Delivery fiber assembly and a broad band source

Abstract

The invention comprises a delivery fiber assembly suitable for delivering broad band light. The delivery fiber assembly comprises a delivery fiber and a connector member. The deliver has a length, an input end for launching light and a delivery end for delivering light, where the delivery fiber comprises along its length a core region and a cladding region surrounding the core region. The cladding region comprises a cladding background material having a refractive index N.sub.bg and a plurality of inclusions of solid material having refractive index up to N.sub.inc and extending in the length of the longitudinal axis of the delivery fiber, wherein N.sub.inc<N.sub.bg and the plurality of inclusions in the cladding region is arranged in a cross-sectional pattern comprising at least two rings of inclusions surrounding the core region. The connector is mounted to the delivery fiber at a delivery end section of the delivery fiber comprising said delivery end. The delivery fiber has a transmission bandwidth of about 200 nm or more, such as of about 300 nm or more, such as of about 400 nm or more, such as of about 500 nm or more.

Claims

1. A spectral engine light source for supplying light to an apparatus, comprising: a microstructured delivery fiber assembly configured for delivering broad band light and comprising a microstructured delivery fiber and a connector member, said delivery fiber having a longitudinal axis, an input end for launching light and a delivery end for delivering light, said delivery fiber comprises a core region and a cladding region surrounding the core region, wherein the cladding region comprises a cladding background material having a refractive index Nbg and a plurality of inclusions of solid material having a refractive index up to Ninc and extending in the direction of longitudinal axis of the delivery fiber, wherein Ninc<Nbg and the plurality of inclusions in the cladding region is arranged in a cross-sectional pattern comprising at least two rings of inclusions surrounding the core region, said core region having a diameter up to about 15 μm, said connector member being mounted to said delivery fiber at a delivery end section of the delivery fiber, said delivery fiber defining a bandwidth of about 200 nm or more in which a transmission loss is less than 0.5 dB/m at all wavelengths within the bandwidth, said spectral engine light source further comprising a spectral engine, said spectral engine comprising two or more lasers emitting respective laser beams, said with wavelength(s) that differ with at least one wavelength; and a multiplexer, wherein the multiplexer is configured for receiving at least a portion of the laser beams of each of the lasers and for collimating the received light to a multiplexed beam, and wherein said microstructured delivery fiber is arranged to receive said multiplexed beam and to deliver at least a part of said received multiplexed beam to the apparatus.

2. The spectral engine light source of claim 1, wherein an inclusion of said plurality of inclusions has a higher refractive index than another inclusion of said plurality of inclusions.

3. The spectral engine light source of claim 1, wherein one of said laser beams of said spectral engine emitted from said two or more lasers comprises at least one wavelength below 500 nm and one of said laser beams emitted from said two or more lasers comprises at least one wavelength above 800 nm.

4. The spectral engine light source of claim 1, wherein at least one of said laser beams of said spectral engine emitted from said two or more lasers has a bandwidth of about 50 nm or less.

5. The spectral engine light source of claim 1, wherein the apparatus comprises an illumination apparatus configured for illuminating a target.

6. The spectral engine light source of claim 1 wherein said two or more lasers comprise at least three lasers, wherein a first laser of the lasers is adapted for emitting a laser beam comprising at least one wavelength below 450 nm, a second laser of the lasers is adapted for emitting a laser beam comprising at least one wavelength in the range from 500 nm to 700 nm, and a third of the lasers is adapted for emitting a laser beam comprising at least one wavelength above 800 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and/or additional objects, features and advantages of the present invention, will be further elucidated by the following illustrative and non-limiting detailed description of embodiments of the present invention, with reference to the appended drawings.

(2) FIG. 1a shows a cross-section of a delivery fiber of an embodiment of a delivery fiber assembly of the invention.

(3) FIG. 1b shows a wavelength profile in form of a transmission loss spectrum for a delivery fiber as shown in FIG. 1a.

(4) FIG. 1c shows an example of a PM fiber, where the dark regions are inclusions doped with another material, such as e.g. boron

(5) FIG. 1d shows an example of the long wavelength transmission edge and short wavelength transmission edge versus the pitch for a fiber according to the invention.

(6) FIG. 2 shows a perspective view of a part of an embodiment of the delivery fiber assembly of the invention.

(7) FIG. 3 is a schematic illustration of an embodiment of a broad band source of the invention.

(8) FIG. 4 is a schematic illustration of another embodiment of a broad band source of the invention.

(9) FIG. 5 is a schematic illustration of yet another embodiment of a broad band source of the invention.

(10) FIG. 6 is a schematic illustration of an embodiment of an apparatus of the invention in form of an interferometer.

(11) FIG. 7 is a schematic illustration of an embodiment of an apparatus of the invention in form of another type of interferometer.

(12) FIG. 8 is a schematic illustration of an embodiment of a spectral engine source of the invention.

(13) FIG. 9 is a schematic illustration of another embodiment of a spectral engine source of the invention.

(14) FIG. 10 is an illustration of an apparatus of an embodiment of the invention

(15) FIG. 11 is an illustration of another apparatus of an embodiment of the invention

(16) The figures are schematic and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

(17) FIG. 1a shows a cross-section of a delivery fiber 5 of a delivery fiber assembly. The delivery fiber 5 comprises a core region with a refractive index n.sub.core. The core is surrounded by a cladding region comprising a background material having a refractive index N.sub.bg and a plurality of microstructures in the form of inclusions 2a, 2b of solid material having refractive index up to N.sub.inc and extending in the length of the longitudinal axis of the delivery fiber, wherein N.sub.inc<N.sub.bg. The plurality of inclusions 2a, 2b in the cladding region is arranged in a cross-sectional pattern comprising at least 6 rings of inclusions surrounding the core region. In the shown embodiment, the 3 in radial direction innermost rings of inclusions 2a have a lower refractive index than the 3 in radial direction outermost rings of inclusions 2b. In the shown embodiments the inclusions have substantially equal diameter. As explained above it may for some applications be advantageous to have different diameters for one ring of inclusions relative to another ring of inclusions.

(18) FIG. 1b shows a transmission loss spectrum of a fiber corresponding to the delivery fiber shown in FIG. 1 with six rings of inclusions, but where all inclusions have same refractive index. In this example the core has a diameter of 10 μm, the inclusions have a refractive index which is 1.2% lower than the refractive index of the core and the cladding background silica material at 635 nm. The center to center distance between the inclusions in the cladding (also known as the pitch) is 6 μm and the diameter of the inclusions is 3 μm.

(19) The spectrum is obtained by sending light from a broad band spectrum light source through the fiber and performing a cut-back to separate the coupling loss. The peak at around 1400 nm is due to water absorption. The delivery fiber is single-mode in the entire transmission bandwidth of the delivery fiber. It can be seen that the delivery fiber has a very broad transmission bandwidth extending from about 425 nm to about 1500 nm.

(20) The delivery fiber shown in FIG. 1c is an example of a PM fiber comprising a core region with a refractive index n.sub.core. The core is surrounded by a cladding region comprising a background material having a refractive index N.sub.bg and a plurality of microstructures in the form of inclusions 7a, 8b of solid material having refractive index up to N.sub.inc and extending in the length of the longitudinal axis of the delivery fiber, wherein N.sub.inc<N.sub.bg. The plurality of inclusions 7a, 7b in the cladding region is arranged in a cross-sectional pattern comprising at least 6 rings of inclusions surrounding the core region. In the shown embodiment, a number of inclusions b with a higher refractive index than the other inclusions 7a is arranged in two opposite clusters for forming stress elements. The inclusions 7b with the higher refractive index are e.g. doped with boron.

(21) In an embodiment of the of the delivery fiber is has been found that the diameter (d) of the inclusions in the cladding relative to the pitch (Λ) may have large influence on the guiding properties of the delivery fiber. In an embodiment the transmission loss is large if the d/Λ is less than about 0.4. In an embodiment the fiber is multimode if d/Λ is more than about 0.6.

(22) In an embodiment of the invention is has been found that the pitch (Λ) of the delivery fiber may have large influence on the spectral transmission bandwidth of the delivery fiber.

(23) In particular it was found that the short wavelength transmission edge sets a upper limit to the pitch and where this limit increases with the required short wavelength edge, such that e.g. a short wavelength edge of 300 nm requires a pitch of less than 6 μm whereas a short wavelength edge of 600 nm requires a pitch of less than 9 μm.

(24) Further it was found that the long wavelength transmission edge sets a lower limit to the pitch and where this limit increases with the required long wavelength edge, such that e.g. a long wavelength edge of 800 nm requires a pitch of at least 3.2 μm whereas a long wavelength edge of 1500 nm requires a pitch of at least 6 μm.

(25) FIG. 1d shows the pitch shows an example of the long wavelength transmission edge (201) and short wavelength transmission edge (202) versus the pitch for a fiber according to the invention having a d/Λ of about 0.5.

(26) In an example the mode field diameter of the delivery fiber varies from about 8.0 μm at 500 nm to about 9.0 μm at 900 nm. In an embodiment the mode filed diameter of the fiber varies by less than about 20% from 500 nm to 900 nm.

(27) FIG. 2 shows a part of a delivery fiber assembly comprising the delivery fiber 5 and a connector member 6 mounted to the delivery fiber at a delivery end section of the delivery fiber comprising the delivery end 5a. As it can be seen the delivery fiber comprises a protection coating, such as a polymer protection coating.

(28) The connector member is advantageously an optical fiber connector of the type which in the prior art is commonly used to terminate the end of an optical standard fiber to enable easy connection and disconnection of two standard optical fibers with low loss.

(29) During mounting, the optical fiber is typically aligned inside the optical connector member, so that the core region of the optical delivery fiber is centered inside a connector plane of the connector member. For a polarizing or polarization maintaining fiber it is also possible to rotate the fiber so that the polarization axis is in a predetermined plane. Furthermore it is ensured that the end facet of the fiber is in the output plane of the connector member. This can e.g. be achieved by polishing the connector and fiber end facets.

(30) If light is sent through the delivery fiber assembly with a connector member on the output end, then the position of the light being emitted from the output of the connector member is well known. For a standard all-solid single mode fiber the light will have its focal plane and thereby waist at the output plane of the connector.

(31) Many different types of connectors have been introduced to the marked, such as e.g. FC, E-2000, SMA connectors, as well as connectors with built in beam expansion.

(32) It is desired to use fiber connector members having low loss and high power handling, as they should advantageously be capable of handling average powers such as up to 100 mW or even up to several Watts.

(33) The broad band source 10 shown in FIG. 3 comprises a broad band laser pulse generator 1 comprising a not shown optical pump source operable to generate pump pulses and a not shown microstructured optical fiber for generating broad band light pulses upon feeding of pump light where the optical pump source is arranged to launch pump pulses to the microstructured optical fiber. In the shown embodiment the broad band laser pulse generator 1 is in the form of a SuperK™ system marketed by NKT Photonics Denmark. The broad band source further comprises a delivery fiber 5 comprising solid inclusions as described above. The delivery fiber 5 is arranged for receiving at least a portion of at least some of said broad band light pulses. In the shown embodiment the broad band source 10 further comprises an optical component 3, preferably a filter 3 arranged between the broad band laser pulse generator 1 and the delivery fiber 5. The optical component 3 is for example a polarizer, a spectral filter (preferably tunable) and/or a beam splitter.

(34) At the output end section of the delivery fiber 5, the delivery fiber comprises a connector member 6 e.g. as described above. The connector member 6 is advantageously configured for delivering at least a part of said received portion of said broad band light pulses to an apparatus as described above.

(35) In the embodiment shown in FIG. 4 the broad band source 10 is coupled to an optical waveguide arranged for receiving light from the delivery fiber, here called the first delivery fiber. In this embodiment the optical waveguide arranged for receiving light from the first delivery fiber is in form of an additional delivery assembly comprising a second delivery optical fiber 22 and a second delivery fiber inlet end connector member 21 and a second delivery fiber output end termination unit 23. The connector member 6 of the delivery fiber assembly 5, 6 in the following referred to as the first delivery fiber assembly 5,6 is connected to the second delivery fiber inlet end connector member 21 using a mating sleeve 20.

(36) By using a mating sleeve the connectors mechanically couple the core regions of the first and the second delivery fibers 5, 22 so that light can pass from the first delivery fiber 5 to the second delivery fiber 22 with low loss. Preferably the connector members are spring-loaded, so the fiber faces are pressed together when the connector members 6, 21 are mated. The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers.

(37) The fiber termination unit 23 is advantageously a connector member, a collimator, a ball lens, grin lens or any other suitable termination unit.

(38) The second optical delivery fiber 22 can in principle be any kind of optical fiber, preferably having a relative broad transmission bandwidth e.g. at least about 200 nm or more, and preferably the transmission bandwidth of the second optical delivery fiber 22 at least partially overlaps the transmission bandwidth of the first delivery fiber 5.

(39) In an embodiment the second optical delivery fiber 22 is substantially identical to the first delivery fiber 5.

(40) In an embodiment the broad band source 10 comprising the broad band laser pulse generator 1 and the first fiber delivery assembly 5,6 can be replaced without replacing the second fiber delivery assembly 21, 22, 23 or vice versa.

(41) In an embodiment the broad band source 10 and said second fiber delivery assembly 21, 22, 23 is built into an apparatus or alternatively the second fiber delivery assembly 21, 22, 23 is built into an apparatus while the broad band source 10 is arranged to feed light to the apparatus via the connection between the connector members 6, 21. Examples of such apparatus are microscopes, bio-imaging systems (such as e.g. OCT, SLO, STED, CARS and photoacoustic systems), alignment or overlay system and manufacturing equipment (such as e.g. semiconductor manufacturing equipment). This embodiment of the invention enables that the broad band source 10 easily can be disconnected for service and/or can be replaced independently of said second fiber assembly 21, 22, 23, which e.g. may be more difficult to disconnect from the remainder of the apparatus. For example the supercontinuum source and first fiber delivery assemble constituting a broad band source of an embodiment of the invention can be comprised in a first module, whereas the second fiber assembly 21, 22, 23 is part of a second module such as e.g. an alignment sensor in a semiconductor wafer scribing system. In this example the invention enables a modular build-up of the semiconductor wafer scribing system. If the semiconductor wafer scribing system breaks down, then the error can be located to the specific module which has failed, and this can be replaced independently of the other modules. This improves risk management for the semiconductor wafer scribing system compared to having to replace both modules at the same time.

(42) In an embodiment the second fiber delivery assembly 21, 22, 23 is used in bio-medical imaging or surgical applications. Examples of such embodiments include endoscopy, colonoscopy, rhinoscopy and bronoscopy as well as other applications where a part of the second optical fiber enters inside either a human or animal body. In such embodiments the broad band source 10 as shown in FIG. 3 can easily be connected to the connection member 21 as described above.

(43) In an embodiment the second fiber delivery assembly is sterilized before use.

(44) In an embodiment the second fiber delivery assembly is disposable.

(45) FIG. 5 is a schematic illustration of another embodiment of a broad band source of the invention. The broad band system 10 may be as described above and the second optical delivery fiber assembly 21, 22, 23 may be as described in FIG. 4.

(46) The fiber termination unit 23 advantageously is or comprises a collimator for focusing light towards a sample 30.

(47) Advantageously the second fiber delivery assembly 21, 22, 23 is built into an apparatus and the broad band source 10 is optionally arranged as a built in module in the apparatus and is arranged to feed light to the apparatus via the connection between the connector members 6, 21. The source 10 comprises or is optically connected to an optical detector 34, and the optical component 3 comprises an additional filter 32 arranged to direct a portion of light 33 reflected by the sample and guided by the fibers 5 and 22. The additional filter is advantageously a splitter.

(48) In an embodiment the delivery fiber 5 and the second optical fiber 22 are double clad fibers. Thereby a portion of the light 31 reflected by the sample can be guided to the optical detector via the second optical delivery fiber assembly 21, 22, 23 and the first delivery fiber assembly 5, 6. In an embodiment the delivery fiber 5 and the second optical fiber 22 comprise a cladding with an NA of at least 0.1, such as at least 0.15, such as at least 0.22. Also in this embodiment the fibers 5, 22 will guide some of the light 31 which is being reflected from the sample under test.

(49) In an embodiment the optical component 3 comprises means to separate the light that is reflected from the sample and guided by the fibers 33 from at least some of the light from the broad band source. Such means is for example a beam splitter 32.

(50) In an alternative embodiment a double-clad fiber coupler is applied instead of a splitter for example by providing a double-clad fiber coupler at the input end of the first delivery fiber. The double-clad fiber coupler is advantageously configured for separating core and cladding light, e.g. by having a 2×2 port structure comprising multimode double clad fibers on two ports of the coupler and single mode double clad fibers on the other two ports, such as e.g. the DC1300 LEB offered by Thorlabs. In principle a portion or all of the reflected light could be separated from the major part of the light from the broad band source but any other means known to the skilled person.

(51) Advantageously the reflected and separated light is transmitted to an optical detector 34, such as e.g. a photodiode or a spectrometer.

(52) FIG. 6 is a schematic illustration of an embodiment of an apparatus of the invention in form of an interferometer e.g. for use in optical coherence tomography (OCT) e.g. for visualization of internal tissue. The interferometer comprises a first delivery fiber assembly 105a, 106a comprising a fused coupler delivery fiber assembly 105b, 106b where the first delivery fiber assembly 105a, 106a and the fused coupler delivery fiber assembly 106b is fused in a component section 100. The interferometer comprises a broad band source comprising an optical pump source 101a operable to generate pump pulses an air hole microstructured optical fiber 101b for generating broad band light pulses upon feeding of pump pulses from said optical pump source 101a and the first delivery fiber assembly 105a, 106a comprising a delivery fiber 105a comprising solid inclusions as described above and a connector member 106a also as described above. The first delivery fiber assembly 105a, 106a is connected to the microstructured optical fiber via a delivery fiber connector member 106c which is advantageously as the connector member described above, and an end cap connection member 101c. In the end cap connection member 101c the air holes along less than a few mm of the air hole microstructured optical fiber 101b are collapsed and the light beam is collimated by a not shown lens. The delivery fiber connector member 106c and the end cap connection member 101c are mated and held together by a mating sleeve 20c. In an alternative embodiment the air hole microstructured optical fiber 101b is spliced to the delivery fiber 105 by splicing and/or by using a using a GRIN lens as described above.

(53) The interferometer comprises a second fiber assembly 21a, 22a, 23a which advantageously is as the second fiber assembly 21, 22, 23 described above, and the connector members 106a, 21a are connected and hold together by mating sleeve 20a.

(54) The fused coupler delivery fiber assembly 105b, 106b is connected to a third fiber assembly 21b, 22b, 23b which advantageously is as the second fiber assembly 21, 22, 23 described above, and the connector members 106b, 21b are connected and held together by mating sleeve 20b. The interferometer further comprises a mirror 40 or another reference unit arranged to reflect light emitted via the fiber termination unit 23b. In an alternative embodiment the reference unit is not included in the apparatus but can be selected by the user.

(55) The fused coupler delivery fiber assembly 105b is further connected to a detector 124, such as a spectrometer. The broad band source may comprise one or more tunable or non-tunable filters and or a pulse picker and one or more amplifiers such as it is well known in the art.

(56) In general a coupler has a bar port, where the light goes straight through from one top arm to the other top arm (or from the bottom arm to the other bottom arm), and a cross port where the light goes from the top arm to bottom arm, or vice versa. Often couplers are close to have a very low loss such that all the light is send to the bar port or the cross port. In this embodiment the two top arms are provided by the delivery fiber 105a on either side of the component section 100 and the bottom arms are provided by the delivery fiber 105b on either side of the component section. The bar ports and the cross port are provided by the component section 100. The bar port has a transmission coefficient of x and the cross arm a transmission coefficient of (1−x). The transmission coefficient is the same irrespective of which direction the coupler is traversed.

(57) In use broad band light pulses are transmitted to the delivery fiber 105a and as marked on the illustration in the end of the delivery fiber 105a nearest to the microstructured optical fiber the light pulses power is set to be 100%=“1”. At the fused component section 100, some of the light (x) is transmitted further via the delivery fiber 105a and some of the light (1−x) is transmitted further via the fused coupler delivery fiber 105b.

(58) The light portion (X) transmitted from the fused component section 100 and via the delivery fiber 105a is transmitted to the second fiber assembly 21a, 22a, 23a and via the fiber termination unit 23a the light pulses are emitted towards a sample 30 and reflected light 31a is transmitted in the opposite direction via the second fiber 22a and the delivery fiber 105a until the remitted light reaches the fused component section 100. From there a portion of remitted light is transmitted further via the fused coupler delivery fiber 105b to the detector 104.

(59) The light portion (1−X) transmitted from the fused component section 100 and via the fused coupler delivery fiber 105b is transmitted to the third fiber assembly 21b, 22b, 23b and via the fiber termination unit 23b the light pulses are emitted towards a mirror 40 and reflected light 31b is transmitted in the opposite direction via the third fiber 22b and the fused coupler delivery fiber 105b until the remitted light reaches the fused component section 100. From there a portion of remitted light is transmitted further via the fused coupler delivery fiber 105b to the detector 104. Advantageously the mirror reflects substantially all of the light that is incident on it.

(60) As explained the interferometer thereby has two interferometer arms, one that is guiding light to a sample and re-transmit reflected light and one that is guiding light to a reference unit (e.g. a mirror) and re-transmits reflected light. In an embodiment one interferometer arm is configured for being focused onto a tissue sample and for scanning the sample in an X-Y longitudinal raster pattern. The other interferometer arm is bounced off the reference mirror. Reflected light from the tissue sample is combined with reflected light from the reference.

(61) As mentioned above in the embodiment shown in FIG. 6 the light goes from the broad band laser goes through the cross port of the coupler to reach the mirror 40. It is reflected from the mirror and goes back through the bar port of the coupler to reach the detector 124. Assuming that the reflection is loss less the transmission coefficient for the entire path is the product of the two transmission coefficients, i.e. x(1−x).

(62) FIG. 7 is a schematic illustration of an embodiment of a delivery fiber of the invention comprising a combiner.

(63) Advantageously all of the delivery fibers 105a, 105b, 22a, 22b are all solid fibers comprising microstructures in form of inclusions as described above and preferably all of the delivery fibers 105a, 105b, 22a, 22b have a transmission bandwidth of 200 nm or more, preferably the transmission bandwidths are overlapping or identical.

(64) FIG. 7 is a schematic illustration of an embodiment of an apparatus of the invention in form of another type of interferometer e.g. for use in optical metrology e.g. for thin film, wafer, optical critical dimension (OCD), overlay and wafer stress for transistor and interconnect metrology applications.

(65) Parts of the interferometer of FIG. 7 are similar to corresponding parts of the interferometer of FIG. 6. The interferometer comprises a first delivery fiber assembly 105a, 106a comprising a fused splitter delivery fiber assembly 105b, 106b where the first delivery fiber assembly 105a, 106a and the fused splitter delivery fiber assembly 106b is fused in a component section 100. The interferometer comprises a broad band source comprising an optical pump source 101a operable to generate pump pulse, a microstructured optical fiber 101b for generating broad band light pulses upon feeding of pump pulses from said optical pump source 101a and the first delivery fiber assembly 105a, 106a comprising a delivery fiber 105a comprising solid inclusions as described above and a connector member 106a also as described above. The first delivery fiber assembly 105a, 106a is connected to the microstructured optical fiber via a filter 32 arranged to directing a portion of reflected light 33 reflected by the sample 30e and the reference unit 40 towards an optical detector 34. The remaining parts are as in the example of FIG. 7.

(66) FIG. 8 illustrates a spectral engine source suitably for supplying light to an apparatus. The spectral engine source comprises three lasers 121, 222, 123 emitting laser beams 121a, 122a, 123a respectively. The laser beams 121a, 122a, 123a differs from each other with at least one wavelength as described above.

(67) The lasers 121, 222, 123 may be of same or of different types, such as one or more gas lasers, one or more chemical lasers, one or more metal-vapor lasers and/or one or more semiconductor lasers.

(68) The spectral engine source further comprises a multiplexer M here illustrated by a number of mirrors arranged to combine the beams 121a, 122a, 123a into one single multiplexed beam M. It should be understood that the multiplexer may be any kind of multiplexer or combiner capable of combining least a portion of the laser beams of each of the lasers and for collimating the received light to a multiplexed beam. The multiplexer M collimates the 121a, 122a, 123a sufficiently close to be received by the delivery fiber of the spectral engine source of the invention. For simplification the delivery fiber is not shown of the spectral engine source, however the delivery fiber is arranged to collect the multiplexed beam M and to delivering at least a part of the received multiplexed beam M to the apparatus,

(69) FIG. 9 illustrates another spectral engine source suitably for supplying light to an apparatus. The spectral engine source comprises 5 lasers 131, 232, 133, 134, 135 emitting laser beams 131a, 132a, 133a, 134a, 135a respectively. The laser beams 131a, 132a, 133a, 134a, 135a differs from each other with at least one wavelength. For example laser beam 131a may comprise wavelength (s) in the range of 400-500 nm, laser beam 132a may comprise wavelength (s) in the range of 500-600 nm, laser beam 133a may comprise wavelength (s) in the range of 600-700 nm, laser beam 135a may comprise wavelength (s) in the range of 800-900 nm.

(70) The spectral engine source further comprises a multiplexer M here illustrated by a number of mirrors arranged to combine the beams 131a, 132a, 133a, 134a, 135a into one single multiplexed beam M. The spectral engine source also comprises a not shown delivery fiber as described above for receiving the multiplexed beam and to delivering at least a part of the received multiplexed beam M to an apparatus,

(71) FIG. 10 illustrates an apparatus of an embodiment of the invention comprising a light source LS selected from a broad band source, a broad band source system or a spectral engine source with a delivery fiber DL as described above. The apparatus is a lithographic apparatus and comprises an illumination system (illuminator) IL arranged to receive the light from the delivery fiber of the light source LS. The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam received from the light source LS. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation bean, to have a desired uniformity and intensity distribution in its cross-section.

(72) The radiation beam B is incident on a patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in FIG. 1) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The apparatus may for example operate as described in US2007013921

(73) FIG. 11 illustrates an apparatus of an embodiment of the invention comprising scanning microscope that is embodied as a confocal scanning microscope and a light source LS selected from a broad band source, a broad band source system or a spectral engine source with a delivery fiber DL as described above. The light source LS delivers an illuminating light beam 211 via the delivery fiber DL

(74) The scanning microscope comprises an acoustooptical component 213 that is embodied as AOTF 215. From acoustooptical component 213, light 212, selected out of illuminating light beam 211, arrives at a beam deflection device 17 that contains a gimbal-mounted scanning mirror 19 and that guides illuminating light beam 211 through scanning optical system 221, tube optical system 223, and objective 225 over or through specimen 227. Detected light beam 229 coming from the specimen travels in the opposite direction through scanning optical system 221, tube optical system 223, and objective 225, and arrives via scanning mirror 219 at acoustooptical component 213 which conveys detected light beam 229 to detector 231, which is embodied as a multi-band detector. Illuminating light beam 211 is depicted as a solid line in the drawing, and detected light beam 229 as a dashed line. Illumination pinhole 233 and detection pinhole 235 that are usually provided in a confocal scanning microscope are schematically drawn in for the sake of completeness. Omitted in the interest of better clarity, however, are certain optical elements for guiding and shaping the light beam.

(75) Acoustooptical component 213, which serves to select the wavelength spectrum that is chosen, is configured as AOTF 215, through which an acoustic wave passes. The acoustic wave is generated by an electrically activated piezo acoustic generator 237. Activation is accomplished by a high-frequency source 239 that generates an electromagnetic high-frequency wave that exhibits an adjustable HF spectrum. The HF spectrum is chosen in such a way that only those portions of illuminating light beam 211 having the desired wavelength arrive at beam deflection device 217. The other portions of illuminating light beam 211 not influenced by the acoustic excitation are directed into a beam trap 241. The power level of the illuminating light beam 211 can be selected by varying the amplitude of the acoustic wave. The crystal sectioning and orientation of acoustooptical component 213 are selected in such a way that with a single coupling-in direction, different wavelengths are deflected in the same direction. A computer 243 is used to choose a second or third wavelength spectrum. Monitor 247 of computer2 43 serves as the display for the spectral composition. Selection of the wavelength spectrum together with its spectral composition is accomplished on the basis of a graph G within a coordinate system having two coordinate axes X, Y. The wavelength of the light is plotted on coordinate axis X, and its power level on coordinate axis Y. Computer 243 controls high-frequency source 239 in accordance with the user's stipulation. The user makes adjustments using computer mouse 257. Depicted on monitor 247 is a slider 259 that serves for adjustment of the overall light power level of illuminating light beam 11 or detected light beam 229.

(76) Although embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.