System and method for transmitting parallel signals via an optical transmission path

• US 5,539,846 A
• Filed: 03/24/1995
• Issued: 07/23/1996
• Est. Priority Date: 03/25/1994
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Furusawa, Satoshi, Takechi, Hideaki, Morikura, Susumu
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US08/410,313
• Time in Patent Office: 487 Days
• Field of Search: 385/24, 359/110, 359/118, 359/136, 359/165, 370/10, 370/13, 370/85.5
• US Class Current: 385/24
• CPC Class Codes: H04J 3/0623 Synchronous multiplexing systems, e.g. synchronous digital hierarchy/synchronous optical network (SDH/SONET), synchronisation with a pointer process

Abstract

A parallel signal transmission system for transmitting parallel signals from a transmission unit to a reception unit via an optical fiber, at a low cost without spoiling their quality. The transmission unit converts received parallel signals into serial signals frame by frame, by means of a frame sync signal, and further converts the serial signals into direct current equilibrium signals which are either CMI codes or DMI codes. At the same time, the direct current equilibrium signals are multiplexed with the frame sync signal in accordance with the code ruling violation in order to drive a laser diode having a 0.78 μm wavelength and output intensity-modulated optical signals to the optical transmission path. As the optical transmission path, a plastic clad fiber is used whose core diameter is 200 μm or larger in order to agree with the laser diode having a 0.78 μm wavelength. In the reception unit, the optical signals are photo/electric converted by means of a silicone photo diode, amplified into direct current equilibrium signals having a predetermined amplitude by means of an alternating current coupling type amplifier. The amplified direct current equilibrium signals are divided into serial signals and the frame sync signal by detecting a coding rule violation, and reproduced into original parallel signals by using the divided frame sync signal.

Claims

1. A parallel signal transmission system for transmitting parallel signals composed of a plurality of bits from a transmission unit to a reception unit via an optical transmission path, wherein

said transmission unit comprises:

a parallel/serial signal conversion means for converting received parallel signals into serial signals frame by frame, said frame being composed of the plurality of bits, in accordance with a 1-bit frame sync signal, and outputting the serial signals;

an encoding means for converting the serial signals outputted from said parallel/serial signal conversion means into direct current equilibrium signals to be used as transmission path signals in conformance with a characteristic of said optical transmission path, and for, at a same time, multiplexing a predetermined bit of the direct current equilibrium signals with the 1-bit frame sync signal by using code rule violation; and

an electric/photo signal conversion unit for driving a laser diode having a laser beam of 0.78 μ

m wavelength in accordance with the direct current equilibrium signals multiplexed with the 1-bit frame sync signal and outputting optical signals intensity-modulated by the laser diode;

said optical transmission path is composed of a plastic clad fiber and directly connected with the laser diode without a lens therebetween;

said reception unit comprises;

a photo/electric conversion means for receiving optical signals sent through said optical transmission path by means of a light reception element made of a silicone photo diode, converting the received optical signals into electric signals, amplifying the electric signals into direct current equilibrium signals having a predetermined amplitude with an alternating current coupling type amplifier, and outputting the direct current equilibrium signals;

a decoding means for receiving and decoding the direct current equilibrium signals into serial signals and for outputting the serial signals separately from the 1-bit frame sync signal by detecting a coding rule violation; and

a serial/parallel signal conversion means for receiving the serial signals and the 1-bit frame sync signal separately, converting the serial signals into original parallel signals frame by frame in accordance with the 1-bit frame sync signal, and outputting the original parallel signals.

2. The optical transmission system of claim 1, wherein the direct current equilibrium signals to be used as the transmission path signals are one of coded mark invention codes and differential mode invention codes which are both 1B/2B signals.

3. The optical transmission system of claim 2, wherein

the 1-bit frame sync signal is multiplexed with the converted direct current equilibrium signals in a predetermined timing of the serial signals outputted from said parallel/serial signal conversion means, and

a longest duration of light emission of the laser diode is dependent on a signal transmission rate on said optical transmission path and a number of consecutive positive-signed signals to be formed by the multiplexing with the 1-bit frame sync signal.

4. The optical transmission system of claim 3, wherein an average direct current voltage of the direct current equilibrium signals is one of being fixed to 1/2 of the signal amplitude and slightly fluctuating when a violation is generated by the multiplexing with the 1-bit frame sync signal, said fluctuation being restricted to an ignorable degree by optimizing a frequency of multiplexing of the 1-bit frame sync signal.

5. The optical transmission system of claim 1, wherein the plastic clad fiber has a core whose diameter is large enough to receive an entire laser beam emitted from the laser diode.

6. The optical transmission system of claim 5, wherein

the diameter of the core of the plastic clad fiber is 200 μ

m or larger in order to agree with the laser diode having a 0.78 μ

m wavelength, and

the plastic clad fiber has a wavelength which has a lowest transmission loss in a light emitting band width of the laser diode.

7. The optical transmission system of claim 6, wherein the silicon photo diode has a core whose diameter is large enough to receive an entire laser beam emitted from the plastic clad fiber.

8. The optical transmission system of claim 7, wherein the alternating current coupling type amplifier uses the direct current voltage of received signals as an operational bias voltage.

9. A parallel signal transmission method for transmitting parallel signals composed of a plurality of bits from a transmission unit to a reception unit via an optical transmission path, said method comprising the steps of:

converting parallel signals into serial signals frame by frame each composed of the plurality of bits, by using a 1-bit frame sync signal;

converting obtained serial signals into direct current equilibrium signals;

multiplexing a predetermined bit of direct current equilibrium signals with the 1-bit frame sync signal at a predetermined frequency;

driving a laser diode in accordance with the direct current equilibrium signals multiplexed with the 1-bit frame sync signal and converting into intensity-modulated optical signals;

receiving the intensity-modulated optical signals outputted from said transmission unit and transmitting to said reception unit via an optical fiber having a predetermined length, said optical fiber having a plurality of coupling portions;

receiving the intensity-modulated optical signals sent through said optical fiber and converting into electric signals;

converting the electric signals into direct current equilibrium signals having a predetermined amplitude;

detecting a coding rule violation in the direct current equilibrium signals;

separating the 1-bit frame sync signal from the direct current equilibrium signals in accordance with the detected coding rule violation;

decoding the direct current equilibrium signals separated from the 1-bit frame sync signal into serial signals; and

converting the serial signals into parallels signals frame by frame in accordance with the separated 1-bit frame sync signal.

10. The parallel signal transmission method of claim 9, wherein the direct current equilibrium signals in the step of converting the serial signals into direct current equilibrium signals are one of coded mark invention codes and differential mode invention codes, which are both 1B/2B codes.