JPH0371115A - Optical circuit for light amplification - Google Patents

Abstract

PURPOSE:To obtain a light amplifying optical circuit capable of guaranteeing integration and stable operation by using a plane type quartz glass waveguide formed on a substrate consisting of Si or the like and unitedly forming an amplifying medium and a multiplexing/demultiplexing optical circuit. CONSTITUTION:The quartz glass waveguide to which Er is added is used to constitute the optical circuit for multiplexing/demultiplexing pump light and signal light and the amplifying waveguide on the same substrate 9. In order to drive an optical amplifier utilizing the optical circuit, an output from a pump light LDla and signal light propagated through an optical fiber 3a are respectively made incident upon the ports A, B of a directional coupler I. Since the coupling efficiency values of the pump light and the signal light in the directional coupler are 99% and 0%, both of them are transmitted to a port C. Thereby, the signal light and the pump light are transmitted through the Er-added optical waveguide after the port C, and during the period, the signal light is amplified. Then the pump light is separated from the signal light by a direction coupler II utilizing the same principle as the directional coupler I and the signal light is measured by a photodetector 5a.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to optical components constituting optical amplifiers.
This invention relates to the structure of an optical circuit that amplifies signal light in the band and 1.5 μm band.

(Prior Art) Recently, optical amplification using an Er-doped silica optical fiber has been developed.
It was revealed that it operates with extremely high efficiency in the 5 μm band. This utilizes the laser emission that Er has at 1.5 μm, and it propagates through an Er-doped optical fiber.
A signal light in the μm band is optically amplified by simultaneously incident pump light. In this case, a pump light compatible with absorption of Er is used, and the energy distribution of Er is changed to population inversion to cause optical amplification.

Compared to optical amplifiers using semiconductor lasers as the amplification medium, optical amplifiers using optical fibers have almost the same components and core diameters as the transmission optical fiber and the amplification optical fiber, so there is almost no coupling loss. There are advantages such as:

A specific configuration of an optical amplifier using an Er-doped optical fiber is shown in FIG. In Fig. 4, ■ is a semiconductor laser (LD) for pumping, 2 is a light source of signal light, 1, 54
μm LD, 3 is single mode optical fiber for transmission, 4,4
A is a dielectric multilayer film with a reflectance of 1 at 1.54 μm.
00%, and the transmittance is 100% at the wavelength of the pump light. 5 is a photodetector (PD), 6.6a.

6b, 6c, and 6d are lenses, and 7 is an Er-doped optical fiber. In order to operate the optical amplifier having the configuration shown in FIG. 4, the pump light 1 and the signal light propagated through the optical fiber 3 are made to enter the rare earth-doped optical fiber through the dielectric layer 4. The pump light and signal light propagated through the optical fiber are separated by a dielectric mirror 4a, and the signal light intensity is measured by a photodetector 5. When the pump light intensity is increased in this system, the signal light begins to be amplified.

1, D, fir which can be used as pump light
wavelength 0.98μm or 1.48μm according to the absorption of
is possible.

The problem with the second configuration is that optical components such as lenses and mirrors are used when the optical amplifier is actually introduced into the transmission line, so it is difficult to make it compact. Furthermore, the optical axis was easily misaligned due to impacts, temperature changes, etc.

(Problem B to be Solved by the Invention) The present invention provides a structure of an optical circuit for optical amplification that enables integration and stable operation when configuring an optical amplifier using a rare earth-doped optical waveguide. be.

(Means for Solving the Problems) The optical circuit for optical amplification of the present invention integrates an amplification medium and an optical circuit for multiplexing and demultiplexing using a planar silica-based glass waveguide formed on a substrate such as Si. The configuration is as follows. In an optical amplification circuit in which a glass optical waveguide consisting of a core portion through which light propagates and a cladding layer with a low refractive index surrounding the core portion is fabricated on a flat substrate, rare earth elements Nd or E are used.
having at least a part of the optical waveguide doped with r, and 2
It has two or more optical circuits that multiplex and demultiplex light that is larger than waves.

According to the present invention, it is possible to integrate on the same substrate an optical amplifier, which was conventionally composed of optical components for multiplexing and demultiplexing pump light and signal light, and a rare earth-doped single moat optical fiber. This has the advantage that optical axis misalignment is less likely to occur due to such factors.

Furthermore, according to this method, the optical amplifier can be constructed using a technique substantially similar to the LSI process, so that mass production is possible and the optical amplifier can be manufactured at low cost. Furthermore, the coupling loss between the transmission optical fiber and the silica waveguide made of the same material is very low, 0.5 dB or less, and is stable against temperature changes.

The optical amplification characteristics of the rare earth doped waveguide will be discussed below. If the signal light and pump light intensities propagating through the waveguide are respectively Ts and Ip, their changes are expressed by the following equations.

I, h=hνp/εσ9τ (1) ip−
rp/Ith (2)il
-7Is/ε1th (3)
σ2ν.

Here, h Ni blank constant ν9: Pump light frequency νS: Signal light frequency σp: Pump light absorption cross section σ5: Signal light absorption cross section ε Ni branch ratio τ: Fluorescence lifetime ρ: Er'' + concentration 2: Waveguide length The results calculated based on (1) to (6) are shown in Fig. 5. In Fig. 5, the excitation wavelength is 0.98 μm and 1.47 μm.
μm, output 40n+W, core Er” concentration 1.8
Calculated as 10"cm-' (3500ppm).

From Figure 5, the excitation wavelength is 0.98 μm or 1,47 μm.
It can be seen that if the LD is used to pump the signal light, it is possible to amplify the signal light by about 20 dB in an Er-doped waveguide with a length of 10 cm.

(Example) The present invention will be described in detail below using the drawings.

Practical Example In this example, a single-mode quartz-based glass waveguide doped with Er was fabricated on a St substrate, and a circuit for multiplexing and demultiplexing pump light and signal light and an amplification waveguide were constructed. A glass waveguide consists of a core portion through which light propagates, and a cladding layer with a low refractive index surrounding the core portion.

Figure 1 shows the structure of this embodiment, 1a is L for pump light.
D (wavelength 1.47 μm), 3a is a single mode optical fiber for transmission, 5a is a PD for signal light detection, 8 is an Er quartz optical waveguide, and 9 is an optical directional coupler made of an Er-doped silica optical waveguide. It is a Si substrate. The Si substrate 9 consists of two directional couplers (I and ■) and a lower amplification waveguide.

To fabricate an Er-doped quartz-based guiding waveguide, first, a glass film with an Er concentration of 3000 is deposited on the Si substrate 9 as a core layer glass film.
ppm, a film thickness of 8 μm, and a relative refractive index difference of 0.7%. Next, a waveguide (width 8 .mu.m) having a structure not shown in FIG. 1 was etched by a photolithography process similar to the LSI process, and then an overclad glass film was formed. The overall size of the substrate was 30 mm x 60 mm. In the directional coupler, the wavelength is 1.47μm and the wavelength is 1.5μm.
The coupling efficiency at 4 μm was set to 99% and 0%, respectively.

In order to operate the optical amplifier using the optical circuit shown in FIG. incident on A and B.

Since the coupling efficiency of the directional coupler for the pump light and the signal light is 99% and 0%, respectively, both propagate to the port. Therefore, the signal light and pump light are connected to port C.
The signal light propagates through the subsequent Er-doped optical waveguide, during which time the signal light is amplified. After that, the pump light and signal light are separated in the directional coupler ■ using the same principle as in the case of the directional coupler I.
The signal light is measured by a photodetector 5a.

When we conducted an amplification experiment using the optical amplifier shown in Figure 1 using a pump light LD with an output of 25 mW, we found that the wavelength was 1.54 μm.
It was confirmed that it was possible to amplify signal light of m by 5 dB, and that it has a wide range of applications as a small and simple optical amplifier.

In this example, an optical circuit for multiplexing and demultiplexing pump light and signal light and an amplification waveguide are constructed on the same substrate using a quartz-based glass waveguide doped with Er as in Example 1. did. However, instead of a directional coupler, a Matsuhatsu Ender interferometer was used to combine and demultiplex the pump light and signal light.

Figure 2 shows the structure of this embodiment, where 1b' is the pump light L.
D (wavelength: 0.98 μm), 3b is a single mode optical fiber for transmission, 5b is a PD for signal light detection, and 10 is a Si substrate that constitutes an Er-doped silica optical waveguide and an optical multiplexing/demultiplexing circuit. Of the optical waveguides fabricated on the Si substrate 10, only the optical waveguide within the shaded area is an Er-doped optical waveguide, and the optical waveguide outside the shaded area is a silica-based optical waveguide not doped with Er.

The advantage of multiplexing using the Matsuhatsu-Ender interferometer shown in FIG. 2 is that the coupling rate can be adjusted with high accuracy for light with a large wavelength interval. Therefore, when using LDs with wavelengths of 0.98 .mu.m and 1.54 .mu.m as pump light and signal light, the Matsuhatsu Ender type interferometer is advantageous. In fact, in the optical amplifier shown in Figure 2, the wavelength is 0.
．． The coupling efficiency was adjusted to 0 and 100% at 98 μm and 1.54 μm, respectively, and the wavelength 1.
It was possible to amplify 54 μm signal light by 8 dB.

Fact history In this example, a single mode optical fiber doped with high concentration Er is embedded in a silica-based glass waveguide, an optical circuit for multiplexing and demultiplexing pump light and signal light is formed on the same substrate, and an optical amplifier is constructed. was configured. Figure 3 shows the structure of this embodiment, where IC is a pump light LD (wavelength 1.47 μm), 3c is a single mode optical fiber for transmission, 5C is a PD for signal light detection, and 11 is an optical multiplexing/demultiplexing circuit. The constructed Si substrate 12 is a high concentration I! It is an r-doped single mode optical fiber. In order to embed the highly concentrated Er-doped single mode optical fiber 12 in the Si substrate constituting the glass waveguide, the fiber embedding portion was etched by a photolithography process, and an appropriate length of the optical fiber was fixed with adhesive.

The operating principle of the optical amplifier shown in Fig. 3 is the same as that shown in Fig. 1, and when an amplification experiment was conducted using this optical amplifier using a pump light LD with an output of 25 mW, it was found that the wavelength was 1.5 μm.
m signal light could be amplified by 10 dB, and the amplification factor could be improved compared to the case of Example 1.

0 In Examples 1 to 3, the Er-doped waveguide was used to
．． A 5 μm band amplifier was constructed, but Nd was used instead of Er0.
By pumping at 0.83 .mu.m using a 1.3 .mu.m band, it is possible to amplify the 1.3 .mu.m band with an optical circuit having almost the same structure.

(Effects of the Invention) As explained above, the optical circuit for optical amplification of the present invention configures an optical amplifier using an integrated optical circuit using a glass waveguide on one substrate. Significant downsizing can be achieved compared to the case of using optical fibers, ■ No deterioration of amplification characteristics due to shock, temperature changes, etc. ■ Silica-based glass has excellent heat resistance and corrosion resistance, so it can be used for a long time. The advantages include that it is possible to create optical amplifiers with excellent stability and performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an optical amplification circuit according to Embodiment 1 of the present invention, FIG. 2 is a diagram showing the configuration of an optical amplification circuit according to Embodiment 2 of the present invention, and FIG. 3 is a diagram illustrating the configuration of an optical amplification circuit according to Embodiment 2 of the present invention. 4 is a diagram showing the configuration of an optical amplifier using a conventional Er-doped optical fiber. FIG. 5 is a diagram showing the configuration of an optical amplifier using a conventional Er-doped optical fiber. FIG. 3 is a diagram showing the dependence of amplification factor on waveguide length (calculation results). 1, Di, Ib, lc-for pump light 1.1]2
...LD for signal light 3, 3a, 3b, 3c...Transmission capacity - 7-t optical fiber 4.4a...Dielectric multilayer film 5, 5a, 5b+5c'' Photodetector 6 6a 6
b, 6c, 6d-lens 7... [! R-doped single mode optical fiber 8...Er-doped silica-based leading waveguide 9...Si substrate 10 in which the optical directional coupler is constructed of an Er-doped silica-based optical waveguide...Matsuhatsu Ender-type optical multiplexing/demultiplexing circuit Si substrate with quartz waveguide formed

Claims (1)

[Claims] 1. In an optical amplification circuit in which a glass optical waveguide consisting of a core part that propagates light and a cladding layer with a low refractive index around the core part is fabricated on a flat substrate, an optical guide doped with rare earth elements Nd or Er is used. 1. An optical circuit for optical amplification, characterized in that it has a wave path in at least a portion thereof, and has two or more optical circuits for multiplexing and demultiplexing two or more waves of light.