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Fiber Optic Design

Fiber Optic System Designer

Drag-drop optical network designer with a bidirectional link-budget engine, WDM wavelength routing, ITU-T compliance check, OSNR and chromatic dispersion budgets, and an interactive OTDR trace view per node. The engineering core for any fiber project from FTTH access to DWDM long-haul.

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Welcome card with template / blank / help quick-start.
Welcome card with template / blank / help quick-start.
Generic-named component palette grouped by engineering role.
Generic-named component palette grouped by engineering role.
Drag-from-port-to-port wiring with hover-revealed labels.
Drag-from-port-to-port wiring with hover-revealed labels.
Component properties modal with field-level help.
Component properties modal with field-level help.
Interactive OTDR trace with pan / zoom / event navigation.
Interactive OTDR trace with pan / zoom / event navigation.

Overview

A fiber project lives or dies on its link budget, and the link budget is where the errors hide. Every connectorised node adds pigtail loss, every fiber span adds attenuation and chromatic dispersion, every fan-out at a splitter or a demux divides the power, and every amplifier in a long-haul chain adds ASE noise that erodes OSNR. Compute it by hand in a spreadsheet and the bidirectional case (a GPON drop carries downstream at one wavelength and upstream at another), the wavelength routing through the WDM elements, and the ITU-T budget class each design satisfies all become separate manual exercises that drift out of step with the topology.

The noIM₃ Fiber Optic System Designer is the engineering layer of a fiber project on one canvas. Drag components from the palette (transmitter, receiver, transponder, fiber span, splice, connector, patch panel, attenuators, monitor tap, isolator, splitter, the full WDM suite, and optical amplifier) onto a node graph, wire output ports to input ports, and the engine recomputes the whole link budget on every change. Each fan-out is treated as a distinct path, so every TX to RX pair reports its own hop-by-hop waterfall, cumulative loss, Rx power, margin against sensitivity and overload, OSNR, and accumulated chromatic dispersion.

Bidirectional analysis runs a reverse pass so downstream and upstream margins sit side by side, with isolators correctly blocking the reverse direction and transponders terminating it. WDM elements are wavelength-aware, so a transmitter wired to a mux port tagged a different wavelength is blocked at the mux with a validation note rather than silently producing the wrong answer. Compliance auto-matches forward paths against the ITU-T GPON, XG-PON, XGS-PON and NG-PON2 budget classes including a system reserve, and a continuous validation pass surfaces polish mismatches, band errors, amplifier saturation, splitter starvation, and receiver overload by severity.

Right-click any node for an OTDR Trace From Here. The interactive OTDR view renders reflections as reflectance-proportional bell curves convolved with the selected pulse width and splices as faster-sloping sections of the trace, just like a field instrument, so a target trace can be generated for the install crew before the fiber is ever laid. Projects auto-save to browser storage, support a versioned .fsd file format, ship with a templates library spanning GPON, CWDM/DWDM, ROADM, long-haul EDFA chains, mine backbone, and data-centre short-reach designs, and offer full undo, redo, copy, paste, pan and zoom.

Capabilities

Drag-drop node-graph canvas

An SVG canvas with a palette grouped by engineering role: Endpoints (transmitter, receiver, transponder), Fiber and Passives (fiber span, splice, connector, patch panel), Loss Elements (fixed and variable attenuator, monitor tap, isolator), Power Branching (splitter), the WDM Suite (multiplexer, demultiplexer, add/drop, reconfigurable add/drop, channel filter, dispersion compensator), and Active (optical amplifier). Drag a component onto the canvas, then wire output ports to input ports by dragging port to port or click-then-click. Pan, wheel-zoom anchored on the cursor, fit-to-content and 1:1 reset keep large topologies workable. Wire-creation validation blocks self-loops, wrong-direction wires, and cycles.

Bidirectional link-budget engine

Forward (TX to RX) and reverse (RX to TX) traversals run from every endpoint. Loss is applied per output port, so a monitor-tap MAIN port differs from its MON port, an add/drop express path differs from its drop path, and a ROADM line-out differs from its drop. Equipment pigtail loss (0.3 dB IN plus 0.3 dB OUT per connectorised node) is baked into every traversal, and fiber spans include a configurable per-end termination loss (default 0.35 dB, one connector mate plus one fusion splice). Optical amplifier output saturates at its configured ceiling; transponders regenerate, resetting power, wavelength, noise, and dispersion. Every TX to RX pair reports its own waterfall, cumulative loss, Rx power, margin, OSNR, and dispersion.

WDM wavelength routing

Mux input ports, demux output ports, channel-filter pass-band, add/drop drop-wavelength, and the ROADM drop-wavelength list all filter on the path wavelength using a configurable per-port channel plan. A 1530 nm transmitter wired to a mux port tagged 1550 nm is blocked at the mux with a validation note instead of silently routing the wrong answer. The wavelength match tolerance is 0.4 nm, half a 100 GHz ITU channel, so adjacent grid channels never accidentally match. Default channel plans seed the ITU 100 GHz C-band grid with a one-click reseed in the properties modal.

ITU-T compliance check

Auto-matches every forward path against the standard budget classes: GPON G.984 A (20 dB), B (25 dB), B+ (28 dB), C (30 dB), C+ (32 dB); and XG-PON / XGS-PON / NG-PON2 (G.987 / G.9807 / G.989) N1 (29 dB), N2 (31 dB), E1 (33 dB), E2 (35 dB). A 1.3 dB system reserve (aging 0.5, repair 0.5, temperature 0.3) is included, and the engine picks the smallest class whose budget covers the path. The section header reports the best-fit standard across all paths, and per-path headroom is shown so upgrades can be sized.

OSNR and chromatic dispersion budgets

Each optical amplifier accumulates ASE noise per its noise figure using a −58 dBm reference at 0.1 nm bandwidth, so OSNR at the receiver is signal power minus accumulated noise. A receiver optional OSNR requirement triggers an OSNR-marginal warning within 3 dB of the floor and an OSNR-fail error below it. Fiber spans accumulate chromatic dispersion using their per-span ps/(nm·km) coefficient times length; a dispersion compensator subtracts its ps/nm value and a transponder resets it to zero. The receiver optional dispersion tolerance triggers a dispersion-fail error when net accumulated CD exceeds it.

Interactive OTDR trace per node

Right-click any node and pick OTDR Trace From Here for a field-style trace view. The engine auto-picks the direction (forward or reverse) with the most reachable content. Reflections render as smooth sin(πt) bell curves with height proportional to reflectance (APC faint, UPC a visible bump, an open end a towering Fresnel) and width set by the selectable pulse width (5 / 10 / 30 / 100 / 300 ns, 1 / 10 µs). Splices and equipment bulk loss render as faster-sloping smoothstep sections. The test wavelength selector (1310 / 1490 / 1550 / 1577 / 1625 / 850 nm) re-runs the trace against the per-fiber-type attenuation table. Wheel zooms on the cursor, drag pans, clicking an event row centres the chart, and the event table exports to CSV.

Structural validation engine

A validation pass runs continuously and groups issues by severity: APC to UPC connector polish mismatch (reflection risk), wavelength outside the fiber type operating band (for example 850 nm into G.652 SMF), EDFA driven into saturation, VOA set-point outside its operating range, fiber attenuation outside the plausible envelope per fiber type, unwired transmitter output, unreached receiver, mux/demux wavelength mismatch, splitter starvation, receiver overload, OSNR floor violation, and chromatic dispersion tolerance violation. Each issue carries a clear engineering explanation and links back to the affected node.

Per-path waterfall and status pills

Each path renders its own card: mini-stat tiles for total loss, Rx power, margin, OSNR, and accumulated chromatic dispersion sit above a hop-by-hop waterfall table that lists the hop label, type, delta dB, cumulative loss, and power-out at every node, with the terminating receiver row highlighted. The Bidirectional Links table pairs each downstream path with its upstream twin, showing DL and UL margin side by side and combining them into a single status pill (OK / MARG / UNDER / OL). A Link Budget Summary card headlines DL and UL path counts and the worst-case margin across both directions.

Multi-tab projects, auto-save, and templates

A tab strip keeps several independent designs in one project, each with its own undo/redo history (Ctrl+Z / Ctrl+Y). The whole project auto-saves to browser localStorage on every change (400 ms debounce) with a "saved Xs ago" status pill in the header that turns red on a storage failure. The versioned .fsd project file (v2, with v1 legacy compatibility) moves work between machines. A templates library ships nine starter designs, GPON 1:32, GPON 1:64 two-stage, P2P with EDFA, a 3-amp EDFA chain at 240 km, 4-channel CWDM, 8-channel DWDM with EDFA, ROADM with add/drop, OM4 data-centre short reach, and a mine backbone with a monitor tap, each seeded to realistic engineering defaults.

Standards & methodology

  • ITU-T G.984 GPON budget classes A (20 dB) / B (25 dB) / B+ (28 dB) / C (30 dB) / C+ (32 dB)
  • ITU-T G.987 XG-PON, G.9807 XGS-PON, and G.989 NG-PON2 classes N1 (29 dB) / N2 (31 dB) / E1 (33 dB) / E2 (35 dB)
  • System reserve 1.3 dB (aging 0.5 + repair 0.5 + temperature 0.3) applied to every path
  • ITU-T G.652 standard single-mode fiber and G.657 bend-insensitive single-mode fiber
  • ITU-T G.671 typical splitter loss
  • ITU 100 GHz C-band channel grid with 0.4 nm wavelength match tolerance
  • OSNR reference floor −58 dBm at 0.1 nm bandwidth

When to use this tool

  • Design a greenfield FTTH GPON access link and verify it fits the GPON B+ / C+ class budget
  • Plan an XGS-PON upgrade from an existing GPON plant and check the same fiber and splitter still work at 1577 / 1270 nm
  • Size the splitter ratio and feeder length for an FTTH deployment from optical headroom and OSNR target
  • Verify a long-haul C-band DWDM link end to end including ASE noise from a chain of EDFAs and chromatic dispersion against the receiver tolerance
  • Plan a ROADM with add/drop on a multi-channel trunk and verify the per-channel routing is correct
  • Audit a vendor-supplied design against an independent ITU-T budget model with all reserves visible
  • Generate a target OTDR trace for the field tech before installation so they know what events to expect and at what distance
  • Diagnose an in-service link by mirroring the as-built topology and matching the live OTDR trace against the modelled one
  • Decide between APC and UPC polish for a planned drop cable and flag the polish-mismatch risk before procurement
  • Plan a mine backbone with an inline monitor tap and quantify the loss penalty of the live-fiber OTDR access point
  • Verify a data-centre OM4 short-reach link at 850 nm against channel loss limits
  • Run the same topology through GPON / XG-PON / XGS-PON / NG-PON2 budget classes and quantify the upgrade headroom

Is this the right tool for you?

Reach for the Fiber Optic System Designer in any of the following situations.

  • You are planning a new FTTH GPON drop and need to confirm the splitter ratio and feeder length leave enough margin to satisfy a B+ or C+ budget class.
  • You are upgrading an existing GPON plant to XGS-PON and need to verify the in-place fiber and splitter still close at the XGS-PON wavelengths before committing to the swap.
  • You are verifying a long-haul DWDM link with a chain of EDFAs and need OSNR accumulated across every amplifier and chromatic dispersion checked against the receiver tolerance.
  • You are routing channels through a ROADM with add/drop on a multi-channel trunk and need to confirm each channel reaches the right drop without a wavelength clash.
  • You have a vendor-supplied design and need to audit it against an independent ITU-T budget model with the aging, repair, and temperature reserves made explicit.
  • You are about to send a crew to install a span and want a target OTDR trace so they know which events to expect and at what distance before they connect anything.
  • You are diagnosing an in-service fault and need to mirror the as-built topology so the modelled OTDR trace can be compared against the live instrument trace.
  • You are specifying a drop cable and need the polish-mismatch (APC to UPC) reflection risk flagged before the connectors are ordered.
  • You are designing a mine backbone with an inline monitor tap and need to quantify the loss penalty the live-fiber access point adds to the budget.
  • You are keeping several candidate designs side by side in one project and need per-tab undo and an auto-saved, shareable .fsd file.

Frequently asked questions

What does the link-budget engine actually account for?

It traces every TX to RX path and accumulates fiber attenuation, splice loss, connector loss, patch-panel loss, splitter and WDM fan-out loss, and equipment pigtail loss (0.3 dB IN plus 0.3 dB OUT per connectorised node). Fiber spans include a configurable per-end termination loss (default 0.35 dB, one connector mate plus one fusion splice). Each fan-out is a distinct path, so every TX to RX pair gets its own hop-by-hop waterfall, cumulative loss, Rx power, margin against sensitivity and overload, OSNR, and accumulated chromatic dispersion.

How does the bidirectional (downstream and upstream) analysis work?

Downstream paths originate at transmitters and terminate at receivers. Upstream paths originate at receivers using their optional return TX power and return wavelength (for example an ONT TX at 1310 nm in a GPON design) and terminate at transmitters. The engine runs both traversals so downstream and upstream margins sit side by side in the Bidirectional Links table, combined into a single status pill. Isolators correctly block the reverse direction and transponders terminate it.

Which ITU-T standards does the compliance check cover?

It auto-matches every forward path against the GPON G.984 classes A (20 dB), B (25 dB), B+ (28 dB), C (30 dB), and C+ (32 dB), and the XG-PON / XGS-PON / NG-PON2 classes (G.987 / G.9807 / G.989) N1 (29 dB), N2 (31 dB), E1 (33 dB), and E2 (35 dB). A 1.3 dB system reserve (aging 0.5, repair 0.5, temperature 0.3) is included, and the engine picks the smallest class whose budget covers the path, reporting the best-fit standard across all paths in the section header.

How is OSNR computed through a chain of amplifiers?

Each optical amplifier accumulates ASE noise per its noise figure using a −58 dBm reference at 0.1 nm bandwidth, with the running noise level carried through the traversal. OSNR at the receiver is signal power minus accumulated noise. If a receiver has an optional OSNR requirement set, the engine flags an OSNR-marginal warning within 3 dB of the floor and an OSNR-fail error below it.

Does the OTDR view behave like a real field instrument?

It is a field-style modelled trace. Reflections render as smooth sin(πt) bell curves with height proportional to the event reflectance (APC faint, UPC a visible bump, an open end a towering Fresnel) and width set by the selectable pulse width from 5 ns to 10 µs, so long pulses smear closely-spaced events the way a real OTDR struggles to resolve them. Splices and equipment bulk loss appear as faster-sloping sections of the trace. The test wavelength selector re-runs the trace against the per-fiber-type attenuation table, and the event table exports to CSV.

How does the tool stop a wavelength from being routed to the wrong port?

WDM elements are wavelength-aware. Mux input ports, demux output ports, channel-filter pass-bands, add/drop drop-wavelengths, and the ROADM drop-wavelength list all filter on the path wavelength against a configurable per-port plan. A transmitter wired to a port tagged a different wavelength is blocked there with a validation note rather than silently producing the wrong answer. The match tolerance is 0.4 nm, half a 100 GHz ITU channel, so adjacent grid channels never accidentally match.

Is my design saved, and can I move it between machines?

The whole project auto-saves to browser localStorage on every change (400 ms debounce) with a "saved Xs ago" status pill in the header that turns red on a storage failure. You can keep several independent designs in one multi-tab project, each with its own undo/redo history. The versioned .fsd project file (v2, with v1 legacy compatibility) lets you save and load across sessions and machines.