Q-switched fiber laser operating at 1.5 μm based on WTe_2

Compared with the extensively studied MoS2 and WS2, WTe_2 owns a smaller bandgap, which is applicable to a near-infrared system in photodetectors, communications, and ultrafast optics. In this work, the WTe_2 saturable absorber(SA) with the tapered fiber structure is prepared by the magnetron-sputtering technology, which enables the prepared SA to be low in cost and have strong nonlinearity. The modulation depth of the prepared WTe_2 SA is measured as 31.06%. The Q-switched fiber laser operating at 1.5 μm is successfully investigated by incorporating the proposed SA into the prepared ring cavity. To the best of our knowledge, this is the first attempt of WTe_2 in the Q-switched fiber laser at 1.5 μm.     

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.     

Polarization entanglement generation at 1.5 μm based on walk-off effect due to fiber birefringence

In this Letter, a linear scheme to generate polarization entanglement at 1.5 μm based on commercial polarization maintained dispersion shifted fiber (PM-DSF) is proposed. The birefringent walk-off effect of the pulsed pump light in the PM-DSF provides an effective way to suppress the vector scattering processes of spontaneous four-wave mixing. A 90 deg offset of fiber polarization axes is introduced at the midpoint of the fiber to realize the quantum superposition of the two correlated photon states generated by the two scalar processes on different fiber polarization axes, leading to polarization entanglement generation. Experiments of the indistinguishable property on single-side and two-photon interference in two nonorthogonal polarization bases are demonstrated. A two-photon interference fringe visibility of 89±3% is achieved without subtracting the background counts, demonstrating its great potential in developing highly a efficient and stable fiber based polarization-entangled quantum light source at the optical communication band.     

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.     

Geometrical dependence of optical negative index meta-materials at 1.55 μm

We have studied the geometry dependency of fishnet-like negative refractive index meta-materials (NIMs), and developed a process to fabricate such NIMs using nanoimprint lithography (NIL) in a controlled way for it to achieve negative refractive index in the desired frequency range. As an example, we fabricated a fishnet structure with a minimum negative refractive index of −1.7 at 1560 nm, which was only 10 nm off the targeted wavelength of 1550 nm.     

High-power diode-pumped fiber laser operating at 3 μm

A high-power diode-cladding-pumped Ho3?-doped fluoride glass fiber laser operating in cascade mode is demonstrated. The ?I?→?I? and ?I?→?I? laser transitions produced 0.77 W at a measured slope efficiency of 12.4% and 0.24 W at a measured slope efficiency of 5.2%, respectively. Using a long fiber length, which forced a large threshold for the ?I?→?I? transition, a wavelength of 3.002 μm was measured at maximum output power, making this system the first watt-level fiber laser operating in the mid-IR.     

1.56 μm and 2.86 μm Raman lasers based on gas-filled anti-resonance hollow-core fiber

We report here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage. The maximum output powers at 1.56 and 2.86 μm are 27 and 8.5 m W with Raman conversion efficiency of 30% and 42%, respectively. The results offer a new method to produce a 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.     

Economic evaluations and forecasts for optical fibre transmission systems at 1.2–1.5 μm

Inherent characteristics of optical fibres make them suitable for telecommunication networks. This can become a matter of fact provided that costs of fibres and of related components make optical systems more convenient than copper cable ones. Economic evaluations of convenience limits, especially for systems operating at 1.2–1.5m are given, as well as an estimate of the percentage of links in different areas of a typical network (in Italy) that can be realized without intermediate repeaters using optical fibres at 0.8–0.9m or at 1.2–1.5m.     

1.8 μm optical parametric oscillator based on KTiOPO4

A 1.8 ??m optical parametric oscillator pumped by a diode end-pumped acousto-optically Q-switched Nd:YAG is demonstrated. A 30-mm-long KTiOPO₄ crystal cut with an angle of ?? = 59.4°, ?? = 0° is employed as the OPO crystal. 685 mW signal laser at 1.8 ??m is obtained at the diode pump power of 13 W and the pulse repetition rate of 25 kHz. Simultaneously, 265 mW idler emission at 2.6 ??m is obtained. The corresponded diode-to-OPO conversion efficiency is 7.3%. The pulse width of the signal and idler wave are measured to be 4.5 and 2.5 ns, respectively. This gives a peak power of 6.1 and 4.2 kW, respectively.     

Coherent beam combination of narrow-linewidth 1.5 μm fiber amplifiers in a long-pulse regime

We report what we believe to be the first experimental demonstration of coherent beam combining of two fiber amplifiers in a 100 ns pulse regime using a signal leak between the pulses. Pulses of ～100 W stimulated-Brillouin-scattering limited peak power are combined with 95% efficiency, a residual phase error of λ/27, and no significant beam quality degradation.     

Mode-locked thulium-doped fiber laser based on 0.3 nm diameter single-walled carbon nanotubes at 1.95 μm

Employing 0.3 nm diameter single-walled carbon nanotubes(SWCNTs)as saturable absorbers,we demonstrate a passively mode-locked fiber laser operating at 1950 nm.The 0.3 nm diameter SWCNTs are prepared by pyrolyzing dipropylamine in the channels of zeolite crystals Mg APO-11(AEL).The laser pumped by a 1550 nm laser source produces 972 fs pulses with a spectral width at half-maximum of 4.2 nm and a repetition rate of 21.05 MHz,an average output power of 2.3 mW corresponding to the maximum pump power of 420 mW with a 10%output coupler.     

125 μm fiber based all-optical ultrasound probes for pulse-echo imaging

All-optical ultrasound probes that contain a photoacoustically-based ultrasound generator paired with a photonic acoustic sensor provide a promising imaging modality for diagnostic and MRI-compatible applications.Here, we demonstrate the fabrication of a fiber-based all-optical ultrasound probe and its applications in pulseecho ultrasound imaging. The ultrasound generator is fabricated on a 125 μm multimode optical fiber by forming a light-absorbing multiwalled carbon nanotube(MWCNT)-polydimethylsiloxane(PDMS) composite coating on its distal end. A peak-to-peak acoustic pressure of 0.95 MPa was achieved with laser irradiation at 2.46 μJ by chemically functionalizing the fiber surface to enable a strong adsorption. Ultrasound reception was performed by a fiber-laser ultrasound sensor that translates ultrasound pressure into differential lasing-frequency changes.By linearly scanning the probe, ex vivo two-and three-dimensional imaging of a segment of swine trachea was demonstrated by detecting the echo ultrasound signals and reconstructing the acoustic scatterers.The probe presents axial and lateral resolutions at 150 and 62 μm, respectively. The small-sized, side-looking all-fiber ultrasound probe presents a promising approach for assembling an interventional endoscopy.     

1 μm wavelength swept fiber laser based on dispersion-tuning technique

We report a wavelength swept fiber laser at the 1 μm region based on an actively mode-locked dispersion-tuning technique. The ring-cavity laser uses a 70 cm ytterbium-doped fiber as a gain medium. Mode locking is achieved by the direct modulation of the amplitude modulator, and a ～1000 m single-mode fiber is used to provide the desired intracavity dispersion. By sine-modulating the modulation frequency, a wavelength swept laser with a range of ～30 nm can be achieved at a sweeping rate of 50 Hz. The characteristics of the laser, such as its singlewavelength tuning range, tuning sensitivity, static linewidth and sweeping rate, are also studied experimentally.     

Generation of 400 μW at 17.5 μm using a two-color Yb fiber chirped pulse amplifier

We have demonstrated the generation of 400 μW of power at ~18 μm by difference-frequency mixing the 1038 and 1105 nm from a two-color, chirped pulse amplification Yb fiber system. A two-color seed is selected from a continuum source and amplified to 300 mW of total power in a two-stage Yb fiber amplifier.     

Superfluorescent fiber source at 3.9 μm in the attenuation minimum of the atmospheric window 3–5 μm

Superfluorescence has been demonstrated for the first time at 3.9m in holmium-doped fluoride glass optical fiber. Fluorescence measurements were possible at room temperature while pumping around 650 nm. Cooled to 173 K superfluorescence was obtained.     

Dependence of Er:Yb-codoped 1.5 μm amplifier on wavelength-tuned auxiliary seed signal at 1 μm wavelength

We report on experiments performed with a cladding-pumped single-mode Er:Yb-codoped single-frequency fiber amplifier simultaneously seeded by a distributed-feedback diode at 1556 nm and a tunable external-cavity diode laser emitting at a wavelength of about 1 μm wavelength. The influence of the output wavelength of the external-cavity laser on amplification and reabsorption behavior of the Yb emission as well as the amplifier performance at a wavelength of 1556 nm is examined experimentally.     

High-gain fiber, optical-parametric, chirped-pulse amplification of femtosecond pulses at 1 μm

Fiber-based optical-parametric chirped-pulse amplification is reported at 1μm in a microstructured fiber in the femtosecond regime. The signal has been highly stretched by an ?ffner triplet and then amplified with an all-fiber, pulsed-pump, fiber optical-parametric amplifier. More than 30dB gain has been achieved over 8.3nm, and the amplified signal has been recompressed.     

How good must single photon sources and detectors be for efficient linear optical quantum computation?

We present a scheme for linear optical quantum computation that is highly robust to imperfect single photon sources and inefficient detectors. In particular we show that if the product of the detector efficiency with the source efficiency is greater than 2/3, then efficient linear optical quantum computation is possible. This high threshold is achieved within the cluster state paradigm for quantum computation.     

Nonlinear properties of quantum dot semiconductor optical amplifiers at 1.3 μm： errata

The authors regret that one of the coauthors was inadvertently omitted in the previous paper. E. Varene was a member of the Institut fur Festk6rperphysik at the Technische Universitat Berlin and contributed to the results on cross-phase modulation.     

12 W Q-switched Er:ZBLAN fiber laser at 2.8 μm

A diode-pumped, actively Q-switched 2.8 μm fiber laser oscillator with an average output power of more than 12 W has been realized through the use of a 35 μm core erbium-doped ZBLAN fiber and an acousto-optic modulator; to our knowledge, this is the first 3 μm pulsed fiber laser in the 10 W class. Pulse energy up to 100 μJ and pulse duration down to 90 ns, corresponding to a peak power of 0.9 kW, were achieved at a repetition rate of 120 kHz.