A new comprehensive method to suppress the spurious modes in a BPF is proposed taking the multi-strip resonator BPF as an example. It consists of disturbing the resonant frequency, coupling coefficient and external Q of the higher-order modes at the same time. The designed example has shown an extraordinarily good out-of-band response in the computer simulation.

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This paper presents a highly efficient multi-band power amplifier (PA) with a novel reconfigurable configuration. It consists of band-switchable matching networks (BS-MNs) and a biasing network (BS-BN) that are available for multi-band operation. BS-MNs with a susceptance block (SB) require a shorter transmission line (TL) than those without the SB at some target impedances. This paper theoretically derives the relationships of the required TL lengths for the BS-MN with or without the SB and the target impedances. The required TL lengths at the target impedances are evaluated numerically in order to discuss the advantages of the proposed configuration. The BS-BN employing switches for band switching can supply DC power to an amplification device without additional DC power dissipation because the DC bias current does not flow through the switches. Numerical analyses confirm that a BS-BN can be configured with low loss in multiple bands. Based on the proposed configuration, a 1/1.5/1.9/2.5-GHz quad-band reconfigurable PA is designed and fabricated employing RF microelectro mechanical systems switches and partitioned low temperature co-fired ceramics substrates. The fabricated 1W-class PA achieves a high output power of greater than 30dBm and a maximum power added efficiency of over 40% in all operating modes.

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An inter-modulation distortion (IMD) compensation method for thermal memory effect using a multistage RC-ladder circuit has been proposed. The IMD caused by the thermal memory effect on an InGaP/GaAs HBT amplifier was compensated for by inserting a multistage RC-ladder circuit in the base bias circuit of the amplifier. Since heat flux owing to self-heating in the transistor can be approximated with a multistage thermal RC-ladder circuit, the canceling of IMD by an additional electrical memory effect generated from the RC-ladder circuit is predicted. The memory effects cause asymmetrical characteristics between upper and lower IMD. The IMD caused by the memory effects is expressed as a vector sum of each origin. By adjusting an electrical reactance characteristic for sub-harmonics affected by the thermal memory effect in the amplifier circuit, the asymmetric characteristic is symmetrized. The parameters of the RC-ladder circuit were estimated so that the adjusted electrical reactance characteristic is reproduced in simulation. A fabricated InGaP/GaAs HBT amplifier with the thermal memory effect compensation circuit exhibited a symmetrized and suppressed IMD characteristics.

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An analog pre-distortion linearizer employing a radio frequency (RF) transistor with a self base bias control circuit is proposed. The self base bias control circuit extracts the envelope from the modulated input RF signal of the RF transistor and automatically controls its base current according to the extracted envelope. As a result, the proposed linearizer realizes positive gain deviation at high input power level. By adding a resistor between the RF transistor and the self base bias control circuit, the negative gain deviation can be derived. The design of the proposed lineaizer is described with taking the envelope frequency response of the self base bias control circuit into consideration. The fabricated linearizer achieves the adjacent channel power leakage ratio (ACLR) improvement of 8.1dB for a 2GHz-band, 10W-class GaAs FET high-power amplifier (HPA) with negative gain deviation for W-CDMA base stations. It also achieves the ACLR improvement of 8.3dB for a LDMOS HPA with positive gain deviation for the same application.

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This paper presents a digital predistorter with a wideband memory effect compensator for a Doherty power amplifier (PA). A simple memory-predistortion model, which consists of a look-up-table (LUT) and an adaptive filter equalizing memory effects, and a new memory effect estimation algorithm using a direct-learning architecture are proposed. The proposed estimation algorithm has an advantage that a transfer function of a feedback circuit does not affect the learning process. The predistorter is implemented in a field programmable gate array (FPGA) and a digital signal processor (DSP). The transmitter has achieved distortion level of -50.8dBr at signal bandwidth away from the carrier, and PA module efficiency of 24% with output power of 43dBm at 2595MHz under a 20MHz-bandwidth orthogonal frequency division multiplexing (OFDM) signal using laterally diffused metal oxide semiconductor (LDMOS) FETs.

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Orthogonal frequency division multiplexing (OFDM) signals have high peak-to-average power ratio (PAPR) and cause large nonlinear distortions in power amplifiers (PAs). Memory effects in PAs also become no longer ignorable for the wide bandwidth of OFDM signals. Digital baseband predistorter is a highly efficient technique to compensate the nonlinear distortions. But it usually has many parameters and takes long time to converge. This paper presents a novel predistorter design using a set of orthogonal polynomials to increase the convergence speed and the compensation quality. Because OFDM signals are approximately complex Gaussian distributed, the complex Hermite polynomials which have a closed-form expression can be used as a set of orthogonal polynomials for OFDM signals. A differential envelope model is adopted in the predistorter design to compensate nonlinear PAs with memory effects. This model is superior to other predistorter models in parameter number to calculate. We inspect the proposed predistorter performance by using an OFDM signal referred to the IEEE 802.11a WLAN standard. Simulation results show that the proposed predistorter is efficient in compensating memory PAs. It is also demonstrated that the proposal acquires a faster convergence speed and a better compensation effect than conventional predistorters.

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This paper describes a time-domain expression based on the physical model of power amplifiers where electric memory effect is considered to be caused by even-order nonlinearity and bias impedance. It is demonstrated that the time-domain expression is consistent with the general memory polynomial reported by D.R. Morgan et al. To confirm validity of the physical model, a simple method is proposed to measure amplitude and phase of IMD by two tone test: the phase is extracted from measured small signal S-parameters of the amplifier under test. The method is applied to a GaN FET amplifier under condition that memory effect is enhanced by applying inductive cable for DC supply. Frequency dependent IMD is fitted by a parallel connection of L, C, and R: it has been confirmed that the frequency dependence of IMD is given by the bias impedance at even order harmonics of envelope frequency. The frequency dependence assures the validity of the physical model as well as the time-domain expression.

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In this paper, the 8th harmonic Push-Push oscillator is successfully presented. The Push-Push principle and the excellent harmonic coherency in a microwave resonator are effectively utilized. The proposed oscillator consists of two sub-circuits, a microstrip ring resonator and an output circuit. The concept of the simplified structure harmonic oscillator (SSHO) is adopted in the proposed oscillator. The microstrip ring resonator plays two roles of the common resonator and the power combiner circuit. This kind of Push-Push oscillator has practical advantages of the easy circuit design due to the simple circuit configuration and the miniaturization of the circuit size. Using the Push-Push principle and the effective circuit configuration of the output circuit, the desired 8th harmonic signal is effectively enhanced. This Push-Push oscillator achieves good millimeter-wave oscillation in V band using inexpensively available X band HEMTs. The estimated output power of -6dBm at the frequency of 51GHz is obtained with the phase noise of -93dBc/Hz at the offset frequency of 1MHz.

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A method to realize the fine frequency-tuning steps using tiny capacitors instead of Metal-Insulator-Metal (MIM) capacitors is proposed for a digitally controlled oscillator (DCO). The tiny capacitors are realized by the coplanar transmission lines which are arranged unsymmetrical in a 6 metal layers (M6) foundry of 0.18µm CMOS technology. These transmission line based capacitors are designed by using electro-magnetic field simulator, and co-designed by using SPICE simulator. Finally, these capacitors are employed to design 15bit DCO and fabricated the proposed DCO in 0.18µm CMOS technology, and tested. The measured phase noise of DCO was -118.3dBc/Hz (@1MHz offset frequency), and the oscillating frequency tuned from 4.86GHz to 5.36GHz in the minimum frequency-tuning step of 18kHz.

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This paper presents a novel spur suppression technique using a three-phase holding pulse for a direct digital synthesizer (DDS) with a two-phase holding digital-to-analog converter (2PH-DAC). A 2PH-DAC, which uses a reverse-sign step-function as a sampling pulse waveform instead of a commonly-used gate function of zeroth-order hold, enhances the first image of aliasing, which is of higher frequency than the fundamental. Therefore, the first image can be treated as a desired signal, while the fundamental and the second image are spurs for a DDS with a 2PH-DAC (2PH-DDS). The main problem of the 2PH-DDS is close spurs in the case that signal frequency is near Nyquist frequency or sampling frequency. This paper proposes a novel spur suppression technique for a 2PH-DDS. A configuration of a 2PH-DDS is first explained, and spectral properties are analyzed. Based on the analysis, a technique using a three-phase holding pulse to cancel spurs is proposed. Evaluated spur levels of the proposed synthesizer are from -51 to -34dBc, and are improved by 25dB or more by the proposed technique.

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The purpose of this paper is to propose an efficient and effective design scheme to implement compact, high-performance wideband bandpass filters based on a novel compound three-line unit consisting of a stub-loaded short-circuited parallel-coupled three-line structure and two lead lines. Firstly, a simulative investigation is conducted on the transmission characteristics of the proposed coupling unit. The results show that the bandwidth of such structure can be predicted by a symmetric parallel-coupled short-circuited three-line unit, whereas the transmission zeros by a three-section stub composed of the loaded stub, one of the parallel-coupled three lines and the lead line. Accordingly, given specifications, a pseudo-elliptical filter can be designed in an novel three-coupled-line based two-step design scheme: 1. after the derivation of the new closed-form synthesis formulae, a Chebyshev ultra-wideband (UWB) filter is synthesized on a desired passband using symmetric three-line coupling units. 2. By designing the stubs and choosing the proper lengths of the lead lines, multiple transmission zeros are then introduced to improve the skirt and stopband characteristics, whereas the equiripple characteristics are kept in passband. As an example, a UWB bandpass filter covering the Japan's lower UWB band (BW: 3.1-4.8GHz, FBW: 43%) is designed to describe the proposed design procedure. The measured filtering characteristics agree very well with the theoretical predictions, which validate the effectiveness of the proposed new coupling structure and corresponding filter design technique. In addition, the designed filters exhibit good characteristics, such as steep skirt selectivity, very wide stopbands, a compact size compared with the filter based on short-circuited three-line structure, etc.

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A high directivity microstrip coupler suppressing leak coupling with a cancellation circuit of a Wilkinson divider is presented. The presented coupler utilizes a cancellation circuit between a coupling port and an isolation port of the conventional microstrip coupler to enhance the isolation. The cancellation circuit consists of the Wilkinson divider, the multistage attenuator, and the phase offset line. The frequency to enhance the isolation is controlled by the attenuators. As the directivity is improved without the modification of the conventional coupler, the cancellation circuit can be applied to the fabricated conventional couplers. The measured directivity of the presented 1/18 λ coupler is improved from 4.8dB to 43.0dB at 2.6GHz, compared with the conventional 1/4 λ coupler with -20dB coupling. Simultaneously, the 27.4% relative bandwidth with the 20dB directivity is achieved.

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Post-wall waveguide slot arrays are potential candidates for millimeter-wave systems. The modeling of the post-walls by the equivalent solid-walls in terms of guided wavelength is indispensable for intensive optimization of slot design for reducing computational load. In the single mode waveguide slot arrays, the modeling errors of the post-wall waveguide by the solid-wall waveguide are serious especially for the transversely located slots. The S-parameter prediction errors become larger as we increase the height of the waveguide to utilize the low-loss advantage of the waveguide. The authors propose a novel post-wall waveguide structure, named as a connected post-wall (C-PW), to enhance the equivalence. The C-PW waveguide keeps enhanced equivalence to the solid-walls even for a larger substrate height. The predictions are confirmed by simulations and measurements. An 8-element linear array of reflection-cancelling slot pairs is designed by using the equivalent solid-wall model to demonstrate the feasibility of the simple design in the C-PW.

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A post-wall center-feed waveguide consisting of T-junctions is proposed for reducing the slot-free area of a parallel plate slot array antenna. The width of the slot-free area is reduced from 2.6 λ₀ to 2.1 λ₀. A sidelobe level in the E-plane is expected to be suppressed lower than that of the conventional center-feed antenna using cross-junctions. The method of moments with solid-wall replacement designs initially the T-junctions and HFSS including the post surfaces modifies only the reflection cancelling post. We have designed and fabricated a 61.25GHz model antenna with uniform aperture illumination. The sidelobe level in the E-plane is suppressed to -9.5dB while that of a conventional cross-junction type is -7.8dB. Also, we suppress it to -13.8dB by introducing a -8.3dB amplitude tapered distribution in the array of the radiation slot pairs.

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A composite right/left-handed transmission line (CRLH-TL) using substrate integrated waveguide (SIW) with floating-conductor (SIW-type CRLH-TL) for microwave and millimeter wave frequencies has been proposed by the authors. This paper proposes a new configuration that is shield type of the SIW-type CRLH-TL, which can suppress the radiation from the exposed floating-conductors, and shows that even if the shielded structure is used, the SIW-type CRLH-TL supports the LH mode as well as the prototype. Proposed CRLH-TL consists of a SIW with slot apertures (part 1), a dielectric film with floating-conductors (part 2) and a SIW without lower conductor (part 3). A shielded SIW-type CRLH-TL for X - K band (with wide LH mode bandwidth of 6GHz and transition frequency of 16GHz) that satisfies the balance condition is designed. Dispersion diagram and S-parameters are derived numerically, and typical field distributions of RH and LH transmission and the zeroth-order resonance are shown. Measured result agrees well with theoretical result, by considering the accuracy performance and loss factors of the fabricated CRLH-TL. Proposed CRLH-TL has advantage of simple manufacturing, because the parts 1 - 3 are composed of simple planar periodic structure. It is expected to be one of the basic structure of CRLH-TL or components such as LH coupler above 10GHz or millimeter wave frequency.

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Multilayered volumetric composite right/left handed metamaterial structures are investigated. The present structure is composed of conducting mesh plates and dielectric layers including dielectric resonators. The 2-D composite right/left handed metamaterial structure is designed for the in-plane propagation. Propagation mode analysis was made for the volumetric structure under the periodic boundary condition along the normal to the layers as well as for finite number of layered type for comparison. The negative-refractive-index planar lenses were designed and fabricated for the demonstration. It is found from the numerical simulation that the beam focusing through the planar lens with large number of layers is clearly confirmed in both magnitude and phase distribution of the fields. On the other hand, for small number of layers, the beam spot is not found in the magnitude distribution due to the effect of discontinuities between air and designed structure at the top and bottom surfaces, but is still found in the phase distribution. The effect of number of stacked layers on the propagation characteristics is discussed by comparing the numerical simulation results with the measurement.

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This paper treats a band-broadening design technique of a dual-band branch-line coupler with matching networks composed of an impedance step and a short-circuited stub based on the equivalent admittance approach. By replacing each right-handed transmission line (RH-TL) with a composite right/left-handed transmission line (CRLH-TL), very flat couplings over a relative bandwidth of about 10% can be obtained at two arbitrary operating frequencies in comparison with previous CRLH-TLs branch-line couplers. Furthermore, by adding periodical open-circuited stubs into RH-TLs of the designed CRLH-TLs branch-line coupler with matching networks, the entire size of the coupler can be reduced to about 50%. Verification of these band-broadening and size-reduction design techniques can be also shown by an electromagnetic simulation and experiment.

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In this paper, a resonator based on composite right/left handed transmission line concept is discussed. This resonator excites -1st order resonance mode. We start with half-wave resonators consisting of two unit cells of a composite right/left handed transmission line. From the simulated field distributions, the center of these half-wave resonators can be short-circuited to obtain a quarter-wave resonator in the -1st mode. Susceptance slope parameters are calculated for the resonator. Then this resonator is applied for a 2-pole filter made by LTCC, which can be designed with standard filter design theory owing to the slope parameter. The dimension of the experimental filter implemented by LTCC is 2.5mm by 1.35mm by 0.52mm. The insertion loss is 1.80dB at the 2.4GHz band. Good agreement between measured and computed results is obtained.

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Beam steering of leaky wave radiation from a nonreciprocal composite right/left handed transmission line with a ferrite substrate is proposed. The nonreciprocal phase constants of the line were tuned by changing the applied DC magnetic field normal to the ferrite substrate. In the numerical simulation and the experiment, the nonreciprocal phase characteristics and leaky wave radiation are investigated for the ferrite substrate with the magnetization not only in the saturated region, but also in the unsaturated region. The numerical simulation results are in good agreement with the measurement. It is confirmed that the beam directions of the obliquely unidirectional leaky wave radiation for two different power directions are continuously tunable.

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It has been reported that by adding two folded elements, bow-tie antenna can be miniaturized, but the antenna has VSWR degradation problem. In this paper, the details of the VSWR degradation are investigated and the physical mechanism of the degradation is clarified. The best position for folded element is also shown. Moreover, the bow-tie antenna is bent in half in order to realize more size reduction. When the two folded elements are added to the half bent bow-tie antenna, the lowest operation frequency goes down and the proposed antenna can be more downsized than the previous proposed antenna. The gain is slightly lower than that of the previous model, however, the antenna area is reduced from 31%, which is the antenna area ratio of privious proposed antenna and conventional bow-tie antenna, to 19%. The bandwidth of 92% is obtained for VSWR≤2.

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A novel broad-band ring-slot array antenna for simultaneous use of orthogonal polarizations is presented in this paper. In this antenna, the broad-band performance is obtained by integrating a 2×2 ring-slot array antenna and a broad-band π/2 hybrid circuit. The simultaneous use of the right-hand circular polarization (RHCP) and the left-hand circular polarization (LHCP) is achieved using orthogonal feed circuits on three layers. The both-sided MIC technology is effectively employed in forming this type of slot array antenna. Experimental results show that the proposed antenna has good circular polarization characteristics for both the LHCP and the RHCP. The measured impedance-bandwidth of return loss better than -10dB are about 47% both for the LHCP and the RHCP. The 3dB axial ratio bandwidths are 25% (RHCP) and 29% (LHCP). The isolation between the two input ports is better than -35dB at center frequency of 7.5GHz.

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This paper proposes a concept of a concurrent configuration of radio-frequency (RF) micromachined and micro-electro-mechanical-system (MEMS) devices. The devices are fabricated on an originally developed dielectric-air-metal (DAM) structure that suits for fabrication of various devices all together. The DAM structure can propose membrane-supported hollow elements embedded in a silicon wafer by creating cavities in it. Even though the devices have different cavity depths, they are processed by just one planarization. In addition, since the structure is worked only from the front side of the wafer, no flipping process as well as no wafer bonding process is required, and the fact realizes low-cost concurrent integration. As applications of the DAM structures, a hollow grounded co-planar waveguide, lumped element circuitries, and an MEMS switch are demonstrated.

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Newly developed multi-layer inductors on GaAs three-dimensional MMICs are presented. We analyzed single-, double-, triple-, and quadruple-layer stacked-type inductors in what may be the first report on inductors on a GaAs MMIC with three or more layers. The performance of single- and multi-layer inductors was measured and calculated by electromagnetic field simulation. The multi-layer inductors produce 2-11 times higher inductance than that of conventional inductors on 2D-MMICs although they are the same size. This means that the proposed multi-layer inductors have smaller areas with the same inductances than those of conventional inductors. We also conducted the first-ever investigation of how performance factors such as parasitic capacitance, Q-factor, and self-resonant frequency are degraded in multi-layer inductors vis-à-vis those of conventional inductors. A microwave amplifier using multi-layer inductors was demonstrated and found to reduce circuit size by 20%.

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A circular cavity resonance method is improved to measure the frequency dependence of complex permittivity of a dielectric plate by using multimode TE_0m1 with integer m. The measurement principle is based on a rigorous analysis by the Ritz-Galerkin method. A new circular cavity with lowered height is designed from a mode chart of a cavity to decrease the number of unwanted modes near the TE_0m1 modes. A copper cavity having 20GHz for the TE₀₁₁ mode was constructed based on this design. For glass cloth PTFE, RT/duroid 6010 and FR-4 dielectric plates, the frequency dependences are measured from resonant frequencies for the TE_0m1 (m =1, 2, 3 . . .) modes. These measured results agree well with ones measured by using the conventional four different size cavities with TE₀₁₁ mode. It is verified that the designed cavity structure is useful to measure the frequency dependence of low loss dielectric plates.

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A new type of the wide-band BPF made up of an inter-digital resonator and parallel-coupled lines was proposed. The bandwidth of the inter-digital resonator becomes wider by increasing the number of fingers. The design of the parallel-coupled line was performed by optimazing the structural parameters so that the bandwidth is the same as that of the inter-digital resonator. The measured results of the combination of above elements for the BPF agreed well with the simulated ones such that the insertion loss is less than 0.67dB and that the sharp skirt characteristics are realized by attenuation poles near the edges of the passband.

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In this paper, a microstrip lowpass filter using hairpin structure and Chip-Capacitor is proposed. Firstly, the LPF with one hairpin element is briefly designed and optimized with LC prototype structure using circuit simulator. With the capacitor loaded the proposed LPF illustrates the sharp attenuation performance near the cut-off frequency and the wideband rejection characteristics. Then, in order to improve the stopband attenuation the three-hairpin LPF is studied. By optimazing its design the attenuation is improved by 32dB.

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This paper presents spectral multi-level (M-ary) amplitude shift keying (ASK) optical code-division-multiplexing (OCDM) as a key technology for future optical access network. A novel transmitter configuration to achieve flexible scalability that is required in future optical access network is proposed. The transmitter employs pre-biasing circuits and dummy data input. Pre-biasing circuits enable us to achieve high tolerance to multiple access interference by compensating for the nonlinearity of the M-ary ASK and increase the number of multiplexed binary data streams. By inputting the dummy data into the transmitter so that the total number of multiplexed binary data streams including those that actually accommodate users/services and the dummy streams remains constant, the number of users/services can be increased up to the total number of data streams without changing the parameters for pre-biasing. Therefore, the proposed transmitter can flexibly enhance the scalability of the spectral M-ary ASK OCDM. The formulas for calculating the bit error rate characteristics are described when using the conventional and proposed transmitters. The feasibility of the proposed transmitter is verified theoretically using the established formulas.

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This paper reviews next generation optical access network standardization activities, focusing on 10-Gbps class TDM PON, and introduces key technologies for their co-existence with deployed systems.

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The optical access fiber network is spreading rapidly as a result of the progress made on optical communication technologies and the availability of a wide range of broadband Internet content. If the optical access network is not properly maintained, the service quality will decrease. This paper describes some effective technologies that have been researched and developed to maintain a high quality of service, and to achieve efficient maintenance and operation.

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10G-EPON systems have attracted a great deal of attention as a way of exceeding to realize over 10Gb/s for optical subscriber networking. Rapid burst-mode transmitting/receiving techniques are the key technologies enabling the burst-mode upstream transmission of 10G-EPON systems. In this paper, we have developed a OLT burst-mode 3R receiver incorporating a burst-mode AGC optical receiver and an 82.5GS/s over-sampling burst-mode CDR and a ONU burst-mode transmitter with high launch power DFB-LD of 1.27µm wavelength to fully compliant with IEEE802.3av 10G-EPON PR30 standards. The transmitting characteristics of a fast LD turn-on/off time of less than 6ns and a high launch power of more than +8.0dBm, and the receiving characteristics of receiver sensitivity of -30.1dBm and the upstream power budget of 38.1dB are successfully achieved.

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Passive optical network topology has been widely adopted in access networks due to its low-cost and yet flexible network structure. To further promote the passive optical networks, the cost reduction of optical modules is critical. Relatively expensive combination of a conventional index-coupled distributed feedback laser diode (IC-DFB-LD) and an optical isolator is commonly used for passive optical networks with transmission distance more than 30km. Although gain-coupled DFB-LDs (GC-DFB-LD) have been widely investigated in the hope of eliminating the isolator in optical modules, their limited output power keeps them from practical use in passive optical networks. In this paper, we describe the development of 1.31µm and 1.49µm GC-DFB-LDs with high output power and optical feed back tolerance for isolator-free optical modules in access networks. The relative intensity noise (RIN) degradation was well suppressed below -120dB/Hz at -8dB optical feedback in the temperatures range from 0°C to 85°C from both 1.31µm and 1.49µm GC-DFB-LDs. Optical feedback tolerance of 1.31µm and 1.49µm GC-DFB-LDs were improved by more than 6dB and 4dB as compared with conventional IC-DFB-LDs. Dispersion power penalty after over 30km transmission at 1.25Gbps were achieved less than 0.3dB and 0.7dB under -15dB optical feedback conditions. The proposed 1.31µm GC-DFB-LD prototypes experimentally demonstrated 14mW output power with over 5, 000-hour operation at 85°C. Our devices are found to fully complying IEEE 802.3ah standard and seem to be promising for the low-cost optical modules in long-reach access network applications. The details of the device structure as well as transmission experiments are also reported.

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Various types of optical connector with a precise alignment mechanism and long-term reliability have been researched, developed and improved during about 30 years since practical optical communication systems were first introduced in Japan in 1981. The main issues related to optical fiber connector development changed from performance improvement to miniaturization, cost reduction and ease of field assembly when optical communication systems expanded from optical trunk networks to optical access networks. Various different key technologies for optical connectors have been developed to meet these requirements, and a large number of optical connectors are currently being used for the flexible and efficient construction, maintenance and operation of optical access networks. This paper describes the structure, features, and basic technologies of the optical connectors employed in optical access networks in Japan and their standardization and future prospects.

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Broadband optical access services are spreading throughout the world, and the number of fiber to the home (FTTH) subscribers is increasing rapidly. Telecom operators are constructing passive optical networks (PONs) to provide optical access services. Externally installed optical splitters for PONs are very important passive devices in optical access networks, and they must provide satisfactory performance as outdoor plant over long periods. Therefore, we calculate the failure rate of optical access networks and assign a failure rate to the optical splitters in optical access networks. The maximum cumulative failure rate of 1 × 8 optical splitters was calculated as 0.025 for an optical access fiber length of 2.1km and a 20-year operating lifetime. We examined planar lightwave circuit (PLC) type optical splitters for use as outside plant in terms of their optical characteristics and environmental reliability. We confirmed that PLC type optical splitters have sufficient optical performance for a PON splitter and sufficient reliability as outside plant in accordance with ITU-T standard values. We estimated the lifetimes of three kinds of PLC type optical splitters by using accelerated aging tests. The estimated failure rate of these splitters installed in optical access networks was below the target value for the cumulative failure rate, and we confirmed that they have sufficient reliability to maintain the quality of the network service. We developed 1 × 8 optical splitter modules with plug and socket type optical connectors and optical fiber cords for optical aerial closures designed for use as outside plant. These technologies make it easy to install optical splitters in an aerial optical closure. The optical splitter modules have sufficient optical performance levels for PONs because the insertion loss at the commercially used wavelengths of 1.31 and 1.55µm is less than the criterion established by ITU-T Recommendation G.671 for optical splitters. We performed a temperature cycling test, and a low temperature storage and damp heat test to confirm the long-term reliability of these modules. They exhibited sufficient reliability as regards heat and moisture because the maximum loss change was less than 0.3dB.

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We present a full description of a polarization-independent athermal differential quadrature phase shift keying (DQPSK) demodulator that employs silica-based planar lightwave circuit (PLC) technology. Silica-based PLC DQPSK demodulator has good characteristics including low polarization dependence, mass producibility, etc. However delay line interferometer (DLI) of demodulator had the large temperature dependence of its optical characteristics, so it required large power consumption to stabilize the chip temperature by the thermo-electric cooler (TEC). We previously made a quick report about an athermal DLI to reduce a power consumption by removing the TEC. In this paper, we focus on the details of the design and the fabrication method we used to achieve the athermal characteristics, and we describe the thermal stability of the signal demodulation and the reliability of our demodulator. We described two athermalization methods; the athermalization of the transmission spectrum and the athermalization of the polarization property. These methods were successfully demonstrated with keeping a high extinction ratio and a small footprint by introducing a novel interwoven DLI configuration. This configuration can also limit the degradation of the polarization dependent phase shift (PDf) to less than 1/10 that with the conventional configuration when the phase shifters on the waveguide are driven. We used our demodulator and examined its demodulation performance for a 43Gbit/s DQPSK signal. We also verified its long-term reliability and thermal stability against the rapid temperature change. As a result, we confirmed that our athermal demodulator performed sufficiently well for use in DQPSK systems.

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In this paper, we present a new composite transistor circuit design technique that provides superior performance enhancement to analog circuits. By adding a composite transistor to the cascode-compensated amplifier, it has achieved a 102dB DC gain, and a 37.6MHz unity gain bandwidth while driving a 2nF heavy capacitive load at a single 1.8V supply. In the comparison of power-bandwidth and power-speed efficiencies on figures of merit, it offers significantly high values with respect to the reported state-of-the-art works. By employing the composite transistor in a linear regulator powered by a 3.3V supply to generate a 1.8V output voltage, it has shown fast recovery response at various load current transients, having a 1% settling time of 0.1µS for a 50mA or 100mA step, while a 1% settling time of 0.36µS for a maximum 735mA step under a capacitive load of 10µF with a 1Ω ESR resistor. The simulated load regulation is 0.035% and line regulation is 0.488%. Comparing its results with other state-of-art LDO reported results, it also validates the significant enhanced performance of the proposed composite-transistor-based design in terms of speed, current driving capability and stability against changes in environmental parameters. All the proposed designs are simulated using chartered semiconductor (CSM) 1.8V/3.3V 0.18µm CMOS triple-well process technology with thin/thick oxide options and BSIM3 model parameters.

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