JP2004347709A - Reciprocating optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reciprocating optical modulator which supplies a modulation signal via an electric supply line with a band width narrower than a frequency of the modulation signal although it can modulate light with a modulation signal of a wide band width. <P>SOLUTION: The reciprocating optical modulator is disposed on an individual optical crystal block or multiple optical crystal blocks and exists on a continuous optical path and is equipped with an optical path 3 with an amplifying function (1), an optical modulation part 4 formed on the optical path with the amplifying function (2), a first light wave filter 2 and a second light wave filter 6 arranged so as to put the optical modulation part in between (3) and a construction (wavelength-multiplexer 8) to introduce pump light to excite the optical path 3 with the amplifying function (4). Also the first light wave filter is constructed so as to input incident light and to reflect modulated light of the incident light (5) and the second light wave filter is constructed so as to reflect the incident light and to output the modulated light of the incident light (6). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reciprocating optical modulator that can modulate light with a high-frequency signal with a simple configuration and that can be downsized.
[0002]
[Prior art]
A configuration in which a laser beam is introduced into a kind of light reflection resonator, and a higher-order sideband is obtained by modulating the light a plurality of times while the light reciprocates therethrough. Patent Document 1 discloses a multiplied light modulation device that has a bandpass filter that allows a sideband wave to pass through, and that can obtain light whose intensity is modulated at a frequency that is an integral multiple of the frequency of an input high-frequency electric signal. . Patent Document 1 also discloses a configuration in which an optical amplifier is provided in the reflection resonator.
[0003]
Further, Non-Patent Document 1 discloses a laser device shown in FIG. 6 in which an optical path, a reflective layer, and a grating region for reflection are provided in a lithium niobate (LiNbO ₃ ) crystal mixed with erbium (Er). I have.
[0004]
In addition, as shown in FIG. 7, a laser device in which a reflection grating region is provided instead of the above-described reflection layer, and a region sandwiched between the two reflection grating regions is an optical resonator is disclosed in Non-Patent Document 1. It is described in reference 2.
[0005]
An optical modulator in which a Mach-Zehnder optical interferometer is formed on a lithium niobate (LiNbO ₃ ) crystal is already well known.
[0006]
According to the present invention, with respect to output light whose intensity is modulated at a frequency that is an integral multiple of the frequency of the input high-frequency electric signal, light having higher intensity can be easily obtained than the invention described in Patent Document 1.
[0007]
[Patent Document 1]
JP 2000-6275 A
[Non-patent document 1]
Ch. Becker, et al. , "Integrated optical Ti: Er: LiNbO ₃ distributed Bragg reflector laser with a fixed photorefractive grating", OPTICS RETTERS, Vol. 23, No. 15, 1194-1196, August 1, 1998.
[Non-patent document 2]
B. K. Das, et al. _{, "Single-frequency Ti: Er} : LiNbO 3 distributedBragg reflector waveguide laser with thermally fixed photorefractive cavity", Appl. Phys. , B73, 439-442 (2001).
[0009]
[Problems to be solved by the invention]
The multiplied light modulation device disclosed in Patent Document 1 can obtain modulated light including a higher-order sideband, but the higher the order, the lower the obtained output intensity tends to be. Therefore, a configuration using an optical amplifier to increase the output intensity is disclosed. Generally, in order to improve the response speed, it is necessary to shorten the length of the reciprocating optical path. However, a configuration that can be downsized is not disclosed, and modulation cannot be performed with a modulation signal having a wide bandwidth. Further, the laser device described in Non-Patent Document 1 or 2 can be used as an oscillator or an amplifier, but cannot be used as an optical modulator. Further, in a Mach-Zehnder type optical modulator formed on a lithium niobate (LiNbO ₃ ) crystal, it is difficult to obtain a high-order sideband with a high-frequency electric signal having a small amplitude.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above, and it is possible to easily modulate light with a high-frequency signal with a simple configuration and to reduce the size, even though the modulation can be performed with a modulation signal having a wide bandwidth. The present invention relates to a reciprocating frequency doubler optical modulator that can be used.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the first feature of the present invention is not limited to whether it is formed and provided in a single optical crystal, or formed and provided in a plurality of optical crystals, Each of the following is formed on a continuous optical path, (1) an optical path having an amplifying action, (2) an optical modulator formed on the optical path having an amplifying action, and (3) A first optical filter and a second optical filter provided so as to sandwich the optical modulator, and (4) a configuration for introducing excitation light for exciting the optical path having the amplifying action. (5) The first optical filter is configured to input the incident light and reflect the modulated light, and (6) the second optical filter reflects the incident light and reflects the incident light. And outputting the modulated light.
[0012]
The second feature is that the third optical filter is provided in particular. However, as a whole, the optical filter is formed and provided on a single optical crystal, or is formed separately on a plurality of optical crystals. The following are formed on a continuous optical path, regardless of whether they are formed. (1) An optical path having an amplifying action, and (2) An optical path having an amplifying action. An optical modulator, (3) a first optical filter and a second optical filter provided so as to sandwich the optical modulator, and (4) an optical modulator between the optical modulator and the second optical filter. A third optical filter for removing incident light, and (5) a configuration for introducing excitation light for exciting the optical path having the amplifying action, and (6) first optical filtering. The filter is configured to receive the incident light and reflect the modulated light, and (7) the second optical filter includes: Reflect light, it is to have a structure that outputs light obtained by modulating the incident light.
[0013]
The third feature is that (1) the optical crystal is lithium niobate (LiNbO ₃ ), and (2) the light modulating section is a voltage applied to an electrode on an optical path provided by diffusing impurities. (3) an optical path having an amplifying action is formed by doping the optical crystal with erbium (Er); 4) The first optical filter and the second optical filter, or the first optical filter, the second optical filter, and the third optical filter use the periodic pattern provided on the optical crystal. That is, it uses an optical filter that has been used.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Unless otherwise specified, the same reference numerals are used for the same components or components having the same functions in the drawings.
[0015]
An embodiment of the present invention is shown in the block diagram of FIG. The input light in FIG. 1 is light having a single frequency f ₀ , but the configuration in FIG. 1 uses an excitation light and a multiplexing unit 8 to excite an optical path having an amplifying function described later. And enters the first optical filter 2. The first optical filter 2 is a narrow band filter. This is the input light of frequency f ₀ is transmitted, the light slightly displaced from the frequency is a filter having a characteristic that reflects. The optical path 3 having an amplifying action is formed in a region 12 doped with Er (erbium), and is excited by the excitation light source 7. The optical modulator 4 is a light intensity modulator that can modulate the light from the first optical filter 2 to the second optical filter 6 or the light in the opposite direction with the same characteristic of the modulation frequency fm. It is a vessel. The second optical filter 6 is a band limiting filter that reflects up to an n-th (n ≧ 3, for example, n = 3) sideband, but transmits other light. Has characteristics. The third optical filter 5, in order to prevent the use of excitation energy stored in the exciting medium in the optical path 3 with amplification effect wasted, thereby preventing the input light frequency f _0. Even if the third optical filter 5 is not provided, the reciprocating optical modulator of the present invention operates, but is preferably provided to prevent useless amplification. Further, the optical path 3 having the amplifying function compensates for the attenuation of the light intensity occurring in the first, second or third optical filter or the optical modulator. It is possible to operate without it.
[0016]
When configured as above, as shown in FIG. 2, the incident light of frequency f ₀ inputted through the first optical filter is amplified in the optical path with amplification function, is modulated, shown in FIG. 1 (b) Although sidebands occur, linear modulation is assumed to be performed for simplicity, and therefore only the carrier and the first double-sideband are generated. This light is input to the third optical filter, and the incident light is suppressed. Since the input light having the frequency f ₀ is removed by the third optical filter, the light returns to the first optical filter again, and the reflected light becomes only the sideband, and the input light is not amplified. Therefore, it is possible to prevent energy consumption for that purpose.
[0017]
The light once modulated and reflected by the second optical filter passes through the light intensity modulator again. At this time, both sidebands are modulated, resulting in a spectrum shown in FIG. Of these lights, the carrier is suppressed by the third optical filter, so that almost only the sideband is present as shown in FIG. This light is amplified in the optical path 3 to recover the loss, is reflected again, is further modulated, and has the spectrum shown in FIG. Due to this modulation, first-order and third-order sidebands are generated. The third-order sidebands shown in FIG. 1 (g) pass through the band-limiting filters of the second optical filters so that the third-order sidebands pass therethrough. Give a limiting characteristic. With this setting, the first-order sideband shown in FIG. 1F is reflected. As described above, the third-order sideband is output from the band-limiting filter.
[0018]
In the above description, the optical modulator is an intensity modulator. However, it can be easily understood that the same effect can be obtained even if a phase modulator or a single sideband modulator is used. The modulator applicable to the present invention includes a resonance type modulator and a traveling wave type modulator. As is natural for a resonance type modulator, even for a traveling wave type modulator, it is possible to modulate light in either direction with the same characteristics by providing electrodes at both ends and inputting a modulation signal from them. it can.
[0019]
The optical path 3, the modulating unit 4, the first optical filter 2, the second optical filter 6, and the third optical filter 5 having an amplifying function in FIG. 1 are composed of, for example, one LiNbO ₃ crystal as shown in FIG. It is formed above. The method of forming each part is already well known, and can be formed, for example, as follows. First, an X-cut LiNbO ₃ crystal 20 is prepared so that its longitudinal direction is the C-axis of the crystal. Next, Er (erbium) is doped to form an optical path having an amplifying action, and Fe (iron) is doped to portions where the first, second, and third optical filters are formed. Next, a waveguide serving as an optical path is formed by diffusing Ti (titanium). The optical modulator shown in FIG. 3 is of a Mach-Zehnder type. Next, a diffraction grating is formed by holography using an argon ion laser while heating the LiNbO ₃ crystal. Further, a film of silicon oxide is formed on the LiNbO ₃ crystal, and a gold electrode is formed to form an optical modulator.
[0020]
In the configuration of FIG. 1, the excitation light is incident from the first optical filter 2, but it is also effective to enter the excitation light from the second optical filter 6 as shown in FIG. By entering from both of these, more effective excitation is performed.
[0021]
Each part shown in FIG. 1 or FIG. 4 does not necessarily need to be formed on one LiNbO ₃ crystal 20 as shown in FIG. 3. For example, as shown in FIG. If the LiNbO ₃ crystal 21 or LiNbO ₃ crystal 23 in the direction does not coincide with the LiNbO ₃ crystal 22 in the crystal direction in which the modulation portion is easily formed, each is formed on a different crystal, and then bonded with an adhesive. , And FIG. In this way, the method of manufacturing each part separately and then joining them has an advantage that each part can be optimized and manufactured.
[0022]
1, 3, 4 or 5 is a laser beam having a wavelength of 1,550 nm. The excitation light source 7 of the optical modulator 4 is a semiconductor laser having a wavelength of 980 nm and an output of 200 mW. Laser light output from the semiconductor laser is introduced into an optical path by a multiplexer 8. At this time, it is desirable to use the isolator 9 in order to prevent the excitation light source from becoming unstable due to the reflected light. The Er ions are excited by the laser light from the excitation light source 7, and the input light or its modulated light is amplified by the excitation. The purpose of this amplification is to compensate for the attenuation of light that occurs in the optical path, the optical modulator, the first optical filter, the second optical filter, or the third optical filter, and the amplification degree is too large, and When an optical resonator is formed by reflection occurring in the first optical filter and reflection occurring in the second optical filter, laser oscillation may occur here. For this reason, it can be seen that there is an optimum region for the amplification degree of the optical path having the amplification effect.
[0023]
A modulation signal is supplied to the optical modulator, and when this modulation signal uses, for example, a third (or n) -order sideband, a frequency of 1/3 (or 1 / n) of a target modulation frequency is used. May be supplied. For this reason, when a third-order sideband is used, a signal near 1 GHz may be used as a modulation signal even when the modulation frequency is, for example, a signal near 3 GHz, which makes it difficult to amplify or transmit the modulation signal. Is greatly reduced.
[0024]
【The invention's effect】
According to the present invention, there are provided (1) an optical path having an amplifying action, and (2) an optical modulator formed on the optical path having an amplifying action, on a continuous optical path provided in one or a plurality of optical crystals. (3) a first optical filter and a second optical filter provided so as to sandwich the optical modulator, and (4) an excitation light for introducing an optical path having an amplifying action. And (5) the first optical filter is configured to input the incident light and reflect the modulated light, and (6) the second optical filter reflects the incident light. Then, it is configured to output the light obtained by modulating the incident light and to output the optical sideband wave which is a natural number multiple of the modulation signal. Therefore, the configuration is simple and small, and the amplifier of the modulation signal is relatively narrow bandwidth. And the power can be supplied using a power supply line, and the handling of the modulated signal becomes easy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of the present invention.
FIG. 2 is a block diagram showing an operation of reciprocating multiplication optical modulation.
FIG. 3 is an overhead view showing an embodiment of the present invention using a single crystal.
FIG. 4 is an overhead view showing an embodiment of the present invention using two excitation light sources.
FIG. 5 is an overhead view showing an embodiment of the present invention using a plurality of crystals.
FIG. 6 is a bird's-eye view showing a laser using a LiNbO ₃ crystal, which is a first conventional example.
FIG. 7 is a bird's-eye view showing a laser using a LiNbO ₃ crystal, which is a second conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 Reciprocating frequency modulator 2 First filter 3 Optical path with amplifying action 4 Optical modulator 5 Third filter 6 Second filter 7 Excitation light source 8 Multiplexer 9 Amplifier 10 Waveguide 11 Modulation electrode 12 Er is doped Regions 20, 21, 22, 23 LiNbO ₃ crystal

Claims (3)

(1) an optical path having an amplifying action and (2) an optical modulation section formed on the optical path having an amplifying action provided on one or a plurality of optical crystals and on a continuous optical path; A) a first optical filter and a second optical filter provided so as to sandwich the optical modulator, and (4) a configuration for introducing excitation light for exciting the optical path having an amplification effect. (5) The first optical filter is configured to input the incident light and reflect the modulated light, and (6) the second optical filter reflects the incident light and reflects the incident light. A reciprocating frequency doubler optical modulator having a configuration for outputting modulated light. (1) an optical path having an amplifying action and (2) an optical modulation section formed on the optical path having an amplifying action provided on one or a plurality of optical crystals and on a continuous optical path; And (4) a first optical filter and a second optical filter provided so as to sandwich the optical modulator, and (4) an optical filter provided between the optical modulator and the second optical filter. A third optical filter that removes the light; and (5) a configuration for introducing excitation light that excites the optical path having the amplifying action. (6) The first optical filter receives incident light. And (7) the second optical filter is configured to reflect the incident light and output the modulated light. Light modulator. (1) The optical crystal is made of lithium niobate (LiNbO ₃ ), and (2) the light modulating section controls the electro-optical effect induced according to the voltage applied to the electrode on the optical path provided by diffusing the impurities. (3) an optical path having an amplifying action is formed by doping erbium (Er) into the optical crystal, and (4) a first optical filter and The second optical filter, or the first optical filter, the second optical filter, and the third optical filter, each using an optical filter using a periodic pattern provided on the optical crystal. The reciprocating optical modulator according to claim 1 or 2, wherein:

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