FEATURE
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Lighting up the silver screen

Jessica Rowbury on how lasers are improving the viewing experience for cinema goers

Although 3D laser projection technology has received quite a bit of attention in the last year or two, up until recently, it has only been demonstrated at industry screenings or at trade shows. This year, however, it has started to make its way into mainstream cinemas. IMAX will introduce laser projectors for 3D screenings of the latest Hobbit film in December, and a laser projector developed by Barco that won two awards in August and September − one from the Beijing International Radio, TV and Film Equipment Exhibition (BIRTV), and another from the 3D International Society − will be delivered to a couple of dozen cinemas around the globe in the coming months ready for The Hobbit: Battle of the Five Armies.

The development of these new projectors has been made possible as laser diodes have become more affordable and higher power. However, although laser technology promises better viewing experiences and longer lifetimes, bringing lasers into a completely new application field is not without its challenges.

A brighter light source

Film piracy poses a big threat to cinema, and with more and more people opting to stream movies online rather than paying for theatre tickets, the capability to provide an immersive and impressive experience has become increasingly important for cinemas. Because laser projectors can offer brightness levels of more than double that of lamps – laser systems offering 60,000 lumens or more are available – the picture quality is significantly better. ‘The most important benefit of a laser projector is proving brighter pictures which contribute to the level of immersion and to the experience of cinema audiences,’ said Goran Stojmenovik, product manager for laser projection at Barco. ‘In many cinemas today, 3D presentations are very dark; it is not appreciated by a number of people.’

Laser projectors also offer cost benefits compared to lamp projectors, as they are more energy-efficient and have a longer lifetime. ‘A standard projector uses a large lamp and you have to change the lamp every 500 to 1,000 hours, and that’s at quite some cost,’ said Dr Jörg Neukum, director of sales and marketing at laser diode company Dilas. ‘And, the lamp is not very efficient... laser diodes have efficiencies up to 50 per cent. This is an improvement over lamps by at least a factor of 10.’

In general terms, laser projectors consist of three light sources – one red, green and blue – and a dichroic mirror used to combine the beams to produce white light. To deflect the beams, a scanning mirror, or micro-mirror arrays are typically used. ‘So, you fire the laser on the mirror and when you put a signal onto the mirror the mirror bends and deflects the laser beam into the direction you need it,’ said Neukum.

In September, Barco won the Lumière Award from the International 3D Society for its 4K laser-illuminated projector, the DP4K-60L, which has already been installed in two cinemas − one in the US and one in China. The projector has a combination of VCSEL-based green lasers and direct diode red and blue lasers, which are mounted in ‘free space’, in enclosed opto-mechanical structures. The light from the laser diodes is then accumulated and collimated through a series of mirrors and lenses to fill the etendue space of the 1.38-inch 4K digital micro mirror devices.

Because the projector uses a ‘six primary system’, whereby each primary colour is made by not one but two sets of wavelengths, the need for a second projector and an intermediate polarisation system is eliminated. ‘A classical approach would be to have a laser projector with only three laser wavelengths for one eye and another projector with three wavelengths for the other eye. In our case we have put all of the wavelengths into one projector,’ explained Stojmenovik. ‘We are the only ones that integrate everything into the single projector. We use two bands of wavelengths for each primary colour, in order to facilitate 3D stereoscopic presentation by colour separation… So you can produce 3D without the need for an intermediate element; you only need 3D glasses for separation.’

To reduce an effect known as speckle, which occurs when a single laser wavelength is reflected from the screen and interferes with itself, appearing as bright and dark spots on the screen, the projector uses a variety of wavelengths integrated into a single projector. ‘Speckle is really important when you produce an image using laser light, because speckle interferes with the sharpness of the image and can be really disturbing,’ Stojmenovik said. ‘We use direct coupling − direct because there is no intermediate fibre. All of the lasers are safely enclosed inside the projector. This concept allows us to have a variety of wavelengths, a variety of polarisation directions, and a variety of angles, all of which contributes to de-speckling. The more diversity you have in the light − wavelengths, polarisation angles, directions – the less speckle you perceive.’

Laser projectors have only just started to enter the market this year, and the improved laser diode technology is what has enabled these developments. High-powered red light sources are important for creating rich images because the human eye is much less sensitive to this colour than with green or blue. Although not yet commercially available, Dilas recently delivered its first red diode laser module with 80W of power at 638nm, double the power of its existing 40Wt red diode laser product. It is the surrounding optics that is crucial for these high-brightness high-power red laser sources. ‘It is our in-house beam shaping technology and the mounting technology of these laser bars [that make them so bright], ’ explained Neukum.

The mounting and optical alignment are both very precise in order to get the light from so many different sources into a 400µm fibre. The device has free beam shaping, using microptomechanical technologies.

Although laser projectors are just starting to make their way into cinemas, the technology could be applied to other applications. In particular, they are bright enough for screening video during the day. ‘If you have enough power you could also do illumination in daylight events. If you think of a sports stadium in bright sunlight when you want to have a video screen somewhere, you need lots of light to compete with the outside sunlight. With high-power lasers you actually get the possibility to do that,’ Neukum said.

However, because the benefits of lasers will make the largest and most immediate improvement in cinema, this is the market that is currently being targeted by projector companies. ‘Having a lot of light out of a single projection lens is definitely appealing to many other applications like sporting events, concerts, projection mapping with buildings, theme parks and so on,’ said Barco’s Stojmenovik. ‘However, cinema is the market that has long running hours and needs high brightness, where the two benefits of high-end laser projectors are immediately appreciated, so it was logical to start there. We began in cinema, but without a doubt we will continue this trend to enter other markets.’

Because laser projection technology has just started to be installed this year, primarily into large, premium cinemas, it will be a few years until lasers will become the standard choice of illumination for this market. According to Stojmenovik, there are two approaches for which the technology will be adopted: ‘High-end, high-brightness projectors for premium cinemas – where the lamp operational costs are highest, but the image quality benefit for audiences are also highest – and low-end, low brightness blue-pumped laser-phosphor projectors, where the price difference to lamp projectors is traded off against the ease of use and maintenance,’ he said.

‘In the future these two market approaches and technologies will push towards the mainstream cinema applications. As the technology matures, it will become more efficient, and we also expect the prices of lasers to go down with a wider adoption of the laser illuminated projection. We expect that, in a couple of years, laser illumination will be the dominant technology for cinema projectors.’

Laser light shows

The laser light show market is more established than the cinema market, but it has recently experienced strong growth as laser diodes have become cheaper and more reliable. ‘For a long time, the laser light show industry was the “little kid” on the block,’ Justin Perry, COO at Pangolin, said. ‘However in recent years, improvements in laser technology have helped make the laser entertainment equipment easier to use and substantially more cost effective to work with. And as a result, we are seeing rapid growth within our industry. In fact, many large-scale production and lighting companies are now turning to lasers as an alternative light source to LEDs. In the past, laser entertainment may have accounted for less than one per cent of the global laser market; now we’re nearly a half billion dollar industry, and growing. We’re not such a small kid on the block anymore.’

Just as cinema laser projectors can provide a brighter, more immersive viewing experience than traditional xenon lamp projectors, lasers used for laser light shows can create much more spectacular effects than the more conventional LEDs. ‘When you think of a laser as your artistic tool or medium, you soon recognise that lasers can create a much wider degree of effects and colours − LEDs can only do so much. With lasers, you can create stunning aerial beam effects, as well as crisp and clean graphics, logos, and text. These are effects that LEDs try to replicate – but, no matter how hard they try, there is still a stark difference in what the end result looks like,’ Perry remarked.

The lasers used for laser light shows vary widely in terms of output powers, and this generally depends on the type of venue and application where the laser projector will be used. ‘Typically, indoor events (again, depending on the size of the venue) will use between 500mW up to 5W in output power, while outdoor events can use laser projectors ranging from 10, 20, 30, or even 40 watts or more.’ Perry continued: ‘A lot of factors come into play when determining the amount of laser output power needed for a show (such as the amount of ambient light at the venue) – but, in general, indoor events use between 500mW to 5W in power, and outdoor events can range from, on average, 10W in power, up to 20W or more.’

Safety first

When dealing with high-power lasers, safety always has to be considered. However, because cinema is a new application area, a lack of information and a set of appropriate standards have created some challenges for the adoption of this technology in the cinema space. According to Barco’s Stojmenovik, the safety regulations are too restrictive; they were produced a long time ago, before today’s laser projectors were developed, and were mainly meant for laser light shows that use higher power lasers closer to audiences. Current projectors include safety mechanisms that minimise the risk. ‘The lasers that are contained in our projector are class four, but we do all we can to make the light less collimated to fit it into a typical projector optical path [the laser]. Once it [the light] is coming out of the lens, there is absolutely no difference between a laser projector and a xenon projector, because the light is mixed − it goes in all different directions within a certain zoom angle, depending on the lens between the screen,’ Stojmenovik explained. ‘But the regulations are much more restrictive because there is a laser inside.’

The key to moving things forward is to educate customers and develop more appropriate safety regulations. ‘The challenge is rather a lack of information and knowledge of safety procedures, than actual hurdles in installing laser projectors. Barco is actively working on training programmes on laser safety and providing safety information and guidance to our customers. One of our laser safety officers is also member of LIPA [Laser Illuminated Projector Association] and is very active in standard participation, where LIPA is trying to come to safe but sensibly adapted international safety standards for laser illuminated projection,’ Stojmenovik said.

The laser light show application area is more advanced, so several technologies have been developed that can ensure the safety of laser light shows, even for effects like audience scanning, when lasers are scanned close over the heads of a crowd. The Professional Audience Safety System (PASS) developed by Pangolin has enabled the US, and more recently, the UK government to allow these types of effects, as long as the technology is installed inside of the laser projectors being used. The PASS system monitors the output power of the laser projector in real-time and ensures that the power levels remain at a safe level. ‘We believe this has been a game changer for laser light shows allowing people to do audience scanning,’ stated Perry. ‘If it detects at any time that there is a problem with the laser sources − if it is outputting more power than is safe, or if there is a problem with the scanning system − the system will shut the entire projector down.’

Other technologies used to make laser light shows safe include a safety lens which can be installed onto the output window of a laser projector to increase the divergence of the laser beams fired into the audience.

By increasing the beam’s divergence, for example, from 2mm to 10mm or 20mm, the laser beams become a lot safer.

Pangolin also provides a beam attenuation map safety feature inside of its software, which is used to control the output powers of each laser in the projector, depending on how close those laser beams will be to the audience.

‘If you have a 20W projector, the beams that go over people’s heads would be full power at 20W; the beams that go into another safe area could only be 10W, and the beams that project into the audience can be less than 1W of power,’ explained Perry.