Optical Transmission Characteristics Research Articles

OPTICAL SOLITON COMMUNICATION RESEARCH IN CHINA

The optical soliton communication research in China, which began in 1984, is reviewed briefly in this paper. The main theoretical works include: optical soliton transmission characteristics, optimal design of optical soliton communication system and theories related to the key components such as soliton sources, EDFA, etc. An experimental system with 2.5 Gb/s, 21 km has been developed. Possible developments in the near future is viewed.

Projection moire´ deflectometry for the automatic measurement of phase objects

A computer-based method for measuring the local refractive index gradient of phase objects using the projection moire´ technique is presented. A phase object is placed in front of the projected grating pattern. The image of the projected grating pattern deforms in accordance with the variation of the refractive index of the phase object. The moire´ fringe is generated by superimposing two images of the projected gratings pattern (the original pattern and the deformed pattern). The optical transmission characteristics of projection moire´ fringe is discussed. The moire´ deflectogram is analyzed by Fourier filtering and the phasemeasuring technique.

Elliptically birefringent optical fiber transmission characteristics

Abstract This paper presents a rigorous analysis of spun hi-bi (highly birefringent) fibers, loosely categorized as elliptically bi fibers, via the initial value problem approach. Two kinds of transmission problem are treated. In the single-eigenmode transmission regime, it is found that the major technological difficulty inherent to spun hi-bi fibers concerns excitation of the eigenmode, which strictly requires that the launched light be exactly oriented in conformity with one or the other local principal axes of the fiber and, meanwhile, that the ellipticity of the launched light be exactly equal to the eigen-ellipticity of the same fiber. In the second kind of problem that involves the interaction of two eigenmodes, a basic result is derived to show that an arbitrary polarization mode of excitation will reproduce itself in integer multiples of the local beat length. Such a kind of transmission regime is relieved of the excitation difficulty but, because of being severely length-sensitive, is inherently...

Transmission characteristics of copper mesh at 118.8 μm

An experimental investigation of the optical transmission characteristics of an electroformed copper wire mesh at an angle of 45° to incident radiation at 118.8 μm is reported. It is shown that the transmission coefficient is highly sensitive to the input beam polarization and the results obtained are in good agreement with those reported elsewhere. A comparison, however, with previously reported results for a mesh of the same type shows that microscopic differences in the physical dimensions of the mesh give rise to sizeable differences in the magnitude of the transmission coefficient, which is an important consideration in the design of multi-mesh beam-splitting systems when precise beam splitting ratios are required.

Some recent developments in glasses for nonlinear optics

The development of glasses with high χ(3) values is discussed. The glasses considered contain oxides such as PbO, Bi2O3, La2O3, Nb2O5 and TiO2 in combination with B2O3 or Ga2O3 to encourage glass formation. New glass-forming systems have been identified, in particular the PbO-Bi2O3-TiO2 system, and fundamental properties such as refractive index dispersion curves, optical transmission, and crystallization characteristics have been determined. Some glasses have predicted n 2 values up to 35 times that for silica, and this figure has been confirmed by experiment.

Transparent Conducting Films Grown By Pulsed Laser Deposition

AbstractWe have studied the properties of two types of transparent conducting oxides grown by pulsed laser deposition (PLD) on quartz substrates. We have grown films of ITO with resistivity as low as 250 μΩ-cm and with absorption coefficient < 600 cm−1 throughout the visible spectrum. Even films deposited at room temperature can have ρ < 500 μΩ-cm, although the optical transmission characteristics are worse than those of commercially available ITO. Important parameters governing film quality include the oxygen partial pressure during film deposition and substrate temperature. GaInO3 is a recently identified transparent conducting material which is structurally distinct from ITO. Films have been grown with no intentional dopants and with either Ge substitution for Ga or Sn substitution for In. Doping concentrations as high as 10 at. % have been studied. There is no evidence for dopant segregation. Films with resistivities as low as 3 μΩ-cm have been achieved, and the absorption coefficient can be less than 500 cm−1 throughout the entire visible spectrum.

Room temperature spontaneous emission in five-micron-long Fabry–Pérot vertical cavities

Five-micron long AlGaAs/GaAs Fabry–Pérot vertical cavities with thin GaAs active regions of two different thicknesses are analyzed both theoretically and experimentally in terms of their optical transmission characteristics, spontaneous radiation patterns, and spontaneous spectral emission characteristics. The effects on spontaneous emission of the precise placement of the GaAs active region and also the thickness of this region, as compared to the emitted wavelength, are demonstrated. The measured results are compared with theoretical calculations which are based on the first-order perturbation field theory presented in an earlier publication. Good agreement is found in the comparison between the theoretical predictions and the experimental results, and indicates the controllable spontaneous emission in these long vertical cavities.

Modification of the optical spectra of glass by metal ion implantation

We have carried out some exploratory investigations of the effect of metal ion implantation on the optical transmission characteristics of glass. The implants were done using the vacuum-arc-based high current metal ion implantation facility developed at Berkeley. The implanted doses were from 3 × 10 16 to 1 × 10 17 cm −2 and the energy was mostly 60 keV. A range of different metal ion species was used, including C, Al, Si, Ti, Fe, Ni, Cu, Y, Ag, Pt and Au. We used soda lime-silica glass (window glass), boron-silica glass (microscope slides), and tin oxide coated glass. The transmission of the glass samples to optical radiation in the wavelength range 300 to 2400 nm was measured. Here we outline the procedure and describe the results of the optical transmission measurements.

Partially exposed polymer dispersed liquid crystals for boundary layer investigations

A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.

Effects of space exposure on optical filters

Optical transmittance characteristics of nine optical filters were remeasured after nearly 6 years in space aboard the NASA Long-Duration Exposure Facility. Three different filter types were included. In general, transmittance decreased for most filters. The center frequency and bandpass of a narrow-band filter under an aluminum cover were unchanged, while narrow-band filters exposed directly to the space environment tended to show a shift in center frequency and increased bandwidth. A pair of infraredreflecting mirrors exhibited reduced transmittance in the visible, with a mirror under an aluminum cover less degraded than a mirror exposed to space. The bandpass was unchanged for both of these mirrors. Neutral density filters showed a slight increase in transmittance for an uncovered filter; essentially no change for the filter under the aluminum cover.

Wide-gap semiconductor InGaN and InGaAln grown by MOVPE

We have achieved InGaN growth on sapphire substrates at temperatures substantially higher than conventional growth temperatures for InGaN. When the growth temperature was changed from 500 (conventional) to 800° C (this work) in InGaN, the x-ray diffraction line width (full width at half maximum) decreased from 100 to 30 min. At 77 K, edge emission was observed in PL. In order to further improve crystalline quality, we have investigated ZnO as a lattice-matching substrate. First, the surface treatment and the resistance to the reducing atmosphere at high temperatures was briefly investigated. We report the first successful lattice-matched growth of InGaN. The x-ray diffraction line width of InGaN grown on ZnO was about 20% smaller than that of films grown on sapphire substrates, thus using lattice-matched substrates was shown to have an effect on improving the crystalline quality of InGaN. Single crystal InGaAlN has been also realized on sapphire substrates. The indium, gallium and aluminum contents were 2.2, 22.5 and 74.3%, respectively. The optical transmission characteristic of this InGaAlN was measured.

Observation of the optical analogue of quantized conductance of a point contact

DIFFRACTION of light by an aperture is a well-known manifestation of the wave nature of light. The most familiar case is that of an incident plane wave, which is diffracted into a spatial pattern that is sensitive to the properties of the aperture: the ratio of transmitted power to incident flux (the transmission cross-section σ) depends in a complicated way on the aperture area A (refs 1–3). For diffuse (that is, isotropic rather than plane-wave) illumination, however, the situation is much simpler4: in three dimensions, σ increases with A in a series of steps of equal height λ2/2π (where λ is the wavelength of the light), and is thus independent of the detailed aperture shape. A similar simplification occurs for two-dimensional diffuse illumination of a slit: the transmission cross-section per unit slit length increases in stepwise fashion as a function of the slit width W, with steps of height λ/2 occurring whenever W = nλ/2 (n = 1,2,3,…)—that is, whenever a new mode is enabled in the slit. Although the optical transmission characteristics of slits have been studied extensively for plane-wave illumination5–8, we know of no investigation of this predicted staircase dependence for diffuse illumination. Here we report the observation of such an effect, and suggest that it may play a part in any process of wave propagation through a constriction.

Femtosecond soliton transmission in 18 km-long dispersion-shifted, distributed erbium-doped fibre amplifier

Femtosecond optical soliton transmission characteristics in a dispersion-shifted, distributed erbium-doped fibre amplifier as long as 18.2 km have been investigated. The erbium fibre has a dual shape core structure with a doping concentration of 0.5 ppm. Solitons (A = 0.7−1.2) with a pulse width of about 450 fs have been successfully transmitted, and even a slight narrowing was observed. When the soliton width was reduced to 260 fs, the output pulse width always broadened up to around 470 fs.

Performance of lightwave systems incorporating multilongitudinal mode laser and optically preamplified receiver combinations

The performance of optical communication systems employing multilongitudinal mode laser and semiconductor laser preamplified receiver combinations is investigated theoretically, emphasis being placed on the influence of mode partition noise (MPN). Two types of MPN are considered in the analysis: one owing to wavelength-dependent fibre dispersion and the other owing to the wavelength-dependent attenuation mechanism associated with both the amplifier gain and optical filter transmission characteristics. To reduce the influence of amplifier gain ripple and to ensure high receiver performance the mode spacing and the centre mode wavelength of the laser source may need to match closely those of the amplifier, especially for high internal amplifier gains and substantial facet reflectivity. For example, for 1% amplifier facet reflectivity, 30 dB internal optical gain, and 3 nm half-spectral-width laser the receiver sensitivity degrades by 5.1 dB when the lengths of the laser and the amplifier differ by 5%. In contrast with 0.1 and 0.01% reflectivity this reduces to 1.95 dB and 0.4 dB, respectively. We also show that for multimode laser operation there is an optimum bandwidth for the bandpass optical filter at which the required detectable optical power for a given bit error rate (BER) is minimum. Operating with filter bandwidth less than this optimum value will degrade dramatically the sensitivity and may, even in the absence of fibre dispersion, lead to a BER floor in the presence of MPN. The analysis presented here may be used to provide guidelines for the design of optical systems based on laser amplifiers and multimode or nearly single mode laser sources.

Anisotropic transport and optical properties of superconducting (La1-xSrx)2CuO4single crystal thin films

Abstract An experimental study on the resistivity, Hall coefficient, upper critical field, and optical reflection and transmission characteristics is described for single-crystalline superconducting (La1-xSrx)2CuO4 thin films epitaxially grown on SrTiO3 single crystal substrates by rf magnetron sputtering. These properties exhibit pronounced anisotropy between the c-axis direction and the Cu-O plane. The characteristics are consistently explained from the point of view of the two-diemensional (2D) electronic structure. The most noteworthy implication of the experimental results is that the transport along the c-axis is far from an itinerant picture. This leads to the idea that the superconductivity in the series of cuprate materials is caused by the 2D electronic system arising from the Cu-O planes, and some interactions between them, which is not possibly due to itinerant carriers.

Performance of optically preamplified direct detection receivers in presence of laser chirp. Part 2: Near travelling-wave and Fabry-Perot amplifier cases

For pt.I see ibid., vol.136, no.5, p.249-55 (1989). The paper is concerned with performance degradation caused by laser chirp for optical receivers incorporating semiconductor laser preamplifiers with nonzero facet reflectivity. Transmission at 4 Gbit/s through a single-mode fibre (SMF) is specifically simulated, taking into account the interaction between laser wavelength chirp and both fibre chromatic dispersion and the optical amplifier transmission characteristics. The results indicate that the penalty, arising from the transiently varying mismatch between the instantaneous laser wavelength and the peak gain-wavelength of the amplifier, has strong dependence on both amplifier gain G/sub 0/ and facet reflectivity R, and may lead to severe performance degradation even in the absence of fibre chromatic dispersion. Biasing the laser source well above threshold-to reduce chirp-does not guarantee a reduction in the dynamic mismatch penalty, and it leads to a higher extinction ratio penalty which is again found to be an increasing function of both G/sub 0/ and R. To reduce the mismatch penalty the amplifier peak gain-wavelength should be tuned to be slightly shorter than the laser CW wavelength. Using this approach a 0.7 AA detuning can offer more than a 20 dB reduction in the mismatch penalty for Fabry-Perot amplifiers (FPAs) operating at high optical gain.

Zinc sulphide films doped with terbium chloride and samarium chloride, prepared by spray pyrolysis

Undoped, TbCl3-doped and SmCl3-doped zinc sulphide films have been prepared by the spray pyrolysis technique using air as the carrier gas at atmospheric pressure. The doped films show strong photoluminescent emission with a dominant peak at about 460 nm. This peak is characteristic of chlorine-doped zinc sulphide phosphors. The films have poor crystallinity with a cubic crystalline structure. The optical transmission characteristics of these films show an absorption edge shifted to shorter wavelengths compared with those of the undoped films.

Silicon thin films for optoelectronic temperature sensors

The optical transmission characteristics of polycrystalline thin films of silicon are reported with a view to fabricating a compact, intensity-modulated, opto-electronic temperature sensor for real-time temperature measurement in industrial environments and inside high-voltage electrical machines.

Electromagnetic transmission and reflection characteristics of anisotropic multilayered structures

A rigorous electromagnetic analysis method, using a 4 × 4 matrix formulation in combination with discrete Fourier-transform techniques, is presented as a straightforward way of analyzing the optical transmission and reflection characteristics of anisotropic multilayered structures. Three examples illustrating the method are presented. First, the previous ellipsometric and polarimetric work of Zander et al. [ Optik70, 6 ( 1985)] is extended to cases in which coupling between orthogonally polarized plane waves exists at interfaces. Second, Williamson’s multiple-pass birefringent spectral filter [ J. Opt. Soc. Am.61, 767 ( 1971)] is reevaluated; results including and excluding interference effects are presented. Third, the design of a new, very-narrow-band (typically 0.01 nm), tunable spectral filter called the Fabry–Perot/Šolc filter is introduced. Several versions of the Fabry–Perot/Šolc filter, each employing different materials, are analyzed. One version exhibits a total tuning range of 40 nm, and another version has an effective finesse of approximately 1300.

Physical properties of sapphire fibretips for laser angioplasty

The physical properties of sapphire contact probes were examined with respect to their use in laser angioplasty. The rounded and bullet-shaped probes are mechanically atraumatic and provide tactile feedback during laser angioplasty. The optical transmission characteristics of the flat, rounded and bullet-shaped probes were measured and the propagated laser beam profiles photographed in air and water. These properties are largely wavelenght independent in the small part of the spectrum currently used for laser angioplasty. Sapphire contact probes may heat up from direct absorption of laser light at the interfaces, but they probably also heat up by conduction from the heated tissue with which they are in contact. The rounded and bullet shaped probes focus light to a rather diffuse waist in air, but in water this focusing effect is lost. The divergence angle of the bare fibre is reduced in water. Transmittance characteristics depend on surface reflection, absorption, probe shape and surface smoothness. The flat probes transmitted 85% of the incident light, but the rounded and bullet probes absorbed and scattered almost half of the light.