Optical Transceiver Built-In Test Using Light Pipe
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Solution Overview
Problem
Current Built-In Test (BIT) methods for optical transceivers are inadequate for ensuring robust operability across various configurations, particularly in systems where transmit and detection bands overlap, as they rely on simple flash detection and do not effectively measure alignment errors or beam power.
Innovation Solution
A light pipe is used to intercept and redirect a portion of the collimated transmit beam, creating a virtual object in the receiver field-of-view, allowing the same detector to perform more comprehensive tests, including alignment verification and radiometry, while preserving collimation and reducing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate BIT detector is used to detect the transmit beam flash, then the BIT can be performed, but the device complexity increases and the same detector cannot be used for both normal operation and testing
Solution Approach 1:
The receiver detector is designed to serve dual purposes: detecting target signatures during normal operation and detecting the transmit beam flash during BIT. The light pipe enables the detector to access the transmit beam path without requiring a separate dedicated BIT detector, making the detection system universal for both functions.
Solution Approach 2:
A light pipe is introduced as an intermediary optical element that redirects a portion of the transmit beam to the receiver detector. This mediator allows the detector to receive light from the transmit beam during BIT without interfering with the normal target detection function, enabling seamless dual-purpose operation.
2Reliability
If the eye is rotated 180 degrees to perform BIT in a gimballed system, then the transmit beam can be directed back into the detector, but the operation complexity increases and normal operation is interrupted
Solution Approach 1:
The light pipe is pre-positioned and optically aligned during system assembly to intercept the transmit beam at the desired angle. This preliminary configuration eliminates the need for dynamic gimbal rotation during BIT, as the optical path is already established to redirect light to the detector in the normal operational position.
Solution Approach 2:
The mechanical gimbal rotation mechanism is replaced with a fixed optical redirection system using the light pipe. Instead of mechanically rotating the detector or optics to perform BIT, the light pipe provides a fixed optical path that achieves the same effect without mechanical movement, simplifying the operation.
3Productivity
If simple flash detection is used for BIT, then the test can be performed quickly, but the measurement precision is insufficient to detect alignment errors or measure beam power
Solution Approach 1:
The light pipe intercepts only a portion of the transmit beam (partial action) rather than the entire beam, redirecting a sample to the detector. This partial interception is sufficient to provide measurable light for both flash detection and precise measurements of alignment and power, without requiring full beam manipulation.
Solution Approach 2:
The system provides feedback to the processor about the detected light characteristics, enabling the processor to determine not only whether the transmit source is operational but also to measure alignment accuracy and beam power. This feedback mechanism transforms simple flash detection into a comprehensive diagnostic tool.
4Adaptability or versatility
If the light pipe intercepts a portion of the collimated transmit beam, then comprehensive tests can be performed using the same detector, but the light pipe must be precisely aligned to preserve collimation
Solution Approach 1:
The light pipe is designed with specific angular parameters (e.g., 45-degree angles) that define its optical path. By carefully selecting and controlling these angular parameters during manufacturing and assembly, the system ensures that the redirected beam maintains collimation and properly enters the receiver optical path, achieving both versatility and precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables more robust BITs that confirm transceiver operability, measure alignment errors, and assess beam power using the same detector and electronics, improving the reliability of optical transceivers in diverse configurations.
Implementation Method 1
The light pipe comprises an input face and first reflective surface in the transmitter FOV to intercept a portion of the beam along a first axis and re-direct the beam, a second reflective surface and output face in the receiver FOV that re-directs the portion of the beam along a second axis towards the receiver
Implementation Method 2
an optical channel that guides the redirected portion of the beam from the first reflective surface to the second reflective surface to offset the second axis from the first axis
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
An optical transceiver is provided with a light pipe (50) that intercepts, offsets and redirects a portion of the collimated transmit beam to create a virtual object in the receiver field- of -view (22 ) to perform the BIT. The light pipe comprises an input face and first reflective surface in the transmitter FOV (20) to intercept a portion of the beam along a first axis (38) and re-direct the beam, a second reflective surface and output face in the receiver FOV (22) that re-directs the portion of the beam along a second axis (30) towards the receiver to create the virtual object in the receiver FOV and an optical channel that guides the redirected portion of the beam from the first reflective surface to the second reflective surface to offset the second axis from the first axis. The same detector used during normal operation of the transceiver is used to perform the BIT, which may include a simple "on/off test or a radiometry test. The light pipe may be designed with an acceptance FOV that preserves collimation, which facilitates a measurement of alignment error between the transmit beam and receiver.