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Optical angular momentum (OAM) doubling of continuous-wave optical-vortices (OVs) in telecommunication wavelength is demonstrated via single-pass SHG in a PPLN. By measuring SHG-OVs output power, optical-optical conversion efficiencies depending on OAMs are investigated.
We develop a periodically poled LiNbO3 (PPLN) ridge waveguide device and experimentally demonstrate a phase-sensitive amplification based on a cascaded SHG and OPA process. We successfully obtain the high phase-sensitive parametric gain of 21.9 dB.
We propose a global simulation scheme for studying the output characteristics of quantum cascade lasers subjected to near-infrared optical pulses with a wide range of injection powers. We treat nonresonant excitations where the photon energy of the injected pulse is far from that of QCLs. To maintain consistency even at large injection powers wherein thermal effects become non-negligible, internal...
1-THz continuous-wave signal is generated by an optical frequency comb generator utilized as a 41st-order multiplier. Phase noise characteristics of generated signal are evaluated by heterodyne detector and microwave electrical spectrum analyzer.
Envelope-detector-based transceiver configurations are useful for both digital signal transmission and radar systems in the terahertz band. A dual-purpose transceiver is demonstrated using a 1-Gb/s on-off keying signal and 12.5-GHz-bandwidth frequency-modulated continuous-wave radar.
This paper presents a wideband differential amplifier operating at 138 GHz in 40-nm CMOS. It is composed of five differential common source stages with cross-coupled capacitors. A small-signal gain of 18 dB at 138 GHz and a 3-dB bandwidth of 27 GHz are achieved. It consumes 75 mW from a 0.94-V voltage supply. The die area with balun and pads is 945 × 842 μm2 and the core size not including input/output...
This paper presents a compact wideband amplifier at 160 GHz in 40-nm CMOS. Typical wideband amplifier design requires higher-order matching networks and more gain stages, both of which demand larger die area. The presented 8-stage amplifier uses a compact “fishbone” layout technique, and its core size is as small as 190 × 123 µm2. A small-signal gain of 15 dB at 160 GHz and a 3-dB bandwidth of 41...
Optimizing high-power ultrashort pulse amplifier using double-clad Yb-doped fiber, maximum output power of >3 W with a pulse width of 110 fs without pedestal component is obtained. Using this pulse, high-power high-efficiency broadband THz pulse generation is expected.
We present a new analytical model combining the heat equation with rate equations to reproduce experimentally obtained output intensity of terahertz quantum-cascade lasers subject to optical pulse injection and demonstrate good agreement with the experiments.
Optimizing high-power ultrashort pulse amplifier using double-clad Yb-doped fiber, maximum output power of >3 W with a pulse width of 110 fs without pedestal component is obtained. Using this pulse, high-power THz pulse generation is measured by a pyroelectric detector with a low sensitivity.
We have demonstrated amplitude modulation of terahertz quantum cascade lasers by means of the injection of near-infrared laser pulses. Injected 818nm and 1350nm laser pulses had greatly suppressed the output power.
We evaluated performance of zero-bias, square-law GaAsSb/InAlAs/InGaAs tunnel diodes at frequencies up to 220 GHz. The detectors with submicron cross-sectional area demonstrated sensitivities above 500 V/W, and curvature coefficients of 20 V−1.
We have investigated intensity change of terahertz emission from terahertz quantum cascade lasers under optical injection of near-infrared femtosecond laser pulses. THz intensities were suppressed by optical injections and their extinction ratios were dependent on the time delay of optical pulses. Recovery times from the suppressed states to the pre-excited states, for interband and intersubband excitations,...
We develop a mode-locked Yb-doped fiber laser system and obtain ultra-short pulses, toward high-intensity THz frequency comb generation. By using these pulses, we attempt to generate THz pulse from an InAs substrate and confirm it. By improving our system, higher intensity THz frequency comb generation is expected.
We have investigated the light-current characteristics of terahertz quantum cascade lasers using an external light whose energy is below the bandgap energy of the host material. It is found that light injection induces a large modulation depth, up to 100%.
Terahertz imaging and sensing have attracted much attention in recent years, because they can be applied to many application fields. A terahertz real-time imaging technologies considered increasingly important in the future (Terahertz Camera) was developed. The terahertz camera consists of a light source (Terahertz quantum cascade laser) and a un-cooled micro-bolometer array, which can easily get...
The portability of a terahertz imaging system is crucial for practical applications because most of the measured objects are generally fixed and cannot be moved from their locations. We have developed a portable imaging system using a terahertz quantum cascade laser and a microbolometer focal plane array. We also obtained a direct image of the focused beam of the laser.
Transmission spectra of thin films of niobium nitride grown on a magnesium oxide substrate were measured by terahertz time-domain spectroscopy under several temperature conditions. Clear changes in the transparent terahertz waveform and transmission spectra of under / above a phase transition temperature were observed.
In this paper, we have calculated performance of the novel four-level THz-QCLs with the non-equilibrium Green's function (NEGF) method. The calculation result for 40 K showed that the indirect-pump QCL has the largest THz gain. The main origin for this is that almost all electrons contribute to lasing in the new scheme. However, the advantage of gain deteriorates at 200 K due to thermally activated...
Bolometer-type uncooled infrared QVGAs (Quarter Video Graphics Arrays, namely, 320times240) were modified to improve their sensitivities at 3 THz. High transmission materials were investigated and it is found that high resistivity silicon with anti-reflection coating of Parylene or Silicon Dioxide is suitable. Using this material, THz lens was fabricated and handy THz camera which operates at TV frame...
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