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Different fibers generally have different mode characteristics so their connections in many practical applications often require mode conversion. The feasibility of mode conversion between fibers with different refractive index distributions based on adiabatically tapered structures is theoretically analyzed. The first kind of mode conversion is between ring core fiber and convex core fiber; the second kind is between multicore fiber and single-core fiber. Three common tapered structures are investigated: tapered core, diffused core, and tapered cladding. The analysis results show that mode conversion by a tapered structure is not suitable for all the modes for a ring core fiber and a convex core fiber; however, it can be accomplished for multicore fiber and single-core fiber.

Mode characteristics of a tapered double clad fiber should be analyzed based on three-layer waveguide model, so it is more complicated than that of a single clad fiber. In this paper, a method based on coupled local mode theory is introduced to calculate the mode evolution process in a tapered double clad fiber. Mode field characteristics of double clad fiber are calculated analytically with weak guidance approximation, and the expression of mode coupling coefficient is derived. Based on this, the local mode characteristics and mode coupling characteristics in a tapered double clad fiber are analyzed. The mode evolution characteristics of tapered double clad fibers with different parameters are simulated. As an example, the structure optimization process of a tapered double clad fiber is introduced. High efficiency coupling with a six-mode single clad fiber is realized, and the theoretical transmission loss is less than 0.3 dB.

Irradiating experiments with a 532nm laser were conducted to investigate the effect of integration time on crosstalk line intensity for IT-CCD. Crosstalk lines were observed in all the experimental images with different integration times when laser power was high enough. Crosstalk line gray value was calculated by eliminating the impact of background light and main spot. Calculation results show that crosstalk line intensity is independence of integration time while proportional to laser power. According to the working principle of IT-CCD image sensor, the formation mechanism of crosstalk line is the quantitative overflow of stored charges from photodiode to vertical CCD in the process of vertical transfer. According to the working principle of electric shutter, the reason of the independence of integration time on crosstalk line intensity is that the period of shutter pulse is an invariant. This research enriches the knowledge of crosstalk effects for IT-CCD, and provides important support for deep searching the mechanism of laser jamming on CCD.

According to the demands of laser energy control and test in Hardware-in-the Loop (HWIL) simulation systems for laser jamming CCD sensors effects applications, the laser propagation regulars in the system and the ways to describe laser energy simulations are provided. The basic theoretical analysis to calculate the laser energy distribution in far field and the method to achieve the simulation equipment are also discussed. Based on the Virtual Instrument (VI) technology, the ways for random phase screens formed by multiple layers of atmospheric turbulence as while as wave fronts retrieval based on a spatial Light Modulators(SLMs) set are derived. In the CCD sensors’ jamming effects experiments with different laser parameters such as repeat frequency, the lasers and their energy control equipment were utilized so as to form the distributions of laser light random phase and the undulations of laser beam intension in far field. By using the simulations system, the realization to generate different far field laser propagation effects at real time and to prove the efficiency of the laser energy control and test based on the platform of Windows+ LabVIEW+IMAQ Vision technology in simulations were experienced for CVIs. The analysis of error factors in simulation system was also provided. It is shown that the rhetorical method, devices and the analysis to simulation dynamic effects for laser propagation, which can provide the specialties of real-time, dynamic control, expansibility and can also be applied to beam quality, energy control and test in the HWIL simulation systems for laser jamming CCD sensors experiments.

Beam combining is one of the most potential methods to break through the output power limitations of a single fiber laser. In this letter, we report a high-power experimental result achieved by incoherent beam combining based on a $7\times 1$ all-fiber signal combiner. The final output power is 6.26 kW with high beam quality ( $M^{2}\approx 4.3$ ). Beam quality of the incoherent combination laser is analyzed both by theory and experiment in details. Experimental measured values fit well with the simulation results. These results can demonstrate the feasibility of high-power high-brightness incoherent beam combining based on all-fiber signal combiners.

The CMOS Image Sensor (CIS) is photoelectricity image device which focused the photosensitive array, amplifier, A/D transfer, storage, DSP, computer interface circuit on the same silicon substrate[1]. It has low power consumption, high integration,low cost etc. With large scale integrated circuit technology progress, the noise suppression level of CIS is enhanced unceasingly, and its image quality is getting better and better. It has been in the security monitoring, biometrice, detection and imaging and even military reconnaissance and other field is widely used. CIS is easily disturbed and damaged while it is irradiated by laser. It is of great significance to study the effect of laser irradiation on optoelectronic countermeasure and device for the laser strengthening resistance is of great significance. There are some researchers have studied the laser induced disturbed and damaged of CIS. They focused on the saturation, supersaturated effects, and they observed different effects as for unsaturation, saturation, supersaturated, allsaturated and pixel flip etc. This paper research 1064nm laser interference effect in a typical before type CMOS, and observring the saturated crosstalk and half the crosstalk line. This paper extracted from cmos devices working principle and signal detection methods such as the Angle of the formation mechanism of the crosstalk line phenomenon are analyzed.

We investigate N ×1 pump coupler theoretically and experimentally. Firstly the influence of lengths of the transitional region and the waist region of tapered fiber bundle on the efficiency of a 7×1 pump combiner is numerically analyzed. The results suggest that there is a minimum length for the transitional region in order to achieve high efficiency; meanwhile, the waist region should be as short as possible. Then a 7×1 pump combiner is fabricated. The transmission efficiencies of all 7 ports are higher than 98% and the final total output power is as high as 3.81 kW with 98.4% transmission efficiency. This is the highest output power reported to date and improvement further is possible by better cleaving, splicing and using LD with higher power. The experimental result verifies the simulation which can be applied in the fabrication of N ×1 pump combiners.

We report a novel method to obtain high-power near-infrared broadband supercontinuum based on amplified spontaneous emission (ASE) source. Firstly two kinds of ASE seed sources, without and with parasitic laser, are amplified to be 19.1 and 19.9 W, respectively, using a fiber amplifier. Then, comparative experiments are performed by using these two sources to pump different fibers. When using the ASE source without parasitic laser to pump a piece of 1000-m single-mode fiber, six orders Stokes waves are generated to extend the spectrum to beyond 1500 nm. But the spectrum is not flat with clear discrete Stokes peaks. When a section of 150-m double-clad passive fiber is pumped by the ASE source with parasitic laser, 18.3 W supercontinuum with 20 dB spectral range covering from 1030 to 1650 nm is generated. And the continuous ASE source becomes a stochastic pulsed light owing to parasitic lasing and self-pulse effect without any artificial modulation. This method combines the merits of ASE source and pulsed light, which are simplicity and low cost of the former and high peak power of the latter.

A high-power ultraflat near-infrared supercontinuum (SC) is generated in a section of photonic crystal fiber (PCF) pumped by an amplified spontaneous emission (ASE) source instead of continuous-wave (CW) and pulsed lasers. A low-power ASE seed at 1 $\mu\hbox{m} $ is amplified to be 90.9 W by two fiber amplifiers and then emitted from a 10- $\mu\hbox{m} $ -core fiber. Using this ASE source to pump a section of 100-m-long PCF, a 49.5-W near-infrared SC is obtained, and the 5-dB spectral bandwidth is 760 nm, covering from 1062 to 1822 nm. This is the reported highest power of ASE-pumped SC source. A comparative experiment is taken with a 122-W CW laser at 1090 nm to pump the same PCF. A 56.2-W SC source is generated with 5-dB spectral width of 605 nm from 1082 to 1687 nm. The conversion efficiency to SC is higher, and the spectrum is broader and flatter using the ASE source as the pump. Conclusively, pump incoherence can aid the SC generation and spectral flatness.

All-fiber signal combiner is a key component for augmenting the fiber laser power. Presently the reported 7×1 signal combiners are all have output fibers with core diameters larger than 100 μm. In order to improve the beam quality of the combiner, a fiber with smaller core of 50 μm diameter is chose to be the output fiber. An all-fiber 7×1 signal combiner is fabricated with measured power transmission efficiency around 99% for each port. The beam quality is improved and the measured M2 are around 6 which are matched well with the theoretically calculated results.

Multicore photonic crystal fiber is an important research direction to realize high-power supercontiuum. We report two post processing methods based on air hole collapse technique to generate Gaussian-like mode field in a seven-core photonic crystal fiber (SCPCF) for low loss splicing. By heating and collapsing all air holes in the meantime, the mode field of SCPCF becomes more concentrated and the valleys between separated core modes become much flatter. Another method to generate Gaussian-like mode field is selectively collapsing the central air holes between the seven cores, which can form an integrated larger core. Theoretical simulation results are confirmed by experiment and both methods are used to decrease mode field mismatch between SCPCF and double clad fiber with splicing losses as low as 0.46 and 0.22 dB, respectively.

The obstacles of power scaling the supercontinuum (SC) source based on single-core photonic crystal fiber (PCF) are analyzed. The combination of high-power fiber lasers and multi-core PCFs would be a feasible method to obtain an all-fiber-integrated high-power broadband SC source (covering visible range). In this paper, we present a comprehensive study of high-power SC generation in multi-core PCFs. Comparative experiments are performed by using a high-power pulse-repetition-rate-tunable picosecond fiber laser to pump two kinds of home-made seven-core PCFs. The influences of PCF structure (fiber dispersion property) and pulse repetition rate (pulse peak power) on the SC generation in multi-core PCFs are investigated in detail. When the picosecond fiber laser at a pulse repetition rate of 1.9 GHz is adopted as the pump, 116 W SC spanning from 800 to 1700 nm is generated in 1# seven-core PCF. Also 64 W visible SC spanning at least 500-1700 nm is demonstrated in 2# seven-core PCF at a pump pulse repetition rate of 480 MHz. The potential of extending the spectral range and scaling the output power for the SC source based on multi-core PCFs are analyzed and discussed.

The main source of light transmission loss between single-mode fiber (SMF) and large mode area (LMA) fiber is from the mode field mismatch. Thermally expanded core (TEC) technique was introduced to realize mode field adaptation between them. The SMF was heated by a H2–O2 flame to increase the mode field diameter (MFD) which can result in a mode field match with LMA. Both numerical calculation and experiment results show it is workable to realize mode field adaptation and get a low transmission loss by this method. For HI1060 (d=5 μm, NA=0.14) and LMA-GDF-15/130(d=15 μm, NA=0.08), a low-loss with 0.4 dB was obtained for SMF–LMA–SMF from 6.4 dB with TEC processing experimentally.

We demonstrate Watt-level flat visible supercontinuum (SC) generation in photonic crystal fibers, which is directly pumped by broadband noise-like pulses from an Yb-doped all-fiber oscillator. The novel SC generator is featured with elegant all-fiber-integrated architecture, high spectral flatness and high efficiency. Wide optical spectrum spanning from 500 nm to 2300 nm with 1.02 W optical power is obtained under the pump of 1.4 W noise-like pulse. The flatness of the spectrum in the range of 700 nm~1600 nm is less than 5 dB (including the pump residue). The exceptional simplicity, economical efficiency and the comparable performances make the noise-like pulse oscillator a competitive candidate to the widely used cascade amplified coherent pulse as the pump source of broadband SC. To the best of our knowledge, this is the first demonstration of SC generation which is directly pumped by an all-fiber noise-like pulse oscillator.

A method based on controlled air hole collapse for low-loss fusion splicing small-core photonic crystal fibers (PCFs) and single-mode fibers (SMFs) was demonstrated. A taper rig was used to control air hole collapse accurately to enlarge the MFDs of PCFs which was then spliced with SMFs using a fusion splicer. An optimum mode field match at the interface of PCF-SMF was achieved and a low-loss with 0.64 dB was obtained from 3.57 dB for a PCF with 4 μm MFD and a SMF with 10.4 μm MFD experimentally.

We report an incoherently combined near-infrared supercontinuum (SC) source with >200 W output power using a 3×1 broadband fiber power combiner. A broadband fiber power combiner is designed and theoretically investigated. The power transmission efficiencies of light at different wavelengths of the combiner are calculated, and the combiner is verified to be capable of combining broadband sources efficiently. Then a combiner is fabricated. Three ∼70 W near-infrared SC sources are constructed and then, using the combiner, a >200 W near-infrared SC source is obtained. Conclusively, using incoherently combining method we can obtain a high-power SC source, and the thermo-management can be realized easily. We believe that this is a suitable method to obtain a higher-power SC source.

A high-efficiency pump-signal combiner for high power fiber amplifiers based on thermally expanded core (TEC) technique is reported in this paper. TEC technique is used to fabricate mode-field adapter which allows optimization of signal fibers in a monolithic (6+1) ×1 fiber combiner. The combiner is fabricated by connecting a tapered fiber bundle (TFB) to a passive 25/250 (NA=0.06/0.46) double-clad fiber (DCF). By this method, the coupling efficiency of SMF-28 signal fiber at 1064nm improves from 54% to 92.7%. The average pump coupling efficiencies of six 105/125 (NA=0.15) fibers are measured to be 96.7% at 976nm. Furthermore, the average signal transmission efficiency is around 93.3%. The fabricated fiber combiner is spliced to an Yb-doped DCF for use as an all-fiber amplifier. The slope efficiency is measured to be 71.6%.

We study the mode evolution properties in a 3 x 1 adiabatic tapered single-mode fiber combiner (ATSMFC) in theory. The fabrication of the combiner for single mode fibers based on adiabatic tapered fused bundle (TFB) technique with the assistant of low index glass capillary is introduced. The whole taper region can be seen as three phase: single-mode fibers, multi-core fiber and multi-mode fiber. Supermodes of three-core fiber with scalar mode results are derived based on coupling mode theory. The analysis is verified with numerical examples by fully vectorial finite element mode solver (Cosmol Multiphysics). Simulation results show that the three input core modes in single-mode fibers gradually evolve into three supermodes in three-core fiber and then evolve into three low-order modes in the multi-core fiber. Effective indices for different modes are calculated which can depict the evolution process vividly. The results may be useful for practical high power fiber laser systems.

Pumping coupler technology is one of the critical technologies for high power laser and amplifier. Side-pumping technology can couple pumping beam into inner cladding of the double-clad fiber through the side of the fiber. Compared to the end-pumping technology by tapered fused bundle (TFB), it has many superiorities. That the signal fiber was not disconnected guarantees high transmission efficiency, providing the possibility of transmitting a high power signal. Additionally, the pump light is coupled into the double-cladding fiber all along the coupler’s body (~5-10 cm long), which reduces the thermal effects caused by leakage of pumping light, resulting in high pump power handling capabilities. For the realization of reliable, rugged and efficient high power fiber amplifiers and fiber laser systems, a novel kind of fused side-pumping coupler based on twisting is developed. The complete simulations were carried out for the process of side-pumping. From detailed information about simulations, we found that the pump efficiencies, one of the vital parameters of pumping coupler, have a significant influence with coupling length, the numerical aperture (NA) and taper ratio of pump fiber. However, the diversification of the parameters drops the high transmission efficiency barely. Optimized the parameters in the simulations, the pump and signal coupling efficiencies are 97.3% and 99.4%, respectively. Based on theoretical analysis, the side-pumping coupler was demonstrated at the pump and signal coupling efficiencies are 91.2% and 98.4%, respectively. This fiber coupler can be implemented in almost any fiber laser or amplifier architecture.

We report a method to fabricate a mode-field adaptor (MFA) for a large-mode-area (LMA) fiber and single-mode fibers (SMFs) based on fiber tapering and the thermally expanded core (TEC) technique. Through adiabatically tapering a LMA fiber by an oxygen–hydrogen flame, the mode-field diameter is decreased effectively with nearly no extra loss, which makes it possible to realize mode-field adaptation between the LMA fiber and SMFs. Both numerical calculation and experimental results show it is workable to realize fundamental mode propagation in LMA fiber and get a low insertion loss by this method. For a LMA fiber (d=25 μm, NA=0.06) and a SMF (d=4 μm, NA=0.2), a low loss with less than 0.4 dB has been obtained both in the forward and backward directions experimentally.

Broadband 1.9-3.9 μm supercontinuum generation in a ZBLAN fiber pumped by 2 μm pulsed laser and amplifier system is demonstrated with 7.11 W output power and 3.52 W at wavelengths longer than 2.5 μm.

In this paper, we present the design, construction, and testing of a monolithic fiber end cap collimator for high-power free-space fiber-fiber coupling applications. The collimator is based on a large-sized fiber end cap and a spherical lens design on the output facet. Values of the spot size and working distance are theoretically analyzed based on Gaussian approximation and ABCD transmission matrix. The free-space fiber-fiber coupling process is also analyzed for different lens curvature radii and coupling distances. In the experiment, a collimated laser beam is obtained with Rayleigh length of about 400 mm. A high-power laser with 1.1 kW output is tested on the end cap collimator, which only heats up by 7°C at the output facet without active cooling. Free-space fiber-fiber coupling between two 20/400 μm fibers is achieved based on these collimators, with measured coupling loss lower than 0.3 dB.

We report an experiment of incoherent beam combining based on a 7×1 all-fiber signal combiner with output power up to 6.08 kW. Properties of transmission efficiency and beam quality are analyzed by beam propagation method. Based on the calculative results, a 7×1 all-fiber signal combiner is fabricated. The handle power capacity is tested with average transmission efficiency of 98.9% and beam quality of M2≈10.

Core mode cutoff is a useful concept not only for a tapered single-core fiber (SCF) but also for a tapered multicore fiber (MCF) to realize cladding mode transmission. In this paper, cut-off conditions of either core mode for tapered SCFs or supermodes for MCFs are theoretically investigated. Rigorous analytical formulas are derived for the modes of SCF by a three-layer waveguide model, and an approximation formula of the cut-off condition is given for the LP01 mode. The supermodes of MCFs are analyzed by the coupling mode theory, and the cut-off condition is calculated by a numerical method. Simulation results show that the in-phase supermode of MCFs has a similar cut-off condition with that of SCF. Based on this property, a convenient approximate formula is given to estimate the cut-off condition of the in-phase supermode for tapered MCFs.

We reported diverse soliton operations in a thulium/holmium-doped fiber laser by taking advantage of a tapered fiber-based topological insulator (TI) Bi2Te3 saturable absorber (SA). The SA had a nonsaturable loss of ∼53.5% and a modulation depth of 9.8%. Stable fundamentally mode-locked solitons at 1909.5 nm with distinct Kelly sidebands on the output spectrum, a pulse repetition rate of 21.5 MHz, and a measured pulse width of 1.26 ps were observed in the work. By increasing the pump power, both bunched solitons with soliton number up to 15 and harmonically mode-locked solitons with harmonic order up to 10 were obtained. To our knowledge, this is the first report of both bunched solitons and harmonically mode-locked solitons in a fiber laser at 2 μm region incorporated with TIs.

We present an all-fiber 7×1 signal combiner for high power fiber lasers. Through theoretical analysis, the fabrication method is confirmed and the taper length of the fiber bundle is chosen to be 1 cm to ensure a high transmission efficiency of the combiner. Based on the theoretical results, an all-fiber 7×1 signal combiner with high transmission efficiency is fabricated. A capillary with low refractive index is fused around the bundle of signal fibers to make an additional cladding layer. Then the fiber bundle is tapered to match the core of the output fiber and then spliced with the output fiber. The combiner is tested with a 500 W fiber laser and a temperature increase of 13°C/kW without any active cooling is observed in the combiner. The power transmission efficiency is measured to be close to 99% for each input port and the beam quality M2 is around 10.

High power all fiber mid-IR supercontinuum (SC) generation in a ZBLAN fiber pumped by a 2 μm master oscillator power amplifier (MOPA) system is demonstrated. A semiconductor saturable absorber mirror (SESAM) passively mode-locked laser with pulse width of 26 ps at 1960 nm is used as the seed of the MOPA system. A laser spectrum extending from ~1.9 μm to beyond 2.6 μm is generated in a subsequent thulium-doped fiber amplifier (TDFA). Then, the spectrum is further broadened to the mid-IR region in the ZBLAN fiber. A mid-IR SC extending from 1.9 to 3.9 μm with 7.11 W average output power is obtained based on a large mode area TDFA, the SC power for wavelengths longer than 2.5 μm is 3.52 W with a power ratio of 49.5% with respect to the total SC power. The overall optical conversion efficiency from the 790 nm pump of the large mode area TDFA to the total SC output is 10.4%. To the best of our knowledge, both the 7.11 W total average power and 3.52 W average power in wavelengths beyond 2.5 μm are the highest power ever reported for a mid-IR SC generation in ZBLAN fiber pumped by 2 μm fiber lasers and TDFAs.

A new approach for an all-fiber coherent beam combining by active phasing a fiber combiner is presented, and effect of fill factor of the fiber combiner on the all-fiber coherent combining is also numerical analyzed. Experimental results show that the power in the bucket (PIB) increases more than a factor of 2.35. The results validate the feasibility of coherent combining using a fiber combiner. The PIBs with different fill factors are calculated and the results show that the coherent combining is reduced with the increasing fill factor.