Beam modulators (optical modulators)

01

Choose electro-optic or acousto-optic

RP Photonics, a laser-technology encyclopedia, defines an optical modulator as a device for manipulating a property of light, used across a wide range of application areas. [1] Electro-optic modulators (EOMs) control power, phase or polarization with an electrical signal; RP writes "Usually, such a device is based on the linear electro-optic effect (also called the Pockels effect)", a field-induced change in a nonlinear crystal's refractive index; types include phase modulators, polarization modulators acting as voltage-controlled waveplates, and amplitude modulators that add a polarizer. Their half-wave voltage Vπ — the voltage for a phase shift of π — is hundreds or thousands of volts for typical Pockels cells, needing a high-voltage amplifier. Bulk modulators pass a free-space beam through a crystal, while waveguide modulators confine light in a channel on a chip — for example on lithium niobate — allowing lower voltages and higher modulation frequencies; travelling-wave designs reach the gigahertz region, and resonant EOMs give large modulation depth at one fixed frequency. [2] Acousto-optic modulators (AOMs) use a piezoelectric transducer driven by an RF signal to launch a sound wave — RP cites around 100 MHz, with 10–100 µm acoustic wavelength and 1–10 W acoustic power — whose refractive-index grating diffracts the light; they switch or adjust beam power, and serve in Q-switching, cavity dumping, mode locking, pulse picking and laser printers. AOM materials RP lists include tellurium dioxide, crystalline quartz and fused silica, germanium for the infrared, and lithium niobate for high-frequency or integrated devices. [3]

Editorial calculation: acoustic wavelength times frequency gives the sound speed, so 10–100 µm at 100 MHz implies 1,000–10,000 m/s; since RP says AOM switching time is limited by the time sound takes to cross the beam, a 1 mm beam would switch in roughly 0.1–1 µs, and focusing to 0.1 mm would cut that tenfold at some cost in efficiency. [3]

Give the supplier the wavelength, beam diameter and power (average and peak), the property to modulate (intensity, phase, polarization, frequency), modulation bandwidth or switching time, extinction or contrast ratio, insertion loss limit, free-space or fibre-coupled format, driver type and input signal, cooling, size and mounting, and quantity.

02

Set aperture, efficiency and the driver

RP Photonics lists aperture size, power handling, switching speed and insertion loss among key EOM parameters, and stresses thermal drift compensation and a matched electronic driver. Crystal choice sets the limits of bulk EOMs: KD*P offers high optical quality and extinction for large apertures and is standard for Q-switches but is hygroscopic and rings piezoelectrically at high repetition rates, while BBO handles higher average power and switching frequencies but needs higher voltages and smaller apertures. [2] For AOMs, diffraction efficiency rises with RF drive power up to saturation and depends on wavelength and beam divergence; switching time is set by the acoustic transit time across the beam, so larger beams are slower, and focusing speeds switching but can lower efficiency. [3]

Editorial note: ask for the driver to be specified with the modulator — its voltage or RF power, rise time and input interface — since RP treats the matched driver as part of the modulator's performance. [2]

03

Read a measured waveguide modulator data set

RP Photonics gives no full data set for one waveguide device, so this section uses one published device to show what a full waveguide EOM data set contains. [2] Li et al. (Huazhong University of Science and Technology with Fudan University and other groups, Nature Communications 2026) built a thin-film lithium niobate (TFLN) Mach-Zehnder modulator with two 3-dB power splitters, a 9-mm-long electro-optic modulation section, a thermo-optic phase shifter for bias and two spot-size converters as edge couplers. It operates continuously from 1260 to 2060 nm, with a 3-dB EO bandwidth above 67 GHz across the O to U bands, about 100 GHz at 1310, 1485, 1550 and 1590 nm, and above 50 GHz in the 2-µm band. [4]

The authors trace the rise in loss toward longer wavelengths mainly to absorption by the metal electrodes, and they report single-lane PAM-4 transmission of 240 to 280 Gbps across the O to U bands and 170 Gbps at the 2-µm band. [4]

Editorial calculation: dividing the reported Vπ·L of 2.61 V·cm by the 0.9 cm electrode length gives a half-wave voltage of about 2.9 V at 1550 nm, against the hundreds to thousands of volts RP Photonics gives for bulk Pockels cells. [4] [2] When comparing quotes, ask for Vπ at your wavelength together with electrode length, 3-dB EO bandwidth, on-chip and fibre-to-fibre insertion loss, and extinction ratio, because each of these figures changes with wavelength in the data above.

04

Compare what suppliers offer

Suppliers linked to this page list optical modulators; each card links to the page reviewed.

Listings include lithium niobate multifunction integrated-optic chips among fibre-optic sources and amplifiers; ask each for wavelength, Vπ, bandwidth, insertion loss and extinction ratio data.

05

Trace the modulator system

This is a functional reference built from the sources cited; it is not one maker's design.

06

Fill the specification fields with values for your project

A beam modulator quotation needs values for your project. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the beam, modulation and driver needs together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Beam: [wavelength; diameter; power]
Modulation: [intensity; phase; polarization; frequency]
Speed: [bandwidth; switching time]
Performance: [extinction; insertion loss]
Format: [free-space; fibre-coupled]
Driver: [HV; RF; input]
Quantity: [units]

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