Lightwave Components Research Articles

Frequency domain optical network analysis using integrated optics

Frequency domain based measurements of optical networks and components are reviewed. A measurement system for performing optical network analysis is described in detail. The application of a Ti:LiNbO/sub 3/ Mach-Zehnder modulator in such a network analyzer is discussed. The integrated optic modulator makes it possible to characterize both the amplitude and phase of the modulation response of lightwave components. The modulator operates at both 1300 and 1550 nm. Design considerations and tradeoffs are described to obtain the wide wavelength coverage, as well as low switching voltage and a stable frequency response which can be calibrated. Device pigtailing, packaging, and reliability are discussed as they relate to overall instrument reliability. Stability considerations including bias drift and acoustic resonances are detailed for both x- and z-cut modulators. >

Fiber optic microcellular radio

A distributed antenna system consisting of optical fiber connected canisters is proposed to replace or supplement the base station antennas required for cell splitting of growing cellular mobile radio systems. The end-to-end linear transmission of RF signal voltage can be maintained over the wide dynamic range of mobile radio. The technical feasibility of multiplexed subcarrier transmission using available lightwave components has been verified by signal-to-noise ratio and intermodulation distortion measurements. Measurements of a two-way audio link over both simulated and real radio paths have demonstrated the compatibility of a prototype lightwave transceiver, designed for the canister, with the existing base station and mobile equipment. >

Lightwave scalar network analyser employing optical heterodyne detection

A new system for measuring the transmittance and reflectance characteristics of lightwave components is described. By employing frequency-tracked narrowband detection after optical heterodyning, a resolution bandwidth as narrow as 3 MHz with a dynamic range of 50 dB is achieved at a scanning speed of 1 GHz/s. The shot-noise-limited sensitivity of the system is also discussed.

Optical measurements based on RF modulation techniques

A characterization concept is introduced for high-speed lightwave components based on high-frequency RF modulation of the test signals. The concept is explained by using the example of optical transmission measurements covering optical loss, modulation bandwidth, and length measurements. Optical reflection measurements are investigated with the capability of separating multiple reflections. Responsivity measurements of electrooptical devices such as lasers and photodiodes are investigated. The described concepts are utilized in the first commercially available instrumentation systems covering a modulation bandwidth up to 20 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave-frequency carriers on optical fibres

The use of microwave carrier frequencies in wideband optical-fibre networks is a promising new approach to the distribution of voice, data and video services to subscribers. This paper discusses the general features and design rules of microwave multiplexed wideband optical-fibre systems and reports on several specific systems developed at GTE Laboratories. These include transmission of 60 frequency modulated (FM) video channels multiplexed on carriers in the 2.7-5.2 GHz band, and the transmission of 20 frequency-shift-keyed (FSK) 100 Mb s -1 digital video channels in the 2-6 GHz band. A hybrid system is also described that transmits a 100 Mb s -1 baseband signal in addition to the 60 FM video channels. These transmission experiments illustrate the large bandwidth capability and design flexibility of microwave-multiplexed lightwave systems. As lightwave systems push towards larger and larger bandwidths, microwave-multiplexing may emerge as the more natural way to exploit the enormous bandwidth of lightwave components.

Optical Reflection Measurement System Using A Swept Modulation Frequency Technique

A measurement system has been developed capable of mea-suring reflected optical power as low as 0.0025% with a spot size diam-eter of 24 Am. One application for this system is the characterization of small-area photodetectors. The operation of the measurement system is simple, allowing the operator to quickly make multiple reflection measurements, and it does not require a darkroom. The measurement system merges a microscope, for visual alignment and focusing of the laser beam, with a lightwave component analyzer using modulation vec-tor error correction. A measurement comparison between the analyzer-based system and a power-meter-based system showed that each sys-tem can measure reflections as low as 0.0025%. However, the analyzer-based system offers the advantage of identifying the location and magnitude of system reflections. The system operates at a wavelength of 1310 nm.

Microwave-multiplexed lightwave systems: A new approach to wideband networks

For the last fifteen years the attention of the fibre-optic community has been principally focused on developing baseband digital transmission system for transmitting time-division-multiplexed voice channels over long distance and interoffice routes. Attention has now shifted to extending the fibreoptic network to the subscriber loop and to providing a multitude of new services through lightwave networks. Based on the results reviewed here, it is apparent that microwave-multiplexing techniques provide a new and attractive way to transmit wideband services over optical fibre. By allowing lightwave systems designers to use and combine the complete range of available electronics, including both analog and digital electronics, and both baseband and microwave techniques, a great number of new possibilities arise for exploiting the bandwidth of lightwave components and for designing wideband lightwave networks. Over the next few years the microwave-multiplexing techniques described in this article may fundamentally change the way we use lightwave technology.

Subcarrier multiplexing for multiple-access lightwave networks

This paper describes the applicability of subcarrier multiplexing to lightwave multiple-access networks. It is shown how currently available microwave and lightwave components can be used, by using subcarrier multiplexing, to provide high-capacity networks. For example, the proposed multiple-access network can support 1024 users at a continuous bit rate of 1.5 Mbit/s, per user.

Trends in U.S. Broad-Band Fiber Optic Transmission Systems

Fiber optic media are rapidly penetrating the telecommunications network. They are used as undersea and terrestial trunk lines, central-office loops, optical data links, and will eventually be included within the distribution plant which connects directly into individual premises. The rapid implementation of lightwave systems is occurring because the high bandwidths and low losses of optical fibers enable broad-band communication services to be provided between widely spaced repeaters and also allows users to upgrade currently installed systems to meet future needs. This paper will describe current applications and show how future trends will depend upon the continuing evolution of lightwave components and optical fiber designs.

Improved distributed-index planar microlens and its application to 2-D lightwave components

A recent improvement of a 2-D array of distributed-index (DI) planar microlenses is presented to demonstrate a 2-D integrated optical component using a planar microlens array. These components are made by stacking planar microlens arrays and other planar optical devices. The improved planar microlens has f = 2.0 mm, a N.A. = 0.23, and its spherical aberration is very small. A fiber coupler is demonstrated. From a preliminary experiment, it is shown that the coupling loss of each channel is <0.5 dB for coupling 50-micron core DI fibers.

Long-wavelength optical fiber communication

Recent research on long-wavelength lightwave communication utilizing the wavelength region between 1.3 and 1.6 µm is reviewed with an eye toward future system development. The attraction of the long-wavelength region is the availability of the ultimately low-loss and wide-band features of the silica fiber, where minimum loss is 0.27 dB/km at a wavelength of 1.3 µm and 0.16 dB/km at 1.55 µm. The single-mode fiber has found its first significant applications in long-wavelength systems. The specific characteristics of lightwave components are discussed with focus on physical fundamentals. The practical performance of fibers and lightwave devices is surveyed. The dynamic properties of long-wavelength laser diodes are discussed in relation to fiber characteristics. The noise characteristics of long-wavelength detectors are considered for the purpose of specifying the repeater spacing. Some system studies are reviewed, for example, 1.3-µm-wavelength lightwave systems, which have demonstrated bandwidth-distance products of about 40 GHz ċ km. Various approaches to extend the capacity of long-wavelength lightwave transmission are given. In the future, the 1.5-µm wavelength system could operate at the lowest loss wavelength region extending from 1.5 to 1.65 µm. Much higher performance, for example, bandwidth-distance products of 185 GHz ċ km, achieved by further continuation of research and development on lightwave sources as well as fibers. Because of the author's familiarity with work in Japan, that work is emphasized and most frequently cited.