JP3117098B2 - External modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external modulator using a Mach-Zehnder type optical modulator.

[0002]

2. Description of the Related Art Conventionally, there has been known an external modulator using a Mach-Zehnder type optical modulator which is used by being incorporated in an optical transmitter or the like of an optical fiber transmission system.

FIG. 2 shows an example of a conventional external modulator of this type, in which a laser beam 1 emitted from a light source (not shown) is input to a Mach-Zehnder type optical modulator 2, and
An electric modulation signal, for example, a frequency-division multiplexed modulation signal 3 is applied to the Mach-Zehnder type optical modulator 2 and its optical loss is changed to output a laser light 4 with light intensity modulation. I was

FIG. 3 shows the relationship between the modulated signal and the output light in the device shown in FIG.
Indicates that the laser light 4 having a light intensity corresponding to the voltage value of the modulation signal 3 is output in accordance with the curve A showing the applied voltage versus light loss, that is, the output light intensity characteristic.

[0005]

By the way, the curve A
Shows a substantially linear characteristic within a predetermined voltage range (hereinafter, this is referred to as a half-wavelength voltage of the Mach-Zehnder type optical modulator). Therefore, when the peak voltage of the modulation signal 3 exceeds the half-wavelength voltage of the Mach-Zehnder optical modulator 2 as shown by points 3a and 3b in FIG. 3, the output waveform of the laser light 4 in FIG. There is a problem that the distortion occurs as shown by points 4a and 4b.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, an object of the present invention is to provide an external modulator in which output light is not distorted even if the peak voltage of a modulation signal exceeds a half-wavelength voltage of a Mach-Zehnder type optical modulator. .

[0007]

According to the present invention, in order to achieve the above object, a laser beam emitted from a light source is input to a Mach-Zehnder type optical modulator to which an electric modulation signal is added, so that light intensity modulation is performed. In the external modulation device that
The peak voltage does not exceed the half-wavelength voltage of the Mach-Zehnder optical modulator , and the waveform near the peak voltage changes smoothly.
The present invention proposes an external modulation device in which a modulation signal is applied to a Mach-Zehnder optical modulator via a voltage compressor that compresses the signal.

[0008]

According to the present invention, the peak voltage of the modulation signal does not exceed the half-wavelength voltage of the Mach-Zehnder optical modulator due to the voltage compressor , and the waveform near the peak voltage is gentle.
Since the laser light is compressed so as to change , the Mach-Zehnder optical modulator outputs a laser light whose light intensity is modulated without distortion.

[0009]

FIG. 1 shows an embodiment of an external modulation device according to the present invention. In the drawing, the same components as those of the conventional example are denoted by the same reference numerals. That is, 1, 4 'is a laser beam, 2 is a Mach-Zehnder optical modulator, 3, 3' is a modulation signal, and 5 is a voltage compressor.

In the above configuration, the laser light 1 emitted from a light source (not shown) is input to the Mach-Zehnder type optical modulator 2 as in the case of the conventional example.
For example, the frequency division multiplexed modulated signal 3 is input to the voltage compressor 5.

The voltage compressor 5 is designed so that the peak voltage of the input electric signal does not exceed the half-wavelength voltage of the Mach-Zehnder type optical modulator 2 and the waveform near the peak voltage changes smoothly. Compress and output.

FIG. 4 shows a relationship between an input signal and an output signal in the voltage compressor 5, and according to a curve B showing an input voltage-output voltage characteristic in the voltage compressor 5, the Mach-Zehnder type of the modulation signal 3 is obtained. Points that exceed the half-wave voltage of the optical modulator 2, for example, 3a and 3b, are respectively referred to as points 3a '.
And 3b 'indicate that a compressed modulated signal 3' is output.

The modulation signal 3 'output from the voltage compressor 5 is applied to the Mach-Zehnder type optical modulator 2, and the light loss is changed to modulate the light intensity of the laser light 1 to obtain a laser light 4'. Output.

FIG. 5 shows the relationship between the modulated signal and the output light in the device shown in FIG.
Indicates that a laser beam 4 ′ having a light intensity corresponding to the voltage value of the modulation signal 3 ′ obtained by compressing the modulation signal 3 is output according to a curve A showing the applied voltage versus output light intensity characteristic in FIG. It can be seen that no distortion occurs in the points 4a 'and 4b' of the laser beam 4 'corresponding to the points 3a and 3b of the signal 3 which exceed the half-wavelength voltage of the Mach-Zehnder optical modulator 2, respectively.

[0015]

As described above, according to the present invention, the external modulation for modulating the light intensity by inputting the laser light emitted from the light source to the Mach-Zehnder type optical modulator to which the electric modulation signal is added. In the device, the peak voltage does not exceed the half-wave voltage of the Mach-Zehnder optical modulator , and
The modulation signal is applied to the Mach-Zehnder optical modulator through a voltage compressor that compresses the waveform near the peak voltage so that the waveform changes gradually. A modulation signal that does not exceed the voltage is applied, whereby a laser light whose light intensity is modulated without distortion is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an external modulation device of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional external modulation device.

FIG. 3 is an explanatory diagram showing a relationship between a modulated signal and output light in the device of FIG. 2;

FIG. 4 is an explanatory diagram showing a relationship between an input signal and an output signal in the voltage compressor in FIG.

FIG. 5 is an explanatory diagram showing a relationship between a modulation signal and output light in the device of FIG. 1;

[Explanation of symbols]

1: laser light, 2: Mach-Zehnder optical modulator, 3, 3
'... Modulation signal, 5 ... Voltage compressor, 4' ... Light intensity modulated laser light.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-122613 (JP, A) JP-A-1-237516 (JP, A) JP-A-4-192729 (JP, A) 251815 (JP, A) JP-A-1-195418 (JP, A) JP-A-63-232506 (JP, A) JP-B-54-6902 (JP, B2) (58) Fields investigated (Int. ⁷ , DB name) G02F 1/01 G02F 1/313 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. An external modulator that modulates light intensity by inputting a laser beam emitted from a light source to a Mach-Zehnder type optical modulator to which an electric modulation signal is added, wherein the peak voltage is a Mach-Zehnder type optical modulator. Waveform does not exceed the half-wave voltage , and the waveform near the peak voltage changes smoothly.
An external modulator, wherein a modulation signal is applied to a Mach-Zehnder optical modulator via a voltage compressor that compresses the data to be modulated.