Based on customer input, we offer the Model 21x7 higher-gain, lower-bandwidth balanced photoreceivers with the same adjustable-gain and -bandwidth settings as our popular 20x1 laboratory photoreceivers. Ideal for coherent heterodyne-detection applications including doppler LIDAR, and optical coherence tomography (OCT), these 10-MHz balanced photoreceivers can make the difference when you need to see a small signal.Just like our other balanced photoreceivers, the Models 2107 and 2117 balanced photoreceivers work by subtracting the photocurrent from two well-matched photodetectors. Common-mode noise that is present on both the reference and signal beams (such as laser intensity noise) is cancelled out and doesnt appear as part of the signal. Any imbalance between the photocurrents generated by the reference and signal photodetectors, whether intentional or unintentional, is ampliﬁed and is seen as the signal.Both free-space (FS) and FC-connectorized versions are available as well as metric-compatible versions. For your convenience, the Model 21x7 balanced photoreceivers can run off batteries or your own DC power supply. To ensure safe operation, we strongly recommend our Model 0901 power supply.