Holographic Versatile Disc

The smaller disc size was aimed to reduce costs and materials used. It employs a technique known as collinear holography, whereby a blue-green and red laser beam are collimated in a single beam. The blue-green laser read data encoded as laser interference fringes from a holographic layer near the top of the disc. A red laser is used as the reference beam to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed among the data. A dichroic mirror layer between the holographic data and the servo data reflects the blue-green laser while letting the red laser pass through. This prevents interference from refraction of the blue-green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology .

Standards for 100 GB read-only holographic discs and 200 GB recordable cartridges were published by ECMA in 2007 but no further holographic disc product has ever appeared in the market. A number of release dates were announced, all since passed, likely due to the actual high costs of the drives and discs, lack of compatibility with existing or new standards, and competition from more established optical disc Blu-ray and video streaming.

Technology

Current optical storage saves one bit per pulse, and the HVD alliance hoped to improve this efficiency with capabilities of around 60,000 bits per pulse in an inverted, truncated cone shape that has a 200 μm diameter at the bottom and a 500 μm diameter at the top. High densities are possible by moving these closer on the tracks: 100 GB at 18 μm separation, 200 GB at 13 μm, 500 GB at 8 μm, and most demonstrated of 5 TB for 3 μm on a 10 cm disc.

The system used a green laser, with an output power of 1 watt which is high power for a consumer device laser. Possible solutions include improving the sensitivity of the polymer used, or developing and commoditizing a laser capable of higher power output while being suitable for a consumer unit.