Device including a ring optical resonator

Abstract

An apparatus includes an optical resonator having four ports, the four ports including a first port, a second port, a third port, and a fourth port. A first electronic circuit is configured to calculate first information representing a power difference between optical signals provided by two of the four ports. A method of operating the apparatus is also disclosed.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from French patent application No. 1856692, filed on July 19, 2018, which is incorporated herein by reference. Technical Field

[0003] The present disclosure generally relates to devices including ring optical resonators, for example, gyroscopes including such ring optical resonators. Background Art

[0004] Gyroscopes that include a ring optical resonator are known. In such gyroscopes, when the ring optical resonator is not rotating about its axis and an optical signal propagates through the resonator, the resonator exhibits a resonant wavelength, the interval between two consecutive resonant wavelengths being constant and generally referred to as the free spectral range (FSR). Considering a fixed-order resonance (having a resonant wavelength λR at rest), when the ring optical resonator is rotated about its axis, the optical signal propagating in the resonator in the same direction as the rotation experiences an increase in the resonant wavelength relative to the wavelength λR at rest, while the optical signal propagating in the resonator in the opposite direction to the rotation experiences a decrease in the resonant wavelength relative to the wavelength λR at rest. The difference between the resonant wavelength λR at rest and the resonant wavelength during rotation depends on the rotational speed of the resonator, making it possible to determine the rotational speed of the gyroscope. Summary of the Invention

[0005] Embodiments overcome all or part of the disadvantages of known devices comprising optical resonators, and in particular known devices comprising ring optical resonators using, for example, resonant ring waveguides.

[0006] Embodiments provide a gyroscope including a resonant ring waveguide, wherein the rotational speed is determined with higher accuracy than known gyroscopes including a resonant ring waveguide.

[0007] Embodiments provide a gyroscope including a resonant ring waveguide in which certain variations, such as temperature variations, do not affect the calculation of rotational speed.

[0008] Embodiments provide a gyroscope including a resonant ring waveguide, wherein measurement noise is reduced relative to measurement noise of known gyroscopes including a resonant ring waveguide.

[0009] An embodiment provides an apparatus including: an optical resonator having a first port, a second port, a third port, and a fourth port; and a first electronic circuit for calculating first information representing a power difference between optical signals provided by two of the four ports.

[0010] According to one embodiment, an optical resonator comprises a first ring waveguide.

[0011] According to one embodiment, the resonator further comprises: a second waveguide coupled to the first waveguide and linking the first port to the second port; and a third waveguide coupled to the first waveguide and linking the third port to the fourth port.

[0012] According to one embodiment, when the first optical signal is provided to the first port, the first signal is transmitted to the second port and the third port.

[0013] According to one embodiment, the second port and the third port form said two ports of the four ports.

[0014] According to one embodiment, the apparatus further comprises a second electronic circuit for calculating second information representing a power difference between the optical signals provided by the other two of the four ports.

[0015] According to one embodiment, the apparatus further comprises a laser source linked to the first port and the second port.

[0016] According to one embodiment, the laser source has a wavelength that is adjustable according to a control signal.

[0017] According to one embodiment, the resonant wavelength of the resonator is adjustable according to a control signal.

[0018] According to one embodiment, the second circuit determines the control signal based on the second information.

[0019] According to one embodiment, the second circuit determines the control signal such that the second information represents zero disparity.

[0020] According to one embodiment, the device further comprises at least one optical modulator.

[0021] According to one embodiment, the optical modulator is configured such that the optical signals provided to the first port and the second port are modulated at different frequencies.

[0022] According to one embodiment, the first circuit is configured to determine the angular velocity based on the first information.

[0023] An embodiment provides a gyroscope comprising the apparatus as defined above.

[0024] An embodiment provides an integrated circuit comprising the apparatus as defined above or the gyroscope as defined above.

[0025] An embodiment provides a method for determining a rotational speed of an apparatus as defined above or a gyroscope as defined above, wherein the rotational speed is determined based on first information. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments taken in conjunction with the accompanying drawings, in which:

[0027] Figure 1 An embodiment of a device comprising a ring optical resonator is schematically presented;

[0028] Figure 2 Shown Figure 1 a variation in the power transmission coefficient of an optical signal between ports of the device as a function of wavelength; and

[0029] Figure 3 A further embodiment of a device comprising a ring optical resonator is schematically presented. DETAILED DESCRIPTION

[0030] In different drawings, the same elements are represented by the same reference numerals. In particular, structural and / or functional elements common to different embodiments may be represented by the same reference numerals and may have the same structure, size and material properties.

[0031] For clarity, only those steps and elements useful for understanding the described embodiments are shown and described in detail. In particular, the operation of current optical and electro-optical components such as modulators, switches, couplers, splitters, circulators, etc. is not described.

[0032] Unless otherwise specified, when referring to two elements being connected to each other (electrically or optically), this means being directly connected without intermediate elements other than conductors or waveguides, and when referring to two elements being linked to each other (electrically or optically), this means that the two elements may be connected or linked (electrically or optically) via one or more other elements. Additionally, when referring to two elements being linked or connected together without further detail, this means that the two elements are optically linked or connected.

[0033] Unless otherwise stated, when referring to two waveguides being coupled together, this means that the waveguides include portions that are sufficiently close to each other that a signal passes from one waveguide to the other by evanescent coupling.

[0034] Unless otherwise indicated, the terms "about," "approximately," and "on the order of" are used herein to indicate a tolerance of plus or minus 10%, preferably plus or minus 5%, of the value in question.

[0035] Figure 1 An embodiment of a device 1 , here a gyroscope comprising a ring optical resonator, is schematically presented.

[0036] Device 1 includes an optical resonator 101 having four ports 103, 105, 107, and 109. More specifically, resonator 101 includes a ring waveguide 111, a waveguide 113, and a waveguide 115. Waveguide 113 is coupled to waveguide 111 and links the input / output ports 103 and 105 of resonator 101. Waveguide 115 is coupled to waveguide 111 and links the output ports 107 and 109 of resonator 101.

[0037] Ports 103 and 105 are linked to an input port 117 of the apparatus 1, which is linked (preferably connected) to a laser source 119 which may or may not form part of the apparatus 1. As an example, the laser source 119 provides a signal having an infrared wavelength (e.g., in the range of about 750 nm to about 3000 nm), it being understood that the apparatus described may be adapted to operate at other wavelengths.

[0038] In this embodiment, ports 103 and 105 are further connected to respective photodetectors 121 ( PD1 ) and 123 ( PD2 ), for example photodiodes. A connection network 125 enables linking ports 103 and 105 to port 117 and to respective photodetectors 121 and 123 .

[0039] exist Figure 1 In the example shown, connection network 125 includes an optical splitter 127 and two optical couplers 129 and 131 (here, X couplers). The input of optical splitter 127 is connected (preferably connected) to port 117. The output of splitter 127 is connected to port 103 via coupler 129, which also connects port 103 to photodetector 121. The other output of splitter 127 is connected to port 105 via coupler 131, which also connects port 105 to photodetector 123.

[0040] Ports 107 and 109 are linked (preferably connected) to respective photodetectors 133 ( PD3 ) and 135 ( PD4 ) (eg, photodiodes).

[0041] Device 1 includes an electronic circuit 137 (CIRC1). Circuit 137 is configured to calculate information representing the power difference between the two output signals of resonator 101 provided by ports 105 and 107. More specifically, circuit 137 calculates the difference between the output signals of photodetectors 123 and 133 (e.g., currents I2 and I3, respectively, representing the optical power received by these photodetectors). Therefore, circuit 137 is electrically linked (preferably electrically connected) to photodetectors 123 and 133 to receive output signals I2, I3.

[0042] The device 1 further includes an electronic circuit 139 (CIRC2). Circuit 139 calculates information representing the power difference between the two output signals of resonator 101 provided by ports 103 and 109. More specifically, circuit 139 is configured to calculate the difference between the output signals of photodetectors 121 and 135 (e.g., currents I1 and I4, respectively, representing the optical power received by these photodetectors). Therefore, circuit 139 is electrically linked (preferably electrically connected) to photodetectors 121 and 135 to receive output signals I1, I4. As an example, circuit 139 implements a feedback loop that receives I1 and I4 as input signals and outputs a control signal cmd, and the calculation of the difference between signals I1 and I4 is implemented in the feedback loop.

[0043] In this embodiment, the resonator 101 has an adjustable resonant wavelength, considering a fixed-order resonance. The value of the resonant wavelength of the resonator 101 (in other words, the value of the resonant wavelength of the waveguide 111) is determined by a control signal cmd provided by the circuit 139. As an example, the waveguide 111 includes at least one phase modulator 141, such as at least one accumulation, injection, or loss phase modulator, or preferably at least one thermal phase modulator, which receives the signal cmd.

[0044] In an alternative embodiment not shown, the laser source 119 has an adjustable operating wavelength. In this variant, the value of the operating wavelength of the source 119 is determined by a control signal provided by the circuit 139. This alternative embodiment can be implemented in combination or independently, given that the resonant wavelength of the resonator 101 is adjustable for a fixed-order resonance.

[0045] In apparatus 1, when source 119 provides an optical signal L to port 117, connection network 125, in this example, provides corresponding signals L1 and L2 to respective ports 103 and 105 via respective couplers 129 and 131. A portion of the power of signal L1 is then transmitted from port 103 to port 105 in this example, and then transmitted to photodetector 123 via coupler 131. Another portion of the power of signal L1 is transmitted from port 103 to port 107, which is linked to photodetector 133, via coupling between waveguides 113, 111, and 115. Symmetrically, a portion of the power of signal L2 is transmitted from port 105 to port 103 in this example, and then transmitted to photodetector 121 via coupler 129, while another portion of the power of signal L2 is transmitted from port 105 to port 109. Signals L1 and L2 then propagate in opposite directions relative to each other in waveguide 111.

[0046] Figure 2The figure shows the variation of the transmission coefficient T (ordinate) of the power of the signals L1 and L2 between the different ports of the device 1 as a function of the wavelength λ (abscissa) at three operation steps A, B and C. More specifically, curves 201 and 203 show the variation of the coefficient T of the signal L1 between the ports 103 and 105 and between the ports 103 and 107, respectively, and curves 205 and 207 show the variation of the coefficient T of the signal L2 between the ports 105 and 103 and between the ports 105 and 109, respectively.

[0047] At step A, the device 1 is not rotated about the axis of the ring waveguide 111, and the resonant wavelength λR of the ring waveguide 111 is not yet controlled by the circuit 139 for a fixed-order resonance. The laser source 119 provides a signal L having a wavelength λL to the device 1, and the ring waveguide 111 resonates at the wavelength λR. As the wavelengths of the signals L1 and L2 are varied, it can be observed that at wavelength λR, the power of the signal L1 transmitted from port 103 to port 105 (curve 201) and the power of the signal L2 transmitted from port 105 to port 103 (curve 205) are minimum, while the power of the signal L1 transmitted from port 103 to port 107 (curve 203) and the power of the signal L2 transmitted from port 105 to port 109 (curve 207) are maximum. Furthermore, the further the wavelength is from the wavelength λR, the more reversible this phenomenon becomes. Due to the fact that the device 1 is not rotating, the curves 201 and 203 (signal L1 ) are confused with the corresponding curves 205 and 207 (signal L2 ).

[0048] At step B, circuit 139 provides a control signal cmd to waveguide 111 to modify the resonant wavelength λR of waveguide 111. More specifically, circuit 139 calculates the difference between the output signals I1 and I4 of photodetectors 121 and 135. Such a difference or information represents the difference between the power of signal L2 provided by port 103 and the power of signal L2 provided by port 109, and therefore represents the difference between curves 205 and 207. Circuit 139 is configured to determine signal cmd based on this information so that at the wavelength λL of signals L1 and L2, the power of signal L2 transmitted to port 103 (curve 205) is approximately equal to (preferably equal to) the power of signal L2 transmitted to port 109 (curve 207). This is equivalent to, at the intersection of curves 205 and 207, as shown in FIG. Figure 2 This is shown in step B. Since the device is not rotating, curves 201 and 203 (signal L1) are still confused with corresponding curves 205 and 207 (signal L2).

[0049] At step C, the device 1 is moved relative to the central axis of the waveguide 111 at an angular velocity Ω( Figure 1) rotation. The Sagnac effect generated by this rotation causes the waveguide 111 to resonate at a wavelength λR1 greater than the wavelength λR of step B for a signal L1 traveling through the waveguide 111 in the direction of rotation of the waveguide 111, and conversely, the waveguide 111 to resonate at a wavelength λR2 less than the wavelength λR of step B for a signal L2 traveling through the waveguide in a direction opposite to the direction of rotation of the waveguide 111.

[0050] Therefore, curves 201 and 203 are shifted relative to curves 205 and 207. At the same time, the resonant wavelength λR2 of the waveguide 111 is controlled by the circuit 139 so that the curves 205 and 207 intersect each other at the wavelength λL of the laser light source 119. Then, the intersection of the curves 201 and 203 occurs near the wavelength λL, and at the wavelength λL, the curves 201 and 203 exhibit a slope.

[0051] Circuit 137 calculates the difference between the output signals I2 and I3 of photodetectors 123 and 133. This difference, or information, represents the difference between the power of signal L1 transmitted to port 105 (coefficient T2, curve 201) and the power of signal L1 transmitted to port 107 (coefficient T3, curve 203), or in other words, the difference between coefficients T2 and T3. Due to the Sagnac effect, the difference between coefficients T2 and T3 is roughly proportional to the offset between curves 201, 203 and curves 205, 207. Therefore, the difference between coefficients T2 and T3 is roughly proportional to the rotational speed Ω of waveguide 111, and therefore roughly proportional to the rotational speed of device 1.

[0052] The circuit 137 is configured to derive the value SΩ of the speed Ω from the difference between the signals I2 and I3 ( Figure 1 ), for example by means of a look-up table with rotational speed values, wherein such a table may be determined during a previous calibration step and stored, for example, in a static memory ( Figure 1 Not shown).

[0053] The advantage of calculating velocity Ω based on the difference between currents I2 and I4 (particularly near the intersection of curves 201 and 203) is that the gain in detecting changes in velocity Ω is greater than when velocity Ω is calculated directly from the difference between wavelengths λR1 and λR2. This is particularly true as the slopes of curves 201 and 203 increase with the quality factor due to the high quality factor of resonator 101.

[0054] In an apparatus where the minimum values ​​of currents I1 and I2 are detected to measure the difference between wavelengths λR1 and λR2, the dark current component will be significant compared to the photogenerated current component for each current I1 and I2 measured at its minimum. In apparatus 1, near the intersection of curves 201 and 203, the dark current component in each of currents I2 and I3 is small compared to the photogenerated current component, for example, at least two times smaller. This reduction in the dark current component in the measured current used to determine the speed Ω results in an increase in the accuracy of the speed determination.

[0055] An advantage of controlling the wavelength λR2 based on the difference between the output signals of the photodetectors 121 and 135 is that the difference between the output signals of the photodetectors 123 and 133 (and therefore the speed Ω calculated from this difference) is insensitive to slow variations relative to the update time of the signal cmd that allows such control, i.e., variations in frequency that are less than the bandwidth of the feedback loop of the circuit 139. Variations in the temperature of the device 1, and in particular in the temperature of the waveguide 111, are examples of slow variations relative to the response time of the device 1.

[0056] The above operation can be applied to the case where the circuit 139 controls the wavelength λL instead of the resonant wavelength λR2 of the waveguide 111. This operation can also be applied to the case where the circuit 139 controls the resonant wavelength λR2 of the waveguide 111 and the wavelength λL of the laser source 119.

[0057] In a variation not shown, the power of signals L1 and L2 supplied to respective ports 103 and 105 is modulated at different frequencies, for example, at a frequency of one or more hundreds of kilohertz. The power of signal L1 received by each of photodetectors 123 and 133 is then detected synchronously with respect to the modulation frequency of signal L1, while the power of signal L2 received by each of photodetectors 121 and 135 is detected synchronously with respect to the modulation frequency of signal L2. This reduces or even suppresses measurement noise. In particular, it reduces or even suppresses noise generated in the measurement of the power of signal L1 due to parasitic reflections of signal L2 up to photodetectors 123 and / or 133, as well as noise generated in the measurement of the power of signal L2 due to parasitic reflections of signal L1 up to photodetectors 121 and / or 135. As a result, the value SΩ of velocity Ω is calculated with greater accuracy.

[0058] As an example, in the device 1 this change is achieved by adding a modulator between the splitter 127 and the coupler 129, and between the splitter 127 and the coupler 131, the modulators being, for example, of the Mach-Zehnder or electro-absorption type.

[0059] In combination Figure 1In other alternative embodiments of the described apparatus 1, the connection network 125 may be modified. In particular, the couplers 129, 131 may be implemented as optical circulators instead of X-couplers. The advantages of optical circulators over X-couplers are reduced power consumption and parasitic reflections.

[0060] Figure 3 A further embodiment of a device 3 is schematically presented, here a gyroscope comprising a resonant ring waveguide.

[0061] As with device 1, device 3 includes resonator 101; photodetectors 133 and 135, linked (preferably connected) to respective ports 107 and 109; circuit 137, electrically linked (preferably electrically connected) to photodetector 133; circuit 139, electrically linked (preferably electrically connected) to photodetector 135; and port 117, linked (preferably connected) to laser source 119.

[0062] However, unlike device 1, in device 3, ports 103 and 105 of the resonator are alternately connected to the same photodetector 301 (PD) (e.g., a photodiode) via an optical switch 303 (e.g., a Mach-Zehnder modulator). Port 117 is also alternately connected to ports 103 and 105 via switch 303. Thus, switch 303 acts as a connecting network. Two circuits 137 and 139 are electrically connected (preferably electrically connected) to the output of photodetector 301 to receive the output signal of the photodetector. In this example, current I represents the power of the optical signal received by the photodetector.

[0063] The device 3 operates by alternating first and second operating phases.

[0064] In the first operation phase corresponding to the first state of the switch 303, based on the signal L, the switch provides the signal L2 to the port 105 and links the port 103 to the photodetector 301, so that the signal L2 provided by the port 103 is always transmitted to the photodetector 301. Then, the output signal I of the photodetector 301 represents the power of the signal L2 transmitted from the port 105 to the port 103. Figure 2 As described, circuit 139 then determines signal cmd based on the difference between signals I and I4.

[0065] In the second operating phase corresponding to the second state of the switch 303, the switch provides the signal L1 from the signal L to the port 103 and links the port 105 to the photodetector 301 so that the signal L1 provided by the port 105 is transmitted to the photodetector 301. Then, the output signal I of the photodetector 301 represents the power of the signal L1 transmitted from the port 103 to the port 105. Figure 2 As already described, the circuit 137 then determines the value SΩ of the speed Ω based on the difference between the signals I and I3. In this second operating phase, the circuit 139 is preferably configured to maintain the signal cmd at the value determined during the previous first phase.

[0066] The frequency of the first and second phases is preferably greater than the frequency of the changes to which the device 3 is subject (e.g., changes in temperature, changes in speed Ω, etc.), for example, at least ten times greater. For example, the duration of each first phase and each second phase is in the range of about 1 μs to about 1 ms. As an example, the alternation between the first and second phases can be controlled by a signal (e.g., periodic), which is then provided to the switch 303 and to the circuits 137 and 139.

[0067] Due to the fact that during each of the first and second phases a single signal L1 or L2 flows through the device 3 , this makes it possible to suppress possible influences of the signal L2 on the measurements performed from the signal L1 , and vice versa.

[0068] Furthermore, the speed Ω is calculated in the same manner in both devices 1 and 3 , with device 3 benefiting from the same advantages as device 1 regarding the calculation of the speed Ω.

[0069] Furthermore, as in device 1, in a variant embodiment of device 3 (not shown), signals L1 and L2 are modulated at different frequencies. In this case, the measurement of currents I and I4 during the first phase is performed in synchronization with the modulation frequency of signal L2, and the measurement of currents I and I3 during the second phase is performed in synchronization with the modulation frequency of signal L1.

[0070] As an example, this alternative embodiment is implemented by providing a first modulator between the switch 303 and the port 103 to modulate the power of the signal L1, and providing a second modulator between the switch 303 and the port 105 to modulate the power of the signal L2. In addition to reducing or even suppressing the measurement noise, such a configuration can avoid that part of the power of the signal L is returned to the laser 119. Preferably, the first modulator is active only during the second operating phase and the second modulator is active only during the first operating phase.

[0071] In the above description, a ring waveguide refers to a waveguide that is closed on itself, for example a circular or rectangular waveguide or a spiral waveguide. It should be noted that, for the same occupied surface area, the use of a spiral waveguide 111 enables the formation of a longer waveguide than a waveguide 111 which is already circular.

[0072] In a preferred embodiment, the above-mentioned devices 1 or 3 are implemented in the same chip or in the same integrated circuit. For example, the same silicon layer comprises the waveguides, optoelectronic components and electronic components (circuits CIRC1 and CIRC2) of the device.

[0073] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these various embodiments and variations may be combined, and that other variations will occur to those skilled in the art. In particular, although circuits 137 and 139 have been shown and described as two separate electronic circuits, circuits 137 and 139 may correspond to a single electronic circuit.

[0074] In addition, although not described, the value of the angular velocity can also be derived from the difference between the first signal and the second signal, the first signal representing the difference between the power of the signal L2 provided by the port 103 and the power of the signal L2 provided by the port 109, and the second signal representing the difference between the power of the signal L1 provided by the port 105 and the power of the signal L1 provided by the port 107, for example, the first and second signals are provided by the corresponding circuits CIRC2 and CIRC1.

[0075] Finally, based on the functional indications given above, the actual implementation of the described embodiments and variants is within the capabilities of a person skilled in the art. In particular, in the described embodiments and variants, the resonator 101, the optical and optoelectronic components, and the circuits 137 and 139 can be formed on the same chip, or at least a portion of the resonator can be formed on a different chip from the chip forming the circuits 137 and 139 to benefit from different manufacturing technologies.

Claims

1. A device comprising: an optical resonator having four ports including a first port, a second port, a third port, and a fourth port; a first electronic circuit configured to calculate first information representing a power difference between a second port optical signal provided by the second port and a third port optical signal provided by the third port, the second port optical signal and the third port optical signal originating from a laser source; a second electronic circuit configured to calculate second information, wherein the second information represents a power difference between a first-port optical signal provided by the first port and a fourth-port optical signal provided by the fourth port, the first-port optical signal and the fourth-port optical signal originating from the laser source, the second information being used to control a resonant wavelength of the optical resonator so that the power difference between the first-port optical signal and the fourth-port optical signal is zero at a wavelength of the laser source; as well as an optical modulator configured such that the optical signals supplied to the first port and the second port are modulated at different frequencies, wherein detection of the powers of the second-port optical signal and the third-port optical signal is performed synchronously with respect to the modulation frequency of the optical signal supplied to the first port, and detection of the powers of the first-port optical signal and the fourth-port optical signal is performed synchronously with respect to the modulation frequency of the optical signal supplied to the second port.

2. The apparatus of claim 1, wherein the optical resonator comprises a first ring waveguide.

3. The apparatus of claim 2, wherein the optical resonator further comprises: a second waveguide coupled to the first ring waveguide and linking the first port to the second port; and a third waveguide coupled to the first ring waveguide and linking the third port to the fourth port.

4. The apparatus according to claim 3, wherein the apparatus is configured such that an initial optical signal is provided to the first port, a first portion of the initial optical signal is transmitted by the second waveguide to the second port to generate the second-port optical signal, and wherein a second portion of the initial optical signal is transmitted through the first ring waveguide to the third port to generate the third-port optical signal.

5. The apparatus of claim 1, wherein the laser source is linked to the first port and the second port. The apparatus according to claim 5 , wherein the laser source has a wavelength adjustable according to a control signal. The apparatus of claim 6 , wherein the second electronic circuit determines the control signal based on the second information. 8 . The apparatus of claim 7 , wherein the second electronic circuit is configured to determine the control signal such that the second information represents zero disparity.

9. The apparatus of claim 1, wherein the first electronic circuit is configured to determine an angular velocity based on the first information.

10. A device comprising: an optical resonator comprising a first port, a second port, a third port, and a fourth port; a laser source connected to the first port and the second port; a first electronic circuit configured to calculate first information representing a power difference between a second-port optical signal provided by the second port and a third-port optical signal provided by the third port, the second-port optical signal and the third-port optical signal originating from the laser source; a second electronic circuit configured to calculate second information, wherein the second information represents a power difference between a first-port optical signal provided by the first port and a fourth-port optical signal provided by the fourth port, the first-port optical signal and the fourth-port optical signal originating from the laser source; and the second information is used to control a resonant wavelength of the optical resonator so that the power difference between the first-port optical signal and the fourth-port optical signal is zero at a wavelength of the laser source; as well as an optical modulator configured such that the optical signals supplied to the first port and the second port are modulated at different frequencies, wherein detection of the powers of the second-port optical signal and the third-port optical signal is performed synchronously with respect to the modulation frequency of the optical signal supplied to the first port, and detection of the powers of the first-port optical signal and the fourth-port optical signal is performed synchronously with respect to the modulation frequency of the optical signal supplied to the second port.

11. The apparatus of claim 10, wherein the optical resonator comprises: a first ring waveguide; a second waveguide coupled to the first ring waveguide and linking the first port to the second port; as well as A third waveguide is coupled to the first ring waveguide and links the third port to the fourth port.

12. The apparatus according to claim 11, wherein the apparatus is configured such that an initial optical signal is provided by the laser source to the first port, and a first portion of the initial optical signal is transmitted by the second waveguide to the second port to generate the second-port optical signal, and wherein a second portion of the initial optical signal is transmitted through the first ring waveguide to the third port to generate the third-port optical signal.

13. The apparatus of claim 10, wherein the laser source has a wavelength adjustable according to a control signal, wherein the second electronic circuit is configured to determine the control signal based on the second information. The apparatus of claim 13 , wherein the second electronic circuit is configured to determine the control signal such that the second information represents zero disparity.

15. A method for determining a rotational speed of a device, the device comprising an optical resonator, the optical resonator comprising a first port, a second port, a third port, and a fourth port, the method comprising: transmitting an initial optical signal from a laser source to the first port; guiding a first portion of the initial optical signal to the third port via a first ring waveguide to generate a third port optical signal; directing a second portion of the initial optical signal to the second port via a second waveguide to generate a second port optical signal; calculating first information, where the first information represents a power difference between the optical signal at the second port and the optical signal at the third port; as well as determining a rotational speed of the device relative to a central axis of the first ring waveguide based on the first information; transmitting a second initial optical signal from the laser source to the second port; guiding a first portion of the second initial optical signal to the fourth port via the first ring waveguide to generate a fourth port optical signal; guiding a second portion of the second initial optical signal to the first port via the second waveguide to generate a first-port optical signal; and calculating second information representing a power difference between the fourth-port optical signal and the first-port optical signal; and using the second information to control a resonant wavelength of the optical resonator so that a power difference between the first port optical signal and the fourth port optical signal is zero at the wavelength of the laser source; The optical signals provided to the first port and the second port are modulated at different frequencies, the power detection of the second port optical signal and the third port optical signal is performed synchronously with respect to the modulation frequency of the optical signal provided to the first port, and the power detection of the first port optical signal and the fourth port optical signal is performed synchronously with respect to the modulation frequency of the optical signal provided to the second port.

16. The method according to claim 15, further comprising: When a first optical signal is provided to the first port, the first signal is transmitted to the second port and the third port.

17. The method according to claim 15, further comprising: An angular velocity is determined based on the first information.

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