PHASECam is the fringe tracker for the Large Binocular Telescope Interferometer (LBTI). It is a near-infrared camera that is used to measure both tip/tilt and fringe phase variations between the two adaptive optics-corrected apertures of the Large Binocular Telescope (LBT). Tip/tilt and phase sensing are currently performed in the H (1.65 μm) and K (2.2 μm) bands at 1 kHz, but only the K-band phase telemetry is used to send corrections to the system in order to maintain fringe coherence and visibility. However, due to the cyclic nature of the fringe phase, only the phase, modulo 360 deg, can be measured. PHASECam’s phase unwrapping algorithm, which attempts to mitigate this issue, occasionally fails in cases of fast, large phase variations or low signal-to-noise ratio. This can cause a fringe jump in which case the optical path difference correction will be incorrect by a wavelength. This can currently be manually corrected by the operator. However, as the LBTI commissions further modes that require robust, active phase control and for which fringe jumps are harder to detect, including multiaxial (Fizeau) interferometry and dual-aperture nonredundant aperture masking interferometry, a more reliable and automated solution is desired. We present a multiwavelength method of fringe jump capture and correction that involves direct comparison between the K-band and H-band phase telemetry. We demonstrate the method utilizing archival PHASECam telemetry, showing it provides a robust, reliable way of detecting fringe jumps that can potentially recover a significant fraction of the data lost to them.

中文翻译：

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为大型双筒望远镜干涉仪的相位传感器PHASECam实现多波长条纹跟踪

PHASECam是大型双筒望远镜干涉仪（LBTI）的边缘跟踪器。这是一台近红外照相机，用于测量大型双筒望远镜（LBT）的两个自适应光学校正孔径之间的尖端/倾斜角和边缘相位变化。倾斜/倾斜和相位感测当前在1 kHz的H（1.65μm）和K（2.2μm）波段中执行，但是仅使用K波段相位遥测技术向系统发送校正，以保持边缘相干性和能见度。但是，由于条纹相的循环特性，只能测量模数为360度的相。PHASECam的相位展开算法试图缓解这一问题，但在快速，大的相位变化或低信噪比的情况下，有时会失败。这可能会导致条纹跳跃，在这种情况下，光程差校正在波长上是不正确的。当前可以由操作员手动纠正。但是，随着LBTI调试需要鲁棒，主动相位控制且条纹跳变更难检测的其他模式，包括多轴（Fizeau）干涉测量法和双孔非冗余孔径掩膜干涉测量法，需要一种更可靠和自动化的解决方案。我们提出了一种边缘跳跃捕获和校正的多波长方法，该方法涉及在K波段和H波段相位遥测之间进行直接比较。我们演示了利用档案PHASECam遥测技术的方法，表明该方法提供了一种检测边缘跳跃的鲁棒，可靠的方法，可以潜在地恢复丢失给他们的数据的很大一部分。