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An all-fiber amplification and compression system seed is demonstrated by using a chirped pulse oscillator at the telecommunication band. Dispersion management is applied successfully both in the oscillator and amplifier, allowing dissipative soliton (DS) generation and amplification. The oscillator generates 4-ps chirped pulses with 130 mW (4.55 nJ) average power. Benefiting from large chirp and the high energy of DSs from the oscillator, the amplification system can be simplified. The average power after amplification is increased to 324.2 mW, corresponding to a single pulse energy of 11.3 nJ. The minimum pulse duration is 190 fs after the single-mode fiber (SMF) is employed to compress the pulses. The repetition rate of pulses is 28.6 MHz.

Though normal-dispersion mode-locked fiber lasers generally work on a single-pulse regime due to the large chirp of the pulses, we observe bound states of one kind of dissipative solitons in the laser. The separation between the bounded pulses in such soliton molecules increases with the pump power, and also varies with the settings of polarization controllers, which is consistent with other kinds of bounded pulses such as solitons. Our study indicates that the bound state of pulses is an intrinsic feature of mode-locked lasers and is independent of pulse profiles, stimulated by overdriving of mode-locking mechanisms.

We present an all-fiber self-starting high-energy soliton laser based on a chirped fiber Bragg grating (CFBG). The oscillator is mode-locked by nonlinear polarization rotation (NPR). As the net dispersion is greatly increased by the CFBG, the pulse energy can be increased correspondingly. The single pulse energy is 4.8 nJ, and the pulse duration is 4.4 ps with a repetition rate of 16.6 MHz.

We experimentally demonstrate direct generation of 51 nJ, 284-fs ultrashort pulses in an all-fiber cavity-optimized erbium-doped laser with a low repetition rate of 2.68 MHz. The conversion efficiency of the laser is about 10%. The laser is mode-locked by nonlinear polarization rotation. Such high energy and ultrashort duration benefits from using large output ratio (90%), elongating the cavity length, dispersion management, and bidirectional high-power pumping in the laser. Further decreasing the net dispersion of the laser by using a dispersion-compensated fiber can reduce the pulse duration to 160 fs. In addition, variation of spectral width due to an invisible filter in the laser is experimentally demonstrated.

Modulation instability (MI) in passively mode-locked dissipative solitons lasers has been studied. The factors that affect MI, including the intensity of the nonlinear wave and the linear phase delay of the cavity, have been experimentally studied. It's found that MI induces sidebands in the spectrum of dissipative solitons. The sidebands can cause the pedestal on the pulse in time domain and thus limit the pulse duration. Additionally, a simple method to eliminate the sidebands is proposed and nearly pedestal free pulses are generated correspondingly. Finally, based on MI, a method to measure the cavity net dispersion is proposed and applied to two dissipative soliton lasers with different net dispersion. It's shown that the positions of the adjacent spectral sidebands can determine the intracavity net dispersion, and the measurement error is limited by the accuracy of the optical spectrum analyzer. This indicates it is a simple and precise method to measure the intracavity net dispersion.

By optimizing critical parameters including period, thickness, hole shape and diameter, a tri-color filter based on extraordinary optical transmission through periodic hole array on metallic film is designed for OLED display, which shows high purity, narrow bandwidth and large resonant peak in simulation, and experimentally study. Also, its practicability gets confirmed by further verifications in structure’s angle invariance, oblique incidence transmission efficiency and polarized incidence independence. The 0.2 × 0.2 mm2 tiny fabrication scale and as more than 360 periods array dense qualify for UVGA (1600 × 1200) resolution.

A novel concept of individually switchable and widely tunable erbium-doped multiwavelength fiber laser (MWFL) is proposed and experimentally demonstrated. The key component of the laser is a channel transmissivity individually variable comb filter composed of two cascaded different-length long-period fiber gratings (LPFGs), named cascaded mismatching LPFGs. When inserted into the laser cavity, this polarization-dependent comb filter functions as the wavelength selector and switching filter simultaneously. By properly adjusting the polarization controllers (PCs) in the laser cavity and in the high birefringence Sagnac loop mirror (HiBi-SLM), eleven individually switchable wavelengths with different flexible lasing states, including successively tunable adjacent single-, dual- and triple-wavelength outputs, nonadjacent dual- and triple-wavelength outputs, as well as quadruple- and quintuple-wavelength outputs, have been achieved. This MWFL may be useful in optical fiber sensing or other fields desiring very flexible optical source.

We experimentally demonstrated the generation of transform-limit Gaussian ultrashort pulses as short as 70 fs from a dispersion-managed mode-locked erbium-doped fibre (EDF) laser. The output spectrum is close to the Gaussian profile with a full-width half-maximum (FWHM) output of 49 nm, and the measured autocorrelation trace exhibits the Gaussian profile. The shortest pulse duration of 70 fs was observed after external recompression. The time-band product is 0.44, showing the best transform limit pulse.

We report a simple fabricating approach to control the mode couplings in long-period fiber gratings (LPFGs) through side exposing fiber to long-pulse-10.6-μm laser from a cheap, internally modulated CO2 tube. By tuning focused-spot size on fibers, not only circularly symmetric mode coupling but also asymmetric mode couplings can be effectively achieved. Simulation of mode profiles in grating cross-section with Finite Element Method (FEM), and LPFG-cladding etching experiment with hydrofluoric acid (HF), support our explanation that asymmetric mode coupling in LPFGs depends on local refractive-index (RI) change within an azimuthally thin cladding layer, resulted from large-spot method induced deep melt flow on fiber surface during CO2 laser irradiation.

A period-chirped long-period fiber grating (CLPFG), using ordinary multi-mode fiber (MMF), for broadband mode conversion (60 nm bandwidth of coupling efficiency >90%) has been proposed. Through using such a MMF-CLPFG, a broad-spectrum pulse can be converted into LP 02 for femtosecond pulse distortion-free delivery in MMF. The simulation shows that the pulse suffers less nonlinear distortion than that in a single-mode fiber. In addition, the negative pre-chirp introduced by MMF-CLPFG can offset the linear and positive SPM-induced frequency chirp and thus compress the pulse. Using this scheme, an initial 18 kW peak power 75 fs pulse distortion-free delivery in MMF has been numerically demonstrated.

A high-power low-noise fiber Brillouin amplifier (FBA) has been demonstrated for slow-light delay buffer. Its features including gain, gain saturation, and noise figure (NF), have been characterized. Among them, the gain saturation is highlighted because it is a fundamental limitation for FBA-based slow-light buffer. It is testified that the gain saturation is more easily achieved for lower signal-to-pump ratio (SPR), and the NF is reduced at higher pump level when below Brillouin threshold. The experiment demonstrated that up to 20-ns delay enhancement could be obtained in this high-power FBA for a -30-dBm input signal, as well as with low NF. Besides, the analysis on how the performance of the high power FBA affects the slow-light delay buffer has been presented.

A CO 2 laser and point-by-point method are used for fabricating step-changed period chirped long-period fiber gratings (LPFG). Several types of period chirped LPFGs have been demonstrated, such as, linearly chirp, peak-shape chirp, and cascaded linearly chirp. Unlike uniform LPFGs, the spectrum change such as multiple attenuation peaks, broader spectrum can be seen in these chirp gratings, and the spectral shape can be controlled by the grating period. Especially, the cascaded linearly chirped LPFGs performs a multi-peak as interference between the core mode and cladding mode, which can be used as multi-wavelength filters in fiber optic communication and fiber optic sensors. Also, a linear tuning range of 1.6 nm with –0.559 pm/μe tuning rate is achieved in these types of devices by applying an axial strain.

We propose a sub-wavelength structured metal film with two sets of grooves with different periods. It can enhance the second harmonic generation (SHG) based on phase-matching. Meanwhile, we reduce the thickness of metal film to excite long-range surface plasma wave for improving the interaction length of SHG. The numerical study shows that this structure greatly improves the conversion efficiency of SHG for about 106 times, and that the SHG light is emitted in a direction perpendicular to the metal surface. This new type of structure could contribute to high conversion efficiency of SHG for the virtues of low loss and extremely compact structure.

We have experimentally demonstrated the direct generation of 128-fs pulses in an all-anomalous-dispersion all-fiber mode-locked laser. The laser is free of dispersion compensation in the cavity based on standard single mode fiber (SMF). The time-bandwidth product is 0.536. The laser is achieved by using two mode-lockers, one is nonlinear polarization rotation (NPR), and the other is nonlinear amplifying loop mirror. The coexistence of dual mode-locking mechanisms can decrease the cavity length to 12-m, and also results in producing high-quality pulses with a Gaussian shape both on the pulse profile and spectrum, but without Kelly sidebands.

We have demonstrated the direct generation of 4.6-nJ 78.9-fs ultrashort pulses with 58 kW peak power in an all-fiber net-normal-dispersion oscillator. Such high peak power is a record in an all-fiber oscillator and is comparable to chirped-pulse amplification systems. The corresponding spectrum has steep spectral edges, which is the typical shape of dissipative solitons (DS). Also, we find that the spectral width is tunable from 40 to 58 nm by adjusting polarization controllers, and the pulse duration can be tuned from 1.7 ps to 120 fs through increasing the pump power, which is attractive to applications. Besides, we demonstrate experimentally the relationship between spectral width and the pump power of DS laser for the first time.

The alignment of azobenzene molecules in DR19-PUI film induced by all-optical poling is identified. When the writing beams of frequencies ω and 2ω are both linearly polarized with their polarization directions parallel to each other, azobenzene molecules tend to reorient to perpendicular direction (i.e. direction perpendicular to the polarization of writing beams). At the end of the writing process more molecules orient in perpendicular direction than those in parallel direction (i.e. direction parallel to the polarization of writing beams). The alignment of molecules in parallel or perpendicular direction is, respectively, characteristic of noncentrosymmetry or centrosymmetry. It is the alignment of molecules in parallel direction that results in the second-order nonlinearity in the poled film.

The temperature dependence of all-optical poling of azobenzene–polyimide films was experimentally investigated. The poling efficiency decreased with the increase of the sample temperature during the optical poling processes. The experimental result can be explained by considering the relation between the lifetime of the triplet-state of the azobenzene molecule and the repetition rate of the laser pulses used in the poling processes.

We proposed and demonstrated a new concept of switchable multiwavelength erbium-doped fiber ring laser with a multisection high-birefringence fiber loop mirror (HiBi-FLM). The HiBi-FLM results in the laser operating on different allowed wavelengths. The wavelength switching can be achieved by modifying the reflection spectrum of HiBi-FLM through two polarization controllers. The experiment demonstrates the switchable lasing operation within the random combination of three wavelengths, as well as with a large (/spl sim/40 dB) output signal to background noise ratio.

Transitions between different kinds of soliton solutions of Ginzburg-Landau equation (GLE) have been studied experimentally in a mode-locked fiber laser. It is demonstrated that the different kinds of solitons corresponding to different solutions of GLE can be generated in a single mode-locked laser. Dispersion-managed solitons (DM), all-normal-dispersion solitons (ANDi) and similaritons can be emitted respectively depending on the parameter of the intensity of the light field and the birefringence effect. The three nonlinear waves show different features especially the spectrum shapes and dynamics accompanying with pump power scaling. Such phenomenon reveals the properties of GLE, which is not only scientifically interesting but also valuable to practical applications of mode-locked fiber lasers., Comment: 5 pages, 9 figures

We experimentally demonstrate an all-fiber similariton generation, amplification and compression laser system for the first time. The system can generate 4.1 nJ, 75.6-fs pedestal free pulses with 54 kW peak power. In addition, the pulse duration can be tuned through modifying the pump power. The corresponding spectrum width is 51 nm, and without spectral spikes. Such high quality ultra-short pulses are benefited from the linear chirp of similaritons. The seeded similariton is generated in a soliton-similariton switchable oscillator, in which, soliton or similariton can be chosen to emit alternatively by controlling polarization. Furthermore, we experimentally demonstrated the relationship between the gain and the spectral width of similaritons.

We report superluminal propagation in optical fibers using Brillouin lasing oscillation in a ring cavity. Negative group velocity propagation through a 10-m single mode fiber has been experimentally demonstrated. An advancement of 221.2 ns was observed before the input signal, which was achieved with a very high slope efficiency of $211.3\text{ }\text{ }\mathrm{ns}/\mathrm{dB}$. This indicates that this way is suitable for long-distance low-loss superluminal propagation via optical fibers. Correspondingly, the group velocity is $\ensuremath{-}0.151c$ and the group index is $\ensuremath{-}6.636$---the highest group velocity ever reported for optical fibers.

We proposed and demonstrated the propagation of slow/fast light in erbium-doped fiber through gain cross modulation. We observed the ultraslow light with a group velocity of 6.1×10-3 c and the superluminal propagation with a negative group velocity of -5.1 ×10-4c. (2 pages)

The cascaded asymmetric exposure long-period fiber gratings are fabricated by CO(2) laser, which provide multi-wavelength filters with anisotropic transmission spectrum under different states of polarization. Inserting this device in the ring cavity of an erbium-doped fiber laser, a triple-wavelength switchable lasing laser with equal spacing of 2.6 nm has been obtained. Owing to the polarization dependent loss of the new cascaded long-period fiber grating, the wavelength switching of random combination of C(1) (3), C (2) (3), and C(3) (3) is demonstrated through the polarization controlling. We derive the wavelength switch to the polarization characteristic of cascaded asymmetric exposure long-period fiber gratings.

We have demonstrated a novel multiwavelength Brillouin-erbium fiber laser (BEFL), in which the Brillouin pump is self-excited within the linear cavity, instead of the injection from the external cavity or direct generation in the intracavity. By using this simple scheme, the generation of more than 160 Brillouin Stokes lines has been experimentally demonstrated, which is the largest one achieved in BEFLs to the best of our knowledge. Also, the single longitudinal mode operation and the low noise performance of output wavelength line have been confirmed. Meanwhile, the experiment demonstrates that the BEFL performs good stability on both the operating wavelengths and the output power of each wavelength.

A low noise figure (NF), all-optical gain-clamped C+L band erbium-doped fiber amplifier (EDFA) has been demonstrated. A parallel configuration is employed to avoid the crosstalk between the C- and L-band signals. Half of the amplified spontaneous emission from the output signal is filtered by an interleaver and fed back to the parallel EDFA to form lasing cavity. Two lasers in the C- and L-band, respectively, formed in the cavity clamp the C- and L-band signals simultaneously. In the L-band, the double-pass configuration with a fiber Bragg grating is used to improve the gain and NF. Furthermore, co-propagation of the signal and the lasing power leads to a low NF, while the amplified signals are exported separately from the lasing power. Finally, a wide gain-clamping range up to -10dBm and ~5.5dB NF are obtained.

The alignment of dye molecules in optically poled polymer films is modeled. We point out that when writing beams (fundamental and second harmonic) are linearly polarized with their polarization directions parallel, the majority of the dye molecules in a poled film are axially oriented perpendicular to the writing-beam polarization, whereas the minority are polar oriented parallel to the writing-beam polarization. Only the latter, however, contribute to the second-order nonlinearity of the film. This model is verified by experiments. Based on the model, a new method of improving optical poling efficiency is put forward.

We proposed and demonstrated a new configuration of the low noise figure C+L- band erbium- doped fiber amplifier. In the configuration, a preamplifier is used to reduce the noise figure, and an improved double-pass configuration with a fiber Bragg grating was employed to enhance the L-band gain and while to reduce the noise figure. The experiment demonstrated that the noise figure in the new broad-band amplifier was improved by ~2 dB, and the gain was enhanced up to above 25dB over the region from 1525 to 1605nm.

The recent observation of enhanced optical transmission through a periodic array of subwavelength apertures in a metal film has elicited significant interest both because it represents a novel phenomenon and because it raises the prospect of a series of new applications. Recently, an ~10 4 increase in conversion efficiency of second harmonic generation (SHG) from a periodically nanostructured silver film structure consisting of a single subwavelength aperture surrounded by a set of concentric surface grooves was reported. Although the phase-matching condition for extraordinary transmission has been discussed by many researchers, the phase-matching conditions of SHG process was neglected in former experiments. In this paper, we design a silver film with two different sets of periods on a quartz substrate with the silver thickness of 20nm in order to excite long-range surface plasma wave that could transmit millimeter-order distance in the metal surface, which greatly contribution to the improvement of the conversion efficiency of SHG for about 10 2 times. The fundamental light is perpendicularly coupled into the metal film with about 29 percent coupling efficiency, and the direction of the transmitted SH light is also perpendicular to the metal surface. Furthermore, this new type of structure could contribute to high conversion efficiency of SHG for the virtues of low losses, extremely compact structure and easily fabrication process.

The temperature-dependent insertion-loss of volume phase holographic wavelength-division demultiplexers(WDDM) is analyzed using Bragg diffraction theory in this paper. We demonstrate that most of the temperature-induced insertion-loss results from the diffraction deflection. Finally, we propose a new way to improve the temperature characteristics of volume phase holographic demultiplexers if we have a suitable choice between the thermal expansion coefficients of the gratings and the thermal coefficients of the gratings index. This result is useful to design a self-temperature compensation WDDM.

We experimentally demonstrate an all-fiber ultrashort pulse amplification and compression system seeded by similaritons at an erbium-doped wavelength band. By optimizing the compressor, our system can generate 4.1 nJ, 75.6 fs pedestal-free pulses with 54 kW peak power. The corresponding spectrum width is 51 nm and has no spectral spikes. Such high-quality ultrashort pulses benefit from the linear chirp of similaritons. Furthermore, we experimentally demonstrate the variation of the similariton spectral width and compressed pulse duration to the amplifier gain, which is consistent with theoretical study.

Two identical long-period fiber gratings (LPFGs) are difficult to produce in practice, notably for CO2-laser or arc-discharge induced LPFGs. So it is meaningful to study the spectrum evolution of cascaded LPFGs with some deviation, named “mismatching” LPFGs. Theory and experiment demonstrate that the upper envelope of the fringe pattern is intrinsically curved but less dramatically than the lower envelope. Bending the grating pair to introduce proper cladding-mode loss can improve the contrast of the fringe pattern at a desired wavelength, which indicates that cascaded mismatching LPFGs can be used as high-quality comb filters or fiber sensors. © 2012 Optical Society of America OCIS codes: 060.2340, 060.2330, 050.2770, 280.4788.

A multiwavelength erbium-doped fiber (EDF) laser based on a nonlinear amplifying loop mirror (NALM) is proposed and experimentally demonstrated. The NALM provides intensity-dependent transmissivity to equalize different-wavelength powers and the transmission can be uniquely optimized by controlling the cavity loss associated with a section of un-pumped EDF, which also enhances the output signal-to-noise ratio (SNR). Through adjusting the polarization controllers (PCs), under only 70 mW pump power, up to 62-wavelength output with channel spacing of 0.45 nm has been achieved. Also, the lasing tunability and stability are verified.

The operation of a passively mode-locked erbium-doped fiber ring laser in two-color pulse mode has been experimentally observed. The experiments demonstrate that the wavelengths of two-color pulses can be switched among three wavelength bands. Through carefully controlling the polarization states of the laser cavity, various modulation patterns of the two-color pulses are obtained, which are due to the interaction of two different-wavelength pulses. Single- and three-color pulses are also observed. Multiwavelength oscillation is ascribed to the wavelength-dependent transmission induced by birefringence, and can synchronously mode-lock through nonlinear polarization rotation.

We report the amplitude-equalized high order arbitrary numerator rational harmonic mode-locked (RHMLed) pulse generations based on the technique of nonlinear polarization rotation in the fiber-ring laser. The numerator effect on the amplitude uniformity of RHMLed pulse train is first investigated. It is demonstrated that the high order RHMLed pulse train with uniform amplitude can be achieved by choosing a proper numerator. The pulse amplitude equalization in up to the 10th order RHMLed pulse train is observed when the numerator is equal to 3 instead of 1. It is important that the technique may be useful to generate the high-speed pulse trains with uniform amplitude by using the high order RHMLing technique.