35 research outputs found
A full degree-of-freedom photonic crystal spatial light modulator
Harnessing the full complexity of optical fields requires complete control of
all degrees-of-freedom within a region of space and time -- an open goal for
present-day spatial light modulators (SLMs), active metasurfaces, and optical
phased arrays. Here, we solve this challenge with a programmable photonic
crystal cavity array enabled by four key advances: (i) near-unity vertical
coupling to high-finesse microcavities through inverse design, (ii) scalable
fabrication by optimized, 300 mm full-wafer processing, (iii)
picometer-precision resonance alignment using automated, closed-loop
"holographic trimming", and (iv) out-of-plane cavity control via a high-speed
micro-LED array. Combining each, we demonstrate near-complete spatiotemporal
control of a 64-resonator, two-dimensional SLM with nanosecond- and
femtojoule-order switching. Simultaneously operating wavelength-scale modes
near the space- and time-bandwidth limits, this work opens a new regime of
programmability at the fundamental limits of multimode optical control.Comment: 25 pages, 20 figure
A full degree-of-freedom spatiotemporal light modulator
Harnessing the full complexity of optical fields requires complete control of all degrees-of-freedom within a region of space and time — an open goal for present-day spatial light modulators (SLMs), active metasurfaces, and optical phased arrays. Here, we solve this challenge with a programmable photonic crystal cavity array enabled by four key advances: (i) near-unity vertical coupling to high-finesse microcavities through inverse design, (ii) scalable fabrication by optimized, 300 mm full-wafer processing, (iii) picometer-precision resonance alignment using automated, closed-loop “holographic trimming”, and (iv) out-of-plane cavity control via a high-speed µLED array. Combining each, we demonstrate near-complete spatiotemporal control of a 64-resonator, two-dimensional SLM with nanosecond- and femtojoule-order switching. Simultaneously operating wavelength-scale modes near the space- and time-bandwidth limits, this work opens a new regime of programmability at the fundamental limits of multimode optical control
Determination of Thermal Damage Threshold in THz Photomixers Using Raman Spectroscopy
The increase of device lifetime and reliability of THz photomixers will play an essential role in their possible future application. Therefore, their optimal work conditions/operation range, i.e., the maximal incident optical power should be experimentally estimated. We fabricated and tested THz photomixer devices based on nitrogen-implanted GaAs integrated with a Bragg reflector. Raman spectroscopy was applied to investigate the material properties and to disclose any reversible or irreversible material changes. The results indicate that degradation effects in the photomixer structures/material could be avoided if the total optical power density does not exceed levels of about 0.7 mW/µm2 for 100 min of operation. Furthermore, the investigations performed during 1000 min of optical exposure on the photomixer devices’ central region comprising interdigitated metal-semiconductor-metal (MSM) structures suggest a reversible “curing” mechanism if the power density level of ~0.58 mW/µm2 is not exceeded. Long-term operation (up to 1000 h) reveals that the photomixer structures can withstand an average optical power density of up to ~0.4 mW/µm2 without degradation when biased at 10 V. Besides the decrease of the position of the A1g (LO) Raman mode from ~291 cm−1 down to ~288 cm−1 with increasing optical power density and operation time, broad Raman modes evolve at about 210 cm−1, which can be attributed to degradation effects in the active photomixer/MSM area. In addition, the performed carrier lifetime and photomixer experiments demonstrated that these structures generated continuous wave sub-THz radiation efficiently as long as their optimal work conditions/operation range were within the limits established by our Raman studies