JPH0222631A - Detector for frequency multiplex optical communication - Google Patents

Abstract

PURPOSE:To provide a high frequency resolution to cover a wide wavelength range by providing a resonator which has transmission characteristics by positions of plural frequencies whose intervals are different from those of frequencies of plural transmission light. CONSTITUTION:A frequency selecting means which detects the light having a desired frequency from transmission light having plural frequencies is provided with a Fabry-Perot laser 3 which has oscillation characteristics in positions of plural frequencies whose intervals are different from those of frequencies of plural transmission light and a control means which controls this resonator to select the light having a desired frequency. It is preferable that a Fabry-Perot etalon resonator where the resonator length can be controlled spatially or by the change of the refractive index or a resonator where the equivalent resonator length can be controlled is used as this resonator. Thus, a wide wavelength range is covered for frequency multiplex optical communication.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a detection device for optical communication, and particularly to a detection device capable of covering a wide wavelength range for frequency multiplexed optical communication.

[Conventional technology]

Frequency separation in the receiving system of conventional frequency-division optical communication is (
1) Spatial separation using a diffraction grating using the principle of a conventional spectrometer (1986 IEICE General Conference 10)
50 (Page 4-221 of the Proceedings, (2) I!i using the frequency characteristics of a directional coupler (1985 IEICE Information Systems Division National Conference 330 (Proceedings 2-6)
(1 page)), (3) Method for interfering with single mode oscillating semiconductor lasers (IEICE Technical Report Quantum Electronics 0QE78-139 (1978, p. 61)
) etc. were considered.

[Problem to be solved by the invention]

The above conventional technology had the following advantages. In other words, the conventional techniques (1) and (2) above have poor frequency resolution;
Since the frequency resolution for light with a wavelength of 1.5 - is approximately 27 GHz or more (wavelength resolution of about 2 people), there is a problem that the frequency density cannot be increased. Also, (2
) has the problem of requiring multiple duplexers with different characteristics because the transmission band of periodic filtering and the far range are the same. In method (1), the configuration is complicated as it involves mechanically changing the angle of the diffraction grating, and (2)
), there is a problem in that the loss in one directional coupler is accumulated in a plurality of directional couplers, resulting in a large loss.

Furthermore, the prior art (3) does not have the above problem.

Since one oscillation light must cover a wide wavelength range, there is a problem in that a large control input is required. This will be explained using FIG.

From the transmitting side, signals are carried on light of a plurality of frequencies with a frequency interval Δf and are sent (FIG. 2(a)). On the other hand, the receiving side has a window of one frequency f' (Fig. 2(b)).
), which in coherent optical communications becomes a single mode local oscillator laser. By changing the frequency characteristics of this window, e.g.

As shown in Figure 2(c), f' can be adjusted to f4 to receive light at the frequency of f4, or as shown in Figure 2(d), f' can be adjusted to f4,
It was tuned to receive light at this frequency. In actual equipment, a local oscillation laser that can change the temperature or a special wavelength tunable laser has been used. However, in such a device, when the frequency range f1 to fn widens, it becomes difficult to make the receiving side window directly follow this.

An object of the present invention is to provide a detection device for frequency multiplexed optical communication that has high frequency resolution and can cover a wide wavelength range.

[Means to solve the problem]

The above object is a detection device for frequency multiplexing optical communication having a frequency selection means for detecting light of a desired frequency from transmitted light using light of a plurality of frequencies, wherein the frequency selection means detects a frequency of the plurality of transmitted lights. Frequency multiplexed optical communication characterized by having a resonator having transmission characteristics at positions of a plurality of frequencies at intervals different from the interval of , and a control means for controlling the resonator to select light of a desired frequency. or a frequency multiplexing optical communication detection device having frequency selection means for detecting light of a desired frequency from transmitted light using light of a plurality of frequencies, the frequency selection means detecting light of a desired frequency from transmitted light using light of a plurality of frequencies. a Fabry-Perot laser having oscillation characteristics at a plurality of frequency positions at frequency intervals and different intervals;
This is achieved by a detection device for frequency multiplexed optical communication characterized by comprising a control means for controlling the resonator to select light of a desired frequency.

The resonator used in the present invention is preferably a Fabry-Perot etalon resonator whose resonator length can be controlled spatially or by changing the refractive index or a resonator whose isometric resonator length can be controlled.

In these Fabry-Perot etalon resonators or Fabry-Perot lasers, the frequency interval difference δf is the number m of multiplexed frequencies with the minimum interval Δfllin of the transmitting side frequency interval
It is preferable that the value is smaller than the value divided by +1 and wider than the full width at half maximum f of the transmission value in the frequency characteristics of the receiving side or the full width at half maximum f of the oscillation characteristics. This f is the cut frequency width, and if it deviates from the center by more than f72, the characteristics will deteriorate significantly. That is, Δf m; 11/ (m + 1) ) δf〉f/2
It is preferable that the following formula is satisfied.

[Effect]

The principle of the present invention will be explained using FIG. Figure 1(a)
As shown in FIG. 2, signals are sent from the transmitting side on light beams of a plurality of frequencies separated by a frequency interval of Δf. On the other hand, on the receiving side, Δf+δ is slightly wider than this frequency interval.
A Fabry-Perot etalon having transmission characteristics or a Fabry-Perot laser having oscillation characteristics having a frequency interval Δf' of f (or a narrow Δf−δf) is prepared. This region with high transmittance or oscillation is called a window.The interval between the windows of the Fabry-Perot etalon resonator is determined by the interval between the two reflecting plates forming the etalon, n1, and the refractive index n between the reflecting plates.

If the wavelength is λ, then λ2 difference δf is the minimum frequency interval Δf 1lli on the transmitting side.
smaller than the value obtained by dividing n by the number of multiplexed frequencies m plus 1, and the full width at half maximum of the transmission value in the frequency characteristics of the receiving side (full width at half maximum of the window) or the full width at half maximum of the oscillation characteristic (full width at half maximum of the window) The value should be wider than Vf. Namely.

Let Δf man/ (m + 1 )〉δf〉V, f (Fig. 1(b)).

In this way, for multiple signal lights sent from the transmitting side, for example, if the f4' window on the receiving side matches the light of frequency f4, there is no window on the receiving side that matches the light from other transmitting sides. Therefore, the received signal light is f.

Only light with a frequency of
This time, the light at f7 overlaps with the window f7/, and only the light at f7 is obtained as the received signal light (FIG. 1(d)).

By doing this, conventionally, when you wanted to change the received signal light from f to f7, you needed a control input that gave a frequency change of 3Δf, but with this configuration, a signal input that gives a frequency change of 3δf is sufficient. becomes.

In the above frequency configuration, all frequency ranges can be covered by a control input that provides a frequency change of Δf.

In this Fabry-Perot etalon, the width of the window is 100.
It is possible to narrow it down to about MHz (7.5 x 10-'' nm).

If this method is used, it is sufficient to move the window on the receiving side by 2XAf, regardless of m, although it would normally be necessary to move the window on the receiving side to cover the frequency range of m×Δf. The effect of this method becomes particularly noticeable when the length of 1 m becomes large.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. Third
A first embodiment is shown in Figure (a).Each light emitted from an optical fiber 1 through which light of five different frequencies has been propagated is focused on a light receiver 4 via a focusing lens 2. The settings are as follows. A Fabry-Perot etalon 3 consisting of reflective plates 3-1 and 3-2 coated with a reflectance of 98%, a column 3-3, and a piezoelectric element PZT 3-4 is inserted between the focusing lens 2 and the light receiver 4. The wavelength of the five different propagating lights is ~1.54uIm, and the frequency interval is 12.6GHz
(one person per wavelength interval), whereas the interval between the two reflectors 3-1 and 3-2 of the Fabry-Perot etalon 3 is 1
Set to 0.8mm. As a result, the frequency interval of the transmission characteristic window of Fabry-Perot etalon 3 is 13.9 GH.
z (1.1 people per wavelength interval), the full width at half maximum of the window on the receiving side at this time is ~100 Mfh. The 0 frequency shown in FIG. 3(b) in the received light spectrum with respect to the voltage of PZT is shifted by 12.6 GHz, but with the setting of the Fabry-Perot etalon, the interval appears to be reduced to 1.26 GIk. Therefore, in the above configuration, 12
．． There is no need to move the window that supports 6GHz, and δf
Tuning can be achieved by changing the PZT voltage by 1.26GHz. For example, if you want to obtain an optical signal with a frequency of f4, as shown in Figure 3(b), 3X1,2
6 GHz, that is, the resonator length is 0.23. Just change it. In this configuration, the wavelength is 1.54. half of 0
．． If a voltage for controlling 77 can be applied, all frequency ranges can be covered.

Next, a second embodiment will be explained using FIG. 4.

The configuration is shown in 4th (a). Each of the propagating lights through the optical fiber 1 through which lights of five different frequencies have been propagated is focused on the external resonator semiconductor laser 8 via the focusing lens 2, and the propagating lights are coupled to the semiconductor laser 8. . The configuration of the external cavity semiconductor laser 8 is shown in FIG. 4(b). The component is a semiconductor laser 8- with anti-reflection coating 8-3.
1 also includes a focusing gradient lens 8-2 coated with a non-reflective coating 8-4, a reflector plate 8-5 coated with a reflective coating, and a support base 8-6. The resonator of this external cavity semiconductor laser 8 is formed by the cleavage surface 8-0 of the semiconductor laser 8-1 and the reflecting plate 8-5. The resonance length of this resonator was set to have the same optical path length as in the first embodiment. A DC bias current is applied to this semiconductor laser 8-1 by a DC power supply 7. This amplifies the light. The propagating light is coupled to the cleavage surface 8-0 of the semiconductor laser. At this time, only the light with the frequency corresponding to the Fabry-Perot mode of the external cavity semiconductor laser 8 is strongly amplified, but especially the light with the frequency matching the Fabry-Perot mode of the laser in the coupled light is amplified. The purpose is to apply a mode lock and emit particularly strong light. If this phenomenon is viewed from the viewpoint of one frequency characteristic, it is the same as the received signal light shown in FIG. In the configuration shown in FIG. 4, frequency tuning is performed using the semiconductor laser 8-
The control circuit 5 controls the current to inject the temperature of 1 into the Peltier element 6.
By changing the refractive index within the semiconductor laser 8-1, the Fabry-Perot resonance frequency (amplification frequency) can be changed. The received signal received by the light receiver 4 at that time is shown in FIG. 4(c).Similar to Example 1, by changing the Peltier current, δ shown by the arrow in FIG. 4(b)
Tuning can be performed at intervals corresponding to fΣ1.26 GHz.

〔Effect of the invention〕

According to the present invention, frequency selection on the receiving side in single frequency multiplexing optical communication can be performed with a control input as low as 1/n or less with respect to the frequency multiplexing factor n, resulting in miniaturization of the control device and energy saving.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram for explaining the present invention in detail, Fig. 2 is an explanatory diagram for explaining the conventional system, Fig. 3 is an explanatory diagram of the first embodiment of the invention, Fig. 4 FIG. 2 is an explanatory diagram of a second embodiment of the present invention. 1... Optical fiber 2... Focusing lens 3.
...Fabry-Perot etalon 4...Receiver 5...Control circuit 6...
- Peltier element 7... DC power supply 8... External resonator semiconductor laser 3-1.3-2... Reflector plate 3-3... Support column 3-4
...P Z T 8-0...Shoulder surface 8
-1...Semiconductor laser 8-2...Graded lens for external resonator 8-3.
8-4...Non-reflective coating 8-5...Reflective coating 8-6...Support stand attorney Junnosuke Nakamura Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A detection device for frequency multiplexing optical communication having a frequency selection means for detecting light of a desired frequency from transmitted light using light of a plurality of frequencies, wherein the frequency selection means detects light of a desired frequency from transmitted light using light of a plurality of frequencies. It is characterized by comprising a resonator having transmission characteristics at a plurality of frequency positions at intervals different from the frequency interval of the transmitted light, and a control means for controlling the resonator to select light of a desired frequency. Detection device for frequency multiplexed optical communication. 2. The detection device for frequency multiplexed optical communication according to claim 1, wherein the resonator is a Fabry-Perot etalon resonator. 3. With respect to the frequency interval Δf of the transmitted light, the frequency difference δf between the frequency interval of the light passing through the resonator on the detection side and Δf is set as Δf/(m+1)≧δf>Δf/2 for the frequency multiplicity m, where 2. The detection device for frequency multiplexed optical communication according to claim 1, wherein Δf is a cut frequency width for obtaining a sufficient extinction ratio, and further comprising means for controlling an optical resonator length. 4. In a frequency multiplexing optical communication detection device having a frequency selection means for detecting light of a desired frequency from transmitted light using light of a plurality of frequencies, the frequency selection means selects an interval between the frequencies of the plurality of transmitted lights. Detection for frequency multiplexed optical communication, characterized by comprising a Fabry-Perot laser having oscillation characteristics at a plurality of frequency positions at different intervals, and a control means for controlling the laser to select light of a desired frequency. Device.