JPH03171787A - Wavelength conversion system and wavelength converter device - Google Patents

Abstract

PURPOSE:To control efficiency of wavelength conversion by producing tertiary nonlinear polarization which is required to produce four-optical wave mixing effect in a semiconductor laser medium by injecting a proper sine-wave current to the semiconductor laser medium by superposing it to a direct current. CONSTITUTION:Signal light and excitation light which are projected from semiconductor lasers 11, 12 are coupled by a single mode optical fiber coupler 31 and injected to a semiconductor laser medium 5. Wavelength conversion light which is newly produced by four-light wave mixing effect in the semiconductor laser medium 5 is taken out by an optical fiber 4 after separated to a signal light and excitation light by an optical filter 50. Meanwhile, excitation light and signal light are partially accepted by a light detecting device 201 which consists of InGaAs avalanche photodiode and output thereof is amplified by an amplifying circuit 301 and input to a sine-wave oscillator 7. A sine-wave current from the sine-wave oscillator 7 and a direct current from a direct power source 6 are superposed by a synthetic circuit 9 and supplied to the semiconductor laser medium 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wavelength conversion method and a wavelength converter used in optical communication, optical switching, etc. (Conventional technology) In recent years, as the amount of information transmission has expanded, high-density wavelength division multiplexing optical fiber transmission technology that sets the channel spacing from several GHz to several tens of GHz, and swapping of wavelengths between multiple channels have become popular. Research and development on wavelength-division optical switching technology is actively progressing (for example, Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 72 (1989), No. 2, 1).
(pages 41-156). Optical fiber transmission and
Optical switching requires the realization of a wavelength conversion function that converts the wavelength of signal light into a different wavelength. As one of the methods that enables such wavelength conversion, a method that utilizes the four-wave mixing effect of a semiconductor laser medium has recently attracted attention (for example, IEICE technical research report, No. OQE-
Volume 88 (1988), pages 69-74). In this method, excitation light with an angular frequency ωp is incident on a semiconductor laser medium together with a signal light with an angular frequency ωa whose wavelength is to be converted.
A light wave with an angular frequency Ω = 2ωp - ωa newly generated by the four-wave mixing effect in this semiconductor laser medium is extracted and used as wavelength-converted light. Here, the four-wave mixing effect in the semiconductor laser medium is mainly caused by pulsations in the carrier density corresponding to the difference frequency between the pump light and the signal light, and third-order nonlinear polarization is induced in the medium. do. (Problem to be solved by the invention U> Wavelength conversion using the four-wave mixing effect of this semiconductor laser medium has high conversion efficiency, and a relatively low input of pumping light power of 1 nW or less is sufficient. However, the pulsation of carrier density The magnitude of the resulting third-order nonlinear polarization depends on the values of the pump light power, signal light power, and their difference frequency.On the other hand, these values generally cannot be arbitrarily selected due to system design constraints. Therefore, in the conventional wavelength conversion method that uses the four-wave mixing effect, it is difficult to set the wavelength conversion efficiency and the obtained wavelength-converted optical power to a predetermined value. The wavelength conversion method has a problem that needs to be solved regarding the control of the power of the wavelength converted light.The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology and improve the wavelength conversion efficiency, that is, the power of the wavelength converted light. An object of the present invention is to provide a wavelength conversion method and a wavelength converter that use the four-wave mixing effect of a semiconductor laser medium that can be set to a predetermined value. Excitation light with an angular frequency ωp and an angular frequency ωa are applied to the semiconductor laser medium into which a DC current is injected.
The angular frequency newly generated by the four-wave mixing effect in the semiconductor laser medium is ω.
A wavelength conversion method for extracting wavelength-converted light of a=2ωp-ωa is characterized in that a sinusoidal current with an angular frequency of Ω=1ωp-ωa1 is injected into the semiconductor laser medium in a manner superimposed on a direct current. Another wavelength conversion method of the present invention is that in the wavelength conversion method described above, when the time is expressed as t, and the signal light of angular frequency ωa is modulated by a function of Fa(t), 1=Ia @+I&@F@ (t) Sin[ (ω# −
ωa ) tl, where Io: DC current value I1. injected into the semiconductor laser medium. :It is characterized by injecting a current expressed as an AC current value into the semiconductor laser medium. The wavelength converter of the present invention includes a semiconductor laser medium, a pumping light source that outputs pumping light with an angular frequency ωp, and an angular frequency ωa modulated by an information signal Fa(t).
an optical branching means for branching the input signal light, and the angular frequency ω
means for combining one of the excitation light a and the input signal light of angular frequency ωa branched by the optical branching means and inputting it into the semiconductor laser medium; and an input of the angular frequency ωa branched by the optical branching means. an optical receiver that receives the other signal light and outputs a current corresponding to the information signal Fa(t); and an angular frequency Ω=1ωp−ωa whose amplitude and phase can be changed.
The present invention is characterized by comprising a sine wave oscillator that outputs a sine wave current of I, and a drive circuit that adds a direct current to the product of the outputs of the optical receiver and the sine wave oscillator and injects it into the semiconductor laser medium. (Function) As mentioned above, the four-wave mixing effect in the semiconductor laser medium is caused by third-order nonlinear polarization caused by carrier density pulsations equal to the difference frequency Ω=1ωpωa1 between the excitation light and the signal light.In the present invention, In addition to the original third-order nonlinear polarization caused by this light wave, pseudo third-order nonlinear polarization is induced by supplying a sinusoidal current with an angular frequency Ω having an appropriate amplitude and phase to the semiconductor laser medium. That is, The third-order nonlinear polarization PML in the present invention is PML"Popt Pele"
However, P: nonlinear polarization due to light waves opt P: nonlinear polarization ee due to sinusoidal current application. As a result, the present invention has the advantage of being able to artificially control the magnitude of third-order nonlinear polarization and, by extension, the wavelength conversion process due to the four-wave mixing effect.
Here, Pele and P. The relative signs between pt can be made either the same or opposite by changing the phase of the applied sinusoidal current. Therefore, this method has the advantage that the overall PML can be controlled freely.
By the way, nonlinear polarization Pele due to the application of a sinusoidal current is induced regardless of the presence or absence of light waves. Therefore, when the signal light is modulated by the information signal Fa(t),
If a sinusoidal current is continuously injected, an information signal cannot be added to the wavelength-converted light. However, even when the signal light is modulated by the information signal Fa(t), Fa(t) can be detected using an appropriate method and T=Iac+IacF* (t) sin[(ωp −
(aha) t] However, Io: DC current value injected into the semiconductor laser medium ■1. :By injecting a current that can be expressed as an alternating current value into the semiconductor laser medium, wavelength conversion can be performed without losing the information signal. In the wavelength converter of the present invention, Fa(1) is detected using part of the signal light. (Example) Next, the wavelength conversion method and wavelength converter of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a diagram of a first embodiment of a wavelength converter according to the present invention. In this figure, the semiconductor laser medium 5 is
A low-reflection coating with a reflectance of 0.1% or less is applied to both end faces of a normal InGaAsP/InP buried structure semiconductor laser device, and the active layer has a thickness of 0.2μ-
, the width is 1μ finger and the length is 300μm. In this semiconductor laser medium 5, when a DC current of 10(l^) is injected, a small signal gain of about 15 dB is obtained by increasing the wavelength by 1.55 μ. Furthermore, both the signal light source 11 and the pumping light source 12 have an oscillation wavelength L of 55 μ. - InGaAsP/PnP distributed feedback semiconductor laser, optical coupling system 21, 22, 23, 24 is selfoc lens with tip, optical multiplexer 31 is single mode optical fiber coupler, photodetector 201 is T nGaAs avalanche photo The diode and sine wave oscillator 7 is a phase locked loop (PLL) oscillator that can oscillate synchronously with external input from frequencies IGHZ to 5GHz.
Synthesizing circuit 9 is a bias-tay circuit. Furthermore, the optical filter 50 is made of a Fapuri-Perot etalon. In FIG. 1, signal light and excitation light respectively emitted from semiconductor lasers 11 and 12 are combined by a single mode optical fiber coupler 31 and input into a semiconductor laser medium 5. The wavelength-converted light newly generated by the four-wave mixing effect in the semiconductor laser medium 5 is separated into signal light and excitation light by an optical filter 50, and then extracted by the optical fiber 4. In this example, the frequency difference between the signal light and the excitation light is 20Hz,
The spectral spacing of the optical filter 50 made of Fabry Vero etalon was set to IOGHZ. On the other hand, a part of the excitation light and the signal light are used to synchronize the carrier density pulsations induced in the semiconductor laser medium 5 with the injected sinusoidal current.
The light is received by a photodetector 201 made of a GaAs avalanche photodiode, and its output is amplified by an amplifier circuit 301 and input to a sine wave oscillator 7. The semiconductor laser medium 5 is supplied with a sine wave current from the sine wave oscillator 7 and a DC current from the DC power source 6 in a superimposed manner by a combining circuit 9. Here, the phase of the applied sine wave current is adjusted by a delay line 8. FIG. 2 is a diagram showing the dependence of the wavelength-converted optical power obtained at the top of FIG. 1 on the applied sinusoidal current. however,
In this case, the pumping light power is O dBn (1nW), the signal light power is -3068n (lμga), the frequency difference between both light waves and the frequency of the sine wave current is 2GHz, and the DC f4 current is 1
It is 00ll^. Furthermore, the two curves correspond to the case where the phase of the sine wave current is set so that the increase rate or decrease rate of the wavelength-converted optical power becomes maximum when the sine wave current is increased. As is clear from this figure, in this example, by changing the sine wave current value to Ion^, the wavelength converted optical power can be changed from approximately -40 dBI1 to 0.
It can be seen that the dBn can be varied over an extremely wide range, and this range can be made wider by further increasing the sine wave current value. FIG. 3 is an elliptical diagram of a second embodiment of the wavelength converter according to the present invention. The difference from the first embodiment is that the output of a semiconductor laser 11, which is a signal light source, is modulated by an optical modulator 10. A part of the modulated signal light is detected using an optical demultiplexer 32, a photodetector 202, an amplifier circuit 302, and a detection circuit 60, and the detected output modulates a sine wave current. In this figure, an optical modulator 10 is an optical intensity modulator made of LiNbO3, an optical demultiplexer 32 is a single mode optical fiber coupler, and a photodetector 20
2 is an InGaAs photodiode. The other precepts are the same as in Figure 1, so the same elements are given the same numbers. In this embodiment, the signal light from the semiconductor laser 11 is modulated at 50 Hb/s by the optical modulator 10, and then combined with the excitation light by the multiplexer 31, which is a single mode optical fiber coupler, to the semiconductor laser medium. It is being incident. Further, in order to detect the 50 Hb/s modulated signal, a part of the modulated signal light is extracted by the optical demultiplexer 32 and received by the photodetector 202. The received light output is regenerated into a modulated signal by the amplifier circuit 302 and the detection circuit 60, and then input to the mixer circuit 40, where it modulates the sine wave current from the sine wave oscillator 7. This modulated sinusoidal current is superimposed on a direct current by a combining circuit 9 consisting of a bias tee circuit, and is supplied to the semiconductor laser medium 5. When the present example was operated under the same conditions as the first example, the wavelength-converted optical power was changed over a very wide range, almost the same as in Fig. 2, without losing the 50 Wb/s modulation signal. It has been confirmed that this can be done. Above, the wavelength conversion method and wavelength converter according to the present invention have been explained using practical examples, but the present invention is not limited to these embodiments, and several modifications can be made. For example, in this embodiment, I n is used as the semiconductor laser medium.
GaAsP/I nP material was used, but GaAjAs
Other materials such as /GaAs may also be used. In addition, the excitation light source and signal light source may be a semiconductor laser made of other steel or materials, or an aW! laser such as a gas laser. It goes without saying that any structure or type of optical coupling system, optical multiplexer/demultiplexer, various electric circuits, etc. may be used as long as it has the performance. <<Effects of the Invention>> As explained above, in the wavelength conversion method and wavelength converter of the present invention, the third-order nonlinear polarization necessary for the four-wave mixing effect to occur in the semiconductor laser medium can be applied to the semiconductor laser medium. It is generated by injecting an appropriate sinusoidal current superimposed on a direct current. Therefore, by adopting the method and converter of the present invention, the wavelength conversion efficiency can be increased by f! of the injected alternating current. It can be controlled by width and phase.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a first embodiment of the wavelength converter according to the present invention, and Fig. 2 is a characteristic diagram showing the wavelength-converted optical power with respect to the applied sinusoidal current obtained by the first embodiment of the wavelength converter. , FIG. 3 is a schematic diagram of a second embodiment of the wavelength converter according to the present invention. In the figure, 11... signal light source, 12... excitation light source, 21, 22
, 23.24... Optical coupling system, 31... Optical multiplexer, 3
2... Optical demultiplexer, 4... Optical fiber, 5... Semiconductor laser medium, 6... DC power supply, 7... Sine wave oscillator, 8... Delay line, 9... Synthesizing circuit, 10... Optical modulator, 201, 202... Photodetector, 301.30
2...Amplification circuit, 40...Mixer circuit, 50...
- Optical filter, 60...detection circuit.

Claims (3)

[Claims] (1) A pump light with an angular frequency ω_p and a signal light with an angular frequency ω_a are respectively incident on a semiconductor laser medium into which a direct current is injected, and the angular frequency newly generated by the four-wave mixing effect in the semiconductor laser medium is ω_a=2ω_p
In a wavelength conversion method that extracts wavelength-converted light of −ω_a, the semiconductor laser medium has an angular frequency of Ω=|ω_p−ω
A wavelength conversion method characterized by superimposing and injecting a sine wave current of __a| on a direct current. (2) In the wavelength conversion method according to claim 1, when time is expressed as t, the signal light of angular frequency ω_a is F_a(t)
When the semiconductor laser medium is modulated by a function of I=I_d_c+I_a_cF_a(t)sin[(ω
_p-ω_a)t] However, I_d_c: DC current value I_ injected into the semiconductor laser medium
a_c: A wavelength conversion method characterized by injecting a current represented by an injection alternating current value into a semiconductor laser medium. (3) a semiconductor laser medium, an excitation light source that outputs excitation light with an angular frequency ω_p, an optical branching means that branches an input signal light with an angular frequency ω_a modulated by the information signal F_a(t), and the angular frequency ω_p means for combining one of the excitation light and the input signal light having an angular frequency ω_a branched by the light branching means and inputting it into the semiconductor laser medium; and an input signal having an angular frequency ω_a branched by the light branching means. an optical receiver that receives the other light and outputs a current corresponding to the information signal F_a(t); and a sine wave oscillator that outputs a sine wave current with an angular frequency Ω=ω_p−ω_a whose amplitude and phase can be changed. A wavelength converter comprising: a drive circuit that adds a direct current to the product of the output of the optical receiver and the sine wave oscillator and injects the DC current into the semiconductor laser medium.