DE102011089482A1 - Laser with monitored fiber optic path - Google Patents

Abstract

It is a laser with a laser source (2) which is operable with power and generates a first laser radiation as a function of the supplied current, an inlet and an outlet end (13, 12) having optical fiber path (5) into which the first laser radiation coupled via the inlet end (13) and which emits a second laser radiation via the outlet end (12) as a function of the coupled-in first laser radiation, a measuring unit (14, 15), the laser radiation, which at one between the inlet and the outlet end (13 , 12) of the optical fiber section (5), measures and generates a measurement signal based thereon, and provides a control module (6) based on the laser source (2) current supplied continuously a first threshold (Ss1 (t)) and / or a second limit value (Ss2 (t)) which, based on the measuring signal of the measuring unit (14, 15), continuously determines an actual signal (S1 (t)) and the actual signal (S1 (t)) continuously compares with the first threshold (Ss1 (t)) and turns off the laser source (2) when the actual signal (S1 (t)) is less than the first threshold (Ss1 (t)) and / or the actual signal (S1 (t )) continuously compares with the second threshold (Ss2 (t)) and turns off the laser source (2) when the actual signal (S1 (t)) is greater than the second threshold.

Description

The present invention relates to a laser having a laser source which is operable with current and generates a first laser radiation in response to the supplied current, and an inlet and an outlet end having optical fiber link into which the first laser radiation is coupled via the input end and in Dependence of the coupled-in first laser radiation emits a second laser radiation via the outlet end.

Since the leadership of the laser radiation takes place in the Lichtleitfaserstrecke, a closed light guide is in contrast to a possible open light guide, in which the laser radiation is guided by mirrors to the exit end of the laser.

When guiding the laser radiation in an optical fiber path, there is a difficulty in that until the laser radiation exits the outlet end there is no freely accessible point at which a part of the laser radiation for regulating the laser can be coupled out, for example by means of a coupling-out mirror. Since an optical fiber path as a light-guiding medium for the laser radiation usually contains glass fibers or glass fiber components, there is the risk of destruction of the optical fiber link, for example by fiber breakage or thermally induced melting of a fiber connection point. In the case of such a destruction, the laser radiation would emerge freely at least in the interior of the laser and, with a correspondingly high power of the laser (of, for example, 1 kW or more), cause considerable damage to the laser as well as endangering the operating personnel.

Particularly critical in lasers with an optical fiber link are the splices in which fiber end faces are fused together, and fiber couplers, in particular for running in the opposite direction of propagation laser radiation significantly lower damage threshold than in the intended direction of propagation. Such reverse propagation of laser radiation can occur when the laser radiation emitted by the laser is reflected back from the workpiece to be machined in the Lichtleitfaserstrecke.

Thus, in a laser having an optical fiber link, there is a problem that destruction may be caused by the primarily generated forward laser light as well as backward running laser light reflected from the workpiece to be processed, for example. Since there are no freely accessible locations for obtaining measurement signals in the optical fiber link in comparison to open beam lasers, it is already difficult to obtain corresponding measurement signals for monitoring the optical fiber path of the laser.

It is known in light-conducting cables to detect the destruction (eg in the form of a fiber break) by embedding a detection wire running next to the light-guiding fiber. The detection wire can be a wire or a conductor track deposited on the primary coating of the fiber ( US 4,883,054 ), which changes the conductivity in case of fiber breakage. Furthermore, a second optical waveguide fiber into which a second, very low-power light source is coupled and detected at the exit end can be provided, as in US Pat DE 40 107 89 A1 is described. Such an embedding of an electrical or "optical" wire is not or not consistently possible in a laser with an optical fiber link (especially if it is designed for high power), since such an electrical or optical wire can not be integrated in important fiber components such as a high power fiber coupler is.

Furthermore, it is known to monitor an optical waveguide by specially multilayer fiber layers, which allows loss radiation to pass through conversion processes from a first layer to a second layer, and which is then guided to a detector ( DE 43 140 31 A1 ). Again, however, there is the difficulty that specially prepared glass fibers are needed, which often can not be used in a laser with a Lichtleitfaserstrecke (especially for high power).

Furthermore, it is known to provide photodetectors for detecting stray light at the input end and at the output end of the fiber in conjunction with a suitable evaluation electronics which compares the two signals ( US 4,812,641 ) or with a fixed threshold ( US 7,146,073 ).

Such a configuration thus relates to a focus in a light guide and the exit from the light guide, so the case of an interrupted beam, which is not present in a laser with a Lichtleitfaserstrecke just. In addition, the signals for the photodetectors are obtained directly at the input and the output end, including in the US 7,146,073 a special preparation of the fiber ends is described. Such a preparation precludes use of commercially available high performance fiber optic cable provided with standard plug dimensions.

Furthermore, it is known to carry out the measurement at the fiber input and at the fiber output in such a way that the signal is direction-dependent at the fiber output in order to draw conclusions about the material processing process with regard to back-reflection and defocusing ( US 5,319,195 ).

Again, there is the case of an interrupted beam guidance in order to win the corresponding measurement signals can. The measurement signal at the output end is further influenced by light reflected from the workpiece, which is indeed taken into account, but the evaluation still difficult.

Proceeding from this, it is an object of the invention to provide a laser with a laser source and an inlet and an outlet end having optical fiber link, in which destruction of the optical fiber during operation of the laser as possible prevented or at least minimized.

According to the invention, the object is achieved by a laser having a laser source which can be operated or pumped with current and generates a first laser radiation as a function of the supplied current, an inlet and an outlet end having optical fiber link, into which the first laser radiation coupled via the inlet end is and which emits a second laser radiation via the outlet end depending on the coupled first laser radiation, a measuring unit, the laser radiation which exits at a lying between the inlet and the outlet end of the optical fiber passage, measures and based thereon generates a measurement signal and a control module, based on the current supplied to the laser source continuously determines a first and a second limit, which continuously determines based on the measurement signal of the measuring unit an actual signal and continuously compares the actual signal with the first limit and the laser source switches off, who n the actual signal is smaller than the first limit value and / or the actual signal continuously compares with the second limit value and the laser source switches off when the actual signal is greater than the second limit value.

A decrease in the actual signal below the first threshold indicates a loss of laser radiation in the optical fiber link, e.g. occurs when the guided in the Lichtleitfaserstrecke laser radiation thermally damaged part of the Lichtleitfaserstrecke or if, for example, a mechanical damage is present. With an appropriate choice of the size of the first limit value can thus be safely prevented further damage to the optical fiber link.

If the actual signal exceeds the second threshold, this is indicated e.g. on that reflected back laser radiation is coupled into the optical fiber link and it passes in the opposite direction, the optical fiber link. This can occur when machining workpieces, e.g. during material processing a highly reflective melt is formed. With a corresponding choice of the second limit, damage that would cause the reflected back laser radiation can be prevented. Of course, can be prevented by the comparison of the actual signal with the second limit and damage by laser radiation that passes through the optical fiber for other reasons in the opposite direction. The second threshold is preferably greater than the second threshold.

By continuous monitoring is meant in particular that the system is continuously monitored, for example, with an analog electronic circuit, or that the system is monitored at successive times, wherein the distance between successive monitoring times can be chosen so short that one in the meantime either defect would not lead to the destruction of other components of the system or would normally not at least endanger human and environmental health. The second-mentioned training of a continuous monitoring can be formed, for example, with a digital electronics, in which, for example, a controller repeatedly compares the actual values with the limit values in an infinitely loop realized in the program. For example, the time duration between two monitoring times may be a few μs. For the sake of completeness, it should be mentioned that the time period between two monitoring times, e.g. either always the same or different.

In the case of the laser according to the invention, the control module can switch off the laser source by switching off the power supply to the laser source.

Switching off the laser is understood here in particular to mean that the laser power is reduced to such an extent that no damage of components can occur or that no danger can emanate from the laser. The shutdown can, but need not, be made such that the laser current is brought to zero. This can be done for example by switching off the laser current or alternatively by shorting the laser current. The short-circuiting of the laser current can advantageously take place in the immediate vicinity of the laser, for example with a MOSFET or a bipolar transistor. To switch off the laser, however, it is also sufficient if the current is not completely switched off, but is reduced to such an extent that the laser threshold is not reached. The optical fiber link is preferably connected directly to the laser source, so that there is no free beam access between the laser source and the optical fiber link. In particular, there is no free beam access from the laser source to the exit end of the optical fiber path, so that the laser has a completely closed beam path.

Under free-jet access, here is e.g. understood that the laser radiation is guided over a certain length in air, so that in this area, for. a decoupling signal for decoupling a small portion of the laser radiation can be positioned. However, the free path, for example between a diode laser and the FAC lens or within a compact fiber optic coupling optics for a diode laser is not to be understood as free beam access in this sense, because there is no space for a device for decoupling provided. In contrast, a free-beam access is present in an optical telescope for coupling the radiation from one fiber to another fiber, since a device for coupling out a measuring beam can be provided in the collimated beam section. However, such free beam access is not present if it is a system in which the fibers are spliced together or connected via face coupling. In such a system then no free beam access is available.

Furthermore, in the case of the laser according to the invention, the optical fiber path can have at least one optical fiber with core and cladding and the measuring unit can measure the laser radiation emerging from the cladding. This radiation is often referred to as a sheath light. The optical fiber can be formed so that it emits such a jacket light at a predetermined location. For this, e.g. microscopic disturbances in the transition from the core to the cladding are provided. It can also be roughened a small portion of the fiber cladding, whereby a scattering of the jacket light takes place. Additionally or alternatively, the optical fiber may be intentionally bent so that due to the bending of the cladding light emerges. It is also possible to apply to the lateral surface of a medium having a higher refractive index than the cladding, so that no total reflection takes place at the interface between the cladding and the applied medium and thus cladding light is coupled out.

The laser radiation measured by the measuring unit preferably exits transversely to the propagation direction of the laser radiation in the optical fiber path.

The decoupled laser radiation preferably has only a fraction of the average power of the laser radiation guided in the optical fiber path. In particular, the fraction may be in the per thousand range.

In the case of the laser according to the invention, the optical fiber path can have at least two optical fibers spliced together and the measuring unit can measure the laser radiation exiting at the splice point.

Furthermore, the optical fiber path may comprise a plurality of optical fibers, which are coupled by means of a fiber coupler with a single optical fiber, wherein the measuring unit measures the emerging from the fiber coupler laser radiation.

In both cases (measurement at the splice point as well as measurement at the fiber coupler), the invention makes use of the fact that the laser radiation emerging there is measured and used to monitor the safety of the optical fiber link according to the invention.

In the case of the laser according to the invention, the optical fiber link can be designed as a passive optical fiber link. In this case, only the first laser radiation of the laser source is guided over the optical fiber path, so that the second laser radiation coupled out via the outlet end of the optical fiber path corresponds to the first laser radiation.

Of course, it is also possible that the optical fiber link has an active fiber which is pumped with the laser radiation of the laser source. In this case, a fiber laser is present, so that the decoupled second laser radiation is the laser radiation of the fiber laser and the coupled first laser radiation is the pump radiation of the fiber laser. In this case, the pumping radiation and / or the second laser radiation generated by means of the fiber laser can be measured by means of the measuring unit as emerging laser radiation.

The laser source may have at least one laser diode. It may preferably have a plurality of laser diodes which are supplied with current, for example, in series or parallel circuits. However, other laser sources are also possible which can be operated with electricity or are electrically pumpable. In particular, electrically pumped semiconductor lasers can generally be used. It is also possible to pump a solid-state laser by means of one or more electrically pumped semiconductor lasers, thereby realizing the laser source.

The control module may increase the first and / or second threshold as the pumping current increases. This takes into account the fact that with increasing pumping current increases the average laser power and thus the risk of a defect in the optical fiber link.

In particular, the control module increases the first limit as it increases Pumping current through so that the increase increases with increasing pumping current. Thus, the larger the pumping current becomes, the greater the increase becomes, whereby better protection is achieved. Furthermore, the control module can perform the increase of the second limit value so that the increase of the second limit value decreases with increasing pumping current. As the pumping current increases, the increase for the second threshold value decreases as the increase continues, which in turn leads to better protection of the laser. For example, the width of the window defined by both limits may decrease with increasing pumping current. Only when the actual value is in the window, the laser is not switched off.

In the laser according to the invention, the current supplied to the laser source may vary over time, e.g. To produce pulsed laser radiation or to vary the beam power in continuous stitching operation. In this case, the actual signal as well as the first and / or second limit value preferably vary in time in the same way. This ensures that the first and / or second limit are ideally adapted to the respective laser conditions and thus the first and / or second threshold can be selected very close to the actual value, so that the intended operation can be safely performed and at the same time the desired Security (ie the fast shutdown, if necessary) is guaranteed.

The laser is designed especially for high power. This is understood in particular to mean that the average power in continuous-wave mode or the peak pulse power in pulsed operation of the laser radiation emitted via the outlet end is at least 1 kW.

The optical fiber path can also be designed such that laser radiation emerges at several points between the inlet and the outlet end. In this case, the measuring unit is preferably designed so that it measures at each of these multiple locations the exiting laser radiation and generates corresponding measurement signals. The control module then determined based on the measurement signals for each exit point continuously a corresponding actual signal and compares all actual signals continuously with the first limit and / or the second limit. If at least one of the actual signals is smaller than the first limit value, the control module carries out the shutdown of the laser source. Furthermore, the control module also shuts off the laser source when at least one of the actual signals is greater than the second threshold.

The optical fiber path can also be designed such that it has a plurality of light entry ends. In particular, the exit end can also be used as entry end. This is the case, for example, with a double ended end-pumped fiber laser. There, the exit end of the laser radiation of the active fiber can simultaneously be the inlet end for the pump radiation. The pump radiation and emerging laser radiation may have different wavelengths, so that a separation of the beam paths, for example with a wavelength-selective mirror element is possible.

The laser can emit pulsed laser radiation or continuous wave radiation.

There is further provided a method of operating a laser having a laser source which is operable with current and generates a first laser radiation in response to the supplied current, and having an inlet and an outlet end having optical fiber in which the first laser radiation over the Input end coupled and output in response to the coupled first laser radiation, a second laser radiation over the exit end, the current being supplied to the laser source so that it generates the first laser radiation, laser radiation emerging at a lying between the inlet and the outlet end of the optical fiber link , Measured and based on a measurement signal is generated based on the current supplied to the laser source continuously a first and / or a second limit is determined based on the measurement signal continuously an actual signal is determined and the actual signal continuously with the first limit value compared and the laser source is turned off when the actual signal is smaller than the first threshold, and / or the actual signal continuously compared with the second threshold and the laser source is turned off when the actual signal is greater than the second threshold. In this case, the actual signal may be equal to the measurement signal, or the actual signal may additionally include, for example, a dependent of the time change of the measurement signal portion, which is referred to as a differential part, or for example an integral part, which depends on the accumulated over a certain period control deviation. Such a differential portion results in faster shutdown in the event of sudden deviations of the actual value from the target base value, i. in case of sudden deviations.

With the method according to the invention for operating a laser, the destruction of the optical fiber path can be reliably prevented or at least an occurring destruction can be minimized.

The inventive method for operating a laser can be further formed so that the laser according to the invention can be operated including its developments. In particular, the inventive method can contained in the context of the laser according to the invention described method steps.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it:

1 a schematic view of a first embodiment of the laser according to the invention;

2 an enlarged schematic sectional view of a fiber optic element of the optical fiber path of the laser according to the invention;

3a - 3c Diagrams for explaining the monitoring according to the invention of the optical fiber path of the laser according to 1 ;

4a - 4c Diagrams for explaining the monitoring according to the invention of the optical fiber path of the laser according to 1 ;

5a - 5c Diagrams for explaining the monitoring according to the invention of the optical fiber path of the laser according to 1 ;

6a - 6c Diagrams for explaining the monitoring according to the invention of the optical fiber path of the laser according to 1 ;

7 a schematic representation of the signal acquisition and processing by the control module of the laser according to the invention, and

8th a schematic representation for explaining the rule-technical realization of the monitoring of the optical fiber link.

The optical fiber link may include optical fibers, optical fibers and optical cables or other fiber optic components.

At the in 1 embodiment shown, the laser according to the invention 1 a laser source 2 with three laser diodes 3 ₁ , 3 ₂ and 3 ₃ , a power source 4 for operating the laser diodes 3 ₁ - 3 ₃ , an optical fiber link 5 and a control module 6 on. The laser source 2 Of course, more than three or less than three laser diodes 3 ₁ - 3 ₃ included. The number of three laser diodes 3 ₁ - 3 ₃ is just an example.

The fiber optic route 5 points for each laser diode 3 ₁ - 3 ₃ a first optical fiber and thus here three first optical fibers 7 ₁ , 7 ₂ and 7 ₃ , wherein each first optical fiber 7 ₁ - 7 ₃ exactly one laser diode 3 ₁ - 3 _{3 is associated} so that a first end of each first optical fiber 7 ₁ - 7 ₃ with the associated laser diode 3 ₁ - 3 _{3 is} connected. The other end of the first optical fibers 7 ₁ - 7 ₃ is with second optical fibers 8th ₁ - 8th _{3 of} a fiber coupler 9 welded. The fiber coupler 9 has a third optical fiber on the output side 10 on top of that from the fiber coupler 9 groundbreaking end with a fourth optical fiber 11 is welded, of which the third optical fiber 10 opposite end of an outlet end 12 the optical fiber link 5 forms. The entry end 13 the optical fiber link 5 gets through with the laser diodes 3 ₁ - 3 ₃ connected ends of the first optical fiber 7 ₁ - 7 ₃ formed.

The laser 1 further includes first and second photodetectors 14 . 15 , with which side of the optical fiber link 5 between inlet and outlet ends 13 . 12 emerging laser radiation (by arrows 16 . 17 indicated) can be measured. This will be for a safety shutdown of the laser 1 used, as will be described in detail below. The measuring signals of the photodetectors 14 . 15 be the control module 6 fed.

To operate the laser 1 become the laser diodes 3 ₁ - 3 ₃ with power source 4 applied. In the 1 shown series connection of the laser diodes 3 ₁ - 3 ₃ is only an example. There are also other types of wiring possible. In particular, a parallel connection is possible.

By applying current generate the laser diodes 3 ₁ - 3 ₃ laser radiation into the respective first optical fiber 7 ₁ - 7 _{3 is} coupled and via the fiber coupler 9 to the exit end 12 the optical fiber link 5 to be led. In the embodiment described here, the optical fiber link is 5 purely passive. It is thus only the laser radiation of the laser diodes 3 ₁ - 3 ₃ to the exit end 12 guided. However, it is also possible in the Lichtleitfaserstrecke 5 to arrange an active fiber with the laser radiation of the laser diodes 3 ₁ - 3 _{3 is} pumped. In this case, a fiber laser is present whose laser radiation as desired laser radiation over the exit end 12 is delivered. The at the exit end 12 emerging laser radiation 18 can for example be used for cutting, welding or hardening of various workpieces W and here has an average power of at least 1kW. The current to be delivered for the laser diodes 3 ₁ - 3 ₃ can by the user of the laser 1 from the outside via a connection 19 the power source 4 be determined.

At the in 1 shown laser is a closed beam guide, since the laser radiation of the laser diode 3 ₁ - 3 ₃ directly into the first optical fibers 7 ₁ - 7 _{3 is} coupled and the optical fibers 7 ₁ - 7 ₃ , 8th ₁ - 8th ₃ , 10 and 11 by means of splices V1 and V2, in which the fiber end faces are welded together, and thus the laser radiation of the laser diodes 3 ₁ - 3 ₃ over the exit end 12 the optical fiber link 5 is decoupled. The laser according to 1 can therefore also be referred to as an all-fiber laser.

The optical fibers 7 ₁ - 7 ₃ , 8th ₁ - 8th ₃ , 10 and 11 the optical fiber link 5 are fiber optic components, which may differ in detail depending on the concrete design, but are always similar in their basic structure.

In 2 is shown schematically in an enlarged sectional view of the basic structure of such an optical fiber with a stepped refractive index profile, wherein the optical fiber is a light-guiding core 20 has, which is usually formed of quartz glass. The refractive index of the quartz glass of the core 20 is greater than the refractive index of the immediately adjacent cladding 21 , which leads to a total internal reflection at the boundary core-cladding and thus to the light-guiding property of the fiber. The coat 21 may for example be formed from fluorine-doped quartz glass.

To make the fiber pliable and mechanically robust is on the mantle 21 a plastic layer 22 applied, which is often referred to as coating or buffer. The plastic layer 22 Can be made from a primary, soft coating 23 and a secondary, harder coating 24 consist. In the training as fiber optic cables still more sheaths are often provided to increase the robustness. On the other hand, for example, in the case of fiber couplers, it is possible to apply coating 22 be waived.

The in conjunction with 2 described optical fiber has between core 20 and coat 21 a stepped refractive index profile, so that such fibers are also often called step index fibers. Instead of being formed as a step-index fiber, the optical fibers can also be designed as so-called gradient index fibers in which the refractive index continuously decreases towards the outside from the fiber center.

Because the laser 1 has the described closed beam guide, is subject to the Lichtleitfaserstrecke 5 the risk of destruction, for example in the form of a fiber breakage or a thermally induced melting of a splice point V1, V2. In the case of such destruction, the laser radiation could at least in the interior of the laser 1 free escape and cause the possible high power of, for example 1kW and more significant damage in the device and a threat to the operator.

Furthermore, undesirably, the over the outlet end 12 emitted laser radiation 18 from the workpiece W to be processed back into the Lichtleitfaserstrecke 5 are reflected, so that there is an undesirable reverse propagation. Especially the fiber coupler 9 can have a significantly smaller destruction threshold for laser radiation in the reverse propagation direction than in the intended propagation direction.

To a destruction of the optical fiber link 5 and to prevent a hazard to persons or at least the extent of the destruction of the optical fiber link 5 is minimized, the fact is exploited that a clear functional relationship between the generated laser power and the supplied current to operate the laser diodes 3 ₁ - 3 ₃ is present. This is used in the way that is based on the current to drive the laser diodes 3 ₁ - 3 _3, a first limit value S _s1 (t) is derived and a (first) actual signal S ₁ (t) to be compared therewith from the measurement signal of the first photodetector 14 is derived. The first limit value S _s1 (t), which can also be referred to as the first threshold value or the first setpoint value, and the actual signal S ₁ (t), which can also be referred to as the actual value, become in the control module 6 continuously compared with each other, and when the actual signal S ₁ (t) is smaller than the first threshold value S _s1 (t), causes the control module 6 via the power source 4 a shutdown of the laser 1 , Such a decrease of the actual signal S ₁ (t) shows namely that laser power in the optical fiber path 5 "get lost". This occurs, for example, when a melting begins at a splice connection V1, V2.

This type of control or monitoring of the laser 1 should be discussed in detail below in connection with 3a - 3c to be discribed. It is assumed that the operating current I (t) for operating the laser diodes 3 ₁ - 3 _{3 is} constant in time, as in 3a is shown.

Based on this time constant operating current I (t), the control module determines 6 the first limit S _s1 (t), as shown in 3b is shown schematically.

In 3c is in addition to the first threshold S _s1 (t) that of the control module 6 based on the measurement signal of the first photodetector 14 determined actual signal S ₁ (t) located. Since this actual signal S ₁ (t) is always above the first limit value S _s1 (t), the laser 1 not switched off. In 3c is still another actual signal S ' ₁ (t) located, from the it is assumed that it decreases to the first limit value S _s1 at time t1. In such an actual signal S ' ₁ (t), the control module switches 6 at time t1, the power source 4 so that the laser diodes 3 ₁ - 3 _{3 are} no longer energized. This leads to the shutdown of the laser 1 ,

In 4a - 4c the case is shown in which the operating current I is time modulated as intended. This then likewise leads to a time-modulated first limit value S _s1 (t), as in _FIG 4b is shown. During normal operation of the laser 1 should then also the actual signal S ₁ (t) have the same temporal modulation, if the laser 1 has no error, as in 4c is indicated. A temporally constant first limit value would not be meaningful for this operation, since the intended temporal modulation of the actual signal S ₁ (t) would lead to a falling below the temporally constant first limit value, so that undesirably the laser 1 would be turned off. In order to prevent this, the distance between the temporally constant first limit value and the expected actual signal would have to be so large that it would no longer be safe to destroy the optical fiber link 5 prevented or at least prevented quickly.

The one from the first photodetector 14 detected laser radiation is preferably coupled out in such a way that it only a small fraction of the light from the over the exit end 12 emerging laser radiation amounts. Typically, the fraction is in the range of a few per thousand. This can be achieved in particular by decoupling light from the cladding of the corresponding optical fiber. For such decoupling, microscopic perturbations in the transition from the core to the cladding can be provided. Furthermore, known methods for generating cladding light can be used. For example, a small area of the fiber cladding can be roughened, whereby the cladding light is scattered out. It is also possible to apply to the lateral surface of a medium having a higher refractive index than the cladding, so that no total reflection takes place at the interface between the cladding and the applied medium.

Furthermore, the scattered light produced at the splices V1, V2 can also be detected. This is in 1 for the splice point V1 indicated, wherein the corresponding scattered light 17 by means of the second detector 15 is measured. Based on the measurement signal of the second detector 15 determines the control module 6 a second time-dependent actual signal, which is continuously compared in the same way as the first actual signal with the first limit value. When the second actual signal drops to the first limit value, the control module switches 6 the laser 1 for security reasons.

To the risk of coupled in the wrong direction laser radiation in the Lichtleitfaserstrecke 5 to minimize, a second threshold S _s2 (t), which may also be referred to as second threshold or second setpoint, may be determined, which is an upper limit to the actual value. If this upper limit is exceeded by the actual value, the control module will execute 6 turn off the laser 1 by. In order to measure the laser radiation injected in the wrong direction, it is again possible to measure jacket light which is produced when laser radiation reflected back from the workpiece W via the outlet end 12 in the optical fiber route 5 is coupled again. Since, in this case, there are generally no optimum coupling-in conditions with regard to the numerical aperture of the fiber and / or with regard to spot size and angle of incidence in the fiber core, overblasting will take place, which can be detected.

This type of safety shutdown of the laser 1 will be described in more detail below.

In 5a is the same as in 3a the time course of the current for the laser diodes 3 ₁ - 3 ₃ , in which case a constant current is assumed.

Based on this current, the control module determines 6 in addition to the first limit value S _s1 (t), a second limit value S _s2 (t) as the upper limit, which in 5b in the same way as in 3b are drawn.

As long as the actual value S ₁ (t) lies between the two limit values S _s1 and S _{s2, it} is considered that the laser operates as intended and in accordance with its intended purpose 1 went out. However, should the actual value S '' ₁ rise above the second threshold S _s2 , as in 5c is indicated, the control module switches 6 the laser 1 by stopping the power supply. This is in the illustration according to 5c at time t2 the case.

In the same way, a shutdown takes place if the actual value S ' _{1 reaches} the first limit value S _s1 . This is according to the representation of 5c at time t1 the case.

Thus, a window for the actual value S _{1 is} given by the two limit values S _s1 and S _s2 . As long as the actual value lies in this window, the operation of the laser is considered as intended 1 went out. If the actual value S ₁ leaves this window, the laser becomes 1 off.

In 6a - 6c is the case with the lower and upper limit S _s1 and S _s2 case for the one time varying operating current I. shown. As long as the corresponding time-varying actual value S _{1 is} within the window specified by the two limit values S _s1 and S _s2 , it is assumed that the operation is as intended and the laser is not switched off. If the actual value S _{1 reaches} the upper or lower limit (ie the first or second limit value S _s1 , S _s2 ), the automatic shutdown takes place.

Of course it is possible the laser 1 form so that only a comparison of the actual value S _{1 is performed} with the second threshold S _s2 .

In 7 is schematically the signal acquisition and processing by the control module 6 for the case with the lower and upper limit values S _s1 (t) and S _s2 (t).

The control module 6 includes a current detector 25 and a first to third electronic circuit 26 . 27 and 28 , The current detector 25 determined by means of the laser diodes 3 ₁ - 3 ₃ supplied operating current I (t) a target base signal S ₀ (t), which is for example an electrical voltage signal. This nominal base signal S ₀ (t) becomes the first electronic circuit 26 supplied therefrom, which determines therefrom the lower and upper limit value S _s1 (t) and S _s2 (t) according to the following formulas S _s1 (t) = S ₀ (t) - ΔS _low S _s2 (t) = S ₀ (t) + ΔS _high

The values for ΔS _low and ΔS _high may be the same or different. The values are suitably determined to realize the desired protective function. In particular, the values .DELTA.S _low and .DELTA.S _{high can} with increasing pumping current of the laser diodes 3 ₁ - 3 _{3 are} chosen smaller. Thus, the higher risk of destruction with increasing laser power can be considered. It should also be remembered that the relative inaccuracies just above the lasing threshold are particularly high. In this operating range, therefore, there is a particular risk that it will lead to faulty laser shutdown, without a fiber defect is present. This can be countered by the fact that in the lower power range, a magnitude greater percentage deviation ΔS _low / S ₀ and / or ΔS _high / S _{0 is} allowed. It may or may not even allow for a larger absolute deviation for ΔS _low and ΔS _high in the range just above the lasing threshold compared to operation at rated power.

The second electronic circuit 27 generated based on the measurement signal supplied to the first photodetector 14 the first actual signal S ₁ (t), which in turn may be a voltage signal.

The first actual signal S ₁ (t) and the two limit values S _s1 (t) and S _s2 (t) become the third electronic circuit 28 supplied, the described comparison of the signals (eg according to 5c and 6c ) and outputs an output signal S _out .

The third electronic circuit 28 For example, it can be designed as a window discriminator which compares the first actual signal S ₁ (t) with the two limit values S _s1 (t) and S _s2 (t). Depending on the comparison result, the level of the output signal S _{out is} generated. If the actual value is within the limits, the level of the output signal S _{out may be} low, for example. If the actual signal is not within the limits, the level of the output signal S _{out may be} high, which then causes the current source to be turned off. Of course, the window discriminator 28 Also be designed so that it outputs the signal S _out only when the actual signal S ₁ (t) is not within the limits. In this case, the current source is designed so that a shutdown is effected upon application of the signal S _out .

The reaction time from the detection of a threshold overshoot or undershoot to the shutdown of the laser 1 depends essentially on the speed of the photodetectors 14 . 15 and the signal processing electronics and software of the control module 6 from. Since laser-induced destruction is based on thermal effects, reaction times in the range of a few microseconds should be aimed for, in particular in the event of a preventive shutdown before the onset of fiber destruction. The need for microsecond response times can be estimated as greatly simplified as follows. If, for example, the fiber coupler 9 As a critical point, a small area V1 of an estimated 0.01 mm ³ volume content could be melted. For this purpose, a heat energy Q = ρ · V · c · ΔT must be introduced, with a density of the quartz glass ρ = 2.2 g / cm ³ , a heat capacity of c = 1 J / (gK) and a melting point of the quartz glass of about 1660th ° C. This results in a heat energy Q of about 0.03 J = 0.03 Ws. With complete absorption of the laser radiation, a laser power of P = 1kW must act for about 30μs long to deposit this heat energy. Therefore, the reaction time should be in the range of a few microseconds.

Should in the laser according to the invention 1 primarily consequential damage after destruction of a fiber optic component of the optical fiber link 5 can be prevented, the reaction time can be selected so long as the housing or other shields safely prevent leakage of laser radiation into the environment. These reaction times are then longer than those mentioned some Microseconds in the event of preventive shutdown of the laser 1 ,

In 8th is shown schematically the control engineering view of another embodiment. From the continuously monitored measured value of the power P (t) and the instantaneous desired base value S ₀ (t) calculated from the laser current, the control deviation R ₁ (t) is formed as the difference. From this, a proportional value is formed by multiplication by a coefficient P (coefficient for the proportional component) (by block 30 indicated). Furthermore, an integral value can be formed by the summation over previous control deviation values multiplied by an integral coefficient m _i (by block 31 indicated). Further, by taking the difference between, for example, two consecutive control deviation values multiplied by a coefficient m _d for the differential component, a differential value can be formed (by block 32 indicated). These three values can be summed up to the actual value S ₁ (t). This continuously formed actual value S ₁ (t) is continuously updated with a window discriminator 28 then monitors whether it falls below a lower value of the control deviation .DELTA.S _low or exceeds an upper permissible value of the control deviation .DELTA.S _high , these two limit values from the target base value S ₀ (t) are continuously recalculated (by blocks 33 and 34 indicated).

In this exemplary embodiment, the comparison of the actual signal S ₁ (t) with the limit values takes place in such a way that first the nominal base value S ₀ (t) is subtracted from the measured value P (t), adding to the difference in the above-mentioned manner proportional, differential and integral components and this sum (actual value) S ₁ (t) are then compared with the permissible control deviations. These control deviations are respectively the differences ΔS _high and ΔS _low from the upper limit value S _s1 (t) and the nominal base value S ₀ (t) or the nominal base value S ₀ (t) and the lower nominal value S _s2 (t). Of course, it is not always necessary to add to the control deviation R ₁ (t) the proportional, differential and integral components. It can also only one of the shares or it can be added to two of the shares to the control deviation. This method of performing the comparison is not only in this specific embodiment, but also generally equivalent to a direct comparison of an actual value, which is calculated on the basis of the measured value without deduction of the target base value, with the upper and lower limits S _high and S _low .

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4883054 [0006]
• DE 4010789 A1 [0006]
• DE 4314031 A1 [0007]
• US 4812641 [0008]
• US 7146073 [0008, 0009]
• US 5319195 [0010]

Claims (16)

Laser with a laser source ( 2 ), which is operable with current and generates a first laser radiation in dependence of the supplied current, one of an inlet and an outlet end ( 13 . 12 ) having optical fiber link ( 5 ), into which the first laser radiation via the entrance end ( 13 ) is coupled in and the second laser radiation in dependence on the coupled-in first laser radiation via the outlet end ( 12 ), a measuring unit ( 14 . 15 ), the laser radiation, which at one between the entrance and the exit end ( 13 . 12 ) of the fiber optic fiber link ( 5 ), measures and generates a measurement signal based thereon, and a control module ( 6 ) based on the laser source ( 2 ) supplied current a first threshold (S _s1 (t)) and / or a second threshold (S _s2 (t)) determined based on the measurement signal of the measuring unit ( 14 . 15 ) an actual signal (S ₁ (t)) is determined and the actual signal (S ₁ (t)) is continuously compared with the first limit value (S _s1 (t), and the laser source ( 2 ) turns off when the actual signal (S ₁ (t)) is smaller than the first limit value (S _s1 (t)) and / or the actual signal (S ₁ (t)) continuously with the second limit value (S _s2 (t)) compares and the laser source ( 2 ) turns off when the actual signal (S ₁ (t)) is greater than the second threshold (S _s2 (t)). Laser according to Claim 1, in which the control module ( 6 ) increases the first limit as the pumping current increases. Laser according to Claim 2, in which the control module ( 6 ) increases the first limit value (S _s1 (t)) with increasing pumping current so that the increase increases with increasing pumping current. Laser according to one of the preceding claims, in which the control module ( 6 ) increases the second threshold (S _s2 (t)) as the pumping current increases. The laser of claim 4, wherein the control module increases the second threshold so that as the pumping current increases, the boost decreases. Laser according to one of the above claims, in which the current supplied to the laser source varies over time and the actual signal (S ₁ (t)) and the first and / or second limit value (S _s1 (t), S _s2 (t)) in the same way vary in time. Laser according to one of the preceding claims, in which the control module ( 6 ) the laser source ( 2 ) by switching off the power supply to the laser source ( 2 ) turns off. Laser according to one of the preceding claims, in which the optical fiber path ( 5 ) at least one optical fiber ( 7 ₁ , 7 ₂ , 7 ₃ ; 8th ₁ , 8th ₂ , 8th ₃ ; 10 ; 11 ) with core ( 20 ) and coat ( 21 ) and the measuring unit ( 14 . 15 ) Measures the emerging from the jacket laser radiation. Laser according to one of the preceding claims, in which the optical fiber path ( 5 ) at least two optical fibers spliced together ( 7 ₁ , 7 ₂ , 7 ₃ ; 8th ₁ , 8th ₂ , 8th ₃ ; 10 ; 11 ) and the measuring unit ( 14 . 15 ) measures the laser radiation emerging at the splice point (V1, V2). Laser according to one of the preceding claims, in which the optical fiber path ( 5 ) several optical fibers ( 7 ₁ , 7 ₂ , 7 ₃ ), which by means of a fiber coupler ( 9 ) with a single optical fiber ( 10 ), and the measuring unit ( 14 . 15 ) from the fiber coupler ( 9 ) Exiting laser radiation measures. Laser according to one of the preceding claims, in which the optical fiber path ( 5 ) as a passive optical fiber link ( 5 ) is trained. Laser according to one of Claims 1 to 10, in which the optical fiber link ( 5 ) has an active fiber which is connected to the laser radiation of the laser source ( 2 ) is pumped. Laser according to one of the preceding claims, in which the laser source ( 2 ) at least one laser diode ( 3 ₁ , 3 ₂ , 3 ₃ ). Laser according to one of the preceding claims, which is designed so that the average power in the continuous wave mode or the pulse peak power in the pulse mode of the over the output end ( 12 ) emitted laser radiation ( 18 ) is at least 1kW. Laser according to one of the preceding claims, derived from the laser source ( 2 ) or the entrance end of the optical fiber path to the exit end ( 12 ) of the optical fiber link ( 5 ) is formed without free beam access. A method of operating a laser having a laser source that is operable with current and generates a first laser radiation in response to the supplied current, and having an inlet and an outlet end having optical fiber link into which the first laser radiation coupled via the input end and in dependence the second laser radiation is output via the output end, the laser source is supplied with current, so that it generates the first load radiation, laser radiation, at a lying between the inlet and the outlet end of the optical fiber path outlet, measured and based on a measurement signal is generated based on the laser source current supplied continuously a first and / or a second limit is determined based on the measurement signal continuously an actual signal is determined and the actual signal continuously compared with the first limit and the Laser source is switched off when the actual signal is smaller than the first threshold, and / or the actual signal continuously compared with the second threshold and the laser source is turned off when the actual signal is greater than the second threshold.

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