pursuit mode when the goal is to overlap the projected pattern of another transceiver or escape mode when the goal is to avoid overlap by the pattern projected by another transceiver the modulation frequency of the infrared light is characteristic of a particular transceiver so that detection of another transceiver 39 s modulation frequency is indicative of pattern overlap as in fig2 the area of overlap 47 is a large percentage of the projected light pattern area fig5 shows various ways to achieve the function of the optical switch of fig4 in fig5 a the transceiver focusing element lens 63 establishes optical beam path 62 a small mirror 58 is mounted on a slide switch platform 61 in the position shown the mirror 58 intercepts received energy along beam path 62 and directs it along path 60 to detector 59 when slide switch platform 61 is translated in the direction of the arrow light emitting diode 56 has an unobstructed projection path 57 in fig5 b transceiver focusing element lens 64 establishes beam path 65 mirror 68 is provided with rotational means so that in one position it may intercept received light along path 65 and reflect it along path 66 to detector 67 in another position 70 it may allow transmission of light from light emitting diode 69 along paths 71 and 65 fig5 c shows transceiver focusing element lens 72 establishing beam path 73 both light emitting diode 74 and detector 75 are mounted on slide switch platform 76 so that either device may be positioned in beam path 73 the optical switch function of fig4.