JP2706439B2 - Optical integrated circuit type light intensity modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an optical integrated circuit type light intensity modulator capable of adjusting the light amplitude intensity. 2. Description of the Related Art Hitherto, an optical integrated circuit type optical intensity modulator using a branch interference type optical switch has been known. This conventional optical integrated circuit type optical intensity modulator is formed by combining two Y-branch waveguides, and coherent light propagating through an input optical waveguide is divided into two equal parts by the Y-branch waveguide. The coherent light divided into two equally passes through the first waveguide and the second waveguide, respectively, is merged in the output optical waveguide, and is extracted as outgoing light, and the first waveguide and the second waveguide are extracted. When the phase difference of the coherent light passing through the optical waveguide becomes π, the emitted light emitted from the output optical waveguide disappears due to the interference. Therefore, the optical path length is provided in at least one of the first waveguide and the second waveguide. An electrode is provided as an optical path length changing means for changing the wavelength, and the electrode is controlled such that the phase difference of the coherent light becomes π. [0003] By the way, an intensity modulator not only enables intensity modulation at a desired modulation frequency but also modulates the optical amplitude intensity at the desired modulation frequency. It is more desirable to be able to adjust. However, the conventional optical integrated circuit type optical intensity modulator can only set the modulation frequency, and cannot adjust the optical amplitude intensity. The present invention has been made in view of the above circumstances, and an object of the present invention is to perform intensity modulation at a desired modulation frequency and to control the light amplitude intensity at the desired modulation frequency. It is an object of the present invention to provide an optical integrated circuit type light intensity modulator which can adjust the intensity. In order to achieve this object, an optical integrated circuit type optical intensity modulator according to the present invention comprises a first optical waveguide for splitting coherent light emitted from a light source. A first merging waveguide for merging coherent light passing through the first and second optical waveguides, and a coherent beam passing through a third optical waveguide and a fourth optical waveguide branched from the first merging waveguide, respectively. A second merging waveguide for merging light; first optical path length changing means for changing an optical path length of the first optical waveguide; and second optical path length changing means for changing an optical path length of the third optical waveguide. ,
One of the first optical path length changing means and the second optical path length changing means is controlled by a signal of a periodic wave whose number of cycles is variable in order to change a modulation frequency, and one of the other is an optical amplitude. It is configured to be controlled by a signal whose level is adjusted to change the intensity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical integrated circuit type optical intensity modulator according to the present invention will be described below with reference to the drawings for convenience. FIG. 1 is a schematic view of an optical integrated circuit type optical intensity modulator according to the present reference example.
Denotes an optical integrated circuit board, and a material having an electro-optical effect is used for the optical integrated circuit board 1. The optical integrated circuit substrate 1 includes an incident optical waveguide 2, an output optical waveguide 3,
Reference optical waveguide 4, first optical waveguide 5, and second optical waveguide 6
And a third optical waveguide 7. Reference optical waveguide 4,
The first optical waveguide 5, the second optical waveguide 6, and the third optical waveguide 7 are configured to be branched from the incident optical waveguide 2 and to join again at the output optical waveguide 3. [0008] Coherent light P from a light source (not shown) is incident on the incident optical waveguide 1, and the coherent light P is transmitted through the reference optical waveguide 4, the first optical waveguide 5, and the second optical waveguide 6. , To the third optical waveguide 7, and the reference optical waveguide 4,
After passing through the first optical waveguide 5, the second optical waveguide 6, and the third optical waveguide 7, they are joined again in the output optical waveguide 3, and output from the output optical waveguide 3 as modulated light P ′. Here, the wavelength of the coherent light P lambda, and the incident light amplitude intensity and I _i, the light amplitude intensity of the modulated light P'and I _o. The first optical waveguide 5, the second optical waveguide 6, and the third optical waveguide 7 are provided in parallel with the reference optical waveguide 4, respectively. The reference optical waveguide 4 is an optical waveguide used as a reference for the optical path length, and the optical path length is X. Here, the first optical waveguide 5, the second optical waveguide 6, and the third optical waveguide 7
Each optical path length of the X _1, X _2, X _3, the first reference the optical path length for the optical path length X of the optical waveguide 4 X _1, X _2, X _3, second and third optical path difference δ Assuming that ₁ , δ ₂ and δ ₃ , X ₁ = X + δ ₁ X ₂ = X + δ ₂ X ₃ = X + δ ₃ . The first optical waveguide 5 has a first optical path length difference δ _1.
The first optical path difference changing means 8 for changing the optical path length with time is provided, and the second optical waveguide 6 is provided with the second optical path difference changing means 9 for relatively setting the second optical path difference δ _2. the third optical path length difference changing means 10 for changing the third optical path length difference [delta] ₃ temporally is provided in the third optical waveguide 7. The first, second, and third optical path length difference changing means 8, 9, and 10 are provided near the first, second, and third optical waveguides 5, 6, and 7, respectively. It is formed by the second and third electrodes. Voltages V ₁ , V ₂ and V ₃ as shown in FIG. ₂ are applied to the _first , _second and _third electrodes. The voltage V ₁ is a triangular wave having a constant period. The difference between the minimum voltage V ₁ min and the maximum voltage V _1max is that the first optical path length difference δ ₁ is an integral multiple of half the wavelength λ of the coherent light P. It is desirable to determine so that. By doing so, the waveform of the modulated light P ′ emitted from the emission optical waveguide 3 becomes a preferable periodic wave. The voltage V ₂ is a constant voltage with respect to time, and its voltage value can be appropriately set. Voltage V
₃ is a triangular wave having a constant period obtained by the voltage V ₂ is added to the voltage V _1, the voltage V _3, the voltage V _1, the voltage V ₂ is set so as to satisfy the formula shown below. V ₃ = V ₁ + V _{2 When} the relationship between the voltage V ₃ , the voltage V ₁ , and the voltage V ₂ is thus determined, the sum of the first optical path difference δ ₁ and the second optical path difference δ ₂ is obtained. Are equal to the third optical path length difference δ _3, and the respective optical path lengths X ₁ , X ₂ , X ₃ can be relatively changed. Here, the reference optical waveguide 4, the first optical waveguide,
The wave functions of the coherent light P passing through the third optical waveguides 5, 6, and 7 are given by: When expressed, the light intensity amplitude I of the modulated light P ′ can be expressed based on the following equation. Here, k is a wave number, 2π / λ
It is. ## EQU2 ## This equation can be modified as shown below. [Equation 3] The above equation finally becomes the following equation. I = 4 (1 + cosKδ ₁ ) +4 cosKδ ₂ (1 + cosKδ ₁ ) = 4 (1 + cosKδ ₁ ) · (1 + cosKδ ₂ ) (1) In equation (1), 4 (1 + cosKδ ₁ ) is the first optical path length difference δ.
_{Since 1} is periodically changed, this is a term that changes the light amplitude intensity in each cycle, and includes a modulation frequency. In contrast, (1) (1 + cosKδ 2) of the formula, by adjusting the second optical path length difference [delta] _2, the maximum amplitude value of the light amplitude intensity I _o changes. That is, (1 + cosKδ ₂ ) is a term that gives the maximum amplitude value of the modulated light P ′. [0018] For example, setting the second optical path length difference [delta] ₂ to n ₁ lambda, the maximum amplitude value of the modulated light P'As shown in Figure 2 is I _o, and the second optical path length difference [delta] ₂ n ₁ When it is set to λ + λ / 4, the maximum amplitude value of the modulated light P ′ is I _o / 2. FIG. 3 shows an embodiment of the optical integrated circuit type optical intensity modulator according to the present invention. The first optical waveguide 11 for splitting the coherent light P incident on the incident optical waveguide 2 is shown in FIG. And coherent light P ₁ passing through the second optical waveguide 12 and
The first merging waveguide 13 for merging P ₂ is connected to the optical integrated circuit board 1.
In addition, a third optical waveguide 14 and a fourth optical waveguide 15 are formed on the optical integrated circuit substrate 1 by branching from the first merged waveguide 13, and the third optical waveguide 14 and the fourth optical waveguide 15 are formed. And the coherent light beams P ₃ and P ₄ passing through the first optical waveguide 11 are changed by changing the optical path length of the first optical waveguide 11 to the first optical waveguide 11. A first optical path length changing means 16 for changing the optical path length of the third optical waveguide 14 is provided on the third optical waveguide 14, and the first optical path length changing means 16 and 2 Optical path length changing means 17
Is controlled so as to change the optical path length at the frequency at which the intensity modulation is desired, and the other is controlled so as to change the optical amplitude intensity. Here, the second optical waveguide 12 and the fourth optical waveguide 15
Is equivalent to the reference optical waveguide 4 of the reference example, the optical path length is X, the optical path length of the first optical waveguide 11 is X ₁ , the optical path length of the third optical waveguide 14 is X _2, and the second optical waveguide 4 is If the optical path length difference of the first optical waveguide 11 with respect to the optical path length X of the optical path 12 is δ ₁ , and the optical path length difference of the third optical waveguide 14 with respect to the fourth optical waveguide 15 is δ ₂ , the following equation is obtained. X ₁ = X + δ ₁ X ₂ = X + δ _{2 In} this embodiment, the first optical path length changing means 16 and the second optical path length changing means 17 are respectively composed of the first optical waveguide 11 and the third optical waveguide 14.
First provided in the vicinity of, is constituted by the second electrode, the first electrode voltage V ₄ for setting the modulation frequency is applied, the voltage for the second electrode to adjust the light amplitude intensity V
₅ is to be applied. The voltage V ₄ is the fourth
As shown in the figure, the triangular wave has a predetermined period, and its voltage V ₅
Is a constant voltage over time. Here, the modulated light P 'emitted from the emission optical waveguide 3 is obtained by synthesizing the light that has passed through the four paths a to d, and the wave function corresponding to each of the paths a to d. Is [Equation 4] Then, the light amplitude intensity I of the modulated light P 'is given based on the following equation. (Equation 5) This equation can be modified as shown below. [Equation 6] This equation is finally the same as equation (1). [0025] Thus, the raise or lower the voltage V ₅ varies the amplitude value, that the modulation frequency changes the cycle of the voltage V ₄ changes are the same as reference example. Since the optical integrated circuit type optical intensity modulator according to the present invention is constructed as described above, it is possible to perform intensity modulation at a desired frequency, This has an effect that the light amplitude intensity can be adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an optical integrated circuit type strong modulator according to a reference example. FIG. 2 is an explanatory diagram for explaining an operation of the optical integrated circuit type strong modulator according to FIG. 1; FIG. 3 is a schematic diagram of an optical integrated circuit type strong modulator according to the present invention. FIG. 4 is an explanatory diagram for explaining an operation of the optical integrated circuit type strong modulator according to FIG. 3; [Description of Signs] 4 ... Reference optical waveguides 5, 11 ... First optical waveguides 6, 12 ... Second optical waveguides 7, 14 ... Third optical waveguides 8 ... First optical path length difference changing means 9 ... Second optical path length differences Changing means 10: third optical path length difference changing means 15: fourth optical waveguide 16: first optical path length changing means 17: second optical path length changing means

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Satoru Niimura               75-1, Hasunumacho, Itabashi-ku, Tokyo               In Pucon                (56) References JP-A-62-48823 (JP, A)                 JP-A-59-24827 (JP, A)

Claims (1)

(57) [Claims] A first merging waveguide for merging the coherent lights respectively passing through the first optical waveguide and the second optical waveguide for splitting the coherent light emitted from the light source, and branching from the first merging waveguide A second merging waveguide for merging coherent light passing through the third and fourth optical waveguides, and the first merging waveguide;
First optical path length changing means for changing the optical path length of the optical waveguide;
A second optical path length changing unit for changing an optical path length of the third optical waveguide, wherein one of the first optical path length changing unit and the second optical path length changing unit is used to change a modulation frequency. Controlled by a periodic wave signal with a variable period, one of which is
An optical integrated circuit type light intensity modulator controlled by a signal whose level is adjusted to change the light amplitude intensity. 2. The first optical path length changing means is formed of a first electrode provided near the first optical waveguide and to which a voltage is applied, and is controlled by a triangular wave voltage signal having a variable period for changing a modulation frequency. The second optical path length changing means is formed from a second electrode provided near the third optical waveguide and to which a voltage is applied, and is controlled by a constant voltage signal that can be adjusted to change the light amplitude intensity. 2. The method according to claim 1, wherein
3. An optical integrated circuit type optical intensity modulator according to claim 1.