JPS635306A - Optical demultiplex element - Google Patents

Abstract

PURPOSE:To divide optical signals having narrow wavelength intervals with a small extinction ratio, by installing a means which gives an optical loss to at least one of two optical waveguides. CONSTITUTION:When multiplexed optical signals lambda1 and lambda2, whose wavelengths are about 1.55mum and wavelength intervals are about 0.1nm, are inputted, the optical signal lambda1 and lambda2 are branched at a ratio of about 1:1 by means of an optical coupler 3 and propagated to two optical waveguides 2a and 2b having different optical paths. Since the optical waveguides 2a and 2b have different optical paths, radii of curvature, etc., their propagation losses are different from each other and, as the waveguide 2b has a longer optical path and smaller radius of curvature as compared with the other waveguide 2a, the propagation loss of the wavelength 2b is larger than that of the other waveguide 2a by about 1dB. Therefore, the optical signals lambda1 and lambda2 propagated through the optical waveguide 2b become smaller in power than those propagated through the other waveguide 2 by about 1dB. Accordingly, a voltage of about 10V is impressed across electrodes 4 and sothat the specific refractive index of the optical waveguide 2a' can be made smaller and the radiation mode can be made larger. Thus the powers of the optical signals lambda1 and lambda2 propagated through the optical waveguides 2a are made smaller by about 0.5dB so as to make the difference in propagation loss between the two optical waveguides 2a and 2b smaller by about 0.5dB.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical demultiplexing element used in an optical fiber wavelength multiplexing/demultiplexing transmission system.

(Prior Art) Optical fiber wavelength division multiplexing and demultiplexing transmission has recently been actively researched and developed because the transmission capacity increases dramatically. In particular, an optical demultiplexer that demultiplexes multiplexed optical signals is one of the important devices for realizing optical fiber wavelength division multiplexing and demultiplexing transmission.
It is one. Conventionally, as an optical demultiplexing element, there is one that demultiplexes an optical signal using a dielectric multilayer film or a diffraction grating.

For details, please refer to the Optical Communication Handbook of Kagaku Shinbunsha Co., Ltd., first published in August 1984 (edited by Editor-in-Chief Hirata, etc.)
It is described on pages 573 to 583 of . With this type, it is difficult to narrow the wavelength interval of the optical signals to be demultiplexed, so the number of wavelengths that can be transmitted is small (1
(approximately 0 waves), which has the disadvantage that large-capacity transmission is difficult. To this end, the Matsuhatsu Enda Interferometric Optical Demultiplexing Element, which can demultiplex optical signals with narrow wavelength intervals by using optical interference, has recently been developed, and is capable of demultiplexing approximately 100 or more wavelengths. It is being This splits the multiplexed signals of different wavelengths into two optical waveguides,
The difference in optical path length gives a phase difference between the branched optical signals, and then they are combined again in a 2x2 optical coupler with a 1:1 splitting ratio to cause interference. It separates optical signals of each wavelength to each of two output ends. For details of this optical demultiplexing element e, please refer to No. 10-35 of the lecture proceedings of the 1985 IEICE General Conference.
The paper by Mr. Inoue et al. (lecture number 264) listed on page 9
6).

(Problem that the invention seeks to solve) - Generally, the Matsuhatsu Enda interferometric optical demultiplexing element interferes with optical signals of different phases and separates them depending on the brightness and darkness of the optical signals, as mentioned above. , it is necessary that the propagation losses of the two optical waveguides giving the phase difference are the same.

If there is a difference in propagation loss, an optical signal of a different wavelength will mix into the demultiplexed optical signal of any wavelength, and the extinction ratio of the demultiplexed optical signal will increase, resulting in a deterioration of the S/N ratio. becomes. However, it is not necessarily easy to fabricate two optical waveguides with no difference in propagation loss, and there is a major drawback in that it is difficult to improve the extinction ratio of the split optical signal.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above drawbacks and provide an optical demultiplexing element that can demultiplex optical signals with narrow wavelength intervals with a small extinction ratio.

(Means for Solving the Problems) The present invention provides a Matsuhatsu Interferometric optical demultiplexing element having two optical waveguides that give a phase difference to input optical signals of different wavelengths, wherein at least one of the two optical waveguides is The apparatus is characterized by comprising means for imparting a propagation loss to the input signal.

(Function) If there is a difference in propagation loss between the two optical waveguides, the intensities of the optical signals propagating in each will differ between the two optical waveguides. As a result, when optical signals of wavelengths with different intensities are combined using a 2 x 2 optical coupler with a 1:1 branching ratio, one of the two output ends of the optical coupler receives a signal with a higher intensity due to interference. A matching optical signal can be obtained. Also, at the other output end, the optical signal strength of the wavelength branched to the other output end should be zero, but since the power of the optical signal is different, it may not be completely zero. First, the optical signal can no longer be output. Therefore, when optical signals of different wavelengths are demultiplexed, the optical signals of different wavelengths will be mixed into the optical signals of the respective wavelengths demultiplexed to the two output ends of the optical coupler. On the other hand, if the difference in propagation loss in the two optical waveguides is made zero, the power of the optical signals is the same, so optical signals with different wavelengths can be completely demultiplexed, and optical signals with a small extinction ratio can be separated. I get a signal. In the present invention, the above-mentioned difference in propagation loss can be reduced by providing means for imparting an input signal propagation loss to at least one of the two optical waveguides.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing the configuration of an embodiment of the present invention. Width 8- with Ti diffused on the surface of LiNbO5 substrate 1
An optical waveguide 2 having a relative refractive index of about 0.3% was formed.

By forming the two optical waveguides 2 close to each other, the first and second directional integrator type optical couplers 3, 3' with a branching ratio of about 1:1 for light with a wavelength of 1.55P@ are formed. In order to provide a phase difference between optical signals, two optical waveguides 2a and 2b having different optical path lengths are formed between optical couplers 3 and 3'. Note that the optical path difference is approximately 0.1 wavelength interval of the optical signal.
The width is about 5 mm so that it is 5 nm. An optical waveguide 2a' having a relatively small refractive index of 0.2% is inserted into the optical waveguide 2a having a short optical path length, and electrodes 4 are formed on both sides of the optical waveguide 2a'. With such a configuration, when a voltage is applied to the electrode 4, LiNb0. Due to the electro-optic effect, the relative refractive index of the optical waveguide 2a' further decreases, thereby increasing the radiation mode of the optical signal propagating there, and thus increasing the loss of the optical signal.

Now, with the above-described configuration, a multiplexed optical signal λ1° having a wavelength of about 155p and a wavelength interval of about 0.1 nm is input. Then, the optical coupler 3 generates an optical signal ^1. λ is split approximately 1:1 into two optical waveguides 2a with different optical path lengths.
, 2b. Here, two optical waveguides 2a,
2b have different optical path lengths, radii of curvature, etc., and therefore have different propagation losses. In this embodiment, as can be seen from the figure, the optical waveguide 2b has a longer optical path length and a smaller radius of curvature than the optical waveguide 2a, so the propagation loss is about 1 dB larger. Therefore, the optical signal λ1 . The power of λ is about 1 dB smaller. Therefore, by applying a voltage of about 10 V to the electrode 4 and decreasing the relative refractive index of the optical waveguide 2a', the radiation mode is increased and the optical signal λ3. The input power is reduced by about 0.5 dB, and the difference in propagation loss between the two optical waveguides 2a and 2b is reduced to 0.5 dB.
It was reduced to about dB. By doing this, the optical signals λ1, . The extinction ratio of λ is -20
I was able to improve it from dB to -30dB. Note that the optical waveguide 2a
The increase in the loss of the demultiplexing element due to the increase in the propagation loss of ' is as small as 0.25 dB.

In the above embodiment, LiNbQ was used as the material, but the material is not limited to this, and semiconductor materials (e.g. GaAs, In
P, etc.), quartz glass, etc. may be used.

Furthermore, in the above embodiments, the electro-optic effect was used as a means to increase the propagation loss, but the invention is not limited to this. For example, if a semiconductor material is used, a light absorption effect by carrier injection, a plasma effect, etc. may be used, or a quartz fiber If it is used, the effect of increasing loss due to bending may be used.

Further, in the embodiment described above, a configuration is provided in which loss is provided only to one of the two optical waveguides 2a and 2b, but it is of course possible to provide the loss to both optical waveguides.

Further, in the above embodiment, an optical signal multiplexed with two wavelengths is used, but the present invention is not limited to this, and an optical signal multiplexed with three or more wavelengths may be used.

(Effects of the Invention) As described above, by providing means for imparting optical loss to at least one of the two optical waveguides providing optical path length,
An optical demultiplexing element capable of demultiplexing optical signals with narrow wavelength intervals with a small extinction ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of an embodiment of the present invention. 1...LiNb0. Substrate, 2, 2a, 2a'
, 2b... optical waveguide, 3.3'... optical coupler,
4... Electrode.

Claims (1)

[Claims] In a Mach-Zehnder interferometric optical demultiplexing element that has two optical waveguides that give a phase difference to input optical signals of different wavelengths,
An optical demultiplexing element characterized in that at least one of the two waveguides is provided with means for imparting a propagation loss to the input optical signal.