All-Optical Control & Multiplexed Readout

• All-optical control and multiplexed readout are techniques that manipulate and measure information using light alone, bypassing traditional electronic modulation.
• They employ versatile platforms like diffractive networks, graphene metamaterials, and fiber reconfigurators to achieve ultrafast, high-dimensional signal processing.
• These methods enable scalable, secure applications in quantum computing, telecommunications, and integrated photonic circuits by reducing latency and power consumption.

All-optical control and multiplexed readout encompass a range of photonic, quantum, and opto-electronic protocols in which the manipulation and measurement of information channels occur through light alone, without intermediary electronic modulation or detection. This approach features in quantum dot spin qubits, ultrafast metamaterials, diffractive diffractive neural networks, all-optical fibre switches, and cryogenic quantum technologies. Central to these advances are schemes for directly steering multiple photonic degrees of freedom (DoFs)—including amplitude, phase, polarization, spectral channel, spatial mode, and spin angular momentum—by entirely optical means, often with parallel (multiplexed) readout. The following sections review the underpinning architectures, physical control mechanisms, ultrafast and high-dimensional operation modes, multiplexed detection paradigms, experimental benchmarks, and prospects for scale-out into dense photonic or quantum networks.

1. Photonic System Architectures for All-Optical Control

Contemporary all-optical control schemes cover diverse platforms and device classes, each engineered to leverage photon–photon interactions or photonic structure for DoF steering.

• Reconfigurable Diffractive Networks: Layered phase-only diffractive structures, such as the mechanically reconfigurable R-D2NN, employ $K$ rotatable layers where each layer $l$ can be oriented in $4$ discrete angles ($\theta_l=0°,90°,180°,270°$). This encoding yields $N_\text{ops}=4^K$ independent linear transformations, specifically high-dimensional permutation operations between an input and output field-of-view. Changing the orientation of a subset of these $K$ layers physically remaps the permutation executed by the optical network (Ma et al., 4 Feb 2024).
• Ultrafast Metamaterial Modulators: Dual-stack graphene nanoribbon arrays, integrated within a dielectric host, provide independently addressable localized surface plasmon resonances ($\omega_x,\,\omega_y$) in two perpendicular orientations. Tuning is achieved via the Fermi level ($E_{F,1},\,E_{F,2}$) or via ultrafast optical pumping of electron temperatures ($T_1,\,T_2$), enabling selective amplitude, phase, and polarization modulation with sub-picosecond response (Matthaiakakis et al., 9 Jul 2025).
• All-Optical Fibre Reconfigurators: By counterpropagating a high-power control beam and a weak probe within few-mode or multicore fibers, a temporally and spatially tailored Kerr-nonlinear index grating enables dynamic mode conversion, core switching, and power splitting. The transformation on the probe is set by the instantaneous mode composition and power of the control beam; the theory is captured by a unitary $N$-mode transfer matrix $M=\exp(iAL)$ (Ji et al., 24 Sep 2024).
• Atomic and Solid-State Multilevel Systems: Lambda ($\Lambda$) and ladder schemes in multilevel atoms or quantum dots leverage near-degenerate trion transitions and large Zeeman or crystal-field splittings, allowing multiple pathways for optical initialization, state transfer, and readout by selective excitation of cycling transitions (Éthier-Majcher et al., 2015). In cavity-based systems, dual-wavelength multi-state switching is implemented by correlated four-wave-mixing processes (Sheng et al., 2013).
• Cryogenic Quantum Circuits—Optical I/O: Superconducting circuits and single-photon detectors remove traditional coaxial wiring by using optical fibers for both control and readout. Control signals are impressed on an optical carrier at room temperature and delivered via fiber to a cryogenic photodiode (for microwave regeneration) (Lecocq et al., 2020, Pan et al., 24 Dec 2025), while readout is implemented via amplitude- or frequency-multiplexed modulation of a cryogenic laser or Brillouin transduction and optically delivered to room-temperature detectors (Thiele et al., 21 Mar 2024, Pan et al., 24 Dec 2025).

2. Physical Mechanisms Enabling All-Optical Control

Distinct physical processes underpin the realization of functionally complete all-optical control:

• Diffractive Propagation and Multiplexed Layer Orientations: Sequential angular spectrum propagation through transmissive phase masks transforms input fields according to the calculated transmission matrices for each rotational layer configuration. The combination of phase profiles and rotation uniquely encodes permutations (Ma et al., 4 Feb 2024).
• Material Nonlinearities and Kerr Effects: In optical fibers, strong control beams induce transient nonlinear index gratings via the Kerr effect ($n=n_0+n_2I$). Cross-phase modulation and intermodal coupling steer probe energy among modes or cores, governed by a Hermitian coupling matrix $A$ (Ji et al., 24 Sep 2024).
• Plasmonic and Thermal-Carrier Modulation: In dual-stack graphene structures, localized plasmon modes in orthogonal nanoribbon arrays permit independent or joint amplitude and phase control of transmitted fields. Dynamic, broadband modulation results from the ultrafast thermalization of hot carriers following pulsed pump irradiation, modifying the Drude weight $D(T)$ and scattering rate $\Gamma(T)$ on femtosecond timescales (Matthaiakakis et al., 9 Jul 2025).
• Trion-Enabled Selection Rules & Lambda Systems: In quantum dot/nitrogen-pair systems, selective spin-qubit operations are orchestrated by addressing specific trion states (light- or heavy-hole) with laser fields of defined polarization and detuning, with initialization, control, and readout all performed optically via tailored selection rules (Éthier-Majcher et al., 2015).
• Brillouin, Piezo, and Optomechanical Transduction: Superconducting qubit signals are up-converted to optical via a traveling-wave Brillouin transducer—a piezoelectrically-induced traveling phonon mixes with a strong optical pump to generate an optical sideband, realizing broad (>200 MHz) microwave-to-optical conversion with sufficient efficiency for frequency-division multiplexed parallel qubit readout (Pan et al., 24 Dec 2025).

3. Multiplexed Readout Paradigms

All-optical schemes enable concurrent, distinct channel readout via channelization in spatial, spectral, modal, or amplitude domains:

• Spatial/Permutation Multiplexing: In diffractive networks, each physical orientation of the $K$-layer stack conjures a distinct permutation $P_i$ acting on input fields; a reverse operation $P_i^{-1}$ decrypts the output, while non-matching inverses yield apparent scrambling (speckle) (Ma et al., 4 Feb 2024).
• Spectral/Wavelength Channelization: Quantum and classical multi-channel readout is achieved by up-converting distinct frequency bands (e.g., qubit resonators at $\omega_{r,1}$, $\omega_{r,2}$) to unique optical sidebands via simultaneous optical pumping with multiple wavelengths (e.g., 1550.00 nm, 1560.95 nm), then using heterodyne or photodetection multiplexing (Pan et al., 24 Dec 2025, Lecocq et al., 2020). In atomic cavity devices, wavelength-separated outputs (e.g., 795 nm signal, 780 nm Stokes) are split via grating or dichroic optics, with measured inter-channel extinction $>25$ dB (Sheng et al., 2013).
• Polarization and Angular-Momentum Decomposition: Dual-stack metamaterials inherently support Stokes-parameter and handedness analysis, extractable by downstream polarization optics and modal sorters. Amplitude, ellipticity ($\eta$), optical rotation ($\alpha$), and spin purity are resolved in parallel (Matthaiakakis et al., 9 Jul 2025).
• Amplitude Multiplexing: In SNSPD arrays, simultaneous firing of $k$ nanowires produces pulses of amplitude $k V_1(t)$, propagating through the cryogenic amplifier and laser, and read out as quantized amplitude steps. Demultiplexing on the receiving photoreceiver enables quasi-photon-number resolution (Thiele et al., 21 Mar 2024).
• Mode/Spatial Multiplexing: Mode decomposition in reconfigurable fibers is realized by reconstructing the input amplitude and phase (e.g., $\Delta\phi_{in}$ with precision $\pm0.05$ rad) from the dependence of output modal weights on the control beam configuration (Ji et al., 24 Sep 2024).

4. Experimental Demonstrations and Performance Metrics

Representative platforms have achieved the following experimental benchmarks:

Platform/type	Multiplexing/Control Mechanism	Performance Highlights
Diffractive network (Ma et al., 4 Feb 2024)	K-layer orientation permutation	$4^K$ ops; NMSE $\approx 3\times 10^{-6}$; 20+ dB PSNR
Graphene meta-device (Matthaiakakis et al., 9 Jul 2025)	Fermi level, pump tuning	$\sim$200 fs rise, $>$100 GHz bandwidth, $\sim$2 pJ/switch
All-optical fiber (Ji et al., 24 Sep 2024)	Kerr CNLSE, control beam	Sub-nanosecond, $\geq$98% conversion, $<$1 dB IL
SNSPD array (Thiele et al., 21 Mar 2024)	Amplitude multiplexing, laser	$>79\%$ SDE, 3 ns rise time, multi-channel
Superconducting qubit (Pan et al., 24 Dec 2025Lecocq et al., 2020)	Brillouin, photodiode, optical I/O	$<$0.2% gate fidelity loss, $>40$ channels/fiber

• Thermal and Power Considerations: Optical fibers confer order-of-magnitude reductions in cryogenic heat load compared to coaxes—fibers: $\sim$1 $\mu$W/K, coaxes: $\sim$100 mW/K per line. All-optical bias/readout chains for SNSPDs operate at 2.6 mW passive dissipation (Thiele et al., 21 Mar 2024), while photonic qubit links have supported up to $10^6$ channels for 20 $\mu$W cooling power at typical 1% duty cycle (Lecocq et al., 2020).
• Crosstalk Rejection: Dichroic and grating-based separation achieves $>$30 dB (atomic cavity), heavy-hole trion frequency splitting is $\sim$150 GHz with %%%%45$M=\exp(iAL)$46%%%% cross-excitation probability (Éthier-Majcher et al., 2015).
• Timing Metrics: Metamaterial modulators exhibit modulation rise $\sim$200 fs (graphene), fiber switches achieve $<$1 ns operation (Kerr grating control), SNSPDs preserve nanosecond-level rise times (Thiele et al., 21 Mar 2024, Matthaiakakis et al., 9 Jul 2025, Ji et al., 24 Sep 2024).
• Scalability: R-D2NNs with $K=4$ demonstrate $256$ permutations in a monolithic device; frequency-multiplexed qubit readout supports 40–200 channels/fiber (Ma et al., 4 Feb 2024, Pan et al., 24 Dec 2025).

5. Applications and Integration Pathways

All-optical control and multiplexed readout underpin advanced photonic, quantum, and opto-electronic applications:

• Telecommunications and Switching: Rotation-multiplexed diffractive networks implement ultra-dense channel shuffling for demultiplexing and switching high-dimensional data streams without electronic drivers (Ma et al., 4 Feb 2024).
• Quantum Information Processing: All-optical I/O architectures directly support scaling to hundreds or thousands of superconducting qubits by decoupling I/O bandwidth from cryogenic constraints (Pan et al., 24 Dec 2025, Lecocq et al., 2020). Optical multiplexing enables parallel, crosstalk-suppressed readout of quantum states and classical detector arrays (Thiele et al., 21 Mar 2024).
• Encryption and Secure Transmission: Permutation operations and inverse decoding with physically unclonable configurations enable on-the-fly data encryption at the physical layer (diffractive, fiber, or trion-level) (Ma et al., 4 Feb 2024, Éthier-Majcher et al., 2015).
• Integrated Photonic Circuits: Ultrafast, low-energy optical control is compatible with planar, CMOS-ready architectures and on-chip waveguide networks. Fiber-based and metamaterial approaches feed directly into the design of scalable, reconfigurable photonic processors (Matthaiakakis et al., 9 Jul 2025, Ji et al., 24 Sep 2024).

6. Underlying Limitations and Future Perspectives

Current limitations and development trajectories include:

• Material Quality and Loss: High-quality, low-loss graphene ($\mu \geq 27000$ cm$^2$/Vs) and low-loss optical fibers are critical for maximizing Q and bandwidth (Matthaiakakis et al., 9 Jul 2025, Ji et al., 24 Sep 2024). Fabrication challenges and integration of cryogenic optoelectronics (e.g., low-jitter packaged lasers) remain nontrivial in SNSPD systems (Thiele et al., 21 Mar 2024).
• Signal-to-Noise and Crosstalk: Multiplexing amplitude levels is limited by system SNR, with $\mathcal{O}(10)$ channels achievable per fiber/line with typical noise margins (Thiele et al., 21 Mar 2024).
• Energy-per-Bit and Speed: Sub-picosecond switching and $<$1 pJ/bit operation are attainable in advanced nonlinear and metamaterial platforms, but require further optimization of cooling and heat dissipation strategies.
• Scalability: The matrix-based formalism ($M=\exp(iA L)$) for fiber and waveguide meshes naturally scales to large $N$, suggesting straightforward extension to integrated, chalcogenide, or silicon-photonic networks with femtosecond switching (Ji et al., 24 Sep 2024).
• Hybridization: Combining all-optical reconfiguration with electronic or memory elements and leveraging on-chip integration for simultaneous spatial, modal, and spectral multiplexing remain core areas for ongoing research and development.

The intersection of all-optical control and multiplexed readout thus represents a convergent path for high-dimensional, scalable, and low-latency manipulation of photonic and quantum information resources across multiple technology domains.