Lab practice
The bench itself: instruments, alignment, fixturing, test procedures, and the working habits that separate clean data from artifacts.
55 articles · 171 glossary terms · 17 tools
Start here: The optics bench in 10 pages
The instruments and habits behind clean optical measurements.
- 1Optical power meterGlossary
- 2Optical Spectrum Analyzers: Operating Principles and Measurement ConfigurationArticle
- 3Beam profilerGlossary
- 4Knife-edge measurementGlossary
- 5Coupling a Free-Space Beam into Single-Mode Fiber: Lens Choice and AlignmentArticle
- 6Fiber connectors: PC, UPC, APCGlossary
- 7Fiber Connector Inspection and Cleaning: Dry and Wet-Dry MethodsArticle
- 8Measuring Insertion Loss and Return Loss of a Fiber ComponentArticle
- 9Lock-in amplifierGlossary
- 10Setting Up a Temperature-Controlled Laser Characterization BenchArticle
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.
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
Ring Resonator Explorer
Simulate and fit microring resonators: live spectrum, phase and group delay, a true-scale field view, and measured-scan fitting that extracts Q, coupling, and loss with both branches.
PIC characterization
Grating Coupler Spectrum Fitter
Extract de-embedding numbers from a pasted loopback scan: center wavelength, per-coupler insertion loss, 1 dB and 3 dB bandwidths, and ripple-period analysis that locates the parasitic Fabry-Perot cavity.
PIC characterization
Vπ Fitter
Fit a pasted modulator bias sweep to the full cosine transfer function: half-wave voltage, VπL, extinction ratio, bias phase, and quadrature point, with residuals and built-in validation.
Optical coatings
Thin-Film Reflectance Calculator
Reflectance and transmittance of any dielectric layer stack by the characteristic-matrix method, s and p polarization at any angle, with presets for anti-reflection coatings, quarter-wave Bragg mirrors, laser facet coatings, and etalons, live spectrum and angle plots, and a 16-row validation table.
Imaging and diffraction
Airy Disk Calculator
Airy disk radius and diameter, FWHM, dark and bright rings, encircled energy, and the Rayleigh, Sparrow and Abbe resolution limits for any wavelength and f-number, aperture and focal length, or numerical aperture, with angular resolution for telescopes, pixel sampling for cameras, a rendered pattern, and an 18-row validation table.
Detectors and noise
Photodiode Noise Calculator
Which noise source limits a PIN or avalanche photodiode receiver, and what is the weakest signal it can see: signal shot, dark-current shot, thermal and amplifier noise summed over the bandwidth into SNR, noise-equivalent power, minimum detectable power, the shot-noise crossover power and the optimum APD gain, with the shot-noise limit, noise and SNR plots, guided experiments and a validation table.
Units and conversions
Photonics Unit Converter
Optical power between dBm, mW, W and dBW; gain and loss as dB, linear and field ratios, percent and optical density; wavelength to frequency, photon energy and wavenumber; and linewidth between Δν, Δλ and Δσ, with photon flux, ideal responsivity, telecom band, nearest DWDM channel, coherence length and a validation table.
Beams and focusing
Gaussian Beam Calculator
Rayleigh range, depth of focus, divergence and beam parameter product of a Gaussian or M² beam; beam radius, wavefront curvature, Gouy phase, peak intensity and aperture transmission at any distance; and the focused waist size and position behind a thin lens, with beam plots, presets, guided experiments and a validation table.
Imaging and diffraction
Diffraction Grating Calculator
Diffraction angles of every propagating order, the Littrow angle, angular and linear dispersion, resolving power, spectrometer resolution for a given slit, free spectral range and beam width ratio for any groove density, wavelength, incidence and order, with a ray diagram, angle-versus-wavelength curves, presets, guided experiments and a validation table.
Imaging and diffraction
Slit Diffraction Calculator
Single-slit, double-slit and multi-slit Fraunhofer patterns: first minimum angle, central maximum width on a screen, fringe spacing, fringes inside the envelope, missing orders and the Fresnel number, with the intensity plotted and drawn as it looks on the screen, presets, guided experiments and a validation table.
Polarization
Jones Calculus Calculator
Any input polarization through up to four polarizers, half-wave and quarter-wave plates, retarders and rotators: transmitted intensity, output Jones vector, Stokes parameters, azimuth, ellipticity and handedness, with the polarization ellipse, an intensity-versus-angle plot, presets, guided experiments and a validation table.
Units and conversions
Optical Density Calculator
Optical density, transmission, decibels and attenuation factor from any one of them, the total of a stack of neutral-density filters and the power it passes, the OD needed to reach a target power, and the absorbance and transmittance of an absorbing sample with its surface reflections, with plots, presets, guided experiments and a validation table.
Articles
- Wavemeter vs Optical Spectrum Analyzer: Measuring a Laser's Wavelength and SpectrumWhen to use a wavemeter and when to use an optical spectrum analyzer to measure a laser: what each reports, accuracy and resolution compared in picometers and megahertz, single-mode and multimode sources, side-mode suppression, tuning and mode hops, with worked numbers at 1550 nm.
- Raman Spectroscopy Setup: Laser, Filters, Spectrometer and CalibrationHow a Raman spectroscopy setup is built and calibrated: choosing the excitation wavelength (532, 785 or 1064 nm), laser and filter requirements, collection optics, the spectrometer's resolution and coverage with a worked example, detectors, wavenumber calibration with silicon and lamp lines, and common problems such as fluorescence and sample heating.
- Photonics Engineer Interview Questions, with Worked AnswersTechnical questions commonly asked in interviews for photonics, optical and laser engineering roles, grouped by fundamentals, fibers, lasers, detectors and noise, integrated photonics and lab practice, each with a short worked answer, the numbers to quote and links to the full explanation.
- How to Read an Optics Spec Sheet: Lenses, Mirrors, Windows and FiltersWhat each line on a lens, mirror, window or filter specification means and how to judge whether it is good enough: dimensions and tolerances, material, focal length, surface flatness and irregularity, transmitted and reflected wavefront, surface quality, roughness, wedge and centration, clear aperture, coatings and damage threshold, with worked numbers.
- How to Measure a Detector's NEP and D*Procedure for measuring the noise equivalent power (NEP) and specific detectivity (D*) of a photodetector: measuring the dark noise spectrum, removing the amplifier's contribution, measuring responsivity, normalizing to bandwidth and area, with a worked InGaAs example in which the feedback resistor, not the photodiode, sets the NEP.
- How to Calibrate and Cross-Check an Optical Power MeterProcedure for checking an optical power meter between calibrations: zeroing, comparison with a reference meter, the wavelength setting, linearity by the superposition method, fiber connector repeatability, and a simple uncertainty budget, with worked numbers in percent and dB.
- Choosing a Laser Power Meter: Photodiode, Thermal or Pyroelectric SensorHow to choose a laser power or energy meter: photodiode, thermopile and pyroelectric sensors compared, with power ranges, wavelength coverage, speed, aperture and damage limits, worked examples for wavelength-setting errors, overfilled apertures and pulsed beams, and a checklist.
- Wafer-Level Optical Testing of Photonic Chips: Setup, Alignment and Test FlowHow silicon photonic wafers are tested optically before dicing: the optical probe station, fiber probes over grating couplers, per-die alignment and its share of test time, reference structures, wafer maps of loss and resonance, probe calibration, and the failure modes of an automated flow.
- How to Measure Ultrashort Pulse Duration: Autocorrelation, FROG and SPIDERProcedures and choices for measuring femtosecond and picosecond laser pulses: the intensity autocorrelator and its calibration, the deconvolution factor and what it hides, checking against the spectrum with the time-bandwidth product, interferometric autocorrelation, and when FROG, SPIDER or d-scan is needed.
- Measuring Polarization Extinction Ratio and Polarization-Dependent LossProcedure for measuring PER of polarization-maintaining fiber and components, and PDL of fiber-pigtailed devices: why a single rotating-polarizer reading can hide a misaligned launch, the heat or stretch method, and the all-states and Mueller four-state methods for PDL with a worked example.
- Measuring Insertion Loss and Return Loss of a Fiber ComponentProcedure for measuring the insertion loss and return loss of fiber-pigtailed and connectorized components: reference methods and which connections they include, launch conditions, the continuous-wave reflectometer method with background subtraction, and the errors that dominate at the 0.1 dB and 50 dB level.
- How to Measure Refractive Index: Prism, Refractometer, Prism Coupler, Ellipsometry and FringesMethods for measuring the refractive index of bulk glass and crystals, liquids, thin films and waveguides: minimum deviation with a prism, critical-angle refractometers, the prism coupler, spectroscopic ellipsometry, and interference fringes, with the accuracy of each, worked examples, and the difference between phase and group index.
- How to Measure Photodetector Bandwidth and Frequency ResponseProcedure for measuring the frequency response and 3 dB bandwidth of a photodiode or optical receiver: the calibrated-modulator network-analyzer method, the optical heterodyne method with its expected RF power, the impulse-response method, de-embedding the RF path, and the bias and photocurrent dependences that change the answer.
- How to Measure OSNR: Interpolation, Integration and In-Band MethodsProcedure for measuring optical signal-to-noise ratio with an optical spectrum analyzer: the 0.1 nm reference bandwidth, the IEC interpolation method and its bandwidth corrections, integrating wide coherent channels, and the in-band methods needed when filtering or dense spacing hides the noise floor.
- How to Measure Electro-Optic Modulator Bandwidth: S21 Setup, Conventions and LimitsProcedure for measuring the small-signal electro-optic bandwidth of Mach-Zehnder and phase modulators with a network analyzer: the setup and calibration, bias and drive level, removing the photodiode's response, the electrical and optical 3 dB conventions, and the velocity-mismatch and electrode-loss limits that set the result.
- How to Measure the Focal Length of a Lens: Bench Methods and AccuracyProcedures for measuring a lens's focal length on the optical bench: the distant-object and collimated-laser methods for back focal length, autocollimation, the Bessel displacement method that needs no principal-plane location, the magnification method, and the errors that limit each.
- How to Measure Fiber Attenuation and Bend Loss: Cutback, OTDR and Mandrel MethodsProcedures for measuring the attenuation of optical fiber in dB/km by the cutback method and by OTDR, the spectral attenuation curve, and macrobend loss by mandrel wrapping, with launch conditions, a worked cutback example, and the errors that dominate each measurement.
- How to Measure Laser Beam Divergence: Two-Point and Focal-Plane MethodsProcedure for measuring the far-field divergence of a laser beam: the two-point method and why it underestimates inside the Rayleigh range, the focal-plane lens method that works on any bench, width definitions, half versus full angle, and a worked example.
- How to Collimate a Laser Beam: Lens Choice, Waist Placement and CheckingProcedure for collimating the output of a fiber or laser diode: what a collimated Gaussian beam can and cannot do, choosing the focal length from the beam size wanted, how far away the waist can be placed, setting the lens distance, and checking collimation with distance measurements or a shear plate.
- Coupling a Free-Space Beam into Single-Mode Fiber: Lens Choice and AlignmentProcedure for coupling a collimated laser beam into single-mode fiber: choosing the lens focal length to match the mode field diameter, the 1 dB tolerances in offset, angle and focus with a worked example at 1550 nm, beam walking with two mirrors, back-propagation, APC fiber, and verifying the efficiency.
- Focusing a Laser Beam: Spot Size, Depth of Focus and DamageHow to focus a laser beam to a chosen spot: the focused spot size from wavelength, focal length, input beam diameter and M², the trade against depth of focus, choosing and orienting the lens, peak irradiance and fluence at the focus, damage thresholds, and how to measure the spot.
- Fiber vs CO₂ vs Nd:YAG Lasers for Cutting, Welding and MarkingHow fiber, CO₂ and Nd:YAG lasers compare for materials processing: wavelength and absorption, focused spot size and depth of focus, beam delivery, efficiency, and which laser suits metal cutting, welding, marking, wood, acrylic, glass and copper, with worked numbers.
- Fiber-to-Chip Coupling for Silicon Photonics: Methods, Alignment and LossHow light gets between optical fiber and a silicon photonic chip: the mode-size problem in numbers, edge couplers, grating couplers and their alternatives, the active alignment loop, fiber-array roll alignment, and how to measure and de-embed coupling loss. A guide to the site's detailed procedures.
- Fiber Optic Connector Types: LC, SC, FC, ST, MPO and Very Small Form FactorReference to the optical fiber connector types in use: LC, SC, FC, ST, MU and E2000 single-fiber connectors, MPO multi-fiber connectors and their polarity, the very small form factor SN, MDC and CS connectors, ferrule sizes, polish and color codes, typical losses, and which connector suits which job.
- Fiber Connector Inspection and Cleaning: Dry and Wet-Dry MethodsProcedure for inspecting and cleaning fiber connector end faces before every mate: what a particle on the core costs in insertion and return loss, choosing an inspection tip, the dry and wet-dry cleaning sequence, bulkheads and transceiver ports, MPO connectors, and when to stop cleaning and replace.
- Fiber Array Attach to Photonic Chips: V-Groove Arrays, Alignment Tolerances, Epoxy, and the Loss BudgetProcedure for attaching a V-groove fiber array unit to a photonic integrated circuit: array specifications and their tolerances, the alignment arithmetic for edge and grating couplers, choosing and curing the epoxy, the loss budget per channel, and the Telcordia tests the joint has to survive.
- Thermal Tuning and Locking of Ring ResonatorsHow far a ring resonance moves per kelvin on silicon, silicon nitride, silica, and lithium niobate, computed from the thermo-optic coefficient and group index; what a heater costs per free spectral range and why undercut buys efficiency at the price of speed; thermal bistability under high circulating power; and the locking methods that keep a ring on its channel, with the numbers that decide between them.
- Laser Diode Lifetime: How an MTTF Claim Is BuiltThe arithmetic behind a laser diode lifetime specification: the Arrhenius temperature acceleration and the current acceleration exponent, worked with realistic activation energies; how a few thousand hours of stress on a few dozen devices becomes a million-hour mean time to failure and what confidence that number carries; the failure criteria that define a failure; what burn-in catches and does not; and how to derate a laser from the claim to an operating point.
- Why L-I Curves KinkWhat a kink in a laser diode's light-current curve is, the lateral-mode and beam-steering mechanism that produces most of them in ridge lasers, how mode hops, polarization switches, and facet damage look different, how to read the signature, and how kink-free power is measured and specified.
- Three Ways to Measure Waveguide Loss, ComparedCutback, Fabry-Perot fringe contrast, and ring-resonator Q extraction measure the same propagation loss with different structures, different dominant uncertainties, and different failure modes. Worked numbers for each, a decision rule for which to use at what loss level, and what to expect when two of them disagree.
- Measuring Optical Density Beyond the Stray-Light FloorWhy a spectrophotometer cannot verify an OD 6 filter, why the light source has to be spectrally cleaner than the filter under test, and a laser-and-detector procedure with an error budget that reaches OD 7: source clean-up, detector linearity by a calibrated attenuator chain, baffling, the stacked-filter floor test, and how to report the result.
- Common-Mode Rejection in Balanced DetectorsWhere the common-mode rejection ratio of a balanced photodetector comes from (responsivity mismatch, path-delay mismatch, bandwidth mismatch), the formula that gives CMRR as a function of frequency with worked numbers, what a given CMRR buys against local-oscillator intensity noise, and a step-by-step measurement and trimming procedure.
- Measuring TDECQ on a PAM4 TransmitterProcedure for measuring TDECQ on 100G and 200G per lane PAM4 optical transmitters: the reference receiver chain, capture requirements, pattern and clock recovery setup, the histogram-and-noise computation, companion metrics (OMA, ER, RLM), and the bench failure modes that corrupt the number.
- Measuring Modulator Vπ and Electro-Optic BandwidthProcedure for measuring the half-wave voltage and EO bandwidth of Mach-Zehnder and phase modulators: DC transfer-curve fitting, the Bessel-null method, small-signal quadrature slope, and swept-frequency S21, with the dominant error sources and a worked example.
- De-Embedding Coupler Loss with Reference StructuresProcedure for separating fiber-to-chip coupler loss from device loss using back-to-back reference structures: loopback measurement, per-coupler spectra, spectral subtraction, alignment repeatability protocol, and Fabry-Perot ripple diagnosis, with worked numbers.
- Measuring 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.
- Laser Diode Packages: TO-Can, C-Mount, CoS, and ButterflyA working guide to the standard laser diode packages. What each is for, thermal paths, monitor and TEC contents, the wiring-variant traps, and how to choose for a bench experiment versus a product.
- How to Read a Laser Diode DatasheetA working engineer's walkthrough of a laser diode datasheet: what threshold, slope efficiency, kink-free power, SMSR, RIN, and tracking error actually promise, the conditions-column traps, and the specs that are missing when a vendor hopes you won't ask.
- How to Measure Laser Linewidth: Choosing the Right MethodA selection guide for the four standard linewidth measurements: DSH, heterodyne, frequency-noise discriminator, and coherent receiver. Covers the fiber-length math, what each method actually reports, and the mistakes that skew results.
- Edge Coupler vs Grating Coupler: Choosing Fiber I/O for a Photonic ChipThe decision every PIC project makes once: edge coupling or grating coupling. Loss, bandwidth, polarization, wafer-level test, packaging, and the hybrid strategy most real programs land on.
- Anti-Reflection Coating Design: The Quarter-Wave ConditionHow single-layer anti-reflection coatings work and how to design one: the quarter-wave thickness condition, the ideal-index rule, worked examples on glass and silicon, and when a single layer isn't enough.
- Photodetector Characterization: Responsivity, NEP, and BandwidthProcedures for measuring the three primary parameters of photodetectors used in photonics (wavelength-dependent responsivity, noise-equivalent power, and 3-dB electrical bandwidth), with focus on the standard measurement configurations for InGaAs PIN photodiodes.
- DFB Laser Characterization: Full Parameter Extraction WorkflowComplete characterization workflow for a distributed-feedback (DFB) semiconductor laser, integrating LIV, spectral, temperature-dependent, and noise measurements to extract the parameters required for telecom and sensing applications.
- Optical Spectrum Analyzers: Operating Principles and Measurement ConfigurationReference for optical spectrum analyzers (OSAs) including diffraction grating, Fabry-Pérot, and Fourier-transform variants, resolution bandwidth and dynamic range specifications, and the standard measurement configurations for laser source characterization, OSNR measurement, and EDFA gain characterization.
- How to Compute Wall-Plug Efficiency from an LIV CurveStep-by-step procedure for turning a laser diode's LIV sweep into its wall-plug efficiency curve: the definition, why the peak sits at a few times threshold, the three factors that set it, a worked example with numbers, the measurement errors that bias it, and typical peak values from telecom DFBs to pump diodes.
- Setting Up a Temperature-Controlled Laser Characterization BenchEquipment selection, thermal mounting, electrical configuration, and noise mitigation for a benchtop laser diode characterization setup, with focus on the configuration choices that determine measurement quality.
- Active Fiber Alignment to Edge Couplers on Photonic Integrated CircuitsProcedure for alignment of optical fiber to edge coupler structures on photonic integrated circuits using lensed fibers and inverse-taper couplers, with discussion of butt-coupling, anti-reflection cleaving, and the distinct failure modes compared to grating coupler alignment.
- Pulsed versus Continuous-Wave LIV Measurement: Self-Heating and MethodologyComparison of pulsed and continuous-wave measurement modes for semiconductor laser LIV characterization, with quantification of self-heating bias, duty cycle requirements, and equipment configuration.
- Threshold Current Extraction Methods ComparedComparison of the four standard methods for extracting threshold current from a semiconductor laser LIV curve, applied to a single dataset, with discussion of when each method is preferred and the systematic differences between them.
- How to Measure M² Beam Quality: Camera and Knife-Edge MethodsProcedure for measuring laser beam quality (M²) per ISO 11146 with a beam-profiling camera or a knife edge: second-moment (D4σ) widths and why baseline noise inflates them, the caustic scan through a focus, hyperbolic fitting, automated M² systems, and the dominant errors.
- Loaded and Intrinsic Q Factor Extraction from Ring Resonator Transmission SpectraProcedure for extracting loaded and intrinsic quality factors of integrated ring resonators from measured transmission spectra, including fit methodology, the all-pass / add-drop distinction, and resolution of the coupling regime ambiguity.
- Waveguide Propagation Loss by the Cutback MethodProcedure for measuring optical propagation loss in integrated photonic waveguides using the cutback method, including paired-device variants used in foundry process control, fit methodology, and uncertainty analysis.
- Slope Efficiency and Differential Quantum Efficiency from LIV MeasurementsProcedure for extracting slope efficiency and external differential quantum efficiency from laser diode LIV data, with discussion of measurement geometry, facet-collection considerations, and common extraction errors.
- Characteristic Temperature Extraction from LIV MeasurementsProcedure for extracting the characteristic temperature T₀ of a semiconductor laser diode from temperature-dependent threshold current measurements, with worked example and discussion of extraction errors.
- Grating Coupler Fiber Alignment: Finding First LightActive alignment of a single-mode fiber to a silicon photonics grating coupler: height, 40 × 40 μm raster, polarization, fine search, expected loss, failure modes.
Glossary
- Acousto-optic modulator (AOM)
- Adaptive optics
- Anti-reflection coating (AR)
- Arc lamp (xenon, mercury)
- Autocorrelation (pulse measurement)
- Beam diameter (1/e², FWHM and D4σ)
- Beam dump (beam block)
- Beam expander
- Beam profiler
- Beam quality (M²)
- Beam splitter
- Bias tee
- Boxcar averager (gated integrator)
- Burn-in
- CCD vs CMOS image sensors
- Characteristic matrix method (transfer matrix for thin films)
- Characteristic temperature (T₀)
- Cold finger
- Collimation
- Confocal microscopy
- Cube beamsplitter
- Cutback method
- De-embedding
- Delayed self-heterodyne
- Dichroic mirror
- Die-level test
- Differential resistance
- Diffraction grating
- Diffuser
- Distributed acoustic sensing (DAS)
- Distributed temperature sensing (Raman DTS)
- Dither locking (top-of-fringe lock)
- Doppler shift
- Duty cycle
- Dynamic range
- Edge coupler
- Electrical spectrum analyzer (ESA, RF spectrum analyzer)
- Ellipsometry
- Etalon
- Eye diagram
- Far-field divergence
- Faraday rotator
- FBG sensor
- Fiber array (FAU)
- Fiber Bragg grating (FBG)
- Fiber cleaving
- Fiber connector types
- Fiber connectors: PC, UPC, APC
- Fiber patch cord (jumper)
- Fiber polishing
- Fiber-optic gyroscope
- Fiber-optic sensor
- First light
- Fizeau interferometer
- Fluorescence
- Fluorescence microscopy
- Forward voltage (V_f)
- FROG (frequency-resolved optical gating)
- FTIR spectroscopy
- Fusion splicing
- Galvo scanner
- Gaussian beam
- Grating coupler
- Hakki-Paoli method
- Hyperspectral imaging
- Impedance matching (50 Ω termination)
- Index-matching gel
- Insertion loss (IL)
- Integrating sphere
- Integration time (exposure time)
- Interferometer
- Irradiance
- Junction temperature
- Knife-edge measurement
- Laser Doppler vibrometry
- Laser machining
- Laser pointer
- Lensed fiber
- Linear optical sampling (LOS)
- LIV curve
- LIV kink
- Lock-in amplifier
- Malus's law
- Mode matching
- Mode mismatch loss
- Mode scrambler
- Monochromator
- Near field and far field
- Network analyzer
- Neutral-density filter
- Noise bandwidth (equivalent noise bandwidth)
- Notch filter
- Optical circulator
- Optical coherence tomography (OCT)
- Optical delay line
- Optical density (OD)
- Optical filter
- Optical frequency domain reflectometry (OFDR)
- Optical isolator
- Optical phase-locked loop (OPLL)
- Optical power meter
- Optical return loss
- Optical spectrum analyzer (OSA)
- Optical time-domain reflectometry (OTDR)
- Optical window
- Pellicle beamsplitter
- Photoacoustics
- Photodiode array
- Photoluminescence (PL)
- Photon transfer curve
- Photonic wire bonding
- Picosecond laser
- Pigtailing
- Polarization controller
- Polarization extinction ratio (PER)
- Polarization-maintaining (PM) fiber
- Polarized light microscopy
- Polarizer
- Pound-Drever-Hall locking (PDH)
- Power density
- Prism coupler
- Probe station
- Pseudo-random binary sequence (PRBS)
- Pulse duration
- Pulse energy
- Pump-probe spectroscopy
- Pyroelectric detector
- Radiometry vs photometry
- Raman spectroscopy
- Rayleigh range
- Resolution bandwidth
- Retroreflector
- Rise time (10–90%)
- Sampling oscilloscope
- Scanning Fabry-Perot interferometer
- Series resistance
- Shack-Hartmann wavefront sensor
- Side-mode suppression ratio (SMSR)
- Slope efficiency
- Source-measure unit (SMU)
- Spatial filter
- Speckle
- Spectrometer
- Stray light
- Streak camera
- Strehl ratio
- Submount
- SWIR camera
- TDECQ
- Thermal resistance
- Thermistor (NTC)
- Thermoelectric cooler (TEC)
- Thermopile
- Time of flight (ToF)
- Time-bandwidth product
- Time-correlated single-photon counting (TCSPC)
- Tracking error
- Transmittance
- Tunable diode laser absorption spectroscopy (TDLAS)
- Ultrastable optical cavity
- Vacuum chuck
- Variable optical attenuator (VOA)
- Wafer-level test
- Wall-plug efficiency
- Wavefront error
- Wavemeter
- Waveplate (retarder)
- Wire bonding
- X-ray diffraction (XRD)
- Zernike polynomials
- β-separation line