measured and reported in this paper. The dc-drift can be minimized using polarization-insensitive LiNbO 3 unbalanced Mach-Zehnder interferometers.Index Terms-Lithium niobate LiNbO 3 , dielectric electro-optic sensors, wide-band electric field sensing, optical retarders.

The topic of spectral line suppression is of major importance when designing impulse radio ultrawideband (IR-UWB) systems. The presence of spectral lines in the power spectral density (PSD) may limit the maximum transmission power to comply with UWB regulations, thus, affecting the system performance. Although previous works have shown the advantages of IR-UWB over fiber (UWBoF) implementations, the topic of spectral line suppression in PSD in such systems has not been entirely addressed. This letter proposes a simple IR-UWBoF system using spectral line free (SLF) convolutional codes to address this topic. Experimental results show that the proposed system offers improved PSD characteristics compared to conventional IR-UWBoF implementations. Furthermore, it is demonstrated that the proposed system is able to deliver SLF IR-UWB signals over single-mode fibers up to 30 km.ABSTRACT: This article presents a novel active W-band phase shifter implemented using IHP SiGe Heterojunction Bipolar Transistor (HBT) 0.25-mm SG25H1 technology with three vector (0 -120 -240 ) sum technique. The integrated chip consists of a 3-way Wilkinson power divider/ combiner with 0 -120 -240 phase shifting lines and three low-noise amplifiers (LNA) working at 77 GHz, which comprises a total of 1.5 3 Figure 5 Degradation of SFL convolutionally coded Q-BOPPM TH-IR UWB signals after the fiber transmission: (a) MATLAB signal; (b) as measured at point A in Figure 3; (c) as measured in B2B configuration at point B in Figure 3; (d) as measured after 20-km SMF transmission; and (e) as measured after 30-km SMF transmission. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

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