OTDM vs OWDM: Understanding the Differences

This page explores the differences between OTDM (Optical Time Division Multiplexing) and OWDM (Optical Wavelength Division Multiplexing) optical multi-channel systems. We’ll delve into their principles, advantages, and disadvantages.

Both OTDM and OWDM serve as optical multi-channel systems, multiplexing optical signals either in the time domain or the wavelength domain.

• OTDM: Achieved in the time domain using ultra-short pulse transmission.
• OWDM: Achieved in the wavelength domain using a large number of carrier wavelengths within the same fiber.

Refer to this tutorial on fiber optical communication for a more in-depth look.

OTDM: Optical Time Division Multiplexing

In OTDM, different data channels occupy distinct time slots, denoted as ‘T’, without overlapping. These slots are fully overlapped in the optical frequency domain. This time-domain separation ensures no crosstalk between channels.

OWDM: Optical Wavelength Division Multiplexing

In OWDM, data channels are separated in the frequency domain. They are placed in non-overlapping frequency bands (Bch). All channels can fully overlap in the time domain without any crosstalk.

Check out this tutorial on DWDM system basics for more information.

OTDM vs OWDM: Key Differences

Common Optical Components

Both OTDM and OWDM systems utilize the following components:

• Optical Modulator and Demodulator
• Optical Multiplexer and De-Multiplexer
• Laser Pulse generator at the transmit end
• Photodetector at the receive end
• Optical Amplifier to enhance signal strength
• Clock extraction at the receiver for information recovery
• Wavelength filters to extract desired wavelengths

Refer to these links for basics on various Optical Components.

Advantages and Disadvantages of OWDM

Advantages:

• Relatively low data rate per optical channel with modest requirements for dispersion and electronic speed.
• Data format and timing of the channels are independent of each other.

Disadvantages:

• Challenging requirements for the wavelength MUX and DEMUX regarding wavelength control, filter characteristics ($Δλ~0.5-1.2$ nm), crosstalk, and thermal stability.
• Large component count.
• Highly stable optical frequency generation and small oscillator bandwidth (~MHz).
• High total operational power ($N_{opt} \times P_{op,channel}$; typically $200 \times 1$ mW/ch = $200$ mW) in the fiber can result in optical nonlinearities.