RESUMEN
Recent advancements in silicon photonics are enabling the development of chip-scale photonics devices for sensing and signal processing applications, among which on-chip spectrometers are of particular interest for precision wavelength monitoring and related applications. Most chip-scale spectrometers suffer from a resolution-bandwidth trade-off, thus limiting the uses of the device. Here we report on a novel passive, chip-scale, hybrid speckle-enhanced Fourier transform device that exhibits a two order-of-magnitude improvement in finesse (bandwidth/resolution) over the state-of-the art chip-scale speckle and Fourier transform spectrometers. In our proof-of-principle device, we demonstrate a spectral resolution of 140 MHz with 12-nm bandwidth for a finesse of 104 that can operate over a range of 1500-1600 nm. This chip-scale spectrometer structure implements a typical spatial heterodyne discrete Fourier transform interferometer network that is enhanced by speckle generated from the wafer substrate. This latter effect, which is extremely simple to invoke, superimposes the high wavelength resolution intrinsic to speckle generated from a strongly guiding waveguide with a more broadband but lower resolution discrete Fourier transform modality of the overarching waveguide structure. This hybrid approach signifies a new pathway for realizing chip-scale spectrometers capable of ultra-high resolution and broadband performance.
RESUMEN
We demonstrate a technique for SBS reduction in a nanosecond Yb-fiber amplifier by imposing 1.19 GHz/ns frequency chirp on the seed pulses with a pulse-driven phase modulator. A nearly 9-fold increase in the SBS threshold was observed for 8.4 ns pulses. SBS threshold data and transient SBS gain for various degrees of chirp are reported and compared with theoretical calculations. We further demonstrate the recovery of the input narrowband spectrum by applying an opposite chirp with a second phase modulator after the amplification.
RESUMEN
We report 1645 nm narrowband operation of a monolithic Er:YAG nonplanar ring oscillator resonantly pumped at 1532 nm. Unidirectional cw power up to 0.5 W was obtained with a measured linewidth of 21 kHz.
RESUMEN
The cw and Q-switched performance of Er:YAG lasers operating at 1645 nm were measured. Guided by previous work in the literature, we sought to improve efficiency at low pulse repetition frequencies by decreasing the doping level from 0.5 to 0.25 at.% to reduce upconversion losses. Only a small improvement was obtained with this first-time-tested lower-doped material. Measurements of the fluorescence due to upconversion directly indicated that loss due to this process could not account for the observed power loss at low pulse repetition frequencies. Enhanced green emission during Q-switched operation, resulting from two-photon absorption of 1645 nm intracavity laser light, is reported for what we believe to be the first time. Measurements indicated that the output loss from this process is negligible.
RESUMEN
A time-gated filter is demonstrated that converts a double-sideband radio-frequency (rf) waveform on a pulsed optically chirped carrier into a single sideband (SSB) waveform. Electrical technology to produce SSB modulation is currently limited to rfs less than 20 GHz, while our filter operates up to the maximum frequency available from optical modulators. Application of the filter in photonic time-stretch analog-to-digital converters (TS-ADCs) mitigates severe frequency fading owing to the dispersion penalty that limits the rf input signal bandwidth and time aperture. Here we show that frequency fading owing to the presence of both upper and lower sidebands in the TS-ADC can be reduced by over 20 dB and that a TS-ADC using this filter can digitize electrical signals with rfs beyond 100 GHz.
