Gain Compression Factor Research Articles

Small-signal resonance distortion of semiconductor lasers

Small-signal expressions for the second- and third-order resonance distortion of a semiconductor injection laser are reported. Results are valid even if the frequencies involved are not closely spaced, and are applicable to high-power lasers for which previously published results may not be valid. The new results are more accurate than prior results when the product of the gain compression factor and the photon density is relatively large, or when low frequencies are of interest. The second-order distortion-to-carrier ratio depends on the resultant frequency but not on the individual frequencies involved in nonlinear mixing. The third-order distortion-to-carrier ratio in general depends on individual mixing frequencies, but if all frequencies are small compared to the resonance frequency, then this result also depends primarily on the resultant frequency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anomalous damping in MQW lasers due to slow inter-well transport

The authors present a model for MQW (multiple quantum well) lasers, using the laser rate equations, which includes transport of carriers between the individual wells of MQW lasers. This model provides the first consistent explanation for the anomalously high damping in MQW lasers. It is found that, while electron and hole transfer times both are of the order of 3 ps for typical InGaAs/InGaAlAs structures, hole transfer is much slower than electron transfer in InGaAs/InGaAsP structures, with the hole transfer time being of the order of 100 ps. Since the stimulated recombination times are of the order of 100 ps, this means that one may expect an inhomogeneous hole distribution for the latter case, whereas the carrier distribution is homogeneous for the former case. The effective differential gain derived from the resonance frequency vs. power is found to be almost equal for the two types of lasers. There is a significantly higher damping for the InGaAs/InGaAsP laser, which can be described by an effective gain compression factor almost four times higher than for InGaAs/InGaAlAs.

Experimental determination of gain compression factors of a DFB laser in the presence of TM light injection

Compared to direct current modulation, an optical modulation scheme of laser diodes exhibits no rolling off characteristics due to the electrical parasitics existing in the laser diodes. In particular, in the TM light injection scheme, no injection locking phenomena take place. A number of applications of TM light injection have been reported. In relation to these, determining the gain compression factors of laser diodes in the presence of TM light injection is essential. A new technique for determining these factors is presented. The technique is shown to be viable for measuring the gain compression of distributed feedback (DFB) lasers. >

Transport limits in high-speed quantum-well lasers: experiment and theory

It is shown experimentally that the modulation bandwidth of quantum well lasers can be reduced by a factor of six due to carrier transport across undoped layers of the laser as in the separate confinement heterostructure (SCH). Analytical expressions are given for the modulation response function, resonance frequency, damping rate and K factor to include carrier transport, and it is shown that carrier transport is responsible for a low-frequency rolloff which limits the modulation response of quantum-well lasers. It also shown that carrier transport leads to a reduction in the effective differential gain, while the gain compression factor remains largely unaffected by it.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High speed quantum-well lasers and carrier transport effects

Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as a factor of six in quantum-well lasers. They also show that, in addition, it leads to a reduction in the effective differential gain and thus the resonance frequency, while the nonlinear gain compression factor remains largely unaffected by it. The authors present the temperature dependence data for the K factor as further evidence for the effects of carrier transport. >

Single quantum well strained InGaAs/GaAs lasers with large modulation bandwidth and low damping

Strained In/sub 0.2/Ga/sub 0.8/As/GaAs single quantum well polyimide buried ridge waveguide lasers with 3 dB modulation bandwidths of 15 GHz and gain compression factors in as small as 9.98*10/sup -18/cm/sup -3/ have been fabricated. The authors have also observed that the gain compression factor is not larger than in lasers with bulk active areas, and is lower for structures with a smaller number of wells and shorter cavity lengths.

Gain compression and phase-amplitude coupling in GaInAs quantum well lasers with three, five and seven wells

The gain compression and phase-amplitude coupling factors are measured along with the differential gain in GaInAs/GaInAsP quantum well lasers with three, five and seven wells. Results are compared with those obtained for a conventional bulk laser of the same quaternary material. The ultimate modulation bandwidth deduced from the measurements is shown to increase with the number of wells. For the seven well laser, the ultimate modulation bandwidth is found to reasonably approach that obtained for the bulk laser while the phase-amplitude coupling factor is 2.6 times smaller.

Effect of the nonlinear gain in semiconductor lasers on the performance of multigigabit-per-second lightwave systems

The implications on performance of the functional form of the nonlinear gain in single-mode semiconductor lasers are studied for multigigabit-per-second, intensity-modulation, direct-detection lightwave systems. Compared to a previously used functional dependence on the photon and carrier densities, a new result due to G. Agrawal (1988) can, depending on the fiber dispersion and gain compression factor, yield quite different receiver sensitivities. >

Gain-switched picosecond pulse (&amp;gt;10 ps) generation from 1.3 mu m InGaAsP laser diodes

Fabry-Perot-type laser diodes with high injection efficiency were found to be suitable for ultrashort pulse generation. By decreasing cavity length, the shortest pulsewidth of 6.7 ps at a repetition rate of 100 MHz was achieved under a gain switching scheme. A systematic investigation of bias-level-dependence of pulsewidth, peak output power, as well as the effect of cavity-length shortening was performed. Suppression of facet reflection of a laser diode with a normal cavity length was effective in reducing the pulsewidth (from 16.6 to 10.2 ps). It was found that the optimum condition both for minimizing pulsewidth and for maximizing peak output power can be obtained by selecting the DC bias level. The rate equation analysis also indicated that the gain compression factor may not influence the multimode lasers as much under the gain switching condition as single-mode lasers. The influence of electrical parasitics of the lasers is briefly discussed. >

Optimization of Third-Order Intermodulation Product and Output Power from an X-Band MESFET Amplifier Using Volterra Series Analysis

A third-order analysis for accurately predicting large-signal power and intermodulation distortion performance for GaAs MESFET amplifiers is presented. The analysis is carried out for both single- and two-tone input signals using the Volterra series representation and is based only on small-signal measurements. Simple expressions for the nonlinear power gain frequency response, the output power, the gain compression factor, and the third-order intermodulation (IM/sub 3/) power are presented. The major sources of gain compression and intermodulation distortion are identified. Based on the developed nonlinear analysis in conjunction with the device nonlinear model, a systematic procedure for designing a MESFET amplifier under large-signal conditions for optimum output power and IM/sub 3/ performance is proposed. The method utilizes out of band computed matching compensation through a nonlinear model of the amplifier. The accuracy of the device large-signal and IM/sub 3/ distortion characterization and the practicability of the proposed method are illustrated through comparison between measured and predicted results.

Clinical experience in hearing-aid adjustment by means of BER amplitudes

Assuming that brain-stem-evoked response (BER) amplitudes are correlated with actual loudness, the dynamic range of individual hearing can be determined by means of normal and pathologic amplitude characteristics. This permits an estimation of gain requirement and compression factor in hearing-aid evaluation. Clinical importance and validity of the procedure is investigated in a group of 59 children with impaired hearing. The method yields reasonable values of hearing-aid parameters, which are comparable with those usually obtained by speech audiometry.