JPH11311716A - Optical processor, and formation of optical processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the wavelength difference of insertion loss caused on an optical fiber transmission light in a wide wavelength range and to uniformize wavelength characteristics of the light loss in a specific wavelength range without adding any active optical function means. SOLUTION: An optical modulator module 100 is equipped with an optical modulator 110 having an optical waveguide 112 formed. Further, the optical modulator module 100 is equipped with a 1st lens 122, which is put in focus on light of the shortest wavelength λmin in a set wavelength range (shortest wavelength λmin to longest wavelength λmax), on an end surface of the optical waveguide 112 formed on a 1st end surface 110a of the optical modulator 110. Polarized waves of light signals P1 and P2 to be modulated are so set that their components of wavelength λmin are maximum with the insertion loss when the optical modulator module 100 is inserted into the optical transmission line. In this constitution, the optical modulator module 100 has the wavelength difference of the insertion loss reduced since wavelength characteristics of coupling loss and propagation loss cancel each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical processing device having at least an optical modulator and a method of forming the optical processing device.

[0002]

2. Description of the Related Art An electro-absorption type optical modulator using a semiconductor is
It is an optical function element that modulates light in an optical waveguide to be built by utilizing an electric field absorption effect of a semiconductor, and can realize conversion of an electric signal into an optical signal. Since such an electro-absorption type optical modulator can perform a high-speed optical modulation operation, in recent years, a single-wavelength optical communication system, particularly, a time-division multiplex (Time-Division Multi) has been proposed.
iplexing: Hereinafter, referred to as “TDM”. ) -Based optical communication systems are used to generate ultra-high-speed optical signals.

In recent years, there has been an increasing demand for an optical communication system having a Tbit / s class information capacity. Recently, an electro-absorption type optical modulator has become one of the next-generation large-capacity optical communication systems. Wave-division multiplexing (Wave-Divisional Mu) has attracted attention as a promising information transmission method.
ltiplexing: Hereinafter, referred to as “WDM”. Application to optical communication systems, WDM optical cross-connects, and the like, is also being studied.

Here, from the viewpoint of application to WDM optical communication systems (including WDM optical cross-connects), optical modulators currently on the market, including electroabsorption type optical modulators, will be examined. In a WDM optical communication system,
Light of a plurality of wavelengths is used as a carrier for information. Even in a WDM optical communication system, in a system configuration in which a certain optical modulator and a certain carrier correspond one-to-one, as in the case of the single-wavelength optical communication system, the optical communication is performed according to the corresponding wavelength. The optimum design of the modulator can be made individually.

[0005] However, if a system configuration in which a plurality of carriers are input to one optical modulator is adopted, it is necessary to modulate light of a plurality of wavelengths with one optical modulator. Therefore, for example, in an optical modulator in which characteristics such as insertion loss and extinction characteristics change remarkably for each wavelength, and driving conditions such as a bias voltage and a modulation amplitude voltage differ for each wavelength,
It becomes impossible to drive. The insertion loss refers to a loss of a signal generated in a transmission line due to insertion of a transducer, and in an optical communication system, an optical loss (Fi) when an optical processing device is inserted in an optical fiber transmission line.
bar-to-fiber transmission
n) corresponds to this.

From the above study, an optical modulator which has a small difference in characteristics over the range of wavelengths input into the system and can be driven under the same conditions is excellent from the viewpoint of application to a WDM optical communication system. You can see that it is. Also, in a WDM optical communication system, the polarization (polarization) of light used as a carrier may not be constant, so that an optical modulator applied to the WDM optical communication system is required to have characteristics that do not depend on polarization. You.

Conventionally, optical modulators operating at high speed mainly include:
There have been proposed two types, a Mach-Zehnder interference type using the principle of interference and an electro-absorption type using absorption change of a semiconductor. Among them, the Mach-Zehnder interference type optical modulator is not suitable for a system configuration in which a plurality of carriers are input because the driving conditions need to be largely changed for different wavelengths. In general, the polarization dependence is extremely large, and cannot be used particularly for WDM optical cross-connects.

On the other hand, the electro-absorption type optical modulator is smaller than the Mach-Zehnder interference type optical modulator in both the wavelength difference and the polarization dependence of the driving conditions. However, the extinction characteristic and the insertion loss of the electroabsorption optical modulator essentially have wavelength dependence as described below. That is, for the longest wavelength in the used wavelength region (hereinafter, referred to as “longest wavelength”), the insertion loss is the best, but the extinction efficiency is the worst. Also, conversely,
For the shortest wavelength (hereinafter referred to as “shortest wavelength”), the extinction efficiency is the best, but the insertion loss is the largest.

Regarding the wavelength difference of the extinction characteristic among the essential characteristics of the electro-absorption optical modulator having the wavelength dependency,
By setting the amplitude voltage in accordance with the longest wavelength, the required extinction ratio can be satisfied even at the shortest wavelength. That is, the wavelength difference of the extinction characteristic can be covered by the driving conditions.

However, it is difficult to compensate for the wavelength difference of the insertion loss by simply adjusting the setting of the driving condition. Although it is certain that the wavelength difference of the insertion loss can be reduced to some extent by making the bias voltage shallow, this method still has a problem that the effect of the pattern effect and the deterioration of the response speed occur. For this reason, when the electroabsorption optical modulator is applied to a WDM optical communication system, how to suppress the wavelength fluctuation of the insertion loss (the worst value can be obtained at the shortest wavelength) in the wavelength range of the input light is determined. This is an important issue.

As a conventional optical processing apparatus to which an optical modulator is applied, for example, “High-speed Tandem”
of MQW Modulators for Co
ded Pulse generation with
14-dB Fiber-to-Fiber Gai
n "F. Devaux, N .; Souli, A .; Ouga
zzaden, F.S. Huet, and M.S. Carr
e, IEEE Photonics Technology
oggy Letters, vol. 8, NO. 2, p
p. 218-220, 1996. There is an optical processing device disclosed in US Pat.

It is considered that such a conventional optical processing device has not been developed for the purpose of applying an optical modulator to a WDM optical communication system. However, in the above literature, an effect that is consistent with the object of the present invention, that is, an effect that the wavelength dependence of the insertion loss generated in the optical fiber transmission system is reduced, is briefly introduced below.

The optical processing apparatus described in the above document employs a configuration in which an optical modulator and an optical amplifier having the same structure of a light absorption layer and an active layer are integrated on the same substrate. FIG.
2 shows the wavelength dependence of the insertion loss generated in the optical fiber transmission system by the conventional optical processing device. As can be seen from FIG. 8, this optical processing device has a small wavelength difference of the insertion loss caused in the transmission system. In particular, focusing on the second solid line from the bottom in FIG.
It can be seen that the wavelength dependence of the insertion loss is extremely small in the wavelength range of μm. This is because the optical loss caused by the optical modulator is compensated by the optical amplifier integrated on the same substrate. Referring to FIG. 7, the optical loss caused by the optical modulator (discrete modulator) is changed by the gain (discrete amplifier) of the optical amplifier.
It is easily understood that is compensated.

[0014]

However, in the above-mentioned conventional optical processing device, the optical amplifier also amplifies the interference effect due to the residual reflection of the end face of the optical waveguide, so that the wavelength characteristic of the optical signal is oscillated (ripple). Occurs. In addition, the above-mentioned conventional optical processing device has an A
SE (Amplified Spontaneous)
In order to remove the emission, it is necessary to provide a narrow band wavelength filter that transmits only light in a predetermined wavelength range outside the device. Furthermore, the above-mentioned conventional optical processing device
Since the optical modulator and the optical amplifier are integrated on the same substrate, electrical crosstalk and thermal crosstalk occur between the two elements, and there is a problem in long-term reliability and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional optical processing apparatus, and has a new and improved structure in which the wavelength difference of insertion loss caused in an optical fiber transmission line in a wide wavelength band is reduced. It is an object of the present invention to provide a light processing device and a method for forming the light processing device. further,
Another object of the present invention is to provide a new and improved optical processing apparatus and optical processing apparatus capable of equalizing the wavelength characteristics of optical loss in a predetermined wavelength region without adding an active optical function means. It is an object to provide a forming method. Still further, the present invention provides a new and improved optical processing apparatus and an optical processing apparatus which do not cause inconveniences such as an increase in price, instability of operation, generation of noise, and the like even after achieving the above object. It is also an object to provide a method.

[0016]

The insertion loss that occurs in an optical fiber transmission line due to the insertion of an optical processing device includes (1) a reflection loss that occurs when light enters and exits each optical element that constitutes the optical processing device. It can be expressed as the sum of 2) the propagation loss that occurs during propagation in each optical element and (3) the coupling loss that occurs when light enters each optical element. Therefore, if the cancellation of the wavelength characteristics among the reflection loss, the propagation loss, and the coupling loss is realized, as a result, the insertion loss can make the wavelength characteristics uniform by reducing the wavelength difference.

Therefore, the first aspect of the present invention provides an optical modulator having an optical waveguide and optical modulation means for modulating light propagating through the optical waveguide, and an optical coupling element for optically coupling light to the optical waveguide. The optical modulator and the optical coupling element adopt a configuration in which the optical modulator and the optical coupling element are optically aligned with the shortest wavelength light in a preset wavelength region as reference light.

The reason why the wavelength difference of the insertion loss is reduced by the invention according to claim 1 having such a configuration will be described. Generally, in a waveguide type optical element including an optical modulator, an anti-reflection coating is applied to an input / output end face of light. In such a configuration, the reflection at the incident / exit end face of the light is suppressed, and the reflection loss generated at the time of entering / exiting the light can be reduced to a negligible level. Therefore, it is generally considered that the optical loss that affects the insertion loss generated in the optical transmission line by the waveguide type optical element is a propagation loss and a coupling loss.

A description will be given of the propagation loss among the optical losses that affect the insertion loss. When the intensity of light is modulated using an electro-absorption type optical modulator, the wavelength of the intensity-modulated light is usually the light absorption layer of the optical waveguide. Is set to a longer wavelength side than the bandgap wavelength. At this time, since the difference between the wavelength of light and the band gap wavelength is generally about several tens to hundreds of nm, even a slight wavelength difference causes a difference in light absorption by the light absorbing layer due to the effect of band filling. In particular, several tens of nm
When the degree is reduced, the difference in light absorption becomes significant. In the electro-absorption optical modulator, such a difference in light absorption is a main cause of a wavelength difference in propagation loss. Under normal driving conditions, the resulting propagation loss in the optical waveguide of the optical modulator becomes maximum at the shortest wavelength and conversely becomes minimum at the longest wavelength.

One coupling loss will be described. The coupling loss of the waveguide type optical element to the optical waveguide is caused by, for example, a mode mismatch of light. Normally, the coupling loss becomes the smallest with respect to the reference light for optical alignment, and becomes larger as the wavelength is farther from the reference light. In this specification, the optical alignment refers to adjusting the positional relationship between the optical elements in order to make the optical coupling between the optical elements optimal for a predetermined reference light.

According to the first aspect of the present invention, the optical modulator and the optical coupling element are optically aligned using light having the shortest wavelength in the wavelength region as reference light. Therefore, according to the first aspect of the present invention, the coupling loss of light that occurs when the light enters the optical modulator has a wavelength characteristic that minimizes the light of the shortest wavelength in the wavelength region and conversely maximizes the light of the longest wavelength. have. That is, according to the first aspect of the invention, the propagation loss and the coupling loss show wavelength changes in directions opposite to each other. As a result, according to the first aspect of the present invention, the wavelength characteristic of the coupling loss and the wavelength characteristic of the transmission loss cancel each other, and the wavelength difference of the insertion loss is reduced.

As described above, according to the first aspect of the present invention, there is provided an optical processing apparatus capable of reducing insertion loss without specially using an active optical functional element such as an optical amplifier. be able to. Therefore, the WDM of the optical modulator
It is possible to suitably apply the transmission method to an optical communication system.

In a configuration in which the optical coupling element and the optical modulator are optically aligned at the longest wavelength in the wavelength region, the propagation loss and the coupling loss are opposite to the configuration according to the first aspect of the present invention. Both are minimum at the longest wavelength and maximum at the shortest wavelength. Therefore, the difference in insertion loss between the shortest wavelength and the longest wavelength is maximized. In a configuration in which an optical coupling element and an optical modulator are aligned with broad light including light between the longest wavelength and the shortest wavelength in the wavelength region or light from the longest wavelength to the shortest wavelength, the optical transmission line The difference due to the wavelength of the insertion loss occurring in the first embodiment is about the middle between the configuration according to the first aspect of the invention and the configuration optically aligned at the longest wavelength.

According to a first aspect of the present invention, for example, as in the second aspect of the present invention, the optical waveguide has an end face through which light enters and exits. , The shortest wavelength light may be converged on the end face.

Further, the polarization of light incident on the optical modulator is:
It is preferable to adopt a configuration in which the insertion loss is maximized in the light of the shortest wavelength. According to the third aspect of the present invention having such a configuration, even when the polarization of the light to be processed is not constant and the insertion loss generated in the optical processing device shows polarization dependence, the light is inserted within a predetermined wavelength range. Loss averaging can be achieved.

According to another aspect of the present invention, there is provided an optical processing apparatus comprising at least an optical modulator having an optical waveguide and an optical modulator for modulating light propagating through the optical waveguide. An apparatus comprising: a light propagation path including an optical waveguide of an optical modulator; and a wavelength filter means interposed in the propagation path to cancel light loss in the optical modulator.
The configuration provided is adopted.

According to the fourth aspect of the present invention, the wavelength difference of the insertion loss occurring in the optical modulator can be compensated by the wavelength filter means of which various designs have been proposed. In general, since the wavelength filter means can be formed by a passive optical element, according to the fourth aspect of the present invention, the optical and thermal crosstalk and the energy consumption can be suppressed, and the WDM transmission type light can be suppressed. The application of the optical modulator to a communication system becomes possible.

According to a fourth aspect of the present invention, as in the fifth aspect, the wavelength filter means may be a wavelength filter element. According to the fifth aspect of the present invention, the wavelength characteristics of the insertion loss can be easily made uniform by employing a wavelength filter element having various functions and configurations conventionally proposed as the wavelength filter means. Can be. Further, as in the invention according to claim 6, the wavelength filter means may be a light transmitting film formed on the end face of the optical waveguide of the optical modulator. According to the fourth aspect of the present invention having such a configuration, the number of parts can be reduced, and the simplification of the device scale and the miniaturization can be realized.

Further, according to the invention of claim 7,
A method for forming an optical processing device, comprising at least an optical modulator having an optical waveguide and an optical modulator for modulating light propagating in the optical waveguide, and an optical coupling element for optically coupling light to the optical waveguide; The above object is achieved by a configuration including a step of setting a predetermined wavelength region where optical processing is required and a step of aligning the optical modulator and the optical coupling element with light having the shortest wavelength in the wavelength region. .

Further, the invention according to claim 8 is a method for forming an optical processing device, comprising an optical modulator having at least an optical waveguide and an optical modulator for modulating light propagating through the optical waveguide. Measuring the wavelength characteristic of the optical loss occurring in the optical modulator, and arranging a wavelength filter means having a wavelength characteristic that cancels out the wavelength characteristic of the optical loss. Solve.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical modulator module or an optical modulator according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description will be omitted.

(First Embodiment) First, a first embodiment in which the present invention is applied to an optical modulator module will be described.
This will be described with reference to FIGS. In addition, FIG.
FIG. 2 is an explanatory diagram of a schematic configuration of the optical modulator module 100 according to the present embodiment, and FIG. 2 is an explanatory diagram of a wavelength characteristic of optical loss generated in the optical modulator module 100.

As shown in FIG. 2, the optical modulator module 100 according to this embodiment has a wavelength range of λmin to λm.
ax is set, and light modulation is performed on light within this wavelength range. As shown in FIG.
In order to realize such a function, an optical modulator 110, which is a one-chip semiconductor electroabsorption optical element, and an optical system 120 for inputting light input via an optical fiber 126 to the optical modulator are shown in FIG. ， Provides as a main component.
In the optical modulator module 100, these optical modulators 1
The optical system 10 and the optical system 120 are arranged so as to align the optical axis substantially on a straight line AA ′ to be modularized.

In the optical modulator module 100, the optical modulator 110 has a first end face 110a and a second end face 110b both coated with an anti-reflection film AR. In the optical modulator, a light absorption layer 112a that continuously absorbs light by applying an electric field is formed over the first end face 110a and the second end face 110b. Further, in the optical modulator 110, the first clad layer 114a and the second clad layer 11 sandwiching the light absorption layer 112a are provided in order to confine light in the light absorption layer 112a.
4b are formed. With such a configuration, in the optical modulator 110, the optical waveguide 112 having the light absorption layer 112a as a core is formed.

Further, in the optical modulator 110, a first electrode 116a is provided on the first cladding layer 114a, and a second electrode 116b is provided on the second cladding layer 114b. As a result, an electric field can be applied to the light absorbing layer 112a, and the light guided by the optical waveguide 112, that is, the light that is optically coupled (coupled) to the light absorbing layer 112a and propagates in the optical waveguide 112 can be obtained. It is possible to run the modulation.

Since the optical modulator 110 has the above configuration, the light incident from the first end face 110a can be modulated in the optical waveguide 112 and emitted from the second end face 110b. Further, the light incident from the second end face 110a can be similarly modulated in the optical waveguide 112 and emitted from the first end face 110a.

The optical system 120 has a wavelength of the shortest wavelength λ.
It is formed by aligning the first lens 122, the second lens 124, and the optical fiber 126 using light of min. The first lens 122 corresponding to the optical coupling element in the optical modulator module 100 has a wavelength λ.
The focal point for the light of min is arranged so as to match the end face of the optical waveguide 112 formed on the first end face 112a. Further, the second lens 124 is disposed so that the focal point for the light having the wavelength λmin matches the end face of the optical fiber 126. Then, the first lens 122 and the second lens 12
4 are arranged substantially parallel to each other so that collimated light can be received as it is on the other hand.

That is, in the optical modulator module 100 according to the present embodiment, the optical modulator 110 and the optical fiber 126 are optically aligned via the optical system 120 using the shortest wavelength λmin as reference light. Will be. Therefore, the optical modulator 110 and the optical fiber 126
Optical coupling is best for light with the shortest wavelength λmin

The wavelength characteristics of the insertion loss that occurs in the optical fiber transmission system when the optical modulator module 100 configured as described above is inserted will be studied with reference to FIG. When the optical signal P1 transmitted through the optical fiber 126 is collected and input to the end face of the optical waveguide 112 formed on the first end face 110a of the optical modulator 110, or the optical signal P1 is modulated from the second end face 110b side. When the light P2 input to the optical waveguide 110 and propagated through the optical waveguide 112 is output from the optical waveguide 112 formed on the first end face 110a and coupled to the optical fiber 126, coupling loss occurs due to a mode mismatch of the light. As already mentioned, the optical coupling between the optical elements is best at the wavelength at which the alignment is performed and degrades as one moves away from that wavelength.

As described above, in the present embodiment, the alignment between the optical modulator 110 and the optical fiber 126 is performed via the optical system 120 using the shortest wavelength λmin as the reference light. Therefore, as shown in FIGS. 2A and 2B, for the light having the shortest wavelength λmin, the propagation loss is maximum, but the coupling loss can be minimized. On the other hand, at the longest wavelength λmax, the propagation loss is the smallest, but the coupling loss is the largest. As a result, the wavelength range λmin
In the case of .lambda.max, the wavelength characteristic of the propagation loss shown in FIG. 2A and the wavelength characteristic of the coupling loss shown in FIG. 2B cancel each other, and as shown in FIG. Small insertion loss is realized.

Further, in the present embodiment, the optical signals P1 and P1 input to the optical modulator module 100 are
By setting the two polarizations so that the insertion loss is the largest in the component of the shortest wavelength λmin, the wavelength difference of the insertion loss when the polarization is not constant can be reduced. This is because the polarization of the incident light is set so that the insertion loss due to the optical modulator is the largest at a certain wavelength component of the incident light, and the optical coupling device and the optical modulator are set so that the insertion loss is minimized at that wavelength. This is based on the fact that the difference in insertion loss due to the difference in polarization can be reduced by optically aligning.

Here, in this embodiment, a description will be given of a verification experiment performed by the inventor regarding the setting for maximizing the insertion loss of the optical modulator with respect to the shortest wavelength component of the polarization of the optical signal to be modulated. . In this verification experiment, the inventor
Assuming a wavelength region of 1.545 μm to 1.558 μm, an input light wavelength of 1.545 μm and an input light wavelength of 1.558 μm
The insertion loss of an optical modulator module to which several electro-absorption optical modulators actually manufactured were measured for μm. The electro-absorption type optical modulator manufactured by the inventor is an I-type optical modulator.
A light absorbing layer composed of nGaAsP and having a bandgap wavelength of about 1.47 μm and a thickness of about 0.26 μm
m and the element length are about 250 μm. In the verification, a dispersion fiber is usually used as an optical fiber 126, and an optical coupling system using two aspheric lenses is used as an optical system 120.

In this verification experiment, the shortest wavelength was 1.54
The average of the difference between the wavelengths of the insertion loss at both wavelengths when the alignment is performed at the polarization at which the insertion loss is the maximum at 5 μm is about 0.52
dB (about 10%). In contrast, the longest wavelength 1.
The average of the wavelength difference of the insertion loss at both wavelengths when the alignment is performed at the polarization at which the insertion loss is minimized at 558 μm is about 0.5.
It was 84 dB (about 20%). From these verification results,
It is confirmed that the wavelength characteristics of the insertion loss can be greatly improved by performing alignment so that the insertion loss is maximized at the shortest wavelength in the wavelength region.

As described above, according to the present embodiment, the wavelength difference of the insertion loss is reduced without modifying the optical modulator itself. In addition, the optical modulator can be driven without changing the driving conditions, even when light of a plurality of wavelengths is input or when the wavelength is input with a random polarization. Therefore, according to the present invention, it is possible to provide an optical modulator module that can be applied to a low-cost and highly reliable WDM transmission communication system.

Further, in this embodiment, the wavelength difference of the insertion loss can be reduced without making the bias voltage applied to the optical modulator shallow, so that the influence of the pattern effect and the deterioration of the response speed can be avoided. it can. Further, according to the present embodiment, it is not necessary to provide a gain means for compensating for the loss, for example, an optical amplifier. Therefore, an optical modulator module having low noise and good long-term operation stability without ASE or ripple amplification is realized.

(Second Embodiment) Next, FIGS. 3 and 4 show a second embodiment in which the present invention is applied to an optical modulator module in the same manner as in the first embodiment. It will be described with reference to FIG. FIG. 3 is an explanatory diagram of a schematic configuration of the optical modulator module 200 according to the present embodiment, and FIG. 4 is an explanatory diagram of an insertion loss of the optical modulator module 200. As shown in FIG. 3, an optical modulator module 200 according to the present embodiment includes
An optical modulator 210 having substantially the same basic configuration as the optical modulator 110 applied to the optical modulator module 100 shown in FIG.

In the optical modulator module 200, a lens 222a is arranged on the first end face 210a side of the optical modulator 210 so as to focus on the end face on the first end face 210a of the optical waveguide 212. . Further, a lens 224a is disposed on the first end face 210a side substantially in parallel with the lens 222a so as to receive light emitted from the optical modulator 210 and collimated by the lens 222a. Furthermore, the optical fiber 226a
The lens 224a is arranged such that the end face is aligned with the focal point located on the opposite side of the lens 222a.

The second end face 210b of the optical modulator 210
On the side, optical elements similar to those on the first end face 210a side are arranged in the same manner as on the first end face 210a side. That is, a lens 222b focused on the end face on the first end face 210b of the optical waveguide 212, a lens 224b capable of receiving light emitted from the optical modulator 210 and collimated by the lens 222b, and an end face at the focus of the lens 224b. And an optical fiber 226b that is matched.

In the optical modulator module 200 according to the present embodiment, a wavelength filter 220 is disposed on the second end face 210b side between the lens 222b and the lens 224b, substantially in parallel with the lens 222b and the lens 224b. I have. The wavelength filter 220 is designed to have a wavelength characteristic of a light transmittance that cancels a wavelength characteristic of another optical loss generated in the optical modulator module 200. Therefore, the wavelength filter 220 is
By performing a filtering process on the parallel beam propagating between b and the lens 224b, it is possible to compensate for the wavelength difference of the optical loss generated in the optical modulator 210.

Specifically, the wavelength filter 220 can reduce the optical loss occurring in the optical modulator module 200 when the wavelength filter 220 is not installed by various methods,
For example, it can be obtained by actual measurement or calculation by simulation, and can be designed based on the obtained result.

Here, such a design will be schematically described with reference to FIG. In the optical modulator module 200, the optical loss that occurs when the wavelength filter 220 is not installed mainly occurs due to the optical modulator 210, which is an electroabsorption optical modulator, and is coupled to the optical modulator 210. It is about the sum of the loss and the propagation loss in the optical modulator 210. In such a case, the optical loss that occurs in the optical modulator module is the largest in the light of the shortest wavelength, and becomes smaller toward the longer wavelength side. Therefore, the wavelength filter 220 is designed to have a light transmittance that is minimum in the shortest wavelength light and increases toward the long wavelength side.

As described above, according to the present embodiment, the wavelength difference of the insertion loss caused by the optical modulator module can be suppressed by using the wavelength filter of which various configurations and functions have been conventionally proposed. it can. That is, according to the present embodiment, the application of the optical modulator to the WDM optical communication system of the optical modulator can be easily realized.

Further, by combining the configuration of this embodiment with the configuration of the first embodiment, it is possible to suppress the wavelength difference of the insertion loss to a required value or less even in a large input light wavelength range. It is. According to the inventor's knowledge, by combining the configuration of the present embodiment with the configuration of the first embodiment, a wider input of about 20 nm or more than the case where the configuration of the first embodiment is used alone is used. Even in the optical wavelength range, a wavelength difference of insertion loss equal to or less than a required value is achieved.

(Third Embodiment) Next, a third embodiment in which the present invention is applied to an optical modulator will be described with reference to FIG.
This will be described with reference to FIG. FIG. 5 is an explanatory diagram of a schematic configuration of the optical modulator 310 according to the present embodiment, and FIG. 6 is an explanatory diagram of an insertion loss generated in the optical transmission line by the optical modulator 310. As shown in FIG. 3, the optical modulator 310 according to the present embodiment is a one-chip electro-absorption optical modulator, and the basic configuration is used in the first embodiment shown in FIG. The optical modulator 110 is substantially the same as the optical modulator 110.

However, the optical modulator 3 according to the present embodiment
In 10, the second end face 310b is set as a light incident end face, and the first end face 310a is set as a light output end face. Then, on the second end face 310b, which is the light emission end face, the end face film 320 according to the present embodiment, whose light reflectance has wavelength dependence, is formed.

In the optical modulator 110, the end face film 310b
Is a light reflectance that cancels out the sum of the wavelength dependence of the propagation loss of light generated during propagation through the optical waveguide 312 of the optical modulator 310 and the coupling loss of light generated when entering and exiting the optical waveguide. It is designed to have. Such an end face film 310b
Can be designed using a known technique.

The design of the end face film 310b according to the present embodiment is performed in the same manner as the design of the wavelength filter 220 according to the second embodiment shown in FIG. Therefore, as shown in FIG. 6, the end face film 310b according to the present embodiment is formed.
Is designed to have a light transmittance that is minimum in the light of the shortest wavelength and increases toward the longer wavelength side.

In the optical modulator 310, a non-reflection film AR is formed on the first end face 310 a which is a light exit end face, and the first end face 31 is emitted when the light exits from the optical modulator 310.
A configuration is employed in which light is reflected at 0a and does not return into the optical waveguide 312. With this configuration, it is possible to reduce the interference phenomenon in the optical modulator 310 as much as possible by suppressing the reflected return light.

As described above, according to the present embodiment, it is possible to reduce the wavelength difference of the insertion loss without increasing the number of optical elements, and it is possible to apply the optical modulator to a WDM optical communication system. Become possible. Further, by combining the configuration according to the present embodiment with the configuration according to the first or second embodiment or the configuration according to the first and second embodiments, the insertion loss can be more effectively reduced. The wavelength difference can be reduced.

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to such configurations. Within the scope of the technical idea described in the appended claims, those skilled in the art will be able to conceive various changes and modifications, and those changes and modifications are also within the technical scope of the present invention. It is understood that it belongs to.

For example, in the verification described in the above embodiment, an optical modulator and an optical modulator module whose input wavelength is around 1.55 μm have been described as examples, but the present invention is not limited to such a configuration. The present invention can be applied to an optical modulator and an optical modulator module in which various other input wavelengths are set.

Further, in the above embodiment, the optical modulator module using the aspherical lens as the optical coupling element has been described as an example, but the present invention is not limited to this configuration. The present invention relates to various other optical coupling elements such as a spherical optical fiber and a computer generated hologram (Computer).
The present invention can also be applied to an optical modulator module to which a Generated Hologram (CGH) element or the like is applied.

Further, in the above embodiment, the optical modulator module applied to the optical fiber transmission line of the ordinary dispersion optical fiber has been described as an example, but the present invention is not limited to this configuration. The present invention can be applied to an optical modulator module applied to various other optical fiber transmission lines.

Further, in the present invention, the position of the wavelength filter exemplified in the above embodiment is not limited. In the present invention, the insertion position of the wavelength filter may be anywhere in the light propagation path.

Further, the configuration of the optical modulator applied to the present invention is not limited except that it is a waveguide type optical modulator. The present invention is applicable to optical modulators using various semiconductor materials, for example, InP-based materials, GaAs-based materials, or Si-based materials. Also,
Optical modulators having various structures and dimensions can be applied to the present invention. Further, it is obvious that the wavelength region applicable to the present invention is not limited to the input light wavelength band exemplified in the above embodiment.

[0066]

According to the present invention, the wavelength characteristic of the insertion loss caused in the optical fiber transmission line by the insertion, which has not been realized in the optical processing apparatus using the conventional optical modulator, is within a predetermined wavelength range. Flat characteristics can be realized. Therefore, an optical modulator can be applied to a WDM optical communication system using a wavelength multiplexed optical signal as a transmission signal.

Further, in the present invention, there is no other active optical element such as an amplifier for compensating for the wavelength difference of the optical loss generated in the optical modulator. Therefore, there is no influence caused by other optical elements, such as crosstalk and amplification of noise, and no increase in power consumption. As a result, according to the present invention, it is possible to provide an inexpensive optical processing device capable of performing a stable operation.

[Brief description of the drawings]

FIG. 1 is a schematic structural explanatory view of an optical modulator module to which the present invention can be applied.

FIG. 2 is an explanatory diagram of characteristics of the optical modulator module shown in FIG.

FIG. 3 is a schematic structural explanatory view of another optical modulator module to which the present invention can be applied.

FIG. 4 is an explanatory diagram of characteristics of the optical modulator module shown in FIG.

FIG. 5 is a schematic diagram illustrating the configuration of an optical modulator to which the present invention can be applied.

FIG. 6 is an explanatory diagram of characteristics of the optical modulator shown in FIG.

FIG. 7 is an explanatory diagram showing characteristics of a conventional optical processing device.

FIG. 8 is an explanatory diagram showing characteristics of a conventional optical processing device.

[Explanation of symbols]

 100, 200 Optical modulator module 110, 210, 310 Optical modulator 110a, 110b End face 112 Optical waveguide 122 Lens 220 Wavelength filter 320 End face film P1, P2 Optical signal λmin Shortest wavelength λmax Longest wavelength

Claims (8)

[Claims] 1. An optical processing apparatus comprising at least an optical modulator having an optical waveguide and optical modulation means for modulating light propagating through the optical waveguide, and an optical coupling element for optically coupling the light to the optical waveguide. An optical processing apparatus, wherein the optical modulator and the optical coupling element are optically aligned with light having a shortest wavelength in a preset wavelength region as reference light. 2. The optical waveguide according to claim 1, wherein the optical waveguide has an end face through which light enters and exits, and the optical coupling element focuses the light having the shortest wavelength on the end face. 2. The light processing device according to 1. 3. The optical processing device according to claim 1, wherein the polarization of the light is set so that the insertion loss is maximized in the light having the shortest wavelength. 4. An optical processing apparatus, comprising: an optical modulator having at least an optical waveguide and an optical modulator for modulating light propagating through the optical waveguide; and an optical processing apparatus including the optical waveguide of the optical modulator. And a propagation path interposed between the
An optical processing device, comprising: wavelength filter means for canceling the light loss in the optical modulator. 5. The optical processing apparatus according to claim 4, wherein said wavelength filter means is a wavelength filter element. 6. The optical processing apparatus according to claim 4, wherein said wavelength filter means is a light transmitting film formed on an end face of said optical waveguide of said optical modulator. 7. An optical processing device comprising at least an optical modulator having an optical waveguide and optical modulation means for modulating light propagating through the optical waveguide, and an optical coupling element for optically coupling the light to the optical waveguide. A method for forming a device; setting a predetermined wavelength region in which light processing is required; and optically coupling the optical modulator and the optical coupling element with light having the shortest wavelength in the wavelength region as reference light. A method of forming an optical processing device. 8. A method for forming an optical processing device, comprising: an optical modulator having at least an optical waveguide and an optical modulator for modulating light propagating through the optical waveguide; an optical loss generated in the optical modulator. And a step of arranging wavelength filter means having a wavelength characteristic for canceling the wavelength characteristic of the optical loss.