What is an optical delay line (ODL)?

An Optical Delay Line (ODL) is an electric-optic-electric instrument. It performs fixed time delay(s), between a few nanoseconds up to several hundred microseconds, for RF signals from 10MHz up to 40GHz and more. The RF input signal is converted into an optical modulated signal. The optical signal is transmitted into a long single mode fiber, usually at a 1.55 micron wavelength or similar. Passing the fiber, the optical signal is converted back into an electrical RF signal. The electrical control on the ODL elects the optical system automatically, with no need for tuning by the operator.

What components does an Optical Delay Line incorporate?

An Optical Delay Lines system (ODL) incorporates high performance lasers such as DFBs, optical modulators for high operation frequencies, photodiodes, and optionally other components such as optical dispersion compensators, optical switches, optical amplifiers and pre- and post RF amplifiers to provide exceptionally high performance. The ODL optical system supports very high bandwidths of analog signals, high sensitivity with wide dynamic range, for various delays.

What is light coefficient?

Light coefficient refers to light traveling at a different velocity in glass fiber and its index of refraction is 1.5. That means that 10 kilometer range in the air is equivalent to 6.666 kilometers in fiber and vice versa. Usually, RFOptic requests data from the user in order to provide microseconds from the fiber so it will be easy to prepare the spools.

Can an Optical Delay Line support more than 1 ODL?

Yes, RFOptic standard Optical Delay Lines can support up to 8 distinct delay lines. RFOptic has a range of products that support more than one delay line. The customer can also extend it later by adding additional spools. Eight (8) delay lines that can create 255 combinations of delay lines are standard.

How can I protect my Optical Delay Line investment?

The most expensive portion of an Optical Delay Line (ODL) is the transceiver. It is therefore important to design an Optical Delay Line that also captures your ODL needs in the future and/or with different applications. If you are not sure of the number of delay lines that may be required, contact us directly. We provide specific Optical Delay Lines that allow for the possibility to add more delay lines as needed in the future.

What is a progressive Optical Delay Line?

Our progressive Optical Delay Lines combine distinct delay line to create additional delay lines.  Progressive delay lines are used if the customer needs more than eight (8) delay lines.  Progressive Optical Delay Lines can be used to provide up to 256 delay lines. One classic application is for phased radar arrays where on top of a base delay line, the delays have to be entered in equal steps.  For example, this solution would allow for creating delay lines from 1 microsecond to 255 microseconds with 1 microsecond step.

What is a variable Optical Delay LIne?

Our variable Optical Delay Lines are especially suited for a variety of applications including radar range simulation and signal processing. There are two basic techniques to consider; Switched RF and Switched Fiber.

Switched RF uses multiple delay lines and RF switches to select various delay values. This technique has a good performance but is relatively expensive because multiple delay lines are required.

Switched Fiber delay systems are more cost effective, since they include several different delay lines. Two optical matrices (e.g., 1:2, 1:4 or 1:8) select (either manually or through PC) the desired delay line (i.e. DL 1 to DL 8).

A third approach for a variable delay system is an ODL system configuration which includes cascaded 1:2 and 2:2 optical matrices with several different delay lines in between (replacing the above two optical switch matrix 1:8.

What are the minimum and minimum delay amounts?

RFOptic has created optical delay lines solutions that range from a few nanosecond up to 1000 nanosecond and more.

When is dispersion compensation needed?

As the signal frequency and the delay line length increase, the optical signal can be dispersed and weaken significantly. As needed, RFOptic incorporates DCM (Dispersion Compensation Module) in its ODL solutions.

Optical dispersion of long fibers at high RF frequencies causes additional insertion loss at specific frequency ranges per defined delay line length(s), where the insertion loss deep can reach 20 dB and more. The optical dispersion loss can be eliminated by using an optical dispersion unit connected to the long delay line for compensating the undesired dispersion loss.

Why is ODL System Gain important?

Since ODL typically involves fairly long delay lines, the link budget calculation becomes important.  Based on the requirements, pre- and post LNA are used.

Our online Link Gain Calculator calculates the link gain and the optical predicted parameters for RFOptic’s RFoF programmable product line – 2.5 GHz, 3 GHz, 4 GHz and 6 GHz. It is especially designed for the users of programmable RFoF family solutions in order to determine how the embedded LNA and attenuator should be set up to meet their required RFoF link budget.

How do I manage my RFOptic Optical Delay Line?

Our Optical Delay Lines can be controlled manually using the push button on the unit, or remotely through an RS-232 or Ethernet connection

What is the delivery time once I purchase an Optical Delay Line?

Usually, all RFoF products are sold from stock which means that the delivery time is about 2 weeks. Since an Optical Delay Line is a customized product, it can be delivered in less than 4 weeks (depending on the complexity of the system).