{"id":1353,"date":"2026-01-26T07:41:20","date_gmt":"2026-01-26T07:41:20","guid":{"rendered":"https:\/\/photo-detector.com\/?p=1353"},"modified":"2026-01-26T07:41:23","modified_gmt":"2026-01-26T07:41:23","slug":"ingaas-vs-silizium-fotodioden","status":"publish","type":"post","link":"https:\/\/photo-detector.com\/de\/ingaas-vs-silicon-photodiodes\/","title":{"rendered":"InGaAs vs. Silizium-Photodioden: Die Wahl des richtigen Detektors f\u00fcr OTDR-Ger\u00e4te"},"content":{"rendered":"\n

So, you\u2019re in the middle of designing your next-generation OTDR (Optical Time Domain Reflectometer). You\u2019ve got the laser sources figured out, the pulse width modulation is looking good, but now you\u2019re staring at the receiver end. The detector.<\/p>\n\n\n\n

It\u2019s always the same debate in the R&D lab, isn’t it? Do we try to cut costs with Silicon (Si), or do we commit to Indium Gallium Arsenide (InGaAs)?<\/p>\n\n\n\n

If you look at the datasheets quickly, you might think you have wiggle room. But here is the hard truth: if your equipment is targeting the standard telecom windows (1310nm and 1550nm), getting the wrong photodiode isn’t just a minor spec difference\u2014it\u2019s the difference between a top-tier instrument and a paperweight.<\/p>\n\n\n\n

At BeePhoton<\/strong>, we’ve seen plenty of engineers try to “hack” the system by pushing detectors to their absolute limits. Sometimes it works. Most of the time, it results in a noisy mess. Today, I want to walk you through the real, gritty differences between InGaAs vs Silicon photodiodes<\/strong>, specifically for fiber optic testing components. No fluff, just the engineering reality.<\/p>\n\n\n\n

The Wavelength Battleground: Where Physics Draws the Line<\/h2>\n\n\n\n

Before we even talk about pricing or packaging, we have to respect the physics. The fundamental difference between these two materials lies in their bandgap energy. This isn’t just textbook theory; it dictates the upper limit of the wavelength your OTDR detector can actually see.<\/p>\n\n\n\n

Silicon: The King of Short Range (850nm)<\/h3>\n\n\n\n

Silicon is cheap. It’s abundant. The manufacturing processes are mature because the entire semiconductor industry runs on it.<\/p>\n\n\n\n

Silicon has a bandgap energy of approximately 1.12 eV<\/strong> at room temperature. What does that mean for us? It means Silicon is fantastic at absorbing photons in the visible range and the Near-Infrared (NIR) up to about 1000nm or 1100nm.<\/p>\n\n\n\n

If you are building an OTDR specifically for Multimode Fiber (MMF) testing\u2014mostly LANs and data centers running at 850nm<\/strong>\u2014Silicon is your best friend. It has peak responsivity right around 900nm.<\/p>\n\n\n\n

However<\/strong>, and this is a big however, once you push past 1100nm, Silicon becomes transparent. The photons from a 1310nm laser just pass right through the material without generating electron-hole pairs. No current. No signal.<\/p>\n\n\n\n

InGaAs: The Telecom Standard (1310nm\/1550nm\/1625nm)<\/h3>\n\n\n\n

This is where InGaAs PIN photodiodes<\/strong> enter the chat. Indium Gallium Arsenide has a smaller bandgap (around 0.75 eV<\/strong> depending on the alloy ratio). This allows it to absorb lower-energy photons\u2014specifically those found in the Single Mode Fiber (SMF) bands.<\/p>\n\n\n\n

For an OTDR measuring long-haul networks, FTTx, or PONs, you are working at 1310nm, 1490nm, 1550nm, and 1625nm<\/strong>. Silicon is useless here. You literally have no choice but to go with InGaAs if you want to detect anything.<\/p>\n\n\n\n

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Engineer’s Note:<\/strong> I once saw a competitor try to market a “universal” probe using a Ge (Germanium) detector to save money over InGaAs. Germanium works in these wavelengths, but the dark current (noise) is significantly higher. If you care about dynamic range (and in OTDRs, dynamic range is everything), InGaAs is superior to Germanium.<\/p>\n<\/blockquote>\n\n\n\n

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Si PIN Photodiode with NIR sensitivity enchanced (430-1100nm) PDCP08-201<\/a><\/h2>\n\n
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The\u00a0<\/span>PDCP08-201<\/span><\/strong>\u00a0is a high-performance\u00a0<\/span>SMD Si PIN Photodiode<\/span><\/strong>\u00a0designed for precision optical communication and medical sensing.[<\/span>1<\/span><\/a>] Featuring a large 2.9\u00d72.9 mm active area with enhanced NIR sensitivity (0.70 A\/W) and ultra-low dark current (20 pA), this\u00a0<\/span>SMD Si PIN Photodiode<\/span><\/strong>\u00a0ensures superior signal detection and reliability in a compact surface-mount package.<\/span><\/p>\n\n\t\t\t<\/div><\/div>\n\n\n

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Key Technical Specs: Responsivity and Noise<\/h2>\n\n\n\n

Let\u2019s get into the math. Don’t worry, I know standard WordPress editors hate LaTeX, so I\u2019ll keep these formulas clean and copy-paste friendly.<\/p>\n\n\n\n

When you are selecting a OTDR detector<\/strong>, you are balancing two things: How much signal can I get (Responsivity) and how little noise can I tolerate (NEP\/Dark Current).<\/p>\n\n\n\n

1. Responsivity (R)<\/h3>\n\n\n\n

Responsivity tells you how much electrical current you get for a given amount of optical power. The formula looks like this:<\/p>\n\n\n\n

R = Ip \/ Popt<\/strong><\/p>\n\n\n\n

Where:<\/p>\n\n\n\n