JPH08146366A - Light modulator - Google Patents

Abstract

(57) [Summary] [Object] To provide an optical modulator capable of modulating an optical signal at a higher speed than a conventional optical modulator. An optical modulator that modulates the phase difference of a light wave that has passed through two branched optical paths that share the same light source by a change in the refractive index of a variable refractive index medium, and uses the resulting change in light intensity due to the interference effect of the light wave. In the above, both the optical intensity modulator and the optical amplifier are provided, and the phase difference is modulated between π and a certain value of θ, and the θ is between 0.5π and 0.98π. In the optical amplifier, the output light from the light intensity modulator is 1 / [10 sin ² (δφ when the phase difference is δφ).
/ 2)] times or more and 10 / [sin ² (δφ / 2)] times or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator required for various devices such as optical communication and optical calculation.

[0002]

2. Description of the Related Art In a conventional optical modulator utilizing the change in refractive index of a variable refractive index medium, δφ shown in (1) and (2) below is used.
Alternatively, the light intensity is modulated by changing δψ between 0 and π. (1) When utilizing the interference effect of light waves that have passed through two branched optical paths, the phase difference δφ when the two light waves are combined. (2) When utilizing the intensity change of a specific linearly polarized light component due to the modulation of the phase difference between two orthogonally polarized light components of light having a single polarized light component (in a pure state with respect to the polarization direction), Phase difference δψ. In the case of (1), if δφ is π, the two light waves cancel each other due to the interference effect, the output light intensity is 0, and, for example, the signal is in the off state. On the contrary, if δφ is 0, it is turned on. In the case of (2), δψ is 0
If so, the output light becomes linearly polarized light, and if δψ is π, it becomes linearly polarized light in a direction orthogonal thereto. When the polarization modulation is converted into the light intensity modulation by using the polarizer installed so as to be orthogonal to the latter linearly polarized light, the transmitted light intensity of the polarizer becomes 0 if δψ is π, and the signal is in the off state. If δψ is 0, it is turned on.

Δφ or δψ does not necessarily have to be changed between 0 and π, and is described in Applied Physics Letters, Vol. 59, No. 21, page 2651 (1991) or Japanese Patent Laid-Open No. 4-264746. As described above, there is also a method of slightly changing δφ or δψ within 1 mrad or less to perform light intensity modulation. In this case, δφ
Alternatively, compared to the method of limiting the modulation of δψ between 0 and π, high-speed modulation is possible, but the light intensity modulation width is very small, and it becomes difficult to distinguish the ON state and the OFF state of the signal. Did not work as a light modulator. In general, in order to reduce the crosstalk between the ON state and the OFF state as much as possible, it has been devised to make δφ or δψ as close to 0 as possible in the OFF state and as close to π as possible in the ON state.

Here, the variable refractive index medium means an electric field, a magnetic field,
The refractive index changes due to light, pressure, heat, etc. For example, in an optical modulator that uses the Pockels effect, which is a phenomenon in which the refractive index changes due to an electric field, the light of the same light source is split into two, and the Pockels effect installed in one of the two optical paths is expressed. By applying an electric field to the medium, its refractive index is changed, and the interference effect of light at the confluence point, which is generated by recombining two light waves that have passed through the respective optical paths, is utilized. GHz
In order to realize high-speed modulation on the order, an ultra-short electrical signal pulse is propagated in the same direction as the traveling direction of light to the electrode along the refractive index variable medium that induces the Pockels effect, and the traveling wave operation is performed. A method of modulating the phase difference between light waves propagating in two optical paths between 0 and π is generally adopted.

[0005]

In the conventional optical modulator utilizing the change in the refractive index of the variable refractive index medium, in order to change δφ or δψ between 0 and π, the optical modulation is performed for the following reason. There was a problem that the speed was limited to a certain value or less.

For example, in an optical modulator utilizing the Pockels effect, which is a phenomenon in which the refractive index changes with an electric field, the maximum modulation speed f _m , the optical path length L in the variable refractive index medium, and the variable refractive index medium are generally applied. There is the following relationship between the electric field intensities E to be generated.

F _m L = 2 c / (π [n _m −n _o ]) L = 3λ / (n _o ³ rE) where c is the speed of light, _nm is the equivalent refractive index of microwaves, and n is
_o is the equivalent refractive index of the light wave, λ is the wavelength of the input light, and r is the Pockels constant. When the optical path length L of the variable refractive index medium is increased in order to reduce the electric field strength E, the maximum modulation speed f is due to the phase speed mismatch that the microwave speed (modulation electric signal transmission speed) is slower than the light wave. _m is limited.
Further, if the optical path length L is shortened to increase the maximum modulation speed f _m , the electric field strength E must be increased. However, in the high band of gigahertz order, the voltage strength that can be generated by the current modulation electric signal generation technology becomes. There is a limit. Due to the above trade-off relationship, there is a physical limit to the maximum feasible modulation speed f _m in the conventional optical modulator using the Pockels effect. The value of f _m L is the integrated optical circuit and components (I
ntegrated OpticalCircuit and Components ； SK Kor
otky and RC Alferness, Marcel Dekker, 1987
(Year), page 203, when LiNbO ₃ is used as the refractive index variable medium, about 9.6 GHz cm,
When an organic polymer is used, it is about 150 GHz cm.

In the optical modulator utilizing the phenomenon that the refractive index changes due to the temperature change, it is necessary to reduce the optical path length or temperature change width in the refractive index variable medium in order to increase the modulation speed. However, since the product of the optical path length and the temperature change width in the variable refractive index medium determines the phase modulation range, one parameter is set small in order to modulate the phase difference δφ or δψ between 0 and π. Then, the other becomes bigger. As a result, there is a limit to the maximum modulation speed that can be achieved.

As described above, 1 mrad of δφ or δψ
There is also a method of performing high-speed light intensity modulation as compared with the method of inducing the following minute change by the change of the refractive index of the variable refractive index medium and limiting the modulation range of δφ or δψ between 0 and π. However, this method has a problem that the crosstalk becomes very large or the output light intensity becomes very small, so that it is difficult to use it as an optical modulator.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical modulator capable of modulating an optical signal at a higher speed than conventional optical modulators.

In order to achieve the above object, the optical modulator of the present invention is characterized by having both a light intensity modulation function and an optical amplification function. Further, the light intensity modulator uses the change in the refractive index of the variable refractive index medium, and (1) changes in the light intensity due to the interference effect of the light wave having the phase difference δφ that has passed through two branched optical paths that share the same light source, ) Intensity change of specific linear polarization component due to modulation of phase difference δψ of two polarization components orthogonal to each other of light composed of a single polarization component (in a pure state with respect to polarization direction) (1), (2) Is a light intensity modulation method that uses one of the
In the case of the light intensity modulation method by the above method (1), the output light from the light intensity modulation unit is changed in the light amplification unit in the range of π and θ (0.5π <θ <0.98π). Is 1 / [10sin ²
(δφ / 2)] times or more and 10 / [sin ² (δφ / 2)] times or less, 1 / in the case of the light intensity modulation method by the above method (2)
^{[10sin 2 (δψ / 2)} ] ^{times, 10 / [sin 2 (δψ} /
2)] It is characterized in that the light is amplified by a factor of 2 or less.

As described in the previous section, δφ or δψ
There has been a method of increasing the modulation speed without limiting the modulation range of 0 to π (Applied Physics Letters, Vol. 59, No. 21, 2651).
Page (1991) or JP-A-4-264746)
However, it is difficult to use as an optical modulator because of problems such as deterioration of crosstalk and weakening of output light intensity. We have added a light amplification function to the light modulation device in addition to the light intensity modulation function, and
By inputting light of 1 μW or more and 20 μW or less and operating this device in the above phase modulation range and optical amplification range, a) 2 to 50 compared to the method of modulating δφ or δψ between 0 and π. It has been found that it is possible to simultaneously realize three points, that is, high speed modulation of about twice, b) crosstalk of -20 dB or less, and c) output light intensity at a level almost equal to the input light. So far, there is no optical modulator that satisfies these three points at the same time.
An optical modulator having an optical amplification function and satisfying these three points can be realized only by operating under the above conditions. b and c indicate that the device of the present invention works well as an optical modulator, and a indicates that the device of the present invention enables transmission of a large amount of information that is impossible with conventional modulators. Shows.

The phase modulation range and the optical amplification magnification range are experimentally determined, and the theoretical basis has not been clarified yet. When operated outside this condition, for example, the input light intensity from the light intensity modulator to the light amplifier decreases,
It is necessary to increase the optical amplification factor, which is due to spontaneous emission of the optical amplification medium (Amplified Stimulated Emissi
on; ASE), and as a result, the crosstalk of this device deteriorates.

Here, the variable refractive index medium means an electric field, a magnetic field,
The refractive index changes due to light, pressure, heat, etc. For example, a phenomenon in which the refractive index changes due to an electric field is called the Pockels effect, and the variable index medium has an electro-optical (E-Optic; E) that exhibits a second-order nonlinear optical effect.
O) material, which is an inorganic ferroelectric substance such as LiNbO ₃ or KTiOPO ₄ , a semiconductor such as GaAs, an organic crystal such as 2-methyl-4-nitroaniline, a hyperpolarization such as a polyimide containing oriented Disperse Red 1. Any substance that exhibits the Pockels effect may be used, such as a polymer or a solution containing a molecule with a high ratio. The light propagation path may be a solid such as an optical waveguide, a solution such as ethylene glycol, a gas such as air, a vacuum, or a combination thereof.

In the case of performing the light intensity modulation by the above method (1), the light of the same light source is divided into two, and the refractive index of the variable refractive index medium installed in one of the two optical paths is changed. Then, the interference effect of light at the merging point, which is generated by recombining the two light waves having the phase difference Δφ that have passed through the respective optical paths, is used. The structure of the optical path is Mach-Zehnder optical interferometer type or Michelson optical interferometer type,
Anything that utilizes the interference effect of light split into two from the same light source may be used. The control of δφ is performed by changing the refractive index of the variable refractive index medium by an electric field, a magnetic field, light, pressure, heat or the like. When δφ is π, the output light intensity is 0, and the optical signal is off. When δφ is shifted from π, the output light is not 0, and the optical signal is in the ON state.

The OFF state may be set by setting the difference between the two optical path lengths to be precisely equivalent to the phase difference π of the light wave, or the refractive index of the variable refractive index medium provided in one of the optical paths may be set to the electric field. It may be adjusted by magnetic field, light, pressure, heat, etc. As the refractive index variable medium for setting the off state, a refractive index variable medium different from the refractive index variable medium for optical modulation may be provided, or the refractive index variable medium for optical modulation may be shared for the off state setting. Good. In the latter case, two types of refractive index modulation signals are sent to the same refractive index variable medium. If the refractive index of the two optical paths changes due to changes in the operating environment of this device such as temperature changes, and the phase difference of the light waves from the two optical paths fluctuates due to causes other than the refractive index modulation signal, this OFF state setting The variable refractive index medium is adjusted for offset setting.

When an optical modulation signal such as electricity or light is input to the refractive index variable medium for optical signal modulation, the optical modulation input signal is turned off even if the output light of the optical intensity modulator becomes 0. In the state, the output light of the light intensity modulator may be 0 or either. In the former case, when the optical modulation signal is input, the offset is adjusted so that the phase difference between the two light waves becomes π, and in the latter case, when the optical modulation signal is not input. , The offset is adjusted so that the phase difference between the two light waves becomes π.

In the case of performing the light intensity modulation by the method (2), the phase difference between two polarization components orthogonal to each other of light having a single polarization component (in a pure state with respect to the polarization direction) is modulated. , The intensity change of the specific linearly polarized light component accompanying this is utilized. For example, linearly polarized light is passed through a variable index medium. Here, linearly polarized light is
It can be considered to be combined light having an intensity ratio of 1: 1 and a phase difference of 0 between two polarization components that form an angle of 5 degrees and are orthogonal to each other. When the difference in refractive index between two polarization components orthogonal to each other is changed by the refractive index variable medium,
A phase difference δψ occurs between the two polarization components, and as a result, the incident light of linearly polarized light is generally converted to elliptically polarized light by the variable refractive index medium and to linearly polarized light in the special case where the phase difference becomes π. . By passing such polarization-modulated light through a polarizer, intensity-modulated light can be obtained.

Polarization modulation is performed between elliptically polarized light and linearly polarized light. The output light from the variable refractive index medium generally does not become linearly polarized light due to the refractive index anisotropy of the variable refractive index medium, etc. Therefore, depending on the case, it may be orthogonal to each other, such as a Soleil-Ubabinet phase compensator or a Faraday cell. Insert a phase difference adjusting element for two polarization components before entering the polarizer.
It is necessary to adjust the offset of. The offset is adjusted by adjusting the output light from the variable refractive index medium when the optical modulation signal such as electricity or light is input to the variable refractive index medium or not input. Is set to be linearly polarized light. By the polarizer set in the direction orthogonal to the polarization direction of this linearly polarized light,
Linearly polarized light is converted into light having an intensity of 0 (off state), and elliptically polarized light is converted into light having a nonzero intensity (on state). With the above method,
Light intensity modulation is performed by changing the refractive index of the variable refractive index medium.

The light emitting medium of the optical amplifier is an optical fiber doped with erbium ions, a semiconductor such as GaInAsP, or N.
Any substance that emits light at the wavelength of the signal light, such as a solid such as d: YAG or a solution containing a dye such as rhodamine 6G, may be used. The optical amplification section is configured to pass the output light from the light intensity modulation section through the light emitting medium, and amplifies the light by stimulated emission.
The causes of deteriorating the crosstalk of the optical modulator of the present invention are 1) leakage light from the light intensity modulator in the off state, and 2) light emission (ASE) from the optical amplifier due to spontaneous emission of the optical amplification medium. . In order to improve the crosstalk of the output light, in some cases, the output light from the optical amplifying section is mixed with a medium (a solid such as glass, a material containing a saturable absorption dye,
Liquid such as ethylene glycol). in this case,
It is necessary to set the most efficient concentration of the saturable absorbing dye so that the signal light is transmitted while the noise light is transmitted.

Among the various light intensity modulators and the light amplifiers described above, the light intensity modulator utilizing the Mach-Zehnder type Pockels effect using an optical waveguide and the light amplification by a semiconductor such as GaInAsP to which a voltage is applied are utilized. By using the function expressing section, the optical modulator of the present invention can be made into a compact one-chip element. By using a Mach-Zehnder type optical waveguide for the optical modulation function manifesting part, and
The optical amplification function expressing section is made compact by using a semiconductor. Optical amplification using semiconductors also has the advantage that no other light source is required. Light intensity modulation using the Pockels effect can be performed at a higher speed than light intensity modulation using the change in refractive index due to pressure and heat, and can be realized with a more compact device than light intensity modulation using light. .
It is necessary to perform the traveling wave operation in order to perform high-speed modulation of the light intensity modulator using the Pockels effect. As described above, the conventional method has a problem that the modulation speed is limited due to the traveling wave operation, but the apparatus of the present invention performs high-speed modulation of about 2 to 50 times the maximum modulation speed of the conventional method. Is realized.

[0022]

As described above, in the optical modulator of the present invention,
(1) Change in light intensity due to the interference effect of light waves having a phase difference δφ that has passed through two branched optical paths that share the same light source, (2)
Phase difference δ of two polarization components that are orthogonal to each other for light that is composed of a single polarization component (pure state in the polarization direction)
An optical intensity modulation method that uses one of (1) and (2) of the intensity change of a specific linearly polarized light component due to the modulation of ψ, and δφ or δψ is defined as π and θ (0.5π <θ <0. 98
π), and the output light from the light intensity modulator in the light amplifier is multiplied by 1 / [10 sin ² (δφ / 2)] in the case of the light intensity modulation method according to method (1). Above, 10 / [si
n ² (δφ / 2)] times or less, and in the case of the light intensity modulation method by the above method (2), 1 / [10 sin ² (δψ / 2)] times or more, 1
The following three points a, b, and c were realized at the same time by optical amplification to 0 / [sin ² (δψ / 2)] times or less. a) δ
Compared to the method that modulates φ or δψ between 0 and π, 2
˜50 times high-speed modulation, b) -20 dB or less crosstalk, and c) output light intensity at almost the same level as the input light.
The conventional optical modulator cannot satisfy three points at the same time. However, the optical modulator has not only a light intensity modulating function but also an optical amplifying function, and by operating under the above conditions. For the first time, an optical modulator satisfying the three points was realized. As described in a), the device of the present invention enables the transmission of large amounts of information, which is impossible with conventional modulators.

[0023]

The present invention will be described in more detail with reference to examples.

(Embodiment 1) FIGS. 1 and 2 show the configuration of an optical modulator of the present embodiment. Figure 1 shows a Mach-Zehnder optical interferometer type optical intensity modulator using the Pockels effect and Ga
1 is a schematic diagram of an optical modulator equipped with an optical amplification section that utilizes light emission by current injection into InAsP. FIG. 2 is a sectional view taken along the broken line in FIG. This device includes a light source (diode laser: GaInAsP) 1, a single mode optical waveguide 2, a branch 3, a branch 4, a modulated electric signal propagation electrode 5, a modulated electric signal source 6, a bias voltage application electrode 7, Bias voltage source 8, Y-shaped branch 9, photodetector (photodiode) 10,
Optical amplification medium GaInAsP11, light emitting diode power supply 12, the signal light outgoing light 13, the light modulation variable refractive index medium (LiNbO ₃₎
14, variable refractive index medium for bias (LiNbO ₃ ) 15,
It comprises a clad layer 16, a ground electrode 17, and a substrate 18. The signal light has a wavelength of 1.5 μm and uses GaInAsP as a light source.

The optical path length difference between the branch paths 3 and 4 is set so that the phase difference δφ of the light waves passing through the branch paths 3 and 4 is approximately π. LiNbO installed in branch 4
_An electric field is applied to the electrode 315 by using the bias voltage applying electrode 7 to change the refractive index of LiNbO ₃ 15 so that δφ becomes π when the modulated electric signal is in the off state. . Since the refractive indexes of the branch paths 3 and 4 change due to changes in the operating environment of the device such as temperature fluctuations, δφ when the modulated electrical signal is in the off state
May deviate from π. In order to keep this at π at all times, a part of the output light from the light intensity modulation section branched by the Y-shaped branch path 9 is monitored by the photodetector 10, and the photodetector is always detected when the modulated electric signal is in the off state. LiNbO branch passage 4 so that the light intensity detected is 0 to 10 ₃ 15
The voltage applied to is adjusted by the bias power supply. The branch path 3 is a portion for modulating the refractive index of LiNbO ₃ 14 installed in the branch path 3 by the propagation of the modulated electric signal. The length of the modulated electric signal propagation electrode 5 and LiNbO ₃ 14 installed in the branch 3 is 1 mm.

As a result of separately preparing and examining a waveguide having the same structure except that the interaction length of the electric field and light in the branch 3 was changed, the phase difference δφ of the light waves from the branch 3 and the branch 4 was set to 0. It was found that an interaction length of about 5 mm is required to modulate between π. At this time, the applied electric field strength was set to 1 V / μm in consideration of the characteristics of the high-speed electric signal generation source. When performing optical modulation with a high-speed modulated electrical signal by a traveling wave operation that propagates the modulated electrical signal and input light in the same direction,
Since it is necessary to match the phase velocity of the modulated electric signal with the input light, the modulation velocity of the modulated electric signal is limited. In the case of LiNbO ₃ , the product of the maximum modulation speed and the interaction length is, Integrated Optical Circuit and Components (Integrated Optical Circuit and Components;
SK Korotky and RC Alferness, Marcel Dekker
, 1987), the maximum modulation frequency of the modulated electric signal is about 20 GHz in the conventional method of modulating δφ between 0 and π. Presumed to be.

A 90 GHz sinusoidal electric signal is input as a modulated electric signal to the optical modulator of the present invention, and 90 GHz is inputted.
It was investigated whether or not the modulation at was possible. 0 from the light source.
90 m of cw input light of 5 mW is input to the light intensity modulator.
A Hz sinusoidal modulated electrical signal was propagated to the electrode 5 of the branch 3. The peak intensity of the output light from the light modulator was 20 μW. This is the phase difference δ of the light waves from the branch 3 and the branch 4.
It suggests that φ is 0.4 rad. The output light from the light intensity modulator was sent to the optical amplifier and optically amplified. As a result, the detected waveform of the optical signal had no distortion reflecting the waveform of the input electric signal. This shows that this device can perform high-speed modulation of 90 GHz, which cannot be realized by the conventional optical modulation method. The peak intensity of output light is about 0.5mW
And the amplification factor is about 25 times. At this time, the ASE intensity was 1 μW or less and the crosstalk was −20 dB or less. The above results indicate that the present apparatus is a) high speed modulation of about 2 to 50 times as compared with the method of modulating δφ between 0 and π.
It is shown that three points of b) crosstalk of −20 dB or less and c) output light intensity of the level almost equal to the input light are simultaneously realized.

(Embodiment 2) FIG. 3 shows an optical modulator having another structure. In this device, the light intensity modulation is performed by utilizing the phase difference δψ between the two polarization components orthogonal to each other of the light having the single polarization component. This apparatus includes a light source (cwNd: YAG laser) 19, a polarizer 20, polarization modulators 21 to 25, a Soleil-Yu-Babinet compensator 26, a polarizer 27, and an amplification medium (N.
d: YAG) 28, amplification light source 29, saturable absorption dye 30
Consists of FIG. 4 shows a detailed view of the polarization modulators 21-25. The polarization modulators 21 to 25 include a modulated electric signal propagation electrode 31, a ground electrode 32, a modulated electric signal source 33, an EO polymer 34, and an insulator substrate 35 having a mirror-like surface. When the modulated electric signal flows through the modulated electric signal propagation electrode 31, FIG.
An electric field is applied vertically. As the EO polymer 34, a polymer having Disperse Red 1 as a side chain was used and was formed as a polymer having a thickness of 150 μm on the insulating substrate 35 with an electrode. A polymer having an EO constant of 15 pm / V obtained by performing the electric field orientation of the nonlinear molecule in the vertical direction of FIG. 4 was used.

The signal light is cw light of 1064 nm using an Nd: YAG laser as the light source 19. The light from the light source 19 passes through the polarizer 20 and becomes linearly polarized light. The average output of this linearly polarized light is 10 mW. At this time, the polarization direction of the linearly polarized light is 4 with respect to the electric field direction generated in the EO polymer 34.
Make an angle of 5 degrees. Input light is polarization modulator 2
1, 22, 23, 24, and 25, and passes through a Soleil-Ubavinet phase compensation plate 26 and a polarizer 27, and then an optical amplification unit 28.
It is amplified by and output. Not only when the modulated electric signal is in the ON state but also when it is in the OFF state, the input light that is linearly polarized changes to elliptically polarized light while being repeatedly reflected by the polarization modulators 21 to 25 due to the polarization characteristic of reflection and the like. By the method described below, the intensity of output light passing through the polarizer when the modulated electric signal is in the off state is set to be less than one-millionth of the input light. The elliptically polarized light generated by the reflection with the polarization modulators 21 to 25 is reflected by the Soleil-Babinet phase compensation plate 26.
Is converted to linearly polarized light. The polarizer 27 is set in the direction orthogonal to the polarization direction of this linearly polarized light.

When the electric field applied to the EO polymer 34 is modulated, the phase difference δψ between two polarization components of the input light which are orthogonal to each other is modulated by the EO effect, so that the polarization state of the laser light changes. As a result of operating only one of the five polarization modulators 21 to 25, the peak intensity of the laser light passing through the polarizer 27 was 2.5 μW when the polarization modulator was in the ON state. This is due to reflection from one polarization modulator, and δψ is a modulated electrical signal of 0.03 rad.
It shows that it is subject to modulation. The output light from the polarizer 27 is diode laser pumped Nd: YAG rod 2.
Then, the signal was amplified by about 4,000 times to obtain an optical signal having the same intensity level as the input light.

The modulated electric signals in the five polarization modulators are synchronized as shown in FIG. 5, and each modulated electric pulse is provided with a constant delay time. As a result of the laser light interacting with the five modulated electrical signals 36-40, the output light 41 passing through the polarizer 27 will be as shown in FIG. These pulses are optically amplified by the Nd: YAG rod 28 and have almost the same peak intensity as the input light.

[0032]

According to the present invention, it is possible to provide an optical modulator capable of modulating an optical signal at a higher speed than the conventional optical modulator.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration example of an optical modulator of the present invention.

FIG. 2 is an explanatory diagram showing a configuration example of an optical modulator of the present invention.

FIG. 3 is an explanatory diagram showing a configuration example of an optical modulator of the present invention.

FIG. 4 is an explanatory diagram showing a configuration example of an optical modulator of the present invention.

FIG. 5 is a timing chart showing a temporal relationship between a modulated electric signal and a modulated optical signal in the optical modulator of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Single mode optical waveguide, 3, 4 ... Branch path, 5 ... Modulation electric signal propagation electrode, 6 ... Modulation electric signal source, 7 ... Bias voltage applying electrode, 8 ... Bias voltage source, 9 ... Y-shaped branch path, 10 ... Photodetector, 11 ... Optical amplification medium GaInAsP, 12 ... Light emitting diode power supply, 13 ... Signal light emission light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Tsunoda 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (4)

[Claims] 1. A light which utilizes a change in light intensity due to a resulting interference effect of a light wave, which modulates a phase difference of a light wave passing through two branched optical paths having the same light source by a change in a refractive index of a variable refractive index medium. The modulator includes both an optical intensity modulator and an optical amplifier, modulates the phase difference between π and a certain value of θ, and θ is between 0.5π and 0.98π, In the light amplification section, the output light from the light intensity modulation section is 1 / [10 sin ² (δφ when the phase difference is δφ).
/ 2)] times or more and 10 / [sin ² (δφ / 2)] times or less, and an optical modulator is characterized. 2. A phase difference between two polarization components orthogonal to each other of light composed of a single polarization component is modulated by a change in the refractive index of a variable refractive index medium, and the resulting intensity change of a specific linear polarization component is used. The optical modulator that includes both the optical intensity modulator and the optical amplifier, modulates the phase difference between π and a certain value of θ, and θ is between 0.5π and 0.98π. 1 / [10si when the phase difference is δψ and the output light from the light intensity modulator is present in the optical amplifier.
An optical modulator characterized by performing optical amplification at least n ² (δψ / 2) times and at most 10 / [sin ² (δψ / 2)] times. 3. The optical modulator according to claim 1, wherein the refractive index change of the variable refractive index medium is induced by an electric field, a magnetic field, light, pressure, or heat. 4. The refraction index change of the refractive index variable medium is induced by a Pockels effect generated by applying an electric field to the refractive index variable medium, and the electric field is induced by the Pockels effect. A light intensity modulation function manifesting part of a Mach-Zehnder type optical waveguide that applies an ultrashort electrical signal pulse to the electrode along the variable rate medium by a traveling wave operation that propagates the ultrashort electrical signal pulse in the same direction as the traveling direction of the light, and a semiconductor that emits light when a voltage is applied. An optical modulation device comprising a light amplification function expressing section consisting of 1 on a single chip.