Improved drawing conditions for very low loss 1.55-μm dispersion-shifted fiber

Fiber drawing conditions (temperature, speed, tension) have been investigated to reach very low losses (0.20 dB/km at 1.55 μm) with MCVD triangular core-profile preforms. Such dispersion-shifted fibers exhibit good mechanical, splicing, cabling, and ageing properties.     

Passive polarization rotator based on silica photonic crystal fiber for 1.31-μm and 1.55-μm bands via adjusting the fiber length

A new polarization rotator based on the silica photonic crystal fiber is proposed. The proposed polarization rotator photonic crystal fiber （PR-PCF） possesses a triangle jigsaw-shape core region. The full-vector finite-element method is used to analyze the phenomenon of polarization conversion between the quasi-TE and quasi-TM modes. Numerical simulations show that the wavelengths of 1.31 μm and 1.55 μm are converted with a nearly 100% polarization conversion ratio with their matched coupling length and has a relatively strong realistic fabrication tolerance - 100 nm on the y axis and 50 nm on the x axis. The full vectorial finite difference beam propagation method is used to confirm the performance of the proposed PR-PCF.     

Diode-pumped 200 μm diameter core, gain-guided, index-antiguided single mode fiber laser

Single mode laser action in a diode-pumped gain-guided, index- antiguided Nd³⁺-doped phosphate glass fiber having a 200-μm-diameter core is demonstrated. Near-Gaussian beam quality was maintained, even when pumped up to four times the threshold pump power, indicating robust lowest order mode oscillation. Subtle differences associated with the effectiveness of diode pumping gain-guided, index-antiguided fibers are discussed. PACS 42.55.Wd; 42.55.Xi     

Self-swept erbium fiber laser around 1.56 μm

Self-swept erbium fiber laser emitting around 1.56?μm is reported in detail. Both sweep directions were registered: pointing toward longer and shorter wavelengths, redshift and blueshift sweeping, respectively. We describe method of determining the direction of the wavelength drift using the monochromator based optical spectrum analyzer. Possible root for this sweeping regime, i.e., the gain modulation along active fiber, is discussed with the help of a simple model calculating the overall cavity gain that can predict the direction of the laser wavelength sweeping.     

A self-seeded fiber laser incorporated with a fiber Bragg grating external cavity semiconductor laser

A self-seeded fiber laser incorporated with a fiber Bragg grating external cavity semiconductor laser (FBG-ECL) and a Mach-Zehnder interferometer (MZI) were reported in this paper. The MZI provided a Q-switching with response time in the order of micro-seconds. The FBG-ECL provided narrow pulses as seeds to shorten the Q-switched pulses. Experimentally, pulse width of 0.8 μs was measured, which was one fifth of the pulse width without self-seeding.     

126-W all-fiberized single-mode laser from an 11-μm small-core fiber

We demonstrate a 126-W all-fiberized single-mode laser from an 11-μm small-core fiber. The active fiber is a strictly single-mode fiber that produces pure single-mode. The optical to optical efficiency of the fiber laser is 68.2% with ASE suppressed by a factor of ∼35 dB and no power-roll. The output power is only limited by the available pump source, scaling the pump power may achieve much higher output power using the 11 μm small-core fiber.     

Erbium-doped CW and Q-switched fiber ring laser with fiber grating Michelson interferometer

The band-pass characteristic of fiber grating Michelson interferometer is analyzed, which acts as bothband-pass filter and Q-switch. An erbium-doped fiber ring laser based on fiber grating Michelsoninterferometer is implemented for producing single longitudinal mode CW operation with 5 MHz spectrallinewidth and up to 6 mW output power. In Q-switched operation, stable fiber laser output pulses withrepetition rate of 800 Hz, pulse width of 0.6 μs, average power of 1.8 mW and peak power of 3.4 W aredemonstrated. The peak power and average power of the Q-switched pulses are varied with the repetitionrate.     

2-μm mode-locked nanosecond fiber laser based on MoS_2 saturable absorber

We demonstrated a 2-μm passively mode-locked nanosecond fiber laser based on a MoS_2 saturable absorber(SA).Owing to the effect of nonlinear absorption in the MoS_2 SA, the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W. The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm, respectively. Experimental results show that MoS_2 is a promising material for a 2-μm mode-locked fiber laser.     

Narrow-beam divergence 1.55μm laser diodes with integrated self-aligned spotsize converter

This paper describes the high performance of narrow-beam divergence spot size converter(SSC)integratedseparately confined heterostructure(SCH)LD.The upper optical confinement layer (OCL) and thebutt-coupled tapered thickness waveguide were regrown simultaneously,which not only offered theseparated optimization of the active region and the integrated spotsize converter,but also reduced thedifficulty of the butt-joint selective regrowth. The threshold current was as low as 5.4 mA,the outputpower at 55 mA was 10.1 mW, the vertical and horizontal far field divergence angles were as low as 9°and 15°,and the 1-dB misalignment tolerances were 3.6 and 3.4 μm, respectively.     

Supercontinuum generation at 1.55μm using highly nonlinear photonic crystal fiber for telecommunication and medical applications

In this paper, we present a theoretical calculation of a highly nonlinear germanium (Ge) doped photonic crystal fiber with all-normal group velocity dispersion to design a supercontinuum (SC) light source at 1.55 μm. By doping 3% higher refractive index Ge inside the host silica, the nonlinear coefficient is increased to a value as large as 60.5 W^?1 km^?1 at 1.55 μm. A 10 dB bandwidth of a 120 nm SC spectrum for a 2.5 ps input optical pulse and a 10 dB bandwidth of a 190 nm SC spectrum for a 1.0 ps input optical pulse have been found using the same fiber length of 200m and input optical power of 18 W. The coherent lengths of the generated SC light sources are found to be 8.8 μm for a 2.5 ps input optical pulse and 5.6 μm for a 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution at 1.55 μm is found to be about 4.0 μm for biological tissues.     

1.55μm大光腔激光器

高功率1.55μm激光器长期以来一直为人们所重视和追求.本文通过合理设计,采用适宜的生长技术,首次成功地制备了大光腔结构,从而实现了脉冲输出功率高达2W以上的激光器.器件还具有阈值电流低(宽接触型结构的J_(th)≤2.7kA/cm~2),温度稳定性高(T_0≈130K)的特点,同时具有良好的光谱模式,是这一波段的理想光源.     

1.55-μm Si-based MOEMS optical tunable filter

A prototype 1.55-μm Si-based micro-opto-electro-mechanical-systems (MOEMS) tunable filter is fabricated, employing surface micromachining technology. Full-width-at-half-maximum (FWHM) of the transmission spectrum is 23 nm. The tuning range is 30 nm under 50-V applied voltage. The device can be readily integrated with resonant cavity enhanced (RCE) detector and vertical cavity surface emitting laser (VCSEL) to fabricate tunable active devices.     

Graphene-based passively Q-switched 2 μm thulium-doped fiber laser

We demonstrated stable pulses generation at 2 μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5 mW and the single pulse energy was 85 nJ at 53 kHz repetition rate, and the pulse width was about 1.4 μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2 μm fiber lasers.     

Sb_2Te_3 mode-locked ultrafast fiber laser at 1.93μm

Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb_2Te_3with the modulation depth,non-saturable loss,and saturable intensity of 38%,31.2%,and 3.3 MW/cm~2,respectively.Stable soliton pulses emitting at 1930.07 nm were obtained with pulse duration of 1.24 ps,a 3-dB spectral bandwidth of 3.87 nm,an average output power of 130 m W,and signal-to-noise ratio(SNR)of 84 dB.To our knowledge,this is the first demonstration of Sb_2Te_3-based SA in fiber lasers at 2-μm regime.     

1.30μm／1.55μm SiGe多模干涉滤波器

用多模干涉原理分析和设计了光通信波长（１．３０μｍ～１．５５μｍ）的Ｓｉ１－ｘＧｅｘ／Ｓｉ滤波器，并用模的传播分析方法对其传输特性进行了研究。结果发现，在Ｇｅ含量ｘ＝０．０４时，干涉区的脊高和宽度分别为６．３５μｍ和８μｍ。如果多模干涉区长度ＬＭ＝２３０２．５μｍ，可滤１．３０μｍ而通１．５５μｍ的波长。且具有３１ｄＢ的对比度和０．０１ｄＢ的插入损耗；如果多模干涉区长度ＬＭ＝２５１２．５μｍ，可滤１．５５μｍ而通１．３０μｍ的波长。具有１６ｄＢ的对比度和０．０９ｄＢ的插入损耗。     

Operation of Tm3+ fiber laser at λ = 2.3 μm coupled to a silica fiber Bragg grating

A wavelength tunable all fibre laser which utilizes Tm³⁺-doped fluoride fibre as a gain mechanism emitting around a wavelength of = 2.3 m is reported. Tm³⁺-doped fluoride fibre was coupled to a fibre Bragg grating inscribed in silica. This laser was evaluated by employing it as a wavelength tunable source in a methane gas optical sensor. A minimum gas detectivity of 100 ppm m limited by the ability to prepare low concentrations of gases was achieved. Emission wavelength control was implemented by thermally tuning the grating, although this method may prove to be too slow and cumbersome for practical use. A model describing the coupling between the silica fibre Bragg grating and the Tm³⁺-doped fibre was developed and integrated with a fibre laser model. This theoretical framework was used to examine the optimum silica and fluoride fibre parameters to achieve the maximum coupling between the fibres, with the aim of further reducing the fibre laser threshold.     

AlGaInAs multiple-quantum-well 1.2-μm semiconductor laser in-well pumped by an Yb-doped pulsed fiber amplifier

An AlGaInAs multiple quantum well structure is reported as an effective gain medium of the in-well pumped high-peak-power semiconductor disk laser at 1.2 μm. We use an Yb-doped pulsed fiber amplifier as the pump source to effectively optimize the output characteristics. The maximum average output power of 1.28 W and peak output power of 0.76 kW is obtained at 1225 nm lasing wavelength under 60 kHz pump repetition rate and 28 ns pump pulse width.