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5.1 (a) Each single pixel on the THz SLM contains a 4 × 4 mm2, ~2500
element array of metamaterial SRRs. These elements are connected
together with metal wires to serve as a metallic (Schottky) gate. An
external voltage bias controls the substrate charge carrier density
near the split gaps, tuning the strength of the resonance, (b)
Diagram of the substrate and the depletion region near the split gap
of a single SRR, where the gray scale indicates the free charge carrier
density, (c) The THz SLM (not drawn to scale) is a 4 × 4 array of
individual pixels in (a). Each pixel is independently controlled by an
external voltage between the 1 × 1 mm2 Schottky electric pad and
the ohmic contact............................. 43
5.2 (a) THz amplitude transmission spectra for one of the 16 pixels of the
THz SLM without voltage bias (dashed) and with 14V bias (solid). A
large modulation depth is observed at 0.36 THz, the design resonant
frequency, (b) A transmission image of the 4-by-4 array at 0.36 THz,
with two pixels turned off (biased), and the rest turned on (zero bias). 44
5.3 Noise-to-signal power ratio (dashed) and noise-plus-crosstalk-to-signal
power ratio (dotted) across frequency, from which we obtain the
crosstalk level (solid). Above 0.33 THz (in the shaded area), crosstalk
is buried in noise, and is therefore unmeasurable. These ratios are
calculated from their corresponding transmission images of the 4-by-4
array of the THz SLM at every frequency. In the inset image at 0.36
THz, two pixels are under a square voltage bias and the rest are
unbiased. A THz modulation (differential) signal is measured at each
pixel using the lock-in amplifier referenced to the square voltage. ... 46