Excellent Single Mode Research Articles

Multi-layered cladding based ultra-low loss, single mode antiresonant hollow core fibers

In reality, an efficient platform for high-power laser delivery is highly important, which can be justified by readily available fiber lasers, and hollow-core fiber can be the best platform for guiding high optical power over long distances. The constraints include designing new cladding geometry, which may lead to a higher laser induced damage threshold in the fiber’s structure, having low losses along with a single mode nature. This article reports a new antiresonant fiber that has a hollow core and a triple-layered cladding configuration with only circular tube elements. The effects of multiple layers corresponding to the number of tube rings in the cladding geometry are well explored, which leads to understanding the physical insight of inter-layers. In comparison to double-layered cladding elements fiber, the proposed fiber significantly reduces loss by an order of two and reveals a minimum leakage loss of 5.82 × 10−5 dB/km at the chosen wavelength of 1.06 µm through the proper arrangement of cladding elements. We achieved a maximal higher order mode extinction ratio of about 104 (indicates the excellent single mode properties) and comparatively a little bending-induced loss of 9.00 × 10−4 dB/km, when the radius of bending is 14 cm. As a result, our studies on new multilayer fiber designs are not only useful for delivering high laser power but also serve as guidelines for the experimental realization of future multilayered cladding fibers.

Bend-resistant stress-type segmented cladding large-mode-area single-mode fibers.

We propose a novel bend-resistant stress-type large-mode-area fiber with segmented cladding, to the best of our knowledge, in which a high refractive index stress rod is introduced at the core, to improve the loss ratio between the least high-order mode (HOM) and fundamental mode loss, and to reduce the fundamental mode loss effectively. The mode loss and effective mode field area with or without heat load, and mode field evolution between the straight and bending transition are investigated, by utilizing the finite element method and the coupled-mode theory. The results show that the effective mode field area and the loss of the fundamental mode can reach up to 1050.1 µm2 and 0.0055d B⋅m -1, respectively, and the loss ratio between the least loss HOM and fundamental mode loss is greater than 210. The coupling efficient of the fundamental mode in the straight-bending transition reaches 0.85 at a wavelength of 1.064µm and a bending radius of 24cm. In addition, the fiber is insensitive to the bending direction and has excellent single-mode performance in any bending direction; the fiber maintains single-mode operation under heat load from 0 to 8W/m. This fiber has potential application in compact fiber lasers and amplifiers.

Tailored vortex lasing based on hybrid waveguide-grating architecture in solid-state crystal

We report a hybrid waveguide-grating vortex laser emitter processed based on femtosecond laser direct writing of the Nd:YVO4 crystal. The cladding waveguide together with the fork grating features both excellent single-mode guidance and vortex diffraction properties. The confocal micro-Raman characterization results reveal the mechanism of the periodic refractive index modulation of the fork grating. Vortex lasers at the milliwatt level are achieved at a wavelength of 1064.7 nm under optical pump laser at 809.3 nm. The numerical simulation of the near-field diffraction propagation demonstrates the generation process of the vortex beams. Our results suggest that the waveguide-grating configuration is of great potential for optical-field steering applications in integrated photonics.

Wideband low confinement loss anti-resonant hollow core fiber with nested U-shape tube.

We propose a nested U-shape tube anti-resonant hollow core fiber (UARF) that can effectively reduce the confinement loss (CL) as well as the loss oscillations. The key parameters of UARF have been optimized via numerical analysis. Simulation results show that the CL of proposed UARF is lower than 0.01dB/km over a 550 nm operational bandwidth range from 1.3 µm to 1.85 µm. This CL is nearly one order of magnitude lower than the nested anti-resonant nodeless fiber (NANF). Moreover, the loss ratio between higher-order modes to the fundamental mode is verified to be more than 100,000 over a ultrawide bandwidth of 1000 nm, which indicates its excellent single mode performance. The tolerance towards the structure deformation of UARF has been evaluated for the purpose of practical fiber fabrication. Thus, the proposed UARF has potential application in large capacity data transmission, nonlinear optics, gas sensing and so on.

Gain-Coupled 4 × 25 Gb/s EML Array Based on an Identical Epitaxial Layer Integration Scheme

Gain-coupled 4 × 25 Gb/s electroabsorption modulated laser (EML) array is implemented by an identical epitaxial layer integration scheme. Gain-coupling is incorporated via absorptive gratings to improve the single mode yield of the device. The EML array exhibits excellent single-mode performance, high extinction ratio, and a modulation bandwidth over 28 GHz. Clear eye opening under 28-Gb/s nonreturn-to-zero modulation has been demonstrated for all four channels. Transmission performance of the EML array over 20- and 40-km single-mode fiber is tested, confirming its potential for 100 GbE applications.

基于TDLAS的气体检测技术算法

Tunable diode laser absorption spectroscopy(TDLAS) is a high sensitive and high resolution gas absorption spectrum detection technology, with fast response, high precision, excellent single mode characteristics and strong versatility. The temperature and concentration of the detected gas were calculated by measuring the absolute absorption intensity in the direct absorption method of TDLAS, but was easily affected by particle concentration and fluctuation of laser intensity. The laser was modulated through high frequency sinusoidal signal in the wavelength modulation method of TDLAS, making the laser output frequency and intensity modulated simultaneously, with the characteristics of high signal-to-noise ratio and sensitivity, but the gas parameters were determined by calibration experiments or complex algorithms. Therefore, the expression of harmonic terms containing molecular absorption information was deduced through the theory of absorption spectrum and wavelength modulation, and the relationship between harmonic signal and absolute absorption intensity of detected gas was analysed, establishing the measurement algorithm of absolute absorption intensity based on harmonic signal. The absorption spectral line of NH3 molecule near 1 531 nm was taken as an example for numerical analysis, and the relative errors between theoretical calculation (a=0) and simulation values were no more than 2% when the modulation amplitude reached up to a=0.032 cm-1(m=2), which further proved the reliability of on-line measurement algorithm.

Design and experimental analysis of self-sensing SSDNC technique for semi-active vibration control

A semi-active vibration control technique using nonlinear synchronized switch damping on negative capacitance (SSDNC) is proposed in this article. SSDNC, as one of the effective nonlinear vibration damping techniques, has been intensively investigated and discussed in recent years. In comparison with the classical SSDNC technique, the proposed self-sensing approach realizes the SSDNC technique by using analog circuits, which require neither external sensors nor controllers. In particular, the stability of the switching shunt circuit using negative capacitance (NC) is addressed. The theoretical and experimental analysis reveals that the saturation of the operational amplifier in synthetic NC can prevent the proposed SSDNC circuit from trapping into instability and yielding the best attenuation performance. The final experiments show that the proposed approach exhibits excellent single-mode damping performance and is sufficiently robust.

Single-mode channel waveguide at 1540 nm in Er-doped ZnO thin film

Er-doped ZnO thin film is fabricated by radio frequency magnetron sputtering technology. It is found that the Er:ZnO film has good film quality with excellent single-mode characteristic. When the film is stimulated by 532nm laser, one waveguide mode at 1540nm can be excited. By confining the lateral width of planar waveguide, a single-mode channel waveguide at 1540nm is fabricated by focused-ion-beam etching. This kind of waveguide meets the requirements of single-mode and low loss in optical communication, which could be a choice for future optical design.

Semi-active vibration control featuring a self-sensing SSDV approach

Abstract A self-sensing vibration control technique using nonlinear synchronized switch damping on the voltage sources (SSDV) is proposed in this article. SSDV, as one of effectively nonlinear vibration damping techniques, has been developed into several extensions in recent years, such as enhanced SSDV and adaptive SSDV. However, in the original SSDV and its extensions, the switch algorithm for the principle of SSDV technique is carried out by active real-time controllers (e.g., DSpace systems/Digital Signal Processors (DSPs)). In addition, external sensors are applied to measure the moment of the displacement extrema for the switch algorithm. By comparison, the proposed approach can realize the SSDV technique without real-time controllers and external sensors. Experimental investigations showed that the proposed technique exhibits excellent single-mode damping performance and is easy to implement.

Single-Mode Vertical-Cavity Surface-Emitting Lasers Array With Zn-Diffusion Aperture for High-Power, Single-Spot, and Narrow Divergence Angle Performance

A single-mode vertical-cavity surface-emitting laser (VCSEL) array at 850 nm with excellent performance in terms of high output power, single-lobe far-field, and narrow divergence angle has been demonstrated. By use of the Zn-diffusion process with proper sizes of oxide current-confined and Zn-diffusion optical apertures, each unit of VCSEL in the demonstrated array is highly single-mode (side-mode suppression ratio 30 dB) with a narrow far-field divergence angle (~5°) and an extremely high maximum single-mode output power (~7.1 mW). Due to the excellent single-mode performance of each VCSEL unit, the 10 × 10 array exhibits a single-lobe and nearly circular symmetric far-field pattern, very narrow divergence angle (~4°), and output power as high as around 187.4 mW. Furthermore, its bias-dependent output optical spectra measured in different positions of array shows very high similarity. This result indicates that the excellent uniformity of single-mode performance of each VCSEL unit in the array. The far-field pattern simulation results indicate that although the coherence in our array is low, its output beam quality is as high as that of a single-mode unit VCSEL, which exhibits a near diffraction limited M square factor (M 2 ≈ 2).

In Situ Heterogeneous Catalysis Monitoring in a Hollow‐Core Photonic Crystal Fiber Microflow Reactor

A novel process for uniform deposition of noble-metal catalyst nanoparticles on the inner core wall of a hollow-core photonic crystal fiber is presented. The resulting continuous flow microreactor enables heterogeneous catalysis reactions on extremely low (sub-μL) sample volumes. Strikingly, the excellent single mode transmission properties of the HC-PCF are preserved after the deposition process, allowing sensitive in situ spectroscopy measurements over unprecedented length scales of up to 50 cm.

Tunable-diode-laser spectroscopy of C_2H_2 using a 303 μm GaInAsSb/AlGaInAsSb distributed-feedback laser

The mid-IR region beyond 3 microm is very attractive for gas sensing, since the fundamental absorption bands of several hydrocarbons are located in this range. We demonstrated, for the first time to our knowledge, the use of a novel GaInAsSb/AlGaInAsSb distributed-feedback laser emitting around 3.03 microm in a tunable-diode laser-spectroscopy application. The laser operates in continuous mode at room temperature with excellent single-mode and tuning properties. A comparison of the measurement results was made with the recently updated data on C212H(2) found in the HITRAN 2008 compilation. A good agreement was found between the measurements and the database. Wavelength modulation spectroscopy of acetylene at ambient conditions was made, and a sensitivity of 18 ppb (parts per billion) per meter at an integration time of 3 s corresponding to a relative absorption of 5 x 10(-6) was obtained. The optimum detection limit of the acetylene measurement in this wavelength modulation spectroscopy setup was better than 1.5 ppb m at an integration time of 600 seconds.

Nano-polymer-dispersed liquid crystal as phase modulator for a tunable vertical-cavity surface-emitting laser at 155 μm

We demonstrate what we believe is the first nonmechanical tunable vertical-cavity surface-emitting laser operating in the C band. This was achieved as a result of the combination of an InGaAs quantum well structure with a 6lambda thickness tunable index nano-polymer-dispersed liquid-crystal material. Experimental results exhibited a potential tunable range close to 10 nm, in the preliminary version, and excellent single mode locking due to the side-mode suppression ratio (more than 20 dB) over the whole spectral range. Another decisive advantage, compared to mechanical solutions, was the tuning response time of a few tens of microseconds (>30 micros) to scan the full spectral range (10 nm), making this device appropriate for some access network functions, as well as being robust and low cost. The voltage values are the main limitation to wavelength range extension. We present a first version of the device optically pumped. The next version will be electrically pumped as required for the access network applications targeted here.

Transverse junction stripe laser with a lateral heterobarrier by diffusion enhanced alloy disordering

We report the first cw, room-temperature multiple quantum well transverse junction stripe laser (MQW TJS) with an alloy disordered heterobarrier. The addition of a lateral heterobarrier by zinc diffusion enhanced alloy disordering reduces the laser threshold by a factor of 3 compared to standard transverse junction stripe lasers processed simultaneously. The reduction in threshold and excellent single mode performance of the MQW TJS are attributed to the superior carrier and optical confinement of a single heterojunction compared to a homojunction. We demonstrate for the first time lateral injection in a multiple quantum well where the diffused junction plays an active (not passive) role in the injection process and that the transition region between complete disorder and no disorder forms the active region of the laser.

A 10 W single mode Pyrex waveguide CO2laser

Describes a Pyrex waveguide carbon dioxide laser operating at a maximum single line power of about 10 W. Although construction is straightforward, excellent single mode purity is achieved in a far simpler way than most conventional systems.