Hamamatsu Photonics continuously works on ways to reduce phase noise in its liquid crystal on silicon spatial light modulators, which are crucial for applications like quantum computing, quantum key distribution, and high-precision manufacturing.
Hamamatsu's latest range of LCOS-SLMs has a low-noise mode that limits phase ripples to less than 4 mrad (peak-to-peak), which is two orders of magnitude lower than some of the LCOS-SLMs on the market today.
Origin of Jitter and Phase Retardation in LCOS-SLMs
In LCOS-SLMs, phase retardation at a specific pixel is controlled by the orientation of liquid crystal (LC) molecules, which is determined by the drive voltage provided to the electrodes in that pixel.
Hamamatsu LCOS-SLMs are driven by an AC voltage whose magnitude at a pixel is proportional to the desired phase retardation. The drive voltage frequency is faster than the LC molecules' response time to the driving electric field.
As a result, the LC molecules twitch briefly during each cycle of the AC drive voltage, but their average orientation remains constant. However, the LC molecules' twitching causes minor shifts or oscillations in the beam pattern, which are undesirable in some applications.
In contrast, some manufacturers utilize pulse-width modulation (PWM) to power LC molecules.1 In PWM, the magnitude and frequency of the drive voltage stay constant, while the duty cycle varies depending on the desired phase retardation. This mechanism causes LC molecules to twitch, resulting in jitters in the beam pattern.
Hamamatsu Photonics' X15223 Series Cooled LCOS-SLM. Image Credit: Hamamatsu Photonics Europe
Significance of Jitter in Certain Beam-Shaping Applications
High Precision Manufacturing
Laser material processing applications, such as marking and high-precision manufacturing, can benefit from LCOS-SLM-based beam-shaping technologies that increase throughput. However, jitter in the beam pattern can sometimes have an unfavorable effect on output quality.
Quantum Computing and Quantum Key Distribution
In atom trap-based quantum computing, LCOS-SLMs generate laser spot arrays that serve as potential wells for trapping atoms. Jitter can influence the potential wells' steepness and positioning precision, leading to unstable atom traps, erroneous quantum state readouts, and limited scalability for the quantum computer.
Similarly, in quantum key distribution (QKD), LCOS-SLMs encode quantum keys as beam patterns, which are then sent via optical networks. Phase noise directly impacts the integrity of quantum keys, the distance they can be transferred, and their susceptibility to interception by other parties.
Certain QKD techniques employ interference between keys and jitter, impairing the reading of interference patterns. Finally, phase noise raises the burden of error correction techniques, reducing overall efficiency.
Low Noise Mode of LCOS-SLMs from Hamamatsu
Hamamatsu's LCOS-SLMs are well-known for their low-phase noise caused by LC molecules twitching. Even at the highest drive voltage, peak-to-peak phase noise is as low as 8 mrad (Figure 1).
Hamamatsu engineers have created a low noise mode to further reduce phase noise. As a result, the variation in phase retardation is reduced by 60% (Figure 1), and the peak-to-peak value of phase fluctuations is just a few mrad, which is extraordinarily low for LCOS-SLMs.
The low-noise mode of Hamamatsu's LCOS-SLMs efficiently tackles these issues while needing no changes to the product integration. However, one disadvantage to the low-noise mode is that LC molecules respond relatively slowly.
In situations where beam shaping accuracy and stability are more important than fast refresh rates, Hamamatsu's LCOS-SLMs' revolutionary low-phase noise feature is appealing.
Peak-to-peak phase noise due to fluctuations of LC molecules in normal and low noise modes of Hamamatsu’s LCOS-SLMs. Image Credit: Hamamatsu Photonics Europe
The quest for stability in optical applications is more than a technological problem. Precision and accuracy are critical to industry success.
The low-noise mode in LCOS-SLMs is intended to help engineers achieve accuracy, accelerating the development of applications such as high-precision manufacturing, quantum computing, and communications. Every detail in our intimately connected world is critical to a future defined by precision and dependability.
References
- Collings, N., et al. (2011). The Applications and Technology of Phase-Only Liquid Crystal on Silicon Devices. Journal of Display Technology, 7(3), pp.112–119. https://doi.org/10.1109/jdt.2010.2049337.
This information has been sourced, reviewed and adapted from materials provided by Hamamatsu Photonics Europe.
For more information on this source, please visit Hamamatsu Photonics Europe.