Beam-Steered Diffractive Grating True Time Delay
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Solution Overview
Problem
Current microwave photonic systems face challenges in achieving rapid tuning and fine delay resolution at 10 GHz and beyond, with existing delay lines suffering from high optical loss, coarse delay increments, and limited phase and amplitude control due to group delay ripples and slow tuning speeds.
Innovation Solution
A time delay device and method utilizing a beam deflector, imaging device, and stationary diffractive grating to introduce a relative phase delay in an optical beam, allowing for continuous tunability and fine delay resolution, featuring a beam-steered diffraction grating true time delay system with a rotatable mirror or acousto-optic beam deflector, and a focusing element to change the optical path length, enabling rapid tuning and minimal dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If discrete fiber Bragg grating delay lines are used, then delay resolution is provided, but the delay increments are coarse (minimum 10 ps, translating to 36° RF phase step at 10 GHz)
Solution Approach 1:
The patent replaces the mechanical/discrete FBG delay line system with an optical scanning system using a diffractive grating and scanned beam approach. This substitution enables continuous delay tuning instead of discrete 10 ps steps, achieving fine phase control at 10 GHz and beyond by dynamically scanning the optical beam across the grating aperture.
Solution Approach 2:
The invention introduces dynamic beam scanning across the diffractive grating aperture, transforming the static discrete delay line into a dynamic continuous tuning system. The scanned beam position is controlled by a voltage signal, enabling real-time continuous adjustment of the optical path length and thus achieving fine phase control without the 10 ps quantization limitation.
2Speed
If integrated-optic switch delay lines are used, then fast tuning is achieved, but optical loss becomes prohibitive at large bit-depths
Solution Approach 1:
The patent extracts the switching function from the delay line structure itself and separates it into a beam scanning mechanism. Instead of using integrated-optic switches within the delay line that cause high loss at large bit-depths, the invention uses an external scanned beam approach where the optical path is dynamically selected without inserting lossy switching elements in the signal path.
Solution Approach 2:
The diffractive grating serves as an intermediary element that enables delay tuning without requiring high-loss switching mechanisms. The scanned beam interacts with the grating to select different optical path lengths, providing fast tuning capability while avoiding the prohibitive optical loss that plagues integrated-optic switch delay lines at large bit-depths.
3Measurement precision
If piezoelectric fiber stretchers are used, then fine delay resolution and low optical loss are achieved, but tuning range is limited (on the order of 10 ps) and tuning speed is slow
Solution Approach 1:
The patent replaces the piezoelectric mechanical stretching mechanism with an optical scanning mechanism using a diffractive grating. This substitution removes the fundamental limitations of piezoelectric stretchers: the slow tuning speed and limited 10 ps tuning range. The scanned beam approach enables both fine delay resolution and rapid tuning by electronically controlling beam position without mechanical deformation.
Solution Approach 2:
The invention changes the fundamental operating parameter from mechanical strain (piezoelectric effect) to optical path length variation through beam scanning. By controlling the scanned beam position across the diffractive grating with voltage signals, the system achieves both fine delay resolution and fast tuning speeds, overcoming the dual limitations of piezoelectric fiber stretchers.
4Adaptability or versatility
If chirped fiber gratings are used, then delay tuning is achieved, but group delay ripple (non-linear variations in group delay) limits achievable phase and amplitude control
Solution Approach 1:
The patent replaces the chirped fiber grating structure with a scanned beam diffractive grating system. This substitution eliminates the group delay ripple problem inherent in chirped gratings by using a different physical mechanism: dynamic beam scanning across a grating aperture. The scanned beam approach provides linear delay tuning without the non-linear group delay variations that limit phase and amplitude control in chirped grating systems.
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
The solution provides high-resolution time delay control with minimal dispersion and optical loss, enabling true-time-delay for microwave signals across a wide frequency range, improving delay ripple and tuning speed compared to existing systems, and supporting high-performance agile photonic systems.
Implementation Method 1
a beam deflector to change a beam deflection angle of the optical beam
Implementation Method 2
a focusing element arranged between the beam deflector and the stationary diffractive grating
Implementation Method 3
a stationary diffractive grating arranged in an optical path with the beam deflector... a change in optical path length experienced by the optical beam as the beam moves across the grating surface results in a relative phase delay
Implementation Method 4
an imaging device configured to image optical beam onto the beam deflector
Data Source
AI summary
A system testing the speed of a microwave photonic system, having a Mach Zehnder interferometer that includes a first arm with a photonic system to be tested and an amplifier arranged to amplify the output of the photonic system, and a second arm with an attenuator configured to match the output power of the amplifier, with at least one filter arranged at the output of the Mach Zehnder interferometer, the filter having a pass band that includes the center frequency of a continuous wave microwave signal applied to the Mach Zehnder interferometer arms. A continuous wave microwave signal is applied to the input of the Mach Zehnder interferometer, a signal is applied to only the second arm with the photonic link, and the output of the bandpass filter is measured with an oscilloscope and a microwave power detector.