Cavity-length Mismatch Research Articles

Cavity Mode-Matching InGaN Aperture-Emitting Device with a Nanoporous GaN Reflector via Ion Implantation

Cavity mode-matching InGaN resonant-cavity light-emitting diodes (RC-LEDs) with aperture size-dependent emission have been demonstrated through nitrogen ion (N+) implantation and electrochemical wet etching processes. The RC-LED structure consisted of 570 nm-depth ion-implanted regions and an embedded 17-pair nanoporous-GaN/n-GaN distributed Bragg reflector (DBR) outside the aperture, while there existed a full 20-pair DBR structure within the aperture regions. Shorter and mode-matching cavity lengths were fabricated, confirmed by transmission electron microscopy and angle-resolved photoluminescence spectra inside the aperture area without subjecting to the N+ implantation. By reducing the aperture sizes, higher current density and narrower far-field electroluminescence emission patterns were observed in the RC-LED with an aperture size of 40 μm-diameter. These results demonstrate that the cavity mode-matching RC-LEDs with optical/electrical confinements and controllable cavity length mismatch features can be applied in a wide range of optoelectronic-based device applications.

C-band dual-wavelength synchronized mode-locked erbium-doped fiber laser using a common absorber

We demonstrate a C-band dual-wavelength synchronized mode-locked erbium-doped fiber laser based on a common single-wall carbon nanotube saturable absorber and two loop resonators. The synchronous mode-locked pulses laser is with a repetition rate of 16.28 MHz and durations of 1.95 ps and 1.21 ps at 1533 nm and 1562 nm, respectively. The tolerance of a cavity-length mismatch is about 830μm. The proposed dual-wavelength laser system exhibits a flexibly controlled performance and a long-term stability, which offers great potential for a number of applications, such as difference-frequency terahertz-wave generation and field-enhancement Raman microscopy.

Temporal cavity solitons in a laser-based microcomb: a path to a self-starting pulsed laser without saturable absorption.

We theoretically present a design of self-starting operation of microcombs based on laser-cavity solitons in a system composed of a micro-resonator nested in and coupled to an amplifying laser cavity. We demonstrate that it is possible to engineer the modulational-instability gain of the system's zero state to allow the start-up with a well-defined number of robust solitons. The approach can be implemented by using the system parameters, such as the cavity length mismatch and the gain shape, to control the number and repetition rate of the generated solitons. Because the setting does not require saturation of the gain, the results offer an alternative to standard techniques that provide laser mode-locking.

Carbon nanotube-synchronized dual-color fiber laser for coherent anti-Stokes Raman scattering microscopy.

In this Letter, we present a passively synchronized dual-color fiber laser at 1.03 and 1.53 µm for coherent anti-Stokes Raman scattering (CARS) microscopy. This fiber laser consists of both Yb- and Er-doped laser cavities, combined by an ∼1.2m common branch with a single-walled carbon-nanotube-based saturable absorber. Stable passively synchronized mode-locked state is obtained within a total cavity length mismatch of 50 µm. We demonstrate the capability of the synchronized dual-color fiber laser for CARS spectroscopy in both low- and high-wavenumber regions, with a resolution of 6.6cm-1. Furthermore, a CARS image in the field of view 150×60µm2 of polystyrene at the Raman shift of 3041cm-1 has also been achieved. The results show the feasibility of our passively synchronized dual-color fiber laser to be employed as a stable and low-cost ultrafast laser source for CARS.

Passively synchronized dual-color mode-locked fiber lasers based on nonlinear amplifying loop mirrors.

We have proposed and implemented a scheme for passive all-optical synchronization between erbium and ytterbium mode-locked fiber lasers. The passive locking of repetition rates for the dual-color pulses was realized by cross-phase modulation within phase-biased nonlinear amplifying loop mirrors. In contrast to previous demonstrations, the synchronization system was configured in an all-polarization-maintaining structure, thus gaining substantially improved stability and robustness. Consequently, the maximum tolerance of a cavity-length mismatch of 16.2mm was achieved unprecedentedly, which was at least one order of magnitude longer than previously reported results for comparable temporal durations of involved pulses. The corresponding relative timing jitter was measured to be 31fs within a 1MHz bandwidth. Such a tight and robust synchronization fiber laser system offers great potential for various applications such as pump-probe microscopy, Raman scattering spectroscopy, and nonlinear frequency generation.

Wavelength-spacing controllable, dual-wavelength synchronously mode locked Er:fiber laser oscillator based on dual-branch nonlinear polarization rotation technique.

A wavelength-spacing controllable, dual-wavelength synchronously mode locked Er:fiber laser oscillator based on dual-branch nonlinear polarization rotation (NPR) technique was presented. The center wavelengths were at 1542 nm and 1561 nm, which had pulse durations of 1.38 ps and 1.70 ps, respectively. Experimentally, the synchronous mode locking was achieved by precisely adjusting the cavity length of one branch. A tolerance in the cavity length mismatch of 0.46 mm for synchronous mode locking was demonstrated. The frequency difference of the two pulse trains was measured to be less than 1 mHz. Additionally, this synchronously mode locked dual-wavelength laser had a wavelength tunable range of about 5.6 nm, and a controllable wavelength spacing from 10.5 nm to 28.2 nm, corresponding to a tunable frequency difference from 1.32 THz to 3.26 THz. To the best of our knowledge, this is the first demonstration of synchronously mode locked dual-wavelength output directly from a Er:fiber laser oscillator, using dual-branch NPR technique.

Stretched-pulse mode-locking synchronously triggered by a femtosecond master laser at sub-megahertz repetition rate

A stretched-pulse mode-locked ytterbium-doped fiber laser was passively synchronized to a femtosecond Ti:sapphire laser at a low repetition rate of 240 kHz through large cross absorption modulation along additional 1-m-long erbium-doped fiber. The synchronous fiber laser with an ultra-long fiber cavity could produce not only nanosecond flat-top pulses with tunable pulse duration but also Gaussian-shape stretched pulses with its minimum pulse duration of ∼450 ps as confirmed by cross-correlation measurement. When operating in the stretched pulse regime, the sub-nanosecond fiber laser could be synchronously triggered by the master injection with the cavity-length mismatch tolerance up to ∼7.8 cm and timing jitter less than 400 fs, confirming that the stretched-pulse mode-locking of the ultra-long slave fiber laser could be robustly controlled by cross absorption modulation effects in the erbium-doped fiber with appropriate femtosecond master injection.

Independently tunable 13 W femtosecond Ti:sapphire lasers passively synchronized with attosecond timing jitter and ultrahigh robustness

A stable passively synchronized femtosecond laser has been realized by coupling two 1.3 W mode-locked Ti:sapphire lasers with a Kerr medium. An ultralong tolerance of 10 microm for the cavity length mismatch and a timing jitter of less than 0.4 fs were obtained. The relative carrier-envelope phase slip was directly observed by measuring the heterodyne output between the two lasers.

Global view of nonlinear dynamics in coupled-cavity lasers – a bifurcation study

This paper investigates nonlinear behavior of coupled lasers. Composite-cavity-mode approach and a class-B description of the active medium are used to describe nonlinearities associated with population dynamics and optical coupling. The multimode equations are studied using bifurcation analysis to identify regions of stable locking, periodic oscillations, and complicated dynamics in the parameter space of coupling-mirror transmission T and normalized cavity-length mismatch dL/λ. We further investigate the evolution of the key bifurcations with the linewidth enhancement factor α. In particular, our analysis reveals the formation of a gap in the lockband that is gradually occupied by instabilities. We also investigate effects of the cavity-length on chaotic dynamics.

Passive synchronization between femtosecond Ti:sapphire and Cr:forsterite lasers

Two independent femtosecond Ti:sapphire and Cr:forsterite lasers were stably synchronized by crossing both lasers inside the Ti:sapphire crystal. We obtained two-color femtosecond pulse trains at the completely different wavelengths of around 820 nm and 1250 nm respectively. This new technique overcomes the gain competition and enables us to greatly broaden the tunable ranges. By optimizing the overlap of the beams, we realized a large tolerance of cavity-length mismatch of 5 μm and demonstrated long-term synchronization that continuously remained over several hours. The measured FWHM of the cross-correlation trace is 74±2 fs based on the 43±2-fs Ti:sapphire and 52±1-fs Cr:forsterite lasers. The exact coincidence with the theoretical calculated value infers the two-color laser being synchronized with a timing jitter of only a few femtoseconds.

Generation of two-color femtosecond pulses by self-synchronizing Ti:sapphire and Cr:forsterite lasers

We report a novel technique for the synchronization of two different femtosecond solid-state lasers by crossing of both laser pulses in a Kerr medium. Stable dual-wavelength femtosecond pulses at central wavelengths of 820 and 1250 nm have been obtained. The tolerance of cavity-length mismatch is ~0.6mum , where the pulse widths of the Ti:sapphire and the Cr:forsterite lasers are 18 and 40 fs, respectively, at average powers of 600 and 110 mW. The typical timing jitter derived from the cross correlation is less than 3 fs.

Fiber-grating-based self-matched additive-pulse mode-locked fiber lasers

Fiber-grating-based self-matched additive-pulse mode-locked (APM) fiber lasers were investigated both theoretically and experimentally. With three fiber gratings to form the linearly coupled cavities, such a fiber laser system could generate stable mode-locked output without critical cavity length control. It was shown that the wavelength dependence of the effective penetration length of a fiber grating led to the self-matching of the cavity lengths of the coupled cavities. A millimeter-order cavity-length mismatch could be tolerated. In a similar laser structure using chirped fiber gratings with a designated arrangement of the grating polarities, the APM fiber laser could have the advantages of higher tolerance of cavity-length mismatch and stretched-pulse amplification. After pulse compression with a piece of single-mode fiber, output pulses with full-width at half-maximum pulsewidths of 930 fs were obtained.

Dynamic instabilities in an additive-pulse mode-locked Nd:YAG laser

An additive-pulse mode-locked Nd:YAG laser is studied experimentally and numerically. We observe dynamic instabilities such as period doubling, quasi-periodicity, and high-dimensional chaos. Dependence on control parameters such as peak nonlinear phase shift and cavity-length mismatch are discussed. We provide evidence for instabilities in the temporal profiles of the individual pulses.

Silver thiogallate, singly resonant optical parametric oscillator pumped by a continuous-wave mode-locked Nd:YAG laser

We describe a silver thiogallate (AgGaS(2)) singly resonant optical parametric oscillator (OPO), synchronously pumped by a continuous-wave actively mode-locked Nd:YAG laser. The OPO is operated with a signal wavelength near 1.319 microm and an idler wavelength near 5.505 microm. At optimum output coupling, 100 mW of useful signal power and 6 mW of idler power are generated from 625 mW of pump power. The pump is mechanically chopped at a 32:1 duty cycle to prevent thermal lensing of the AgGaS(2) crystals. Pump depletion is as high as 63%. The signal has pulse widths ranging from 45 to 80 ps and spectral widths ranging from below 0.1 to 0.3 nm. The OPO signal can oscillate over a 2-mm range of round-trip cavity-length mismatch.

Simple method for eliminating the warming-up time of an Antares cw mode-locked Nd:YLF laser

Mode locking of a cw Nd:YLF laser is sensitive to cavity-length mismatch. When a cw mode-locked Nd:YLF laser is turned on the power dissipation from the lamps causes a slow change in the cavity length because of heating of mechanical resonator parts. A method is presented to eliminate these warming-up effects.

On the design of synchronously pumped mode-locked dye lasers with improved noise characteristics

An analysis of a synchronously pumped mode-locked (SPML) dye laser that is less susceptible to external noise sources is presented. Approximate, analytic formulas for the pulsewidth and peak intensity of an SPML dye laser are derived in the limit of a short pump pulse and a short coherence time. Using these expressions the sensitivity of the pulsewidth, the peak intensity, and a pulse energy on the cavity length mismatch and the pump level are explored. It is found that the detrimental effects of pump laser jitter (level and timing) can be decreased if a higher pumping level is achieved. Long-term pulse-to-pulse fluctuations in energy can be reduced by increasing the cavity losses. >

Spectral and temporal characterizations of coupled-cavity mode locking in a KCl:Tl color center laser

The authors present experimental results on the spectral and temporal characteristics of a coupled-cavity mode-locked (CCM) KCl:Tl color center laser where a 2.8-m length of anomalously dispersive fiber was used in the control cavity. Under different operating conditions, both symmetrical and peak-featured spectra of the CCM laser were observed. Interrelationships between the spectral broadening and the cavity-length mismatch were determined experimentally.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Study of synchronously mode-locked and internally frequency-doubledcw dye laser

The analysis of the characteristics of a synchronously mode-locked and internally frequency-doubled dye laser is presented. Dependence of dye laser pulse characteristics on the cavity length mismatch of the pump laser and dye laser is studied. Variation of the minimum pulsewidth with intracavity bandwidth and the harmonic conversion efficiency is presented in the form of graphs.

Limits to pulse advance and delay in mode-locked lasers

A fundamental limitation on pulse advance or delay in mode-locked lasers is described by the impulse response of the intracavity bandwidth limitation, which is roughly equal to the inverse bandwidth (1/ωc) in seconds. In sync-pumped and active systems this restricts the allowable range of cavity-length mismatch for proper mode locking, explaining micrometer sensitivities in some cases. The master equation of mode locking cannot predict this behavior, which affects active, passive, and sync-pumped mode-locked lasers. We also note that the intrinsic recovery time of the pulse width τ in a mode-locked laser is (ωcτ/2)2 round trips, where [1 − (ω2/ωc2)] approximates the field response of the intracavity filter.

Dual picosecond dye lasers synchronously pumped by a mode locked cw yag laser

The performance of a novel dual dye laser system synchronously pumped by the frequency doubled output of a mode-locked CW-YAG laser is evaluated in relation to pulsewidth, pulse substructure, pulse spectral width and timing jitter. The behavior of the system is adequately described by a theoretical model which includes the time dependent gain and losses due to frequency bandwidth, cavity length mismatch and output coupler. The jitter is significantly reduced from that obtained with CW gas laser pumping as a result of the shorter pump pulse (50 ns instead of ≈100 ps). A routine operating condition uses 2-plate birefringen filters, 0.8 W pump power at 532 nm, to yield two 2.0 ps pulses having a cross correlation width of 3.8 ps, and 30 mW average power from each laser.