DE10357212B4 - Clock regenerator for high-speed optical time-division multiplex signals - Google Patents

Abstract

Clock regenerator for a time-division multiplex signal (TDM) for generating a sub-clock signal (f _K ) with a ring laser (13, 15, 18) to which the time-division multiplex signal (TDM) is fed via a coupler (2) and which contains a modulator (3) which modulates the time division multiplexed signal (TDM) with a sub-data rate of the time division multiplexed signal (TDM),
with a splitter (4, 5), via which a signal component is coupled out of the ring laser (18, 13, 15),
with a first filter (6) connected downstream of the splitter (4, 5) for selecting a first optical comparison signal (λ _LM ) having the wavelength of the freely oscillating ring laser (13, 15, 18),
with a second filter (7) connected downstream of the same splitter (4, 5) or a further splitter (20) for decoupling a second optical comparison _signal (λ _TDS ) _having the wavelength of the time-division multiplex signal (TDM),
with optical-electrical converters (8, 9), which convert the optical comparison signals (λ _LM , λ _TDS ) into electrical comparison signals (V1, V2),
with a control device (10, 19), which compares the electrical comparison signals (V1, ...

Description

The The invention relates to a clock regenerator for optical time division multiplexed signals, preferably with bit rates ≥ 80 Transfer Gbit / s become.

at optical transmission systems with extremely high data rates is the recovery of the system clock from an intensity modulated Time-division multiplex signal (OTDM signal) problematic, since in today Prior art, an electrical recovery of the system clock by means of phase locked loops is not yet possible. Therefore, time division multiplexed signals are used first a division of the received signal to individual channels; out the individual data signals of lower data rate is then respectively derived a data clock signal.

In "Lasers and Electro-Optics Society ", LEOS 2001, The 14th Annual Meeting of the IEEE, Vol. 2, pp. 721-722. J. M. Roth et al. is a ring laser system for generating a clock signal described.

In US 5,548,433 Such a ring system is used to recover the clock signal of a supplied data signal.

In an article from the Lucent Technologies Bell Laboratories "High Speed Clock Recovery using Optoelectronic Phase Locked Loop Implemented with Balanced Photodetection "by Dennis T.K. Tong, et al; Holmdel, NJ 07733, USA; 0-7803-9 / 99 1999 IEEE, On pages 349, 350, a phase locked loop is described which includes the incoming signal directly a data clock signal with a sub-data rate wins in the over a modulator the incoming OTDM signal with this clock signal is modulated and compared the output signal of the modulator with the attenuated received signal becomes. The error signal thus obtained controls via a low-pass filter Oscillator.

In Electronic Letters, 2001, Vol. 37, No. 8, pages 509 and 510 described another clock regenerator, which is also a subharmonic clock signal generated. This arrangement uses a tunable mode-locked laser (TMLL), which is controlled by a controllable oscillator. The Output signal and the data signal are called a SLALOM (Laser Amplifier in a loop mirror) supplied, the output signal via a Bandpass or low-pass filter of a photodiode is supplied. Its output signal, as in the previous circuit is with the muted received signal compared and controls over a bandpass the oscillator. Through a special transmission code or through a scrambler must have a constant ratio of logical zeros and ones are generated. In this arrangement is simultaneously generates an electrical and an optical clock signal. However, this circuit is expensive.

These Circuit was made by the same inventors in Proc. 27th European Conference to Opt. Communication, ECOC 01-Amsterdamur, pages 721-722 yet through a semiconductor amplifier added.

task The invention is therefore a more easily realizable clock regenerator for optical signals specify.

These Task is solved by the clock regenerator according to claim 1.

at This clock regenerator, a comparison between signals is performed, the generated by the TDM signal and a laser-active medium. With appropriate execution the control circuit, this comparison is largely independent of the 1-0 distribution of the data signals. Preferably, a subfrequency generates the data rate of a data signal (channel) of the wavelength division multiplexed signal equivalent.

Farther is advantageous that also an electrical and an optical Clock signal is generated. The sub-clock signals will be corresponding generates the frequency of a data signal.

One embodiment The invention will be explained in more detail with reference to figures.

It demonstrate

1 a schematic diagram of the clock regenerator,

2 the power ratios in an asynchronous control loop and

3 the power ratios in a synchronous control loop.

The in the 1 The arrangement shown is a block diagram of a particularly advantageous embodiment of the invention, in which only essential elements are shown.

The core of the clock regenerator is a feedback fiber ring laser 18 . 13 . 15 which basically consists of a pump laser 13 , a laser-active medium 15 and an optical fiber 18 is formed. In the fiber 18 is via a coupler 2 on at the signal input 1 a time-division multiplexed TDS signal coupled in a connection fiber in the RZ format (return to zero). This signal usually consists of several data signals (channels) of the same Da tenrate. The time-division multiplex signal TDS becomes a modulator 3 supplied and modulated with the modulation signal f _K , whose frequency corresponds to the data rate of a sub-signal, preferably a data signal. For example, at a data rate of 10 Gbit / s of a data signal, the modulation frequency is 10 GHz. The modulation signal is at the same time as a data clock signal at the clock output 12 led out. The modulated time division multiplexed signal, in contrast, is transmitted via a coupler 14 and the laser-active medium 15 , For example, a doped fiber to the modulator 3 recycled. The laser 13 pumps the laser-active medium 15 whose wavelength-dependent gain maximum is chosen to be shifted by several nm (nanometers) from the wavelength, the "carrier frequency", of the time division multiplexed signal.

From the ring laser are over splitter 4 and 5 and filters 6 and 7 coupled out a first comparison signal _LM λ the wavelength of the free-running laser, and a second comparison signal _TDS λ the wavelength of the time division multiplexed signal TDS and in each case by a photodiode 8th and 9 converted into electrical comparison signals V1 and V2, via a comparator 10 controlling the controllable oscillator to oscillate at the frequency of a sub-data rate, here a data signal. An attenuator 19 can for level matching of the comparison signals in the connecting line between photodiode 9 and comparators 10 to be on.

2 shows the levels of the first comparison signal λ _LM (laser intensity) at the wavelength of the free-oscillating ring laser and the second comparison signal λ _TDS (carrier intensity) with the wavelength of the time-division multiplex signal TDS for the asynchronous case.

A free-running ring laser RL will resonate at the wavelength at which the laser-active medium 15 has a maximum gain. This also applies if the modulation frequency f _{K of} the oscillator 11 does not coincide with a sub-data rate of the received time division multiplex signal TDS. The level of the first comparison signal λ _LM is then greater than that of the second comparison signal λ _TDS, and the control voltage obtained from the subtraction of the corresponding electrical signals is used in the case in which 2 case illustrated the frequency of the oscillator 11 to decrease until the frequency f _{K of} the oscillator 11 is equal to the data rate of a data signal. Then, the injection of a synchronous to the mode frequency of the laser light image will cause the ring laser to oscillate with the wavelength of the incoming time-division multiplex signal and amplify this signal.

If the oscillator frequency and the sub-data rate coincide, a level ratio becomes corresponding 3 reached, wherein the level of the second comparison signal is substantially increased compared to the level of the first comparison signal. With a corresponding design of the control loop, a phase-locked sub-clock signal (data clock signal) f _{K is obtained} . By multiple delay of the recovered data clock signal, the clock signals for the other data signals can be derived.

By the decoupling of laser and TDM signal from the ring laser results a high sensitivity, since both comparison signals dependent on change from the modulation frequency. There by the time constant of the ring laser even with several successive following logical zeros (no signal) the comparison voltages decay only slowly, is largely independent of reaches the 1-0 distribution of the time division multiplex signal. The reinforcement profile VP of the laser-active medium can be relatively flat.

Is instead of the second comparison signal λ _TDS a from the TDM signal on a broken line splitter 20 directly coupled alternative comparison _signal λ _TDS2 or, at constant level _ratios , a constant second comparison value used, the arrangement is less sensitive.

An optical data clock signal f _KQ can be sent via another splitter 16 be disconnected and then lies at the exit 17 at.

It can also choose an arrangement where the direction of laser oscillation is not optical Elements is specified. The error signal for the control of the oscillator then becomes a comparison of the laser intensity in the direction of the data signal and the carrier intensity in opposite Direction won.

Claims (1)

Clock regenerator for a time-division multiplex signal (TDM) for generating a sub-clock signal (f _K ) with a ring laser ( 13 . 15 . 18 ), via a coupler ( 2 ) the time-division multiplex signal (TDM) is supplied and the one modulator ( 3 ) which modulates the time division multiplexed signal (TDM) with a sub-data rate of the time division multiplexed signal (TDM), with a splitter ( 4 . 5 ), via which a signal component from the ring laser ( 18 . 13 . 15 ), with a splitter ( 4 . 5 ) downstream first filter ( 6 ) for selecting a first optical comparison signal (λ _LM ), the wavelength of the free-oscillating ring laser ( 13 . 15 . 18 ), with a same splitter ( 4 . 5 ) or another splitter ( 20 ) downstream second filter ( 7 ) for coupling out a second optical comparison _signal (λ _TDS ) _having the wavelength of the time division multiplexed signal (TDM), with optical-electrical converters ( 8th . 9 ), which convert the optical comparison signals (λ _LM , λ _TDS ) into electrical comparison signals (V1, V2), with a control device ( 10 . 19 ), which are supplied with the electrical comparison signals (V1, V2) and which outputs a control signal (U _R ), and with a controllable oscillator ( 3 ), to which the control signal (U _R ) is supplied and which generates the sub-clock signal (f _K ), which as a modulation signal modulator ( 3 ) controls.