JP2010102170A - Optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical modulator that can be driven by a simple driving circuit. <P>SOLUTION: The optical modulator 1 comprises a core layer 2 having a predetermined width and a thickness extending in a longitudinal direction for transmitting light in the longitudinal direction, and a first clad layer 3u and a second clad layer 3d interposing the core layer 2 in a thickness direction. The core layer 2 is formed of an optical material having an electro-optic effect with a refractive index variable depending on an electric field. A first electrode 4u and a second electrode 4d forming an electric field in the core layer 2 are formed on faces of the first clad layer 3u and the second clad layer 3d, respectively, which intersect the thickness direction and are not in contact with the core layer 2; and at least one of the first electrode 4u and the second electrode 4d has a side 5 inclined from a light-entrance side to the width direction with respect to the longitudinal direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical modulator that can be driven by a simple drive circuit.

  There are two types of devices (optical modulators) that convert electrical signals into optical signals and transmit them, that is, those using ICs and those using waveguides.

  In the case of using an IC, on the transmission side, an electric signal representing information by a change in voltage is received once by a driver IC for driving a light emitting element, and the driver IC generates a driving current based on the electric signal to generate a laser diode or the like. The light-emitting element is turned on and off, and an optical signal is transmitted. In the optical receiver, an amplification IC amplifies a light receiving current from a light receiving element such as a photodiode to which an optical signal is incident, and an electric signal is obtained.

  In the case of using a waveguide, the light emitting element emits light having a constant intensity (CW light), and this CW light is incident from a single mode optical fiber to two branch paths constituting the Mach-Zehnder waveguide, and one of the branches. By applying an electric field to the path, a phase difference is generated in the light of both branch paths. Since the emitted light is modulated in accordance with the phase difference, the electric signal can be converted into an optical signal and transmitted. The optical receiver is the same as described above. Since this method uses the phase difference of light, precise control of the driving voltage for applying an electric field to the branch path in the Mach-Zehnder waveguide is required.

JP-A-3-244231

  Both of the conventional two types of optical modulators have a complicated configuration.

  In the case of using an IC, a temperature correction circuit is provided in the driver IC so that an optical signal does not fluctuate due to temperature because the driving condition of the light emitting element has temperature dependency. In the driver IC, it is necessary to convert an electric signal that is a voltage signal into a drive current. For these reasons, the internal configuration of the driver IC is complicated.

  A device using a waveguide requires a precise control of a driving voltage for driving a light emitting element in order to obtain CW light, so that a driving circuit is also complicated. In the case of using the waveguide, the light intensity drifts with respect to the voltage of the electric signal.

  Accordingly, an object of the present invention is to solve the above problems and provide an optical modulator that can be driven by a simple drive circuit.

  To achieve the above object, the present invention provides a core layer having a predetermined width and thickness and extending in the longitudinal direction so as to transmit light in the longitudinal direction, a first cladding layer sandwiching the core layer from the thickness direction, and a first cladding layer. An optical modulator having two cladding layers, wherein the core layer is formed of an electro-optic effect optical material whose refractive index changes according to an electric field, and the thickness direction of the first cladding layer and the second cladding layer; A first electrode and a second electrode that form an electric field in the core layer are formed on each of the surfaces that are not in contact with the core layer, and at least one of the first electrode and the second electrode extends in the longitudinal direction. On the other hand, it has sides inclined in the width direction from the light incident side.

  At least one of the first electrode and the second electrode may include a plurality of electrodes that form different electric fields with the inclined side as a boundary.

  A voltage is applied between the first electrode and the second electrode, and the refractive index of the core layer located on the light incident side from the inclined side is larger than the refractive side of the core layer. An electric field may be formed so that the refractive index of the core layer located is low.

  The present invention exhibits the following excellent effects.

  (1) It can be driven by a simple drive circuit.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIGS. 1A to 1C, an optical modulator 1 according to this embodiment includes a core having a predetermined width and thickness and extending in the longitudinal direction so as to transmit light in the longitudinal direction. An optical modulator 1 having a layer 2 and a first cladding layer 3u and a second cladding layer 3d sandwiching the core layer 2 from the thickness direction, wherein the core layer 2 has an electric power whose refractive index changes according to an electric field. An electric field is formed in the core layer 2 on the surfaces of the first cladding layer 3u and the second cladding layer 3d in the thickness direction and on the side not in contact with the core layer 2 formed of an optical effect optical material. The first electrode 4u and the second electrode 4d are formed, and at least one of the first electrode 4u and the second electrode 4d has a side (slope side) 5 inclined in the width direction from the light incident side with respect to the longitudinal direction. It is what you have.

  Here, the left side of the optical modulator 1 is the light incident side. The right side of the drawing is sometimes referred to as the emission side for convenience, although light may or may not be emitted in the present invention. The incident direction of light is the longitudinal direction of the light modulator 1.

  The core layer 2 is formed of a uniform electro-optic effect optical material over the entire region in the width direction and the longitudinal direction. The electro-optic effect optical material has a property that the refractive index changes when a voltage is applied. Either an electro-optic effect optical material whose refractive index increases when a voltage is applied or an electro-optic effect optical material whose refractive index decreases when a voltage is applied, which one is used depends on the first electrode 4u and This relates to the shape and arrangement of the second electrode 4d. Further, the difference in refractive index between when the voltage is applied and when it is not applied is related to the critical angle at which total reflection of light occurs, and is therefore related to the inclination angle of the hypotenuse 5 of the first electrode 4u or the second electrode 4d.

  Various electro-optic effect optical materials are known. For example, LN (lithium niobate) other semiconductor materials, polymer materials, DRI (dispersed reds produced by Aldrich) oriented by poling, PN junction semiconductors Some of them change the refractive index by charge injection.

  The first cladding layer 3u and the second cladding layer 3d are formed of a material having a refractive index lower than that of the core layer 2 when the refractive index is controlled to be high. Needless to say, the core layer 2, the first cladding layer 3u, and the second cladding layer 3d are transparent in the wavelength band of light used for optical signals.

  The electrode formed on the surface not contacting the core layer 2 of the first cladding layer 3u is referred to as a first electrode 4u, and the electrode formed on the surface not contacting the core layer 2 of the second cladding layer 3d is referred to as the second electrode 4d. Call. These electrodes are, for example, thin film electrodes.

  In the present embodiment, the second electrode 4d is conducted to the GND (ground) potential, and a desired electrical signal is input to the first electrode 4u. The second electrode 4d is formed in a rectangular shape over the entire surface in the width direction and the longitudinal direction, and the first electrode 4u is formed in a shape having a hypotenuse. The second electrode 4d may have the same shape as the first electrode 4u and may be disposed to face the first electrode 4u. Alternatively, the second electrode 4d may not be set to the GND potential, and an electric signal that changes in an opposite phase to the electric signal input to the first electrode 4u may be input to the second electrode 4d.

  Corresponding to the electrode arrangement of the present embodiment, an electro-optic effect optical material for the core layer 2 is used whose refractive index decreases when a voltage is applied.

  As shown in FIG. 1A, the first electrode 4u is formed in an isosceles triangle shape having a vertex at the center position in the width direction on the incident side and a base extending over the entire width on the emission side. The two oblique sides 5 of the isosceles first electrode 4u are inclined in the width direction with respect to the longitudinal direction (light incident direction) of the optical modulator. This inclination angle is an angle at which light is totally reflected (an angle exceeding the critical angle).

  The operation of the optical modulator of FIG. 1 will be described.

  When the optical modulator 1 has the same potential between the first electrode 4u and the second electrode 4d and no electric field is formed in the core layer 2 by the first electrode 4u and the second electrode 4d, the width of the core layer 2 is reduced. Since the refractive index is uniform over the entire region in the direction and the longitudinal direction, the light incident on the incident side is transmitted in the longitudinal direction of the core layer 2 and emitted from the emission side.

  When a voltage is applied between the first electrode 4u and the second electrode 4d, an electric field is formed in the core layer 2 by the first electrode 4u and the second electrode 4d. In the core layer 2, the refractive index changes low in the core layer 2a located in the illustrated isosceles triangular region immediately below the first electrode 4u. In the core layer 2b located in the other region, the refractive index does not change and remains unchanged. For this reason, the boundary surface along the oblique side 5 of the first electrode 4u is the total reflection surface. Since the light incident on the incident side is totally reflected by the total reflection surface, the light cannot propagate through the region of the core layer 2a immediately below the first electrode 4u. Therefore, no light is emitted from the emission side of the optical modulator 1.

  When the voltage application between the first electrode 4u and the second electrode 4d is stopped, the electric field in the core layer 2 disappears. Again, since the refractive index of the core layer 2 is uniform over the entire region in the width direction and the longitudinal direction, the light incident on the incident side is transmitted in the longitudinal direction of the core layer 2 and emitted from the exit side.

  As described above, according to the optical modulator 1 of the above embodiment, when an electric field is formed in the core layer 2 by the first electrode 4u and the second electrode 4d, the core layer 2 has a high refractive index (no electric field). It is divided into a portion (core layer 2b) and a portion (core layer 2a) having a low refractive index (electric field), and a total reflection surface is formed along the oblique side 5 of the first electrode 4u. The light is not emitted from. Therefore, a light source (not shown) is arranged on the incident side of the optical modulator 1 so that light having a constant intensity is incident, and the light modulation driving circuit in FIG. 2 is connected between the first electrode 4u and the second electrode 4d. When a voltage of a desired electric signal is applied, an electric field is formed such that the refractive index of the core layer 2a is lowered and the refractive index of the core layer 2b is relatively high (original refractive index). As a result, an optical signal whose light intensity is modulated according to the electrical signal is emitted on the emission side.

  FIG. 2 shows the signal timing of optical modulation.

  As shown in FIG. 2A, an electrical signal in which a predetermined voltage higher than the GND voltage and a GND voltage (voltage zero) alternately appear is applied to the first electrode 4u. A transient waveform in switching between the predetermined voltage and the GND voltage is indicated by hatching. The time axis is arbitrary time.

  As shown in FIG. 2B, when the electrical signal is a GND voltage, the portion immediately below the first electrode 4u (the emission side 6 of the oblique side 5) has a high refractive index (original refractive index). When the electrical signal is at a predetermined voltage, the portion immediately below the first electrode 4u (the emission side 6 of the oblique side 5) has a low refractive index. The transient waveform at the change of the refractive index is shown by hatching.

  Although the refractive index of the portion not directly under the first electrode 4u (incident side 7 from the oblique side 5) is not shown, the refractive index does not change throughout the entire time. Therefore, the amount of transmitted light (the intensity of the emitted optical signal) changes according to the voltage change in FIG. 2A and the refractive index change in FIG. That is, as shown in FIG. 2 (c), the amount of transmitted light is maximum when the electrical signal is at the GND voltage, and is non-transmitted (zero) when the electrical signal is at the predetermined voltage. Note that when the electrical signal has a predetermined voltage as shown by the broken line, there is no transmission (zero), but a value smaller than the maximum value (however, a detector optically connected to the optical modulator 1 is output from the optical modulator 1) Communication is possible even with a large amount of light (when the electrical signal is a GND voltage) and a small amount of light (when the electrical signal is a predetermined voltage).

  The effects of the present invention according to the above embodiment are as follows.

  Since the light modulator 1 of the above embodiment uses the phenomenon of total reflection of light at the boundary surface where the difference in refractive index occurs, the on / off of light (with or without outgoing light) can be clearly controlled. Therefore, it is optimal for converting an electric signal modulated by turning on and off the voltage into an optical signal and emitting it.

  The optical modulator 1 of the above embodiment can apply the voltage of the electric signal to the first electrode 4u and the second electrode 4d as it is. Therefore, a circuit for converting an electric signal, which is a voltage signal, into a driving current as in the conventional method using an IC becomes unnecessary, and the driving circuit is simplified.

  In the optical modulator 1 of the above embodiment, the incident light may be so-called CW light having a constant intensity, so that the control circuit of the light source is simpler than the method using the conventional IC.

  In the optical modulator 1 of the above embodiment, even if the voltage of the electric signal drifts, the emitted light is turned on / off depending on the presence or absence of total reflection of light, so that the voltage drift is canceled (the signal component due to the voltage drift is an optical signal). Not communicated to). Therefore, the optical signal does not become unstable due to the influence of voltage drift as in the conventional method using the waveguide.

  In the optical modulator 1 of the above embodiment, the refractive index of the electro-optic effect optical material forming the core layer 2 immediately changes with respect to the formation of the electric field. That is, the response time of the refractive index change with respect to voltage application is short. Therefore, the response time of the change of the optical signal with respect to the change of the electric signal is shorter than the conventional one, and the electric signal faster than the conventional one can be converted into the optical signal. Therefore, an optical modulator that is faster than the conventional one can be manufactured.

  The optical modulator 1 of the above embodiment has an effect of correcting the waveform disturbance in the electric signal. This is because controlling transmission of light depending on whether total reflection occurs or not corresponds to applying a threshold to an electric signal.

  Since the optical modulator 1 of the above embodiment does not require encoding of an optical signal, the circuit on the transmission side and the circuit of the optical receiver are simplified. The encoding will be described later.

  By the way, in the said embodiment, the 1st electrode 4u was formed in the isosceles triangle shape which has a vertex in the center position of the width direction in the incident side, and has a base over the full width in the output side. On the contrary, the isosceles triangle shape may be a portion without the first electrode, and the first electrode 4u may be formed into two right triangle shapes sandwiching the isosceles triangle shape. In this case, an electro-optic effect optical material for the core layer 2 is used whose refractive index increases when a voltage is applied. When an electric field is formed in the core layer 2 by the first electrode 4u and the second electrode 4d, the refractive index increases in the right triangle region, and the refractive index is relatively low in the isosceles region. Therefore, the boundary surface along the hypotenuse 5 becomes the total reflection surface. Thus, the shape and arrangement of the electrodes may be changed depending on the characteristics of the electro-optic effect material used for the core layer 2 (relationship between applied voltage and refractive index change).

  Next, another embodiment of the present invention will be described.

  As shown in FIGS. 3A and 3B, the optical modulator 41 according to the present embodiment has a predetermined light transmission rate in the longitudinal direction, similar to the embodiment shown in FIG. An optical modulator 41 having a core layer 2 having a width and a thickness and extending in the longitudinal direction, and a first cladding layer 3u and a second cladding layer 3d sandwiching the core layer 2 from the thickness direction, 2 is formed of an electro-optic effect optical material whose refractive index changes according to an electric field, and is a surface of the first cladding layer 3u and the second cladding layer 3d in the thickness direction and on the side not in contact with the core layer 2 A first electrode 4u and a second electrode 4d for forming an electric field are formed on the core layer 2, respectively, and at least one of the first electrode 4u and the second electrode 4d is inclined in the width direction with respect to the longitudinal direction. It has a side (slope side) 5.

  When the difference from the embodiment of FIG. 1 is described, two types of first electrodes 4u (first first electrode 4u1 and second first electrode 4u2) are provided on the surface of the first cladding layer 3u that is not in contact with the core layer 2. It is formed. That is, the first first electrode 4u1 is formed in an isosceles triangle shape having a vertex at the center position in the width direction on the incident side and a base extending over the entire width on the emission side. The second first electrode 4u2 is formed in two right triangle shapes sandwiching the isosceles triangle shape. The second electrode 4d is formed in a rectangular shape over the entire surface in the width direction and the longitudinal direction. Similarly to the first electrode 4u, the second electrode 4d may be divided into two types and arranged so as to face the first electrodes 4u1 and 4u2, respectively.

  The region of the core layer 2 immediately below the first first electrode 4u1 is referred to as a first region S1, and the region of the core layer 2 immediately below the second first electrode 4u2 is referred to as a second region S2.

  In this embodiment, a PDATA line, which is one of the differential signals, is electrically connected to the first first electrode 4u1 so that differential signals can be input to the two types of first electrodes 4u1 and 4u2. The NDATA line, which is the other side of the differential signal, is electrically connected to the first electrode 4u2. The second electrode 4d is electrically connected to GND which is a neutral potential of the differential signal.

  As shown in FIG. 4A, one differential signal PDATA in which a predetermined high voltage and a predetermined low voltage appear alternately is applied to the first first electrode 4u1. The other differential signal NDATA in which a predetermined high voltage and a predetermined low voltage appear alternately at the opposite timing is applied to the second first electrode 4u2.

  As shown in FIG. 4B, when the differential signal PDATA has a predetermined low voltage, the first region S1 (exit side of the oblique side 5) S1 directly under the first first electrode 4u1 has a high refractive index ( When the differential signal NDATA has a predetermined high voltage, the second region (incident side of the oblique side 5) S2 immediately below the second first electrode 4u2 has a low refractive index. At this time, since the first region S1 has a higher refractive index than the second region S2, an electric field is not formed in the core layer 2 described in the above embodiment, and the light is refracted over the entire width direction and longitudinal direction of the core layer 2. The effect that the light incident on the incident side is transmitted and emitted from the emission side is greater than when the rate is uniform.

  When the differential signal PDATA has a predetermined high voltage, the first region (exit side of the oblique side 5) immediately below the first first electrode 4u1 has a low refractive index, and when the differential signal NDATA has a predetermined low voltage, The second region (incident side of the oblique side 5) immediately below the second first electrode 4u2 has a high refractive index (original refractive index). A total reflection surface is formed along the oblique side 5, and the light incident on the incident side is totally reflected by the total reflection surface, and thus cannot be transmitted to the first region S1. Therefore, no light is emitted from the emission side of the light modulator 41.

  As a result, the optical signal modulated by the differential signal as shown in FIG. 4C is emitted from the optical modulator.

  Next, an embodiment of arraying according to the present invention will be described.

  As shown in FIG. 5, the optical modulator 61 according to the present embodiment includes a plurality of N optical modulators 1 shown in FIG. 1 arranged in the width direction of the core layer 2. N waveguides ch1 to chN are optically connected to the emission side of the core layer 2 in each row. On the other hand, one common CW light source is provided on the incident side of the core layer 2 in each row. N signal lines for inputting different electric signals of ch1 to chN are electrically connected to the first electrode 4u of each column. The second electrode 4d in each column is electrically connected to a common GND.

  The modulation operation in the individual optical modulators 1 for each column is as described above. In the optical modulator 61, different electrical signals are input to the first electrodes 4u in each column, and the CW light is modulated into an optical signal. Since each optical signal is transmitted to the outside through N waveguides, N-channel parallel transmission is realized. Thereby, for example, multi-channel parallel transmission such as 16 channels and 32 channels becomes possible.

  In the conventional optical modulator, the light source and the drive circuit are required for the number of channels for parallel transmission. However, the optical modulator of the present invention can be driven by a simple drive circuit, and can be applied to all channels. Since only one light source is required, the overall configuration including the light source and the light modulator is greatly simplified.

  As shown in FIG. 6, the optical modulator 71 according to the present embodiment is configured by arranging a plurality of N optical modulators 41 shown in FIG. 3 in the width direction of the core layer 2.

  The modulation operation in the optical modulator 41 for each column is as described above. As described with reference to FIG. 5, the optical modulator 71 can perform parallel transmission and can be driven by a simple drive circuit.

  As shown in FIG. 7, the optical modulator 81 according to the present embodiment has the same structure as the optical modulator 61 of FIG. 5 in the core layer 2, the first electrode 4 u, and the second electrode 4 d, but the channel The number of columns is double, and the signal lines electrically connected to the first electrodes 4u in each column and the waveguides optically connected to the emission side of the core layer 2 in each column are different. That is, the signal line of the differential signal PDATA of the first channel is electrically connected to the first electrode 4u of the first column, and another differential signal of the first channel is connected to the first electrode 4u of the second column. The NDATA signal line is electrically connected. In this way, the signal line of the Nth channel differential signal PDATA is electrically connected to the first electrode 4u of the 2N-1th column, and the other electrode of the Nth channel is connected to the first electrode 4u of the 2Nth column. A signal line for one differential signal NDATA is electrically connected. 2N waveguides are optically connected to the output side of the core layer 2 in each column, and the optical signal of the differential signal PDATA and the optical signal of the differential signal NDATA of each channel are transmitted.

  As shown in FIG. 8, the optical modulator 91 according to the present embodiment has the same structure as the optical modulator 71 of FIG. 6, except for the core layer 2, the first electrode 4u, and the second electrode 4d. The number of columns is double, and the signal lines connected to the first electrodes in each column and the waveguides optically connected to the emission side of the core layer 2 in each column are different. That is, the signal line of the differential signal PDATA of the first channel is electrically connected to the first first electrode 4u1 of the first column, and another one of the first channel is connected to the second first electrode 4u2 of the first column. Are connected to the signal line of the differential signal NDATA. Opposite to the first column, a signal line for the differential signal NDATA of the first channel is electrically connected to the first first electrode 4u1 of the second column, and the second first electrode 4u2 of the second column is connected to the second first electrode 4u2. A signal line of the differential signal PDATA for one channel is electrically connected.

  In this way, in the 2nd (N-1) th row, the signal line of the N-th channel differential signal PDATA is electrically connected to the first first electrode 4u1, and another one of the N-th channel is connected to the second first electrode 4u2. Are connected to the signal line of the differential signal NDATA. In the second N column, contrary to the second N-1 column, the signal line of the N-channel differential signal NDATA is electrically connected to the first first electrode 4u1, and the Nth channel is connected to the second first electrode 4u2. The signal lines of the differential signal PDATA are electrically connected.

  2N waveguides are optically connected to the output side of the core layer 2 in each column, and the optical signal P is transmitted by the differential signal PDATA and the differential signal NDATA of each channel in the odd-numbered waveguides. In the even-numbered waveguides, the optical signal N is transmitted by the differential signal NDATA and the differential signal PDATA of each channel. The optical signal P transmitted through the even-numbered waveguides in the same channel and the optical signal N transmitted through the even-numbered waveguides have opposite phases.

  The optical modulator 101 shown in FIG. 9 is obtained by arranging a plurality of N rows of optical modulators 1 shown in FIG. 1 in the width direction of the core layer 2. At this time, the core layer 2 and the core layer in each row The light absorption layer 6 is provided between the two. The light absorbing layer 6 is made of a light absorbing material and is for reflecting light having a traveling component in the width direction of the core layer 2 by being reflected by the total reflection surface along the oblique side 5.

  Thereby, when a plurality of N rows of optical modulators 1 are arranged in the width direction of the core layer 2, it is possible to prevent light having a traveling component in the width direction from entering and leaving between the core layers 2 of adjacent rows.

  When the optical modulators 1 are arranged in a plurality of N rows in the width direction of the core layer 2, the adjacent core layers 2 are not in contact with each other, but a space (air layer) is provided between the core layers 2 or the cladding A layer may be formed.

  Next, the electrodes (first electrode 4u, second electrode 4d) will be described.

  It is important that the electrode has a hypotenuse 5 in order to form a total reflection surface, but the size of the electrode is not particularly important. Increasing the electrode decreases the electrode impedance.

  The core layer 2, the first clad layer 3u, and the second clad layer 3d are made of resin. However, when the thickness of the core layer 2, the first clad layer 3u, and the second clad layer 3d is reduced, the impedance between the electrodes is lowered. Further, when the conductivity of the material used for the electrode is increased, the impedance is lowered.

  Reflection can be eliminated by matching the impedance of the electrode with the impedance of the signal line. 50Ω for single end and 100Ω for differential are desirable. Impedance may be adjusted by inserting a parallel resistor between the first electrode 4u and the voltage source or between the second electrode 4d and the voltage source.

  Next, an optical receiver corresponding to the optical modulator of the present invention described so far will be described.

  As shown in FIG. 10, the optical receiver 111 includes a light receiving element 112 such as a PD (photodiode) on which an optical signal emitted from the waveguide of FIGS. 5 to 8 is incident, and one end of the light receiving element 112. A ground resistor 113 electrically connected to the capacitor, a capacitor 114 having one electrode electrically connected to a connection point between the ground resistor 113 and the light receiving element 112, and an electrode electrically connected to the opposite electrode of the capacitor 114. Received signal line 115.

  A direct current voltage is applied to the light receiving element 112 from a direct current power source, and the voltage of the ground resistor 113 changes according to the light reception current by the incident optical signal. By guiding this voltage to the reception signal line 115 via the capacitor 114, an AC component (voltage change) can be extracted from the voltage of the ground resistor 113.

  In the conventional optical modulator, even when the electrical signal is an electrical signal having a high voltage state and a low voltage state with the same sign, the electrical signal has a positive voltage state and a negative electrical signal state. The optical signal also has a state in which the light intensity is large and a state in which the light intensity is not zero but small. An optical receiver that receives such an optical signal needs to generate a reference optical intensity from the received optical signal in order to correctly detect a state in which the light intensity is high and a state in which the light intensity is not zero but low. there were. In order to stably obtain the standard light intensity, the information code carried in the original electrical signal is processed and encoded into an optical communication code that keeps the average light intensity within a relatively short time. There is a need to. For this reason, in the conventional optical modulator, an encoding circuit is built in the driver IC, and the optical receiver requires a decoding circuit that decodes the optical communication code into the information code of the original electrical signal.

  In contrast, in the optical modulator of the present invention, the optical signal has a state where the light intensity is a predetermined magnitude and a state where the light intensity is zero. Since the state where the light intensity is zero is an absolute reference, it is not necessary to generate a reference light intensity in the optical receiver. For this reason, the average light intensity may not be constant. Therefore, it is not necessary to encode the information code into an optical communication code by the optical modulator, and it is not necessary to decode by the optical receiver. Therefore, as shown in FIG. 2, the optical modulation driving circuit is simplified, the optical modulator is simplified, and the counterpart optical receiver is also simplified.

  Next, a modified example of the present invention will be described.

  The optical modulator 121 shown in FIG. 11 includes a core layer 2 (see FIG. 1B) having a predetermined width and thickness and extending in the longitudinal direction so as to transmit light in the longitudinal direction. An optical modulator 121 having a first cladding layer 3u and a second cladding layer 3d sandwiched from the thickness direction, wherein the core layer 2 is formed of an electro-optic effect optical material whose refractive index changes according to an electric field, A first electrode 4u and a second electrode 4d that form an electric field in the core layer 2 in the thickness direction of the first clad layer 3u and the second clad layer 3d and on the surfaces that are not in contact with the core layer 2, respectively. And at least one of the first electrode 4 u and the second electrode 4 d is narrower than the core layer 2.

  Here, the first electrode 4 u is formed to be narrower than the core layer 2. The first electrode 4u extends in the longitudinal direction from the emission side and is formed partway on the incident side. The first electrode 4 u is provided at the center in the width direction of the core layer 2. Similar to the previous embodiments, the second electrode 4d covers the entire surface of the core layer 2 or faces the first electrode 4u in the same shape as the first electrode 4u. On the exit side of the core layer 2, a waveguide (or optical fiber) 122 connected to an optical receiver (not shown) is provided at the same position as the first electrode 4 u. The width of the waveguide 112 is narrower than the width of the core layer 2. A light source (not shown) for CW light is provided on the incident side.

  When no voltage is applied between the first electrode 4u and the second electrode 4d, the electro-optic effect optical material of the core layer 2 has a uniform refractive index regardless of the location. Is transmitted to the emission side. An amount of light according to the ratio to the width of the core layer 2 enters the waveguide 122.

  When a voltage is applied between the first electrode 4u and the second electrode 4d, the refractive index of the electro-optical effect optical material of the core layer 2 is higher or lower than that of the surroundings only under the first electrode 4u (electro-optical). Depending on the effect optical material).

  Assuming that the refractive index is higher than the surroundings just below the first electrode 4 u, the light density increases in that region, so that a larger amount of light enters the waveguide 122. Assuming that the refractive index is lower than the surroundings just below the first electrode 4u, the light density in that region is low, so that a smaller amount of light enters the waveguide 122.

  It is assumed that an electro-optic effect optical material whose refractive index is linearly proportional to the electric field strength (for example, a material that increases the refractive index when the electric field strength is increased) is used for the core layer 2. In this case, as shown in FIG. 12, when the voltage applied between the first electrode 4u and the second electrode 4d is linearly changed from V0 to V1, the amount of light incident on the waveguide 122 is from I0. It changes linearly up to I1. Therefore, the optical modulator 121 can convert an analog electrical signal into an analog optical signal.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure of the optical modulator which shows one Embodiment of this invention, (a) is a top view, (b) is a sectional side view with a circuit diagram, (c) is AA sectional drawing. 2 is a timing chart of an electric signal, a refractive index, and an optical signal when the optical modulator of FIG. 1 is operated. It is a figure of the optical modulator which shows other embodiment of this invention, (a) is a top view, (b) is a sectional side view with a circuit diagram. 4 is a timing chart of an electric signal, a refractive index, and an optical signal when the optical modulator of FIG. 3 is operated. It is a top view with a circuit diagram of the optical modulator which shows other embodiment of this invention. It is a top view with a circuit diagram of the optical modulator which shows other embodiment of this invention. It is a top view with a circuit diagram of the optical modulator which shows other embodiment of this invention. It is a top view with a circuit diagram of the optical modulator which shows other embodiment of this invention. It is a top view of the optical modulator which shows other embodiment of this invention. It is a circuit diagram of the optical receiver corresponding to the optical modulator of this invention. It is a top view of the optical modulator which shows the modification of this invention. FIG. 12 is a characteristic diagram of voltage versus optical signal in the optical modulator of FIG. 11.

Explanation of symbols

1, 41, 61, 71, 81, 91, 101, 121 Optical modulator 2 Core layer 3d Second cladding layer 3u First cladding layer 4d Second electrode 4u First electrode 4u1 First first electrode 4u2 Second first Electrode 5 hypotenuse

Claims (3)

A core layer having a predetermined width and thickness and extending in the longitudinal direction to transmit light in the longitudinal direction;
An optical modulator having a first cladding layer and a second cladding layer sandwiching the core layer from the thickness direction,
The core layer is formed of an electro-optic effect optical material whose refractive index changes according to an electric field,
A first electrode and a second electrode for forming an electric field in the core layer are formed in the thickness direction of the first clad layer and the second clad layer, and on each of the surfaces not in contact with the core layer,
At least one of the first electrode and the second electrode has a side inclined in the width direction from the light incident side with respect to the longitudinal direction.   2. The optical modulator according to claim 1, wherein at least one of the first electrode and the second electrode includes a plurality of electrodes that form different electric fields with the inclined side as a boundary. A voltage is applied between the first electrode and the second electrode,
An electric field is formed so that the refractive index of the core layer located on the light emission side from the inclined side is lower than the refractive index of the core layer located on the light incident side from the inclined side. The optical modulator according to claim 1.

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