Relative intensity noise characteristics of injection-locked semiconductor lasers

Abstract

An experimental and theoretical study of relative intensity noise �RIN� spectra of side-mode injection-locked Fabry-Pérot semiconductor lasers is reported. It is shown that the injection-locking technique effectively increases the relaxation oscillation frequency from 4.5 GHz �free-running mode� to 12 GHz �injection-locked mode� and enhances relaxation peaks of the slave laser RIN spectra. Results from our theoretical model, which include the key parameters for semiconductor quantum-well lasers, such as the linewidth enhancement factor, the nonlinear gain saturation coefficients, and optical confinement factor, show good agreement with our experimental results. © 2000 American Institute of Physics. �S0003-6951�00�03435-5� Considerable attention has recently been paid to injec tion locking in semiconductor lasers due to the desire to develop broader-bandwidth laser systems. Several studies have predicted that the modulation bandwidth of strongly injection-locked semiconductor lasers can be significantly improved compared to the free-running case. 1,2 This is very attractive since it may allow one to achieve large modulation bandwidths with conventional semiconductor lasers at room temperature, avoiding the use of advanced devices and the need for complicated fabrication techniques. Injection lock ing influencing the modulation bandwidth of semiconductor lasers was shown experimentally and theoretically. 3 Simpson and Liu indirectly observed the increase of the relaxation frequency 1 and presented the noise reduction for an injection-locked laser. 4 Meng, Chau, and Wu 5 reported ex perimental data directly demonstrating the improvement of modulation responses. Measurements of the eye diagrams of injection-locked lasers also confirm the bandwidth improvement. 6 However, little experimental work on the relative inten sity noise �RIN� and the variation of the relaxation oscilla tion frequency for injection-locked semiconductor lasers are available in the literature. 4,7 Several theoretical simulations of noise characteristics have been reported, 4,8-11 with one of them predicting the relaxation frequency enhancement. 4 In this letter, we report experimental results and theoretical cal culations of RIN spectra of an injection-locked Fabry-Pérot �FP� laser, and show very good agreement between the theory and experiment. We also compare the RIN spectra of the free-running laser with the injection-locked laser and show an increase of relaxation frequency from 4.5 GHz �free running� to 12 GHz �injection locked�.The experimental setup is shown in Fig. 1. The injection signal from a single-mode distributed-feedback �DFB� mas ter laser passes through an erbium-doped fiber-optical ampli fier �EDFA�. The EDFA is used to amplify the pump DFB laser power and control its injection power into the slave laser over a range up to a few milliwatts. A tunable 3-nm a� Electronic mail: s-chuang@uiuc.edu bandwidth optical filter is used to remove excess signals on the side modes. The injection level is monitored by an opti cal power meter...

Bandwidth enhancement of Fabry-Perot quantum-well lasers by injection-locking

“…This is very attractive since it may allow one to achieve large modula tion bandwidths with conventional semiconductor lasers at room temperature, avoiding the use of advanced devices and the need for complicated fabrication techniques. Fur thermore injection locking in semiconductor lasers is an attractive method to ensure single mode operation [13], reduce the linewidth of a free-running laser [14], and eliminate mode partition noise [15], mode hopping, and fre quency chirp from modulated lasers [16]. The injectionlocking technique may also prevent spurious feedback effects that are random and difficult to avoid and can strongly disturb the behavior of the laser.…”

Phase space of tristability in dual injection-locked Fabry-Perot laser diodes

“…Introduction of IL in the mode M = {−5}at longwavelength side with respect to the central mode, creates a valley in the phase plot(solid lines), that can lead to the occurrence of two new stationary points n st (1) andn st (2) , as well as to a reduced value of n st (3) <n th [14]. Analysis shows that n st (2) is different from the other two stationary points in terms of stability [3].…”

“…By reading the phase plot, we can see that the rate of concentration change dn/dt would become negative, causing a further decrease in concentration that would push the system away fromn st (2) and into n st (1) (depicted with arrows on the phase plot for P −5 inj = −17 dBm). By analogy, a perturbation that would increase the concentration, would push the system into n st (3) . Hence n st (2) is a repulsive stationary point, unlike n st (1) and n st (3) , that act as attractive stationary points and can be stable in terms of the small signal analysis.…”

“…The technique of injection-locking, in which light from one (master) laser is injected into the cavity of the slave laser, arises as a promising tool for improving various aspects of photonic components, as well as for realization of novel all-optical ones. One of the historically first noticed benefits of injection-locking is frequency chirping, linewidth, and relative intensity noise reduction in directly modulated lasers [1][2][3]. However, the concept of intermodal injection-locking, in which light from the master laser is injected with a frequency close to one of the slave laser's side-modes, paved the way for utilizing this technique for wavelength conversion [4], transmitter design for wavelength-division-multiplexing passive optical networks (WDM PONs) [5], Radio-over-Fiber systems [6], improved CATV transmission [7], all-optical memories [8], all-optical regenerators [9], or conversion of advanced modulation formats [10].…”

Dynamic Characteristics and Linewidth Enhancement Factor of Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

“…The RIN peaks of a semiconductor laser are at the resonance frequencies of the small-signal modulation response of the laser [7]. The resonance frequency determines the modulation bandwidth of the semiconductor laser.…”