JP2004163675A - Organic waveguide type optical modulator with monitor, optical modulation apparatus and optical integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic waveguide type optical modulator with a monitor which can reliably detect monitoring light, eliminate a temperature drift and DC drift and can be driven at a high speed and with a low driving voltage. <P>SOLUTION: The modulator is a Mach-Zehnder type organic waveguide type optical modulator and is equipped with: a control circuit 40 which controls the DC bias voltage to be applied to control electrodes 203 to 205 to set the operation point for optical modulation; and a photodetector 50 for monitoring the radiated light 300 generated in the multiplexing part of guided light the phase of which has been modified. The control circuit 40 adjusts the operating point by controlling the DC bias voltage in accordance with the intensity of the radiated light. The optical waveguide 200 is provided with a crystal of 4-N,N-dimethylamino-4'-N-methylstilbazolium tosylate (DAST) being an electro-optic effect medium as the core layer with the b-axis aligned to the waveguide direction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic waveguide type optical modulator with a monitor, an optical modulator, and an optical integrated circuit.
[0002]
[Prior art]
With the development of large-capacity and high-speed optical communication, "information transmission using light" has been proposed not only for trunk networks but also for LANs, network terminals, electronic devices, boards, and between LSI chips. ing.
In the “optical interconnection” in which electronic devices, boards, and LSI chips are connected by light, the power supply voltage of the mounted LSI chips has been reduced and the optical interconnects have been designed to prevent noise from being applied to the LSI chips. Devices used for connection are required to lower the power supply voltage.
[0003]
As one of the devices used for optical interconnection, there is an “optical modulator that modulates the intensity of light according to an electric signal and uses it as a signal light”, but in combination with the demand for low power consumption of the entire system, There is a strong demand for lowering the driving voltage.
[0004]
As one of the optical modulators, a “Mach-Zehnder type optical modulator” is known.
[0005]
Conventionally, as this type of optical modulator, LiNbO which is an inorganic ferroelectric crystal is used.₃(Hereinafter, LN crystal is abbreviated as LN crystal). However, since the dielectric constant of LN crystal is as large as about 28, the modulation band is limited. It is necessary to reduce the length of the electrode to reduce the interaction length between the signal microwave and the light wave, and if this is done, the driving voltage for modulation will increase. Is difficult to achieve.
[0006]
In a Mach-Zehnder type optical modulator currently using an LN crystal, a driving voltage: 5 V and a modulation frequency: 10 Gps are generally used, and the driving voltage is two to three times the power supply voltage of the LSI chip. Size.
[0007]
An optical modulator using an LN crystal is generally a discrete device and a “high-cost device”. That is, processing of an inorganic material such as LN is a high-temperature process, and the configuration of an optical integrated circuit in which electric wiring and an optical waveguide are incorporated is different from hybrid mounting, and alignment is complicated and cost is likely to be high.
[0008]
On the other hand, organic materials have a smaller dielectric constant than inorganic materials, are easily thinned, and have large electro-optic constants. Is expected to be realized. However, "organic polymer materials" have a low glass transition point, and polarization is relaxed by temperature and changes over time, so when used in an optical modulator, how to ensure reliability as an optical modulator Is a problem.
[0009]
Mach-Zehnder type optical modulators are also known to have problems called “DC drift” and “temperature drift”.
In a Mach-Zehnder type optical modulator, a DC bias voltage is applied to set an “operating point” which is a reference of a modulated optical output. Then, a high-frequency signal voltage is applied to the “traveling wave control electrode” so as to be superimposed on the DC bias voltage.
“DC drift” is a phenomenon in which the operating point fluctuates with time due to the application of the DC bias voltage.
The “temperature drift” is a phenomenon in which an operating point fluctuates with time due to a temperature change in a portion of an optical modulator where an electric field is applied.
When a DC drift or a temperature drift occurs, distortion of a modulation waveform or deterioration of an extinction ratio occurs.
[0010]
As a method to cope with these DC drift and temperature drift, a part of the signal light or “radiation light radiated from the multiplexing point of the Mach-Zehnder type optical waveguide” is guided to a photodetector by an optical fiber and monitored. There has been proposed a method of adjusting the magnitude of a DC bias voltage so as to compensate for an optical output changed by a DC drift or a temperature drift (see Patent Documents 1 to 3).
[0011]
However, these methods relate to “a conventional discrete optical modulator in which signal light propagates through an optical fiber”, and an organic conductive circuit that can integrate a plurality of optical modulators or form a monolithic optical integrated circuit. Even when applied to a waveguide optical modulator, there are cases where monitor light cannot be extracted or a photodetector cannot be provided.
[0012]
[Patent Document 1]
Patent No. 2738078
[Patent Document 2]
JP-A-5-100194
[Patent Document 3]
JP 2001-209018 A
[0013]
[Problems to be solved by the invention]
The present invention relates to a Mach-Zehnder organic waveguide type optical modulator with a monitor that can reliably detect monitor light and effectively eliminate the problems of temperature drift and DC drift in an organic waveguide type optical modulator that can be integrated. Another object of the present invention is to realize an optical modulator in which two or more of these are integrated, and an optical integrated circuit using them.
[0014]
[Means for Solving the Problems]
The organic waveguide type optical modulator with monitor according to the present invention is a “Mach-Zehnder type organic waveguide type optical modulator”.
[0015]
An organic waveguide type optical modulator with a monitor according to a first aspect has a control circuit and a photodetector for monitoring.
The “control circuit” controls a “DC bias voltage for setting an operating point of light modulation” applied to a control electrode that generates an electric field for modulating the phase of guided light.
[0016]
The “monitoring photodetector” detects, via the clad portion, radiation light generated at the multiplexing portion where the phase-modulated guided light is multiplexed.
[0017]
The control circuit controls the DC bias voltage in accordance with the intensity of the emitted light detected by the monitoring photodetector to adjust the operating point of the light modulation.
[0018]
In the optical waveguide, a crystal of DAST (4-N, N-dimethylamino-4′-N-methylstilbazolium tosylate) is used as an electro-optic effect medium that modulates the phase of guided light by an electric field. Are arranged as a core layer such that the axis becomes the b-axis.
[0019]
In the organic waveguide optical modulator with a monitor according to the first aspect, the radiated light propagates through a reflection mirror that changes the direction of “radiated light generated at a multiplexing unit where the phase-modulated guided light is multiplexed”. The reflecting mirror may be provided in the clad portion (claim 2), and the reflecting mirror may be configured to "convert the direction of the radiated light to a direction crossing the substrate surface on which the optical waveguide is formed" (claim 3).
[0020]
The "organic waveguide type optical modulator with monitor" according to claim 4 has a control circuit, a monitor photodetector, a monitor light branching unit, and an optical path conversion unit.
The “control circuit” controls a “DC bias voltage for setting an operating point of light modulation” applied to a control electrode that generates an electric field for modulating the phase of guided light.
The "monitoring photodetector" detects a part of the phase-modulated and multiplexed signal light as monitor light.
[0021]
The “monitor light branching unit” branches a part of the signal light as monitor light.
The "optical path conversion means" is means for converting the direction of the monitor light branched by the monitor light branching means into a direction crossing the substrate surface on which the optical waveguide is formed.
The control circuit controls the DC bias voltage in accordance with the intensity of the emitted light detected by the monitoring photodetector to adjust the operating point of the light modulation.
[0022]
In the optical waveguide, a DAST crystal as an electro-optic effect medium for modulating the phase of guided light by an electric field is provided as a core layer such that the waveguide direction is the b-axis.
[0023]
The "optical path conversion means" in the organic waveguide type optical modulator with monitor according to claim 4 may be a "reflection mirror" (claim 5) or a "grating coupler" (claim). 6).
[0024]
The "monitor light branching means for branching monitor light from signal light" in the organic waveguide type optical modulator with monitor according to claim 4 or 5 or 6 may be a "branch waveguide". , A "directional coupler" (claim 8), and a "two-input, two-output multi-mode interference optical waveguide" (claim 9).
[0025]
An optical modulator according to the present invention is characterized in that two or more organic waveguide optical modulators with a monitor according to any one of the first to ninth aspects are integrated on the same substrate. Claim 10).
[0026]
An optical integrated circuit according to the present invention has at least one organic waveguide type optical modulator with monitor according to any one of claims 1 to 9 on the same substrate, and has an output terminal of an electronic device and an organic waveguide with monitor. By electrically connecting the control electrode of the waveguide type optical modulator, light from the light emitting element is output as one or more modulated lights corresponding to an electric signal from an output terminal, and the output modulated light is optically transmitted. This is configured to be transmitted by a unit (claim 11).
[0027]
The above-mentioned “DAST” is an “organic crystal” having the structural formula shown in FIG. 1, and since it is an organic crystal, “polarization treatment required for an organic polymer” is not required. There is no. Further, it has an extremely large nonlinear optical constant (d11 = 1010 pm / V (λ = 1.3 μm)) and an electro-optical constant (r11 = 75 pm / V (λ = 820 nm)), and has a low dielectric constant (ε1) unique to an organic crystal. = 5.2).
[0028]
The present invention has been made by paying attention to the fact that the above-mentioned characteristics of DAST are extremely suitable for a Mach-Zehnder type optical waveguide type optical modulator, and by using this, high-speed modulation with low voltage driving can be realized. is there. As far as the inventor knows, an optical waveguide type optical modulator using DAST is not known.
[0029]
Since DAST is an organic crystal, it has a larger coefficient of thermal expansion than inorganic materials and is more susceptible to temperature, so that temperature drift is likely to occur. However, the optical modulator of the present invention "detects a part of the radiated light or the signal light by the monitoring photodetector and adjusts the DC bias voltage based on the detection result". Can be reliably removed.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments will be described.
FIGS. 2A and 2B are diagrams showing an embodiment of the organic waveguide type optical modulator with a monitor according to claims 1 to 3, wherein FIG. 2A is a top view, and FIG. 2B is a monitor portion including a reflection mirror. FIG.
[0031]
The organic waveguide type optical modulator with a monitor is a Mach-Zehnder type optical modulator, which optically modulates incident light incident from the left side in (a) and emits it as signal light from the right side of the optical modulator.
[0032]
The organic waveguide type optical modulator with monitor has a structure in which a lower clad 20 and an upper clad 30 are laminated on a substrate 10 as shown in FIG. It is formed on the clad 20. A monitoring photodetector 50 is provided on the upper clad 30, and a reflection mirror 60 is provided on the lower clad 20.
[0033]
As shown in FIG. 2A, the optical waveguide 200 is directed from the incident side to the emission side, and is branched in a Y-shape in the middle into two paths, and each of the divided parts constitutes an “arm part”. The downstream side of the arm merges into a Y-shape to the injection section. DASTs 201 and 202 having an “electro-optic effect” are arranged in each of the arm portions, and the remaining optical waveguide portions (which do not require the electro-optic effect) are formed as “known resin optical waveguides”.
[0034]
As shown in FIG. 2A, control electrodes 203, 204, and 205 are formed on the upper surface of the upper clad 30 as shown. The control electrodes 203 to 205 are “traveling wave type electrodes”, the control electrodes 204 and 205 are set to the ground potential, and the control electrode 203 is grounded via a termination resistor 206 of 50Ω.
[0035]
When a high-frequency signal voltage (microwave voltage) is applied to the control electrode 203 by the signal power supply 207, a micro electromagnetic wave acts on each of the DAST 201 and 202.
[0036]
In DASTs 201 and 202, the crystal orientation is set so that the b-axis of the crystal is in the waveguide direction in order to effectively use the largest electro-optic constant: r11. A voltage is applied in the a-axis direction of the crystal, and the plane of polarization of the incident light is also parallel to the a-axis.
[0037]
In the embodiment of FIG. 2, the crystal axes of DAST 201 and DAST 202 have their crystal axis directions set so that the a-axis is parallel to substrate 10, and the electric field is also parallel to the substrate. Further, since the a-axis directions of DAST 201 and 202 in both arm portions are the same direction, when control electrodes 204 and 205 are grounded and microwave voltage is applied to control electrode 203 by signal power supply 207, DAST 201 and 202 Opposite electric fields act (in the vertical direction in FIG. 2A).
[0038]
When a light from a light source (semiconductor laser) (not shown) enters the optical waveguide 200, it is equally divided and guided to each arm at the Y-shaped branch. When the micro electromagnetic wave acts while being guided through the DAST 201 and 202 in each arm part, the refractive index changes due to the electro-optic effect in the DAST 201 and 202, but the direction of the acting electric field is opposite between the DAST 201 and 202. Therefore, one of the phase velocities of the light guided through the DASTs 201 and 202 is large and the other is small, and a phase difference is generated between the lights guided through the DASTs 201 and 202.
[0039]
When the lights whose phases have been changed in the DAST 201 and 202 are combined in a Y-shape and multiplexed, they interfere with each other to cause a difference in light intensity. The intensity of the light intensity corresponds to a change in the signal voltage applied to the control electrode 203, and the output light emitted from the optical waveguide is “signal light whose light intensity is modulated according to the signal voltage”.
[0040]
By using the electrodes 203 to 205 as “traveling wave electrodes”, it is possible to eliminate the influence of capacitance and to cope with very high-speed light modulation.
[0041]
The relationship between the light intensity of the signal light modulated as described above and emitted from the emission unit and the voltage applied to the control electrode is represented by a relationship shown by a solid line in FIG. 3 (this relationship is a Mach-Zehnder type). The initial operating point is a voltage that gives the maximum optical output of the signal light (0 V in the figure) and a voltage that gives the minimum optical output: V_πVoltage in between: V_{π / 2}It is preferable to set For this reason, a DC bias voltage (the above-mentioned voltage: V_{π / 2}) Is applied.
[0042]
However, the application of the DC bias voltage causes a DC drift of the operating point. In addition, a temperature drift occurs due to the influence of the DAST temperature change.
[0043]
On the other hand, at a portion where the guided lights phase-modulated by the DASTs 201 and 203 are multiplexed, radiation light 300 leaking from the optical waveguide to the cladding portion is generated, and propagates in the lower cladding layer 20. The light intensity of the radiated light 300 generated in this manner has a “complementary relationship with the light intensity of the signal light” as shown by a broken line in FIG. That is, when the light intensity of the signal light is maximum, the light intensity of the emitted light is minimum, and when the light intensity of the signal light is minimum, the light intensity of the emitted light is maximum.
[0044]
Therefore, by monitoring a part of the emitted light 300, the shift of the operating point due to the temperature drift or the DC drift is detected by the control circuit 40, and is fed back to the signal power supply 207 to adjust the DC bias voltage so as to be always appropriate. Operating point can be maintained.
[0045]
In this embodiment, as shown in FIG. 2B, the radiation light 300 propagating in the lower clad 20 is changed its optical path to the upper clad 30 by a reflecting mirror 60 provided on the lower clad 20. , Are detected by the monitoring photodetector 50 provided on the upper clad 30.
[0046]
That is, the optical modulator whose embodiment is shown in FIG. 2 is a Mach-Zehnder type organic waveguide type optical modulator, in which the electrodes 203 to 205 for generating an electric field for modulating the phase of the guided light have optical modulation. And a control circuit 40 for controlling a DC bias voltage applied to set the operating point of the light, and a radiated light 300 generated at a multiplexing portion where the phase-modulated guided light is multiplexed. The control circuit 40 controls the DC bias voltage according to the intensity of the radiated light detected by the monitor photodetector 50 to adjust the operating point of light modulation. A monitor-equipped organic material having DAST crystals 201 and 202 as an electro-optic effect medium for modulating the phase of guided light by an electric field in the optical waveguide and having a b-axis in the waveguide direction. Waveguide type A modulator (claim 1).
[0047]
The clad portion 20 through which the radiated light 300 propagates has a reflection mirror 60 that changes the direction of the radiated light 300 generated at the multiplexing portion where the phase-modulated guided light is multiplexed (claim 2). The reflecting mirror 60 converts the direction of the radiated light 300 into a direction (upward) crossing the substrate surface 10 on which the optical waveguide is formed (claim 3).
[0048]
【Example】
Hereinafter, a specific example of the embodiment of FIG. 2 will be described.
A “polyimide substrate” is used as the substrate 10, and a lower clad 20 serving as an optical waveguide clad is formed on the substrate 10 by spin coating of a polyimide resin.
Further, using a pattern mask corresponding to the Mach-Zehnder optical waveguide 200, “core grooves according to the optical waveguide pattern” are formed by photolithography and reactive ion etching using oxygen gas.
[0049]
The core groove is filled with “polyimide resin having a large refractive index” serving as a core to form the low-loss optical waveguide 200. Next, lithography and etching are performed again only on the “portion where DAST 201 and 202 are selectively formed” to form a core groove.
[0050]
The DAST crystal is grown in the groove thus formed again by the "slow cooling method using methanol as a solvent". At this time, a “crystal waveguide direction is set to the b-axis” using a seed crystal. In this way, a DAST single crystal can be formed in a form in which the core groove is buried such that the direction substantially perpendicular to the b-axis becomes the a-axis.
[0051]
When the DAST crystal is grown, the DAST “grows other than the core groove”. Therefore, the polishing is performed using a foamed urethane pad: IC-1000 / SUBAIV (trade name: Rodale) and abrasive particles of silica, and the other than the core groove. Of unnecessary DAST is removed, and DAST is left only in a desired core groove.
[0052]
In addition to the above “Formation of DAST crystal by slow cooling method using seed crystal”, Appl. Phys. Lett. Vol. 74 (1999) 635, and a DAST crystal can be formed by an MOVPE (Organic Vapor Phase Deposition) method.
[0053]
The upper layer on which the Mach-Zehnder type optical waveguide 200 is formed is spin-coated with the same polyimide resin as the material of the lower cladding 20 to form an upper cladding 30 having a thickness of 2 μm, and an optical waveguide portion for guiding input light and signal light. Then, an optical waveguide portion is formed by DASTs 201 and 202 that generate an electro-optic effect by applying a voltage.
[0054]
Next, a V-shaped groove having an inclination angle of 45 degrees with respect to the substrate surface is formed on the back surface of the substrate 10 by using a dicing saw to form a reflection mirror 60. The radiated light 300 emitted from the multiplexing point of the Mach-Zehnder optical waveguide is totally reflected at the interface between the polyimide resin (the lower clad 20) and the air according to Snell's law, is emitted from the upper surface of the upper clad 30, and is monitored. It is detected by the detector 50.
[0055]
The “optical path conversion of radiation light” by the reflection mirror 60 has a small wavelength dependence and is easy to design.
A “coplanar line type gold electrode” is formed on the upper clad 30 as the control electrodes 203 to 205 by a sputtering method, and a terminating resistor 206 of 50Ω is attached to the end to form a traveling wave type electrode. Further, a “photodetector” is mounted on the upper clad 30 as a monitoring photodetector 50 for monitoring the radiated light 300 emitted from the upper surface of the upper clad 30.
[0056]
The optical output of the emitted light 300 in the structure obtained in this manner is detected by the monitoring photodetector 50, and the detected output is taken into the control circuit 40. When the optical output fluctuates, a desired optical output is obtained. The DC bias voltage is controlled so that the
[0057]
When a modulation signal was input between the control electrodes 203 to 205 via a coaxial cable while a laser beam having a wavelength of 1.3 μm was incident, an ultra-high-speed light intensity modulation was performed at a “low drive voltage” of about 1.5 V. Was effective.
[0058]
Since a low-cost organic material is used for the structure including the optical waveguide and can be formed by a low-temperature process, a low-cost organic waveguide type optical modulator with monitor can be realized. Further, since the emitted light 300 is monitored without branching the signal light, the intensity of the signal light does not decrease, and the operating point of the optical modulation is feedback-controlled, so that it is stable without being affected by temperature drift and DC drift. Light modulation can be realized.
[0059]
In the above example, the semiconductor microfabrication by photolithography and etching was used as a patterning method of the Mach-Zehnder type optical waveguide, but it may be formed by imprinting or die molding such as a stamper. The part may be formed of a photosensitive resin.
[0060]
The substrate 10 is made of SiO₂Substrates of inorganic materials such as silicon and GaAs, organic materials such as mylar, and hybrid materials such as glass epoxy used for printed boards can also be used.
[0061]
Further, the “core portion other than DAST” in the optical waveguide is not limited to the above-described polyimide resin, but various resins such as epoxy resin, PMMA, acrylate-based resin, silicon resin, cyanurate resin, and SiO 2₂It may be configured using any inorganic film of Si, Si, or SiN, or may be configured using a “photonic crystal having a periodic fine structure”.
[0062]
As a method for forming the reflection mirror 60, in addition to the above-mentioned “method of forming a V-shaped groove using a dicing saw”, processing by a stamper or the like, formation by photolithography and etching using a light and shade mask, laser ablation, or the like A method is also possible. A metal film such as Au, Ag, or Al may be formed on the surface of the reflection mirror 60 to improve the reflectance.
[0063]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 4 shows an embodiment of the optical modulator according to the tenth aspect.
This optical modulator is obtained by integrating two organic waveguide type optical modulators with a monitor on the same substrate. The integrated two organic waveguide type optical modulators with monitor are as described in claim 4.
[0064]
In order to avoid complication, the same reference numerals as those in FIG. Further, since the two integrated organic waveguide type optical modulators with monitor are "the same", these same parts are denoted by "the same numeral and a code by a combination of A and B". Each optical modulator is distinguished by A and B in the code. Since these two organic waveguide type optical modulators with monitor have the same configuration and the same function, the configuration and function of one optical modulator will be described.
[0065]
In FIG. 4, reference numeral 2 denotes a structure in which a lower clad and an upper clad are stacked on the same substrate as described with reference to FIG. Each optical waveguide is formed in the lower cladding.
[0066]
The optical waveguide 200A is formed from the incident side (the left side in the figure) to the emission side (the right side in the figure). At the downstream side, it merges into a Y-shape and goes to the injection section. DASTs 201A and 202A having an “electro-optic effect” are arranged in each of the arm portions, and the remaining optical waveguide portions (which do not require the electro-optic effect) are formed of “known resin optical waveguides”.
[0067]
The control electrodes 203A, 204A and 205A formed on the upper surface of the upper clad as shown in the figure are "traveling wave type electrodes", the control electrodes 204A and 205A are set to the ground potential, and the control electrode 203A is connected via a 50Ω termination resistor 206A. Grounded.
[0068]
When a high-frequency signal voltage (microwave voltage) is applied to the control electrode 203 by the signal power supply 207A, a micro-electromagnetic wave acts on each of the DASTs 201A and 202A, and “signal light” is generated by the same operation as the optical modulator of FIG. can get.
[0069]
The optical waveguide 200B is the same as the optical waveguide 200A, and the illustration of the “control circuit, signal power supply, and terminating resistor” is omitted on the optical waveguide 200B side.
[0070]
The difference between the two organic waveguide type optical modulators with monitor and that shown in FIG. 2 is as follows.
That is, in the embodiment shown in FIG. 4, in the optical waveguides 200A and 200B of the organic waveguide type optical modulator with monitor, the guided lights phase-modulated in the DAST 201A (201B) and 202A (202B) are combined. The wave is turned into a signal light, which is guided and emitted through the signal light waveguide 211A (211B), and "a part of the signal light" is branched to the branch waveguide 212A (212B) as monitor light.
[0071]
The monitor light branched in this manner is reflected by the reflection mirrors 60A and 60B (these are the same as the reflection mirror 60 shown in FIG. 2) formed at the end of the branch waveguide 212A (212B). The light is reflected, emitted to the upper clad surface side, detected by the monitoring photodetector 50A (50B), and monitored by the control circuit.
[0072]
Compared to the case of monitoring the emitted light 300 as in the embodiment of FIG. 2, the embodiment of FIG. 4 directly monitors a part of the signal light, so that the embodiment of FIG. "More accurate monitoring" is possible.
[0073]
In the embodiment of FIG. 4, the “monitor light branching unit that branches a part of the signal light as the monitor light” is an “asymmetric two-branch waveguide”, and the intensity ratio between the signal light and the “branched monitor light” is determined. Since it can be adjusted by the branch angle between the optical waveguide for signal light 211A (211B) and the branch waveguide 212A (212B), it suffices to branch by the amount of light necessary for monitoring, and the wavelength band of the used light is relatively wide.
[0074]
By monitoring the monitor light, it is possible to detect a shift in the operating point due to a temperature drift, a DC drift, or the like in the control circuit unit, and feed back to the signal power supply 207A (207B) to always maintain an appropriate operating point.
[0075]
The optical waveguides 200A, 200B, DAST 201A (201B), 202A (202B), control electrodes 203A to 205A (203B to 205B), reflection mirror 60A (60B), and the like are the same as those in the above-described embodiment of the embodiment of FIG. The monitoring photodetector 50A (50B) can be mounted in the same manner as in the above embodiment.
[0076]
As for the material of each part, it is possible to use various materials described in the above-described embodiment, and it is also possible to improve the reflectance by forming a reflection mirror and forming a metal film on the reflection surface. Same as in the case.
[0077]
Each of the optical modulators of the optical modulator shown in FIG. 4 according to the embodiment is actually manufactured by using the same material and method as in the example of the embodiment in FIG. When a modulation signal was input to the control electrode via the coaxial cable while the light was being incident, an ultra-high-speed light intensity modulation could be realized with a drive voltage as low as about 1.5V.
[0078]
In addition, since monitor light for monitoring is extracted from the upper surface of the upper clad, the monitor photodetector can be arranged so as not to interfere with the optical waveguide or the `` monitor photodetector of another optical modulator ''. Optical modulators can be integrated.
[0079]
FIG. 5 is a modification of the embodiment shown in FIG. In order to avoid complication, the same portions as those in FIG. 4 are denoted by the same reference numerals as those in FIG. 4, and the description regarding FIG.
[0080]
In this embodiment, as a monitor light branching means for branching a part of the signal light as monitor light, a branch waveguide (a directional coupler) is formed at the same time as another optical waveguide portion other than the portion where the DAST is provided. 213A (213B) is used.
[0081]
The monitor light guided through the branch waveguide 213A (213B) is emitted to the upper clad surface side by the grating coupler 61A (61B) and is monitored by the monitor photodetector 50A (50B) mounted on the upper clad. Is detected.
[0082]
By monitoring the monitor light, it is possible to detect a shift in the operating point due to a temperature drift, a DC drift, or the like in the control circuit, and to feed back to the signal power source to always maintain an appropriate operating point.
[0083]
The grating coupler includes a refractive index modulation type and a relief type grating, and a curved grating having a light collecting function can also be formed. For the patterning of the grating, the surface of the resin optical waveguide (branch waveguide) is patterned by photolithography and etching using a mask. At this time, a blazed high-efficiency grating coupler can be formed by using the obliquely incident ion beam. A two-beam interference method in which exposure is performed by interfering two coherent light waves, an electron beam drawing method in which a pattern is formed using an electron beam, and the like can also be used as the grating patterning method.
[0084]
The optical waveguides 200A, 200B, DAST 201A (201B), 202A (202B), control electrodes 203A to 205A (203B to 205B), the reflection mirror 60A (60B), and the like are the same as those in the embodiment of the embodiment shown in FIG. The monitoring photodetector 50A (50B) can be mounted in the same manner as in the previous embodiment.
[0085]
The material of each part can also use the various materials described in the above-described embodiment, and it is also possible to improve the reflectance by forming a reflection mirror and forming a metal film on the reflection surface, as in the above-described embodiment. The same is true.
[0086]
FIG. 6 is another modification of the embodiment shown in FIG. In order to avoid complication, the same portions as those in FIG. 4 are denoted by the same reference numerals as those in FIG. 4, and the description regarding FIG.
[0087]
In this embodiment, a “two-input, two-output multimode interference type optical waveguide” is used as a monitor light branching unit that branches a part of signal light as monitor light.
[0088]
The light phase-modulated by the DAST 201A (201B) and 202A (202B) is split at an intensity ratio of 1: 1 by a two-input two-output multi-mode interferometer optical waveguide 215A (215B) formed in the multiplexing unit. Are guided and emitted as signal light through the signal light optical waveguide 211A (211B).
[0089]
The other of the branched light is guided as a monitor light through the branch waveguide 216A (216B), reflected by the reflection mirror 60A (60B) and emitted to the upper clad surface, and is mounted on the upper surface. It is detected by 50A and 50B.
[0090]
Also in this case, "more accurate monitoring" can be performed because the signal light is directly monitored as compared with the case where the emitted light is monitored. In the two-input, two-output multimode interferometer optical waveguide 215A (215B), the operating point can be "controlled so as to be shifted by a phase of π / 2" in advance, as shown in the embodiment of FIG. As compared with the "directional coupler" used, the tolerance for fabrication is loose, and the wavelength dependence is small as in the "branch waveguide" used in the embodiment of FIG.
[0091]
While monitoring the monitor light, the control circuit can detect a shift in the operating point due to a temperature drift, a DC drift, or the like, and feed back to an input signal to always maintain an appropriate operating point.
[0092]
The two-input two-output multi-mode interferometer optical waveguide 215A (215B) and the monitor light branching waveguide 216A (218B) are formed as resin optical waveguides at the same time as the "other optical waveguide parts other than the part where the DAST is provided". You.
[0093]
The optical waveguides 200A, 200B, DAST 201A (201B), 202A (202B), control electrodes 203A to 205A (203B to 205B), the reflection mirror 60A (60B), and the like are the same as those in the embodiment of the embodiment shown in FIG. The monitoring photodetector 50A (50B) can be mounted in the same manner as in the previous embodiment.
[0094]
As for the material of each part, various materials described in the above embodiment can be used, and the same as in the case of the above embodiment, it is also possible to improve the reflectance by forming a reflection mirror and forming a metal film on the reflection surface. is there.
[0095]
In the optical modulators shown in the embodiments of FIGS. 4 to 6, each “organic waveguide optical modulator with monitor” integrated on the same substrate is a Mach-Zehnder organic waveguide optical modulator. A control circuit 40A for controlling a DC bias voltage applied to electrodes 201A to 203A (201B to 203B) for generating an electric field for modulating the phase of the guided light to set an operating point of light modulation; A monitoring light detector 50A (50B) for detecting a part of the phase-modulated and multiplexed signal light as monitor light, and monitor light branching means 212A (212B) for branching a part of the signal light as monitor light; 213A (213B), 215A (215B), and 216A (216B) intersect the direction of the monitor light branched by the monitor light branching means with the substrate surface on which the optical waveguide is formed. The optical path changing means 60A (60B) and 61A (61B) for converting the light in the direction, and the DC bias voltage is controlled by the control circuit 40A according to the intensity of the radiated light detected by the monitoring photodetector 50A (50B). Then, the operating point of light modulation is adjusted, and DAST is provided in the optical waveguide 200A (200B) as electro-optical effect media 201A (201B) and 202A (202B) for modulating the phase of guided light by an electric field. Is provided as a core layer such that the waveguide direction is the b-axis (claim 4).
[0096]
The "optical path conversion means" is a reflection mirror 60A (60B) in the embodiment of FIGS. 4 and 6 (claim 5), and is a grating coupler 61A (61B) in the embodiment of FIG. Claim 6).
[0097]
The "monitor light branching means for branching the monitor light from the signal light" is the branch waveguide 212A (212B) in the embodiment of FIG. 4 (claim 7), and the directional coupler 213A in the embodiment of FIG. (213B) (claim 8), and in the embodiment of FIG. 6, it is a two-input, two-output multimode interference type optical waveguide 215A (215B) (claim 9).
[0098]
Therefore, an optical modulator according to an embodiment shown in FIGS. 4 to 6 has two or more organic waveguide type optical modulators with a monitor according to any one of claims 4 to 9 integrated on the same substrate. (Claim 10).
[0099]
FIG. 7 is a diagram showing one embodiment of the optical integrated circuit.
This optical integrated circuit realizes optical wiring between a plurality of ICs 410 and 420 arranged on a printed circuit board 400. The printed circuit board 400 is made of glass, ceramic, a resin film, or the like. “Optical wiring” is used for fast signal lines, and slow signal lines are electrical wiring. Electric wiring and optical wiring are mixed on the printed circuit board 400, such as power supply to the light emitting elements 431 and 432 and wiring to control electrodes to the optical modulators 440 i arranged in an array.
[0100]
As each light modulator of the light modulator array in the light output unit (composed of a light emitting element and a light modulator array), an “organic waveguide light modulator with monitor” of the type shown in FIG. 4 is used. . That is, the optical modulator array is an optical modulator in which a plurality of the organic waveguide type optical modulators with monitor shown in FIG. 5 are formed and arranged on the same printed circuit board 400.
[0101]
Since the organic waveguide type optical modulator with monitor of the present invention can be formed at a low temperature, it can be monolithically formed on the printed circuit board 400 on which the electric wiring is formed.
[0102]
On the printed circuit board 400 on which electric wiring has been formed in advance, each optical waveguide is formed using a polyimide resin in the same manner as in the above-described embodiment, and DAST is formed only in the arm portion by a slow cooling method from methanol and subsequent polishing. I do. The branch waveguide for branching the monitor light is formed at the same time when the groove of each optical waveguide is formed, and the resin is filled with the same resin as the portion outside the DAST formation site.
[0103]
The reflection mirror that reflects the monitor light toward the monitor photodetector was formed as a V-shaped groove having an inclination angle of 45 degrees from the back surface side of the printed circuit board 400. Further, each control electrode was formed by AU vapor deposition, and the optical modulator array was formed monolithically. The photodetector for detecting the monitor light was mounted in a hybrid together with a light emitting element and a light receiving element for light output and light input.
[0104]
That is, the polyimide on the electric wiring is removed, and flip-chip mounting is performed to form an optical integrated circuit. The output from the monitoring photodetector is taken into a control circuit, and when the optical output fluctuates, the DC bias of each optical modulator is controlled so that a desired optical output is obtained.
[0105]
Light emitted from the hybrid-mounted light emitting elements 431 and 432 is branched and guided to each optical modulator through an optical waveguide. Here, the electrical signals output from the plurality of output terminals of the ICs 410 and 420 are integrated by a demultiplexer (not shown), and four monitor-equipped organic waveguide type optical modulators 440i and the like constituting an optical modulator array are provided. (I = 1 to 4), modulated by an optical modulator driver (not shown) according to the output electric signal, guided to the light receiving element arrays 471 and 472 through the optical waveguide 460, and possibly passed through an amplifier to a multiplexer (not shown). It is then converted back to the original bits and transmitted to another IC.
In this embodiment, the input / output device has two optical outputs and optical inputs to enable bidirectional optical transmission. Although this is a preferred example, the optical integrated circuit of the present invention is limited to such a configuration. However, if there is a configuration having an optical output unit including an optical modulator in which DAST is selectively arranged, the optical input unit does not have to be on the same substrate, and conversely, other optical components are not required. There is no problem even if there is.
[0106]
In the embodiment shown in FIG. 7, since the organic optical modulator can perform very high-speed modulation, an electric signal is processed using a multiplexer and a demultiplexer, and the transmission path is utilized by utilizing the high speed of the optical modulator. However, the optical modulation may be performed by associating each optical modulator with each output terminal of the IC.
As described above, by using the organic waveguide type optical modulator with a monitor using the organic crystal: DAST, the fluctuation of the operating point due to the temperature drift, the DC drift of the modulation signal, and the like is removed, and the low voltage driving is enabled. A stable optical integrated circuit can be realized at low cost.
[0107]
【The invention's effect】
As described above, according to the present invention, an organic waveguide type optical modulator with a monitor, an optical modulation device, and an optical integrated circuit can be realized.
The organic waveguide type optical modulator with monitor according to the present invention can realize high-speed optical modulation by low voltage driving by using DAST as a Mach-Zehnder type optical waveguide type optical modulator, and can monitor the emission light and the signal light by the monitor. By detecting the parts and adjusting the DC bias voltage based on the detection results, the effects of temperature drift and DC drift can be reliably removed, and each part can be configured and integrated in a low-temperature process, realizing low cost. it can. Therefore, an optical modulator in which a plurality of organic waveguide type optical modulators with a monitor of the present invention are integrated on the same substrate, and an optical integrated circuit in which electric elements are further integrated can be realized at low cost and have high reliability. In addition, high-speed signal transmission / reception at a low voltage is possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing the molecular structure of DAST.
FIG. 2 is a diagram for explaining an embodiment of an organic waveguide type optical modulator with a monitor.
FIG. 3 is a diagram for explaining the light output of signal light and the light intensity of emitted light.
FIG. 4 is a diagram for explaining an embodiment of an optical modulation device having two organic waveguide type optical modulators with a monitor.
FIG. 5 is a diagram for explaining another embodiment of an optical modulation device having two organic waveguide type optical modulators with a monitor.
FIG. 6 is a diagram for explaining another embodiment of the light modulation device having two organic waveguide type light modulators with a monitor.
FIG. 7 is a diagram illustrating one embodiment of an optical integrated circuit.
[Explanation of symbols]
200 Mach-Zehnder optical waveguide
201, 202 DAST
203, 204, 205 control electrode
207 Signal power supply
50 Photodetectors for monitors
60 reflection mirror

Claims (11)

A Mach-Zehnder type organic waveguide type optical modulator,
A control circuit that controls a DC bias voltage applied to set an operating point of light modulation on a control electrode that generates an electric field for modulating the phase of the guided light,
A radiation light generated at a multiplexing portion where the phase-modulated guided light is multiplexed, having a monitoring photodetector for detecting via a cladding portion,
According to the intensity of the emitted light detected by the monitoring photodetector, the DC bias voltage is controlled by the control circuit to adjust an operating point of light modulation,
In the optical waveguide, 4-N, N-dimethylamino-4′-N-methylstilbazolium tosylate (4-N, N-dimethylamino-) is used as an electro-optic effect medium for modulating the phase of guided light by the electric field. A 4′-N-methyl-stilbazolium tosylate (hereinafter abbreviated as DAST) crystal as a core layer with a b-axis in a waveguide direction, and a monitor-equipped organic waveguide optical modulator having a monitor. . The organic waveguide type optical modulator with monitor according to claim 1,
An organic waveguide type with a monitor, characterized in that a reflection mirror for changing the direction of emitted light, which is generated at a multiplexing portion where the phase-modulated guided light is multiplexed, is provided in a clad portion through which the radiated light propagates. Light modulator. The organic waveguide type optical modulator with monitor according to claim 2,
An organic waveguide type optical modulator with a monitor, characterized in that the reflection mirror changes the direction of emitted light to a direction crossing the substrate surface on which the optical waveguide is formed. A Mach-Zehnder type organic waveguide type optical modulator,
A control circuit that controls a DC bias voltage applied to set an operating point of light modulation on a control electrode that generates an electric field for modulating the phase of the guided light,
A monitoring photodetector for detecting a part of the phase-modulated and combined signal light as monitor light,
Monitor light branching means for branching a part of the signal light as monitor light;
Optical path conversion means for converting the direction of the monitor light branched by the monitor light branching means into a direction crossing the substrate surface on which the optical waveguide is formed,
According to the intensity of the monitor light detected by the monitor photodetector, the DC bias voltage is controlled by the control circuit to adjust the operating point of light modulation,
An organic with monitor characterized in that a DAST crystal is provided as a core layer in an optical waveguide as an electro-optic effect medium for modulating the phase of guided light by the electric field so that the waveguide direction is the b-axis. Waveguide type optical modulator. The organic waveguide type optical modulator with monitor according to claim 4,
An organic waveguide type optical modulator with a monitor, wherein the optical path conversion means is a reflection mirror. The organic waveguide type optical modulator with monitor according to claim 4,
An organic waveguide type optical modulator with a monitor, wherein the optical path conversion means is a grating coupler. The organic waveguide type optical modulator with monitor according to claim 4, 5, or 6,
An organic waveguide type optical modulator with a monitor, wherein the monitor light branching means for branching the monitor light from the signal light is a branch waveguide. The organic waveguide type optical modulator with monitor according to claim 4, 5, or 6,
An organic waveguide type optical modulator with a monitor, wherein the monitor light branching means for branching the monitor light from the signal light is a directional coupler. The organic waveguide type optical modulator with monitor according to claim 4, 5, or 6,
An organic waveguide type optical modulator with a monitor, wherein the monitor light splitting means for splitting the monitor light from the signal light is a multi-mode interference type optical waveguide having two inputs and two outputs. 10. An optical modulator, wherein two or more organic waveguide optical modulators with a monitor according to claim 1 are integrated on the same substrate. 10. An organic waveguide optical modulator with a monitor according to claim 1 on one or more substrates, wherein an output terminal of an electronic device and control of the organic waveguide optical modulator with a monitor are controlled. By electrically connecting the electrodes, the light from the light emitting element is output as one or more modulated lights corresponding to the electric signal from the output terminal, and the output modulated light is transmitted by the optical transmission unit. The configured optical integrated circuit.

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