The name is absent

59

becomes more challenging because a single chip surface would not be able to provide
enough space for both the pixels and their connecting wires to their respective schot-
tky pads. Moreover, for such a large number of pixels, the current packaging of the
SLM with many ribbon cables will be too bulky.

One solution is to design a THz SLM to be used for a reflection, instead of trans-
mission, setup. The resulting chip will have multiple layers with the connecting wires
beneath the pixels. Each pixel can be as small as the size of a single split-ring res-
onator, but cannot be smaller than the diffraction limit at the operating frequency.
Not only will this design pack more pixels into a single chip, but also will allow more
compact circuit and packaging similar to Texas Instrument’s digital micromirror de-
vice (DMD) [78].

Another drawback of the current metamaterial-based THz SLM is its limited
modulation depth, and its narrowband operation. The modulation depth at each
pixel is constrained by the depletion between the split gap of the resonator elements
and the n-doped substrate. The highest modulation depth demonstrated is 55% at
0.81 THz [12]. The modulation occurs in a relatively narrow frequency range around
the resonant frequency, making the device best applicable to continuous-wave THz
systems. A more desirable SLM would be a DMD with mirrors optimized for a wide
range of THz frequencies. This solution can provide broadband modulation at 100%
depth, but loses the ability to tune the modulation depth at each pixel which is
essential for applications such as THz beam steering and beam focusing.

6.2.2 Terahertz source power and receiver dynamic range

The performance of the single-pixel CS THz imager relies on its ability to detect a
small change in the overall THz signal caused by the modulation at a single SLM

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