In this paper, we demonstrate the monolithic integration of two resonant tunneling diodes (RTD) to make a THz mixer circuit. The circuit uses two RTDs, which are integrated in one carrier substrate. The RTDs are biased independently. The fist RTD operates as an oscillator and provides the local oscillator signal for the second RTD operating as a mixer. The measurements demonstrate that a monolithic integration of several RTDs in one substrate is feasible. This offers new possibilities for RTD based wireless communication and sensing systems.
Developing terahertz integration technology is essential for practical use of terahertz electromagnetic waves (0.1–10 THz) in various applications including broadband wireless communication, spectroscopic sensing, and nondestructive imaging. In this paper, we present our recent challenges towards terahertz system integration based on photonic crystal technology such as the development of terahertz transceivers. We use photonic-crystal slabs consisting of a twodimensional lattice of air holes formed in a silicon slab to develop low loss compact terahertz components in planar structures. The demonstration of ultralow loss (< 0.1 dB/cm) waveguides and integrated transceiver devices in the 0.3 THz band shows the potential for the application of photonic crystals to terahertz integration technology. Improving the coupling efficiency between the photonic crystal waveguide and resonant tunneling diode is important to take full advantage of the ultralow loss photonic crystal waveguides.
For high-power THz wave generation by photomixing of two lightwaves, we proposed the synchronous power combiner which consists of eight-arrayed photomixers/antennas and the THz phase control system. We experimentally confirmed the effectiveness of the power combination by synchronizing the phases of the THz wave by the mechanical optical delay lines and also demonstrated the same functionality at the lightwave-circuit-based optical phase control system. We found that the directional gain is increasing with increasing the number of photomixers from two to three and it reached up to 4.5 dB.
Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-of frequency. This work is an
overview of some recent results concerning the low temperatures operation, linearity, and circular polarization studies of
nanometer scale field effect transistors for the detection of terahertz radiation. Also first results on graphene transistors
are discussed.
We show that phohtonic technologies developed for conventional fiber-optic communications have potential for use in
contemporary terahertz-wave applications, such as remote sensing and wireless communications. Advanced unitravelling
photodiodes (UTC-PDs) can produce output power of 0.5 mW at 350 GHz and 10 μW at 1 THz. Using the
UTC-PD and other optical devices, we demonstrate a time-continuous terahertz-wave signal generator that can tune the
output signal over a wide frequency range with very narrow spectral linewidth and gas-sensing with the terahertz-wave
source. We also show some preliminary results for terahertz-wave wireless communications using photonic technologies.
We developed an active gas sensing system with a highly- sensitive sub-terahertz (THz) wave receiver consisting of a
superconductor-insulator-superconductor mixer and a photonics-based THz-wave local oscillator. Continuous
monitoring of the gas contents in the gas cell was successfully carried out with the developed system. The high
sensitivity of the developed THz-wave receiver makes it possible to extend the detection range up to 30 m.
Metal gap optical waveguides support propagation and strong confinement of coupled surface plasmon polariton
in nano-region. We study efficient transmission through a plasmonic T-branch with a mesa structure in metal
gap optical waveguides. Transmissivity through the branch with various mesa geometries is investigated by
numerical simulations. It is found that transmissivity through the branch can be improved by introducing thin
metal barrier into dielectric gap. We can achieve more than four times enhancement in the transmissivity.
We have developed a 120-GHz-band wireless communication link that uses photonic and electronic technologies for the
generation, modulation, and amplification of 125-GHz signals. Photonic technologies are suitable for generating ultra-high
frequency signals, and enable long-distance wired transmission and the distribution of millimeter-wave signals.
All-electronic systems, on the other hand, have the advantages of being compact and inexpensive, especially when the
transceiver functions are implemented with monolithic microwave integrated circuits (MMICs). We succeeded in the
error-free transmission of a 10-Gbit/s data signal over a distance of 450 m, and estimated the maximum transmission
distance to be about 2 km.
The uni-traveling-carrier photodiode (UTC-PD) is a novel photodiode that utilizes only electrons as the active carriers.
This unique feature is the key to realize its excellent high-speed and high-output characteristics simultaneously. To date,
a record 3-dB bandwidth (f3dB) of 310 GHz and a very high millimeter (mm)-wave output power of over 17 mW at 120
GHz have been achieved. These superior characteristics are essential for the detection of high-bit-rate optical signal in
communications systems and for the generation of high-frequency electro-magnetic waves in measurement and sensing
systems. For optical communications, we have realized a photoreceiver operating at up to 160 Gbit/s and an avalanche
photodiode with a record f3dB of 40 GHz. For generating mm-/sub-mm-wave signals, we have developed a compact
UTC-PD module with a rectangular waveguide output port for operation at up to 325 GHz. We have also fabricated a
quasi-optical module for operation at higher frequencies integrating a UTC-PDs and a planar log-periodic antenna. This
module can be operated at up to 1.6 THz with a maximum output-power of 2.6 μW at 1.04 THz. The UTC-PD has been
used successfully for several applications, such as mm-wave imaging and photonic local signal supply for radio
telescopes, demonstrating its feasibility for high-frequency measurement and sensing systems. As a challenge for future
high-sensitivity sensing systems, the possibility of UTC-PD modules operating at a very low temperature of 15 K has
also been demonstrated.
The uni-traveling-carrier photodiode (UTC-PD) is a novel photodiode that utilizes only electrons as the active carriers. This unique feature is the key to achieving excellent high-speed and high-output characteristics simultaneously. A record 3-dB bandwidth of 310 GHz and a millimeter-wave output power of over 20 mW at 100 GHz have already been achieved. The superior capability of the UTC-PD for generating very-large high-bit-rate electrical signals as well as a very-high output power in millimeter/sub-millimeter ranges can innovate various systems, such as broadband optical communications systems, wireless communications systems, and high-frequency measurement systems. Achievements include photoreceivers of up to 80 Gbit/s, DEMUX operations using an integrated optical gate of up to 320 Gbit/s, and a 10-Gbit/s millimeter-wave wireless link at 120 GHz. Also achieved has been high-power millimeter generation of 17 mW at 120 GHz with a waveguide-output UTC-PD module, considered for use in the photonic-local system of radio telescopes.
The uni-traveling-carrier photodiode (UTC-PD) is a newly developed photodiode that utilizes only electrons as the active carriers. This unique feature enables a UTC-PD to achieve excellent high-speed and high-output characteristics simultaneously. Fabricated devices exhibit a record 3-dB bandwidth of 310 GHz, a very-short electrical output pulse of less than 1 ps, high-power millimeter-wave generation at 100 GHz with an output power of over 20 mW, and a sub-millimeter-wave emission at frequencies of up to 800 GHz. The superior capabilities of the UTC-PD for generating wideband millimeter/sub-millimeter waves and very-short electrical pulse signals can innovate various measurement and sensing systems, for instance, millimeter-wave imaging or network analysis. A waveguide-output UTC-PD module with a maximum output power of over 10 mW at 100 GHz is practically important for the photonic-local system in radio telescopes.
Ultrafast photodiode is a key device, which links electronics and photonics technologies, especially in measurement, sensing and communications systems. Uni-traveling-carrier photodiode UTC-PD is unique in that it provides both a large bandwidth and a high saturation output current at 1.55-m wavelength. In this paper, we describe recent progress in UTC-PD technologies and their analog and digital applications in the frequency regions from giga-hertz to tera-hertz. First, operation principle and characteristics of InP/InGaAs UTC-PDs are shown. Time-domain response exhibited 1-ps pulse width, which corresponds to the 3-dB bandwidth of over 300 GHz. To enhance the output power, resonant-operation of the UTC-PD integrated with a matching circuit is proposed. The CW output power exceeds 20 mW at 100 GHz. Photonically-generated electrical signals are applied as stimulus to ultrafast measurement systems such as IC testers and network analyzers. By integrating PDs with planar antennas in monolithic as well as hybrid fashions, millimeter and submillimeter-wave emitters are developed. These photonic emitters are used as signal sources for transmitters in millimeter-wave wireless links, imaging applications, and local oscillators in radio-astronomy receivers. Finally, a novel functional device, in which an electro-absorption modulator is integrated with the PD, is demonstrated as a demultiplexer for over 300-Gb/s optical communications systems.
Thick-gold-multilevel damascene-interconnect technology makes it possible to fabricate >10-micrometers -feature ultrahigh-speed devices on Si. Adding H2O2 to a conventional KIO3-based slurry triples the removal rate of gold in chemical mechanical polishing (CMP). A ratio of H2O2 to slurry of approximately 1:1 is found to be the optimum for obtaining the highest gold removal rate. X-ray photoelectron spectroscopy (XPS) analyses show that gold is oxidized in spite of its chemical stability when the removal rate is high. The gold is oxidized due to the reduction of iodine at the optimum H2O2 mixture ratio. This CMP of gold enabled us to make a thick (>10 micrometers ) gold-multilevel damascene-interconnection structure for the first time. Integration of full-wafer wafer-bonded uni-traveling carrier photodiodes (UTC-PDs) with the gold multilevel interconnections as coplanar waveguides (CPWs) on a Si wafer has been achieved using this gold-CMP process.
Microfabrication technologies for use as practical methods in > 10-micrometers featured high-speed device fabrication have been developed: the thick polyimide-used damascene process, electroless plating of Ru/Ni on Cu interconnections, the area-restricted chemical mechanical planarization to polish thick polyimide films. Applying their technologies to fabricate RF-components and millimeter-wave components on Si demonstrates excellent characteristics: high-quality factor (Q-factor) in spiral inductor, low transmission loss for sidewall coplanar waveguide (CPW), high-power radiation in CPW-fed sot antenna. The Si-technology-based approach to achieve seamless integration of different kinds of devices, i.e., photonic devices, ULSIs, RF-devices, and millimeter- wave devices are promising ways to fabricate high-speed systems on Si.
Integrated Packaging (IP) technology was developed to enable further application of ultrahigh-speed Uni-Traveling-Carrier photodiodes (UTC-PDs). In IP modules, devices are fabricated on the package substrate together with all interconnections using standard semiconductor processing techniques after wafer bonding of device epitaxial layers. Thus, problems associated with substrate discontinuity and wire/solder interconnections encountered in conventional hybrid packaging of > 100 GHz devices are eliminated. UTC-PDs, integrated with millimeter-wave coplanar waveguides (CPWs), were fabricated on package compatible sapphire with high yield. Device performance was not affected by wafer bonding. Furthermore, devices with record 3-dB bandwidth of 174 GHz were obtained. These devices produced output voltages of 1.45 V (29 mA) at higher input levels while maintaining 3-dB bandwidth above 150 GHz. CPWs fabricated on sapphire exhibited low dispersion. Thus, wafer bonding on sapphire is a promising technique for IP module fabrication.
An electro-optical polymer was synthesized where a diazo dye with a dicyanovinyl group as an electron acceptor and a diethylamino group as a donor is attached to the polymer chain. The electro-optical coefficient (r) reached 30 pm/V. It was found that the edge absorption of the chromophore caused a loss increase in the near infrared region, which indicates that the increase in the r value leads to a propagation loss increase in the material. The loss is around 1.0 dB/cm in a single-mode waveguide fabricated by using oxygen reactive ion etching. The polymer waveguide is applied to two types of devices, a Mach-Zehnder optical modulator and a vertically stacked directional coupler, which both achieve electro-optical modulation. As another application, electro-optical measurement of an electric field in a high-speed circuit device is demonstrated, where the polymer is processed into a chip film probe and patched to an integrated circuit, thus enabling the electric signal to be detected.
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