Patent GB-1171184-A (GB)
Title: Semiconductor Junction Laser
Inventor: FENNER GUNTHER ERWIN
IPC: H01S5/062
Filed: 1967-01-16
Abstract: 1,171,184. Laser deflectors. GENERAL ELECTRIC CO. 16 Jan., 1967 [7 March, 1966], No. 2243/67. Heading H4F. [Also in Division H1] One of the opposite conductivity type regions of a semiconductor junction laser is divided into a plurality of zones for separately energizing the portions of the junction regions underlying said zones so that the output beam may be displaced or deflected. In the arrangement of Fig. 1 a groove 17 is etched in the P region 11 of a PN junction diode 10 made from semi-conductors or alloys thereof of Group III-V elements so as to leave a bridge portion 16 connecting zones 14, 15. Faces 25, 26 are polished to form a resonant cavity and faces 32, 33 are roughened and tapered. Zones 14, 15 may be formed by diffusion of impurities through a mask to obtain a high resistance between the zones. When pulsed D.C. or continuous D.C. bias is applied to terminals 18, 19 from a D.C. source via a variable potentiometer, Fig. 2 (not shown), an output beam is obtained at some indeterminate location, depending upon groove non-uniformities, along face 25 between non-reflecting faces 32, 33 if the biases are equal. When the current density in zone 15 exceeds that in zone 14 then the index of refraction within the portion of junction 13 underlying zone 14 exceeds that underlying zone 15 so that the output beam is deflected away from the normal to surface 25. Similarly, if the current density in zone 14 exceeds that in zone 15 the beam is deflected away from the normal to surface 25 in the opposite direction. If the beams are in close proximity to either surfaces 32 or 33 the beam effectively remains in zones underlying 15 or 14 and since there is very little internal refraction the beam emerges perpendicular to surface 25 at the corners and discontinuous shifting of the output beam is obtained. Discontinuous shifting of the laser beam is also obtained by using the arrangement of Fig. 4A and Fig, 4B (not shown) in which diode 40 has a pair of crossed grooves 41, 42 and two pairs of reflecting surfaces 43, 44 and 45, 46. With the D.C. sources connected as shown to the various zones when zones 47, 48 have equal currents the laser beam is generated along axis of the junction lying midway between faces 45, 46. If currents in zones 47, 48 are reduced to just below the laser threshold value and current is applied to zone 49 the output beam is displaced to a location adjacent face 45. Similarly, if zone 50 is energized the laser beam is displaced adjacent face 46. If the roles of zones 47, 48 are replaced by zones 49, 50 the beam emerges from face 45. A convex lens may be placed in front of the emitting surface. Continuous scanning of the laser beam across the junction may be obtained by using non-linear grooves, Fig. 7 and Figs. 5, 6, 8 (not shown). It is shown that by adjusting the gains of the various zones there exists a unique distance along the junction from a non-reflecting face at which the gain is a maximum and laser oscillations occur at this point. Thus, upon proper variations of the voltage amplitudes applied to the three zones continuous beam-scanning occurs. Beam deflection also can be produced. Four of the diodes shown in Fig. 7 may be placed adjacent one another with a non-reflecting surface of one diode in contact with that of another diode, with the centre zones of each diode in a pair in contact with each other, Fig. 9A (not shown). Alternatively the diodes may form an integral structure, Fig. 9B (not shown). Fig. 10 shows a many zoned diode 140 with parallel Fabry-Perot faces 142, 143. Current to the various zones is supplied from a triangular wave current generator 150 synchronously driven by clock pulse generator. In operation, heavy current in zone 1 decreases while current in zones I<SP>1</SP>, I<SP>11</SP> builds towards a maximum, Fig. 11 (not shown). Cessation of current in zone 1 and initiation of increasing in current in zone 2 occurs when the current in zones 1<SP>1</SP>, I<SP>11</SP> begins to decrease. When the current in zone 2 reaches a maximum and begins to decrease the current in zones 1<SP>1</SP>, 1<SP>11</SP> ceases and current in zones 2<SP>11</SP>, 2<SP>1</SP> begins to increase. Thus as the high-gain region of diode 140 progresses through the various diodes in unison with the high current density sections the laser beam progresses along face 142 until it reaches the end when it re-emerges in the first diode again. The diode of Fig. 10 may be formed in the shape of a cylinder, Fig. 11 (not shown), having a cylindrical PN junction in which case the laser beam has a circular scan.