GB2317709A - Optical protection device - Google Patents
Optical protection device Download PDFInfo
- Publication number
- GB2317709A GB2317709A GB9501805A GB9501805A GB2317709A GB 2317709 A GB2317709 A GB 2317709A GB 9501805 A GB9501805 A GB 9501805A GB 9501805 A GB9501805 A GB 9501805A GB 2317709 A GB2317709 A GB 2317709A
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- GB
- United Kingdom
- Prior art keywords
- signal
- wave
- entrance
- pump
- exit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 25
- 239000000463 material Substances 0.000 claims abstract description 22
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 6
- 229910052709 silver Inorganic materials 0.000 claims description 6
- 239000004332 silver Substances 0.000 claims description 6
- 229910017214 AsGa Inorganic materials 0.000 claims description 3
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 claims description 3
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 3
- UKDIAJWKFXFVFG-UHFFFAOYSA-N potassium;oxido(dioxo)niobium Chemical compound [K+].[O-][Nb](=O)=O UKDIAJWKFXFVFG-UHFFFAOYSA-N 0.000 claims description 3
- 230000003993 interaction Effects 0.000 description 4
- 238000010521 absorption reaction Methods 0.000 description 3
- 230000010355 oscillation Effects 0.000 description 3
- 230000006399 behavior Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000005374 Kerr effect Effects 0.000 description 1
- 229910007475 ZnGeP2 Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000005693 optoelectronics Effects 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/39—Non-linear optics for parametric generation or amplification of light, infrared or ultraviolet waves
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F9/00—Methods or devices for treatment of the eyes; Devices for putting-in contact lenses; Devices to correct squinting; Apparatus to guide the blind; Protective devices for the eyes, carried on the body or in the hand
- A61F9/02—Goggles
- A61F9/022—Use of special optical filters, e.g. multiple layers, filters for protection against laser light or light from nuclear explosions, screens with different filter properties on different parts of the screen; Rotating slit-discs
- A61F9/023—Use of special optical filters, e.g. multiple layers, filters for protection against laser light or light from nuclear explosions, screens with different filter properties on different parts of the screen; Rotating slit-discs with variable transmission, e.g. photochromic
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Nonlinear Science (AREA)
- Optics & Photonics (AREA)
- Heart & Thoracic Surgery (AREA)
- Ophthalmology & Optometry (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- General Physics & Mathematics (AREA)
- Vascular Medicine (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
This optical protection device consists of an element of non-linear material (1) including an entrance face (10) and an exit face (11) each possessing a mirror (2, 3) reflecting the light towards the element of non-linear material. The entrance and exit mirrors are at least partially reflecting in respect of the signal and idler waves generated from a pump wave within the non-linear medium. As regards the pump wave, these mirrors are preferably transparent. Thus above a certain level of the pump wave, the latter being transformed into signal and idler waves, a device (4) will be protected from the pump wave.
Description
2317709 OPTICAL PROTECTION DEVICE The invention relates to an optical
protection device applicable to the protection of optical sensors and allowing in particular protection against optical beams of high intensity.
In numerous optronic applications, it is neces sary to protect the sensors (optoelectronic,...) against optical attackers such as lasers. Several solutions are already used or under study such as band-stop filters, inverse saturable absorption systems, index variations induced by the Kerr effect,... In numerous cases, these techniques rely on absorption effects which may bring about substantial heat-up of the devices and even destruction if the incident laser power from which it is is sought to be protected is too substantial. Moreover, in certain cases, to obtain adequate sensitivity, there may be cause to use interactions of the resonant type, thus naturally limiting the spectral ranges of use. The invention offers the advantage of using principles which in their nature are purely dispersive (no absorption) and are based on certain properties of parametric oscillators.
The invention therefore relates to an optical protection device characterized in that it includes an element of non-linear material including an entrance face and an exit face each possessing a mirror reflecting the light towards the element of non-linear material, the entrance and exit mirrors being at least partially reflecting in respect of the signal and idler waves generated from a pump wave within the non-linear medium.
The various subjects and features of the inven tion will emerge more clearly in the description which follows and in the appended figures which represent:
- Figure 1, an example embodiment of the device; - Figures 2a to 3e, optical transmission curves for the device of Figure 1 as a function of the reflec tion coefficients of the rairrors of the device; - Figures 4 to 7, characteristic curves demonstrating the effectiveness of the device of the invention.
Hence, an example embodiment of the device according to the invention will be described whilst referring to Figure 1.
This device includes a medium 1 made of a nonlinear material possessing an entrance face 10 and an exit face 11. An entrance mirror 2 is arranged on the entrance face 10 side and an exit mirror is arranged on the exit face 11 side. Preferably, these mirrors 2 and 3 are adjoined to the respective faces 10 and 11. More precisely, the f aces 10 and 11 can be treated so as to have the reflection characteristics which will be indicated below.
The non-linear material medium 1 can be AsGa, ZnGeP2 silver selenogallate (AgGaSe2), silver thiogallate, lithium niobate or potassium niobate.
This medium 1 can be an assemblage of laminae or of layers of non-linear materials, which non-linear materials can be chosen from the above materials.
The role of the protection device is to protect a device 4 situated to the right against overly high incident optical powers (pump wave) arriving on the entrance mirror.
As will be described later, the incident pump wave of wavelength Xp penetrates the non-linear material medium. The pump wave is transformed into a signal wave of wavelength Xs and an idler wave of wavelength Xi such that Xs + Xi = Xp. Beyond a specified power, the pump wave is transformed almost totally into a signal wave and an idler wave. Beyond this power of the pump wave the device 4 is therefore protected against the action of this wave.
There is provision for the entrance mirror 2 to be reflecting to the signal waves (reflecting towards the non-linear The exit mirror 3 is likewise reflecting to the sign-Al;';and idler waves (likewise towards the non-linear medium) Moreover, the exit mirror 3 can be transparent to the pump wave. Possibly, the entrance mirror 2 may likewise be transparent (in both directions) to the pump wave.
The operation of the device described above with reference to Figure 1 relies on the particular properties of optical parametric oscillators (OPO). Considering the non-linear medium 1 to be transparent to the optical wavelengths used. This medium is placed in a cavity of the Fabry P6rot type forming the basic element of an optical oscillator. The optical wave of frequency ú2p (pump wave) is incident on the non-linear medium 1. Through a secondorder non-linear optical effect it can be shown that two new frequencies 2. and 2, (OS: signal, Qi: idler frequency) are generated in the crystal whose exact is values depend on the capacities to produce phase tuning. If the gain of the non-linear interaction is sufficient, the system can oscillate and thus constitute an optical source which is continuously tunable through modification of the phase tuning conditions already mentioned. The oscillation threshold depends naturally on the losses in the cavity and on the gain of the interaction which is strongly related to the magnitude of the non-linearities of the material used. In pulse mode, this threshold depends also on the length of the cavity (return journey time of the light in the cavity compared with the width of the pump pulse).
Once the threshold is exceeded, all the residual energy in the pump pulse is initially converted into the signal and idler waves, the pump power stabilizing at the level of the threshold of an equivalent OPO operating in continuous mode. In fact, the reality is more complex since, the idler and signal powers in the cavity being substantial, it is not possible to neglect the phenomenon which is the inverse of interaction, namely reconversion of the idler and of the signal to regenerate the pump. These phenomena are illustrated in Figure 2a. which shows the incident and transmitted pump pulses and the signal pulse transmitted in the case in which the mirrors are perfectly transparent to the pump wave. The entrance mirror is totally reflecting to the idler and signal waves and the exit mirror transparent in respect of the idler and partially reflecting in respect of the signal. In this case, it is observed --that no pump wave is recreated in the contrapropagative direction relative to the incident pump but that a certain amount is transmitted by the OPO. The "rebound" in the transmitted pump pulse, corresponding to the recreation of the pump by the idler and the intracavity signal, is also clearly distin- guishable. The magnitude of this pump regeneration depends on the parameters of the cavity, on the incident pump power (operation of the OPO more or less above the threshold), etc.
The phenomenon of interest to the invention is appears when considering the case of an OPO whose two mirrors are always perfectly transparent in respect of the pump wave but partially (or totally) reflecting in respect of the idler and signal waves. When the reflection coefficients in respect of the idler and signal waves are increased, the first consequence is a reduction in the oscillation threshold (reduction in the losses through the coupling of the waves to the outside of the cavity).
In an application in which the purpose is to generate tunable idler/signal frequencies, it will of course be sought to optimize the cavity to obtain maximum power at the output of the system by considering the output/threshold compromise. By the invention, it is sought to protect a device. A solution is to find the conditions of operation of the device which minimize the transmitted pump power and maximize the reflected pump power. Consequently, a sensor situated downstream of the device within the optical reception chain will thus become protected.
Behaviour of this type is illustrated by Figures 3, which represent the behaviours of parametric oscillators in which the mirrors of the cavity have substantial reflection coefficients in respeCt of the signal and idler waves and maximum transmission coefficients in respect of the pump wave. The important point is that, in these cases, the pump wave is negligible at the exit of the device (exit mirror 3 side) and almost totally reflected by the parametric oscillator once the oscillation threshold is attained, thus forming a non-linear mirror which is indeed the function sought.
Figures 2a, 2b and 3a to 3e represent the incident, and then transmitted pump pulses, and output signal (the idler pulse is identical to the signal pulse and is not represented) for various modes of operation of the device of the invention.
In Figures 2a and 2b:
- the pump energy is 4 mJ - the width of the pump pulse at mid-height is 10 ns - the length of the non-linear medium 1 is 1 cm and the cavity is constituted by the faces of the medium 1 (cavity length = 1 cm) - the coefficient of non-linearity is deff 14.2 pm/V - the reflection coefficients of the entrance mirror are: zero f or the pump wave and 0. 9 9 f or the signal wave and the idler wave - the wavelength of the pump wave is 1.06 gm and the signal and idler waves have a wavelength XS = Xi = 2.12 gm - the exit mirror has a zero reflection coeffi cient in respect of the pump wave - the radius of the pump beam is 1.6 ran.
In Figure 2a, the reflection coefficients of the exit mirror in respect of the signal and idler waves are 60%; the following energies are obtained for the pump, signal and idler waves:
- signal wave 0.94 mJ - idler wave 0.94 mJ - transmitted pump wave = 0.60 mJ - reflected pump wave = 1.52 mJ In Figure 2b, the reflection coefficierits of the exit mirror in respect of the signal and idler waves are 50%; the following energies are obtained for the pump, signal and idler waves:
- signal wave 1.06 mi - idler wave 1.06 mi - transmitted pump wave 0.84 mJ - reflected pump wave = 1.04 mJ In Figures 3a to 3e:
- the pump energy is 0.1 mJ - the width of the pump pulse at mid-height is 10 ns - the non-linear coefficient is deff = 150 pm/V - the reflection coefficients of the entrance mirror are:
zero for the pump wave is and 100% for the signal wave and the idler wave - the exit mirror has a zero reflection coeffi cient in respect of the pump wave For Figures 3a to 3c:
- the radius of the pump beam is 1.6 mm - the wavelength is 1.06 g and the signal and idler waves have a wavelength ds = di = 2.12 gm - the length of the non-linear medium 1 (and of the cavity) is 0.2 em - the reflection coefficients of the exit mirror in respect of the signal and idler waves are respectively: 90% (Figure 3a), 95% (Figure 3b) and 99% (Figure 3c) For Figures 3d and 3e:
- the pump wavelength is 3.5 gm and the signal and idler waves have a wavelength ds = di 7 gm - the length of the non-linear medium 1 (and of the cavity) is 0.5 em - the reflection coefficients of the exit mirror in respect of the signal and idler waves are 95% - the radii of the pump beam are respectively 1.6 mm (Figure 3d) and 0.2 mm (Figure 3e).
Figure 3d corresponds to a pump wave focused to a radius of 1.6 mm and Figure 3e to a pump wave focused to a radius of.2 mm. It is thus seen that the triggering threshold (threshold of the OPO) can naturally be adjusted by modifying the incident optical intensity.
Againi the material used can be a semiconductor with artificial phase tuning.
It is therefore seen that an incident pump wave Xp is transformed into two waves, signal Xs and idler Xi, which are reflected by the exit mirror 3. These two waves recombine in principle partially into a pump wave which passes through the entrance mirror 2 and is therefore returned in a direction substantially reverse to the incident pump wave. The signal and idler waves which have is not recombined are reflected by the entrance mirror 2. They recombine to give a new pump wave. It is noted that this new pump wave is cancelled out and is not transmitted to the device 4.
Figures 4 to 7 demonstrate the effectiveness of the invention.
For example, for a laser of length 0.4 gm, a pump beam pulse of midheight width 10 ns, an illumination spot of radius 1.6 mm and a nonlinear medium with nonlinear coef f icient d = 14 pm/V and thickness Ep = 1 mm with an exit mirror reflecting the signal and idler waves to 0.95%, curves 4 to 6 are obtained, having the incident energies of the pump beam as abscissae and as ordinates:
- for Figure 4, the energy of the pump beam transmitted - for Figure 5, the energy of the pump beam reflected - for Figure 6, the percentage of the pump beam transmitted.
In the same way, for a pump laser of wavelength 3.5 gm exhibiting 10 ns pulses, an illumination spot of radius 1.6 mm and a non-linear medium with non-linear coefficient d = 150 pm/V and thickness Ep = 5 mm with an exit mirror reflecting the signal and idler waves to 95%, the curve of Figure 7 is obtained in which the energy transmitted by the device is represented as a function of the incident pump energy.
Claims (5)
1. An optical protection device comprising an element of nonlinear material including an entrance face and an exit face each possessing a mirror reflecting the light towards the element of non-linear material, the entrance and exit mirrors being at least partially reflecting in respect of the signal and idler waves generated from a pump wave within the non-linear medium.
2. A device according to claim 1, wherein the exit mirror is transparent in respect of the pump wave.
3. A device according to claim 2, wherein the entrance mirror is transparent in respect of the pump wave.
4. A device according to claim 1, wherein the entrance and exit mirrors are totally or near-totally reflecting in respect of the signal and idler. waves- 5_ A device according to claim 4, wherein the reflection coefficients of the entrance and exit mirrors, in respect of the signal and idler waves, are greater than 90%.
6. A device according to claim 1, wherein the non-linear material is lithium niobate or potassium niobate, silver selenogallate (Ag Ga Se 2), or silver thiogallate, ZnGeP 2 or AsGa.
7_ A device according to claim 1, wherein the non-linear material is an assemblage of laminae or of layers of non-linear material.
8. An optical protection device substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in Figure 1 of these drawings.
Amendments to the claims have been filed as follows CLAIMS.:
I. An optical protection device for protecting an optical device from an incident optical wave comprising an element of non-linear material includina an entrance face and an exit face each possessing a mirror reflecting light towards the element of non-linear material, the entrance and exit mirrors being at least partially reflecting in respect of signal and idler waves generated from the incident optical wave acting as a pump wave within the nonlinear medium, said mirrors being transparent to the incident wave.
2. A device according to claim 1, wherein the reflection coefficients of the entrance and exit mirrors, in respect of the signal and idler waves, are gr2ater than 90?).
3. A device according to claim 1, wherein the non-linear material is lithium niobate or potassium niobate, silver selenogallate (Ag Ga Se2)' or silver thiogallate, ZnGeP 2 or AsGa.
4. A device according to claim 1, wherein the non-linear material is an assemblage of laminae or of layers of non-linear material.
5. An optical protection device substantially as described hereinbefore with reference to the accompanying drawings and as illustrated in Figure 1 of these drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9401270A FR2751435A1 (en) | 1994-02-04 | 1994-02-04 | OPTICAL PROTECTION DEVICE |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9501805D0 GB9501805D0 (en) | 1997-12-24 |
| GB2317709A true GB2317709A (en) | 1998-04-01 |
| GB2317709B GB2317709B (en) | 1998-07-08 |
Family
ID=9459788
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9501805A Expired - Fee Related GB2317709B (en) | 1994-02-04 | 1995-01-31 | Optical protection device |
Country Status (2)
| Country | Link |
|---|---|
| FR (1) | FR2751435A1 (en) |
| GB (1) | GB2317709B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2831722A1 (en) * | 2001-10-30 | 2003-05-02 | Thales Sa | OPTICAL PARAMETRIC OSCILLATOR WITH HIGH BEAM QUALITY |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4180751A (en) * | 1978-09-08 | 1979-12-25 | Gte Sylvania Incorporated | Mode-locked optical parametric oscillator apparatus |
| US4909609A (en) * | 1988-08-04 | 1990-03-20 | The United States Of America As Represented By The Secretary Of The Navy | Nonlinear optical protection against frequency agile lasers |
| US5053641A (en) * | 1989-07-14 | 1991-10-01 | Cornell Research Foundation, Inc. | Tunable optical parametric oscillator |
| US5088096A (en) * | 1989-07-11 | 1992-02-11 | Thomson-Csf | Tunable power laser |
| US5181211A (en) * | 1991-05-20 | 1993-01-19 | Fibertek, Inc. | Eye-safe laser system |
-
1994
- 1994-02-04 FR FR9401270A patent/FR2751435A1/en active Pending
-
1995
- 1995-01-31 GB GB9501805A patent/GB2317709B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4180751A (en) * | 1978-09-08 | 1979-12-25 | Gte Sylvania Incorporated | Mode-locked optical parametric oscillator apparatus |
| US4909609A (en) * | 1988-08-04 | 1990-03-20 | The United States Of America As Represented By The Secretary Of The Navy | Nonlinear optical protection against frequency agile lasers |
| US5088096A (en) * | 1989-07-11 | 1992-02-11 | Thomson-Csf | Tunable power laser |
| US5053641A (en) * | 1989-07-14 | 1991-10-01 | Cornell Research Foundation, Inc. | Tunable optical parametric oscillator |
| US5181211A (en) * | 1991-05-20 | 1993-01-19 | Fibertek, Inc. | Eye-safe laser system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2317709B (en) | 1998-07-08 |
| FR2751435A1 (en) | 1998-01-23 |
| GB9501805D0 (en) | 1997-12-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20010131 |