Method and apparatus for photomixing

• US 6,825,455 B1
• Filed: 03/04/1999
• Issued: 11/30/2004
• Est. Priority Date: 09/05/1996
• Status: Expired due to Term

• Current Assignee: Rudolf Schwarte
• Original Assignee: Rudolf Schwarte
• Inventors: Schwarte, Rudolf
• Primary Examiner(s): Luu, Thanh X.
• Application Number:
  US09/254,333
• Time in Patent Office: 2,098 Days
• Field of Search: 250/214.1, 250/214.R, 257/222, 257/435
• US Class Current: 250/214.1
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4914 of detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement

Abstract

A method and corresponding device for determining the phase- and/or amplitude data of an electromagnetic wave. In order to bring about the spatial depth resolution of the image data obtained, the method according to the invention comprises the following steps: an electromagnetic wave is beamed onto the surface of a photonic mixed element comprising at least one pixel, the pixel having at least two light-sensitive modulation light gates G_am and G_bm and associated accumulation gates G_a and G_b; modulation light gate voltages U_am(t) and U_bm(t), which are configured as U_am(t)=U_o+U_m(t) and U_bm(t)=U_o−U_m(t), are applied to the modulation light gates G_am and G_bm; a direct voltage, whose magnitude is at least the same as that of the total of U_o and the amplitude of the modulation voltage U_m(t), is applied to the accumulation gates G_a and G_b; the charge carriers produced in the space charge region of the modulation light gates G_am and G_bm by the incident electromagnetic wave are subjected, as a function of the polarity of the modulation light gate voltages U_am(t) and U_bm(t), to the potential gradient of a drift field and drift to the corresponding accumulation gate G_a or G_b; and the charges q_a and q_b which have drifted to the accumulation gates G_a and G_b, respectively, are diverted. The corresponding photonic mixed element has at least one pixel which comprises at least two light-sensitive modulation light gates (G_am, G_bm) and accumulation gates (G_a, G_b) which are associated with the modulation light gates and are partitioned with respect to the incident electromagnetic wave. A plurality of photonic mixed elements can be assembled to form an array.

Claims

1. A method of determining the phase and/or amplitude information of an electromagnetic wave

in which an electromagnetic wave is radiated onto the surface of a photonic mixing element having at least one pixel, wherein the pixel has at least two light-sensitive modulation photogates G_am and G_bm and associated accumulation gates G_a and G_b,

in which there are applied to the modulation photogates G_am and G_bm modulation photogate voltages U_am(t) and U_bm(t) which are in the form of U_am(t)=U_o+U_m(t) and U_bm(t)=U_o−

U_m(t), wherein U_o represents a bias voltage of the accumulation gates G_a and G_b,

wherein applied to the accumulation gates G_a and G_b is a dc voltage whose magnitude is at least as great as the magnitude of the sum of U_o and the amplitude of the modulation voltage U_m(t),

in which charge carriers produced in a space charge zone of the modulation photogates G_am and G_bm by the electromagnetic wave are exposed to a potential gradient of a drift field in dependence on the polarity of the modulation photogate voltages U_am(t) and U_bm(t) and drift to the corresponding accumulation gate G_a and G_b, and

in which charges q_a and q_b which have drifted to the respective accumulation gates G_a and G_b are taken off.

2. A method according to claim 1

in which the electromagnetic wave is irradiated by a transmitter,

in which the electromagnetic wave reflected by an object is radiated onto the surface of the photonic mixing element,

in which the modulation photogate voltages U_am(t) and U_bm(t) are in fixed phase relationship with the phase of the electromagnetic wave irradiated by the transmitter, and

in which the charge carriers produced are additionally exposed to the potential gradient of a drift field in dependence on the phase of push-pull modulation photogate voltages U_am(t) and U_bm(t).

3. A method according to claim 2

in which for two different phase shifts Δ

φ

₁ and Δ

φ

₂ of the modulation photogate voltages U_am(t) and U_bm(t) relative to the phase of the electromagnetic wave irradiated by the transmitter and charges q_a1 and q_b1 as well as q_a2 and q_b2 are taken off and the charge differences (q_a1−

q_b1) and (q_a2−

q_b2) are formed, and

in which in accordance with the equation $\begin{array}{cc}{\mathrm{\varphi <br><br>}}_{\mathrm{opt}}=\frac{q_{\mathrm{a2}}-q_{\mathrm{b2}}}{q_{\mathrm{a1}}-q_{\mathrm{b1}}}& \text{\hspace{1em}<br><br>}\end{array}$

the pixel phase φ

opt of the electromagnetic wave is determined relative to the phase of the electromagnetic wave irradiated by the transmitter and thus the transit time of the electromagnetic wave received by the pixel is determined.

4. A method according to claim 3

in which by means of four modulation photogates G_am, G_bm, G_cm and G_dm and four associated accumulation gates G_a, G_b, G_c and G_d, for two different phase shifts Δ

φ

₁ and Δ

φ

₂ of the modulation photogate voltages U_am(t)=U₀+U_m1(t) and U_bm(t)=U₀−

U_m1(t) and U_cm(t)=U₁+U_m2(t) and U_dm(t)=U₁−

U_m2(t) relative to the phase of the electromagnetic wave irradiated by the transmitter, at the same time charges q_a, q_b, q_c and q_d are separated and taken off, and

in accordance with the equation ${\mathrm{\varphi <br><br>}}_{\mathrm{opt}}=\frac{q_c-q_d}{q_a-q_b}$

the pixel phase φ

_opt of the electromagnetic wave irradiated by the transmitter and therewith the transit time of the electromagnetic wave received by the pixel is determined.

5. A method according to claim 2

in which the photonic mixing element has a plurality of pixels,

in which at least one pixel is directly radiated with a part of the electromagnetic wave from the transmitter and

in which calibration of the phase shift between the electromagnetic wave and modulation photogate voltages U_am(t) and U_bm(t) is implemented from a phase shift measured with said pixel.

6. A method according to claim 1

in which the electromagnetic wave with independently excited, unknown intensity modulation is radiated onto the surface of the photonic mixing element,

in which the modulation photogate voltages U_am(t) and U_bm(t) are produced by a tunable modulation generator,

in which the charge carriers produced are additionally exposed to a potential gradient of a drift field in dependence on the phase of push-pull modulation photogate voltages U_am(t) and U_bm(t), and

in which the photonic mixing element and the modulation generator form at least one phase-lock loop and the electromagnetic wave is measured in accordance with a lock-in method.

7. A method according to claim 1 in which a continuous or discontinuous HF-modulation is used as modulation for the electromagnetic wave, and pseudo-noise modulation or chirp modulation is used as modulation for the modulation photogate voltages.

8. A method according to claim 7 in which the modulation photogate voltage is HF-modulation and the charges q_a and q_b for the phase shifts Δ

φ

=0°

/180° and

90°

/270°

are taken off.

9. A method according to claim 8 in which the charges q_c and q_d are taken off.

10. A method according to claim 1 in which a steady-state modulation is used with modulation photogate voltages U_am=U_o+U_m0 and U_bm=U₀−

U_m0 with a settable modulation dc voltage U_m0 which is constant in respect of time and with which a difference image from the difference of the charges q_a and q_b is specifically weighted.

11. A method according to claim 1 in which the charges q_a and q_b beneath the accumulation gates G_a and G_b are integrated and read out with a multiplex structure.

12. A method according to claim 11 in which the charges q_a and q_b beneath the accumulation gates G_a and G_b are integrated and read out with a CCD-structure.

13. A method according to claim 1 in which the accumulation gates G_a and G_b are in the form of pn-diodes, and in which the charges q_a and q_b are read out directly as voltage or as current.

14. A method according to claim 13 in which the charges q_c and q_d are read out directly as voltage or as current.

15. A method according to claim 13 in which the pn-diodes are blocked, low-capacitance pn-diodes.

16. A method according to claim 13, in which the structure is made in CMOS technology.

17. A method according to claim 13 in which the pixel phase or the pixel transit time and the pixel brightness are ascertained directly by means of an active pixel sensor structure (APS).

18. A method according to claim 17 in which the pixel phase or the pixel transit time and the pixel brightness are selectively and/or serially read out only way of an on-chip multiplex structure.

19. A method according to claim 1 in which brightness of the pixel is respectively evaluated as the sum of the charges of the associated accumulation gates as a grey value image.

20. A method according to one of claims 1 to 19 characterized in that in background lighting or an external, non-modulated additional lighting, a difference between grey value images taken with and without exposure of the photonic mixing element to the electromagnetic wave is used as a correction parameter.

21. A method according to one of claims 1 to 19 characterised in that the photonic mixing element comprises a plurality of pixels used in a linear, surface or spatial array.

22. A method according to claim 21 characterised in that at least one of the pixels is directly radiated with a part of an intensity-modulated electromagnetic wave serving as lighting and that the measurement at said at least one pixel is used for calibration of other phases and brightness results, wherein reference pixel or pixels is or are acted upon by a transmitter with different levels of intensity or levels of intensity which can be differently set.

23. A photonic mixing element

with at least one pixel (1),

which has at least two light-sensitive modulation photogates (G_am, G_bm) comprising terminals for and adapted to receive modulation photogate voltages U_am(t) and U_bm(t) which are in the form of U_am(t)=U_o+U_m(t) and U_bm(t)=U_o−

U_m(t), and

accumulation gates (G_a, G_b) which are associated with the modulation photogates (G_am, G_bm) and which are shaded relative to an incident electromagnetic wave, wherein U_o represents a bias voltage of the accumulation gates (G_a, G_b).

24. A mixing element according to claim 23 characterized in that a middle gate (G_o) is arranged between the modulation photogates (G_am, G_bm).

25. A mixing element according to claim 23 characterised in that the at least one pixel (1) has four, symmetrically arranged, modulation photogates (G_am, G_bm, G_cm, G_dm) and accumulation gates (G_a, G_b, G_c, G_d).

26. A mixing element according to one of claims 23 to 25 characterised in that the accumulation gates (G_a, G_b) are in the form of pn-diodes, and the charges q_a, q_b can be read out directly as voltage or current.

27. A mixing element according to claim 26 characterised in that the charges q_c, q_d can be read out directly as voltage or current.

28. A mixing element according to claim 26 in which the pn-diodes are blocked, low capacitance pn-diodes.

29. A mixing element according to claim 26 in which the pn-diodes comprise CMOS technology pn-diodes.

30. A mixing element according to claim 23 characterised in that for the purposes of increasing a maximum modulation speed the pixel is produced using buried channel GaAs-technology and with an integrated drift field.

31. A mixing element according to claim 23 characterised in that the at least one pixel (1) is in the form of an active pixel sensor structure with partially pixel-related signal processing and partially line- or matrix-related signal processing.

32. A mixing element according to claim 23 characterised in that the shading is also extended onto edge regions of the modulation photogates.

33. A mixing element arrangement having at least two photonic mixing elements according to claim 23 characterised in that the photonic mixing elements are arranged in a one-dimensional, two-dimensional or three-dimensional arrangement.

34. A mixing element arrangement according to claim 33 characterised in that modulation photogates (G_am,n, G_am,n+1) and (G_bm,n, G_bm,n+1) respectively associated with two adjacently arranged, different pixels (n, n+1) respectively have a common accumulation gate (G_s) and that the modulation photogates (G_am,n, G_am,n+1) and (G_bm, G_bm,n+1) respectively are acted upon by the same modulation photogate voltages U_am(t) and U_bm(t).

35. A mixing element arrangement according to claim 33 characterised in that there are provided devices for direct irradiation of the at least one pixel (1) as a reference pixel, by means of which a part of the incident electromagnetic wave emitted by a transmitter is directed onto the at least one pixel.

36. A mixing element arrangement according to claim 35 characterised in that the devices for direct irradiation are equipped for a variation in respect of space and/or time of the intensity of the direct irradiation.

37. A one-dimensional or multi-dimensional mixing element arrangement according to claim 33 characterised in that the at least one pixel (1) are embodied using MOS-technology on a silicon substrate (2) and can be read out with a multiplex CCD-structure.

38. A mixing element arrangement according to claim 33 characterised in that there is provided a microlens optical system which produces substantially for each mixing element used for image recording its own microlens by which the incident electromagnetic wave is focussed onto a central region of the mixing element which can thus be reduced in size.

39. Apparatus for determining phase information of an electromagnetic wave

having at least one photonic mixing element comprising:

at least one pixel (1),

which has at least two light-sensitive modulation photogates (G_am, G_bm) comprising terminals for and adapted to receive modulation photogate voltages U_am(t) and U_bm(t) which are in the form of U_am(t)=U_o+U_m(t) and U_bm(t)=U_o−

U_m(t),

accumulation gates (G_a, G_b) which are associated with the modulation photogates (G_am, G_bm) and which are shaded relative to an incident electromagnetic wave, wherein U_o represents a bias voltage of the accumulation gates G_a and G_b, and

having a modulation generator (10, 13), and

having a transmitter (4) that irradiates the electromagnetic wave which is intensity-modulated by the modulation generator (10, 13) in predetermined manner,

wherein the electromagnetic wave which is reflected by an object (6) is radiated onto the surface of the photonic mixing element, and

wherein the modulation generator (10, 13) supplies the photonic mixing element with modulation voltages U_m(t) which are in a predetermined phase relationship with respect to the phase of the electromagnetic wave that is irradiated from the transmitter.

40. Apparatus according to claim 39 characterised in that there are provided an optical system (7) and a mixing element arrangement, wherein the optical system (7) forms an image of the reflected electromagnetic wave that is radiated onto the surface of the photonic mixing element.

41. Apparatus according to claim 39 or 40 characterised in that there are provided a mixing element arrangement with associated optical receiving system, electronic evaluation and signal processing system for difference signals, sum signals and reference signals, with a digital memory for a grey value image and a transit time or distance image, a transmitter for lighting a three-dimensional scene with modulated electromagnetic waves, and with an adjustable optical transmitting system corresponding to the optical receiving system, forming a digital 3D-photographic camera in the form of a compact unit.

42. Apparatus according to claim 39 or 40 characterized in that to form a digital, three-dimensionally recording video camera, there are provided mixing clement arrangement with associated optical receiving system, electronic evaluation and signal processing system for the difference signals, sum signals and reference signals, with a digital memory for a grey value image and a transit time or distance image, a transmitter for lighting a three-dimensional scene with modulated electromagnetic waves, and with an adjustable optical transmitting system corresponding to the optical receiving system, wherein there are further provided memory means for storage of digital image sequences.

43. Apparatus according to claim 41 characterised in that the transmitter is provided with devices for emitting light waves in various spectral regions for producing colour images or colour image components.