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Optical beam scanning is a widely utilized function in optical systems and a compact nonmechanical solid-state device has long been anticipated. Here, we have studied such a device consisting of photonic crystal slow-light waveguides and switch trees, fabricated by a Si photonics process, employing a bespoke prism lens for beam collimation. Further in this study, we particularly demonstrated the operation of the device only by the thermo-optic (TO) tuning of its components, at a fixed wavelength of light. A spot beam of ∼0.1° divergence, was scanned in two dimensions, in the angular range of 40° × 8.8° and average power consumption of < 0.7 W. Neglecting some disordered beams caused by the non-uniformity of the fabricated device, the estimated number of resolution points was 400 × 32 = 12,800, which required a significant effort in the device fabrication and calibration, utilizing optical-phased arrays, if the same performance was targeted.

The doubly periodic Si photonic crystal waveguide operates as a nonmechanical beam-steering device that can be applied in light detection and ranging. In this Letter, we develop and describe a prism lens that collimates a fan-shaped beam, emitted from the waveguide independent of the steering angle. Its fundamental profile is investigated using a theoretical analysis for thick lenses, and then, its detailed aspherical design is obtained. In ray tracing, this prism lens suppresses the beam divergence to less than the diffraction limit in most of the targeted beam-steering range. The prism lens is fabricated by acrylic cutting, and its expected characteristics are observed.

This paper proposes and demonstrates an optical leaky wave antenna (OWLA) excited by a beam expander consisting of a slab waveguide and parabolic photonic bandgap (PBG) reflector. Conventional OLWAs are usually excited through an adiabatic taper waveguide, but its large size is a drawback. The PBG reflector is easy to fabricate with the OLWA using Si photonics technology and its size is ten times smaller than that of the adiabatic taper waveguide. We confirmed the excitation of a shallow grating waveguide, which is a kind of OLWAs, through the beam expander in simulations and measurements.

In this chapter, the authors discuss some spontaneous emission characteristics in microcavity surface emitting lasers (SELs). Modified distribution of modes in the SEL is calculated and displayed over the optical wave vector space (k-space). The spontaneous emission factor is calculated to evaluate the amount of spontaneous emission control in the SELs and the possibility of the thresholdless operation. The spontaneous emission factor for the Bragg resonant mode in microcavity SELs is as large as 103 to 105 times that in conventional horizontal cavities. It is not so dependent on the vertical cavity quality but is almost inversely proportional to the cavity lateral size. To realize such an SEL experimentally, the reduction of the nonradiative recombination at the microcavity surface will be the important issue. In addition, investigation of the absolutely closed cavity structure will provide more remarkable effects of the microcavities.

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.

We modeled the photonic bands of S i O 2 -cladded Si lattice-shifted photonic crystal waveguides via machine learning and found a structure that generates low-dispersion slow light with a group index of approximately 20 in the full C-band at telecom wavelengths. The normalized delay-bandwidth product is as large as 0.45, which is close to the theoretical upper limit. The transition structure between this waveguide and a Si-channel waveguide was designed using an evolutional optimization, and a C-band average loss of 0.116 dB/transition was calculated. These results prove the possibility of further enhancing the versatility of slow light.

Semiconductor ion sensors that respond to the surface electric charge in a solution are used for chemical and biological sensing. Photonic sensors exploiting such a response in the photoluminescence intensity enable a simple system consisting only of a photopump source and a photodiode; however, their sensitivity is usually lower than that of electric sensors, such as ion-sensitive field-effect transistors. This study employed a GaInAsP semiconductor honeycomb photonic crystal slab as a photonic sensor structure and obtained a high ion sensitivity. The surface recombination, which is the origin of the ion sensitivity, was enhanced by increasing the surface-to-volume ratio and moderately suppressing the photopump level. Nevertheless, a sufficient signal-to-noise ratio was maintained by improving the light extraction efficiency. Moreover, a high pH sensitivity of 0.27 dB/pH, which is six times that without photonic crystals, was obtained and resulted in a pH resolution of 0.011 at pH ∼7 comparable with that of electric sensors.

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.

Slow light generated through silicon (Si) photonic crystal waveguides (PCWs) is useful for improving the performance of Si photonic devices. However, the accumulation of coupling loss between a PCW and Si optical wiring waveguides is a problem when slow-light devices are connected in a series in a photonic integrated circuit. Previously, we reported a tapered transition structure between these waveguides and observed a coupling loss of 0.46 dB per transition. This Letter employed particle swarm optimization to engineer the arrangement of photonic crystal holes to reduce loss and succeeded in demonstrating theoretical loss value of 0.12 dB on average in the wavelength range of 1540–1560 nm and an experimental one of 0.21 dB. Crucially, this structure enhances the versatility of slow light.

The light emission characteristics of GaInAsP semiconductors in aqueous solutions are modified by the surface charge, depending on the balance between radiative and nonradiative recombination. This Letter demonstrates the application of a GaInAsP photonic crystal band-edge laser in sensing a solution pH, which reflects the surface charge. The sensitivity is enhanced by a hybrid of fractal honeycomb and close-packed structures with a large surface-to-volume ratio and a high quality factor ( Q ), which allows a low threshold carrier density. We experimentally obtained a maximum pH sensitivity of 1.9 dB/pH near the threshold and a signal-to-noise ratio of 52/pH (pH resolution of 0.019) at a pump power 2.4 times the threshold where the intensity noise diminished.

We demonstrate a GaInAsP photonic crystal bandedge laser whose emission intensity shows 4× higher sensitivity and 5× higher S/N than H0 nanolaser's. It will be a versatile sensor for simply detecting chemicals and biomolecules, such as CRMP2 biomarker for Alzheimer's disease.

We demonstrate a nonmechanical, on-chip optical beam-steering device using a photonic-crystal waveguide with a doubly periodic structure that repeats the increase and decrease of the hole diameter. We fabricated the device using a complementary metal–oxide–semiconductor process. We obtained a beam-deflection angle of 24° in the longitudinal direction, while maintaining a divergence angle of 0.3°. Four such waveguides were integrated, and one was selected by a Mach–Zehnder optical switch. We obtained lateral beam steering by placing a cylindrical lens above these waveguides. By combining the lateral and longitudinal beam steering, we were able to scan the collimated beam in two dimensions, with 80 × 4 resolution points.

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.

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.

Silica-clad silicon photonic crystal waveguides (PCWs) are promising components for various applications because of their simple fabrication and generation of slow light. However, an optical loss higher than 4 dB occurs when they are simply coupled to input/output silicon wire waveguides. To reduce the optical loss, we proposed a junction structure in which light in the waveguide is first coupled to a high-group-velocity radiation mode at an expanded core and subsequently converted to the slow-light mode in a tapered core of the PCW. The coupling loss at a junction is calculated to be 0.28 dB at its minimum and less than 0.5 dB for the wavelength range of 12 nm. We measured a coupling loss of 0.46 dB for the device fabricated by the silicon photonics process. This low-loss junction well supports the practical use of PCWs.

We propose an ultra-compact solid-state auto-correlator fabricated by Si photonics technology. The correlation waveform is obtained by detecting the overlap of two slow-light pulses counter-propagating in a photonic crystal waveguide integrated with two-photon absorption photodiode array. Since the device does not need a mechanical delay scanner, the full integration on a silicon-on-insulator, easy operation and high reliability are available. Different from conventional single-shot auto-correlators, it shows a much higher sensitivity for low-power pulses owing to the strong confinement and nonlinear enhancement of slow light. We succeeded in acquiring the auto-correlation waveform of pico-second pulses. The detection limit evaluated from the product of peak and average powers was of the order of 10−7 W2, which is equal to or even better than that of the commercial auto-correlators and 107 times better than the single-shot one's.

A lattice-shifted photonic crystal waveguide (LSPCW) maintains slow light as a guided mode and works as an optical antenna when a kind of double periodicity is introduced. Selecting one LSPCW from its array and converting the fan beam to a spot beam using a collimator lens allows non-mechanical, two-dimensional beam steering. We employed a shallow-etched grating into the LSPCW as the double periodicity to increase the upward emission efficiency and designed a bespoke prism lens to convert the steering angle in a desired direction while maintaining the collimation condition for the steered beam. As a result, a sharp spot beam with an average beam divergence of 0.15° was steered in the range of 40 ∘ × 4.4 ∘ without precise adjustment of the lens position. The number of resolution points obtained was 4256. This method did not require complicated and power-consuming optical phase control like that in optical phased arrays, so it is expected to be applied in complete solid-state light detection and ranging.

The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible to perform biosensing without a fluorescent label or a chromogenic substrate. The most common phenomenon between many photonic sensors is that the resonance wavelength reflects the refractive index of attached media; an index change of 2.5 × 10−4 in the surrounding liquid can be measured through an emission wavelength shift without stabilization. This effect is applicable to detecting environmental toxins and cell behaviors. The laser emission intensity also reflects the electric charge of surface ions. The intensity varies when an electrolyte or a negatively charged deoxyribonucleic acid (DNA), which is positively or negatively charged in water, is accumulated on the surface. This effect allows us to detect the antigen-antibody reaction of a biomarker protein from only the emission intensity without any kind of spectroscopy. In detecting a small amount of DNA or protein, a wavelength shift also appears from its concentration that is 2–3 orders of magnitude lower than those of the conventional chemical methods, such as the enzyme-linked immuno-solvent assay. It is unlikely that this wavelength behavior at such low concentrations is due to the refractive index of the biomolecules. It is observed that the electric charge of surface ions is induced by various means, including plasma exposure and an electrochemical circuit shifting the wavelength. This suggests that the superhigh sensitivity is also due to the effect of charged ions. Thus, we call this device an iontronic photonic sensor. This paper focuses on such a novel sensing scheme of nanolaser sensor, as an example of resonator-based photonic sensors, in addition to the conventional refractive index sensing.

In this study, we fabricated a photoelectrochemical circuit using GaInAsP photonic crystal nanolasers as a working electrode. Then, we controlled the emission intensity and lasing wavelength of these nanolasers by applying a bias voltage in an ionic solution. The electrochemical working points for the emission intensity and wavelength were observed for the backward and forward biases, respectively. We confirmed that the emission intensity is primarily changed by the surface recombination, which is enhanced by the Schottky barrier near the solid–liquid interface. The wavelength shift is also assumed to be caused by the Pockels effect in the electric double layer of the solution. This control method can maximize and stabilize the performance of photonic biochemical sensors and also become an option in controlling the laser diode characteristics., This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in (Yoshito Saijo et al 2019 App. Phy. Let. 114 221105) and may be found at http://doi.org/10.1063/1.5098119.

We demonstrate an ultra-compact solid-state auto-correlator without delay scanning. We observe counter-propagating slow light pulses in a Si photonic crystal waveguide with a two-photon-absorption photodiode array. Sensitive detection is available for picosecond pules.

GaInAsP photonic crystal nanolaser is a tiny semiconductor laser, which can fabricated by simple HI etching process and operated by room-temperature photopumping. It can be used as a ultra-sensitive bio-sensor, since its wavelength and emission intensity are greatly influenced by the environmental index and charges. This paper reports the detection of prostate-specific antigen from a concentration of 1 fM even when the analyte includes 10-billion higher concentration of BSA as a contaminant. It also demonstrates various bio-sensings such as a biomarker for Alzheimer's disease, endotoxin, DNA and living cells.

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.

GaInAsP photonic crystal (PC) point-shift nanolasers operate at room temperature and under pulsed and continuous-wave condition by photopumping, with an effective threshold of ～1 μW, a single mode peak of over 40 dB, and a small modal volume of -0.2 times the cubic wavelength. We report the details of its design, fabrication process, measurement method, and lasing characteristics. In particular, we reveal that wide spectral broadening often observed for nanolasers under pulsed condition is caused by large thermal chirping. Then, we focus on a nanolaser-based liquid index sensor, which is also applicable to detecting gases and bio-molecules. The dependence of the laser's sensitivity and resolution on the modal profile and spectral linewidth are investigated. We also configure the laser in a large-scale array, and demonstrate spectrometer-free sensor system. Finally, we present a nanoslot nanolaser, which is particularly suitable for further reducing the modal volume and enhancing light-matter interaction and sensor performance. Additionally, we demonstrate that high sensitivity and spectral narrowing by the unique optical confinement in the nanoslot gives rise to.

We proposed and demonstrated a wavelength-division multiplexing (WDM) optical beam-steering device consisting of a thermally controlled doubly periodic Si two-dimensional bulk photonic crystal waveguide and coupled microring multiplexers. Beam forming and steering while maintaining a sharp profile is much easier in this device than with optical phased arrays which need the fine phase control. By dividing the range of beam-steering angles into different wavelength channels, it is possible to cover a wide range of angles, even when each angle is small. In this study, we fabricated a device with four wavelength channels, each of which showed beam steering of 4°-5° as a result of heating, resulting in a total of 16°. Two-dimensional steering is also achieved by loading a collimator lens and selecting one waveguide from those arrayed. We evaluated 112 resolution points with four wavelengths and 448 points in total by switching four waveguides. If this WDM concept is introduced into light detection and ranging and the number of wavelengths is increased, it will be possible to increase the sensing throughput, which is usually constrained by the round-trip time of light, by simultaneous parallel operation.

Photonic crystals (PCs) are multi-dimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the PC. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored using photonic band theory. The negative refraction enables novel prism, collimation, and lens effects. Because PCs usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The PC slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid reflection and diffraction losses. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects. The collimation effect is obtainable not only inside but also outside of the PC by optimizing negative refractive condition.

We report an on-chip autocorrelator comprising a Si rib waveguide and two-photon-absorption photodiodes in which two pulses simultaneously propagate in opposite directions, and their correlation is acquired. The rib waveguide's broadband guiding mode and moderately low group index allow the device to operate over a wide wavelength range with high resolution. We confirm that the waveguide has a transmission band of at least 1300-1630 nm and observed correlation waveforms for pulses of the order of several hundred femtoseconds to several picoseconds, with a range of at least the entire C band region.

Light focusing characteristics of a negative refractive lens fabricated out of a silicon-on-insulator photonic crystal (PC) slab are investigated theoretically and experimentally. It focuses in the near infrared, but the focal spot is degraded by a lens aberration. To reduce the aberration, we designed a composite PC that gives rise to a narrower focal spot. In addition, two unique functions of this lens are demonstrated: refocusing outside of the PC and parallel focusing, enabling image transfer and real image formation, respectively. These results prove the feasibility of an in-plane free space optical network based on negative refraction.

Slow light with a remarkably low group velocity is a promising solution for buffering and time-domain processing of optical signals. It also offers the possibility for spatial compression of optical energy and the enhancement of linear and nonlinear optical effects. Photonic-crystal devices are especially attractive for generating slow light, as they are compatible with on-chip integration and room-temperature operation, and can offer wide-bandwidth and dispersion-free propagation. Here the background theory, recent experimental demonstrations and progress towards tunable slow-light structures based on photonic-band engineering are reviewed. Practical issues related to real devices and their applications are also discussed. The unique properties of wide-bandwidth and dispersion-free propagation in photonic-crystal devices have made them a good candidate for slow-light generation. This article gives the background theory of slow light, as well as an overview of recent experimental demonstrations based on photonic-band engineering.

Photonic crystals are multidimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the crystals. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored based on photonic band theory. Negative refraction enables novel prism, collimation, and lens effects. Because photonic crystals usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The photonic-crystal slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid unwanted reflection and diffraction. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects.

We demonstrate a Si sub-bandgap photodiode in a photonic crystal slow-light waveguide that operates at telecom wavelengths and can be fabricated using a Ge-free, standard Si-photonics CMOS process. In photodiodes based on absorption via mid-bandgap states, the slow-light enhancement enables performance that is well balanced among high responsivity, low dark current, high speed, wide working spectrum, and CMOS-process compatibility, all of which are otherwise difficult to achieve simultaneously. Owing to the slow-light effect and supplemental gain at a high reverse bias, the photodiode shows a responsivity of 0.15 A/W with a low dark current of 40 nA, which is attributed to no particular processes such as ion implantation and excess exposure of the Si surface. The maximum responsivity was 0.36 A/W. The modest gain allows for sufficient frequency bandwidth to observe an eye opening at up to 30 Gb/s.

Photonic crystal nanolaser is an easily fabricated and operated semiconductor laser, which can be a high performance biosensor chip. It detects not only the environmental index of adsorbed bio-molecules as the laser wavelength shift but also the surface charge as the change in the emission intensity. This capability allows the simultaneous analysis of optical and electrical properties of target bio-molecules. Such multi-sensing is demonstrated for hybridization of DNAs. This nanolaser also shows ultrahigh sensitivity for antibody-antigen reactions of biomarker proteins and ultrahigh selectivity against contaminants, which are promising to medical diagnoses. For example, PSA for prostatic cancer is detected from 1 fM even with 10 µM contaminants, and CRMP2 for Alzheimer disease is detected from 10 pM in animal-derived sample. It is also applicable to detecting endotoxin, the environmental toxin, which must be removed in clinical treatments. A low concentration of 0.001 EU/ml is detected within 33 min by monitoring limulus amebocyte lysate reaction with endotoxin.

We designed and fabricated 70×75 µm2 arrayed waveguide grating demultiplexer consisting of Si slab and wire waveguides on a silicon-on-insulator substrate. By optimizing the connection between components and the layout of arrayed waveguides, internal light scattering and the increase in phase error were suppressed. As a result, clear demultiplexing characteristics were observed with a channel spacing of 8 nm and a sidelobe level of -22 dB in the wavelength range from 1.5 to 1.6 µm.

An ultralow group velocity of light in a III–V semiconductor photonic crystal (PC) waveguide is expected to enhance the optical gain per unit length of the waveguide. We discuss the possibility of a compact semiconductor optical amplifier that utilizes a single-line-defect PC waveguide fabricated from an all semiconductor low-Δ slab with deep airholes. From photonic band and traveling-wave rate equation analysis, a gain of larger than 20 dB is expected in a short active PC waveguide of 10 µm length, although the waveguide mode has a large radiation loss. We experimentally demonstrate such a waveguide in the passive wavelength regime. The waveguide is fabricated into a GaInAsP/InP wafer with high-mesa input/output waveguides. We show that the observed transmission characteristics of light correspond well to the photonic band theory.

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 quasi-periodic PC microlaser, because the hole burning by the whispering gallery mode of this cavity suppresses the carrier leakage.

In this paper, we discuss unique light localizations in photonic crystal line defect waveguides based on two different concepts. The first concept is an additional defect doping that breaks the symmetry of the line defect. Even though such a defect is open to the line defect, the optical field is well confined around the defect at cutoff frequencies of the line defect. This expands the design flexibility of microcavities, and allows effective mode controls such as the single-mode operation. The lasing action of such cavities in a GaInAsP photonic crystal slab was experimentally observed by photopumping at room temperature. The second concept is a chirping of the waveguide structure. The photonic band of a waveguide mode has a band edge, at which the group velocity becomes zero. The band-edge condition shifts in a chirped line defect waveguide, so guided light reaches a zero group velocity point and is localized. A macroscopic behavior of this phenomenon was experimentally observed in a waveguide fabricated into a silicon-on-insulator substrate. In addition, a microscopic behavior was theoretically investigated, which suggested its applicability to a group delay device.

We theoretically and experimentally investigated lasing and resonant characteristics in photonic crystal lasers with point defects and/or point and line composite defects. The finite-difference time domain simulation showed that various resonant modes can occur in arbitrary defect geometries. A GaInAsP airbridge photonic crystal slab with a lattice constant of /spl sim/0.42 /spl mu/m, a hole diameter of /spl sim/0.25 /spl mu/m, a sidewall angle of /spl sim/90/spl deg/, and a sidewall roughness of /spl sim/10 nm, was fabricated by Cl/sub 2//Xe inductively coupled plasma etching, in which ions and radicals were balanced by optimizing the gas pressure and the bias voltage. The room temperature pulsed lasing was observed with a threshold irradiated power of 1.4 mW by photopumping. The possibility of the continuous-wave (CW) lasing was also discussed with the estimation of the thermal resistance. The mode control in some composite defects was confirmed from resonant photoluminescence peaks under CW condition.

Electronic devices and their highly integrated components formed from semiconductor crystals contain complex three-dimensional (3D) arrangements of elements and wiring. Photonic crystals, being analogous to semiconductor crystals, are expected to require a 3D structure to form successful optoelectronic devices. Here, we report a novel fabrication technology for a semiconductor 3D photonic crystal by uniting integrated circuit processing technology with micromanipulation. Four- to twenty-layered (five periods) crystals, including one with a controlled defect, for infrared wavelengths of 3-4.5 microm, were integrated at predetermined positions on a chip (structural error

The GaInAsP microgear laser is a kind of microdisk laser but has a rotationally symmetric grating, which matches with the profile of the whispering gallery mode. In this study, we achieved the room temperature continuous-wave lasing with a threshold photopump power of 14 /spl mu/W for the smallest gear diameter of 2.02 /spl mu/m. We also observed the single-mode lasing in a deep grating device, where the /spl pi/-phase-shifted nonlasing mode completely disappeared. The experimental results were well explained by a three-dimensional finite-difference time-domain calculation and a consideration on the surface recombination. In addition, to increase the variety of the microgear, we proposed its fusion with a quasi-periodic photonic crystal (QPC), which also has a rotational symmetry. We theoretically estimated a sufficiently high Q of 21 600 for a QPC gear with a point defect of 1.6-/spl mu/m diameter, which is the smallest limit for a normal microdisk at a wavelength of 1.5-1.6 /spl mu/m.

In this paper, we discuss the Purcell effect, which enhances the spontaneous emission rate, in microdisk lasers operating at room temperature by continuous wave photopumping. We theoretically analyzed the Purcell effect at room temperature by using the four-level rate equations that include the intraband relaxation and the nonradiative effect. We also fabricated 1.55-/spl mu/m GaInAsP microdisk lasers with a minimum diameter of 1.7 /spl mu/m and a minimum threshold power of 19 /spl mu/W. Then, we measured the carrier lifetime in a 2.6-/spl mu/m-diameter device by the phase-resolved spectroscopy method, and confirmed that the carrier lifetime was shortened to 1/10 of that in the as-grown epitaxial wafer at a low pump level. From the comparison between the theory and the experiment, we estimated the Purcell factor to be 6.7, the spontaneous emission factor to be 0.11, and the nonradiative lifetime to be 4 ns. The nonradiative lifetime was consistent with that estimated by another methods. We believe that this is the first demonstration of the Purcell effect in semiconductor microcavities at room temperature.

We fabricated a GaInAsP microdisk laser using a benzocyclobutene (BCB) polymer cladding, which decreased the fragility and the thermal resistance of the conventional air cladding device and simplified the current injection using the metal pad electrode. The threshold current for a 7-µm-diameter device was 0.4 mA at room temperature, which was almost the same as that for the air cladding device. The red shift of the resonant spectrum against the continuous wave current was reduced by 54% in the BCB cladding device. Nearly 90% of this reduction is attributed to the reduction in thermal resistance. The remaining 10% is due to the reduction in temperature dependence (athermal effect) by the BCB cladding which has a negative temperature dependence of the refractive index. An analysis shows that the microdisk laser with a polymer cladding can function as an athermal laser when the disk thickness is reduced to 50–80 nm.

We propose an ultra-compact solid-state autocorrelator fabricated using Si photonics technology that obtains correlation by detecting the overlap of two slow light pulses counter-propagating in a photonic crystal waveguide integrated with a two-photon absorption photodiode array. As the device does not require a mechanical delay scanner, it can be integrated onto a chip and operated without alignment. Using the correlator, we successfully acquired the autocorrelation of picosecond pulses. The nonlinear enhancement of slow light improves sensitivity, resulting in an evaluated detection limit in terms of the product of the peak and average power on the order of 10−7 W2, which is equal to or even better than that of commercial scanning autocorrelators and 107-fold better than that of conventional single-shot autocorrelators.

We developed a 25-Gb/s silicon modulator with 9.83-dB·V αV π L, which is smallest of those operated at 25 Gb/s and higher. We used forward-biased diode operations, which enables small V π L with moderately doped low-loss waveguides.

Third-harmonic generation enhanced by slow-light pulses in a photonic crystal waveguide offers a way to generate green light emission from silicon.

This paper experimentally demonstrates the strong enhancement of light extraction efficiency in two-dimensionally arranged microcolumns. They were designed like a honeycomb photonic crystal and fabricated into GaInAsP-InP wafers by using the inductively coupled plasma etching: For the laterally directed light passing through the microcolumns, peculiar transmission characteristics were observed, which could be explained by the Bragg reflection theory, namely, the photonic bandgap (PBG), The measurement of spontaneous lifetime showed that the internal efficiency in the microcolumns was reduced by the surface recombination at sidewalls. In contrast, the light extraction efficiency evaluated from the measured photoluminescence intensity, and the internal efficiency was more than ten times that for a planar wafer, This was thought to be due to the expanded escape cone of internal light by the low effective refractive index, and also due to the strong diffraction and scattering of laterally directed light, which corresponds to the second-order Bragg condition. Such effects are expected not only in photonic crystals but also in some disordered structures. We expect this structure to allow a high-efficiency light-emitting diode (LED), since electronic elements needed for current injection devices can be added independently of the effects.

We have calculated lasing characteristics of current injection microdisk lasers of several microns in diameter, taking account of the scattering loss at center posts and the carrier diffusion effect. We found that the optimum width of the disk wing exposed to the air is 0.6-0.7 /spl mu/m and the minimum threshold current is nearly 10 /spl mu/A for the disk diameter of 2 /spl mu/m. The internal differential quantum efficiency can be 95% if the transparent carrier density is reduced to 7.5/spl times/10/sup 17/ cm/sup -3/ and the diffusion constant is increased to 8 cm/sup 2//s. In the experiment, we have obtained the room temperature continuous-wave operation of a GaInAsP-InP device of 3 /spl mu/m in diameter, for the first time, with a record low threshold of 150 /spl mu/A. This achievement was mainly owing to the reduction of the scattering loss at the disk edge, and hence the reduction of the threshold current density. The spontaneous emission factor was estimated to be 6/spl times/10/sup -3/. This value was much reduced by the large detuning of the lasing wavelength against the spontaneous emission peak. A larger value over 0.1, which is expected for such a small device, will be obtained by the wavelength tuning and the narrowing of the spontaneous emission spectrum.

We investigated the inductively coupled plasma etching of InP-based materials for photonic-crystal (PC) device fabrication. By optimizing bias power and gas pressure, circular holes with a diameter of

25 Gbps operation was obtained with extinction ratios of 2 - 4 dB for V pp = 1.00 - 1.75 V in MZI modulator consisting of 200-μm photonic crystal slow light waveguide phase shifters.

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.

We demonstrate the high-speed electrical delay tuning of slow light pulses using Si photonic crystal waveguides. The device has an i-region-chirped pin diode, within which thermo-optic and carrier plasma effects are generated by forward bias. The former changes the delay up to 62 ps for the DC bias. The latter changes the delay for 1 Gbps pseudo random bit sequence tuning signals, which will be applicable to advanced time-domain optical signal processing.