Active Mode-locked Fiber Laser Research Articles

Transmission performance of a 1.96 µm active mode-locked laser in smoke channel.

We demonstrate the data transmission characteristics of a 1.96 µm laser in an indoor simulated smoke channel. An active mode-locked thulium-doped fiber laser at 1961.63 nm can be generated, and the repetition rate is 2.11 GHz corresponding pulse duration of 12.47 ps. Therefore, the pulse can be modulated by a 2.11 Gb/s digital sequence to act as a carrier light source. The transmission characteristics of signal light under different visibility conditions of 0.5, 0.05, and 0.005 km are studied. Compared with the back-to-back conditions, the signal-to-noise ratios of the carrier can decrease after passing through the smoke channels, which are 3.93, 7.1, and 9.08 dB, respectively. At the same time, the received power jitter can increase from ±0.16 to ±1.14dB. The sensitivity can be -19.52dBm at the visibility of 0.005 km. The experimental results show that thulium-doped mode-locked laser has an excellent performance in a smoke channel.

Multiple fiber Bragg grating sensing system based on active mode-locking fiber laser

In this paper, a new multiple fiber Bragg grating (FBG) sensing system based on active mode-locking fiber laser is proposed. The active mode-locking fiber laser is composed of a linear cavity with an Fabry–Perot laser diode (F-P LD) as a reflective cavity mirror, and the erbium-doped fiber as the gain medium. Meanwhile, the F-P LD is also used as the modulating element of the fiber laser. Multiple FBGs cascaded in a long fiber are used as both the sensors in the system and the components for wavelength selection in the active mode-locking fiber laser. The capacity of the proposed sensing system to interrogate multiple FBGs in wavelength and spatial domain is investigated. The proposed sensing system has the characteristics of low cost, good stability, good compatibility, and can be used in quasi-distributed multi-point sensing.

Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging

Optical coherence tomography (OCT) is a noninvasive imaging modality that can provide high-resolution, cross-sectional images of tissues. Especially in retinal imaging, OCT has become one of the most valuable imaging tools for diagnosing eye diseases. Considering the scattering and absorption properties of the eye, the 1000-nm OCT system is preferred for retinal imaging. In this study, we describe the use of an akinetic swept-source OCT system based on a pulse-modulated active mode locking (AML) fiber laser at a 1080-nm wavelength for in-vivo human retinal imaging. The akinetic AML wavelength-swept fiber laser was constructed with polarization-maintaining fiber that has an average linewidth of 0.625 nm, a spectral bandwidth of 81.15 nm, and duty ratio of 90% without the buffering method. We successfully obtained in-vivo human retinal images using the proposed OCT system without the additional k-clock and the frequency shifter that provides a wide field of view of 43.1°. The main retina layers, such as the retinal pigment epithelium, can be distinguished from the OCT image with an axial resolution of 6.3 μm with this OCT system.

Scintillation index reducing based on wide-spectral mode-locking fiber laser carriers in a simulated atmospheric turbulent channel.

We report on a communication link demonstration in a 1km simulated atmospheric turbulent channel with a wide-spectral mode-locking fiber laser. Wide-spectral beams are part of the supercontinuum, which is generated from pumping a dispersion-shifted fiber by an active mode-locked fiber laser. In addition, the propagation effects of wide-spectral beams were investigated experimentally in a simulated atmosphere channel. The characteristics of bit error rate and eye pattern before and after turbulence were analyzed, respectively. The experimental results showed that the sensitivity of the whole link reaches -40 dBm. The scintillation index of free-space optical communication between wide-spectral partially coherent and narrow-spectral coherent beams was compared, which indicates that the wide-spectral partially coherent optical communication link is more resistant to atmospheric turbulence. We experimentally verified that the scintillation index of wide-spectral carriers is dependent on coherent degree rather than spectral width.

Effect of narrow spectral filter position on the characteristics of active similariton mode-locked femtosecond fiber laser.

A significant change in active similariton characteristics, both numerically and experimentally, is observed as a function of the location of the lumped spectral filter. The closer the spectral filter is to the input of the Yb(3+)-doped fiber, the shorter the de-chirped pulse width. The peak power of the de-chirped pulse has its maximum value at a certain location of the spectral filter. Four different positions of the spectral filter inside the laser cavity have been theoretically studied and two of them have been verified experimentally.

Linearized Wavelength Interrogation System of Fiber Bragg Grating Strain Sensor Based on Wavelength-Swept Active Mode Locking Fiber Laser

We demonstrated a linearized wavelength interrogation system of fiber Bragg grating (FBG) strain sensors, based on a wavelength-swept active mode locking (AML) fiber laser. Since the wavelength sweeping mechanism of the AML fiber laser does not depend on the wavelength selecting filter, we can easily demonstrate the wavelength-linear sweeping by applying a programmable electrical signal to the laser cavity. Both static and dynamic strain measurements of FBG sensors were characterized with high linearity, which has an R-square value of 0.9999 at a sweep rate of 50 kHz.

Simultaneous Dual-Band Wavelength-Swept Fiber Laser Based on Active Mode Locking

We report a simultaneous dual-band wavelength-swept laser based on the active mode locking method. By applying a single modulation signal, synchronized sweeping of two lasing-wavelengths is demonstrated without the use of a mechanical wavelength-selecting filter. Two free spectral ranges are independently controlled with a dual path-length configuration of a laser cavity. The static and dynamic performances of a dual-band wavelength-swept active mode locking fiber laser are characterized in both the time and wavelength regions. Two lasing wavelengths were swept simultaneously from 1263.0 to 1333.3 nm for the 1310 nm band and from 1493 to 1563.3 nm for the 1550 nm band. The application of a dual-band wavelength-swept fiber laser was also demonstrated with a dual-band optical coherence tomography imaging system.

Numerical simulation of a dispersion-managed active harmonically mode-locked fiber laser using a spectral double-grid technique

A comprehensive lumped model approach has been presented in this paper for the simulation of a dispersion-managed active mode-locked fiber laser. A key aspect of our model is that it operates simultaneously at two different spectral scales, corresponding to the gain bandwidth of the erbium-doped fiber and the frequency content of the mode-locked laser (MLL) pulse. The lumped model consists of a detailed amplifier model that is evolved using a predictor–corrector-based adaptive approach. Convergence analysis of this algorithm is also presented in this paper, highlighting the step size reduction achieved when the amplifier migrates from linear to saturation regime. A simple adaptive frequency domain approach is followed to control the fine grid spectral points and the coarse grid wavelengths. Such an approach has been used to simulate a harmonic MLL cavity in two widely different dispersion regimes facilitated by a pair of chirped fiber Bragg gratings. We validate our model by comparing such simulated results with carefully planned experiments.

Phase modulator birefringence effect on multibound soliton formation in an active mode-locked fiber laser

Multibound solitons generated in an active mode-locked fiber ring resonator can be considered to offer some significant applications in the coding for optical packet transmission. Optical phase modulators (PMs) incorporated in such fiber ring resonators are fabricated in uniaxial birefringent crystal substrate and thus influence both polarized modes of a coupled linearly polarized mode from a weakly guiding fiber forming the ring. Thus there are two polarized rings in such a structure of the active mode-locked fiber ring resonators. They are coupled and interact with each other in the generation of multibound solitons. This paper thus studies the influence of two types of electrodes for phase modulation, lumped and traveling wave, in such birefringent fiber active ring resonators, and hence the transitional formation of multibound solitons. It is shown that there exist comblike spectral components in the ring cavity due to the birefringence property of the PM. Furthermore, the narrow free spectral range of the ring resonator limits the pulse shortening and hence the formation of the multibinding of solitons.

Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier

The static and dynamic characteristics of a wavelength-swept active mode locking (AML) fiber laser are presented in both the time-region and wavelength-region. This paper shows experimentally that the linewidth of a laser spectrum and the bandwidth of the sweeping wavelength are dependent directly on the length and dispersion of the fiber cavity as well as the modulation frequency and sweeping rate under the mode-locking condition. To achieve a narrower linewidth, a longer length and higher dispersion of the fiber cavity as well as a higher order mode locking condition are required simultaneously. For a broader bandwidth, a lower order of the mode locking condition is required using a lower modulation frequency. The dynamic sweeping performance is also analyzed experimentally to determine its applicability to optical coherence tomography imaging. It is shown that the maximum sweeping rate can be improved by the increased free spectral range from the shorter length of the fiber cavity. A reflective semiconductor optical amplifier (RSOA) was used to enhance the modulation and dispersion efficiency. Overall a triangular electrical signal can be used instead of the sinusoidal signal to sweep the lasing wavelength at a high sweeping rate due to the lack of mechanical restrictions in the wavelength sweeping mechanism.

Microwave photonic filter’s application on the microwave signal generation based on an active mode-locked fiber laser

A novel scheme which utilizes the microwave photonic filter technique for the optical generation of a microwave signal based on an active mode-locked fiber laser is proposed. A microwave signal generator using a microwave photonic filter based on a 2: 1 optical coupler with a fiber loop which can effectively suppress a low-order frequency component of the microwave signal is demonstrated and a ∼10-GHz microwave signal is achieved based on an active mode-locked fiber laser with the original pulse repetition rate of ∼5 GHz.

Generation of bound solitons in actively phase modulation mode-locked fiber ring resonators

Bound solitons generated in actively mode-locked lasers enable new forms of pulse pairs and multiple pairs or groups of solitons in optical transmission or logics. In this paper, we present the generation of stable bound states of multiple solitons in an active mode-locked fiber laser using continuous phase modulation for wideband phase matching. Not only that dual-soliton bound states but also the triple- and quadruple-soliton pulses can be established. Simulation of the generated solitons are demonstrated. We have also prove by simulation that experimental relative phase difference and chirping caused by phase modulation of LiNbO3 modulator in the fiber loop significantly influences the interaction between the solitons and hence their stability as they circulate in the anomalous path-averaged dispersion fiber loop.

Dual Orthogonal Polarization States in an Active Mode-Locked Birefringent Fiber Ring Laser

We report the generation of dual amplitude pulses in an active mode-locked fiber laser within a birefringent cavity. Different to normal mode-locked pulses with identical amplitude and polarization state, and pulses polarized on both x- and y-axes simultaneously exist in the output pulse train. The two orthogonal pulse sequences have different amplitudes and lase at different wavelengths. Dual wavelengths are the result of red shift and blue shift of the x- and y-polarization states of the generated pulses, respectively, due to the detuning phenomena. Locking to individual x- or y-polarized pulse is also obtained by adjusting polarization controllers

Polarization-Dependent Locking in SOA Harmonic Mode-Locked Fiber Laser

Polarization-dependent states of the output pulse train generated from an active harmonic mode-locked fiber laser by exploiting the birefringence of the fiber ring is reported for the first time. There exist two different fundamental frequencies for each polarization-mode lasing and hence the laser can be forced to mode-locking states of the two orthogonal polarization regimes by tuning or detuning the modulation frequency. Theoretical equations for predicting the tuning frequencies are described and good agreement with experimental results is obtained

Active mode locking of tunable multi-wavelength fiber ring laser

We report an active mode-locked tunable multiple-wavelength fiber laser constructed using a unidirectional ring cavity combined with an amplitude modulator and a single sampled fiber Bragg grating (SFBG). Simultaneous generation of up to six-wavelength picosecond pulses with identical repetition rate and a wavelength spacing of about 1.6 nm (200 GHz) is demonstrated. The spectral width and side-mode suppression ratio are 0.01 nm and 40 dB for all the wavelengths. The average output power is 4.5 dBm and the supermode noise suppression is more than 40 dB. The equal-step wavelength tuning over a range of 1.6 nm for all the wavelengths has also been achieved by applying tension to the SFBG.