Simultaneously Improving Power Consumption and Linearity of Digital-to-Optical Converters (DOCs) for Energy-Efficient Optical Data Transmission

This paper presents a novel design for Digital-to-Optical Converters (DOCs) aimed at improving both the power efficiency and linearity of optical data transmission. The work focuses on optimizing the performance of DOCs for high-frequency, high-density optical communication systems, particularly for applications such as 5G and beyond.

Key Contributions:

1. Improved Linearity with ESL-DOCs*:

• The paper introduces ESL-DOCs*, a design technique that enables DOCs to achieve near-zero Integral Non-Linearity (INL) and Differential Non-Linearity (DNL) while using only log2(N) inputs for Pulse-Amplitude Modulation (PAM-N). This reduces the number of inputs compared to previous designs (which required N-1 inputs), lowering power consumption significantly by reducing the number of electronic drivers.

• The segment lengths for the electrodes are optimized through inverse design techniques, achieving superior linearity compared to previous designs.

2. Power Consumption Reduction:

• The ESL-DOC* reduces the power consumption of electronic drivers by a factor of 3.82× for PAM-16 when compared to thermometer-coded Engineered Segment Length (ESL) DOCs. This is achieved by reducing the number of drivers required from N-1 to log2(N), thus enhancing energy efficiency.

3. Fabrication and Experimental Results:

• ESL-DOCs* were fabricated using Lithium Niobate (TFLN), implementing PAM-16. The fabricated devices demonstrated significant improvements in INL and DNL, with 3.7× better INL and 2.1× better DNL compared to previous binary DOC designs.

• Experimental measurements showed a Root-Mean-Squared (RMS) INL of 0.28 Least Significant Bits (LSBs) and RMS DNL of 0.20 LSBs, confirming the high linearity and reduced non-linearity of the ESL*-DOC.

4. Comparison to Other MZM Architectures:

• No need for a Digital-to-Analog Converter (DAC),

• Near-zero INL and DNL,

• Fewer digital inputs (log2(N)).

• The ESL-DOC* was compared to traditional Binary MZM and Thermometer ESL-DOCs. It was found to simultaneously achieve:

• The comparison shows that ESL*-DOCs offer better linearity, fewer required inputs, and lower power consumption.

5. Measurement Setup and Results:

• The experimental setup included edge-coupled fiber arrays and a photodiode to measure optical power, demonstrating the effectiveness of the ESL*-DOC design in real-world conditions. Eye diagrams and INL/DNL measurements confirmed the performance improvements.

• Measured results showed that the ESL*-DOC offers superior optical power transmission characteristics, with consistent output across different input signals, further supporting its practicality for high-frequency communication.

Conclusion:
This work introduces ESL*-DOCs, an energy-efficient and high-performance solution for digital-to-optical conversion in high-speed optical communication systems. By optimizing the segment lengths of the electrodes and reducing the number of required digital inputs, ESL*-DOCs achieve improved linearity and significant power savings. The results indicate that ESL*-DOCs offer a promising approach for future optical data transmission, addressing key challenges related to energy efficiency, bandwidth, and system complexity in next-generation wireless communication.