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Next-Gen Storage: Getting to Terabytes with Holographic Storage (10/2005)
by Douglas Dixon
This is the promise of holographic storage -- the far-out dreams of Star Trek coming back to earth in real products, promising 200 GB in 2006, with a path to 1 TB and beyond. That's a trillion bytes, over 200X the capacity of a DVD, on a disc with the same form factor!
The possibilities for holographic storage were featured at the Next Generation DVD Summit, sponsored by the DVD Association (DVDA, www.dvda.org), in coordination with the National Institute of Standards and Technology (NIST, www.nist.gov) in Gaithersburg, Maryland in June 2005 (www.dvda.org/html/nist-conference.php).
At the DVD Summit, Nelson Diaz, president and CEO of InPhase Technologies and Hideyoshi Horimai, founder and CTO of Optiware Corporation, presented their views of the state of the industry, with both promising 200 to 300 GB discs as early as 2006, albeit targeted and priced for professional markets.
InPhase Technologies, a spin-out from Bell Labs / Lucent Technologies, developed practical holographic material and holds over 40 related patents (www.inphase-tech.com). It licenses and sells its Tapestry brand holographic media, and is also developing storage drive products, targeting 300 GB capacity in 2006 and 1.6 TB in 2009. The media supports both discs and other form factors, such as postage-stamp memory cards.
Optiware Corporation (www.optware.co.jp/english) developed a Collinear Holographic Technology technique that permits storage on spinning media, offering backward compatibility with current red- and blue-laser optical drives. It is working with ECMA to standardize its Holographic Versatile Disc (HVD) format, targeting 200 GB capacity in 2006, growing to 1 TB and then 3.9 TB in the same form factor.
This is not just claims and mirrors: Both companies have developed significant backing from major development partners and investors. InPhase closed a $32.1 million third round of funding in May 2005, with support from partners and investors including Bayer MaterialScience AG, Mitsubishi, Hitachi Maxell, ALPS, and New Venture Partners. And Optiware announced a $14 million fifth round of funding in July 2005, from new investors including Toshiba, joining previous investments from partners and investors including Fuji Photo Film, Matsushita Electric, Pulstec, Konica, and Intel Capital.
So how does this holography magic work? It's all in the concept of volumetric recording: Instead of using a laser to burn and read a pit, as with conventional CD and DVD, essentially storing each individual bit as a two-dimensional circle, holography stores a three-dimensional volume of data with each flash of light. Each such pulse of light is called a page, with the data represented as a two-dimensional pattern or array (although more complicated as a simple pattern of bits or bar code). Holography therefore provides parallel access to data, and even multiplexed storage in the same location.
In holographic data storage, the laser beam is divided into a signal beam and a reference beam. The signal beam conveys the data, and is combined with the reference beam to create a complex three-dimensional interference pattern that is stored three-dimensionally in the photopolymer storage medium. It sounds like science fiction, but given the holographic material, the rest of the system leverages existing technology: the pattern can be generated using a conventional spatial light modulator (SLM) such as a digital micromirror device (DMD, as used in digital projectors), and then read back using CMOS pixel detector arrays (as in digital cameras).
Data is moved in parallel with each flash of light, providing rapid access and data transfer rates. One version of the Optiware system, for example, can store 60,000 bits per pulse/page, with 23,000 pulses per second, on a disc rotating at 300 rpm.
Even better, holographic material can store not only two-dimensional pages of data, but also extend to store 3-D layers of data. For example, the InPhase Tapestry blue media (for blue laser) can store a collection of multiple pages (called a book) at the same location by varying the angle or wavelength of the reference beam, and then overlap the locations to further increase the storage density. Approximately 1 million bits of data can be recorded per page, 252 pages per book, and fifteen books then overlaid in one location.
As a bonus, besides its advantages in high storage density and rapid data transfer, these developers of holographic media also promise lower costs than traditional optical media (an order of magnitude lower then DVD), and ease in handling and storage. Since holography is a photographic process, recordable media does need to be protected until it is used, but once the media is exposed to light the images are permanently stored, as on film. Optware describes the archival quality of its media as at least 50 years.
InPhase Technologies was founded in 2000 as a Lucent Technologies venture, and is now based in Colorado (www.inphase-tech.com). Based on seven years of research on holographic materials and systems at Bell Labs, InPhase has rights to over 40 Bell Labs patents associated with holographic technology, and has assembled core patents in holographic data storage media, holographic recording process, recording drive, and the manufacturing process.
The challenges for designing holographic polymer material include the need to cover a broad dynamic range, be light-sensitive and, still highly transparent, dimensionally stable, and insensitive to temperature fluctuations. Requirements included high dynamic range, high photosensitivity, dimensional stability, optical clarity and flatness, nondestructive readout, millimeter thickness, and environmental and thermal stability.
InPhase has been shipping holographic media since 2001, and in February 2004 extended its Tapestry brand of green-wavelength media to include blue wavelength media for use with 400 to 410 nm lasers developed for blue-laser DVD.
InPhase also sells holographic media testers and drive development systems to companies developing next-generation optical drive systems. InPhase media customers that have publicly stated they are investigating holographic storage include Pioneer, MEI, NHK, Sony, Thomson, Samsung, Daewoo, JVC, and Optware. Companies that have purchased testers include NHK and Sony.
In April 2005 at the National Association of Broadcasters (NAB) conference, InPhase held the first public demonstration of its prototype Tapestry holographic drive with Hitachi Maxell at the Maxell Corporation of America booth. The drive records data into InPhase's patented two-chemistry Tapestry photopolymer write-once material. The recording material is 1.5 mm thick and is sandwiched between two 130 mm diameter transmissive plastic substrates.
InPhase demonstrated a data density of 200 gigabits per square inch, and a transfer rate of 27 megabytes (MB) per second. By varying the angle of incidence and wavelength of the reference beam in the material (angle multiplexing with polytopic multiplexing), multiple holograms to be stored in the same volume of material by overlapping not only pages, but also books of data. Each exposure of the laser records a data page of approximately 1 million bits. There are collected into a book of 252 pages, and then fifteen books of data are overlaid in one location.
Among InPhase's partners and investors, Bayer MaterialScience AG is developing polymers for optical data storage, and investigating possible applications outside the storage market, for example in displays and sensors in car interiors, projection surfaces, and signal lights (www.bayermaterialscience.com). Hitachi Maxell is developing high-volume media manufacturing technologies, and has developed a disk cartridge for easy integration in automated library systems (www.maxell.com).
The first generation InPhase drive, to be introduced at the end of 2006, are write-once discs designed for professional archiving, targeted at 300 GB capacity. This will be followed by re-writable discs, with capacities ranging to 1.6 TB capacity in 2009. InPhase sees opportunities for holographic storage for a wide range of products, ranging from consumer handheld devices to enterprise storage, with 2 GB on a postage stamp, 210 GB on a credit card.
Optware Corporation, based in Yokohama, Japan, was established in 1999 as a development venture for holographic recording technology (www.optware.co.jp/english). Optware's team of former Sony Corp. optical engineers has developed a new method of holographic storage, called Collinear Holographic Versatile Disc (HVD), designed to enable storage of up to 3.9 TB of data on a CD sized disc at data rates exceeding 1 Gbits/sec.
Traditional holography uses separate signal (data) and reference beams to create the interference pattern stored in the holographic material. These separate beams obviously require precise alignment, especially for use on rotating media compatible with CD and DVD drive designs. Instead, the Optware collinear approach aligns the two laser beams into a single beam of coaxial light, creating a three-dimensional hologram composed of data fringes.
The system uses a single objective, and a servo system for the pickup system to maintain tracking and focus. The system can lay down 23,000 pulses a second while the media is rotating at 300 rpm. The lens floats above the moving disc and micro adjusts to compensate for vibration and flutter, as in ruggedized DVD drives.
The system uses beams of two different wavelengths: a 532 nm green solid laser for data recording and reading, and a red semi-conductor laser (that does not photosensitize the holographic recording material) to control the tracking and focus servo. The red laser reads a built-in reference track on the media, a pitted aluminum substrate, and the retirned signal is split to a separate sensor to keep the optics on target.
The two beams are put into the same optical path by the dichroic mirror installed before the objective lens, and are then incident to the same objective lens. The recording medium is coated with a reflection film, and the objective lens is controlled so that the beam is brought into focus on this film.
The recording laser beam is first divided by beam splitters into an information beam and a reference beam. The information beam is converted into two-dimensional page data by the digital micro mirror device (DMD). These two beams are again merged into one on the same optical axis by beam splitters and are incident to the objective lens. The data is then recorded onto the holographic recording medium in the form of interference patterns.
To reconstruct the information from the stored hologram, only the reference beam is incident to the objective lens, and the reconstruction beam passes through the objective lens and is returned to be received by the CMOS sensor and decoded using a FFT.
HVD storage also offers interesting possibilities for data protection. The 3-D hologram is recorded using the two-dimensional page data which is surrounded by a reference pattern, formed together on the mirrors of the DMD device. The page data then cannot be read out except by the reproducing the exact reference pattern. In this form of encryption, there are over a million key combinations per page, and each page can have a different reference key. Since the HVD system writes 23,000 pages/sec., a fully encrypted disc would require 22 giga keys/sec. to unlock.
For mass production, holographic media can be replicated very efficiently in one simultaneous transfer from a master. But once written, the replicated discs cannot be used as masters for further copying.
To promote the development of the Holographic Versatile Disc format, six companies joined to form the HVD Alliance in February 2005 (www.hvd-alliance.org): CMC Magnetics, Fuji Photo Film, Nippon Paint, Optware, Pulstec Industrial, and Toagosei. Fuji Photo Film is working closely with Optware on manufacturing and materials technology, especially the design of a light-tight cartridge system to protect the photo-sensitive material before it is exposed (www.fujifilm.com).
Optware is also working to standardize the HVD format through the Ecma International industry association (www.ecma-international.org), which develops standards for Information and Communication Technology (ICT) and Consumer Electronics (CE). Ecma technical committee TC44 was formed in December 2004 to standardize Holographic Information Storage Systems (HISS). TC44 will begin standardizing three different storage media: 200 GB cartridge, 100 GB HVD read-only disc, and 30 GB HVC card. Its charter also includes related other subjects like case, volume and file structure, as well as the development of guidelines for media archival life, testing, and handling (www.ecma-international.org/memento/TC44.htm).
The goal for TC44 is to develop a standard by mid-2006, and then submit the standards to ISO in December 2006 for fast-track processing. Based on the standard, Optware will begin shipping the first HVD devices with 200 GB capacity, soon after 1 TB going to 3.9 TB. Increasing the data density for larger capacity will require both stacking data pages closer together and improving the signal to noise in the media.
This is not some futuristic virtual reality generated on the Star Trek holodeck -- several very serious consortiums, funded by multiple rounds of significant investments, are developing holographic storage systems, and targeting first products as early as 2006.
The first products will support 200 to 300 GB capacity, and will be targeted to enterprise mass storage systems (such as currently use magnetic tape). Planned follow-up products will include rewritable media, and expand capacity to the range of 1, 2, or 4 TB.
Holographic storage also has a promising future in mass-market consumer products, offering inexpensive higher-capacity replacements for solid state media.
So the race is on, between the expanding capacity of traditional solid-state storage with multiple gigabytes, the promise of blue-laser DVD with multiple layers for tens to hundreds of gigabytes, and then holographic storage with multiple hundreds of gigabytes up into terabytes. Storage may actually catch up to the demands of applications like a consumer's entire video collection, or a full-bandwidth uncompressed HD recorder.
Next Generation DVD Summit, June 2005
DVD Association (DVDA)
National Institute of Standards and Technology (NIST)
Bayer MaterialScience AG
Fuji Photo Film
HVD Alliance -- Holographic Versatile Disc
ECMA International - TC44 - Holographic Information Storage Systems (HISS)