Increasing attention has been devoted to pulse generation from nitridebased semiconductor blue lasers by gainswitching technique 14,15,16,17, which is a simple and inexpensive technique of shortpulse generation through direct modulation of semiconductor lasers. Rp photonics encyclopedia gain switching, gainswitched. Fp semiconductor laser is much smaller than that in a gainswitched singlemode distributed feedback. Because laser operation starts with some low level of fluorescence light, which first needs to be amplified in a number of resonator roundtrips, the pulses are emitted with some temporal delay. Gainswitched semiconductor lasers have been used as compact picosecond optical sources in many applications, such as distance measurements 1,2,3, nonlinear microscope imaging 4,5, and optical communications 6,7. The spectral and temporal characteristics of the pulses obtained with the proposed technique are investigated with numerical simulations. The average output powers in short pulses are usually limited to at most a few milliwatts, except for optically pumped surfaceemitting externalcavity semiconductor lasers vecsels, which can generate multiwatt average output. Gain switching is a method for pulse generation by quickly modulating the laser gain via the pump power. Transient gain analysis of gainswitched semiconductor.
The present work presents the study of an ultrashort pulse high quality laser source. Gainswitched pulse generation with semiconductor lasers. Pdf frequency dynamics of gainswitched injectionlocked. The degree of temporal synchronization of the pulse. Optical frequency comb generation from semiconductor lasers systematically analyzed. Gainguided laser diodes dont mode hop, they mode ooze as the modes and gain peak shift.
Pdf steppulse modulation of gainswitched semiconductor. Gainswitched semiconductor lasers are good candidates for use as seed lasers 11,12,14,15,16,17, owing to their many unique properties including their simplicity, frequencytunable capability. The requirements for low time jitter and reduced frequency chirp operation. The simplest way to analyze and understand laser dynamics is using rate equations. If one follows a guided mode through one complete roundtrip of the cavity, one finds that the change in optical power after one. Gain modulation by graphene plasmons in aperiodic lattice.
Gain switching is one of the most interesting methods used. The temporal and spectral characteristics of the resulting pulses are compared. Figure 1b shows the shortest pulses of the gainswitched semiconductor lasers achieved in the past 40 years both via electrical and optical pumping 24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39. Semiconductor lasers are essentially diodes which produces coherent light through the process of stimulated emission. Read semiconductor lasers and herterojunction leds quantum electronics principles and applications. We propose a pulse shaping and shortening technique for pulses generated from gain switched single mode semiconductor lasers, based on a mach zehnder interferometer with variable delay. Frequency dynamics of gainswitched injectionlocked. All the semiconductor lasers were pumped with impulse optical pumping, and all the generated gainswitched output pulses were well described by exponential functions in their rise parts, wherein the transient gains were. Single peak gainswitched optical pulses with pulse widths less than or equal to 40 ps and optical powers equal to 100 mw are observed when electrical pulses with duration of 800 ps are applied. This in turn requires high doping and current levels. The effect of nonlinear gain on the frequency response of semiconductor lasers at high bias powers is analysed using the multimode rate equations.
Gain switching of a doublecorewaveguide semiconductor. The frequency dynamics of gainswitched singlemode semiconductor lasers subject to optical injection is investigated. Effect of nonlinear gain on the bandwidth of semiconductor. In this chapter, we will setup laser rate equations using the fabryperot optical cavity as a model.
Highenergy subnanosecond optical pulse generation with a. However, it was very difficult to obtain short pulses with duration shorter than. Once the laser is pumped above threshold, a surge of stimulated emission depletes the carriers faster than they can be injected, resulting in a very short, high power spike the gain switch spike of the pulsed dbr laser. The goal of this paper is to present and compare measured results from bulk and quantum well laser diodes utilizing the. The gainswitching dynamics of singlemode pulses were studied in blue ingan multiplequantumwell verticalcavity surfaceemitting lasers vcsels through impulsive optical pumping. Semiconductor lasers types, applications, construction. Optical injection may improve or deteriorates the optical frequency comb quality. A systematic analysis of the influence of the capture, interlevel relaxation and exciton dephasing time constants on the dynamic behavior of quantum dot fabryperot semiconductor lasers is done taking into account the lasing from the ground and excited states. The simulation results show that the carrier time constants studied influence significantly the. The spectral and temporal characteristics of the pulses obtained with the proposed technique are investigated with. Light is emitted at a junction between two regions of opposite doping as shown in gure 4. Dynamics of gainswitched and modelocked semiconductor lasers. Osa gainswitching dynamics in optically pumped single. Suppose the modal gain is ag and the facet reflectivities are r1 and r2.
Ultrashort pulses were observed early in the development of diode lasers. Comb coherence relies on nonfull extinction of stimulated emission between pulses. If a high pump power is suddenly applied to a laser, laser emission sets in only with a certain delay, as it starts with weak fluorescence light, which first needs to be amplified in a number of resonator round trips. To analyze the gainswitching dynamics of the ld endpumped nd. In lasers, mirrors form a resonator or cavity that is used to circulate light. Common materials for semiconductor lasers and for other optoelectronic devices are. When the gain of a semiconductor laser is switched by a short electrical pulse from a state below threshold into gain inversion, the light emitted from the laser exhibits relaxation oscillations. The temperature dependence of the gain in semiconductor. The gainswitched laser pulses with controllable repetitionrate from 1hz to 4khz and pulse width of 16 ns are obtained.
The temperature dependence of the gain in semiconductor lasers paul togher september 1996 a thesis submitted to the university of surrey for the degree of doctor of philosophy. Experimental study of optical frequency comb generation in. To find the modal gain, one starts from the requirement that the emission as well as absorption of photons, must conserve. Abstract the two processes of gain switching and modelocking in a semiconductor laser are studied within a single theoretical framework. Some gas lasers can be operated with a pulsed excitation current. The mode of operation is somewhat di erent than that of the laser described in the previous chapter. Ultrafast pulse generation by semiconductor lasers. Among the three main strategies for generating ofcs from semiconductor lasers, namely mode locking, gain switching and electrooptic modulation, gain switching has attracted specific attention due to its easy implementation, high flexibility in the selection of the repetition frequency and low losses. From cost point of view the semiconductor lasers are economical. Pdf fast phenomena in semiconductor lasers researchgate. As a result, we can acquire the output pulse with a higher peak power the. Suppression of the power overshoot, typical during gainswitched operation, can be.
The compact, inexpensive, and easytooperate gainswitched semiconductor lasers have wide potential applications as pulse light sources in industries and medical treatments 1. Semiconductor laser is well suited for interface with fiber optic cables used in communication. The gain switching of the laser using a high power sine wave signal that drives the laser gain above and below the lasing threshold is a. However, there are also optically pumped semiconductor lasers, where carriers are generated by absorbed pump light, and quantum cascade lasers, where intraband transitions are utilized. Steppulse modulation of gainswitched semiconductor pulsed laser article pdf available in applied sciences 93. Yvo 4 microchip laser, a theoretical model has been developed. A study of the gainswitching process in gainn mqw laser diodes is reported.
The generation of picosecond optical pulses using the gainswitching method is examined using two different types of current drive at 1 ghz. Lasers emit coherent light at wavelengths that are well defined. Pdf the effect of strong externalinjection into a commercial semiconductor diode to increase the laser bandwidth such that gainswitched pulses can. Gain switching of a laser diode is easily achieved by capitalizing the first period of the relaxation oscillation which is generated by switching on a diode laser biased just below threshold56 with injected electrical or optical excitations. Our conclusion is that we will have net optical gain, i. Timing and amplitude jitter in a gainswitched multimode. Department of physics, university of surrey, guildford, surrey, gu2 5xh, u. In many cases, distributed feedback dfb lasers are used to meet the requirements of high pulse peak power andor singlemode. Gain switching is a technique for generating short optical pulses in a laser by. These wavelengths are usually fixed once the device has been fabricated. We call the device that delivers energy to the gain medium e.
However, the result is not necessarily gain switching in the sense of using the first emitted spike. This is often done with tea carbon dioxide lasers co 2 lasers, which are suitable only for pulsed operation. Pdf high frequency pulse generation using a gainswitched. Emission, absorption and modal gain the analysis of a semiconductor laser diode requires a detailed knowledge of the modal gain, which quantifies the amplification of light confined to the lasing mode. Highenergy picosecond pulse generation by gain switching in. Also, semiconductor lasers can be used for the generation of ultrashort pulses with mode locking or gain switching. Laser dynamics singlemode the larger this product the larger is the small signal gain g 0 achievable with a certain laser material. Femtosecond pulse generation beyond photon lifetime limit. In contrast to q switching, where the resonator losses are modulated, gain switching is the generation of short optical pulses by modulating the pump power. Gain switching occurs as a large number of carriers are initially pumped into the active region of the laser.
Theory of ultrashort pulse generation and amplification by gain. The frequency dynamics of gain switched singlemode semiconductor lasers subject to optical injection is investigated. We analyzed the transient gain properties of three gainswitched semiconductor lasers with different materials and cavity structures during pulse lasing. Spectral dynamics of picosecond gainswitched pulses from. Download semiconductor lasers and herterojunction leds quantum electronics principles and applications ebook free in pdf and epub format. The limiting factors in short pulse generation by gain switching of semiconductor lasers are analyzed using an approach parallel to conventional q switching analysis. The limiting factors in short pulse generation by gain switching of semiconductor lasers.
The initial gain and the cavity photon lifetime, respectively, limit the rise and. Rp photonics encyclopedia semiconductor lasers, laser diodes. This source is based on gain switching diode lasers and pulse compression schemes. Gainswitching conditions are determinant for the frequency comb quality. Smaller size and appearance make them good choice for many applications. The advantage of using the gain switched pulses is the. The influence of the photon lifetime in the laser cavity has been examined for both types of drive, and it is shown. Semiconductor lasers and light emitting diodes 222 variety of forms including optical, electrical, or chemical. Steppulse modulation of gainswitched semiconductor pulsed laser. Gainswitching is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, of the order of picoseconds 10. Gainswitched semiconductor lasers provide an alternative solution, which have performed shortest pulses of picoseconds duration since 1970s. The value of the material gain that satisfies the lasing condition, 2 1 1 2 r r e ag l. The model is based on the rate equations of fourlevel systems and some practical physics conditions. The gain medium is pumped by an external source, which is electrical in nature in case of semiconductor lasers 3.
One method to create ofcs is by gainswitching a semiconductor laser 410. Femtosecond pulse generation beyond photon lifetime limit in gain. Chapter 7 lasers after having derived the quantum mechanically correct suszeptibility for an inverted atomic system that can provide gain, we can use the twolevel model to study the laser and its dynamics. A theory of the nonlinear ultrashort dynamic response of unbiased gainswitched. The standard gain switching arrangement is to drive a laser, biased below threshold, with an electrical rf generator. It is shown that the pulse profiles generated for each process are governed by essentially the same equations, and that the difference between the two cases lies merely in the value of a timescale. Linear and nonlinear pulse compression for inp monolithic. Pulse widths of gainswitched pulses range from several tens to several hundreds.
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