A. P. Astakhova

Experimental observation of whispering gallery modes in sector disk lasers

The existence of the whispering gallery modes in a sector disk resonator has been demonstrated theoretically and experimentally observed in a disk, half-disk, and quarter-disk semiconductor lasers. The half-disk and quarter-disk lasers are fabricated from 285μm diameter disks emitted near 2.13μm at room temperature with continuous wave threshold currents of 55–60mA. Mode spacing in emission spectra of the half-disk lasers was the same as for the whole disk and doubled for the quarter disk as expected from the theoretical analysis. Half-disk lasers emit two parallel beams from the cleaved facet, while the two output beams are perpendicular in quarter-disk devices.

High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring

High efficient LED structures covering the spectral range of 1.6–2.4 µm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached.

Infrared whispering-gallery-mode lasers (λ= 2.4 μm) with convex disk cavity operating at room temperature

A whispering gallery mode (WGM) semiconductor laser with a convex disk cavity operating at room temperature in the middle-IR range (λ = 2.4 μm) has been created for the first time. The convex cavity was formed by etching in a specially selected CrO3-HF-H2O mixture. The room-temperature emission spectra have been measured. The laser generates WGMs at room temperature in a pulsed regime.

Semiconductor WGM lasers for the mid-IR spectral range

Disk-cavity whispering-gallery-mode (WGM) semiconductor lasers for the mid-IR spectral range have been developed. The specific properties of these devices are investigated.

LEDs based on InAs/InAsSb heterostructures for CO2 spectroscopy (λ = 4.3 μm)

Light-emitting diodes (LEDs) operating in a 4.1–4.3 μm wavelength range have been created on the basis of InAs/InAsSb heterostructures grown by metalorganic vapor-phase epitaxy. The output radiation power of LEDs is increased using flip-chip design. Investigation of the electrolumuinescent properties of LEDs with smooth and profiled output edge surface showed that the latter LEDs possess a greater efficiency, which is related to an increase in the radiation yield due to multiply repeated reflection from the curved surface. The output power of LED operating in a quasi-continuous wave mode was 30 μW at a current of 200 mA and that in a pulse mode was 0.6 mW at a current pulse amplitude of 2 A.

Portable optical water-and-oil analyzer based on a mid-IR (1.6–2.4 μm) optron consisting of an LED array and a wideband photodiode

An optical method for measuring the water and oil content using mid-IR (1.6–2.4 μm) LEDs and a wideband photodiode is suggested for the first time. This method is developed based on the absorption spectra of pure water, dewatered oil, and water—oil emulsions (cut oil) with different content of water and uses 10 types of LEDs in the spectral range 1.6–2.4 μm. It is shown that pure water heavily absorbs the LED radiation in the spectral range 1.85–2.05 μm, oil absorbs in the range 1.67–1.87 μm, and the LED radiation with a maximum at 2.20 μm is equally weakly absorbed by water and oil. An optical cell of the water-and-oil analyzer is designed on the basis of a three-element diode array with radiation maxima at 1.65 (detection of oil), 1.94 (detection of water), and 2.2 μm (reference signal) wideband photodiode covering the spectral range 1.3–2.4 μm. A calibration curve is derived that represents the dependence of the water concentration in oil on the amplitude of the reduced signal obtained by processing three signals from the LEDs. This optical method of measuring the water content in oil underlies a portable analyzer making possible online measurements directly in an oil well.

High-power InAs/InAsSbP heterostructure leds for methane spectroscopy (λ ≈ 3.3 μm)

Two designs of light-emitting diodes (LEDs) based on InAsSbP/InAs/InAsSbP double hetero-structures grown by metal-organic vapor phase epitaxy on p− and n-InAs substrates have been studied. The current-voltage and electroluminescence characteristics of the LEDs are analyzed. It is shown that the LED design with a light-emitting crystal (chip) mounted with the epitaxial layer down on the LED case and emission extracted through the n-InAs substrate provides better heat removal. As a result, the spectral characteristics remain stable at increased injection currents and the quantum efficiency of radiative recombination is higher. The internal quantum efficiency of light-em itting structures with an emission wavelength λ = 3.3–3.4 μm is as high as 22.3%. The optical emission power of the LEDs is 140 μW at a current of 1 A in the quasi-continuous mode and reaches a value of 5.5 mW at a current of 9 A in the pulsed mode.

Optical parameters of diode lasers based on an InAsSb/InAsSbP heterostructure

The rates of radiative recombination (including transitions induced by enhanced luminescence) and nonradiative recombination, internal quantum yield of luminescence, and the matrix element for band-to-band optical transitions were determined for the first time for InAsSb/InAsSbP diode lasers oscillating at wavelengths of 3.1–3.2 μm. It is established that the contribution of nonradiative recombination to the lasing threshold can be as large as 97%. The internal quantum yield of luminescence for the InAs0.97Sb0.03 compound is no higher than 3%. Most likely, the nonradiative channel is formed with involvement of Auger recombination with the constant C = 4.2 × 10−38 m6s−1 (T = 77 K). The studied samples of lasers feature relatively low optical losses ρ = 900 m−1 and internal quantum efficiency of emission at the level of 0.6. The spontaneous lifetime of nonequilibrium charge carriers as determined from the radiative-recombination rate is equal to 6 × 10−8 s, which is consistent with known published data.

Impact-ionization-stimulated electroluminescence in isotype n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures

We have studied electroluminescence in n-GaSb/n-AlGaAsSb/n-GaInAsSb heterostructures with isotype heterojunctions, in which the quantum efficiency of emission is increased due to the additional production of electron-hole pairs as a result of the impact ionization that takes place near the heterointerface. The impact ionization in such heterostructures is possible due to the presence of deep wells in the energy band structure.

Current and temperature tuning of quantum-well lasers operating in 2.0-to 2.4-µm range

Radiation spectra of GaInAsSb/GaAlAsSb-based quantum-well diode lasers in pulsed and quasi-continuous operation modes were studied in the temperatures range from −10 to +20°C with driving currents varying from 50 to 200 mA. For currents exceeding the threshold value by no more than 30%, a single-mode lasing was usually observed. A further increase in current leads, as a rule, to the appearance of 3–5 additional long-wavelength cavity modes, which suggests the growth of gain in this spectral range due to the interaction of modes. In single-mode conditions, the lasing wavelength is red-shifted with temperature at a rate of 2–3 Å/K because of the current-induced heating of the laser and the corresponding increase in the refractive index. The rate of this heating is estimated at 0.1 µs.