JPH05267765A - Pulse frequency variable mode locking device - Google Patents

Abstract

PURPOSE:To realize a pulse period variable mode locking device of simple structure by a method wherein a first optical waveguide where mirrors are arranged at both its end its ends is provided, oscillation light is propagated to a second waveguide to circuit, and a resonator is elongated in length by a length corresponding to the second waveguide which the laser beam travels. CONSTITUTION:Light propagated to a first optical waveguide 1 is made to pass through the intermediary of a synchronizing circuit 9 when no voltage is applied to an optical switch or switched over to a second optical waveguide 6 or a third optical waveguide 8 when a voltage is applied onto the optical switch. A resonator is composed of a first and a second mirror, 2 and 3, and light traveling the second optical waveguide 6 can be controlled in traveling distance by controlling a first optical switch in switching time. By this setup, as a resonator is elongated in length by a length corresponding to the second waveguide which the laser beam travels, a pulse laser whose pulse period is proportional to the sum of the length of the first optical waveguide 1 and the integral multiple of the length of the second optical waveguide 6 can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mode lock device used as one of laser oscillation control methods, and more particularly to a mode lock device capable of changing a pulse period.

[0002]

2. Description of the Related Art FIG. 4 is a view showing a schematic structure of a conventionally known synchronous mode-locked dye laser. A mode-locked argon ion laser between the first and second mirrors,
A diffraction mode lock device driven by a frequency synthesizing rf driver is arranged, and a sub-picosecond pulse can be generated between a second resonator composed of a third mirror, a laser medium and a fourth mirror. ..

[0003]

However, since the conventional mode lock device has a fixed resonance length,
There was a problem that the pulse period could not be changed. That is, in order to change the pulse frequency in the above configuration, it is sufficient to move the fourth mirror, but there is a problem in that a precise moving mechanism and a device are increased in size.

The present invention has been made in order to solve the above-mentioned conventional problems. A resonator is composed of two resonators, a first resonator and a second resonator, and an optical path changeover switch is used. An object of the present invention is to provide a mode-lock device in which the pulse period is variable by guiding light into the second resonator, controlling the time for circulating the light in the second resonator, and artificially changing the resonance length.

[0005]

In order to solve the above problems, the present invention provides a first optical waveguide in which a first mirror is arranged at an incident end and a second mirror is arranged at an outgoing end, and a first optical waveguide of the first optical waveguide. A laser medium provided near the entrance end and a laser medium formed near the exit end of the first optical waveguide for propagating light propagating in the first optical waveguide to the second optical waveguide side and to the second optical waveguide side. A first optical switch for propagating the propagated light again to the first optical waveguide side, and a first optical switch disposed between the first optical switch and the laser medium for branching the light propagating in the first optical waveguide Two optical switches and a synchronous circuit for switching the first and second optical switches in a predetermined cycle are provided.

[0006]

The pumping light propagates through the first mirror to the first optical waveguide. This first mirror has a high transmittance for the excitation light wavelength and functions as a mirror having a high reflectance for the oscillation wavelength. The laser medium amplifies and oscillates the oscillation light inside the resonator by the propagating excitation light. The first optical switch switches the oscillation light propagating through the first optical waveguide to the second optical waveguide, and further switches the oscillation light circulating in the second optical waveguide to the first optical waveguide. The second optical switch switches the oscillated light traveling back and forth in the first optical waveguide to the third optical waveguide. The synchronizing circuit controls the timing of the first and second optical switches.

[0007]

1 is a block diagram showing an embodiment of a variable pulse period mode lock device of the present invention. In the figure, 1
Is a first optical waveguide, 2 is a first mirror arranged at the input end of the first optical waveguide 1, and 3 is a second mirror also arranged at the output end. Reference numeral 4 is a laser medium arranged on the input end side of the first optical waveguide 1, 5 is a first optical switch also arranged on the output end side of the first optical waveguide 1, and the first optical switch 5 has an annular shape. The second optical waveguide 6 formed in is connected. Reference numeral 7 is a second optical switch formed between the laser medium 4 and the first optical switch. The second optical switch 7 is connected to a third optical optical waveguide 8 whose both ends are open. Reference numeral 9 is a synchronizing circuit for controlling the switching time of the first and second optical switches.

FIG. 2 is an enlarged plan view showing the configuration of the first and second optical switches 5 and 7, and the first optical waveguide 1 and the second or third optical waveguide 6, 8 are formed in parallel and close to each other. Directional coupler is used. In this optical switch, when the light of P _i propagated to the first optical waveguide 1 is not applied to the optical switch via the synchronizing circuit 9, the optical waveguide P =
When a voltage is applied, it is switched to the second or third optical waveguide 6 or 8 side as P ×. The optical switch and the optical waveguide are formed on a LiNbO ₃ substrate, for example.

In the above structure, the excitation light is propagated from the laser light source (not shown) to the first optical waveguide 1 in a state where no voltage is applied to the first and second switches 5 and 7 (OFF). As the excitation light, for example, the second harmonic of Ar laser or Nd: YAG laser is used, and as the laser medium 4, Ti: A is used.
l ₂ O ₃ is used. The pumped laser light that has propagated excites the laser medium, and the oscillated light is amplified by the laser medium and oscillates while reciprocating between the first and second mirrors. It is conceivable that the oscillated light propagated in the second optical waveguide 6 is attenuated as it travels through the waveguide. In such a case, a known optical amplifier may be inserted in the waveguide 6. Good.

Next, mode lock and pulse period conversion will be described with reference to FIG. In the figure, "a" indicates the on / off state of the second optical switch 7, "b" indicates the on / off state of the first optical switch 5, "x" indicates the switch is on, and "=" indicates the switch is off. Shows.

Now, suppose that the oscillation light reflected by the first mirror 2 travels toward the second mirror 3 side at time 0. This light is at time 1
At, the second optical switch 7 reaches the first optical switch 5 since the second optical switch 7 is in the off (=) state at this time (after the light passes through the second optical switch, Switch is on). At this time, since the first optical switch 5 is in the on (x) state, the oscillated light propagates to the second optical waveguide 6.

After the light has propagated to the second optical waveguide 6, this first
The optical switch 5 is turned off while the oscillation light does not go around the second optical waveguide 6 once. As a result, the light passes through the second optical waveguide 6
The first optical switch 5 is turned on when the time 3 is reached, but the oscillated light propagates again to the first optical waveguide 1 (this switch is turned off after the light passes through the first optical switch). ).

The oscillated light propagating in the first optical waveguide 1 is reflected by the second mirror 3 at time 4 and passes through the second switch 7 again at time 5, but at this time this switch 7 is off. Pass as it is. Next, when the time 6 is reached, the second optical switch 7 is turned off, and the oscillated light passes through as it is and is reflected by the first mirror 2 at the time 7 to return to the initial state. In this way, the first
A resonator is formed between the second mirrors. The light oscillated at a timing other than the above timing is emitted from the third optical waveguide via the second optical switch 7.

According to the above arrangement, the switching time of the first optical switch 5 can be controlled to control the distance that light travels in the second optical waveguide 6. This is the same as extending the distance between the first and second mirrors. Further, since only the light of a certain specific timing is selected by switching the first and second optical switches, it is equivalent to the mode-locking technique in which the loss is modulated in the resonator. The laser oscillation period at the time of mode locking is the period T = a / c (c is the speed of light) for the resonator length a. In the present invention, the resonator length a
Can be lengthened by the amount of light passing through the second optical waveguide 6, so that a pulse laser whose pulse period is proportional to the sum of the length of the first optical waveguide 1 and the length of the second optical waveguide 6 is multiplied. You can

As described above in detail with reference to the embodiments, the pulse-cycle variable mode lock device of the present invention provides a first optical waveguide in which mirrors are arranged at both ends and oscillation light of the first optical waveguide. Since the resonator length a is propagated and circulated to the side of the second optical waveguide, and the resonator length a is lengthened by the amount of traveling through the second optical waveguide, it is possible to realize a mode-lock device having a variable pulse period with a simple configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a variable pulse period mode lock device of the present invention.

FIG. 2 is an enlarged plan view showing a configuration of first and second optical switches.

FIG. 3 is an explanatory diagram related to mode lock and pulse period conversion.

FIG. 4 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 1 1st optical waveguide 2 1st mirror 3 2nd mirror 4 laser medium 5 1st optical switch 6 2nd optical waveguide 7 2nd optical switch 8 3rd optical waveguide 9 Synchronous circuit

Claims (1)

[Claims] 1. A first optical waveguide having a first mirror at an incident end and a second mirror at an outgoing end, a laser medium provided near the incident end of the first optical waveguide, and the first optical waveguide. The light which is formed in the vicinity of the emitting end of the first optical waveguide and propagates through the first optical waveguide to the second optical waveguide side and the light propagated to the second optical waveguide side to the first optical waveguide side again A first optical switch for propagating, a second optical switch arranged between the first optical switch and the laser medium for branching light propagating in the first optical waveguide, and the first and second optical switches A variable pulse period type mode lock device, characterized in that a synchronous circuit is provided for switching at a predetermined period.