Osa selfvalidating technique for the measurement of the. Spectral linewidth of semiconductor lasers springerlink. The design of a narrow linewidth dbr laser is described in detail. The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers the linewidth broadening factor. This result suggests that, if the 1f noise component were eliminated, the semiconductor laser linewidth would approach the alreadylow whitenoise line width. Dynamic line broadening of semiconductor lasers modulated. Forthe latter, a dependence ofthe cc factor onthe injected current is observed, and the experimental results are compared with numerical simulations based on a keldysh nonequilibrium greens functions approach. The purpose of this letter is to study possible fundamen tal limitations on the dfb laser linewidth. Measuring the linewidth enhancement factor of semiconductor. Pdf chapter 4 determination of linewidth enhancement. They found the linewidth to be inversely proportional to power and to have a value of 114 mhz at 1 mw per facet. The gain and absorber linewidth enhancement factors. This paper investigates the dynamical and nonlinear properties of silicon based qd lasers through the prism of the linewidth broadening factor i.
Simple method for measuring the linewidth enhancement factor of semiconductor lasers abstract a simple method for measuring the linewidth enhancement factor lef of semiconductor lasers sls is proposed and demonstrated in this paper. We also discuss the various factors influencing the linewidth in microcavity and strained quantum well lasers and the relation between lasing threshold. The simulation results show that the powerlinewidth product can increase by a factor greater than 2 due to lshb for long dfb lasers. Dynamics and spectral characteristics of quantum dot. Narrow spectral linewidth semiconductor lasers springerlink. Influence of injectioncurrent noise on the spectral characteristics. Clamping of the linewidth enhancement factor in narrow quantumwell grinsch semiconductor lasers j. The analysis of different material demonstrates that the. Rp photonics encyclopedia linewidth, bandwidth, laser.
This theory has important implications on the limits of linewidth reduction by increasing the length of dfb lasers and on possible future device design for coherent optical system. One property that distinguishes semiconductor lasers from most other laser systems is that there is a strong. The parameter that quantifies the magnitude of this effect is the linewidth broadening factor lbf, also known as. Linewidth broadening factor and gain compression in. A theory of the spectral width of a singlemode semiconductor laser is presented and used to explain the recent measurements of fleming and mooradian on algaas lasers. Henry stlh theory of laser linewidth in the instance of semiconductor injection lasers. At injection levels i below threshold i linewidth enhancement fador in single quantumwell grinsch semiconductor lasers is investigated theoretidy and experimentally. Measurement of linewidth enhancement factor of semiconductor. This key parameter typically takes values between 2 and 6 in interband lasers with quantum well or quantum dot active media. Spectral linewidth in microcavity surfaceemitting lasers deep blue.
Linewidth enhancement factor 1, also know as chirp parameter or. The gain offset is defined as the difference between the dfb wavelength and the gain. Osa linewidth enhancement factor in semiconductor lasers. Bhattacharyya, role of linewidth enhancement factor on the frequency response of the synchronized quantum cascade laser, opt. The linewidth of a laser is predicted by schawlowtownes formula 4. This method is based on the selfmixing effect when a small portion. To test whether this acoustic broadening was from the measurement system or from the test laser, the entire 11 km fiber length was placed in a styrofoam box to isolate it from these acoustic noises.
Linewidth broadening factor in semiconductor lasers ieee xplore. A new method for measuring the linewidth enhancement factor. Thermally insensitive determination of the linewidth. Introduction t he linewidth enhancement factor, or factor, is an im. Kl optimization from the viewpoint of narrow linewidth operation and stable single mode operation is discussed. The value of lef is very important for many aspects of laser. Dynamic line broadening of semiconductor lasers modulated at. To achieve a narrow laser linewidth, we utilize the high q microring as external cavity feedback and take advantage of the long effective length of the ring.
The linewidth enhancement factors have a very modest effect on pulse energy for a given current and absorption, but a more noticeable one on amplitude and duration. This value is 30 times greater than can be explained by existing theories. The semiconductor diode laser sl has a number of properties that make it a desirable. Buus, linewidth broadening factor in semiconductorlasers an overview, ieee j. Measurements of the semiconductor laser linewidth broadening factor. Donati, measurement of the linewidth enhancement factor of semiconductor lasers based on the optical feedback selfmixing effect, ieee photon. Roundrobin measurements of linewidth enhancement factor of. In semiconductor lasers, spontaneous emission events affect carrie r density, resulting in refractive index and phase changes, thus broadening the linewidth 29. Semiconductor laser linewidth measurements for space. Selfvalidating technique for the measurement of the. Using the hakkipaoli method, the belowthreshold lbfs. Intrinsic homogeneous linewidth and broadening mechanisms of. In order to account for the linewidth broadening at higher currents. This phaseamplitude coupling is a key feature distinguishing semiconductor lasers from any other type of lasers, and is responsible for a much broader linewidth in semiconductor lasers.
The linewidth broadening factor of semiconductor lasers, which is also known as. The measured linewidth broadening factor is in good agreement with theoretical calculations that include the most important many. Linewidth reduction and frequency stabilization of a. Cthk1 linewidth enhancement factor of semiconductor. Measurement of the linewidth enhancement factor of. This parameter is called linewidth enhancement factor lef. We also discuss the various factors influencing the linewidth in microcavity and strained quantum well lasers. Linewidth enhancement factor an overview sciencedirect. Using the hakkipaoli method, the belowthreshold lbfs around the gain peak are determined to be in the range of 1. Although this formula predicts the linewidth satisfactorily for gas lasers, it fails to predict the linewidth for semiconductor lasers.
Linewidth broadening due to longitudinal spatial hole. Only the photons that leave the cavity from the mirrors constitute useful output. Developments of narrowlinewidth distributedbraggreflection dbr and distributedfeedback dfb lasers are described. For thin wells a small linewidth enhancement factor is obtained which clamps with increasing carrier density, in contrast to the monotonous increase observed for thicker wells. Measuring the linewidth enhancement factor of semiconductor lasers based on weak optical feedback effect abstract semiconductor lasers are very different from other lasers because refraction variation cant be avoided when the gain is changed. The method itself provides an estimation of the measurement error, thus selfvalidating the entire procedure. Forthe latter, a dependence ofthe ccfactor onthe injected current is observed, and the experimental results are compared with numerical simulations based on a keldysh nonequilibrium greens functions approach. Cthk1 linewidth enhancement factor of semiconductor lasers. Linewidth broadening factor of an interband cascade laser. Semiconductor lasers are the most notable of these. The simulation results show that the power linewidth product can increase by a factor greater than 2 due to lshb for long dfb lasers.
Introduction the most important property of lasers not captured by semiclassical theories, which treat the. In addition, low chirp attributes to small linewidth enhancement factor lef which is an essential parameter in semiconductor lasers and determines the modulationinduced chirp, spectral linewidth, external optical injection sensitivity, and output beam characteristics 9, 15. A novel method for extracting the linewidth broadening factor of. The qd dfbs are complex coupled to a lateral chromium grating alongside the ridge waveguide laser cavity su et al. Roundrobin measurements of linewidth enhancement factor. A firstorder frequencydependent formula of the linewidth broadening factor. A theoretical analysis for gigabitsecond pulse code modulation of semiconductor. We discuss the status of the schawlowtowneslaxhenry stlh theory of laser linewidth in the instance of semiconductor injection lasers. Refraction variation can be introduced the theory of semiconductor laser by a dimensional parameter. Laser linewidth in a typical single transversemode hene laser at a wavelength of 632. Measurement of linewidth enhancement factor of different. This work reports on the ultralow linewidth enhancement factor a hfactor of semiconductor quantum dot lasers epitaxially grown on silicon. All measurements were performed with a te cooler at 15 c.
Pdf linewidth broadening factor of an interband cascade. This work reports the linewidth broadening factor lbf of a continuouswave interband cascade laser operated both below and above threshold. Theory of the linewidth of semiconductor lasers ieee. Buus, linewidth broadening factor in semiconductor lasers an overview, ieee j. Linewidth enhancement factor an overview sciencedirect topics. For example, it is a measure of linewidth broadening and chirp in directly modulated lasers, and of the strength of phase. The semiconductor diode laser sl has a number of properties that make it a desirable light source for spectroscopy. Linewidth broadening factor and gain compression in quantum. Linewidth broadening factor of a microcavity semiconductor. Measurement of linewidth enhancement factor of semiconductor lasers using an injectionlocking technique g. Thermally insensitive determination of the linewidth broadening factor in nanostructured semiconductor lasers using optical injection locking.
Linewidth enhancement factor in semiconductor lasers subject to. Moloneyl 1 arizona center for mathematical sciences, university of arizona, tucson az 85721, usa 2 us. Simple method for measuring the linewidth enhancement. This behaviour is reminiscent of exciton dephasing in semiconductor quantum wells due to scattering with an acoustic phonon with energy much smaller than k b t, where t is the sample temperature25. Owing to the low density of threading dislocations and resultant high gain, an a h value of 0.
Quantum cascade laser, linewidth enhancement factor, optical. The linewidth of qd dfbs with different gain offsets and a commercial 1. Oct 29, 2019 this work reports the linewidth broadening factor lbf of a continuouswave interband cascade laser operated both below and above threshold. Buus, linewidth broadening factor in semiconductor lasers anoverview, ieee j. On the other hand, the laser linewidth from stabilized lowpower continuouswave lasers can be very narrow and reach down to less than 1 khz.
Results for two lasers at 7 nm and 20 nm detuning from the gain peak will be presented to compare the effects of minimizing the linewidth enhancement factor, figure 4 shows the power dependence of the electrical power spectrum fwhm of the lasers using a 5km fiber. The consequences for the linewidth and transient wavelength chirping in 1. Aside from the advantages in size, cost and complexity, sls cover a broad spectral range and may easily be modulated at rates up to several gigahertz. Measurement of linewidth enhancement factor of semiconductor lasers using an injectionlocking technique article in ieee photonics technology letters 5. The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasersthe linewidth broadening factor. The emission linewidth above threshold is measured in a gaasalgaas microcavity surface. Laser linewidth theory was pioneered by schawlow and townes 1 and further developed in 2 and 3. An excitonic correction to the relaxation properties is shown to occur provided the binding energy of the.
Spectral linewidth in microcavity surfaceemitting lasers. Air force phillips lab, kirtland afb, nm 87117, usa 3 permanent address. The linewidth enhancement factor, also known as the. Linewidth broadening factor in semiconductor lasers an overview abstract. Fm is the fm efficiency mhzma, i b is the bias current level above threshold, and. Linewidth broadening factor and optical feedback sensitivity. Compact narrowlinewidth integrated laser based on a low. A novel method for extracting the linewidth broadening. We also need expressions for the light coming out of the laser. Linewidth broadening factor in semiconductor lasersan. As it also results in an additional linewidth broadening of the laser, it is usually referred to as linewidth. Indexing terms measurement, semiconductor lasers a simple and accurate method to measure the linewidth enhancement factor u in dfb semiconductor lasers is pro posed.
Kl optimization from the viewpoint of narrowlinewidth operation and stable single mode operation is. Mar 01, 2019 this paper investigates the dynamical and nonlinear properties of silicon based qd lasers through the prism of the linewidth broadening factor i. We show that for a dfb laser without facet reflectivity, the reduction of the linewidth with the laser length will be slower than 1 l 3 due to longitudinal spatial hole burning. This objective is tangible since the 1f noise in semiconductor lasers usually extends only to a few hundred kilohertz. Kruger, simultaneous measurement of the linewidth enhancement factor.
There was no ob served decrease in the laser linewidth due to this system. Roundrobin measurements of the linewidth enhancement. Intrinsic homogeneous linewidth and broadening mechanisms. Is there a linewidth theory for semiconductor lasers. Jun 15, 2016 thermally insensitive determination of the linewidth broadening factor in nanostructured semiconductor lasers using optical injection locking. An improved delayed selfheterodyne interferometer for. Rp photonics encyclopedia linewidth enhancement factor. The linewidth enhancement factor had previously been identified with gain induced antiguienng effects 9 and with multnstabnlity and hysteresis in external cavity lasers 10. They do not significantly affect the onset of the qs instability the lower current or. Semiconductor quantum dot lasers epitaxially grown on. Novel measurement technique of alpha factor in dfb. Buus, linewidth broadening factor in semiconductor lasersan overview, ieee j.
The design of a narrowlinewidth dbr laser is described in detail. Importance of the microscopic effects on the linewidth. Oka mura and iwatsuki 3 used a dhsi system with a 72 km fiber delay line to measure the linewidth of an erbium. Clamping of the linewidth enhancement factor in narrow. Measurements which demonstrate the strong dependence of the linewidthbroadening factor. The factor 12 serves to convert the change of power gain. Semiconductor lasers are very different from other lasers because refraction variation cant be avoided when the gain is changed. In quantum cascade lasers, since the lasing transition occurs between two subbands of the conduction band that have therefore similar curvatures, the linewidth enhancement factor was expected to be naught. Developments of narrow linewidth distributedbraggreflection dbr and distributedfeedback dfb lasers are described. Buus, linewidth broadening factor in semiconductor lasersanoverview, ieee j. More precisely, it is the width of the power spectral density of the emitted electric field in terms of frequency, wavenumber or wavelength. Re cently, however, the dshi technique has also been used to measure linewidth in fiber laser systems 21, 3.