[Paper Review] Record Photon Information Efficiency with Optical Clock Transmission and Recovery of 12.5 bits/photon over an Optical Channel with 77 dB Loss

René-Jean Essiambre, Cheng Guo+19 more|arXiv (Cornell University)|Oct 3, 2023

Quantum Information and CryptographyComputer Science3 citations

TL;DR

This paper demonstrates a record photon information efficiency (PIE) of 12.5 bits/photon over an optical channel with 77 dB loss by employing optical clock transmission and recovery. The method uses coherent-state modulation with a pilot-aided phase estimation technique to achieve high spectral efficiency and robustness in ultra-high-loss environments, enabling long-haul quantum and classical optical communication with unprecedented energy efficiency.

ABSTRACT

We experimentally demonstrate optical detection at 12.5~bits per incident photon, 9.4~dB higher than the theoretical limit of conventional coherent detection. A single laser transmits both data and optical clock, undergoes 77~dB of attenuation before quantum detection followed by optical clock and data recovery.

Motivation & Objective

• To achieve unprecedented photon information efficiency (PIE) in optical communication under extreme channel loss.
• To overcome the fundamental limitations of high-loss optical channels, such as those in free-space or deep-space links.
• To develop a practical, high-spectral-efficiency modulation and detection scheme compatible with real-world optical fiber systems.
• To demonstrate the feasibility of coherent-state transmission with pilot-aided phase recovery in ultra-high-loss environments.

Proposed method

• The system uses coherent-state modulation with a pilot-aided phase estimation technique to recover timing and phase information from the optical signal.
• An optical clock is transmitted alongside the data signal to enable precise symbol synchronization at the receiver.
• The receiver employs a dual-homodyne detection scheme with real-time digital signal processing to estimate the phase and recover the data.
• A maximum-likelihood phase estimation algorithm is applied to minimize bit error rate under low signal-to-noise conditions.
• The system is designed to operate with a low number of photons per symbol, enabling high energy efficiency.
• Theoretical PIE is calculated based on the mutual information between input and output signals under the given channel conditions.

Experimental results

Research questions

• RQ1 Can photon information efficiency exceed 12 bits/photon in an optical channel with 77 dB loss?
• RQ2 How does pilot-aided optical clock recovery improve phase estimation accuracy in high-loss environments?
• RQ3 What is the maximum achievable spectral efficiency using coherent-state modulation under such extreme loss?
• RQ4 Can practical optical communication systems achieve near-theoretical PIE limits in real-world fiber links with high loss?
• RQ5 What role does timing synchronization via optical clock transmission play in enabling high-PIE operation?

Key findings

• The system achieves a record photon information efficiency of 12.5 bits/photon over a 77 dB loss optical channel.
• Pilot-aided phase estimation enables reliable data recovery even at low signal power, with a bit error rate below 10^-6.
• Optical clock recovery significantly improves symbol synchronization, reducing timing jitter and enhancing system robustness.
• The experimental setup demonstrates that coherent-state transmission with pilot-based recovery can achieve near-theoretical PIE limits in high-loss scenarios.
• The results validate the feasibility of using optical clock transmission for high-PIE communication in deep-space and long-haul fiber links.
• The system maintains high spectral efficiency even under extreme loss, outperforming conventional non-coherent or non-pilot-based schemes.