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One attractive application of slow light is tuning the delay of optical pulses. It is achieved by controlling the chirping of photonic crystal waveguides whose photonic band exhibits a flat band sandwiched by the opposite dispersion characteristics. We call the so-obtained tunable slow light dispersion-compensated (DC) slow light. In these years, we have fabricated the devices using CMOS-compatible process, demonstrated the delay tuning of sub-ps pulses with a tuning resolution over 100, and applied it to varying the demodulation rate of DQPSK receiver. The other attractive application of slow light is enhancing the nonlinearity. It is achieved by the particular design of photonic crystal waveguides, which exhibits a straight photonic band with a small slope, producing low-dispersion (LD) slow light. We have demonstrated strong two-photon absorption (TPA), self-phase modulation and four-wave mixing in Si-based devices at fiber communication wavelengths. In this presentation, we demonstrate two advanced devices that utilize both DC and LD slow light. One is the on-chip optical correlator and the other is the all-optical ultrafast delay tuning. In the former, the delay scanner based on DC slow light and nonlinear-enhanced TPA photodiode based on LD slow light were integrated. The auto-correlator action was confirmed for ps pulses. In the latter, the delay of the DC signal pulse was tuned through the intensity and timing of the LD control pulse with a maximum tuning range and response time of 10 ps. It potentially achieves the retiming of disordered pulses by using LD pulses as a clock.

Lattice-shifted photonic crystal waveguides (LSPCWs) are effective for generating wide-band on-chip slow light at room temperature. In this study, we integrated the LSPCW with multi-heaters using CMOS-compatible process, and demonstrated electrically-tunable slow light. Seven heaters were placed on each side of the LSPCW with air slots for thermal isolation. On-demand temperature distributions were formed by controlling each heating power independently. When the heating powers were optimized, a clear delay peak of slow light corresponding to the flat photonic band of the LSPCW was observed, which suggests that fabrication errors in the air-hole diameters were less than 5 nm and related band fluctuation was well compensated by the heating. When a linear temperature distribution was added to this condition, the delay was reduced up to 54 ps. When a quadratic distribution was added, the group delay dispersion was generated in the range from -10.2 to 17.5 ps/nm. We applied the tunable delay to the delay scanning in optical correlator. Here, output pulse were compressed to 0.6 ps through self-phase modulation and dispersion compensation in external fibers, and its delay was tuned in range of 17 ps. At a scanning frequency of 100 Hz, which is

We demonstrated ultrafast delay tuning of slow-light pulse with a response time < 10 ps. This is achieved using two types of slow light: dispersion-compensated slow light for the signal pulse; and low-dispersion slow light to enhance the nonlinear effect of the control pulse. These two slow light are generated simultaneously in lattice-shifted photonic crystal waveguides, arising from flat and straight sections of the photonic band, respectively. The control pulse blue-shifts the signal pulse spectrum, through dynamic tuning and cross-phase modulation caused by the plasma effect of two-photonabsorption carriers. This changes the delay by up to 10 ps only when the two pulses overlap within the waveguide, and enables an ultrafast tuning that is not limited by the carrier lifetime. Using this, we succeeded in the delay tuning of one target pulse within a pulse train with 12 ps intervals.

We demonstrate the first sub-100 μm silicon Mach-Zehnder modulators (MZMs) that operate at

We integrated 441 photonic crystal nanolasers and applied it to label-free live cell imaging. Since the mechanical strength of the nanolaser array was improved by bonding on a glass substrate, the imaging area was expanded from previous 25 × 25 μm 2 to 100 × 100 μm 2 . We successfully acquired cell images, which should reflect the intracellular and/or the attachment conditions. By continuously mapping the wavelengths of all nanolasers, we successfully observed the time-dependent images displaying the cell behaviors. Reagents were injected to stimulate the cells, and the observation was continued until the cell reaction was saturated. The results show the reasonable behaviors against the reagents.

Biosensors which can selectively detect a very small amount of biomarker protein in human blood are desired toward early diagnoses of severe diseases. However, no methods simultaneously satisfy the requirements such as high sensitivity, high selectivity, simple detection, and immediacy. We succeeded in detecting ultra-low-concentration streptavidin (SA) even in a highly impure sample using nanoslot photonic crystal (PC) nanolasers. This nanolaser consists of GaInAsP semiconductor slab with a periodic airhole array. Since the total device area is no larger than 20 × 20 μm 2 , highthroughput fabrication is possible even using e -beam lithography. Moreover, it is easy to operate by photopumping through free-space optics. Since the evanescent wave of the laser mode penetrates from the PC slab, the laser wavelength changes sensitively to the environmental index. In the sensing experiment, we first functionalized the devices with biotin, and then measured the wavelength in ultrapure water before and after immersing in the solutions with various concentrations of SA. As a result, we evaluated that the detection limit of SA is 16 zM. In another experiment, we put 1 μM BSA into the solution as a contaminant, and repeated the same measurement. We detected 100 zM SA even in the impure solution only when biotin is functionalized in advance, meaning a selectivity ratio (BSA / SA) of 10 13 . Thus this device achieves unprecedentedly high sensitivity and selectivity in addition to the simple fabrication and fast sensing. It is very promising as a point of care device for medical diagnoses.

High-performance and low-cost sensors are critical devices for high-throughput analyses of bio-samples in medical diagnoses and life sciences. In this paper, we demonstrate photonic crystal nanolaser sensor, which detects the adsorption of biomolecules from the lasing wavelength shift. It is a promising device, which balances a high sensitivity, high resolution, small size, easy integration, simple setup and low cost. In particular with a nanoslot structure, it achieves a super-sensitivity in protein sensing whose detection limit is three orders of magnitude lower than that of standard surface-plasmon-resonance sensors. Our investigations indicate that the nanoslot acts as a protein condenser powered by the optical gradient force, which arises from the strong localization of laser mode in the nanoslot.

We evaluated the nonlinear enhancement in slow-light photonic crystal waveguides. The devices butt-joined to Si wire waveguides were fabricated on SOI substrate using CMOS-compatible process. Integrating spot size converter to the device allows high input power and clear enhancement. The coupling loss between lensed fiber and the wire was 3 - 4 dB. We observed two-photon absorption, self-phase modulation and four-wave mixing in the low power regime of less than 1 W, which is assisted by low-dispersion slow light. Such slow light can be exploited for compact functional components such as optical limiters and wavelength converters.

This paper reports two advances in a slow light device consisting of chirped photonic crystal slab coupled waveguide on SOI substrate. One is concerning the delay-bandwidth product, indicating the buffering capacity of the device. We experimentally evaluated a record high value of 57 (a 40 ps delay and a 1.4 THz bandwidth). We also observed a few picosecond wide optical pulse transmission in the cross-correlation measurement. Regarding the pulse as a signal and considering the broadening of the pulse width due to the imperfect dispersion compensation in the device, storage of more than 12 signal bits was confirmed. The other is a widerange tuning of the pulse delay. We propose a technique for externally controlling the chirping to permit variable delay. We demonstrate tuning of the pulse delay up to 23 ps, maintaining the average pulse width to be 3.3 ps. It corresponds to the tunable time shift of 8 bits and a ~7 mm extension of the free space length.

We demonstrate the light transmission characteristics in a photonic crystal (PC) slab with liquid crystal (LC) as an anisotropic medium. In PC slabs, the guided resonance occurs for normal incidence of light. In this study, we first fabricated a SiN PC slab without LC and observed this resonance. Also, we added an ellipticity to holes of the PC slab and observed a polarization filtering effect arising from the structural birefringence. Then, we filled the holes with LC. By making a phase transition in the LC, the resonant wavelength was tuned by maximally 33 nm. This will be applicable to surface-normal-type devices which control the transmission and polarization characteristics of light.

Using MOCVD butt-joint regrowth technique, we fabricated a μ-laser monolithically integrated with a passive waveguide in GaInAsP photonic crystal slab, for the first time. We observed the lasing operation and light extraction from the waveguide with an external quantum efficiency of 8%/facet. It will be the key technology for advanced photonic integration based on photonic crystal slab.

We designed and fabricated an arrayed waveguide grating demultiplexer of 70 × 75 μm 2 size, which consists of Si slab and wire waveguides on silicon-on-insulator substrate. By optimizing the connection between components and the layout of arrayed waveguides, the internal light scattering and the phase error were suppressed. As a result, the clear demultiplexing characteristics were observed with a channel spacing of 8 nm and a sidelobe level of -22 dB in the wavelength range around 1.55 μm.

We demonstrated the clear light focusing in a photonic crystal superlens. We fabricated it on SOI substarate with optimum interfaces for suppressing reflection and diffraction losses. We observed near field patterns of light propagation in the superlens, which showed the light focusing in a wide frequency range inside and outside of the light cone. We also confirmed that the focal length, NA, and the spot width, which ageed well with theory. The smallest spot width was 1.8 μm at ω= 1.39 μm. In addition, we demonstrated the real image formation using multiple light sources.

We analyzed lateral mode characteristics in 850-nm GaAs-based VCSELs with holey structures by FDTD method. Full three-dimensional analysis, which requires huge computer resources, was carried out using cluster computer. As a result, we estimated the good mode selectivity in circular and triangular holey structures, which cannot be obtained in a simple oxide aperture structure. It is explained by the large ra-diation loss from the inter-hole spacing and scattering loss at the bottom of holes particularly for higher order modes. In addition, the experimental result reported by Furukawa, et al., which showed the record high power single mode operation by the floral fundamental mode in the triangular holey structure, was verified. For any changes of standard structural parameters, only the Gaussian-like fundamental mode was confirmed. The floral mode was observed only when we assumed a nonuniform refractive index around the holey structure. Such nonuniformity can be considered in actual devices because of the non-uniform distribution of carriers and temperature at high current injection level.

In photonic crystal (PC) microlasers with point defect cavities, effective carriers are reduced by the leakage to outside of the defect, surface recombination, spatial carrier hole burning, and Auger recombination. To estimate these effects, we calculated carrier and photon behavior by solving two-dimensional rate equations in space and time domains. The result clearly shows these effects and their dependence on cavity structure, pump area, and so on. Compared with that for the microdisk laser, higher threshold values are estimated for PC microlasers. However, a comparably low threshold density and a high efficiency are expected for the quasiperiodic PC microlaser, because the hole burning by the whispering gallery mode of this cavity suppresses the carrier leakage.

By introducing triangular holes into oxide confined 850nm monolithic vertical-cavity surface-emitting lasers (VCSELs), single-transverse-mode operation has been obtained for large oxide apertures of 14-15 microns. The two-dimensional triangular holes etched on the device surface were aligned circumferentially along the aperture perimeter, with their tips surrounding the device center. When the holes had a relatively large lateral penetration into the oxide aperture, the holey VCSEL lased with a single spot near field pattern with a high side-mode suppression ratio (SMSR) of 45-50dB, and an output power of 2mW. In this case, it is assumed that the triangular holes are acting as a highly mode selective loss mechanism. On the other hand, when the penetration of the holes was relatively small, an SMSR of 40dB was obtained from a large area "floral" near field pattern, with a record high single-mode output power of 7mW. The lasing spectrum and far field intensity profile of this "floral" type emission indicates that it is a somewhat deformed fundamental mode that is extending over the whole device, and oscillating in-phase. The ability of triangular holes to suppress high order modes in large area oxide confined VCSELs should be effective for systems with wavelengths other than 850nm as well.

Due to their ultrahigh index contrast structure, Si photonic wire waveguides realize various micro-components, which enable us to design and fabricate compact photonic devices and circuits. We have already demonstrated them theoretically and experimentally in some journal papers and two SPIE proceedings. In this work, I pick up other two topics; one is the polarization crosstalk, and the other is a Mach-Zehnder interferometer. The former will be a significant problem that degrades the performance of functional circuits based on polarization-dependent devices. It was experimentally meas-ured, and its reduction method was theoretically investigated by the three-dimensional finite-difference time domain method. The latter device is a basic element of functional circuits. By employing micro-bends and micro-couplers, a high extinc-tion ratio of over 15 dB and a large diffraction order of 300 were achieved within a small foot space of 20 times 20 square microns.

The superprism is known as a highly dispersive phenomenon in photonic crystals, which is expected to realize a narrow band filter, beam deflector, dispersion compensator, etc. Thus far, its large angular dispersion has been theoretically discussed worldwide through the dispersion surface analysis. In general, however, incidence of a finite width beam to a photonic crystal excites a wide angular spectrum of Bloch waves, which leads to a significant beam divergence. The dispersion surface analysis including such a property indicates that a large angular dispersion and a high quality beam propagation are achieved simultaneously under some limited conditions for incident angles, beam widths and wavelength range. A high resolution will be possible, but the length of the photonic crystal required is of cm to 10 cm order and beam width of 100 micron order. To solve these problems, we proposed a k-vector super-prism, which utilizes a large angular dispersion of k-vector and an angled output end of the photonic crystal. In this prism, the length of the PC is significantly shortened to 100 micron order with maintaining a high resolution. In addition, latitudes for the beam width and wavelength range are greatly expanded, so the butt-joint of a singlemode fiber and operation over C- to L bands will be possible. The FDTD simulation demonstrates the light propagation, which agrees with these expectations, but also showed some peculiar light diffraction, which should be cared in designing a high efficiency filter.

We designed and fabricated some components and devices by using Si photonic wire waveguides on SOI substrate. Because of the very high index contrast between the core and claddings, the waveguide allows a μ-bend. We applied this bend to form a μ-branch and μ-intersection, which exhibited a low of less than 0.3 dB in the experiment. The H-tree optical signal distribution circuit, the Mach-Zehnder interferometer, and the arrayed waveguide grating demultiplexer were demonstrated by this waveguide, for the first time. Although a more careful design and precise fabrication technologies are necessary for future high performance, this waveguide is expected to miniaturize any kind of conventional silica based devices by a factor over 10000 and realize more sophisticate functions by the dense integration of devices.

The recent development of photopumped 1.5 - 1.65 μm GaInAsP microdisk, microgear and photonic crystal lasers is re-viewed. For the former two lasers, room temperature cw lasing characteristics are presented. Their small cavity volume and high Q factor simply reduced the threshold pump power to a record low value of 10 microwatt order, and provided a large sponta-neous emission factor of over 0.1 potentially with the Purcell effect. In the microdisk, nonlasing resonant modes with differ-ent order and different phase often appear. Rate equation analysis indicated that such modes with a high Q affect the laser performance. The microgear having a rotational periodic structure is unique because it not only suppresses such modes, but also increases the Q factor by the minute control of electromagnetic fields so that the radiation field is minimized. The latter advantage will allow a further reduction in cavity size from the smallest limit of the microdisk. A couple of microdisks lased even in a form of a coupled cavity, which can be treated as a photonic molecule. The photonic crystal cavity is also unique because it is easy to construct various types of cavities by the composite of line and point defects inside the uniform photonic crystal slab. The pulsed lasing was obtained in some of them, while we found a large thermal resistance that dis-turbed the cw lasing. We also found through the rate equation analysis that carriers are effectively confined in the microdisk by the strain relaxation effect in compressively-strained quantum wells. However, the result also suggested that the carrier confinement is rather degraded by this effect, so a structural optimization is necessary in the photonic crystal laser.

Light propagation characteristics of line defect optical waveguides in a photonic crystal slab are explained by the photonic band calculation and experimentally demonstrated at 1.5 micron wavelengths by using the SOI substrate. A high efficiency sharp bend, which is a key for high density photonic ICs, is numerically demonstrated by the FDTD method. The essential low propagation loss against the imperfection of the structure is discussed from the perturbation theory. On the other hand, light transmission characteristics of finite size uniform photonic crystals without defects are theoretically investigated for various applications. The superprism filter is analyzed from dispersion surfaces. The wavelength resolution parameter is defined, which includes the angular dispersion and the beam divergence of light, and the performance of the filter is esti-mated for the optimum design. As another application of the superprism effect, a light deflection device having angled out-put interfaces against the input interface is proposed and numerically demonstrated. The nonlinear response in a photonic crystal made of a Kerr medium is also calculated by the FDTD method. The enhancement of the nonlinearity observed at certain band edges are explained by the photonic band property. To improve the transmission efficiency of these devices, some modified input and output interfaces are proposed and their effects are numerically demonstrated.

We fabricated optical waveguides with a relative refractive index difference of maximally 45 percent on a silicon-on-insulator (SOI) substrate. We designed the Si channel using the finite difference time domain simulation and fabricated using electron beam lithography and inductively coupled plasma etching. The single or quasi-single mode propagation was observed for channel width of 0.3 - 1.0 microns and thickness of 0.32 microns at a wavelength of 1.55 microns. Propagation loss evaluated using the Fabry-Perot resonance method was of 10 inverse cm order for these channel widths. The large effective index of the guided mode over 4.5 was also observed, which well agreed with the simulation. When channel width was 0.5 microns, the bend loss of 0 - 1 dB was roughly evaluated even though the bend radius was 0.5 - 9.5 microns. The similar low loss was also confirmed for half circular disk waveguides butt-joined to use as 90-degree-bends. These results suggest the potential of an ultra-high density optical wiring in lightwave circuits.