Tynax ~ Patent Library

Patent for Sale:

Infra-red Shutter    

An Infra-red shutter for thermal imaging and optical modulation with simpler operation, higher modulation speed, shrunken dimensions, resistance to mechanical shocks.


Solid-state modulators/shutters based on the electro-refractive effect have been proposed and researched to replace the mechanical counterpart. In the heart of our modulator is a technology based on the fusion of micro- and nano-patterned surfaces with the electro-refractive effect. This technology allows to produces a semiconductor optical structure fully transparent for the middle and far infra red radiation in a passive state. Pumping optically the free charge carriers into the structure activates the modulator. At a specific charge density the structure will almost completely block the incoming radiation. Periodically driven excitation of the structure modulates a passing through signal synchronised with the external driver. The speed of the modulation can reach GHz regime with the modulation contrast above 90%. Moreover the modulation occurs over a narrow band around a specific resonance infra-red frequency given by the properties of the structure.

Key Benefits are:
-- Smaller, faster and quieter than current mechanical shutters
-- Provides control over available shutter speeds with the theoretical limit in GHz frequencies regime
-- Operable over selected relatively narrow frequency bands
-- Operable in environments with high g-forces
-- Allows stroboscopic and 3D measurements
-- Provides capability for high-frequency sampling rate needed to improve image quality and the signal- to-noise ratio
-- Exhibits robust manufacturing technology
-- Extends capabilities of IR and thermal imaging to new markets and applications, such as gaming and position tracking
-- Allows IR camera systems to operate without interference from laser-induced dazzle effects

This technology overcomes the limitations of mechanical shutters which, despite an apparent simplicity, are based on moving parts, which restricts applications of thermal imaging for high-speed measurements and in environments with high g-forces. The mechanical shutter is relatively bulky as it requires a space to accommodate the blade, energy inefficient and inherently limited to slow speed of the modulation.

Primary Application of the Technology

-- Infra red camera systems
-- Discriminative imaging systems (hyperspectral imaging)
-- Automotive 3D sensor systems
-- Telecommunications

The Problem Solved by the Technology

Current IR imaging devices employ mechanical modulators to block incoming IR radiation by dropping a shutter. The purpose is often to enable background measurements to taken, which can be employed to enhance an IR image. However, the speed of such mechanical shutters is limited and the structure is typically bulky and noisy when in use.

There are also known attempts to provide modulators exploiting the Kerr effect, liquid crystals and acousto-optical characteristics. However, these are not widely implemented for the reasons explained below.

Kerr effect modulators are fast, but usually have bulky dimensions, a small aperture and require the application of high voltages. However, the major drawback with Kerr effect modulators is that they are birefringent.

For infrared light modulation an active layer consisting of liquid crystals must be relatively thick, corresponding to the wavelength to be absorbed. This results in poor response to applied pulses and a low extinction ratio. Almost all types of liquid crystals show slow response, narrow bandwidth and birefringence.

Acousto-optical modulators usually do not consume electrical power significantly and have good extinction ratio, but they are bulky in comparison to devices in microelectronics, have low bandwidth and relatively slow response in modulators with large apertures.

An aim of the present invention is therefore to provide an optical absorber which can be employed in an electro-optical modulator and which helps to address the above-mentioned problems.

How the Technology Solves the Problem

An optical absorber comprising: a semiconductor micro or nano scale structured array configured for transmission of electromagnetic (EM) radiation when in a passive state and for absorption and/or reflection of electromagnetic (EM) radiation when in an active state; and an activator arranged to inject free carriers into the structured array to activate said array on demand.

The optical absorber can be activated-on-demand to switch between a passive transmitting state and an active absorbing state. Accordingly, the optical absorber may be configured as an anti-reflective coating (i.e. fully or substantially transparent) when passive and as a total or substantial absorber (i.e. light blocker or reflector) when active. In other embodiments, the injection of free carriers can be controlled to alter the transparency of the array to a desired degree (e.g. to make it partially transparent and partially absorptive) to provide attenuation of a transmitted signal.

Advantageously, the optical absorber is based on proven physical principles and does not require complex fabrication technology or exotic materials. For example, it could be easily integrated into silicon devices. An optical absorber according to an embodiment of the present invention may be employed as an ultrafast shutter to block incoming radiation for a specified period of time.

The modulator may be configured to achieve up to a GHz repetition rate. Furthermore, modulators according to embodiments of the present invention (e.g. configured for a typically-sized uncooled IR sensor for a commercial camera) may have low power consumption (e.g. below 1 W) and can be optimised for improved performance and efficiency.

The optical absorber may be configured for transmission and/or absorption and/or reflection of EM radiation over a selected frequency bandwidth. In certain embodiments, the EM radiation comprises IR radiation. In other embodiments, the EM radiation comprises visible light. In particular embodiments, the optical absorber may be configured for transmission and/or absorption and/or reflection over a relatively narrow bandwidth (e.g. near, mid or far IR).

In certain embodiments, the optical absorber may be configured such that, when active, the array is substantially transparent at a first wavelength and substantially reflective at a second wavelength. In which case, the optical absorber may be employed as a beam splitter.

It will be understood that the dimensions and distribution of the structures in the array, in combination with the injection of free carriers and, optionally, the doping of the semiconductor material by donors or acceptors, can be tailored to provide a nearly transparent (passive) and/or strongly absorptive/reflective (active) optical response at a desired wavelength. More specifically, in an ideal case, the optical absorber may have a frequency response having a Lorentzian shape, with its centre in the frequency domain being determined by the concentration of injected free carriers and the width being determined by the scattering rate of the array. Both of these parameters are therefore tunable to some extent and, thus, the frequency response can be manipulated in terms of its position and shape.

Competitive Advantage

The optoelectronic device may be configured for use in signal detection; gated signal detection; filters; spectral pulse shaping; tuned IR emitters; 3D topography imaging; position and/or speed detection; reconnaissance, surveillance and target acquisition technology; optical thermal imaging (e.g. to identify objects in the dark or in difficult environments such as smoke or fog); industrial process control; pyrometers; or vision enhancement for automotive, aviation or seafaring applications. Thus, the optoelectronic device may be configured for use by, for example, fire-fighters, law enforcement officers, emergency personnel, border patrol, coast guards, rescue teams, security guards, maintenance engineers, building inspectors or military personnel.

More specifically, an optoelectronic device according to an embodiment of the invention may be configured for shortwave or near IR use (e.g. wavelengths of approximately 0.7 to 5 microns) and may be employed in active vision enhancement (e.g. where an IR light source is employed), high temperature thermography or material analysis. An optoelectronic device according to another embodiment of the invention may be configured for medium wave or mid IR use (e.g. wavelengths of approximately 5 to 40 microns) and may be employed in thermography, passive vision enhancement (e.g. night vision) or material analysis. An optoelectronic device according to a further embodiment of the invention may be configured for long wave or far IR use (e.g. wavelengths of approximately 40 to 350 microns) and may be employed in thermography or passive vision enhancement.

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