Free Space Optics (FSO) takes a line-of-sight approach to telecommunications in which modulated infrared laser light is transmitted through the air, from one building to another, to form broadband data channels. Each point in an FSO network is defined by a transceiver that sends and recieves optical signals which carry voice, video, and other types of digital data. Transmission rates are generally in the gigabytes-per-second range.

What to look for in a light detector for an FSO network:

What is the bandwidth of the system?
This will determine the size of the detector's active area. For data transmission at 1 Gbps, a PIN photodiode or an avalanche photodiode (APD) with an active area of 200 um to 500 um is required.

How far apart are the transceivers?
The farther a laser beam has to travel, the more sensitive its detector must be. Long distances typically call for an APD, which provides high sensitivity through built-in gain amplification. By contrast, silicon PIN photodiodes are sufficient for handling short distances.

• Detectors and emitters for spatial light transmission
• Silicon avalanche photodiodes: high gain, fast time response, low dark current, and high sensitivity in the UV to near infrared region. Active areas range from 0.2 mm to 5.0 mm in diameter.
• C5658 APD module: detects optical signals at 1 GHz with high sensitivity.
• C5331 APD module: operates an APD with single 5 W supply.
• S9717 series silicon APD: 200 um to 500 um active area in a surface mount package. Peak wavelength: 800 nm. Max. cut off at 1 GHz.
• S2382 silicon APD: 500 um active area in a TO-18 package. Peak wavelength: 800 nm. Max. cut off at 900 MHz.
• S2381 silicon APD: 200 um active area in a TO-18 package. Peak wavelength: 800 nm. Max. cut off at 1 GHz.
• Continuous wave laser diodes: a variety of single-element laser diodes with radiant output power ranging from 0.5 W to 5 W.

Please contact us for information on other products which can be used for this application.