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Register a new userGenerations of high efficiency, high purity, and broadband Laguerre-Gaussian modes from a Janus optical parametric oscillator
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Laguerre-Gaussian (LG) modes, carrying orbital angular momentum of light, are critical for important applications such as high-capacity optical communications, super-resolution imaging, and multi-dimensional quantum entanglement. Advanced developments in these applications strongly demand reliable and tunable LG mode laser sources, which, however, do not yet exist. Here, we experimentally demonstrate highly-efficient, highly-pure, broadly-tunable, and topological-charge-controllable LG modes from a Janus optical parametric oscillator (OPO). Janus OPO featuring two-face cavity mode is designed to guarantee an efficient evolution from a Gaussian-shaped fundamental pumping mode to a desired LG parametric mode. The output LG mode has a tunable wavelength between 1.5 um and 1.6 um with a conversion efficiency above 15%, a topological charge switchable from -4 to 4, and a mode purity as high as 97%, which provides a high-performance solid-state light source for high-end demands in multi-dimensional multiplexing/demultiplexing, control of spin-orbital coupling between light and atoms, and so on.
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We have investigated the generation of highly pure higher-order Laguerre-Gauss (LG) beams at high laser power of order 100W, the same regime that will be used by 2nd generation gravitational wave interferometers such as Advanced LIGO. We report on the generation of a helical type LG33 mode with a purity of order 97% at a power of 83W, the highest power ever reported in literature for a higher-order LG mode.
We study optical parametric oscillations in Kerr-nonlinear microresonators, revealing an intricate solution space -- parameterized by the pump-to-signal conversion efficiency -- that arises from an interplay of nonlinear processes. Using a three-mode approximation, we derive an efficiency-maximizing relation between pump power and frequency mismatch. To move beyond a three-mode approximation, a necessity for geometries such as integrated microring resonators, we numerically simulate the Lugiato-Lefever Equation that accounts for the full spectrum of nonlinearly-coupled resonator modes. We observe and characterize two nonlinear phenomena linked to parametric oscillations in multi-mode resonators: Mode competition and cross phase modulation-induced modulation instability. Both processes may impact conversion efficiency. Finally, we show how to increase the conversion efficiency by tuning the microresonator loss rates. Our analysis will guide microresonator designs that aim for high conversion efficiency and output power.
Vast geographical distances in Africa are a leading cause for the so-called digital divide due to the high cost of installing fibre. Free-Space Optical (FSO) communications offer a convenient and higher bandwidth alternative to point-to-point radio microwave links, with the possibility of re-purposing existing infrastructure. Unfortunately, the range of high bandwidth FSO remains limited. While there has been extensive research into an optimal mode set for FSO to achieve maximum data throughput by mode division multiplexing, there has been relatively little work investigating optical modes to improve the resilience of FSO links. Here we experimentally show that a carefully chosen subset of Hermite-Gaussian modes is more resilient to atmospheric turbulence than similar Laguerre-Gauss beams, theoretically resulting in a 167% theoretical increase of propagation distance at a mode dependent loss of 50%.
We report a 65MHz-bandwidth triangular-shaped optical parametric oscillator (OPO) for squeezed vacuum generation at 860nm. The triangle structure of our OPO enables the round-trip length to reach 45mm as a ring cavity, which provides a counter circulating optical path available for introducing a probe beam or generating another squeezed vacuum. Hence our OPO is suitable for the applications in high-speed quantum information processing where two or more squeezed vacua form a complicated interferometer, like continuous-variable quantum teleportation. With a homemade, broadband and low-loss homodyne detector, a direct measurement shows 8.4dB of squeezing at 3MHz and also 2.4dB of squeezing at 100MHz.
The multiple lobes of high order Hermite-Gaussian (HG) laser modes differ in terms of shape, size, and optical energy distribution. Here, we introduce a generic numerical method that redistributes optical energy among the lobes of high order HG modes such that all the identical low intense lobes become both moderate or high intense lobes and vice-versa, in a controlled manner. Further, the modes which consist of only two types of intensity distribution among its multiple lobes are transformed together into all high intense lobes. Furthermore, in some cases, moderate intense lobes together with high intense lobes become high intense lobes, and moderate intense lobes together with low intense lobes become high intense lobes. Such controlled modulation of optical energy may offer efficient and selective utilization of each lobe of HG modes in most applications like particle manipulation, optical lithography, and the method can be used in other fields like nonlinear frequency conversion and shaping ultrafast optical pulses.
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