Dynamics and pulsepackage oscillations in broadarea. Laser dynamics singlemode the larger this product the larger is the small signal gain g 0 achievable with. Due to the effect of laser relaxationoscillations on the relative intensity noise rin, there is rin peak at the laser relaxationoscillation frequency 1, which limits the applications of the lasers. The additive feedback level enhances the light intensity, and the relaxation oscillation frequency of the laser can be broadened by adding the current and the dualfeedback level. In this region, we experimentally observed pulsepackage oscillations. Relaxationoscillationfree semiconductor laser with optical. Laser dynamics singlemode the larger this product the larger is the small signal gain g. The ro frequency is high relationship between the relaxation oscillation frequency of a laser diode and its external cavity length ieee conference publication. The laser emits continuouswave optical signal with pe. Experimental investigation of relaxation oscillations.
Enhancing the relaxation oscillation frequency of a. Spectral signature of relaxation oscillations in semiconductor lasers m. Calculations of relaxation phenomena can be based on the dynamic equations as presented in the article on laser dynamics, which can for small fluctuations, not for. In this case, the dynamical response of a laser is highly. Abinitio theory of quantum fluctuations and relaxation oscillations in.
By continuing to use this site you agree to our use of cookies. Semiconductor lasers are described by two rate equations, one for the photon density and another for the carrier density. In other type lfibased applications, dynamics of laser are used and the laser operates at relaxation oscillation state. The broadening of the relaxation oscillation peak with increasing carrier noise level is interpreted as an increase of the nonlinear gain compression with noise. More interestingly, the relaxation oscillation frequency or period could be clearly extracted from the autocorrelation function acf of the temporal waveform which was the inverse fourier transform of the power spectrum. The classa dynamics of this laser, free of relaxation oscillations, enables one to suppress the electrical phase noise in excess that is.
Oct 28, 20 suppression of relaxation oscillation dynamics in semiconductor lasers with external feedback. Osa nonequilibrium and manybody coulomb effects in the. Relaxation oscillations in lasers ultrafast laser physics. Relaxation oscillation enhancelnent and coherence collapse. Influence of lateral field on the relaxation oscillation. Due to the effect of laser relaxation oscillations on the relative intensity noise rin, there is rin peak at the laser relaxation oscillation frequency 1, which limits the applications of the lasers. Relaxation oscillation enhancement and coherence collapse in. The delay in the laser turnon is independent of the current ramp.
Relaxation oscillation noise suppression in fibre dfb lasers using a semiconductor optical amplifier. Osa experimental demonstration of a tunable dualfrequency. Relaxation oscillation dynamics in semiconductor diode lasers with optical feedback article pdf available in ieee photonics technology letters 2515 march 20 with 225 reads. Thus, precision measurement of the relaxation frequency is important. However, the bandwidth is limited to less than 30ghz. A drawback of such method is that delayed feedback can easily lead to sustained relaxation oscillations ro. We also need expressions for the light coming out of the laser. Ultrafast laser eth zurich physics ursula keller lukas gallmann eth zurich, physics department, switzerland. To reduce the rin magnitude or push the rin peak to. The key to chaos in the laser is the relaxation oscillation which becomes undamped due to the presence of the external feedback. A formula for frequency detuning of the optical dualfeedback is developed to demonstrate that frequency detuning is added with the additive optical feedback.
Pdf relaxation oscillations in a semiconductor quantum. The specific case of a verticalcavity surfaceemitting laser is treated. Diodepumped solidstate lasers longitudinal pumping transversal pumping. Rate equations for a twinemitter phasedarray semiconductor laser are used to show that active optical modulation above the relaxation oscillation frequency can be achieved by introducing a 180 relative phase shift in the emitter current modulation.
Chapter 11 basics of semiconductor lasers cornell university. To find out more, see our privacy and cookies policy. Only the photons that leave the cavity from the mirrors constitute useful output. Simultaneous and robust oscillation of the two orthogonally polarized eigenstates is achieved by reducing their overlap in the optical active medium.
Enhancing the relaxation oscillation frequency of a chaotic. Relaxation oscillation dynamics in semiconductor diode lasers. It is found, for some laser parameters, that gainguided semiconductor lasers with narrow stripe can exhibit higher relaxation oscillation frequency than indexguided devices. Suppression of relaxation oscillation in strong optical. Relaxation oscillation enhancelnent and coherence collapse in. Builtup of laser power from spontaneous emission noise. The ro frequency is high relationship between the relaxation oscillation frequency of a laser diode and its external cavity length.
Understand the relaxation oscillations and dynamics. A treatment of the dynamics in a semiconductor laser that is based on the coupled maxwellsemiconductor bloch equations is described. Rp photonics encyclopedia relaxation oscillations, solid. Relationship between the relaxation oscillation frequency of. Relaxationoscillationfree semiconductor laser with. The oscillation frequency is similar to the inverse period of the spikes.
For operation just above the laser threshold, the relaxation oscillations are slow, and their damping time is about twice the upperstate lifetime of the gain medium. Suppression of relaxation oscillation dynamics in semiconductor lasers with external feedback. Relaxation oscillations rp photonics consulting on laser. Harmonic content and relaxation resonant frequency of a. Figure 2 shows the frequency responses of optical injectionlocked dfb laser across the locking range. Relationship between the relaxation oscillation frequency. Index termsdelay systems, laser theory, optical feedback, relaxation oscillation, semiconductor lasers.
In the latter case, the period of the oscillation is proportional to the relaxation time time constant of the system, hence the term relaxation oscillation. Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback. The oscillation is commonly observed when the injection is moderately strong and positively detuned from the hopf bifurcation boundary. For fourlevel lasers, the damping time is inversely proportional to the pump parameter r note that a saturable absorber in the laser. Pdf we study relaxation oscillations in a semiconductor quantumdot laser using the electronhole asymmetry model m. Pdf relaxation oscillation dynamics in semiconductor. In semiconductor optical amplifiers soas, photons multiplied via stimulated emission.
Introduction semiconductor lasers are important as transmit. Us6943939b1 optical amplifier with damped relaxation. Relaxation oscillation enhancement and coherence collapse. Detailed analysis of coherence collapse in semiconductor. We find experimentally that the relaxation oscillation peak in the relative intensity noise spectrum of a semiconductor laser has a higher damping and lower frequency when we add low frequency noise to the pump current. Abstractthe nonlinear dynamical periodone oscillation of an optically injected semiconductor laser is investigated analytically. Modulation of relaxation oscillation frequency of a dfb laser. Relaxation oscillation noise suppression in fibre dfb. Spectral signature of relaxation oscillations in semiconductor lasers. Instantaneous frequency measurement applied to semiconductor.
Relaxationoscillation phenomena in an injectionlocked. Relaxation oscillation dynamics in semiconductor diode. In this operation region, a semiconductor laser shows a smooth curve, where we can observe uncertainty into defining the onset of laser oscillation. Chaotic oscillations from such a laser are strongly affected by the relaxation oscillation frequency. To the best of our knowledge, no one has considered the problem of harmonic content in the optical frequency response of a laser diode, from an optimization point of view. Zeijlmans abstracta new and relatively simple expression is given for the optical spectrum of a singlemode semiconductor laser which, due to the presence of relaxation oscillations, consists. Relaxationoscillationfree semiconductor laser with optical feedback. Rate equations for a twinemitter phasedarray semiconductor laser are used to show that active optical modulation above the relaxation oscillation frequency can be achieved by introducing a 180deg relative phase shift in the.
A laser diode ld with external feedback can generate undamped relaxation oscillation ro under a certain operational condition. In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave. Pdf relaxation oscillations in a semiconductor quantumdot. Semiconductor optoelectronics farhan rana, cornell university p p p p np n v the number of photons leaving the cavity from the mirrors is therefore, p p p o p p o n n v the output power p of the laser is.
Ultrahighspeed operation of laser diode by crossgain. Us6943939b1 us10101,761 us10176102a us6943939b1 us 6943939 b1 us6943939 b1 us 6943939b1 us 10176102 a us10176102 a us 10176102a us 6943939 b1 us6943939 b1 us 6943939b1 authority us united states prior art keywords optical amplifier reflector laser signal optical prior art date 20020319 legal status the legal status is an assumption and is not a. Here we have approached to establish the reason of relaxation oscillation in semiconductor laser, a matter of discussion over several years, by theoretical considerations relating, the carrier concentration in its active region with the relaxation oscillation i. A drawback of such method is that delayed feedback can easily lead to sustained relaxation. Conference on lasers and electrooptics, quantum electronics and laser science conference, san francisco. For higher powers, the oscillations can faster, and the damping time gets shorter. A desirable feature of a laser is the constant amplitude, shown in figure. Selfmodulation above the relaxation oscillation frequency has been previously observed in a phasedarray semiconductor lasers. One of the characteristic frequencies of chaotic oscillations in semicon ductor lasers with optical feedback is the relaxation oscillation frequency. The classa dynamics of this laser, free of relaxation oscillations, en. Experimental investigation of relaxation oscillations resonance in modelocked fabryperot semiconductor lasers v. Relaxation oscillation of semiconductor laser figure 6. The frequency response of the freerunning dfb laser is shown by the black curve, having a freerunning relaxation oscillation frequency of 3 ghz. The frequency of relaxation oscillations in the output power of lasers, particularly semiconductor lasers, is an important parameter which can be used to inform other fundamental laser variables, for comparison with expected theory, and to show the effect of external influences, such as optical feedback, by a change in value.
Pdf relaxationoscillationfree semiconductor laser with optical. The laser relaxation oscillation ro frequency is proportional to the injected current. Relaxation oscillation dynamics in semiconductor diode lasers with optical feedback daan lenstra, senior member, ieee abstractwe theoretically investigate the stability of a singlemode semiconductor laser with weak optical feedback in the short externaldelay regime. Relaxation oscillations and pulse stability in harmonically modelocked semiconductor lasers farhan rana and paul george abstractin this paper, we discuss pulse dynamics in harmonically modelocked semiconductor lasers and present the conditions necessary for stability. The theoretical model is based on external injection locking il in a sld. Here, the term short indicates that the external mirror is positioned at less than the length corresponding to the laser relaxation oscillation frequency.
The selfpulsation frequency shows up as an enhancement of the oscillation of the laser emission if the two frequencies coincide. The classa dynamics of this laser, free of relaxation oscillations, enables one to suppress the electrical phase noise in. Experimental demonstration of a tunable dualfrequency. Pdf relaxation oscillation dynamics in semiconductor diode. Rate equations for a twinemitter phasedarray semiconductor laser are used to show that active optical modulation above the relaxation oscillation frequency can be achieved by introducing a 180deg relative phase shift in the emitter current modulation. Relaxation oscillation frequency is produced when a laser is operated in the low laser threshold current region. It is well known that laser output power jumps with. It is shown that intraband carrier dynamics and interband coulomb interactions significantly affect the damping of relaxation oscillations. The relaxation oscillation plays an important role in the system. The modulation response has a resonance at the ro frequency. The third scanning fabryperot was a con focal resonator with fsr 750 mhz and finesse 300, and was used to view narrowing of the laser linewidth at weak. Modulation of relaxation oscillation frequency of a dfb. A method to enhance the relaxation oscillation frequency and carrier bandwidth of a delayed feedback semiconductor laser transmitter is presented using additive optical feedback light.
The circuit consists of a feedback loop containing a switching device such as a transistor, comparator, relay, op amp, or a negative resistance device like a tunnel diode, that repetitively charges a capacitor. Semiconductor lasers often make use of external optical feedback, for various reasons, like singlemode selection, stabilization or linewidth narrowing. We investigated the relaxation oscillation enhancement and coherence collapse state of the laser oscillation based on the laser rate equations. Tunable dualfrequency oscillation is demonstrated in a vertical externalcavity surfaceemitting laser.
Mar 07, 2014 semiconductor lasers often make use of external optical feedback, for various reasons, like singlemode selection, stabilization or linewidth narrowing. Influence of current noise on the relaxation oscillation. Relaxation oscillations are small mutually coupled oscillations of the laser. Modulation of twinemitter semiconductor lasers beyond the. The nonlinear laser equations can easily be solved. This paper investigates theoretically the suppression of relaxation oscillation ro in strong optical injectionlocked semiconductor laser diode sld. Montrosset, near threshold operation of semiconductor lasers and resonanttype laser amplifiers, ieee j. The broadening of the relaxation oscillation peak with increasing carrier noise level is interpreted as an increase of the nonlinear gain compression with noise strength. A semiconductor laser having high speed modulation function over a wide temperature range can be attained by making an active layer region 305 of a semiconductor laser as a multiple quantum well structure of ingaalas or ingaas material system, and defining the bandgap wavelength of the barrier layer to less than 950nm, or alternatively, by making the bandgap. In our simulation, an adaptive fourthorder rungekutta algorithm is used to solve the rate equations of injectionlocked sld, the temporal evolution of. This meant that the chaotic carrier had a signature of laser relaxation oscillation. The relaxation oscillation is defined as the small oscillations of. Pdf semiconductor lasers often make use of external optical feedback, for various reasons, like singlemode selection, stabilization or linewidth. Right after the laser turns on, the amplitude varies for a while and then gets stabilized to a constant.
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