Low-phase noise adjustable signal generator

Abstract

The invention relates to a phase-noise-free adjustable signal generator, comprising • an optical signal source (OQ) which coherently generates a plurality of optical signals (f1,f2,...), • an optical signal splitter (BS) which divides the incoming plurality of optical signals (f1,f2,...) into at least a first arm and a second arm, • a first bandpass filter (BPF1) located in the first arm and a second bandpass filter (BPF2) located in the second arm, wherein both the first bandpass filter (BPF1) and the second bandpass filter (BPF2) each allow one signal from the plurality of optical signals (f1,f2,...) to pass through, • wherein a first modulator (Δf) is further arranged in the first arm, wherein the modulator (Δf1) is controlled by an adjustable oscillator (f) ref ) is targeted, • an optical signal combiner (BC) which combines the signals from the first arm and the second arm to provide a phase-deficient output signal.

Description

[0001] The invention relates to a low-phase noise adjustable signal generator. background

[0002] Signal generators are required in many areas of technology. There are adjustable signal generators and fixed-frequency signal generators. It should be noted that the effort required to ensure stable operation of such signal generators depends on the available frequencies.

[0003] However, many applications require particularly low-noise signal generators.

[0004] Previous signal generators use reference oscillators in the low-frequency range <20 GHz and then upconvert them to the desired band using low-noise frequency multipliers. Even with an ideal (i.e., noise-free) frequency multiplier, the phase noise increases by 20log10(N). An example of this is the setup in the article "A fully integrated 77-GHz radar transmitter based on a low phase-noise 19.25-GHz fundamental VCO" by F. Starzer, A. Fischer, HP Forstner, H. Knapp, F. Wiesinger, and A. Stelzer, published in the 2010 IEEE Bipolar / BiCMOS Circuits and Technology Meeting (BCTM), Austin, TX, USA, 2010, pp. 65-68, doi: 10.1109 / BIPOL.2010.5667953.

[0005] This problem has already been recognized in the state of the art and other optical approaches have been presented.

[0006] A similar system is known from the article "Optical Millimeter-Wave Signal Generation Via Frequency 12-Tupling" by P.-T. Shih et al., published in Journal of Lightwave Technology, vol. 28, no. 1, pp. 71-78, Jan. 1, 2010, doi: 10.1109 / JLT.2009.2035452, in which the frequency multiplication is performed in the optical domain. In the first step, a dual-parallel Mach-Zehnder modulator is operated at its maximum power. This first achieves frequency multiplication. A further frequency multiplication is then achieved using four-wave mixing, an optical nonlinear Kerr effect. However, the fundamental problem remains unchanged, as the phase noise is also increased by 20log10(N).

[0007] However, approaches that exhibit high phase noise cannot be used to upconvert optoelectronic PLLs.

[0008] The article "A low-noise photonic heterodyne synthesizer and its application to millimeter-wave radar" by Kittlaus, Eric A., Eliyahu, Danny, Ganji, Setareh, Williams, Skip, Matsko, Andrey B., Cooper, Ken B., and Forouhar, Siamak, published in 2021 Nature Communications, 12, issue 1, pp. 1-10, https: / / EconPapers.repec.org / RePEc:nat:natcom:v:12:y:2021:i:1:d:10.1038_s41467-021-24637-0, describes a system that directs the light from two lasers of different frequencies onto a photodiode. The photodiode converts the optical frequency difference into an electrical signal. However, this system also has disadvantages: To generate a stable signal with low phase noise, the optical sources must be aligned with extreme precision using complex and expensive hardware. This increases both the costs and the complexity of the entire system.

[0009] Furthermore, a system that uses a mode-locked laser as a comb generator is known from the article "A fully photonics-based coherent radar system" by Ghelfi, P., Laghezza, F., Scotti, F. et al., published in Nature 507, pp. 341-345 (2014). https: / / doi.org / 10.1038 / nature13078. Two bands are selected using optical bandpass filters, a baseband signal is modulated using a Mach-Zehnder modulator (MZM), and the frequency is fine-tuned using a frequency shifter. However, the system shown cannot be used as a frequency generator, but can only be used to mix any baseband signal into a higher RF band. Furthermore, detuning is not possible.

[0010] In addition, none of the systems offers an optical output signal.

[0011] Based on this situation, the object of the invention is to provide a low-phase noise adjustable signal generator that makes it possible to generate arbitrarily high signals with low phase noise.

[0012] The object is achieved by a device according to claim 1. Further advantageous embodiments are the subject matter of the dependent claims.

[0013] The invention is explained in more detail below with reference to the figures, which show: Fig. 1 is a schematic block diagram of an embodiment of the invention with an electrical output, Fig. 2 a schematic block diagram of an embodiment of the invention with an optical output Fig. 3 a schematic block diagram of another embodiment of the invention with an electrical output, and Fig. 4 a schematic block diagram of another embodiment of the invention with an optical output.

[0014] The invention will be described in more detail below with reference to the figures. It should be noted that various aspects are described, each of which can be used individually or in combination. This means that any aspect can be used with different embodiments of the invention unless explicitly presented as a mere alternative.

[0015] Furthermore, for the sake of simplicity, reference will generally only be made to one entity in the following. Unless explicitly stated, the invention may also comprise several of the entities in question. Therefore, the use of the words "a," "an," and "another" is to be understood merely as an indication that at least one entity is used in a simple embodiment.

[0016] Where procedures are described below, the individual steps of a procedure can be arranged and / or combined in any order, unless the context explicitly indicates otherwise. Furthermore, the procedures can be combined with one another unless expressly indicated otherwise.

[0017] Numerical values ​​are generally not to be understood as exact values ​​but also include a tolerance of + / - 1% up to + / - 10%.

[0018] References to standards or specifications are to be understood as references to standards or specifications that are / were in effect at the time of the application and / or, if priority is claimed, at the time of the priority application. However, this does not imply a general exclusion of applicability to subsequent or replacing standards or specifications.

[0019] Fig. show exemplary embodiments of the invention.

[0020] In embodiments of the invention, a low-phase noise adjustable signal generator is provided.

[0021] The low-phase-noise adjustable signal generator according to the invention has an optical signal source OQ which coherently generates a plurality of optical signals f1,f2,...

[0022] For example, the optical signal source OQ can be an optical comb generator, e.g. an optical frequency comb can be realized using a mode-locked laser MLL or a Kerr resonator.

[0023] Furthermore, the low-phase-noise adjustable signal generator according to the invention has an optical signal splitter BS, which divides the incoming plurality of optical signals f1, f2,... into at least a first arm and a second arm.

[0024] Furthermore, the low-phase-noise adjustable signal generator according to the invention has a first bandpass filter BPF1, which is arranged in the first arm, and a second bandpass filter BPF2, which is arranged in the second arm, wherein both the first bandpass filter BPF1 and the second bandpass filter BPF2 each allow a signal from the plurality of optical signals f1, f2,... to pass.

[0025] By means of the (adjustable) first optical bandpass filter BPF1 and the second (adjustable) bandpass filter BPF2, (different) optical bands can be selected and, depending on the implementation, the frequency of one arm or both arms can be detuned.

[0026] A pre-adjustment of the current output frequency of the system can be determined by the difference between the two optical bands.

[0027] In the first arm, a first modulator Δf1 is further arranged, wherein the first modulator Δf1 is controlled by an adjustable oscillator f ref is controlled.

[0028] Furthermore, the low-phase noise adjustable signal generator according to the invention has an optical signal combiner BC, which combines the signals from the first arm and the second arm to provide a low-phase output signal.

[0029] Since the phase noise of the system of this invention follows the phase noise of the signal generator, the appropriate signal generator can be selected depending on the application requirements.

[0030] In one embodiment of the invention, the optical signal source OQ generates an optical comb of equidistant optical signals f1,f2,....

[0031] According to a further embodiment, the optical signal source OQ comprises a mode-locked laser or a Kerr resonator.

[0032] In one embodiment of the invention, the first bandpass filter BPF1 and / or the second bandpass filter BPF2 are adjustable.

[0033] In another embodiment of the invention, the optical signal splitter BS is a 3 dB splitter. Likewise, in one embodiment of the invention, the optical signal combiner BC can be a 3 dB combiner.

[0034] According to a further embodiment of the invention, the (first and / or second) modulator Δf provides single sideband modulation.

[0035] According to yet another embodiment of the invention - see Fig. 3 and Fig. 4 - a second modulator Δ f2 is arranged in the second arm, wherein the second modulator Δ f2 is supplied by a second signal source f arbThis means that it is also possible to apply / modulate an external modulation – e.g., a ramp or an OFDM signal – to the output signal using a second frequency shifter.

[0036] In one embodiment of the invention, the combined optical signal is fed to an opto-electrical conversion unit OE, in particular a photodiode, after the optical signal combiner BC. In the opto-electrical conversion unit OE, the optical difference frequency can be evaluated and made available as an electrical signal.

[0037] According to a further embodiment of the invention, the adjustable oscillator f ref an optoelectric PLL.

[0038] Preferably, the repetition frequency of the first MLL lies between fmax / N and fmax of the reference signal generator. Once the maximum or minimum output frequency of the reference signal generator is reached, a higher or lower optical band should be selected using the optical bandpass filters.

[0039] For low phase noise, a signal generator locked to either an atomic clock or an MLL is preferred, such as the OEPLL from the article "Locking of microwave oscillators on the interharmonics of mode-locked laser signals" by Bahmanian M, Kress C, and Scheytt JC, published in Optics Express. 2022 Feb;30(5):7763-7771. DOI: 10.1364 / oe.451894. PMID: 35299531.

[0040] The architecture presented in this invention makes it possible to generate signals of any magnitude with very low phase noise.

[0041] This invention is freely tunable, thus overcoming a major limitation of the prior art systems. The embodiment of the Fig. and Fig. They also have an optical output, which allows the optical signal to be transmitted and split over any distance, allowing a channel to be precisely characterized, for example.

[0042] Furthermore, the system can be designed to be completely monolithic and integrated, which can significantly reduce the overall costs.

[0043] In the embodiments of the invention, the phase noise is only slightly increased compared to the reference source, but significantly lower than in the prior art.

[0044] Since in the embodiments of the invention the signal can be realized by means of two lines of a laser, two lasers do not have to be locked onto each other.

[0045] The system can be used as a signal generator since all embodiments offer detunability.

[0046] In addition, in embodiments of the invention - see Fig. 2 and Fig. 4 - possible to provide optical outputs. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] A fully integrated 77-GHz radar transmitter based on a low phase-noise 19.25-GHz fundamental VCO“ der Autoren F. Starzer, A. Fischer, H. P. Forstner, H. Knapp, F. Wiesinger and A. Stelzer, veröffentlicht in 2010 IEEE Bipolar / BiCMOS Circuits and Technology Meeting (BCTM), Austin, TX, USA, 2010, pp. 65-68, doi: 10.1109 / BIPOL.2010.5667953

[0004] Optical Millimeter-Wave Signal Generation Via Frequency 12-Tupling“ der Autoren P. -T. Shih et al., veröffentlicht in Journal of Lightwave Technology, vol. 28, no. 1, pp. 71-78, Jan.1, 2010, doi: 10.1109 / JLT.2009.2035452

[0006] A low-noise photonic heterodyne synthesizer and its application to millimeter-wave radar“ der Autoren Kittlaus, Eric A., Eliyahu, Danny, Ganji, Setareh, Williams, Skip, Matsko, Andrey B., Cooper, Ken B. and Forouhar, Siamak, vveröffentlicht in 2021 Nature Communications, 12, issue 1, p. 1-10, https: / / EconPapers.repec.org / RePEc:nat:natcom:v:12:y:2021:i:1:d:10.1038_s41467-021-24637-0

[0008] A fully photonics-based coherent radar system" by Ghelfi, P., Laghezza, F., Scotti, F. et al., published in Nature 507, 341-345 (2014). https: / / doi.org / 10.1038 / nature13078

[0009] OEPLL from the article "Locking of microwave oscillators on the interharmonics of mode-locked laser signals" by Bahmanian M, Kress C, and Scheytt JC, published in Optics Express. 2022 Feb;30(5):7763-7771. DOI: 10.1364 / oe.451894. PMID: 35299531

[0039]

Claims

[1] Low-phase noise adjustable signal generator comprising • an optical signal source (OQ) which coherently generates a plurality of optical signals (f1,f2,...), • an optical signal splitter (BS) which divides the incoming plurality of optical signals (f1,f2,...) into at least a first arm and a second arm, • a first bandpass filter (BPF1) arranged in the first arm, and a second bandpass filter (BPF2) arranged in the second arm, wherein both the first bandpass filter (BPF1) and the second bandpass filter (BPF2) each allow a signal from the plurality of optical signals (f1, f2,...) to pass through, • wherein a first modulator (Δf1) is further arranged in the first arm, wherein the first modulator (Δf1) is controlled by an adjustable oscillator (f ref ) is controlled, • an optical signal combiner (BC) which combines the signals from the first arm and the second arm to provide a low-phase output signal. [2] Low-phase noise adjustable signal generator according to claim 1, characterized by that the optical signal source (OQ) generates an optical comb of equidistant optical signals (f1,f2,...). [3] Low-phase noise adjustable signal generator according to claim 1, characterized by that the optical signal source (OQ) comprises a mode-locked laser or a Kerr resonator. [4] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the first bandpass filter (BPF1) and / or the second bandpass filter (BPF2) are adjustable. [5] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the optical signal splitter (BS) is a 3dB splitter. [6] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the optical signal combiner (BC) is a 3dB combiner. [7] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the first modulator (Δf1) provides single sideband modulation. [8] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that a second modulator (Δ f2) is arranged in the second arm, wherein the second modulator (Δ f2) is controlled by a second signal source (f arb ) is controlled. [9] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the combined optical signal is fed to an opto-electrical conversion unit (OE) after the optical signal combiner (BC). [10] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the combined optical signal is fed to a photodiode (OE) after the optical signal combiner (BC) [11] Low-phase noise adjustable signal generator according to one of the preceding claims, characterized by that the adjustable oscillator (f ref ) has an opto-electrical PLL.

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