Search

The compact, high-speed, low-power consumption Mach–Zehnder interferometer (MZI)-type optical switch using thermo-optical effect is a key device in future optical integrated circuits. In this study, we achieved ultra-high-speed switching operation of 0.4 μs and low electrical power operation of 23 mW with a small device footprint by loading an asymmetric doped MZI structure and an integrated heat sink. This optical switch can be fabricated in the standard manufacturing process of silicon photonic devices, has high practicality and will be a useful tool in various optical integrated circuits.

Age, growth, and gonadal condition of the Giant mottled eel, Anguilla marmorata, were estimated from 303 specimens collected at Okinawa-jima Island, Japan. Otolith opaque zones that formed every year correlated with high water temperature and were thought to be annual rings. The growth of this species differed between males and females, and females were longer lived and larger than males. The mean gonadosomatic index (GSI) and the appearance of silver eels showed no clear seasonality. Comparing life history characteristics of this species between natural (northern specimens) and urban rivers (southern specimens), the growth of southern specimens was faster than that of the northern specimens, leading to the development of gonads and their downstream migration at younger ages. Therefore, we conclude that the life history characteristics of A. marmorata strongly influence by the river environments.

To realize fast switching of a few μs and low-power consumption, we apply a differential control method to a thermo-optic Mach–Zehnder interferometer optical switch loaded with a direct-current injection-type phase shifter using multimode interference. We achieve ultrafast switching of several tens of ns, which is considerably higher than the conventional switching speed. With differential control, we demonstrate extremely fast optical switching with τ rise = 36 ns and τ fall = 24 ns. This method can be widely applied to similar devices and can contribute significantly to the speedup of other thermo-optic switches.

In this study, by loading a Si optical modulator with an integrated polarizer using a curved waveguide, we developed a Si optical modulator with a high extinction ratio of over 50 dB. It can be applied to a wide range of applications from digital coherent optical communication to sensing.

Optical phased arrays (OPAs) have received considerable attention as solid-state beam scanners. However, conventional OPAs that actively control the phase difference between arrays are characterized by excessive power consumption for high-precision beam emission. In this study, we fabricated an OPA comprising Bragg grating and arrayed waveguide grating (AWG). Multi-mode waveguide is used in AWG to reduce the effect of manufacturing error. This device realizes wide and high-resolution two-dimensional beam steering only by sweeping wavelength. FWHM of the emitted beam is 0.534° × 2.27°, and the steering range is 43.9° × 13.5° with 1/64 of the power consumption of conventional OPA.

High-power electric propulsion systems are promising for future large-scale space missions. To develop a high-power Hall thruster cluster system, researchers at the Gifu University have been investigating the effects of plume interference using 500 W class side-by-side (SBS) systems having two magnetic-layer heads. In this study, to investigate the dependencies of discharge characteristics and thrust performance on the axial position of a cathode, we measured the discharge currents and the thrusts for various axial positions. The optimum cathode position for the thrust performance was examined using the results. As the cathode shifted downstream, thrust decreased more than 10% for each operation. The results also revealed that at a high voltage in the SBS operations, the thrust performance increases for shifting the cathode close to the head end.

We propose a carrier-depletion type Si optical modulator for transverse electric (TE) polarization loaded with an integrated polarizer. The integrated TE-pass polarizer with a bent waveguide has a compact and simple structure and demonstrate a polarization extinction ratio of 41.3 dB and insertion loss of 0.67 dB. This Si optical modulator loaded with the integrated polarizer achieved a maximum extinction ratio of 54.5 dB. It is expected to have a wide range of applications in digital coherent optical communication and optical sensing fields.

We demonstrated a Si-photonics-based heterogeneous tunable laser in the 1.55- µm- band with quantum dot reflective semiconductor optical amplifier. Relatively low threshold current could be achieved owing to high gain characteristic.

We propose a tunable dual-wavelength heterogeneous quantum dot laser diode. The tunable dual-wavelength laser consists of a quantum dot semiconductor optical amplifier as the optical gain medium and an external cavity fabricated from silicon photonics technology as the wavelength tunable filter. We successfully demonstrated dual-wavelength lasing oscillation by tuning the difference frequency from approximately 34 to 400 GHz.

We propose a thermo-optic phase shifter which uses multimode interference. Electrodes are attached to the section where the multimode interference has minimum optical power in the sidewalls. We use the Silicon large thermo-optic constant to create an integrated optical device to control the state of light in several microseconds, for both heating and cooling times.

Thermo-optic coefficients of organic-inorganic hybrid polymers with rutile-TiO 2 nanoparticles were carefully estimated using SOI ring resonators. Athermal operation of the SOI ring resonators with TiO 2 hybrid-polymer claddings was achieved. The hybrid-polymer cladding can be applied to diverse silicon waveguide structures to control the temperature dependence of silicon photonic devices.

We investigate a structure to reduce the wavelength-dependence of a ring resonator's transmission characteristics by replacing the conventional directional coupler of the racetrack resonator with a curved directional coupler. We show its potential as a filter for broadband wavelength tunable single mode lasers

We demonstrated wavelength tunable laser diodes with Si-wire waveguide ring resonators as an external optical cavity. The footprint of the optical cavity including the semiconductor optical amplifier is as small as 0.8 mm × 0.6 mm which is less 1/10 of those made of silicon oxinitride material. Wavelength tuning range of approximately 55 nm was demonstrated, which covers entire L-band of the optical communication wavelength system. Furthermore, a spectral linewidth narrower than 100 kHz was obtained by optimizing the design of the external optical cavity. The optical nonlinearity of silicon is described and the influence on laser oscillation is also discussed.

We propose a tunable two-wavelength heterogeneous quantum dot laser diode. The tunable two-wavelength laser consists of a quantum dot semiconductor optical amplifier and an external cavity fabricated from silicon photonics technology as the two-wavelength tunable filter. We successfully demonstrated two-wavelength lasing oscillation by tuning the difference frequency from approximately 34 GHz to 400 GHz.

In this paper, we experimentally characterize the sensitivity of different types of multimode Bragg gratings in Silicon-On-Insulator and demonstrate a high sensitivity of 120 nm per refractive index unit using Bragg gratings for TM polarized light.

We present a Si-photonics-based quantum dot heterogeneous tunable lasers in the 1-µm band. Optical devices using Si-photonics-based PIC in the 1-µm band probably have not been reported yet.

Si-photonic hybrid ring external cavity wavelength tunable lasers by passive alignment techniques with more than 100-mW fiber-coupled power and linewidth narrower than 15 kHz along the whole C-band are demonstrated. These attractive performances are achieved due to very low loss Si-wire waveguides, of which loss is lower than 0.5 dB/cm. Obtained results show excellent features of Si-photonics toward commercial products.

We proposed and demonstrated a compact and low propagation loss thermo-optical phase shifter using a multi-mode interference. The calculated insertion loss of designed MMI phase shifter was approximately 0.05 dB. The fabricated phase shifter shows high speed and low power consumption. The wavelength tunable laser diode with two ring resonators loaded the MMI phase shifters was fabricated. The wavelength tuning operation with low power consumption was successfully demonstrated.

Presently, silicon photonics is receiving considerable attention because it provides a promising platform for fabrication of highly integrated photonic devices. In addition, silicon photonic devices can be fabricated using the mature fabrication technologies of electric integrated circuits. We focused on an integrated light source and developed wavelength tunable lasers using silicon photonic technologies. The narrow spectral linewidth heterogeneous laser diode with high optical output power was realized for optical digital coherent communication systems[1]. The recent studies for expanding the availability of heterogeneous lasers will be presented.

Quantum dot (QD) is one of the attractive materials. In this paper, we focus on advanced photonic devices using QD structure and its applications for the next generation access networks.

We proposed a tunable dual-mode heterogeneous quantum dot laser diode with a Si-photonics-based photonic integrated circuit, and successfully demonstrated dual-mode lasing oscillation by tuning the differential frequency from approximately 20 GHz to 200 GHz.

We fabricated wavelength-tunable laser diodes using a Si photonic wavelength filter that consists of ring resonators and an asymmetric Mach-Zehnder interferometer. The footprint of the optical cavity including the semiconductor optical amplifier is small, 2.6 mm × 0.5 mm, which is about 1/9 of those for tunable laser diodes made of silicon oxynitride. The wavelength could be tuned over approximately 62 nm, which covers the entire L-band of the optical communication wavelength range. The maximum output power reaches 42.2 mW. Furthermore, a spectral line width narrower than 100 kHz was obtained. Such tunable laser diodes with narrow spectral line widths are suitable as light sources integrated into other digital coherent devices.

In this paper we experimentally demonstrate the possibility of detecting an object using a rectangular resonator with a surface area of 200 μm2. The optical biosensor is fabricated on the standard silicon-on-insulator platform, and the object is sensed with the evanescent field that extends from the top of the device. It is possible to detect the presence of the object by measuring the shift of the resonant wavelengths in the transmission spectrum. We compare the performance of the device when it is operated in TE and TM polarization, obtaining superior performance with TM polarization, whereby it achieves a shift of 1.5 nm when a large element is placed on its surface.

In this work, 1 GHz video data was collected by a CMOS camera and successfully transmitted by the electro-optic (EO) modulator driven by an external modulation module integrated onto the same chip. For this application, the EO modulator component included a polymer waveguide modulator, which performed a 20 GHz bandwidth, clear eye diagram opening with a Q factor of 10.3 at 32 Gbit/s and a drive voltage of 1.5 Vpp. By utilizing a thermally stable EO polymer, the wide-band polymer modular can yield a photonic integrated camera sensor system which is a reliable processing platform for real-time data processing.

In this paper we present a compact direct current injection thermo-optic switch based on a Mach-Zehnder Interferometer configuration that is suitable for autonomous vehicle applications as it has a low heating resistance value of 97 Ω, a rapid 2.16 μs switching time constant, and a Pπ of 28 mW. The device relies on multimode interference to achieve low optical insertion losses of less than 1.1 dB per device, while allowing direct current injection to heat the waveguide and achieve fast operation speeds. Furthermore, the total resistive value can be tailored as the heating elements are placed in parallel.

A compact narrow-linewidth semiconductor laser is demonstrated by hybridly integrating an optical filter constructed from Si waveguides with a single-mode semiconductor laser, whose spectral linewidth is narrowed through optical negative feedback. We design the optimum structure of a reflective ring filter for an optical negative feedback laser, and a narrow spectral linewidth of 160 kHz is realized by the hybridly integrated laser source whose effective device length is less than 1.5 mm.

We propose a narrow-spectral-linewidth silicon photonic wavelength-tunable laser with a novel external wavelength-tunable filter, which consists of two silicon ring resonators with different circumferences and a highly asymmetric Mach–Zehnder interferometer (MZI), the two optical paths of which have significantly different lengths. Calculations and experimental results indicated that the gain difference between longitudinal modes was increased by the highly asymmetric MZI. Consequently, a narrow spectral linewidth of 12 kHz and a stable single-mode oscillation were obtained.

Ultra-compact wavelength tunable laser diode with wide tunability was successfully developed with combining quantum dot optical amplifier and silicon micro-ring filters. The single mode laser oscillation was demonstrated with 25 nm wavelength tuning range.

Quantum-dot nanotechnology is attractive for use in advanced photonic devices that will augment the available optical-frequency resources and will increase the number of wavelength channels usable by wired and wireless networks in short/middle-range communication systems.

We have fabricated a three terminal device integrating a (Ga,Mn)As Esaki diode and a light emitting diode (LED) to investigate the bias-voltage dependence of the injection of spin polarized electrons. The electroluminescence polarization (PEL) from the LED was measured under Faraday configuration as a function of bias voltages applied independently to the Esaki diode and to the LED. The polarization shows strong dependence on the bias applied to the Esaki diode when the LED bias is fixed. The maximum PEL of 32.4% was observed when the valence electrons near the Fermi energy of (Ga,Mn)As are injected into the LED. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We first report 0.5(2e2/h) conductance quantization in adiabatic quantum point contacts (QPCs) fabricated at high In-content InGaAs/InAlAs single heterojunctions under no magnetic field. This quantization seems difficult to understand, since the spin one-dimensional (1D) subbands in the QPCs are generally degenerated when B=0. However, this observation is reproducible in various QPC samples with different dimensions but not likely so definite as the conductance quantization in usual QPCs. It is noted that this particular heterojunction 2DEG is found to have high electron mobility of