Method and Photodiode Device for the Coherent Detection of an Optical Signal

Abstract

Provided is a device which includes a method for the coherent detection of an optical signal, including the following steps of providing a vertically illuminable photodiode; producing an optical reference signal; radiating the optical signal and the reference signal into the photodiode in such a way that the two signals at least partially interfere with each other. Radiating the optical signal into the photodiode is effected via a first side of the photodiode, and radiating the reference signal into the photodiode is effected via a second side of the photodiode, or, vice versa, the reference signal is radiated into the photodiode via the first side of the photodiode and the optical signal is radiated into the photodiode via the second side.

Claims

1. A method for the coherent detection of at least one optical signal, comprising the steps of: providing at least one vertically illuminable photodiode; producing at least one optical reference signal; and radiating the optical signal and the reference signal into the photodiode in such a way that the two signals at least partially interfere with each other, wherein radiating the optical signal into the photodiode is effected via a first side of the photodiode, and radiating the reference signal (LO) into the photodiode is effected via a second side of the photodiode, or, vice versa, the reference signal is radiated into the photodiode via the first side of the photodiode and the optical signal is radiated into the photodiode via the second side.

2. The method according to claim 1, wherein the optical signal and the reference signal are radiated into the photodiode substantially collinearly.

3. The method according to claim 1, wherein the first side faces away from the second side.

4. The method according to claim 1, wherein the first side is formed by a substrate of the photodiode or a semiconductor layer of the photodiode arranged on a substrate.

5. The method according to claim 4, wherein at least one of the optical signal and the reference signal (LO) is radiated in at an angle relative to the substrate or the semiconductor layer.

6. The method according to claim 1, wherein the wavelengths of the optical signal and the reference signal are at least approximately the same.

7. The method according to claim 1, wherein the optical signal and the reference signal are produced by means of the same optical light source.

8. The method according to claim 1, wherein the wavelengths of the optical signal and the reference signal are different and preferably their differential frequency maximally corresponds to the 3 dB cut-off frequency of the photodiode or is not much greater than the 3 dB cut-off frequency of the photodiode.

9. The method according to claim 1, wherein the optical signal and the reference signal are radiated into the photodiode such that they interfere with each other at least in an absorber layer of the photodiode.

10. The method according to claim 1, wherein for spatially scanning the optical signal the reference signal is radiated in at different angles relative to the first or second side of the photodiode and for each of the angles an interference signal is registered by the photodiode.

11. The method according to claim 1, wherein the reference signal is radiated in via an adjustable deflection unit, wherein the photodiode registers an interference signal produced by the interference of the optical signal with the reference signal, which substantially depends on a fraction of the optical signal that is incident on the photodiode collinearly to the reference signal.

12. The method according to claim 1, wherein a plurality of optical signals is radiated in from different solid angles, wherein the aperture of the photodiode is chosen in such a way that the normalized intensity of the interference signal of incident optical signals from solid angles outside a specified solid angle resolution is not greater than 0.1 or greater than 0.05.

13. The method according to claim 1, wherein the reference signal is radiated in diffusely so that a detection is possible from several solid angles at the same time.

14. The method according to claim 1, wherein the photodiode has an aperture which amounts to at least 0.5 mm or at least 1 mm.

15. The method according to claim 1, wherein there is provided an array of photodiodes, wherein at least one optical signal is each radiated into the photodiodes via the first side or the second side, wherein the reference signal is each radiated in via the other side of the photodiodes, wherein each of the photodiodes registers an interference signal produced by the interference of the optical signal with the reference signal, which substantially depends on a fraction of the optical signal which is incident on the photodiode collinearly to the reference signal.

16. A photodiode device for the coherent detection of at least one optical signal, comprising: at least one vertically illuminable photodiode; and a light irradiating device for radiating the optical signal and a reference signal into the photodiode in such a way that the two signals at least partially interfere with each other, wherein the light irradiating device is configured such that the optical signal entering into or impinging on the light irradiating device is radiated into the photodiode via a first side of the photodiode and the reference signal entering into or impinging on the light irradiating device is radiated into the photodiode via a second side of the photodiode, or, vice versa, the reference signal is radiated in via the first side and the optical signal is radiated in via the second side.

17. The photodiode device according to claim 16, wherein the light irradiating device comprises a first deflection device for deflecting the optical signal or the reference signal and a second deflection device for deflecting the reference signal or the optical signal.

18. The photodiode device according to claim 17, wherein the light irradiating device comprises a waveguide for guiding the optical signal or the reference signal, wherein the first deflecting device is formed by an end face of the waveguide.

19. An array with a plurality of photodiode devices according to claim 16.

20. The array according to claim 19, wherein the light irradiating devices of the photodiode devices are designed and arranged such that the photodiodes of several of the photodiode devices can be illuminated with the same reference signal.

21. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The proposed solution will be explained in detail below by means of exemplary embodiments with reference to the Figures.

[0037] FIG. 1 schematically shows a photodiode device for the coherent detection according to a first exemplary embodiment of the solution;

[0038] FIG. 2 shows a photodiode device for the coherent detection according to a second exemplary embodiment of the solution; and

[0039] FIG. 3 shows the normalized intensity of the interference signal to be detected in dependence on the angular difference between the direction of the optical signal and the reference signal.

DESCRIPTION OF THE INVENTION

[0040] The photodiode device 100 according to the solution as shown in FIG. 1 for the coherent detection of an optical signal OS comprises a photodiode 10. The photodiode 10 includes a plurality of semiconductor layers 2 to 4 arranged one above the other on a substrate 1. The lowermost layer 2 represents an n-doped contact layer, while the uppermost layer 4 is a p-doped contact layer. Between the two contact layers 2, 4 the absorber layer 3 is disposed, so that the layers 2 to 4 form a p-i-n junction. Alternatively, it is possible that the n-doped contact layer is arranged above the absorber layer 3 and the p-doped contact layer extends below the absorber layer 3 adjacent to the substrate 1. For electrically contacting the n-contact layer 2 n-contacts 21 are used, while the p-contact layer 4 is contacted via p-contacts 42.

[0041] The photodiode device 100 furthermore comprises a light irradiating device (not shown in FIG. 1) by means of which the optical signal OS to be detected is coupled into the photodiode 10 via a first side of the photodiode 10, namely via an underside 11 of the substrate 1 (through the underside 11). By means of the light irradiating device a reference signal in the form of a local-oscillator signal LO furthermore is coupled into the photodiode 10 via a second side of the same (through the second side). The second side of the photodiode 10 is formed by its upper side, i.e. by an outwardly facing side 41 of the p-contact layer 4. It is of course also possible that the optical signal OS conversely is coupled into the photodiode 10 via the upper side of the photodiode 10, i.e. the side 41 of the layer 4, and the local-oscillator signal LO is coupled into the photodiode 10 via its underside, i.e. the side 11 of the substrate 1.

[0042] Thus, the optical signal OS is mixed with the local-oscillator signal LO in the manner of the coherent detection. At the same time, there is produced a detector signal (photodiode signal) dependent on the mixed signal formed by this mixture. With reference to this detector signal, properties of the optical signal OS can be determined in the manner of the coherent detection known per se. In particular, the photodiode device according to the solution also comprises an evaluation unit for evaluating the detector signal. It is also conceivable that, as already explained above, the direction of incidence of the local-oscillator signal LO is changed in order to obtain information with respect to the direction of the optical signal OS or to perform the detection in a direction-selective manner.

[0043] FIG. 2 shows a more concrete exemplary embodiment of the photodiode device 100 according to the solution. Analogous to FIG. 1, the photodiode 10 of the photodiode device 100 includes an n-doped contact layer (n-contact layer 2) and a p-doped contact layer (p-contact layer 4), between which an absorber layer 3 is disposed.

[0044] The light irradiating device 20 of the photodiode device 100 comprises an optically integrated waveguide 210 formed by semiconductor layers 211 arranged on the substrate 1, into which the optical signal OS to be detected is coupled. A cutout 212 extends through the semiconductor layers 211 of the waveguide 210 (and for example also through the n-contact layer 2). The cutout 212 extends at an angle to the substrate 1 and the waveguide 210 (for example at an angle of 45°) so that the waveguide 210 has an end face 213 adjacent to the cutout 212 and extending at this angle. This end face 213 forms a first deflection device in the form of a deflecting surface which diverts the light of the optical signal OS guided in the waveguide 210 by an angle dependent on the course of the cutout 212 (in the present case 90) in the direction of the photodiode 10. Thus, the optical signal OS in turn enters into the photodiode 10 via an underside of the photodiode 10, which in this case is formed by an underside 22 of the n-contact layer 2.

[0045] Furthermore, the light irradiating device 20 comprises a second deflection device in the form of a (for example cylindrical) lens 220. The lens 220 is arranged such that the local-oscillator signal LO radiated into the same is deflected in the direction of the upper side of the photodiode 10, i.e. the upper side 41 of the p-contact layer 4, and is coupled into the photodiode 10 via the side 41 of the p-contact layer 4. Analogous to FIG. 1, a superposition of the optical signal OS and the local-oscillator signal LO occurs in the absorber layer 3. It is also conceivable here that the direction of incidence of the local-oscillator signal LO is varied in order to spatially scan the optical signal OS.

[0046] As already mentioned in connection with FIG. 1, the optical signal OS and the local-oscillator signal LO can of course also be interchanged, i.e. the local-oscillator signal LO might be coupled into the photodiode 10 via the waveguide 210, and the optical signal OS might be coupled into the photodiode 10 via the lens 220.

[0047] Furthermore, instead of the illustrated conventional photodiode there might also be used an avalanche photodiode which in addition to the absorber layer contains a multiplier layer, among other things. It is also possible that several of the photodiode devices 100 of FIGS. 1 and 2 are connected to form an array, in order to realize for example an imaging sensor.

[0048] FIG. 3 shows the normalized intensity (relative to a collinear incidence of the optical signal and the reference signal) of the interference signal to be detected in dependence on the angular difference (“relative propagation angle”) between the direction of the optical signal and the direction of the reference signal for different apertures of the photodiode or a lens upstream of the photodiode. For all apertures, the intensity of the interference signal decreases with increasing angular difference, with the intensity curve dropping most steeply for the smallest aperture (10 μm).