Device and method for combining light beams

Abstract

A light source device includes a first light source to provide a first input light beam in the direction of a central axis of the light source device, a second light source to provide a second input light beam in the direction of the central axis, a central reflector, a catadioptric reflector to focus light of the first input light beam to the central reflector, and to focus light of the second input light beam to the central reflector, and at least one actuator to change the angular position of the central reflector, so as to cause the central reflector to form an output beam by sequentially reflecting light of the first input light beam and light of the second input light beam to the axial direction.

Claims

1. A light source device comprising: a first light source to provide a first input light beam in the direction of a central axis of the light source device, a second light source to provide a second input light beam in the direction of the central axis, a central reflector, and, at least one actuator to change the angular position of the central reflector, so as to cause the central reflector to form an output light beam by sequentially reflecting light of the first input light beam and light of the second input light beam to the axial direction, and a catadioptric reflector to focus light of the first input light beam to the central reflector, and to focus light of the second input light beam to the central reflector, wherein the catadioptric reflector is arranged to provide a first external inclined light beam, which is focused to the central reflector, wherein the catadioptric reflector comprises a refracting input surface, a first reflecting surface, a second reflecting surface and a refracting output surface, wherein the input surface is arranged to form a first internal axial light beam from the first input light beam, the first reflecting surface is arranged to form a first converging light beam from the first internal axial light beam, the second reflecting surface is arranged to form a first internal inclined light beam from the first converging light beam, and the output surface is arranged to form the first external inclined light beam from the first internal inclined light beam.

2. The device of claim 1, wherein the catadioptric reflector is arranged to form the first external inclined light beam from light of the first input light beam, wherein the catadioptric reflector is arranged to form a second external inclined light beam from light of the second input light beam, wherein the central reflector is arranged to form the output light beam by reflecting light of the first external inclined light beam to the axial direction during a first time period, and by reflecting light of the second external inclined light beam to the axial direction during a second time period.

3. The device of claim 1, wherein the curvature of the first reflecting surface has been selected such that the first external inclined beam has a focused spot at the central reflector.

4. The device of claim 1, wherein the curvature of the first reflecting surface has been selected to compensate a diverging effect of the second reflecting surface, such that the first external inclined beam has a focused spot at the central reflector.

5. The device of claim 1, wherein the input surface is axially symmetric with respect to the central axis.

6. The device of claim 1, wherein the input surface is a planar surface.

7. The device of claim 1, wherein the second reflecting surface is a conical surface.

8. The device of claim 1, wherein the output surface is a conical surface.

9. The device of claim 1, wherein a first actuator is arranged to tilt the central reflector about a first tilt axis, and wherein a second actuator is arranged to tilt the central reflector about a second tilt axis, so as to cause rotation of the normal of the central reflector around the central axis.

10. The device of claim 1, comprising a plurality of light sources to provide input light beams, wherein the light sources are positioned along a circle.

11. The device of claim 1, wherein the first input light beam spatially overlaps the second input light beam at the input surface.

12. The device of claim 1, wherein the first reflecting surface is arranged to form the first converging light beam from light of the first input light beam, and the first reflecting surface is arranged to form a second converging light beam from light of the second input light beam, wherein the first converging light beam spatially overlaps the second converging light beam.

13. The device of claim 1, further comprising a tunable optical filter to form filtered output light by filtering light of the output light beam.

14. A method, comprising providing an output light beam by using a light source device, which comprises a plurality of light sources, a central reflector, and at least one actuator, wherein said providing of the output light beam comprises: providing a first input light beam in the direction of a central axis of the light source device, wherein the first input light beam is provided by using a first light source, providing a second input light beam in the direction of the central axis, wherein the second input light beam is provided by using a second light source, changing the angular position of the central reflector, so as to cause the central reflector to form the output light beam by sequentially reflecting light of the first input light beam and light of the second input light beam to the axial direction, wherein the angular position of the central reflector is changed by using the at least one actuator, focusing light of the first input light beam to the central reflector by using a catadioptric reflector, and focusing light of the second input light beam to the central reflector by using the catadioptric reflector, wherein the catadioptric reflector is arranged to provide a first external inclined light beam, which is focused to the central reflector, wherein the catadioptric reflector comprises a refracting input surface, a first reflecting surface, a second reflecting surface and a refracting output surface, wherein the input surface is arranged to form a first internal axial light beam from the first input light beam, the first reflecting surface is arranged to form a first converging light beam from the first internal axial light beam, the second reflecting surface is arranged to form a first internal inclined light beam from the first converging light beam, and the output surface is arranged to form the first external inclined light beam from the first internal inclined light beam.

15. The method of claim 14, further comprising: illuminating an object with light of the output light beam, capturing a first digital image of the object when the output light beam comprises light at a wavelength of the first input light beam, and capturing a second digital image of the object when the output light beam comprises light at a wavelength of the second input light beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following examples, several variations will be described in more detail with reference to the appended drawings, in which

(2) FIG. 1a shows, by way of example, in a three-dimensional view, a light source device,

(3) FIG. 1b shows, by way of example, in an axial view, light beams of the light source device,

(4) FIG. 1c shows, by way of example, in an axial view, light beams of the light source device,

(5) FIG. 2 shows, by way of example, wavelengths of the input beams, and corresponding temporal evolution of wavelength of the output beam,

(6) FIG. 3a shows, by way of example, temporal evolution of wavelength of the output beam,

(7) FIG. 3b shows, by way of example, temporal evolution of wavelength of the output beam,

(8) FIG. 4 shows, by way of example, in a cross-sectional side view, the light source device,

(9) FIG. 5 shows, by way of example, in a three-dimensional view, the catadioptric reflector of the light source device,

(10) FIG. 6a shows, by way of example, in a cross-sectional side view, dimensions of the catadioptric reflector,

(11) FIG. 6b shows, by way of example, in an axial unfolded view, dimensions of the catadioptric reflector,

(12) FIG. 7a shows, by way of example, in a cross-sectional side view, dimensions of the catadioptric reflector,

(13) FIG. 7b shows, by way of example, in an axial view, dimensions of the catadioptric reflector,

(14) FIG. 8a shows, by way of example, in a cross-sectional side view, dimensions of the catadioptric reflector,

(15) FIG. 8b shows, by way of example, in an axial view, dimensions of the catadioptric reflector,

(16) FIG. 9 shows, by way of example, in a three-dimensional view, a catadioptric reflector of the light source device,

(17) FIG. 10 shows, by way of example, a control system of a light source, which comprises the light source device,

(18) FIG. 11 shows, by way of example, timing of operation of light emitters according to angular position of the central reflector,

(19) FIG. 12a shows, by way of example, an optical apparatus, which comprises the light source,

(20) FIG. 12b shows, by way of example, an optical apparatus, which comprises the light source, and

(21) FIG. 12c shows, by way of example, an optical imaging apparatus, which comprises the light source.

DETAILED DESCRIPTION

(22) Referring to FIG. 1a, the light source device 500 may comprise a plurality of light sources LED.sub.1, LED.sub.2, LED.sub.3, a catadioptric reflector unit 100, and a central mirror M1. The light sources LED.sub.1, LED.sub.2, LED.sub.3 may provide axial input light beams B0.sub.1, B0.sub.2, B0.sub.3 of different wavelengths ?.sub.1, ?.sub.2, ?.sub.3, . . . . The catadioptric reflector unit 100 may form focused inclined light beams B4.sub.1, B4.sub.2, B4.sub.3 by reflecting and refracting light of the axial input light beams B0.sub.1, B0.sub.2, B0.sub.3. The catadioptric reflector unit 100 may form the inclined light beams B4.sub.1, B4.sub.2, B4.sub.3 such that each inclined light beam B4.sub.1, B4.sub.2, B4.sub.3 has a focused spot SP1 at the central mirror M1. The position of the focused spot SP1 of each inclined light beam B4.sub.1, B4.sub.2, B4.sub.3 may substantially coincide with the central axis AX1 of the light source device 500. The direction SZ may be parallel with the central axis AX1. The catadioptric reflector unit 100 may form a first focused inclined beam B4.sub.1 by reflecting and refracting light of a first light source LED.sub.1. The catadioptric reflector unit 100 may form a second focused inclined beam B4.sub.2 by reflecting and refracting light of a second light source LED.sub.2. The light source device 500 may be arranged to form an output light beam B5 by reflecting light of the inclined light beams B4.sub.1, B4.sub.2, B4.sub.3. The central mirror M1 may be arranged to form the output light beam B5 by reflecting light of the inclined light beams B4.sub.1, B4.sub.2, B4.sub.3. The tilt angle (?1, ?2) of the central mirror M1 may varied so that the central mirror M1 may sequentially reflect light of the inclined light beams B4.sub.1, B4.sub.2, B4.sub.3 to the direction of the central axis AX1. In particular, the central mirror M1 may be arranged to reflect light of first inclined beam B4.sub.1 to the axial direction SZ during a first time period (T.sub.1,1), and the central mirror M1 may be arranged to reflect light of a second inclined beam B4.sub.2 to the axial direction SZ during a second time period (T.sub.1,2). The first inclined beam B4.sub.1 may have a first wavelength 21. The second inclined beam B4.sub.2 may have a second different wavelength 22. The output light beam B5 may have the first wavelength ?1 during the first time period (T.sub.1,1), and the output light beam B5 may have the second wavelength 22 during the second time period (T.sub.1,2).

(23) The catadioptric reflector 100 may comprise a refracting input surface (SRF1), a first reflecting surface SRF2, a second reflecting surface SRF3 and a refracting output surface SRF4. A first light source LED.sub.1 of the light source device 500 may be arranged to provide a first axial input light beam B0.sub.1. The input surface SRF1 may be arranged to form a first internal axial light beam B1.sub.1 from the first input light beam B0.sub.1. The first reflecting surface SRF2 may be arranged to form a first converging light beam B2.sub.1 from the internal axial light beam B1.sub.1. The second reflecting surface SRF3 may be arranged to form an internal inclined light beam B3.sub.1 from the converging light beam B2.sub.1. The output surface SRF4 (or a facet of the surface SRF4) may be arranged to form an external inclined light beam B4.sub.1 from the internal inclined light beam B3.sub.1.

(24) The catadioptric reflector 100 may be arranged to provide an external inclined light beam (B4.sub.1), which is focused to the central reflector M1, wherein the catadioptric reflector 100 may comprise a refracting input surface SRF1, a first reflecting surface SRF2, a second reflecting surface SRF3 and a refracting output surface SRF4, wherein the input surface SRF1 may be arranged to form an internal axial light beam (B1.sub.1) from the first input light beam (B0.sub.1), the first reflecting surface SRF2 may be arranged to form a converging light beam (B2.sub.1) from the internal axial light beam (B1.sub.1), the second reflecting surface (SRF3) is arranged to form an internal inclined light beam (B3.sub.1) from the converging light beam (B2.sub.1), the output surface SRF4 (or a facet of the surface SRF4) may be arranged to form the external inclined light beam (B4.sub.1) from the internal inclined light beam (B3.sub.1).

(25) The catadioptric reflector 100 may form a first external inclined light beam (B4.sub.1) from light of a first input light beam (B0.sub.1), wherein the catadioptric reflector 100 may form a second external inclined light beam (B4.sub.2) from light of a second input light beam (B0.sub.2), wherein the central reflector M1 may form the output beam B5 by reflecting light of the first primary output beam (B4.sub.1) to the axial direction (SZ) during a first time period (T.sub.1,1), and by reflecting light of the second primary output beam (B4.sub.2) to the axial direction (SZ) during a second time period (T.sub.1,2).

(26) In an embodiment, the first reflecting surface SRF2 and/or the second reflecting surface SRF3 may be arranged to reflect light by total internal reflection (TIR).

(27) The central mirror M1 may also be called e.g. as a tilted mirror or as a tiltable mirror. The central mirror M1 may also be called e.g. as a central reflector M1.

(28) Each light source LED.sub.1, LED.sub.2, LED.sub.3 may provide an axial input light beam B0.sub.1, B0.sub.2, B0.sub.3. Each input light beam B0.sub.1, B0.sub.2, B0.sub.3 may have a wavelength ?.sub.1, ?.sub.2, ?.sub.3. Each light source LED.sub.1, LED.sub.2, LED.sub.3 may be positioned e.g. on a circle CIRC1. The axial input light beams B0.sub.1, B0.sub.2, B0.sub.3 may be substantially parallel with the central axis AX1 of the light source device 500.

(29) The first light source LED.sub.1 may be arranged to emit first light B0.sub.1, which has a first spectrum, and the second light source LED.sub.2 may be arranged to emit second light B0.sub.2, which has a second different spectrum. The first light source LED.sub.1 may be arranged to emit light B0.sub.1 at a first wavelength M, and the second light source LED.sub.2 may be arranged to emit light B0.sub.2 at a second different wavelength 22 such that the first light source LED.sub.1 does not emit light at the second wavelength 22. One or more of the light sources LED.sub.1, LED.sub.2, LED.sub.3 may also be arranged to emit broadband light and/or white light.

(30) The light source device 500 may comprise one or more actuators ACU1, ACU2 for changing the angular position (?1, ?2) of the central reflector M1 (see FIG. 10). For example, a first actuator ACU1 may be arranged to periodically tilt the central mirror M1 about a first tilt axis AX11, and a second actuator ACU2 may be arranged to periodically tilt the central mirror M1 about a second tilt axis AX12, so as to cause rotation of the normal N1 of the central mirror M1 about the central axis AX1 of the light source device 500. The normal N1 of the central mirror M1 is shown e.g. in FIG. 4. The central mirror M1 may sinusoidally oscillate about the first tilt axis AX11, the central mirror M1 may sinusoidally oscillate about the second tilt axis AX12, and the phase difference between said two oscillations may be substantially equal to 90? so as to cause rotation of the normal N1 of the central mirror M1 about the central axis AX1. ?1(t) denotes time-dependent angular velocity of the central mirror M1 about the first tilt axis AX11. ?2(t) denotes time-dependent angular velocity of the central mirror M1 about the second tilt axis AX12.

(31) An actuator ACU1 may also be arranged to rotate a tilted central mirror M1 about the central axis AX1, so as to cause rotation of the normal N1 of the central mirror M1 about the central axis AX1 of the light source device 500.

(32) The one or more actuators ACU1, ACU2 may be arranged to adjust the angular position (?1, ?2) of the central reflector M1 around at least axis (AX11, AX12).

(33) The frequency of mechanical oscillation of the central mirror may be e.g. greater than 0.1 Hz, greater than 1 Hz, greater than 10 Hz, greater than 100 Hz, greater than 1 kHz, or even greater than 10 KHz. The frequency of mechanical oscillation of the central mirror may be e.g. in the range of 0.1 Hz to 20 KHz. The speed of rotation of the normal N1 of the central mirror M1 may be e.g. greater than 0.1, greater than 1.0, greater than 10, greater than 100, greater than 1000, or even greater than 10000 revolutions per second. The speed of rotation of the normal N1 may be e.g. in the range of 0.1 to 20000 revolutions per second.

(34) The central mirror may be tilted e.g. in a predetermined angular range. The central mirror may be tilted e.g. in the angular range of ?15? to +15?. The diameter of the central mirror may be e.g. smaller than 5 mm so as to reduce the oscillating mass. The diameter of the central mirror may be e.g. in the range of 0.3 mm to 3 mm.

(35) SX, SY and SZ denote orthogonal directions. The direction SZ is parallel with the central axis AX1 of the light source device 500.

(36) The light source device 500 may comprise a control system SYS1 for synchronizing tilting of the central reflector M1 with operation of the light sources LED.sub.1, LED.sub.2, LED.sub.3 (see FIG. 10).

(37) P1 denotes a point where the centerline of an axial external beam B0 (e.g. B0.sub.1) intersects the input surface SRF1 of the catadioptric reflector unit 100.

(38) P2 denotes a point where the centerline of an axial internal beam B1 (e.g. B1.sub.1) intersects the first reflective surface SRF2 of the catadioptric reflector unit 100.

(39) P3 denotes a point where the centerline of a converging beam B2 (e.g. B2.sub.1) intersects the second reflective surface SRF3 of the catadioptric reflector unit 100.

(40) P4 denotes a point where the centerline of an inclined beam B3 (e.g. B3.sub.1) intersects the output surface SRF4 of the catadioptric reflector unit 100.

(41) P5 denotes a point where the centerline of an external inclined beam B4 (e.g. B4.sub.1) has the narrowest width. In other words, the point P5 denotes the center of the waist (SP1) of the focused inclined beam B4. The waist SP1 may also be called as the focused spot.

(42) The light source device 500 may be arranged to operate such that the centerline of each external inclined beam B4 may intersect the reflective surface of the central mirror M1 substantially at the centerline AX1 of the light source device 500. The light source device 500 may be arranged to operate such that the waist SP1 of each external inclined beam B4 may substantially coincide with the reflective surface of the central mirror M1.

(43) The light source device 500 may optionally comprise beam modifying optics LNS1 e.g. for focusing or collimating light of the output beam B5. The optics LNS1 may comprise e.g. one or more lenses for forming a focused or collimated light beam B6 from the output beam B5.

(44) FIG. 1b shows, by way of example, in an axial view, light beams of the light source device 500. The symbol ?? denotes the angle between centerlines of adjacent inclined beams B4.sub.1, B4.sub.2. The symbol ?? may also denote the difference between azimuthal directions of adjacent inclined beams B4.sub.1, B4.sub.2.

(45) FIG. 1b shows a situation where the first axial beam B1.sub.1 does not overlap the second axial beam B12.

(46) FIG. 1c shows, by way of example, in an axial view, light beams of the light source device 500. FIG. 1c shows a situation where the first axial beam B1.sub.1 overlaps the second axial beam B12.

(47) The first reflecting surface SRF2 may be axially symmetric with respect to the central axis AX1. Consequently, the catadioptric reflector may form a focused spot (SP1) from light of a first light source (LED.sub.1) also in a situation where the light beam (B1.sub.1) of the first light source (LED.sub.1) spatially overlaps the light beam (B12) of a second light source (LED.sub.1) on the first reflecting surface SRF2 of the catadioptric reflector 100. This may allow reducing the distance between adjacent light sources (LED.sub.1, LED.sub.2). This may allow using an increased number of light sources (LED.sub.1, LED.sub.2, LED.sub.3, . . . )

(48) The first reflecting surface SRF2 may be arranged to form a first converging light beam (B2.sub.1) from light of the first input light beam (B0.sub.1), and the first reflecting surface SRF2 may be arranged to form a second converging light beam (B2.sub.2) from light of the second input light beam (B0.sub.2), wherein the first converging light beam (B2.sub.1) may spatially overlap the second converging light beam (B2.sub.2).

(49) FIG. 2 shows, by way of example, spectral intensity distributions of several input beams, and temporal evolution of wavelength of the formed output beam. The output light beam B5 may comprise one or more sequences SEQ1 of light pulses B5.sub.1,1, B5.sub.1,2, B5.sub.1,3, B5.sub.1,4, B5.sub.1,5, B5.sub.1,6, . . . .

(50) FIG. 2 shows, by way of example, forming the output light beam B5 from six input light beams, but the number of the input light beams may also be smaller or greater.

(51) Referring to the uppermost curve of FIG. 2, the first light source LED.sub.1 may provide first input light B0.sub.1 at a first wavelength 21. The first light source LED.sub.1 may be arranged to provide the first input light B0.sub.1 during time periods T.sub.1,1, T.sub.2,1, T.sub.3,1, . . . . The first input light B0.sub.1 may have a spectral intensity distribution dl/d?. The spectral intensity distribution dl/d? of the first input light B0.sub.1 may have a maximum value MAX1. The first wavelength 21 may mean e.g. the spectral position of the maximum of the spectral intensity distribution dl/d? of the first input light B0.sub.1.

(52) The first light source LED.sub.1 may be arranged to operate such that the first light source LED.sub.1 does not provide the first input light B0.sub.1 between the time periods T.sub.1,1, T.sub.2,1, T.sub.3,1, . . . . For example, the first light source LED.sub.1 may be switched off between the time periods T.sub.1,1, T.sub.2,1, T.sub.3,1, . . . .

(53) Referring to the second curve from the top, the second light source LED.sub.2 may provide second input light B0.sub.2 at a second wavelength 12 during time periods T.sub.1,2, T.sub.2,2, T.sub.3,2, . . . . The spectral intensity distribution dl/d? of the second input light B0.sub.2 may have a maximum value MAX2.

(54) Referring to the third curve from the top, the third light source LED.sub.3 may provide third input light B0.sub.3 at a third wavelength 23 during time periods T.sub.1,3, T.sub.2,3, T.sub.3,3, . . . . The spectral intensity distribution dl/d? of the third input light B0.sub.3 may have a maximum value MAX3.

(55) A fourth light source LED.sub.4 may provide input light B04 during time periods T.sub.1,4, T.sub.2,4, T.sub.3,4, . . . MAX4 may denote the maximum of the intensity distribution of the input light B04. A fifth light source LED.sub.5 may provide input light B05 during time periods T.sub.1,5, T.sub.2,5, T.sub.3,5, . . . MAX5 may denote the maximum of the intensity distribution of the input light B05. A sixth light source LED.sub.6 may provide input light B0.sub.6 during time periods T.sub.1,6, T.sub.2,6, T.sub.3,6, . . . MAX6 may denote the maximum of the intensity distribution of the input light B0.sub.6.

(56) Referring to the lowermost curve of FIG. 2, the output light beam B5 may be formed of consecutive light pulses B5.sub.1,1, B5.sub.1,2, B5.sub.1,3, B5.sub.1,4, B5.sub.1,5, B5.sub.1,6, . . . B5.sub.2,1, B5.sub.2,2, B5.sub.2,3, B5.sub.2,4, B5.sub.2,5, B5.sub.2,6, which have the different wavelengths ?1, ?2, ?3, ?4, ?5, ?6. The output light beam B5 may have the first wavelength 21 during the time periods T.sub.1,1, T.sub.2,1, T.sub.3,1, . . . . The output light beam B5 may have the second wavelength 22 during the time periods T.sub.1,2, T.sub.2,2, T.sub.3,2, . . . . The output light beam B5 may have the third wavelength 23 during the time periods T.sub.1,3, T.sub.2,3, T.sub.3,3, . . . T.sub.off denotes a time period between consecutive light pulses B5.sub.1,1, B5.sub.1,2 of the output light beam B5.

(57) The device 500 may be arranged to operate such that the intensity of the output beam B5 is substantially equal to zero between the time periods T.sub.1,1, T.sub.1,2. The times t.sub.1,1, t.sub.1,2, t.sub.1,3, . . . may denote the start times of the time periods T.sub.1,1, T.sub.1,2, T.sub.1,3, . . . .

(58) Referring to FIG. 3a, the duration of the light pulses may be increased such that the blanking time T.sub.off between consecutive light pulses becomes short or zero.

(59) Referring to FIG. 3b, the duration of the light pulses may also be increased such that a first light pulse B5.sub.1,1 may temporally overlap with one or more other pulses B5.sub.1,2, B5.sub.1,3.

(60) For example, the first light pulse B5.sub.1,1 of the output light beam B5 may temporally overlap with a second light pulse B5.sub.1,2 of the output light beam B5 during a time period T.sub.ON2. For example, the central mirror M1 may be arranged to simultaneously reflect light of a first inclined beam B4.sub.1 and light of a second inclined beam B4.sub.2 so that the light pulses (B5.sub.1,1, B5.sub.1,2) at the wavelengths 21, 12 may be simultaneously gathered e.g. by the optics LNS1. The output light beam B5 may simultaneously comprise the first light pulse B5.sub.1,1 and the second light pulse B5.sub.1,2 during the time period T.sub.ON2.

(61) The central mirror M1 may be arranged to simultaneously reflect light of a first inclined beam B4.sub.1 and light of a second inclined beam B4.sub.2 substantially to the direction SZ of the central axis SX1 so that the angle between the centerline of the first light pulse B5.sub.1,1 and the centerline of the second light pulse B5.sub.1,2 is smaller than a predetermined limit.

(62) The instantaneous position of the centerline of the reflected light (B5.sub.1,1) of the first inclined beam B4.sub.1 may slightly deviate from the central axis AX1 according to the instantaneous angular position of the tilting or rotating central mirror M1.

(63) The instantaneous position of the centerline of the reflected light (B5.sub.1,2) of the second inclined beam B4.sub.2 may slightly deviate from the central axis AX1 according to the instantaneous angular position of the tilting or rotating central mirror M1.

(64) The instantaneous position of the centerline of the reflected light (B5.sub.1,1) of the first inclined beam B4.sub.1 may slightly deviate from the instantaneous position of the centerline of the reflected light (B5.sub.1,2) of the second inclined beam B4.sub.2 according to the instantaneous angular position of the tilting or rotating central mirror M1.

(65) The first light pulse B5.sub.1,1 may temporally overlap with a second light pulse B5.sub.1,2 and with a third light pulse B5.sub.1,3 during a time period T.sub.ON3. The central mirror M1 may be arranged to simultaneously reflect light of a first inclined beam B4.sub.1, light of a second inclined beam B4.sub.2, and light of a third inclined beam B4.sub.3 substantially to the direction SZ of the central axis SX1.

(66) FIG. 4 shows, by way of example, in a cross-sectional side view, the light source device 500. The catadioptric reflector 100 may have the input surface SRF1, the first reflective surface SRF2, the second reflective surface SRF3, and the output surface SRF4. Each light source LED may provide an external input beam B0. The input surface SRF1 may form an internal axial beam B1 by refracting light of the input beam B0. The first reflective surface SRF2 may form a converging beam B2 by reflecting light of the internal axial beam B1. The second reflective surface SRF3 may form an internal inclined beam B3 by reflecting light of the converging beam B2. The output surface SRF4 may form an inclined external beam B4 by refracting light of the internal inclined beam B3. The central mirror M1 may form output light beam B5 by reflecting light of the inclined external beam B4 to the direction SZ of the central axis AX1.

(67) The input surface SRF1 may be e.g. a planar surface. The second reflective surface SRF3 may be e.g. a conical surface. The angle ?3 may denote the angle between the second reflective surface SRF3 and the axial direction SZ. The output surface SRF4 may be e.g. a conical surface. The angle ?4 may denote the angle between the output surface SRF4 and the axial direction SZ.

(68) The catadioptric reflector 100 may optionally comprise central surfaces SRF5, SRF6 for allowing the output light B5 to pass through a central region of the catadioptric reflector 100. The central surfaces SRF5, SRF6 may be e.g. planar surfaces.

(69) The central surface SRF5 and/or SRF6 may also be e.g. a spherical surface or an aspherical surface, e.g. to focus or collimate output light B5.

(70) The catadioptric reflector 100 may be arranged to operate such that the converging beams B2 do not intersect (reach) the central axis AX1. The catadioptric reflector 100 may also comprise a central hole for allowing the output light B5 to pass through a central region of the catadioptric reflector 100.

(71) L0 may denote a distance between each light source LED.sub.1 and the central axis AX1.

(72) The output light beam B5 may be understood to pass through a target area AREA1. The target area AREA1 may also be called e.g. as an output area. The target area AREA1 may have a width WAREA1. The target area AREA1 may be defined e.g. by an optical aperture. The target area AREA1 may be defined e.g. by an optical aperture of the optics LNS1. The output light beam B5 may have a width WB5. The output light beam may be arranged to pass through the output area AREA1 of the device 500. The angular position of the central mirror M1 may be varied so as to sequentially couple each light source LED.sub.1, LED.sub.2 to an output area AREA1 of the device 500.

(73) The catadioptric reflector 100 may comprise or consist of transparent material.

(74) The material of the catadioptric reflector 100 may be e.g. polymethyl meth-acrylate (PMMA), polycarbonate, glass, or sapphire. The catadioptric reflector 100 may be produced e.g. by molding, mechanical machining and/or 3D printing. In an embodiment, the catadioptric reflector 100 may be a single piece of transparent material. The material may be selected such that it is substantially transparent at all wavelengths 21, 22, 23 of the output beam B5.

(75) The surface SRF1, SRF2, SRF3, and/or SRF4 may be axially symmetric with respect to the central axis AX1. The axially symmetric shape may facilitate manufacturing of the catadioptric reflector 100. The axially symmetric shape may facilitate assembly of the light source device 500, as it is not necessary to pay attention to the angular position of the catadioptric reflector 100 with respect to the light sources LED.sub.1, LED.sub.2, . . . .

(76) Referring to FIG. 5, The catadioptric reflector may be arranged to focus light of the inclined beams to the central mirror M1. The curvature of the first reflective surface SRF2 may be selected such that each inclined beam B4 may have a focused spot at the central mirror M1. The first reflective surface SRF2 may operate as a concave focusing mirror for the light, which propagates within the catadioptric reflector.

(77) CU2H denotes a curve defined by the intersection of a horizontal plane with the first reflective surface SRF2. CU2V denotes a curve defined by the intersection of a vertical plane with the first reflective surface SRF2, wherein said vertical plane also includes the central axis SX1. Peripheral rays of the axial input beam B1 may meet the curve CU2H at points P21, P22. Peripheral rays of the axial input beam B1 may meet the curve CU2V at points P23, P24. The centerline of the axial input beam B1 may meet the first reflective surface SRF2 at the point P2.

(78) The point P2 may be at a distance R20 from the central axis AX1, as shown in FIG. 7a. The curve CU2V may have a radius R2V of curvature, e.g. as shown in FIG. 7a. The curve CU2H may have a radius R2H of curvature, e.g. as shown in FIG. 7b.

(79) The second reflective surface SRF3 and/or the refractive output surface SRF4 may be e.g. conical surfaces. To the first approximation, the conical reflective surface SRF3 may operate locally as a cylindrical reflector. To the first approximation, the conical refractive surface SRF4 may operate locally as a cylindrical lens. Consequently, the surfaces SRF3, SRF4 may deform a focal spot formed on the central mirror M1 in a similar manner as cylindrical lenses.

(80) The first radius R2V of curvature may be different from the second radius R2H of curvature, so that the first reflective surface SRF2 may compensate a deforming effect of the second reflective surface SRF3 and/or compensate a deforming effect of the refractive output surface SRF4.

(81) For example, the curvature (1/R2V, 1/R2H) of the first reflecting surface SRF2 may be selected such that the first external inclined beam (B4.sub.1) has a focused spot (SP1) at the central reflector M1. The curvature (1/R2V, 1/R2H) of the first reflecting surface (SRF2) may be selected to compensate a diverging effect of the second reflecting surface (SRF3), such that the first external inclined beam (B4.sub.1) has a focused spot (SP1) at the central reflector M1.

(82) The curvature of a surface may mean the reciprocal (=1/R) of the radius of curvature (R) of said surface. The curvature of a surface at a point of said surface may be specified e.g. by a first radius (R2V) of curvature and/or by a second radius (R2H) of curvature. The first radius (R2V) may specify a vertical curvature (=1/R2V) of the surface. The second radius (R2H) may specify a horizontal curvature (=1/R2V) of the surface.

(83) FIGS. 6a and 6b illustrate how the first reflective surface SRF2 may compensate a deforming effect of the conical surfaces SRF3, SRF4.

(84) FIG. 6a shows, in a cross-sectional side view, propagation of light in the catadioptric reflector unit 100. A point light source LED.sub.1 may be positioned at the source point P0. The axial external beam B0 has a centerline from the point P0 to the point P1. The point P1 is located on the input surface SRF1. The internal axial beam B1 has a centerline from the point P1 to the point P2. The point P2 is located on the reflective surface SRF2. The converging beam B2 has a centerline from the point P2 to the point P3. The point P3 is on the second reflective surface SRF3. The inclined internal beam B3 has a centerline from the point P3 to the point P4. The point P4 is on the output surface SRF4. The inclined external beam B4 has a centerline from the point P4 to the point P5. The point P5 may be located at the centerline AX1 of the catadioptric reflector 100. The point P5 may be located on the reflective surface of the central mirror M1. The catadioptric reflector 100 may be arranged to form a sharp focused image of the light source LED1 on the reflective surface of the central mirror M1. The sharp focused image may be located on the central axis AX1. The catadioptric reflector 100 may be arranged to form a sharp focused spot at the point P5, which may be located on the central axis AX1 and also on the reflective surface of the central mirror M1. L.sub.P0P1 denotes the distance between the points P0 and P1. L.sub.P1P2 denotes the distance between the points P1 and P2. L.sub.P2P3 denotes the distance between the points P2 and P3. L.sub.P3P4 denotes the distance between the points P3 and P4. L.sub.P4P5 denotes the distance between the points P4 and P5.

(85) The beam B1 comprises peripheral light rays LR13, LR14. The beam B2 comprises peripheral light rays LR23, LR24. The beam B3 comprises peripheral light rays LR33, LR34. The beam B4 comprises peripheral light rays LR43, LR44. The light rays LR13, LR23 meet the reflective surface SRF2 at the point P23. The light rays LR14, LR24 meet the reflective surface SRF2 at the point P24.

(86) TP3V denotes a target point for the upper and lower light rays LR23, LR24 of the converging beam B2. The radius of curvature of the first reflecting surface SRF2 may be selected such that the extension of the upper and lower light rays LR23, LR24 meet at the target point TP3V. L.sub.TP3V denotes the distance between the point TP3V and the point P3 of the surface SRF3.

(87) TP3H denotes a target point for the lateral light rays LR21, LR22 of the converging beam B3 (FIG. 6b). The radius of curvature of the first reflecting surface SRF2 may be selected such that the extension of the latera light rays LR21, LR22 meet at the target point TP3H. L.sub.TP3H denotes the distance between the point TP3H and the point P3 of the surface SRF3.

(88) The distance L.sub.TP3V may be greater than the distance L.sub.TP3H, so that the catadioptric reflector 100 may form a sharp focal spot at the point P5. The first radius (R2V) of curvature of the first reflecting surface SRF2 may be different from the second radius (R2H) of curvature of the first reflecting surface SRF2, so that the catadioptric reflector 100 may form a sharp focal spot at the point P5.

(89) The point O3 is located on the central axis AX1 such that the line from the point O3 to the point P3 is perpendicular to the surface SRF3 at the point P3. R.sub.SRF3 denotes the distance between the points O3 and P3. The distance R.sub.SRF3 may represent the radius curvature of the surface SRF3 at the point P3.

(90) The point O4 is located on the central axis AX1 such that the line from the point O4 to the point P4 is perpendicular to the surface at the point P4. R.sub.SRF4 denotes the distance between the points O4 and P4. The distance R.sub.SRF4 may represent the radius curvature of the surface SRF4 at the point P4.

(91) FIG. 6b shows, in an axial unfolded view, propagation of light in the catadioptric reflector unit 100. The inclined optical path from the point P3 to the point P5 has been unfolded to the plane of the drawing.

(92) The axial beam B1 may have a circular shape, when viewed in the axial direction. The converging beam B2 has peripheral light rays LR21, LR22. The inclined internal beam B3 has peripheral light rays LR31, LR32. The conical surface SRF3 may form the peripheral light rays LR31, LR32 by reflecting the peripheral light rays LR21, LR22. The light rays LR21, LR31 meet the surface SRF3 at the point P31. The light rays LR22, LR32 meet the surface SRF3 at the point P32. The output surface SRF4 may form peripheral light rays LR41, LR42 of the inclined external beam B4 by refracting the light rays LR31, LR32 of the inclined internal beam B3.

(93) The curve CU3H may represent the curvature of the conical reflecting surface SRF3. The curve CU2H may represent the curvature of the first reflecting surface SRF2.

(94) TP3H denotes a target point for the lateral light rays LR21, LR22 of the converging beam B3. The radius of curvature of the first reflecting surface SRF2 may be selected such that the extension of the lateral light rays LR21, LR22 meet at the target point TP3H. L.sub.TP3H denotes the distance between the point TP3H and the point P3 of the surface SRF3. FP3 may denote a focal point of the conical reflective surface SRF3. f3 denotes the distance between the focal point FP3 and the point P3 on the surface SRF3. The curvature of the first reflective surface SRF2 may be selected so as to compensate the diverging effect of the curvature of the second first reflective surface SRF2 on the direction of the peripheral light rays LR31, LR32.

(95) Consequently, the catadioptric reflector 100 may be arranged to focus all peripheral light rays LR41, LR42, LR43, LR44 to the same point P5.

(96) Referring to FIGS. 7a and 7b, the first reflective surface SRF2 may have a first radius R2V of curvature and a second radius R2H of curvature at the point P2 on the surface SRF2. R20 may denote the distance between the point P2 and the central axis AX1.

(97) The surfaces SRF1, SRF2, SRF3, SRF4 may be axially symmetric with respect to the central axis AX1. The axially symmetric surfaces may allow operation such that a first axial beam B1.sub.1 of a first light source LED.sub.1 may spatially overlap a second axial beam B12 of a second light source LED.sub.2.

(98) FIGS. 8a and 8b show a catadioptric reflector 100, which comprises multiple facets. For example, the first reflecting surface SRF2 may comprise a plurality of reflective facets F2a, F2b, F2c and/or the second reflective surface SRF3 may comprise a plurality of reflective facets F3a, F3b, F3c. The facets F2a, F3a may be arranged to reflect light of a first light source LED.sub.1. A facet F2a may have a radius R2H (and R2V) of curvature. The radius R2H may have an end point O2H. The end point O2H of the radius of curvature of the facet F2a may be displaced with respect to the central axis AX1. The facets F2b, F3b may be arranged to reflect light of a second light source LED.sub.2. The facets F2c, F3c may be arranged to reflect light of a third light source LED.sub.3.

(99) The axially symmetric catadioptric reflector 100 may allow using a higher number of light sources than the catadioptric reflector 100 of FIG. 8b.

(100) Referring to FIG. 9, the light source device 500 may further comprise a plurality of beam-modifying lenses or curved facets LNS0, which may be positioned between the light sources LED.sub.1, LED.sub.2 and the catadioptric reflector 100. A plurality of beam-modifying lenses or curved facets LNS0 may be implemented on the input surface SRF0.

(101) The axially symmetric catadioptric reflector 100 may allow using a higher number of light sources than the catadioptric reflector 100 of FIG. 9.

(102) FIG. 9 shows, by way of example, a control system SYS1 of a light source device 500. The control system SYS1 may comprise a control unit CNT1 and one or more actuators ACU1, ACU2.

(103) The control unit CNT1 may be arranged to control operation of the actuators ACU1, ACU2 and the light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . such that the central mirror M1 may sequentially reflect light of the light sources to the axial direction. The control unit CNT1 may provide control signals S.sub.1, S.sub.2, S.sub.3, . . . , S16 for the light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . , LED.sub.16 for timing of operation of the light sources. The control unit CNT1 may e.g. provide control signals SA1, SA2 for controlling operation of the actuators ACU1, ACU2.

(104) The device 500 may comprise a memory MEM1 for storing computer program code PROC1. The program code PROC1, when executed by one or more data processors of the control unit CNT1, may cause the device 500 to form the output light B5 from the light of the light sources, as described above.

(105) The device 500 may comprise a memory MEM2 for storing operating parameters PAR1. The operating parameters PAR1 may e.g. specify duration of light pulses, power of light pulses and/or duration of a blank time (T.sub.off) between consecutive light pulses.

(106) The device 500 may comprise a communication unit COM1 to provide or receive a synchronization signal S.sub.SYNC1, so as to allow synchronization of operation with an optical system 700. The optical system may comprise e.g. a camera for capturing images of a target in a situation where the target is sequentially illuminated with the output light B5 of the device 500.

(107) FIG. 11 shows, by way of example, timing of operation of light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . . LED.sub.16 for forming an output beam B5. The uppermost curve shows angular position ?1(t) of a first actuator ACU1 as a function of time t. The second curve from the top shows angular position ?2(t) of a second actuator ACU2 as a function of time t. The phase difference between the actuators ACU1, ACU2 may be substantially equal to 90? so that the normal N1 of the central mirror M1 may rotate around the central axis AX1. The operation of the actuators ACU1, ACU2 may be synchronized with the operation of the light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . . LED.sub.16 (or vice versa). T.sub.CYC1 may denote a duration of a sequence of light pulses obtained from the light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . . LED.sub.16. The angular position ?1(t) may oscillate between values ??.sub.MAX and +?.sub.MAX. The angular position ?2(t) may oscillate between values ??.sub.MAX and +?.sub.MAX.

(108) Referring to FIG. 12a, an optical apparatus 1000 may comprise the light source device 500, a filter FIL1, and a detector DET1. The light source device 500 may provide light B6, B7 for an optical system 700. The light source device 500 may provide output light B6, which comprises a sequence of light pulses at several different wavelengths ?.sub.1, ?.sub.2, ?.sub.3, . . . . The filter FIL1 may be e.g. a tunable Fabry-Perot interferometer, which may provide filtered light B7. The filter FIL1 may reduce spectral bandwidth of one or more light pulses of the output light B6. The spectral bandwidth of one or more light pulses of the filtered light B7 may be narrower than the spectral bandwidth of one or more light pulses of the output light B6. The operation of a tunable filter FIL1 may be synchronized with the operation of the light source device 500, e.g. by using the synchronization signal S.sub.SYNC. The output light B6 or the filtered output light B7 may be directed to an object OBJ1. The object OBJ1 may be e.g. a sample, which may be analyzed by using the optical apparatus 1000. The object OBJ1 may be e.g. a biological tissue sample. The object OBJ1 may be e.g. a piece of food. The object OBJ1 may be e.g. a chemical substance.

(109) The object OBJ1 may provide sample light pulses B8 by reflecting, transmitting and/or scattering the output light B6, B7. The detector DET1 may be arranged to detect the intensity of light pulses of the sample light B8. The apparatus 100 may provide spectral data from the object OBJ1 at a plurality of different wavelengths ?.sub.1, ?.sub.2, ?.sub.3, . . . . The apparatus 1000 may be arranged to obtain detected intensity values, and the apparatus 1000 may be arranged to associate each detected intensity value with the corresponding wavelength ?.sub.1, ?.sub.2, ?.sub.3, . . . . For example, the apparatus 1000 may provide a transmittance spectrum or a reflectance spectrum of the object OBJ1.

(110) In an embodiment, a tunable light source apparatus 1000 may comprise the light source device 500 and a tunable optical bandpass filter FIL1. The tunable bandpass filter FIL1 may allow e.g. only one narrow spectral band to be transmitted. The spectral band may have a selectable center wavelength.

(111) The tunable light source apparatus may provide light pulses at selectable wavelengths, e.g. in the spectral range of 400 nm to 1100 nm.

(112) For example, when using a tilting Fabry-Perot interferometer as a filter, the spectral (FWHM) width of the spectral band of the filtered light may be e.g. in the range of 3 nm to 8 nm.

(113) For example, when using a piezo-actuated Fabry-Perot interferometer, which has silver alloy mirrors, the spectral (FWHM) width of the spectral band may be e.g. in the range of 9 nm to 15 nm. FWHM denotes full width at half maximum.

(114) The tunable light source apparatus may provide light pulses at selectable wavelengths, e.g. in the spectral range of 420 nm to 660 nm. The tunable light source apparatus may provide light pulses at selectable wavelengths, e.g. in the spectral range of 450 nm to 850 nm. The tunable light source apparatus may provide light pulses at selectable wavelengths, e.g. in the spectral range of 500 nm to 1050 nm. The tunable light source apparatus may cover the spectral range of 420 nm to 660 nm, 450 nm to 850 nm, or 500 nm to 1050 nm.

(115) Referring to FIG. 12b, an optical apparatus 1000 may comprise the light source device 500, and a spectrometer SPEC1. The light source device 500 may provide light B6 for an optical system 700, which comprises a spectrometer. The spectrometer SPEC1 may comprise e.g. a tunable Fabry-Perot interferometer and a detector (DET1). The optical apparatus 1000 may be arranged to measure a spectrum of an object OBJ1.

(116) Referring to FIG. 12c, an optical apparatus 1000 may comprise the light source device 500, and a digital camera CAM1. The light source device 500 may provide light B5 for an optical system 700, which comprises an imaging device (camera). The light source device 500 may be arranged to illuminate an object OBJ1 with a sequence of light pulses B5.sub.1,1, B5.sub.1,2, B5.sub.1,3, . . . of different wavelengths ?.sub.1, ?.sub.2, ?.sub.3, . . . . The camera CAM1 may be arranged to capture images DIMG1_?1, DIMG1_?2, . . . of the illuminated object OBJ1. For example, a first image DIMG1_?1 may be captured when the object is illuminated with a light pulse B5, which has a first wavelength 21. A second image DIMG1_?2 may be captured when the object is illuminated with a light pulse B5, which has a second wavelength 22. The camera CAM1 may comprise imaging optics LNS2 and an image sensor SEN1. The imaging optics LNS2 may form an optical image IMG1 of an object OBJ1 on the image sensor SEN1. The image sensor SEN1 may convert the optical image IMG1 into a digital image DIMG. The digital images may be communicated to a memory as an image signal S.sub.IMG1. The apparatus 100 may comprise a memory MEM3 for storing the captured images DIMG1_?1, DIMG1_?2. The images DIMG1_?1, DIMG1_?2 may be optionally combined to form a multi-spectral composite image. For example, the apparatus 100 may be arranged to capture M images of the same object OBJ1 at M different wavelengths ?.sub.1, ?.sub.2, ?.sub.3, . . . . The number M may be e.g. greater than 10, greater than 20, greater than 30, greater than 40, or even greater than 50. The apparatus 1000 may comprise a control unit CNT2 for controlling operation of the apparatus 1000. The operation of the apparatus 1000 may be synchronized with the operation of the light source device 500 by using the synchronization signal S.sub.SYNC. The apparatus 1000 may be e.g. a hyperspectral imaging apparatus.

(117) The apparatus 1000 may be e.g. an imaging microscope. The apparatus 1000 may be arranged to illuminate an object OBJ1 with the light B5, B6, or the filtered output light B7, e.g. in order to capture a microscope images (DIMG1_?1, DIMG1_?2) at different wavelengths.

(118) The output light B5, B6, or the filtered output light B7 may be delivered to the object OBJ1 or an optical unit e.g. via one or more optical fibers. The apparatus 1000 may comprise one or more optical fibers to guide the light B5, B6, B7. For example, the light B5, B6, B7 may be guided to a cavity via an optical fiber bundle.

(119) The term catadioptric means that reflector 100 is arranged to refract and reflect light. The catadioptric reflector 100 may be arranged to refract and reflect light of the light sources LED.sub.1, LED.sub.2, LED.sub.3, . . . .

(120) The conical surface (e.g. SRF3, SRF4) may mean a surface, which is defined by sections of straight lines that pass through a common fixed point (i.e. the apex point), which is located at a symmetry axis (AX1). The conical surface may be axially symmetric with respect to the symmetry axis (AX1). The apex angle of the conical surface may be smaller than 180?.

(121) For the person skilled in the art, it will be clear that modifications and variations of the devices and methods according to the present disclosure are perceivable. The figures are schematic. The particular embodiments described above with reference to the accompanying drawings are illustrative only and not meant to limit the scope of the present disclosure, which is defined by the appended claims.