Controlling the radiation spectrum of quantum-well heterostructure lasers by ultrasonic strain
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Controlling the Radiation Spectrum of Quantum-Well Heterostructure Lasers by Ultrasonic Strain L. A. Kulakova*, N. A. Pikhtin, S. O. Slipchenko, and I. S. Tarasov Ioffe Physicotechnical Institute, Russian Academy of Sciences, ul. Politekhnicheskaya 26, St. Petersburg, 194021 Russia *e-mail: [email protected] Received October 16, 2006
Abstract—The radiation of a semiconductor laser has been modulated in frequency by variable strain. The strain is excited by injecting bulk or surface ultrasonic waves. Dynamic and static analyses of the variations in the spectral characteristics of the radiation in the presence of sound are performed. A model is suggested and the data obtained are analyzed theoretically. The radiation frequency modulation in InGaAsP/InP heterostructures produced by surface waves is shown to be determined mainly by the band gap modulation of the active region. PACS numbers: 42.55.Px, 42.60.Jf, 73.50.Rb, 74.25.Ld, 78.20.Hp DOI: 10.1134/S1063776107050020
1. INTRODUCTION Optical interferometric measuring systems have increasingly used the frequency modulation of semiconductor lasers since the 1990s [1]. Frequency-tuned diode lasers are also used to create ultrahigh-resolution spectrometers. The simplest frequency tuning method is to vary the operating current [2]. The situation with the frequency tuning in multiple-section diode lasers is technologically more complex [3]. The radiation frequency tuning produced by thermal effects can be used in certain spectrometers [4]. These methods have the following major flaw: the frequency is reproducible relatively inaccurately as it is tuned. On the other hand, elastic strain in semiconductors is known to change both the permittivity [5, 6] and the properties of the electron subsystem [7, 8]. Owing to the photoelastic effect [5], the strain Smn in crystals causes a change in permittivity ∆εik: ∆ε ik = – ε ij p jlmn ε lk S mn ,
(1)
where pjlmn is the photoelasticity tensor component and i, j, k, l, m, n = 1, 2, 3. In what follows, the summation is over the repetitive indices. A moving diffraction grating emerges in the case of elastic waves (Smn ∝ sin(Qx – Ωt), where Q is the wave number and Ω = 2πF is the sound wave frequency). The so-called acoustooptic interaction results in the diffraction of light by this grating. The light beam aperture a is much larger than the sound wavelength Λs, a Λs. The Doppler effect causes the frequency of the diffracted light to be shifted by the sound frequency, i.e., by a value of the order of several hundred megahertz. The situation becomes nontraditional when the ultrasound propagates across a thin nanosized (a in
thickness) semiconductor layer (e.g., in the form of an optical resonator), where a Λs. This means that the permittivity for the light in a resonator may be assumed to vary with time as the strain in a sound wave. Similar variations with time defined by the strain potential constant Λmn [7] can also occur with the band gap Eg: ∆E g = Λ mn S mn .
(2)
One might expect these effects to mani
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