Automated control algorithms for silicon photonic polarization receiver

Adaptive polarization control for a fiber system based on the optimized AdamSPGD algorithm

In this work, an adaptive control scheme based on the optimized AdamSPGD algorithm is proposed to maintain the stable state of polarization (SOP) of the optical signal in a fiber system. The search space can be reduced by half with the guidance of the physical equation of optical intensity that passes through a liner polarizer, leading to an increase in the speed and stability. Moreover, the robustness is guaranteed by the adoption of AdamSPGD as the optimization object. In the experiment, the input optical signals with random SOPs are successfully controlled to a stable output SOP. Compared to the original algorithm, the speed is increased by 44.73%, and the standard deviation of the required number of iterations is reduced by 21.27%.

High-speed polarization tracking using thin film lithium niobate integrated dynamic polarization controller

Dynamic polarization controllers (DPCs) are essential devices in various optical applications. We develop a thin film lithium niobate (TFLN) integrated DPC driven by the real-time implemented Jacobian control algorithm for fast polarization tracking. Experimental results demonstrate a high polarization tracking speed of 100 krad/s when targeting a specific linear state of polarization, with a low control loop delay of 420 ns, half-wave control voltages of 2.75 V, and a fast polarization restoring time of 1.6 us. Compared to previously reported integrated DPCs, the TFLN-based DPC achieves significantly higher tracking speed and lower loop delay. The results highlight the effectiveness of the Jacobian method and the outstanding performance of TFLN-based DPCs. The study opens up possibilities for further advancements in DPC solutions using TFLN technology.

Active polarization controller based on micro-ring resonators

On-chip polarization handling is of great significance for optical interconnects to overcome polarization sensitivity. In this Letter, we propose and experimentally demonstrate a novel, to the best of our knowledge, on-chip polarization controller (PC) on a 220 nm silicon-on-insulator (SOI) platform. It is the first demonstration of a PC based on micro-ring resonators. Any input polarization states can be actively converted to the standard transverse-electric (TE) mode under the phase manipulation. Experimental results show that the insertion loss is less than 0.8 dB and the polarization dependent loss (PDL) is around 0.5 dB. The proposed device also exhibits excellent performances in wavelength tunability over the C band and 35 Gbps data transmission.

Online polarization error suppressed optical vector analyzer based on Bayesian optimization

An optical vector analyzer (OVA) based on orthogonal polarization interrogation and polarization diversity detection is widely used to measure an optical device's loss, delay, or polarization-dependent features. Polarization misalignment is the OVA's primary error source. Conventional offline polarization alignment using a calibrator greatly reduces the measurement reliability and efficiency. In this Letter, we propose an online polarization error suppression method using Bayesian optimization. Our measurement results are verified by a commercial OVA instrument that uses the offline alignment method. The OVA featuring online error suppression will be widely used in the production of optical devices, not just in the laboratory.

Jacobian methods for dynamic polarization control in optical applications

Dynamic polarization control (DPC) is beneficial for many optical applications. It is often realized via tunable waveplates to perform automatic polarization tracking and manipulation. Efficient algorithms are essential to realize an endless polarization control process at high speed. However, the standard gradient-based algorithm is not well analyzed. Here, we model the DPC with a Jacobian-based control theory framework that finds a lot in common with robot kinematics. We then give a detailed analysis of the condition of the Stokes vector gradient as a Jacobian matrix. We identify the multi-stage DPC as a redundant system enabling control algorithms with null-space operations. An efficient, reset-free algorithm can be found. We anticipate more customized DPC algorithms to follow the same framework in various optical systems.

Reset-free adaptive polarization controller on a silicon-photonic platform for a self-coherent communication system

To give full play to the advantages of the self-coherent systems in the data center scene, the problem of the random walk of the polarization state of the delivered local oscillator must be solved. An adaptive polarization controller (APC) is an effective solution, with the characteristics of easy integration, low complexity, being reset-free, and so on. In this work, we experimentally demonstrated an endlessly APC based on a Mach-Zehnder interferometer on a silicon-photonic integrated circuit. The APC is thermally tuned with only two control electrodes. It endlessly stabilizes the arbitrary state of polarization (SOP) of the light to a state of equal power of the two orthogonal polarizations (X and Y). A polarization tracking speed of up to 800 rad/s is achieved.

Circuit-level convergence of electronics and photonics: basic concepts and recent advances

Integrated photonics is widely regarded as an important post-Moore's law research direction. However, it suffers from intrinsic limitations, such as lack of control and satisfactory photonic memory, that cannot be solved in the optical domain and must be combined with electronics for practical use. Inevitably, electronics and photonics will converge. The photonic fabrication and integration technology is gradually maturing and electronics-photonics convergence (EPC) is experiencing a transition from device integration to circuit design. We derive a conceptual framework consisting of regulator, oscillator, and memory for scalable integrated circuits based on the fundamental concepts of purposeful behavior in cybernetics, entropy in information theory, and symmetry breaking in physics. Leveraging this framework and emulating the successes experienced by electronic integrated circuits, we identify the key building blocks for the integrated circuits for EPC and review the recent advances.

High-performance polarization management devices based on thin-film lithium niobate

High-speed polarization management is highly desirable for many applications, such as remote sensing, telecommunication, and medical diagnosis. However, most of the approaches for polarization management rely on bulky optical components that are slow to respond, cumbersome to use, and sometimes with high drive voltages. Here, we overcome these limitations by harnessing photonic integrated circuits based on thin-film lithium niobate platform. We successfully realize a portfolio of thin-film lithium niobate devices for essential polarization management functionalities, including arbitrary polarization generation, fast polarization measurement, polarization scrambling, and automatic polarization control. The present devices feature ultra-fast control speeds, low drive voltages, low optical losses and compact footprints. Using these devices, we achieve high fidelity polarization generation with a polarization extinction ratio up to 41.9 dB and fast polarization scrambling with a scrambling rate up to 65 Mrad s^-1, both of which are best results in integrated optics. We also demonstrate the endless polarization state tracking operation in our devices. The demonstrated devices unlock a drastically new level of performance and scales in polarization management devices, leading to a paradigm shift in polarization management.