A reference for working photonics engineers
Tutorials, references, and tools for the engineering of light.
Photonica covers the bench-level procedures that journal papers and vendor datasheets do not: laser characterization, photonic integrated circuit testing, and lab practice. Currently 25 tutorials, 262 definitions, 6 material references, and 7 calculators, with sources.
Tools
All tools →Laser characterization
T₀ Extraction Calculator
Fit the characteristic temperature T₀ and pre-exponential I₀ from threshold current vs. temperature data.
Laser characterization
Wall-Plug Efficiency Calculator
Compute wall-plug efficiency from LIV data point-by-point and identify the peak operating current.
Optical alignment
Fiber Coupling Efficiency Calculator
Estimate Gaussian beam to single-mode fiber coupling efficiency from beam waist, fiber MFD, and alignment offsets.
PIC design
Bragg Wavelength Calculator
Convert between grating period and Bragg wavelength for DFB/DBR lasers and integrated photonic Bragg gratings.
Optical coatings
AR Coating Thickness Calculator
Quarter-wave anti-reflection design: film thickness, ideal index, and residual reflectance with a live spectrum plot.
Laser characterization
Junction Temperature Calculator
Extract junction temperature rise and thermal resistance from a DFB wavelength shift, or predict junction temperature from known R_th.
PIC characterization
Q Factor to Propagation Loss Converter
Convert intrinsic Q to waveguide propagation loss for ring resonators, with platform presets for SOI, SiN, InP, and LNOI.
Glossary
Full glossary →ABCDEFGHIJKLMNOPQRSTUVWXYZ
- Aberrations
- Departures from ideal image formation in real optical systems. The principal categories (spherical, coma, astigmatism, field curvature, distortion, and chromatic) are the main targets of lens design and correction.
- Acceptance angle
- The maximum incidence angle at which light can enter an optical fiber or waveguide and still be guided. Geometrically related to the numerical aperture.
- Acceptance bandwidth
- The range of input wavelengths, incidence angles, or polarization conditions over which a nonlinear or wavelength-selective optical process operates efficiently. Sets the wavelength tolerance of frequency conversion crystals, filters, and gratings.
- Acousto-optic modulator (AOM)
- An optical device that diffracts and frequency-shifts light using an acoustic wave traveling through a transparent crystal. Used for laser intensity modulation, frequency shifting, beam deflection, and Q-switching.
- Airy disk
- The diffraction pattern formed in the focal plane of an ideal lens or telescope from a uniformly-illuminated circular aperture. A central bright disk surrounded by concentric rings of decreasing intensity, setting the resolution limit of imaging systems.
- Amplified spontaneous emission (ASE)
- Broadband incoherent optical power produced by spontaneous emission events that are subsequently amplified by stimulated emission in an optical amplifier. The fundamental noise source in optical amplifiers.
- Anti-reflection coating (AR)
- A thin-film stack designed to reduce the reflectance of an optical surface by destructive interference between front- and back-surface reflections. The standard surface treatment for any high-performance optical element.
- Apodization
- Smooth variation of a periodic structure's strength along its length to control the spectral response. The standard technique for sidelobe suppression in gratings, filters, and resonators.
Recently published
All articles →- Jul 26, 2026Reference · Optical networkingWDM Mux/Demux Technologies: Thin-Film Filters vs AWG vs FBGThe three ways to split wavelengths: cascaded thin-film filters, arrayed waveguide gratings, and fiber Bragg gratings with circulators. Compared on loss, channel count, isolation, temperature behavior, and cost.
- Jul 26, 2026Reference · MaterialsThermo-Optic Coefficients of Photonic Materials: Reference Tabledn/dT values for silicon, silicon nitride, silica, InP, GaAs, lithium niobate, and polymers at telecom wavelengths. Includes the resonator-shift formula, athermal design logic, and the caveats that make coefficients composition-dependent.
- Jul 26, 2026Reference · Optical networkingOptical Amplifiers Compared: SOA vs EDFA vs RamanThe three amplifier technologies compared on the numbers that decide between them: gain, noise figure, saturation power, bandwidth, and dynamics. With the use cases where each is the only sensible answer.
- Jul 26, 2026Reference · Laser physicsOptical Feedback in Semiconductor Lasers: The Five Regimes and Coherence CollapseWhat back-reflections actually do to a laser: the Tkach–Chraplyvy feedback regimes, why coherence collapse destroys linewidth and RIN, which devices are sensitive and why, and the isolation budget that keeps links stable.
- Jul 26, 2026Procedure · Laser characterizationMeasuring Laser Diode Junction Temperature and Thermal ResistanceTwo bench methods for finding the actual temperature of a laser chip: the DFB wavelength-shift method and the forward-voltage method. Includes the pulsed-vs-CW logic, worked numbers, and thermal resistance extraction.
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Not sure where to start?
Three good entry points, depending on what brought you here.
If you’re setting up a bench
Laser characterization bench setup
What actually goes on the table, what each instrument needs to do, and the mistakes that cost the most time to find.
If you have data and need a number
T₀ extraction from LIV measurements
The full procedure, a worked example, and where extraction quietly goes wrong. There’s a calculator to go with it.
If nothing is coupling
First light on a grating coupler
Getting from zero signal to first light, in the order that finds problems fastest.