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We propose and demonstrate a simple all-optic control for Si photonics using a photo-thermal heater. The control light is absorbed in a heavily doped control waveguide and the signal light phase is tuned through thermal diffusion in a signal waveguide adjacent to but not optically coupled with the control waveguide. We designed and fabricated Mach–Zehnder- and microring-type devices requiring 17 (π-phase shift) and 4 (switching between resonance and non-resonance with 6 dB extinction) mW of control power, respectively. We confirmed that the heating efficiency of all-optic control exceeded that of an electrical heater placed above the signal waveguide.

In this paper, we propose and demonstrate a frequency-modulated continuous-wave light detection and ranging (LiDAR) with a Si photonic crystal beam scanner, simultaneously enabling scanning laser Doppler measurements. This nonmechanical solid-state device can reduce the size of conventional scanning laser Doppler vibrometers, making LiDAR a multimodal imaging sensor, which can measure the distributions of distance, velocity, and vibration frequency. We fabricated this device using Si photonics process and confirmed the expected operations. Distance and velocity resolutions were less than 15 mm and 19 mm/s, respectively. The detection limit of the vibration amplitude determined by the signal-to-noise ratio was 2.5 nm.

We propose an electromagnetic wave imaging system using Si photonics microring modulators (MRMs) as radio over fiber components. In this system, radio frequency signals detected at microwave probes are applied to the connected MRMs; an MRM is tuned to the laser wavelength using the thermo-optic effect to read-out through the optical transmission. By repeating this process for all MRMs and mapping the read-out signals in two dimensions, the distribution of electromagnetic waves can be visualized. Such system operation was demonstrated at 3.5 GHz in a 37.5 × 37.5 mm2 probing area, for which we confirmed the agreement with theoretical simulations.

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 demonstrate 64 Gbps operation in a compact Si photonic crystal optical modulator that employs meander line electrodes and compensate for the phase mismatch between slow light and RF signals. Although low dispersion slow light increases the modulation efficiency, maintaining a sufficiently wide working spectrum, the phase mismatch becomes a limiting factor on the operation speed even when the phase shifter length is as short as 200 μm. Meander line electrodes broke this limit and enhanced the cutoff frequency by up to 31 and 38 GHz using 50 Ω and 20 Ω termination resistors, respectively. This allowed to use a group index of slow light higher than 20, and greatly improved the quality of the modulation characteristics at 25 and 32 Gbps. Clear open eye was observed even at 40–64 Gbps.

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 label-free imaging of living cells using a GaInAsP semiconductor imaging plate. The photoluminescence (PL) intensity is changed by immersing the semiconductor wafer in different pH solutions and by depositing charged polyelectrolytes on the wafer. Various observations indicate that this phenomenon arises from the radiative and surface recombination rates modified by the Schottky barrier at the charged semiconductor surface. HeLa cancer cells were cultured on the semiconductor, and PL was observed using a near-infrared camera. The semiconductor areas with the cells attached exhibited characteristic PL profiles, which might reflect the attachment and surface condition of the cells, cellular matrix, and other substances.

The detection of low-concentration biomarkers is expected to facilitate the early diagnosis of severe diseases, including malignant tumors. Using photonic crystal nanolaser sensors, we detected prostate-specific antigen (PSA) from a concentration of 1 fM, which is difficult to detect by conventional enzyme-linked immunosorbent assay. The signal intensity and stability were improved by using a surfactant (i.e., ethanolamine). Even when a contaminant such as bovine serum albumin was mixed into the PSA sample, thereby increasing the concentration of the contaminant ten billion times, it was still possible to maintain a high level of detection.

Optical nonlinearity can be enhanced by the combination of highly nonlinear chalcogenide glass and photonic crystal waveguides (PCWs) providing strong optical confinement and slow-light effects. In a Ag-As(2)Se(3) chalcogenide PCW, the effective nonlinear parameter γeff reaches 6.3 × 10(4) W(-1)m(-1), which is 200 times larger than that in Si photonic wire waveguides. In this paper, we report the detailed design, fabrication process, and the linear and nonlinear characteristics of this waveguide at silica fiber communication wavelengths. We show that the waveguide exhibits negligible two-photon absorption, and also high-efficiency self-phase modulation and four-wave mixing, which are assisted by low-dispersion slow light.

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.

We demonstrate a Si photonic crystal waveguide Mach-Zehnder modulator that incorporates meander-line electrodes to compensate for the phase mismatch between slow light and RF signals. We first employed commonized ground electrodes in the modulator to suppress undesired fluctuations in the electro-optic (EO) response due to coupled slot-line modes of RF signals. Then, we theoretically and experimentally investigated the effect of the phase mismatch on the EO response. We confirmed that meander-line electrodes improve the EO response, particularly in the absence of internal reflection of the RF signals. The cut-off frequency of this device can reach 27 GHz, which allows high-speed modulation up to 50 Gbps.

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.

A GaInAsP photonic crystal slab microlaser with an integrated passive waveguide was fabricated by a MOCVD butt-joint regrowth process. The boundary between the active and passive regions was optimized for high light transmission. In addition, the edge of the waveguide was designed to output a narrow beam, and the light detection was improved. Consequently, a maximum output power of 0.17 mW was obtained with a differential quantum efficiency of 20%, which would increase to more than 40% under ideal detection conditions.

We report on the fabrication and evaluation of a directional coupler consisting of two different chirped photonic crystal (PC) waveguides that can generate wideband, low dispersion slow light. The directional coupler was fabricated from a silicon-on-insulator PC slab with airhole diameter chirping. For both waveguides, we observed a group index of 60-80 near the photonic band edge and opposite dispersion characteristics. In the directional coupler, we evaluated a group index of 30-40 in a wavelength bandwidth of 32 nm. The experimental results agree with the theoretical relation between the group index and bandwidth.

We propose and demonstrate an on-chip optical correlator, in which two types of photonic crystal slow-light waveguides are integrated and operated as an optical delay scanner and a two-photon-absorption photodetector. The footprint of the device, which was fabricated using a CMOS-compatible process, was 1.0 × 0.3 mm(2), which is substantially smaller than that of conventional optical correlators with free-space optics. We observed optical pulses using this device and confirmed the correspondence of pulse waveforms with those observed using a commercial correlator when the pulse width was 5-7 ps. This device will achieve one-chipping of an optical correlator and related measurement instruments.

In general, biochemical sensors based on photonic cavities are used to detect changes in the refractive index of the environment. In this study, however, a GaInAsP semiconductor photonic-crystal nanolaser sensor that we recently developed was found to detect not only the environmental refractive index but also the surface charge. In contrast to the pH sensitivity we reported previously, this is an ultra-sensitive detection mechanism capable of identifying proteins and deoxyribonucleic acids (DNA) at a femtomolar-order or lower concentrations. When the device is exposed to plasma or DNA solutions, the laser wavelength simultaneously changes with the zeta potential and the flat-band potential of the semiconductor surface. This indicates that the charged functional groups on the surface, which are formed by these treatments, modify the Schottky barrier near the semiconductor surface, trap the excited carriers in the barrier, and change the refractive index of the semiconductor via the carrier effects. These findings also suggest that some other photonic sensors may also exhibit similar electrochemical and optoelectronic effects.

We report a silicon DQPSK receiver whose symbol rate can be varied by a tunable one-bit delay line including an all-pass micro-ring slow-light device. It also consists of Si-wire waveguides with spot-size converters, optimized splitters/couplers, heater-controlled Mach-Zehnder attenuators and phase shifters, 90° hybrid with a low-loss crossing and balanced Ge photodiodes, all of which are fabricated by using CMOS-compatible process. Demodulation was confirmed at symbol-rates of 7.4 − 9.0 Gbaud, corresponding to bit-rates of 14.8 − 18.0 Gb/s.

The slow light device based on photonic crystal coupled waveguide was fabricated, and a tunable delay of 72 ps was obtained for 2-ps-wide slow light pulses by local heating, which corresponds to a tunable fractional delay of 36. This value was further enhanced to 110 by compressing the output pulses through self-phase modulation and dispersion compensation in external fibers. We applied this device to optical correlator as a delay scanner, where the fractional delay determines the resolution of the delay scanning. Using this correlator, we successfully observed sub-picosecond pulses at a scan frequency up to 2 kHz, which is 100 times faster than that of mechanical scanners in conventional correlators.

We have studied low-dispersion slow light and its nonlinear enhancement in photonic crystal waveguides. In this work, we fabricated the waveguides using Si CMOS-compatible process. It enables us to integrate spotsize converters, which greatly simplifies the optical coupling from fibers as well as demonstration of the nonlinear enhancement. Two-photon absorption, self-phase modulation and four-wave mixing were observed clearly for picosecond pulses in a 200-μm-long device. In comparison with Si wire waveguides, a 60 − 120 fold higher nonlinearity was evaluated for a group index of 51. Unique intensity response also occurred due to the specific transmission spectrum and enhanced nonlinearities. Such slow light may add various functionalities in Si photonics, while loss reduction is desired for ensuring the advantage of slow light.

Microphotonic sensors have been actively studied with increasing demands for label-free biosensing in medical diagnoses and life sciences. For high-throughput and low-cost sensing, a high sensitivity is crucial for eliminating the pre-concentration process, while a simple setup of sensors is also desirable. This paper demonstrates a super-sensitivity for protein, which satisfies these requirements. The key device is a photonic crystal nanolaser, in particular with a nanoslot. Even using a simple setup, the nanolaser achieves an extraordinary-low detection limit for BSA protein, i.e. 255 fM on an average, which cannot be explained by its bulk index sensitivity. The specific adsorption of the protein is observed only around the nanoslot with strong laser intensity. This suggests that the super-sensitivity arises from the effective trapping of protein in the nanoslot.

We report the first experimental demonstration of 10 Gb/s modulation in a photonic crystal silicon optical modulator. The device consists of a 200 μm-long SiO2-clad photonic crystal waveguide, with an embedded p-n junction, incorporated into an asymmetric Mach-Zehnder interferometer. The device is integrated on a SOI chip and fabricated by CMOS-compatible processes. With the bias voltage set at 0 V, we measure a V(π)L0.056 V∙cm. Optical modulation is demonstrated by electrically driving the device with a 2(31) - 1 bit non-return-to-zero pseudo-random bit sequence signal. An open eye pattern is observed at bitrates of 10 Gb/s and 2 Gb/s, with and without pre-emphasis of the drive signal, respectively.

We experimentally demonstrate a tunable slow-light device consisting of all-pass Si microrings. A compact device of 0.014 mm2 footprint is fabricated by using CMOS-compatible process, and its center wavelength, bandwidth and delay are continuously tuned by integrated heaters. The tuning range is 300 ps at fixed wavelengths with a 1 nm bandwidth. Eye opening of 40 Gbps non-return-to-zero signals is observed at up to a 150 ps delay and a 4 bit buffering capacity is confirmed, which corresponds to a spatial buffering density of 0.29 kbit/mm2.

We report on the fabrication of chalcogenide glass (Ag-As(2)Se(3)) photonic crystal waveguides and the first detailed characterization of the linear and nonlinear optical properties. The waveguides, fabricated by e-beam lithography and ICP etching exhibit typical transmission spectra of photonic crystal waveguides, and exhibit high optical nonlinearity. Nonlinear phase shift of 1.5pi through self-phase modulation is observed at 0.78 W input peak power in a 400 microm long device. The effective nonlinear parameter gamma(eff) estimated from this result reaches 2.6 x 10(4) W(-1)m(-1). Four-wave mixing is also observed in the waveguide, while two-photon absorption at optical communication wavelengths is sufficiently small and the corresponding figure of merit is larger than 11.

We experimentally demonstrate wideband dispersion-free slow light in chirped photonic crystal coupled waveguides (PCCW). In unchirped PCCWs, the zero group velocity can occur at an inflection point of a photonic band of even symmetric mode. The even symmetric mode is selectively excited by connecting the device with input and output waveguides through optimized branch and confluence structures. In the device fabricated on SOI substrate, a large increase in group delay was observed with a maximum group index of 140 and the zero group velocity dispersion at the inflection point. Photonic bands estimated from the group delay characteristics corresponded to calculated ones. In the chirped PCCWs, the group velocity dispersion was internally compensated and the nearly constant group index of 50-60 was obtained in a wavelength bandwidth of 10 nm. The dispersion compensation was also confirmed through the transmission measurement of sub-ps optical pulses.

We propose a novel compact wavelength demultiplexer, for which two functions arising from the anomalous dispersion characteristics of photonic crystals are combined. One is the superprism that exhibits large angular dispersion and expansion of light beam. The other is the superlens used for the focusing of the expanded light beam. Theoretically, a high resolution of 0.4 nm will be realized in the 1.55 μm wavelength range with device areas of 0.2 and 2.0 mm2, respectively, for available bandwidths of 3 and 35 nm. Also, a low insertion loss of less than 1 dB is expected by the optimization of input and output ends of the photonic crystals. The demultiplexing function is clearly demonstrated in finite-difference time-domain simulation.

Previously, we discussed an optical delay device consisting of a directional coupler of two different photonic crystal (PC) waveguides. It generates wideband and low dispersion slow light. However, it is easily degraded by a large reflection loss for a small imperfection of the coupling condition. In this paper, we propose and theoretically discuss a PC coupled waveguide, which allows more robust slow light with lower loss. For this device, unique photonic bands with a zero or negative group velocity at the inflection point can be designed by the structural tuning. Finite difference time domain simulation demonstrates the stopping and/or back and forth motion of an ultrashort optical pulse in the device combined with the chirped structure. For a signal bandwidth of 40 GHz, the average group index of the slow light will be 450, which gives a 1 ns delay for a device length of 670 microm. The theoretical total insertion loss at the device and input/output structures is as low as 0.11 dB.

We demonstrated the first room temperature continuous wave lasing in InAs quantum-dot microdisk lasers with a standard air-cladding optical confinement structure. The spectrum shows the single strong lasing peak at a wavelength of 1280 nm. The threshold pump power is 410 muW, and the corresponding effective threshold obtained by considering the absorption efficiency is 81 muW. This achievement is mainly attributed to the increase in Q factor by the improved disk shape.

Input and output boundaries of a photonic crystal (PC) are optimized so that the superprism exhibits low insertion loss. It is shown that projected-airhole and half-circular airhole interfaces achieve transmission loss of 0.3 dB and 1.0 dB, respectively, for small and large incident angles of light against normal to boundaries. The finite-difference time-domain simulation shows that a low loss is essentially realized by a periodic phase modulation of the incident beam by the interfaces. It also demonstrates the clear steering of collimated light beam with varying wavelength. The enhancement of angular dispersion is also demonstrated by a PC composed of a dispersive medium.

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 ~1 ps 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 wide-range 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, corresponding to a ~7 mm extension of the free space length.

We demonstrate refractive index sensing using photonic crystal point shift nanolasers. These lasers operate continuously at room temperature by photopumping in a liquid, and exhibit a 50-dB peak intensity over the background level and a spectral linewidth of < 26 pm, the resolution limit of the present experiment. The lasing wavelength shifts by soaking in different liquids; the wavelength to index sensitivity was 350 nm/RIU, the highest value recorded to date for nanocavity- based sensors. An index resolution of 9.0 x 10(-5) was thus confirmed, leading to an expectation of a resolution of < 10(-6). We propose and demonstrate a spectrometer-free sensor based on nanolasers in an array configuration. These will be disposable sensors with very simple optical I/O. They are anticipated to be integrated with biochips and used for label-free single molecule detection.

We have developed compact Si Mach-Zehnder modulators that are assisted by wideband low-dispersion slow light in lattice-shifted photonic crystal waveguides. We have also developed Si triangular-shaped coupled-microring multiplexers that allow a box-like spectrum, a wide free spectral range, and an efficient thermal tuning. In this study, we integrated three sets of these devices in a small footprint of 2.0 × 0.7 mm(2) and achieved their 25 Gbps/ch operation as a wavelength division multiplexing transmitter. Moreover, we demonstrated hitless wavelength tuning using thermo-optic switches loaded in the bus waveguide.

We proposed and demonstrated a label-free imaging method for living cells using a GaInAsP H0-type photonic crystal nanolaser array. We integrated 441 nanolasers in an arrayed configuration and achieved photopumped lasing with a 100% yield. Then, we attached HeLa cells on it, measured the wavelengths of all nanolasers and used them as pixel information. We acquired cell images, which partially corresponds to optical micrographs and probably reflects the attachment condition of the cells. We improved the refractive index resolution from ~10(-2) to 2 × 10(-3) by incorporating a nanoslot into each nanolaser and compensating the nonuniformity of each index sensitivity.

Biosensors selectively detecting a very small amount of biomarker protein in human blood are desired for early and reliable diagnoses of severe diseases. This paper reports the detection of protein (streptavidin: SA) in ultra-low concentration, with an ultra-high selectivity against contaminants, using photonic crystal nanolasers. For biotin-modified nanolasers in pure water with SA, an extremely-low detection limit of 16 zM is evaluated. Even in a mixture with 1 μM bovine serum albumin as the contaminant, 100 zM SA is detected, meaning a selectivity of 10(13). These are remarkable capabilities that are promising for practical biosensing in the medical applications mentioned above.

We demonstrate the first sub-100 μm silicon Mach-Zehnder modulators (MZMs) that operate at >10 Gb/s, by exploiting low-dispersion slow-light in lattice-shifted photonic crystal waveguides (LSPCWs). We use two LSPCW-MZM structures, one with LSPCWs in both arms of the MZM, and the other with an LSPCW in only one of the arms. Using the first structure we demonstrate 10 Gb/s operation with a operating bandwidth of 12.5 nm, in a device with a phase-shifter length of only 50 μm. Using the second structure, owing to a larger group index as well as lower spectral noise, we demonstrate 40 Gb/s operation with a phase-shifter length of only 90 μm, which is more than an order-of-magnitude shorter than most 40 Gb/s MZMs.