JPS62273510A - Optical modulator - Google Patents

Abstract

PURPOSE:To obtain laser light having a prescribed output waveform, by setting optional voltage waveform data and generating a high voltage corresponding to the data, and then, applying the high voltage across an electrooptic crystal. CONSTITUTION:Optical voltage waveform data are set in a storage section 6 from a data setting section 7. When trigger signals 9 are inputted to the storage section 6, the already set voltage waveform data are successively outputted and converted into voltage waveform by means of a DA converter 5 and the outputs of the converter 5 are amplified to high voltages by using a high-voltage amplifier 4 and impressed across an electrooptic crystal 1. When a high voltage V is impressed across the electrooptic crystal 1, the polarized light of laser light passed through the inside of the crystal 1 is changed proportionally to the high voltage. Therefore, the incident laser light 10 is optically modulated by the electrooptic crystal 1 and polarizers 2 and 3 provided on both sides of the transmissive optical axis of the crystal under a condition where their transmissive axes intersect with each other at right angles and the gain saturation, etc., of a laser amplifier 8 can be corrected. As a result, a necessary amplified laser waveform 12 is obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical modulator, and particularly to an optical modulator that performs amplitude using an electro-optic effect.

[Conventional technology]

Conventional optical modulators use a laser amplifier to amplify the laser oscillator output in order to obtain laser light with high output energy.

FIG. 3 shows an example of waveforms at various parts in such an optical modulator.

The vertical axis of this figure shows the relative value normalized by the peak value of each waveform. Incident laser beam 10 with a constant peak value that is normally obtained
If this is amplified using the laser amplifier 8, the resulting amplified laser beam 13 will have a peak value several tens of times different at the beginning and end of the laser pulse.

[Problem that the invention seeks to solve]

That is, in the conventional optical modulator described above, when the output energy becomes large in the laser amplifier, the gain becomes saturated and decreases over time.

Therefore, there is a drawback that the waveform of the amplified laser light that has passed through the laser amplifier changes with respect to the waveform of the incident laser light, making it impossible to obtain laser light with the desired output waveform.

[Means for solving problems]

The optical modulator of the present invention is for optically modulating an incident laser beam so that the waveform of the amplified laser beam becomes a necessary arbitrary waveform, taking into account the gain saturation of the laser amplifier, and includes an electro-optic crystal; a pair of polarizers placed on both sides of the transmission optical axis; a storage section for holding arbitrary voltage waveform data;
a data setting section for setting the data; a D/A converter for converting the storage section data into a voltage waveform;
and a high voltage amplifier for amplifying the output to a high voltage and applying it to the electro-optic crystal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the optical modulator shown in FIG. 1, arbitrary voltage waveform data is set from the data setting section 7 to the storage section 6. When the trigger signal 8 enters the storage section 6, the already set voltage waveform data is sequentially outputted and converted into a stain pressure waveform by the D/A converter 5. The output is amplified to a high voltage using a high voltage amplifier 4 and applied to the electro-optic crystal 1. When a high voltage V is applied to the electro-optic crystal 1, the polarization of laser light passing through the crystal changes in proportion to the high voltage.

Therefore, polarizers 2 and 3 are placed on both sides of the electro-optic crystal 1 and its transmission optical axis so that their transmission axes are perpendicular to each other.
The incident laser beam 10 undergoes optical modulation. This transmittance T is generally expressed by the following equation (1), where the half-wave voltage of the electro-optic crystal 1 is Vλ/2.

Next, the optical modulation shown in FIG. 1 will be explained with reference to an example of the time waveform of each part shown in FIG. 2.

The waveform diagram shown in FIG. 2 shows a case where the present invention is used to amplify a laser pulse train and make the peak value of the amplified laser light constant.

Similarly to the waveform diagram of the conventional optical modulator shown in FIG. 3, FIG. 2 also shows relative values standardized by the peak value or average value of each waveform.

Generally, the laser amplifier 8 has a transmittance T that corrects the gain waveform of the laser amplifier 8 because the gain at the rear of the laser pulse train temporally decreases due to factors such as gain saturation and becomes like the amplified laser beam 13. 1) Apply a high voltage waveform to the electro-optic crystal 1 using the /A converter 5 and the high voltage amplifier 4, and set the corresponding voltage waveform data in the storage unit 6 using the data setting unit 7. is optically modulated to produce a transmitted laser beam 11.

When this transmitted laser beam 11 is amplified by the laser amplifier 8, an amplified laser beam 12 having a flat envelope whose peak value stability is within a few degrees is obtained.

〔Effect of the invention〕

The optical modulator of the present invention sets arbitrary voltage waveform data,
By generating a corresponding high voltage and applying it to the electro-optic crystal, any transmitted laser waveform can be obtained within the range that satisfies the speed of the D/A converter, so the gain saturation of the laser amplifier can also be corrected. This has the effect that the necessary amplified laser waveform can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing an example of a time waveform using the embodiment shown in FIG. 1, and FIG. 3 is a time waveform using a conventional example. FIG. 1... Electro-optic crystal, 2, 3... Polarizer, 4...-High voltage amplifier, 2... D/A converter, 6... ... Storage section, 7 ... Data setting section, 8 ... Laser amplifier, 9 ... Trigger signal, 10 ... Incident laser beam, 11 ...・
...Transmitted laser light, 12.13...Amplified laser light, 14...Gain. Agent: Susumu Uchihara, patent attorney) 1 @ Kaya 2 Fu Kaya 3 Rhyme

Claims (1)

[Claims] An electro-optic crystal, a pair of polarizers arranged on both sides of a transmission optical axis of the electro-optic crystal, a storage section for holding arbitrary voltage waveform data, and a data setting section for setting the voltage waveform data. , a D/A converter for converting the voltage waveform data into a voltage waveform, and a high voltage amplifier for amplifying the voltage waveform obtained by the conversion to a high voltage and applying it to the electro-optic crystal. An optical modulator comprising: