JPS6028621A - Optical modulator and optical frequency controller - Google Patents

Abstract

PURPOSE:To obtain easily an intended stable phase difference and to make manufacture easy by providing a difference in optical path to two branch waveguides. CONSTITUTION:An input waveguide 2 is branched to two waveguides 3, 4 at a point B and are joined to each other at a point E to form an output waveguide 5. The waveguide 4 has the path length longer by 1384Angstrom which is half the wavelength 2768Angstrom of the light-emitted from an He-Ne laser in the crystal than the other waveguide 4. All the waveguides 2-5 have about 5-10mum path width. The two waveguides 3, 4 are parallel straight lines spaced at about 100mum in the parts CD, FG forming electrodes 6, 7. The electrodes 6, 7 exist right above said parallel straight lines and have about 5-10mum width and 5mm. length. When the electrodes are formed in the above-mentioned difference in path length, about 2mm. is required as the length of BC(BF). Optical fibers, etc. are connected to an input part A and an output part H.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to optical modulators and optical frequency controllers, and more particularly, to a stable optical amplitude modulator and a method for generating a stable frequency difference from a single frequency input light. This invention relates to an optical frequency controller that provides two types of light.

Prior Art and Problems Optical heterogain measurements are possible by controlling the optical frequency, but in order to perform these measurements accurately and efficiently, it is necessary to obtain two lights with a stable frequency difference. Conventionally, devices for providing such light (optical frequency controllers) have utilized the Zeeman effect or optical diffraction caused by ultrasonic waves to generate two lights with different frequencies.

In an optical frequency controller that uses the Zeeman effect, a magnetic field is applied to the laser to cause Zeeman separation, and two
Two lights with different frequencies are obtained by extracting the two lights as right-handed and left-handed circularly polarized lights, and then separating them using a quarter-wave plate and a polarization series. However, with this optical frequency controller, the difference in frequency between the two obtained lights depends on the magnetic field, it is difficult to set the magnetic field arbitrarily, so there is a limit to the frequency difference, and linearly polarized light is emitted. There are problems such as the inability to apply a semiconductor laser and the inability to miniaturize the device because a quarter-wave plate and polarizing prism are used.

In an optical frequency controller using ultrasonic waves, a laser beam is split into two by a half mirror, one of the beams is used as is, and the other beam is guided to an ultrasonic frequency modulator.
By performing frequency modulation using the black reflection condition, light having a frequency different from that of the other light is obtained. However, with this optical frequency controller, there is a limit to the frequency difference that can be set due to the plastic reflection conditions, and ultrasonic frequency modulators generate heat because they require large driving power, so countermeasures are needed. There are problems such as being

In addition, as an optical modulator used in such optical frequency controllers, a Gutshisol type optical path using a Matsuno-Zehnder interferometer, that is, one optical path is once branched into two optical paths, and then one In an optical path that has a unified optical path, an electric field is applied to the two branched optical paths to change the refractive index, causing a phase change that is equal in size and opposite in sign, and A material with a different refractive index is inserted into one of the optical paths of the branched paths, and the refractive index is changed using an external electric field to change the phase of the light.
Some devices modulate the amplitude of light by combining light from two optical paths. However, the method of inserting substances with different refractive indexes into the optical path is difficult to control, and it is difficult to obtain a specific phase change. In addition, the method of changing the refractive index by applying an external electric field to one branch path causes the phase change to vary;
There are disadvantages such as requiring an extra IU source.

Purpose of the Invention In view of the prior art as described above, the present invention provides an easy-to-manufacture optical modulator that provides stable optical amplitude modulation, and
2 with a more stable frequency difference from a single frequency input light
The present invention aims to provide an optical frequency controller that provides two types of light.

Structure of the Invention In order to achieve the above object, the present invention forms a Matsuhatsu Enda-shaped waveguide in or on a dielectric substrate, and utilizes electro-optic effect, magneto-optic effect, etc. in the two branch waveguides. The two branch waveguides are configured so that they can give refractive index changes of equal magnitude and opposite sign, and the phase of the input light is changed to the equivalent of a half wavelength without changing the refractive index due to electro-optic effects, etc. To provide an optical modulator having a path length difference such that the path length is changed by a certain amount.

Since the optical modulator according to the present invention has a structure that provides a phase difference to light by providing a path length difference between two branch waveguides, it is easy to obtain a desired phase difference and it is advantageous. The resulting phase difference is stable and easy to manufacture, making it suitable for mass production.

The type of light applicable to the optical modulator according to the present invention is not particularly limited. However, the commonly used light is, for example, a He-No laser beam with a wavelength of 6328X, a wavelength of 8500X or 13000X, a 1550X
Examples include 0X semiconductor laser light.

In order to achieve the above object, the present invention similarly provides two optical modulators according to the present invention in or on a dielectric substrate.
At the same time, the input light is split into two and input into the two optical modulators, the outputs from the two optical modulators are each split into two, and the two sets of branched outputs are each split into two. An optical frequency controller is provided in which a waveguide network is formed to synthesize signals with a phase difference of ±90° corresponding to a quarter wavelength.

The present invention will be explained in detail below using examples.

Embodiment of the Invention FIG. 1 shows an optical modulator according to an embodiment of the invention. FIG. 2 is a sectional view taken along line 1--2 in FIG.

Lithium niobate (LtNb) with dimensions of approximately 5x15m++ and thickness of approximately 0.5wII++, with the crystal C axis in the thickness direction.
o5) Spread titanium on the main plane of crystal plate 1 to a thickness of several hundred
After a certain degree of vapor deposition, the titanium is turned by i4 and heat treated at 950° C. for several hours to thermally diffuse the titanium, thereby forming waveguides 2 and 3°4.5. Next, alumina is deposited as a buffer layer directly above the two branched waveguides 3 and 4, and then aluminum electrodes 6 and 7 are deposited. Formation of a buffer layer is optional.

In FIG. 1, the input waveguide 2 is connected to the two waveguides 3 at point B.
, 4, and then merge at point E to form an output waveguide 5.
become. One branch waveguide 4 and another branch waveguide 3
The wavelength of the light emitted by the He-Ne laser in the crystal is 27.
It has a long path length of 1384X, which is half of 68X. Waveguides 2, 3, 4゜5 all have a path width of 5 to 10I.
It is about NL. Moreover, the two branch waveguides 3 and 4 are spaced apart by 100 μm in the portions CD and FG forming the electrodes 6 and 7.
They form parallel straight lines of about m. The electrodes 6 and 7 are located directly above this parallel straight line portion, and have a width of about 5 to 10 tails and a length of about 5 mm. When such an electrode is formed with the above path length difference, the length of BC (BF) is approximately 2 mm. Note that an optical fiber or the like is connected to the input section A1 and the output section H.

The wavelength 632 emitted by the Ha-No radar to this optical modulator
When 8X light is input, if no voltage is applied to the electrode 6.7, 180
Since a phase difference of 0 occurs, the output becomes 0. Electrodes 6, 7
When a voltage V is applied to the waveguides 3 and 4, an electric field of equal magnitude but opposite direction is applied to the waveguides 3 and 4, causing a change in the refractive index of equal magnitude but opposite sign due to the electro-optic effect. A phase difference of (k is a proportionality constant) is created. When the light waves that have a phase difference kv due to the electric field are combined at point E, they are combined with the above 180° phase difference! 111
An output (amplitude) proportional to 1 kV is given, and if kV is not very large, amplitude modulation proportional to V is applied.

FIG. 3 shows an optical frequency controller that is an embodiment of the present invention.

This optical frequency controller is also manufactured by thermally diffusing titanium onto a lithium niobate crystal plate 10 to form a waveguide 11, using the same method as in the manufacturing of the optical modulator described above.
3, 14, and 15 were formed. In the figure, the input waveguide IJ branches into two waveguides JB' and J13''.
becomes. The waveguide JB' branches into two waveguides B'σσ
Bi and! After becoming 3'F'σ Bi, the waveguide E'! Similarly, the waveguide JB" is branched into two waveguides B〃σ'TfF!' and B"rσ'B, and then the waveguides pj/f lc are combined. Electrodes 12.13 and 14.15 are formed directly above the unified tail sections C', D', F'G', and C"D"IF".

The waveguide JB' to the waveguide tH''t and the waveguide JR'' to the waveguide E!'1f' are substantially the same as the optical modulator shown in FIG. 1 described above.

The waveguides B' and B'Ir' are each branched into two, one each for H' and l('K, and the other for H').
'M and fM are combined into output waveguides KL and MN, respectively. Here, the waveguide H' has a waveguide EffK.
The path length is also shorter by a quarter of the wavelength of the Ha-Ne laser. Similarly, the waveguide fM has a shorter path length than the waveguide πM by a quarter of the wavelength.

Light of a single frequency ω is input to the input side IJ of this optical frequency controller, and Vl==V(11(nΔωt
1 electrode 14.15 V2 = V6ccsΔωt [in the formula,
vo represents a constant voltage of 2 to 3V, Δω represents a modulation frequency, and t represents time. ) is applied at the same time, the output side KL
and MN with the same wave numbers ω+Δω and ω−Δω are independently obtained. For details of the basic principle of this optical frequency fii controller, please refer to the specification and drawings of the patent application (Japanese Patent Application No. 58-76574) proposed by the present inventors. By separating the light of ω into two parts, giving them a phase difference of 90' and amplitude modulating them at a modulation frequency Δω, and combining the two obtained lights with a phase difference of ±90', the frequencies ω + Δω and ω − Δω are obtained. It is something that gives you the light of. According to this proposal, which is also adopted in the present invention, light having a stable frequency difference can be obtained. In the present invention, the above-described optical modulator structure is further incorporated into a dielectric crystal to obtain an external optical frequency controller that provides a more stable frequency difference and is small and easy to manufacture.

In the above example, in order to change the refractive index of the two branch waveguides of the optical modulator so that the sizes are equal and the signs are opposite, an electrode was formed directly above the waveguide and a voltage was applied. It is also possible to utilize the magneto-optical effect (electro-optic effect) by arranging an electromagnet with opposite polarity directly above the waveguide. Examples of dielectric crystals include LiNbO3 and L
Examples include iTaOx. The method of forming the waveguide, the type of electrode material, etc. are not limited to the above embodiments. Furthermore, when providing a path length difference in order to give a phase difference to light in an optical modulator or optical frequency controller, the path length difference is typically set to a half wavelength or a quarter wavelength, but an integer wavelength plus A path length difference of minus half wavelength or quarter wavelength may be used.

Effects of the Invention As is clear from the above questions, the present invention provides a compact optical modulator and optical frequency controller that achieve stable amplitude modulation and frequency control and are easy to control and manufacture.

[Brief explanation of the drawing]

Figure 1 is a plan view of the optical modulator, and Figure 2 is the line segment ■- in Figure 1.
3 is a cross-sectional view taken along section (3) and a plan view of the optical frequency controller. 1.10...dielectric, 2,3,4.5.1.1...
Waveguide, 6, 7, 12, 13, 14. 15... electrode.

Claims (1)

[Scope of Claims] (-1. A waveguide network is formed by branching a power waveguide in a substrate or on a substrate into two, and reuniting the branched waveguides to form an output waveguide; Electro-optic effect for the book branch waveguide,
A state in which the refractive index change is configured to be equal in magnitude and opposite in sign by utilizing a magneto-optic effect, and there is no change in the refractive index by providing a path length difference between the two branch waveguides. An optical modulator characterized in that the phase of input light is different by an amount equivalent to a half wavelength. 2. Branching the input waveguide into a first and second waveguide in or on the substrate, branching the first waveguide into a third and fourth waveguide, and branching the input waveguide into a third and fourth waveguide. waveguides are combined to form a fifth waveguide, the second waveguide is branched into a sixth and seventh waveguide, and the sixth and seventh waveguides are combined to form an eighth waveguide. waveguide, and the fifth waveguide is the ninth waveguide.
and branches into a tenth waveguide, and connects the eighth waveguide to the first waveguide.
The ninth and eleventh waveguides branch into the first and twelfth waveguides.
waveguides are combined to form a first output waveguide, and the first output waveguide is
A waveguide network is formed by combining the 0 and 12 waveguides to form a second output waveguide, and the phase of the input light to the third and fourth waveguides is different by an amount equivalent to a half wavelength. a path length difference such that the third and fourth waveguides are equal in size and opposite in sign; What is the phase of the input light to the waveguide? A path length difference is provided such that the path length differs by an amount equivalent to a half wavelength, and the refractive index change is configured to be equal in size and opposite in sign to the sixth and seventh waveguides, and A path length difference is given to the ninth waveguide so as to advance the phase of the input light by an amount equivalent to a quarter wavelength with respect to the eleventh waveguide, and An optical frequency controller characterized by providing a wave path with a path length difference that delays the phase of input light by an amount equivalent to a quarter wavelength.