Quality Of Light Beam Research Articles

Study on narrow linewidth 2.1 μm self-optical parametric oscillator based on Nd:MgO:PPLN

We report a 2.1 µm miniaturized narrow linewidth self-optical parametric oscillator (SOPO) based on Nd:MgO:PPLN crystal. We attained 2.1 µm narrow linewidth laser output by incorporating an Fabry-Perot (F-P) etalon into the SOPO. By controlling the crystal temperature uniformly, a stable 2.1 µm degenerate light output is obtained at 71 °C. Finally, when inserting the F-P etalon with a thickness of 2.5 mm, a maximum average output power of 0.65 W is obtained, corresponding pulse repetition rate is 60 kHz, the pulse width is 7.77 ns, the degenerate light beam quality M2 < 2. And the linewidth of 2168 nm laser is narrowed from 67.53 nm to 2.23 nm. It is proved by experiments that adding F-P etalon to the SOPO can narrow the linewidth of the 2.1 μm laser and optimize the beam quality. These findings provide technical support for the realization and application of narrow linewidth 2.1 µm laser, which is great significance for the further development of related fields.

Sixty-Nine-Element Voice Coil Deformable Mirror for Visible Light Communication

To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized from the aspects of thermal deformation, response time, coupling coefficient, and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized voice coil deformable mirror (VCDM) has a large phase stroke, good thermal stability, a short response time of less than 0.7 ms, and a large first resonance of 2045 Hz. The fitting residuals of the VCDM for the first 10 Zernike modes with a PV value of 8 μm are all below 10 nm (RMS). Compared with a similar DM, the obtained results from our compact VCDM indicate that it has a higher wavefront fitting precision. VCDM corrected complex random aberrations in the VLC scenario and improved the coupling efficiency of the signal beam, proving that the compact VCDM with high performance and low cost has a good application prospect in VLC systems.

A modified structure with asymmetric and doping barrier interlayers of GaAs-based laser diodes with both small vertical divergence angle and low threshold current

The vertical divergence angle of GaAs-based laser diodes (LD) can be reduced by usually increasing waveguide thickness and inserting low index layers between waveguide layers and cladding layers, but it will also induce an increase of the threshold current. It is proposed to make the inserted low index interlayers doped and asymmetric to simultaneously reduce vertical divergence angle and alleviate the deterioration of threshold current. The simulation results indicate that the carrier leakage and injection are improved due to the change of energy band profile. The characteristics of newly designed laser structure indicate a satisfactory light beam quality and a relatively low threshold current density.

A Novel Kind of Transverse Micro-Stack High-Power Diode Bars

Novel transverse micro-stack semiconductor laser bars are put forward to improve the output optical power of semiconductor laser bars at low injection current. More importantly, the novel laser bars have a coupled large optical cavity, which can overcome the problem of catastrophic optical damage and improve light beam quality due to the coherently coupled emitting along the transverse direction. The micro-stack tunnel regeneration tri-active region laser structure was grown by metal organic chemical vapour deposition. For a weakly coupled uncoated device, the optical power exceeds 60W under 50A driving current and the slope efficiency reaches 1.55W/A. Further experiments show that the perpendicular divergence of 23° is achieved from transverse strongly coupled devices.

Ultra-fast speed, low grating lobe optical beam steering using unequally spaced phased array technique

In this paper, we present a low grating lobe optical beam steering technique using an unequally spaced phased array, in which the required spacings among the phase elements are quantitatively analyzed so that the grating lobe can be minimized by destructive interference. A large grating lobe is one of the major drawbacks of optical phased array technology because it limits the light efficiency and the quality of the light beam. Thus, the low grating lobe technique presented in this paper could substantially improve the light efficiency and the quality of light beam, and could potentially be used in a variety of applications such as fast speed ladar beam steering, large size high resolution displays, and wide bandwidth free space optics communications.

NOVEL COUPLED MULTI-ACTIVE REGION HIGH POWER SEMICONDUCTOR LASERS CASCADED VIA T UNNEL JUNCTION

A novel semiconductor laser structure is put forward to resolve the major difficulties of high power laser diodes. In this structure, several active regions are cascaded by tunnel junctions to form a large optical cavity and to achieve super high efficiency. This structure can solve the problems of catastrophic optical damage of facet, thermal damage and poor light beam quality effectively. Low-pressure metalorganic chemical vapor deposition method is adopted to grow the novel semiconductor laser structures, which are composed of Si:GaAs/C:GaAs tunnel junctions, GaAs/InGaAs strain quantum well active regions. External differential q uantum efficiency as high as 2.2 and light power output of 2.5W per facet (under 2A drive current) are achieved from an uncoated novel laser device with three a ctive regions.

Generalized Siegman formula and comments on the inequality M 2 ⩾ 1 for light-beam quality

An generalized version of the Siegman formula which comes directly from Helmholtz equation is reported in this paper. Based on this formula, a comparison between the two definitions of the light beam far-field divergence angle is made. It is discovered the Siegman's moment definition for divergence angle would not make sense if the light beam could not be approximated to the slowly varying one. The proof of inequality M2 ⩾ 1 given by Chen and Qiu would fail if the evanescence wave effects are considered.