This paper describes the outline of recent standardization activities for Radio on Fiber (RoF) transmitter by IEC TC103/WG5. RoF transmitter consists of optical fibers, electrical to optical (E/O) converter, and optical to electrical (O/E) converter. IEC TC103/WG5 is working on standardization on measurement method of E/O and O/E devices, and technical specification of RoF transmitter. This paper overviews those standardization activities which are being developed by TC103/WG5 as well as the National Committee of WG5.

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This paper describes mobile backhaul optical access network designs for future cellular systems, in particular, for those systems that exploit coordinated multipoints (CoMP) transmission/reception techniques. Wavelength-division-multiplexing passive optical networks (WDM-PON) are primarily considered and two proposals to enhance mobile backhaul capability of WDM-PONs for CoMP are presented. One is physical X2 links that support dedicated low latency and high capacity data exchange between base stations (BSs). The other is multicasting in WDM-PONs. It effectively reduces data/control transmission time from central node to multiple BSs joining CoMP. Evaluation results verify that the proposed X2 links and the multicasting enable more BSs to join CoMP by enhancing the mobile backhaul capability, which results in improved service quality for users.

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We propose a coherent optical and radio seamless network concept that allows broadband access without deployment of additional optical fibers within an optical fiber dead zone while enhancing network resilience to disasters. Recently developed radio-over-fiber (RoF) and digital coherent detection technologies can seamlessly convert between optical and radio signals. A millimeter-wave radio with a capacity greater than 10Gb/s and high-speed digital signal processing is feasible for this purpose. We provide a preliminary demonstration of a high-speed, W-band (75-110GHz) radio that is seamlessly connected to an optical RoF transmitter using a highly accurate optical modulation technique to stabilize the center frequencies of radio signals. Using a W-band digital receiver with a sensitivity of -37dBm, we successfully transmitted an 18.6Gb/s quadrature-phase-shift-keying signal through both air and an optical fiber.

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In this paper, a novel interference suppression technique from added RoF (Radio-on-Fiber) system is proposed. In general RoF system, received RF (radio frequency) signal intensity is periodically varied depending on chromatic dispersion that is known as fading phenomenon. In proposed technique null points of this fading phenomenon are intentionally applied to minimize signal interferences. This technique can realize two types of multiplexing RoF signal. In the first configuration, a single optical carrier is modulated twice using two optical modulators connected in series. In second configuration, new RoF signal is added to the existing network using individual light source. Multiplexing RoF signals of 10GHz-band with data of 30Mbps 64QAM is experimentally demonstrated.

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Radio on fiber (RoF) — distributed antenna system (DAS) over wavelength division multiplexing — passive optical network (WDM-PON) with multiple — input multiple — output (MIMO) has been proposed as a next generation radio access network (RAN). The system employs optical time division multiplexing (OTDM) over one WDM channel as a backhaul for RAN to flexibly transmit various types of radio air interfaces. To cover a wider wireless service area, the WDM-PON has a combination of double and bus topologies. This paper analyses the channel capacity in the MIMO cell provided by the RoF-DAS over WDM-PON with computer simulation considering noise power added in the RoF link, and discusses the trade-off between losses in RoF and wireless channel appeared in the channel capacity. Then, this paper clarifies a method to derive the optimal cell size to obtain the highest channel capacity.

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In this paper, we propose a high-speed full-duplex optical wireless communication system using a single channel imaging receiver for personal area network applications. This receiver is composed of an imaging lens, a small sensitive-area photodiode, and a 2-aixs actuator and it can reject most of the background light. Compared with the previously proposed system with single wide field-of-view (FOV) non-imaging receiver, the coverage area at 12.5Gb/s is extended by > 20%. Furthermore, since the rough location information of the user is available in our proposed system, instead of searching for the focused light spot over a large area on the focal plane of the lens, only a small possible area needs to be scanned. In addition, by pre-setting a proper comparison threshold when searching for the focused light spot, the time needed for searching can be further reduced. Proof-of-concept experiments have been carried out and the results show that with this partial searching algorithm and pre-set threshold, better performance is achieved.

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The quantum dot optical frequency comb laser (QD-CML) is an attractive photonic device for generating a stable emission of fine multiple-wavelength peaks. In the present paper, 1.0-GHz and ∼10-ps-order short optical pulsation is successfully demonstrated from a hybrid mode-locked QD-CML with an ultrabroadband wavelength tuning range in the T+O band. In addition, 10-GHz high-repetition intensity-stable short optical pulse generation with a high S/N ratio is successfully demonstrated using an external-cavity QD-CML with a 10th-harmonic mode-locking technique.

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We propose a method of the precise frequency tuning in millimeter wave (MMW) generation using a Mach-Zehnder-modulator-based flat comb generator (MZ-FCG). The MZ-FCG generates a flat comb signal where the comb spacing is exactly the same as the frequency of a radio-frequency signal driving the MZ-FCG. Two modes are extracted from the comb signal by using optical filters. One of them was modulated by a phase modulator, creating precisely frequency-controllable sidebands. In the experiment, typical phase modulation was used. By photomixing of the extracted two modes using a high-speed photodiode, MMW signals with precisely frequency-controllable sidebands are generated. By changing the modulation frequency, the frequency of MMW signals can be continuously tuned. In this scheme, there are two methods for the frequency tuning of MMW signals; one is a coarse adjustment which corresponds to the comb spacing, and the other is fine tuning by the phase-modulation. It was demonstrated that the intensity fluctuation of the upper sideband of the modulated MMW signal was less than 1dB, and the frequency fluctuation was less than the measurement resolution (300Hz).

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A large-range switchable RF signal generator is demonstrated using a triple-wavelength fiber laser with uneven-frequency-spacing. Due to the birefringence characteristics of the triple-wavelength fiber laser, switchable dual-wavelength operation can be obtained by adjusting a polarization controller. Therefore, we can achieve a stable RF signals at microwave or millimeter-wave band.

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To obtain an ultra-short high-intensity pulse source, we investigated the amplification characteristics of two types of pulses (dissipative soliton and stretched pulses) produced by our Yb-doped fiber laser oscillator. Our results show that the dissipative soliton pulse can be amplified with less deterioration than the stretched pulse.

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We propose new electro-optic modulators using a double antenna-coupled electrode structure for radio-over-fiber systems. The proposed modulators are composed of a pair of patch antennas and a standing-wave resonant electrode. By utilizing a pair of patch antennas on SiO₂ substrates and a coupled-microstrip line resonant electrode on a LiNbO₃ substrate with a symmetric configuration, high-efficiency optical modulation is obtainable for 2 ∼ 4 optical waveguides at the same time. The proposed modulators were designed at 58GHz and their basic operations were demonstrated successfully with an improvement of 9dB compared to a single antenna-coupled electrode device on a LiNbO₃ substrate in our previous work.

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Quasi-phase-matching (QPM) electro-optic modulators using gap-embedded patch-antennas were proposed for improving wireless microwave-optical signal conversion. The proposed QPM devices can receive wireless microwave signals and convert them to optical signals directly. The QPM structures enable us to have twice antenna elements in the fixed device length. The device operations with improved conversion efficiency of ∼10dB were experimentally demonstrated at a wireless signal frequency of 26GHz. The proposed QPM devices were also tested to a wireless-over-fiber link.

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We report a 40-Gb/s and highly accurate intensity limiter with a single Erbium-Doped Fiber Amplifier (EDFA) for low-power-consumption driving intensity limiting. The intensity limiter based on self-phase modulation with an appropriate pre-chirping procedure makes it possible, which provides a highly accurate limiting of less than 0.01dB. We fed 40-Gb/s signals with 2.69dB intensity fluctuation and 4.7dB improvement on the receiver sensitivity was obtained for a bit error rate of 10^-9 by using a numerical simulation.

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We report a trial of 100-GS/s optical quantization with 5-bit resolution using soliton self-frequency shift (SSFS) and spectral compression. We confirm that 100-GS/s 5-bit optical quantization is realized to quantize a 5.0-GHz sinusoid electrical signal in simulation. In order to experimentally verify the possibility of 100-GS/s 5-bit optical quantization, we execute 5-bit optical quantization by using two sampled signals with 10-ps intervals.

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This article describes the frequency response and the applications of the optical electric-field sensor consisting of a 1mm × 1mm × 1mm CdTe crystal mounted on the tip of an optical fiber, which theoretically possesses the potential to cover the frequency band from below megahertz to terahertz. We utilize a capacitor, GTEM-Cell, and standard gain horn antennas for applying a free-space electric field to the optical sensor at frequencies from 20kHz to 1GHz, from 1GHz to 18GHz, and from 10 to 180GHz, respectively. An electric-field measurement demonstrates its flat frequency response within a 6-dB range from 20kHz to 50GHz except for the resonance due to the piezo-electric effect at a frequency around 1MHz. The sensitivity increases due to the resonance of the radio frequency wave propagating in the crystal at the frequencies higher than 50GHz. These experimental results demonstrate that the optical electric-field sensor is a superior tool for the wide-band measurement which is impossible with conventional sensors such as a dipole, a loop, and a horn antenna. In transient electrostatic discharge measurements, electric-field mapping, and near-field antenna measurements, the optical electric-field sensor provide the useful information for the deterioration diagnosis and the lifetime prognosis of electric circuits and devices. These applications of the optical electric-field sensor are regarded as promising ways for sowing the seeds of evolution in electric-field measurements for antenna measurement, EMC, and EMI.

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This paper describes two promising millimeter-wave measurement techniques suitable for biological materials. One is reflection-geometry imaging using a low-coherence signal, and the other is millimeter-wave ellipsometry. Imaging porcine tissue during the desiccation process, we found the temporal variation of the reflection intensity to be well explained by an exponential decrease of the relative dielectric constant. Ellipsometry results showed that the complex relative dielectric constant also decreased exponentially with time during the desiccation process and that for bovine tissue the gradients for the real and imaginary parts of the constant were different. The implications of these results on the distribution of water in biological tissues are discussed.

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We evaluated the single side-band phase noise of a 40GHz beat signal generated by two free-running lasers. This allowed us to verify the utility of the two free-running lasers is verified as a light source for a next-generation radio-over-fiber system using frequency such as those in the millimeter-wave and terahertz bands. We also measured the phase noise of a frequency quadrupler using a Mach-Zehnder modulator for comparison. The phase noise of the two free-running lasers and the frequency quadrupler are -63.85 and -95.22dBc/Hz at a 10kHz offset frequency, respectively.

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The author developed a wideband precise I/Q modulator using GaAs pHEMT technology. In this technology, pHEMT has 0.22µm metallurgical gate length and f_t=51GHz at V_ds=5V. With the careful design of the wideband phase shifter, this IQ modulator achieved a large wideband frequency range of 250MHz to 8GHz and good EVM performance after calibration. For overall frequency range, low distortion performance is obtained, where third order intermodulation is less than -42dBc. Also the ACPR at 2.2GHz for W-CDMA application is less than -74dBc.

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A LNA, an RF front-end and a 6th-order complex BPF for reconfigurable low-IF receivers are demonstrated in this work. Due to the noise cancellation, the two-stage LNA presents a low NF of 2.8 to 3.3dB from 0.8 to 6GHz. Moreover, the LNA delivers two kinds of gain curves with IIP₃ of -2.6dBm by employing the capacitive degeneration and the resistive gain-curve shaping in the second stage. The flicker noise corner frequency of the down-converter has been considered and the measured f_C of the RF front-end is 200kHz. The RF front-end also provides two kinds of gain curves. For the low-frequency mode, the conversion gain is 28.8∼31.1dB from 800MHz to 2.4GHz. For the high-frequency mode, the conversion gain is 26.8∼27.4dB from 3 to 5GHz. The complex BPF is realized with gm-C LPFs by shifting the low-pass frequency response. With variable transconductances and capacitors, a fixed ratio of the centre frequency to the bandwidth (∼2) is achieved by varying the bandwidth and the centre frequency of the LPF simultaneously. The complex BPF has a variable bandwidth from 200kHz to 6.4MHz while achieving an image rejection of 44dB.

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High phase noise is a common problem in ring oscillators. Continuous conduction of the transistor in an analog tuning method degrades the phase noise of ring oscillators. In this paper, a digital control tuning which completely switches the transistors on and off, and a 1/f noise reduction technique are employed to reduce the phase noise. A 14-bit control signal is employed to obtain a small frequency step and a wide tuning range. Furthermore, multiphase ring oscillator with a sub-feedback loop topology is used to obtain a stable quadrature outputs with even number of stages and to increase the output frequency. The measured DCO has a frequency tuning range from 554MHz to 2.405GHz. The power dissipation is 112mW from 1.8V power supply. The phase noise at 4MHz offset and 2.4GHz center frequency is -134.82dBc/Hz. The FoM is -169.9dBc/Hz which is a 6.3dB improvement over the previous oscillator design.

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This paper presents the design of a second-order and a fourth-order bandpass filter (BPF) for 60GHz millimeter-wave applications in 0.18µm CMOS technology. The proposed on-chip BPFs employ the folded open loop structure designed on pattern ground shields. The adoption of a folded structure and utilization of multiple transmission zeros in the stopband permit the compact size and high selectivity for the BPF. Moreover, the pattern ground shields obviously slow down the guided waves which enable further reduction in the physical length of the resonator, and this, in turn, results in improvement of the insertion losses. A very good agreement between the electromagnetic (EM) simulations and measurement results has been achieved. As a result, the second-order BPF has the center frequency of 57.5GHz, insertion loss of 2.77dB, bandwidth of 14GHz, return loss less than 27.5dB and chip size of 650µm × 810µm (including bonding pads) while the fourth-order BPF has the center frequency of 57GHz, insertion loss of 3.06dB, bandwidth of 12GHz, return loss less than 30dB with chip size of 905µm × 810µm (including bonding pads).

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We suggest a novel digitally-controlled SMPS using a high-resolution DPWM generator. In the proposed circuit, the duty ratio of the DPWM is determined by the voltage slope control of an internal capacitor using a pseudo relaxation-oscillation technique. This new control method has a simpler structure, and consumes less power compared to a conventional digitally-controlled SMPS. Therefore, the proposed circuit is able to operate at a high switching frequency (1MHz∼10MHz) obtained from a relatively low internal operating frequency (10MHz∼100MHz) with a small area. The maximum current of the core circuit is 2.7mA, and the total current of the entire circuit, including the output buffer driver, is 15mA at 10MHz switching frequency. The proposed circuit is designed to supply a maximum 1A with maximum DPWM duty ratio of 90%. The output voltage ripple is 7mV at 3.3V output voltage. To verify the operation of the proposed circuit, we performed a simulation with Dongbu Hitek BCD 0.35µm technology.

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A multigate polycrystalline-silicon (poly-Si) thin-film transistor (TFT) is a recently popular topic in the field of Si devices. In this study, self-aligned planar metal double-gate poly-Si TFTs consisting of an embedded bottom metal gate, a top metal gate fabricated by a self-alignment process, and a lateral poly-Si film with a grain size greater than 2µm were fabricated on a glass substrate at 550°C. The nominal field-effect mobility of an n-channel TFT is 530cm²/Vs, and its subthreshold slope is 140mV/dec. The performance of the proposed TFTs is superior to that of top-gate TFTs fabricated using equivalent processes.

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We have investigated on a random-texturing process for multi-crystalline Si solar cells by plasmaless dry etching, with chlorine trifluoride (ClF₃) gas treatments. The reflectance of textured surfaces was reduced to below 20% at a wavelength of 600nm. In this study, we tried to improve the electrical characteristics by modifying the fabrication process. The substrate surfaces were dry etched by chlorine trifluoride gas and subsequently etched with an acid solution to form appropriate textured structures. The improved electrical characteristics were demonstrated.

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This paper proposes a new BIST (Built-In Self-Test) method for static testing of an ADC (Analog-to-Digital Converter) with transition detection method. The proposed BIST uses a triangle-wave as an input test stimulus and calculates the ADC's static parameters. Simulation results show that the proposed BIST can test both rising and falling transitions with minimal hardware overhead.

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