# Integrated Optical Phased Arrays for Beam Forming and Steering
## 5 Material Platforms
### Si Photonics Platforms
#### 5.1.1 OPAs Based on the Si Platform
As the electronic wirings for controlled phase shifters occupy an increasingly large area with the growing number of elements on OPAs, it is quite challenging to realize large-scale OPAs integrated with electronic controls on a single chip. Monolithically integrated OPAs provide a reliable and low-cost solution with densely distributed circuits and reduced footprints [16; 86; 122]. The first monolithically integrated OPA transceiver with individual amplitude and phase control is presented in Figure 10b [86]. This 8 \(\times\) 8 OPA chip included TO phase shifters and attenuators, WGAs, and control electronics, and there were in total more than 300 optical components and over 74,000 electrical components. The OPA enabled a narrow FOV of 1.6\({}^{\circ}\)\(\times\) 1.6\({}^{\circ}\) and a sidelobe suppression ratio of 11 dB [86]. Another monolithically integrated OPA chip consisted of 1024 uniformly spaced WGAs, 1192 phase shifters, and 168 attenuators. The OPA with an aperture size of 5.7 \(\times\) 6.4 mm\({}^{2}\) presented a  
Figure 10: Typical OPA structures based on the Si platform. (**a**) The structure of an OPA chip with a plateau envelope. Reprinted with permission from [59] © The Optical Society. (**b**) An 8 \(\times\) 8 monolithic OPA. Reprinted with permission from [86] © The Optical Society. (**c**) A 1D aperiodic high-resolution aliasing-free OPA. Reprinted with permission from [12] © The Optical Society. (**d**) A 2D aperiodic Si-based OPA with independently tunable phase shifters. Reprinted with permission from [87] © The Optical Society. directional beam with a narrow beamwidth of 0.03\({}^{\circ}\), which can be steered in a wide FOV of 45\({}^{\circ}\)[16]. Typically, well-designed aperiodic OPAs have wide FOVs. The aperiodic large-scale OPA presented in Figure 10c enabled a dramatical 2D beam steering capability of having more than 60,000 resolvable points within an FOV of 80\({}^{\circ}\)\(\times\) 17\({}^{\circ}\), enabled by the great beam directionality with a narrow beamwidth of 0.14\({}^{\circ}\)\(\times\) 0.14\({}^{\circ}\)[12]. The 2D 8 \(\times\) 8 aperiodic Si OPA shown in Figure 10d consisted of individually controlled phase shifters, allowing both amplitude and phase engineering of the emitted optical beam from the OPA. The demonstrated OPA also enabled sidelobe suppression [87]. A 128-element aperiodic Si OPA based on a two-chip solution enabled a greatly high FOV-to-beamwidth ratio of 16\({}^{\circ}\)/0.8\({}^{\circ}\)[45]. For the OPAs based on directional couplers to distribute input power into each output channels, the minimal spacing between adjacent antennas is limited by the size of directional couplers, which might result in a relatively narrow FOV of the OPA. In addition, an OPA using directional couplers generally takes a large overall size. A novel serial WGA-based Si OPA significantly reduced the overall chip size and increased power efficiency while maintaining comparable far-field performance [123]. In addition to the above-mentioned OPA transmitters, integrated OPA receivers can also be demonstrated on the Si platform. The first 1D Si OPA receiver with an aperture size of 96 \(\times\) 50 \(\upmu\)m\({}^{2}\) presented an FOV of 30\({}^{\circ}\) and a beamwidth of 0.74\({}^{\circ}\)[69]. The first 2D OPA receiver on the Si platform was shown with an FOV of 8\({}^{\circ}\)\(\times\) 8\({}^{\circ}\) and a beamwidth of 0.75\({}^{\circ}\)\(\times\) 0.75\({}^{\circ}\)[43]. A wide variety of novel integrated OPAs have also been implemented on the Si photonics platform. Some examples are shown as follows. A half-wavelength-pitch EF OPA with an FOV of 180\({}^{\circ}\) was demonstrated by minimizing the mode overlaps of waveguides in the phase space [94]. A sparse aperiodic OPA based on WGAs provided beam steering in the full visible space while preserving a narrow beamwidth of \(\sim\)0.1\({}^{\circ}\) and a high SMSR of 13.5 dB [114].