Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

A marriage of optical fibre fabrication technology and LSI microfabrication technology gave birth to fibre-matched silica waveguides on silicon: thick glass layers of high-silica-content glass are deposited on silicon by flame hydrolysis, a method originally developed for fibre preform fabrication. Silica channel waveguides are then formed by photolithographic pattern definition processes followed by reactive ion etching. This ‘high silica (HiS) technology’ offers the possibility of integrating a number of passive functions on a single silicon chip, as well as the possibility of the hybrid integration of both active and passive devices on silicon. This paper reviews the NTT HiS technology and its application to integrated-optic components such as optical beam splitters, optical switches, wavelength-division multi/demultiplexers and optical frequency-division multi/demultiplexers. The clear and simple waveguide structures produced by the HiS technology make it possible to design and fabricate these components with high precision and excellent reproducibility.

Silica waveguides on silicon and their application to integrated-optic components

TUTORIAL REVIEW Silica waveguides on silicon and their application to integrated-optic components

Methods are provided for forming optical devices, such as waveguides, with minimal defect formation. In one aspect, the invention provides a method for forming a waveguide structure on a substrate surface including forming a cladding layer on the substrate surface, forming a core layer on the cladding layer, depositing an amorphous carbon hardmask on the core layer, forming a patterned photoresist layer on the amorphous carbon hardmask, etching the amorphous carbon hardmask, and etching the core material.

Use of amorphous carbon film as a hardmask in the fabrication of optical waveguides

Various embodiments described herein include rare earth doped glass compositions that may be used in optical fiber and rods having large core sizes. Such optical fibers and rods may be employed in fiber lasers and amplifiers. The index of refraction of the glass may be substantially uniform and may be close to that of silica in some embodiments. Possible advantages to such features include reduction of formation of additional waveguides within the core, which becomes increasingly a problem with larger core sizes.

Rare earth doped and large effective area optical fibers for fiber lasers and amplifiers

40 Gbit/s direct modulation of a 1.3 /spl mu/m distributed feedback laser is reported for very-short-reach optical links. Error-free operation is accomplished by using a negative dispersion fibre.

40 Gbit/s direct modulation of distributed feedback laser for very-short-reach optical links

An optical fiber connector with an adjusting mechanism using double eccentric tubes is reported. Tolerable impairment values of possible factors affecting connection loss are evaluated. The main factors of the connection loss are mutual core displacement and fiber axis tilt. By using a double eccentric adjusting mechanism, a 0.57-dB average connecting loss between step index multimode fibers is obtained without matching material. The connection loss can be attributed quantitatively to several impairment factors. Using a transparent thin film in the connecting section, the reflection can be reduced as low as about −25 dB, and the average connecting loss was improved to about 0.20 dB.

Double eccentric connectors for optical fibers

Halides of Si and Ti, B, P, or Ge and oxygen or steam are introduced into a reaction vessel and heated in a vapor phase to form fine glass particles by oxidation or hydrolysis. The fine glass particles are deposited on a substrate. The deposited fine glass particles are heated and vitrified into a transparent glass layer, which is etched to form a core having a desired pattern by a reactive sputter etching process using Freon gas. The core is coated by a clad. In a waveguide thus formed, the cross sectional configuration and dimensions of the core layer and the refractive index difference are precisely controlled. The waveguide is manufactured with good reproducibility. The fabrication method is suitable for mass production of waveguides. An expansion coefficient transient layer is provided between the core layer and the substrate to prevent a crack in the waveguide. The glass softening temperature of the cladding layer is set lower than that of the core layer, so that the cross sectional configuration and dimensions of the core layer is unchanged against the heat in the vitrification process of the cladding layer. The refractive index is reduced in the vicinity of the boundary between the core and clad to prevent the loss of light due to light scattering on the core side faces.

Method of making glass waveguide for optical circuit

Embedded single and multimode waveguides on fused quartz substrates have been fabricated by high‐speed silica deposition and accurate reactive sputter etching by a C2F6 gas plasma. These waveguides have rectangular cross sections with an aspect ratio close to unity. Total waveguide loss was approximately 5 dB/cm, and absorption loss measured by laser calorimetry at 637‐nm wavelength was less than 0.1 dB/cm.

Deposited silica waveguide for intergrated optical circuits

Splicing between an optical fibre and a planar deposited silica waveguide was performed by using a CO2 laser as a heat source. The average splicing loss of 30 samples between a multimode graded-index fibre and a deposited silica waveguide was 0.18 dB. Reflection from the joining point disappeared by the fusion splicing.

Nobuo Shimizu

Papers

40 Gbit/s direct modulation of distributed feedback laser for very-short-reach optical links

Double eccentric connectors for optical fibers

Method of making glass waveguide for optical circuit

Deposited silica waveguide for intergrated optical circuits

Fusion splicing between optical circuits and optical fibres