High efficiency lasing of a dye-doped polymer laser with 1.06 μm pumping

For the first time, tunable lasing from a dye laser with an active polymer medium has been obtained using 1.06 μm pumping. The conversion efficiency of 43% and the tunable range of Δλ=63 nm have been reached with the use of polymethine dye in a polyurethane matrix. Received: 20 April 2001 / Revised version: 16 July 2001 / Published online: 19 September 2001     

Development of proposed federal standard 1070: 62.5/125-μm graded-index,multimode optical fiber waveguides for on-premises applications

This paper describes a process that has been successful in generating a specification to guide the user community in the procurement of single-size, multimode optical fiber for on-premises applications. This process began with an attempt to adopt an industry standard as a federal standard that would eliminate a multiplicity of choices available from the marketplace. The initial EIA-458-A Standard contained four “preferred” sizes. Discussions both in a government standards committee and in an applications-oriented industry (EIA) working group indicated the desirability of recommending a single fiber size. The process by which the industry committee selected the 62.5-μm core diameter/125-μm cladding diameter multimode fiber is presented.

The next element of the process was that of selecting the appropriate standard performance measures and attributes that would assure minimum performance of graded parameters such as attenuation and bandwidth, as well as a uniform specification of the product. The vehicle selected for this specification was the EIA 492-Series Generic, Sectional, and Blank Detail Specifications. Inputs were solicited from all of the identified U.S. manufacturers of this fiber size. Those inputs were coordinated and integrated into a detail specification, which is now being circulated by the EIA on a standards proposal ballot. After ballot approval, it will be published as an ANSIIEIA standard specification. Similar work has been initiated to develop a detail specification for fiber optic cables based on a related set (472-Series) of EIA specifications.

The process of developing a detail specification that assures conformance of the product to dimensional and strength tolerances as well as performance measures requires considerable coordination and iteration. No proprietary information or processes are contained in the specification so that the industry participants are free to compete on price and performance as long as compliance with the specification can be demonstrated.     

1.5μm, 8×12.5Gb/s of hybrid-integrated TOSA with isolators and ROSA for 100GbE application

Compact transmitter and receiver optical sub-assemblies(TOSA and ROSA) are fabricated in our laboratory and have an aggregated capacity of 100 Gb/s. Specially, directly modulated laser(DML) drivers with two layers of electrical circuit boards are designed to inject RF signals and bias currents separately. For all the lanes, the3 dB bandwidth of the cascade of the TOSA and ROSA exceeds 9 GHz, which allows the 12.5 Gb/s operation.With the 12.5 Gb/s × 8-lane operation, clear eye diagrams for back-to-back and 30-km amplified transmission with a dispersion compensation fiber are achieved. Low cost and simple processing technology make it possible to realize commercial production.     

Improving robustness of GGNMOS with P-base layer for electrostatic discharge protection in 0.5-μm BCD process

Gate-grounded N-channel MOSFET(GGNMOS) has been extensively used for on-chip electrostatic discharge(ESD)protection. However, the ESD performance of the conventional GGNMOS is significantly degraded by the current crowding effect. In this paper, an enhanced GGNMOS with P-base layer(PB-NMOS) are proposed to improve the ESD robustness in BCD process without the increase in layout area or additional layer. TCAD simulations are carried out to explain the underlying mechanisms of that utilizing the P-base layer can effectively restrain the current crowing effect in proposed devices. All devices are fabricated in a 0.5-μm BCD process and measured using the transmission line pulsing(TLP)tester. Compared with the conventional GGNMOS, the proposed PB-NMOS devices offer a higher failure current than its conventional counterpart, which can be increased by 15.38%. Furthermore, the PB-NMOS type 3 possesses a considerably lower trigger voltage than the conventional GGNMOS to protect core circuit effectively.     

Thermal optimization of 1.55 μm OP-VECSEL with hybrid metal–metamorphic mirror for single-mode high power operation

We report on the thermal design and the characterization of InP-based 1.55 μm wavelength large diameter (～100 μm) optically pumped vertical external cavity surface emitting lasers (OP-VECSELs). The device is thermally optimized for high power ( > 70 mW) room-temperature (RT) continuous-wave (CW) single-mode operation. Efficient bottom heat dissipation in the 1/2-VCSEL chip is obtained thanks to the use of a hybrid metal– metamorphic GaAs/AlAs mirror integrated to the InP-based active region, and to subsequent soldering on a SiC substrate. A single-mode output power of 77mW is obtained under CW-RT laser operation, limited by the pump power. Moreover thermal simulations and characterizations of the 1/2-VCSEL chip show that even higher power could be obtained at higher pumping levels, using a CVD diamond substrate.     

Experimental generation of optical non-classical states of light with 1.34 <Emphasis Type="Italic">μ</Emphasis>m wavelength

We report the experimental generation of the optical non-classical states with 1.34 μm wavelength which is close to one of the fiber telecommunication windows (1.31 μm). The single-mode amplitude squeezed states with quantum fluctuation of 2.3 ± 0.1 dB below the shot noise limit (SNL) and the entangled states with quantum correlation of 1.1 ± 0.1 dB below the SNL are produced by an optical parametric amplifier with a type-I phase-matched PPKTP crystal and a pair of properly oriented type-II phase-matched KTP crystals, respectively.     

Measurement and analysis of optical gain spectra in 1.6 to 1.8 μm InAs/InP (100) quantum-dot amplifiers

Small signal modal gain measurements have been performed on two-section ridge waveguide InAs/InP (100) quantum-dot amplifiers that we have fabricated with a peak gain wavelength around 1.70 μm. The amplifier structure is suitable for monolithic active-passive integration, and the wavelength region and wide gain bandwidth are of interest for integrated devices in biophotonic applications. A 65 nm blue shift of the peak wavelength in the gain spectrum has been observed with an increase in injection current density from 1,000 to 3,000 A/cm². The quantum-dot amplifier gain spectra have been analyzed using a quantum-dot rate-equation model that considers only the carrier dynamics. The comparison between measured and simulated spectra shows that two effects in the quantum-dot material introduce this large blue shift in the gain spectrum. The first effect is the carrier concentration dependent state filling with carriers of the bound excited and ground states in the dots. The second effect is the decrease in carrier escape time from the dots to the wetting layer with decreasing dot size.     

1.82-μm distributed feedback lasers with InGaAs/InGaAsP multiple-quantum wells for a H2 O sensing system

High-strained InGaAs/InGaAsP multiple quantum wells （MQWs） distributed feedback （DFB） lasers, fabricated using metal organic chemical vapor deposition, are presented at 1.82 μm with a high side-mode-suppression ratio of 49.53 dB. The current- and temperature-tuning rates of the DFB mode wavelength are 0.01 nm/mA and 0.13 nm/℃, respectively. A characteristic temperature of 51 K is also confirmed. The DFB laser demonstrates good performance and can be applied to H₂ O concentration sensing.     

Electrical and optical characteristics of the InAs/InAs0.7Sb0.1P0.2 single heterojunction photodiodes for the spectral range 1.6-3.5 μm

The electrical end optical characteristics of InAs/InAs_0.7Sb_0.1P_0.2 heterojunctions were studied. The dark current mechanisms in the heterostructures were investigated at several temperatures. The experimental results shows that, the low temperature region the tunneling mechanism of the current flow dominates in both, forward and reverse biases. At high temperatures region and in the range of voltage from 0.1 V to 1 V, the reverse current was defined by diffusion mechanism.     

Molecular beam epitaxial growth of high quality InAs/GaAs quantum dots for 1.3-μm quantum dot lasers

Systematic investigation of InAs quantum dot(QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots.By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved.The areal quantum dot density is 5.9× 10~(10) cm~(-2), almost double the conventional density(3.0 × 1010 cm~(-2)).Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density.These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.     

Thermal and optical properties of Tm: Li6Gd(BO3)3 crystal: A potential candidate for 1.83 μm lasers

Single crystal of Tm³⁺: Li₆Gd (BO₃)₃ was grown by the Czochralski method. The heat capacity was measured from 308 to 673 K. The absorption spectra of the crystal in three mutually perpendicular arbitrary directions were measured at room temperature. Based on the Judd-Ofelt theory and the spectra measured in three mutually perpendicular directions, the intensity parameters Ω_t (t=2, 4, 6), the line strengths, the oscillator strengths, the radiative rates, radiative lifetimes and fluorescent branching ratios were calculated. We calculated the emission cross-section by the reciprocity method and also obtained the gain cross-section.     

Multispectrum fitting of line parameters for C2H2 in the 3.8-μm spectral region

Using FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈ 0.001 cm⁻¹) of acetylene ¹²C₂H₂, absolute positions and intensities have been measured for about 250 lines between 2600 and 2800 cm⁻¹ in the and cold bands, and in the and hot bands. These measurements improve the accuracy of wavenumbers previously available and lead to individual line intensities for the first time in this spectral region. A multispectrum fitting procedure has been used to retrieve line parameters from five experimental spectra recorded at different pressures. The frequencies of the ν₃ band of ¹²C¹⁶O₂ allowed to perform an absolute wavenumber calibration. The accuracy of the amount of ¹²C₂H₂ in the sample has been checked using the cold band around 2100 cm⁻¹, and has been estimated to be around ±2%. The average absolute accuracy of the line parameters obtained in this work has then been estimated to be ±0.0002 cm⁻¹ for line positions, and ±5% for line intensities. For each studied band, the vibrational transition dipole moment squared value has been determined, as also empirical Herman-Wallis coefficients. A complete line list containing positions and intensities for the five strongest bands around 3.8 μm has been set up for atmospheric applications.     

Bleaching effect in passive regions of powerful 1.02 μm InGaAs/AlGaAs DQW laser diodes with ridged waveguide structure

It has been shown that the cavity trapped amplified luminescence (CTAL) flux formed within the active region of a powerful 1.02 μm InGaAs/AlGaAs DQW laser diode (LD) with a ridged waveguide structure, can cause the bleaching of passive areas leading to abrupt hysteresis-type changes in the light–current and spectral characteristics. The post-threshold rise of the CTAL flux within the non-lasing parts of the active region is most likely to play significant role in the nonlinear optical phenomena observed in investigated LDs. The frequency-integrated CTAL flux density at which bleaching takes place is equal to 6.5×10⁸ W/m². The hysteresis-type loop can be removed through the LD “run-in” procedure or high-temperature annealing of the LD chip in an hydrogen atmosphere. PACS 42.55.Px; 42.70.Hj     

Atomically controlled surfaces with step and terrace of β-Ga2O3 single crystal substrates for thin film growth

The surface of β-Ga₂O₃ (1 0 0) single crystal grown with floating zone method was treated by chemical-mechanical-polishing (CMP) for 30-120 min followed by annealing in oxygen atmosphere at temperature 600-1100 °C for 3-6 h. The evolution of the step arrangement was investigated with reflection high energy electron diffraction and atomic force microscopy. Atomically smooth surfaces with atomic step and terrace structure of β-Ga₂O₃ substrates were successfully obtained after just CMP treatment as well as CMP treatment and post annealing at 1100 °C for 3 h. The uniform step height was 0.57 nm, and smooth terrace width was 100 nm, where the misorientation angle was about 0.36°. The obtained atomically smooth surface provides a potential application for the high-quality epitaxial film growth.     

Measurement of absorption spectra for atmospheric methane by a lidar system with tunable emission wavelength in the range 1.41–4.24 μm

We have developed, built, and tested an automated differential lidar system for measuring low concentrations of atmospheric gases, based on an optical parametric oscillator tunable in the near IR region. We have calculated the spectral shift of the relative intensities of the individual lines in the ν₃ absorption band of methane. In comparing the measured and calculated spectra, we did not observe any shifts in the ν₃ absorption band of methane. At the same time, in the experimental spectra we observe broadening of the Q branch and the individual lines of the P branch. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 285–290, March–April, 2009.     

Hetero-epitaxy of L_g= 0.13-μm metamorphic AlInAs/GaInAs HEMT on Si substrates by MOCVD for logic applications

In this work, a hetero-epitaxial Al0.49In0.51As/Ga0.47In0.53 As metamorphic high electron mobility transistor(mHEMT) grown by metal–organic chemical vapor deposition(MOCVD) on p-type silicon substrate has been successfully demonstrated. A novel AlGaAs/Al As period multiple quantum well(MQW) composite buffer scheme is developed to effectively tune the leakage current from the buffer layer. The quantized room-temperature Hall mobility of the twodimensional electron gas(2DEG) is larger than 7800 cm2/V·s, with an average sheet carrier density of 4.6×1012cm-2.Two-stage electron beam(EB) lithography technology by a JBX-6300 e-beam lithography system is developed to realize a 0.13-μm m HEMT device on Si substrate. A maximum transconductance Gm of up to 854 mS/mm is achieved, and is comparable to that of m HEMT technology on Ga As substrate with the same dimension. The fTand fmax are 135 GHz and120 GHz, respectively.     

Tunable diode laser measurement of pressure-induced shift coefficients of CO2 around 2.05 μm for Lidar application

Atmospheric carbon dioxide (CO₂) is one of the main contributors to the greenhouse effect. A global monitoring of CO₂ from space is foreseen as a key issue to quantify its sources and sinks at a regional scale and to better predict future levels of CO₂ and their effect on climate change. Differential Absorption Lidar (DiAL) is a promising and novel spectroscopic technique for remote sensing CO₂ spatial and temporal concentration distribution with a high level of accuracy. However, a precise knowledge of spectroscopic parameters of CO₂ molecular transitions and their dependence with temperature and pressure is required for reducing the uncertainty on DiAl measurements. Hence, to support remote sensing of carbon dioxide in the troposphere, we report on the accurate determination of air pressure-induced shift coefficients for eight absorption lines belonging to the R branch of (20⁰1)_III←(00⁰0)_I band of CO₂ at 2.05 μm. Purposely, a high-resolution tunable diode laser absorption spectrometer (TDLAS) coupled to a cryogenically cooled optical cell was implemented. From these measurements, we have further determined the temperature-dependencies of the air pressure-induced shift coefficients.     

The 2ν3 band of CH4 revisited with line mixing: Consequences for spectroscopy and atmospheric retrievals at 1.67 μm

This paper presents a study of absorption in N₂-broadened P and R manifolds of the 2ν₃ band of CH₄ near 6000 cm⁻¹ using high resolution laboratory and atmospheric spectra. This region is of prime importance for the retrieval of methane abundances in the Earth's atmosphere using ground-based or space-borne spectrometers. Recent laboratory investigations have been devoted to the methane spectroscopic parameters in this band, motivated by their previous poor knowledge and their increasing use by remote sensing experiments. In the absence of a better model, previous studies have used Voigt line shapes and thus purposely neglected line mixing (LM). In this paper, we first present direct comparisons between measured laboratory spectra and the results of a model which accounts for LM without adjusting any of the spectroscopic parameters. A good agreement is obtained and the results show that LM does have a significant influence on the shapes of P and R manifolds. Hence, most previously observed discrepancies were not due to improper broadening and shifting coefficients but to the neglect of this effect. This also confirms that widths and shifts derived in recent 2ν₃ band studies neglecting LM are “effective” and lack physical meaning, as suggested in a previous work [17] (Frankenberg et al., 2008). In a second step, the conclusions from the laboratory data are tested using ground-based atmospheric solar absorption spectra. The fit residuals obtained confirm the quality of the proposed model and evidence the impact of line mixing on CH₄ atmospheric spectra. The present results also confirm that laboratory and atmospheric spectra can alternatively be accurately modeled neglecting LM and using ad hoc broadening and shifting parameters. Conclusions of this exercise can be drawn from two perspectives. From the point of view of spectroscopy and understanding of processes, accurate line parameters will not be deduced from fits of laboratory measurements unless line-mixing effects are included in the spectral-shape model. In the meantime, and from the point of view of atmospheric retrievals, neglecting LM with suitable effective line parameters is convenient and accurate (within current retrieval uncertainties). Note that this is only true if this approach is not used for total pressures significantly above 1 atm (e.g. Jupiter).     

1.4 μm emission properties and local environments of Tm ions in tellurite glass modified with MoO3

The 1.4 μm emission properties of Tm³⁺ ions embedded in tellurite glass containing MoO₃ have been investigated in an effort to develop non-crystalline materials for ultra broadband optical amplifier. Spectral lineshape and bandwidth of the 1.4 μm emission exhibited a negligible dependence on amount of MoO₃, while the measured lifetime of the Tm³⁺:³H₄ state decreased with increase in MoO₃ content. Multiphonon relaxation turned out to become stronger with increase in MoO₃ amount, which coincided with the further broadened Raman scattering bandwidth of the MoO₃-containing tellurite glass. The spectroscopic properties of Tm³⁺ ions doped in our modified tellurite glasses are discussed in connection with the local structural parameters obtained from Tm L₃-edge EXAFS analysis.