Magnet-less non-reciprocal metamaterial (MNM) synthesise artificial magnetic gyrotropy by metal ring resonator with unilateral component insertion. Clear advantage to natural magnetic material is full integrated circuit ingredient compatibility but still suffers from drawbacks of consumption power in active component and footprint of ring resonator. A new MNM structure by a varactor inserted figure of eight resonator is introduced, which enables reduction of active components by half and even smaller footprint to the original simple ring resonator structure in addition to frequency tunability.

This paper presents a novel isolator that employs a varactor that tunes the operating frequency for use in future multi-band mobile handsets. The proposed isolator employs only one varactor for compactness and has a three-fold symmetric structure to reduce the parasitic reactance at each port. Analytical and experimental results clarify the tuning range of the proposed isolator. This paper presents the fundamental characteristics of the proposed isolator such as the insertion loss, isolation, and adjacent channel leakage ratio (ACLR) using a W-CDMA signal. The impact of the proposed isolator on the system performance is described based on experimental evaluation of the ACLR with a multi-band transmission system consisting of a power amplifier and the proposed isolator.

Tunnel diodes are some of 2-port devices with negative differential resistance (NDR). In this paper, we propose a low insertion loss isolator, which can be designed to operate up to sub-millimeter region, by using resonant tunneling diodes (RTDs) and a HEMT. Small-signal analyses are performed to confirm insertion loss and unidirectional characteristics for the proposed active isolator. It is found that unidirectional amplifications as well as isolation characteristics could be expected below sub-millimeter waveband as a result of numerical calculations.

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 30 km. 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 1.31 µm and 1.49 µm 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 -120 dB/Hz at -8 dB optical feedback in the temperatures range from 0 to 85 from both 1.31 µm and 1.49 µm GC-DFB-LDs. Optical feedback tolerance of 1.31 µm and 1.49 µm GC-DFB-LDs were improved by more than 6 dB and 4 dB as compared with conventional IC-DFB-LDs. Dispersion power penalty after over 30 km transmission at 1.25 Gbps were achieved less than 0.3 dB and 0.7 dB under -15 dB optical feedback conditions. The proposed 1.31 µm GC-DFB-LD prototypes experimentally demonstrated 14 mW output power with over 5,000-hour operation at 85. 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.

This paper introduces a new approach to realize a multi-state operation on the microwave isolator using ferrite edge-mode. The voltage control of total transmission on the isolator is realized. The operation is based on the unique property of ferrite edge-mode and the variable resistance of PIN diodes. On the isolator, the frequency response is investigated both experimentally and numerically. The numerical analysis is performed by the FDTD method. Both numerical and experimental results have shown that the transmission between two ports can be totally controlled by the applied voltage for the diodes. The experimental results indicate that the transmission direction can be controlled at 11 GHz, and the isolation ratio can be controlled for more than 30 dB.

This paper introduces a new type of microwave isolator. The operation is based on the two phenomena; the ferrite edge-mode and the photo-generated plasma on silicon substrate. Conventional ferrite edge-mode isolator has been made of the ferrite and the resistive material. The later is used to absorb the reverse-propagating wave of the isolator. An inadequate choice of the resistive body leads to the imperfect absorption; the isolation ratio decreases. In this paper, the isolation-variable isolator is introduced by using this change of isolation. The control is realized by the change of the surface resistance on the silicon. On this isolator, the frequency response is investigated both experimentally and numerically. The numerical analysis is conducted by FDTD method. The experiment is carried out on the prototype isolator. Both experimental and numerical results have shown that the isolation ratio can be controlled for 39 dB at 12 GHz by the irradiation.

Recently optical-microwave interactions in the yttrium iron garnet (YIG) film have been extensively studied due to its importance in the new, high speed optical signal processing devices. In this work, we present the experimental results on the simultaneous operation of optical isolator and optical modulator in a microstrip line on YIG single crystal. Optical isolation of more than 20 dB has been observed experimentally together with optical modulation by magnetostatic backward volume wave (MSBVW) in the frequency range from 1.5 GHz to 4.5 GHz. Theoretical results on the combined isolator-modulator in magneto-optic media based on the tensor form of dielectric constant are also discussed.

This letter describes our DFB-LD module for use in WDM optical access networks. We realized an isolator-free DFB-LD module with a thermo-electric cooler in aim of stabilizing the emission wavelength for WDM systems. Silicon waferboard technology was employed to achieve simple assembly and small size of the module. This small size contributed to low TEC power. Our fabricated module demonstrated low-noise and stable emission wavelength characteristics under 156 Mbit/s pseudo random modulation.

By optimizing the structure of erbium-doped fibers, high efficiency such as a gain coefficient of 6.3dB/mW, or a slope efficiency of 92.6% have been realized with very flat wavelength dependence. Though the optimized structure has high NA, the splice loss with standard fibers can be lowered by the additional arc technique. The carbon coated fiber with a fatigue parameter over 150 guarantees the reliability, even when wounded on a small coil. In-line isolators and WDM couplers have been also developed. An amplifier module has been assembled, resulting in an output power more than +16dBm owing to the high performance of each component.