Key Applications of Optical Switches in Fiber-Optic Communication Networks: Protection Switching and Optical Cross-Connect

I. Lifeline Protection: The Application of Optical Switches in Fiber-Optic Protection Switching Systems

Fiber-optic networks inevitably experience unexpected outages, such as construction disruptions, natural disasters, and equipment failures. How can services be restored quickly within tens of milliseconds? This is the core mission of the Optical Line Protection (OLP) switching system, and the optical switch is the “fast switch” that executes this action.

Operating Principle (using 1+1 protection as an example):

1. The primary fiber (working fiber) and the backup fiber (protection fiber) simultaneously transmit the same service signal (broadcasting is achieved by the transmitting optical splitter).

2. At the receiving end, the 1×2 optical switch (or 2×2 optical switch configuration) defaults to receiving the signal from the primary fiber.

3. When the system’s real-time monitoring (through optical power or OSNR, etc.) detects that the primary fiber signal fails or its quality degrades beyond a threshold, the control unit immediately issues a command.
4. The optical switch switches to the backup fiber port within an extremely short time (typically <50ms, or even <20ms), receiving the signal transmitted by the backup fiber.
5. Service restoration is seamless, with users barely noticing.

Key requirements for optical switches:

Ultra-fast switching speed: Milliseconds are the baseline, and the shorter the better (MEMS and electro-optical switches offer significant advantages).

High reliability: Reliable operation at critical moments and long life are essential.

Low insertion loss & high isolation: Minimize signal impact and ensure signal quality after switching.

Stability: Stable performance under various environmental conditions.

II. The Core of Network Flexibility: The Application of Optical Switches in Optical Cross-Connects (OXCs) and ROADMs

With the growth of network traffic and the diversification of services, traditional electrical-layer cross-connects are inefficient and costly. All-optical-layer cross-connects are becoming an inevitable trend. This is the core function of optical cross-connect equipment, and modern ROADM nodes also rely on this technology.

Working Principle:
The core of an OXC/ROADM is a large optical switch matrix (such as an MxN MEMS optical switch).
Optical signals from different directions and wavelengths enter the node.
According to instructions from the network control plane, the optical switch matrix dynamically cross-connects any wavelength channel on any input port to any output port.
This enables dynamic routing, wavelength add/drop, and (optional) wavelength conversion of optical layer services.

The core value of optical switches in this application:
Dynamic and flexible networking: No manual fiber patching is required; software-defined optical channels can be quickly established, modified, or removed.
Improved resource utilization: Flexible sharing and on-demand allocation of wavelength-level resources are achieved.
Simplified operations and maintenance: Significantly reduces the complexity and time of network configuration and fault recovery.
Support for new services: Providing the underlying support for bandwidth-on-demand services.

Key requirements for the optical switch matrix:
Large port count: Support for dozens or even hundreds of ports is required (MEMS technology offers significant advantages).
Low insertion loss and low crosstalk: Maintaining good optical performance in a large-scale matrix is a significant challenge. High reliability and stability: Core node equipment must operate reliably and uninterruptedly 24/7.

Rapid reconfiguration capabilities: Support dynamic business adjustments.