Application 1: Detector Systems

Figure 1: PCX Lens as FOV Limit in Detector Application [View Larger Image]

Every optical system requires some sort of preliminary design. Getting started with the design is often the most intimidating step, but identifying several important specifications of the system will help establish an initial plan. The following questions will illustrate the process of designing a simple detector or emitter system.

Goal: Where Will the Light Go?

Although simple lenses are often used in imaging applications, in many cases their goal is to project light from one point to another within a system. Nearly all emitters, detectors, lasers, and fiber optics require a lens for this type of light manipulation. Before determining which type of system to design, an important question to answer is "Where will the light go?" If the goal of the design is to get all incident light to fill a detector, with as few aberrations as possible, then a simple singlet lens, such as a plano-convex (PCX) lens or double-convex (DCX) lens, can be used.

Figure 1 shows a PCX lens, along with several important specifications: Diameter of the lens (D₁) and Focal Length (f). Figure 1 also illustrates how the diameter of the detector limits the Field of View (FOV) of the system, as shown by the approximation for Full Field of View (FFOV):

(1.1)

Or, by the exact equation:

(1.2)

For detectors used in scanning systems, the important measure is the Instantaneous Field of View (IFOV), which is the angle subtended by the detector at any instant during scanning.

(1.3)

Figure 2: Instantaneous FOV [View Larger Image]

Figure 3: PCX Lens as FOV Limit in Emitter Application [View Larger Image]

Considered in reverse, Figure 1 can also represent an emitting system (Figure 3), with the lens used to collimate the light. This setup will be the premise of the application example.

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