# Integrated Optical Phased Arrays for Beam Forming and Steering
## 7 Performances
### Power Consumption  
Typically, 1D long-WGA-based OPAs and 2D WGA-based OPAs can be used to achieve 2D beam forming and steering. Expensive precisely tunable lasers are necessary for 1D long-WGA-based OPAs. Grating-dispersion-based OPAs with compromised spectral purities, multi-beam projection capabilities [45] have wavelength-dependent components such as input grating couplers and power splitters [64]. 2D WGA-based OPAs are superior to 1D long-WGA-based OPAs without these compromises. However, a challenge for large-scale 2D OPAs is high power consumption [75]. Large-scale OPAs are highly needed for high-performance applications. Large-scale antennas are crucial to increase the aperture sizes of OPAs. Total power consumption of phase shifters and corresponding driver circuits are usually proportional to the number of antennas [45]. High-performance beam steering is hindered by thermal managements and power consumption [15]. Typically, a power-hungry TO phase shifter of a long-range (over 100 m) OPA application (like LiDAR) consumes a power of tens of milliwatts. Overall power consumption of hundreds of watts is needed for an OPA with thousands of power-hungry phase shifters [103]. However, due to the power capacity of demonstrated OPAs, large-scale OPAs are limited by the unaffordable power level [103]. The overwhelming power consumption of OPAs should be decreased. The simplest way to lower the power consumption of large-scale OPAs is to decrease the number of phase shifters [74; 113]. Additionally, the power consumption can be decreased by adoptions of EO phase shifters [11; 42] and multi-pass structures [15; 103]. Furthermore, a high-swing pulse-width modulation driving circuit can also be used to reduce the power consumption of OPAs [45; 143]. For a 2D \(N\times N\) OPA, the total power consumption can be significantly reduced by decreasing the number of phase shifters to only 2\(N\)[74]. As presented in Figure 14a, an 8 \(\times\) 8 OPA was implemented using 16 phase shifters placed outside of the array aperture [74]. Compared with a typical OPA with the same angular range and beamwidth, a multi-beam steering OPA contained fewer phase shifters [113]. Low power consumption can be achieved by the multi-beam steering OPAs. OPAs require densely integrated high-performance power-efficient phase shifters [126]. The maximum static power consumption of an EO phase shifter of OPAs for long-range LiDAR and free-space communications was only 2 uW for a 2\(\pi\) phase shift. It was orders of magnitude less than TO shifters [11]. A III-V/Si heterogeneous phase shifter shown in Figure 14b provided a greatly low static power consumption (<3 nW) and a high speed (>1 GHz) [126]. Another heterogeneous phase-shifter-based OPA utilizing III-V multiple-quantum-well structures achieved a low operating voltage of 0.45 V and low power consumption of less than 3 nW for a 2\(\pi\) phase shift [42]. A multi-pass photonic structure shown in Figure 14c relied on spatial mode multiplexing to circulate light multiple times through a phase shifter [103]. A conversion to a different orthogonal spatial mode occurred each time when light was recirculated, eliminating unwanted interference, and maintaining broadband operation. By embedding a TO phase shifter in the multi-pass structure, a 2D 512-element OPA based on this structure achieved an FOV of 70\({}^{\circ}\)\(\times\) 6\({}^{\circ}\) and consumed power of 1.9 W. The power consumption of the TO phase shifter was 1.7 mW/\(\pi\)[103]. TO phase shifters of a sparse OPA system shown in Figure 14d were electrically routed in a row-column fashion to reduce the number of electrical drivers. A custom pulse-width-modulated CMOS electronic chip reduced the power consumption of drivers [143]. By leveraging recent advances in the monolithic integration of photonic and electronic circuits, a large-scale coherent detector array with 512 pixels achieved an accuracy of 3.1 mm at 75 m when using only 4 mW of radiated optical power.