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REVIEW 4 major objections 5 minor 1 cited by

Phase Biasing System for Optical Gyroscope Using Passive Non-Reciprocal Polarization Techniques

T0 review · 4 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read This paper seeks to establish that a passive non-reciprocal polarization phase shifter can replace active modulation in a fiber-optic gyroscope, producing two simultaneous quadrature signals and cutting simulated angular random walk by up…

desk verdict Interesting passive-biasing idea for IFOGs, but the 40x ARW claim is an artifact of a noiseless simulation. read the letter →

arxiv 2505.19331 v1 pith:AMKUAZJG submitted 2025-05-25 physics.app-ph physics.optics

Onder Akcaalan , Melike Gumus Akcaalan This is my paper · ORCID
classification physics.app-phphysics.optics
keywords interferometricfiber-opticgyroscopepassivephasebiasingnon-reciprocalpolarization-dependentshifterquadraturepointsangularrandomwalkSagnaceffectJonescalculusbalanceddetection
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper seeks to establish that a passive optical element, the Non-Reciprocal Polarization-Dependent Phase Shifter (NRPPS), can replace the active phase modulator in an interferometric fiber-optic gyroscope. Using Jones calculus, the authors show that an eighth-wave plate inside the NRPPS gives the counter-propagating beams a fixed $\pi/2$ relative phase and produces two interference outputs at the quadrature points $\pi/2$ and $3\pi/2$. Their simulations compare this NRPPS-IFOG with a conventional actively biased gyroscope and report angular random walk values roughly 10, 30, and 40 times lower for 200 m, 1000 m, and 2000 m fiber coils. If this holds in hardware, gyroscopes could run without active modulators, with less power, fewer drift sources, and simpler readout.

What carries the argument

The central object is the Non-Reciprocal Polarization-Dependent Phase Shifter (NRPPS): a passive chain consisting of a polarizing beam splitter, a non-reciprocal element that rotates polarization by +45 degrees on each pass, an eighth-wave plate retarder, and a mirror. Because the clockwise beam crosses the retarder with its fast axis matched while the counter-clockwise beam crosses with its slow axis matched, the round trip adds phase $2\phi_r$ to the counter-clockwise beam and no net phase to the clockwise beam; with $\phi_r = \pi/4$ this is exactly $\pi/2$. Two output ports then supply the quadrature signals at relative phases $\pi + 2\phi_r$ and $2\phi_r$, which become $3\pi/2$ and $\pi/2$ when the retarder is an eighth-wave plate. The paper derives this with Jones matrices for each polarization state.

What would settle it

Measure the overlapping Allan variance of the difference of the two detector outputs in a stationary NRPPS-IFOG while attenuating the optical power; if the noise floor scales with the individual detector shot-noise slopes instead of vanishing, the simulated 10-40x ARW improvement is not attainable.

Watch

Extended reading notes

Core claim

The central discovery is that passive quadrature biasing can be obtained in an IFOG by inserting an NRPPS into the beam path. The non-reciprocal polarization rotation makes the clockwise and counter-clockwise beams experience different retarder alignments, so one round trip accumulates a phase $2\phi_r$ while the other accumulates none. Setting the retarder as an eighth-wave plate, $\phi_r = \pi/4$, places the two interference outputs at the quadrature points $\pi/2$ and $3\pi/2$, giving complementary readouts. The paper claims this is the first IFOG configuration to operate at two quadrature points simultaneously without active modulation, and that the complementary readouts support common-mode noise cancellation that reduces angular random walk by factors of about 10, 30, and 40 for 200 m, 1000 m, and 2000 m fiber coils.

Load-bearing premise

The load-bearing premise is that the two photodetector outputs share perfectly correlated, time-matched noise so that subtracting them removes all noise; the paper simulates this ideal cancellation and does not model detector shot noise, thermal noise, or polarization drift, which are not common-mode in a real gyroscope.

Editorial extensions

If this is right

  • Replacing the active modulator with the NRPPS removes the drive electronics, power supply, and thermal stabilization that conventional MIOC or piezoelectric biasing requires.
  • Because the two readouts sit at $\pi/2$ and $3\pi/2$, the gyroscope can produce one rotation-rate data point per coil cycle rather than one per two cycles, giving continuous readout.
  • The coil length no longer has to respect modulation timing constraints, so designers can choose longer fiber coils for higher sensitivity without changing the biasing scheme.
  • If the simulated common-mode noise cancellation is real, angular random walk falls by roughly 10x, 30x, and 40x for 200 m, 1000 m, and 2000 m coils compared with a conventional IFOG.
  • The passive bias principle generalizes to other interferometric gyroscopes and Sagnac sensors that need a fixed phase bias between counter-propagating beams.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The paper's own caveat that a perfect temporal match makes the system noiseless implies the 40x gain is an idealization: real detector shot noise and thermal noise are not common-mode, so the gain in hardware is likely smaller.
  • A closed-loop variant is implicit in the design: placing a piezoelectric actuator behind the NRPPS mirror, as the paper mentions for future work, would allow feedback to hold the quadrature bias point and extend dynamic range.
  • The two-quadrature readout resembles balanced detection, so the scheme could be adapted to other Sagnac interferometers, including chip-scale or resonant gyroscopes, wherever a passive $\pi/2$ bias is needed.
  • A direct experimental check is to measure the Allan variance of the PD2 minus PD3 signal with the input beam blocked; if the residual noise is set by the detector floors, the ARW improvement will be bounded by detector performance.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. The manuscript proposes a passive phase-biasing scheme for an interferometric fiber optic gyroscope (IFOG) based on a Non-Reciprocal Polarization-Dependent Phase Shifter (NRPPS). The central claim is that the NRPPS introduces a fixed π/2 phase shift between counter-propagating beams without active modulation, enabling simultaneous operation at two quadrature points (π/2 and 3π/2) and providing natural noise suppression. The authors present a qualitative optical architecture, a Jones calculus model of the NRPPS element, and MATLAB simulations comparing the angular random walk (ARW) of their NRPPS-IFOG with a conventional IFOG for 200 m, 1000 m, and 2000 m fiber coils. They report ARW improvements of roughly 10×, 30×, and 40×, respectively, and argue that passive biasing reduces power consumption, complexity, and long-term drift.

Significance. If the proposed scheme worked as described, it would be a useful contribution to IFOG design: passive biasing at two quadrature points would eliminate active modulators and their associated control electronics, with potential benefits in power, robustness, and miniaturization. The manuscript correctly identifies a real problem and engages with relevant prior work on passive biasing, and the explicit attempt to provide a Jones calculus model and a parametric simulation study is commendable. However, the significance is not established by the present manuscript. The Jones calculus contains a load-bearing error (the PBS is set to the identity matrix, which removes the polarization-dependent routing the entire architecture relies on), the phase budget that yields the quadrature points omits the necessary explanation of the π shift at the coupler, and the quantitative ARW improvement is derived from a simulation with no stochastic noise model. The claimed 40× improvement is therefore unsupported by the evidence presented.

major comments (4)
  1. [Section 2, Eq. (11) and Eqs. (17)-(19)] Setting the PBS Jones matrix J_PBS to the 2×2 identity removes the polarization-dependent routing that the entire NRPPS architecture relies on. The text explains that the CW beam passes straight through the PBS while the CCW beam is reflected, and that after the double pass the rotated polarization is rerouted to a different output port. With J_PBS=I, Eqs. (18)-(19) describe a single spatial path with no polarization-dependent separation; the Jcoll2(90°) matrix at the output is then applied without physical justification, and the claimed result E_CW_out=H does not follow from the stated matrices. A valid model requires separate transmission and reflection matrices for the two orthogonal polarizations, or a 4-port scattering description of the PBS.
  2. [Section 2, Eqs. (1)-(8) and Eqs. (20)-(24)] The phase budget that leads to the claimed quadrature operation is inconsistent. The Jones calculation in Eq. (22) yields a relative phase of 2ϕr between the two counter-propagating outputs, but Eq. (1) assigns a relative phase of π+2ϕr to the PD2 interference without deriving the π term from a coupler scattering matrix or from an explicit path difference. Since the claimed simultaneous operation at π/2 and 3π/2 depends directly on this π, the reader cannot verify the core bias mechanism from the presented equations. In addition, Eq. (15) defines the retarder with diag(e^{iϕr}, e^{-iϕr}); for a true eighth-wave plate the retardance should be π/4, implying ϕr=π/8, not ϕr=π/4 as stated. The value ϕr=π/4 corresponds to a quarter-wave retardance, which changes the output phases and needs to be reconciled.
  3. [Simulation section, Tables 1-2] The reported ARW improvement is an artifact of a noiseless deterministic model. The text states that 'perfect temporal match makes the system noiseless' and introduces only a 3 m fiber delay between PD2 and PD3; no stochastic noise source is modeled, including detector shot noise, thermal noise, relative intensity noise, polarization drift, or thermal phase noise. Subtracting or combining two deterministic signals that are identical apart from a time delay cannot produce a physically meaningful Allan variance, and the reported values such as 0.00002 °/√hr for the 2000 m coil are orders of magnitude below any realistic shot-noise-limited estimate for a 100 mW source at 1550 nm with typical losses. The comparison in Table 1 is therefore not a valid basis for the claimed 10×-40× improvement in ARW.
  4. [Simulation section, paragraph beginning 'In the simulation, sensitivity was calculated...'] The input rotation rate is stated as 'Earth's rotation (15°/s)', but the Earth's rotation rate is 15°/hour, not 15°/s. This factor-3600 error enters the Sagnac phase and all rotation-rate-dependent quantities used in the Allan variance analysis. The simulation parameters must be corrected and the ARW comparison re-run before the quantitative claims can be assessed.
minor comments (5)
  1. [Section 2, Eq. (20)] E_CCW_in is set equal to H, although the text describes the CCW beam as vertically polarized when it enters the PBS; this is inconsistent with the stated routing and should be corrected.
  2. [Section 2, Eqs. (22)-(24)] The output of the CCW-path calculation is labeled E_CW_out in Eqs. (22)-(24); these labels should be E_CCW_out to avoid confusion with the CW-path result in Eq. (19).
  3. [Throughout] The text repeatedly uses '8-wave plate' and '8-wave retarder' where 'eighth-wave plate' is meant; given Eq. (15), the value ϕr=π/4 corresponds to a quarter-wave retardance, so the terminology and the numerical value are inconsistent.
  4. [Figure 3 and accompanying text] The text says that without considering losses the PD3 signal will be half of the PD2 level, but Eqs. (4) and (8) predict identical functional forms (2I(1+cos(...))) apart from the phase, so the origin of the 1/2 factor is not explained.
  5. [Conclusion and Table 1] The conclusion states a '40×' improvement, but Table 1 shows a 40× ratio only for the 2000 m coil; the ratios for 200 m and 1000 m are approximately 12× and 28×. The approximate statement '10×, 30×, and 40×' should be aligned with the table values.

Circularity Check

1 steps flagged · score 6.0 of 10

The reported 40x ARW improvement is a built-in consequence of assuming PD2 and PD3 carry identical noiseless signals; the simulation's 'noiseless' idealization makes the quantitative claim reduce to its inputs.

  1. other [Simulation section, paragraph describing PD2/PD3 temporal offset (after Table 1, before Table 2)]
    "Photodetectors in Fig.- 2, PD2 and PD3 were used to calculate the rotation rate, with a 3-meter fiber length difference introduced to create a temporal offset between the signals. Otherwise, perfect temporal match makes the system noiseless, which will be addressed for the future papers in terms of detailed investigation of the NRPPS-IFOG system."

    The paper attributes the ARW gain to 'the use of PD2 and PD3, which are actually same signal but receive π-phase-shifted quadrature components,' i.e., the two channels are assumed to have perfectly correlated signals. The quoted sentence then states the direct consequence: in the simulation, perfect temporal matching makes the system noiseless. Because no independent detector noise (shot noise, thermal noise, or decorrelated RIN) is modeled, the reported ARW values and the 10-40x improvement are generated by the ad hoc 3 m offset rather than predicted from a physical noise source. The quantitative central claim therefore reduces by construction to the input assumption that the two photodetectors see the same common-mode signal.

full rationale

The passive π/2 biasing derivation is self-contained: the Jones-matrix calculation (Eqs. 17-24) shows that a retarder with φr = π/4 produces a 2φr = π/2 phase shift after double pass, and simultaneous quadrature detection at PD2/PD3 follows algebraically from Eqs. (4) and (8). This is a design choice, not a fitted result, and no self-citation is load-bearing. The circularity concern is limited to the headline ARW claim. The paper explicitly says the simulation is noiseless when PD2 and PD3 are temporally matched and introduces a 3 m fiber delay to generate the plotted Allan-variance behavior. Since PD2 and PD3 are assumed to be 'actually same signal,' common-mode noise cancellation is built into the input; the 40x improvement is therefore an artifact of the simulation construction rather than an independent prediction. The passive-bias concept itself retains independent content, so the score is moderate (6), not extreme.

Assumptions & free parameters 2 free parameters · 3 assumptions · 0 invented entities

The central claim depends on three main assumptions: an ideal non-reciprocal rotator, ideal lossless components, and perfectly correlated noise between the two detector channels. The first two come from the Jones model; the third is the source of the simulated ARW improvement and is the most fragile.

free parameters (2)
  • retarder phase phi_r = pi/4 (eighth-wave plate)
    Chosen by hand so that 2*phi_r = pi/2, producing the claimed quadrature bias. It is a design parameter, not fitted to measured data.
  • temporal offset fiber length = 3 m (also 20, 50, 100 m tested)
    Hand-chosen delay between PD2 and PD3; the shortest 3 m offset gives the best ARW (Table 2), so the headline 40x improvement depends on this choice.
assumptions (3)
  • domain assumption The non-reciprocal element rotates polarization by exactly +45 degrees for both beam directions and introduces no phase or loss.
    Assumed in Jones matrices (Eq. 14) and used throughout the derivation; real Faraday rotators have wavelength-dependent rotation and temperature sensitivity.
  • domain assumption The two photodetectors PD2 and PD3 measure perfectly correlated (common-mode) noise so that subtraction cancels all noise.
    Stated in the simulation paragraph: 'perfect temporal match makes the system noiseless'. This is the basis for the ARW improvement and is not physically justified for shot, thermal, or detector noise.
  • domain assumption Optical components (PBS, retarder, mirror) are ideal and lossless.
    The Jones derivation ignores component losses and the actual polarization-dependent routing of the PBS, treating it as the identity matrix (Eq. 11).

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Cite this review

Pith. "Pith review of Phase Biasing System for Optical Gyroscope Using Passive Non-Reciprocal Polarization Techniques." pith.science (2026). https://pith.science/paper/AMKUAZJG

@misc{pith2026250519331,
  author       = {Pith},
  title        = {Pith review of: Phase Biasing System for Optical Gyroscope Using Passive Non-Reciprocal Polarization Techniques},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/AMKUAZJG}},
  note         = {Machine review of arXiv:2505.19331}
}
abstract

Interferometric Fiber Optic Gyroscopes (IFOGs) are widely used in precision navigation systems due to their high sensitivity, robustness, and solid-state nature. To ensure linear response and accurate angular velocity measurement, a fixed $\pi/2$ phase bias is typically introduced between the clockwise (CW) and counter-clockwise (CCW) beams using active modulation components. However, these active elements increase system complexity, power consumption, cost, and susceptibility to thermal drift and long-term degradation. In this work, we present a novel IFOG configuration that, to the best of our knowledge, achieves for the first time, simultaneous operation at two quadrature points ($\pi/2$ and $3\pi/2$), providing natural noise suppression without relying on active components. This is made possible through the integration of a Non-Reciprocal Polarization-Dependent Phase Shifter (NRPPS), which introduces a pure $\pi/2$ passive phase shift. We detail the optical architecture and provide theoretical modeling using Jones calculus to demonstrate how the NRPPS element introduces passive quadrature biasing. Simulation results show that the proposed NRPPS-IFOG achieves significantly improved sensitivity, with Angular Random Walk (ARW) values up to 40x lower than those of conventional IFOGs, depending on the fiber coil length. The design further leverages quadrature-phase signal detection and adjustable temporal offsets between photodetectors to enhance noise suppression. This passive biasing approach eliminates the need for active modulation, offering reduced power consumption, improved stability, and enhanced long-term reliability.

Figures

Figures reproduced from arXiv: 2505.19331 by the authors.

Figure 1
Figure 1. (Left) A multi-integrated optical circuit (MIOC) integrated conventional IFOG, (right) Piezoelectric ceramic [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. A Non-Reciprocal Polarization Phase Shifter based IFOG system. [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Output signals of PD2 and PD3 section for NRPPS-IFOG while rest and with rotation [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: (left) Non-Reciprocal Polarization Phase Shifted Design with respect to CW beam, (right) Non-Reciprocal [PITH_FULL_IMAGE:figures/full_fig_p006_4.png]
Figure 5
Figure 5. Figure 5: (left) The input signal source for conventional-IFOG simulation as number of samples in 2 cycles, (right) [PITH_FULL_IMAGE:figures/full_fig_p006_5.png]

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. A Simple and Novel Passive Double-Sensitivity Optical Gyroscope Based on Non-Reciprocal Polarization Techniques

    physics.app-ph 2025-06 reject novelty 5.0 of 10

    The DS-NRPPS-IFOG combines a passive polarization phase shifter with a double-pass fiber coil to operate at two quadrature points, yielding simulated angular random walk up to 50x lower than a conventional double-sens...

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