In this paper, we present a new photonic technique for producing large time delay of radio-frequency (RF)
modulated optical signals and its application in a novel true-time-delay (TTD) multiple beam-forming system
for wideband RF phased-array antennas using Fourier optics. The RF signal to be delayed is modulated onto
a broadband optical carrier in a frequency-mapped manner by an acousto-optic tunable filter (AOTF). Due to
the phased-matched acousto-optic interaction and the moving nature of the acoustic waves in the AOTF, di.erent
frequency components of the optical carrier are only modulated and Doppler-shifted by the corresponding
frequencies of the modulating RF signal. Heterodyne detection between the modulated optical beam and a timealigned
reference beam from the same light source can recover the modulating RF signal. When a small optical
path length di.erence is introduced between the heterodyne beams, a large RF time delay magnified by the
frequency ratio between the optics and the RF will be generated, which we refer to as the sluggish-light effect.
Sluggish light has potential applications in TTD beam forming for wideband RF phased-array antennas and
proof-of-concept experiments of the sluggish-light based TTD beam forming for an emulated 2- and 4-channel
RF array will be presented in this paper.
In this paper, we present a novel approach for broadband RF photonic signal processing using a femtosecond laser and an Acousto-Optic Tunable Filter (AOTF). We demonstrate that by using spectral filtering in the AOTF, we are able to map each frequency component of the broadband RF signal onto a corresponding set of frequency comb lines of a femtosecond pulse train. The time domain interpretation of this RF to optical frequency mapping yields a femtosecond pulse shaping operation, which is in distinct contrast to the conventional double sideband amplitude modulation of a CW carrier used in RF photonic links. The interaction with a traveling acoustic wave in the AOTF leads to Doppler shift of each frequency comb line by its corresponding RF conterpart, which allows the recovery of the encoded RF signal by heterodyne detection with an unmodulated reference pulse train. As a proof of concept, we experimentally demonstrated mapping of 10 MHz bandwidth RF signals onto 65 nm FWHM optical bandwidth of a 2 GHz repetition rate femtosecond laser using a commercial AOTF and a 40 MHz bandwidth RF signal mapping using a supercontinuum source. Optical processing functions such as RF bandpass/notch filtering can be achieved in the optical domain using optical filters, thereby avoiding the limitations of RF analog filters. Down-conversion naturally occurs based on the laser repetition rate.
We present an optimized design of an acousto-optic tunable filter (AOTF) using a phased-array transducer for a spectrally-multiplexed
ultrafast pulse-shaping RF beamformer application. The momentum-space interaction geometry is used to optimize an AOTF using acoustic beam-steering techniques in combination with acoustic anisotropy in order to linearly map the applied RF frequency to the filtered output optical frequency. The appropriate crystal orientation and phased-array transducer design are determined to linearize the RF to optical frequency mapping even in the presence of optical dispersion of the birefringence. After optimizing the phased-array transducer, acoustic anisotropy, and optical anisotropic diffraction geometry, the designed AOTF will compensate for the birefringent dispersion of TeO2 to give a linear modulation of RF frequencies onto the corresponding optical frequencies. This linearized frequency mapped AOTF is required for a squint-compensated, wavelength-multiplexed, optically processed RF imager.
We demonstrate a compact optical transducer (~50μm) based on a gold film perforated with a square array of square holes. The lattice constant (separation between nearest holes) is chosen to be a ~1μm to detect refractive index change around (n~1.4) with resonant wavelength (λ~1.5μm). Both reflectance measurement and finite difference time domain (FDTD) simulations are performed to evaluate the performance of the sensors. The responsivity of the resonant wavelength is measured to be Δλ/Δn ~835nm RIU-1 (RIU= refractive index unit). The linewidth and contrast of resonance are compared with different size of holes from experimental measurement and FDTD simulations. Coupled mode theory analysis is also used to understand the change reflectance spectrum as a function of hole width.
Spatial dragging of optical solitons is an asymmetric interaction in which a weak signal soliton propagating at a tilted angle can drag an
initially overlapping strong pump soliton with orthogonal polarization to the side, thus missing a spatial aperture at the output. A novel ultrafast all-optical wavelength converter based on (3+1)-D soliton dragging interaction between frequency shifted
solitons is demonstrated in this paper using numerical simulations. This device is not rate limited by carrier life time as previously demonstrated wavelength converters and potentially can reach
a bit rate of 2TB/sec. The proposed wavelength converter can be used in future multi-wavelength soliton communication network or multi-wavelength optical logic based computing systems.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.