# MEMS Mirrors Questions & Answers

What type of MEMS mirror does Hamamatsu make?

Hamamatsu makes electromagnetic mirrors, which consist of a magnet and a MEMS mirror chip. The basic operating principle of electromagnetic mirrors is shown in the figure below. When an electrical current flows into the coil on the MEMS mirror, the mirror tilts according to the Lorentz force.

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Figure 1. An electromagnetic mirror’s structure and basic operating principle

What are the advantages of electromagnetic mirrors?

The advantages of electromagnetic mirrors include the following:

• Low voltage operation (up to 12 V)
• Large torque
• Large tilt angle

What is the relationship between mechanical deflection angle and optical deflection angle?

As shown in the figure below, the mechanical deflection angle and optical deflection angle have the following relationship:

Optical deflection angle = 2 x Mechanical deflection angle

Hamamatsu uses the optical deflection angle in our datasheets.

Figure 2. Optical deflection angle

Can you sell MEMS mirrors in chip form?

We do not sell MEMS mirrors in chip form. The MEMS mirror packaging and assembly are very critical factors for obtaining the performance described in the datasheet. Therefore, we cannot sell these components separately.

What is the relationship between resolution and frame rate?

In raster scanning, there is a trade-off between vertical resolution and frame rate. The horizontal scanning time is determined by the resonant frequency of the fast axis (fixed frequency). When you increase the horizontal resolution, the time to scan a whole frame also increases. Therefore, it results in a slower frame rate. Typical vertical resolution and frame rate values are shown in the table below.

Table 1. Vertical resolution and frame rate values

What is a MEMS mirror?

MEMS stands for micro-electro-mechanical systems, and a MEMS mirror is a small moving mirror etched on a silicon wafer using MEMS technology. By using a MEMS mirror, you can reduce the size of the whole scanner to a few cm cube.

How are resonant and linear mirrors different?

A resonant mirror moves in a continuous sinusoidal motion at the fixed frequency, usually 1 kHz to tens of kHz. You can get a wide mirror angle with a small driving electric current. For example, our S13989-01H resonant mirror is capable of +/-20 deg. optical angles with +/-25 mA driving current.

A linear mirror tilts its angle according to the driving current. You can stop the mirror at the desired angle or operate it in continuous movement. However, in continuous mode the speed is usually limited to tens of Hz.

Why do you need a feedback loop for the resonant axis frequency?

The mirror’s tilt angle is significantly affected by even a slight shift in the resonant frequency. The resonant frequency can shift over time and when the temperature changes. The feedback loop adjusts the mirror driver frequency to match the shifted resonant frequency, so it can minimize the tilt angle instability.