Takuya Aizawa

Polarization-independent quantum-confined Stark effect in an InGaAs/InP tensile-strained quantum well

We present a theoretical analysis and experimental studies on the control of the polarization-dependent characteristics of the refractive index change and the absorption change due to the quantum-confined Stark effect in an InGaAs/InP quantum-well structure. The polarization dependency which arises from the energy level splitting of heavy-hole and light-hole states in the quantum well can be controlled by inducing an appropriate amount of tensile strain in the quantum well. Measurements were carried out on the polarization dependency of the refractive index change and the absorption change in unstrained, 0.15, 0.3, and 0.45% tensile-strained 11.5-nm-thick InGaAs quantum-well structures through the whole spectral range, i.e., near and below the transition energy. We found that by inducing a 0.3% tensile strain in the 11.5-nm quantum well, the spectral profiles for the transverse electric and the transverse magnetic modes are brought closer to each other, with the peaks of the negative index changes corresponding to both modes occurring at the same wavelength with a slight difference in their absolute values. Moreover, in the long wavelength region, the refractive index change for both modes coincides in the wavelength as well as the absolute value. Based on these results, we have fabricated an absorption modulator and controlled the modulation characteristics with respect to the incident light polarization. >

Polarization-independent field-induced absorption-coefficient variation spectrum in an InGaAs/InP tensile-strained quantum well

The authors report the absorption-coefficient variation of a tensile-strained InGaAs/InP quantum well measured throughout the spectral range near and away from the bandgap. They discuss the spectral absorption-coefficient variation spectra of an unstrained, a 0.15%, a 0.30%, and a 0.45% tensile-strained quantum well and show that the difference between the wavelengths of absorption-coefficient variation peaks for TE and TM modes becomes zero with 0.3% tensile strain. It is shown that this wavelength difference varies linearly with the magnitude of the strain.<<ETX>>

Observation of polarization independent electric field effect in InGaAs/InP tensile strained quantum well and its proposal for optical switch

We have experimentally observed the polarization independent electric field induced absorption coefficient variation in an InGaAs/InP tensile strained quantum well (QW) structure for the first time. We have also found that the field induced absorption coefficient/refractive index variation of strained QW for the transverse electric (TE) mode does not change appreciably from that of an unstrained one. Based on these results, we propose tensile strained QW for polarization independent optical switch/modulator.

Polarization-independent switching operation in directional coupler using tensile-strained multi-quantum well

Polarization-independent switching operation in a multi-quantum well directional coupler is obtained for the first time, with a bar-state crosstalk of -12 dB. By introducing tensile strain in an InGaAs-InP multi-quantum well, polarization-independent switching voltage is as small as 3 V, with the coupling length being 1.2 mm. The cross-state crosstalk that is obtained at zero-applied voltage, is less than -8 dB with respect to TE and TM polarized lights.<<ETX>>

Effect of spectral-hole burning on multi-channel EDFA gain profile

We show that a spectral gain profile of a multichannel erbium-doped fiber amplifier (EDFA) changes associated with the change in multichannel location, which is well described by a summation of hole burning caused by each signal.

Thin Film Magneto-Impedance Sensor Integrated Into

A linear magneto-impedance (MI) sensor integrated into a FePt thin film bias magnet which has in-plane isotropic magnetic property was investigated. The maximal bias field of 13.1 Oe was obtained after magnetizing a 1.3-mum thick FePt film in longitudinal direction of the sensor element. The bias field changed with the magnetizing angle. By controlling the angle in the magnetizing direction of the bias magnet and sensing direction, it was shown to be able to adjust the effective bias field after fabrication of the sensor element.

{\rm L}1_{0}

We report on a compact InGaAsP/InP MQW directional coupler switch with spacing between the waveguides at the input and the output facets larger than 125 /spl mu/m, required for the fiber-array coupling, by employing small low-loss bends. The total device length, including both the coupling and the bending regions, with the different optical confinements in the lateral direction is 2 mm. The coupling region of the switch is 420 /spl mu/m, and the voltage-length product at switching is around 6 Vmm.<<ETX>>

FePt Thin Film Bias Magnet

This paper presents a CMOS voltage controlled oscillator (VCO) with a high-Q inductor fabricated by using a commercial wafer-level-package (WLP) technology. A new topology suitable for CMOS VCOs with high-Q WLP inductors is proposed. Measured Q of a WLP inductor is 40 in differential mode at around 1.9 GHz. A phase noise is -134.4 dBc/Hz at a 1 MHz offset for 1.9 GHz carrier frequency, and a FoM is -193 dBc/Hz. The VCO with the WLP inductor improves a phase noise of 6.4 dB as compared to VCOs with conventional on-chip inductors.

InGaAsP/InP MQW directional coupler switch with small and low-loss bends for fiber-array coupling

The barrier layer thickness dependence on crystal quality of the multi-quantum well (MQW) structure with compressively strained InGaAs wells and InGaAsP (λg=1.15 µm) barriers is investigated. The lattice mismatch Δa/a for a 15-period MQW structure with a 1%-strained 5 nm InGaAs (In0.68Ga0.32As) well layer is improved by increasing the thickness of the barrier layer, and it becomes saturated over 15 nm to around 0.2%. The X-ray diffraction peak intensity becomes saturated over 10 nm. The strongest exciton peak intensity and the sharpest peak width are observed for a 10 nm barrier. The optimum well volume ratio for a MQW, shown as W/(W+B), is around 0.3 from the results of the X-ray diffraction peak intensity and the exciton peak width and intensity (W: well thickness, B: barrier thickness).

A low phase noise LC-VCO with a high-Q inductor fabricated by wafer level package technology

This paper presents a feasibility study on VCO using RF SiP technology, which is an RF application of stacked SiP. An off-chip inductor is implemented in a separated chip, and measured Q factor is 130. A phase noise is -119 dBc/Hz at 1 MHz offset for a 5.84-GHz carrier frequency, and frequency tuning range is 5.73 GHz-5.95 GHz. Power consumption is 1.93 mW, and 180 nm CMOS process is utilized. FOM is -192dBc/Hz.