JP2000010137A - Wavelength converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable wavelength conversion near to signal light by outputting only the wavelength conversion light without using an optical filter with a wavelength converter utilizing the oscillation suppression phenomenon of a semiconductor laser. SOLUTION: An optical amplifier region is inserted into two arm waveguides 13a, 13b of a symmetrical Mach-Zehnder interferometer. The wavelength converter has a light reflection means for reflecting the light of a wavelength Ac to input/output ports which are the cross ports of the symmetrical Mach- Zehnder interferometer. A laser resonator is formed by this light reflection means and the optical amplifier region to induce the laser oscillation of the wavelength λc. At this time, intensity modulation signal light of a wavelength λs is inputted from the port to which the light reflection means is not connected. The wavelength conversion light formed by the complementary modulation of the laser oscillation light of the wavelength λc by the intensity modulation signal light of the wavelength λs is separated from the intensity modulation signal light and is outputted from the different port.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength converter for converting the wavelength of an optical signal into another wavelength.

[0002]

2. Description of the Related Art As wavelength converters, those utilizing the oscillation suppression phenomenon of a semiconductor laser are known. This is because a semiconductor laser oscillating at a wavelength λc has a wavelength λs (≠ λ
When the light of c) is input from outside, the carrier in the laser is consumed by the external input light, and the oscillation of the wavelength λc is stopped. The configuration is such that, as shown in FIG. 4A, an intensity-modulated signal light having a wavelength λs is input to a semiconductor laser 41 oscillating at a wavelength λc.

In the semiconductor laser 41, the oscillation is turned off when the intensity modulated signal light having the wavelength λs is on, and the oscillation is turned on when it is off. That is, the oscillation light having the wavelength λc
s will be complementarily modulated by the intensity-modulated signal light. This is substantially equivalent to the wavelength conversion of the signal light having the wavelength λs into the signal light having the wavelength λc.

[0004]

In the configuration shown in FIG. 4A,
The original signal light (wavelength λ) together with the wavelength-converted light (wavelength λc)
s) is also output at the same time. Therefore, if it is desired to obtain only the wavelength-converted light, it is necessary to provide an optical filter for blocking the original signal light, which complicates the device configuration.

In this case, it is necessary that the wavelength of the converted light and the wavelength of the original signal light are separated from each other by an optical filter. Furthermore, when the input signal light wavelength is near the laser oscillation wavelength, a phenomenon (laser injection locking) in which laser oscillation is synchronized with the input signal light occurs. In this case, the above-described wavelength conversion effect cannot be obtained. In a semiconductor laser, such injection locking is unavoidable, so that the wavelength cannot be converted to a wavelength near the signal light, and the application range to the system is limited.

On the other hand, as shown in FIG. 4B, laser oscillation light (wavelength-converted light) having a wavelength of λc is extracted from the incident end face of the intensity-modulated signal light having a wavelength of λs in the semiconductor laser 41.
By employing a configuration in which the wavelength-converted light (wavelength λc) and the intensity-modulated signal light (wavelength λs) are separated by the optical demultiplexer 42, it is possible in principle to extract only the wavelength-converted light. However, in practice, the signal light component of the wavelength λs output together with the converted wavelength light cannot be made completely zero due to the residual reflection of the semiconductor laser end face. Therefore, similarly to the case where an optical filter is used, it is necessary that the converted light wavelength and the original signal light wavelength are separated from each other so as to be separated by the optical demultiplexer.
In addition, even if the configuration shown in FIG. 4B is used, the injection locking phenomenon cannot be avoided, so that conversion to a wavelength near the signal light is still impossible.

According to the present invention, in a wavelength converter utilizing the oscillation suppression phenomenon of a semiconductor laser, it is possible to output only wavelength-converted light without using an optical filter and to enable wavelength conversion to near signal light. It is an object to provide a wavelength converter.

[0008]

The wavelength converter according to the present invention comprises:
An optical amplification region is inserted between the two arm waveguides of the symmetric Mach-Zehnder interferometer, the loop waveguide of the loop mirror, or the 3 dB coupler of the Michelson interferometer and the light reflector, and the cross port of the symmetric Mach-Zehnder interferometer is inserted. A light reflecting means for reflecting light of wavelength λc is provided at an input / output port, one port of a loop mirror, or one port of a Michelson interferometer, and a laser resonator is formed by the light reflecting means and an optical amplification region. This is the configuration. Then, laser oscillation of the wavelength λc occurs.

At this time, when an intensity-modulated signal light having a wavelength λs is input from a port to which no light reflecting means is connected, a wavelength λs
The laser oscillation light of c is complementarily modulated by the intensity-modulated signal light of wavelength λs, separated from the intensity-modulated signal light as wavelength-converted light, and output from a different port.

[0010]

(First Embodiment) FIG. 1 shows a configuration example of a first embodiment of the present invention.

The wavelength converter of this embodiment has a configuration based on a symmetric Mach-Zehnder interferometer. The symmetric Mach-Zehnder interferometer has a 3 dB coupler 11 having one of two ports as input ports A and B, a 3 dB coupler 12 having one of two ports as output ports C and D, and a 3 dB coupler 11,
12 of the same optical length that connects the other two ports of each other
It is composed of the arm waveguides 13a and 13b.
In this configuration, input port A and output port D, input port B and output port C are cross ports, input port A and output port C, input port B and output port D are through ports.

As the wavelength converter, optical amplification regions 14a and 14b having the same characteristics are inserted into the respective arm waveguides 13a and 13b of the symmetric Mach-Zehnder interferometer, and are placed on the optical waveguides connected to the input port B and the output port C. , Reflection wavelength λc
The Bragg reflection (DBR) regions 15a and 15b are formed, and an intensity-modulated signal light having a wavelength λs is input from an input port A.

In this configuration, a reflection wavelength λc is provided on both sides of an input port B and an output port C which are cross ports of a symmetric Mach-Zehnder interferometer including the optical amplification regions 14a and 14b.
Are arranged to form a laser resonator.

That is, the light of the wavelength λc reflected by one DBR region 15a is transmitted from the input port B to the 3 dB coupler 11b.
, The light is branched into two by the 3 dB coupler 11, and the arm waveguides 13a and 13b, the optical amplification regions 14a and
The signal is multiplexed by the 3 dB coupler 12 via 14b. At this time, since the two paths through which the light having the wavelength λc has passed are completely symmetric, the multiplexed light having the wavelength λc is output to the output port C which is a cross port with respect to the input port B. The light of wavelength λc output from the output port C is
The light is reflected by the area 15b, and is again input from the output port C to the 3dB coupler 12. The light having the wavelength λc is output to the input port B by following the reverse path, and is output to the DBR region 15.
The light is reflected at a and re-input to the symmetric Mach-Zehnder interferometer, and the reciprocation described above is repeated thereafter.

In such a resonator configuration for light having the wavelength λc, if the gains of the optical amplification regions 14a and 14b are sufficient, laser oscillation will occur at the wavelength λc. Part of the laser oscillation light is output via the DBR regions 15a and 15b.

On the other hand, when laser oscillation is performed at the wavelength λc, an intensity-modulated signal light having the wavelength λs is input from the input port A to the symmetric Mach-Zehnder interferometer. The intensity-modulated signal light having the wavelength λs is branched into two by the 3 dB coupler 11, and the light is amplified by the optical amplification region 14 via the arm waveguides 13a and 13b, respectively.
a and 14b. In each optical amplification region, the excitation carrier is consumed by turning on and off the intensity modulation signal light, and if the intensity modulation signal light power is sufficient, the carrier consumption is large and the laser oscillation of the wavelength λc stops. That is, since the laser oscillation is suppressed by the external input light, the wavelength conversion from the wavelength λs to λc is realized as in the related art.

The intensity-modulated signal light that has passed through each optical amplification region is multiplexed by the 3 dB coupler 12. At this time, since the two paths through which the intensity-modulated signal light has passed are completely symmetric, the combined intensity-modulated signal light is output to the output port D which is a cross port with respect to the input port A.

As described above, by using a perfect symmetric Mach-Zehnder interferometer, it is possible to completely separate the intensity-modulated signal light having the wavelength λs and the laser oscillation light (wavelength-converted light) having the wavelength λc into different output ports. Further, since the intensity-modulated signal light does not enter the laser resonator having the two DBR regions 15a and 15b at both ends, injection locking does not occur even if λs and λc are close to each other. Therefore, wavelength conversion near the input wavelength becomes possible.

In this embodiment, the laser resonator is formed by the two DBR regions. However, even if one of the DBR regions reflects light without wavelength dependence like a cleavage plane. Good.

Further, as the wavelength converter, a wavelength conversion that does not depend on the polarization state of the input signal light is desirable. For that purpose, the gain characteristics of the optical amplification regions 14a and 14b need to be polarization-independent. However, in this case, the polarization state of the laser oscillation light having the wavelength λc is not determined, and the noise of the wavelength-converted light may increase due to mode competition noise between the polarizations. To avoid this, the DBR area 15
What is necessary is just to make a and 15b strongly reflect the light of a specific polarization state. Then, laser oscillation occurs in the state of polarization, and polarization mode competition noise can be avoided. Alternatively, the input port B of the 3 dB coupler 11 and the DBR region 15
a or between the output ports C and D of the 3 dB coupler 12
A means for transmitting light in a specific polarization state, for example, a polarizer using a hybrid integration technique may be inserted between the BR region 15b.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
1 shows a configuration example of the embodiment. The wavelength converter of the present embodiment has a configuration based on a loop mirror. The loop mirror uses one of the two ports of the 3 dB coupler 21 as input / output ports A and B, and uses the other two ports C and D as loop waveguides 2.
This is a configuration connected by 2.

As a wavelength converter, an optical amplification region 23 is inserted into the loop waveguide 22, and a Bragg reflection (DBR) region 24 having a reflection wavelength λc is formed on the optical waveguide connected to the input / output port B. An intensity-modulated signal light having a wavelength λs is input from the output port A.

In this configuration, the laser resonator is formed by arranging the DBR region 24 having the reflection wavelength λc at the input / output port B of the loop mirror including the optical amplification region 23. That is, when the light having the wavelength λc reflected by the DBR region 24 is input from the input / output port B to the 3 dB coupler 21, the light is branched into two by the 3 dB coupler 21, respectively, follows the loop waveguide 22 in the opposite direction, and travels in the opposite direction. And are multiplexed by the 3 dB coupler 21. At this time, since the path of the wavelength λc propagating in the opposite direction is the same, the multiplexed light is output from the input / output port B to which the light is input. The light having the wavelength λc output from the input / output port B is reflected by the DBR region 24, input again from the input / output port B to the 3 dB coupler 21, and follows the same path.

In such a resonator configuration for light of wavelength λc, if the gain of the optical amplification region 23 is sufficient, laser oscillation will occur at wavelength λc. Part of this laser oscillation light is output via the DBR region 24.

On the other hand, when the laser is oscillating at the wavelength λc, the intensity-modulated signal light having the wavelength λs is input from the input / output port A to the loop mirror. The intensity-modulated signal light having the wavelength λs is branched into two by the 3 dB coupler 21, respectively, follows the loop waveguide 22 in the opposite direction, and is input to the optical amplification region 23. In the optical amplification region 23, the excitation carrier is consumed by turning on and off the intensity modulation signal light, and if the intensity modulation signal light power is sufficient, the carrier consumption is large and the laser oscillation of the wavelength λc is stopped. That is, since the laser oscillation is suppressed by the external input light, the wavelength λ is
The wavelength conversion from s to λc is realized.

The intensity-modulated signal lights that have passed through the optical amplification region 23 in opposite directions are multiplexed by the 3 dB coupler 21. At this time, since the paths through which the intensity-modulated signal lights have passed are the same, the multiplexed intensity-modulated signal light is output from the input / output port A to which the input.

As described above, by using the loop mirror, the intensity modulated signal light having the wavelength λs and the laser oscillation light (wavelength converted light) having the wavelength λc can be completely separated and output to different ports. Further, since the intensity-modulated signal light does not enter the laser resonator constituted by the DBR region 24 and the loop mirror, injection locking does not occur even if λs and λc are close to each other. Therefore, wavelength conversion near the input wavelength becomes possible.

(Third Embodiment) FIG. 3 shows a third embodiment of the present invention.
1 shows a configuration example of the embodiment. The wavelength converter of the present embodiment has a configuration based on a Michelson interferometer. In the Michelson interferometer, one of two ports of the 3 dB coupler 31 is used as input / output ports A and B, and the other ports C and D are connected to optical waveguides 32a and 32b, and one of the optical waveguides 32 is used.
This configuration is such that a phase shifter 33 is inserted into a, and reflection mirrors 34a and 34b are provided at the other end of each optical waveguide.

As the wavelength converter, the optical waveguides 32a, 32
2b, optical amplification regions 35a and 35b having the same characteristics are inserted,
A reflection wavelength λ is provided on the optical waveguide connected to the input / output port B.
A Bragg reflection (DBR) region 36 is formed, and an intensity-modulated signal light having a wavelength λs is input from the input / output port A. The light amplification regions 35a and 35b may be semiconductor light amplification regions, and the cleavage planes may be reflection mirrors 34a and 34b.

In this configuration, the laser resonator is formed by arranging the DBR region 26 having the reflection wavelength λc at the input / output port B of the Michelson interferometer including the optical amplification regions 35a and 35b. That is, the wavelength λc reflected by the DBR region 36
Is input to the 3 dB coupler 31 from the input / output port B, the light is branched into two by the 3 dB coupler 31, and reflected by the reflection mirrors 34a and 34b via the optical waveguides 32a and 32b and the optical amplification regions 35a and 35b, respectively. The signals are multiplexed by the 3 dB coupler 31 following the opposite direction. At this time, by setting the phase shifter 33, most of the light having the wavelength λc is output to the input / output port B. As a result, the light of wavelength λc multiplexed by the 3 dB coupler 31 is output from the input / output port B to which the light is input. The light having the wavelength λc output from the input / output port B is reflected by the DBR region 36, input again from the input / output port B to the 3 dB coupler 31, and follows the same path.

In such a resonator configuration for light having the wavelength λc, if the gains of the optical amplification regions 35a and 35b are sufficient, laser oscillation will occur at the wavelength λc. Part of this laser oscillation light is output via the DBR region 36.

On the other hand, when laser oscillation is performed at the wavelength λc, an intensity-modulated signal light having the wavelength λs is input from the input / output port A to the Michelson interferometer. The intensity-modulated signal light having the wavelength λs is split into two by the 3 dB coupler 31, and the optical amplification regions 35a and 35a are respectively transmitted through the optical waveguides 32a and 32b.
b. In the optical amplification regions 35a and 35b, the excitation carriers are consumed by turning on and off the intensity modulation signal light, and if the intensity modulation signal light power is sufficient, the carrier consumption is large and the laser oscillation of the wavelength λc is stopped. That is, since the laser oscillation is suppressed by the external input light, the wavelength conversion from the wavelength λs to λc is realized as in the related art.

The intensity-modulated signal light having passed through the optical amplification regions 35a and 35b is reflected by the reflection mirrors 34a and 34b, traced in opposite directions, and multiplexed by the 3dB coupler 31.
At this time, by adjusting the phase shifter 33 so that the reciprocating optical lengths formed between the ports C and D and the reflection mirrors 34a and 34b are different by λs / 2, the multiplexed intensity modulated signal light is adjusted. Is output from the input / output port A.

As described above, by using the Michelson interferometer, the intensity-modulated signal light having the wavelength λs and the laser oscillation light (wavelength-converted light) having the wavelength λc can be separated into different output ports. However, a slight crosstalk of the wavelength-converted light having the wavelength λc is output to the input / output port A to / from which the intensity-modulated signal light having the wavelength λs is input / output. Only output. Further, since the intensity-modulated signal light does not enter the laser resonator constituted by the DBR region 36 and the Michelson interferometer,
Even if λs and λc are close to each other, injection locking does not occur. Therefore, wavelength conversion near the input wavelength becomes possible.

Incidentally, if the reflecting mirrors 34a and 34b in the third embodiment are configured symmetrically with respect to the axis of symmetry, and the phase shifter 33 is set so that the optical lengths of the two arm waveguides are different by λs / 2. , A wavelength converter using an asymmetric Mach-Zehnder interferometer.

The components of each embodiment described above can be partially or wholly integrated on a semiconductor substrate. Further, among the components of each embodiment described above, some or all of the components other than the amplification region can be formed of a glass waveguide.

[0037]

As described above, according to the wavelength converter of the present invention, the input signal light and the wavelength-converted light can be converted without using an optical filter by the functions of a symmetric Mach-Zehnder interferometer, a loop mirror and a Michelson interferometer. Since they can be separated and output, wavelength conversion to near the input wavelength is also possible.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration example of a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration example of a conventional wavelength converter using a semiconductor laser.

[Explanation of symbols]

11, 12, 21, 31 3dB coupler 13a, 13b Arm waveguide 14a, 14b, 23, 35a, 35b Optical amplification region 15a, 15b, 24, 36 Bragg reflection (DBR)
Area 22 Loop waveguide 32a, 32b Optical waveguide 33 Phase shifter 34a, 34b Reflection mirror 41 Semiconductor laser 42 Optical demultiplexer

Claims (8)

[Claims] 1. A first 3 dB coupler having one of two ports as input ports A and B, a second 3 dB coupler having one of two ports as output ports C and D, and first and second 3 dB. A symmetric Mach-Zehnder interferometer composed of two arm waveguides having the same optical length connecting the other two ports of the coupler, and light having the same characteristics inserted into each arm waveguide of the symmetric Mach-Zehnder interferometer Amplifying region, first light reflecting means connected to the input port B for reflecting light of wavelength λc, light of wavelength λc connected to the output port C in a cross-port relationship with the input port B And a second light reflecting means for reflecting light, wherein a laser resonator is formed by the first light reflecting means, the second light reflecting means, and the light amplifying region disposed therebetween, and a laser oscillation of wavelength λc is provided. Originate And receives the intensity modulated signal light having a wavelength λs from the input port A at that time,
The first light reflecting means or the second light reflecting means outputs wavelength-converted light of wavelength λc in which laser oscillation light of wavelength λc is complementarily modulated by intensity-modulated signal light of wavelength λs. A wavelength converter characterized in that: 2. The wavelength converter according to claim 1, wherein one of the two light reflecting units has a configuration that does not have wavelength dependence. 3. The wavelength converter according to claim 1, wherein the optical amplifying means has a gain characteristic having no polarization dependency, and whether the light reflecting means reflects a specific polarization. A wavelength converter comprising means for transmitting a specific polarized wave between a 3 dB coupler and light reflecting means. 4. A loop mirror constituted by a 3 dB coupler having one of two ports as input / output ports A and B, a loop waveguide connecting the other two ports in a loop, and a loop guide of the loop mirror. A light amplifying area inserted into the wave path; and a light reflecting means connected to the input / output port B for reflecting light having a wavelength of λc, wherein a laser resonator is formed by the light reflecting means, the loop mirror, and the light amplifying area. To cause laser oscillation of the wavelength λc, and at that time, the wavelength λs
And a wavelength-converted light having a wavelength λc in which the laser oscillation light having a wavelength λc is complementarily modulated by the intensity-modulated signal light having a wavelength λs from the light reflecting means. Characteristic wavelength converter. 5. A 3 dB coupler having one of the two ports as input / output ports A and B, a light reflecting portion connected to the other two ports C and D, and a light reflecting portion between the ports C and D and the respective light reflecting portions. A Michelson interferometer composed of optical phase adjusting means for adjusting the reciprocating optical length formed therebetween so as to differ by λs / 2, and inserted between the ports C and D and each light reflecting portion. A light amplification region connected to the input / output port B and reflecting light having a wavelength of λc; and the light reflection unit and the light reflection unit of the Michelson interferometer and the light reflection unit disposed therebetween. A laser resonator is formed by the optical amplification region to cause laser oscillation of wavelength λc. At this time, intensity modulated signal light of wavelength λs is input from the input / output port A, and laser oscillation of wavelength λc is The light is intensity modulated signal light of wavelength λs A wavelength converter configured to output wavelength-converted light having a wavelength λc that is complementarily modulated by the wavelength converter. 6. The wavelength converter according to claim 5, wherein the light amplification region is formed by a semiconductor light amplification region, and a cleavage end face thereof is a light reflection portion. 7. The wavelength converter according to claim 1, wherein a part or all of the components are integrated on a semiconductor substrate. 8. The wavelength converter according to claim 1, wherein a part or all of the components other than the optical amplification region are formed of a glass waveguide. .