Lithium niobate (LN) modulators have been for years the devices of choice for the telecommunication market due to
their high modulation rate and their robustness. Matching RF and optical velocities has been the most critical factor that
limited this technology to 40 Gb/s since the early 2000's. However, recent interest in millimeter-wave (mmW) imaging,
which requires good resolution images for object recognition, has led to significant progress in modulator's design and
fabrication techniques . 100 GHz modulation bandwidth has been reported .
For passive mmW imaging purpose at 77 GHz and beyond, we have developed an electro-optic phase modulator that can
work up to 220 GHz. Modulator design and fabrication techniques are presented, supported by experimental
measurements of optical response. We demonstrate optical upconversion up to 220 GHz by achieving RF and optical
index matching combined with substrate modes elimination and low dielectric and conduction losses. The RF index is
matched to the optical group velocity at 2.19 through CPW ridged structure and silicon dioxide layer deposition.
Accurate index matching is obtained by controlling the thickness and the topology of the silicon dioxide layer, whereas
substrate modes are reduced by thinning the LN substrate down to 50 μm. A fiber-modulator-fiber optical insertion loss
of 4.5 dB also ensures good optical upconversion efficiency. We have applied the phase modulator to our mmW imaging
system and obtained high quality mmW images in W-band.
The integration of an opto-electronic mmW module for application to RF sensing and imaging is
presented. Component integration consisting of ultra-broad band antennas, PIN switching, low
noise amplifiers, and photonic phase modulator, is discussed. A fully integrated module working
up to 130GHz is characterized and presented. Applications in a distributed aperture RF imaging
system are discussed.
Millimetre-wave (mmW) imaging has attracted significant research interests for the promises of allweather
imaging and security scanning for military applications. Recently, we have developed a highsensitivity
mmW imaging system based on photonic devices, which relies on optical up-conversion of the
received mmW signal to generate detectable sidebands. For system with lower detector reponsivity,
higher resolution and wider separation between sidebands and optical carrier, a high efficiency EO
modulator that works in W-band is required. Since such system does not exist commercially, we were
motivated to develop our own 94GHz phase modulator. In our previous publications, we have presented
design, fabrication and preliminary characterization of Lithium Niobate (LN) based devices. We continue
in this paper with our post-processing techniques, updated characterization results and the packaging
method between antenna and modulator. Modulation efficiency >1W-1 has been achieved over W-band.
Using a fin-coupler for antenna integration, we have obtained insertion loss less than 3dB. The packaged
modulator has been installed in our imager. Initial scanning showed high-quality images of various
Millimeter wave (mmW) imaging is continually being researched for its applicability in all weather imaging. While
previous accounts of our imaging system utilized Q-band frequencies (33-50 GHz), we have implemented a system that
now achieves far-field imaging at W-band frequencies (75-110 GHz). Our mmW imaging approach is unique due to the
fact that optical upconversion is used as the method of detection. Optical modulators are not commercially available at
W-band frequencies; therefore, we have designed our own optical modulator that functions at this frequency range.
Imaging at higher frequencies increases our overall resolution two to three times over what was achieved at Q-band
frequencies with our system. Herein, we present imaging results obtained using this novel detector setup, as well as key
imager metrics that have been experimentally validated.
Recently, our group has developed a high-sensitivity millimeter-wave (mmW) imaging system based on optical
upconversion. In such a system, native mmW radiation of objects is first collected by a broadband horn antenna, which
feed the mmW signal to Co-Planar Waveguide (CPW) on a Lithium Niobate(LN) Electro Optical (EO) modulator. The
mmW power is then transferred to the sidebands of an optical carrier due to phase modulation. Detection is realized by
measuring the optical power transferred to the sidebands. The overall performance of the imaging system is highly
dependent on the conversion efficiency of the EO modulator, which is a function of the frequency of the collected
millimeter-wave energy. In this paper, we present the design, fabrication and experimental results towards realizing LN
EO modulators for use in the 95 GHz imaging band.