Ameliorating the stability of erbium-doped fiber laser using saturable absorber fabricated by the pulsed laser deposition technique.

In this paper, we present the performance and stability of an erbium-doped fiber laser (EDFL) based on ZnO saturable-absorber (SA) prepared using two schemes: solution method (SM) and pulsed laser deposition technique (PLDT). It was observed that EDFL with ZnO-SA prepared using SM emits at 1561.25 nm under a pump power of 230 mW. As the pump power is increased from 22.2 mW to 75.3 mW, the pulse duration decreases from 24.91 to 10.69 µs, and the pulse repetition rates increase from 11.59 to 40.91 kHz. Besides at pump power of 75.3 mW, the peak power, pulse energy, and average output power are measured as 0.327 mW, 2.86 nJ, and 0.18 mW, respectively. However, when PLDT-based SA was incorporated into the ring cavity, the emission wavelength is noticed at 1568.21 nm at a pump power of 230 mW. With the increase in pump power from 22.2 mW to 418 mW, the pulse repetition rates increase from 10.79 to 79.37 kHz and the pulse width decreases from 23.58 to 5.6 µs. Furthermore, the peak power, pulse energy, and average output power are observed to be 10.9 mW, 74 nJ, and 5.35 mW, respectively. The stability of EDFL based on SAs prepared using SM and PLDT has also been investigated. To the best of the author's knowledge, it is the first comparison of performance and long-term stability of EDFL based on two experimental techniques SM and PLDT-based SAs. These findings suggest that PLDT-based SAs provides optimum stability over a long period and enhanced the performance of fiber lasers compared to the SAs prepared using the conventional SM technique. This study paves the way for the development of ultra-stable SAs for their potential applications in pulsed laser sources and photonic devices.

Stabilization of self-mode-locked QDash lasers subject to simultaneous continuous-wave optical injection and optical feedback.

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. With continuous-wave optical injection, various wavelengths spanning a range from 1568 to 1578 nm were investigated and optimum wavelengths (1571.210 to 1572.710) yielding the narrowest RF linewidth and reduced timing jitter of slave laser were identified. In addition, the dependence of RF linewidth and pulse repetition rate on injected wavelength was further explored. Our results indicate that simultaneous optical feedback and optical injection significantly improves the RF linewidth across the widest delay range compared to optical feedback alone. Under fully resonant feedback and optimum injection parameters, a minimum RF linewidth of 1 kHz (instrument limited) was achieved with simultaneous optical injection plus optical feedback, which was >2× lower than optical feedback alone and more than 100× lower than free-running. 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.

Stabilization of self-mode-locked quantum dash lasers by symmetric dual-loop optical feedback.

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.

Asymmetric dual-loop feedback to suppress spurious tones and reduce timing jitter in self-mode-locked quantum-dash lasers emitting at 1.55 µm.

We demonstrate an asymmetric dual-loop feedback method to suppress external cavity side-modes induced in self-mode-locked quantum-dash lasers with conventional single- and dual-loop feedback. In this Letter, we report optimal suppression of spurious tones by optimizing the delay in the second loop. We observed that asymmetric dual-loop feedback, with large (∼8×) disparity in loop lengths, gives significant suppression in external-cavity side-modes and produces flat radio frequency (RF) spectra close to the main peak with a low timing jitter, compared to single-loop feedback. Significant reduction in RF linewidth and timing jitter was produced by optimizing the delay time in the second feedback loop. Experimental results based on this feedback configuration validate predictions of recently published numerical simulations. This asymmetric dual-loop feedback scheme provides simple, efficient, and cost-effective stabilization of optoelectronic oscillators based on mode-locked lasers.

Optimum stabilization of self-mode-locked quantum dash lasers using dual optical feedback with improved tolerance against phase delay mismatch.

We experimentally investigate the RF linewidth and timing jitter over a wide range of delay tuning in a self-mode-locked two-section quantum dash lasers emitting at ~ 1.55µm and operating at ~ 21 GHz repetition rate subject to single and dual optical feedback into gain section. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual loop configurations. We demonstrate that dual loop feedback, with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, unlike single loop feedback. In addition, for dual loop configurations, under fully resonant conditions, integrated timing jitter is reduced from 3.9 ps to 295 fs [10 kHz-100 MHz], the RF linewidth narrows from 100 kHz to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual loop optical feedback with separate fine tuning of both external cavities is far superior to single loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

Simultaneous achievement of narrow pulse width and low pulse-to-pulse timing jitter in 1.3 microm passively mode-locked quantum-dot lasers.

We have analyzed pulse width and timing jitter in passively mode-locked two-section InAs quantum-dot lasers emitting at 1310 nm and have identified two distinct, extensive mode-locked regions with robust short pulses and low timing jitter. A record combination of 2 ps pulses and 25 fs/cycle timing jitter (500 fs, 1-100 MHz), with 1 mW average output power per facet, is demonstrated.

Dynamics of traveling waves in the transverse section of a laser.

We analyze the general features of the formation and interaction of transverse traveling waves and the appearance of filamentation in broad area semiconductor lasers with current profiling. For small apertures, the emitted profile is symmetric consisting of two counterpropagating transverse traveling waves, both emanating from the center of the device. For larger apertures, the emission becomes asymmetric as one of the traveling waves expands to occupy an increased area while the other occupies the remaining, smaller spatial region. In both devices, the pattern becomes unstable at higher injection currents due to optical filamentation, although an intermediate state is present in the wider device whereby the dominant wave undergoes a Hopf bifurcation before filamentation occurs.

Femtosecond measurements of two-photon absorption coefficients at lambda = 264 nm in glasses, crystals, and liquids.

Using ultraviolet femtosecond pulses with high irradiance stability, we measured the two-photon absorption (TPA) coefficients in a number of substances with a total accuracy of approximately 10%. Six commercial fused-silica samples (KU-1, Coming 7940, SQ, Suprasil, Herasil, and Infrasil) possess TPA coefficients (beta values) of approximately 2 x 10(-11) cm/W. For crystalline quartz and sapphire, the following beta values were obtained: (1.2 +/- 0.2) x 10(-11) and (9.4 +/- 1.2) x 10(-11) cm/W, respectively. In beta-barium borate crystal the TPA coefficient depends on crystal cut, beam polarization, or both and varies from (47 +/- 5) x 10(-11) to (68 +/- 6) x 10(-11) cm/W. For eight liquids that were studied (water, heavy water, ethanol, methanol, hexane, cyclohexane, 1,2-dichloroethane, and chloroform) the beta value lies from (34 +/- 3) x 10(-11) to (95 +/- 11) x 10(-11) cm/W.