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Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation leading to the change of signal frequency and wavenumber. The interaction of light with such fronts allows frequency conversion, light stopping, optical delays as well as bandwidth and pulse duration manipulation. We will present theoretical and experimental examples of signal transmission, reflection and trapping by the front and highlight special situations such as light stopping, time reversal or optical push broom effect. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrodinger equation which follows from the slowly varying envelope approximation of the wave equation. In particular, for highly dispersive waveguides a temporal evolution of the spatial wave envelopes are considered in contrast to conventional spatial evolution of temporal envelopes. Further, we will present an overview of experimental results and estimate the maximal achievable effects for each of the application in different waveguide systems.

Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation. The interaction of light with that front allows frequency conversion, light stopping, optical delays, and bandwidth and pulse duration manipulation. Here, we present examples of signal transmission, reflection, trapping and stopping. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrodinger equation which follows from the slowly varying envelope approximation of the wave equation.

We have studied a Si photonics non-mechanical beam steering device for LiDARs. We exploit a doubly periodic Si photonic crystal waveguide (PCW) with a collimator lens, which emits a single-peaked optical beam. Thanks to the slow light effect in the PCW, wide range beam steering can be obtained in the longitudinal direction with maintaining a small beam divergence by a small change of the wavelength and/or index of the PCW. However, due to the symmetric crosssection of the PCW, the emission occurs in both upward and downward directions, which causes a 3-dB loss in the transmission of the optical beam. The downward beam is partly reflected by the substrate, and the reflected beam interferes with the upward beam and modifies the far field pattern, which further increases the loss at particular beam angles. In LiDARs, this loss is repeated at the reception of returned light, resulting in a severe loss penalty. In this study, we investigated the unidirectional upward emission in some PCW structures with vertical asymmetries. We found theoretically that a shallow etched grating on top of the Si layer, which overlaps with the PCW holes significantly increases the upward emission. We fabricated such a device using Si photonics CMOS process and observed 2-8 times stronger upward emission as compared with that of the symmetric PCW. Furthermore, we integrated 32 PCWs in parallel configuration and selected one working PCW so that its relative position against a collimator lens is switched and the beam is steered in the lateral direction. We observed over 400×32 resolution points.

The optical beam steering device is essential for LiDARs and non-mechanical ones have been developed extensively. We have studied the one based on a Si photonic crystal waveguide (PCW) that guides slow light. In LiDARs, the beam hits a distant object. Then, reflected light is scattered hemispherically and a part of it is returned and received by the PCW. In this process, a long PCW aperture is expected to increase the reception intensity. However, since the PCW has a propagation loss of the order of 10 dB/cm, the reception intensity is not increased by simply lengthening the PCW. In this study, in order to suppress the total loss of the PCW, we proposed and fabricated a serial array of PCWs, in which light is received by multiple and short PCWs and then summed by using Si wire waveguide and coupler. We first estimate the transmission and reception characteristics of the PCW array. The effective aperture radiating light is lengthened by dividing the PCW, so the beam divergence becomes small and the reception intensity is improved. Also, we measured the transmission characteristics of the PCW array. We obtained a 0.046° beam divergence by controlling the phase between the PCWs. In the beam steering by the wavelength scanning or heating, we confirmed that the phase matching angular step appears stepwise. If we use the angular step as a resolution point, we can obtain the beam steering without the phase control.

We demonstrate a non-mechanical on-chip optical beam steering device using the photonic crystal waveguide with a double periodic structure that repeats the increase and decrease of hole diameter. Guided slow light in this waveguide is radiated to be a light beam. Slow light shows strong dispersion, which allows a deflection angle of approximately 10 times that of a normal diffraction grating. We fabricated the device using complementary metal oxide semiconductor process and observed a beam deflection angle of 24° in the longitudinal direction with maintaining the divergence angle of 0.3° when the wavelength was changed by 27 nm. Four such waveguides were integrated, and one of them was selected by a Mach-Zehnder optical switch. Then, the lateral beam steering was obtained when a cylindrical lens was placed above these waveguides. By combining the longitudinal and lateral beam steering, the collimated beam was scanned two-dimensionally with 80 × 4 resolution points.

We have developed GaInAsP semiconductor photonic crystal nanolaser biosensor, which detects the adsorption of proteins and DNAs from ultralow concentrations via the wavelength shift. In general, bio-chemical sensors based on photonic cavities are considered to detect the environmental refractive index change. In this study, however, we observed various evidence that the wavelength shift of the nanolaser sensor reflects not only the environmental index but also the surface charge of biomolecules and/or environmental ions. Different from the pH-sensitivity in the laser emission intensity we reported previously, the wavelength shift is extremely sensitive to the surface charge and ions so that we can detect the biomolecules from fM to aM. To investigate the mechanism, we exposed the device to plasma or DNA solution, and measured the zeta potential and flatband potential as well as the wavelength shift. From the consistent behaviors between them, we constructed a physical model that the surface charge modifies the Schottky barrier near the semiconductor surface, trap the excited carriers in the barrier, and produce the carrier plasma shift in the wavelength. Since the change of the flatband potential is already observed for fM DNA, we suppose a phenomenon such that a small number of charged molecules act as a trigger for changing the charged functional group on the device surface. These results also suggest the possibility that some other photonic sensors also involves similar electrochemical effects.

The double-periodic Si photonic crystal waveguide radiates guided slow light into free space as an optical beam. It also functions as a beam steering device, in which the steering angle is changed widely by the slight wavelength variant thanks to the large dispersion of slow light. A similar function is obtainable when the wavelength is fixed and the refractive index of the waveguide is changed. In this study, we integrated two kinds of heater structures in the waveguide and demonstrated the beam steering by the thermo-optic effect. For a p-i-p doped heater structure, we implanted a p-type dopant except around the waveguide core, and observed a beam steering angle Δθ = 26°, which is close to a theoretical value, with a relatively low heating power P = 1.6 W and high-speed response of 100 kHz order. However, the beam divergence increased up to δθ = 5°, which seemed to reflect the temperature nonuniformity in the Si slab. On the other hand, for the TiN heaters placed away from the waveguide core, we obtained a comparable steering angle with a narrower beam divergence of δθ < 0.3°. However, the required heating power was as large as P = 4.8 W, and the response speed was slow, reflecting its low heating efficiency and large heat capacity. We expect these problems to be solved by homogenizing the current and temperature distributions for the former and by optimizing the positioning of the heaters for the latter.

Time of flight LiDARs are used for auto-driving of vehicles, while FMCW LiDARs potentially achieve a higher sensitivity. In this study, we fabricated and tested each component of a FMCW LiDAR based on Si photonics and experimentally simulated the ranging action. Here, we drove a Si photonic crystal slow light modulator with linearly frequency-chirped signal in the frequency band of 500–1000 MHz and a repetition frequency of 100 kHz, to generate FM-signal light from a narrow-linewidth laser source. Next, we branched the signal light into two paths. One was inserted into a fiber delay line of 20–320 m and its output was irradiated to a photonic crystal slow beam steering device acting as an optical antenna via the free-space transmission. When the irradiation angle was optimized so that the antenna gain took maximum for a set laser wavelength, light was efficiently coupled into the antenna. We mixed the light output from the antenna with reference light of the other path with no delay, and detected it by balanced photodiodes. We observed a beat signal whose frequency well agreed with the theoretical value predicted from the length of the delay line. Thus, we succeeded in the experimental simulation of the FMCW LiDAR. We also observed a spectral sequence around the beat spectrum, in which the inter-frequency spacing equals the repetition frequency and corresponds to a range resolution of 30 cm which will be improved by expanding the modulation bandwidth.

We have developed GaInAsP semiconductor photonic crystal nanolaser biosensor and demonstrated the detection of ultralow-concentration (fM to aM) proteins and deoxyribonucleic acids (DNAs) adsorbed on the device surface. In general, this type of photonic sensors exploiting optical resonance has been considered to detect the refractive index of biomolecules via the wavelength shift. However, this principle cannot explain the detection of such ultralowconcentration. Therefore, we investigated another candidate principle, i.e., ion sensitivity. We consider such a process that 1) the electric charge of biomolecules changes the nanolaser’s surface charge, 2) the Schottky barrier near the semiconductor surface is increased or decreased, 3) the distribution of photopumped carriers is modified by the barrier, 4) the refractive index of the semiconductor is changed by the carrier effects, and 5) the laser wavelength shifts. To confirm this process, we electrochemically measured the zeta and flatband potentials when charged electrolyte polymers were adsorbed in water. We clearly observed that these potentials temporally behaved consistently with that of the laser wavelength, which suggests that polymers significantly acted on the Schottky barrier. The same behaviors were also observed for the adsorption of 1 fM DNA. We consider that a limited number of charged DNA changed the surface functional group of the entire device surface. Such charge effects will be the key that achieves the ultrahigh sensitivity in the nanolaser biosensor.

Slow light in photonic crystal waveguides allows the phase shifters in Si MZ modulators to enhance the modulator efficiency. In this study, the group index and bandwidth product is maximized, the mode penetration into photonic crystal claddings and electrical series resistance are balanced, and the p-n junction profile is optimized. The device is fabricated on 200 mm wafer using KrF exposure, and practical performance (bitrates up to 32 Gbps, 3 dB extinction ratio, 1.75 V PPG voltage

We report what we call co- and counter propagating slow-light systems based on the high nonlinearity in Si lattice-shifted photonic crystal waveguides (LSPCWs). The intense slow-light pulse, as a control pulse, efficiently generates two-photon absorption and carrier plasma effects, which tunes the dispersion characteristics of the LSPCWs and spectrum of copropagating or counter-propagating slow-light pulse, as a signal pulse. Using the control pulse, we succeeded in experimentally demonstrating adiabatic wavelength conversion and its enhancement, delay tuning of up to 10 ps with a response time

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.

Si photonics enables the integration of photonics with electronics, making it to be an attractive platform for compact and highly functional devices. By incorporating photonics crystal waveguides (PCWs) and other slow-light nanostructures, optical devices can be made compact as well as having additional functionality. Furthermore, fabricating these devices using existing CMOS process is crucial for their low-cost mass production. In this paper, we report our recent results on CMOS-fabricated, integrated PCW and other slow-light devices, including tunable delays, high-nonlinearity devices, optical modulators and DQPSK receivers.

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.

We demonstrate a fast optical correlator using tunable delay of slow light in chirped photonic crystal coupled waveguide. Laser heating was performed for the tuning with a response speed up to several kHz. We clearly observed the crosscorrelation trace of 1.8 ps pulses. The tuning range was limited up to 8.7 ps, but will be extended to several 10 ps by long length devices. As the response is >100 times faster than conventional mechanical methods, the device is suitable for fast data mapping in optical correlation systems such as OCT.

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.

Light showing extremely slow propagation (known as "slow light") can produce various effects such as compression of optical signals, buffering, convolution integral calculation, beam forming, enhancement of optical absorption, gain, non-linearity, and so on. To generate such light, very large material and structural dispersions are used. Photonic crystal waveguides are good candidates for many device applications since they can easily generate slow light at room temperature. This paper discusses the potential of slow light devices while explaining some critical issues, such as the delay-band product and the dispersion compensation.

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.

The microdisk laser is a microcavity laser, which strongly confines the whispering gallery mode and realizes the ultralow threshold lasing and large scale integration. This paper presents two recent topics related with this laser. The first topic is the microdisk with InAs quantum-dot active layer. It is not only promising for ultimate low threshold operation but also has the potential of a high-speed single photon emitter because of the atom-like electron transition in quantum-dots and the large Purcell effect in the microcavity. In this study, we obtained the room temperature operation in this device, for the first time, by photopumping with a low effective threshold of less than 1 milliwatt. The second topic is the photonic molecule consisting of evanescent-coupled multiple microdisks based on GaInAsP materials. As well as the unique behavior of coupled modes in this structure, we also observed the bistable lasing by the nonuniform photopumping, which was considered to be arising from the saturable absorption. Due to its low threshold of 70 microwatts, this device is expected to be an optical memory and flip-flop device by photonic integration.

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.