Quasi-light Storage for Optical Data Packets

Summary

The article describes a procedure to store optical data packets with an arbitrary modulation, wavelength, and data rate. These packets are the basis of modern telecommunications.

Abstract

Today's telecommunication is based on optical packets which transmit the information in optical fiber networks around the world. Currently, the processing of the signals is done in the electrical domain. Direct storage in the optical domain would avoid the transfer of the packets to the electrical and back to the optical domain in every network node and, therefore, increase the speed and possibly reduce the energy consumption of telecommunications. However, light consists of photons which propagate with the speed of light in vacuum. Thus, the storage of light is a big challenge. There exist some methods to slow down the speed of the light, or to store it in excitations of a medium. However, these methods cannot be used for the storage of optical data packets used in telecommunications networks. Here we show how the time-frequency-coherence, which holds for every signal and therefore for optical packets as well, can be exploited to build an optical memory. We will review the background and show in detail and through examples, how a frequency comb can be used for the copying of an optical packet which enters the memory. One of these time domain copies is then extracted from the memory by a time domain switch. We will show this method for intensity as well as for phase modulated signals.

Introduction

The data transport in the telecommunications networks is optically, since only optical fibers offer the capacity required for today's data traffic transmitted around the world. However, in every node of the network the optical signal has to be transferred into the electrical domain in order to process it. After processing the signal is converted back to the optical domain for further transmission. This double-transfer between the domains is both time and power consuming. In order to use an all-optical processing of the data, the problem of the intermediate storage has to be solved. Thus, lots of methods for the storage or buffering of the optical signals have been sug....

Protocol

1. Preparing the System (Figure 4)

1. Insert the laser diodes LD1 and LD2 in the specific mount and connect it with the current (LDC) and temperature controllers (TEC). Turn the devices on and check the functionality of the laser diodes with the optical spectrum analyzer. Usually, a telecom wavelength around 1,550 nm is used.
2. Connect the laser diode to the modulators (IM/PM and MZM1) according to the setup in Figure 4. The optical connectors need to be cleaned before use, to ensure the clean surface for coupling. Connect the power supply (not shown) and the signal from the waveform generator (AWG) with an additional electrical ampli....

Results

For the measurement a 10110101 intensity modulated data pattern with a data rate of 1 Gbps was used. The black line in Figure 6 represents the original signal and the colored lines represent the different storage times achieved with the QLS.  The reference is measured without the QLS and the deactivated switch at the output. Under ideal conditions storage times up to 100 nsec are achievable. The results for the stored 11001101 data pattern of a phase modulated signal, again with a data rate of 1 Gbps can.......

Discussion

The most critical step during the experiment is the adjustment of the frequency comb, i.e. the bandwidth, flatness and position in respect to the data signal in the frequency domain. According to the sampling theorem in frequency domain, signal distortions are avoided if the whole bandwidth of the optical packet is sampled with an ideally flat comb. Thus, the bandwidth of the optical packet defines the minimum bandwidth of the frequency comb and in this bandwidth the comb has to be as flat as possible. A nonidea.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Laser diode	3S Photonics	A1905LMI	2x
Laser Mount	Tektronix	LDH BFY-B2	2x
Temperature Controller	LightWave	LDT-5948	2x
Current Controller	LightWave	LDX-3220	2x
Optical amplifier	High-Wave	HWT-EDFA-B-30-1-FC/PC
Circulator	OFR	OCT-3-IR2
Waveform Generator	Tektronix	AWG7102
Fiber 20 km	OFS	AllWave-ZWP G652C-D
Polarization Controller	Thorlabs	Fiber Pol. Contr. IPC030	2x
Modulator	Avanex	IM-10-P	Phase
Modulator	Avanex	SD20	Amplitude, extract
Modulator	Avanex	PowerBit F-10	Amplitude, data
Modulator	Covega	Mach10	Amplitude, comb
Optical Spectrum Analyzer	Yokogawa	AQ6370C
Oscilloscope	Agilent	DCA-J 86100C
Measurement Module	Agilent	86106B
Fiber Laser	Koheras	Adjustik
Coupler	Newport	F-CPL-L22151-P	Ratio: 90/10
Coupler	Newport	F-CPL-L12155-P	Ratio: 50/50
Power supply	Zentro-Elektrik	LD 2x15/1 GB
Electrical amplifier	SHF	826H
Supply port	SHF	B826
Electrical amplifier	Amplifier Research	10W1000
Photodiode	Newport	D-8ir
Electrical spectrum analyzer	HP	8563E