JPH05323247A - Optical resonator array - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a practical optical resonator array with high stability and no error between resonators. In an optical resonator array in which a plurality of waveguide type resonators are provided adjacent to each other in parallel on the same substrate, the plurality of waveguide type resonators 2 are made of a waveguide medium having an electro-optical effect. Means for controlling the refractive index of the waveguide medium by applying a predetermined voltage and the temperature stabilizing device 11 are provided. A reference light modulated at a predetermined frequency is incident on one of the plurality of waveguide resonators 2, and a deviation between the reference light and one resonance frequency of the waveguide resonator 2 is given. Means are provided for returning an electric signal to the waveguide medium and the temperature stabilizing device 11 via electrodes to control the refractive index of the waveguide medium. Further, the reference light is made incident on one of the plurality of waveguide type resonators 2 while modulating the length of the waveguide type resonator at a predetermined frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical resonator array, and more particularly to an optical resonator used as an optical frequency standard of a transmission source and an optical frequency selection filter of a receiving unit in large-capacity frequency division multiplexing optical communication. It is about arrays.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a schematic configuration of a conventional optical resonator array, 1 is an optical medium substrate on which a waveguide type resonator 2 is formed, 2 is a waveguide type resonator, Three
Is a high reflection film, 4 is incident light, and 5 is outgoing light. In FIG. 7, only three waveguide type resonators 2 are shown, but actually, several tens or more waveguide type resonators 2 are included.

In the optical resonator array having such a structure, a plurality of incident lights 4 are incident on the waveguide type resonator (core) 2. The waveguide resonator 2 has the resonance peak characteristic shown in FIG. 8 of the resonance frequency interval determined by the interval of the reflection film 3. When a plurality of incident lights 4 are incident, a plurality of emitted lights 5 that pass through this resonance characteristic are obtained.

[0004]

However, in such a conventional optical resonator array, due to the temperature dependence and thermal expansion of the refractive index of the optical medium used as the waveguide type resonator 2, its resonance is caused by the fluctuation of the outside air temperature. The characteristics will change. In addition, due to variations in the waveguide length of each waveguide resonator 2, no matter how much effort is made to make them uniform, the resonance characteristics are not uniform.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a practical optical resonance having a high stability without an error between waveguide type resonators. To provide an instrument array.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0007]

In order to solve the above-mentioned problems, the means (1) of the present invention is an optical system in which a plurality of waveguide type resonators are provided adjacent to each other in parallel on the same substrate. In the resonator array, the plurality of waveguide type resonators are made of a waveguide medium having an electro-optical effect, a means for applying a predetermined voltage to control the refractive index of the waveguide medium, and a temperature stabilizing device. Is the most important feature.

According to a second aspect of the present invention, in the optical resonator array according to the first aspect, one of the plurality of waveguide type resonators has a reference light modulated at a predetermined frequency. Of the reference light and one of the resonance frequencies of the waveguide type resonator is returned to the waveguide medium and the temperature stabilizing device via an electrode as an electric signal, It is characterized in that means for controlling the refractive index is provided.

According to a third aspect of the present invention, in the optical resonator array according to the first aspect, the plurality of waveguide type resonators are modulated while modulating the length of the waveguide type resonator at a predetermined frequency. A reference light is made incident on one of the two, and a deviation between the reference light and one resonance frequency of the waveguide type resonator is fed back to the waveguide medium and the temperature stabilizing device as an electric signal via an electrode. However, a means for controlling the refractive index of the waveguide medium is provided.

[0010]

According to the above-mentioned means, a plurality of waveguide type resonators are formed on the same substrate, and further, the plurality of waveguide type resonators are made of a waveguide medium having an electro-optical effect, and are temperature stable. The stability is improved by having a chemical device. Further, the reference light is made incident on one of the plurality of waveguide type resonators, and a deviation between the reference light and one resonance frequency of the waveguide type resonator is converted into an electric signal as an electric signal through the electrode to form the waveguide medium. Also, the resonance frequency is stabilized by returning to the temperature stabilization device and controlling the refractive index of the waveguide medium, thus realizing a highly accurate and highly stable optical resonator array that could not be achieved until now. can do.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[Embodiment 1] FIG. 1 is a perspective view showing an external configuration of an optical resonator array of Embodiment 1 of the present invention, and FIG. 2 is a block diagram showing a schematic configuration of FIG. Example 1
As shown in FIGS. 1 and 2, the optical resonator array of is an optical medium substrate (optical resonator waveguide substrate) 1 on which a plurality of waveguide type resonators 2 are formed, and a waveguide type resonance including a waveguide. Stabilizing device (temperature adjusting device) 11, which includes a resonator (optical resonator) 2, a highly reflective film 3, a Peltier element, and the like, an electrode 12,
A weighting circuit 13 is provided. In FIG. 2, only three waveguide type resonators 2 are shown, but actually, several tens or more waveguide type resonators 2 are included.

In the waveguide type resonator 2, when the voltage between the electrodes 12 is changed, the refractive index is changed due to the electro-optical effect, and therefore the resonance frequency is changed, and the transmission characteristic corresponding to the change is obtained.

By the way, no matter how much the two end faces of the waveguide type resonator 2 are made parallel, an error of about 0.1 degree occurs, so that, for example, 100 waveguide type resonators 2 are formed every 250 μm. If formed, the required optical medium substrate 1
Has a length W of 25 mm, and the error length ΔLe of the length L of the first and the 100th waveguide resonators 2 is

[0015]

## EQU1 ## ΔLe = W × tan (0.1 °) = 0.044 mm (1) For example, frequency division multiplexing (F
DM) When it is intended to be used for optical communication, its waveguide type resonator length L is

[0016]

L = C / (2n ₁ f) (2) where C is the speed of light (2.998 × 10 ⁸ m / s), n ₁ is the refractive index of the waveguide, and for example LiNbO ₃ is 2.14, f
Is the frequency interval (2.5 GHz). Therefore, if the waveguide type resonator length L is 28 mm, then ΔLe / L
= 0.0063, an error of ± 63 MHz occurs.

Therefore, the voltage is generated in advance in the electrode 12 through the weighting circuit 13 so as to compensate for the error.

The stability of the resonance peak frequency of the waveguide resonator 2 was examined in order to consider the influence of the fluctuation of the waveguide resonator length L on the characteristics of the waveguide resonator 2. For example, the temperature coefficient of the refractive index of LiNbO ₃ is Δn _T / n ₁ = 3.
8 × 10 ⁻⁵ deg ⁻¹ , thermal expansion coefficient ΔL _T / L = 1 × 1
It is about 0 ^-6 deg ^-1 , and the temperature coefficient of the refractive index is extremely large, and the thermal expansion coefficient can be ignored. Temperature 1 degree (de
g. When the temperature change of f per) is Δf _T , from equation (2),

[0019]

[Equation 3]

[0020]

By the way, a certain resonance peak frequency is F
₀ (193420 GHz, wavelength λ = 1.55 μm), and the number of modes is m,

[0022]

Equation 4] _{F 0 = mc / (n 1} L) = a mf (4), the temperature change △ f ₀ of f ₀ per 1deg is

[0023]

ΔF ₀ = mΔf _T = −7.4 GHz / deg (5)

Therefore, when the ambient temperature is controlled to ± 0.01 ° C. or lower by using the temperature stabilizer 11, about ± 7
A 0 MHz stability was obtained.

[Second Embodiment] FIG. 3 is a block diagram showing a schematic structure of a stabilized optical resonator array according to a second embodiment of the present invention. In the second embodiment, as shown in FIG. 3, an optical medium substrate (optical resonator waveguide substrate) 1 on which a plurality of waveguide type resonators (optical resonators) 2 are formed, and a waveguide type including a waveguide A resonator (optical resonator) 2, a highly reflective film 3, a temperature stabilizing device (temperature adjusting device) 11 including a Peltier element, an electrode 12, a weighting circuit 13 such as an electric filter, a reference semiconductor that oscillates at a predetermined optical frequency. A laser 21, a photoelectric conversion light receiver 22, a high frequency electric signal oscillator 23, a phase detector or a lock-in amplifier 24 are provided. In Figure 3,
Similar to FIG. 2, only three waveguide resonators 2 are shown,
Actually, it is composed of several tens of waveguide type resonators 2.

In the waveguide type resonator (optical resonator) 2, by changing the voltage between the electrodes 12, the refractive index is changed by the electro-optical effect, and therefore the resonance frequency is changed, and the transmission characteristics are changed accordingly. Is obtained.

Next, the operation of the stabilized optical resonator array of the second embodiment will be described with reference to FIG.

The emitted light from the reference semiconductor laser 21 passes through one of the waveguide resonators 2 and is photoelectrically converted by the photoelectric conversion light receiver 22. At that time, the reference semiconductor laser 2
Reference numeral 1 refers to the modulation signal from the high-frequency electrical signal oscillator 23 and is subjected to predetermined frequency modulation, and outputs frequency-modulated light. In the waveguide resonator 2, a frequency change of light is converted into a light intensity change due to the frequency dependence of the transmittance. That is, the frequency difference between the center frequency of the frequency-modulated light and one resonance peak frequency of the waveguide resonator 2 is detected.

The transmitted light of the waveguide resonator 2 is received by the photoelectric conversion photodetector 22, converted from an optical signal to an electric signal, and sent to the phase detector 24. The phase detector 24 compares the phase with the reference signal of the high frequency electric signal oscillator 23 to generate an error signal according to the frequency difference, and the error signal is generated by the electric filter, the weighting circuit 13, the temperature stabilizing device (temperature adjusting device). An electric field is applied to the optical medium through the (device) 11 and the electrode 12, and the refractive index of the optical medium is changed to stabilize the waveguide resonator length L.

For example, in the device configuration shown in FIG. 3, In oscillating in the wavelength of 1.55 μm as the reference semiconductor laser 21
GaAsP distributed feedback semiconductor laser (DFB type L
D) which was stabilized using an isotope-substituted acetylene gas ( ¹³ C ₂ H ₂ ) as a frequency reference was used. The frequency of the high frequency electric signal oscillator 23 was 100 MHz. This frequency-stabilized light was made incident on the waveguide resonator (optical resonator) 2.
As the optical medium substrate (optical resonator waveguide substrate) 1, Li
NbO ₃ was used. The resonance frequency interval is 2.5 GHz. Waveguide loss is 0.2 dB / cm, reflectance is 80%
Is. 100 waveguide type resonators 2 were formed every 0.25 mm.

Here, the optical path length is stabilized by the Pockels effect. With the maximum possible applied electric field of 10 V / μm,
A change of Δn = 1.6 × 10 ⁻³ is obtained. This corresponds to a resonance frequency change of about 300 GHz, which is sufficient as a variable range. The variable width is ± 10 GHz and can be controlled by an applied voltage of ± 300 mV.

The phase detector 24 detects the phase of the 100 MHz modulated light component of the reference semiconductor laser 21, and the resonator length of the waveguide resonator 2 is stabilized to ± 2 MHz (applied voltage 60 μV) or less. The stabilization band is 100 ns. This stability corresponds to 3 / ± 10000 ° C. when converted into temperature fluctuation.

By the way, the frequency shift amount per degree is 7.
At 4 GHz, as can be seen from equations (3) and (5),
Since it is a constant value regardless of the resonator length of the waveguide resonator 2, the similar effect can be obtained by the similar stabilization even in the adjacent waveguide resonator 2. FIG. 4 shows a transmission characteristic diagram of the optical waveguide array in which the resonance peaks are mutually stabilized. It can be seen that the resonance peaks of the adjacent waveguide resonators 2 overlap.

[Embodiment 3] FIG. 5 is a block diagram showing a schematic construction of Embodiment 3 of the optical resonator array of the present invention. Instead of modulating the reference semiconductor laser 21 of Embodiment 2, a waveguide is used. This is an example of a case where the waveguide length of the mold resonator 2 is modulated to obtain an error signal. In this case, since a means for modulating the laser is unnecessary, a very compact system can be realized.

As described above, the optical resonator array in which the resonance frequency is stabilized can be used as the optical frequency standard of the transmission source and the optical frequency selection filter of the reception source in large capacity frequency division multiplexing optical communication. If used as an optical frequency standard, for example, 10G
A plurality of laser light sources stabilized for each Hz can be realized.

FIG. 6 is a block diagram showing a schematic configuration of an example in which a plurality of lasers are simultaneously stabilized by using the stabilizing optical resonator of the third embodiment, and 51 and 51 'are a plurality of frequency multiplexing units. Lasers (stabilized lasers) 52 and 52 'are photodetectors and 53 and 53' are phase detectors. The modulation signal of the high frequency electric signal oscillator (modulator) 23 is applied to the electrode 12 of the waveguide resonator 2 to obtain an error signal between the resonance peak of the waveguide resonator 2 and the oscillation frequency of the laser, and the laser is fed to the laser. It is stabilized by negative feedback.

As the optical medium, LiNbO ₃ and LiTa are used.
O ₃ , LiIO ₃ , BaTiO ₃ , GaAs, ZnO, P
bMoO ₄ , ADP (NH ₄ H ₂ PO ₄ ), KDP (KH ₂
PO ₄ ), RDA (RbH ₂ AsO ₄ ), CDA (C ₂ H ₂
AsO ₄ ) or Ba ₂ NaNb ₅ O ₁₆ can also be used.

Although the direct modulation is used for the modulation of the reference semiconductor laser 21 in FIG. 3, the same effect can be obtained by using a modulator having another structure such as an acousto-optic modulator or an electro-optic modulator. Can be obtained.

Although the present invention has been specifically described based on the embodiments, it is needless to say that the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. ..

[0040]

As described above, according to the present invention, a plurality of waveguide type resonators are formed on the same substrate, and the plurality of waveguide type resonators have an electro-optical effect. Stability can be improved by including a medium and providing a temperature stabilizing device. Further, the reference light is made incident on one of the plurality of waveguide resonators, and the deviation between the reference light and one resonance frequency of the resonator is fed back to the waveguide medium and the temperature stabilizing device as an electric signal. However, by controlling the refractive index of the waveguide medium and stabilizing the resonance frequency, it is possible to realize a highly accurate and highly stable optical resonator array that has not been achieved so far.

[Brief description of drawings]

FIG. 1 is a perspective view showing an external configuration of a first embodiment of an optical resonator array of the present invention,

FIG. 2 is a block configuration diagram showing a schematic configuration of Example 1 of the optical resonator array of the present invention,

FIG. 3 is a block configuration diagram showing a schematic configuration of a stabilized optical resonator array according to a second embodiment of the present invention,

FIG. 4 is a diagram for explaining an example of a resonance peak when stabilized in the second embodiment;

FIG. 5 is a block configuration diagram showing a schematic configuration of Example 3 of the optical resonator array of the present invention,

FIG. 6 is a block configuration diagram showing a schematic configuration of an example in which the stabilized optical resonator array of Example 3 of the present invention is applied to stabilization of a plurality of semiconductor lasers,

FIG. 7 is a block configuration diagram showing a schematic configuration of a conventional optical resonator array,

FIG. 8 is a diagram for explaining resonance peaks of a plurality of optical resonators.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical medium substrate (optical resonator waveguide substrate), 2 ... Waveguide type resonator (optical resonator), 3 ... High reflection film, 4 ... Incident light, 5 ... Emission light, 11 ... Temperature stabilizing device, 12 ... electrodes,
13 ... Weighting circuit, 21 ... Reference semiconductor laser, 22 ...
Photoelectric conversion photodetector, 52, 52 '... Photodetector, 23 ... High-frequency electrical signal oscillator, 24, 53, 53' ... Phase detector,
51,51 '... Stabilized laser.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Ito 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. An optical resonator array in which a plurality of waveguide type resonators are provided adjacent to each other in parallel on the same substrate, wherein the plurality of waveguide type resonators are made of a waveguide medium having an electro-optical effect. An optical resonator array comprising: a means for controlling a refractive index of the waveguide medium by applying a predetermined voltage; and a temperature stabilizing device. 2. The optical resonator array according to claim 1, wherein a reference light modulated at a predetermined frequency is incident on one of the plurality of waveguide resonators, and the reference light and the reference light are combined. A means for controlling a refractive index of the waveguide medium by returning a deviation from one resonance frequency of the waveguide resonator to the waveguide medium and the temperature stabilizing device via an electrode as an electric signal is provided. An optical resonator array characterized in that 3. The optical resonator array according to claim 1, wherein the reference light is incident on one of the plurality of waveguide resonators while modulating the waveguide resonator length at a predetermined frequency. Then, the deviation between the reference light and one resonance frequency of the waveguide resonator is returned to the waveguide medium and the temperature stabilizing device as an electric signal through the electrode, and the refractive index of the waveguide medium is returned. An optical resonator array, characterized in that means for controlling the optical resonator are provided.