Optical time-division multiplexing transmitter module

Details Optical time-division multiplexing transmitter module Optical time-division multiplexing transmitter module

1998-10-13

2001-12-11

Pascal, Leslie (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200

Reexamination Certificate

active

06330089

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical transmitter module for time-division multiplexing in an optical communication field.
BACKGROUND OF THE INVENTION
A conventional optical time-division multiplexing (OTDM) system is described, for example, in Proceedings of the 21st European Conference on Optical Communications (ECOC '95-Brussels) Th. A. 3. 5, pp. 983-986. An optical transmitter described in this publication has an optical signal (clock) generator which includes a laser diode and an optical electro-absorption (EA) modulator and generates a 10 Gbit/s pulse beam.
In the conventional transmitter, an RZ (return-to-zero) pulse train signal from the optical signal generator is split into two signals via an optical coupler. Then the split signals are modulated by an LiNbO
3
modulator. After one of the modulated signals is delayed, both signals are multiplexed via another optical coupler.
There are some problems with the conventional optical time-division multiplexing transmitter module. Since the conventional transmitter employs an LiNbO
3
modulator for modulating the optical signals, it is difficult to minimize the overall module size. In the case of employing a relatively smaller EA modulator instead of the LiNbO
3
modulator, connections between its input/output ports and other components require optical fibers, which prevents further size reduction. Moreover, especially in the case of a multi-tap module with a PLC substrate (a planer lightwave circuit formed on a semiconductor substrate), it is difficult to align optical axes of EA modulator chips and the PLC substrate.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to solve the above-described problems to provide an optical time-division multiplexing transmitter module which is compact and makes alignment of the optical axes easy.
According to the present invention, there is provided an optical time-division multiplexing transmitter module which includes an optical circulator, an optical coupler which splits in two an optical signal in the form of a pulse beam output from the circulator, first and second double-pass electro-absorption (DPEA) modulators positioned respectively to receive and modulate one and the other of the two split signals, and reflect the modulated signals back through the coupler to the circulator. The coupler multiplexes the reflected signals and directs the multiplexed signals to the circular which then guides them to exit through a circulator output port. An optical delay circuit is positioned between in the path of one of the split signals so as to delay it relative to the other.
By employing DPEA modulators, the number of the optical components is reduced thereby making it is possible to make the module more compact. Further, according to the invention, compared to the prior art, it is easy to align the optical axes.


REFERENCES:
patent: 5615037 (1997-03-01), Betts et al.
patent: 5781003 (1998-07-01), Kondo
patent: 5796764 (1998-08-01), Corsini et al.
patent: 5835646 (1998-11-01), Yoshikawa
patent: 5889607 (1999-03-01), Suzuki et al.
patent: 5926297 (1999-07-01), Ishikawa et al.
patent: 11160663-A (1999-06-01), None
20Git/s, 8100km Straight-line Single-Channel Solution-based RZ Transmission Experiment Using Periodic Dispersion Compensation. pp. 983-986.

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