Pilot Tone Modulation involves adding a slight low-frequency sine or cosine modulation to each wavelength in wavelength division multiplexing systems to encode signals. Different wavelengths use different modulation frequencies to mark their signals. When these low-frequency signals are added to optical wavelengths, they create modulation amplitudes at the peaks of the optical signal, known as Pilot Tone Modulation signals.

These signals are transmitted alongside original signals through optical networks, with their frequencies within the bandwidth of the message channel. To prevent interference with data signals, their frequencies must be lower than the minimum cutoff frequency of the data channel. However, to avoid affecting the dynamic gain characteristics of EDFA (Erbium-Doped Fiber Amplifier), their frequencies cannot be too low. Therefore, Pilot Tone Modulation signals typically operate between 10 kHz and 1 MHz, categorized as low-frequency micro-disturbance signals. These signals are transmitted using Manchester coding, which ensures synchronization between transmission and reception. Optical modules require an integrated Manchester codec to generate and decode Manchester code, distinguishing Pilot Tone Modulation optical modules from general optical modules (Figure 1 illustrates the built-in Manchester codec in the optical module).

Figure 1: Manchester Codec

Nuvoton Technology has unveiled the pioneering Nuvoton M031G series, the world's first hardware Pilot Tone Modulation MCU. This series integrates a dedicated hardware Manchester codec, enabling rapid modulation and demodulation of Manchester code tailored specifically for Pilot Tone Modulation signals. It supports amplitude modulation (AM) and frequency modulation (FM) modes, catering comprehensively to the requirements of telecommunications operators and equipment manufacturers.

Figure 2: Pilot Tone Modulation Module MCU

The NuMicro M031G series integrates a hardware Manchester codec with CRC support for modulating and demodulating low-frequency micro-disturbance signals. It also includes a DAC supporting automatic data generation, which can produce sine waves at 500 kHz for frequency modulation (Figure 3 illustrates sine wave Modulation signal generation). Testing has demonstrated the DAC's capability to generate smooth sine wave Modulation reliably signals at 500 kHz (Figure 4 shows the measured MANCH_TX output from DAC0).

Figure 3: Sine Wave Modulation Signal Generation

Figure 4: MANCH_TX Output Measured from DAC0

NuMicro M031G Series Features:

• Hardware Manchester codec (M031G series): Used for modulating and demodulating low-frequency micro-disturbance signals.
• DAC with automatic data generation capability (M031G series): Can generate 32-point smooth sine waves at 500 kHz for Pilot Tone Modulation applications.
• Built-in temperature sensor: Accuracy of ±1.6°C within the range of 0°C to 70°C; accuracy of ±2°C within the range of -40°C to 105°C.
• Compact package: QFN24 3x3 mm; QFN33 4x4 mm.
• I²C: Supports 1 MHz slave mode without holding SCL, with a pre-burned I²C bootloader.

The NuMicro M029G/M030G/M031G series provides a comprehensive solution for optical module applications, with the M031G series being the world's first hardware Pilot Tone Modulation optical module. Thus, it satisfies the requirements for both general optical module and Pilot Tone Modulation module applications.