Box 122, beijing university of posts and telecommunications, beijing 100876, peoples republic of. Passive mode locking in a passively modelocked laser, the loss modulation is done by a saturable absorber, such as a sesam p. A mode locking mechanism by active gain modulation is studied numerically and experimentally. The second one is optical kerreffect based mode locking, for example, nonlinear polarization rotation npr technology 17 19.
Of the transient evolution of am modelocking tea c02 laser. Cntbased saturable absorbers with scalable modulation. Active mode locking in an actively modelocked laser, as. Modelocking via active gain modulation in quantum cascade. Monolayer graphene has a remarkably large modulation depth of 65. The extinction ratio will be close to, but not exceed, the extinction ratio of the modulator. Selfstarting mode locking of the laser occurred at the incident pump power of about mw. Frequencymodulation mode locking of a semiconductor laser article pdf available in optics letters 1622. Saturable plasmonic metasurfaces for laser mode locking. A new modelocking method of tunable dye laser is described. By employing the ccg as a feedback element,33,34 steady single mode thz qcl operation can be obtained with relatively high output power. We give a comprehensive overview on passive mode locking of solidstate lasers with slow saturable absorbers, based on analytical and numerical calculations.
Based on acoustooptic or electrooptic elements, modelocking has been demonstrated in various earlier reports on lasers 1417. However, strong thermal effects and photorefractive bleaching characteristic for lif crystals delimqswitched mode locking in diode pumped lasers 318 optoelectron. For picosecond lasers, we present a simple equation to estimate the obtained pulse duration and compare the results to those for mode locking with fast saturable absorbers. Numerical study on the minimum modulation depth of a saturable absorber for stable fiber laser mode locking article pdf available in journal of the optical society of america b 321 january. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Introduction commonly used method to generate nanosecond or sub. The amplitude modulation am modulation depth figure is complementary to the modulation index. The detection power does not describe the detected power at locking status. It is a modulation on a different frequency from the original signal, to transfer out of f 1 noise fig. Monolayer graphene as a saturable absorber in a mode. It can be explained by the value of the modulation depth required for modelocking. Active modelocking via pump modulation in a tmdoped.
Harmonic modelocking and wavelengthtunable qswitching. Mode locking with crossphase and selfphase modulation. Semiconductor saturable absorber mirrors sesams are the most traditional sas and are 1commonly used in solidstate and fiber lasers. In this paper the study of frequency modulation harmonic modelocking for ytterbium doped fiber laser is presented. Cvdgrown mose2 with high modulation depth for ultrafast.
Reliable selfstart mode locking of a fiber laser can be ensured when the saturation energy of an absorber is one order of magnitude lower than the circulating pulse energy in a resonator, while the minimum modulation depth must be higher than 4 %. We demonstrate that a 100% modulation depth can be achieved as a consequence of a strong interaction of the. Experimental setup figure 3 shows the schematic of the bp qswitched and modelocked er. This article is about modelocking in lasers, which is fine, but modelocking is a more general topic applicable to all sorts of nonlinear oscillatory systems.
We also discuss how much shorter the pulse duration can. The shorter pulse width obtained could be understood from the large normalized modulation depth of the graphene. We also discuss how much shorter the pulse duration can be. Depending on a pulse fluence, the optical properties of sesam can be modified in two. Iondoped crystals are another type of sa frequently used in mode locking or qswitching applications2. Cvdgrown mose2 with high modulation depth for ultrafast mode. A modelocking mechanism by active gain modulation is studied numerically and experimentally. This article is about mode locking in lasers, which is fine, but mode locking is a more general topic applicable to all sorts of nonlinear oscillatory systems. The frequency response of the modulation depth of a semiconductor optical amplifier can be improved in a. A modulation index of 1 is the maximum level of modulation that can normally be applied and occurs when the envelope increases by a factor of 1, i. In general modulation depth will find over in the carrier signal am i correct. The minimum achievable pulse duration and the output power decrease by increasing the modulation depth. A modulation depth of 100% thus corresponds to a situation where the minimum value of the modulated quantity is zero, and the maximum is twice the mean value.
Narrowing linewidth of wavelengthswept active mode locking. A passive modelocked diodepumped selffrequencydoubling yb. This mechanism allows us to generate shorter pulses than with active mode locking. For lif modulators we observed much longer envelopes with the modulations depths much better than 50%. The frequency response of the modulation depth of a semiconductor optical. Theory of lock in modulation and demodulation 1 general scheme of lock in ring the synchronous moddemod is also called lock in modulationfig. Passive mode locking in a passively mode locked laser, the loss modulation is done by a saturable absorber, such as a sesam p. Based on acoustooptic or electrooptic elements, modelocking has been demonstrated in. Terahertz thz frequency technology has many potential applications in nondestructive imaging, spectroscopic sensing, and highbitrate freespace communications, with an optical modulator being a key component. Pdf frequencymodulation mode locking of a semiconductor laser. We have investigated the broadband saturable absorption property of graphenebi 2 te 3 heterostructures and demonstrated their applications for stable harmonic modelocking operation in a ybdoped fiber laser and wavelengthtunable qswitching operation in an erdoped fiber laser. Yab laser with a low modulation depth semiconductor saturable absorber mirror operating at 374 mhz is demonstrated. Selfmodelocking of quantum cascade lasers with giant.
Integrated terahertz graphene modulator with 100% modulation. This technique is called fm mode locking fm frequency modulation, although the term phase modulation mode locking would seem to be more appropriate. Nonlinear multimodal interference for ytterbiumdoped all. Understand the principle of amplitude modulation know how to modulate a signal to a certain frequency know how to demodulate a signal back to the baseband can write the equation and draw block diagram for both modulation and demodulation can plot the signal spectrum after modulation and demodulation. Modulation and demodulation medium, it would be dif. The reason is that the shorter the circulating pulses become, the faster the loss modulation. Nonlinear multimodal interference for ytterbiumdoped allfiber modelocking noiselike pulse generation zhiguo lv, zhi yang, dongdong song, feng li, xiaojun yang, yang yang, yishan wang, qianglong li, and wei zhao state key laboratory of transient optics and photonics, xian institute of optics and precision mechanics, chinese academy of sciences, xian 710119.
This device, when placed in a laser cavity and driven with an electrical signal, induces a small, sinusoidally varying frequency shift in the light passing through it. We conducted a numerical study to investigate the minimum modulation depth of a saturable absorber that is essentially required for stable optical pulses to be generated from a passively modelocked fiber laser cavity. Introduction semiconductor saturable absorber mirrors are important components used for passive mode locking and q. The reason is that the shorter the circulating pulses. It is shown that the buildup time to reach steady state can be, depending on the modulation depth, considerably larger than the duration of the pulse train. To our knowledge, it is the first time to experimentally demonstrate the saturable absorption property of the bp beyond 3 m. Harmonic mode locking with 850fs pulse duration, 202. We conducted a numerical study to investigate the minimum modulation depth of a saturable absorber that is essentially required for stable optical pulses to be generated from a passively mode locked fiber laser cavity. Therein, the nonlinear absorp tion and modulation depth of the all. Cvdgrown mose2 with high modulation depth for ultrafast modelocked erbiumdoped.
The second one is optical kerreffect based modelocking, for example, nonlinear polarization rotation npr technology 17 19. Lowthreshold continuouswave modelocking is achieved with a transformlimited pulse width of 4. A passive mode locked diodepumped selffrequencydoubling yb. Monolayer graphene as a saturable absorber in a modelocked. However, it has proved challenging to achieve highspeed modulation with a high modulation depth across a broad bandwidth of thz frequencies. Selfmodelocking of quantum cascade lasers with giant ultrafast optical nonlinearities roberto paiella,1 federico capasso,1 claire gmachl,1 deborah l. Somewhat less obviously, active mode locking also works with a periodic phase modulation instead of amplitude modulation e. Iondoped crystals are another type of sa frequently used in modelocking or qswitching applications2.
Theory of lock in modulation and demodulation 1 general scheme of lock in ring the synchronous moddemod is also called lock in modulation fig. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. Passive mode locking with slow saturable absorbers. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone.
The multifarious performance comparisons indicate that the cvdbased mose. Pdf narrowing linewidth of wavelengthswept active mode. By adopting sesam with 3% modulation depth, stable femtosecond modelocking of tm. Lowthreshold continuouswave mode locking is achieved with a transformlimited pulse width of 4. Numerical study on the soliton modelocking of the er3.
The pulse duration and signaltonoise ratio of the laser are 207fs and 85db, respectively. Generally, soliton lasers operating in anomalous dispersion like ours requires. As known, the active modelocking technique can be achieved using amplitude or frequency modulation. The modulation depth of a graphenebi 2 te 3 heterostructure saturable absorber gbi 2 te 3sa is. Sb4o5cl2 for 34thorderharmonic mode locking sciencedirect. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium. Mode locked lasers are routinely used for a wide variety of applications since they can provide optical pulses ranging in widths from a few femtoseconds to hundreds of picoseconds.
The parameter window for the emission of stable pulse trains was found. The mode locking state could then be maintained to the maximum accessible pump. We demonstrate a novel narrowlinewidth configuration of a wavelengthswept active mode locking aml fiber laser. On the other hand, the modulation depth of the tipcf sa would be high enough for stable femtosecond pulse modelocking, considering that another ti sa with 1. Crossphase and selfphase modulation are used for selfsustained mode locking of a highpower neodymium glass fiber laser. Active modelocking via pump modulation in a tmdoped fiber. Pdf frequencymodulation mode locking of a semiconductor. We think this work opens novel avenues toward optoelectronics device based on sb 4 o 5 cl 2. Kgdwo42 laser leads to significant pulse shortening. Cntbased saturable absorbers with scalable modulation depth. Rp photonics encyclopedia modulation depth, modulator. The radiofrequency rf spectrum of mode locking was shown in fig. Modelocking via active gain modulation in quantum cascade lasers.
Passive mode locking with slow saturable absorbers springerlink. Chapter 5 active mode locking forsimplicity, we assume, that the laser operates inthe transverse fundamental modes and, therefore, we only have to treat the longitudinal modes of the laser similar to a simple plane parallel fabryperot resonator figure. Osa numerical study on the minimum modulation depth of a. Sesamassisted klm has peaktopeak amplitude fluctuations modulation am, active mode locking is frequency modulation fm mode locking, which uses a modulator device based on the acoustooptic effect. Modulation depth ni community national instruments. Rp photonics has a deep expertise on different modelocking techniques, types or designs of modelocked lasers, etc. This simplified modelocking of lowpulseenergy systems, such as highrepetition rate solid. Maybe someone can write a more general description for mode locking and perhaps this article can be retitled modelocking lasers, or something similar, to better reflect its content. Integrated terahertz graphene modulator with 100% modulation depth.
We propose and experimentally realize a new class of actively modelocking technique using pump modulation for rareearth doped fiber lasers. A larger normalized modulation depth would result in shorter mode locked pulses. Here, the modulation amplitude is half the mean value. Nonlinear multimodal interference for ytterbiumdoped allfiber mode locking noiselike pulse generation zhiguo lv, zhi yang, dongdong song, feng li, xiaojun yang, yang yang, yishan wang, qianglong li, and wei zhao state key laboratory of transient optics and photonics, xian institute of optics and precision mechanics, chinese academy of sciences, xian 710119.
The saturation intensity and modulation depth are 402. Nevertheless, it can reliably start klm operation, with good daytoday reproducibility. Stable pulses with a fwhm as short as 70 fs and pulse energies of as much as 1 nj are generated at a wavelength of 1. We use the geom to actively modelock an erbiumdoped fiber laser with output pulse duration of 1. Rp photonics encyclopedia active mode locking, actively. Pdf numerical study on the minimum modulation depth of a. From the fitting curve, we can obtain the modulation depth of 7. Actively modelocked laser with an amplitude modulator. Active modelocking via pump modulation in a tmdoped fiber laser. Reliable selfstart modelocking of a fiber laser can be ensured when the saturation energy of an absorber is one order of magnitude lower than the circulating pulse energy in a resonator, while the minimum modulation depth must be higher than 4 %. Pulses as short as 100 fs were obtained with a 2% modulation depth saturable absorber.