Short-wavelength Band Research Articles

A Partial Double-Pass S-Band Erbium-Doped Fibre Amplifier

An efficient and low noise short wavelength band erbium-doped fibreamplifier (S-band EDFA) is proposed and demonstrated using double-passconfiguration. This amplifier provides a gain of 1500 nm signal as highas 26.9 dB, which is 9.6 dB higher than the two-stage single-passamplifier. The corresponding noise figure obtained is 7.5 dB, which isof the same level as in the single-pass amplifier and more than 2 dBlower than the previously reported double-pass amplifier [IEICEElectron. Express 2 (2005) 182]. The gain enhancement is due to thedouble pass-propagation of the test signal in the second stage, whichincreases the effective erbium-doped fibre (EDF) length. The low noiseis attributed to the optical circulator between EDFs, which preventsthe backward amplified spontaneous emission from propagating into theinput part of the amplifier. The proposed amplifier is expected to playan important role in the development of a practical S-band EDFA.

An efficient S-band brillouin erbium fiber laser with additional EDFA

A short wavelength band brillouin–erbium fiber laser (S-band BEFL) with enhanced characteristics is demonstrated using an additional erbium-doped fiber amplifier (EDFA) in the sub-loop of the laser system. Compared with the conventional BEFL without the additional EDFA, the enhanced BEFL has improved the number of channels as well as the flatness of the brillouin Stoke's peak power. By incorporating a double-pass EDFA, a stable output laser comb up to 8 channels was obtained at 1503 nm wavelength region with peak power variation for the first three Stokes is reduced from 30.9 to 5.4 dB. The incorporation of additional EDFA also increases the tuning range of the BEFL, which the maximum tuning range of 1.8 nm was obtained with the single-pass scheme. The S-band BEFL has constant spacing of 0.09 nm or 11 GHz, which has a potential application in dense wavelength division multiplexed system.

Luminescence of crystals of divalent tungstates

Crystals of divalent tungstates are characterized by two main luminescence spectral ranges: a short-wavelength (blue) luminescence band in the range 390–420 nm and a group (often two groups) of longer wavelength (green) bands in the range 480–520 nm. For crystals of calcium, strontium, barium, cadmium, magnesium, zinc, and lead tungstates, it is shown that the wavelength corresponding to the maximum of the blue luminescence band (λmax) correlates with the melting temperature (T m) of these compounds. The position of the blue luminescence band is the same (in the range 510–530 nm) for crystals with different divalent cations. Annealing in vacuum and electron irradiation decrease the intensity of both blue and green luminescence bands but do not change the ratio of their maximum intensities. This circumstance suggests that vacancies serve as luminescence quenchers to a greater extent rather than facilitate the formation of emission centers responsible for a particular luminescence band.

Photophysics and Biological Applications of the Environment-Sensitive Fluorophore 6-N,N-Dimethylamino-2,3-naphthalimide

We have synthesized a new environment-sensitive fluorophore, 6-N,N-dimethylamino-2,3-naphthalimide (6DMN). This chromophore exhibits valuable fluorescent properties as a biological probe with emission in the 500-600 nm range and a marked response to changes in the environment polarity. The 6DMN fluorescence is red-shifted in polar protic environments, with the maximum emission intensity shifting more than 100 nm from 491 nm in toluene to 592 nm in water. Additionally, the fluorescence quantum yield decreases more than 100-fold from chloroform (Phi = 0.225) to water (Phi = 0.002). The scope and applications of the 6DMN probe are expanded with the synthesis of an Fmoc-protected amino acid derivative (5), which contains the fluorophore. This unnatural amino acid has been introduced into several peptides, demonstrating that it can be manipulated under standard solid-phase peptide synthesis conditions. Peptides incorporating the new residue can be implemented for monitoring protein-protein interactions as exemplified in studies with Src homology 2 (SH2) phosphotyrosine binding domains. The designed peptides exhibit a significant increase in the quantum yield of the long wavelength fluorescence emission band (596 nm) upon binding to selected SH2 domains (e.g., Crk SH2, Abl SH2, and PI3K SH2). The peptides can be used as ratiometric sensors, since the short wavelength band (460 nm) was found almost invariable throughout the titrations.

S-band Brillouin erbium fibre laser

A multi-wavelength Brillouin erbium fibre laser, which operates in short wavelength band (S-band), is proposed and demonstrated. The system employs both linear gain and nonlinear gain from a 20 m S-band erbium-doped fibre and a 500 m singlemode fibre, respectively, to generate an optical wavelength comb with spacing of approximately 0.084 nm. Two 80/20 couplers were used in the system as an internal feedback of generated Stokes signal to produce cascaded Brillouin Stokes for multiwavelength operation. A stable output laser comb of up to seven lines was obtained with a Brillouin pump of 3.5 mW and a 980 nm pump of 200 mW.

Electronic Structure of the cis and trans Isomers of Benzimidazo Perylene Derivatives and their Use as Black Pigments

Peryleneimide compounds are industrially important pigments in paint industries as well as in electronics areas. We have focused on the title compound (BIP) as a potential substitute for carbon black used widely as the black pigment. For this reason, electronic characterization of the cis and trans form of BIP has been carried out on the basis of the crystal structure and intermolecular interactions. The black color is characterized by two absorption bands in the visible region in both isomers: the former, shorterwavelength band is due to individual molecules and the latter, longer-wavelength band appears as a result of excitonic interactions between transition dipoles. The stack molecule-pairs, among others, play the determinant role in the appearance of the longer-wavelength band to cover the whole visible region together with the molecular band.

An enhanced S-band brillouin/erbium fiber laser with an additional EDFA in sub-loop

An enhanced short wavelength band brillouin erbium fiber laser (S-band BEFL) is demonstrated using an additional erbium-doped fiber amplifier (EDFA) in the sub-loop of the laser system. Compared with the conventional BEFL without the EDFA, the enhanced BEFL has improved the number of channels as well as the tuning range which are determined by the re-injected signal power. The incorporation of the EDFA also reduces the power difference between the first Stokes and the second Stokes from 17.2dB in conventional BEFL to 3.8dB in the proposed BEFL. A stable output laser comb with 8 channels was obtained with Brillouin pump of 5mW and signal at 1502nm. The BEFL has the potential to be used in the future dense wavelength division multiplexing communication system.

An efficient S-band erbium-doped fiber amplifier using double-pass configuration

An efficient short wavelength band erbium-doped fiber amplifier (S-band EDFA) is proposed and demonstrated using double-pass configuration. This amplifier provides a gain as high as 30dB, but using only 15m depressed cladding erbium-doped fiber (EDF) and 130mW of 980nm pump power. Compared to the single-pass configuration, this amplifier shows a gain enhancement of about 14dB for pump powers above 120mW. However, noise figures penalties of about 0.5 ∼ 0.9dB are obtained for these pump powers. The proposed double-pass amplifier will play an important role in the development of a practical S-band EDFA from perspective of economical usage of EDF and pump power.

Gain control in S-band erbium-doped fiber amplifier using a fiber bragg grating

A gain-clamped short wavelength band erbium-doped fiber amplifier (S-band EDFA) is demonstrated utilizing a fiber Bragg grating (FBG). The amplification in S-band is achieved using an erbium-doped fiber (EDF) with depressed cladding design, which suppressed amplified spontaneous emission (ASE) at longer wavelength. The gain clamping is achieved by routing back the forward ASE into the feedback loop as to create a ring laser. The clamped gain is controlled using a variable optical attenuator (VOA) as to generate a gain of 14.6 to 25.2dB for input signal at 1504nm. At VOA = 0dB, the gain is clamped at 14.6dB with a gain variation of less than ±0.5dB for input signal at 1504nm with power dynamic range of -40 to -5dBm. The noise figure penalty is less than 0.8dB in this amplifier since the laser is arranged to be co-propagated with the signal.

Gain-clamped double-pass S-band erbium-doped fiber amplifier

Gain clamping in double-pass short-wavelength band erbium-doped fiber amplifier (S-band EDFA) is demonstrated. It uses a fiber Bragg grating, which operates in conventional-band to form an oscillating laser in the cavity using an erbium-doped fiber (EDF) gain at around 1530nm. This new technique has shown a good gain clamping effect with gain variation of less than 1.0dB from -40 to -14dBm input signal powers for 1500nm signal. The gain can be controlled within 18 to 20dB by varying a variable optical attenuator from 0 to 8dB. Compared with an unclamped amplifier, the noise figures for small signals are slightly improved due to the suppression of amplified spontaneous emission (ASE). However, the noise figure level is still considerably high due to the double-pass scheme and unoptimised splicing between a depressed cladding EDF and a standard single mode fiber. The advantage of this gain clamped amplifier is that the oscillating light operates at wavelength outside S-band region, which prevent the wavelength division multiplexed system from being disturbed.

Photoacoustic spectrum of samarium phthalocyanine powder

Photoacoustic spectrum of samarium phthalocyanine powder is recorded and compared with previously reported UV–vis absorption spectra of the same dissolved in different liquid and solid host media. The Davidov splitting of Q band is observed in the PA spectrum but the two bands are overlapped considerably and the shorter wavelength band is more intense and dominating one in the powder spectrum.

원자외선분광기 FIMS 자료의 자세정보 및 노출시간 보정

국내 최초의 과학위성인 과학기술위성 1호(STSAT-1)의 주 탑재체 원자외선분광기(FIMS; Far-utraviolet IMaging Spectrograph)는 2003년 9월 발사된 이후로, 다양한 관측을 수행하고 있으나 위성체에서 제공하는 자세정보의 시각오차의 문제점이 발견되어 시각오차를 보정하기 위한 연구가 수행되었다. 시각오차의 보정 후에 잘 알려진 천체의 관측결과를 이용하여 FIMS와 위성체 좌표계 사이의 기계적인 정렬오차에 의해 발행하는 FIMS의 시선방향과 위성체에서 제공하는 자세의 차이를 단파장대와 장파장대에 대하여 각각 계산하였다. 또한, 자세정보의 월별 상태 및 정밀도를 조사하였다. FIMS의 관측방법의 특성상 FIMS로부터 얻어진 영상은 위치별로 서로 다른 노출시간을 갖는다. 이러한 노출시간을 보정하는 방법을 기술하였다. 이 연구의 결과는 FIMS 자료분석을 위해 반드시 필요한 내용이며 추후 좀 더 정밀한 자세정보 보정을 위한 참고 자료로 활용될 것이다. The FIMS (Far-ultraviolet IMaging Spectrograph), the main payload onboard the first Korean science satellite STSAT-1, has performed various observations since its launch on September 2003. It has been found that the attitude informations provided by spacecraft bus system have a time offset problem, and the problem has been extensively studied. After the time offset correction, boresight offsets between FIMS fields of view, of long and short wavelength bands, respectivley, and spacecraft attitude systems, which are mainly due to alignment error between the FIMS and spacecraft mechanical systems, were calculated through the observations of well known calibration targets. Monthly status and precision of the attitude information are also described. Correction methods for spatially variable exposure, intrinsic to FIMS data, are discussed. These results are essential to the FIMS data analysis, and will be used as references for subsequent studies on more accurate attitude corrections.

One-dimensional heterostructural metallodielectric photonic band gap material for the modification of emission spectrum of BaF2 scintillator

One-dimensional metallodielectric heterostructural photonic band gap (PBG) material is designed to reach high transmittance band in short wavelength, broad and deep forbidden band in long wavelength, especially sharp cutoff edge between the transmission and forbidden bands. The designed PBG material is applied to modify the emission spectrum of a BaF2 scintillator and is proved to be adequate to suppress the slow component of the scintillation light. The suppression ratio of the slow to the fast component reaches 28dB with a tolerable attenuation of the fast component.

Free Surface Flow in High Speed Fiber Drawing With Large-Diameter Glass Preforms

This paper presents a complete two-dimensional (2D) thermofluid model for predicting the neck-down shape in the fiber drawing process. This model uses the controlled draw tension to calculate the Neumann boundary condition at the furnace exit; thus, it does not require specifying the speed (or diameter) of the fiber as most previous studies did. The model presented here can be applied to optimization of the high-speed draw process with large-diameter preforms. In this study, the radiative transfer equation is directly solved for the radiation fluxes using the discrete ordinate method coupled with the solution of the free surface flow, which does not assume that the glass is optically thick and does not neglect the glass absorption at the short-wavelength band. The artificial compressibility method is used to solve the Navier-Stokes equations. A staggered-grid computation scheme that is shown to be efficient and robust was used to reduce the computation load in solving the complete 2D model. The neck-down profile of a large preform (9 cm dia) drawn at a relatively high speed of 25 m/s was experimentally measured. The measured profile well matches that derived numerically. Results also show that the free surface calculated using the Dirichlet boundary condition deviates considerably from the measured profile, particularly near the furnace exit where the actual diameter (and, hence, the speed of the glass) is essentially unknown. Although the difference between the numerical results obtained from the full and semi-2D models was small, this difference could be significant if the location at which the glass converges to 125 μm dia is of interest, especially when the preform has a large diameter drawn at a high speed.

Electronic absorption spectra of symmetric cationic dye in constant electric field

The electronic absorption coefficient of polymer films doped with symmetric cationic polymethine dye external electric field constant changes is researched. This effect is characterised by the short-wavelength band edge intensity increases and it decreases on the long-wavelength edge. The dye cation charge distribution in the model electric field 10 8 V m −1 of point charges was calculated by the method AM1. On the basis of the quantum chemical calculations the spectral regularities in electric field is interpreted by the cation electronic charge changes. The theoretical model, based on the eigenfrequencies value changes of the charged anharmonic oscillators under operation field is offered for the observed effects description. The experimental spectra well correlate with the theoretically calculated.

Transformation of a short-wavelength emission band of a double-charged intrinsic acceptor into a long-wavelength band in GaSb-based LEDs

GaSb-based crystals shaped like a stepped pyramid with smoothed steps are obtained. The crystals are intended for the fabrication of light-emitting diodes in which the short-wavelength emission band of a double-charged intrinsic acceptor is transformed into the long-wavelength band without loss in the amount of photons emitted. It is shown experimentally and theoretically that an increase in the ratio of the area of the light-emitting diode crystal to its volume increases the external quantum yield of photons. A yield of 5.1% for the intrinsic acceptor in GaSb is attained.

Coaxial Gyrotrons: Past, Present, and Future (Review)

Most of the present-day millimeter-wave gyrotrons developed for plasma experiments in controlled fusion reactors utilize cylindrical cavities operating in high-order modes. The choice of modes should obey certain restrictions dictated by the achievable mode selection and the maximum admissible level of the density of microwave ohmic losses in the cavity walls. Even with these restrictions, developers have successfully manufactured quasi-continuous-wave gyrotrons operating in the short millimeter wavelength bands that are capable of delivering microwave power on the order of 1 MW. To upgrade gyrotron power to the level of several megawatts, more complicated coaxial microwave circuits should be used. This statement is also valid for relativistic gyroklystrons, which are currently under development for driving future linear accelerators. This paper presents an overview of the history of the development of coaxial gyrodevices, a discussion of the physics-based issues which are the most important for their operation, a description of the state of the art in the development of coaxial gyrodevices for the above-mentioned applications, and a brief forecast for their future.

Gold particle interaction in regular arrays probed by surface enhanced Raman scattering.

Lithographically designed two-dimensional arrays consisting of gold nanoparticles deposited on a smooth gold film are used as substrate to examine the SERS effect of the trans-1,2-bis (4-pyridyl) ethylene molecule. These arrays display two plasmon bands instead of the single one observed for the same arrays of particles but deposited on indium tin oxide coated glass. Laser excitation within the short wavelength band does not bring about any SERS spectrum, while excitation within the long wavelength band yields SERS spectra with a gain per molecule rising up to 10(8). The simultaneous investigation of extinction and Raman spectra of arrays exhibiting various topography parameters enables us to suggest an interpretation for both the occurrence of the two plasmon resonances and for the high Raman enhancement. We suggest to assign the short wavelength band to a plasmon wave propagating at the gold glass interface and the long wavelength one to an air/gold surface plasmon mode modified by particle-particle interaction.

Effects of Radiative Transfer Modeling on Transient Temperature Distribution in Semitransparent Glass Rod

This paper presents a method of modeling the radiative energy transfer that takes place during the transient of joining two concentric, semitransparent glass cylinders. Specifically, we predict the two-dimensional transient temperature and heat flux distributions to a ramp input which advances the cylinders into a furnace at high temperature. In this paper, we discretize the fully conservative form of two-dimensional Radiative Transfer Equation (RTE) in both curvilinear and cylindrical coordinate systems so that it can be used for arbitrary axisymmetric cylindrical geometry. We compute the transient temperature field using both the Discrete Ordinate Method (DOM) and the widely used Rosseland’s approximation. The comparison shows that Rosseland’s approximation fails badly near the gap inside the glass media and when the radiative heat flux is dominant at short wavelengths where the spectral absorption coefficient is relatively small. Most prior studies of optical fiber drawing processes at the melting point (generally used Myers’ two-step band model at room temperature) neglect the effects of the spectral absorption coefficient at short wavelengths λ<3μm. In this study, we suggest a modified band model that includes the glass absorption coefficient in the short-wavelength band. Our results show that although the spectral absorption coefficient at short wavelengths is relatively small, its effects on the temperature and heat flux are considerable.

Noise-reduction capabilities of a Raman-mediated wavelength converter

We describe ultrawideband Raman-mediated wavelength conversion. The nonlinear conversion transfer function is calculated analytically and simulated numerically in the cw regime, and the predicted performance is confirmed experimentally. Data conversion from long- to short-wavelength bands with signal reshaping and significant noise reduction are demonstrated experimentally at 10 Gbits/s and modeled by numerical simulations. Q factors and extinction ratios that are both larger than 10 dB are possible over an effective conversion bandwidth of 35 nm.