Electro-optical regulation loop

Abstract

The invention relates to an electro-optical regulation loop (1) with an input for light of a laser source (LD) and an optical IQ generator (OIQ) for generating two separate phase-shifted signals (E I , E Q ), which regulation loop further has an analog phase difference detector (Δφ) for determining the phase difference between the two phase-shifted signals (E I , E Q ), wherein the phase difference detector (Δφ) generates in operation a control variable, which is provided indirectly or directly to the optical IQ generator (OIQ) for readjusting the phase difference of the phase-shifted signals (E I , E Q ).

Description

Technical Field

[0001] This invention relates to an electro-optical modulation circuit. Background Technology

[0002] In many systems, regulation loops are required.

[0003] The following discussion uses a wireless array antenna as an example to illustrate a series of problems that may also exist at least in part in other systems, such as those in communication technologies, and the present invention can also provide advantageous solutions to these problems.

[0004] From a series of publications, such as Li et al.'s "Demonstration of a microwave photonic synthetic aperture radar based on photonic-assisted signal generation and stretch processing" published in Opt. Express 25, 14334-14340 (2017); Ghelfi et al.'s "A Fully Photonics-Based Coherent Radar System" published in Nature, vol. 507, pp. 341EP-, March 2014; Preusler et al.'s "Optical Signal Generation and Distribution for Large Aperture Radar in Autonomous Driving" published in the 12th German Microwave Conference (GeMiC), Stuttgart, Germany, 2019, pp. 154-157; and Zhang et al.'s work in Opt. Express... In the paper "Photonics-based Broadband Radar for High-Resolution and Real-Time Inverse Synthetic Aperture Imaging" published in 2017 (25, 16274-16281), a wireless system with phased array antennas on both the HF transmitting and receiving circuits is known, partially synchronized with an optical carrier generated at a base station. Signal processing of the received data is also performed at this base station. The analog signal path from the HF receiver to the base station can be implemented using glass fiber.

[0005] Furthermore, this wireless HF receiving system can also be used in harsh environmental conditions, such as in the automotive industry or aircraft manufacturing. In harsh environments, the system is affected by fluctuations in temperature, air pressure, and / or humidity.

[0006] It can be further determined that there are many (wireless) systems, namely QAM-based communication systems, such as fifth-generation mobile radio networks (see, for example, T. Asai’s “5G radio access network and its requirements on mobile optical network”, published at the 2015 International Conference on Optical Network Design and Modeling (ONDM), Pisa, 2015, pp. 7-11), and radar (see, for example, M. Ulrich and Bin Yang’s “IQ and array calibration for FMCW radar”, published at the 18th International Radar Symposium (IRS), Prague, 2017, pp. 1-10), in which the desired information exists in both in-phase and quadrature signals.

[0007] The known system presents a simulated real-time control algorithm to stabilize the IQ signal against environmental conditions, aging effects, and process variations.

[0008] For example, a system for optical transmission of IQ signals is known from US Patent 9,823,540 B2 and from the authors Chung, Hwanseok & Chang, Sun & Lee, Jong & Kim, Kwangjoon in Opt Express. 2013 Oct 21; 21(21):24962-8. doi:10.1364 / OE.21.02496, entitled "Field Trial of automatic bias control scheme for optical IQ modulator and demodulator with directly detected 112Gb / s DQPSK Signal". In this system, the control of the IQ modulator is performed purely electronically using a digital signal processing unit (DSP). This requires two photodiodes and an expensive analog-to-digital converter (ADC) with high bandwidth in the transmit branch to accomplish the task. For IQ generation, a digital DSP and an analog phase shifter are required. To achieve cooperation among these components, both high-bandwidth digital-to-analog converters (DACs) and high-bandwidth analog-to-digital converters (ADCs) are required. Both DACs and ADCs inherently possess quantization noise. However, this no longer guarantees a stable, fixed phase relationship between in-phase and quadrature phases. To avoid this problem, ADCs and DACs must have a large number of active bits (ENOBs).

[0009] Furthermore, the complex Gram-Schmidt orthogonalization method for compensating for IQ errors in coherent optical systems is known from the article "Effect of IQ Mismatch Compensation in an Optical Coherent OFDM Receiver" published by authors H.S. Chung, S.S. Chang, and K. Kim in IEEE Photonics Technology Letters, vol.22, no.5, pp.308-310, March 1, 2010. However, this orthogonalization method is highly susceptible to rounding errors, which can cause quantization noise in the ADC to compromise the stable phase relationship between in-phase and quadrature phases. To avoid this problem, a high-bandwidth ADC with high ENOB must be used.

[0010] Furthermore, from the article "Novel Pilot Scheme for Transmitter IQ Mismatch Compensation in Co-OFDM System" published by J. Lee, Y. Ha, B. Shin, S. Kim, B. Kim and W. Chung in IEEE Photonics Technology Letters, vol. 24, no. 17, pp. 1543-1545, September 1, 2012, it is known that an additional pilot signal is transmitted to characterize the channel, and then the IQ signal can be recovered accordingly.

[0011] Furthermore, from the article "Compensation for In-Phase / Quadrature Imbalance in Coherent-Receiver Front End for OpticalQuadrature Amplitude Modulation" published by authors MS Faruk and K. Kikuchi in IEEE Photonics Journal, vol.5, no.2, pp.7800110-7800110, April 2013, Art no.7800110, it is known that an adaptive FIR filter is used in a butterfly configuration, which allows for compensation of possible IQ imbalance.

[0012] Of the two systems mentioned above, only one static adjustment algorithm is known, which only considers the initial values. That is, it does not consider any possible changes caused by environmental influences.

[0013] A light emitter and a method for generating a light signal are known from patent EP 2 763 333 B1. This requires a compact arrangement of the laser diode and the phase arm. Furthermore, in a flawed solution, the monitoring signal must be generated by multiplying the carrier wave with the output signal. For determination, an error-prone digital phase detector is required.

[0014] Furthermore, US 2014 / 0037286 A1 discloses a method and system for monolithic integration of circuits for monitoring and controlling HF signals. Additionally, US 2018 / 0173023 A1 discloses bias control for an optical modulator. Finally, WO 03 / 049333 A1 discloses modulator control.

[0015] A drawback of all previously known systems is that satisfying a stable phase relationship between in-phase and quadrature phases requires significant design and material overhead to achieve near real-time phase stabilization. Furthermore, not all systems are equally well-suited for maintaining near real-time phase stability under (intensely) changing environmental conditions. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to avoid one or more problems in the prior art, and in particular to provide a low-cost solution.

[0017] The aforementioned technical problem is solved by the electro-optical modulation circuit according to independent claim 1. Advantageous designs are the subject of the dependent claims, the specification, and the drawings. Attached Figure Description

[0018] The invention will now be explained in more detail with reference to the accompanying drawings. In the drawings:

[0019] Figure 1 A block diagram of an electro-optical modulation circuit according to an embodiment of the present invention is shown.

[0020] Figure 2 A first embodiment of an optical IQ generator having an optical orientation coupler and a phase shifter for fine-tuning, according to an embodiment of the present invention, is shown.

[0021] Figure 3 A second embodiment of an optical IQ generator with a 1x2 MMI and a phase shifter according to an embodiment of the present invention is shown.

[0022] Figure 4 A first embodiment of a phase difference detector with an optical directional coupler is shown.

[0023] Figure 5 A second embodiment of a phase difference detector with a multimode interferometer is shown, and

[0024] Figure 6 A first embodiment of the error amplifier is shown, and

[0025] Figure 7 A second embodiment of the error amplifier is shown.

[0026] A phase shifter according to an embodiment of the present invention. Detailed Implementation

[0027] The invention will now be illustrated in more detail with reference to the accompanying drawings. It should be noted that different aspects are described, and these different aspects may be used individually or in combination. That is, each aspect may be used with different embodiments of the invention unless explicitly shown as a purely alternative. Furthermore, for simplicity, only one entity will generally be referred to below. However, unless explicitly stated otherwise, the invention may have multiple involved entities. In this regard, the use of the words “a,” “an,” and “of an” should only be understood as indicating that at least one entity is used in a simplified embodiment.

[0028] With regard to the methods described below, the steps of the methods can be arranged and / or combined in any order, provided that the context does not explicitly suggest otherwise. Furthermore, unless otherwise explicitly stated, these methods can be combined with each other.

[0029] Statements with numerical values ​​should not be interpreted as exact values, but rather include tolerances of + / -1% to + / -10%.

[0030] References to standards or specifications should be understood as references to standards or specifications applicable at the time of application and / or (if priority is claimed) at the time of priority application. However, this does not imply a general exclusion of the applicability of subsequent or alternative standards or specifications.

[0031] exist Figure 1 The diagram illustrates a more complex system that can be divided into two logical sub-regions. These are typically, for example, the left sub-region BS in the base station BS and the right sub-region FE in the front-end FE. Next, we will first consider the sub-regions on the front-end FE side, where similar elements can also be used on the base station BS side.

[0032] exist Figure 1 The diagram shows an electro-optic conditioning circuit 1 with other components. This electro-optic conditioning circuit has an input terminal for light from a laser source LD and a terminal for generating two separate phase-shift signals E. I E Q Optical IQ generator (OIQ).

[0033] The electro-optic conditioning circuit 1 also has a function for determining the two phase shift signals E. I E Q The (simulated) phase difference detector Δφ measures the phase difference between the phases, and generates control parameters during operation. These control parameters are provided indirectly or directly to the optical IQ generator OIQ for readjusting the phase shift signal E. I E Q The phase difference.

[0034] (e.g., an electrical signal V from an HF receiver) I and V Q It can be used in a Mach-Zender interferometer with a phase-stable signal E I and E Q Mixing, such as multiplication, is involved. Therefore, a stable optical IQ signal exists at node 2. The (simulated) phase difference detector Δφ checks the signal E. S and E M The relative phase, in this application, is 90°. The (optical) control signal of the (analog) phase difference detector Δφ is indirectly or directly provided to the optical IQ generator OIQ for readjusting the phase shift signal E. I E Q The phase difference is used to readjust the phase when needed (e.g., with the aid of a phase shifter). Therefore, these units form a simulated electro-optic closed-loop conditioning circuit that adjusts the signal E... S and E M The relative phase is adjusted to 90°. Therefore, coherent detection can be performed, for example, using a 2x4 MZI or an optical directional coupler. Here, the signal E... S It could be an optical carrier signal derived at node (1), whose phase has been readjusted.

[0035] The developed system does not require additional digital components for real-time phase stabilization. In other words, power consumption is reduced by eliminating the need for expensive and power-intensive DSPs. Furthermore, the bandwidth of the ADC used must still be limited to the signal V. I and V Q This satisfies Shannon's theorem, allowing the use of a cheaper ADC with lower power requirements. Furthermore, if the signal V... I and V Q If the analog circuitry is present, then the electro-optic conditioning circuit does not require a DAC. In other words, this can also lead to further cost savings in design and operation.

[0036] In one embodiment of the present invention, the electro-optic modulation circuit 1 further includes two optical modulators MZI1 and MZI2, wherein the first phase shift signal E of the two phase shift signals is modulated. I With the first input signal V I Multiply them, and combine the second phase-shifted signal E from the two phase-shifted signals. Q With the second input signal V Q Multiply.

[0037] In an embodiment of the present invention, the electro-optical modulation circuit 1 has two optical modulators MZI1 and MZI2, wherein the output signals of the two optical modulators MZI1 and MZI2 are guided to a common output terminal (e.g., Figure 1(as shown in the diagram) or a separate output terminal.

[0038] In particular, the optical modulators MZI1 and MZI2 can be Mach-Zender interferometers.

[0039] In one embodiment of the invention, the electro-optic adjustment circuit 1 further includes an error amplifier AMB. Here, the error amplifier AMB can receive control parameters from the phase difference detector Δφ. The error amplifier AMB can (during operation) generate control parameters, which are indirectly or directly provided to the optical IQ generator OIQ for readjusting the phase shift signal E. I E Q The phase difference. That is, the error amplifier AMB can (considering the control signal of the (analog) phase difference detector Δφ) provide readjustment with respect to changing environmental conditions. The error amplifier can be implemented, for example, as a differential amplifier.

[0040] exist Figure 6 and 7 In one embodiment of the invention shown, the error amplifier AMB has at least one photodiode PD0, PD1 and at least one transimpedance amplifier. TIA, where V is the differential voltage of the transimpedance amplifier TIA. out Control parameters for the optical IQ generator OIQ are generated. Here, the implementation of the transimpedance amplifier TIA of the error amplifier AMB can be based on bipolar transistors Q1 and Q2 (…). Figure 6 ) and based on (C)MOS transistors Q1, Q2 ( Figure 7 This is achieved through [the method described in the attached diagram]. DAC and The unit allows for initialization to persistently compensate the (analog) phase difference detector. Possible asymmetries and / or process variations and / or error variations in transistors Q1, Q2 and photodiodes PD0, PD1 of the AMB amplifier.

[0041] When the input signal |E of photodiode PD0 Δφ | 2 When the value is approximately zero, the circuit is in a static state and V... out =0V. Now, when |E = 0V due to environmental influences or process changes, etc. Δφ | 2 When the current is not equal to 0, the photodiode PD0 generates a current I. Δφ ~R|E Δφ | 2 Therefore, node V x The voltage at point V is higher than that at node V. y The voltage at that point is small, and the differential voltage Vout Increase. This output voltage can only be used as a control parameter for controlling the optical IQ generator. For example, the differential voltage V. out This can be used to control one or more phase shifters in the optical IQ generator (OIQ) of the front-end FE and / or the phase shifter (PS) in the base station BS. A closed-loop electro-optic conditioning circuit also exists. For stability reasons, it may be necessary to appropriately select Z. TIA (s) ensures that the system meets the user-selected specifications regarding static settling error, rise rate, overshoot, etc. In particular, Z should also be selected. TIA (s) makes the electro-optical regulation circuit stable.

[0042] In one embodiment of the invention, the optical IQ generator OIQ has an optical orientation coupler RK and a phase shifter PS. The phase shifter PS can provide fine-tuning. All components can be integrated on a single chip. Figure 2 An optical IQ generator (OIQ) based on an optical directional coupler is shown. Since the optical directional coupler RK already produces a 90° phase difference, in this type of optical IQ generation, the phase shifter only needs to compensate for environmental effects, thus the expected control voltage is low.

[0043] In an alternative embodiment of the invention, the optical IQ generator (OIQ) includes an optical power divider, such as a multi-mode interferometer (MMI), particularly a 1x2 MMI or a Y-splitter, and a phase shifter (PS). The phase shifter (PS) can provide fine-tuning. All components can be integrated onto a single chip. For example, since a 1x2 MMI does not produce a phase difference between the two outputs, a phase shift must be provided by additional components. Here, this can be generated together with the phase shifter (PS), thus providing more than just fine-tuning in this case. Figure 2 The implementation differs from that in other systems, so a higher control voltage can be expected.

[0044] In another embodiment of the invention, an optical (analog) phase difference detector Δφ (such as...) Figure 4 (As shown) has an optical directional coupler. If signal E I and E Q With a phase difference of π / 2 + 2πn between them, then |E Δφ | 2 =0.

[0045] In another embodiment of the invention, the (simulated) phase difference detector Δφ (such as...) Figure 5 (As shown) It has an optical power splitter, such as a multimode interferometer (MMI) or a Y-splitter. Its operating principle is similar to... Figure 4The working principle of an optical Δφ detector with a directional coupler. If signal E I and E Q If each has a specific phase difference with respect to the others, for example, π / 2 + 2πn, then |E Δφ | 2 =0. Here, the optical power divider can be designed such that only a certain percentage of the energy is directed to the 2x2 MMI, thus reserving most of the energy for the optical IQ channel.

[0046] Of course, a hybrid system, which is a mixture of two systems, can also be chosen.

[0047] The inventions described above can be used in both wired and wireless systems.

Claims

1. An electro-optic modulation circuit (1), said electro-optic modulation circuit having an input terminal for light from a laser source (LD) and a terminal for generating two separate phase-shift signals (EL). I E Q The optical IQ generator (OIQ) of the system, wherein the adjustment loop also has an analog phase difference detector (Δφ), which is used to determine the two phase shift signals (E). I E Q The phase difference between ) and , where, The simulated phase difference detector (Δφ) generates control parameters during operation, which are indirectly or directly provided to the optical IQ generator (OIQ) for readjusting the phase shift signal (E). I E Q The phase difference of ) The adjustment circuit also includes two optical modulators (MZI1, MZI2), wherein the first phase-shift signal (E) of the two phase-shift signals is converted into an optical modulator. I Multiply by the first input signal (V) I ), and the second phase shift signal (E) of the two phase shift signals Q Multiply by the second input signal (V) Q ).

2. The electro-optical modulation circuit (1) according to claim 1, characterized in that, The regulation circuit also has two optical modulators (MZI1, MZI2), wherein the output signals of the two optical modulators (MZI1, MZI2) are guided to a common output terminal.

3. The electro-optical modulation circuit (1) according to claim 1, characterized in that, The regulation circuit also has two optical modulators (MZI1, MZI2), wherein the output signals of the two optical modulators (MZI1, MZI2) are directed to separate output terminals.

4. The electro-optical adjustment circuit (1) according to any one of claims 1 to 3, characterized in that, The optical modulators (MZI1, MZI2) are Mach-Zehnder interferometers.

5. The electro-optical adjustment circuit (1) according to any one of claims 1 to 4, characterized in that, The adjustment loop also includes an error amplifier (AMB) capable of receiving control parameters from the analog phase difference detector (Δφ), and wherein the error amplifier (AMB) generates control parameters during operation, which are indirectly or directly provided to the optical IQ generator (OIQ) for readjusting the phase shift signal (E). I E Q The phase difference.

6. The electro-optical modulation circuit (1) according to claim 5, characterized in that, The error amplifier (AMB) has at least one photodiode (PD0, PD1) and at least one transimpedance amplifier, wherein the differential voltage of the transimpedance amplifier generates control parameters for the optical IQ generator (OIQ).

7. The electro-optical modulation circuit (1) according to any one of claims 1 to 6, characterized in that, The optical IQ generator (OIQ) has an optical orientation coupler and a phase shifter.

8. The electro-optical modulation circuit (1) according to any one of claims 1 to 6, characterized in that, The optical IQ generator (OIQ) includes a multimode interferometer (MMI) and a phase shifter.

9. The electro-optical modulation circuit (1) according to any one of claims 1 to 6, characterized in that, The optical IQ generator (OIQ) has an optical power divider and a phase shifter.

10. The electro-optical modulation circuit (1) according to any one of the preceding claims, characterized in that, The simulated phase difference detector (Δφ) has an optical directional coupler.

11. The electro-optical modulation circuit (1) according to any one of claims 1 to 7, characterized in that, The simulated phase difference detector (Δφ) has a multimode interferometer (MMI).

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