Highly position-controlled ZnO nanowire arrays are grown on a SiO2-mask-patterned GaN substrate by hydrothermal method. The morphology of ZnO nanowires (NWs) can be modulated, and a comprehensive study is conducted for the first time. The morphology relies on the nucleation process that can be adjusted by varying growth time and solution concentration. Spectral responsibility curve and electroluminescent characteristics (EL) are measured, which both present great ultraviolet (UV) photoelectric properties. Meanwhile, the position of ZnO NWs is highly controllable as designed and the morphology of NWs are largely consistent, which pave the way to fabricate the high performance device resulting from the interaction between light.
In this paper, a variable temperature growth method was proposed and adopted for InGaAs/GaAs multiple quantum wells (MQWs) grown by MOCVD, where the InGaAs well layer and the GaAs barrier were grown under different temperature. A new structure with protection layer was also presented to protect the indium atoms on InGaAs surface from the evaporation during temperature change. The effect of new growth method was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and Photoluminescence (PL). Compared to the conventional constant temperature growth, the surface morphology and crystal quality were improved due to the protection layer and high temperature growth of GaAs. The growth temperature of InGaAs well layer was also optimized in detail, it is found that when the temperature was too high, the surface will be deteriorated, as well the optical properties. The new growth method and tailored structure will help to impro9ve the properties of strained InGaAs/GaAs MQWs materials, and provide the technical support for the performance optimization of semiconductor laser.
Based on the principle of infrared target system, the emissivity and reflectivity of the coating material of the target plate of the infrared target system are studied in depth. The relationship between the emissivity, reflectivity and light wavelength of the target is discussed in this paper. First, 50 target plates are selected and the diffuse reflectance of 1.06 μm laser is measured. The experimental results show that the minimum reflectivity is 0.202 and the maximum reflectivity is 0.217, which is in the range [0.2,0.3]. The average value of reflectivity is 0.20886, and the measurement error is in the range [-0.00686, 0.00814]. Then, the non-uniformity value of each measured value is calculated, the maximum value is 3.89%, less than 7.5%. Finally, the emissivity of the coating material is measured in the wavelength range of 2.5 μm ~ 13.5 μm, and the minimum value is 0.869, better than 0.7. At the same time, four kinds of coating materials are compared and the results show that the coating materials in this paper had higher emissivity. The infrared target system can model all kinds of infrared targets, which provides a method for target attack experiment.
In this paper, the lateral single-mode emission from 1064nm edge-emitting (broad area) BA diode lasers with laterally coupled passive waveguide (LCPW) structures is presented. The LCPW structure is introduced to both sides of the broad active waveguide, and the high-order lateral modes can be tunneled into the LCPW, which results in an increase in higher-order lateral modes loss and an increase in the 2D optical confinement factor difference between fundamental lateral mode and higher-order lateral modes, thereby suppressing the higher-order lateral modes. The influence of LCPW structure on the suppression of higher order lateral modes in broad area lasers are investigated. The results show that for the semiconductor laser with active waveguide width of 15μm, the introduction of LCPW structure effectively eliminates the high-order lateral modes and achieves a single lateral mode output.
In order to complete the detection of small displacements, the principle of grating diffraction interference is used to convert the displacement of the measured target into the change of the light and dark of the fringes after interference. The displacement information is estimated by detecting the change in light intensity. However, this method requires high optical path symmetry and complicated installation. In this regard, by modifying the optical path and using the principle of interference, this article enlarges and visualizes the installation error. Thereby reducing the complexity of installation and adjustment, and improving the accuracy of installation and adjustment.
In this paper, we designed a novel tunable VCSEL structure with a top wave-like mirror for polarization control. Based on rigorous coupled-wave theory, the reflection characteristics of the top wave-like mirror structure for different polarization modes was analyzed. The wave-like structure was designed and optimized to control the output polarization mode of tunable VCSEL. The results show the threshold gain of TM mode is always greater than the TE mode during 84.5nm wavelength tuning range, the maximum increase is more than 10 times. It is indicated that the designed structure of tunable VCSEL can effectively realize stable polarization mode.
Low reverse-bias series resistance tunnel junctions (TJs) are the key to improving the performances of high efficiency multi-junction semiconductor laser diodes (MJLDs). In this paper, InGaAs QW TJ and InGaAs DQW TJ with single InGaAs layer and double InGaAs layers inserted into GaAs TJs separately, are proposed. TJ chips were fabricated by metal organic chemical vapor deposition (MOCVD) technology and semiconductor process. The measurement results of the devices display that the operating voltage of the InGaAs QW TJ and the InGaAs DQW TJ is lower than that of the GaAs TJ under the same injection current, whether it is a small current or a large current, and the InGaAs DQW TJ operating voltage is lower than that of the InGaAs QW TJ. Both GaAs TJ and InGaAs DQW TJ were applied to 1060 nm dual active region semiconductor laser diode. The ridge lasers with a strip width of 100μm and a cavity length of 2 mm were fabricated. The working voltage is reduced from 3.81 V to 3.38 V at 1 A drive current. Further experimental results indicate that the reverse-bias series resistance of InGaAs QW TJ and InGaAs DQW TJ is lower than that of GaAs TJ, and the performances of InGaAs DQW TJ are the best. This is of great significance to reduce the heat loss of MJLDs and improve its performances.
Aiming at the urgent demand of small volume, high efficiency and high power laser source in the field of laser ranging, we proposed a multi-active-regions mini-bar (MAMB) structure of semiconductor laser diodes, in which multi-active regions (or sub-LDs) are cascaded by reverse-biased tunnel junctions (TJs) transversely, meanwhile, several sub-cells composed of sub-LDs form mini-bar laterally. The entire structure was epitaxially grown on GaAs substrate by MOCVD. In order to minimize the additional series resistance introduced by the tunnel junction, InGaAs double quantum wells (DQWs) TJ is adopted. To increase the COMD level, each sub-LD uses an AlGaAs asymmetric large optical cavity, in which the active region is a compressive strained InGaAs DQWs. After the standard chip post-process, the MAMB was fabricated with the ridge-shaped sub-cells, which has a strip width of 200μm and cavity length of 1mm. The MAMB was then soldered on C-mount and mounted on TO3 to test at room temperature with a frequency of 20 Hz and a pulse width of 20 μs. The output power of a MAMB with 3 active regions and 3 sub-cells reaches 47.76 W (28 A), corresponding to a slope efficiency of 2.02 W/A, and the peak wavelength is 1060.6 nm. The results show that the MAMB structure could effectively improve the output power and reduce its volume.
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-2·str-1, 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 μm2, 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, In0.48Ga0.52As0.98Sb0.02/GaAs0.98Sb0.22 has large bandoffset which will offer a better electron confinement. And GaAs0.98Sb0.22 can reduce the effective strain of the highly lattice mismatched InGaAsSb quantum well. The transparent carrier densities of active unit is as low as 0.72×1018 cm-3. 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.
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.
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