Newsroom
- Photonics
6 Oct 2025
What is a lithium-niobate electro-optical modulator?
Definition of an electro-optical modulator
An electro-optical modulator is a component that transforms a continuous optical signal into a ‘modulated’ optical signal (suitable for the transmission channel) under the effect of an electric field. An intensity modulator, for example, works like a photo camera shutter: it closes itself and opens itself at the rhythm of the electrical field applied. The modulator does this billions of times per second (i.e. at the frequency of the applied electric field, expressed in gigahertz - 0.1 to 40 GHz).
A mechanical system would be incapable of opening and closing billions
of times a second, so only the ‘electro-optical’ effect can do this.
This involves passing the light through a particularly sensitive
material, lithium niobate (LiNbO3), to change the behavior of the light as it passes by applying an electric field.
A
modulator therefore consists of an optical circuit 6-9 µm wide and 4-5
µm deep (called a ‘waveguide’), in which the light propagates, and two
gold electrodes that allow voltages to be applied to induce the light to
change some of its characteristics. The optical circuit is made of
lithium niobate ‘doped’ with titanium, and the electrical field will
modify the index of the doped material (the Pockels effect). The light is therefore forced to
follow the modulation of the electric field.
The electro-optic effect is significant in lithium niobate. The
technology, that dates back to the 1980s, makes it easy to produce waveguides, and it is highly compatible
with optical fibers.
Which characteristics of light can be modulated?
Light is an ‘electromagnetic wave’ characterized by a wavelength (the space between two wave crests) and a direction of propagation. But also, by:
An intensity = the amplitude of the wave height
A phase = the speed of the waves at a given moment
A polarization = the orientation of the electromagnetic wave with regards to the direction of propagation
Exail modulators come in three ranges, each of which enables one of these last three characteristics of light to be varied (intensity, phase and polarization modulators). There are also numerous sub-references in the catalogue, not to mention many possible customizations.
What are the main applications of electro-optical modulators?
The best-known application of electro-optical modulation is
telecommunications, for data transmission over optical fibers. The
electro-optical modulator plays an essential role in preparing the
optical signal containing the information to be transmitted before it is
sent down the optical fiber, at very high speeds (up to 70 Gbit/s) and
to the other side of the world.
But
today, electro-optical modulators on lithium niobate are mainly used in
other, more complex applications: wherever an optical signal needs to
be modulated extremely quickly and precisely. With the advent of
photonic technologies, these components are becoming crucial for many
applications, including:
- Fiber-based lasers for high-energy and high-power applications
- Quantum technologies (atom cooling/atom manipulation, quantum communication - QKD, etc.)
- Laser communications in space and other space missions
- Sensing (Lidars, DTS, etc.)
A core component for fiber-optic-gyroscope technology
Exail also manufactures a phase modulator adapted to the needs of fiber-optic-gyroscopes (FOG), an “integrated optical circuit” (IOC) which is connected to the gyroscope's fiber optic coil. This modulator is used to split the optical signal entering the coil into two, to balance the two counter-propagating paths in the coil, and to recombine them at the coil output.
For each FOG, 3 IOCs are required, one for each gyroscope. Exail has sold more than 25000 FOGs over the last decades. Exail's FOG is considered to be the best gyroscope in the world.
Exail produces in-house all the critical elements of its Inertial Navigation Systems (INS) based on FOG technology.
State-of-the-art LiNbO3 electro-optical modulators
Exail has pioneered LiNbO3 modulators since 2000, as the technological knowledge comes from founding members, former researchers at FEMTO ST lab
in Besançon, who developed the lithium niobate technology in the 1980's.
Today, Exail
industrial capabilities support high production of cutting-edge
modulation solutions for advanced applications, such as:
- Phase modulators with low Vπ for Directed Energy Laser, using the Coherent or the Spectral Beam Combination (CBC / SBC)
- Intensity modulators with high extinction ratio for QKD
- Near-infrared dual-stage intensity modulators for high-energy laser facilities
FAQ
A Lithium Niobate modulator is a high-performance guided wave device used to control the phase, intensity, or polarization of light by applying an electric signal. It leverages the Pockels effect of the LiNbO3 crystal, where the refractive index changes linearly with the electric field, allowing for ultra-fast and precise optical signal modulation in telecommunications and sensing applications.
Lithium Niobate is favored because of its excellent electro-optic coefficients, high optical transparency across a wide range of wavelengths, and long-term stability. Compared to other materials, it offers a superior balance between low insertion loss and high-speed operation (up to 40 GHz or more), making it the industry standard for demanding environments like aerospace and subsea defense.
These modulators were developed as critical components in high-bit-rate optical fiber communications. Today they are integrated in high-power lasers, ultra-stable laser sources for quantum application, laser systems and Radio-over-Fiber (RoF) systems. At Exail, they are the core component (called IOC, Integrated Optical Circuits) of Fiber-Optic-Gyroscope (FOG), used in high-precision inertial navigation, where reliability under extreme conditions is paramount.
The Pockels Effect occurs when an external electric field is applied to a non-centrosymmetric crystal, like Lithium Niobate. This field induces a change in the crystal's birefringence, which modifies the phase of the light passing through it. By placing this crystal in an interferometer structure (like a Mach-Zehnder), this phase shift is converted into intensity modulation.
