SMA905-FC spectrometer multimode fiber wiring infrared-IR-200UM-0.22NA 2m

Optical Fiber · SMA905 to FC · Multimode · 200um / 0.22NA · 2 Meter · In stock

What Is This SMA905-FC Multimode Fiber Patch Cord?

This is a 2-meter multimode optical fiber patch cable with an SMA905 connector on one end and an FC connector on the other. The fiber has a 200-micron core diameter and a numerical aperture (NA) of 0.22, optimized for the near-infrared (NIR) range. It is typically used to couple light from a spectrometer, light source, or optical sensor into another instrument — for example, connecting a fiber-coupled spectrometer to a sample probe, or linking a laser to a cuvette holder in an absorption measurement setup.

In short: A 2-meter light pipe with an SMA905 plug on one end and an FC plug on the other, carrying infrared light through a 200-micron glass core — the bridge cable that connects optical instruments with mismatched fiber ports.

Understanding Fiber Specifications for Spectroscopy

1. 200um Core: Why Size Matters for Light Collection

The 200-micron core diameter is the light-carrying channel inside the fiber. A larger core collects more light from a diffuse or extended source — important when you are gathering emission from a fluorescent sample, a scattering medium, or a plasma. The trade-off is that a larger core reduces spectral resolution when coupled to a spectrometer's entrance slit, because the fiber core acts as an extended source at the slit plane. If your spectrometer slit width is 50um or less, much of the light from this 200um fiber will be vignetted (blocked). For highest resolution with this fiber, use a spectrometer with a 100-200um slit.

2. NA 0.22: The Acceptance Cone Angle

Numerical aperture 0.22 means the fiber accepts light entering at up to roughly 12.7 degrees off-axis (half-angle). Light rays outside this acceptance cone escape through the cladding and are lost. When coupling a light source into this fiber, match the source's output NA to 0.22 — a laser with a tight collimated beam (NA ~ 0.01) couples efficiently, while a bare LED with a Lambertian emission (NA ~ 1.0) couples very little power. A focusing lens between the source and the fiber face improves coupling dramatically.

3. Connector Types: SMA905 vs. FC

SMA905 uses a threaded collar with a 1/4-36 thread and a 3.17mm ferrule that seats the fiber end at a fixed physical contact plane — common on spectrometers from Ocean Optics, Avantes, and similar instruments. FC uses a threaded collar with a keyed alignment notch and a 2.5mm ferrule — common on telecom equipment and some laser sources. These connectors are not interchangeable, which is exactly why this hybrid patch cord exists. The keyed FC end ensures the fiber is aligned rotationally; do not force an FC connector if the key does not seat in the mating adapter.

Key Specifications

Frequently Asked Questions

How do I clean the fiber end faces before connecting them?

Dirty connector end faces are the #1 cause of low throughput in fiber-coupled optical systems. Use a fiber optic connector cleaning tool (one-click cleaner) designed for the specific ferrule size — 3.17mm for SMA905, 2.5mm for FC. Alternatively, use lens tissue moistened with isopropyl alcohol (99.9%, not drugstore 70%) and wipe the ferrule tip once in a straight motion — do not rub back and forth. Inspect with a fiber inspection scope if you have one. A single dust particle on the core can block 50% or more of the light, especially with the 200um core.

Can I use this fiber at visible wavelengths like 532nm or 633nm?

This fiber is specified for infrared, which typically means the core material is low-OH (low hydroxyl) silica optimized for transmission above roughly 700nm. At visible wavelengths, low-OH fiber has higher attenuation than UV/VIS-grade (high-OH) fiber, but for a 2-meter length the loss is usually acceptable — you will get light through at 532nm or 633nm. The limit is at the UV end: below about 400nm, low-OH fiber absorbs strongly. If you need UV transmission (below 400nm), look for high-OH (solarization-resistant) fiber instead. Contact us if you need a different wavelength spec.

What is the minimum bend radius for this fiber?

As a general rule for 200um-core multimode fiber with a standard buffer jacket, keep bends no tighter than roughly 30mm radius (60mm diameter). Tighter bends cause light to leak from the core into the cladding — you will see a drop in transmitted power even if the fiber is not permanently damaged. For a permanent installation, secure the fiber so it cannot be pulled tighter than a 50mm radius loop. If you need a cable that can bend around tight corners inside an instrument housing, ask about our bend-insensitive or small-form-factor fiber options.

Why does my spectrometer show lower counts with this fiber compared to a direct free-space coupling?

Every fiber coupling introduces losses: Fresnel reflection at each air-glass interface (~4% per face, so ~8% per connector pair), coupling loss if the source spot is larger than the fiber core, and attenuation along the fiber length. With 200um core and 0.22 NA, a properly coupled system should see 60-80% throughput compared to free-space. If you are getting significantly less, check: (1) SMA905 ferrule fully seated against its mating adapter (these are physical-contact connectors), (2) the source is focused to a spot smaller than 200um at the fiber face, (3) the source NA is less than or equal to 0.22, and (4) both end faces are clean. If all are correct and throughput is still low, the fiber may have an internal break — test with a visible laser pointer and look for light leaking from the jacket.

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