Gain Saturation in (In,Ga)N/GaN/(Al,Ga)N Laser Structures

Abstract

We performed systematic studies of the optical gain and its saturation in (In,Ga)N/GaN/(Al,Ga)N laser structures in dependence on photon energy, excitation density and number of quantum wells. The optical gain and its saturation were obtained by means of the variable stripe-length method under quasi-stationary conditions. The unsaturated gain factor increases with increasing excitation power, i.e increasing modal gain, and reaches its maximum at energies slightly below the spectral position of the gain maximum. High unsaturated gain factors of up to 40 dB at 300 K have been measured.A semiconductor optical amplifier is of general importance in photonics because it is a basic component in most photonic integrated circuits and optical fiber systems [1, 2]. Knowledge of its saturation behavior, in particular the maximum unsaturated modal gain, is important for optical communications. Despite this, a detailed investigation of the saturation behavior of (In,Ga)N/GaN/(Al,Ga)N based optical amplifiers is still lacking.Saturation of an optical amplifier could be caused for two reasons: First, if the stimulated-emission rate, caused by amplification of an input pulse, becomes comparable with the spontaneous and nonradiative recombination in the amplifier, the electron± hole pair density is reduced and saturation sets in. This mechanism limits the maximum unsaturated output power of the amplifier. Second, saturation could be already caused by the internal noise, i.e. spontaneous emission, which is also present without an input signal. The fraction of the spontaneous emission which is coupled into the guided amplifier mode is determined by the spontaneous emission factor b [3]. Amplified spontaneous emission (ASE) of these photons could lead itself to saturation and limits the unsaturated modal gain of the amplifier device.We investigated the gain saturation behavior without external input signal, by systematic studies of (In,Ga)N/GaN/(Al,Ga)N laser structures in dependence on photon energy, excitation density, and number of quantum wells.The structures were grown on SiC substrates by metal organic chemical vapor deposition. The samples consisted of a (Al,Ga)N cladding layer, a GaN waveguide layer, an active layer of (In,Ga)N wells, an (Al,Ga)N spacer layer, a GaN waveguide layer, and an (Al,Ga)N cladding layer. Samples with periods of 3, 4, 5, and 10 2 nm thick P. Michler et al.: Gain Saturation in (In,Ga)N/GaN/(Al,Ga)N Laser Structures 391

Optical gain, gain saturation, and waveguiding in group III‐nitride heterostructures

“…This process limits the unsaturated modal gain of the amplifier device. The saturation of optical gain in (In,Ga)N/GaN/(Al,Ga)N laser structures without application of an external input signal is investigated in detail using the variable stripe-length method [66,67].…”

“…Energy dependence of a) the measured modal gain, b) saturation length Ä×, and c) saturation product ÑÓ Ä× for an (In,Ga)N/GaN/(Al,Ga)N laser structure (3 QW sample) at three different excitation densities, respectively (from Ref [67]…”

Optical amplification and photodegradation in films of spiro-quaterphenyl and its derivatives

“…391.5 nm for spiro-quaterphenyl, 401.5 nm for phenoxyspiro-quaterphenyl and 406 nm for methoxy-spiro-quaterphenyl. The gain in the transparency region (long wavelength edge) is not zero but it has negative values caused by of scattering losses due to roughness of the waveguide [30]. For low pump energy fluence, the spectral width of the gain spectrum is small.…”

Analysis of Gain Saturation Behavior in GaN Based Quantum Well Lasers

“…The saturation depends on the amplifier material and is of profound interest for the design of efficient laser amplifiers. However, just a few detailed studies of saturation of GaN-based optical amplifiers have been conducted up to now [3][4][5].…”