JPH01177519A - Wavelength transducer - Google Patents

Abstract

PURPOSE:To obtain a wavelength transducer whose optical power is low, whose modulation degree of a signal is large, and also, whose optical loss is small by using a light source for executing an oscillation in a single longitudinal mode, and a resonance type optical amplifier having a gain peak in wavelength in the vicinity of oscillation wavelength of this light source. CONSTITUTION:Oscillation wavelength of a semiconductor laser LD 10 which goes to a light source is set in advance in the vicinity of a gain peak wavelength of a resonance type LD optical amplifier 13. In such a state, when a signal light 14 whose wavelength is different from oscillation wavelength of the LD 10 is made incident, a gain spectrum of the resonance type LD optical amplifier 13 is shifted in accordance with the signal light 14. Accordingly, an oscillation light 11a of the LD 10 is taken out from one terminal 15b of a coupler 15 as an optical signal 11b which is modulated in the resonance type LD optical amplifier 13. In such a way, a wavelength transducer whose optical power is low, whose modulation degree of a signal is large, and also, whose optical loss is small is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wavelength converter used in a wavelength division optical exchange or the like.

(Prior Art) In order to realize future broadband communication systems, a transmission and switching system with a wide band is essential. Optical switching systems are highly compatible with optical fiber transmission systems in addition to the inherent broadband properties and non-inductive nature of light, and are considered to be a promising means for realizing broadband switching systems. Light exchange can be roughly divided into spatial division (SD)
Three methods can be considered: , time division (TD), and wavelength division (WD). Among these, the wavelength division (WD) optical switching method is expected to be the method most suitable for large scale. Regarding the WD optical switching system, the Institute of Electronics and Communication Engineers Technical Report 5E86-1
17 (1986), ``A Study of Wavelength Division Wideband Optical Communication Networks.''

A wavelength conversion switch (on switch), which is a basic element of a WD optical switching system, requires a wavelength converter that converts the wavelength of the carrier light while leaving the optical signal transmitted by the optical carrier unchanged. The following methods have been proposed as methods for realizing such a wavelength converter.

FIG. 3 is a diagram showing the configuration of a conventionally proposed wavelength conversion element. Incident light 31 having a wavelength λi to be input to the wavelength converter is input from an input boat 32 to a nonlinear optical element 33 . −
Wavelength λ after actual conversion. DC light 35 from a light source 34 that emits light also enters the nonlinear optical element 33 . Here, the nonlinear optical element 33 has a nonlinear transmittance with respect to the amount of incident light, and a logic etalon using a multiple quantum well (MQW) structure can be used.・Bee (Jo)
urnalof optical 5ociety o
f America B ) J Volume 2.

No. 7, 1985, pp. 1215-1227).

If the intensity of the incident light 31 changes, the light transmittance of the nonlinear optical element 33 changes accordingly, so the DC light 35 is modulated and the signal that was previously transmitted by the incident light 31 of wavelength i to the output port 36 changes to the wavelength i. Enter. It is output as output light 37. Through this process, the signal to be transmitted remains unchanged and the wavelength of the optical carrier is changed from i to λ. It can be converted to .

(Problems to be Solved by the Invention) Since such conventional wavelength converters use passive nonlinear optical elements, the optical power required for operation is large;
There were problems such as: (1) the degree of modulation of the signal was not sufficient; (2) the optical loss was large;

An object of the present invention is to eliminate the above-mentioned problems and provide a wavelength converter with low optical power, high signal modulation degree, and low optical loss.

(Means for Solving the Problems) According to the present invention, there is provided a light source that oscillates in a single longitudinal mode, a resonant optical amplifier having a gain peak at a wavelength near the oscillation wavelength of the light source, and an emitted light of the light source. means for coupling the amplified light of the light emitted from the light source from the output light of the resonant optical amplifier; A wavelength converter is obtained, which is characterized by comprising means for inputting light into a resonant optical amplifier.

(Function) The wavelength converter according to the present invention utilizes the fact that the gain spectrum of a semiconductor laser (LD) type optical amplifier changes depending on the intensity of incident light. In LDs and LD optical amplifiers, the refractive index strongly depends on the excitation Kirlya density even near the peak of the gain spectrum. Therefore, in a resonant LD optical amplification device, when the incident light intensity increases, the gain saturates and the resonant frequency shifts due to the change in the refractive index. Figure 4 shows changes in the gain spectrum due to changes in the intensity of the incident light ('Conference on Lasers and Electro-Optics).
andElectro-Optics: CLEO)
J, 1986-j-' Clinical Digest, Paper No. F H3, pp. 354-35i5).

According to this, it can be seen that a change in the input optical power of about 25 ff causes a gain peak shift of 14 GHz toward the longer wavelength side. Direct current light with a wavelength near the peak of the gain spectrum is guided to this j Since the droplet shifts from the power of the LD% multiplier in accordance with the change in the intensity of the optical signal, it becomes possible to measure the optical signal by the optical signal. If the wavelength of the DC light to be modulated is set to λ in FIG. 4, signals of the same phase can be obtained by setting the signal light to inversion or input. By making the wavelengths of the signal light and the DC light different, wavelength conversion can be realized at the same time. In other words, wavelength conversion is performed while preserving the signal waveform as it is or in an inverted form.

The wavelength converter based on this principle is the 4th r5! As shown in J, there is a gain, so there is no need to consider the problem of loss. Also, as you can see in the figure, the extinction ratio of the operation is very high, and is expressed by the number 1
Operation is possible with extremely low optical power of 0P.

(Embodiment) FIG. 1 shows the configuration of an embodiment of a wavelength converter according to the present invention.

First, the configuration of the embodiment shown in FIG. 1 will be explained. The output light 11a of the single-longitudinal mode oscillation LDIO driven by a DC power supply (omitted in the figure) is converted into a resonant LD by the optical system 12.
The optical amplifier 13 is coupled to the optical amplifier 13 . - The actual signal light 14 is coupled to the resonant LD optical amplifier 13 from the end face on the reflection side via one input end 15a of the optical fiber fused coupler 15.

The oscillation wavelength of the LDIO serving as the light source is set in advance near the gain peak wavelength of the resonant LD optical amplifier 13. In this state, when a signal light 14 having a wavelength different from the oscillation wavelength of the LDIO is made incident, the resonant LD optical amplifier 13 responds to the signal light 14.
The gain spectrum of is shifted. Therefore, the LDIO oscillation light 11a is modulated by the resonant LD optical amplifier 13, and is output as an optical signal 11b from one terminal 15b of the coupler 15. The optical signal 11b is an optical signal obtained by amplifying or inverting the signal light 14 and converting the wavelength.

Next, the resonant LD optical amplifier 13 used in the present invention will be explained. LD amplifiers can be roughly divided into two types: traveling wave type and resonator type.
The resonant type is further divided into Fabry-Perot (F-P
) type and distributed feedback (DFB).

It can be classified as distributed Bragg reflection (DBR) type. Among these, the resonance type that can be used in the present invention has a sharp peak in the gain spectrum. Among the resonance types, in the FP type, gain peaks occur periodically due to Fabry-Perot resonance. In contrast, DFB.

Since the DBR type has gain only for a specific wavelength that satisfies the Bragg reflection condition, it has excellent wavelength selectivity. Among them, a phase shift DFB type LD optical amplifier which has a phase shift section in the middle of a diffraction grating for distributed feedback has a gain peak of 7 in principle at the only wavelength that satisfies the Bragg condition. Therefore, it is most suitable for use in the present invention because it has excellent suppression characteristics of noise light of other wavelengths. This phase shift DF
A B-type LD optical amplifier can be realized by using the phase shift 1-DFB-'LD as is. This phase shift DF
Regarding B-LD, please refer to Magazine 1 I.E.E.E.
Sil-Nal Quantum Electronics (IE)
EE Journal of QuantumElec
tronics) J Vol. QE-22, 1986, pp. 1042-1051, or “Optical Fiber Communications Conference.
ion Conference) 1987 Technical Digest
t) J page 51.

It is described in detail in paper number TuC4, 1987.

FIG. 2 shows the change in the gain spectrum of the input/fourth phase shift DFB type LD optical amplifier due to the injection current. By varying the injection current by several mA, the peak wavelength can be adjusted to 3 to 4.
It can be controlled on the order of a person's level, and the gain bandwidth is as narrow as 1 Å or less.

Next, single longitudinal mode oscillation and Dlo will be explained. Since this LD operates with direct current, a Fabry-Perot type LD can be used as long as conditions are selected, but it is preferable to use a DFB-LD, which has excellent wavelength selectivity. In particular, the resonant LD optical amplifier 13 and the LDIO have the same phase shift DFB-
It is most desirable to use an LD in terms of wavelength matching and wavelength unity. Although not shown in FIG. 1, it may be necessary to insert an optical isolator between the LDIO and the resonant LD optical amplifier 13 in order to eliminate the problem of reflected light.

With the above configuration, the oscillation wavelength of the LDIO can be set to 1.5.
537 pm, the injection current to the resonant LD optical amplifier 13 is 4
When it was set to 5 mA and the signal light 14 of 1.553 was made incident, a modulation degree of ~10 dB was obtained for the optical signal 11b with an optical power of 10 dB.

In the embodiment shown in FIG. 1, a fiber coupler 15 is used to input the signal light 14 and take out the optical signal -8=11b.
By utilizing the difference in the oscillation wavelengths of the signal light 14 and the LDIC+, it is also possible to use an upper-Zender type multiplexing and demultiplexing element. Furthermore, since the configuration shown in FIG. 1 is based on DFB-LD, it is suitable for monolithic integration.
It is also possible to integrate the entire device on a semiconductor substrate.

(Effects of the Invention) As described in detail above, according to the present invention, a wavelength converter with low optical power, high signal modulation degree, and low optical loss can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of a wavelength converter according to the present invention, FIG. 2 is a diagram showing a gain spectrum of a resonant LD optical amplifier used in the present invention, and FIG. 3 is a diagram showing a gain spectrum of a conventional wavelength converter. FIG. 4, which is a diagram showing the configuration, is a characteristic diagram showing changes in the gain spectrum due to changes in the intensity of incident light in the resonant LD optical amplifier. In the figure, lla, llb, 14.31.35
．． 37 is a laser beam, 10 is an LD, 13 is a resonant LD optical amplifier, 15 is a coupler, 15a and 15b are terminals, 12
33 is an optical system; 33 is a nonlinear optical element; 34 is a light source; 32.
36 is an input/output port.

Claims (1)

[Claims] a light source that oscillates in a single longitudinal mode; a resonant optical amplifier having a gain peak at a wavelength near the oscillation wavelength of the light source; and means for coupling light emitted from the light source to the resonant optical amplifier;
comprising means for extracting amplified light emitted from the light source from among the output light of the resonant optical amplifier; and means for inputting signal light having a wavelength different from the wavelength of the light source into the resonant optical amplifier. A wavelength converter featuring: