JPH05121801A - Ring laser - Google Patents

Abstract

(57) [Summary] [Object] To provide a ring laser having a structure capable of manufacturing a ring laser having excellent characteristics at a high yield. [Structure] Ring resonator 1 with one curved optical waveguide
And a directional coupler 2, and one optical waveguide of the directional coupler 2 is connected to the ring resonator 1 in the crossed optical waveguide section 3.
And a ring laser are formed by intersecting with. Directional coupler 2
Since a weak coupling type directional coupler can be used as the optical waveguide, it is possible to use an optical waveguide having a large refractive index difference between the core and the clad, and thus a ring laser having a small pumping light threshold value and high conversion efficiency. Can be manufactured with a high yield.

Description

Detailed Description of the Invention

[0001]

The present invention relates to optical communication, optical information processing,
The present invention relates to an optical waveguide type rare earth ion-doped glass ring laser having a high utility value as a light source in fields such as optical measurement.

[0002]

2. Description of the Related Art A silica-based optical waveguide laser in which rare earth ions are added to the core can obtain an oscillation threshold of low excitation light intensity and high conversion efficiency by utilizing the optical confinement effect of the waveguide structure. Due to its small size, various applications are expected in fields such as optical communication, optical information processing, and optical measurement.

In particular, an optical waveguide type ring laser having a ring resonator formed on the same substrate is suitable for integration because the resonator structure can be manufactured by using a patterning technique, and the oscillation frequency is variable and stable. Because it can be controlled,
Applications are expected in the fields of frequency-multiplexed optical communication and coherent optical communication. In this case, Er ions having an emission band in the 1.5 μm band, Nd and Pr ions having an emission band in the 1.3 μm band, which are important for optical communication, are added as active ions. In the case of Er ions, these ions are 0.82 μm band, 0.98 μm band and 1.48 μm.
m band, 0.75 μm band and 0.80 μm band for Nd ions, and 1.02 μm band for Pr ions have absorption bands in the near-infrared region and have wavelengths suitable for these bands. Can be excited by light.

FIG. 3 shows an example of the structure of a conventional optical waveguide type ring laser disclosed in Japanese Patent Application No. 1-71828. In this ring laser, a ring resonator 11 composed of one closed curve optical waveguide and one optical waveguide for inputting pumping light and outputting laser oscillation light are adjacent to each other to form a directional coupler 12. It has a structure. For example, in the case of an Er-doped ring laser, wavelengths 0.82 μm and 0.98 μm incident from the pumping light input port 13
m or 1.48 μm of the excitation light, and the excitation light introducing unit 14
Through the directional coupler 12. This directional coupler 1
The excitation light is introduced into the ring resonator portion 11 composed of an optical waveguide to which Er ions are added via 2, and the ring resonator 1
The Er ion of 1 is excited to cause laser oscillation, the laser oscillation light is extracted from the directional coupler 12, further extracted from the oscillation light derivation unit 15, and emitted from the oscillation light output port 16. Reference numeral 20 denotes a flat substrate on which the ring laser having the above configuration is arranged.

In such a configuration, one directional coupler 12 is used to introduce pumping light and derive laser oscillation light. For this reason, the directional coupler 12 has been required to have a coupling rate wavelength characteristic as shown in FIG. In order to efficiently couple the pumping light to the ring resonator 11, a coupling rate of 80% or more was required at the pumping light wavelength. Further, in order to obtain a predetermined oscillation light output and reduce the excitation light threshold value required for laser oscillation, it is necessary to have a coupling rate of 5% or more and 10% or less at the oscillation light wavelength. As shown in the characteristics of FIG. 4, in the strong coupling type directional coupler that couples at short wavelengths and does not couple at long wavelengths, two optical waveguides having a small difference in refractive index between the core and the clad are arranged at extremely small intervals. It can be realized by arranging adjacently over a long distance.

[0006]

However, the conventional ring laser has the following problems due to the use of such a strong coupling type directional coupler. Since it is necessary to match the refractive index distribution structure of the waveguide of the strong coupling type directional coupler and the waveguide of the ring resonator,
It has been difficult to construct a laser circuit by using a waveguide having a large refractive index difference between the core and the cladding capable of efficiently exciting r ions in the ring resonator. Moreover, if a strong coupling type directional coupler is constructed by the refractive index distribution of the silica-based optical waveguide,
The change in the coupling rate with respect to the wavelength became steep, and the coupling rate changed sensitively to the change in the device structure. Therefore, the difference in the refractive index between the core and the clad, and a slight manufacturing error in the waveguide width and the waveguide spacing cause the deviation of the coupling wavelength and the variation of the coupling rate at the excitation wavelength and the oscillation wavelength. As a result, there are problems that the characteristics such as the oscillation threshold and the differential efficiency of the optical waveguide type ring laser are limited, the deviation of the oscillation characteristics is large, and the manufacturing yield is low.

Therefore, an object of the present invention is to provide a ring laser having an appropriate structure so that a ring laser having excellent characteristics can be manufactured with a high yield.

[0008]

In order to solve the above-mentioned problems, the present invention is constructed on a flat substrate by an optical waveguide in which at least a part of rare earth ions is added, and pumping light introduction for introducing pumping light is provided. And a ring laser for oscillating laser by dielectric emission of rare earth ions and an oscillating light derivation part for deriving lasing light, which is connected to the excitation light introducing part and the oscillating light deriving part. At least one curved optical waveguide, and at least some of the curved optical waveguides are brought close to each other for at least 1
Individual directional couplers, one of the optical waveguides forming the directional coupler is intersected with the optical waveguide forming the ring resonator to form at least one crossed optical waveguide portion, The curved optical waveguide is arranged such that the optical waveguide is drawn out of the ring resonator through the crossed optical waveguide.

[0009]

In the ring laser of the present invention, by using a weak coupling type directional coupler having a small coupling rate at the excitation wavelength and a large coupling rate at the oscillation wavelength, an optical waveguide with a large refractive index difference between the core and the cladding is used. Since the circuit can be configured, it is possible to realize a ring laser having a small threshold value of excitation light required for laser oscillation and high conversion efficiency. Moreover, since the weak coupling type directional coupler whose coupling rate with respect to wavelength is gradual can obtain the predetermined coupling rate with good reproducibility with the processing accuracy in the usual silica optical waveguide manufacturing process,
INDUSTRIAL APPLICABILITY The present invention can manufacture a ring laser having predetermined characteristics with a high yield.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings.

An embodiment of the optical waveguide type ring laser according to the present invention is shown in FIG. The ring laser of the present embodiment is composed of one curved optical waveguide, and parts of the optical waveguides are brought close to each other to form the directional coupler 2 and the remaining part forms the ring resonator 1 and its direction. One of the optical waveguides forming the directional coupler 2 and the optical waveguide forming the ring resonator 1 are crossed to form the crossed optical waveguide section 3,
One curved optical waveguide is arranged so that the optical waveguide is drawn out of the ring resonator 1 through the crossed optical waveguide portion 3. Reference numeral 10 is a flat substrate on which the ring laser having such a configuration is arranged.

As shown in FIG. 2, the directional coupler 2 used in this ring laser has a low coupling rate at the pumping wavelength,
It is a weak-coupling type that has a high coupling ratio at the oscillation wavelength and can be manufactured using an optical waveguide with a large difference in the refractive index between the core and the cladding, so it is a high NA waveguide that can efficiently excite rare earth ions with a small excitation light. It has the feature that a ring resonator can be configured. Moreover, since the weak coupling type directional coupler has a gradual change in the coupling rate with respect to the wavelength, it is possible to suppress variations in the coupling rate at the excitation wavelength and the oscillation wavelength due to manufacturing errors. For this reason, it is possible to obtain a predetermined coupling rate with good reproducibility with the processing accuracy in the usual quartz optical waveguide manufacturing process.

When the weak coupling type directional coupler is used, it is necessary to provide the crossed optical waveguide portion 3 and draw the optical waveguide to the outside of the ring in order to enter the excitation light and to derive the oscillation light. By setting the angle formed by the two waveguides in the crossed optical waveguide section 3 to 60 degrees or more and 120 degrees or less, excessive loss can be suppressed to 0.1 dB or less.

According to the ring laser of the present invention, a weak coupling type directional coupler capable of using a high NA waveguide and capable of producing the coupling ratio at the excitation wavelength and the oscillation wavelength at a predetermined value with good reproducibility is provided. Since it is used, a ring laser having good oscillation characteristics can be manufactured with a high yield.

Next, the operating principle of the ring laser of the present invention will be described. Since the pumping light incident port and the laser oscillation light emitting port are interchangeable with each other, here, the directional coupler 2 is used.
It is assumed that the excitation light is incident from the end face 4 close to the laser light and the laser oscillation light is extracted from the end face 7 close to the cross optical waveguide portion 3.

Since the coupling ratio of the directional coupler 2 is small at the pumping wavelength, the pumping light incident from the port 4 is guided to the ring resonator 1 where it is absorbed by the rare earth ions. The excited rare earth ions amplify the spontaneous emission light by stimulated emission, and start laser oscillation when the amplification degree per one round of the ring exceeds the optical loss value. The laser oscillation light passes through the cross optical waveguide portion 3 and circulates around the ring resonator 1, and the directional coupler 2
To reach. Since this directional coupler 2 has a high coupling ratio at the oscillation wavelength, most of the laser oscillation light goes around the ring again, and a part of the laser oscillation light crosses the optical waveguide section 3 from the directional coupler 2.
Is led to the emitting end 7 outside the ring resonator.

Since the oscillation wavelength of the ring laser of the present invention is determined by the wavelength characteristics of the amplification and loss of the resonator, it is possible to increase the wavelength from 1.53 μm by incorporating an element having wavelength selectivity inside the ring resonator. 1.60 μm
It can oscillate in the range of up to. As the oscillation wavelength selection element, a waveguide circuit type filter such as a Mach-Zehnder interferometer, a waveguide having a grating structure or a grating waveguide type filter using a waveguide in which a grating is formed by light irradiation, or a groove is formed in the waveguide. It is possible to use a multi-layer film insertion type filter in which the applied dielectric multi-layer film filter is embedded. Particularly, in the waveguide circuit type filter using the Mach-Zehnder interferometer, since the transmission wavelength can be controlled by providing a thin film heater on at least one of the two branched waveguides and heating it, this is used as a wavelength selection element. As a result, a wavelength tunable ring laser can be constructed.

Next, a specific example will be described.

(Embodiment 1) A ring laser is designed based on the constitution of the embodiment of the present invention shown in FIG. 1, and an Er-doped quartz optical waveguide ring laser is manufactured by a flame deposition method and a reactive ion etching method. The variation of circuit element characteristics and ring laser oscillation characteristics was evaluated.

The ring laser is designed to have a core size of 5 μm.
m × 5 μm, the relative refractive index difference between the core and the cladding is 0.75
%, The optical path length of the ring resonator 1 is 10 cm, the coupling rate of the directional coupler 2 at the excitation wavelength of 0.98 μm is 0%, the coupling rate at the oscillation wavelength of 1.60 μm is 92.5%, and the crossed optical waveguide section 3 has The crossing angle was 90 °.

The ring laser is manufactured by depositing a silica-based lower clad layer on a silicon substrate by a flame deposition method, and forming a silica-based core layer to which 1 wt% of Er is added,
A usual Er-doped silica-based optical waveguide circuit manufacturing method was used in which the rectangular core was processed by the reactive ion etching method and then embedded by using the flame deposition method again.

Tables 1 and 2 show the evaluation results of the circuit elements and the ring laser oscillation characteristics. The production quantity was 30 pieces. The coupling ratio of the directional coupler 2 had good characteristics such that the difference between the average value and the design value was small for both the excitation wavelength and the oscillation wavelength, and the standard deviation was also small. The excess loss of the crossed optical waveguide portion 3 was as small as 0.13 dB. The oscillation characteristics of the ring laser have an average oscillation threshold value of 30 mW and a differential efficiency of 2
The characteristics were 0%, and the standard deviation of each was small, which was a good characteristic.

[0023]

[Table 1]

[0024]

[Table 2]

(Comparative Example) Based on the conventional structure shown in FIG. 3, a ring laser was designed, and a ring laser was manufactured by the same method as in Example 1, and variations in circuit element characteristics and ring laser oscillation characteristics were confirmed. evaluated.

The ring laser is designed so that the core size is 7 μm.
m × 7 μm, relative refractive index difference between core and cladding is 0.25
%, The optical path length of the ring resonator 1 is 10 cm, the coupling ratio of the directional coupler 2 at the excitation wavelength of 0.98 μm is 100%,
The coupling rate at the oscillation wavelength of 1.60 μm was 7.5%.

The evaluation results of the circuit elements and the ring laser oscillation characteristics are shown in Tables 3 and 4. The manufacturing quantity is also 30
It was an individual. Regarding the coupling rate of the directional coupler, the difference between the average value and the design value for both the excitation wavelength and the oscillation wavelength was larger than that of Example 1, and the standard deviation was also large. Regarding the oscillation characteristics of the ring laser, the average value of the oscillation threshold value was 60 mW, the differential efficiency was 10%, and the standard deviation of each was large.

[0028]

[Table 3]

[0029]

[Table 4]

From Example 1 and Comparative Example, it is clear that the ring laser structure of the present invention can manufacture a ring laser having good oscillation characteristics with a high yield.

In the above embodiment, the case where the ring laser doped with Er ions is excited in the 0.98 μm band is shown, but the present invention is not limited to this, and for example, 0.82 μm band, 1.48 μm band. Obviously, any absorption wavelength band in the near infrared region of Er ions, such as a band, can be applied to different excitation wavelength bands.

Similarly, the present invention can be applied to other rare earth ions having an absorption wavelength band and an emission wavelength band in the near infrared region such as Nd ions and Pr ions.

Furthermore, the integration technique of integrally forming the rare earth ion-doped core and the undoped core on the same substrate is applied to the present invention, and the rare earth ion is added only to the ring resonator portion to introduce the excitation light. It is effective for improving the characteristics of the ring laser because the excitation light and the oscillation light can be prevented from being attenuated by unnecessary absorption of rare earth ions by configuring the waveguide and the oscillation light derivation part with a waveguide to which rare earth ions are not added. Is.

[0034]

In the ring laser of the present invention, by using a weak coupling type directional coupler having a small coupling rate at the pumping wavelength and a large coupling rate at the oscillation wavelength, an optical waveguide having a large refractive index difference between the core and the cladding is obtained. Since an optical circuit can be configured by this, there is an advantage that a ring laser with a small excitation light threshold required for laser oscillation and high conversion efficiency can be realized. Moreover, since the weak coupling type directional coupler whose coupling rate changes slowly with respect to wavelength can obtain a predetermined coupling rate with good reproducibility with the processing accuracy in the ordinary manufacturing process of the silica-based optical waveguide, the present invention Has an advantage that a ring laser having predetermined characteristics can be manufactured with a high yield.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an embodiment of a ring laser of the present invention.

FIG. 2 is a diagram showing an example of coupling factor wavelength characteristics of a weak coupling type directional coupler used in the ring laser of the present invention.

FIG. 3 is a diagram showing a structure of an example of a conventional ring laser.

FIG. 4 is a diagram showing an example of coupling factor wavelength characteristics of a strong coupling type directional coupler used in a conventional ring laser.

[Explanation of symbols]

 1 Ring Resonator 2 Directional Coupler 3 Crossing Optical Waveguide Section 4 Excitation Light Input Port 5 Excitation Light Introducing Section 6 Oscillation Light Derivation Section 7 Oscillation Light Output Port 10 Planar Substrate 11 Ring Resonator 12 Directional Coupler 13 Excitation Light Input Port 14 Excitation light introduction part 15 Oscillation light derivation part 16 Oscillation light output port 20 Planar substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keizo Suto, 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A pumping light introducing part for introducing pumping light and a ring resonator for laser oscillation by dielectric emission of rare earth ions, which is formed on a flat substrate by an optical waveguide in which at least a part of rare earth ions is added. And a ring laser having an oscillating light lead-out portion for leading out laser oscillated light, comprising one curved optical waveguide connected to the pumping light introducing portion and the oscillating light leading portion, and the curved optical waveguide At least one of the optical waveguides constituting at least one directional coupler is made close to each other, and one of the optical waveguides constituting the directional coupler is intersected with the optical waveguide constituting the ring resonator to form at least one optical waveguide. And the curved optical waveguide is arranged so that the optical waveguide is drawn out of the ring resonator through the intersecting optical waveguide section. Ring lasers.