Recently, strongly modulated photonic crystals, fabricated by the state-of-the-art semiconductor nanofabrication process, have realized various novel optical properties. This paper describes the way in which they differ from other optical media, and clarifies what they can do. In particular, three important issues are considered: light confinement, frequency dispersion and spatial dispersion. First, I describe the latest status and impact of ultra-strong light confinement in a wavelength-cubic volume achieved in photonic crystals. Second, the extreme reduction in the speed of light is reported, which was achieved as a result of frequency dispersion management. Third, strange negative refraction in photonic crystals is introduced, which results from their unique spatial dispersion, and it is clarified how this leads to perfect imaging. The last two sections are devoted to applications of these novel properties. First, I report the fact that strong light confinement and huge light–matter interaction enhancement make strongly modulated photonic crystals promising for on-chip all-optical processing, and present several examples including all-optical switches/memories and optical logics. As a second application, it is shown that the strong light confinement and slow light in strongly modulated photonic crystals enable the adiabatic tuning of light, which leads to various novel ways of controlling light, such as adiabatic frequency conversion, efficient optomechanics systems, photon memories and photons pinning.

https://iopscience.iop.org/article/10.1088/0034-4885/73/9/096501/pdf

Manipulating light with strongly modulated photonic crystals

The ability to directly modulate a nanocavity laser with ultralow power consumption is essential for the realization of a CMOS-integrated, on-chip photonic network, as several thousand lasers must be integrated onto a single chip. Here, we show high-speed direct modulation (3-dB modulation bandwidth of 5.5 GHz) of an ultracompact InP/InGaAsP buried heterostructure photonic-crystal laser at room temperature by optical pumping. The required energy for transmitting one bit is estimated to be 13 fJ. We also achieve a threshold input power of 1.5 µW, which is the lowest observed value for room-temperature continuous-wave operation of any type of laser. The maximum single-mode fibre output power of 0.44 µW is the highest output power, to our knowledge, for photonic-crystal nanocavity lasers under room-temperature continuous-wave operation. Implementing a buried heterostructure leads to excellent device performance, reducing the active region temperature and effectively confining the carriers inside the cavity. Advanced on-chip photonic networks require integrated nanoscale lasers with low power consumption. Researchers have now demonstrated high-speed modulation of a compact heterostructure photonic crystal laser at room temperature with an unprecedented low required energy of ∼13 fJ per bit transmitted.

High-speed ultracompact buried heterostructure photonic-crystal laser with 13 fJ of energy consumed per bit transmitted

Disclosed is an optical transmission fiber having reduced bending and microbending losses that is commercially usable in FTTH or FTTC transmission systems.

Single mode optical fiber

The present invention embraces a single-mode optical fiber that, at a wavelength of 1550 nanometers, has bending losses of 0.15 dB/turn or less for a radius of curvature of 5 millimeters.

Bend-insensitive single-mode optical fiber

High-speed modulation and 4.4 fJ bit−1 data transmission is demonstrated using a photonic-crystal nanocavity laser. Its current threshold of 4.8 µA, modulation current efficiency of 2.0 GHz µA−0.5 and output power of 2.17 µW may enable on-chip photonic networks in combination with recently developed high-sensitivity receivers.

Few-fJ/bit data transmissions using directly modulated lambda-scale embedded active region photonic-crystal lasers

A novel widely tunable optical filter with a ladder-type structure is proposed. The device decreases the electrode area, compared with a tunable filter using an arrayed waveguide grating filter. It is fabricated using the InGaAsP-InP material system, and current injection is employed to change the refractive index of the waveguide. The device exhibits a tuning range of 58 nm and a switching time of less than 10 ns.

A widely tunable optical filter using ladder-type structure

The differential modal gain (DMG) in a few-mode erbium-doped fibre amplifier (FM-EDFA) is successfully improved by employing a ring-core FM erbium-doped fibre (RC-EDF). The DMGs between LP01 and LP11 mode signals in the FM-EDFA with the RC-EDF are 1.8 and 1.6 dB for LP01 and LP11 mode pumping, respectively, whereas those in a FM-EDFA with a conventional step-index FM EDF are 9.2 and 6.1 dB, indicating 7.4 and 4.5 dB DMG improvement for LP01 and LP11 mode pumping, respectively.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/el.2014.3411

Improvement of differential modal gain in few-mode fibre amplifier by employing ring-core erbium-doped fibre

We demonstrate the simultaneous 12-core amplification of a double-clad Er/Yb-doped fiber amplifier by using newly developed free-space coupling pump/signal combiner modules equipped with multi-core fiber pigtails. C-band amplification is successfully achieved using a 5-m long double-clad Er/Yb-doped fiber.

12-Core Double-Clad Er/Yb-Doped Fiber Amplifier Employing Free-space Coupling Pump/Signal Combiner Module

We present a directly modulated membrane laser on high-thermal-conductivity SiC exhibiting >100-GHz bandwidth. A -40GHz relaxation oscillation frequency, owing to low thermal resistance and high optical confinement, and a -95-GHz photon-photon resonance are achieved. Net 239.3-Gbit/s PAM-4 transmission over 2-km standard single-mode fibre is demonstrated.

239.3-Gbit/s net rate PAM-4 transmission using directly modulated membrane lasers on high-thermal-conductivity SiC

An improved method for manufacturing an optical fiber preform uses the CVD method in which a portion of or the whole of the optical fiber preform is formed by depositing glass on the inner wall of the starting tube. The method comprises a first step of depositing glass on the inner wall of the starting tube and collapsing the starting tube so that a silica rod is formed; a second step of removing the starting tube surrounding the silica rod or removing the starting tube and a part of synthetic glass; and a third step of depositing glass on an outer periphery of the silica rod obtained in the second step. By setting the refractive index of the cladding to be less than that of pure silica using the present method, an optical fiber having an extremely low transmission loss may be obtained.

Shoichiro Matsuo

Papers

A widely tunable optical filter using ladder-type structure

Improvement of differential modal gain in few-mode fibre amplifier by employing ring-core erbium-doped fibre

12-Core Double-Clad Er/Yb-Doped Fiber Amplifier Employing Free-space Coupling Pump/Signal Combiner Module

239.3-Gbit/s net rate PAM-4 transmission using directly modulated membrane lasers on high-thermal-conductivity SiC

Optical fiber, optical fiber preform, and method for manufacturing optical fiber preform