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We have developed photonic crystal slow-light devices and photonic integration. Inverse design and compatibility to Si CMOS foundry process enable practically low loss components and demonstrations of LiDAR and high-speed modulator.

We present a dynamically modulated ring resonator on a Si CMOS platform, hosting a synthetic dimension lattice over 180 GHz. The frequency and time domain synthetic band structure was acquired and photonic transport phenomena were explored.

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.

Wide-range nonmechanical beam steering is available by an array of Si photonic crystal slow-light waveguides and their switching without complicated control. FMCW LiDAR action is obtained with this beam steering on a Si photonics chip.

We optimized ultrasmall H0 photonic crystal nanocavity using neural network. Record high $Q$ over one million and 280,000 were calculated in air and water, respectively, for 180 nm slab at a wavelength around 1550 nm.

LiDAR is crucial for future robots/drones, autonomous vehicles, etc. Photonic crystal and Si photonics technologies have potential of non-mechanical beam steering and coherent FMCW LiDAR. We report the current status of their development.

We obtained carrier-suppressed single-sideband signal with a side-mode suppression ratio over 20 dB using photonic crystal I-Q modulator. When we used it for FMCW LiDAR setup, the signal was 5.3 dB higher than double sidebands'.

Photonic crystal has a history of 40 years, and some devices were commercialized recently. But they do not use a photonic band gap, which has been thought as the most important property of photonic crystals and actually produced various unique functions such as slow light. This presentation focuses on modulator and LiDAR, utilizing slow light in photonic crystals fabricated by silicon photonics technology.

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.

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.

For next-era optical interconnects in data centers, development of compact, energy-efficient, low-cost, and high-speed optical transceivers are required, for which high-performance external modulators in silicon photonics will be key components. We present a silicon photonic crystal waveguide slow light Mach-Zehnder modulator suitable for this purpose. The enhancement in the modulation efficiency via the slow light effect reduces the halfwave voltage-length product VπL , maintaining a wide working spectrum over 15 nm. The frequency response of the slow light modulator is constricted by an electrooptic phase mismatch between slow light and RF signals. In this study, this was dramatically improved by matching the phase using meanderline electrodes that delay RF signals. The cutoff frequency was experimentally evaluated to be 32–38 GHz. Using this device, we demonstrated high-speed modulation, including 64-Gbps on-off keying, 100-Gbps pulse amplitude modulation, and 50-Gbps/ch wavelength division multiplexing in 170–200-μm- long devices.

We demonstrate that the lasing wavelength and emission intensity of GaInAsP photonic crystal nanolaser can be controlled by immersing it to an electrolyte and applying a bias voltage. This method gives an option to the control of semiconductor lasers by the iontronic effect.

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.

This paper presents a excitation method of optical leaky waveguide antenna (OLWA) by parabolic reflector using photonic bandgap. We evaluate the performance of OLWA by proposed and conventional excitation method in the simulation. Our proposed method enables to excite OLWA with small feeding circuit.

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.

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.

Photonic crystal nanolasers are fabricated and operated simply, and can be applied as disposable sensors for biomedical applications. They are sensitive to the change with environmental index and surface charge. Functionalizing the nanolaser surface with an antibody, the specific binding of target antigen is detected with a detection limit 2-4 orders lower than that achieved by current standard methods, enzyme-linked immuno-sorbent assay. Nanolasers also detect negatively-charged deoxyribonucleic acid from their emission intensity. This technique requires neither labels nor spectroscopy, which simplifies screening procedures. Its applicability for high-speed detection of endotoxin and for label-fee imaging of living cells are also demonstrated.

We propose and demonstrate triangular-shaped coupled Si microrings for robust wavelength multi-/demultiplexing. Thanks to the geometry, stable interring couplings are obtained at straight waveguides, and heaters for thermal tuning can be isolated maximally with each other so that the thermal crosstalk is suppressed between rings. To suppress the bend loss and enhance the free spectral range (FSR), 2-μm-radius low-loss sharp bends with an optimum waveguide offset are employed. A CMOS-compatible process is used for fabricating second- and fourth-order coupled-microrings designed for the Butterworth and Chebyshev spectral responses, respectively. In the second-order rings, flat-top Box-like drop spectra with fluctuations 30 dB, bandwidth of 2.2 nm, FSR of 19 nm, and thermal tuning up to 8 nm are obtained experimentally. The efficiency of the thermal tuning is better and the thermal crosstalk is lower than those in conventional circular and race-track rings for such wide FSR.

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.

This paper presents a kind of optical leaky waveguide antenna (OLWA), circular waffle waveguide (CWWG), and demonstrates the gain enhancement by reducing perturbations. This antenna is fabricated by silicon photonics which is low-cost and mass-production. The CWWG has circular hole array on the waveguide surface instead of conventional linear grating. These holes reduce perturbations to extend effective antenna aperture, resulting in high antenna gain. To reduce more perturbations, we fabricate shallow hole array on waveguide surface. We confirm the antenna gain enhancement of the CWWG in both the simulation and the experiment.

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.

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.

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

We demonstrate 10 Gb/s modulation in a 200 μm photonic crystal silicon optical modulator, in both carrier-injection and depletion modes. In particular, this is the first demonstration of 10 Gb/s modulation in depletion mode and without pre-emphasis, in a Mach-Zehnder type modulator of this length, although moderate pre-emphasis can improve the signal quality. This is made possible by utilizing the slow-light of the photonic crystal waveguide, where the group index ng is ~ 30 and gives ~ 7 times enhancement in the modulation efficiency compared to rib-waveguide devices. We observe 10 Gb/s modulation at drive voltages as low as 1.6 V and 3.6 V peak-to-peak, in injection- and depletion-modes, respectively.

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.

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.

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.

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 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.

This paper presents experimental performance of Optical Leaky Wave Antenna (OLWA) using waffle waveguide (WWG). The antenna is fabricated by silicon photonics technology to achieve high directivity gain leaky waveguide antenna with small perturbation parameter of WWG. Narrow beam and one-dimensional beam scanning is demonstrated by sweeping input wavelength of OLWA. The measured WWG performance is also compared with a grating waveguide antenna.

Doppler shift of signal light is obtainable by moving photonic bandgap mirror, which is dynamically formed by slow light pulse. Large wavelength shift from several 10 nm to a few 100 nm are numerically demonstrated.

We comprehensively investigated practical silica-clad photonic crystal waveguides, and found two lattice shifts optimum for low-dispersion slow light. Fabricated device shows a high group index of >50, which ensures twice higher performance than conventional ones.

We theoretically investigated the modulation speed of Si photonic crystal slow light modulators. Optimizing the doping profile of p/n junction reduces the RC time constant and enhances the speed to 40 Gbps.

We fabricated a compact on-chip optical correlator using two photonic crystal slow light waveguides, and succeeded in complete on-chip operation. Observed pulse waveform agreed well with the one observed by commercial optical correlator.

We observed the avalanche photodiode operation through defect levels at telecom band in Si photonic crystal slow light modulator. Maximum responsivity was 0.71 A/W with 350 avalanche gain. The eye opened at 20 Gbps.

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.

We fabricated a 12-fold symmetric quasiperiodic photonic crystal (QPC) into a GaInAsP slab, and obtained a lasing action in a single-defect nanocavity and a defect-free area at room temperature. Four defect modes observed by a lithographic tuning were clearly explained by finite-difference time-domain calculation. The lowest threshold was obtained for the quadrupole mode, which has a small modal volume of 0.58 times the cubic wavelength in the cavity, by the fine-tuning of adjacent airholes to the defect. The lasing in the defect-free area was also suggested to be due to the localization of two-dimensional Bragg modes at the photonic gap edge. Because of its high structural flexibility, the QPC nanocavity has the potential of becoming a good alternative to the PC nanocavity.

We propose a photonic molecule consisting of multiple nanocavities in a photonic crystal and demonstrate its lasing and modal characteristics by finite-difference time-domain analysis and by experiments. In the analysis, we show that a point-shift defect and a point-missing defect have s- and p-orbital cavity modes, respectively, and that two adjacent defects exhibit σ- and π-orbital bonding and antibonding modes, which are similar to electronic states in chemical molecules. For such structure, we verify the modal characteristics as photonic molecules, i.e., mode splitting and its dependence on coupling strength, through their fabrication into GalnAsP photonic crystal slabs and the observation of lasing characteristics.