JPH02114241A - Optical coherent frequency shift keying transmitter - Google Patents

Abstract

PURPOSE:To perform easy and stable optical coherent FSK (frequency shift keying) transmission which is free from the modulating speed by providing an optical switch which switches the output rays of light of two lasers which output the rays of light having fixed wavelengths slightly different from each other in accordance with modulated signals. CONSTITUTION:Lasers 10 and 11 are maintained at a fixed temperature by means of a temperature controller 12 and driven with fixed driving currents by means of laser drive circuits 13 and 14. In addition, the frequencies of the lasers 10 and 11 are respectively maintained at lambda1 and lambda2. An optical switch 15 can output one of the output rays of light of the lasers 10 and 11 after switching in accordance with modulated signals. Accordingly, optical signals outputted from the switch 15 and made incident on an optical fiber 16 become optical frequency shift keying (FSK) signals which shift between the frequencies lambda1 and lambda2 in accordance with the modulated signals. Therefore, stable optical coherent FSK transmission can be performed with a simple circuit, since the transmission characteristics are free from the modulating speed and no complicated control is required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a frequency shift keying (hereinafter abbreviated as FSK) transmitter used in optical coherent communications.

2. Description of the Related Art A conventional optical coherent FSK transmitter includes, for example, a transmitter shown in a block diagram as shown in FIG. In FIG. 3, 20 is a laser, 21 is a temperature control device, 22 is an optical fiber, and 23 is a laser drive circuit.

In the conventional optical coherent FSK transmitter configured as described above, the laser 20 is kept at a constant temperature by the temperature control device 21. If this laser 20 is directly modulated by the laser drive circuit 23 by superimposing a minute modulation signal current on the DC drive current, the wavelength of the output light will change from λ to λ2 corresponding to the mark signal and space signal of the modulation signal. or from λ2 to λ1, an optical FSK signal is transmitted through the optical fiber 22.

Problems to be Solved by the Invention However, in the above configuration, when performing FSK,
The wavelength shift of the laser 20 with respect to the modulation signal depends on the modulation speed and does not respond uniformly, and the digital signal after transmission is subject to large distortions, causing deterioration of transmission characteristics (References R, A.

Ring, P, S, Henry Spectrum L3
4-41 Vol, 01 No, 011988-01)
.

In addition, since the wavelength of the output light of the laser 20 changes not only depending on the drive current but also the temperature of the laser itself, the wavelength of the output light is kept at λi or λ2 in consideration of the temperature rise of the laser itself due to Joule heat of the drive current. There must be.

However, complicated control must be performed to keep both output wavelengths stable while responding to the ever-changing drive current and temperature changes caused by Joule heat.

In view of this, an object of the present invention is to provide a simple and stable optical coherence (FSK) transmitter that does not depend on modulation speed.

Means for Solving the Problems The present invention provides two lasers whose output light wavelengths are kept constant and at slightly different wavelengths λ1 and λ2, and an optical switch that switches the output light from the two lasers using a modulation signal. An optical coherent FSK transmitter comprising:

Effect of the Invention With the above-described configuration, the output light from the two lasers is switched by a modulation signal, so that the optical output becomes an FSK-modulated optical signal in accordance with the modulation signal.

Embodiment FIG. 1 shows a block diagram of an optical coherent FSK transmitter in a first embodiment of the present invention.

In FIG. 1, 10 is a first laser, 11 is a second laser, 12 is a temperature control device, 13 is a laser drive circuit that drives the first laser IO, and 14 is a laser that drives the second laser 11. A drive circuit, 15 is an optical switch, and 16 is an optical fiber.

The optical coherent FS of this embodiment configured as above
The operation of the K transmitter will be explained below.

Laser 10 and laser 11 are kept at a constant temperature by temperature control device I2. Laser 10 and laser! 1 is driven with a constant drive current by laser drive circuits 13 and 14 and held at λ and λ2, respectively.

The optical switch 15 receives input laser IO and laser I.
One of the output lights of I can be switched and output according to the modulation signal. Therefore, the optical signal output from the optical switch 15 and input to the optical fiber 1G becomes an optical FSK signal that knots between λ and λ2 according to the modulation signal.

As described above, according to this embodiment, since the laser itself is not directly modulated, the wavelength shift of the laser cannot fully respond to the speed of the modulation signal, and the transmitted digital signal will not be subject to large distortion. It doesn't happen. In addition, since the driving current is constant, the Joule heat generated in the laser is also constant, so the control to keep the output light mh output wavelength constant is 1 m
It can simply be achieved.

FIG. 2 shows an optical coherent F showing a second embodiment of the present invention.
FIG. 3 is a block diagram of the SK transmitter.

In the figure, 10 is a first laser, [1 is a second laser, +2 is a temperature control device, 13 is a laser drive circuit that drives the first laser 10, and 14 is a laser that drives the second laser II. The drive circuit 16 is an optical fiber and has the same structure as that shown in FIG. The difference from the configuration shown in FIG. 1 is that the optical switch I5 is specifically a waveguide type optical switch 17.

The operation of the optical coherent FSK transmitter of the second embodiment configured as described above will be described below.

The waveguide type optical switch 17 usually has two output terminals, OFF and OFF.
When the switch is in the ON state, the incident optical signal is transmitted from the corresponding output terminal, but when the switch is in the ON state, the switch is changed and the optical signal is transmitted from the output terminal opposite to that when the switch is in the OFF state.

When this waveguide type optical switch is used in this embodiment, for example, the light of the wavelength λ of the laser IO input to the first input end when in the OFF state is transmitted from the first output end to the second The light of wavelength λ2 of the laser 2 that is incident on the input end is transmitted from the second output end. When the waveguide type optical switch ■7 turns on, the wavelength λ1 light from the first input end is transmitted from the second output end, and the wavelength λ2 light from the second input end is transmitted from the first output end, as described above. be done. That is, the waveguide type optical switch 17 corresponds to the mark signal and space signal of the modulation signal.
is ON.

Two FSK optical outputs with opposite OF''FL frequency shifts can be obtained simultaneously.

As described above, according to this embodiment, by using a waveguide type optical switch, two Fs whose frequency shifts corresponding to the mark signal and the space signal of the modulation signal are opposite to each other can be used.
It can be obtained when the SK destination is output. FS of this example
By using it in the K transmitter, the same information can be transmitted to two places simultaneously without using a splitter, and the output optical power of the two lasers can be used effectively.

As described in detail, according to the present invention, it is possible to realize an optical coherent FSK transmitter whose transmission characteristics do not depend on modulation speed, does not require complicated control, has a simple circuit, and is stable. Its practical effects are great.

[Brief explanation of drawings]

FIG. 1 shows an optical coherent FS according to one embodiment of the present invention.
FIG. 2 is a block diagram of another embodiment of the present invention, and FIG. 3 is a block diagram of a conventional optical coherent FSK transmitter. 10...first laser, 11...second laser, 1
2...Temperature control device, 13.14...Laser drive circuit, 15...Optical switch, 16...Optical fiber!
7... Waveguide type optical switch, 20... Laser, 21
...Temperature control device, 22...Optical fiber, 23...
・Laser drive circuit. Name of agent: Patent attorney Shigetaka Kurino Figure 1 of Figure 18, Figure 3 of Figure 3

Claims (2)

[Claims] (1) Optical coherent frequency shift keying transmission comprising two lasers whose output light wavelengths are kept constant and slightly different from each other, and an optical switch that switches the output light from the two lasers using a modulation signal. vessel. (2) In claim 1, an optical switch is defined as two
Optical coherent frequency shift keying transmitter with output waveguide type optical switch.