Photodetectors

Photodetectors Shed Light on Optical Sensing

These high-responsivity photodetectors cover wide wavelength ranges for a variety of commercial, industrial, and military applications, including for munitions guidance.

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Light is a form of electromagnetic (EM) energy that plays an important role in battlefield activities. It is being used, for example, for directed-energy weapons using high-power lasers, and is the basis for a number of different detection methods used both for tracking lasers and munitions guidance. In support of such applications is the YAG series of silicon PIN quadrant photodetector diodes from Excelitas. They provide excellent sensitivity and responsivity over the infrared (IR) range of 400 to 1,100 nm, making them strong candidates for optical detection applications at 1,064 nm. The IR detectors employ a circular active area with four pie-shaped quadrants; to minimize noise, a guard ring collects current outside the circular active area.

The YAG series (Fig. 1) includes silicon P- and N-type devices with a breakdown voltage of 180 V dc, and is designed for use at voltages from 0 to 180 V dc. Individual models include the P-type model YAG-444-4AH and N-type model YAG-444N-4AH, both with an active diameter of 11.3 mm. The P-type model YAG-555-44H, in contrast, has an active diameter of 14.1 mm. All three models are supplied in hermetic TO-36 packages for ease of handing and mounting. They can also be provided with additional window anti-reflection coating and built-in heaters.

1. The YAG Series of photodetectors includes silicon P- and N-type devices for optical detection applications from 400 to 1100 nm.

All three photodiodes are characterized by low noise equivalent power and wide detection ranges, as well as excellent responsivity. All provide typical responsivity of 0.60 A/W at 900 nm and 0.44 A/W at 1064 nm, with noise equivalent power of 0.30 pW/(Hz)0.5 measured in a 1-MHz bandwidth at 1064 nm for both P-type devices. For the YAG-444N-4AH, the typical noise equivalent power is 0.25 pW/(Hz)0.5 measured in a 1-MHz bandwidth at 1,064 nm.

The three detectors feature wide fields of view, determined by an angle, α, where the surface of the device is totally illuminated, and angle αʹ where the surface is only partly illuminated. For the YAG-444-4AH and YAG-444N-4AH detectors, α is nominally 110 deg. and αʹ is nominally 160 deg. The larger active area of the YAG-555-4AH reduces α to around 85 deg.

For a 50-Ω load, the photodetectors exhibit 60-MHz bandwidth with 12-ns typical rise time. They operate with good linearity and without dead zones across the dynamic range, with an operating temperature range of –55 to +125ºC.

In support of automotive LIDAR, laser range finding and designation, and high-speed optical communications, the company has also introduced its C30659 Series of Si or InGaAs avalanche photodiodes (APDs), supplied in hermetic TO-8 packages with low-noise GaAs preamplifiers (Fig. 2). These APD-based detectors offer effective detection of wavelengths from UV to 1,550 nm with fast rise and fall times at all wavelengths and system bandwidths of typically 50 to 200 MHz. They are designed to handle high optical power levels without damage.

2. The C30659 Series of Si or InGaAs avalanche photodiodes (APDs) includes low-noise GaAs preamplifiers housed in hermetic TO-8 packages for wavelengths from 830 to 1,550 nm.

The outputs of these detectors should be capacitively or AC-coupled to a 50-Ω termination. The amplifier features an inverting amplifier design with an emitter follower used as an output buffer stage, enabling good low-noise performance and optimized responsivity. The nominal field of view for these APDs is between 136 and 153 deg., depending upon model.

These optical detectors can function effectively in a number of different applications, including for temperature sensing, vehicle safety systems, high-speed free-air communications, and munitions guidance. Both types of detectors are securely packaged and constructed to survive the types of harsh environments associated with some of these applications.

Excelitas Technologies, 22991 Dumberry Rd., Vaudreuil-Dorion, Quebec, Canada J7V 8P7; (450) 424-3300, (800) 775-6786

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