A device that converts optical signals into electrical signals.
The electro-optic mixer addresses the inefficiencies of existing systems by directly converting optical signals to electrical signals using switchable matching networks, reducing complexity and power consumption for efficient wireless data transmission.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-02-01
- Publication Date
- 2026-03-31
AI Technical Summary
Existing optical signal conversion systems for wireless data transmission are complex, costly, and inefficient, with components like transimpedance amplifiers and Mach-Zehnder modulators increasing system size, noise, and power consumption, making them unsuitable for low-power applications.
An electro-optic mixer with switchable matching networks and decoupling elements that convert optical signals directly to electrical signals without a transimpedance amplifier, using H-bridges for mixing and adjustable bandwidth, allowing for frequency selection and power efficiency.
The system reduces complexity, size, noise, and power consumption, enabling efficient conversion and frequency adjustment, suitable for low-power applications and integrated circuits.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to an electro-optical mixer.
Background Art
[0002] In many use cases, optical data is transmitted over long distances using optical fibers. Optical fibers are also used in the radar field for distributing a local oscillator signal (LO). To transmit data or radar signals wirelessly, the optical signal must be converted to an electrical signal before being up-converted.
[0003] The conversion of an optical signal to an electrical signal is performed using a transimpedance amplifier (TIA). Next, up-conversion to the desired RF band is performed using an electrical mixer. The output signal from the TIA can then be further pre-processed using a DC-balanced buffer and a variable gain amplifier (VGA), after which this signal is multiplied by another signal using a mixer.
[0004] A block diagram showing the most relevant prior art is shown in FIG. 1. In this case, the optical signal is routed via fiber from a switching center CO to an optical baseband receiver BPR, where it is pre-processed (by a processing method using, as an example, a photodiode, a transimpedance amplifier, a DC-balanced buffer, and a variable gain amplifier (VGA)), and then up-converted to the desired RF band at an electrical stage TX using a mixer (and a further signal). In this case, the optical baseband receiver BPR and the electrical stage TX are provided, for example, in a BiCMOS integrated circuit.
[0005] In this process, both the transimpedance amplifier and the electrical mixer increase the overall complexity of the system. Further, the transimpedance amplifier requires a separate chip area of about 0.25 mm , , ,
[0004] ,
[0003] , , , 2 ,
[0006] , , , ,
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[0005] in size, which increases the cost of such a system.
[0006] Furthermore, each component has a specific bandwidth. By interconnecting two components, the overall system bandwidth is determined by the bandwidth of the individual components, and therefore by the component with the lowest bandwidth. To detect high-frequency optical signals, a separate TIA must be used to minimize the effects of parasitic capacitance. This TIA generates additional noise.
[0007] These components also generate power losses and impair system efficiency. Therefore, this solution is not suitable for low-power applications or battery-operated systems. It should also be noted that providing a transimpedance amplifier as a separate component increases the risk of overall system failure. In some applications, it may be necessary to use only a specific frequency band from an optical signal of any desired width. This is typically achieved using a filter behind the TIA. This channel selection filter is based on passive components.
[0008] Given that actual passive components always have parasitic resistance, noise increases enormously. Furthermore, (passive) components require a large chip area, thereby significantly increasing system costs. In some applications, it may be necessary to turn off a single unit while data signals and / or clock signals are still being transmitted to other systems via fiber. Various techniques can be used to implement this. A Mach-Zehnder modulator (MZM) prior to the photodiode allows the optical power in the photodiode to be individually set to 0. Such a technique is shown in Figure 2. Here, the optical input signal from the laser diode LD is led to the Mach-Zehnder modulator MZM. The output signal from the Mach-Zehnder modulator MZM is also optical and must still be converted to an electrical signal using a photodiode PD. This electrical signal is a current signal. For further processing, this current signal must still be converted to a voltage signal in a transimpedance amplifier.
[0009] Given that Mach-Zehnder modulators require a very large area and very high control voltages, this solution is disadvantageous, especially for integrated circuits and highly scaled technologies. Therefore, controlling a Mach-Zehnder modulator requires a voltage in the 2-3V range. In modern transistors with dimensions in the nanometer range, this voltage range can already lead to failure of the driver components. Furthermore, these driver components increase mixer noise.
[0010] Furthermore, the MZM requires a chip area of several square millimeters, which increases the overall system cost. Finally, because the MZM only has a bandwidth in the range of less than 30 GHz, this solution is unsuitable for HF applications. As an alternative to a Mach-Zehnder modulator, the supply voltage can be turned off.
[0011] However, a drawback of this technique is that a strong current must flow through the corresponding switching transistor. Cooling capacity must be planned to compensate for the corresponding power dissipation in the transistor, which significantly increases the complexity of the system. Yet another alternative is to use an analog latch to freeze the signal in a DC state after the transimpedance amplifier.
[0012] However, analog latches are very expensive in the mm wave range, significantly increasing system costs. Furthermore, in known systems, since matched networks are designed only as bandpass, as long as they are available, it is, in principle, impossible to select different frequency bands. Based on this, the object of the present invention is to identify solutions that avoid one or more problems in the prior art. [Brief explanation of the drawing]
[0013] This objective is achieved by an electro-optic mixer having the electrical output described in claim 1. Further advantageous embodiments of the present invention are the subject of the dependent claims, specification, and drawings. Embodiments of the present invention will be described by example with reference to the accompanying drawings shown below. [Figure 1] This is an embodiment based on prior art. [Figure 2] This is a further embodiment of the prior art. [Figure 3] This is a schematic diagram of an embodiment of the present invention. [Figure 4] This is a further schematic diagram of a further embodiment of the present invention. [Modes for carrying out the invention]
[0014] The present invention will be described in more detail below with reference to the drawings. It should be noted that various embodiments will be described that can be used individually or in combination. In other words, any embodiment can be used in various embodiments of the present invention unless explicitly stated as a purely alternative.
[0015] Furthermore, for the sake of brevity, only one entity will be referred to in principle below. However, unless explicitly stated otherwise, the present invention may also include multiple related entities. In this regard, the use of the words “a,” “an,” and “one” should be understood only as indicating that at least one entity is used in a single embodiment.
[0016] As long as the method is described below, the individual method steps can be arranged and / or combined in any desired order unless the context explicitly states otherwise. Furthermore, unless otherwise specified, the methods can be combined with each other.
[0017] As a general rule, specifications containing numerical values should not be understood as exact values, but rather as including tolerances of + / -1% to + / -10%. References to standards, specifications, or norms should be understood as references to standards, specifications, or norms that were valid at the time of filing and / or at the time of priority filing, if priority is claimed. However, this should not be understood as a general exclusion of applicability to subsequent or substituting standards, specifications, or norms.
[0018] Figures 3 and 4 show an electro-optic mixer 1 having an electrical output according to an embodiment of the present invention. The electro-optic mixer 1 comprises at least one photodiode PD for converting an incident light signal. The electro-optic mixer 1 further comprises at least one first terminal and at least one second terminal, thereby allowing a first voltage source V1 to be connected (in each case) to the first terminal or to each of the first terminals, and a second voltage source V2 to be connected (in each case) to the second terminal or to each of the second terminals.
[0019] Alternatively, the first power supply I1 may be connected to the first terminal or to each of the first terminals (in each case), and the second power supply I2 may be connected to the second terminal or to each of the second terminals (in each case).
[0020] The electro-optic mixer 1 also includes at least one terminal for small-signal ground potentials for the first voltage source V1 and the second voltage source V2. The small-signal ground potential can be any desired potential, but in particular, it can be the ground potential of the entire circuit.
[0021] The electro-optical mixer 1 includes a first partial matching network represented by Z2 and Z4 disposed on the anode side of the photodiode PD. As a result, a part of the first partial matching network (in this case Z2) can be switchably connected to the terminal for the second voltage source V2 using the switch S2. Thus, another part of the first partial matching network (in this case Z4) can be switchably connected to the terminal for the small-signal ground potential using the switch S2.
[0022] The electro-optical mixer 1 includes a second partial matching network represented by Z1 and Z3 disposed on the cathode side of the photodiode PD. As a result, a part of the second partial matching network (in this case Z1) can be switchably connected to the terminal for the first voltage source V1 using the switch S1. Thus, another part of the second partial matching network (in this case Z3) can be switchably connected to the terminal for the small-signal ground potential using the switch S1'.
[0023] In this case, the matching network must have impedance matching, which means that the AC voltage separation by a single capacitor (as a decoupling element) should not be understood as the matching network. The elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are characterized by inductive characteristics and / or resistive characteristics and / or capacitive characteristics.
[0024] The electro-optical mixer 1 further includes a first decoupling element C1 disposed on the cathode side of the photodiode PD and a second decoupling element C2 disposed on the anode side of the photodiode PD. The first decoupling element C1 and the second decoupling element C2 are characterized by inductive characteristics and / or resistive characteristics and / or capacitive characteristics.
[0025] During operation, an electrical output signal can be provided between the sides facing outward from the photodiodes PD of the first decoupling element C1 and the second decoupling element C2. Using the presented arrangement, a simple, space-saving and frequency-adjustable solution can be provided, which can also be switched off.
[0026] In one embodiment of the invention, the electrical output signal is supplied to the transimpedance amplifiers TIA1, TIA2 respectively. In a further embodiment of the invention, the switches S1, S2, S1´, S2´ are designed as any desired switching elements, but in particular as semiconductor switches, for example as transistors.
[0027] According to one embodiment of the invention, the circuit can operate as an optical receiver when appropriate switch selection is provided. According to yet another embodiment of the invention, the electro-optical mixer can be stopped using the switches S1, S2, S1´, S2´. Without limiting the generality of the invention, the switch positions of the switches S1, S2, S1´, S2´ can be controlled by any desired signal, in particular by an optical signal and / or by an electrical signal and / or by a mechanical signal.
[0028] In one embodiment of the invention, the elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are characterized by inductive properties, whereby the inductive properties are provided by coils and / or lines.
[0029] In one embodiment of the invention, the elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are alternatively or additionally characterized by capacitive properties, whereby the capacitive properties are provided by capacitors and / or lines.
[0030] Without limiting the generality of the present invention, the system is implemented using semiconductor technology, such as BiCMOS. However, the system can also be implemented using individual components. However, obviously, the electro-optic mixer can also be partially integrated and may include individual elements as separate components, for example.
[0031] In all embodiments, the system can be configured to operate using any desired polarization. The system can, in particular, operate using pure TE polarization or pure TM polarization. The system can also operate using both pure TE and pure TM polarization, thus providing, for example, a process for polarization multiplexing.
[0032] In the embodiment shown as an example in Figure 3, an optical signal RF is detected in a photodiode PD and converted into an electrical signal. A first and second partially matched network couple the electrical signals and generate or select a frequency band through impedance matching provided by the first and second partially matched networks.
[0033] In the example shown in Figure 3, the impedances Z1...Z4 are formed by inductors (but not limited to inductors), but the implementation of impedances Z1...Z4 is not limited to coils and capacitors; other passive components can also be used.
[0034] As a result of the anode and cathode impedances of the photodiode PD depending on the operating point, the channel / frequency band can be selected by changing the voltages V1, V2 or currents I1, I2. This is because, for each different voltage, the matching network formed from the first and second partially matching networks interacting with the impedance of the photodiode PD resonates with (other frequencies).
[0035] The actual mixing process is provided by an H-bridge consisting of S1, S2, S1', S2', Z1, Z2, Z3, Z4, and PD.
[0036] If voltage sources V1 and V2 each provide voltages different from 0, which are larger in magnitude compared to the small-signal ground potential, the following may be observed: When switches S1 and S1' are closed and the remaining switch is open, the photodiode PD is in the cutoff direction, and a dark current is detected in addition to the photocurrent. However, when switches S2 and S2' are closed and the remaining switch is open, the diode is operating in the forward direction, the current is dominated by the diode current, and as a result, the photocurrent is no longer detectable.
[0037] However, when switches S1' and S2' are closed and the other switches are open, the bandwidth of the photodiode PD decreases, so only low-frequency signals can be detected. However, when switches S2 and S2' are closed (for a long time) and the remaining switches are open, photo < diode In this case, mixer 1 is turned off.
[0038] These explanations clearly also apply to positive currents I1 and I2 that are not equal to zero. Naturally, it should be noted that if voltage sources V1 and V2 each provide voltages that are not equal to zero (compared to the small-signal mass potential), the explanations specified above are also valid, and the indices should be swapped accordingly. Clearly, these explanations also apply to negative currents I1 and I2 that are not equal to zero.
[0039] Figure 4 shows a further embodiment of the present invention. In this case, the passive core remains, similar to Figure 3. However, when the capacitance is very large, i.e., C1, C2 → ∞, and impedances Z1, Z2, Z3, Z4 (e.g., inductance) are appropriately selected, broadband signals can also be detected.
[0040] In this case, the current can be converted to voltage using transimpedance amplifiers TIA1 and TIA2. However, if power is desired at the output, the voltage can be converted to power at a specific impedance by an optional matching network (at the outputs of transimpedance amplifiers TIA1 and TIA2).
[0041] In addition, the system is not limited to just two transimpedance amplifiers (TIAs). Any desired number of TIAS, sensitive to various frequencies, can be used. After selecting the appropriate transimpedance amplifiers, channel selection can be performed. The embodiment shown in Figure 4 enables both broadband and narrowband operation.
[0042] The embodiments presented herein utilize H-bridges as opposed to Gilbert cells or nonlinearized components. Furthermore, the system can be implemented as a broadband system or using channel selection. The system also offers the option of being deactivatable.
[0043] The electro-optic mixer according to the present invention features an H-bridge that enables direct multiplication of an optical signal with an electrical signal without the presence of a transimpedance amplifier. The electro-optic mixer according to the present invention consumes less power, is less complex, and produces less noise. Depending on the size of the TIA or Mach-Zehnder modulator, the chip area is also smaller. The bandwidth can be adjusted by using a suitable partial matching network. Similarly, the bandwidth can be influenced by the semiconductor technology used. When transistors are used as switches S1, S2, S1', S2', the voltage (compared to a Mach-Zehnder modulator) should be sufficient to reach only a voltage of >3UT (≒75mV), which is significantly less than 2-3V.
Claims
1. A device (1) that converts an optical signal into an electrical signal, - A photodiode (PD) that converts the incident light signal, - The first terminal and, • The second terminal and, - Connected to the first terminal and the first current (I 1 A first power supply that generates ) - Connected to the second terminal and the second current (I ２ A second power supply that generates ) - Multiple terminals for ground potential for the first power supply and the second power supply, - A first partially matched network (Z) located on the anode side of the photodiode (PD) ２ Z ４ ) and the first partially matched network (Z ２ ) part of the switch (S ２ The terminal for the second power supply can be switchedly connected by the first partially matched network (Z ４ Another part of ) is the switch (S' ２ A first partially matched network, which can be switchedly connected to one of the terminals for the ground potential, ・ A second partial matching network (Z １ , Z ３ ) disposed on the cathode side of the photodiode (PD), wherein a part of the second partial matching network (Z １ ) is switchably connectable to the terminal for the first power supply by a switch (S １ ), and another part of the second partial matching network (Z ３ ) is switchably connectable to the other terminal for the ground potential by a switch (S' １ ); a second partial matching network - A first decoupling element positioned on the cathode side of the photodiode (PD), - A second decoupling element disposed on the anode side of the photodiode (PD), A device for converting optical signals into electrical signals, which, during operation, can provide an electrical output signal to the outside of the first decoupling element and the second decoupling element as seen from the photodiode (PD).
2. The aforementioned electrical output signal is transmitted to a transimpedance amplifier (TIA) １ TIA ２ The apparatus according to claim 1, characterized in that it is supplied to each of the following.
3. The aforementioned switch (S １ S ２ , S' １ , S' ２ The apparatus according to claim 1, characterized in that the ) is designed as any desired switching element.
4. The aforementioned switch (S １ S ２ , S' １ , S' ２ The apparatus according to claim 1, characterized in that the ) is designed as a semiconductor switch.
5. The apparatus according to claim 1, characterized in that it can operate as an optical receiver when an appropriate switch selection is given.
6. The aforementioned switch (S １ S ２ , S' １ , S' ２ The apparatus according to claim 1, characterized in that it can be stopped by ).
7. The aforementioned switch (S １ S ２ , S' １ , S' ２ The apparatus according to claim 1, characterized in that the position of ) can be controlled by any desired signal.
8. The aforementioned switch (S １ S ２ , S' １ , S' ２ The apparatus according to claim 1, characterized in that the position of ) can be controlled by an optical signal and / or an electrical signal and / or a mechanical signal.
9. The apparatus according to claim 1, characterized in that the photodiode, the first and second terminals, the first and second power supplies, the plurality of terminals, the first and second partially matched networks, and the first and second decoupling elements are implemented using semiconductor technology.
10. The apparatus according to claim 1, characterized in that it is implemented using individual components.
11. The apparatus according to claim 1, characterized in that the photodiode can operate using any desired polarization.
12. The apparatus according to claim 1, characterized in that the photodiode can operate using pure TE polarization and / or pure TM polarization.
Citation Information
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