Semiconductor optical amplifier-based multi-wavelength ring laser utilizing photonic crystal fiber

A multi-wavelength laser source is demonstrated with a semiconductor optical amplifier (SOA) as a gain medium. A multi-wavelength comb with equal spacing is achieved due to Fabry–Pérot modes of the SOA which oscillates in the ring cavity. A 100 m long photonics crystal fiber (PCF) is inserted in the ring cavity to provide a nonlinear gain by four-wave mixing (FWM) so that the output comb spectrum can be greatly broadened and flattened. The stability of the ring laser is also increased due to the efficient FWM phenomenon occurring in the PCF. The SOA-based laser can generate 35 lasing lines with equal spacing of 0.28 nm and extinction ratios of more than 30 dB at room temperature. The number of channels of the multi-wavelength laser can be controlled flexibly by changing the ratio of the coupler used in the ring cavity configuration as well as controlling the polarization state of the oscillating laser.     

多波长掺镱光纤激光器实验研究

为了产生室温下掺镱光纤激光器稳定的多波长激光振荡,采用两个光纤环镜作为线形腔掺镱光纤激光器的端镜,在其中一个环镜中熔接一段保偏光纤构成梳状滤波器,通过优化掺镱光纤长度和腔损耗,实现了室温下1060nm附近稳定的多波长振荡.实验结果表明,在室温下,掺镱光纤存在比较明显的非均匀加宽效应,从而使得激光器的振荡波长数随泵浦功率的增加而增加.     

Dependence of laser intensity on cavity losses for a detuned, single-mode laser

It is shown that for a detuned, single-mode, homogeneously broadened laser, semiclassical laser theory predicts a transition from a nonlasing state to a lasing state when cavity losses are increased for a range of cavity detunings when dispersion is large. A physical explanation for this behavior is presented in which the influence of dispersion on the cavity resonance frequencies is considered.     

Subluminal and superluminal light propagation via electromagnetically induced transparency in radiatively and inhomogeneously broadened media

Contrary to popular belief, we demonstrate the feasibility of generating superluminal (and subluminal) probe (and signal) light via electromagnetically induced transparency in a medium comprising coupled double-ladder systems. This scheme can be realized in both homogeneously (radiative) as well as in inhomogeneously (Doppler) broadened atomic systems. Unlike more intricate earlier schemes, our scheme is based simply on steady-state propagation dynamics resulting from compensation of the inevitable absorption losses by large nonlinear gain generated through appropriate choice of the pump and coupling fields. We show how easily in this scheme the speed of weak probe (and signal) fields can be switched from subluminal to superluminal by simply varying the strengths of the coherent pump and coupling fields. Furthermore, it is shown that under these conditions both the signal and probe fields are intensity matched and both propagate with the same subluminal (or superluminal) group velocity without suffering loss or gain for long distance in the medium.     

Laser Instabilities and Chaos in Inhomogeneously Broadened Dense Media

Abstract

We study numerically the effects of local-field corrections originating from near dipole—dipole interactions on the dynamics of a single mode, inhomogeneously broadened laser. Our analysis is based on a set of generalized Maxwell–Bloch equations in which the inhomogeneous nature of gain broadening is accounted for by introducing two new dynamical variables and a single parameter that governs the extent of inhomogeneous broadening. Our results show that local-field effects occurring in a dense gain medium reduce the range of continuous wave operation and lead to instabilities and chaos at much lower pumping levels.     

Wavelength switchable L-band erbium-doped fiber laser employing C-band EDFA as gain medium

A new structure for the L-band multiwavelength switchable erbium-doped fiber laser is proposed. Overlapping laser cavities are formed by cascading fiber Bragg gratings as reflectors in a ring structure with a C-band EDFA as a common gain medium. The proposed laser is made to be wavelength-switchable by individually adjusting the loss of each overlapping cavity. Instead of using an L-band EDFA as the gain medium in the L-band fiber laser, we have experimentally demonstrated that by tailoring the gain of the C-band EDFA to have a significant gain tilt in the L-band, a lasing power efficiency of 26% can be achieved over a wide range of switchable lasing wavelengths. Following this optimal design, the side-mode suppression ratio and the minimal separation between two switchable lasing wavelengths were found to be over 42 dB and 0.33 nm, respectively.     

Influence of external cavity length on multimode hopping in microchip Nd:YAG lasers

The influence of external cavity length on multimode hopping in microchip Nd:YAG lasers is investigated experimentally. With an optical feedback loop, the threshold gain of different longitudinal modes are all modulated by changing the external cavity length; a lambda/2 change in the external cavity length causes a one-period oscillation. The longitudinal modes can be divided into groups according to different initial threshold gain variations and modulation trends corresponding to different external cavity phases. Because of the initial gain difference, only one mode in each group is the dominant potential lasing mode, while others are suppressed. During the 2 pi change of the external cavity phase, mode hopping occurs among these potential lasing modes from different groups. Both the intensity waveforms and the number of hopping modes strongly depend on the external cavity length. Experimental results agree well with the theoretical analysis of the phenomenon of multimode hopping subjected to optical feedback in microchip Nd:YAG lasers.     

L-Band multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror and dual-channel Mach–Zehnder interferometer

In this letter, we propose and demonstrate an L-Band linear cavity tunable multi-wavelength erbium-doped fibre laser based on non-linear optical loop mirror (NOLM) and dual-channel Mach–Zehnder interferometer (MZI) . The NOLM provides the intensity-dependent transmissivity, can effectively alleviate the mode competition and beating caused by the homogeneous gain broadening, so that the multi-wavelength lasing can be achieved at room temperature. The dual-channel MZI, configured by linking the two outputs of the single-channel MZI, serves as comb filter. By adjusting the polarization controller in NOLM and pump power, the tunable multi-wavelength output at 1600 nm can be achieved. Moreover, the output stability of the laser has also been accomplished .     

Fringe visibility of multimode laser light scattered through turbid water

Several years ago Swanson [Proc. SPIE 1750, 397 (1992)] performed a simple Michelson interferometric determination of the coherence length of a multimode argon-ion laser after the light passed through a tank of water. As colloidal particles were added to the water the observed coherence length (as measured by twice the distance the mirror moved for fringes to disappear) decreased. Subsequently, a series of careful experiments were performed with a single-mode laser to more accurately measure this change. In these experiments it was found that the 1.5-MHz width of the 514.5-nm line of a single-mode argon-ion laser broadened by as much as 1.3 +/- 0.2 MHz when small colloidal particles were added. At first glance such a broadening should not have resulted in any discernible change in the original Michelson experiment because the gain curve for the multimode laser is of the order of a few gigahertz. The zeros in the fringe visibility function depend on the spectral characteristics of the modes. Upon scattering, the spectral characteristics of the individual laser modes change from Voigt functions, containing both Lorentzian and Gaussian components, to primarily Gaussian. It is this change in the statistical properties of the modes, not the broadening, that accounts for the change in the fringe visibility for a multimode source.     

All-fibre Mach–Zehnder interferometer based on seven-core and coreless fibres for generating stable wavelength-switchable laser

In order to realize a wavelength-tuneable fibre-laser output, a ring-cavity erbium-doped fibre laser based on an all-fibre Mach–Zehnder interferometer (MZI) is proposed and experimentally tested. The MZI consists of a single-mode fibre, two segments of coreless fibre, and a seven-core fibre. For the proposed fibre laser, the length of the gain medium is 4?m and the lasing threshold is 75?mW. By adjusting the loss of the laser cavity, switchable single-wavelength laser emission is realized across the range of 1527.6–1549.9?nm and the wavelength interval is less than 2.4?nm; the peak power difference of each lasing wavelength is less than 7.9?dB. Tuneable dual- and three-wavelength laser outputs were obtained by adjusting the polarization controller. The 3-dB linewidth was less than 0.57?nm. The single- and dual-wavelength laser output power fluctuations were less than 1.4 and 1.7?dB, respectively, when monitored over a period of 30?min.     

Cavity-length optimization for high energy pulse generation in a long cavity passively mode-locked all-fiber ring laser

In order to achieve higher pulse energy in a passively mode-locked fiber ring laser, a long cavity length is commonly implemented. However, a long cavity operating in the anomalous dispersion regime also leads to pulse broadening, which reduces the average pulse power. In this paper, the trade-off between cavity length and average pulse power is investigated with the aim of optimizing the cavity length to achieve maximum pulse energy. Numerical simulation results, presented here, indicate that there exists an optimum cavity length for which the pulse energy is maximum and the optimum length shifts as the pump power changes. The simulation results for a pump power of 500 mW are verified by measurements carried out on a long cavity nonlinear polarization rotation mode-locked all-fiber ring laser operating in the anomalous dispersion regime. With a repetition rate of 266 kHz for the dissipative solitons, we achieve a pulse energy of 139.1 nJ for a cavity length of 700 m. Higher pulse energy can be expected by using a pump laser diode with higher pump power.     

Mode locking in coherently driven laser systems

A new concept of mode locking for a three-level gain medium with two coherent fields is proposed. The strong field applied on the coupling transition produces broadening of the lasing transition. The broadened emission spectrum allows one to generate pulses with durations far beyond limits inherent to a conventional mode-locking technique.     

Gain flattening coatings for improved spectral performance of asymmetric multiple quantum well lasers

A gain flattening coating was designed and fabricated to enhance the wavelength tuning for asymmetric multiple quantum well (AMQW) lasers. After coating, a nonlasing gap in the middle range of the lasing wavelengths, which might exist for AMQW lasers that are operated without an external cavity, was overcome and the total lasing range was increased. With the coating, the tuning range of an AMQW laser, as measured without an external cavity, was increased to 85?nm from 70?nm.     

Three-photon electromagnetically induced absorption and transparency in an inhomogeneously broadened atomic vapour

We study both theoretically and experimentally three-photon electromagnetically induced transparency and electromagnetically induced absorption resonances in inhomogeneously broadened 85 Rb atomic vapour driven by probe and drive laser radiations. We observe narrow Doppler-free absorption as well as transmission resonances for the probe field when the driving laser field is redshifted from the D₁ or D₂ lines of ⁸⁵Rb; the frequency difference between the drive and probe fields is equal to the hyperfine splitting of the ground state of the atoms, and the probe field is tuned to the centre of the Doppler broadened atomic transition. We theoretically study the spectroscopic effect in both homogeneously and inhomogeneously broadened media. Our numerical simulations are in good agreement with the experimental results.     

Cesium lead halide perovskite triangular nanorods as high-gain medium and effective cavities for multiphoton-pumped lasing

High-performance multiphoton-pumped lasers based on cesium lead halide perovskite nanostructures are promising for nonlinear optics and practical frequency upconversion devices in integrated photonics.However,the performance of such lasers is highly dependent on the quality of the material and cavity,which makes their fabrication challenging.Herein,we demonstrate that cesium lead halide perovskite triangular nanorods fabricated via vapor methods can serve as gain media and effective cavities for multiphoton-pumped lasers.We observed blue-shifts of the lasing modes in the excitation fluence-dependent lasing spectra at increased excitation powers,which fits well with the dynamics of Burstein-Moss shifts caused by the band filling effect.Moreover,efficient multiphoton lasing in CsPbBr3 nanorods can be realized in a wide excitation wavelength range (700-1,400 nm).The dynamics of multiphoton lasing were investigated by time-resolved photoluminescence spectroscopy,which indicated that an electron-hole plasma is responsible for the multiphoton-pumped lasing.This work could lead to new opportunities and applications for cesium lead halide perovskite nanostructures in frequency upconversion lasing devices and optical interconnect systems.     

Generation of stable and narrow spacing dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

Abstract

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-μm region.     

Simulation of double quantum well GalnNAs laser diodes

The simulation of double quantum well (QW) GalnNAs ridge-waveguide (RW) lasers is performed over a wide range of cavity lengths and operating temperatures using a comprehensive in-house 2D laser simulator that takes into account all of the major device physics, including current spreading, capture escape processes, drift diffusion in the QW, 2D optical modes and fully resolved lasing spectra. The gain data used by the simulator were fitted to experimental gain spectra measured by the segmented contact method. The gain model includes the band-anticrossing model for the conduction band and a 4 x 4 kldrp model for the valence band. Using a carrier density-dependent and temperature-dependent linewidth broadening parameter, a good fit with experiment over a temperature range of 300-350 K was obtained. A Shockley-Read-Hall (SRH) lifetime of 0.5 ns and an Auger recombination coefficient of 1 x 10^-28 cm⁶/ s, were extracted from the calibration of the laser simulator to experimental device characteristics of broad-area (BA) devices. Using the same set of parameters for BA devices, except for a reduced SRH lifetime of 0.45 ns underneath the etch, 2D simulation results were found to agree well with the measured RW laser operating characteristics. The impact of the various recombination processes in the RW laser at threshold has also been identified using the calibrated laser simulator.     

Random Lasing in π‐Conjugated Films and Infiltrated Opals

The properties of random lasers in π‐conjugated polymer films and solutions infiltrated into opal photonic crystals are reviewed. We show that random lasing is a generic phenomenon that occurs in disordered gain media at an excitation intensity regime higher than that giving rise to amplified spontaneous emission. The emission radiation is coherent as demonstrated by photon statistics methods, and its spectrum contains many laser modes from which a typical cavity length can be obtained using Fourier transform spectroscopy. Since the random cavities are independent from each other, we show that laser emission in several colors is possible when mixing different dyes in the same random cavities. In addition, it is demonstrated that random lasing is formed in many disordered media with various scattering properties ranging from a regime of light prelocalization to that of weak scattering.     

光纤光栅半导体激光器激射波长与Bragg波长的偏离

利用包含光纤布拉格光栅(FBG)反射率分布的光纤光栅外腔半导体激光器(FGSL)的理 论模型,对FGSL 的激射波长进行了研究。结果表明激射波长并不一定在FBG布拉格反射波长处;布拉格反射波长相对于激射波长的偏移量与FBG的反射率分布、半导体增益介质的增益谱分布及增益峰值波长有关;激射波长可大于或小于布拉格反射波长。     

Wavelength tuning in optically mode-locked semiconductor fiber ring lasers with linearly chirped fiber Bragg gratings

We demonstrate wavelength tuning in single-wavelength and multiwavelength semiconductor fiber ring lasers that are mode locked with an optically injected control signal. A semiconductor optical amplifier is used to provide gain as well as to function as an optically controlled mode-locking element. Linearly chirped fiber Bragg gratings--single or superimposed--are used to define the lasing wavelengths as well as to provide wavelength tunability and allow for multiwavelength operation. We obtain pulses of tens of picoseconds in duration when we inject a sinusoidal optical control signal into the laser cavity, and we can tune the lasing wavelength(s) over the reflection bandwidth(s) of the grating(s) by simply changing the frequency of the injected control signal.