GB2416907A - 2-d & 3-d Spontaneous Emission Display - Google Patents

Abstract

A 3-d display comprises two discrete frequency sources (electric arc lamps) tuned to emit two invisible (infra-red) wavelengths. These sources are collimated such that the beams of light are thin and parallel. They are then shone onto mirrors which can be adjusted quickly in 2-d (bearing and elevation). The beams of incident light are then shone into a container of suitable transparent material. Beam A excites the molecules of the target material to an intermediate energy state along its path. If the beams cross within the target material, at the crossing point, beam B excites the molecules from the intermediate energy state to a higher energy state. From this higher energy state, the target material emits visible photons as the electrons spontaneously decay back to their normal state. The beams are then scanned rapidly within the target material generating a 3-d vector (wire frame) or raster image. A 2-d display is made from a flexible sheet of target material (e.g. doped plastic). The incident beams may then be introduced tangentially into the target sheet, and guided using internal reflection. Hence, if the sheet is curved or bent, the incident beams remain within the target material. The beams are then scanned in 1-d (bearing) in order to produce a 2-d vector or raster image.

Description

2-d & 3-d Spontaneous Emission Display This patent relates to a 2-d and 3-

d spontaneous emission display.

Normal flat panel displays (e.g. LCD) displays produce a 2-d raster image. Each pixel requires a separate switch and hence the complexity increases with the square of the linear size of the screen (in pixels). Cathode ray tubes use a simple scanning mechanism to achieve the same effect, but are bulky. A flat 2-d (and coincidentally a 3-d) display using scanning technology would hence be preferable from switched displays.

Two crossing invisible photon sources may be used to produce a visible dot of light (by spontaneous emission) where they cross. This was shown in an experiment (back in 1987) whereby a single ion was held in a magnetic quadrupole trap, in order to investigate the number of hidden variables (randomness) in quantum excitation.

The target, of course, does not need to be an ion. Most neutral (and charged) molecules exhibit distinct emission / adsorption spectra. This is because the energy jumps between energy states of their electrons are discrete. Hence many transparent materials can be used to generate a point of visible light by spontaneous emission.

Two discrete frequency coherent or incoherent light sources are tuned to emit specific frequencies. This is usually achieved by adding impurities to the gas in an electric arc lamp or to the lasing material in a laser cavity.

In the simplest case, source A excites the molecules at the crossing point an intermediate excitation level. The second source B then excites the molecules to a higher excitation level. The molecules then decay back to lower levels, emitting photons of visible energy. The spot is visible from all directions because the emitted photons are generated by spontaneous emission.

This can be used, theoretically, to generate a 2-d and 3-d monochrome display, and with the addition of at least two other frequency sources, a colour display. Since the image is generated by spontaneous emission, it is a ghost image (not holographic).

This is especially useful for vector (wire frame) graphics, but can be used for raster graphics. However, practical problems mean that up until now, such systems are impractical. The main reasons are: 1) The Einstein coefficients of most materials mean that the excited state is very short lived, so that scanning the sources in 2-d or 3-d must be very fast.

2) The power of discrete frequency sources, especially lasers, is too small to generate a bright image. - 2

This patent describes several ways of eliminating these problems. Problem 1 (flickering) may be solved by steering the beams quickly, preferably in solid state.

There are several ways of achieving this: a) Phased arrays of coherent linked sources (e.g. semiconductor laser arrays).

b) Low inertia or solid state reflectors (e.g. semiconductor mirrors) for both coherent and incoherent sources.

c) Low inertia or solid state refractors (e.g. piezo-electric refractors) for both coherent and incoherent sources.

Problem 2 may be solved using primarily high power incoherent, discrete frequency sources. The best sources are arc lamps, which ionise a gas in an electric field, and light generated comes from electrons falling back into ions. The emitted frequencies tend to be discrete and may be tuned slightly, normally by adding other gases.

Note that not all of the sources of incident photons need be beam steered. Some incident photons may be supplied by fixed beams shining though the material. All of the incident photons must be either: 1) of invisible frequency, or; 2) introduced from a direction not visible from viewing positions.

Augmenting the incident power with fixed beams is required if the control (steered) beams are low power. Steering control beams of low power is easier because all current solid state mechanisms above have power constraints. These are low power in the case of phase linked semiconductor lasers, or high adsorption rates by reflectors or refractors, causing excessive heating.

According to the present invention there is provided a 2-d or 3-d display comprising a transparent target material which emits light of visible frequencies. The material is excited by two or more incident discrete frequency sources, such that the material is only excited to the energy state required to emit visible light at the crossing point of the incident sources. The control beams are scanned rapidly in order to generate a flicker free image.

Currently the best solution uses high power coherent or incoherent sources, steered by solid state reflectors or refractors. Solid state reflectors are currently available for applications such as normal projectors. Note that coherence is not required, unless required for phased beam steering.

The power required is quite high, because the image is visible from all angles. Thus for a typical image must be in the order of tens of Watts of light power at all viewing angles. This means that the sources typically require several hundreds of Watts of incident light power because not all of the incident light is adsorbed by the target material. - 3

A specific embodiment of the invention will now be described by way of example with reference to the accompanying figures in which: Figure 1 shows a 3-d display whereby the two discrete frequency sources cross at a point in an inflatable container of transparent gas. Visible light is generated at the crossing point of the incident sources by spontaneous emission of visible photons.

Figure shows the excitation of the material whereby one of the sources is tuned to excite the material from its normal excitation state to an intermediate energy state.

The other source is tuned to excite the material from its intermediate state to a higher energy state. That state then decays back to normal state, emitting visible photons by spontaneous emission during the process.

Figure 3 shows an electric arc lamp generating discrete freciuency light which is collimated into a thin parallel beam. The beam is shone onto one of the steerable (semiconductor) mirrors which are low inertia, allowing rapid scanning in bearing and elevation.

Figure 4 shows a 2-d display whereby the incident control beams are shone into a thin flexible sheet of target material tangentially, using Internal reflection to guide the incident beams, which are scanned in bearing only.

Referring to the figures, the 3-d display comprises an inflatable bag that is filled with the target gas, both of which must be reasonably transparent, and have excitation states that match the incident frequencies such that visible light is only generated at the crossing point of two or more of the incident sources.

The incident control beams are scanned rapidly in bearing and elevation such that the crossing point of the beams traces along a 3-d vector image. The brightness of the image may be varied by varying the intensity of one or more source, or by getting two more more of the incident control beams to miss each other slightly.

Solid state semiconductor mirrors are used because they are low inertia and hence respond quickly. They are controlled electronically in order to steer the beams in the prescribed manner in order to generate the desired image, in the simplest case, a vector or wire frame image.

Raster (or surface) images may be generated also, however the rate of scanning required is much higher. Note that goggles may be required if some of the incident sources are powerful enough and shone in a direction that might cause eye damage to viewers. The power may be augmented by fixed sources shining though the target volume (not shown).

The 2-d display comprises a thin flexible sheet that incorporates the target material (e.g. doped plastic). The control sources are introduced tangentially and scanned in bearing only. If the sheet is curved or bent, the incident control beams are guided by internal reflection.

The frequencies of light visible to humans is in the range 4000 Angstroms (violet) to 7500 Angstroms (far red). The control beams must be of different wavelengths, otherwise two jumps would occur along the primary excitation path. Hence a good choice for two incident beams for a green display are 13000 Angstroms (infra-red) and 8000 Angstroms (infra-red), which provided the target material adsorbs these frequencies, would tend to spontaneously emit light of 4952 Angstroms at the crossing point, depending on the Einstein coefficients of electron transitions of the target material.

Claims (8)

1. A 2-d or 3-d spontaneous emission display comprising a transparent target (of one or more materials) which is excited at the crossing point of two or more incident discrete frequency beams of light such that visible light is generated by spontaneous emission at the crossing point.

2. A 2-d or 3-d display as claimed in Claim 1 whereby the control beams are scanning rapidly though the target material in order to generate a 2d or 3-d image.

3. A 2-d or 3-d display as claimed in Claims 1 & 2 whereby the control beams are steered using phased array steering (coherent sources) or low inertia reflectors or refractors (coherent or incoherent sources).

4. A 2-d or 3-d display as claimed in Claims 1, 2 & 3 whereby rapid beam steering may be achieved using arrays of phase linked semiconductor lasers (coherent sources).

5. A 2-d or 3-d display as claimed in Claims 1, 2 & 3 whereby rapid beam steering may be achieved using solid state reflectors or refractors (coherent or incoherent sources).

6. A 2-d or 3-d display as claimed in Claims 1, 2 & 3 whereby all of the incident sources are invisible from viewing positions because they are of invisible frequency or shone from an invisible direction.

7. A 2-d or 3-d display as claimed in Claims 1, 2 & 3 whereby the power of the steerable control beams may be augmented by fixed non-steered sources.

8. A 2-d display as claimed in Claim 1 whereby some (or all) of the incident sources are introduced tangentially to a flexible sheet of target material (e.g. doped plastic) and are guided using total internal reflection.