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<sup>-1</sup> 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.
We present several novel technologies for sensing millimeter-wave (mmW) radiation for imaging and spectroscopy based on photonic devices. Along these lines, in our high-sensitivity millimeter-wave (mmW) imaging system, which is based on optical upconversion, the power of mmW radiation is transferred to the sidebands on an optical carrier via an electro-optic (EO) modulator fed by a broadband horn antenna. The detection is realized by measuring the transferred optical power of the sidebands. The sensitivity of this detection system is primarily controlled by the conversion efficiency of the EO modulator at the desired mmW frequency (e.g. 95GHz). Thus, modulators are required that exhibit an ultra-broad bandwidth and small drive voltage. In this paper, we present the design, fabrication, and characteristics of LiNbO<sub>3</sub> traveling-wave modulator for the mmW detection system. In a traveling-wave modulator, the bandwidth is limited by the mismatch between electrical and optical propagation constants. We have developed several techniques to finely tune the propagation constant of the mmWs in the modulator and have thereby eliminated this mismatch. Further bandwidth limitations for the modulator arise from losses in the electrode conductor, the substrate and buffer layer dielectrics, and coupling between the traveling-wave mode and the substrate modes. Modulator structures are described to reduce those losses without increasing the device driving voltage. The bandwidth and conversion limits of these structures are also discussed. The mmW detection pixels using the fabricated modulators were assembled, characterized, and analyzed. A high-sensitivity W-band detection system with a low noise-equivalent temperature difference (NETD) has been demonstrated. In addition, we present ongoing work to improve coupling millimeter-wave energy to the modulator at the W-band using techniques viable for packaged devices.
We report the design, fabrication, and characterization of high-speed LiNbO<sub>3</sub> modulator for the millimeter-wave
(MMW) detection system at W band covering atmospheric window at 94 GHz. The LiNbO<sub>3</sub> modulator is used to
convert the collected MMW power into optical frequency, and hence predominantly determines the system sensitivity.
The high sensitivity of detection requires the modulator a broad-band response and a small driving voltage. The ridged
traveling-wave structure has been used in the modulator design. The effects of velocity matching, impedance matching,
and MMW attenuations in this structure on the device's MMW conversion efficiency are investigated. A numerical
model has developed to optimize the device geometric parameters and the fabrication processes. The fabricated
modulator achieved the 3-dB optical bandwidth of 67 GHz and the conversion efficiency of ~0.7 W<sup>-1</sup> at 94 GHz. The
detection pixel based on it has shown a high sensitivity with a noise equivalent temperature difference of ~6 K at a
refreshing rate of 30 Hz.
In this paper we present several novel photonic technologies for sensing millimeter-wave (MMW) radiation for the imaging and spectroscopy applications. Based on the optical up-conversion approach, our high-sensitivity MMW imaging system transfers the power of MMW radiation received from a broadband horn antenna to the sidebands on an optical carrier via an electrooptic (EO) modulator. The detection is realized by measuring the transferred optical power of the sidebands. The sensitivity of this detection system is primarily controlled by the conversion efficiency of the EO modulator
at the desired MMW frequency. In this paper, we present the design, fabrication, and characteristics of the ultra-broadband LiNbO<sub>3</sub> traveling-wave modulator for the MMW detection system working at a frequency of 95 GHz. A numerical model based on the finite element analysis technique has developed to optimize the device geometric parameters and the fabrication processes. A modulation efficiency of ~0.9 W<sup>-1</sup> at 95 GHz has been achieved for the optimized modulator, which corresponds to the half-wave voltages of 9 V and 18 V, at DC and 95 GHz, respectively. The detection pixel based on those modulators has shown a high sensibility with a noise equivalent temperature difference of ~17K at a refreshing rate of 30 Hz.
Recent efforts in our group towards the fabrication of sensors capable of detecting passive levels of millimeter-wave radiation have led to the development of an optically-based detector with sub-picowatt noise equivalent powers. This sensor is based on upconverting the received radiation into sidebands on an optical carrier using electro-optic modulation techniques and, subsequently, suppressing the remaining carrier energy. The noise equivalent power of such detectors is critically dependent on the ability of the electro-optic modulator to efficiently convert frequencies up to and exceeding 95 GHz onto the optical carrier while suppressing potential noise sources. In this paper, we discuss the specific device requirements generated by this unique potential application of high-frequency optical modulators. The effects of various modulator properties, such as half-wave voltage, frequency response, and maximum optical power density are discussed in the context of millimeter-wave detection capability. In addition, we present experimental efforts towards fabricating a passive millimeter-wave detector based on this approach, including efforts to develop an optimized optical modulator technology.
In this paper, antennas that combine transitions from microstrip line / coplanar waveguide (CPW) to horn antenna in a single unit are presented. Conventional single layer microstrip patch antennas inherently suffer narrow operation bandwidth; to widen the frequency bandwidth, stacked patch antennas are used and high gain is achieved from the horn antenna. Here, microstrip line / CPW directly feeds the bottom patch while the top patch couples parasitically to the bottom patch. For -10 dB return loss, 25% bandwidth is achieved for both microstrip line to horn antenna (MSLTHA) at center frequency f<sub>0</sub>=17.5 GHz and for CPW to horn antenna (CPWTHA) at f<sub>0</sub>=97 GHz. The designs were optimized using 3D Finite Element Method (FEM) software HFSS by Ansoft Corporation. The optimal design of MSLTHA has been fabricated and characterized. The return loss and far field radiation pattern are measured and has been found in very good agreement with the simulation results.
In this paper we present the modeling, design and fabrication of high-speed photonic modulators for use at high GHz, namely millimeter wave (MMW), frequencies based on the electro-optic materials, such as LiNbO<sub>3</sub>. To accurately design the traveling wave MMW modulators rigorous EM numerical tools are used to determine the propagation characteristics of both the optical and MMW waveguides. Extensive studies have been made to achieve an optimal design, which includes a close refractive index match between optical and MMW wave and a reduction of MMW propagation loss. The designed devices have been fabricated and tested with a modulation up to 135GHz.