J. Eur. Opt. Society-Rapid Publ. 21, 2( 2025) 21
Table 3. Comparison of research literature on OTTDLs. Structure
Delay accuracy / ps
Adjustable delay range / ps
Scanning range
Frequency / GHz Chip platform Footprint( mm 2)
MRR [ 28 ] |
– |
0 – 236 |
– |
10.7 – 12.75 |
TriPleXTM waveguide |
– |
MRR [ 29 ] |
– |
0 – 500 |
|
10 |
Si 3 N 4 waveguide |
90 |
MRR [ 30 ] |
20 |
0 – 160 |
|
0 – 16 |
SOI |
8 |
GDL [ 33 ] |
6.6 |
60 |
|
10 |
SOI |
|
GDL [ 34 ] |
4.7 |
181.9 |
|
10 |
Si |
|
GDL [ 35 ] |
0.2 |
200 |
�36.8 ° to + 36.8 ° |
8 – 12 |
SOI |
|
PS [ 36 ] |
13.5 |
148.5 |
– |
– |
– |
|
OS [ 37 ] |
2.5 |
0 – 96 |
�75.51 ° to 75.64 ° |
8 – 18 |
SOI |
42.8 |
AWG [ 38 ] |
10.3 |
20,000 |
|
|
|
|
Note: MRR stands for Miniature Resonant Ring; GDL stands for Grating Delay Line; AWG stands for Array Waveguide Grating; PS stands for Path Switching; OS stands for Optical Switch.
waveguide grating. By cascading two stacked array waveguide gratings, the delay can be changed by changing the carrier wavelength.
Duan et al. [ 38 ] improved the multi-channel programmable optical controlled true delay network by dividing the optical signal into 8 channels of single wavelength light. By modulating signals of different wavelengths and passing them through precision fibers of different lengths, they achieved a minimum delay accuracy of 10.3 ps and a maximum adjustable range of 20 ls for the optical true delay line.
5.4.2 Brief summary
The advantages of wavelength selective optical delay lines are easy processing, large adjustable range, and easy integration; The disadvantage is that it requires high continuous adjustability of the laser source [ 39, 40 ].
5.5 General analysis
Table 3 compares different kinds of optical true delay lines based on technical indicators such as delay accuracy, adjustable delay range, and scanning range.
Through analysis and comparison, it can be seen that micro ring resonators are easy to fabricate, have a large adjustable range of optical delay, and can achieve continuous delay, while the beam switching time is relatively long. Grating delay lines are easy to integrate, but cannot achieve continuous adjustment or require changing the wavelength of light for adjustment. The switching speed of the optical switch is fast, reaching ns level speed, however the delay accuracy is low and continuous adjustment cannot be achieved. Wavelength selective optical delay lines are easy to process, have a large adjustable range, and are easy to integrate, but require high continuous tunability of the laser source.
6 Summary and prospect
This article has conducted a study on the theory and related technologies of OTTDLs. It elaborates on the principle of phased array antennas and the reasons for beam squint firstly, and analyzes the impact of true delay on the performance of phased array radar. Then, the basic principle, technological progress, and related applications of optical true delay are introduced. Take four common structures of optical true delay lines as examples, which are micro-ring resonant cavity array, grating true time delay line, multipath switchable OTTDL, and wavelength selective OTTDL. Their performance in delay accuracy, adjustable delay range, and frequency bandwidth are compared.
OTTD and MWPPS technology are the main technical means currently applied in optical controlled beamforming systems. With its advantages of low transmission loss and flat broadband response, the diverse forms of optically controlled phased array technology have gradually improved and been widely applied in fields such as optically controlled phased array radar and atmospheric atmospheric turbulent calculation. There are many aspects that need to be tackled.
Analysis of the impact of parameter errors of OTTDLs on array performance. As a relatively complex multi-channel optoelectronic integrated system, OTTDs inevitably has various parameter errors in the processes of manufacturing, deploying and applicating. Therefore, it is necessary to establish a model of the parameter error of OTTDLs with respect to the performance of optically controlled phased array, which provides important support for optimizing array performance and guiding array design.
Miniaturization and integration. For optical beamforming technology, photon integration technology is a necessary path. It is urgent to study the impact of system packaging on the power consumption, temperature, and other indicators of array chips. Thus achieving efficient microwave packaging and system packaging for broadband beamforming networks.
High precision and efficiency. The number, direction, and shape of beams can be more accurately controlled to transmit energy and information more efficiently by improving photonics signal processing techniques or optimizing subarray partitioning algorithms,.
Intelligence and adaptability. Future optical beamforming technology may include more intelligent and adaptive