Mode-Locked Lasers

Wavelength bistability and tunability are demonstrated in a two-section quantum-dot mode-locked laser with a non-identical capping layer structure. The continuous wave output power of 30 mW (25 mW) and mode-locked average power of 27 mW (20 mW) are achieved for 1245 nm (1295 nm) wavelengths respectively under the injection current of 300 mA. The largest switching range of more than 50 nm and wavelength tuning range with picosecond pulses and stable lasing wavelengths between 1245 nm and 1295 nm are demonstrated for gain current of 300 mA and 330 mA.

We report a wavelength-switchable single-polarization dissipative soliton (DS) mode-locked fiber laser using a chirped fiber Bragg grating (FBG) for spectral filtering. The chirped FBG, when inserted into the ring cavity, provides a stopband from 1045 nm to 1057 nm, which is used for spectral filtering in this all-normal-dispersion mode-locked Yb-doped fiber laser. The combination of the chirped FBG and the Yb gain profile help the formation of the DS. The laser delivers wavelength-switchable and polarized (28 dB) DS of 6.1 nJ and 29 ps at 1032 nm, and 4.3 nJ and 24 ps at 1068 nm, respectively. To the best of our knowledge, this is the direct proof that a bandpass filter is not indispensible to achieve stable DS in ps fiber lasers.

We report on an optical frequency comb with 14nm (∼1.8 THz) spectral bandwidth at-3 dB level that is generated using a passively mode-locked quantum-well (QW) laser in photonic integrated circuits (PICs) fabricated through an InP generic photonic integration technology platform. This 21.5-GHz colliding-pulse modelocked laser cavity is defined by on-chip reflectors incorporating intracavity phase modulators followed by an extra-cavity SOA as booster amplifier. A 1.8-THz-wide optical comb spectrum is presented with ultrafast pulse that is 0.35-ps-wide. The radio frequency beat note has a 3-dB linewidth of 450 kHz and 35-dB SNR.

We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thuliumbismuth co-doped fiber (TBF) as a gain medium in conjunction with a carbon nanotube (CNT)-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 mW. OCIS codes: 320.0320, 140.0140.

This article mainly focuses on the side mode injection locking phenomena when a single-loop optoelectronic oscillator (OEO) is under RF signal injection. The analyses are made regarding lock range, phase noise and locking time. Also, a comparative study has been prepared when the OEO is injection-locked in the first side and the main mode. We show that the lock range is smaller for injection-locked OEO in the first side mode than in the main mode. The phase noise performance of the OEO for both cases is also demonstrated. It is exhibited that the phase noise performance is better in the case of injection-locked OEO at first side mode, particularly in a strong injection regime. The transient behaviour is also approximated by measuring locking time in both cases. The lock range, phase noise and locking time dependency on optical fibre length have also been studied. Finally, we perform experiments to support our analytical findings developed earlier.

Wavelength bistability and tunability are demonstrated in a two-section quantum-dot mode-locked laser with a non-identical capping layer structure. The continuous wave output power of 30 mW (25 mW) and mode-locked average power of 27 mW (20 mW) are achieved for 1245 nm (1295 nm) wavelengths respectively under the injection current of 300 mA. The largest switching range of more than 50 nm and wavelength tuning range with picosecond pulses and stable lasing wavelengths between 1245 nm and 1295 nm are demonstrated for gain current of 300 mA and 330 mA.

We demonstrate the generation of mode-locked pulses in an erbium-doped fiber laser (EDFL) by using a new manganese-doped cadmium selenide quantum-dots-based saturable absorber. The laser produces a soliton pulse train operating at 1561.1 nm with a repetition rate of 1 MHz, as the pump power is varied from 113 to 250 mW. At the maximum pump power, we obtain the pulse duration of 459 ns with a signal-to-noise ratio of 50 dB.

We report a novel spontaneous soliton pattern formation in a figure-of-eight passively mode-locked erbium-doped double-clad fiber laser. It consists in a condensate phase in which there is almost periodic arrangement of alternate crystal and liquid soliton phases. Thanks to an adapted ansatz for the electric field, we perform a reconstruction allowing to clearly identify the soliton distribution along the cavity.

A broadband continuously tunable SESAM all-fiber laser based on optical parametric generation (OPG) for Coherent anti-Stokes Raman Scattering (CARS) imaging applications is presented in this article. This laser structure is built on allpolarization maintaining fibers yielding high environmental stability. The OPG is based on PM photonic crystal fiber as parametric gain pumped by a wavelength-tunable (1025 nm to 1055 nm) and repetition rate-tunable (3 MHz to 500 KHz) Ybdoped pulsed fiber laser. The all-fiber structure features free polarization adjustment in slow-axis tunable operation with a wavelength range from 770 to 940 nm for signal radiation and 1225 to 1510 nm for idler radiation. The pump and signal pulses (CARS-Stokes and CARS-pump respectively) are intrinsically overlapped, both spatially and temporarily, due to the four-wave mixing (FWM) generation and emitted from a single fiber end. The CARS-Stokes and CARS-pump pulse duration vary between 25 to 32 ps and 21 to 24 ps respectively in the whole band, ensuring a good overlap of the generated signals, and both exhibit a Gaussian profile with high spatial beam quality. The frequency conversion allows to obtain a frequency difference between the generated signals from 1100 to 3300 −. The reported low-cost laser source is ideal for bio-imaging applications, especially in CARS imaging, due to its compactness, simplicity, robustness and ease of handling. A patent has been filed based on this technology.

In this paper, optoelectronic oscillators (OEOs) are demonstrated by using direct-modulated edge-emitting lasers under strong optical injection. The optically injection-locked OEO (OIL-OEO) enables a stable optoelectronic oscillation by converting an optical signal to an electrical signal through a long optical fiber loop. Low RF threshold gain of 7 dB for loop oscillation is attained by utilizing the cavity resonance amplification of an injection-locked semiconductor laser. We investigated both the open-and closed-loop characteristics of the OIL-OEO link by varying the injection locking parameters. Using this novel technique with optimized locking parameters, a 20-GHz RF signal with a phase noise of −123 dBc/Hz is successfully achieved without sophisticated frequency or temperature stabilization.

We experimentally demonstrate a dual-frequency comb-based transient absorption (DFC-TA) technique, which has a 12 fs time resolution and an ultrafast scan rate. Here, the fast scan rate is achieved by employing asynchronous optical sampling (ASOPS), which utilizes two independent mode-locked lasers with a slightly detuned repetition rates. The ASOPS approach is advantageous because photodegradation damage of optical sample during TA measurements can be minimized by a gated sampling. We show that the vibrational and electronic population relaxations of near-IR dye molecules in solution that occur in the time range from femtoseconds to nanoseconds can be resolved even with a single time scan measurement. The phase coherent nature of our dual-frequency comb lasers is shown to be the key for successful coherent averaging with femtosecond time resolution preserved over many data acquisitions. We anticipate that the present DFC-TA method without using any pump-probe time delay devices cou...

We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thuliumbismuth co-doped fiber (TBF) as a gain medium in conjunction with a carbon nanotube (CNT)-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 mW. OCIS codes: 320.0320, 140.0140.

A tapered microfiber decorated with titanium dioxide-silicon dioxide nanocomposite saturable absorber (TiO2-SiO2-SA) is demonstrated via alkali fusion method and spincoating technique. The TiO2-SiO2-SA exhibited 17.1% modulation depth, 31.7 µJ/cm 2 saturation fluence and 35.4% non-saturable loss. The TiO2-SiO2-SA was able to generate a pulse duration of 797 fs at a repetition rate of 10.39 MHz and an average output power of 16.57 mW at 1.56 µm. This work presents an enhanced pulse duration within titanium-based saturable absorbers. The high damage threshold of beyond 24.82 GW/cm 2 and excellent stability are believed to have opened a new route of using nanomaterials derived from waste product for next generation ultrafast photonic applications.

A monolithically integrated mode-locked semiconductor laser is proposed. The compound ring cavity is composed of a colliding pulse mode-locking (ML) subcavity and a passive Fabry-Perot feedback subcavity. These two 1.6 mm long subcavities are coupled by using on-chip reflectors at both ends, enabling harmonic mode locking. By changing DC-bias conditions, optical mode spacing from 50 to 450 GHz is experimentally demonstrated. Ultrafast pulses shorter than 0.3 ps emitted from this laser diode are shown in autocorrelation traces.

In this paper, a monolithically integrated ∼1.55 µm semiconductor laser in the fourth harmonic colliding pulse mode locking configuration is reported. This device was developed within a multi-project wafer run at an InP-based active-passive generic foundry. The 1.66-mm Fabry-Pérot cavity is formed with two on-chip reflector building blocks rather than cleaved facets. In the cavity, three absorber sections symmetrically divide the cavity in four gain segments. This laser diode is able to emit 100-GHz pulse trains with 500-fs pulse duration as well as two-tone emissions with a frequency separation of 2.7 THz. The dependence of the spectral behavior on the forward bias current for gain sections and the reverse bias voltage for absorber sections are experimentally demonstrated.

We report on an optical frequency comb with 14nm (∼1.8 THz) spectral bandwidth at-3 dB level that is generated using a passively mode-locked quantum-well (QW) laser in photonic integrated circuits (PICs) fabricated through an InP generic photonic integration technology platform. This 21.5-GHz colliding-pulse modelocked laser cavity is defined by on-chip reflectors incorporating intracavity phase modulators followed by an extra-cavity SOA as booster amplifier. A 1.8-THz-wide optical comb spectrum is presented with ultrafast pulse that is 0.35-ps-wide. The radio frequency beat note has a 3-dB linewidth of 450 kHz and 35-dB SNR.

This Letter presents a photonics-based millimeter wave and terahertz frequency synthesizer using a monolithic InP photonic integrated circuit composed of a mode-locked laser (MLL) and two pulse interleaver stages to multiply the repetition rate frequency. The MLL is a multiple colliding pulse MLL producing an 80 GHz repetition rate pulse train. Through two consecutive monolithic pulse interleaver structures, each doubling the repetition rate, we demonstrate the achievement of 160 and 320 GHz. The fabrication was done on a multi-project wafer run of a generic InP photonic technology platform.

Using an offline cross-correlation technique, we have analyzed the noise behavior of a new type of optical frequency comb (OFC), which is carrier envelope offset (CEO) free by configuration, due to difference frequency generation. In order to evaluate the instrument's ultimate noise floor, the phase and amplitude noise of a stabilized OFC are measured simultaneously using two analog-to-digital converters. Carrier recovery and phase detection are done by post-processing, eliminating the need for external phase-locked loops and complex calibration techniques. In order to adapt the measurement noise floor and the number of averages used in cross correlation, an adaptive frequency resolution for noise measurement is applied. Phase noise results are in excellent agreement with measurements of the fluctuations of the repetition frequency of the OFC obtained from optical signal.

A monolithically integrated mode-locked semiconductor laser is proposed. The compound ring cavity is composed of a colliding pulse mode-locking (ML) subcavity and a passive Fabry-Perot feedback subcavity. These two 1.6 mm long subcavities are coupled by using on-chip reflectors at both ends, enabling harmonic mode locking. By changing DC-bias conditions, optical mode spacing from 50 to 450 GHz is experimentally demonstrated. Ultrafast pulses shorter than 0.3 ps emitted from this laser diode are shown in autocorrelation traces.

We develop a novel description of electrically driven vertical-external-cavity surface-emitting semiconductor lasers (VECSELs) mode-locked by saturable absorber mirrors. Our approach is based on an analytical solution of the bidirectional traveling-wave equations for fundamental transverse mode operation. The resulting time-domain equations describe the evolution of the electric fields and carrier-densities at the quantum-well layers of the emitter and absorber structures which are coupled through delayed boundary conditions. For the design considered, we obtain stable mode-locked pulses of few tens of picoseconds at 15-GHz repetition rate in agreement with recently reported experimental results.

The operation of a passively modelocked figure-eight laser with all fibre repetition rate multiplier is reported. Thirty two times the fundamental repetition rate is achieved with six conventional 3 dB couplers at a repetition rate of 182 MHz. The repetition rate 2 N times multiplication only requires (N + 1) passive fibre couplers and N fibre delay-lines. This method makes it possible to achieve high multiplication and is inexpensive when compared with conventional methods employing sub-ring cavity or special fibre Bragg grating to control repetition rate.

This work highlights the demonstration of a passively Q-switched pulse laser with iron disulfide (FeS2) as a saturable absorber in near-infrared region. The FeS2 saturable absorber is fabricated using liquid exfoliation method. A small piece of the FeS2-SA film is incorporated into the erbium-doped fiber laser ring cavity resulting in stable repetition rate from 80.4 kHz to 88.5 kHz. The laser delivered a pulse duration that decreases from 12.43 μs to 11.3 μs. By tuning the power pump from 125.2 mW to 166.4 mW, maximum output power and pulse energy are recorded at 2.2 mW and 24.8 nJ respectively. Therefore, this work reveals that FeS2 has good nonlinear saturable absorption properties to produce a stable pulse at 1559.8 nm central wavelength.

We report here on a monolithic multisectioned quantum-well laser that operates as multiple colliding pulse mode-lockhg source. With thk type of operation several puises are present wittdn a laser simultaneously and it produces high-repetition rate pulse trains (up to 375 GHz) and pulse widths of around 1-3 ps, as deduced from linear correlation technique measurements. By changing the configuration of the sections 1, 2, 3, cm 4 pulse operation can be selected; frequencyand time-domairl theories have been developed to explain this type of behavior.

We report here on a monolithic multisectioned quantum-well laser that operates as multiple colliding pulse mode-lockhg source. With thk type of operation several puises are present wittdn a laser simultaneously and it produces high-repetition rate pulse trains (up to 375 GHz) and pulse widths of around 1-3 ps, as deduced from linear correlation technique measurements. By changing the configuration of the sections 1, 2, 3, cm 4 pulse operation can be selected; frequencyand time-domairl theories have been developed to explain this type of behavior.

We have studied the mechanism of soliton formation in a passively mode-locked ®bre ring laser when the gain is increased. We show experimentally that new soliton pulses in the laser are generated by soliton shaping of dispersive waves. Our observation is further con®rmed by numerical simulations where an improved model is used that takes into account explicitly the polarization dispersion eect and discrete saturable absorber eect.

We experimentally demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) operation by using a saturable absorber based on Fe3O4 nanoparticles (FONP) in magnetic fluid (MF). As a kind of transition metal oxide, the FONP has a large nonlinear optical response with a fast response time for saturable absorber. By depositing MF at the end of optical fiber ferrule, we fabricated a FONP-based saturable absorber, which enables a strong light-matter interaction owing to the confined transmitted optical field within the single mode fiber. Because of large third-order optical nonlinearities of FONP-based saturable absorber, large modulation depth of 8.2 are demonstrated. As a result, stable passively Q-switched EDFL pulses with maximum output pulse energy of 23.76 nJ, repetition rate of 33.3 kHz, and pulse width of 3.2 μs are achieved when the input pump power is 110 mW at the wavelength of 980 nm. The laser features a low threshold pump power of 15 mW.

We experimentally demonstrate a passively Q-switched, mode-locked fiber laser incorporating a graphene oxide (GO)-deposited side-polished D-shaped fiber. Using both features of nonlinear saturable absorption and large polarization dependence loss of the GO-deposited sidepolished D-shaped fiber, stable Q-switched mode-locked pulses are readily obtained from an erbium fiber ring cavity

All-fiber passively Q-switched fiber lasers have been demonstrated by using graphene oxide (GO) Q-switcher for possible applications in telecommunication, laser processing, fiber sensing and medical community. The GO material was obtained through a modified Hummers method from expanded acid washed graphite flakes and it was embedded into a polyvinyl alcohol (PVA) film to form a saturable absorber (SA) device. The Q-switched pulse operates at 1563.3 nm with a repetition rate that can be tuned from 44.33 kHz to 61.77 kHz as the pump power changes from 39 mW to 96 mW. The highest repetition rate of 61.77 kHz is achieved at a pump power of 96 mW and it is observed that the Q-switched pulse produced maximum pulse energy of 0.054 nJ and pulse width of 5.57 ?s at 96 mW pump power. Full Text: PDF ReferencesJ. Zayhowski and C. Dill, "Coupled-cavity electro-optically Q-switched Nd:YVO4 microchip lasers", Optics letters 20, 716 (1995). CrossRef C.-x. Gao, W. Zhao, Y.-s. Wang, S.-l. Z...

A passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using a black phosphorus saturable absorber as the Q-switcher. The laser generates a stable pulse operating at a wavelength of 1562.35 nm within a pump power region from 7.2 mW to 42.3 mW. At 980 nm pump power of 42.3 mW, the EDFL generates an optical pulse train with a repetition rate of 44.72 kHz and pulse width of 9.8 us. The maximum pulse energy of 81.5 nJ is obtained at a pump power of 35.2 mW. A higher performance Q-switched EDFL is expected to be achieved with the optimization of the saturable absorber and laser cavity. Full Text: PDF ReferencesR. Mas-Balleste, C. Gomez-Navarro, J. Gomez-Herrero and F. Zamora, "2D materials: to graphene and beyond", Nanoscale 3, 20 (2011). CrossRef Z. Sun, T. Hasan, F. Torrisi, D. Popa, G. Privitera, F. Wang, F. Bonaccorso, D. M. Basko and A. C. Ferrari, "Graphene Mode-Locked Ultrafast Laser", ACS nano 4, 803 (2010) CrossRef F. Xia, H. Wang and Y. Jia, ...

In this paper, a passively Q-switched Erbium doped fiber laser (EDFL) by residing Graphene nanoplatelets (GnPs) embedded in polyvinyl alcohol (PVA) based saturable absorber (SA) is demonstrated. To aid the dispersion of GNPs, a surfactant is used and then it is mixed with polyvinyl alcohol (PVA) as host polymer to develop GnPs-PVA film based passive SA. The GnPs-PVA based film then integrated in laser cavity in ring cavity configuration for pulse laser generation. The experimental works show that the proposed passive SA operates at input pump power range from 77 mW to 128 mW with a tunable repetition rate from 78.4 kHz to 114.8 kHz and a shortest pulse width of 3.69 µs. The laser produces maximum instantaneous output peak power and pulse energy of 7.3 mW and 30.46 nJ, respectively and accompanied by signal to noise ratio (SNR) of 64 dB.

В данной работе были рассмотрены применения жидкокристаллических поляризаторов в области фотоники, а именно в обеспечении ними синхронизации мод кольцевых волоконных лазеров. Представлена математическая модель и метод расчета электроуправляемых фазовых пластинок. Были построена зависимость поворота поляризации проходящего лазерного излучения через жидкокристаллическую ячейку от приложенного к ней напряжения. Полученный результат сравнивается с экспериментальной зависимостью. Полученные в работе результаты подтверждают возможность применения жидкокристаллических поляризаторов для обеспечения синхронизации мод волоконных лазеров.

For the first time, we demonstrate a novel passively mode-locked fiber laser operating at 1300 nm using purified singlewalled carbon nanotubes (CNTs) as a saturable absorber. The saturable absorber incorporates diameter-controlled CNTs with peak absorption 1300 nm, guaranteeing mode-locking over the same wavelength region. The ring laser uses praseodymium-doped fiber as a gain medium. The pulse repetition rate is 3.18 MHz, and the spectral half-width is 0.15 nm. Dual-wavelength mode-locking is also demonstrated with a channel spacing of 1.1 nm.

Quantum nanostructure-based semiconductor mode-locked lasers (MLLs) are of increasing interest for various applications including optical sampling [1], frequency comb generation [2], and telecommunications [3]. To improve the performance and to extend the applications of semiconductor MLLs high stabilization in terms of low timing jitter is highly desirable. External optical feedback is a cost effective stabilization technique which suppresses instabilities and reduces the phase-noise by establishing one [4] or more compound cavities [5-7] with external reflectors or resonators. It is desirable for a feedback based stabilization scheme to achieve reduced sensitivity to the detuning of optical delay in the feedback loop. We experimentally demonstrated reduced sensitivity to drift in optical delay using various configurations of dual-loop optical feedback [5-7]. In this paper, we report stabilization of self-mode-locked two-section quantum-dash lasers on the widest range of delay using simultaneous optical-injection and optical feedback. A schematic of our proposed experimental arrangement is shown in Fig. 1(a). With continuous-wave (CW) optical-injection, various wavelengths spanning a range from 1568 to 1578 nm of master laser were investigated and optimum wavelengths (1571.210 to 1572.710 nm) yields narrowest RF linewidth and reduced timing jitter of slave laser were identified. In addition, the relationship of RF linewidth and pulse repetition rate as a function of injected wavelengths was further explored. Our results indicates that simultaneous optical feedback and optical-injection significantly improves the RF linewidth across the widest delay range compared to optical feedback. Measured RF linewidth data for single-loop feedback (black squares) alone and optical feedback plus optical injection (blue triangles) are shown in. Under fully resonant feedback and optimum injection parameters, a minimum RF linewidth of 1 kHz (instrumental limited) was achieved with simultaneous optical-injection plus optical feedback, which was > 2x lower than optical feedback alone and more than 100x than free-running condition. This stabilization technique is implemented in an all optical arrangement without optical/electrical conversion which is ideal for high-repetition-rate devices and photonic integration. Fig. 1 (a). Schematic of the experimental arrangement for single-loop feedback and CW optical-) Measured RF linewidth versus delay with single-loop feedback (black squares) and combined optical feedback and CW optical-injection (blue triangles) REFERENCES [1] T.

We demonstrate a Q-switched Erbium-doped fiber laser (EDFL) using a newly developed gold nanoparticles (GNPs) based saturable absorber (SA) for the first time. The GNPs were embedded in polyvinyl alcohol (PVA) for film-forming and inserted into an Erbium-doped fiber laser (EDFL) cavity to achieve passive Q-switching. The Q-switched EDFL operates at 1560 nm with a pump power threshold of 35 mW, a pulse repetition rate tunable from 19.7 to 89.9 kHz, and the smallest pulse-width of 2.64 μs. The Q-switching pulse shows no spectral modulation with a peak-to-pedestal ratio of 69 dB indicating the high stability of the laser. The highest pulse energy of 103 nJ was obtained at 118 mW pump power. These results show that the GNPs based SA is available for pulsed operation in the 1550 nm spectral range.

We report experimental studies of the influence of symmetric dual-loop optical feedback on the RF linewidth and timing jitter of self-mode-locked two-section quantum dash lasers emitting at 1550 nm. Various feedback schemes were investigated and optimum levels determined for narrowest RF linewidth and low timing jitter, for single-loop and symmetric dual-loop feedback. Two symmetric dual-loop configurations, with balanced and unbalanced feedback ratios, were studied. We demonstrate that unbalanced symmetric dual loop feedback, with the inner cavity resonant and fine delay tuning of the outer loop, gives the narrowest RF linewidth and reduced timing jitter over a wide range of delay, unlike single and balanced symmetric dual-loop configurations. This configuration with feedback lengths of 80 and 140 m narrows the RF linewidth by ∼ 4-67x and ∼ 10-100x, respectively, across the widest delay range, compared to free-running. For symmetric dual-loop feedback, the influence of different power split ratios through the feedback loops was determined. Our results show that symmetric dual-loop feedback is markedly more effective than single-loop feedback in reducing RF linewidth and timing jitter, and is much less sensitive to delay phase, making this technique ideal for applications where robustness and alignment tolerance are essential.

We experimentally demonstrate a passively Q-switched, mode-locked fiber laser incorporating a graphene oxide (GO)-deposited side-polished D-shaped fiber. Using both features of nonlinear saturable absorption and large polarization dependence loss of the GO-deposited sidepolished D-shaped fiber, stable Q-switched mode-locked pulses are readily obtained from an erbium fiber ring cavity

We investigate the influence of symmetric dual-loop feedback (loops with equal length) as a function of full delay tuning on the RF linewidth and timing stability of ~ 21 GHz self-mode-locked quantum dash laser. Various feedback scenarios are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both feedback schemes. Two symmetric dual-loop configurations, subject to balanced (equal feedback strength through either feedback cavity) and unbalanced feedback ratio (~ 4x more power through loop-I relative to other) are presented here. We demonstrated that unbalanced symmetric dual-loop, with the inner cavity fully resonant (at higher feedback intensity) and fine delay tuning of the outer loop (at lower feedback intensity), gives narrow RF linewidth and reduced timing jitter over a wide range of delay detuning, unlike single and balanced symmetric dual-loop configurations. This study reveals that unbalanced symmetric dual-loop with feedback delay lengths 80 and 140 m narrows the RF linewidth by ~ 4-67x (~ 2-9x timing jitter reduction) and ~ 10-100x (~ 2.5-10x timing jitter reduction), respectively, across the widest delay range, compared to free-running condition. The influence of symmetric dual-loop with balanced and unbalanced feedback ratio on the stability of the laser device is further discussed. These results suggests that symmetric dual-loop feedback with controlled feedback strength over each loop and without additional delay time in external feedback loops is significantly more effective than single loop feedback in reducing RF linewidth and timing jitter, across full range of delay phase tuning. Wider resonant feedback regime as a function of full delay tuning achieved with symmetric dual-loop configuration makes this technique ideal for practical applications where robustness and tolerance to misalignment are essential.

We report an experimental study of an actively mode-locked erbium-doped all-fiber laser, based on a standing-wave acoustically-induced superlattice modulation. Our experiments involve the characterization of the laser as a function of the active fiber length, and with different types of delay line fibers. The effect of the modulation on the laser performance was also investigated. Narrower pulses were obtained at higher modulation depths, normal dispersion, and shorter lengths of active fiber. Optical pulses of 160 mW peak power and 630 ps temporal width were obtained at 9 MHz repetition rate.

We report on an examination of pulse timing stability of a home built Erbium Doped Fiber Laser (EDFL) passively mode locked via nonlinear polarization rotation by inserting semiconductor saturable absorber mirror (SESAM) in laser cavity. A very low root mean square (RMS) timing jitter (less than 27 fsec) and faster self-starting mode locking have been established. In order to get clear, low noise signal for time resolving measurements, synchronization of EDFL laser with an external high precision electronic oscil-lator have been established. Subsequently, it is synchronized and optically cross-correlated with a Ti: Sapphire laser source (Micra). The measured relative timing jitter was found to be less than 65 fsec. In this way, the two, well synchronized Ti:Sapphire and EDFL laser pulses prove to be a powerful tool for time resolving measurements.