Optical Phased Array: Scalable Beam Steering

Updated 31 August 2025

Optical phased arrays are integrated photonic devices that electronically control multiple coherent emitters to produce directed, steerable far-field beams.
They leverage advanced phase shifters—including III-V/Si hybrid, thermo-optic, and electro-optic technologies—to achieve sub-millisecond reconfigurability and high spatial resolution.
Scalable architectures using passive matrix addressing and non-uniform array spacing minimize crosstalk and grating lobes, optimizing performance for LiDAR, holography, and sensing applications.

An optical phased array (OPA) is a photonic device that enables solid-state, programmable beam steering by electronically or optically controlling the relative phases of multiple coherent emitters integrated on a chip. OPAs combine a tunable phase-shifter network and a spatially distributed antenna array to generate, with sub-millisecond reconfigurability, directed far-field radiation patterns. These systems underpin advanced technologies in LiDAR, free-space optical communication, sensing, and holography by providing integrated and scalable solutions to the classic problem of agile, non-mechanical beam steering with high spatial resolution and low optical loss.

1. Fundamental Principles of OPA Operation

An OPA consists of a network of coherent light sources (typically single-mode waveguides terminated in grating couplers or end-fire antennas) where each channel’s phase—and, in some architectures, amplitude—can be independently programmed. When illuminated by a coherent source, the far-field radiation is determined by the array factor, set by the position, amplitude, and phase of each emitter. The constructive and destructive interference among the emitters forms a steered, focused beam.

The phase profile across the array is controlled so that for a desired output angle $\psi$ : $\Delta\phi = k_0 d \sin\psi$ where $k_0 = 2\pi/\lambda$ (wavenumber), $d$ is the emitter pitch, and $\lambda$ the operating wavelength. For a 1D OPA, the far-field main lobe direction is thus determined by the imposed linear phase gradient. The full width at half maximum (FWHM) of the beam envelope follows: $\delta \psi \approx \frac{\lambda}{N d}$ with $N$ emitters. Extension to 2D OPAs proceeds via independent phase gradients along orthogonal axes.

2. Enabling Technologies: Phase Shifters and Integration Platforms

Advanced OPA performance depends fundamentally on the characteristics of the phase shifters and integration platform. Major categories include:

III-V/Si Hybrid Phase Shifters: Multiple quantum well (MQW) III–V/Si phase shifters have achieved $V_\pi = 0.45$ V, residual amplitude modulation (RAM) of 0.15 dB, and sub-nanowatt power consumption at $1550$ nm for a $2\pi$ shift. This low voltage/power, combined with large optical bandwidth ( $>1$ GHz across $200$ nm), directly enables high-density, large-scale OPAs due to simplified drive electronics and reduced thermal load (Xie et al., 2019).
Thermo-optic and Microresonator Phase Shifters: Ultralow power, compact microresonator phase shifters with $3\;\mu$ m radius and $2\pi$ phase shift ability have been demonstrated with average static power of $250\;\mu$ W and $50\;\mu$ W for dynamic beamforming in silicon photonic platforms, supporting high-speed operation (~330 kHz) (Chalupnik et al., 2023).
Electro-Optic Platforms: Thin-film lithium niobate (LN) enables high-speed ( $\sim10$ ns), low-power, and ultra-compact phase shifters via the strong Pockels effect, delivering sub-degree FWHM beams ( $0.99^\circ\times0.63^\circ$ ) and wide 2D steering ( $47^\circ\times9.36^\circ$ ) from aperture areas as small as $140\;\mu$ m $\times250\;\mu$ m. Optimization via PSO enables $20$ dB sidelobe suppression in non-uniform arrays (Li et al., 27 Jun 2025).
Passive Delay Lines: Multi-layer OPA architectures can exploit purely passive phase shifters via physical delay lines, achieving dual-axis beam steering solely by wavelength tuning, completely eliminating power consumption and complexity of active phase modulators (Kakdarvishi et al., 23 Nov 2024).

Integration platforms include silicon, silicon-rich silicon nitride, III-V/Si hybrids, and thin-film lithium niobate (see Table 1).

Platform	Phase Tuning Mechanism	Power/Performance
III-V/Si hybrid	MQW electro-absorption	$V_\pi=0.45$ V, <3 nW, 1.65 GHz BW (Xie et al., 2019)
Si photonics	Microheater, resonance	$250\;\mu$ W static, $50\;\mu$ W dynamic, 330 kHz (Chalupnik et al., 2023)
Thin-film LN	Pockels effect	$1.11$ nJ/ $\pi$ , $14.4$ ns, $0.99^\circ\times0.63^\circ$ (Li et al., 27 Jun 2025)
Si-rich SiN	Thermo-optic	$>115^\circ$ FoV, $0.11^\circ$ FWHM (Nejadriahi et al., 2022)
Passive Si stacks	Delay lines, wavelength	78 $^\circ$ vertical FoV, 140 $^\circ$ horiz. FoV (Kakdarvishi et al., 23 Nov 2024)

3. Advanced OPA Architectures and Scalability

Large-scale ( $>1000$ -channel) OPAs present challenges in crosstalk, grating lobes, and control complexity. Key architectural innovations include:

Near-Field Interference Control using Trapezoidal Slab Gratings: A 1000-channel OPA employing a half-wavelength pitch waveguide array and slab grating eliminates grating lobes over 180° FoV, achieving $0.07^\circ\times0.17^\circ$ spot with $-18.7$ dB side-lobe level. Channel crosstalk is minimized through careful routing and width segmentation (Liu et al., 27 Aug 2025).
Passive Matrix Addressing for Scaling: Instead of $N$ independent DAC channels, a passive matrix addressing scheme using $20$ row and $50$ column pulse-width modulation (PWM) signals enables arbitrary control of $1000$ phase shifters, greatly reducing packaging and electronic overhead (Liu et al., 27 Aug 2025).
Superlattice and Non-Uniform Array Spacing: Non-uniform superlattice arrays, optimized via PSO, can combine low crosstalk ( $<-20$ dB) and high angular resolution by apodizing the element spacing, suppressing sidelobes while narrowing the main lobe (Li et al., 27 Jun 2025).

4. Beam Steering Mechanisms and Performance Metrics

OPA beam steering is achieved by tuning the phase across array elements, via electrical (thermo-optic, electro-optic), optical (wavelength tuning), or passive delay (path length) methods.

Phase-Controlled Steering: Imposing a progressive phase delay, $\Delta \phi$ , across an array of emitters steers the main lobe to angle $\theta$ , given by $\sin(\theta) = (\lambda/2\pi d)\Delta\phi$ for linear arrays. Phase errors and amplitude imbalance must be minimized for high-fidelity steering.
Wavelength Tuning: For grating-based OPAs, steering angle also depends on wavelength through the grating equation, e.g., $\sin(\theta) \approx (\lambda - \Lambda n_\mathrm{eff})/n_\mathrm{eff}$ , with steering efficiency typically $0.13^\circ$ /nm (Xie et al., 2019).
Two-Dimensional and Dual Axis Steering: Dual-axis steering may be implemented by stacking (2D arrays), using wavelength/pitch controlled axes, or by serpentine/tiling architectures such as SOPA for raster scanning with minimal active control (Dostart et al., 2020).

Performance metrics typically reported:

Metric	Representative Value/Result	Implementation
Field of View (FoV)	$180^\circ$ , $47^\circ\times9.36^\circ$	1000-channel OPA (Liu et al., 27 Aug 2025), LN OPA (Li et al., 27 Jun 2025)
Side-Lobe Suppression	$-18.7$ dB, $20$ dB	1000-ch Si OPA (Liu et al., 27 Aug 2025), LN OPA (Li et al., 27 Jun 2025)
Beam Width (FWHM)	$0.07^\circ$ , $0.99^\circ$	1000-ch Si OPA, LN OPA
Power Consumption	$<3$ nW/channel, $1.11$ nJ/ $\pi$	III-V/Si (Xie et al., 2019), LNOI (Wang et al., 2023)

5. Challenges: Grating Lobes, Crosstalk, Calibration, and Control

Grating Lobes: Emitter spacing $> \lambda/2$ produces multiple high-intensity beams (ambiguous field of view). Vernier schemes suppress grating lobes by pairing transmit/receive arrays with mismatched pitches, ensuring only the main lobe aligns and unwanted lobes do not overlap (Dostart et al., 2020, Chen et al., 9 Jan 2024).
Crosstalk and Coupling: Dense arrays at half-wavelength pitch can suffer from high inter-channel coupling. Methods such as multi-width superlattice structures and optimized routing/geometries are used to suppress crosstalk to below $-20$ dB (Li et al., 27 Jun 2025, Liu et al., 27 Aug 2025).
Calibration: High-resolution OPAs with many phase shifters require robust calibration. Genetic algorithms and iterative optimization methods are employed to align phases for single-beam, low-divergence output (Guerber et al., 2023).
Control Scalability: Advanced row–column addressing and PWM pulse schemes enable FPGA-driven or ASIC-controlled adjustment of thousands of phase shifters with minimal I/O footprint (Liu et al., 27 Aug 2025).

6. Applications, Emerging Directions, and Outlook

LiDAR and Free-Space Optical Communication: OPA systems are central to integrated solid-state LiDAR. Ultra-wide FoV ( $>160^\circ$ ), high ranging accuracy ( $\sim$ 5.5 mm), and 4D (distance + velocity) imaging have been demonstrated in systems employing Vernier OPA transceivers and flat-top chained grating antennas (Chen et al., 9 Jan 2024).
Holography and Display: Silicon-based, nanoantenna OPAs, numerically optimized with Bragg reflectors, exhibit upward radiation efficiency as high as 90% and can synthesize arbitrary holographic images, supporting applications in AR/VR and next-generation displays (Farheen et al., 2023).
Biomedical Probing: SiN-based OPAs with built-in focusing can produce subcellular ( $1.4\;\mu$ m FWHM) beams for targeted neural excitation or imaging at visible wavelengths (522 nm) (Hosseini et al., 20 Jun 2024).
Non-redundant and Sparse Arrays: Implementation of non-redundant antenna layouts (Costas/Golomb rulers) enables $N^2$ scaling in resolvable beam points with only $N$ phase shifters, dramatically reducing system complexity (Fukui et al., 2021).

Future work involves scaling OPAs beyond $10^3$ channels (Liu et al., 27 Aug 2025), integrating multi-functional photonic circuits (sources, amplifiers, detectors), and improving calibration/self-correction schemes for robust, low-cost, and field-deployable systems.

7. Summary Table: Notable OPA Architectures and Metrics

Architecture	Key Metric(s)	Reference
III-V/Si MQW OPA	$V_\pi = 0.45$ V, RAM 0.15 dB, $>1$ GHz, $<3$ nW	(Xie et al., 2019)
1000-ch Si OPA + Matrix PWM	$180^\circ$ FoV, $0.07^\circ$ spot, $-18.7$ dB SLL	(Liu et al., 27 Aug 2025)
TFLN optimized via PSO	$0.99^\circ\times0.63^\circ$ beam, $47^\circ$ FOV, $20$ dB SLL	(Li et al., 27 Jun 2025)
Thin-film LN (LNOI) OPA	$62.2^\circ \times 8.8^\circ$ FOV, $0.33^\circ$ divergence (sparse)	(Wang et al., 2023)
SiN/SiO₂ multilayer end-fire	3D, $24.78^\circ$ /100 nm tuning, 82% emission	(Wu et al., 2019)
SiN OPA for retina excitation	$1.4\;\mu$ m FWHM, 520 nm, built-in focusing	(Hosseini et al., 20 Jun 2024)
Vernier OPA LiDAR	$160^\circ$ FoV, $<3$ dB variation, 5.5 mm ranging	(Chen et al., 9 Jan 2024)

All values and claims derive directly from the respective papers as indicated.

Optical phased arrays have evolved rapidly, moving from modest demonstration devices to scalable, dense, and efficient beam-steering systems, addressing the key requirements of FoV, resolution, power, and integration for emerging photonic and sensing applications. The engineering of phase shifters, array architecture, and control electronics remains an active area of research with continual improvements in scalability, performance, and manufacturability.