RF photonic channelizers can overcome limitations of conventional electronic methods for analysis of wideband RF spectral content. Here, we will present a recent progress on the RF photonic channelizer systems that are based on optical parametric combs. These systems can analyze very wide RF bandwidths exceeding 100GHz, therefore providing essential capability for the applications demanding a wide-bandwidth spectral analysis. The RF channelizers being presented utilize parametric processes in the highly non-linear fiber mixers to generate a large number of RF signal copies in the optical domain. Two different implementations for generation of RF signal copies will be presented and compared: one using a parametric multicasting and another utilizing a direct comb modulation. Generation of optical combs spanning more than 10THz will be shown. We will also present two distinct system architectures for RF photonic channelizer system: one employing a periodic optical filter such as Fabry-Perot etalon to select channels from the signal comb, and another one utilizing a coherent detection between a frequency-locked signal comb and a parametrically generated local oscillator (LO) comb. The second scheme gives benefit of providing both in-phase and quadrature (I/Q) information on channelized intermediate frequency (IF) signals. We will present a system with 32 implemented channels using a filtered scheme and a 32-channel coherent system with a full-field detection implemented on one tunable channel. Sensitivity and dynamic range as well as benefits of both system architectures will be discussed.
We describe the implementation of a self-heterodyne, tunable down converting RF-IF photonic link as a key component of a wideband microwave signal search and intercept system covering S to Ka bands. The presented architecture uses photomixing of two distributed feedback lasers injection locked to a master external cavity laser, allowing low phase to amplitude noise conversion and improved sensitivity. Coherent detection of the intermediate frequency allows unambiguous recovery of full time-domain information. The practical implementation of a packaged prototype system will be discussed, with emphasis on the system stabilization strategy and performance requirements.
A photonic integrated circuit is designed containing a long grating with spiral geometry. Waveguide width and index
modulation are studied as methods to form the grating structure. Both methods require an initial mask step for
waveguide formation. In the case of width modulation the grating is formed in the same step as the waveguide, whereas
a second mask step is required for index modulation. Thus width modulation removes the alignment tolerances
associated with a two step process. The spiral geometry enables a long grating (~1 m) to be realized in a small area (1
cm2). The ability to form the grating in such a small area enables the use of current lithography mask / projection
equipment. Thus, the requirements for mechanical/optical precision in a customized long fiber Bragg grating fabrication
system is transferred to the precision of commercial lithography mask fabrication and projection equipment.
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