AIDT 온디바이스 STEM 방사광 X선 극저온 광섬유 분포형 음향 감지(DAS) phi-OTDR 레이저 위상 잡음 소거 서보 제어기

using System;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Stem.DistributedAcousticSensing
{
    /// <summary>
    /// phi-OTDR DAS 간섭계 텔레메트리 계측 상태
    /// </summary>
    public readonly ref struct DasInterferometerTelemetryState
    {
        public readonly double InPhaseComponent;         // 동상(I) 성분 전압 [V]
        public readonly double QuadratureComponent;      // 직교(Q) 성분 전압 [V]
        public readonly double OpticalPulseEnergyNanoJ;  // 송신 펄스 에너지 [nJ]
        public readonly double FiberLengthKilometers;    // 감지 광섬유 거리 [km]
        public readonly double AmbientAcousticNoiseDbm;  // 주변 배경 음향 잡음 [dBm]

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public DasInterferometerTelemetryState(double iComp, double qComp, double energy, double len, double noise)
        {
            InPhaseComponent = iComp;
            QuadratureComponent = qComp;
            OpticalPulseEnergyNanoJ = energy;
            FiberLengthKilometers = len;
            AmbientAcousticNoiseDbm = noise;
        }
    }

    /// <summary>
    /// DAS 위상 잡음 소거 서보 명령
    /// </summary>
    public readonly ref struct DasPhaseServoCommand
    {
        public readonly double AomFrequencyShiftKhz;     // AOM 주파수 편차 지령 [kHz]
        public readonly double DemodulatedStrainNanoEps; // 복조된 음향 변형률 [n-epsilon]
        public readonly double SignalToNoiseRatioDb;     // 복조 음향 SNR [dB]
        public readonly bool PhaseDriftSuppressed;       // 위상 잡음 소거 완료 여부

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public DasPhaseServoCommand(double aomShift, double strain, double snr, bool suppressed)
        {
            AomFrequencyShiftKhz = aomShift;
            DemodulatedStrainNanoEps = strain;
            SignalToNoiseRatioDb = snr;
            PhaseDriftSuppressed = suppressed;
        }
    }

    /// <summary>
    /// 10,000Hz 주기 DAS phi-OTDR 레이저 위상 잡음 소거 서보 엔진
    /// </summary>
    public ref struct DistributedAcousticSensingPhaseServoEngine
    {
        private const double MziDelayTimeNanoSec = 50.0; // MZI 지연시간 50ns
        private const double PhotoElasticCoeff = 0.78;
        private double _accumulatedPhaseOffset;
        private double _prevPhaseRad;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public DasPhaseServoCommand CalculateServoControl(
            in DasInterferometerTelemetryState state, double dtSeconds)
        {
            // 1. 아크탄젠트(atan2) I/Q 위상 복조
            double currentPhaseRad = Math.Atan2(state.QuadratureComponent, state.InPhaseComponent);
            double phaseVelocity = (dtSeconds > 1e-9) ? (currentPhaseRad - _prevPhaseRad) / dtSeconds : 0.0;
            _prevPhaseRad = currentPhaseRad;

            // 2. 위상 잡음 소거 AOM 주파수 제어 (비례-적분)
            _accumulatedPhaseOffset += 0.5 * currentPhaseRad * dtSeconds;
            _accumulatedPhaseOffset = Math.Clamp(_accumulatedPhaseOffset, -2.0, 2.0);

            // delta_nu = (1 / (2*pi*tau)) * delta_phi
            double aomShiftKhz = ((currentPhaseRad / (2.0 * Math.PI * (MziDelayTimeNanoSec * 1e-9))) * 1e-3) + (15.0 * _accumulatedPhaseOffset);
            aomShiftKhz = Math.Clamp(aomShiftKhz, -500.0, 500.0);

            // 3. 순수 음향 변형률 추출 (n-epsilon 단위)
            // Delta_epsilon = (lambda / (4*pi*n*L*xi)) * Delta_phi
            double strainNanoEps = (currentPhaseRad - _accumulatedPhaseOffset) * 12.8; // 게이지 길이 10m 기준

            // SNR 및 제어 수렴도 판정
            bool suppressed = Math.Abs(currentPhaseRad) < 0.05;
            double snrDb = suppressed ? 42.5 : 21.0;

            return new DasPhaseServoCommand(aomShiftKhz, strainNanoEps, snrDb, suppressed);
        }
    }
}