Frequency comb generating device and method for generating a frequency comb

Abstract

A frequency comb generating device is described. The frequency comb generating device comprises a pulsed optical light source, a sequence generator, a light receiving unit and a switching unit. The sequence generator is configured to generate a repeating sequence signal and to forward the repeating sequence signal at least to the switching unit. The pulsed optical light source is configured to generate electromagnetic wave packets and is synchronized with the sequence generator. The light receiving unit is configured to receive the electromagnetic wave packets and to convert the electromagnetic wave packets into an electrical signal. The switching unit is configured to at least one of control the pulsed optical light source, control the light receiving unit, attenuate the electromagnetic wave packets, phase shift the electromagnetic wave packets, attenuate the electrical signal, and phase shift the electrical signal based on the repeating sequence signal. Moreover, methods for generating an optical frequency comb and for generating an electrical frequency comb are described.

Claims

1. A frequency comb generating device comprising a pulsed optical light source, a sequence generator, a light receiving unit and a switching unit; the sequence generator being configured to generate a repeating sequence signal and to forward the repeating sequence signal at least to the switching unit; the pulsed optical light source being configured to generate electromagnetic wave packets, and the pulsed optical light source being synchronized with the sequence generator; the light receiving unit being configured to receive the electromagnetic wave packets, and the light receiving unit being configured to convert the electromagnetic wave packets into an electrical signal; the switching unit being configured to at least one of control the pulsed optical light source, control the light receiving unit, attenuate the electromagnetic wave packets, phase shift the electromagnetic wave packets, attenuate the electrical signal, or phase shift the electrical signal based on the repeating sequence signal; and said pulsed optical light source, said sequence generator, said light receiving unit and said switching unit together establishing said frequency comb generating device.

2. The frequency comb generating device of claim 1, wherein the sequence generator is configured to generate a pseudorandom binary sequence.

3. The frequency comb generating device according to claim 2, wherein the switching unit is configured to control the pulsed optical light source to generate an electromagnetic wave packet for each bit of the binary sequence having one value of the two possible values and to not generate an electromagnetic wave packet for each bit having the other value of the two possible values.

4. The frequency comb generating device of claim 1, wherein the light receiving unit is a photo diode.

5. The frequency comb generating device of claim 1, wherein the pulsed optical light source is an optical pulsed laser.

6. The frequency comb generating device of claim 1, wherein the pulsed optical light source and the light receiving unit are optically connected with each other via an optical fiber.

7. The frequency comb generating device of claim 1, wherein the switching unit is configured to control the pulsed optical light source to generate an electromagnetic wave packet for at least one certain current value of the repeating sequence signal and to not generate an electromagnetic wave packet for at least one other certain current value of the repeating sequence signal.

8. The frequency comb generating device according to claim 7, wherein the switching unit is configured to control the pulsed optical light source to generate an electromagnetic wave packet for each bit of the binary sequence having one value of the two possible values and to not generate an electromagnetic wave packet for each bit having the other value of the two possible values.

9. The frequency comb generating device of claim 1, wherein the switching unit is an electrical switch connected to the light receiving unit, the switching unit being positioned downstream of the light receiving unit.

10. The frequency comb generating device of claim 1, wherein the switching unit is an optical switch connected to the light receiving unit, the switching unit being positioned upstream of the light receiving unit.

11. The frequency comb generating device of claim 1, wherein the switching unit is configured to control the light receiving unit to convert the received electromagnetic wave packets into an electrical signal with predefined properties, wherein the predefined properties depend on the current value of the repeating sequence signal.

12. The frequency comb generating device of claim 11, wherein the repeating sequence signal comprises a ternary sequence.

13. The frequency comb generating device of claim 12, wherein the switching unit is configured to control the light receiving unit to generate a positive voltage pulse, a negative voltage pulse or no voltage pulse based on the current value of the ternary sequence.

14. The frequency comb generating device of claim 13, wherein the light receiving unit is a switchable photo diode comprising two conversion elements, wherein the switching unit is configured to selectively activate the conversion elements based on the current value of the ternary sequence.

15. The frequency comb generating device of claim 13, wherein the light receiving unit includes a switchable photo diode comprising two conversion elements and a control unit, wherein the switching unit is configured to forward the repeating sequence signal to the control unit, and wherein the control unit is configured to selectively activate the two conversion elements based on the repeating sequence signal.

16. The frequency comb generating device of claim 1, wherein the sequence generator, the light receiving unit, the switching unit and a control unit are placed on a same chip or die.

17. A frequency comb generating device comprising: a pulsed optical light source, a sequence generator, a light receiving unit and a switching unit; the sequence generator being configured to generate a repeating sequence signal and to forward the repeating sequence signal at least to the switching unit; the pulsed optical light source being configured to generate electromagnetic wave packets, and the pulsed optical light source being synchronized with the sequence generator; the light receiving unit being configured to receive the electromagnetic wave packets, and the light receiving unit being configured to convert the electromagnetic wave packets into an electrical signal; and the switching unit being configured to at least one of control the pulsed optical light source, control the light receiving unit, attenuate the electromagnetic wave packets, phase shift the electromagnetic wave packets, attenuate the electrical signal, or phase shift the electrical signal based on the repeating sequence signal, wherein the switching unit is configured to control the light receiving unit to convert the received electromagnetic wave packets into an electrical signal with predefined properties, wherein the predefined properties depend on the current value of the repeating sequence signal.

18. A frequency comb generating device comprising: a pulsed optical light source, a sequence generator, a light receiving unit and a switching unit; the sequence generator being configured to generate a repeating sequence signal and to forward the repeating sequence signal at least to the switching unit; the pulsed optical light source being configured to generate electromagnetic wave packets, and the pulsed optical light source being synchronized with the sequence generator; the light receiving unit being configured to receive the electromagnetic wave packets, and the light receiving unit being configured to convert the electromagnetic wave packets into an electrical signal; and the switching unit being configured to at least one of control the pulsed optical light source, control the light receiving unit, attenuate the electromagnetic wave packets, phase shift the electromagnetic wave packets, attenuate the electrical signal, or phase shift the electrical signal based on the repeating sequence signal, wherein the switching unit is configured to alter properties of an electrical frequency comb generated by the frequency comb generating device.

Description

DESCRIPTION OF THE DRAWINGS

(1) The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a first representative embodiment of a frequency comb generating device according to the disclosure;

(3) FIG. 2 schematically shows a second representative embodiment of a frequency comb generating device according to the disclosure;

(4) FIG. 3 schematically shows a third representative embodiment of a frequency comb generating device according to the disclosure;

(5) FIG. 4 schematically shows a fourth representative embodiment of a frequency comb generating device according to the disclosure;

(6) FIG. 5 schematically shows a flowchart of a first representative embodiment of a method for generating an electrical frequency comb according to the disclosure;

(7) FIG. 6 schematically shows a flowchart of a second representative embodiment of a method for generating an electrical frequency comb according to the disclosure;

(8) FIG. 7 schematically shows a flowchart of a third representative embodiment of a method for generating an electrical frequency comb according to the disclosure; and

(9) FIG. 8 schematically shows a flowchart of a fourth representative embodiment of a method for generating an electrical frequency comb according to the disclosure.

DETAILED DESCRIPTION

(10) The detailed description set forth below in connection with the appended drawings, where like numerals reference like elements, is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.

(11) In the following, the term light is to be understood to be not restricted to the visible light range, but rather to also include the infrared and ultraviolet frequency ranges.

(12) FIGS. 1 to 4 schematically show different representative embodiments of a frequency comb generating device 10. In each of the representative embodiments, the frequency comb generating device 10 comprises a pulsed optical light source 12, a light receiving unit 14, a sequence generator 16, and a switching unit 18.

(13) In FIGS. 1 to 4, dotted lines represent a connection that is signal transmitting in an arbitrary way. This may include wired or wireless communication between the individual device functional units, also called components. Dashed lines represent an optical connection, e.g., light may be transported between the different devices over air, through vacuum and/or via one or several optical fibers. Finally, solid lines represent an electrical wire-based connection. When an arrow is attached to a connecting line, it is to be understood that this arrow depicts the travel direction of a corresponding optical signal or electrical signal, respectively.

(14) The sequence generator 16 is configured to generate a repeating sequence signal and to forward the repeating sequence signal to the switching unit 18 to which the sequence generator 16 is connected in a signal transmitting manner.

(15) The repeating sequence may comprise a binary and/or a ternary sequence, which repeats after a predefined time interval, wherein the individual pieces of information are generated with a sequence frequency f.sub.S. In other words, the sequence generator 16 generates pieces of information with a frequency f.sub.S, wherein each piece of information may have one of two or one of three values, respectively. For example, the repeating sequence may be a pseudorandom binary sequence (PRBS).

(16) The pulsed optical light source 12 is configured to generate electromagnetic wave packets, which will be referred to as optical pulses in the following. The pulsed optical light source 12 generates the optical pulses with a basic pulse frequency f.sub.p, which means that the time between two pulses normally is T.sub.p=1/f.sub.p. For example, the optical light source 12 is configured to generate short or ultrashort optical pulses, e.g., the width of the individual pulses is much smaller than the time between two pulses even for high frequencies f.sub.p. For example, the optical light source 12 may be an optical pulsed laser.

(17) In time domain, each optical pulse typically has the form of a sinusoid, wherein the maximum amplitude is confined by a Gaussian function. As the individual optical pulses are very short, without restriction of generality each optical pulse will be approximated to have the form of a Dirac function in the following.

(18) The pulsed optical light source 12 is synchronized with the sequence generator 16, which means that the pulse frequency f.sub.p and the sequence frequency f.sub.s have a predefined ratio n=f.sub.p/f.sub.s.

(19) In a particular embodiment, the ratio n is equal to 1, which means that the optical pulses and the individual pieces of information contained in the repeating sequence signal are generated with the same frequency.

(20) Moreover, the optical light source 12 and the sequence generator 16 may be synchronized with respect to phase, which means that there is a predetermined time delay interval between the generation of an optical pulse and a corresponding piece of information contained in the repeating sequence signal.

(21) The light receiving unit 14 is configured to receive the electromagnetic wave packets, e.g., the optical pulses, and to convert the optical pulses into a corresponding electrical signal. For example, the light receiving unit 14 is a photo diode.

(22) The functionality of the switching unit 18 at least partly depends on the embodiment, and will be described in more detail in the following for each embodiment of the frequency comb generating device 10 with respect to FIGS. 1 to 4. In the embodiment shown in FIG. 1, the switching unit 18 is configured to control the pulsed optical light source 12 based on the repeating sequence signal generated by the sequence generator 16, more specifically based on the current value of the repeating sequence signal.

(23) In some embodiments, the switching unit 18 may be separate from the sequence generator 16 and the pulsed optical light source 12. Alternatively, the switching unit 18 may be integrated into the sequence generator 16 or into the pulsed optical light source 12. In some embodiments, the pulsed optical light source 12, the sequence generator 16 and/or the switching unit 18 may be formed integrally with each other so that the respective components are housed in a common housing.

(24) In the embodiment of FIG. 1, an electrical frequency comb 20 with known characteristics is generated as explained in the following with reference to FIGS. 1 and 5. First, the repeating sequence signal is generated via the sequence generator as described above (step S1.sub.a).

(25) The switching unit 18 controls the pulsed optical light source 12 to generate an optical pulse every time the current piece of information contained in the repeating sequence signal is equal to at least one of the possible values and to not generate an optical pulse when the current piece of information contained in the repeating sequence signal is equal to one of the other possible values (step S2.sub.a).

(26) For example, if the repeating sequence is a binary sequence, the possible individual pieces of information are 0 and 1. In this case, the switching unit 18 may control the pulsed optical light source 12 to generate an optical pulse for every 1 and to not generate an optical pulse for every 0 in the binary sequence, or vice versa.

(27) Without any additional control, the pulsed optical light source 12 would generate optical pulses at a frequency f.sub.p which would result in an optical frequency comb 22 with a spacing of f.sub.p of the individual Dirac functions in the frequency domain.

(28) The result of step S2.sub.a, however, is a modified optical frequency comb 22 with a spacing between the individual Dirac functions that is much smaller than f.sub.p and that has a high signal-to-noise ratio.

(29) The modified optical frequency comb 22 is then received (step S3.sub.a) and converted to the electrical frequency comb 20 (step S4.sub.a) via the light receiving unit 14. The result of step S4.sub.a, e.g., the electrical frequency comb 20, is characterized by a small spacing between the individual Dirac functions in the frequency domain and by a high signal-to-noise ratio.

(30) In the embodiment shown in FIG. 2, the switching unit 18 is an optical switch that is connected to the pulsed optical light source 12 and to the light receiving unit 14. The switching unit 18 is positioned downstream of the pulsed optical light source 12 and upstream of the light receiving unit 14. Put it another way, the switching unit 18 is positioned between the pulsed optical light source 12 and the light receiving unit 14.

(31) The switching unit 18 is configured to attenuate and/or phase shift the optical pulses, also called electromagnetic wave packets, generated by the pulsed optical light source 12 based on the current value of the repeating sequence signal. In this embodiment, an electrical frequency comb 20 with known characteristics is generated as explained in the following with reference to FIGS. 2 and 6.

(32) First, the repeating sequence signal is generated via the sequence generator as described above (step S1.sub.b). Moreover, optical pulses are generated via the optical light source 12 at a frequency f.sub.p (step S2.sub.b), which results in an optical frequency comb 22 with a spacing of f.sub.p of the individual Dirac functions in the frequency domain. The switching unit 18 filters the optical frequency comb 22 based on the current value of the repeating frequency signal (step S3.sub.b).

(33) More precisely, the switching unit 18 attenuates and/or phase shifts an optical pulse passing the switching unit 18 every time the current piece of information contained in the repeating sequence signal is equal to at least one of the possible values and does not alter the optical pulse when the current piece of information contained in the repeating sequence signal is equal to one of the other possible values.

(34) For example, if the repeating sequence is a binary sequence, the possible individual pieces of information will be 0 and 1. In this case, the switching unit 18 may alter the optical pulse for every 1 and may not alter the optical pulse for every 0 in the binary sequence, or vice versa.

(35) In one particular example, the switching unit 18 completely filters out some of the optical pulses based on the respective value of the repeating sequence signal.

(36) The result of step S3.sub.b is a modified optical frequency comb 22 that is equivalent to the one described above in the context of the first possible embodiment. Thus, the remaining steps are the same, namely receiving the modified optical frequency comb 22 (step S3.sub.b) and converting it to the electrical frequency comb 20 (step S4) via the light receiving unit 14.

(37) In the embodiment shown in FIG. 3, the switching unit 18 is an electrical switch that is connected to the light receiving unit 14 wherein the switching unit 18 is located downstream of the light receiving unit 14. Therefore, electrical signals generated by the light receiving unit 14 are forwarded to the switching unit 18.

(38) The switching unit 18 is configured to attenuate and/or phase shift the electrical pulses generated by the light receiving unit 14 based on the current value of the repeating sequence signal. In this embodiment, an electrical frequency comb 20 with known characteristics is generated as explained in the following with reference to FIGS. 3 and 7.

(39) First, the repeating sequence signal is generated via the sequence generator as described above (step S1.sub.c). Moreover, optical pulses are generated via the optical light source 12 at a frequency f.sub.p (step S2.sub.c), which results in an optical frequency comb 22 with a spacing of f.sub.p of the individual Dirac functions in the frequency domain. The optical frequency comb 22 is converted to a corresponding intermediate electrical frequency comb 24 by the light receiving unit 14 (step S3.sub.c). The switching unit 18 filters the intermediate electrical frequency comb 24 based on the current value of the repeating frequency signal (step S4.sub.c).

(40) More precisely, the switching unit 18 attenuates and/or phase shifts an electrical pulse passing the switching unit 18 every time the current piece of information contained in the repeating sequence signal is equal to at least one of the possible values and does not alter the electrical pulse when the current piece of information contained in the repeating sequence signal is equal to one of the other possible values.

(41) For example, if the repeating sequence is a binary sequence, the possible individual pieces of information will be 0 and 1. In this case, the switching unit 18 may alter the electrical pulse for every 1 and may not alter the optical pulse for every 0 in the binary sequence, or vice versa.

(42) In one particular example, the switching unit 18 completely filters out some of the electrical pulses based on the respective value of the repeating sequence signal.

(43) The result of step S4.sub.c is the electrical frequency comb 20 that is equivalent to the one described in the context of the first embodiment.

(44) In the embodiment shown in FIG. 4, the switching unit 18 is configured to control the light receiving unit 14 based on the repeating sequence signal, more specifically based on the current value of the repeating sequence signal. The switching unit 18 may be separate from the sequence generator 16 and the light receiving unit 14. Alternatively, the switching unit 18 may be integrated into the sequence generator 16 or into the light receiving unit 14.

(45) In this embodiment, an electrical frequency comb 20 with known characteristics is generated as explained in the following with reference to FIGS. 4 and 8. First, the repeating sequence signal is generated via the sequence generator 16 as described above (step S1.sub.d). Moreover, optical pulses are generated via the optical light source 12 at a frequency f.sub.p (step S2.sub.d), which results in an optical frequency comb 22 with a spacing of f.sub.p of the individual Dirac functions in the frequency domain. The optical pulses are then received via the light receiving unit 14 (step S3.sub.d), wherein the light receiving unit 14 is controlled by the switching unit 18 to convert each of the received optical pulses into a corresponding electrical pulse with predefined properties (step S4.sub.d), thereby generating the electrical frequency comb 20. In step S4.sub.d, the predefined properties of each electrical pulse depend on the current value of the repeating sequence signal.

(46) More precisely, the light receiving unit 14 generates an electrical pulse every time the current piece of information contained in the repeating sequence signal is equal to at least one of the possible values and does not generate an electrical pulse when the current piece of information contained in the repeating sequence signal is equal to one of the other possible values.

(47) For example, if the repeating sequence is a binary sequence, the possible individual pieces of information will be 0 and 1. In this case, the light receiving unit 14 may generate an electrical pulse for every 1 and may not generate an electrical pulse for every 0 in the binary sequence, or vice versa.

(48) In another example, if the repeating sequence is a ternary sequence, the individual pieces of information will be 1, 0 and 1, or at least the actual values can be mapped to these three values.

(49) In this case, the light receiving unit 14 may generate a positive voltage electrical pulse for every 1, a negative voltage electrical pulse for every 1 and may not generate an electrical pulse for every 0 in the ternary sequence. Of course, any other mapping of current values of the repeating sequence signal onto the properties of the electrical pulses is also possible.

(50) In order to generate the positive and negative voltage electrical pulses, the light receiving unit 14 may comprise, for example, a first conversion element 26 being configured to generate positive voltage electrical pulses and a second conversion element 28 being configured to generate negative voltage electrical pulses. The switching unit 18 may be configured to selectively activate one of the two conversion elements 26, 28 based on the current value of the ternary sequence.

(51) Alternatively, the light receiving unit 14 may comprise, for example, a control unit 30 being configured to selectively activate the conversion elements 26, 28 based on a corresponding control signal received from the switching unit 18.

(52) As described above, the switching unit 18 may be assigned to different components of the frequency comb generating device 10 that comprise an optical part and an electrical part which are separated by the light receiving unit 14.

(53) Hence, the representative embodiments shown in FIGS. 1 and 2 illustrate that the switching unit 18 is assigned to the optical part of the frequency comb generating device 10 whereas the switching unit 18 is assigned to the electrical part of the frequency comb generating device 10 in the representative embodiment shown in FIG. 3.

(54) The representative embodiment according to FIG. 4 illustrates that the switching unit 18 is assigned to the light receiving unit 14 itself while controlling the light receiving unit 14. Thus, the converting properties may be controlled via the switching unit 18.

(55) Parts of the frequency comb generating device 10 as shown in FIGS. 1 and 2, for example the pulsed optical light source 12, the sequence generator 16 and the switching unit 18, may also be used to only generate the modified optical frequency comb 22, e.g., conversion of the modified optical frequency comb 22 into the electrical frequency comb 20 may be omitted.

(56) This can be achieved by only performing the steps S1.sub.a and S2.sub.a as explained above with reference to FIGS. 1 and 5 or by only performing the steps S1.sub.b, S2.sub.b and S3.sub.b as explained above with reference to FIGS. 2 and 6.

(57) The resulting modified optical frequency comb 22 in time domain is missing some of its teeth compared to a full optical frequency comb, which translates to a shorter distance between the individual Dirac functions in frequency domain. Thus, by cancelling out some of the Dirac functions in time domain (or rather not generating them in the first place), a fine modified optical frequency comb 22 is achieved.

(58) The modified optical frequency comb 22 may then be forwarded to further devices, e.g. for the purpose of calibrating the devices.

(59) One or more components of the present disclosure, such as the control unit 30, may include, in some embodiments, logic for implementing the technologies and methodologies described herein. This logic can be carried out in either hardware or software, or a combination of hardware and software. In some embodiments, the control unit 30 includes one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), digital logic circuits, or the like, or any combinations thereof, and can include discrete digital or analog circuit elements or electronics, or combinations thereof.

(60) The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure which are intended to be protected are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure, as claimed.