Wavelength Calculator
Calculate wavelength from frequency or frequency from wavelength. Supports all EM spectrum bands, refractive index, photon energy, wave number. Includes spectrum visual and reference table.
SLED (Superluminescent LED) Calculator
Calculate SLED characteristics including spectral width, coherence length, power spectral density, coupling efficiency, and wall-plug efficiency with source comparison table.
nm
nm
mW
%
mA
V
Center Frequency⧉
229.0076 THz
1,310.0 nm
Frequency Bandwidth⧉
6,992.60 GHz
40.0 nm spectral width
Coherence Length⧉
42.90 μm
L_c = λ²/Δλ
Power Spectral Density⧉
0.2500 mW/nm
-6.02 dBm/nm
Coupled Power⧉
5.000 mW
6.99 dBm (50% coupling)
Wall-Plug Efficiency⧉
8.33%
P_elec = 120.0 mW
Slope Efficiency⧉
0.100 mW/mA
Output power per drive current
Spectral Range⧉
1,290.0 – 1,330.0 nm
−3 dB bandwidth
Spectral Profile (Gaussian Approximation)
1,290 nm1,310 nm1,330 nm
SLED vs Other Sources
| Source Type | Spectral Width | Coherence Length | Typical Power | Key Use |
|---|---|---|---|---|
| SLED (this) | 40 nm | 43 μm | 10.0 mW | OCT, fiber sensing |
| DFB Laser | < 0.01 nm | > 10 m | 1–100 mW | Telecom, spectroscopy |
| FP Laser | 1–5 nm | 0.1–1 mm | 1–50 mW | Data links, sensing |
| Standard LED | 30–100 nm | 5–30 μm | 0.1–5 mW | Indicators, illumination |
| ASE Source | 30–80 nm | 10–50 μm | 1–20 mW | WDM testing |
Planning notes, formulas, and examples
About the SLED (Superluminescent LED) Calculator
A Superluminescent Light Emitting Diode (SLED or SLD) is an optical source that combines properties of both LEDs and laser diodes. Like an LED, it produces broadband, low-coherence light. Like a laser diode, it generates high-brightness, spatially coherent output suitable for single-mode fiber coupling. SLEDs are the workhorses of optical coherence tomography (OCT), fiber optic gyroscopes, and white-light interferometry.
The key figure of merit for a SLED is its spectral width — the broader the spectrum, the shorter the coherence length, and the finer the axial resolution in OCT imaging. Typical SLEDs produce 20–80 nm of spectral bandwidth centered at 850 nm, 1310 nm, or 1550 nm. Power levels range from a few milliwatts to tens of milliwatts.
This calculator determines the SLED's frequency bandwidth, coherence length, power spectral density, coupled fiber power, wall-plug efficiency, and slope efficiency. A comparison table shows how SLEDs relate to other optical sources like lasers and LEDs.
When This Page Helps
SLED specifications involve converting between wavelength and frequency domains, computing coherence length from spectral width, and evaluating coupling losses. This calculator is useful when you need to compare OCT source options, estimate usable fiber power, or check whether a source bandwidth supports the axial resolution you need.
How to Use the Inputs
- Enter the center wavelength in nanometers (typically 850, 1310, or 1550 nm).
- Enter the spectral width (FWHM) in nanometers.
- Enter the output power in milliwatts.
- Enter the fiber coupling efficiency as a percentage.
- Enter drive current and forward voltage for efficiency calculations.
- Use preset buttons for common SLED configurations.
- Review the spectral profile visualization and source comparison table.
Formula used
Center Frequency: f = c/λ
Frequency Bandwidth: Δf = c·Δλ/λ²
Coherence Length: L_c = λ²/Δλ
Power Spectral Density: PSD = P/Δλ
Coupled Power: P_fiber = P × η_coupling
Wall-Plug Efficiency: η = P_out / (I × V)
Where:
c = 3×10⁸ m/s
λ = center wavelength
Δλ = spectral width (FWHM)Example Calculation
Result: Coherence length = 42.9 μm, Coupled power = 5.0 mW
A SLED at 1310 nm with 40 nm spectral width has coherence length L_c = (1310 nm)²/(40 nm) ≈ 42.9 μm. With 10 mW output and 50% coupling, 5 mW reaches the fiber. Power spectral density is 10/40 = 0.25 mW/nm.
Tips & Best Practices
- Broader spectral width gives shorter coherence length and better OCT axial resolution.
- SLED output is polarized — use polarization-maintaining fiber for stable coupling.
- Temperature affects center wavelength (~0.4 nm/°C) and output power — use a TEC for stability.
- Optical isolators prevent back-reflections that can cause spectral ripple and instability.
- For OCT applications, a Gaussian spectral shape minimizes sidelobes in the coherence function.
- Multiple SLEDs at different wavelengths can be combined for ultra-broadband sources.
SLED Operating Principle
A SLED is essentially a semiconductor optical amplifier (SOA) with suppressed feedback. One facet is anti-reflection coated (reflectivity < 0.01%) to prevent lasing. Light generated by spontaneous emission is amplified in a single pass through the active region, producing amplified spontaneous emission (ASE). The result is a bright, broadband source with spatial coherence suitable for fiber coupling but low temporal coherence.
Spectral Shaping and Combining
For applications requiring ultra-broad bandwidth, multiple SLEDs centered at different wavelengths can be combined using fiber couplers or wavelength multiplexers. For example, combining an 1260 nm and a 1360 nm SLED can produce a combined bandwidth exceeding 100 nm. The spectral shape affects the point-spread function in OCT — a Gaussian spectrum is ideal, but combining sources may produce ripple that degrades image quality.
SLED vs ASE Source vs LED
SLEDs occupy a unique niche between LEDs and lasers. Standard LEDs produce broadband light but with Lambertian emission patterns, making fiber coupling inefficient. Erbium-doped fiber ASE sources provide excellent broadband output at 1550 nm but are bulky and expensive. SLEDs offer a compact, efficient package with good fiber coupling, making them the preferred choice for portable and clinical OCT systems.
Sources & Methodology
Last updated:
Frequently Asked Questions
A laser has a resonant cavity that produces narrow-linewidth, highly coherent light. A SLED has one facet anti-reflection coated to suppress lasing, producing broadband, low-coherence amplified spontaneous emission (ASE). SLEDs are brighter than LEDs but broader than lasers.
Coherence length is the optical path difference over which interference fringes remain visible. For a SLED, L_c = λ²/Δλ. Shorter coherence length enables finer axial resolution in interferometric measurements like OCT.
OCT requires a broadband, spatially coherent source. SLEDs provide wide spectral bandwidth (short coherence length for fine resolution) with enough power to couple efficiently into single-mode fiber. Their smooth Gaussian-like spectrum produces clean interference signals.
Common center wavelengths are 850 nm (retinal OCT, short fiber links), 1310 nm (low dispersion in fiber, dermal OCT), and 1550 nm (fiber optic gyroscopes, telecom testing). Some specialty SLEDs operate at 1060 nm or 1700 nm.
Coupling efficiency represents how much of the SLED output enters the optical fiber. Typical values are 30-60% for single-mode fiber. Losses come from mode mismatch, alignment, and Fresnel reflections. The coupled power determines the actual signal level in the system.
Not for long-distance telecom because SLEDs have lower spectral efficiency and higher dispersion penalty. However, SLEDs are used in fiber sensing, short-reach links, and wavelength-division multiplexing (WDM) test equipment.
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