Direct answer
A DWDM RFQ should specify nominal center frequency, grid rules and actual passband requirements. Fixed-grid spacing and flex-grid slot width are different fields; wavelength in nm is a conversion aid. Matching frequency alone does not approve module interoperability or a multifiber assembly.
Start from nominal frequency
ITU-T's G.694.1 record marks the 10/2020 edition in force at this review. It defines a DWDM frequency grid anchored at 193.1 THz, covering fixed and flexible grids.
“1550 nm DWDM” is still too broad for procurement. Equipment owners should specify center frequency and passband requirements for filters, multiplexers or tunable optics. Passive jumpers between them separately need connectors, fiber and loss boundaries.
Using THz-to-nm conversion
Frequency and vacuum wavelength follow λ(nm) = 299792.458 / f(THz). Their inverse relationship means a frequency grid does not produce an exactly uniform nm step.
These formula results are rounded label-reading examples, not device measurements. G.694.1 also treats its wavelength table as approximate; DWDM specifications use nominal central frequency.
| Center frequency | Approximate wavelength | Purchasing use |
|---|---|---|
| 193.10 THz | 1552.5244 nm | Retain frequency as the primary field |
| 193.15 THz | 1552.1225 nm | Adjacent frequency difference 50 GHz |
| 193.20 THz | 1551.7208 nm | Wavelength difference changes slightly |
Labels may contain both units. Configure the equipment using its approved grid. Identical channel numbers from different vendors do not independently establish a match.
Spacing, center granularity and slot width
The G.694.1 text gives flex-grid center granularity of 6.25 GHz and slot-width granularity of 12.5 GHz. They describe position and allocated spectral width respectively.
| Field | Object | RFQ check |
|---|---|---|
| Fixed-grid spacing | Spacing in a nominal-frequency set | Same grid rule at both ends |
| Nominal center | Channel or slot center | THz value and units |
| Flex-grid slot width | Allocated continuous frequency range | Width and neighboring allocation |
| Device passband | Specified physical transmission range | Measurement level, temperature and method |
For a hypothetical 193.100 THz center and 75 GHz allocated slot, the geometric edges are 193.0625 and 193.1375 THz. This allocation calculation proves neither loss flatness nor the passage of arbitrary signals.
What “flex-grid support” leaves unspecified
The standard permits different slot combinations; equipment may support only a subset. Obtain supported center positions, widths and software conditions, then have the equipment owner approve the selected combination.
Specify applicable device metrics, such as passband loss and neighboring-channel isolation, separately. An allocated width is not automatically a filter's usable flat passband or proof of end-to-end modulation compatibility.
Input to the fiber-assembly supplier
| Assembly input | Definition | Review |
|---|---|---|
| Optical ports | Approved references and connectors at both ends | Mating, polish and installation |
| Fiber path | Singlemode type, port map and length | Optical route and envelope |
| System test boundary | Operating band, power conditions and loss requirements | Defined optical tests |
| Service labels | Frequency associated with equipment ports | Identification and maintenance |
An ordinary passive jumper does not create a DWDM channel or correct a mismatched passband. The equipment optical system defines the channel plan; the cable assembly follows that approved plan.
Procurement FAQ
- Do matching channel numbers prove compatibility? Verify actual center frequency, grid and equipment numbering.
- Is 50 GHz always the same nm interval? Frequency and wavelength are inversely related; calculate at the actual center.
- Is 6.25 GHz the flex-grid width? It is center-frequency granularity; width is a separate field.
- Does a 75 GHz slot guarantee low loss throughout? Review allocation and physical transmission separately.
- Does using the same singlemode jumper approve the module pair? Optical, host and line conditions still need equipment approval.
Related products and reading
- CWDM wavelength and port checks
- Fiber-path loss budget
- Test-reference configuration
- OEM optical integration
Product pages describe configuration scopes. Actual supply, drawings and performance require project confirmation.
Contact an engineer
Prepare interface drawings, port requirements or existing test records and contact an engineer to discuss fiber-assembly configuration and verification.
Sources and review date
Sources checked on 2026-10-14. Third-party references explain technology and specified configurations, not ARRANEX performance or certification. Purchasing tables are review recommendations; worked examples use stated assumptions.
Sources checked: 2026-10-14