Optical transmitter, optical receiver and optical transmission apparatus and control method of optical receiver

• US 5,274,490 A
• Filed: 04/30/1991
• Issued: 12/28/1993
• Est. Priority Date: 01/20/1988
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Sasaki, Shinya, Tsushima, Hideaki
• Primary Examiner(s): PASCAL, LESLIE C
• Application Number:
  US07/693,584
• Time in Patent Office: 973 Days
• Field of Search: 359/173, 359/180, 359/181, 359/182, 359/184, 359/185, 359/188, 359/191, 359/195
• US Class Current: 398/204
• CPC Class Codes: H04B 10/614 comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers H04J14/06 takes precedence
• CPC Class Codes: H04L 25/4925 using balanced bipolar ternary codes
• CPC Class Codes: H04L 27/10 Frequency-modulated carrier systems, i.e. using frequency-shift keying H04L27/32 takes precedence

Abstract

A unipolar original electrical signal is encoded by alternate mark inversion and combined with a DC bias current for injection of a semiconductor laser to produce a bipolar FSK optical signal that is transmitted to a receiver. At the receiver, the received signal is coupled with optical local power and fed to an optical/electrical transducer, preferably a semiconductor, to produce an electrical signal that is demodulated to produce the original unipolar signal. The demodulator may be of different types, for example employing delaying part of the amplified electrical signal and mixing the delayed part with the original signal for passage of the combined signal through a low pass filter; with proper selection of the delay, an AMI decoder is not needed. The demodulator may also be of the type that has one or more band pass filters to respectively separate the positive mark, space and negative mark signals that may thereafter be added. Filtering and polarization beam splitting may also be used in the demodulator for improving the signal-to-noise ratio and preventing other types of degradation.

Claims

1. A transmitter for an optical coherent communication system, comprising:

an alternate mark inversion (AMI) coder converting a binary information electrical signal into an AMI code baseband electrical signal;

a superposer superposing said AMI coded baseband electrical signal on a bias current to obtain a superposition current signal; and

a semiconductor laser diode driven by said superposition current signal to output an AMI coded frequency shift keying (FSK) optical signal.

2. A receiver for an optical coherent communication system, comprising:

a heterodyne detector converting an AMI coded FSK optical signal into an AMI coded FSK electrical signal, including a semiconductor laser diode producing a local optical signal, an optical coupler combining said AMI coded FSK optical signal with the local optical signal to produce a combination optical signal, and a photo diode detecting the combination optical signal to produce said AMI coded FSK electrical signal; and

a frequency discriminator converting said AMI coded FSK electrical signal into a binary information electrical signal, including a divider dividing said AMI coded FSK electrical signal into two components, a delay line delaying one of said two components relative to the other of said two components by a delay time equal to about n/2f_s, wherein n is a positive natural number including zero and f_s is the frequency corresponding to a space signal of said AMI coded FSK electrical signal, a mixer multiplying the delayed one of said two components and the other of said two components without delay to produce a multiplication component, and a low-pass filter passing the multiplication component to directly produce a binary information electrical signal without necessitating a separate AMI decoder.

3. A receiver for an optical coherent communication system, comprising:

a heterodyne detector converting an AMI coded FSK optical signal into an AMI coded FSK electrical signal, including a semiconductor laser diode producing a local optical signal, an optical coupler combining said AMI coded FSK optical signal with the local optical signal to produce a combination optical signal, and a photo diode detecting the combination optical signal to produce said AMI coded FSK electrical signal;

a band-pass filter having a band-pass frequency corresponding to a space frequency of said AMI coded FSK electrical signal for extracting a space component from the AMI coded FSK electrical signal; and

an envelope detector converting the extracted space component into a binary information electrical signal.

4. An optical communication system, comprising:

a transmitter comprising,

an alternate mark inversion (AMI) coder converting a binary information electrical signal into an AMI coded baseband electrical signal;

a superposer superposing said AMI coded baseband electrical signal on a bias current to obtain a superposition current signal; and

a semiconductor laser diode driven by said superposition current signal to output an AMI coded frequency shift keying (FSK) optical signal;

an optical fiber transmitting said AMI coded frequency shift keying (FSK) optical signal; and

a receiver comprising,

a heterodyne detector converting the AMI coded FSK optical signal into an AMI coded FSK electrical signal, including a semiconductor laser diode producing a local optical signal, an optical coupler combining said AMI coded FSK optical signal with the local optical signal to produce a combination optical signal, and a photo diode detecting the combination optical signal to produce said AMI coded FSK electrical signal, and

a frequency discriminator converting said AMI coded FSK electrical signal into a binary information electrical signal, including a divider dividing said AMI coded FSK electrical signal into two components, a delay line delaying one of said two components relative to the other of said two components by a delay time equal to about n/2f_s, wherein n is a positive natural number including zero and f_s is the frequency corresponding to a space signal of said AMI coded FSK electrical signal, a mixer multiplying the delayed one of said two components and the other of said two components without delay to produce a multiplication component, and a low-pass filter passing the multiplication component to directly produce a binary information electrical signal without necessitating a separate AMI decoder.

5. An optical communication system, comprising:

a transmitter comprising;

an alternate mark inversion (AMI) coder converting a binary information electrical signal into an AMI coded baseband electrical signal,

a superposer superposing said AMI coded baseband electrical signal on a bias current to obtain a superposition current signal, and

a semiconductor laser diode driven by said superposition current signal to output an AMI coded frequency shift keying (FSK) optical signal;

an optical fiber transmitting said AMI coded frequency shift keying (FSK) optical signal; and

a receiver comprising,

a heterodyne detector converting said AMI coded frequency shift keying (FSK) optical signal into an AMI coded FSK electrical signal, including a semiconductor laser diode producing a local optical signal, an optical coupler combining said AMI coded FSK optical signal with the local optical signal to produce a combination optical signal, and a photo diode detecting the combination optical signal to produce said AMI coded FSK electrical signal,

a band-pass filter having a band-pass frequency corresponding to a space frequency of said AMI coded FSK electrical signal for extracting a space component from the AMI coded FSK electrical signal, and

an envelope detector converting the extracted space component into a binary information electrical signal.