JPS5946364B2 - Arbitrary waveform optical pulse generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a simple electric signal such as a sawtooth wave or a sine wave from a continuous oscillation or similar oscillation laser beam to generate a picosecond (10-"2 second) This invention relates to a new type of optical pulse generator that can synthesize arbitrary waveform optical pulses of different orders.

The first possible way to generate optical pulses with arbitrary waveforms is to use an optical modulator, but it is technically very difficult to construct a driving electric circuit on the order of picoseconds. On the other hand, it is easy to obtain a simple picosecond pulse by using laser mode locking, etc., so it is possible to divide this into several pulses, give each one an appropriate delay and intensity, and then superimpose them again to create an arbitrary waveform. Other methods have been proposed and reported, including a method of irradiating this picosecond pulse onto a diffraction grating overlaid with a spatial filter, mask, etc., and utilizing the diffracted light. In these cases, a mode-locked laser capable of obtaining picosecond pulses is required, which increases the overall system size and further limits the usable wavelength range. Furthermore, it has many drawbacks, such as the output waveform changing greatly depending on the nature of the input pulse. In the new device described here, the incident light can be continuous wave light, the type of laser and wavelength are not particularly important, pulse shaping is easy, and it can be configured compactly, making it fully practical as an optoelectronic circuit element. This is what we provide.

Examples will be described below with reference to the drawings.

Incident light 1 enters an electro-optic deflector 2, passes through a distributed phase shifter 3, a distributed intensity aperture 4, and a lens 5 (optional), is diffracted by a diffraction grating 6, and is converted into an arbitrary waveform at a diffracted light output 7. be done. First, with temporally linear deflection, 3,
Consider the case where there is no 4. When a light beam is swung at high speed,
Even though the incident light is continuous, there are 8 waves toward the diffraction grating 6.
The light travels in a band like this. The thickness of this band and the angle it makes with the direction of travel depend on the speed and resolution of the deflection. When the diffraction grating 6 is arranged at an appropriate angle, the bands of diffracted light will be perpendicular to the traveling direction as shown in 9, and the optical waveform will be a pulse with a time width equal to the thickness of the band divided by the speed of light.
If a distributed phase shifter 3 and a distributed intensity aperture 4 are inserted, the shape of the band 8 changes, and the output diffracted light 7 also takes on various waveforms. Next, we will add a more mathematical explanation to understand waveform control.

When passing through the electro-optic deflector, the light beam undergoes an optical phase shift with a linear gradient in the cross-sectional direction (X direction in the figure).
As a result, it is deflected (the phase shift is obtained by changing the refractive index of the deflecting electro-optic crystal due to the applied electric field).
Since the magnitude of this gradient is proportional to the applied voltage, changing the voltage over time sweeps the beam deflection direction. Now, the optical angular frequency of the incident light is ω. Then, the complex amplitude at the exit of the deflector is j(ω) at point X.

−kvX) ・・・・−・・・−・・・・・・・・・
...(1).

Here, t is time, applied voltage, and k is a constant. As the applied voltage, sawtooth V-At (a: constant)...
・・・・・・・・・Considering (2), equation (1) becomes j(ω
o-Kax)T. ．． ．． ．． ．． ．． 、． ．． ,．． ．． (3) e, and apparently the angular frequency ω(x) at point x is ω(x)=
ωo-Kax・・・・・・・・・・・・・・・ (4
), wave sources with linearly different frequencies are distributed in the x direction.

When the light emitted from these wave sources enters the diffraction grating,
Although the incident angle differs slightly depending on the angle, the optical frequency also differs slightly as shown in equation (4), so if the installation angle of the diffraction grating is set appropriately, all the diffracted lights will be in the same direction. As a result, the diffracted light from these sources is completely superimposed.
The installation angle of the diffraction grating in this case is equivalent to the above-mentioned condition in which the bands are perpendicular to the running direction. Now, distributed phase shifter 3,
The complex amplitude distribution of the light immediately after passing through the distribution intensity aperture 4 is:
(3) Instead of (x)Ejq(X). Ej(ω0
-Kax)T. ．． ．． 、． ．． (5) q(x): Amount of distributed phase shift p(x): Represented by the transmission characteristic of the distributed intensity aperture.

Therefore, the diffracted light D(t) is D(t)0C1P(X)Ejq
(X)・Ej((!)0-KaX)1dx...(6)
Then, p(x)Ejq(X) corresponds to the Fourier transform of D(t) (strictly speaking, the Fourier transform of D(t)e-JOOl).

Therefore, if p(x) and q(x) are given by 3 and 4 to match the required D(t), D(t) can be obtained. Also, since the electro-optic deflector has a finite length,
During linear sweeping, a lens effect appears due to the traveling effect of light and reduces the resolution, but this can be compensated for by q(x). As a specific example, a sawtooth voltage of 5 KV/500 ps is applied to an electro-optic deflector using a LiNbO3 crystal using a klytron (a type of high-speed thyratron) to produce Gaussian pulses, triangular pulses, and square pulses with a resolution of about 10 picoseconds. , and other arbitrary waveform pulses can be generated.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the configuration of an embodiment of the optical pulse generator of the present invention. 1...Incoming light, 2...Electro-optic deflector, 3...Distributed phase shifter, 4...Distributed intensity aperture, 5...・Lens, 6... Diffraction grating, 7... Output diffracted light, 8... Light band (before entering the diffraction grating), 9... Light band (after diffraction)
.

Claims (1)

[Claims] 1. A spatially distributed optical phase shifter and a diaphragm or mask with spatially distributed transmittance are arranged at the output part of an electro-optic deflector driven at high speed, and these give the output light an arbitrary phase and intensity distribution. A device that synthesizes arbitrary waveform pulses by irradiating a frequency dispersion element such as a diffraction grating installed at an appropriate angle.