Submarine Systems

The reliability required of undersea communications systems differentiates them from the systems developed for terrestrial applications. Repairs to undersea systems are extremely expensive and require many days to complete. Therefore, for hardware to be placed under the sea, the primary design focus is on reliability. The demand for highly reliable systems leads to a desire for simplicity, limits the complexity of designs and hence the features available, and restricts the choices available for...

Optical Waveguide Modes

The theory of dielectric waveguides is well described in the literature (Snyder and Love 1983 Marcuse 1982, 1991 Tamir 1990 Marz 1994). In this section, we summarize several topics important to the design and simulation of planar waveguide devices, and emphasize the physical principles. An optical waveguide directs the propagation of an electromagnetic field through a nearly lossless doped silica medium. We refer to the propagating field as the lightwave. The field obeys Maxwell's equations....

System Requirements For Wdm Sources

WDM systems are initially proving economical for long-haul applications, where they allow not only lower cost repeaters using EDFAs without regeneration, but also the ability to upgrade gracefully at the terminals by adding incremental capacity with each added channel. Because these applications entail long transmission spans, the initial applications of WDM face, in many instances, all the requirements noted previously for amplified transmission, in addition to those related to WDM. However,...

Volume I1ib

Erbium-Doped Fiber Amplifiers for Optical Communications (Chapter 2) A large part of the economic advantage for lightwave systems stems from the development of the diode-pumped EDFA, which replaced the more expensive and limited electronic regenerators. By remarkable coincidence, the EDFA provides near noise-free gain in the minimum-loss window of silica fiber at f550 nm. It provides format-independent gain over a wide WDM band for a number of novel applications beyond its original use in...

Info

Saturation, erbium-doped liber amplifier. 16-18 for different pump powers. 17 Selective area epitaxy, integrated laser-EA modulator. 128 Selective area etching longitudinal index control, 187-188 semiconductor laser. 187-188 Selective area growth bandgap factors. 182-184 mask. 180-186 problems, 184 channel mesa buried heterostructure device. novel class of light source. 186 semiconductor laser, 179-186 strain, 184 Semiconductor optical switching, 474, 477-479 switch element, 474, 477-479...

Intrinsic Loss Mechanisms Versus Strain

So far, we ascribed the beneficial effects of strain shown in Fig. 5.4 to the reduction of the hole effective mass caused by the modification of the valence band structure. Another possibility is that strain has in some way reduced the internal nonradiative losses in the cavity caused by processes such as Auger recombination (AR) and intervalence band absorption (IVBA). Figure 5.5a illustrates the IVBA process using solid arrows. A photon emitted during the lasing process may be reabsorbed by a...

Receiver Wdm Considerations

WDM complicates the system design, and the role of the optical filter changes dramatically, but the remainder of the receiver is largely unaffected. Among the challenges facing the optical filter on WDM systems are the following The optical filter must perform the same ASE noise reduction that it does in single-carrier systems. It must reject unwanted energy from adjacent carriers. This requires large out-of-band rejection near the desired passband for closely spaced carriers. Achieving high...

Background And Motivation

Time and time again, advances in fiber optics and integrated optics, driven by the compelling economics of ever higher capacity and longer distances between regenerators, have created new possibilities and opportunities for each other. We may begin by citing, for example, the complementary breakthroughs in room-temperature laser diodes and low-loss optical fibers, which occurred in the early 1970s and set the stage for revolutionizing longdistance telecommunications. These pioneering works and...

Linear Arrays

One-dimensional arrays of VCSELs coupled to multimode fiber ribbon cables have been used in prototype parallel data link applications 110-112 . Some illustrations of these results are shown in Fig. 6.30. As indicated, driver and receiver electronics were also developed. These links take advantage of the fact that entire linear arrays of VCSELs can be simultaneously aligned to the elements of a fiber ribbon cable by aligning only the end two lasers and fibers. Thus, these linear arrays...

Important Transmitter Characteristics

There are three major transmitter characteristics that are important in the design of multigigabit laser transmitters used in IM DD systems (1) What is the minimum acceptable extinction ratio for the system (2) What are the requirements for the modulated pulse shape In the next section each of these characteristics is discussed in greater detail An important transmitter parameter is the laser extinction ratio, which is the ratio between the unmodulated optical power and the modulated optical...

Piz

This is not so small, but with quantum-confinement effects used to reduce the wavelength, the lowest electron energy rises, which reduces the net barrier to about 100 meV at 610 nm. With a larger A1 content in the barriers, the conduction band offset is actually reduced, because the indirect bandgap is offset in favor of the valence band. To further improve confinement. one possible approach is to use multiple quantum barriers 36 , as have been applied with some success in edge-emitters. To...

Noise Figure

The amplification of the EDFA is inescapably accompanied by a background of amplified spontaneous emission (ASE). ASE arises when light emitted by spontaneous decay of excited erbium ions is captured by the optical fiber waveguide and then amplified in the EDFA. This ASE background adds noise that degrades amplified signals. The noise figure, defined as the signal-to-noise ratio (SNR) at the output divided by that corresponding to the shot noise of the signal at the input, is a measure of the...

Inline Amplifier

Finally, we consider in-line amplifiers used as repeaters to boost the signal power and extend the transmission distance between digital regenerators. Because in-line amplifiers are used to extend the transmission distance, high output power is required. However, the signals entering in-line amplifiers are weak, so that noise added by each in-line amplifier is important. Therefore, a low noise figure is also required. Thus an in-line amplifier must be both a good preamplifier and a good power...

Mask Layout

As discussed in Section II.C, the geometry of waveguide cores is patterned by the photo-lithographic mask through the photolithography and chemical etching processes. Mask layout connects the optical design to the device fabrication by generating the geometric patterns required by the waveguide device in a format suitable for mask fabrication. Some tools and methods for mask layout are adapted from the electronic integrated circuit industry. However, because of the different propagation...

Terrestrial System Monitoring

Traditionally, systems that employ repeaters have used some form of remote performance monitoring for fault isolation and as an early warning of pending service affecting degradations. Systems that employ chains of fiber amplifiers are not immune to degradations, such as severed fibers or failed pump lasers. To detect remote failures, a method of sensing the failure locally must be devised, and a means to transmit that information to a remote terminal must be established. In some terrestrial...

Acoustooptic Tunable Filters

Tunable filters based on acoustooptic TE < - TM conversion exhibit optical frequency characteristics similar to those of EOTFs, except the TE- and TM-polarized modes are coupled by a surface acoustic wave through the elastooptic effect. Such acoustooptic tunable filters (AOTFs) offer extremely wide tuning ranges and exhibit the unique ability to add or drop several wavelength channels simultaneously. Figure 9.36 shows an example of such a filter on ,v-cut. v-propagation LiNbO,, where an...

Electrooptic Tunable Filters

The electrooptic tunable filter EOTF of Fig. 9.34 is fabricated on x-cut, y-propagation LiNb03 and employs a periodic electrode structure with interdigital finger electrodes of period A, which induce a spatially periodic electric field, E, in the waveguide that couples the TE- and TM-polarized modes by means of the r51 electrooptic coefficient V51 28 X 1012 m V . The TE lt - TM mode conversion is most efficient when the period of the electrode fingers, A, matches the spatial beat period of the...

Acknowledgment Of Optical Fibre

The progress we summarized in this chapter implicitly represents the work of many researchers and developers around the world, and in this short space we were unable to do proper justice to even a fraction of their contributions. We are especially grateful to our colleagues working in this field because each has made a contribution to advancing the technology and has had an influence on our own work. It is our sincere pleasure to acknowledge, in particular, our closest collaborators of many...

References

Dragone, R. C, Kistler, and M. A. Milbrodt. 1993. Broadband array multiplexers made with silica waveguides on silicon. J. Lightwave Tech. 11 212-219. Adar, R C. H. Henry, R. F. Kazarinov, R. C. Kistler, and G. R. Weber. 1992. Adiabatic 3-dB couplers, filters and multiplexers made with silica waveguides on silicon. J. Lightwave Tech. 10 46-50. Adar, R., C. H. Henry, R. C. Kistler, and R. F. Kazarinov. 1992. Polarization independent narrow band Bragg reflection gratings...

Pump Schemes

The most essential component required for EDFAs, after the erbium-doped fiber, is a pump source to supply light at the correct wavelength i.e., one of the erbium pump bands with adequate power to drive the amplifier. The pump sources for the first EDFA demonstrations were an argon ion laser at 514.5 nm1 and a 670-nm dye laser pumped by an argon ion laser.2 These lasers are complicated, are expensive, and occupy a large fraction of an optical bench. The pump source for a practical EDFA should be...