Frequency-Tunable Terahertz-Wave Generation from GaP Using Cr:Forsterite Lasers

We have constructed THz spectrometers using the widely frequency-tunable THz-wave generated from GaP crystal pumped at 1.2 µm region using two Cr:forsterite lasers and compared with that pumped at 1 µm region using a YAG laser and an optical parametric oscillator (OPO). The systems have sufficient resolution for observation of solids and liquids at room temperature. We have measured Terahertz absorption spectra of all 20 kinds of amino acids which form proteins.     

The growth of InAsSb/InAsP strained-layer superlattices for use in infrared emitters

We describe the metalorganic chemical vapor deposition of InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. These SLSs were grown at 500°C, and 200 Torr in a horizontal quartz reactor using TMIn, TESb, AsH₃, and PH₃. By changing the layer thickness and composition, we have prepared structures with low temperature (≤20K) photoluminescence wavelengths ranging from 3.2 to 4.4 μm. Excellent performance was observed for a SLS light emitting diode (LED) and both optically pumped and electrically injected SLS lasers. An optically pumped, double heterostructure laser emitted at 3.86 μm with a maximum operating temperature of 240K and a characteristic temperature of 33K. We have also made electrically injected lasers and LEDs utilizing a GaAsSb/InAs semi-metal injection scheme. The semi-metal injected, broadband LED emitted at 4 μm with 80 μW of power at 300K and 200 mA average current. The InAsSb/InAsP SLS injection laser emitted at 3.6 μm at 120K.     

Optimization of pumping conditions in end pumped Tm:YAP lasers with the consideration of thermal effects

In this work, we presented the measurements and calculations for the optimal pump conditions and their effects on thermal lens, fracture limit and laser efficiencies of end pumped Tm-doped yttrium aluminum perovskite (Tm:YAP) laser rod pumped at 1 064 nm. The results showed that the measured overall efficiency of produced laser at ~1.98 µm is enhanced from 3.9% to 6.9% when the pump spot diameter is reduced from 390 µm to 210 µm. The maximum output power and oscillation threshold are also enhanced with reduced pump spot size. The maximum thermal stress and focal length of thermally induced lens are also addressed.     

Far-infrared hydrazine laser pumped by an N2O laser

We have used an N₂O laser to optically pump N₂H₄ molecules in a far-infrared cavity and observed 17 new laser lines in the wavelength range 93.0 to 374.2 µm, the 136.8 µm line pumped by 10P(16) being a doublet. We measured the frequencies of the laser lines by heterodyne mixing of the far-infrared radiation with radiation from two frequency-stabilized CO₂ lasers.     

Frequency measurements of 3 to 11 THz laser lines of CH3OH

We measured the frequencies of 12 far-infrared laser lines generated in a high- frequency Fabry-Perot laser cavity containing methanol, pumped by a CO₂ laser. The frequencies are in the range 2.8 to 11.4 THz (105.4 to 26.2 µm). Ten of the measured frequencies are higher than 7 THz, and help to fill the laser frequency gaps in this region. Five of the measured lines are new. The 11.4 THz line has the highest frequency of an optically pumped laser ever measured with the CO₂ laser heterodyne technique.     

Optimized operation of optically pumped NH3 laser emission at 12.08 µm and 12.81 µm

Based on the semi-classical density matrix equations, optimized operation of optically pumped NH₃ MIR laser emission at 12.08µm and 12.81µm was studied theoretically and experimentally. The effect of pump power, gas pressure and buffer gas N₂ on MIR output power were discussed in detail.     

Single Mode Laser Oscillation in an Nd‐Doped Large Core Double Clad Fiber Cavity with Concatenated Adiabatic Tapers

We created a new design for an Nd‐doped clad‐pumped silica fiber laser to enhance the pump absorption and lasing efficiency for a butt‐coupled, end‐pumped scheme. Two concatenated adiabatic tapers formed within the laser cavity simultaneously removed higher order modes and were spliced to conventional single mode fibers. We theoretically analyzed mode propagation along the composite cavity and experimentally achieved continuous wave oscillation in the LP₀₁ mode at 1.06 µm and a laser output power of over 820 mW with a slope efficiency of 27%.     

Enhancement of fluorescence emission and signal gain at 1.53 µm in Er3+/Ce3+ co-doped tellurite glass fiber

Er3+/Ce3+ co-doped tellurite glasses with composition of TeO2-GeO2-Li2O-Nb2O5 were prepared using conventional melt-quenching technique for potential applications in Er3+-doped fiber amplifier (EDFA). The absorption spectra, up-conversion spectra and 1.53 µm band fluorescence spectra of glass samples were measured. It is shown that the 1.53 µm band fluorescence emission intensity of Er3+-doped tellurite glass fiber is improved obviously with the introduction of an appropriate amount of Ce3+, which is attributed to the energy transfer (ET) from Er3+ to Ce3+. Meanwhile, the 1.53 µm band optical signal amplification is simulated based on the rate and power propagation equations, and an increment in signal gain of about 2.4 dB at 1 532 nm in the Er3+/Ce3+ co-doped tellurite glass fiber is found. The maximum signal gain reaches 29.3 dB on a 50 cm-long fiber pumped at 980 nm with power of 100 mW. The results indicate that the prepared Er3+/Ce3+ co-doped tellurite glass is a good gain medium applied for 1.53 µm broadband and high-gain EDFA.     

High performance SWIR HgCdTe detector arrays

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 μm and cap layer thickness was ∼0.4 μm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 μm detector on 45 μm × 60 μm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 μm) and Landsat Band 7 (2.08−2.35 μm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 10¹² cm Hz^1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz ^1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally <20 μm μm) planar-mesa diodes to the microlens size of 48 urn. Using microlenses allows array performance to exceed 1-D theory up to a factor of 5.     

One-dimensional photonic crystal obtained by vertical anisotropic etching of silicon

The potentialities of vertical anisotropic etching of (110) silicon for the fabrication of one-dimensional photonic crystal with a high refractive index contrast have been studied. It is shown that advances toward the near-IR spectral range are limited by the mechanical strength of thin silicon walls. The device structures obtained consist of 50 trenches, 114 μm deep, with 1.8-μm-thick Si walls (structure period 8 μm). Their reflectance spectra in the wavelength range 2.5–16.5 μm show good agreement with calculation results, although the main photonic band gap at λ≈28±10 μm remained outside the spectral region of measurements. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 8, 2002, pp. 996–1000. Original Russian Text Copyright ? 2002 by Tolmachev, Granitsyna, Vlasova, Volchek, Nashchekin, Remenyuk, Astrova.     

Infrared Optical Fibers

A state of the art review of nonsilica based infrared fibers is presented. Two types of fiber materials have been investigated--crystals and glasses. Crystal fiber work appears to be focused on development of short haul CO/sub 2/ laser power delivering lines at 10.6 µm. The maximum delivering power of the CW CO/sub 2/ laser has reached up to about 100 W by the polycrystalline KRS-5 fiber. A number of glass fibers are being developed in fluorides, sulfides and heavy metal oxides. The best optical attenuation of each glass fiber has been respectively reduced to 21 dB/km at 2.55 µm for ZrF/sub 4/-based glass fiber with a core-clad structure, 78 dB/km at 2.4 µm for As-S unclad glass fiber, and 13 dB/km at 2.05 µm (70 dB/km at 2.40 µm) for GeO/sub 2/-Sb/sub 2/O/sub 3/ glass fiber with a core-clad structure. Recent progress of these infrared fibers offers great potential for new wavelength fiber finks operating in the 2-10 µm region which have not been realized by silica-based fiber.     

Efficient ER3+-doped CW fluorozirconate fiber laser operating at 2.7 µm pumped at 980 nm

Efficient operation of a cw fluorozirconate fiber laser at 2.7µm pumped at 980 nm is reported. Threshold powers below 1 mW, efficiencies up to 9.3% and output powers up to 6 mW were observed. CW laser operation occurred although the lifetime of the upper laser level is shorter than that of the lower laser level and excited state absorption from the upper laser level additionally weakens population inversion. The mechanisms clarifying cw operation of this self-terminating transition are discussed. The laser operates at several lines between 2.70 and 2.82µm, whereby the operating wavelength increases with increasing pump power.     

Long-wavelength optical fiber communication

Recent research on long-wavelength lightwave communication utilizing the wavelength region between 1.3 and 1.6 µm is reviewed with an eye toward future system development. The attraction of the long-wavelength region is the availability of the ultimately low-loss and wide-band features of the silica fiber, where minimum loss is 0.27 dB/km at a wavelength of 1.3 µm and 0.16 dB/km at 1.55 µm. The single-mode fiber has found its first significant applications in long-wavelength systems. The specific characteristics of lightwave components are discussed with focus on physical fundamentals. The practical performance of fibers and lightwave devices is surveyed. The dynamic properties of long-wavelength laser diodes are discussed in relation to fiber characteristics. The noise characteristics of long-wavelength detectors are considered for the purpose of specifying the repeater spacing. Some system studies are reviewed, for example, 1.3-µm-wavelength lightwave systems, which have demonstrated bandwidth-distance products of about 40 GHz ċ km. Various approaches to extend the capacity of long-wavelength lightwave transmission are given. In the future, the 1.5-µm wavelength system could operate at the lowest loss wavelength region extending from 1.5 to 1.65 µm. Much higher performance, for example, bandwidth-distance products of 185 GHz ċ km, achieved by further continuation of research and development on lightwave sources as well as fibers. Because of the author's familiarity with work in Japan, that work is emphasized and most frequently cited.     

Light emitting diodes for the spectral range λ=3.3–4.3 µm fabricated from InGaAs and InAsSbP solid solutions: Electroluminescence in the temperature range of 20–180°C (Part 2)

Light-emitting diodes (LEDs) based on p-n homo-and heterostructures with InAsSb(P) and InGaAs active layers have been designed and studied. An emission power of 0.2 (λ=4.3 µm) to 1.33 mW (λ=3.3 µm) and a conversion efficiency of 30 (InAsSbP, λ=4.3 µm) to 340 mW/(A cm²) (InAsSb/InAsSbP double heterostructure (DH), λ=4.0 µm) have been achieved. The conversion efficiency decreases with increasing current, mainly owing to the Joule heating of the p-n homojunctions. In DH LEDs, the fact that the output power tends to a constant value with increasing current is not associated with active region heating. On raising the temperature from 20 to 180°C, the emission power of the (λ=3.3 and 4.3 µm) LEDs decreases, respectively, 7-and 14-fold, to become 50 (at 1.5 A) and 7 µW (at 3 A) at 180°C.     

Growth and characterization of GaAs films deposited on Ge/Si composite substrates by metalorganic chemical vapor deposition

We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.     

Comparison of Hg0.6Cd0.4Te LPE layer growth from Te-, Hg-, and HgTe-rich solutions

Hg1-xCdxTe has been grown on CdTe substrates by liquid-phase epitaxy (LPE) from: 1) Te-rich solution at atmospheric pressure in a slider system, 2) Hg-rich solution in a sealed tube dipping system, and 3) HgTe-rich solution in sealed tube tipping and sliding systems. For epitaxial layers grown from Te-rich solution at 500°C, the width of the graded composition region is 3 µm and the compositional variation across the layer and with depth into the layers is less than ±0.01 mole fraction CdTe. The graded composition region for layers grown from Hg-rich solution at 460°C is less than 3 µm; however, there is no uniform composition region because of CdTe depletion from the melt. The graded bandgap region for pseudobinary growth at 700°C is much wider (20 µm) than the other two cases; however, a region of uniform composition can be obtained by growing sufficiently thick layers (> 30 µm). Pseudobinary growth has the theoretical advantage that either p-type or n-type layers may be grown, whereas, only p-type layers may be grown from Te-rich solution at atmospheric pressure.     

Modeling of the seven-terminal transformer implemented in the LTGC-QO

In this paper a seven-terminal transformer has been designed. We have suggested its equivalent-circuit model. This transformer has a primary coil with a center tap and two secondary coils. Based on this transformer, a low-cost transformer-based gate-coupled quadrature oscillator (LTGC-QO) using 0.18 µm CMOS technology has been developed. The LTGC-QO consumes 7 mW at 1 V power supply. The simulated phase noise at 1 MHz offset is–116.3 dBc/Hz. The chip area is 400×500 µm.     

Mini-optically pumped NH3 cavity laser wide band emission at 67.2 µm

The spectral characteristics of mini-optically pumped NH₃ cavity laser emission at 67.2µm was studied. It was found that the spectrum of 67.2µm emission was duality. With low power CO₂-9R(30) pumping condition (lp<1MW/cm²), the spectrum appeared to be two wide FIR laser lines (～4.6GHz for each line), which were the result of competition of multi-Raman processes. With high power pumping condition (lp>2MW/cm²), the spectrum extended to be a very wide band (～14GHz), which was the result of the combination of the competition and interaction enhancement of Raman processes. The wide band spectral characteristics of 67.2 µm would be significant to the tuning of NH₃ OPFIRL.     

Infrared optoelectronic properties of metal-germanium Schottky barriers

An experimental study has been made of the electronic properties of rectifying metal-Ge (n-type) contacts for a range of metals (Au, Cu, Ag, Pb, and Ni) and their optoelectronic characteristics under monochromatic illumination for λ = 0.6328 µm and for 1 µm < λ ≲ 2 µm in the near infrared. For each metal, very idealI-Vcharacteristics were obtained withnvalues from the exponential forward bias region of 1.02 to 1.08 and excellent reverse saturation at 300 K. The dependence of photoresponse on thickness of various metal electrodes (from 50 to more than 1000 Å) was observed.phi_{B}'sfound fromIV C-V, and photoresponse measurements are in close agreement within ±0.03 eV. The dependence of quantum efficiency (QE) upon metal thickness was measured for all metals and these results exhibit the expected decline in QE withd gsim 100Å. Ford lsim 100Å, QE can be as high as 75 percent at λ = 6328 Å, and 48 percent in the wavelength range 1.1 µm < λ < 1.4 µm. QE versushv(1 µm < λ < 2 µm) measurements have identified thresholds for the indirect and direct band-to-band excitation in the germanium and for the internal photoemission of electrons from the metal over the Schottky barrier induced by absorption of the infrared photons.     

Body-driven log/antilog PVT compensated analog computational block

A four quadrant analog multiplier is proposed in this paper. It is using body-driven MOSFETs operating in subthreshold region. In essence, the subthreshold approach is too susceptible to PVT variations. However, these effects have been intrinsically mitigated by the log/antilog characteristics and enable the realization of current-mode multiplication function in simple and power efficient way at the same time. The multiplier is designed in CMOS 0.18 µm 1P6 M process technology. It occupies an active area of 250 µm² and consumes 0.698 µW from ± 0.3 V voltage supply. The results are in agreement with the theory under different conditions.