Broadband resonator optical gyroscope with efficient optical power management for low shot noise

Abstract

A method of operating a resonator optical gyroscope includes generating an optical signal having a broadband frequency range. The method includes coupling an optical signal into an optical resonator (OR) for propagation in a first direction, and coupling the optical signal out of the OR after the optical signal passes through the OR in the first direction. The method includes coupling the optical signal into the OR to propagate in the second direction, and coupling the optical signal out of the OR after the optical signal passes through the OR in the second direction. The method includes amplifying the optical signal coupled out of the OR by the second optical coupler or the optical signal coupled out of the OR by the first optical coupler to produce an amplified optical signal, and producing an electrical signal corresponding to the amplified optical signal. The method includes determining a rotation rate based on the electrical signal.

Description

Background Art

[0001] Resonator fiber gyroscopes (RFOGs) typically utilize a narrow linewidth laser source to generate the optical signal necessary for rotation rate measurement. RFOGs typically operate by propagating an optical signal generated by a laser through an optical resonator in a counter-propagating direction. When the RFOG is subjected to rotation about its sensing axis, the resonant frequency of the optical resonator shifts due to the Sagnac effect. The shift in the resonant frequency can then be used to determine the degree of rotation to which the RFOG has been subjected. Summary of the invention

[0002] In some aspects, the resonator optical gyroscope includes a broadband light source configured to generate an optical signal having a broadband frequency range. The resonator optical gyroscope also includes an optical resonator. The resonator optical gyroscope also includes a first optical coupler coupled to the optical resonator. The first optical coupler is configured to receive an optical signal from the broadband light source and couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in a first direction. The first optical coupler is also configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in a second direction. The resonator optical gyroscope also includes a second optical coupler coupled to the optical resonator. The second optical coupler is configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the first direction. The second optical coupler is also configured to couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in the second direction. The resonator optical gyroscope also includes a gain element configured to amplify the optical signal that has been coupled out of the optical resonator and passed through the optical resonator in the first direction to produce an amplified optical signal. The resonator optical gyroscope also includes a photodetector configured to convert the amplified optical signal into a corresponding electrical signal based on a power level of the amplified optical signal. The resonator optical gyroscope also includes one or more circuits configured to determine a rotation rate based on the corresponding electrical signal.

[0003] In other aspects, the resonator optical gyroscope includes a broadband light source configured to generate an optical signal having a broadband frequency range. The resonator optical gyroscope also includes an optical resonator. The resonator optical gyroscope also includes a first optical coupler coupled to the optical resonator. The first optical coupler is configured to receive an optical signal from the broadband light source and couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in a first direction. The first optical coupler is also configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in a second direction. The resonator optical gyroscope also includes a second optical coupler coupled to the optical resonator. The second optical coupler is configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the first direction. The second optical coupler is also configured to couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in a second direction. The resonator optical gyroscope also includes one or more gain elements configured to amplify an optical signal that has been coupled out of the optical resonator by the second optical coupler and passes through the optical resonator in the first direction and / or an optical signal that has been coupled out of the optical resonator by the first optical coupler and passes through the optical resonator in the second direction. The resonator optical gyroscope also includes a photodetector configured to convert the amplified optical signal into a corresponding electrical signal based on a power level of the amplified optical signal. The resonator optical gyroscope also includes one or more circuits configured to determine a rotation rate based on the corresponding electrical signal.

[0004] In other aspects, a method of operating a resonator optical gyroscope includes generating an optical signal having a broadband frequency range using a broadband light source. The method also includes coupling the optical signal into an optical resonator for propagation in a first direction using a first optical coupler. The method also includes coupling the optical signal out of the optical resonator using a second optical coupler after the optical signal passes through the optical resonator in the first direction. The method also includes coupling the optical signal into the optical resonator for propagation in a second direction using the second optical coupler. The method also includes coupling the optical signal out of the optical resonator using the first optical coupler after the optical signal passes through the optical resonator in the second direction. The method also includes amplifying the optical signal coupled out of the optical resonator by the second optical coupler or the optical signal coupled out of the optical resonator by the first optical coupler using one or more gain elements to generate an amplified optical signal. The method also includes generating an electrical signal corresponding to the amplified optical signal using a photodetector. The method also includes determining a rotation rate based on the electrical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Understanding that the drawings depict only some embodiments and are therefore not to be considered limiting in scope, exemplary embodiments will be described with additional specificity and detail using the accompanying drawings, in which:

[0006] Figure 1A is a block diagram of an exemplary optical gyroscope;

[0007] Figure 1B is a block diagram of an exemplary optical gyroscope;

[0008] Figure 2 is a block diagram of an exemplary optical gyroscope;

[0009] Figure 3 is a block diagram of an exemplary optical gyroscope;

[0010] Figure 4 is a flow chart of an exemplary method for operating an optical gyroscope; and

[0011] Figure 5 is a flow chart of an exemplary method for operating an optical gyroscope.

[0012] As is common practice, the various features described are not necessarily drawn to scale, emphasis instead being placed on specific features relevant to the example embodiments. DETAILED DESCRIPTION

[0013] In the following detailed description, reference is made to the accompanying drawings which form a part thereof, and in which specific illustrative embodiments are shown by way of illustration. However, it should be understood that other embodiments may be utilized, and that logical, mechanical, and electrical changes may be made. In addition, the methods presented in the drawings and the specification should not be interpreted as limiting the order in which the various steps may be performed. Therefore, the following detailed description should not be considered to have a limiting meaning.

[0014] The signals generated by narrow linewidth lasers in RFOGs are generally susceptible to the optical Kerr effect, a nonlinear optical phenomenon that modifies the refractive index depending on the intensity of the optical signal. Broadband lasers (i.e., wide linewidth sources that produce optical signals with a broadband frequency range) can reduce the optical Kerr effect present in RFOGs, but can also cause the output intensity of the optical signal to be significantly reduced after propagating through the optical resonator due to the broadband nature of the laser source and the narrow resonance peak of the optical resonator. The optical resonator essentially operates like a filter so that all non-resonant frequencies are filtered out. Therefore, when a broadband light source is used, the optical signal output from the optical resonator may be too weak for the detection and processing circuits to determine the rotation rate. For high-precision RFOGs, especially when implemented on a chip, power reduction is very problematic because these gyroscopes require high-fineness resonators for accurate rate measurement, and the power of the optical signal output from the optical resonator is inversely proportional to the fineness of the resonator.

[0015] One option to overcome the losses of implementing broadband light sources is to use broadband light sources with high output power. While operational, this approach is not suitable for some applications. For example, for such high-power light sources, the total power consumption can be very high, making them unsuitable for integrated photonic-based gyroscopes or other small-scale RFOG designs.

[0016] The techniques described herein address power loss by utilizing one or more gain elements at various locations on the optical path to amplify an optical signal that has passed through an optical resonator one or more times in order to improve the detectable optical power without increasing the overall power consumption of the gyroscope. In some examples, the gain element is configured to amplify an optical signal that has passed through the optical resonator in a single direction before coupling the optical signal back into the optical resonator. In some examples, the gain element is configured to amplify an optical signal that has passed through the optical resonator in two directions before the optical signal reaches the detector. Further improvements can be achieved by introducing phase modulation to shift the frequency of the optical signal and / or introducing a polarizer to filter out undesirable polarization states.

[0017] Figure 1A A block diagram of an exemplary resonator optical gyroscope 100 is shown in which techniques for efficient optical power management for low shot noise may be implemented. Figure 1A In the example shown, the resonator optical gyroscope 100 includes various components, including a broadband light source 102, a first circulator 104, a first optical coupler 106, an optical resonator 108, a second optical coupler 110, a second circulator 112, a gain element 114, a power monitor 116, a phase modulator 118, a photodetector 120, and a demodulation and rate detection circuit 122. Although in Figure 1A Although not specifically labeled, the components of the resonator optical gyroscope 100 are coupled via suitable guiding optics. For example, the components of the resonator optical gyroscope 100 may be coupled via optical waveguides and / or free-space optics such as lenses, mirrors, and beam splitters. In some examples, the resonator optical gyroscope 100 is implemented on an integrated photonic substrate such as a photonic chip.

[0018] The resonator optical gyroscope 100 generally operates by propagating optical signals through different optical paths, where the optical signals are ultimately processed to determine the rate of rotation experienced by the demodulation and rate detection circuitry 122 of the resonator optical gyroscope 100 .

[0019] The broadband light source 102 is configured to generate an optical signal having a broadband frequency range. In some examples, the broadband light source 102 is a broadband laser configured to generate an optical signal via amplified spontaneous emission (ASE). In some examples, the broadband light source 102 is a rare earth doped optical fiber or other waveguide light source. For example, the broadband light source 102 can be an optical fiber doped with rare earth ions such as erbium, ytterbium, etc. In such examples, the broadband light source 102 is optically pumped (for example, using a 980nm or 1480nm pump laser), absorbs the pump light, and emits an optical signal. In some examples, the broadband light source 102 can be a superluminescent laser diode, a light emitting diode (LED), etc. In any case, the optical signal generated by the broadband light source 102 has a continuous broadband spectrum and low coherence. In some examples, the broadband light source 102 is configured to generate an optical signal of a selected frequency / wavelength range or intensity that reduces the effects from the optical Kerr effect or makes such effects negligible.

[0020] exist Figure 1A In the example shown, the optical signal generated by the broadband light source 102 is provided to the first circulator 104. Figure 1A In the example shown, the first circulator 104 is a three-port device that is configured to output a signal received at one port to another specific port. Figure 1A In the example shown, an optical signal received from a broadband light source 102 at a first port is output to a second port coupled to a first optical coupler 106. Figure 1A In the example shown, the optical signal received from the first optical coupler 106 at the second port is output to the third port connected to the photodetector 120 .

[0021] The first circulator 104 is configured to provide an optical signal received from the broadband light source 102 to the first optical coupler 106, and the first optical coupler 106 is configured to couple at least a portion of the optical signal into the optical resonator 108. In some examples, the optical fiber extending through the first optical coupler 106 is beveled to prevent back reflections of a portion of the optical signal that is not transmitted into the optical resonator 108. In other examples, an optical isolator or similar device may also be used to prevent back reflections. In any case, preventing back reflections ensures that these signals do not interfere with other signals received by the photodetector 120 (including the optical signal generated by the broadband light source 102 and the amplified optical signal or the phase modulated amplified optical signal, as further described herein).

[0022] The optical resonator 108 is configured to pass a portion of the coupled optical signal at one or more resonant frequencies of the optical resonator 108. When the first optical coupler 106 receives the optical signal from the first circulator 104, it directs the optical signal to propagate in the optical resonator 108 in a first direction. Figure 1A In the example shown, the optical signal coupled into the optical resonator 108 by the first optical coupler 106 propagates in a counterclockwise (CCW) direction. However, in other examples, the resonator optical gyroscope 100 may be designed so that the optical signal initially propagates in a clockwise (CW) direction. As the optical signal propagates in the optical resonator 108, some frequency components of the optical signal (particularly frequency components that are not close to the resonant frequency of the optical resonator 108) will destructively interfere and will not resonate. Therefore, the frequency component of the optical signal corresponding to the resonant frequency of the optical resonator 108 will be transmitted to the output port (the second optical coupler 110), while other frequency components will not be transmitted.

[0023] After propagating through the optical resonator 108, a portion of the optical signal is coupled out of the optical resonator 108 via the second optical coupler 110. Optical filtering of the optical signal in the first path through the optical resonator 108 reshapes the broadband spectrum to match the optical resonator transmission line. Figure 1A As shown, the optical signal coupled out of the optical resonator 108 has a significantly reduced power level and is channelized in the CCW direction through multiple resonances.

[0024] The optical signal coupled out of the optical resonator 108 via the second optical coupler 110 is then sent to the second circulator 112. Figure 1A In the example shown, the second circulator 112 is a three-port device that is configured to output a signal received at one port to another specific port. Figure 1A In the example shown, the optical signal received at the first port from the second optical coupler 110 is output to the second port coupled to the first gain element 114. Figure 1A In the example shown, an optical signal received at the third port from the gain element 114 (or from the phase modulator 118 if included) is output to the first port and then to the second optical coupler 110 .

[0025] The gain element 114 (also referred to as a "gain medium") is configured to amplify the optical signal output from the optical resonator 108. In some examples, the gain element 114 is a rare-earth doped amplifier. For example, the gain element 114 can be an optical fiber or waveguide doped with rare earth ions such as erbium, ytterbium, etc. In such examples, the gain element 114 is optically pumped (e.g., using a 980nm or 1480nm pump laser) to provide a desired level of amplification to the optical signal. In other examples, the gain element 114 is a semiconductor optical amplifier. In such examples, the gain element 114 is electrically pumped to provide a desired level of amplification of the optical signal.

[0026] exist Figure 1A In the example shown, the resonator optical gyroscope 100 includes a power monitor 116 configured to measure the power level of the amplified optical signal, and the amount of amplification provided to the optical signal by the gain element 114 is adjustable. In some examples, it is desirable to produce the amplified optical signal at a particular power level during calibration and / or to maintain an approximately constant output power using the gain element 114 during operation. In some examples, the pump power for the optical pump of the gain element 114 (e.g., where the gain element 114 is an EDFA) or the amount of current used for the pump of the gain element 114 (e.g., where the gain element 114 is an SOA) can be adjusted based on the power measurement from the power monitor 116. In some examples, the adjustment is made using a servo mechanism or another control circuit.

[0027] Regardless of the type of gain element 114 used in the resonator optical gyroscope 100, in some examples, the amount of optical or electrical pumping of the gain element 114 is selected based at least in part on the desired overall power consumption of the resonator optical gyroscope 100. For example, the power consumption of pumping the gain element 114 can be limited based on the overall power consumption of the resonator optical gyroscope 100, which includes the power consumption for pumping the broadband light source 102 and the operation of the phase modulator 118 (if included), the photodetector 120, and the demodulation and rate detection circuit 122. By using the gain element 114 to amplify the optical signal after passing through the optical resonator 108, the amount of power (e.g., pump power) used for the broadband light source 102 can be reduced, and the power level of the amplified optical signal at the photodetector 120 will be significantly improved (e.g., by orders of magnitude), even without increasing the power consumption of the entire resonator optical gyroscope 100.

[0028] After amplification, the amplified optical signal is provided to the third port of the second circulator 112, which then passes the amplified optical signal back to the first port of the second circulator 112 and then back to the second optical coupler 110. The second optical coupler 110 is configured to couple at least a portion of the amplified optical signal into the optical resonator 108.

[0029] When some of the signal is coupled into the optical resonator 108, the remaining amount of the signal propagates toward the optical fiber extending through the second optical coupler 110. In some examples, the optical fiber extending through the second optical coupler 110 is beveled to prevent back reflection of a portion of the amplified optical signal that is not transmitted into the optical resonator 108. In other examples, an optical isolator or similar device may also be used to prevent back reflection. In any case, preventing back reflection ensures that these signals do not interfere with other signals received by the second optical coupler 110.

[0030] The second optical coupler 110 couples the amplified optical signal in the second direction through the optical resonator 108. Figure 1A In the example shown, the amplified optical signal propagates in the CW direction.The amplified optical signal having frequency components corresponding to the resonance peak of the optical resonator 108 propagates through the optical resonator 108, while non-resonant frequency components are rejected.

[0031] After the amplified optical signal propagates through the optical resonator 108, the first optical coupler 106 is configured to couple a portion of the amplified optical signal out of the optical resonator 108, and the amplified optical signal is directed to the first circulator 104. Since the amplified optical signal propagates in a direction toward the broadband light source 102 and is received at the second port of the first circulator 104, the first circulator 104 acts as an isolator to direct the amplified optical signal to the photodetector 120 and prevent the amplified optical signal from propagating back to the broadband light source 102.

[0032] The amplified optical signal propagates from the first circulator 104 to the photodetector 120. The photodetector 120 is configured to convert the amplified optical signal from an optical signal to a corresponding electrical signal based on the power of the received amplified optical signal. The electrical signal corresponding to the amplified optical signal is then provided to the demodulation and rate detection circuit 122.

[0033] To determine the rotation rate, the demodulation and rate detection circuit 122 is configured to demodulate the electrical signal and determine the resonant frequency shift based on the power of the demodulated signal corresponding to the amplified optical signal. For example, the received electrical signal may indicate a power difference corresponding to a change in rotation rate.

[0034] In some examples, the resonator optical gyroscope 100 further includes a phase modulator 118 coupled between the gain element 114 and the second circulator 112. In some examples, the phase modulator 118 is configured to receive the optical signal from the second circulator 112 and then amplify the optical signal by the gain element 114 to compensate for the loss introduced by the phase modulator 118. In other examples, such as Figure 1A In the example shown, the phase modulator 118 is configured to receive the amplified optical signal from the gain element 114. Figure 1A Example shown.

[0035] exist Figure 1A In the example shown, after the optical signal is amplified by the gain element 114, the amplified optical signal is provided to the phase modulator 118. The phase modulator 118 is configured to modulate the phase of the amplified optical signal based on the phase modulation signal applied to the amplified optical signal. In some examples, the phase modulator 118 is configured to generate a phase modulated amplified optical signal using a sawtooth waveform. In some examples, the phase modulator 118 is an electro-optical phase modulator. Utilizing such a phase modulator simplifies the architecture of the resonator optical gyroscope 100 and reduces the size and cost of implementing phase modulation of the optical signal compared to previous designs.

[0036] Once modulated by the phase modulator 118, the modulated and amplified optical signal (referred to as a "phase-modulated amplified optical signal") is sent back to the optical resonator 108 in the opposite direction through the second circulator 112 and the second optical coupler 110. After modulation, the phase-modulated amplified optical signal is provided to the third port of the second circulator 112. The phase-modulated amplified optical signal received at the third port of the second circulator 112 is output to the first port of the second circulator 112, which then passes the phase-modulated amplified optical signal back to the second optical coupler 110. The second optical coupler 110 is configured to couple at least a portion of the phase-modulated amplified optical signal into the optical resonator 108.

[0037] After the phase-modulated amplified optical signal propagates through the optical resonator 108, the first optical coupler 106 is configured to couple a portion of the phase-modulated amplified optical signal out of the optical resonator 108, and the phase-modulated amplified optical signal is directed to the first circulator 104. Since the phase-modulated amplified optical signal propagates in a direction toward the broadband light source 102 and is received at the second port of the first circulator 104, the first circulator 104 acts as an isolator to direct the phase-modulated amplified optical signal to the photodetector 120 and prevent the phase-modulated amplified optical signal from propagating back to the broadband light source 102.

[0038] The phase modulated amplified optical signal propagates from the first circulator 104 to the photodetector 120. The photodetector 120 is configured to convert the phase modulated amplified optical signal from an optical signal to a corresponding electrical signal based on the power of the received phase modulated amplified optical signal. The electrical signal corresponding to the phase modulated amplified optical signal is then provided to the demodulation and rate detection circuit 122.

[0039] In some examples, the power level of the phase modulated amplified optical signal at the photodetector 120 can also be used to adjust the slope of the phase modulated signal at the phase modulator 118, and the slope difference between two consecutive cycles of the phase modulated signal can be used to determine the frequency shift. The demodulation and rate detection circuit 122 can then determine the rotation rate based on the frequency shift.

[0040] In some examples, Figure 1A The resonator optical gyroscope 100 shown in FIG. 1 is configured to operate as a closed-loop optical gyroscope because the output from the optical resonator 108 indicating the rotation rate is also used as feedback to adjust the operation of the phase modulator 118 (where “closed loop” includes the propagation of the signal from the phase modulator 118 ultimately to the demodulation and rate detection circuit 122 and the control signal input to the phase modulator 118). In some examples, the demodulation and rate detection circuit 122 includes a control circuit configured to adjust the operation of the phase modulator 118 based on the electrical signal from the photodetector 120. In some examples, the demodulation and rate detection circuit 122 configures at least one parameter of the phase modulator 118, such as a characteristic of the phase modulation signal used by the phase modulator 118 to modulate the optical signal. For example, as previously described, the demodulation and rate detection circuit 122 is configured to adjust the slope of the sawtooth phase modulation signal based on the power change determined from the received electrical signal. The demodulation and rate detection circuit 122 can send a control signal that configures the phase modulator 118. The chirp transponder modulation (sawtooth phase modulation) shifts the frequency of the return beam and makes the frequency overlap with the CW resonance peak of the optical resonator 108 .

[0041] In response to receiving the control signal for adjusting the slope of the phase modulated signal, the phase modulator 118 generates an adjusted phase modulated signal having a slope of a waveform corresponding to the parameters set by the demodulation and rate detection circuit 122. For example, the phase modulated amplified optical signal may have a frequency shift corresponding to the shifted resonant frequency of the optical resonator 108 due to the rotation. In this way, the resonator optical gyroscope 100 (and specifically the demodulation and rate detection circuit 122) can compensate for power variations (e.g., variations caused by rotation) in the average power of the phase modulated amplified optical signal detected by the demodulation and rate detection circuit 122.

[0042] In some examples, to reduce rate measurement errors, the optical resonator 108 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization state. For example, the optical resonator 108 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization mode of the optical resonator 108. Thus, only portions of the optical signal corresponding to a selected polarization mode of the optical resonator 108 are allowed to pass through the polarizer and are transmitted through the optical resonator 108 on each round trip.

[0043] Figure 1B 1 is a block diagram of another exemplary resonator optical gyroscope 150 in which techniques for efficient optical power management for low shot noise may be implemented. The resonator optical gyroscope 150 includes the same Figure 1A Similar elements of the resonator optical gyroscope 100 are described, and therefore only the differences will be discussed. Furthermore, the functional, structural, and other descriptions of the elements of such examples described herein can be applied to similarly named elements of the resonator optical gyroscope 150, and vice versa.

[0044] exist Figure 1B In the example shown, broadband light source 102 is a rare earth doped fiber and gain element 114 is a rare earth doped fiber amplifier. For example, broadband light source 102 and gain element 114 can both be optical fibers doped with rare earth ions such as erbium, ytterbium, or the like.

[0045] exist Figure 1B In the example shown, broadband light source 102 and gain element 114 are coupled to the same pump laser 103 via coupler 105. Pump laser 103 is configured to optically pump both broadband light source 102 and gain element 114 via coupler 105. In some examples, pump laser 103 is a 980 nm or 1480 nm pump laser.

[0046] The coupler 105 can be configured to split the pump power from the pump laser 103 into different desired configurations. For example, the coupler 105 can be configured to achieve a 50 / 50 split ratio of the pump power, such that 50% of the pump power is provided to the broadband light source 102 and 50% of the pump power is provided to the gain element 114. It should be understood that the coupler 105 can also achieve other ratios depending on the desired performance and design constraints.

[0047] exist Figure 1BIn the example shown, power monitor 116 is configured to measure the power level of the amplified optical signal, and the amount of amplification provided to the optical signal by gain element 114 is adjustable. In some examples, it is desirable to produce an amplified optical signal at a particular power level during calibration and / or to maintain an approximately constant output power during operation using gain element 114. In some examples, the pump power for the optical pump of gain element 114 and / or the splitting ratio achieved by coupler 105 can be adjusted based on the power measurement from power monitor 116. In some examples, the adjustment is made using a servo mechanism or another control circuit.

[0048] Figure 2 is a block diagram of another exemplary resonator optical gyroscope 200 in which techniques for efficient optical power management for low shot noise may be implemented. Figure 2 In the example shown, the resonator optical gyroscope 200 includes various components, including a broadband light source 202, a first circulator 204, a first optical coupler 206, an optical resonator 208, a second optical coupler 210, a second circulator 212, a gain element 214, a power monitor 216, a phase modulator 218, a photodetector 220, and a demodulation and rate detection circuit 222. Although in Figure 2 Although not specifically labeled, the components of the resonator optical gyroscope 200 are coupled via suitable guiding optics. For example, the components of the resonator optical gyroscope 200 may be coupled via optical waveguides and / or free-space optics such as lenses, mirrors, and beam splitters. In some examples, the resonator optical gyroscope 200 is implemented on an integrated photonic substrate such as a photonic chip.

[0049] The resonator optical gyroscope 200 generally operates by propagating optical signals through different optical paths, where the optical signals are ultimately processed to determine the rate of rotation experienced by the demodulation and rate detection circuitry 222 of the resonator optical gyroscope 200 .

[0050] The broadband light source 202 is configured to generate an optical signal having a broadband frequency range. In some examples, the broadband light source 202 is a broadband laser configured to generate an optical signal via amplified spontaneous emission (ASE). In some examples, the broadband light source 202 is a rare earth doped optical fiber or other waveguide light source. For example, the broadband light source 202 can be an optical fiber doped with rare earth ions such as erbium, ytterbium, etc. In such examples, the broadband light source 202 is optically pumped (e.g., using a 980nm or 1480nm pump laser). The doped optical fiber absorbs the pump light and emits an optical signal of other wavelengths (e.g., 1550nm). In some examples, the broadband light source 202 can be a superluminescent laser diode, a light emitting diode (LED), etc. In any case, the optical signal generated by the broadband light source 202 has a continuous broadband spectrum and low coherence. In some examples, the broadband light source 202 is configured to generate an optical signal of a selected frequency / wavelength range or intensity that reduces the effects from the optical Kerr effect or makes such effects negligible.

[0051] exist Figure 2 In the example shown, an optical signal generated by a broadband light source 202 is provided to a first circulator 204. Figure 2 In the example shown, the first circulator 204 is a three-port device that is configured to output a signal received at one port to another specific port. Figure 2 In the example shown, an optical signal received from a broadband light source 202 at a first port is output to a second port coupled to a first optical coupler 206. Figure 2 In the example shown, the optical signal received from the first optical coupler 206 at the second port is output to the photodetector 220 through the third port of the first circulator 204 .

[0052] The first circulator 204 is configured to provide an optical signal received from the broadband light source 202 to the first optical coupler 206, and the first optical coupler 206 is configured to couple at least a portion of the optical signal into the optical resonator 208. In some examples, the optical fiber extending through the first optical coupler 206 is beveled to prevent back reflections of a portion of the optical signal that is not transmitted into the optical resonator 208. In other examples, an optical isolator or similar device may also be used to prevent back reflections. In any case, preventing back reflections ensures that these signals do not interfere with other signals received by the photodetector 220 (including optical signals generated by the broadband light source 202 and optical signals coupled out of the optical resonator 208 or phase modulated optical signals, as further described herein).

[0053] The optical resonator 208 is configured to pass a portion of the coupled optical signal at the resonant frequency of the optical resonator 208. When the first optical coupler 206 receives the optical signal from the first circulator 204, it directs the optical signal to propagate in the optical resonator 208 in a first direction. Figure 2 In the example shown, the optical signal coupled into the optical resonator 208 by the first optical coupler 206 propagates in a counterclockwise (CCW) direction. However, in other examples, the resonator optical gyroscope 200 may be designed so that the optical signal initially propagates in a clockwise (CW) direction. As the optical signal propagates in the optical resonator 208, some frequency components of the optical signal (particularly frequency components that are not close to the resonant frequency of the optical resonator 208) will destructively interfere and not resonate. Therefore, the frequency component of the optical signal corresponding to the resonant frequency of the optical resonator 208 will be transmitted to the output port (the second optical coupler 210), while other frequency components will not be transmitted.

[0054] After propagating through the optical resonator 208, a portion of the optical signal is coupled out of the optical resonator 208 via the second optical coupler 210. Optical filtering of the optical signal in the first path through the optical resonator 208 reshapes the broadband spectrum to match the optical resonator transmission line. Figure 2 As shown, the optical signal coupled out of the optical resonator 208 has a significantly reduced power level and is channelized in the CCW direction through multiple resonances.

[0055] The optical signal coupled out of the optical resonator 208 via the second optical coupler 210 is then sent to the second circulator 212. Figure 2 In the example shown, the second circulator 212 is a three-port device that is configured to output a signal received at one port to another specific port. Figure 2 In the example shown, the optical signal received at the first port from the second optical coupler 210 is output to the second port, and the optical signal received at the third port (from the phase modulator 218, if included) is output to the first port and then to the second optical coupler 210. Figure 1A to Figure 1B Unlike the example shown in Figure 2 The illustrated resonator optical gyroscope 200 does not amplify the optical signal after the first pass through the optical resonator 208 .

[0056] When some of the signal is coupled into the optical resonator 208, the remaining amount of the signal propagates toward the optical fiber extending through the second optical coupler 210. In some examples, the optical fiber extending through the second optical coupler 210 is beveled to prevent back reflection of a portion of the amplified optical signal that is not transmitted into the optical resonator 208. In other examples, an optical isolator or similar device may also be used to prevent back reflection. In any case, preventing back reflection ensures that these signals do not interfere with other signals received by the second optical coupler 210.

[0057] The second optical coupler 210 couples the optical signal in the second direction through the optical resonator 208. Figure 2 In the example shown, the optical signal coupled back into the optical resonator 208 by the second optical coupler 210 propagates in the CW direction. The optical signal having frequency components corresponding to the resonance peak of the optical resonator 208 propagates through the optical resonator 208, while non-resonant frequency components are rejected.

[0058] After the optical signal propagates through the optical resonator 208, the first optical coupler 206 is configured to couple a portion of the optical signal out of the optical resonator 208, and the optical signal is directed to the first circulator 204. Since the optical signal propagates in a direction toward the broadband light source 202 and is received at the second port of the first circulator 204, the first circulator 204 acts as an isolator to direct the optical signal to the gain element 214 and prevent the optical signal from propagating back to the broadband light source 202.

[0059] The gain element 214 (also referred to as a “gain medium”) is configured to amplify the optical signal output from the optical resonator 208. Figure 2 In the example shown, the gain element 214 is a rare earth doped amplifier that is optically pumped using a pump laser 215. In some examples, the gain element 214 can be an optical fiber or waveguide doped with rare earth ions such as erbium, ytterbium, etc., and the pump laser 215 is a 980nm or 1480nm pump laser. In other examples, the gain element 214 can be a semiconductor optical amplifier that is electrically pumped to provide a desired level of optical signal amplification.

[0060] exist Figure 2In the example shown, the resonator optical gyroscope 200 includes a power monitor 216 that is configured to measure the power level of the optical signal after a first pass through the optical resonator 208. The amount of amplification provided to the optical signal by the gain element 214 is adjustable. In some examples, the power level of the optical signal after a first pass through the optical resonator 208 can be used to determine the losses due to the optical resonator 208 and can be used to adjust the gain element 214. In some examples, the pump power of the optical pump used for the gain element 214 (e.g., where the gain element 214 is an EDFA) or the amount of current used for the pump of the gain element 214 (e.g., where the gain element 214 is an SOA) can be adjusted based on the power measurement from the power monitor 216. In some examples, the adjustment is made using a servo mechanism or another control circuit.

[0061] Regardless of the type of gain element 214 used in the resonator optical gyroscope, in some examples, the amount of optical or electrical pumping of the gain element 214 is selected based at least in part on the desired overall power consumption of the resonator optical gyroscope 200. For example, the power consumption of pumping the gain element 214 can be limited based on the overall power consumption of the resonator optical gyroscope 200, which includes the power consumption for pumping the broadband light source 202 as well as the operation of the phase modulator 218 (if included), the photodetector 220, and the demodulation and rate detection circuit 222. By using the gain element 214 to amplify the optical signal after the second pass through the optical resonator 208, the amount of power (e.g., pump power) used for the broadband light source 202 can be reduced, and the power level of the amplified optical signal at the photodetector 220 will still be significantly improved (e.g., by orders of magnitude), even without increasing the power consumption of the entire resonator optical gyroscope 200.

[0062] The amplified optical signal propagates from the gain element 214 to the photodetector 220. The photodetector 220 is configured to convert the amplified optical signal from an optical signal to a corresponding electrical signal based on the power of the received amplified optical signal. The electrical signal corresponding to the amplified optical signal is then provided to the demodulation and rate detection circuit 222.

[0063] To determine the rotation rate, the demodulation and rate detection circuit 222 is configured to demodulate the electrical signal and determine the resonant frequency shift based on the power of the demodulated signal corresponding to the amplified optical signal. For example, the received electrical signal may indicate a power difference corresponding to a change in rotation rate.

[0064] In some examples, the resonator optical gyroscope 200 also includes a phase modulator 218 coupled between the second port of the second circulator 212 and the third port of the second circulator 212. The phase modulator 218 is configured to modulate the phase of the optical signal based on the phase modulation signal determined by the demodulation and rate detection circuit 222. In some examples, the phase modulator 218 is configured to generate the phase modulated optical signal using a sawtooth waveform. In some examples, the phase modulator 118 is an electro-optical phase modulator. Utilizing such a phase modulator simplifies the architecture of the resonator optical gyroscope 100 compared to previous designs and reduces the size and cost of implementing phase modulation and frequency shifting of the optical signal.

[0065] Once modulated by the phase modulator 218, the phase modulated optical signal is sent back to the optical resonator 208 in the opposite direction through the second circulator 212 to the second optical coupler 210. After modulation, the phase modulated optical signal is provided to the third port of the second circulator 212. The phase modulated optical signal received at the third port of the second circulator 112 is output to the first port of the second circulator 112, which then passes the phase modulated optical signal back to the second optical coupler 210. The second optical coupler 210 is configured to couple at least a portion of the phase modulated optical signal into the optical resonator 208.

[0066] After the phase-modulated optical signal propagates through the optical resonator 208, the first optical coupler 206 is configured to couple a portion of the phase-modulated optical signal out of the optical resonator 208, and the phase-modulated optical signal is directed to the first circulator 204. Since the phase-modulated optical signal propagates in a direction toward the broadband light source 202 and is received at the second port of the first circulator 204, the first circulator 204 acts as an isolator to direct the phase-modulated optical signal to the gain element 214 and prevent the phase-modulated optical signal from propagating back to the broadband light source 202.

[0067] The phase modulated optical signal propagates from the first circulator 204 to the gain element 214, which amplifies the phase modulated optical signal to produce a phase modulated amplified optical signal. The phase modulated amplified optical signal is provided to the photodetector 120, which is configured to convert the phase modulated amplified optical signal from an optical signal to a corresponding electrical signal based on the power of the received phase modulated amplified optical signal. The electrical signal corresponding to the phase modulated amplified optical signal is then provided to the demodulation and rate detection circuit 222.

[0068] In some examples, the power level of the phase modulated amplified optical signal at the photodetector 220 can also be used to adjust the slope of the phase modulated signal at the phase modulator 218, and the slope difference between two consecutive cycles of the phase modulated signal can be used to determine the frequency shift. The demodulation and rate detection circuit 222 can then determine the rotation rate based on the frequency shift.

[0069] In some examples, Figure 2 The resonator optical gyroscope 200 shown in FIG. 2 is configured to operate as a closed-loop optical gyroscope because the output from the optical resonator 208 indicating the rotation rate is also used as feedback to adjust the operation of the phase modulator 218 (where “closed loop” includes the propagation of the signal from the phase modulator 218 ultimately to the demodulation and rate detection circuit 222 and the control signal input to the phase modulator 218). In some examples, the demodulation and rate detection circuit 222 includes a control circuit configured to adjust the operation of the phase modulator 218 based on the electrical signal from the photodetector 220. In some examples, the demodulation and rate detection circuit 222 configures at least one parameter of the phase modulator 218, such as a characteristic of the phase modulation signal used by the phase modulator 218 to modulate the optical signal. For example, as previously described, the demodulation and rate detection circuit 222 is configured to adjust the slope of the sawtooth phase modulation signal based on the power change determined from the received electrical signal. The demodulation and rate detection circuit 222 can send a control signal that configures the phase modulator 218. The chirp transponder modulation (sawtooth phase modulation) shifts the frequency of the return beam and makes the frequency overlap with the CW resonance peak of the optical resonator 208 .

[0070] In response to receiving the control signal for adjusting the slope of the phase modulated signal, the phase modulator 218 generates an adjusted phase modulated signal having a slope of a waveform corresponding to the parameters set by the demodulation and rate detection circuit 222. For example, the phase modulated optical signal may have a frequency shift corresponding to the shifted resonant frequency of the optical resonator 108 due to the rotation. In this way, the resonator optical gyroscope 200 (and specifically the demodulation and rate detection circuit 222) can compensate for power changes (e.g., changes caused by rotation) in the average power of the phase modulated amplified optical signal detected by the demodulation and rate detection circuit 222.

[0071] In some examples, to reduce rate measurement errors, the optical resonator 208 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization state. For example, the optical resonator 208 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization mode of the optical resonator 208. Thus, only portions of the optical signal corresponding to a selected polarization mode of the optical resonator 208 are allowed to pass through the polarizer and are transmitted through the optical resonator 208 on each round trip.

[0072] Although not explicitly shown, in some examples, Figure 2 The pump laser 215 shown can be used in a manner similar to that described above with respect to Figure 1B The manner described is shared by broadband light source 202 and / or gain element 214. In such examples, the pump power for optical pumping of gain element 214 and / or the splitting ratio achieved by a coupler (not shown) that splits the shared pump laser 215 can be adjusted based on power measurements from power monitor 216. In some examples, the adjustment is made using a servomechanism or another control circuit.

[0073] Furthermore, it should be understood that in some implementations of the resonator optical gyroscope 100, 150, 200, the resonator optical gyroscope 100, 150, 200 may include multiple gain elements 114, 214. For example, the resonator optical gyroscope may include a first gain element (such as gain element 114) configured to amplify the optical signal after the optical signal passes through the optical resonator in the first direction and before the optical signal is coupled into the optical resonator to propagate in the second direction, and the resonator optical gyroscope may include a second gain element (such as gain element 214) configured to amplify the optical signal after the optical signal passes through the optical resonator in the second direction.

[0074] Figure 3 A block diagram of an exemplary resonator optical gyroscope 300 is shown in which techniques for efficient optical power management for low shot noise may be implemented. Figure 3 In the example shown, the resonator optical gyroscope 300 includes various components, including a broadband light source 302, a first optical coupler 306, an optical resonator 308, a second optical coupler 310, a gain element 314, power monitors 311, 316, a fiber Bragg grating 313, a rate photodetector 320, and a demodulation and rate detection circuit 322. Although in Figure 3Although not specifically labeled, the components of the resonator optical gyroscope 300 are coupled via suitable guiding optics. For example, the components of the resonator optical gyroscope 300 may be coupled via optical waveguides and / or free-space optics such as lenses, mirrors, and beam splitters. In some examples, the resonator optical gyroscope 300 is implemented on an integrated photonic substrate such as a photonic chip.

[0075] The resonator optical gyroscope 300 generally operates by propagating optical signals through different optical paths, where the optical signals are ultimately processed to determine the rate of rotation experienced by the demodulation and rate detection circuitry 322 of the resonator optical gyroscope 300 .

[0076] The broadband light source 302 is configured to generate an optical signal having a broadband frequency range. In some examples, the broadband light source 302 is a broadband laser configured to generate an optical signal via amplified spontaneous emission (ASE). Figure 3 In the example shown, the broadband light source 302 is a rare-earth doped optical fiber or other waveguide light source, and the broadband light source 302 is optically pumped using a pump laser 301. In some examples, the broadband light source 302 can be an optical fiber doped with rare earth ions such as erbium, ytterbium, etc., and the pump laser 301 is a 980nm or 1480nm pump laser. In any case, the optical signal generated by the broadband light source 302 has a continuous broadband spectrum and low coherence. In some examples, the broadband light source 302 is configured to generate an optical signal of a selected frequency / wavelength range or intensity that reduces the effects from the optical Kerr effect or makes such effects negligible.

[0077] exist Figure 3 In the example shown, an optical signal generated by a broadband light source 302 is provided to a circulator 304. Figure 3 In the example shown, the circulator 304 is a three-port device that is configured to output a signal received at one port to another specific port. Figure 3 In the example shown, an optical signal received from a broadband light source 302 at a first port is output to a second port coupled to a first optical coupler 306. Figure 3 In the example shown, the optical signal received from the first optical coupler 306 at the second port is output to a third port connected to the photodetector 320 .

[0078] The circulator 304 is configured to provide an optical signal received from the broadband light source 302 to the first optical coupler 306, and the first optical coupler 306 is configured to couple at least a portion of the optical signal into the optical resonator 308. In some examples, the optical fiber extending through the first optical coupler 306 is beveled to prevent back reflections of a portion of the optical signal that is not transmitted into the optical resonator 308. In other examples, an optical isolator or similar device may also be used to prevent back reflections. In any case, preventing back reflections ensures that these signals do not interfere with other signals received by the first optical coupler 306 (including optical signals generated by the broadband light source 302 and amplified optical signals, as further described herein).

[0079] The optical resonator 308 is configured to pass a portion of the coupled optical signal at one or more resonant frequencies of the optical resonator 308. When the first optical coupler 306 receives the optical signal from the broadband light source 302, it directs the optical signal to propagate in the optical resonator 308 in a first direction. Figure 3 In the example shown, the optical signal coupled into the optical resonator 308 by the first optical coupler 306 propagates in a counterclockwise (CCW) direction. However, in other examples, the resonator optical gyroscope 300 may be designed so that the optical signal initially propagates in a clockwise (CW) direction. As the optical signal propagates in the optical resonator 308, some frequency components of the optical signal (particularly frequency components that are not close to the resonant frequency of the optical resonator 308) will destructively interfere and not resonate. Therefore, the frequency component of the optical signal corresponding to the resonant frequency of the optical resonator 308 will be transmitted to the output port (the second optical coupler 310), while other frequency components will not be transmitted.

[0080] After propagating through the optical resonator 308, a portion of the optical signal is coupled out of the optical resonator 308 via the second optical coupler 310. Optical filtering of the optical signal in the first path through the optical resonator 308 reshapes the broadband spectrum to match the optical resonator transmission line. Figure 3 As shown, the optical signal coupled out of the optical resonator 308 has a significantly reduced power level and is channelized in the CCW direction through multiple resonances.

[0081] The optical signal coupled out of the optical resonator 308 via the second optical coupler 310 is then provided to an optical path including a fiber Bragg grating 313 and a gain element 314. Figure 3 In the example shown, the pump laser 301 is configured to optically pump both the broadband light source 302 and the gain element 314. In some examples, the pump laser 103 is a 980 nm or 1480 nm pump laser. Figure 3In the example shown, the optical splitter 303 is used to couple the pump power to the broadband light source 302 and the gain element 314 to split into different desired configurations. For example, the optical splitter 303 can be configured to achieve a 50 / 50 split ratio of the pump power, such that 50% of the pump power is provided to the broadband light source 302 and 50% of the pump power is provided to the gain element 314. It should be understood that the optical splitter 303 can also achieve other ratios depending on the desired performance and design constraints.

[0082] exist Figure 3 In the example shown, gain element 314 is optically pumped in a single direction and provides amplification in a single direction. Figure 3 In the example shown, the optical signal propagates to the fiber Bragg grating 313 and is reflected back. In some examples, the fiber Bragg grating 313 can also be a waveguide reflector (e.g., a grating on a waveguide). After the optical signal is reflected back and propagates in the opposite direction, the gain element 314 is configured to amplify the optical signal. Figure 3 In the example shown, the gain element 314 is a rare earth doped amplifier. For example, the gain element 314 can be an optical fiber or waveguide doped with rare earth ions such as erbium, ytterbium, etc. In such examples, the gain element 314 is optically pumped (e.g., using a 980nm or 1480nm pump laser) to provide a desired level of amplification to an optical signal propagating in a particular direction. In other examples, the gain element 314 is a semiconductor optical amplifier. In such examples, the gain element 314 is electrically pumped to provide a desired level of amplification of the optical signal.

[0083] exist Figure 3 In the example shown, the resonator optical gyroscope 300 includes a plurality of power monitors 311, 316 configured to measure the power level of the amplified optical signal, and the amount of amplification provided to the optical signal by the gain element 314 is adjustable. In some examples, it is desirable to produce the amplified optical signal at a particular power level during calibration and / or to maintain an approximately constant output power using the gain element 314 during operation. In some examples, the pump power of the optical pump for the gain element 314 (e.g., where the gain element 314 is an EDFA) and / or the splitting ratio achieved by the optical splitter 303 can be adjusted based on the power measurements from the power monitors 311, 316. In some examples, the adjustment is made using a servo mechanism or another control circuit.

[0084] Regardless of the type of gain element 314 used in the resonator optical gyroscope, in some examples, the amount of optical or electrical pumping of the gain element 314 is selected based at least in part on the desired overall power consumption of the resonator optical gyroscope. For example, the power consumption of pumping the gain element 314 can be limited based on the overall power consumption of the resonator optical gyroscope 300, which includes the power consumption for pumping the broadband light source 302 and the operation of the photodetector 320 and the demodulation and rate detection circuit 322. By using the gain element 314 to amplify the optical signal after the first pass through the optical resonator 308, the amount of power (e.g., pump power) used for the broadband light source 302 can be reduced, and the power level of the amplified optical signal at the photodetector 320 will be significantly improved (e.g., by orders of magnitude), even without increasing the overall power consumption of the entire resonator optical gyroscope 300.

[0085] The amplified optical signal is provided to the second optical coupler 310. The second optical coupler 310 is configured to couple at least a portion of the amplified optical signal into the optical resonator 308. When some of the signal is coupled into the optical resonator 308, the remaining amount of the signal propagates toward the optical fiber extending through the second optical coupler 310. In some examples, the optical fiber extending through the second optical coupler 310 is beveled to prevent back reflection of a portion of the amplified optical signal that is not transmitted into the optical resonator 308. In other examples, an optical isolator or similar device may also be used to prevent back reflection. In any case, preventing back reflection ensures that these signals do not interfere with other signals received by the second optical coupler 310.

[0086] The second optical coupler 310 couples the amplified optical signal in the second direction through the optical resonator 308. Figure 3 In the example shown, the amplified optical signal propagates in the CW direction.The amplified optical signal having frequency components corresponding to the resonance peak of the optical resonator 308 propagates through the optical resonator 308, while non-resonant frequency components are rejected.

[0087] After the amplified optical signal propagates through the optical resonator 308, the first optical coupler 306 is configured to couple a portion of the amplified optical signal out of the optical resonator 308, and the amplified optical signal is directed to the circulator 304. Since the amplified optical signal propagates in a direction toward the broadband light source 302 and is received at the second port of the circulator 304, the circulator 304 acts as an isolator to direct the amplified optical signal to the photodetector 320 and prevent the amplified optical signal from propagating back to the broadband light source 302.

[0088] The amplified optical signal propagates from the circulator 304 to the photodetector 320. The photodetector 320 is configured to convert the amplified optical signal from an optical signal to a corresponding electrical signal based on the power of the received amplified optical signal. The electrical signal corresponding to the amplified optical signal is then provided to the demodulation and rate detection circuit 322.

[0089] To determine the rotation rate, the demodulation and rate detection circuit 322 is configured to demodulate the electrical signal and determine the resonant frequency shift based on the power of the demodulated signal corresponding to the amplified optical signal. For example, the received electrical signal may indicate a power difference corresponding to a change in rotation rate.

[0090] In some examples, to reduce rate measurement errors, the optical resonator 308 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization state. For example, the optical resonator 308 may include a polarizer (not shown) configured to filter out portions of the optical signal corresponding to an undesired polarization mode of the optical resonator 308. Thus, only portions of the optical signal corresponding to a selected polarization mode of the optical resonator 308 are allowed to pass through the polarizer and are transmitted through the optical resonator 308 on each round trip.

[0091] Additionally, it should be understood that the resonator optical gyroscope may include a second gain element in some implementations of the resonator optical gyroscope 300. For example, the resonator optical gyroscope 300 may include a second gain element (similar to the gain element 214) configured to amplify the optical signal after the optical signal passes through the optical resonator in the second direction.

[0092] Figure 4 A flow chart of an exemplary method 400 of operating a resonator optical gyroscope is shown. Figures 1A to 3 The common features discussed with respect to the exemplary systems in may include similar characteristics to those discussed with respect to method 400, and vice versa. In some examples, blocks of method 400 are performed by the resonator optical gyroscopes 100, 150, 300 described above.

[0093] Method 400 includes generating an optical signal having a broadband frequency range (block 402). In some examples, the optical signal is generated using a broadband light source, which may be an ASE laser, a rare-earth doped optical fiber, a superluminescent laser diode, a light emitting diode, or the like.

[0094] The method 400 also includes coupling an optical signal into the optical resonator to propagate in a first direction (block 404), and coupling the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the first direction (block 406). In some examples, the optical signal is coupled into and out of the optical resonator using a first optical coupler and a second optical coupler, respectively.

[0095] The method 400 also includes amplifying the optical signal coupled out of the optical resonator after the optical signal passes through the optical resonator in the first direction (block 408). In some examples, amplifying the optical signal is performed using a gain element, which may be a rare-earth doped amplifier, a semiconductor optical amplifier, etc. In some examples, the gain element is optically pumped or electrically pumped, and the amount of pump power is determined based at least in part on a desired total power consumption of the resonator optical gyroscope.

[0096] In some examples, phase modulation is not applied to the amplified optical signal. In such examples, method 400 continues by coupling the amplified optical signal into the optical resonator for propagation in the second direction (block 410), and coupling the amplified optical signal out of the optical resonator after the optical signal passes through the optical resonator in the second direction (block 412). In some examples, the optical signal is coupled into and out of the optical resonator using the second optical coupler and the first optical coupler, respectively.

[0097] In examples where phase modulation is not applied to the amplified optical signal, method 400 also includes generating an electrical signal corresponding to the amplified optical signal (block 414). In some examples, the electrical signal is generated by the photodetector based on a power level of the phase modulated amplified optical signal.

[0098] In other examples, method 400 also includes applying phase modulation to the amplified optical signal (block 409). In some examples, applying phase modulation to the amplified optical signal includes using a sawtooth waveform.

[0099] In examples where phase modulation is applied to the amplified optical signal, method 400 also includes coupling the phase modulated amplified optical signal into the optical resonator for propagation in the second direction (block 411), and coupling the phase modulated amplified optical signal out of the optical resonator after the optical signal passes through the optical resonator in the second direction (block 413). In some examples, the optical signal is coupled into and out of the optical resonator using a second optical coupler and a first optical coupler, respectively.

[0100] In examples where phase modulation is applied to the amplified optical signal, method 400 also includes generating an electrical signal corresponding to the phase modulated amplified optical signal (block 415). In some examples, the electrical signal is generated by a photodetector based on a power level of the phase modulated amplified optical signal.

[0101] Regardless of whether phase modulation is applied to the amplified optical signal, method 400 also includes determining a rotation rate based on the electrical signal (block 416). In some examples, determining the rotation rate includes demodulating the electrical signal and determining a resonant frequency shift based on a power of the demodulated electrical signal corresponding to the amplified optical signal or the phase modulated amplified optical signal (depending on the circumstances).

[0102] In some examples, phase modulation (block 409) may be performed prior to amplification (block 408). In such examples, phase modulation is applied to the optical signal coupled out of the optical resonator after the optical signal passes through the optical resonator in the first direction, and the phase modulated optical signal is amplified.

[0103] Figure 5 A flow chart of an exemplary method 500 of operating a resonator optical gyroscope is shown. Figures 1A to 3 The common features discussed with respect to the exemplary systems in may include similar characteristics to those discussed with respect to method 500, and vice versa. In some examples, blocks of method 500 are performed by resonator optical gyroscope 200 described above.

[0104] Method 500 includes generating an optical signal having a broadband frequency range (block 502). In some examples, the optical signal is generated using a broadband light source, which may be an ASE laser, a rare-earth doped optical fiber, a superluminescent laser diode, a light emitting diode, or the like.

[0105] The method 500 also includes coupling an optical signal into the optical resonator to propagate in a first direction (block 504), and coupling the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the first direction (block 506). In some examples, the optical signal is coupled into and out of the optical resonator using a first optical coupler and a second optical coupler, respectively.

[0106] In some examples, phase modulation is not applied to the optical signal. In such examples, method 500 continues by coupling the optical signal into the optical resonator for propagation in the second direction (block 508), and coupling the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the second direction (block 510). In some examples, the optical signal is coupled into and out of the optical resonator using a second optical coupler and a first optical coupler, respectively.

[0107] In examples where phase modulation is not applied to the amplified optical signal, method 500 further includes amplifying the optical signal coupled out of the optical resonator after the optical signal passes through the optical resonator in the second direction (block 512). In some examples, amplifying the optical signal is performed using a gain element, which may be a rare-earth doped amplifier, a semiconductor optical amplifier, etc. In some examples, the gain element is optically pumped or electrically pumped, and the amount of pump power is determined based at least in part on a desired total power consumption of the resonator optical gyroscope.

[0108] In examples where phase modulation is not applied to the amplified optical signal, method 500 also includes generating an electrical signal corresponding to the amplified optical signal (block 514). In some examples, the electrical signal is generated by the photodetector based on a power level of the phase modulated amplified optical signal.

[0109] In other examples, the method 500 further includes applying phase modulation to the amplified optical signal (block 507). In some examples, applying phase modulation to the amplified optical signal includes using a sawtooth waveform.

[0110] In examples where phase modulation is applied to the optical signal, method 500 also includes coupling the phase modulated amplified optical signal into the optical resonator for propagation in the second direction (block 509), and coupling the phase modulated optical signal out of the optical resonator after the optical signal passes through the optical resonator in the second direction (block 511). In some examples, the optical signal is coupled into and out of the optical resonator using a second optical coupler and a first optical coupler, respectively.

[0111] In examples where phase modulation is applied to the amplified optical signal, method 500 further includes amplifying the phase modulated optical signal coupled out of the optical resonator after the phase modulated optical signal passes through the optical resonator in the second direction (block 513). In some examples, amplifying the phase modulated optical signal is performed using a gain element, which may be a rare earth doped amplifier, a semiconductor optical amplifier, etc. In some examples, the gain element is optically pumped or electrically pumped, and the amount of pump power is determined based at least in part on a desired total power consumption of the resonator optical gyroscope.

[0112] In examples where phase modulation is applied to the amplified optical signal, method 500 also includes generating an electrical signal corresponding to the phase modulated amplified optical signal (block 515). In some examples, the electrical signal is generated by a photodetector based on a power level of the phase modulated amplified optical signal.

[0113] Regardless of whether phase modulation is applied to the amplified optical signal, method 500 also includes determining a rotation rate based on the electrical signal (block 516). In some examples, determining the rotation rate includes demodulating the electrical signal and determining a resonant frequency shift based on a power of the demodulated electrical signal corresponding to the amplified optical signal or the phase modulated amplified optical signal (depending on the circumstances).

[0114] By using strategically placed gain elements as described herein, several advantages are achieved over currently available resonator optical gyroscopes that utilize broadband light sources. The power level of the optical signal received at the photodetector of the resonator optical gyroscope described herein is several orders of magnitude higher than other systems. This ensures that the power level of the optical signal at the detector is high enough to reduce the shot noise level, and the increase in power level can be achieved without increasing the overall power consumption of the resonator optical gyroscope. In addition, when a phase modulator and / or polarizer is used in conjunction with the gain element as described herein, the power level of the optical signal can be further improved and the error on the rotation rate measurement reduced.

[0115] In various aspects, the system elements, method steps, or examples described in the present disclosure (such as, for example, the demodulation and rate detection circuit 122 or its components) may be implemented on one or more computer systems including a central processing unit (CPU), a graphics processing unit (GPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), and / or similar devices including hardware execution code for implementing those elements, processes, or examples, the code being stored on a non-transitory data storage device. These devices include or operate using software programs, firmware, or other computer readable instructions for performing various methods, process tasks, calculations, and control functions.

[0116] These instructions are usually stored on any suitable computer storage medium for storing computer-readable instructions or data structures. Computer-readable media can be implemented as any available medium that can be accessed by a general or special-purpose computer or processor or any programmable logic device. Suitable processor-readable media may include storage devices or memory media, such as magnetic media or optical media. For example, storage or memory media may include conventional hard disks, CD-ROMs, volatile or non-volatile media such as random access memories (RAM) (including but not limited to synchronous dynamic random access memories (SDRAM), double data rate (DDR) RAM, RAMBUS dynamic RAM (RDRAM), static RAM (SRAM) etc.), read-only memories (ROM), electrically erasable programmable ROM (EEPROM) and flash memory etc. Suitable processor-readable media may also include transmission media (such as electrical signals, electromagnetic signals or digital signals) transmitted via communication media (such as networks and / or wireless links).

[0117] The methods and techniques described herein may be implemented in part in digital electronic circuits or with a programmable processor (e.g., a special purpose processor or a general purpose processor such as a computer), firmware, software, or a combination thereof. Apparatus embodying these techniques may include appropriate input and output devices, a programmable processor, and a storage medium tangibly embodying program instructions for execution by the programmable processor. Processes embodying these techniques may be performed by a programmable processor executing a program of instructions to perform a desired function by operating on input data and producing appropriate outputs. These techniques may advantageously be implemented in one or more programs executable on a programmable system, the programmable system including at least one programmable processor coupled to receive data and instructions from and transmit data and instructions to a data storage system, at least one input device, and at least one output device. Generally, the processor will receive instructions and data from a read-only memory and / or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including (by way of example) semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and DVD disks. Any of the foregoing may be supplemented by, or incorporated in, specially designed application specific integrated circuits (ASICs).

[0118] Exemplary embodiments

[0119] Embodiment 1 includes a resonator optical gyroscope, the resonator optical gyroscope comprising: a broadband light source, the broadband light source configured to generate an optical signal having a broadband frequency range; an optical resonator; a first optical coupler, the first optical coupler coupled to the optical resonator, wherein the first optical coupler is configured to receive the optical signal from the broadband light source and couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in a first direction, wherein the first optical coupler is further configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in a second direction; a second optical coupler, the second optical coupler coupled to the optical resonator, wherein the second optical coupler a first optical coupler configured to couple the optical signal out of the optical resonator after the optical signal passes through the optical resonator in the first direction, wherein the first optical coupler is further configured to couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in the second direction; a gain element configured to amplify the optical signal that has been coupled out of the optical resonator and passes through the optical resonator in the first direction to produce an amplified optical signal; a photodetector configured to convert the amplified optical signal from a photosensitive element to a corresponding electrical signal based on a power level of the amplified optical signal; and one or more circuits configured to determine a rotation rate based on the corresponding electrical signal.

[0120] Embodiment 2 includes the resonator optical gyroscope of embodiment 1, wherein the gain element is configured to receive an optical signal coupled out of the optical resonator by the second optical coupler, and amplify the optical signal coupled out of the optical resonator by the second optical coupler to produce an amplified optical signal; wherein the second optical coupler is configured to couple the amplified optical signal into the optical resonator so that the amplified optical signal propagates through the optical resonator in the second direction; and wherein the first optical coupler is further configured to couple the amplified optical signal out of the optical resonator after the amplified optical signal passes through the optical resonator in the second direction.

[0121] Embodiment 3 includes the resonator optical gyroscope of embodiment 1, wherein the gain element is configured to: receive an optical signal coupled out of the optical resonator by the first optical coupler; amplify the optical signal coupled out of the optical resonator by the first optical coupler to generate an amplified optical signal; and output the amplified optical signal to the photodetector.

[0122] Embodiment 4 includes the resonator optical gyroscope of any one of Embodiments 1-3, further comprising a first pump laser configured to optically pump the gain element and the broadband light source.

[0123] Embodiment 5 includes the resonator optical gyroscope described in any one of Embodiments 1-4, wherein the resonator optical gyroscope further includes: at least one power monitor, wherein the at least one power monitor is configured to measure the power level of the optical signal; and at least one control circuit, wherein the at least one control circuit is configured to adjust the gain element based on the measured power level of the optical signal.

[0124] Embodiment 6 includes the resonator optical gyroscope described in any one of Embodiments 1-5, wherein the resonator optical gyroscope further includes: a first circulator coupled between the broadband light source and the first optical coupler, wherein the first circulator is configured to provide an optical signal from the broadband light source to the first optical coupler and to provide an optical signal from the first optical coupler to the gain element or the photodetector; and / or a second circulator coupled to the second optical coupler, wherein the second circulator is configured to provide an optical signal from the second optical coupler to the gain element or the phase modulator.

[0125] Embodiment 7 includes the resonator optical gyroscope described in any one of Embodiments 1-6, wherein the resonator optical gyroscope further includes a fiber reflector or a waveguide reflector configured to back-reflect the optical signal toward the gain element or the phase modulator.

[0126] Embodiment 8 includes the resonator optical gyroscope described in any of Embodiments 1-6, further comprising a phase modulator configured to apply phase modulation to an optical signal that has been coupled out of the optical resonator by the second optical coupler and has passed through the optical resonator in the first direction.

[0127] Embodiment 9 includes a resonator optical gyroscope comprising: a broadband light source configured to generate an optical signal having a broadband frequency range; an optical resonator; a first optical coupler coupled to the optical resonator, wherein the first optical coupler is configured to receive the optical signal from the broadband light source and couple the optical signal into the optical resonator such that the optical signal propagates through the optical resonator in a first direction, wherein the first optical coupler is further configured to couple the optical signal out of the optical resonator after the optical signal propagates through the optical resonator in a second direction; and a second optical coupler coupled to the optical resonator, wherein the second optical coupler is configured to couple the optical signal out of the optical resonator after the optical signal propagates through the optical resonator in the first direction. The invention relates to a method for producing a rotational signal comprising: coupling the optical signal out of the optical resonator by the first optical coupler, wherein the first optical coupler is further configured to couple the optical signal into the optical resonator so that the optical signal propagates through the optical resonator in the second direction; one or more gain elements, the one or more gain elements being configured to amplify the optical signal that has been coupled out of the optical resonator by the second optical coupler and passes through the optical resonator in the first direction and / or the optical signal that has been coupled out of the optical resonator by the first optical coupler and passes through the optical resonator in the second direction; a photodetector, the photodetector being configured to convert the amplified optical signal into a corresponding electrical signal based on a power level of the amplified optical signal; and one or more circuits, the one or more circuits being configured to determine a rotation rate based on the corresponding electrical signal.

[0128] Embodiment 10 includes the resonator optical gyroscope of embodiment 9, the resonator optical gyroscope further comprising a phase modulator; wherein the one or more gain elements include a first gain element, the first gain element being configured to receive an optical signal coupled out of the optical resonator by the second optical coupler, and to amplify the optical signal coupled out of the optical resonator by the second optical coupler to produce an amplified optical signal; wherein the phase modulator is configured to receive the amplified optical signal from the first gain element, and to apply phase modulation to the amplified optical signal to produce a phase-modulated amplified optical signal; wherein the second optical coupler is configured to couple the phase-modulated amplified optical signal into the optical resonator so that the phase-modulated amplified optical signal propagates through the optical resonator in the second direction; wherein the first optical coupler is configured to couple the phase-modulated amplified optical signal out of the optical resonator after the phase-modulated amplified optical signal passes through the optical resonator in the second direction.

[0129] Embodiment 11 includes the resonator optical gyroscope of Embodiment 10, wherein the one or more gain elements include a second gain element, the second gain element being configured to receive the phase modulated amplified optical signal coupled out of the optical resonator by the first optical coupler and to further amplify the phase modulated amplified optical signal.

[0130] Embodiment 12 includes the resonator optical gyroscope of embodiment 9, the resonator optical gyroscope further comprising a phase modulator, wherein the phase modulator is configured to receive the optical signal coupled out of the optical resonator by the second optical coupler, and apply phase modulation to the optical signal to produce a phase modulated optical signal; wherein the second optical coupler is configured to couple the phase modulated optical signal into the optical resonator so that the phase modulated optical signal propagates through the optical resonator in the second direction; wherein the first optical coupler is configured to couple the phase modulated optical signal out of the optical resonator after the phase modulated optical signal passes through the optical resonator in the second direction; wherein the one or more gain elements include a first gain element, the first gain element being configured to receive the phase modulated optical signal coupled out of the optical resonator by the first optical coupler, and amplify the phase modulated optical signal to produce a phase modulated amplified optical signal.

[0131] Embodiment 13 includes the resonator optical gyroscope of embodiment 9, wherein the resonator optical gyroscope further includes a phase modulator, wherein the phase modulator is configured to receive the optical signal coupled out of the optical resonator by the second optical coupler, and apply phase modulation to the optical signal to produce a phase-modulated optical signal; wherein the one or more gain elements include a first gain element, wherein the first gain element is configured to receive the phase-modulated optical signal from the phase modulator and amplify the phase-modulated optical signal to produce a phase-modulated amplified optical signal; wherein the second optical coupler is configured to couple the phase-modulated amplified optical signal into the optical resonator so that the phase-modulated amplified optical signal propagates through the optical resonator in the second direction; wherein the first optical coupler is configured to couple the phase-modulated amplified optical signal out of the optical resonator after the phase-modulated amplified optical signal passes through the optical resonator in the second direction.

[0132] Embodiment 14 includes the resonator optical gyroscope of any of Embodiments 9-13, further comprising one or more pump lasers configured to optically pump the broadband light source and the one or more gain elements.

[0133] Embodiment 15 includes the resonator optical gyroscope described in any one of Embodiments 9-14, wherein the resonator optical gyroscope further includes: at least one power monitor, wherein the at least one power monitor is configured to measure the power level of the optical signal; and at least one control circuit, wherein the at least one control circuit is configured to adjust the one or more gain elements based on the measured power level of the optical signal.

[0134] Embodiment 16 includes a method of operating a resonator optical gyroscope, the method comprising: using a broadband light source to generate an optical signal having a broadband frequency range; using a first optical coupler to couple the optical signal into an optical resonator to propagate in a first direction; after the optical signal passes through the optical resonator in the first direction, using a second optical coupler to couple the optical signal out of the optical resonator; using the second optical coupler to couple the optical signal into the optical resonator to propagate in a second direction; after the optical signal passes through the optical resonator in the second direction, using the first optical coupler to couple the optical signal out of the optical resonator; using one or more gain elements to amplify the optical signal coupled out of the optical resonator by the second optical coupler or the optical signal coupled out of the optical resonator by the first optical coupler to generate an amplified optical signal; using a photodetector to generate an electrical signal corresponding to the amplified optical signal; and determining a rotation rate based on the electrical signal.

[0135] Embodiment 17 includes the method of Embodiment 16, wherein amplifying the optical signal coupled out of the optical resonator by the second optical coupler or the optical signal coupled out of the optical resonator by the first optical coupler to produce an amplified optical signal comprises amplifying the optical signal coupled out of the optical resonator by the second optical coupler; wherein the optical signal coupled into the optical resonator using the second optical coupler to propagate in the second direction is the amplified optical signal; wherein the optical signal coupled out of the optical resonator using the first optical coupler is the amplified optical signal.

[0136] Embodiment 18 includes the method of any one of Embodiments 16-17, wherein amplifying the optical signal coupled out of the optical resonator by the second optical coupler or the optical signal coupled out of the optical resonator by the first optical coupler to produce an amplified optical signal includes amplifying the optical signal coupled out of the optical resonator by the first optical coupler.

[0137] Embodiment 19 includes the method of any of Embodiments 16-18, further comprising applying phase modulation to the optical signal coupled out of the optical resonator by the second optical coupler.

[0138] Embodiment 20 includes the method of any of Embodiments 16-19, further comprising optically pumping the broadband light source and the one or more gain elements using a single pump laser.

[0139] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that the present invention be limited only by the claims and the equivalents thereof.

Claims

1. A resonator optical gyroscope (100, 150, 200, 300), the resonator optical gyroscope comprising: A broadband light source (102, 202, 302) configured to generate an optical signal having a broadband frequency range; Optical resonator (108, 208, 308); a first optical coupler (106, 206, 306) coupled to the optical resonator (108, 208, 308), wherein the first optical coupler (106, 206, 306) is configured to receive the optical signal from the broadband light source (102, 202, 302) and couple the optical signal into the optical resonator (108, 208, 308) such that the optical signal propagates through the optical resonator (108, 208, 308) in a first direction, wherein the first optical coupler (106, 206, 306) is further configured to couple the optical signal out of the optical resonator (108, 208, 308) after the optical signal passes through the optical resonator (108, 208, 308) in a second direction; a second optical coupler (110, 210, 310) coupled to the optical resonator (108, 208, 308), wherein the second optical coupler (110, 210, 310) is configured to couple the optical signal out of the optical resonator (108, 208, 308) after the optical signal passes through the optical resonator (108, 208, 308) in the first direction, wherein the first optical coupler (106, 206, 306) is further configured to couple the optical signal into the optical resonator (108, 208, 308) such that the optical signal propagates through the optical resonator (108, 208, 308) in the second direction; a gain element (114, 214, 314) configured to amplify an optical signal that has been coupled out of the optical resonator (108, 208, 308) and passed through the optical resonator (108, 208, 308) in the first direction to produce an amplified optical signal; a photodetector (120, 220, 320) configured to convert the amplified optical signal into a corresponding electrical signal based on a power level of the amplified optical signal; and One or more circuits (122, 222, 322) configured to determine a rotation rate based on the corresponding electrical signal.

2. The resonator optical gyroscope (100, 150, 300) of claim 1, wherein the gain element (114, 314) is configured to receive an optical signal coupled out of the optical resonator (108, 308) by the second optical coupler (110, 310), and to amplify the optical signal coupled out of the optical resonator (108, 308) by the second optical coupler (110, 310) to generate an amplified optical signal; wherein the second optical coupler (110, 310) is configured to couple the amplified optical signal into the optical resonator (108, 308) so that the amplified optical signal propagates through the optical resonator (108, 208, 308) in the second direction; The first optical coupler (106, 306) is further configured to couple the amplified optical signal out of the optical resonator (108, 308) after the amplified optical signal passes through the optical resonator (108, 308) in the second direction.

3. The resonator optical gyroscope (200) of claim 1, wherein the gain element (214) is configured as: receiving an optical signal coupled out of the optical resonator (208) by the first optical coupler (206); amplifying the optical signal coupled out of the optical resonator (208) by the first optical coupler (206) to produce an amplified optical signal; and The amplified optical signal is output to the photodetector (220).

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