JP2667255B2 - Rare earth element doped glass waveguide amplifier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glass waveguide amplifier doped with a rare earth element.

[Related Art] Optical fiber amplifiers and lasers in which a rare earth element is added to the core of an optical fiber have been actively researched, and have been attracting attention as lightwave communication amplifiers and lasers.

Conventionally, as shown in FIG. 7, as an optical fiber amplifier, a signal light is propagated in an optical fiber 32 doped with a rare earth element Er, and an excitation light is used in an optical fiber coupler 33 in the propagation direction of the signal light. A method of amplifying the signal light by forming the inverted distribution state and combining the pump light with the optical fiber coupler 34 from the output side (Kimura, Nakazawa: Oscillation characteristics of optical fiber laser and its Application to Optical Communication, Laser Society of Japan, RTM-87-16, PP.31
37, January 1988).

[Problems to be Solved by the Invention] Optical fiber amplifiers and lasers have (1) 10 core systems.
Because the diameter is as small as about μm, the pump power density increases and the pump efficiency increases, (2) the interaction length can be increased, and (3) the silica-based optical fiber has a very low loss. There is a feature.

However, when attempting to configure a system implemented with a semiconductor laser, a light receiving element, an optical modulation circuit, an optical branching / coupling circuit, an optical switch circuit, an optical multiplexing / demultiplexing circuit, etc. There is a problem that low loss is difficult. In addition, since individual components must be individually adjusted in optical axis and arranged, there are also problems such as an enormous adjustment time, an increase in cost, and a problem in reliability.

Further, in order to realize high gain characteristics, it is necessary to increase the output of the pumping light source, but there is a problem that a high-output pumping light source is expensive.

Further, the problem that the gain of the amplifier fluctuates due to a slight change in the oscillation wavelength of the pump light is also a serious problem in constructing a practical system. This is because the wavelength characteristic of absorption by the excitation light of the optical fiber doped with the rare earth element is extremely sharp. Therefore, it is necessary to stabilize the wavelength of the pumping light source, but there is a problem that the device and the circuit configuration are extremely effective and complicated.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a small-sized, low-loss, high-gain, low-cost reliable amplifier.

[Means for Solving the Problems] A glass waveguide of the present invention having a configuration in which excitation light is coupled from the input side of a rare earth element-doped glass waveguide through which signal light propagates, and the excitation light is extracted from the output side of the waveguide. In a waveguide amplifier, an injection-locked semiconductor laser having an amplifier function is used as the pumping light source, and the pumping light source is synchronized with output light from a reference wavelength stabilized semiconductor laser light source.

In this case, preferably, the coupling of the excitation light to the rare earth element-doped glass waveguide and the extraction of the excitation light from the waveguide are
This is performed by a resonator such as a ring resonator or a directional coupler.
More preferably, the pump light propagation path has a feedback loop configuration.

Although the rare earth element-doped glass waveguide amplifier of the present invention is constituted by a glass waveguide having a planar structure, the rare earth element-doped glass waveguide and the resonator for coupling and extracting the excitation light may be constituted by an optical fiber structure. it can.

[Operation] A signal light is propagated in a glass waveguide to which a rare-earth element is added, and a resonator is provided on an input side of the waveguide to output light of an injection-locked semiconductor laser as excitation light into the waveguide. By coupling and providing a resonator also on the output side of the waveguide to take out the pumping light and input it to the input of the injection-locked semiconductor laser, stabilization of the wavelength of the pumping light and output light And an amplifier with high gain and high stability is realized. In addition, by configuring the above configuration with a glass waveguide having a planar structure, downsizing and low loss can be achieved. Further, since a glass waveguide having a planar structure can be easily realized by applying a semiconductor process, cost reduction and high reliability can be expected.

[Embodiment] FIGS. 1 and 2 show an embodiment of a rare earth element-doped glass waveguide amplifier according to the present invention. This is composed of an embedded glass waveguide, and an injection-locked semiconductor laser 7 whose wavelength is stabilized by being synchronized with the light of a reference wavelength stabilizing semiconductor laser 31 is inserted in the middle of the glass waveguide. ing. FIG. 1 shows a side view of the waveguide amplifier, and FIG. 2 shows a cross section taken along the line II-II.

 First, the configuration of the waveguide will be described.

A buffer layer 2 (refractive index nb) is formed on a substrate 1 (for example, Si, SiO2 glass, glass containing SiO2 containing an additive for controlling the refractive index, GaAs, InP, sapphire, etc.). This buffer layer 2 is made of SiO2 or SiO2 with P, B, Ti, Ge, A
A material containing at least one kind of refractive index control additive such as l or Zn is used. A guide for propagating an optical signal onto the buffer layer 2, that is, the cores 3, 4 and the ring resonator
5,6 are formed. In this embodiment, the cores 3 and 4 are formed parallel to each other, and the ring resonators 5 and 6 are formed between the cores 3 and 4. These guides 3 to 6 have a substantially rectangular cross section, and the refractive index nw is set such that nw> nb with respect to the refractive index nb of the buffer layer 2.

The core 3 contains a rare earth element (Er, Nd, H
o, Yb, Ce, Sm, Tm, Pr, etc.)
It is made of a system glass (SiO2 or SiO2 containing at least one kind of the above-mentioned additive for controlling the refractive index). The rare earth element to be added to the core 3 is a signal light 9 propagating in the core 3.
An element having fluorescence characteristics at the wavelength λs is selected. For example, when a wavelength band of 1.53 μm is used as the wavelength λs, Er or a mixture of Er and Yb can be used as the rare earth element.

For the core 4 and the ring resonators 5 and 6, the above-mentioned SiO2 glass or the same glass as the core 3 can be used.

The entire surface including the buffer layer 2 and the cores 3 and 4 is covered with a clad 8, and the clad 8 has a refractive index nc.
It is selected so as to be lower than nw and is made of the above-mentioned SiO2-based glass.

The ring resonators 5 and 6 are designed to resonate with the oscillation wavelength λp of the injection-locked semiconductor laser 7, and transmit the optical signal of the wavelength λp propagating in the core 4 (3) to the core 3 (4 ) Has the function of selectively binding into It is configured not to resonate with an optical signal of wavelength λs.

The injection-locked semiconductor laser 7 is a light source for excitation, and is synchronized with the wavelength of the output light of the reference wavelength stabilizing semiconductor laser 31 injected through the directional coupler 20 to stabilize the wavelength of the output light. . The output light of the injection-locked semiconductor laser 7 is input into the core 4 as indicated by the arrow 11, and propagates through the ring resonator 5 in the core 3 as indicated by the arrow 12.
The light propagates through the core 4 through the ring resonator 6 as shown by an arrow 13 and is input to the injection-locked semiconductor laser 7.

When the feedback loop as described above is configured, (1) the oscillator wavelength λp can be stabilized, and (2) the injection-locked semiconductor laser 7 can be provided with an amplifying function, and the pump light output with higher output can be achieved. (3) As a result, a stable and high-gain glass waveguide amplifier can be realized. And the whole amplifier can be miniaturized.

Also, as already apparent, since the planar structure is used, the present glass waveguide amplifier is used for forming a glass film, patterning the glass film (photolithography and dry etching processes), forming a glass film, and cutting and polishing. It can be manufactured by a semiconductor process, and a significant cost reduction can be expected by mass production.

Furthermore, the signal light / pumping light transmission waveguide 3, the pumping light transmission waveguide 4, the ring resonators 5 and 6, the directional coupler 20, and the injection-locked semiconductor laser 7 are arranged with mask accuracy. Therefore, the components can be coupled with low loss, and the reliability can be improved.
The input / output section of the injection-locked semiconductor laser 7 and the core 4
A high coupling efficiency may be achieved by using a lens, a refractive index matching agent, or the like.

FIG. 3 and FIG. 4 show another embodiment of the rare-earth element-doped glass waveguide amplifier of the present invention. This is a directional coupler instead of the ring resonators 5 and 6 in FIG.
The pump light 11 is coupled to the core 3 using 14 and 15, and the pump light propagating in the core 3 can be extracted to the core 4.

Also in the case of this embodiment, the signal light 9 propagating in the core 3 is not coupled to the core 4. The signal light 9 is the first
As in the case of the figure, the signal is amplified as it propagates through the core 3 and is extracted as a signal output light 10. That is, the excitation light is coupled into the core 3 through the directional coupler 14, and as the excitation light 12 propagates through the core 3, the excitation light 12 is absorbed by the rare earth element to raise the energy level. As a result, a population inversion occurs, and the signal light 9 is amplified by stimulated emission. This amplification degree depends on the waveguide length of the core 3, the output value of the excitation light, and the concentration of the rare earth element added.

In the case of the present invention, a small-sized and high-gain amplifier is realized by increasing the doping concentration of the rare-earth element and increasing the output value of the pumping light. In addition, the injection-locked semiconductor laser 7 can be more stable by synchronizing with the wavelength of the stable reference semiconductor laser 31 or by forming a feedback loop as described above and further combining it with an injection-locked amplifier. Therefore, a large output can be easily obtained, so that a rare-earth-doped glass waveguide amplifier having high gain and extremely little gain fluctuation can be realized.

FIG. 5 shows another embodiment of the rare-earth element-doped glass waveguide amplifier of the present invention. This is an embodiment in which a glass waveguide having an optical fiber structure is used instead of the planar structure.

That is, an optical fiber 16 having a core of an optical fiber doped with a rare earth element is used as a waveguide for propagating the signal light 9 and the pump light 12, and an optical fiber directional coupler is used as a directional coupler for coupling and extracting pump light. Optical fibers are used as couplers 17 and 18 and as waveguides for propagating pump light 11 and 13.
19 is used. The output light of the reference wavelength stabilized semiconductor laser 31 is input to the injection type semiconductor laser 7 through the optical fiber type directional coupler 29. Although it is difficult to reduce the size and reduce the loss in the configuration using this optical fiber, it is possible to achieve a high gain.

 The present invention is not limited to the above embodiment.

First, as a glass waveguide having a planar structure, a well-known waveguide structure such as a ridge type, a loaded type, or a raised type may be realized in addition to a buried type. When SiO2 glass is used for the substrate 1, the buffer layer 2 need not be formed.

Alternatively, a rectangular groove may be dug in the SiO2 glass substrate, and the cores 3 and 4 may be formed in the groove.

Resonators for coupling or extracting the excitation light to or from the rare-earth-element-doped glass waveguide include ring resonators and directional couplers, as well as tapered directional couplers and fusion-stretched optical fibers. A coupler, a biconical taper type optical fiber coupler, or the like may be used.

The present invention is also suitable for amplifying a plurality of transmission paths. That is, as shown in FIG. 6, when amplifying an optical signal propagating in the two rare earth element-added cores 3 and 21, the output light of one reference wavelength stabilized semiconductor laser 31 is converted by the Y-branch coupler 30. The laser beam is divided into two, and is input to the respective injection-locked semiconductor lasers 7 and 25, whereby the wavelength is synchronized with the wavelength of the semiconductor laser 31. By stabilizing the wavelength and forming a feedback loop, the wavelength is further stabilized and the output is increased, thereby realizing a high gain amplifier.

In FIGS. 1 to 6, the excitation light does not necessarily have to form a feedback loop. The reason is that when the rare earth element-added cores 3 and 21 are sufficiently long, the amount of excitation light fed back is sufficiently small.

[Effects of the Invention] As described above, according to the present invention, a high gain rare earth element-doped glass waveguide amplifier can be realized by using an injection-locked semiconductor laser as an excitation light source. In addition, by using a feedback loop configuration of the pumping light propagation waveguide, it is possible to increase the output of the injection-locked semiconductor laser and stabilize the oscillation wavelength, and realize a stable amplifier with high gain and small gain fluctuation. be able to. Further, by configuring the amplifier with a glass waveguide structure having a planar structure, miniaturization, low loss, low cost, and the like can be expected.

[Brief description of the drawings]

1 to 6 show an embodiment of a rare earth element-doped glass waveguide amplifier according to the present invention. FIG. 1 is a side view of the first embodiment, and FIG. 2 is a sectional view taken along the line II-II of FIG. And FIG. 3 shows the second
FIG. 4 is a sectional view taken along the line IV-IV of FIG. 4, FIG. 5 is a view showing the third embodiment, FIG. 6 is a view showing the fourth embodiment, and FIG. FIG. 2 is a diagram schematically illustrating an optical fiber amplifier. In the figure, 1 is a substrate, 2 is a buffer layer, 3 and 4 are cores, 5 and 6 are ring resonators, 7 is an injection-locked semiconductor laser, 8 is a clad, 9 is a signal light, 10 is a signal output light, 11 , 12, and 13 are pumping lights, 14, 15, and 20 are directional couplers, 16 is a rare earth element-doped optical fiber, 17, 18, and 29 are optical fiber type directional couplers, 19 is an optical fiber for pumping light propagation, Reference numeral 31 denotes a reference wavelength stabilized semiconductor laser.

Claims (5)

(57) [Claims] 1. A glass waveguide amplifier having a configuration in which pumping light is coupled from an input side of a rare earth element-doped glass waveguide through which signal light propagates and the pumping light is extracted from an output side of the waveguide. 1. A rare earth element-doped glass waveguide amplifier, characterized in that an injection-locked semiconductor laser with an amplifier function is used for and is synchronized with the output light of a standard wavelength-stabilized semiconductor laser light source. 2. The method according to claim 1, wherein coupling of the excitation light to the rare earth element-doped glass waveguide and extraction of the excitation light from the waveguide are performed by a resonator such as a ring resonator or a directional coupler. 2. The rare earth element-doped glass waveguide amplifier according to 1. 3. The rare-earth-element-doped glass waveguide amplifier according to claim 2, wherein the pumping light propagation path has a feedback loop configuration. 4. The rare-earth-element-doped glass waveguide amplifier according to claim 1, wherein the rare-earth-element-doped glass waveguide amplifier comprises a glass waveguide having a planar structure. 5. The rare earth element according to claim 1, wherein the resonator for coupling and extracting the rare earth element-doped glass waveguide and the excitation light has an optical fiber structure. Doped glass waveguide amplifier.