JPH05327075A - Monomode oscillation ring laser - Google Patents

Abstract

PURPOSE:To provide a monomode oscillation ring laser of a plain waveguide optical circuit type promising various applications. CONSTITUTION:A loop optical waveguide 12, of which at least one part is doped with a rare earth element and at least one part section is constituted of a plurality of optical waveguides having different optical path length, an optical waveguide part 13 for inputting pump light to the waveguide path 12 and a waveguide path 14 for outputting light from the optical waveguide 12 so as to form a plurality of resonators having a large number of oscillation modes in order to perform monomode oscillation by an oscillation mode having an accorded frequency thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single mode oscillation laser which can be used for optical communication, optical measurement and the like.

[0002]

2. Description of the Related Art In recent years, a loop-shaped optical waveguide doped with a rare earth element (Nd, Er, etc.), an optical waveguide for inputting pump light to the loop-shaped optical waveguide, and the loop-shaped optical waveguide are used. A planar waveguide optical circuit type ring laser in which an optical waveguide for outputting light is formed in one plane has been realized.

FIG. 1 shows an example of the above-mentioned ring laser. In the figure, 1 is an optical waveguide substrate, and 2, 3 and 4 are optical waveguides produced on or within the optical waveguide substrate 1 in one plane. It is a waveguide. The optical waveguide 2 is a loop-shaped optical waveguide at least a part of which is doped with a rare earth element, the optical waveguide 3 is an optical waveguide for inputting pump light to the optical waveguide 2, and the optical waveguide 4 Is an optical waveguide for outputting light from the optical waveguide 2. This ring laser was very small, and its oscillation mode was a narrow linewidth.

[0004]

However, in the conventional ring laser described above, if the length of the loop-shaped optical waveguide 2 is L, the speed of light is c, and the refractive index of the optical waveguide is n, then Δf = c / nL ... … There was a drawback that multiple modes oscillate at the frequency interval given by (1). Since this cannot be doped with a large amount of rare earth elements in principle, the loop length L was made long in order to reduce the oscillation threshold of the laser, and as a result, the formula
This is because, as can be seen from (1), the frequency spacing of the oscillation modes becomes narrower, and many oscillation modes exist within the amplification gain band of the rare earth element. Therefore, the conventional ring laser has a problem that it is not suitable for coherent optical communication using a single mode oscillation laser or optical measurement requiring coherence.

In view of the above problems of the prior art, it is an object of the present invention to provide a planar waveguide optical circuit type single mode oscillation ring laser which can be expected to be applied in various ways.

[0006]

In order to achieve the above object, the present invention provides claim 1 as a loop-shaped optical waveguide, at least a part of which is doped with a rare earth element, and a pumping light for the loop-shaped optical waveguide. An optical waveguide for inputting
In a planar waveguide optical circuit type ring laser in which an optical waveguide for outputting light from the loop-shaped optical waveguide is produced in one plane, at least a section of the loop-shaped optical waveguide has an optical path length of A single mode oscillation ring laser composed of a plurality of different optical waveguides, and as claim 2.
A single mode oscillation ring laser according to claim 1, wherein at least one of the plurality of optical waveguides is provided with a variable phase shifter for changing its optical path length.

[0007]

According to the first aspect of the present invention, since at least a part of the loop-shaped optical waveguide is composed of a plurality of optical waveguides having different optical path lengths, a plurality of resonators having a large number of oscillation modes can be obtained. Single-mode oscillation is performed by the oscillation modes whose frequencies match. According to the second aspect, when the optical path length of at least one of the plurality of optical waveguides is changed by the variable phase shifter, the oscillation mode having the same frequency is changed, and the frequency of single mode oscillation is changed.

[0008]

FIG. 2 shows a first embodiment of a single mode oscillation ring laser of the present invention. In the figure, 11 is an optical waveguide substrate and 12, 13, 14 are on the optical waveguide substrate 11 or inside thereof. In, the optical waveguide manufactured in one plane.

The optical waveguide 12 is a loop-shaped optical waveguide in which at least a part thereof is doped with a rare earth element, and a part of the section is composed of a plurality of optical waveguides 12a and 12b having different optical path lengths. There is. Also, the optical waveguide 1
Reference numeral 3 is an optical waveguide for inputting pump light to the optical waveguide 12, and optical waveguide 14 is an optical waveguide for outputting light from the optical waveguide 12.

In the above structure, the pump light input to the optical waveguide 12 through the optical waveguide 13 passes through the two loops formed by the above-mentioned two optical waveguides 12a and 12b, that is, 12-1 and 12-2. When the rare earth element in the optical waveguide 12 is excited to increase the pump light power, the guide light is output via the optical waveguide 14. At this time, the oscillation frequency of the output signal light is determined as follows.

Now, the two loops 12-1 and 12-
If the lengths of 2 are L1 and L2, respectively, the loop 12
The frequencies allowed to oscillate by the resonators -1 and 12-2 are f = cN1 / nL1 (2) and f = cN2 / nL2 (3) as shown by the solid and broken lines in FIG. 3, respectively. Given (where N1 and N2 are positive integers).

At this time, the loop lengths L1 and L2 are selected to be appropriate lengths in order to lower the oscillation threshold of the laser even if they are long, so that the expression (2) is obtained within the gain band of the rare earth element.
And (3) makes only one frequency satisfied at the same time,
That is, the present ring laser can be oscillated in a single mode.

Here, since the tolerance of the loop lengths L1 and L2 becomes severe, it is practically impossible to manufacture such a ring laser using an optical fiber. However, according to the present invention, Since the ring laser is manufactured by using the technique of the planar waveguide optical circuit, which is also called an optical version of LSI, it is possible to set L1 and L2 with high accuracy.

FIG. 4 shows a second embodiment of the present invention. In the figure, 21 is an optical waveguide substrate, and 22, 23 and 24 are produced on or in the optical waveguide substrate 21 in one plane. The optical waveguide 25 is a variable phase shifter.

The optical waveguide 22 is a loop-shaped optical waveguide at least a part of which is doped with a rare earth element, and a part of the section is composed of a plurality of optical waveguides 22a and 22b having different optical path lengths. There is. In addition, the optical waveguide 2
Reference numeral 3 is an optical waveguide for inputting pump light to the optical waveguide 22, and optical waveguide 24 is an optical waveguide for outputting light from the optical waveguide 22.

The variable phase shifter 25 is for changing the optical path length of either one of the above-mentioned two loop-shaped optical waveguides 22a and 22b, here, 22b, and specifically, the optical waveguide substrate 21. The heater is attached or embedded near the optical waveguide 22b. It is also possible to irradiate a corresponding position of the optical waveguide 22b on the optical waveguide substrate 21 with a light beam and change the optical path length by the thermal effect.

Now, as shown in FIG. 5 (a), the optical waveguide 22
The frequency of the p-th oscillation mode of the loop constituted by a and the q of the loop constituted by the optical waveguide 22b.
It is assumed that the frequency of the second oscillation mode matches and the ring laser is oscillating in a single mode at a frequency f. here,
When the frequency of the p + 1-th oscillation mode and the frequency of the q + 1-th oscillation mode are matched by changing the optical path length of the optical waveguide 22b by the variable phase shifter 25, the ring laser shown in FIG. 5 (b) is obtained. Is the frequency f +
It comes to oscillate at Δf.

Similarly, by further increasing the phase shift amount, single mode oscillation can be performed at a frequency of f + kΔf (k is an integer), and a frequency variable single mode oscillation ring laser can be realized. However, the lengths of the above-mentioned two loops are set to L1 and L2, respectively, similarly to the above, and L1
If .apprxeq.L2 = L, .DELTA.f = c / nL.

Such a ring laser is very suitable as a local light source for channel selection in an optical receiver for optical frequency multiplex communication. This is because if Δf is matched with the inter-channel frequency interval, the frequency of the local oscillation light source can be matched with the frequency assigned to each channel at a high speed with a small phase change, that is, with a small power, and channel selection can be performed. Is possible.

[0020]

As described above, according to claim 1 of the present invention, a loop-shaped optical waveguide, at least a part of which is doped with a rare earth element, and pump light is input to the loop-shaped optical waveguide. In the planar waveguide optical circuit type ring laser in which the optical waveguide of and the optical waveguide for outputting light from the loop-shaped optical waveguide are produced in one plane, at least a part of the loop-shaped optical waveguide Since the section is composed of multiple optical waveguides with different optical path lengths, multiple resonators with multiple oscillation modes can be formed, and single mode oscillation can be performed by the oscillation modes with the same frequency, which is stable. A ring laser that performs single-mode oscillation can be provided.

According to the second aspect of the present invention, since the variable phase shifter for changing the optical path length is provided in at least one of the plurality of optical waveguides, it is possible to change the oscillation mode in which the frequencies match. It is possible to provide a ring laser that can change the oscillation frequency.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional ring laser.

FIG. 2 is a configuration diagram showing a first embodiment of a single mode oscillation ring laser of the present invention.

3 is an explanatory diagram of an oscillation frequency in the device of FIG.

FIG. 4 is a configuration diagram showing a second embodiment of a single mode oscillation ring laser of the present invention.

5 is an explanatory diagram of a frequency variable function in the device of FIG.

[Explanation of symbols]

11, 21 ... Optical waveguide substrate, 12, 12a, 12b, 1
3, 14, 22, 22a, 22b, 23, 24 ... Optical waveguide, 25 ... Variable phase shifter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiya Sato 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp. Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A loop-shaped optical waveguide at least a part of which is doped with a rare earth element, an optical waveguide for inputting pump light to the loop-shaped optical waveguide, and light output from the loop-shaped optical waveguide. In a planar waveguide optical circuit type ring laser in which an optical waveguide for producing is formed in one plane, at least a part of the loop-shaped optical waveguide is configured by a plurality of optical waveguides having different optical path lengths. Characteristic single mode oscillation ring laser. 2. The single mode oscillation ring laser according to claim 1, wherein at least one of the plurality of optical waveguides is provided with a variable phase shifter for changing the optical path length.