We review our recent work on Yb-doped and hybrid-structured solid photonic bandgap fibers (Yb-HS-SPBGFs) for linearly-polarized fiber lasers oscillating in the small gain wavelength range from 1160 nm to 1200 nm. The stack-and-draw or pit-in-jacket method is employed to fabricate two Yb-HS-SPBGFs. Both of the fiber shows optical filtering property for eliminating ASE in the large gain wavelength range from 1030 nm to 1130 nm and enough high birefringence for maintaining linear polarization, thanks to the photonic bandgap effect and the induced birefringence of the hybrid structure. The fiber attenuation of the Yb-HS-SPBGF fabricated by the pit-in-jacket method is much lower than that of the Yb-HS-SPBGF fabricated by stack-and-draw method. Linearly-polarized single stage fiber lasers using Yb-HS-SPBGFs are also demonstrated. Laser oscillation at 1180 nm is confirmed without parasitic lasing in the fiber lasers. High output power and high slope efficiency in linearly-polarized single-cavity fiber laser using the low-loss Yb-HS-SPGF fabricated by the pit-in-jacket method are achieved. Narrow linewidth, high polarization extinction ratio and high beam quality are also confirmed, which are required for high-efficient frequency-doubling. A compact and high-power yellow-orange frequency-doubling laser would be realized by using a linearly-polarized single-cavity fiber laser employing a low-loss Yb-HS-SPBGF.

This paper presents a simplifying method of the two previous fault attacks to pairing and the Miller algorithms based on a practical fault assumption. Our experimental result shows that the assumption is feasible and easy to implement.

The purpose of this work is to synthesize a three-dimension C60 polymer using photo-polymerization method. The used pristine materials were C60 precipitates prepared by a liquid-liquid interfacial precipitation (LLIP) method. The prepared LLIP material was set in the vacuum and was compressed in the anvil with the pressure of 600 MPa or 7 GPa. The 4th harmonics FEL with the wavelength of 500 nm was irradiated with macro-pulses (the pulse width of 20 µs) containing very short micro-pulses (the pulse width of 200 fs). The Raman Ag(2) peak of C60 molecules in the vicinity of 1469 cm-1 becomes broad and shifts to the lower energy region as proceeding of polymerization. Under high pressure and/or FEL irradiation the LLIP crystal revealed the large red-shift and the increment of the half width of the Raman Ag(2) peak. Furthermore the LLIP crystal mixture with iodine revealed the more distinctive red-shift, ca.13cm-1 because of highly packing of C60 molecules. The C60 molecular accession by LLIP process and/or the photo-assisted hole-doping from iodine were promising conditions to promote the photo-polymerization effectively.

To meet the increasing demand to expand wavelength division multiplexing (WDM) transmission capacity, ultrahigh spectral density coherent optical transmission employing multi-level modulation formats has attracted a lot of attention. In particular, ultrahigh multi-level quadrature amplitude modulation (QAM) has an enormous advantage as regards expanding the spectral efficiency to 10 bit/s/Hz and even approaching the Shannon limit. We describe fundamental technologies for ultrahigh spectral density coherent QAM transmission and present experimental results on polarization-multiplexed 256 QAM coherent optical transmission using heterodyne and homodyne detection with a frequency-stabilized laser and an optical phase-locked loop technique. In this experiment, Raman amplifiers are newly adopted to decrease the signal power, which can reduce the fiber nonlinearity. As a result, the power penalty was reduced from 5.3 to 2.0 dB. A 64 Gbit/s data signal is successfully transmitted over 160 km with an optical bandwidth of 5.4 GHz.

We obtained flat optical frequency combs by using the FM laser operation of a fiber ring laser and external intensity modulation. Extremely wide FM spectra can be easily obtained by the moderate internal phase modulation of an FM laser. We used an external intensity modulator to extract a linearly chirped part from the FM light in order to obtain flat spectra. In our experiments, we obtained a flat optical frequency comb with a spectral bandwidth of about 0.5 THz and a power deviation of less than 1.5 dB.

We propose a new parameter-extraction approach based on a mixed-mode genetic algorithm (GA), including the efficient search-space separation and local-minima-convergence prevention process. The technique, substantially extended from our previous work, allows the designed figures-of-merit, such as internal quantum efficiency (ηi) as well as transparency current density (Jtr) of lasers and minimum noise figure (NFmin) as well as associated available gain (GA,assoc) of low-noise amplifiers (LNAs), extracted by an analytical equation-based methodology combined with an evolutionary numerical tool. Extraction results, which agree well with actually measured data, for both state-of-the-art InGaAs quantum-well lasers and advanced SiGe LNAs are presented for the first time to demonstrate this multi-parameter analysis and high-accuracy optimization.

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.

The effect of wavefront compensation in beam transmission is estimated for ground to satellite laser communications. A numerical analysis is performed using the combination of the isoplanatic angle, the atmospheric coherence length and the point-ahead angle to find the aperture size of the beam transmission with which the wavefront compensation effect appears most strongly.

We propose a novel 50 Mb/s optical transmitter fabricated in a 0.6 µm BiCMOS technology for automotive applications. The proposed VCSEL driver chip was designed to operate with a single supply voltage ranging from 3.0 V to 5.25 V. A fully integrated feedforward current control circuit is presented to stabilize the optical output power without any external components. The experimental results show that the optical output power can be stable within a 1.1 dB range and the extinction ratio greater than 14 dB over the automotive environmental temperature range of -40 to 105.

A novel method for tailoring the beam profile of laser diodes that employs Lloyd's mirror interference is investigated. The beam profile in the vertical direction is controlled by inserting a GaAs mirror below the active layer. The experimentally obtained trends are successfully modeled by numerical calculations using Huygens' integral.

We have developed InGaAs-based VCSELs operating around 1.1 µm for high-speed optical interconnections. By applying GaAsP barrier layers, temperature characteristics were considerably improved compared to GaAs barrier layers. As a result, 25 Gbps 100 error-free operation was achieved. These devices also exhibited high reliability. No degradation was observed over 3,000 hours under operation temperature of 150 and current density of 19 kA/cm2. We also developed VCSELs with tunnel junctions for higher speed operation. High modulation bandwidth of 24 GHz and a relaxation oscillation frequency of 27 GHz were achieved. 40 Gbps error-free operation was also demonstrated.

Optical buffer memory for 10-Gb/s data signal is demonstrated experimentally using a polarization bistable vertical-cavity surface-emitting laser (VCSEL). The optical buffer memory is based on an optical AND gate function and the polarization bistability of the VCSEL. Fast AND gate operation responsive to 50-ps-width optical pulses is achieved experimentally by increasing the detuning frequency between an injection light into the VCSEL and a lasing light from the VCSEL. A specified bit is extracted from the 10-Gb/s data signal by the fast AND gate operation and is stored as the polarization state of the VCSEL by the polarization bistability. The corresponding numerical simulations are also performed using two-mode rate equations taking into account the detuning frequency. The simulation results confirm the fast AND gate operation by increasing the detuning frequency as well as the experimental results.

We have developed a high-speed electroabsorption modulator integrated distributed feedback (EA/DFB) lasers. Transmission performance over 10 km was investigated under 25 Gbps and 43 Gbps modulation. In addition, the feasibility of wide temperature range operation was also investigated. An uncooled EA/DFB laser can contribute to the realization of low-power-consumption, small-footprint and cost-effective transceiver module. In this study, we used the temperature-tolerant InGaAlAs materials in an EA modulator. A wide temperature ranged 12 km transmission with over 9.6 dB dynamic extinction ratio was demonstrated under 25 Gbps modulation. A 43 Gbps 10 km transmission was also demonstrated. The laser achieved a clear, opened eye diagram with a dynamic extinction ratio over 7 dB from 25 to 85. The modulated output power was more than +2.9 dBm even at 85. These devices are suitable for next-generation, high-speed network systems, such as 40 Gbps and 100 Gbps Ethernet.

We present a novel high-speed transmitter consisting of a frequency modulated DBR laser and optical filters. The refractive index modulation in the phase control region of the DBR laser allows high-speed frequency modulation. The generated frequency modulated signal is converted to an intensity modulated signal using the edge of the optical filter pass band. We present theoretical simulations of high-speed modulation characteristics and extension of transmission reach. With the proposed transmitter, we review the experimental demonstration of 180-km transmission of a 10-Gb/s signal with a tuning range of 27 nm and 60-km transmission of a 20-Gb/s signal.

We have proposed and successfully demonstrated a two step method for localizing defects on an LSI chip. The first step is the same as a conventional laser-SQUID (L-SQUID) imaging where a SQUID and a laser beam are fixed during LSI chip scanning. The second step is a new L-SQUID imaging where a laser beam is stayed at the point, located in the first step results, during SQUID scanning. In the second step, a SQUID size (Aeff) and the distance between the SQUID and the LSI chip (ΔZ) are key factors limiting spatial resolution. In order to improve the spatial resolution, we have developed a micro-SQUID and the vacuum chamber housing both the micro-SQUID and the LSI chip. The Aeff of the micro-SQUID is a thousand of that of a conventional SQUID. The minimum value of ΔZ was successfully reduced to 25 µm by setting both the micro-SQUID and an LSI chip in the same vacuum chamber. The spatial resolution in the second step was shown to be 53 µm. Demonstration of actual complicated defects localization was succeeded, and this result suggests that the two step localization method is useful for LSI failure analysis.

We fabricated high-power pure blue laser diodes (LDs) by using GaN-based material for full-color laser display. The operating output power, voltage and wall-plug efficiency of the LDs at forward current of 1.0 A were 1.17 W, 4.81 V and 24.3%, respectively. The estimated lifetime of the LDs was over 30,000 hours under continuous-wave operation.

We have proposed a tunable laser with silica-waveguide ring resonators. In this tunable laser, a semiconductor optical amplifier was passively aligned and mounted onto a silica-waveguide substrate. The ring resonators can be tuned by controlling their temperatures using the thermo optic heaters formed on them, and there are no mechanically moving parts. Thus, they are sufficiently stable and reliable for practical use. Our tunable laser exhibits a high fiber-output power of more than 15 dBm and a wide tunable range of 60 nm (L-band, 50 GHz spacing, 147 channels). Moreover, a tunable laser with a much wider tunable range of 96 nm using 100-GHz-FSR ring resonators is also reported.

This paper focuses on optical integration technology and its application in optical microsensors used in biomedical fields. The integration is based on the hybrid integration approach, achieving high performance, small size and weight, and lower cost. First, we describe the key technologies used in hybrid integration, namely passive alignment technology, low temperature bonding technology, and packaging technology for realizing advanced microsensors. Then, we describe an integrated laser Doppler flowmeter that can monitor blood flow in human skin.

The heterodyne laser interferometer acts as an ultra-precise measurement apparatus in semiconductor manufacture. However the periodical nonlinearity property caused from frequency cross-talk is an obstacle to improve the high measurement accuracy in nanometer scale. In order to minimize the nonlinearity error of the heterodyne interferometer, we propose a frequency cross-talk compensation algorithm using an artificial intelligence method. The feedforward neural network trained by back-propagation compensates the nonlinearity error and regulates to minimize the difference with the reference signal. With some experimental results, the improved accuracy is proved through comparison with the position value from a capacitive displacement sensor.

Two-dimensional resonant optical scanners actuated by vertical electrostatic combs with a unique electrical isolation structure have been developed. The isolation on the movable frame surrounding 1 mm-diameter gimbal mirror is made by trenching the top silicon layer of an SOI wafer with leaving the thick bottom layers. Thanks to the large mass of the frame, the resonant frequencies range in 65.0-89.2 Hz for the frame and in 11.9-36.8 kHz for the mirror in a 4 mm4 mm chip. The resultant frequency ratio of the fast/slow axes reaches over 500 and such a high frequency ratio is utilized to display QVGA image by raster scanning of a laser beam.