Temperature Dependence Of Gain Research Articles

Correlation of Barrier Height and Nonradiative Carrier Recombination and the Consequences for Optical Gain in GaN Based Laser Structures

We investigated the photoluminescence intensity and material gain values of GaN based laser structures with various well widths in the active layer by temperature dependent photoluminescence and optical gain measurements. The existence of two different nonradiative recombination channels can be demonstrated by temperature dependent photoluminescence measurements at low excitation densities. This results in two thermal activation energies which can be attributed to distinct activation processes. The influence of the nonradiative recombination is also reflected by the temperature dependence of the required material gain values.

Comparison of temperature dependence in C-band and L-band EDFAs

Temperature-dependent gain and noise characteristics of conventional band and long wavelength band erbium-doped fiber amplifiers are compared. Gain variations and noise figure penalties are shown for 980- and 1480-nm pump wavelength bands at different average inversion levels when the erbium coil temperature is cycled from -10/spl deg/C to 80/spl deg/C. Experimental results demonstrate that the L-band exhibits greater temperature-dependent gain and noise figure excursions compared to the C-band. Furthermore, it is shown that the impact of erbium coil temperature in the L-band is comparatively less dependent upon pump wavelength.

Modeling of current gain's temperature dependence in heterostructure-emitter bipolar transistors

The temperature dependence of the current gain is investigated for GaAs-based heterostructure-emitter bipolar transistors (HEBT's). With the separation of the p-n junction and the heterojunction, the mechanism of hole injection from the base to emitter in the HEBT is different from that of a conventional HBT. Theoretical results demonstrate that the thermionic emission current plays an important role for the hole current which results in a smaller negative or even positive temperature coefficient for the current gain. Experimental data show that the base current for HEBTs is indeed dominated by thermionic emission as predicted. This finding indicates that the HEBT structure is the suitable choice for high power and high speed applications.

Temperature-dependent gain and noise in fiber Raman amplifiers

An experimental investigation of the temperature dependence of the gain and noise performance of a silica-fiber Raman amplifier is described. A decrease in the Raman scattering cross section in a fiber amplifier cooled from a temperature of 300 K to 77 K was measured and found to be in agreement with theoretical values. No difference between the Raman gain coefficients at these two temperatures was observed.

Influence of Barrier Doping and Barrier Composition on Optical Gain in (In,Ga)N MQWs

The influence of barrier doping and barrier composition on the optical gain in (In, Ga)N multiple quantum wells is studied under stationary conditions. Systematic temperature dependent gain measurements are performed by means of the variable-stripe-length method. Furthermore, PL spectra are recorded in order to study the temperature dependence of the quantum efficiency which gives information on activation processes to nonradiative recombination channels. The measured threshold densities and gain can successfully be explained by consideration of localization effects.

Channel temperature measurement using pulse-gate method [power amplifier FET

In this paper, we report on an approach of measuring power amplifier field-effect transistor (FET) channel temperature under real-world operating conditions. The principle of this approach is to compare the magnitude of power amplifier gain at both DC and pulse bias conditions. By utilizing the temperature-dependent gain characteristic of the power amplifier FET and applying pulse-gate control, the gain would gradually decrease with the rising temperature of the hot plate. The channel temperature is then determined when the decreasing gain reaches the level of the base line, which is measured under the specified DC bias and radiofrequency conditions.

Temperature dependent behaviour of C-band and L-band EDFAs: A comparison

Temperature dependent gain and power characteristics of erbium-doped fibre amplifiers operating in the C-band and L-band are compared. Experimental results are shown for the case of 980 and 1480 nm pump wavelength bands over a temperature range of –10 – 80°C. Results indicate that the temperature dependence of signal emission and absorption cross-sections have greater impact on the L-band output power. Furthermore, it is shown that the L-band temperature coefficient (dB/°C) is comparatively less sensitive to pump wavelength.

Reduction of temperature-dependent multichannel gain distortion using a hybrid erbium-doped fiber cascade

Temperature dependent distortion of multichannel gain in the erbium-doped fiber amplifier (EDFA), which is a potential limiting factor in real environment, was successfully compensated by concatenating EDF's of different temperature dependence. A sample case was analyzed through a numerical simulation, for the verification of the suggested idea. Results show that temperature-dependent multichannel gain flatness distortion, except for gain level shifting, can be reduced to 0.5 dB maximum for temperature variation of 25/spl deg/, which is a significant improvement over the case of Al-codoped silica fiber alone (maximum 1.8 dB for 25/spl deg/ variation), or ZBLAN fiber alone (maximum 1.5 dB for 25/spl deg/ variation).

Gain Spectroscopy of HVPE-Grown GaN

We report on photoluminescence and optical gain measurements of highly excited GaN crystals grown by hydride vapor physe epitaxy (HVPE). Inelastic scattering processes of excitons dominate the spontaneous emission spectrum under high excitation up to temperatures of 180 K. Towards room temperature phonon-assisted recombination of excitons and free carriers begins to dominate the spectrum. Similar characteristics are observed in temperature-dependent gain measurements.

Very high characteristic temperature and constant differential quantum efficiency 1.3-μm GaInAsP-InP strained-layer quantum-well lasers by use of temperature dependent reflectivity (TDR) mirror

A very high characteristic temperature T/sub 0/ of 150 K (25-70/spl deg/C) or 450 K (25-50/spl deg/C) and an almost constant differential quantum efficiency operation in the temperature range of 25-70/spl deg/C were achieved in 1.3-/spl mu/m GaInAsP-InP strained-layer quantum-well (SL-QW) lasers by use of a novel temperature dependent reflectivity (TDR) mirror composed of multiple quarter-lambda thickness /spl alpha/-Si-SiOx dielectric films with quarter-lambda shift in the vicinity of center portion, The mechanism of high T/sub 0/ and constant differential quantum efficiency were explained using the structural parameters, transparent current density and gain coefficient of a SL-QW laser that are derived experimentally. The effect of TDR mirror was confirmed by measuring the temperature dependence of net gain of a SL-QW laser with TDR mirror. It was found that less temperature dependent net gain due to the decrease of mirror loss with temperature played an important role for improving the temperature characteristics of threshold current. Almost constant differential quantum efficiency over a wide temperature range is attributed to the increase of the facet reflectivity with temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of oxygen on the behaviour of oxygen-containing groups of soft coal in pyrolysis

A comparison has been made of the processes of thermal and thermo-oxidative decomposition of Kansk-Achinsk brown coal. The composition of the residues formed at different temperatures was studied by elemental and chemical functional analyses and i.r. spectrometry and X-ray diffractometry. Significant differences in the temperature-dependence of gain or loss rates were observed for individual elements, functional groups, molecular structure parameters and the supermolecular organization of the solid products, depending on the gas atmosphere. These differences are mostly due to the fact that with limited access of aerial oxygen, coal degradation proceeds through partial destruction of the stacks of carbon networks.

Analysis of temperature dependent optical gain of strained quantum well taking account of carriers in the SCH layer

The temperature dependence of optical gain in strained quantum well is analyzed taking account of carriers in the separate confinement heterostructure (SCH) layer. Taking account of these carriers in the SCH layer can explain to a considerable extent the difference in the temperature performance between the /spl lambda/=0.98 μm laser and /spl lambda/=1.3 μm laser. It is shown that well depth plays a crucial role for the temperature dependence of optical gain. A strained quantum well on an InGaAs ternary substrate is shown to give a high gain with a small temperature dependence.

Temperature dependent gain of the atomic xenon laser

Measured and calculated gain of the 1.73 μm [5d(3/2)1–6p(5/2)2] and 2.03 μm [5d(3/2)1–6p(3/2)1] atomic xenon transitions for gas temperatures between 290 and 590 K are presented. Fission-fragment excitation was used to generate the gain in Ar/Xe, He/Ar/Xe, and Ne/Ar/Xe gas mixtures at a pump power of 8 W/cm3. For constant gas density, the gain exhibits an approximate Tgas−n dependence with n between 2 and 3. The primary reactions responsible for the temperature dependence of the gain have been identified as dimer formation, dissociative recombination, and enhanced electron collisional mixing of the laser manifold due to an increased electron density.

Base profile tail effects on the low temperature operation of silicon bipolar transistors

This paper reports new results on bandgap narrowing in self aligned polysilicon emitter bipolar transistors. Using temperature dependent current gain measurements, we show that the tail region of the implanted base plays a dominant role in the effective bandgap narrowing of the base. This result will be very important for the development of pseudo-heterojunctions and low temperature-operation bipolar transistors.

The temperature dependent current gain of heterojunction bipolar transistors

A study of the thermal effects on the current gain in different heterojunction bipolar transistor structures is presented. Calculations show that the conventional heterojunction barrier in a graded base transistor is insufficient above room temperature and that a parabolically graded heterojunction is essential for the current gain at elevated temperatures. AlGaAs/GaAs HBTs have been fabricated and characterized up to an ambient temperature of 470 K. The experimental results confirm the theory. An extension of the Gummel-Poon transistor model to include the temperature dependent current gain is proposed. The improvement in correspondence with the measured DC-characteristics over the original model is shown to be substantial.

Temperature dependent gain and noise characteristics of a 1480 nm-pumped erbium-doped fibre amplifier

The gain of a 1480 nm pumped erbium-doped fibre amplifier has been measured over the temperature range −40°C to 60°C. The characteristics can be modelled using emission and absorption cross-section data determined for this temperature range. The temperature dependence of the gain spectrum and noise figure are also predicted.

Temperature-dependent gain and noise of 1.5 μm laser amplifiers

The variations of gain and noise figure with temperature are investigated for a 1.5 μm laser amplifier with angled facets. The gain is decreasing by 4–8 dB for a temperature increase of 20°C and the noise figure is increasing by 2–4 dB. For both parameters the variation is smallest on the high wavelength side of the gain peak.

Characteristics of alexandrite lasers

Alexandrite, BeAl2O4:Cr3+, is a tunable solid-state laser material similar in physical characteristics to ruby but which is capable of four-level vibronic lasing at and above room temperature. The lasing band extends from below 700 nm to over 800 nm and shows a marked dependence of gain on temperature. The vibronic lasing in alexandrite involves a relatively low-emission cross section, which depends strongly on both temperature and wavelength. As a result the optimum optical output coupling is low in comparison with most solid-state insulator lasers. The low-emission cross section implies a high saturation flux, and consequently efficient energy extraction depends on high intra-resonator power densities. As a result optimum energy storage for Q-switched operation is effectively determined by the optical damage limits of resonator components, and there is an increased dependence on the oscillator in contrast to amplifier stages in the design. In the design of the alexandrite laser, optimum departures from conventional Nd:YAG and ruby performance depends on certain relatively minor systems. A broadband pump chamber reflector is required to cover the pump bands of alexandrite which extend from 380 out to 650 nm, yet operation at high average power can tax the chemical stability of many broadband metallic reflectors. The temperature-dependent gain leads to designs that permit the rod temperature to be varied. The highest energy extraction efficiencies are achieved when the rod temperature is near and above 100°C.