Output Coupling Losses Research Articles

Amplified squeezed states: analyzing loss and phase noise

Abstract Phase-sensitive amplification of squeezed states is a technique to mitigate high detection loss, which is especially attractive at 2μm wavelengths. We derived an analytical model proving that amplified squeezed states can mitigate phase noise significantly. Our model discloses two practical parameters: the effective measurable squeezing and the effective detection efficiency of amplified squeezed states. A realistic case study includes the dynamics of the gain-dependent impedance matching conditions of the amplifier. Our results recommend operating the optical parametric amplifier at high gains because of the signal-to-noise ratio’s robustness to phase noise. Amplified squeezed states are relevant in proposed gravitational wave detectors and interesting for applications in quantum systems degraded by the output coupling loss in optical waveguides.

Broadband multi-longitudinal-mode Yb:YAG/YVO4 coupled Raman microchip laser

Broadband lasers oscillating in multiple longitudinal modes have potential applications on high resolution interferometer, optical communication and laser spectroscopy. However, the bandwidth of the laser spectrum is limited by the spectral range of laser materials. Here, a broadband multi-longitudinal-mode laser with bandwidth of 22.4 nm at first-order Stokes wavelength has been achieved in a Yb:YAG/YVO4 Raman microchip laser pumped with a quasi-continuous-wave laser-diode. The output energy is 11.6 mJ at pump energy of 34.4 mJ, and the optical efficiency is 34%. Dramatically expanding multi-longitudinal-mode laser spectrum has been achieved by forming Yb:YAG/YVO4 coupled Raman microchip laser with an external Fabry–Perot mirror to manipulate the output coupling losses at different frequencies for fundamental, first-order and second-order Stokes lasers. The bandwidth of the broadband multi-longitudinal-mode laser is 55.4 nm, which covers from 1041 nm to 1096.4 nm and includes 118 longitudinal modes. This enables compact coupled Raman microchip solid-state lasers for generating broadband multi-longitudinal-mode laser.

Power characteristics of planar index-antiguided waveguide lasers with transverse mode competition

We report comprehensive analysis of output characteristics of homogeneously broadened index-antiguided slab lasers with transverse mode competition. Robust single fundamental mode operation is achieved when the distributive modal loss due to index antiguiding dominates the output coupling loss. Maximal laser efficiency under single fundamental mode operation is investigated numerically for various combinations of single-pass gains and losses. We show analytically that an asymptotic limit of such efficiency exists that is solely determined by the loss ratio between the fundamental and 1st higher-order modes, which equals 66.7% for planar index antiguided lasers.

Optimization and control of the sweeping range in an Yb-doped self-sweeping fiber laser

Influence of the laser cavity parameters (an active fiber length and output coupling losses) and the temperature of elements (active fiber and pump laser diode) on the sweeping range in an Yb-doped self-sweeping laser is investigated. The obtained results show that the sweeping spectral region is shifted to shorter wavelengths for shorter active fibers and with increasing absorbed power. This allows one to obtain self-sweeping operation in a broad range within a ytterbium gain bandwidth from 1028 to 1080 nm. At the same time, there are optimal cavity parameters at which the sweeping span is the broadest (>20 nm). Good agreement between the experimental sweeping range and the calculated maximum gain wavelength is demonstrated.

Evolution of multi-mode operation in vertical-external-cavity surface-emitting lasers

The longitudinal multi-mode emission in a vertical-external-cavity surface-emitting laser is investigated using both single shot streak camera measurements and interferometric measurement techniques. For this, the laser is operated in the single- and two-color emission regime using both an etalon and a free-running configuration without etalon, respectively. The laser emission is analyzed with respect to pump power and output coupling losses for a long and for a short resonator. We observe a steep increase of emission bandwidth close to the laser threshold and monitor the transition between longitudinal single- and multi-mode operation. Additionally, the results indicate that a stable two-color operation is related to a sufficiently high number of oscillating longitudinal modes within each color.

Numerical Modeling and Optimization of Diode Pumped Heavily-Erbium-Doped Fluoride Fiber Lasers

Numerical modeling of heavily-erbium-doped fluoride fiber lasers is presented. Calculations from the model were compared with all previously reported experimental demonstrations of heavily-erbium-doped fluoride fiber lasers. Commensurate with recent modeling studies, good agreement with the measurements was achieved with the use of scaled-down rate parameters for energy transfer that corresponds to weaker interactions between Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. For wavelength-fixed (grating) systems, we show that the measured saturation of the output power results from a combination of changes to the Boltzmann distribution arising from core temperature excursions and pump excited state absorption (ESA). In free-running systems, we show that inter-Stark level transitions that terminate on progressively higher Stark levels within the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13/2</sub> manifold in part describe the non-saturating behavior of the output power at moderate pump levels. The model was used to investigate the influence of dopant concentration, pump wavelength, pump configuration, output coupling and background loss of the fiber on laser performance. In contrast to a number of previous modeling investigations, our results show that the slope efficiency steadily increases with increasing erbium concentration as a result of the reduced rates of energy recycling caused by the weakly interacting Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. The highest slope efficiency was obtained for a pump wavelength of 983 nm due to reduced levels of ESA, however, for both free-running and wavelength-fixed arrangements of the laser, pump ESA may ultimately preclude significant power scaling.

Compact coupling of light from conventional photonic wire to slow light waveguides

In this study, efficient input and output power coupling schemes for transition regions at the interface of conventional and slow light waveguides are investigated. By optimizing the tapered nano-tip of the input and output slab waveguides that support a group index of 3.58, we achieved 97% coupling efficiency to a square-lattice based slow light photonic crystal waveguide with a group index of 1200. The complementary slow waveguide structure based on triangular-lattice is also designed to support same order of magnitude slow light mode and targeted to alleviate the severity of the coupling loss. An acceptable efficiency value is recorded for the second type of slow waveguide mode. For the sake of targeting only input and output coupling losses, we made an assumption that other loss mechanisms are absent in the structure. The successful demonstration of effective and compact slow light couplers will assist the deployment of slow light devices in important applications, such as nonlinear optics, optical buffers, and optical delay lines.

Enhancement of the Mode Area and Modal Discrimination of Microchip Lasers Using Angularly Selective Mirrors

Angularly selective mirrors (ASMs) are proposed as a means to expand the mode area and modal discrimination of microchip lasers. ASMs used as output couplers selectively reflect incoming <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> vectors over a narrow angular range, while they transmit more inclined components. The eigenvalue problem of a microchip resonator equipped with a Gaussian ASM is solved analytically in the paraxial optics approximation using the ABCD matrix formalism. The narrow angular distribution of the reflected beam produces, through the laws of diffraction, a significant increase of the mode size and improved transverse mode discrimination, at the expense of higher oscillation threshold due to larger output coupling losses. Simulations performed using the parameters of Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped YAG material show that one order of magnitude increase of the mode area can reasonably be achieved without causing overheating and thermal fracture. ASMs can be directly deposited on the active material in the form of a resonant grating mirror. This technology involves only planar batch processes that retain the mass production advantage of microchip lasers. The significant increase of brightness of microchips expected from this innovation will give rise to more effective and more compact devices and new applications.

Spatially dependent spontaneous emission and Rabi oscillations of atoms in an open cavity with nonorthogonal eigenmodes

The spatial dependence of the cavity modified spontaneous emission of an atom in a cavity with finite output coupling loss is analyzed. The analysis is based on the quantized nonorthogonal eigenmodes defined by the open cavity boundary condition. The spatial dependence of the Rabi oscillation frequency in the strong coupling regime is also analyzed. For spontaneous decay, the spatial dependence is a sinusoidal modulation on top of a dc value, where the interaction with all cavity modes is considered. For Rabi oscillations, where the atom interacts mainly with only one cavity mode, the oscillation frequency also has a sinusoidal spatial dependence.

Beam steering and tilt coupling in tunable hollow waveguide

We present the new function of tunable hollow waveguides with a variable air core. We show a possibility of wide-angle beam steering from the hollow waveguide and efficient tilt-coupling in narrow air core hollow waveguides. Wide-angle beam steering was demonstrated by calculation and preliminary experiment. In addition, a possibility of an efficient optical coupling with a narrow air core was presented by the tilt-coupling scheme. Input and output coupling losses are 2.5dB and 1dB for 1µm air core, respectively. Wide tunability in sub-wavelength air cores enables us to realize new functions of tunable hollow waveguides and circuits.

Transition, radiation and propagation loss in polymer multimode waveguide bends

Design curves for insertion loss of multimode polymer waveguide 90 masculine bends are reported as a function of bend radius for several waveguide widths. For the first time, to our knowledge, in multimode rectangular waveguides the insertion loss is resolved into its components of transition, radiation and propagation loss, in order of decreasing strength, separating them from input and output coupling loss by calibration and comparison of experimentally measured and beam propagation method (BPM) modeled curves. We used the method of nested bends for the first time in multimode polymer waveguides to calculate the propagation loss on a small substrate without using destructive cut-back. The lowest loss of 0.74 dB occurred for a 50 mum square cross section, Deltan=0.0296, 13.5 mm radius waveguide bend.

Fabrication tolerance of asymmetric silicon-on-insulator polarization rotators

We investigate the fabrication tolerance of novel slanted-angle silicon-on-insulator polarization rotators with asymmetric external waveguiding regions. We also minimize the input and output coupling loss between the polarization rotator and the rib waveguides through a lateral shift in the relative waveguide positions.

Optical cross connect switch based on tip/tilt micromirrors in a white cell

We present a new approach to optical interconnections, based on microelectromechanical system tip/tilt mirror technology and the White cell. This is a free-space approach in which many beams circulate simultaneously in the device, each beam forming a unique spot pattern on the micromirror array. On each bounce, each beam can be switched to any of several White cells, each of which has a different effect on the spot pattern. By appropriate combinations of these White cells, any input beam can be directed to any output. A simple proof-of-concept prototype has been demonstrated, and output coupling loss addressed.

An optical resonator with insertable scraper output coupler for the JAERI far-infrared free-electron laser

The performance of an optical resonator featuring an insertable scraper output coupler was evaluated for the JAERI far-infrared free-electron laser. An efficiency factor of the resonator was introduced for evaluation. The efficiency factor was derived from the amount of the output coupling and diffractive loss of the optical resonator, which were calculated by using an optical mode calculation code, using the iterative computation called Fox–Li procedure. As a result of the evaluation, it was found that the insertable scraper coupler was the most suitable for the far-infrared free-electron lasers.Dependencies of insertion direction and scraper radius were also investigated to find out the optimum geometry of the insertable scraper coupler. It was found that the optimum direction of the scraper was parallel to the wiggling plane of the electron beam and the efficiency of the optical resonator increased with the enlargement of the scraper radius.

Development of an Optical Resonator with High-Efficient Output Coupler for the JAERI Far-Infrared Free-Electron Laser

An optical resonator with a high-efficient output coupler was developed for the JAERI far-infrared free- electron laser. The optical resonator is symmetrical near-concentric geometry with an insertable scraper output coupler. As a result of the development of the optical resonator, the JAERI-FEL has been successfully lased with averaged power over 1kW. Performance of the optical resonator with the output coupler was evaluated at optical wavelength of 22 μm by using an optical mode calculation code. The output coupling and diffractive loss with a dominant eigen-mode of the resonator were calculated using an iterative computation called Fox-Li procedure. An efficiency factor of the optical resonator was introduced for the evaluation of the optical resonator performance. The efficiency factor was derived by the amount of the output coupling and diffractive loss of the optical resonator. It was found that the optical resonator with the insertable scraper coupler was the most suitable to a high-power and high-efficient far-infrared free-electron laser.

A rotary electrostatic micromotor 1×8 optical switch

This paper describes a 1/spl times/8 rotary electrostatic micromotor optical switch fabricated using high-aspect-ratio micromachining technology to produce silicon or nickel components which are subsequently assembled to form a switch. The switch consists of a salient-pole micromotor with 1-mm-diameter 200-/spl mu/m-thick rotor that supports up to a 500-/spl mu/m-tall, 900-/spl mu/m-wide mirror. Typical switches were actuated at 50 V, operated for extended periods in room air, and found to have a rapid rotation with an average optical switching time between two neighboring fiber ports of 18 ms. Optical testing was performed at wavelength of 1310 nm in single- and multimode, and at 850 nm in multimode. The optical beam was propagated in free space with minimal divergence through the use of externally mounted collimating gradient-index lenses. With an aluminum coating, the mirror and external optics exhibited an input to output coupling loss as low as 0.96 dB in multimode and 2.32 dB in single-mode. Interchannel crosstalk was less than -45 dB.

Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser

A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</inf> in Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15/2</inf> in Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf> in Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> in Tm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> F <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2</inf> - <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9/2</inf> transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.

High-silica multimode channel waveguide structure for minimizing fiber-waveguide-fiber coupling loss

The optimum structure for high-silica channel waveguides which are connected to input and output graded-index fibers having a 50-μm core diameter and a 1.0-percent refractive-index difference is studied theoretically and experimentally. Theoretical optimum waveguide structure is obtained on the basis of ray optic analysis. For the step-index waveguide with 1.0-percent refractive-index difference, the theoretical minimum coupling loss (input coupling loss + output coupling loss) is 1.7 dB for an optimum core of 38 μm both in depth and width. For the graded-index waveguide with parabolic-index profile in the depth direction and step-index profile in the width direction, the theoretical coupling loss is 1.1 dB for an optimum core of 38 μm in width and 50 μm in depth. These estimations were in good agreement with the experimental results, which were 1.8 dB for the step-index waveguide and 1.3 dB for the graded-index waveguide.

Exact cavity equations for lasers with large output coupling

The author shows how to write an exact cavity-mode expansion and obtains formally simple yet exact equations of motion for real laser cavities with large output coupling and/or diffraction losses, using the actual transverse eigenmodes of the cavity as a basis set, and including fast transient variations, externally injected signals, and spontaneous emission noise.