The Optical Magic of MEMS in Switches and VOAs

What is MEMS? MEMS (Micro-Electro-Mechanical System) refers to a miniaturized device or system that integrates micro-mechanical components, micro-actuators, signal processing, and control circuits. The fabrication process of micro-mechanical structures involves photolithography, ion beam etching, chemical etching, and wafer bonding. Electrodes are also fabricated on the mechanical structures for electronic control.

A MEMS chip is an integrated circuit that combines micro-mechanical structures with electronic components. It is fabricated using micro- and nano-fabrication techniques to create tiny mechanical elements on a chip surface, which are then interconnected with electrical circuits. These miniature mechanical structures can perform various functions such as sensing, measuring, controlling, and actuating. MEMS chips are typically made of silicon due to its excellent mechanical properties and well-established microfabrication processes. The manufacturing process involves photolithography, thin film deposition, ion etching, and wet etching to precisely construct the tiny structures on the chip.

A MEMS optical switch involves etching tiny mirrors onto a silicon wafer. By applying electrostatic or electromagnetic forces, the mirror array can rotate, thereby altering the propagation direction of the incoming light and achieving optical path switching. The routing of optical waves in a MEMS optical switch is accomplished through external control signals and corresponding high/low voltage levels that control the elevation of the internal mirrors. These switches integrate micro-machines, micro-actuators, signal processing, and control circuits to enable efficient optical signal management.

Figure 1. A schematic diagram of a MEMS optical switch, illustrating its basic components and optical path.

The core components of a MEMS optical switch are tiny mirrors etched onto a silicon wafer. These micromirrors can be rotated using electrostatic or electromagnetic forces, altering the direction of incoming light and effectively switching the optical path on or off.

Figure 2. A schematic diagram showing the arrangement of components in MEMS optical switch

MEMS optical switches typically have two types of port configurations:

Matrix (symmetric): Multiple input and output ports arranged in a matrix format (e.g.,4x4, 8x8, MxN).

Fan-out (asymmetric): A single input port and multiple output ports arranged in a fan-out pattern (e.g., 1x2, 1x4, 1xN).

Figure 3. A schematic diagram showing the arrangement of MEMS torsional mirrors, collimating lenses, and multiple fiber pigtails in a 1xN MEMS optical switch.

A MEMS optical switch operates by directing incoming optical signals to a micro-electromechanical system (MEMS) mirror. This mirror, controlled by external electrical signals, can be tilted or rotated to redirect the light towards the desired output port.

Figure 4. A schematic diagram showing the optical path and mirror movement in a MEMS-based optical switch.

Figure 5. A schematic diagram showing the optical path of a MEMS optical switch from input to output fiber.

Based on the spatial structure, MEMS optical switches can be categorized into two main types:

2D switches: In these switches, the mirrors rotate within a single plane. When the micromirror is horizontal, light passes through; when it's vertical, it reflects the light to the corresponding output port.

Figure 6. A schematic diagram depicting the physical structure of a 2D MEMS optical switch. It illustrates the rotation mechanism of the micromirror and how this movement alters the direction of the incident light, enabling switching between different output ports.

3D switches: These switches feature micromirrors capable of rotating in three-dimensional space, allowing for more complex optical routing. Two mirror arrays are commonly employed for input and output.

Figure 7: A schematic diagram depicting the physical structure of a 3D MEMS optical switch. It illustrates the dual-axis rotation mechanism of the micromirrors and how this movement enables precise control over the direction of the incident light, allowing for complex optical routing.

These advantages make MEMS optical switches suitable for a wide range of applications, including:

Optical cross-connects: This application highlights the ability of MEMS switches to flexibly route optical signals, connecting any input fiber to any output fiber.

Wavelength management: This emphasizes the precision of MEMS switches in manipulating individual wavelengths within a multi-wavelength signal, allowing for fine-grained control of optical networks.

Optical packet switching: This showcases the high-speed switching capabilities of MEMS switches, making them ideal for demanding applications like packet-switched optical networks.

Test and measurement: This application demonstrates the versatility of MEMS switches in optical test equipment, where rapid and precise switching between different optical channels is essential.

Optical sensing: This highlights the sensitivity of MEMS switches to detect the presence or absence of light, enabling their use in optical sensing applications.

While MEMS optical switches offer numerous advantages, they still face challenges such as high cost, limited scalability, and sensitivity to environmental factors. However, ongoing research and development efforts are addressing these issues, paving the way for broader adoption in the rapidly evolving field of optical communications.

MEMS optical switches represent a significant advancement in optical signal management, offering a combination of performance and efficiency that makes them indispensable components in modern fiber-optic networks. As technology continues to evolve, these switches are poised to play an even more pivotal role in shaping the future of optical communications.

Microelectromechanical Systems (MEMS)-based Variable Optical Attenuator (VOA) is a critical component for power regulation in all-optical networks. In all-optical networks, imbalanced channel power can adversely affect the normal operation of the optical network. Variable Optical Attenuators (VOAs) are one of the most widely used basic optical devices for channel equalization.

MEMS micromirror-based Variable Optical Attenuators (VOAs) offer advantages such as simple packaging, small size, low power consumption, and low cost. MEMS VOAs achieve attenuation by deflecting the incident light beam through electrostatic or electromagnetic actuation of a torsional micromirror. Typically, a dual-fiber collimator is coupled with the MEMS chip to realize a compact packaging structure.

Figure 8 illustrates the structure of a MEMS micromirror-based VOA. A pigtail with a dual-fiber collimator serves as the input/output port. The collimated beam is reflected by the MEMS micromirror, connecting the input and output ports. By controlling the deflection angle of the micromirror, the beam is deflected to control the attenuation level.

Figure 8 shows the structure of a MEMS VOA. A MEMS micromirror, actuated to deflect the incident light, is the core component.

MEMS VOAs are primarily used in applications such as pre-setting optical power equalization, channel transmission equalization, automatic gain control, and optical receiver protection. GLSUN's VOA products utilize MEMS control chips and unique optical designs to achieve a more compact size, lower cost, faster response, and higher stability and reliability, making them easier to manufacture.

MEMS chips serve as the foundation for MEMS optical switches and MEMS VOAs, providing miniaturized mechanical structures and control functions. MEMS optical switches and MEMS VOAs represent two crucial applications of MEMS chips in optical communications, respectively used for optical path switching and optical signal power regulation. Both MEMS optical switches and MEMS VOAs offer advantages such as small size, low power consumption, and fast response speed, playing an increasingly significant role in optical communication systems.