Volume Bragg Gratings in Pump Sources: What They Are and How They Differ from FBGs

2026-09-01 0 Leave me a message

What Is a VBG?

A volume Bragg grating (VBG) is a periodic refractive-index structure recorded in bulk glass, commonly PTR glass. It acts as a wavelength-selective reflector, reflecting a narrow spectral band around its Bragg wavelength.

In high-power pump lasers, a VBG is placed in the free-space beam path to provide wavelength-selective optical feedback, helping stabilize the emission wavelength and narrow the output spectrum. Its large aperture also supports relatively large beams and high optical power.

VBGs are angle-selective, so precise alignment is important for achieving the target wavelength. They are widely used for wavelength stabilization and spectral narrowing of high-power multimode pump diodes and laser bars.

What Is an FBG?

A fiber Bragg grating (FBG) is a periodic refractive-index structure written into the core of an optical fiber. It reflects a selected wavelength band around its Bragg wavelength while transmitting most other wavelengths.

In FBG-locked laser sources, the grating provides wavelength-selective optical feedback to the laser diode, helping stabilize the emission wavelength and narrow the output spectrum.

Because the grating is integrated into the fiber, no separate free-space angular alignment is required. This enables compact and robust laser designs and makes FBGs widely used for fiber-coupled wavelength-stabilized laser sources.

VBG vs. FBG:

Aspect	VBG (Volume Bragg Grating)	FBG (Fiber Bragg Grating)
Grating medium	Bulk glass, commonly PTR glass	Optical fiber core
Beam path	Free-space optical path	Fiber-integrated
Typical emitter	High-power multimode pump diodes and diode bars	Fiber-coupled single-mode or few-mode laser sources
Integration & alignment	Requires collimated free-space optics and precise angular alignment	Fiber-integrated; no separate free-space angular alignment
Spectral selectivity	Narrow reflection band; bandwidth depends on grating design	Wavelength-selective reflection band; bandwidth depends on grating design
Power handling	Large aperture; suitable for high-power free-space beams	Depends on fiber type, mode field, and optical power density
Thermal behavior	Bragg wavelength depends on grating and temperature conditions	Bragg wavelength is temperature-sensitive; compensation or athermal designs are available
Typical pump applications	Wavelength stabilization of high-power multimode pump diodes and bars	Wavelength-locked fiber-coupled laser sources and fiber-laser configurations