Glossary
Concise definitions of the photonics, layout, and simulation terms used throughout the Qfactr documentation.
This glossary collects the terms you will meet across the Qfactr docs, from photonic device physics to the file formats you export. Most are standard photonic-integrated-circuit (PIC) vocabulary; a few describe how Qfactr represents a design. Where a term has a dedicated page, it is linked from its definition.
The entries are grouped: core physics and devices, layout and routing, simulation and verification, materials, and data formats. Use the on-this-page navigation to jump to a group, or read top to bottom for a guided tour of the field.
Light, waveguides, and devices
| Term | Definition |
|---|---|
| PIC (photonic integrated circuit) | A chip that guides and manipulates light to perform a function, the optical analogue of an electronic integrated circuit. See Photonic integrated circuits 101. |
| Waveguide | A structure that confines and guides light along a path on the chip. A higher-index core surrounded by lower-index cladding traps light by total internal reflection. See Waveguides & routing. |
| Mode | A stable spatial pattern of the guided optical field that propagates without changing shape. A waveguide that supports exactly one such pattern is single-mode; one that supports several is multi-mode. |
| Index contrast | The difference in refractive index between a waveguide's core and its cladding. Higher contrast confines light more tightly, enabling smaller bends but tightening fabrication tolerances. |
| Directional coupler | Two waveguides placed close enough that light evanescently couples between them; the split ratio depends on the coupling length and gap. Used for splitting, combining, and tapping power. |
| MMI coupler (multimode interference) | A wide multimode section that uses self-imaging to split or combine light at fixed ratios. Compact and fabrication-tolerant, commonly used as a 1x2 or 2x2 splitter. |
| Ring resonator | A looped waveguide coupled to a bus waveguide that resonates at wavelengths fitting a whole number of times around the loop. Used for filtering, modulation, and sensing. The docs reference an example ring with r = 10 µm. |
| MZI (Mach-Zehnder interferometer) | A structure that splits light into two arms and recombines it; a controllable phase difference between the arms sets the output. The basis of many modulators and switches. |
| Phase shifter | An element that changes the optical phase in a waveguide, typically thermo-optic (heating shifts the index) or electro-optic (an applied field shifts it). Used to tune MZIs, rings, and switches. |
| Grating coupler | A periodic grating that couples light between an on-chip waveguide and an out-of-plane optical fiber, used for chip input and output (I/O). |
| Photodetector | A device that converts guided optical power into an electrical signal, the optical-to-electrical endpoint of a link. |
For one-line descriptions of every standard building block and how Qfactr libraries carry them, see Components & building blocks.
Layout and routing
| Term | Definition |
|---|---|
| Pin / port | A physical optical (or electrical) connection point on a component, located at real coordinates. In Qfactr a pin renders red when unconnected and green once a route reaches it. Identifiers look like PS2.out or CMB.in2. |
| Route | An explicit waveguide path drawn between two pins as real S-bend or Manhattan geometry, not an abstract net. See Routing waveguides. |
| S-bend | A smooth, gradually curving waveguide segment that offsets a path laterally while keeping bends gentle to limit radiation loss. |
| Manhattan routing | Routing constrained to orthogonal (horizontal and vertical) segments. Predictable and dense, but every corner is a bend that must respect the minimum bend radius. |
| Bend radius | The radius of a waveguide turn. Below a platform's minimum bend radius, light leaks out of the guide as radiation loss; tighter bends cost more power. |
| Insertion loss | The total optical power lost when light passes through a component or path, usually expressed in decibels (dB). |
| Propagation loss | Power lost per unit length as light travels along a straight waveguide, from scattering and material absorption, typically quoted in dB/cm. |
| Hierarchy / cell | A reusable subcircuit packaged as a block (or cell) with defined external pins and a frozen layout, then instanced into larger systems. See Hierarchical blocks. |
| Netlist | A connectivity-only description listing components and which ports connect to which, with no physical geometry. Qfactr instead keeps connectivity and real layout together in one editable model. |
Simulation and verification
| Term | Definition |
|---|---|
| S-parameters (S-matrix) | A frequency-domain description of how an optical component transmits and reflects power between its ports. Qfactr's PDK-aware parts carry S-matrix data so they behave like the devices they represent. |
| FDTD (finite-difference time-domain) | A full electromagnetic solver that steps Maxwell's equations through space and time. Accurate and general, but computationally heavy, typically used to characterize individual components. |
| EME (eigenmode expansion) | A frequency-domain method that expresses the field as a sum of waveguide modes, efficient for long, slowly varying structures such as tapers and couplers. |
| DRC (design rule check) | Automated verification that a layout obeys a foundry's manufacturability rules (minimum widths, spacings, enclosures). See Process design kits (PDKs). |
Material platforms
| Term | Definition |
|---|---|
| Silicon photonics (SOI) | PICs built on silicon-on-insulator wafers. High index contrast gives compact circuits and reuse of CMOS fabrication, at the cost of higher propagation loss than some alternatives. |
| Silicon nitride (SiN) | A lower-index-contrast platform with very low propagation loss over a broad wavelength range, favored for filters, sensing, and low-loss passive circuits. |
| InP (indium phosphide) | A III-V platform that can generate, amplify, and detect light natively, used where on-chip lasers and active devices are required. |
| Thin-film lithium niobate (TFLN) | A platform with a strong electro-optic effect, enabling high-speed, low-drive-voltage modulators. |
Process kits and data formats
| Term | Definition |
|---|---|
| PDK (process design kit) | A foundry-validated package of components, compact/S-parameter models, design rules, and layer information tied to a specific fabrication process. Qfactr ships a starter Demo-PDK. See Process design kits (PDKs). |
| PCell (parameterized cell) | A component whose geometry is generated from parameters (lengths, radii, gaps) rather than fixed, so one definition produces a family of correctly drawn instances. |
| GDSII (GDS) | The standard binary layout format for the physical mask geometry sent to a foundry, the universal handoff for fabrication. See Export formats. |
| Nazca | A Python-based photonic layout framework. Qfactr exports to Nazca plus GDS to hand off into an existing fabrication flow. |
| SAX / Simphony | Frequency-domain circuit simulators that compose component S-parameters to predict a full circuit's response. |
| PhotonTorch | A time-domain, GPU-accelerated photonic circuit simulator, used for dynamic and large-scale analysis. |
| Verilog-A / SPICE | Modeling languages and simulators from the electronics world, used to co-simulate photonic circuits together with their driving and receiving electronics. |
Qfactr is built on the open-source Lunima engine, which provides the physical layout, PDK-aware components, explicit routing, simulation-aware loss, hierarchy, and these exports.
Next steps
Photonic integrated circuits 101A primer on what PICs are, why photonics, and how light is guided on a chip.Components & building blocksEach standard device, what it does, and a typical use, with how Qfactr libraries carry them.Export formatsA reference table of every export target and what to use each one for.