权利要求：
1. An optical film (140, 540, 640, 740,840, 940, 1040, 1140, 1240, 1340, 1440, 1540, 1640, 1740) having opposed first and second structured surfaces, the optical film (140, 540, 640, 740,840, 940, 1040, 1140, 1240, 1340, 1440, 1540, 1640, 1740) comprising: a plurality of extended prisms (141, 541, 641, 741, 841, 941, 1041, 1141, 1241, 1341, 1441, 1541, 1641, 1741) formed on the first structured surface; and a plurality of extended split spreading structures (142, 542, 642, 742, 842, 942, 1042, 1142, 1242, 1324, 1424, 1524, 1642, 1742) formed on the second structured surface, the split spreading structures (142, 542, 642, 742, 842, 942, 1042, 1142, 1242, 1342, 1424, 1524, 1642, 1742) extending along an elongation axis (144, 1549-2, 1649-2, 1749-2, 1849-2, 1949-2), each split spreading structure (542, 642, 742, 842, 942, 1042, 1142, 1242, 1324, 1424, 1524, 1642, 1742) having a high spreading portion (542a, 642a, 742a, 842a, 942a, 1042a, 1142a, 1242a, 1324a, 1424a, 1524a, 1642a, 1742a) with a high light spreading characteristic disposed alongside a low spreading portion (542b, 642b, 742b, 842b, 942b, 1042b, 1142b, 1242b, 1324b, 1424b, 1524b, 1642b, 1742b) with a low light spreading characteristic; wherein the prisms and the split spreading structures (141,142, 541, 542, 641, 642, 741, 742, 841, 842, 941, 942, 1041, 1042, 1141, 1142, 1241, 1242, 1341, 1342, 1441, 1442, 1541, 1542, 1641, 1642) are arranged in a one-to-one correspondence of prisms (141, 541, 641, 741, 841, 941, 1041, 1141, 1241, 1341, 1441, 1541, 1641, 1741) to split spreading structures (142, 542, 642, 742, 842, 942, 1042, 1142, 1242, 1324, 1424, 1524, 1642, 1742), characterized in that the low spreading portion (542b, 642b, 742b, 842b, 942b, 1042b, 1142b, 1242b, 1324b, 1424b, 1524b, 1642b, 1742b) and the high spreading portion (542a, 642a, 742a, 842a, 942a, 1042a, 1142a, 1242a, 1324a, 1424a, 1524a, 1642a, 1742a) meet along a boundary (542c) that is parallel to the elongation axis of the split spreading structure in plan view.
2. The film of claim 1, wherein, for each of the split spreading structures (542, 642, 742, 842, 942, 1042, 1142, 1242, 1324, 1424, 1524, 1642, 1742), the low spreading portion (142b, 542b, 642b, 742b, 842b, 942b, 1042b, 1142b, 1242b, 1324b, 1424b, 1524b, 1642b, 1742b) has a smooth surface characteristic and the high spreading portion (542a, 642a, 742a, 842a, 942a, 1042a, 1142a, 1242a, 1324a, 1424a, 1524a, 1642a, 1742a) has a roughened surface characteristic.
3. The film of claim 1, wherein each of the split spreading structures (542, 642) comprises a curved segment of the second structured surface, and wherein the low and high spreading portions (542b, 542a, 642b, 642a) of each split spreading structure (542, 642) comprise smooth and roughened portions respectively of the curved segment.
4. The film of claim 1, wherein for each split spreading structure (542, 642, 742, 842, 1324), the high spreading portion (542a, 642a, 842a, 1324a) is a roughened portion and the low spreading portion (542b, 642b, 742b, 842b, 1324b) is a lenslet.
5. The film of claim 1, wherein for each split spreading structure (542, 642, 742, 842, 1324), the high spreading portion (542a, 642a, 842a, 1324a) is a lenslet and the low spreading portion (542b, 642b, 842b, 1324b) is a flat.
6. The film of claim 5, wherein the lenslet of each split spreading structure (542, 642, 742, 842, 1324) is a diverging lenslet.
7. The film of claim 5, wherein the lenslet of each split spreading structure (542, 642, 742, 842, 1324) is a converging lenslet.
8. An optical system (100, 300), comprising: a light guide (150) having a major surface (150a) adapted to emit light; a first and second light source (134, 132) configured to inject light into the light guide (150, 250) along different first and second respective directions; and an optical film (140) according to claim 1, the optical film (140) being disposed proximate the light guide (150, 250) and oriented so that light emitted from the major surface of the light guide (150, 250) is deviated by and passes through the optical film (140) to provide an output beam as a function of which of the first and second light sources (134, 132) are energized; wherein the output beam is a wide output beam when the first light source (134) is energized and the second light source (132) is not energized, and wherein the output beam is a narrow output beam when the second light source (132) is energized and the first light source (134) is not energized.
9. A display system (2100, 2200), comprising: a display panel; a backlight (2130, 2230) disposed behind the display panel, the backlight (2130, 2230) including one or more first light sources (2134, 2234) and one or more second light sources (2132, 2232); and a switch coupled to the one or more first light sources (2134, 2234) and to the one or more second light sources (2132, 2232) to selectively energize such light sources (2134, 2234, 2132, 2232); wherein the backlight (2130, 2230) is configured to provide a first output light beam when the one or more first light sources (2134, 2234) are ON and the one or more second light sources (2132, 2232) are OFF, and is further configured to provide a second output light beam when the one or more first light sources (2134, 2234) are OFF and the one or more second light sources (2134, 2234) are ON; wherein the first output light beam has a wider angular spread than the second output light beam, such that the switch provides the display system with a switchable privacy/sharing function; and wherein the backlight (2130, 2230) includes an optical film (140, 640) according to claim 1.