Fiber-optic Wavelength Research Articles

Amorphous silicon waveguides and light modulators for integrated photonics realized by low-temperature plasma-enhanced chemical-vapor deposition

A new amorphous silicon waveguide is realized by use of amorphous silicon carbon as cladding material. The structure is characterized both experimentally and theoretically, and its application for optical interconnections in photonic integrated circuits on silicon motherboards is proposed. The fabrication process is based on low-temperature (220 degrees C) plasma-enhanced chemical-vapor deposition and is compatible with standard microelectronic processes. Propagation losses of 1.8 dB/cm have been measured at the fiber-optic wavelength of 1.3 microm. A strong thermo-optic coefficient has been measured in this material at this wavelength and exploited for the realization of a light-intensity modulator based on a Fabry-Perot interferometer that is tunable by temperature.

High-isolation demultiplexing in bend-tuned twin-core fiber

By applying a cantilever bend to a twin-core optical fiber wavelength division demultiplexer, isolations of >30 dB have been achieved between channels at 1.33-1.54 /spl mu/m. These bend-tuned TCF's exhibit /spl ges/20 dB isolation over a bandwidth of 32 and 21 nm in the two wavelength windows, respectively. This is significantly better than that typically offered by commercially available, single-stage, tapered coupler demultiplexers. The bend-tuning mechanism is demonstrated experimentally and described theoretically using a coupled local-mode analysis.

Polarization-based optical fiber wavelength filters

Polarization-based in-line wavelength filters have been designed and evaluated. These are compact devices fabricated from single-mode optical fiber possessing high linear birefringence. A minimum passband width of 10 nm has been demonstrated at a passband separation of 60 nm. Both bandpass and bandstop devices can be produced. The filters are constructed from a single strand of fiber, less than 1 m in length, positioned between a pair of polarizers. Rotation of the polarization azimuth at appropriate intervals from the fiber input is achieved by twisting portions of the fiber to induce circular birefringence. Passband widths and separations are selected by choice of the number of twisted sections in the filter, and the lengths and twist angles of such sections.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrooptic sampling evaluation of 1.5 μm metal-semiconductor-metal photodiodes by soliton compressed semiconductor laser pulses

An electrooptic sampling system using soliton compressed pulses from a gain switched laser diode was assembled and used to characterize an InGaAs metal-semiconductor-metal photodetector at the important optical fiber wavelength of 1.55 microns. The measured rise time of the photodiode pulse was 6.5 ps. The pump and probe pulses had a FWHM of 0.6 ps as measured by autocorrelation. The sampling system rise time was evaluated to be 2.0 ps, yielding the estimated intrinsic photodiode rise time of 2.3 ps. By introducing a differential detection scheme and optical filtering, a shot noise limited sensitivity of 0.6 mV/Sqrt[Hz] was achieved. These results represent the fastest rise time, and most sensitive semiconductor laser based, electrooptic sampling system reported to date. >

Study of the crystalline quality of CdTe, CdZnTe and CdMnTe substrates used for liquid phase epitaxy of Cd 0.7Hg 0.3Te

The crystalline quality of epitaxial layers made of Cd 0.7Hg 0.3Te, which is a very good infrared detector at the optimal transmission wavelength (1.3 μm) in optical fibers, is strongly dependent on the crystalline quality of the substrate. Experimental observations, carried out by means of Berg-Barrett topography, cathodoluminescence, etch-pitting, and X-ray double-crystal rocking curve measurements on several CdTe, Cd 0.96Zn 0.04Te, and Cd 0.9Mn 0.1Te substrates confirm that the addition of Zn results in an improvement of the crystalline quality of the CdTe compound. The best results, in this work, were obtained on Cd 0.96Zn 0.04Te material with an etch-pit density of 5×10 4 cm -2 and an X-ray rocking curve linewidth of 25 arc sec. Mn addition, on the other hand, does not show any change in CdTe crystalline quality. Characterization of Cd 0.7Hg 0.3Te layers grown by liquid phase epitaxy (LPE) on two types of substrates (CdTe, Cd 0.96Zn 0.04Te) has demonstrated the better quality of those epitaxial layers grown on the Cd 0.96Zn 0.04Te substrate. This result constitutes an other indication of the improved crystalline quality of the Cd-rich CdZnTe material.

All-fibre Bragg grating strain-sensor demodulationtechnique using a wavelength division coupler

A simple all optical fibre wavelength shift detection scheme, for use with fibre Bragg grating sensing systems, is described. The system is based on the use of a wavelength division coupler designed to exhibit a monotonic dependence of the splitting ratio on wavelength over a 50 nm range.

Determination of monomode fiber buffer properties

Observations of oscillations in bending loss as a function of illuminating wavelength in monomode optical fibers are presented. A model is developed based on the interference between the core-guided mode, and a whispering gallery (WG) mode established by reflection at the buffer-air interface. It is shown that the relative phase of the modes is a function of the dimensions and refractive index of the buffer coating. The phase is determined in experiments where the bend radius and wavelength of illumination are varied, allowing the buffer diameter and refractive index to be determined by a best fit to experimental data. The practicality of this method for the characterisation of buffer properties is discussed. >

Dual wavelength optical fiber HDTV distribution networks using self-synchronization technique and multistar topology

A new optical fiber time-division multiple-access (TDMA) network is proposed for HDTV distributions. It uses two wavelengths to carry optical TDMA and clock signals through the common fibers to each subscriber. At the receiver, both signals are easily separated by using a wavelength division multiplexing (WDM) demultiplexer, and therefore, the frame and time-slot synchronizations are feasibly achieved by using optical fiber delay lines to independently process the separated clock and TDMA signals. This self-synchronization characteristic can be used to improve the network flexibility, which allows one to build a large-scale HDTV distribution network based on a multistar topology. Furthermore, a sensitivity analysis of optical TDMA receivers is carried out. It is shown that, compared with a point-to-point optical fiber digital system, the multi-user optical TDMA system requires a lower extinction ratio to alleviate the performance degradation. >

Analog diversity coding to provide transparent self-healing communication networks

pg 100 diversity coding, as introduced in Ayanoglu et al. (1990), is a method of protection against failures in a communication network or a storage system, which is based on introducing a digital error-correcting code across independent links. This technique makes efficient use of the extra network capacity needed for coding and has the additional advantages of being nearly instantaneous, not requiring a feedback channel, rerouting, or resynchronization. In high-speed (multi Gbps) networks, digital coding will be difficult to implement, and the purpose of the present paper is to demonstrate how diversity coding may be implemented in the analog domain using the discrete fourier transform (DFT). In particular, the authors show that the DFT is a continuous-amplitude maximum-distance separable code over the field of complex numbers when the transform kernel is a prime root of unity. This code can be used to generate self-healing or fault-tolerant communication networks for continuous- or discrete-amplitude signals, as long as continuous-amplitude parity channels are available. The authors describe electrical and optoelectronic implementations, and a signal estimation approach to combat channel noise and thereby improve the performance of the analog diversity coding system. The most important advantage of this technique is in greatly simplifying the encoders and decoders of diversity coding systems for high-speed networks, such as fiber-optic wavelength division multiplexed networks. Application of analog diversity coding to systems with analog sources, such as telemetry systems is also possible.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design and performance of a multiple element slab waveguide spectrograph for multimode fiber-optic WDM systems

A new type of compact (<7 cm/sup 2/) multiple element slab waveguide spectrograph suitable for medium resolution fiber-optic wavelength division multiplexing (WDM) applications in the 700 nm to 900 nm optical band is described. The spectrograph consists of a replicated diffraction grating formed on the convex edge of a multilayer glass-ceramic slab waveguide stack The grating design, based on an aberration corrected derivative of the classic Rowland spectrometer, was first verified holographically, and then implemented by replication from a ruled master grating. A combination of thick-film solder glass glazing, lamination, optical finishing and grating replication was chosen to produce a multiple element spectrograph that enables accurate spectral referencing, and can be interfaced by a passive optical fiber array and detector array alignment procedures.< >

A Limited International Intercomparison of Responsivity Scales at Fiber Optic Wavelengths.

We report here on a recent limited international intercomparison of responsivity scales at wavelengths of interest to the optical communications community. Participants in the comparison were the national laboratories in the United States, the United Kingdom, Germany, and Australia. The wavelengths tested were 1300 and 1550 nm. Data taken at 850 nm are only briefly discussed. The disagreement between the national laboratories’ responsivity scale is comfortably within the uncertainty claimed by each laboratory.

Pilot Study for the International Intercomparison of Responsivity Scales at Fibre Optic Wavelengths

A pilot international intercomparison of spectral responsivity scales at wavelengths important to fibre optics communication was undertaken among national laboratories in the USA, the UK, Germany and Australia. Results are reported for wavelengths of 800 nm, 850 nm, 1 300 nm and 1 550 nm. Based on this study, a larger intercomparison is planned for 1 300 nm and 1 550 nm, using selected germanium photodiodes as transfer standards.

Field analysis of the Cerenkov doubling of infrared coherent radiation utilizing an organic crystal core bounded by a glass capillary

We present a mode field analysis of the second-harmonic electromagnetic wave that radiates from a nonlinear core bounded by a dielectric cladding. With this analysis the ultimate performance of the organic crystal-cored single-mode optical fiber waveguide as a guided-wave frequency doubler is evaluated through the solution of nonlinear parametric equations derived from Maxwell’s equations under some assumptions. As a phase-matching scheme we consider a Cerenkov approach because of advantages in actual device applications, in which the phase matching is achievable between the fundamental guided LP01 mode and the second-harmonic radiation (leaky) mode. Calculated results for organic cores made of benzil, 4-(N, N-dimethyl-amino)-3-acetamidonitrobenzen, 2-methyl-4-nitroaniline, and 4′-nitrobenzilidene-3-acetoamino-4-metxianiline provide useful data for designing an efficient fiber-optic wavelength converter utilizing nonlinear parametric processes. A detailed comparison is made between results for infinite and finite cladding thicknesses.

Transmission Electron Microscopy of InP-Based Compound Semiconductor Materials and Devices

InP/InGaAsP-based heteroepitaxial structures constitute the major optoelectronic devices for state-of-the-art long wavelength optical fiber communication system.s Future advanced device structures will require thin heteroepitaxial quantum wells and superlattices a few tens of {angstrom} or less in thickness, and lateral dimensions ranging from a few tens {angstrom} for quantum dots and wires to a few {mu}m in width for buried heterostructure lasers. Due to the increasing complexity of the device structure required by band-gap engineering, the performance of these devices becomes susceptible to any lattice imperfections present in the structure. Transmission electron microscopy (TEM), therefore, becomes the most important technique in characterizing the structural integrity of these materials. Cross-section transmission electron microscopy (XTEM) not only provides the necessary geometric information on the device structure; a careful study of the materials science behind the observed lattice imperfections provides directions for optimization of both the epitaxial growth parameters and device processing conditions. Furthermore, for device reliability studies, TEM is the only technique that unambiguously identifies the cause of device degradation. In this paper, the authors discuss areas of application of various TEM techniques, describe the TEM sample preparation technique, and review case studies to demonstrate the power of the TEM technique.

Crosstalk penalties in a bidirectional fiber-optic WDM system

Crosstalk power penalties were calculated for a bidirectional fiber-optic wavelength division multiplexed (WDM) system (622 Mb/s at 1300 nm in one direction and 155 Mb/s at 1550 nm in the other) using the system simulation program Simulation of Fiber-Optic Communication Systems (SIFOCS). Nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats were investigated with the result that, in most cases, the power penalty was shown to depend only weakly on individual system properties and is close to the values found in the literature, but there are exceptions where it may be greater than usual (e.g. at 622 Mb/s RZ). These can be detected and investigated with the methods reported. The crosstalk power penalty becomes excessive only for signal-to-crosstalk power ratios well below 10 dB and is negligible for values greater than 15 dB. The calculation methods used can be easily adapted to other systems, e.g. to systems with more closely spaced wavelengths. >

Attenuation coefficient and effective cutoff wavelength of the LP/sub 11/ modes in curved optical fibers

The measured attenuation coefficient of the LP/sub 11/ modes in curved optical fibers for various radii of curvature in the wavelength region below the cutoff wavelength for LP/sub 11/ modes is discussed. The experimental results indicate that the attenuation coefficient may be strongly enhanced at certain wavelengths due to phase-matched coupling between the LP/sub 11/ modes of the fiber core and whispering gallery modes of cladding. Implications for measurements of the effective cutoff wavelength in optical fibers are discussed. >

Echelon grating multiplexers for hierarchically multiplexed fiber-optic communication networks

Echelon gratings have many beneficial properties when used as the dispersing mechanism of a fiber-optic wavelength multiplexer including high optical dispersion, high optical efficiency, greatly reduced sensitivity to polarization, simultaneous utility on many wavelength bands, and a capability for hierarchical multiplexing. The use of echelon multiplexers in a hierarchical environment is discussed, and a prototype echelon multiplexer is constructed and used to demonstrate the unique capabilities of this device for creating wavelength division multiplexing systems.

Advance of optoelectronic devices for long wavelength optical fiber communication in china

Abstract The advance of optoelectronic devices for long wavelength optical fiber communication in China is reviewed. The main features of the long wavelength semiconductor lasers and photodetectors are presented.

Mie scatter in the KFCaF 2AlF 3BeF 2 glass system

Halide glasses are of interest for long wavelength (> 1 μm) optical fiber applications because of potential low Rayleigh scatter and multiphonon losses. However, due to the ionic character of the materials involved, precipitation of one or more phases may readily occur in compound glasses. It is shown, herein, that there are certain quasi-stable regions in the KFF 2AlF 3BeF 2 system that may permit injection from the molten state or pulling from preforms without nucleation of precipitates.

Losses in GaInAs(P)/InP and GaAlSb(As)/GaSb lasers - The influence of the split-off valence band

GaInAs(P)/InP and GaAlSb(As)/GaSb are interesting material systems for long wavelength optical fiber communication. However lasers fabricated from these materials exhibit a substantially higher temperature dependence of the threshold current than GaAs/ GaAlAs lasers ("T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> -problem"). lntervalence band absorption and CHSH-Auger-recombination have been suggested as two possible causes for the strong temperature dependent losses in long wavelength lasers. Both mechanisms, if present, should lead to a population of the split-off valence band. In GaInAsP/InP lasers, we have studied this population by directly observing the radiative high-energy recombination of electrons with holes in the split-off valence band. In the case of the band structure of GaAlSb(As), the band gap energy E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> is close or equal to the spin-orbit splitting energy Δ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> , which favors hole-Auger recombination and intervalence band absorption, as confirmed by our experimental results.