Wavelength Tunable Ultrashort Pulse Research Articles

All-fiber wavelength-tunable mode-locked cylindrical vector beams laser based on multimode interference

Cylindrical vector beams (CVBs) are of increasing concern due to their polarization and axially symmetrical distribution of field intensity. In this paper, we report for the first time an all-fiber single- and dual-wavelength tunable CVBs fiber laser using the nonlinear optical saturation absorption characteristics and filtering properties of nonlinear multimode interference (NL-MMI). In the experiment, the central wavelength of mode-locked CVBs fiber laser can be tuned from 1541 nm to 1564 nm at single-wavelength and from 1542.8 and 1562.925 nm to 1546.52 and 1563.86 nm at dual-wavelength. This NL-MMI-based wavelength-tunable ultrashort pulse CVBs fiber laser has excellent development prospects in optical communication.

Wavelength-tunable mode-locked Yb-doped fiber laser based on nonlinear Kerr beam clean-up effect

We demonstrate a novel approach to achieve wavelength-tunable ultrashort pulses from an all-fiber mode-locked laser with a saturable absorber based on nonlinear Kerr beam clean-up effect. This saturable absorber was formed by a single-mode fiber spliced to a graded-index multimode fiber, and its tunable band-pass filter effect is studied by a numerical model. By adjusting the bending condition of graded-index multimode fiber, the laser could produce dissipative soliton pulses with their central wavelength tunable from1040 nm to 1063 nm. The pulse width of output laser could be compressed externally to 791 fs, and the signal to noise ratio of its radio frequency spectrum was measured to be 75.5 dB. This work provides a new idea for the design of wavelength-tunable mode-locked laser which can be used as an attractive light source in communication system.

Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier**Project supported by the National Basic Research Program of China (Grant No. 2013CB922404), the National Scientific Research Project of China (Grant No. 61177047), and the National Natural Science Foundation of China (Grant No. 61575011).

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power. Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum (center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges. Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm, the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around 1200 nm, and its output power and pulse width are 40 mW and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.

Broadband wavelength tunable mode-locked thulium-doped fiber laser operating in the 2 μm region by using a graphene saturable absorber on microfiber

A broadband wavelength tunable mode-locked Tm3+-doped fiber laser operating in the 2 μm region based on a graphene saturable absorber is experimentally investigated. A section of graphene film is transferred on a microfiber, which allows light-graphene interaction via evanescent field. The microfiber based graphene not only acts as an excellent saturable absorber for mode-locking, but also induces a polarizing effect to form an artificial birefringent filter for wavelength selection. By tuning the polarization states in the laser cavity, the laser exhibits tunable wavelength mode-locked pulses over a wide range from 1880 to 1940 nm. Such a system provides a compact, user friendly and low cost wavelength tunable ultrashort pulse source in the 2 μm region.

Experimental Investigation of Wavelength-Tunable All-Normal-Dispersion Yb-Doped Mode-Locked Fiber Lasers: Compression and Amplification

Wavelength-tunable ultrashort pulse source with high energy is highly desired for a lot of applications. The wavelength-tunable all-normal-dispersion (ANDi) mode-locked fiber laser, which can be compressed easily and amplified by an all-fiber structure, is a promising seed of such a source with compact structures. The pulse compression and amplification at different center wavelengths (from 1026 to 1058 nm) of the tunable ANDi Ybdoped mode-locked fiber lasers that we previously proposed are experimentally investigated in this work. It is found that, for different wavelengths, the duration and chirp of the direct output pulse from the oscillator vary considerably, however, the duration of compressed pulse fluctuates less. For the amplification process, due to the unflat gain spectrum of Yb-doped fiber, the gain at a short wavelength is larger than that at a long wavelength. Consequently, the trends of spectrum distortions induced by the amplification process are different for different wavelengths. These results and analyses will be helpful for the design of a high-energy and wavelength-tunable ultrashort pulse source based on an ANDi seed.

High-speed three-dimensional measurement using electronically controlled wavelength-tunable ultrashort pulse fiber laser

A high-speed three-dimensional measurement system was demonstrated using an electronically controlled wavelength-tunable ultrashort pulse fiber laser and an all-fiber interferometer. A longitudinal scanning range of 2.8 mm and a scanning speed of 100,000 points/s were achieved without moving parts. For a measurement distance of 0.7 m, the sensitivity and accuracy were 70 dB and +/-8 microm, respectively. A clear three-dimensional image of a 100 yen Japanese coin was obtained using this measurement system.

Mode locking of an external cavity asymmetric quantum-well GaAs/AlGaAs semiconductor laser

A theoretical model of the optical gain in asymmetric GaAs/AlGaAs quantum-well lasers is developed. It is demonstrated that the emission spectrum of asymmetric GaAs/AlGaAs quantum-well lasers is much broader than that of standard quantum-well lasers. The experimental samples of such lasers and superluminescent diodes with the emission bandwidth exceeding 50 nm are fabricated. Wavelength tunable ultrashort pulses with duration of 1–2 ps at repetition rates of 0.4–1 GHz are obtained by active mode locking of an external cavity laser.

Novel super-continuum fiber lasers and wavelength-tunable soliton pulses

Advances in ultrashort laser pulse technology have recently generated several new applications in fields as diverse as laser processing, medical and bio-optics, opto-electronics, etc. However, ultrashort-pulse lasers require quiet laboratory environments and water cooling which prevents their use for practical applications. Spectroscopic applications also require a wavelengthtunable ultrashort pulses. The tuning range, however, is generally limited by the gain bandwidth of the laser. Since these pulses are generated with wavelength conversion using nonlinear crystals and mechanical tuning, it is difficult to generate wideband tunable pulses. Of significant interest is the recent development of compact ultrashort-pulse fiber lasers. Since these lasers consist of fiber-optic devices, they produce stable pulses and water cooling is not required. Fiber lasers are also maintenance-free and can work wherever there is electricity. The wavelength of the output pulses, however, can only be changed within the gain bandwidth of the fiber amplifier and the bandwidth is less than 100nm. In our work, we investigate all-fiber wideband utrashort-pulse sources based on ultrashort-pulse fiber lasers and study nonlinear effects in optical fibers. Specialty fibers, such as highly nonlinear fibers and photonic crystal fibers, were recently developed. Their characteristics are determined by their structure and they have demonstrated high energy density and dispersion tunability. Using ultrashort-pulse lasers and suitable specialty fibers, we can generate ultrawideband optical spectra, referred to as a super continuum. All-fiber super-continuum sources have also been reported. However, their noise level is generally high and the super continuum is characterized by excessive fine structure. To date, no practical Figure 1. Optical spectra of wavelength-tunable soliton pulses that were generated through nonlinear effects. As the fiber input power is increased, the center wavelength is continuously red-shifted. We can tune the wavelength from 1.55 to 2.0μm.

Semiconductor saturable absorber mirror with wavelength tailored distributed Bragg reflector

Multi-component semiconductors offer broadband absorption/gain characteristics. In actual devices, however, usable bandwidth of surface-normal devices, e.g. vertical cavity surface emitting lasers, semiconductor saturable absorber mirrors, is limited by the stopband of the distributed Bragg reflector. Using wavelength-tailored distributed Bragg reflectors is a possible solution to extend the operation range in tunable lasers. This study explores the potential of the molecular beam epitaxy technology for preparing monolithic surface-normal semiconductor saturable absorber mirrors for wavelength-tunable ultra-short pulse production. An exceptionally large stopband of a semiconductor saturable absorber mirror of 230 nm, from 1.46 to 1.69 μm, was demonstrated with spatial translation of the wavelength-tailored distributed Bragg reflectors. The tunable operation of the pulsed fiber laser obtained with molecular beam epitaxy grown graded mirrors confirms the capability of this technology. Using these devices as cavity-end mirrors in erbium-doped fiber lasers we could generate and maintain Q-switched and mode-locked picosecond optical pulses over a wavelength range of about 10 nm.

Wavelength tunable ultrashort pulse generation from a passively mode-locked asymmetric-quantum-well semiconductor laser

Optical pulses are generated from a passively mode-locked dual asymmetric-quantum-well semiconductor laser mounted in a linear external cavity. The devices are fabricated with two sections, one of which contains a bend in the waveguide for external cavity coupling. Pulses 2.0–3.9 ps in duration have been generated, which are tunable over 61 nm, from 954 to 1015 nm. Pulse compression yields durations as short as 470 fs with peak powers as high as 1.5 W.

Wavelength Tunable Ultrashort Pulse Fiber Laser.

Compact system of wavelength tunable ultrashort soliton pulse generation has been demonstratedusing modelockedfemtosecond fiber laser and polarization maintaining (PM) fiber. The wavelengths of generated pulsescan be changed continuously by merely varying fiber input power. The generated pulses are almost transformlimited ideal soliton pulses. Two-colored soliton pulses can be generated simultaneously usingthe birefringenceof PM fibers. Using the dispersion shifted PM fibers, in addition to the soliton pulse, the anti-stokespulse is generated at the shorter wavelength side. Using the diameter reduced PM fibers and dispersion shiftedPM fibers, the wavelength tunable ultrashort pulses can be generated in the wide wavelength region of 1.3-2.0μm. In this paper, the characteristics of wavelength tunable soliton pulse are described withthe principles and applications.

Wideband wavelength tunable ultrashort pulse generation using nonlinear effects in optical fibers

Wideband wavelength tunable ultrashort pulse generation using nonlinear effects in optical fibers

Widely wavelength-tunable ultrashort pulse generation using polarization maintaining optical fibers

Characteristics of widely wavelength tunable ultrashort pulse generation using several types of polarization maintaining fibers have been experimentally analyzed. Using the diameter reduced type of polarization maintaining fibers, the wavelength tunable soliton pulse is generated from 1.56 to 2.03 /spl mu/m. It is confirmed that the almost transform-limited 340-fs soliton pulse is generated at a wavelength of around 2 /spl mu/m using a frequency-resolved optical gating method. When low-birefringence fibers are used, it is observed that the orthogonally polarized small pulse spectrum is trapped by the soliton pulse and is also shifted toward the longer wavelength side in the process of soliton self-frequency shift. The wavelength of the orthogonally polarized pulse spectrum is 40-50 nm longer than that of the soliton pulse, and the birefringence of the fiber is compensated by the chromatic dispersion. Finally, a polarization maintaining highly nonlinear dispersion-shifted fiber is used as the sample fiber. When the fiber input power is low, the wavelength-tunable soliton and anti-Stokes pulses are generated. As the fiber input power is increased, the pulse spectra are gradually overlapped and the 1.1-2.1 /spl mu/m widely broadened supercontinuum spectra are generated by only 520 pJ pulse energy.