Liquid-crystal waveguides ready to shine
US optical components maker Digilens has published details of a waveguide-based multiplexing/demultiplexing module (WO 02/063361). The device comprises a demultiplexer (to separate an incoming signal into its constituent wavelengths); an array of waveguides (each of which transports a predefined band of wavelengths); and/or a multiplexer (which takes the beams from the waveguide outputs and recombines them into a composite signal). Each waveguide usually incorporates an optical attenuator. In one version, the core of the waveguides and/or their claddings are made up of a polymer-dispersed liquid-crystal material, the refractive index of which can be varied by the application of an electrical stimulus.
DWDM solution harnesses diffractive optical elements
Ibsen Photonics, the optical components maker based in Copenhagen, Denmark, is patenting a wavelength-division multiplexing (WDM) device based on a transmission-grating spectrometer having at least two diffractive optical elements (WO 02/067475). The module is said to be ideal for a range of applications: combining or separating multiple wavelengths; channel monitoring; and programmable add-drop. Earlier this year, Ibsen unveiled a monitor for real-time measurement of channel power in DWDM systems. The D-MON uses a diffraction grating to split incoming signals onto a custom diode array, simultaneously measuring the individual intensities of up to 80 optical channels at 50 GHz spacing.
Fiber-in-the-sewers: make life easier for the installers
An optical-cable holder that attaches to the ceiling of a sewage pipe is the subject of international patent application WO 02/063734. Developed by Consec Co. of Hiroshima, Japan, the plastic module comprises three bays (each shaped like an inverted U) capable of accommodating a range of cable types. Installation is straightforward. First, the technician presses an integrated fixturing unit, filled with a high-strength adhesive agent, into a drilled hole in the ceiling of the sewage pipe. A plunger pin then forces the adhesive out into the drilled cavity, in turn securing the cable holder to the ceiling.
Dynamic gain equalization: what profile do you want?
A dynamic gain equalizer for applications in wavelength-division multiplexing networks has been developed by Xtellus of New Jersey, US (WO 02/071660). The device uses a dispersive element (such as a grating) to split a composite signal into its constituent wavelength components. Subsequently, the spatially separated wavelengths pass through a linear array of variable optical attenuators (VOAs). These VOAs are based on liquid-crystal phase elements, which modulate the phase of part of the light beam's cross-section. At the output, the attenuated wavelengths are recombined and sent on their way. According to the filing: "The overall wavelength profile of the output light signal can be adjusted to any predefined form, whether a flattened spectral profile, as in gain equalization, or a spectral-compensating or band-blocking profile."
Hybrid wireless link makes optics and RF do the work
Details of a hybrid wireless link capable of providing a gateway between two fiber networks are revealed in international patent application WO 02/071657. Developed by HRL Laboratories in California, US, the link consists of a laser-based free-space optical system and a radiofrequency (RF) wireless system - both of which work in parallel to ensure point-to-point connectivity. Depending on atmospheric conditions, a control unit will switch between laser and RF transmission, using either a binary switch or a variety of latched levels on an incremental switch. The link may be configured for a variety of networks, including multichannel ring topologies.
Optical modulator offers low-loss electrode design
Codeon of the US is patenting an optical modulator design that minimizes coupling of a desired coplanar-waveguide (CPW) electromagnetic wave with spurious modes in non-active sections of the device (WO 02/063379). The modulator includes an electro-optic substrate and a buffer layer, formed on the surface of the substrate. According to Codeon, the buffer layer is made up of a thin portion, which occupies the active section of the electro-optic substrate (where modulation occurs), and a thicker portion, which overlies the electro-optic substrate in one or more non-active sections. The thinner portion of the buffer layer allows significant electro-optical overlap of the CPW electromagnetic wave with an optical wave propagating within the active section of the substrate. At the same time, the thicker portions of the buffer layer prevent the CPW electromagnetic wave from penetrating into the non-active sections of the electro-optic substrate.
Bidirectional WDM system eyes up metro applications
Seneca Networks of Maryland, US, has developed a bidirectional wavelength-division multiplexing (WDM) architecture that, it says, can be used to create scalable network topologies for metro-area applications (WO 02/065679). At the heart of it all is a bidirectional optical waveguide that carries counter-propagating WDM signals. Several optical nodes are positioned along the waveguide, each one including an optically amplified bidirectional add-drop multiplexer (ADM). Each optical node contains at least one transmitter (for supplying an optical channel added by the ADM) and at least one receiver (for detecting an optical channel dropped by the ADM). By measuring optical launch powers and optical-amplifier gain, it is possible to control the power levels of the optical channels to within a specified range.
Memory-controller circuit is tailored for transceivers
Finisar of the US has filed an international patent application on an integrated memory-controller circuit for a fiber-optic transceiver (WO 02/063800). The controller includes memory (for storing information related to the transceiver) and analog-to-digital conversion circuitry (for receiving a number of analog signals from the module's laser transmitter and photodiode receiver, converting those signals into digital values, and storing the digital data in predefined locations within the memory). Logic circuitry compares one or more of these digital values against limit values, generates "flag" values based on the comparisons, and stores the flag values in predefined locations within the memory. Control circuits subsequently adjust the operation of the laser in accordance with one or more values stored within the memory. A serial interface enables a host device to read from and write to locations within the memory.
By Joe McEntee, Editor-in-Chief, FibreSystems magazine group
• This article originally appeared in FibreSystems Europe October 2002 p11