Patent Description:
Gyroscopes are used in a variety of devices, such as smartphones, cars, aircrafts and the like for navigation. As is known, a tradeoff exists between the accuracy of a gyroscope and its size. For example, ring laser gyroscopes or fiber optic gyroscopes with relatively high accuracy are expensive and bulky. Micro electro-mechanical systems (MEMS) based gyroscopes are relatively small but lack precision.

Conventional benchtop laser-based gyroscopes require high precision alignment, clean medium and a high-quality laser source to detect small phase shift (due to Sagnac effect) and to minimize noise.

<CIT>, describes a passive ring resonator laser gyro in which the clockwise and counterclockwise beams do not coexist in the resonator. The laser gyro employs thin film technology. In particular, the preferred laser is a gallium aluminum arsenide laser. Light from the laser is phase-modulated by means of a thin film electro-optic modulator comprising a channel waveguide disposed on an electrically active material and flanked by electrodes for modulating the phase of light from the laser. An electro-optic switch is provided for switching light from the laser to inject alternatingly clockwise and counterclockwise beams into the resonator. The resulting gyro is compact and simply implemented into an integrated, thin film package. Because the clockwise and counterclockwise beams do not coexist in the resonator, various beam interaction effects such as beats, backscatter and feedback into the laser are eliminated.

An optical gyroscope, in accordance with a first aspect of the present invention, includes an optical switch adapted to deliver a laser beam to a first path during a first half of a period and to a second path during a second half of the period, a first optical ring configured to deliver a first portion of the beam received from the first path in a clockwise direction during the first half of the period, and further to deliver a first portion of the beam received from the second path in a counter clockwise direction during the second half of the period, a second optical ring configured to deliver a second portion of the beam received from the first path in a counter clockwise direction during the first half of the period, and further to deliver a second portion of the beam received from the second path in a clockwise direction during the second half of the period, a first photodetector adapted to receive the beams delivered by the first and second optical rings during the first half of the period, a second photodetector adapted to receive the beams delivered by the first and second optical rings during the second half of the period, a first trans-impedance amplifier adapted to amplify the output signal of the first photodetector by a first amplification value, a second trans-impedance amplifier adapted to amplify the output signal of the second photodetector by a second amplification value, a first phase modulator adapted to delay a beam received or delivered by the first optical ring by a first predefined phase value, and a signal combiner adapted to generate a first signal representative of a combined outputs of the first and second trans-impedence amplifiers. In one embodiment, the first predefined phase value is a <NUM>° phase value.

In some embodiments, the optical gyroscope further includes a bandpass filter adapter to filter the first signal. In some embodiments, the optical gyroscope further includes a mixer adapted to downconvert a frequency of the filtered first signal to generate a baseband signal. In some embodiments, the optical gyroscope further includes a controller adapted to convert the baseband signal to a digital signal, and generate a signal representative of a degree of rotation of the optical gyroscope about an axis in response to the digital signal.

In one embodiment, the first and second optical rings are ring resonators. In one embodiment, each of the first and second ring resonators further includes, in part, one or more heating elements adapted to tune the resonator. In one embodiment, the heating elements are resistive heating elements integrated with the first and second ring resonators. In one embodiment, the signal combiner is adapted to add output signals of the first and second trans-impedance amplifiers. In one embodiment, the optical switch includes a Mach Zehnder interferometer.

In one embodiment, the optical gyroscope further includes a second phase modulator adapted to delay a signal received or delivered by the second optical ring by a second predefined phase value. In one embodiment, the second phase value is a <NUM>° phase value.

A method of determining a degree of orientation about an axis, in accordance with a second aspect of the present invention, includes delivering a laser beam to a first path during a first half of a period and to a second path during a second half of the period, delivering a first portion of the beam received from the first path to a first optical ring in a clockwise direction during the first half of the period, delivering a first portion of the beam received from the second path to the first optical ring in a counter clockwise direction during the second half of the period, delivering a second portion of the beam received from the first path to a second optical ring in a counter clockwise direction during the first half of the period, delivering a second portion of the beam received from the second path to the second optical ring in a clockwise direction during the second half of the period, detecting the beams delivered by the first and second optical rings during the first half of the period to generate a first signal, detecting the beams delivered by the first and second optical rings during the second half of the period to generate a second signal, and combining the first and second signals to determine a degree of rotation about the axis, amplifying the first signal by a first amplification value to generate a first amplified signal, amplifying the second signal by a second amplification value to generate a second amplified signal, delaying a beam received or delivered by the first optical ring by a first predefined phase value, and combining the first and second amplified signals to generate a combined signal. In one embodiment, the first predefined phase value is a <NUM>° phase value.

In one embodiment, the method further includes filtering the combined signal to generate a filtered signal. In one embodiment, the method further includes downconverting the frequency of the filtered signal to generate a baseband signal. In one embodiment, the method further includes converting the baseband signal to a digital signal, and generating a value representative of a degree of rotation of the optical gyroscope about an axis in response to the digital signal.

In one embodiment, the first and second optical rings are ring resonators. In one embodiment, the method further includes tuning the first and second ring resonators by applying heat. In one embodiment, combining of the first and second amplified signals includes, adding the first and second amplified signals to another signal. In one embodiment, the method further includes delaying a beam received or delivered by the second optical ring by a second predefined phase value. In one embodiment, the second predefined phase value is a <NUM>° phase value.

The optical gyroscope is an optical gyroscope including first and second optical paths formed using optical waveguides in a semiconductor substrate, a coherent laser source generating two optical signals traveling in the first optical path in one direction and in the second optical path in a second direction opposite the first direction, and a photodetector adapted to receive the beams delivered by the first and second optical paths.

The optical waveguides are optical rings. The optical rings may bearing resonators.

The optical gyroscope includes a switch configured to switch between the outputs of the first and second photodetectors. The optical gyroscope may further include, in part, a heater adapted to heat the ring resonator. The optical gyroscope includes a phase modulator adapted to modulate a phase of the beam delivered to or received from the ring resonator.

In accordance with embodiments of the present invention, an integrated optical gyroscope has a high precision, enhanced immunity to noise and is relatively inexpensive to manufacture.

<FIG> shows an optical ring <NUM> assumed to be a part of a gyroscope and adapted to be able to spin about the z axis (perpendicular to the plane of the page). Assume that two laser beams <NUM> and <NUM> enter the ring at entry point <NUM> at the same time. Assume further that beam <NUM> is caused to travel in a clockwise direction (CW) and beam <NUM> is caused to travel in a counter clockwise direction (CCW). If the force applied to the gyroscope does not cause ring <NUM> to rotate about the z-axis (thereby maintaining ring <NUM> in a stationary state) the position Pi of entry point <NUM> does not change and therefore both beams <NUM> and <NUM> reach the entry point <NUM> at the same, as shown in <FIG>.

Assume, that due to an applied force, optical ring <NUM> is caused to rotate about the z-axis and in a CW direction, as shown in <FIG>, thereby causing a change in position of entry point <NUM> from P<NUM> to P<NUM>. This causes beam <NUM> to travel a longer distance to reach position P<NUM> than it does beam <NUM>. The extra distance traveled by beam <NUM> relative to beam <NUM> causes a time difference Δt defined by the following expression: <MAT>.

In equation (<NUM>), R, ω and A respectively represent the radius, angular velocity and area of optical ring <NUM>, and c represents the speed of light. By measuring the time differenceΔt, the angular velocity ω and hence the degree of orientation about the z- axis is determined. Although not shown, it is understood that a gyroscope has three such rings each adapted to rotate about one of the x, y and z axes.

Conventional optical gyroscopes suffer from a number of sources of noise, such as, for example, (i) thermal noise (thermal fluctuations) inside the waveguide or fiber thus inducing phase shift, (ii) fabrication mismatches, (iii) laser phase noise; and (iv) mode conversion inside the waveguide or fiber. An optical gyroscope, in accordance with embodiments of the present invention, minimizes the above sources of noise.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the amount of spin or rotation about, e.g., the z-axis (perpendicular to the plane of the page). Although not shown, it is understood that optical gyroscope <NUM> also includes similar components adapted to detect the amount of rotations about both x and y axes.

The, e.g., z-axis components of optical ring <NUM> are shown as including an optical switch125, first and second optical paths <NUM>, <NUM>, first and second optical rings <NUM>, <NUM>, and first, second, third, fourth, fifth and sixth directional couplers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and first and second photodetectors <NUM>, <NUM>.

The laser beam supplied by laser source <NUM> is delivered to optical switch <NUM> which has a switching frequency of f<NUM> defined by the period <MAT>. During a first half of each such period T, switch <NUM> of optical switch <NUM> is placed in position <NUM> so as to deliver the laser beam to first optical path <NUM> which is subsequently detected by photodetector <NUM>. During a second half of each such period, optical switch <NUM> is placed in position <NUM> so as to deliver the laser beam to second optical path <NUM> which is subsequently detected by photodetector <NUM>.

The laser beam in path <NUM> (received during the first half of each period T) is delivered to optical ring <NUM> by directional couplers <NUM>, <NUM>, and to optical ring <NUM> by directional couplers <NUM>, <NUM>. The beam so delivered to optical ring <NUM> travels in a counter clock-wise direction and received at photodetector <NUM> via directional couplers <NUM> and <NUM>. In a similar manner, the beam in optical ring <NUM> travels in a clock-wise direction and received at photodetector <NUM> via directional couplers <NUM> and <NUM>.

The laser beam in path <NUM> (received during the second half of each period T) is delivered to optical ring <NUM> by directional couplers <NUM>, <NUM>, and to optical ring <NUM> by directional couplers <NUM>, <NUM>. The beam so delivered to optical ring <NUM> travels in a clock-wise direction and received at photodetector <NUM> via directional couplers <NUM> and <NUM>. In a similar manner, the beam in optical ring <NUM> travels in a counter clock-wise direction and received at photodetector <NUM> via directional couplers <NUM> and <NUM>.

When the direction of the coherent laser beam is switched between paths <NUM> and <NUM>, the common mode of the two output signals generated by photodetectors <NUM> and <NUM> capture the effect of fabrication mismatches, thermal noise, and other sources of mismatch. On the other hand, the differential mode of the two output signals generated by photodetectors <NUM> and <NUM> contains the information regarding the desired signal which is the phase shift due to spinning of the gyroscope. In other words, when the switching frequency of optical switch <NUM> is selected to be relatively high, noise contributions caused, for example, by phase shifts induced by thermal fluctuations (which are in the kHz range) as well as other non-idealities are canceled out. Moreover, because each spin axis of an optical gyroscope includes a pair of rings each enabling the beam to travel in one direction only, back reflections of the beam due to non-ideal characteristics of the waveguides (or fiber) that is common in conventional gyroscopes are inhibited.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the amount of spin or rotation sbout, e.g., the z-axis (perpendicular to the plane of the page). Although not shown, it is understood that optical gyroscope <NUM> also includes similar components adapted to detect the amount of rotations about both x and y axes.

Optical gyroscope <NUM> is similar to optical gyroscope <NUM> except that optical gyroscope <NUM> includes a phase modulator <NUM>, and first and second beam splitters/combiners (Y-junction) <NUM>,<NUM>. Phase modulator <NUM> is adapted to introduce, for example, <NUM>° phase shift to the optical signal delivered to or received from optical ring <NUM>.

The laser beam supplied by laser source <NUM> is delivered to optical switch <NUM> which has a switching frequency of f<NUM> defined by the period <MAT>. During a first half of each such period T, switch <NUM> of optical switch <NUM> is placed in position <NUM> so as to deliver the laser beam to first optical path <NUM>, which is subsequently received and detected by photodetector <NUM>. During a second half of each such period, optical switch <NUM> is placed in position <NUM> so as to deliver the laser beam to second optical path <NUM>, which is subsequently received and detected by photodetector <NUM>.

The optical beam supplied to path <NUM> from path <NUM> through optical coupler <NUM> is split at Y-junction <NUM> into two components. The first component of the beam so split passes through phase modulator <NUM> before entering optical ring <NUM> via optical coupler <NUM>. The second component of the beam travelling on path <NUM> is delivered to optical ring <NUM> via optical coupler <NUM>. The beam traveling in ring <NUM> is delivered to path <NUM> via optical coupler <NUM>. Similarly, the beam traveling in ring <NUM> is delivered to path <NUM> via optical coupler <NUM>. The beams in paths <NUM> and <NUM> are combined by Y-junction <NUM> and received by photodiode <NUM> from path <NUM> via coupler <NUM>.

Similarly, the optical beam supplied to path <NUM> from path <NUM> through optical coupler <NUM> is split at Y-junction <NUM> into two components. The first component of the beam so split enters optical ring <NUM> via optical coupler <NUM>. The second component of the beam travelling in path <NUM> is delivered to optical ring <NUM> via optical coupler <NUM>. The beam traveling in ring <NUM> is delivered to path <NUM>-via coupler <NUM>-and passes through phase modulator <NUM> before reaching Y-junction <NUM>. The beam traveling in ring <NUM> is delivered to path <NUM>-via coupler <NUM> -before reaching Y-junction <NUM>. The beams in paths <NUM> and <NUM> are combined by Y-junction <NUM> and received by photodiode <NUM> from path <NUM> via coupler <NUM>.

Referring to <FIG>, assume that optical rings <NUM> and <NUM> are tuned ring resonators. During the first half of each period <MAT>, when switch <NUM> of optical switch <NUM> is placed in position <NUM> to deliver the beam to optical path <NUM>, the power Pout<NUM> detected by photodetector <NUM> may be defined as: <MAT>.

In equation (<NUM>), Pout<NUM> represents the amount of optical power detected by photo detector <NUM>, Pin is the power supplied by laser source <NUM>, K<NUM> represents the fraction of the laser power delivered to path <NUM> by switch <NUM> (which ideally is equal to <NUM>), α<NUM> represents the coupling coefficient of optical coupler <NUM> (which ideally is equal to <NUM>), α<NUM> represents the coupling coefficient of optical coupler <NUM>, X<NUM> and X<NUM> represent the attenuation coefficients of ring resonators <NUM> and <NUM> respectively, <MAT> represents the electric field in ring <NUM> as the beam travels in a clockwise direction in ring <NUM> during this half period, Ei represents the electric field in ring <NUM> associated with a portion of the beam that travels in a counter clockwise direction in ring <NUM> due to non-ideal characteristics, <MAT> represent the electric field in ring <NUM> as the beam travels in a counter clockwise direction in ring <NUM> during this half period, Eii represents the electric field in ring <NUM> associated with a portion of the beam that travels in a clockwise direction in ring <NUM> due to non-ideal characteristics, ϕ<NUM> represents the phase of the beam as it exits ring <NUM> during this half period, ϕ<NUM> represents the phase of the beam as it exists ring <NUM> during this half period, Δϕther represents the phase shift caused by thermal fluctuations in the rings, S<NUM> and S<NUM> represents the amplifications factors of rings <NUM> and <NUM> respectively due to resonance, δf represents the phase noise of laser beam, Q represents the combined amplification factors of rings <NUM>, <NUM>, and Δϕsag represents the phase shift due to Sagnac effect, that gyroscope <NUM> is adapted to detect.

Given the above definitions, it is seen that: <MAT> <MAT>.

During the first half of each period <MAT>, power Pout<NUM> detected by photodetector <NUM> (due to non-ideal characteristics) may be defined as: <MAT>.

During the second half of each period <MAT>, when switch <NUM> of optical switch <NUM> is in position <NUM> to deliver the beam to optical path <NUM>, power Pout<NUM> detected by photodetector <NUM> may be defined as: <MAT>.

In equation (<NUM>), K<NUM> represents the fraction of the laser power delivered to path <NUM> by switch <NUM> (which ideally is equal to <NUM>). During the second half of each period, power Pout<NUM> detected by photodetector <NUM> may be defined as: <MAT>.

Assuming ideal conditions in which case both K<NUM> and K<NUM> would be equal to <NUM>, during the first period Pout<NUM> would be zero and during the second period Pout<NUM> would be zero. Therefore, under such conditions, signal Pout<NUM> of the first period and signal Pout<NUM> of the second period would not contribute to the combined signals received by photo detectors <NUM> and <NUM> during the sum of the first and second periods. Assuming ideal conditions, such as when α<NUM>= α<NUM> , K<NUM>= K<NUM> , X<NUM>= X<NUM>, and the like, the only difference between signal Pout<NUM> during the first period and signal Pout1 during the second period is the sign of the term Δϕsag. Accordingly, under such ideal conditions, the sum of signal Pout<NUM> of the first period and signal Pout<NUM> of the second is proportional to the term Δϕsαg which is the signal of interest to be detected.

To account for non-ideal characteristics when detecting signal Δϕsag, the output signal of each of photodetectors <NUM> and <NUM> is amplified by the gain of a trans-impedance amplifier before the two output signals are combined. <FIG> shows a simplified schematic block diagram of photodiodes <NUM> and <NUM> (see <FIG>) whose outputs are amplified by trans-impedance amplifiers <NUM> and <NUM> respectively assumed to have gains of Av<NUM> and Av<NUM> respectively. The outputs of trans-impedance amplifiers <NUM> and <NUM> are received by and combined by combiner <NUM> to generate signal Out representative of the degree of rotation along, e.g., the z-axis, as described above. In one embodiment, combiner <NUM> adds the signal Δϕsagrepresentative of the degree of rotation to a base signal during a first half period of each cycle, and subtracts signal Δϕsag from the base signal during a second half period of each cycle.

Accordingly, during the first half of each period <MAT> signal Out may be defined as: <MAT>.

Likewise, during the second half of each period <MAT> signal Out may be defined as: <MAT>.

In simplified equations (<NUM>) and (<NUM>), parametersγ<NUM>, k<NUM>, γ<NUM>, k<NUM>, <MAT> are understood to represent the combined effects of the corresponding parameters shown in equations (<NUM>), (<NUM>), (<NUM>) and (<NUM>). During each half period, signal Out may be made to depend directly on parameter Δϕsαg if the following expression holds: <MAT>.

In deriving equation (<NUM>) it is assumed that <MAT> and <MAT> indicating that when switch <NUM> is placed in position <NUM>, more than <NUM>% of the laser beam power is delivered to path <NUM>, and when switch <NUM> is placed in position <NUM>, more than <NUM>% of the laser beam power is delivered to path <NUM>.

<FIG> is a computer simulation showing the gain in dB of <MAT> along the Y-axis as a function of the number of rotations per minute (RPM) along the X-axis. As is seen from <FIG>, to more accurately determine Δϕsαg as the RPM of the gyroscope decreases, the higher should be the accuracy with which <MAT> is selected.

<FIG> is a high-level block diagram of an integrated optical gyroscope system <NUM>. Gyroscope system <NUM> is adapted to detect the degree of rotations along x, y and z directions and is shown as including in, part, an integrated photonics chip <NUM>. Integrated photonics chip <NUM> may include the gyroscopes <NUM> or <NUM> shown in <FIG> and <FIG> respectively. Output current signals P<NUM> and P<NUM> generated by, e.g., photodetectors <NUM> and <NUM> shown in <FIG> and <FIG>, are amplified by trans-impedance amplifiers <NUM> and <NUM> respectively. The output voltage of trans-impedance amplifiers <NUM> is further amplified by voltage amplifier <NUM> after passing through bypass capacitor <NUM> which is adapted to block DC components of the signal. Similarly, the output voltage of trans-impedance amplifiers <NUM> is further amplified by voltage amplifier <NUM> after passing through bypass capacitor <NUM>.

Variable resistors <NUM>, <NUM> together with amplifier <NUM> and feedback resistor <NUM> are adapted to set the relative gain of the voltages Vi (received from resistor <NUM>) and V<NUM> (received from resistor <NUM>) and add the voltages together. For example, if feedback resistor <NUM> is selected to have a resistance of <NUM> KΩ and resistors <NUM> and <NUM> are selected to have resistances of <NUM> KΩ and <NUM> KΩ respectively, amplifier <NUM> will generate an output voltage defined by 20V<NUM>+10V<NUM>. Resistors <NUM>, <NUM>, by-pass capacitor <NUM>, amplifier <NUM> and resistor <NUM> collectively show one exemplary embodiment of combiner <NUM> shown in <FIG>. Bandpass filter <NUM> is adapted to filter out signal components whose frequencies fall within a selected range. Resistor <NUM> is adapted to match the output impedance of amplifier <NUM> to the input impedance of bandpass filter <NUM>.

The output signal of the bandpass filter <NUM> is further amplified by amplifier <NUM> and its frequency is downconverted to a baseband signal by mixer <NUM> in response to local oscillator (LO) signal <NUM>. The output of mixer <NUM> is filtered by low-pass filter <NUM>. Micro-controller <NUM>, shown as including an analog-to-digital converter <NUM> and a digital signal processor <NUM>, converts the output of low-pass filter <NUM> to a read-out value Sout representative of the degree of rotation of the gyroscope about any of the three axes.

<FIG> shows plots <NUM> and <NUM> of measured output powers in dB as a function of wavelength of the laser beam for two different optical rings that are fabricated close to one another. As is seen from <FIG>, the peaks of the output powers occur at different wavelengths or frequencies for the two optical rings indicating a mismatch between the characteristics of two optical rings even when they are formed near one another.

<FIG> shows plots <NUM> and <NUM> of measured output powers in dB as a function of wavelength for the same optical ring. Plot <NUM> shows the measurement at a first port (e.g., output port) of the ring when the beam is enable to enter the ring from its second port (e.g., input port). Plot <NUM> shows the measurement at the second first port (e.g., input port) of the ring when the beam is enable to enter the ring from its first port (e.g., output port). As is seen from <FIG>, the peaks of plots <NUM> and <NUM> occur at substantially the same frequencies thus indicating that for the same ring the scattering parameters S<NUM> and S<NUM> are substantially equal and thus validating many of the assumptions made above. In other words, an integrated optical gyroscope benefits from the reciprocity of the structures shown above to overcome mode conversion. An integrated optical gyroscope further benefits from the fact that thermal phase noise (phase shift), ring mismatches and laser phase noise are independent of direction, and cancels out such effect.

In some embodiment, optical rings <NUM> and <NUM> may be ring resonators that are tuned, as described above. To tune the ring resonators, the device may include heaters adapted to heat the rings. In some embodiment, the heaters are resistive heaters that may be arranged along portions of the inner areas and/or outer areas of the rings.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the degree of spin along, e.g., the z-axis. Optical gyroscope <NUM> is similar to optical gyroscope <NUM> of <FIG> except that optical gyroscope <NUM> includes resistive heating elements <NUM> positioned adjacent portions of the periphery and within inner areas of rings <NUM> and <NUM>.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the degree of spin along, e.g., the z-axis. Optical gyroscope <NUM> is similar to optical gyroscope <NUM> of <FIG> except that optical gyroscope <NUM> includes resistive heating elements <NUM> positioned adjacent portions of the periphery and within outer areas of rings <NUM> and <NUM>.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the degree of spin along, e.g., the z-axis. Optical gyroscope <NUM> is similar to optical gyroscope <NUM> of <FIG> except that optical gyroscope <NUM> includes resistive heaters <NUM> that partly overlap portions of the rings <NUM> and <NUM> either above or below the rings. In yet other embodiments, not shown, the resistive elements may be positioned within inner areas and outer areas of the rings and furthermore, may overlap the rings.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> adapted to detect the degree of spin along, e.g., the z-axis. Optical gyroscope <NUM> is similar to optical gyroscope <NUM> shown in <FIG> except that optical gyroscope <NUM> includes a second phase modulator <NUM> adapted to introduce, for example, a <NUM>° phase shift to the optical signal delivered to or received from optical ring <NUM>. The optical gyroscope shown in <FIG> does not form part of the invention, but represents subject matter that is useful for understanding the invention.

<FIG> shows an optical gyroscope <NUM>. Optical gyroscope <NUM> is similar to optical gyroscope <NUM> except that optical gyroscope <NUM> includes one optical ring and a waveguide <NUM> in place of optical ring <NUM>.

<FIG> is a simplified high-level block diagram of optical switch <NUM> corresponding to optical switch <NUM> shown for example, in <FIG> and <FIG>. Optical switch <NUM> is a Mach Zehnder interferometer shown as including, in part, first and second phase shifters <NUM>, <NUM> and a <NUM>/<NUM> directional coupler <NUM>.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> together with the control circuitry <NUM> (in a manner similar to combined <FIG> and <FIG>) adapted to detect the degree of spin about, e.g., the z-axis. In the embodiment shown in <FIG>, signal Pout1 generated by photodetector <NUM> is delivered to trans-impedance amplifier <NUM> during the first half of each period <MAT> and signal Pout2 generated by photodetector <NUM> is delivered to trans-impedance amplifier <NUM> during the second half of each period <MAT>. Bypass capacitor <NUM> delivers the output of trans-impedance amplifier <NUM> to variable gain amplifier <NUM> and bypass capacitor <NUM> delivers the output of trans-impedance amplifier <NUM> to variable gain amplifier <NUM>. Electronic switch <NUM> operates to deliver the output of variable gain amplifier <NUM> to resistor <NUM> during the first half of each period <MAT> and to deliver the output of variable gain amplifier <NUM> to resistor <NUM> during the second half of each period <MAT>.

Bandpass filter <NUM>, amplifier <NUM>, mixer <NUM>, low-pass filter <NUM> and controller <NUM> operate in the same manner as described above with respect to <FIG>. Signal Sout is the read-out of controller <NUM> showing the degree of rotation about any of the axis. electronic switch <NUM> operates to deliver signal Pout1 generated by photodetector <NUM> to trans-impedance amplifier <NUM> during the first half of each period <MAT> and to deliver signal Pout2 generated by photodetector <NUM> to trans-impedance amplifier <NUM> during the second half of each period <MAT>.

<FIG> is a simplified high-level block diagram of components of an optical gyroscope <NUM> together with the control circuitry <NUM> adapted to detect the degree of spin along, e.g., the z-axis. In the embodiment shown in <FIG>, phase modulator <NUM> is adapted to further modulate, at a modulation frequency f<NUM>, the phase of the signal received or delivered by optical ring <NUM>. For example, in addition to a phase shift of, e.g., <NUM>°, phase modulator <NUM> modulates this, e.g., <NUM>° phase shift by a predefined amount using at a modulation frequency of f<NUM>. Signal Pout1 generated by photodetector <NUM> is delivered to trans-impedance amplifier <NUM> during the first half of each period <NUM> < <MAT> and signal Pout2 generated by photodetector <NUM> is delivered to trans-impedance amplifier <NUM> during the second half of each <MAT>. The remaining elements of control circuitry <NUM> operate in the same manner as described above with respect to <FIG> except that control circuitry <NUM> generates an in-phase signal I and a quadrature phase signal Q using a local oscillator (LO) signal <NUM> that operates at frequency (f<NUM>+2f<NUM>), The output signals of low-pass filters <NUM> and <NUM> are delivered to controller <NUM> which generates readout signal Sout showing the degree of rotation about any of the axis.

Claim 1:
An optical gyroscope (<NUM>) comprising:
an optical switch (<NUM>) adapted to deliver a laser beam (<NUM>) to a first path (<NUM>) during a first half of a period and to a second path (<NUM>) during a second half of the period;
a first optical ring (<NUM>) configured to deliver a first portion of the beam received from the first path (<NUM>) in a counter clockwise direction during the first half of the period, and further to deliver a first portion of the beam received from the second path (<NUM>) in a clockwise direction during the second half of the period;
a second optical ring (<NUM>) configured to deliver a second portion of the beam received from the first path (<NUM>) in a clockwise direction during the first half of the period, and further to deliver a second portion of the beam received from the second path (<NUM>) in a counter clockwise direction during the second half of the period;
a first photodetector (<NUM>) adapted to receive the beams delivered by the first (<NUM>) and second (<NUM>) optical rings during the second half of the period;
a second photodetector (<NUM>) adapted to receive the beams delivered by the first (<NUM>) and second (<NUM>) optical rings during the first half of the period;
a first trans-impedance amplifier (<NUM>) adapted to amplify an output signal of the first photodetector (<NUM>) by a first amplification value;
a second trans-impedance amplifier (<NUM>) adapted to amplify an output signal of the second photodetector (<NUM>) by a second amplification value;
a first phase modulator (<NUM>) adapted to delay a beam received or delivered by the first optical ring (<NUM>) by a first predefined phase value; and
a signal combiner (<NUM>) adapted to generate a first signal representative of a combined output of the first (<NUM>) and second (<NUM>) trans-impedance amplifiers.