The graphene films have been proved to be potentially useful as optical elements in fiber lasers. In this paper, the graphene films are prepared by both pulsed laser deposition (PLD) method and solution deposition method as saturable absorbers in mode-locked fiber laser. The pulse evolution process in the laser cavity is simulated by RP Fiber Power software. The influence of graphene saturable absorber with different modulation depth on pulse duration and linewidth of laser is analyzed. Finally, a ring-cavity passively mode-locked picosecond pulse Erbium-doped fiber laser based on graphene saturable absorber is constructed experimentally. At the pump power of 30mW, the laser with each saturable absorber can work stably without damage in the mode-locked state.
A novel vertical-cavity surface-emitting laser (VCSEL) with single mode, high-power, low divergence, and temperature stability is presented. The most prominent structural feature of the device is that the high optical loss region is formed by an anti-phase surface relief above the top Distributed Bragg Reflectors (DBRs) and the light-emitting aperture is ringshaped with larger region. The simulation results show the device with 15μm oxide aperture and 5μm width ring light emitting region achieves stable single-higher-order transverse mode emission with a side mode suppression ratio (SMSR) of more than 80dB. The maximum continuous-wave (CW) single mode power is up to 15.2 mW and far-field divergence angle (FWHM) is lower than 4.5°. Moreover, the VCSEL maintains CW single mode emission up to a record high temperature of 450K.
A large size vertical-cavity surface-emitting laser (VCSEL) with multiple concentric ring apertures (MCRA) is investigated. Compared with a typical VCSEL with the same outer dimension, the 804nm VCSEL with MCRA has maximal continuous wave(CW) light output power 0.23 W which is about 3 times that of a typical device. The novel laser also exhibits a stable single-lobed far field pattern with low beam divergence angle, which is suitable for free-space optical communication and optical interconnection applications.
This paper reports a study on the relationship between the combining efficiency and reflectivity of output coupler of diode array in spectral beam combining. The combining efficiency is analyzed theoretically by using principle of the resonator. The simulation shows that high reflectivity will lead to low combining efficiency, and low reflectivity may cause the failure of wavelength locking. With increasing of the reflectivity of the OC, the combining efficiency changes like a downward parabola which has a maximum value of ~10%. The experiments demonstrate that the highest efficiency is obtained at a reflectivity of 10%, and the experimental results agree well with the theoretical analysis.
Fiber-coupled laser diodes have become essential sources for fiber laser pumping and direct energy applications. To obtain high power, high brightness semiconductor laser beam output, a 976nm wavelength fiber coupling module with 12 single-emitter laser diodes has been designed using ZEMAX optical design software, and single-emitter has an output power of 10 W with a 105μm wide emission aperture. The core diameter of output fiber is set as 105μm with a numerical aperture (NA) of 0.15. Finally, the simulated result indicates that the module will have an output power over 100W with the brightness of 16.63MW·cm<sup>-2</sup>·str<sup>-1</sup>, and the coupling efficiency achieved 85%.
The paper study on the effect of index distribution on the mode field and calculated the mode distribution in various index profiles. A single mode gaussian hybrid multicore fiber with 19 hexagonally arranged high index quartz rods is designed and investigated. Theoretical and simulative results are presented and compared to the conventional large mode area double clad fiber, the fundamental mode (FM) area can be reached 694.28 μm<sup>2</sup>, the confinement loss of FM and high order modes (HOMs) are 0.186 dB/m and 1.48 dB/m respectively with the bending radius of 20 cm at 1.064 μm wavelength, moreover, the index distribution can resistant the mode field distortion, which caused by fiber bending. So the FM delivery can be formed and the beam quality can be improved.
The high-performance InGaAsSb/GaAsSb/GaAs lasers emitting 1300 nm is simulated. Compared to the type-II quantum well GaAsSb/GaAs, In<sub>0.48</sub>Ga<sub>0.52</sub>As<sub>0.98</sub>Sb<sub>0.02</sub>/GaAs<sub>0.98</sub>Sb<sub>0.22</sub> has large bandoffset which will offer a better electron confinement. And GaAs<sub>0.98</sub>Sb<sub>0.22</sub> can reduce the effective strain of the highly lattice mismatched InGaAsSb quantum well. The transparent carrier densities of active unit is as low as 0.72×10<sup>18</sup> cm<sup>-3</sup>. The threshold current and slope efficiency of the InGaAsSb/GaAsSb/GaAs three quantum wells laser is equal to 83 mA and 0.62W/A. When the current is over 93 mA, external efficiency will reach 0.72. In order to further enhance the performance of InGaAsSb/GaAsSb quantum well (QW) laser, the asymmetric (0.5 μm/1.5 μm) waveguide structure is also studied.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
KEYWORDS: Optical fibers, Optical filters, High power lasers, Reflectivity, Multiplexing, Fiber lasers, Semiconductor lasers, Diodes, Fiber couplers, Fiber coupled lasers
In this paper, the laser diode (LD) fiber coupling method based on the wavelength multiplexing technique is used. Two different wavelengths of beams from two high power laser diodes are coupled into a single multi-mode fiber via collimating, wavelength combining, focusing and coupling to achieve high efficiently high power output. The output light beam from LD is collimated by using a section of the optical fiber with a diameter of 200μm. According to the basic principle of wavelength multiplexing, the wavelength coupling device is designed. The focusing lens set is designed with the related technical data of fiber and LD. And, two diode laser beams at 808nm and 980nm, light-emitting area of 100μm×1μm, output power of 2W（CW）LDs are coupled into a multi-mode fiber by the above method, with a core diameter of 100μm and a numberical aperture (NA) of 0.22. In the current work, for 808 nm LD and 980 nm LD at a operation current of 2.5 A, the total continuous power output is 4.05 W while the continuous power output is 3.25 W for the optical fiber laser, which gives a total coupling efficiency of as high as 80%.
In this study, uniform InAs QDs were grown on the GaAs (001) substrate by MBE by the S-K mode. The effects of strain reducing layer and rapid thermal anneling on the optical properties of InAs/(In)GaAs QDs were investigated by PL measurements. The annealing results in PL peak energy red-shift which strongly depends on In composition of InxGaAs strained reducing layer , QDs with lower density and/or capped by an InGaAs layer are very sensitive to the annealing. At given annealing conditions, PL peak energy blue-shift of low-density QDs is much larger than that of high density QDs.
Semiconductor laser has the characteristic of high efficiency and small volume,which make it be the best illuminator in the night vision system so that increase the range of observation and improve the image quality of night vision system. But in bad weather, image qualitly will decline because of atmosphere's backward scattering which serious influence the laser beam. To solve this problem, We have studied how to control the working condition of semiconductor laser and make it form a pulse laser which according with range gating technology in night vision system. The result of study indicates that semiconductor laser is feasible as illuminator for night vision system.
The extreme divergence and the astigmatism of the high power laser diode array (LDA) require optics with complex lens structure and high performance. A monolithic micro- optic system is designed to shape the beam of LDA and couple the output of LDA with low NA fiber. The structure and principle of the micro-optic system is described in detail. The actual performance of the micro-optic system is studied by measuring P-I properties for both fiber coupled output and the LDA output, and their dependences on deviations in x, y, z directions. The light output of 980nm, 19-emitter LDA is shaped by this micro-optic system and coupled into a fiber with 400µm diameter, Numerical Aperture (NA) 0.22. The overall efficiency is more than 60%. The main factors effecting coupling efficiency are analyzed.