Wristwatch pulse wave monitoring: assessing daily activity post-catheter ablation for atrial fibrillation.

Aims: Atrial fibrillation (AF) leads to impaired exercise capacity, and catheter ablation (CA) for AF improves exercise capacity. However, the precise changes in daily activities after CA for AF remain unclear. The authors aimed to evaluate the changes in daily activities following CA for AF using a wristwatch-type pulse wave monitor (PWM), which tracks steps and exercise time, estimates burnt daily calories, and records sleep duration, in addition to establishing the rhythm diagnosis of AF or non-AF.

Ultra-compact VCSEL scanner for high power solid-state beam steering.

We demonstrate the lateral monolithic integration of a tunable first-order surface-grating loaded vertical-cavity surface-emitting laser (VCSEL) and slow-light waveguide with fan-beam steering and amplifier function. Shallow Bragg-grating formed on the surface of a VCSEL section enables the selection of a single slow-light mode, which can be coupled into the integrated long waveguide and amplified through pumping the amplifier above threshold. We obtained over 3W amplified slow-light power with single-mode operation and over 4W amplified quasi-single-mode power under pulsed current injection.

Demonstration of real-time structured-light depth sensing based on a solid-state VCSEL beam scanner.

We demonstrated a real-time scanning structured-light depth sensing system based on a solid-state vertical cavity surface-emitting laser (VCSEL) beam scanner integrated with an electro-thermally tunable VCSEL. Through a swept voltage added to the tunable VCSEL, a field of view of 6°×12° could be scanned with a scanning speed of 100 kHz by the beam scanner. Adopting the beam scanner, the real-time depth image with a lateral resolution of 10,000 (20×500) was obtained by measuring a step target placed at 35cm.

Performance of an atrial fibrillation detection algorithm using continuous pulse wave monitoring.

Background: Detecting asymptomatic and undiagnosed atrial fibrillation (AF) is increasingly important. Recently, we developed a wristwatch-based pulse wave monitor (PWM; Seiko Epson, Japan) capable of long-term recording, with an automatic diagnosis algorithm that uses frequency-based pulse wave analysis. The aim of this study was to evaluate the validity of continuous pulse wave monitoring for detection of AF.

Fan-beam steering device using a photonic crystal slow-light waveguide with surface diffraction grating.

Compact non-mechanical beam steering devices are desired not only for current common applications, but also for advanced applications such as light detection and ranging. We use a Si photonic crystal slow-light waveguide with a diffraction grating, which radiates the guided mode to free space and steers a fan beam by sweeping the wavelength. Due to its large angular dispersion, slow light enhances the steering range without degrading the beam quality, resulting in more resolution points.

Enhancing the modulation bandwidth of VCSELs to the millimeter-waveband using strong transverse slow-light feedback.

We present modeling on the millimeter (mm)-wave modulation of vertical-cavity surface-emitting laser (VCSEL) with a transverse coupled cavity (TCC). We show that strong slow-light feedback can induce 300% boosting of the modulation bandwidth of the TCC-VCSEL. Also, the strong lateral feedback can induce resonance modulation over passbands centered on frequencies as high as 3.

Low-voltage, high-speed and compact electro-absorption modulator laterally integrated with 980-nm VCSEL.

We present a compact electro-absorption slow-light modulator laterally-integrated with a 980-nm VCSEL. We figured out the small signal modulation response for different modulator lengths. While the 3-dB small-signal modulation bandwidth of conventional directly modulated VCSELs on the same epi-wafer structure was limited below 10 GHz, we obtained a modulation bandwidth over 21 GHz for a 30 µm long modulator.

Athermal and widely tunable VCSEL with bimorph micromachined mirror.

We demonstrate an athermal and electrostatically-tunable 850 nm-band MEMS VCSEL for the first time. The thermal wavelength drift is compensated by the thermal actuation of a cantilever-suspended mirror with a bimorph effect. At the same time, the resonant wavelength can be continuously tuned by electro-static force as a voltage is applied in the cantilever structure.

Lateral integration of vertical-cavity surface-emitting laser and slow light Bragg reflector waveguide devices.

We present the modeling and the experiment on the lateral integration of a vertical-cavity surface-emitting laser (VCSEL) and slow light Bragg reflector waveguide devices. The modeling shows an efficient direct-lateral coupling from a VCSEL to an integrated slow light waveguide. The calculated result shows a possibility of 13 dB chip gain and an extinction ratio over 5 dB for a compact slow light semiconductor optical amplifier (SOA) and electroabsorption modulator integrated with a VCSEL, respectively.

Ultra-high channel-count wavelength demultiplexer based on a Bragg reflector waveguide with large angular dispersion.

We present a new type of wavelength demultiplexers based on a Bragg reflector waveguide, which provides a large angular dispersion of 1~2°/nm. Benefiting from its large steering bandwidth and sharp divergence angles, we record a number of resolution-points (possible channel-count in demultiplexing) over 200 and 1,000 for active-type and passive-type devices, respectively. It is the highest number in various multiplexing elements ever reported.

Giant and high-resolution beam steering using slow-light waveguide amplifier.

We propose a novel beam-steering device based on a slow-light waveguide amplifier. In this paper, we present the idea of this steering technique and show its modeling characteristics. Giant steering of the radiation beam is obtained by tuning the wavelength of input light, which is coupled into the Bragg reflector waveguide.

Slow-light total-internal-reflection switch with bending angle of 30 deg.

Slowing light in a Bragg reflector waveguide is used to miniaturize optical waveguide switches. We can realize a giant equivalent refractive index change induced by carrier injection near a cutoff wavelength due to its large waveguide dispersion. We fabricate and characterize a reflection-type slow-light switch.

Monolithically integrated multi-wavelength VCSEL arrays using high-contrast gratings.

We propose a novel design for multi-wavelength arrays of vertical cavity surface-emitting lasers (VCSELs) using high-contrast gratings (HCGs) as top mirrors. A range of VCSEL cavity wavelengths in excess of 100 nm is predicted by modifying only the period and duty-cycle of the high-contrast gratings, while leaving the epitaxial layer thickness unchanged. VCSEL arrays fabricated with this novel design can easily accommodate the entire Er-doped fiber amplifier bandwidth with emission wavelengths defined solely by lithography with no restrictions in physical layout.

Greatly increased fiber transmission distance with an optically injection-locked vertical-cavity surface-emitting laser.

We demonstrate single-mode fiber transmission distance enhancement up to 120 km of a directly-modulated injection-locked VCSEL modulated by a 10Gb/s NRZ signal. Injection locking induced data pattern inversion of the VCSEL causes adjustable chirp, which greatly extends reach. Both experiments and simulations are shown to explain this phenomenon.

Wide tunability and ultralarge birefringence with 3D hollow waveguide Bragg reflector.

A tunable Bragg reflector based on a 3D hollow waveguide (HWG) has been proposed. Ultrawide tuning ranges of 152 nm and 164 nm, respectively, in Bragg wavelengths of TE and TM modes of the Bragg reflector have been presented experimentally. With a 3D hat-shaped HWG, a giant birefringence of 0.

Fabrication and characterization of hollow waveguide optical switch with variable air core.

We demonstrate a novel hollow waveguide optical switch composed of an multi-mode interference (MMI) coupler with a variable air core. The numerical simulation and experiment of the proposed optical switch is carried out for investigating the operation of the switch. Switching operation can be obtained by the mechanical displacement of the air core of an MMI hollow waveguide.

Plasmon Enhanced Optical Near-field Probing of Metal Nanoaperture Surface Emitting Laser.

We demonstrate a metal nano-aperture GaAs vertical cavity surface emitting laser (VCSEL) for sub-wavelength optical near-filed probing, which exhibits the strong plasmon enhancement of both optical near-fields and voltage signals with forming a metal nano-particle in the nano-aperture. The threshold current is as low as 300microA, which shows a potential of nano-probing with low power consumption. We achieved the first demonstration of a plasmon enhanced VCSEL near-field probe.

Tunable hollow waveguide distributed Bragg reflectors with variable air core.

We demonstrate a tunable hollow waveguide distributed Bragg reflector consisting of a grating loaded slab hollow waveguide with a variable air-core. The modeling shows that a change in an air-core thickness enables a large shift of several tens of nanometers in Bragg wavelength due to a change of several percents in a propagation constant. We fabricated a slab hollow waveguide Bragg reflector with 620 mum long and, 190 nm deep 1st-order circular grating composed of SiO2, exhibiting strong Bragg reflection at 1558 nm with an air-core thickness of 10 mum for TM mode.

Transverse mode control by etch-depth tuning in 1120-nm GaInAs/GaAs photonic crystal vertical-cavity surface-emitting lasers.

Robust and tolerant single-transverse-mode photonic crystal GaInAs vertical-cavity surface-emitting lasers are fabricated and investigated. Triangular lattice patterns of rectangular air holes of various etch-depths are introduced in the top mirror. The stable single-transversemode operation is observed with a large margin of allowance in the etch depth (t = 2.