Integrated photonics
Waveguides and photonic integrated circuits: platforms, passive building blocks, modulators, couplers, and the loss and index numbers that govern them.
22 articles · 114 glossary terms · 11 tools · 4 materials
Start here: Silicon photonics in 12 pages
From the waveguide to the building blocks of a photonic chip and how it is tested.
- 1Photonic integrated circuit (PIC)Glossary
- 2Silicon-on-insulator (SOI)Glossary
- 3Effective index (n_eff)Glossary
- 4Strip vs rib waveguideGlossary
- 5Propagation lossGlossary
- 6Grating couplerGlossary
- 7Edge Coupler vs Grating Coupler: Choosing Fiber I/O for a Photonic ChipArticle
- 8Directional couplerGlossary
- 9Directional Coupler and MZI CalculatorTool
- 10Ring resonatorGlossary
- 11Mach-Zehnder modulator (MZM)Glossary
- 12Wafer-Level Optical Testing of Photonic Chips: Setup, Alignment and Test FlowArticle
Tools
Convert between grating period and Bragg wavelength for DFB/DBR lasers and integrated photonic Bragg gratings.
Convert intrinsic Q to waveguide propagation loss for ring resonators, with platform presets for SOI, SiN, InP, and LNOI.
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.
Synthesize a 200G-per-lane PAM4 waveform with adjustable bandwidth, noise, jitter, extinction ratio, and level skew, and compute TDECQ through the Bessel-Thomson reference receiver and a 5-tap equalizer, with equalized histograms, tap weights, and guided experiments.
Loss-margin waterfall, per-lane G.652 chromatic dispersion with UI-spread zones, and energy per bit across pluggable, LPO, and CPO at fleet scale, with presets for 400G, 800G, and 1.6T classes and guided experiments.
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.
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.
Free-carrier index and absorption change in silicon from the Soref and Bennett relations at 1310 and 1550 nm and the Nedeljkovic fits at 1550 and 2000 nm: Δn and Δα for any electron and hole density, phase shift and loss for a given length and mode overlap, the length for π and its cost in dB, doped-waveguide loss, and a 17-row validation table.
Solve slab waveguide modes exactly: mode profiles with evanescent tails, an neff-versus-thickness cutoff map, confinement, birefringence, the single-mode window, and a propagating field view for TE and TM.
Free spectral range, finesse, linewidth, Q, photon lifetime, mirror loss, peak transmission, fringe contrast and intracavity power for a plane-parallel or confocal two-mirror cavity of any length, index, reflectivities and internal loss, with exact Airy transmission and reflection spectra, presets from etalons and laser diode chips to ULE reference cavities, guided experiments and a validation table.
Split ratio, crossover length and wavelength range of a directional coupler from the supermode index difference by coupled-mode theory, and the free spectral range, output and extinction ratio of a Mach-Zehnder interferometer built from those couplers, with plots, presets, guided experiments and a validation table.
Articles
- Silicon Photonics Foundries, PDKs and MPW Runs: How a Shuttle WorksHow a photonic chip gets made in a shared foundry run: what a process design kit provides, how a multi-project wafer (MPW) shuttle is organized, the steps from design to tape-out to delivered dies, what to put on a first chip, and the common reasons first silicon disappoints.
- The Silicon Photonics Design Flow: From Mode Solver to Tape-OutThe steps in designing a silicon photonic chip, in order: choosing the platform and waveguide, simulating components, building the circuit from compact models, designing for variation and temperature, layout and verification, tape-out, and testing first silicon, with the site's pages for each step and worked numbers for a ring resonator.
- Bits to Light: How an Optical Transceiver Sends DataThe path a bit takes through an optical link, from the host's SerDes through FEC, the modulation format, the driver and the laser or modulator, the fiber, the photodiode and transimpedance amplifier, to clock recovery and decoding, with the numbers for a 100 Gb/s PAM4 lane: 53.125 GBd, 18.8 ps symbols, the RS(544,514) FEC and the 9.5 dB PAM4 penalty.
- 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 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.
- 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.
- Choosing a Photonics Simulation Method: Mode Solver, EME, BPM, FDTDHow to choose between the main electromagnetic simulation methods for photonic devices: eigenmode solvers, eigenmode expansion, the beam propagation method, FDTD, and circuit-level models, with what each assumes, what it costs, typical meshes and run sizes, and which to use for waveguides, couplers, tapers, gratings, rings and circuits.
- 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.
- 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.
- Why Light Moves Data and Electrons Still ComputeAn honest assessment of optical computing versus optical interconnect: why matrix multiplication in a photonic mesh looks free but is not once conversion and precision are counted, why the same companies pivoted from optical compute to optical interconnect, and where compute by light still fits.
- Optical Circuit Switches in AI Datacenters: How an OCS Works and Why It Is BackHow an optical circuit switch (OCS) works, from the MEMS mirror array that steers each beam to the insertion loss it adds to the link budget; the millisecond-reconfiguration-versus-packet-switching tradeoff it forces; and the traffic patterns of AI training fabrics that make a transparent, protocol-agnostic switch pay off.
- LPO vs LRO vs CPO: Power per Bit at 1.6TAt 1.6T a DSP pluggable runs 13.8 pJ/bit, LPO 7.9 and CPO 6.4. What LRO, LPO and CPO each remove, and what they cost in interoperability and serviceability.
- Light Sources for Co-Packaged OpticsWhy co-packaged optics keeps its lasers outside the package: the thermal, reliability, and yield arguments, the ELSFP and CW-WDM interface standards, the laser-count arithmetic of split-and-modulate architectures, quantum dot combs against Kerr microcombs, and a worked power budget from wall plug to modulator.
- 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.
- Thermo-Optic Coefficient of Silicon Nitride, Silicon, and Other Photonic Materials: dn/dT Reference Tabledn/dT of silicon nitride (2.45 × 10⁻⁵ K⁻¹ for LPCVD Si₃N₄ at 1550 nm) against silicon, silica, InP, GaAs, lithium niobate, and polymers, with sources; the measured ring-resonance drift and heater efficiency that follow from each; a silicon nitride versus silicon platform table; and the film, wavelength, and temperature caveats.
- 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.
- 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.
- 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.
- 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
- Adiabatic coupler
- Apodization (apodized gratings and apodizing filters)
- Arrayed waveguide grating (AWG)
- Barium titanate modulator (BTO)
- Beam steering
- Beat length
- Bend loss
- Bragg condition (Bragg's law)
- Carrier injection
- Co-packaged optics (CPO)
- Confinement factor (Γ)
- Core and cladding
- Coupling coefficient (κ)
- Coupling efficiency
- Critical coupling
- Cutback method
- Cutoff wavelength
- De-embedding
- DFB laser array
- Die-level test
- Directional coupler
- Distributed Bragg reflector (DBR mirror)
- Edge coupler
- Effective area (A_eff)
- Effective index (n_eff)
- Effective index method
- Electro-absorption modulator (EAM)
- Electro-optic effect (Pockels effect)
- Electro-optic modulator (EOM)
- Erbium-doped waveguide amplifier (EDWA)
- Evanescent wave
- External laser source (ELS, ELSFP)
- Extinction ratio (ER)
- Facet (laser and waveguide facets)
- Fiber array (FAU)
- Filling factor
- Finesse
- Finite-difference time-domain (FDTD) method
- Flip-chip bonded laser
- FMCW lidar
- Franz-Keldysh effect
- Free spectral range (FSR)
- Free-carrier absorption (FCA)
- Germanium-on-silicon photodetector
- Grating coupler
- Group index (n_g)
- Guided mode
- Half-wave voltage (Vπ)
- Heterogeneous integration
- Higher-order modes
- Index contrast
- Inverse taper
- Lattice matching
- Leaky mode
- Lensed fiber
- Lithium niobate on insulator (LNOI, TFLN)
- LRO (linear receive optics)
- Mach-Zehnder modulator (MZM)
- Mach–Zehnder interferometer (MZI)
- Metasurface and metalens
- Micro-transfer printing
- Microcomb (Kerr soliton frequency comb)
- Microring modulator
- Modal gain
- Mode field diameter (MFD)
- Mode mismatch loss
- Mode solver
- Multimode interference (MMI) coupler
- Near-packaged optics (NPO)
- Neuromorphic photonics
- Optical computing
- Optical I/O (chiplet optics)
- Optical phase shifter
- Optical phased array (OPA)
- Photonic crystal
- Photonic integrated circuit (PIC)
- Photonic quantum computing
- Photonic tensor core
- Photonic wire bonding
- Pigtailing
- Plasma dispersion effect (Soref-Bennett relations)
- Pockels effect (linear electro-optic effect)
- Polarization splitter-rotator (PSR)
- Prism coupler
- Probe station
- Process design kit (PDK)
- Propagation constant (β)
- Propagation loss
- Quality factor (Q)
- Quantum dot laser
- Quantum photonic integrated circuit (QPIC)
- Quantum-confined Stark effect (QCSE)
- Quasi-phase matching (QPM)
- Ring resonator
- Self-injection locking
- Semiconductor optical amplifier (SOA)
- Sidewall roughness
- Silicon nitride photonics
- Silicon-on-insulator (SOI)
- Slab waveguide
- Spot-size converter (SSC)
- Stop band
- Strip vs rib waveguide
- Substrate leakage
- Surface plasmon (polariton)
- TE and TM polarization
- Thermo-optic phase shifter
- Traveling-wave electrode (velocity matching)
- Two-photon absorption (TPA)
- Wafer-level test
- Whispering-gallery-mode resonator
- Wire bonding
- X-cut lithium niobate
- Y-branch
Materials
The native platform of telecom light. Direct bandgap, lattice-matched quaternaries spanning 1.0–1.65 μm, and monolithic integration of lasers, amplifiers, modulators, and detectors on one substrate.
The electro-optic material. A strong Pockels effect, wide transparency, and ferroelectric poling made bulk LiNbO₃ the telecom modulator standard for decades; thin-film LiNbO₃ has rebuilt the platform at chip scale.
The workhorse of integrated photonics. High index contrast on SOI enables dense circuits at telecom wavelengths, at the cost of two-photon absorption, no native gain, and no second-order nonlinearity.
The low-loss, high-power passive platform. Moderate index contrast, transparency from the visible into the mid-IR, negligible nonlinear absorption at telecom wavelengths. No gain, detection, or fast modulation of its own.