Time and Frequency Transfer and Dissemination Methods Using Optical Fiber Network

Abstract

In the time and frequency transfer and dissemination field, it is important to provide cost effective remote frequency calibration services with an uncertainty of around 10-12 for end users. It is also required to develop ultra precise transfer methods with an order of 10-15 or better uncertainty for the comparison between ultra stable frequency standards which are under developing. This study shows two methods using optical fiber networks to satisfy these demands. First, it is an economical remote calibration method using existing synchronous optical fiber communication networks. The measured frequency stability (the Allan deviation) of the transmission clock is 2×10-13 for an averaging time of one day. The result indicates the method is promising for the simple remote frequency calibration service. Second, it is an ultra precise two-way optical fiber time and frequency transfer method using a newly proposed bi-directional optical amplifier. In this method, wavelength division multiplexing (WDM) signals are transmitted along a single optical fiber. The preliminary measured frequency stability is less than 10-15 (τ=10 4 s) for a 100-km-long fiber with the bi-directional amplifier. It suggests that the method has capability for improving International Atomic Time (TAI) and Coordinated Universal Time (UTC).

Delivering 10 Gb/s optical data with picosecond timing uncertainty over 75 km distance

“…The optical signal is multiplexed into a first fiber spool of 25 km length. To overcome the signal attenuation due to link losses, and to demonstrate the suitability of the method for amplified links, the optical signal is demultiplexed and sent through a quasibidirectional optical line amplifier (OLA) [14]. The quasi-bidirectional amplifier is built up from two semiconductor optical amplifiers (SOAs) equipped with optical isolators (OIs), which limit the influence of backscattered light on the SOAs, thereby allowing operation at high gain.…”

System for precise dissemination of frequency standard via optical fiber

“…The configuration of this device fundamentally consists of the erbium fiber which is the amplification medium, and a wavelength multiplexer/de-multiplexer to separate the bidirectional signal (using a dielectric multilayered film filter), and an optical isolator to prevent reflection, installed in the circuit separated by the above measures [8]. The configuration of this device fundamentally consists of the erbium fiber which is the amplification medium, and a wavelength multiplexer/de-multiplexer to separate the bidirectional signal (using a dielectric multilayered film filter), and an optical isolator to prevent reflection, installed in the circuit separated by the above measures [8].…”

“…In order to transfer a frequency standard directly and over a long distance, the loss in the optical fiber must be compensated, and bidirectional amplification is necessary in order to obtain sufficient optical receiving power, as shown in the previous section. The configuration of this device fundamentally consists of the erbium fiber which is the amplification medium, and a wavelength multiplexer/de-multiplexer to separate the bidirectional signal (using a dielectric multilayered film filter), and an optical isolator to prevent reflection, installed in the circuit separated by the above measures [8]. Isolation between the bidirectional optical signals in this device is a satisfactory value of 65 dB, as shown in Fig.…”

Remote atomic clock synchronization via satellites and optical fibers

“…To cancel long term fiber length variations in time and frequency transfer the two-way method for exchanging optical signals has been investigated (Amemiya et al, 2006). Such an approach was initially proposed in the framework of network synchronization (Kihara and Imaoka, 1995).…”