What is optical delay line?

What is optical delay line?

An electric-optic-electric device is known as an Optical Delay Line (ODL). (In certain literature, an optical delay line is also referred to as a fiber delay line or a fiber optic delay line.) It produces fixed time delays for RF signals from 10MHz to 40GHz and above, ranging from a few nanoseconds to several hundred microseconds. There are ODL versions with low frequencies between 10MHz and 6GHz. Up to 8GHz, 15GHz, 18GHz, 20GHz, and 40GHz are covered by the high-frequency ODLs variants.

Technically speaking, an optical modulated signal is created from the RF input signal. The optical signal is sent into a lengthy single mode fiber, typically at a wavelength of around 1.55 microns. The optical signal is changed back into an electrical RF signal as it travels through the fiber. Without the requirement for operator calibration, the electrical control on the ODL elects the optical system automatically.

To achieve exceptionally high performance, an optical delay line (ODL) system also includes high-performance lasers like DFBs, optical modulators for high operation frequencies, photodiodes, and optionally other components like optical dispersion compensators, optical switches, optical amplifiers, and pre- and post-RF amplifiers. The ODL optical system provides a wide range of delays, high sensitivity analog signal bandwidths, and wide dynamic range.

Radar range modeling and signal processing are two uses for variable optical delay lines, often called progressive optical delay lines (ODLs). The Progressive ODL utilizes the same transceiver for a number of delay lines, with RFOptic performing the customisation.

A cascaded 1:2 and 2:2 optical matrix system with a variety of delay lines in between is the most often used practical method for a variable delay system (replacing the above two optical switch matrix 1:8). The progressive delay configuration depicted below is a cascaded switch matrix.

To specify the necessary delay, the preferred combination of delay lines is chosen. Four progressive delay lines with cascading switch matrices are shown in the diagram below. The user can choose from any of the 16 possible combinations of delay values (16+24) in such a configuration. For instance, a delay similar to Dtot= D1+D2 + D4 or Dtot= D3+D4 etc. can be chosen.)

When the optical signal becomes highly spread and weakened due to an increase in the delay line length and signal frequency, dispersion adjustment may occasionally be required. Our Optical Delay Line (ODL) solutions at RFOptic incorporate DCM (Dispersion Compensation Module) to address this issue.

RFOptic also employs optical amplifiers (EDFAS), which account for optical loss, for very long delay lines. In some circumstances, pre- and post-amplifiers are also necessary.

A user-friendly software interface with an intuitive GUI is used to alter the delay lines and attenuation as needed (Graphic User Interface).