ABSTRACT
Resonant subwavelength gratings (RSGs) offer narrowband high reflectivity with low-reflectivity sidebands. Analysis with the commonly used rigorous coupled-wave analysis assumes an RSG with infinite lateral extent and illumination by plane waves. This analysis is performed with a finite-difference semivectorial high-order accurate two-dimensional Helmholtz code that is able to simulate the entire finite RSG structure in the dimension of the grating vector. We study the effect of finite beam size on RSG reflectivity, resonant wavelength, and spectral response width. Independently, we study the effect of a finite RSG by varying the waveguide length and number of grating periods while fixing the beam size. We show that the placement of the waveguide end facets relative to the termination of the grating has a significant effect on the reflectivity and response width.
ABSTRACT
A new effective index optical model is presented for the analysis of lateral waveguiding effects in verticalcavity surface-emitting lasers. In addition to providing a concise formalism for reducing the dimensionality of the Maxwell equations describing the lasing mode, this model also provides new insights into waveguiding phenomena in vertical-cavity lasers. In particular, it is shown that the effective index responsible for waveguiding is dependent only on lateral changes in the Fabry-Perot resonance frequency. This concept leads naturally to new design methods for these lasers that are expected to result in more eff icient devices with superior modal characteristics.
ABSTRACT
A new beam-propagation method is presented whereby the Padé approximant wide-angle propagation operator is factored into a series of simpler Padé (1, 1) operators, thus leading naturally to a multistep method whose component steps are each solvable by using readily available paraxiallike solution techniques. The resulting method allows accurate approximations to true Helmholtz propagation while incurring only a modest numerical penalty. In addition, the tridiagonal form of the component steps allows the straightforward use of the previously reported transparent boundary condition.
ABSTRACT
A new boundary condition algorithm is presented that passes outgoing radiation freely with a minimum reflection coefficient (typically 10(-5)) while inhibiting the flux of incoming radiation. In contrast to the commonly used absorber method, this algorithm contains no adjustable parameters and is thus problem independent. It adapts naturally to a standard Crank-Nicholson difference scheme and is shown to be accurate and robust for both two-and three-dimensional problems.
ABSTRACT
The use of a two-dimensional coupled-mode theory for modeling buried-ridge-waveguide index-guided arrays in general and leaky-mode arrays in particular is described. This formalism provides a framework for understanding the complicated modal structure of leaky-mode arrays by expressing their modes as linear combinations of the two dimensional modes of the buried-ridge waveguides and the active-region confinement structure. As a result, the inherently large parameter space of these devices may be collapsed dramatically so that the device behavior is describable in terms of only the propagation constant mismatch between the buried-ridge modes and the activeregion modes and their coupling coefficient.
ABSTRACT
A simple formalism is reported for studying the modes of an infinite two-dimensional (2-D) phase-locked array of vertical-cavity surface-emitting diode lasers. In this approach, the Helmholtz equation is approximately separated into products of solutions of the associated one-dimensional (linear) arrays. This formalism allows the knowledge gained from years of research into the modal properties of linear diode arrays to be applied directly to 2-D arrays. As a result, it is expected that both 2-D gain-guided and index-guided arrays (except those with excess gain in the low-index channels) will lase in the high-order mode characterized by emission into four distinct off-axis far-field lobes. In contrast, it is expected that properly constructed 2-D leaky-mode arrays would lase preferentially in the fundamental mode well above threshold.
ABSTRACT
The mode-selection mechanism operative in a new class of large-index-step index-guided arrays is elucidated, and it is shown that such arrays may be designed to operate stably in the fundamental mode at high power levels. In contrast to evanescently coupled arrays, these devices operate in a new set of so-called leaky modes. The calculations demonstrate a significant discrimination between the fundamental and high-order leaky modes that is sensitive to the widths of the high-index coupling regions but insensitive to the drive current. This resulting mode discrimination combined with the inherently large index step present in these devices should allow them to operate stably under cw conditions and/or at high drive currents.
ABSTRACT
We examine the structure and modal gains of the leaky modes of an infinite periodic index-guided array by direct solution of the two-dimensional Helmholtz equation. These findings serve to validate the physical insights suggested by our previous calculations based on the effective-index method and, in particular, confirm the concept of guidewidth tailoring for affecting fundamental-mode operation of these devices at high power levels. Our newer model also provides new insights into the mode-selection mechanism and demonstrates clearly the necessity of a full twodimensional treatment if one is to describe the mode profiles or their relative gains accurately.
ABSTRACT
We present a numerical model for the transient response of a longitudinally pumped miniature solid-state laser. The model is suitable for both regenerative amplifiers and oscillators, provided the latter run in a single mode. The results of our calculations compare well with measurements of the peak output powers and pulse widths for a Nd:YAG rod pumped by a ten-stripe diode laser array. Our model predicts saturation at peak powers of approximately twice the 850 mW reported here due to filling of the lower laser level. To overcome this power limitation due to saturation, we also explore the use of miniature Nd:glass laser amplifiers to boost the single-frequency Nd:YAG pulses to powers exceeding 200 W.
ABSTRACT
Numerical modeling of two-photon-resonant sum-frequency mixing in mercury vapor predicts efficiencies >10% for generation of 130.2-nm oxygen resonance light. The modeling indicates that power broadening of the two-photon resonance due to amplified spontaneous emission from the pumped level strongly influences the mixing process. Measurements of the broadening and the efficiencies for difference-frequency mixing are presented as a check of the model calculations.
ABSTRACT
We report the use of gain switching to obtain 60 mW of single-longitudinal-mode peak output power from a laser-diode-excited monolithic Nd:YAG laser. The device is demonstrated to operate at repetition rates in excess of 1 kHz and exhibits a spectral linewidth of less than 8 MHz. This oscillator provides an ideal source for injection seeding of laboratory Nd:YAG laser systems.
