JP5667514B2 - Phase shifter on semiconductor substrate, polarization separator and polarization synthesizer using the same - Google Patents

Description

  The present invention relates to a phase shifter on a semiconductor substrate, and a polarization separator and a polarization synthesizer using the phase shifter.

  There is a demand for an increase in communication traffic volume via the Internet and the like. Therefore, in a wavelength division multiplexing (WDM) system, an increase in transmission speed per channel and an increase in the number of wavelengths are required. Specifically, high transmission rates such as 40 Gbit / s and 100 Gbit / s are required for transmission in the WDM system.

  However, when the modulation symbol rate is increased for higher speed, there is a problem that the dispersion tolerance is rapidly deteriorated and the transmission distance is shortened. A multilevel technology for increasing the bit rate without increasing the symbol rate. And the need for multiplexing technology is increasing. Various formats have been developed such as DQPSK (Differential Quadrature Shift Keying) optical modulators and DP (Dual Polarization) -QPSK optical modulators in which multiple Mach-Zehnder optical modulators are arranged in parallel. Wave multiplexing techniques are becoming standard.

  In the polarization multiplexing technique, a function necessary for the optical transmitter is to place different modulation signals on the orthogonal polarization components. There are two possible ways to shape it. One is a method (see Non-Patent Document 1) in which one polarization light is modulated, and one of the polarizations is rotated by 90 ° and then combined by a polarization beam combiner (Polarization Beam Combiner). The other is a method in which two polarization components are provided at the time when light enters the optical modulator, and after the incidence, they are separated into orthogonal components by a polarization beam splitter, and the orthogonal components are respectively modulated. (See Non-Patent Document 2).

At present, these technologies are realized by using an LN modulator composed of LiNbO ₃ (lithium niobate; LN). When 100-Gbit / s DP-QPSK becomes popular in the future, The size will increase. In addition, it is necessary to use a driver having a relatively high half-wave voltage and a high voltage output, and thus the power consumption of the driver is increased. In the current communication, it is required to reduce the power consumption while reducing the size, and in the future, there is a limit to solving the above problem using only the LN modulator.

  Therefore, as one means for meeting these requirements, a Mach-Zehnder type semiconductor modulator that changes the refractive index by applying an electric field to a semiconductor element and converts an input electric signal into a phase change of light has attracted attention. The semiconductor modulator has a larger relative refractive index difference between the optical waveguides to be configured and a smaller bending radius than the LN modulator, so that a small circuit layout is possible. In addition, since the drive voltage can be made smaller than that of the LN modulator, it has been attracting attention from the viewpoint of low power consumption. In these semiconductor modulators, as with the LN modulator, a high-speed modulator corresponding to a multilevel transmission format such as DQPSK has already been reported.

Hiroshi Yamazaki et al., “Integrated 100-Gb / s PDM-QPSK modulator using a hybrid assembly technique with silica-based PLCs and LiNbO3 phase modulators,” ECOC 2008, Mo.3.C.1, 2008. C. R. Doerr and L. Zhang, “Monolithic 80-Gb / s Dual Poralization On-Off-Keying Modulator in InP,” OFC, PDP19, 2008. Y. Hashizume, R. Kasahara, T. Saida, Y. Inoue, and M. Okano, “Integrated polarisation beam splitter using waveguide birefringence dependence on waveguide core width,” Electronics Letters, 6 Dec 2001, Vol. 37, No. 25 , pp. 1517-1518. Shigeaki Oie, Yoshio Zhang, Takahiro Okabe, “Electro-optic effect of zinc-blende crystals”, Laser Research, Laser Society of Japan, January 1987, Vol. 15, No. 1, pp. 2-11

  In the prior art, polarization control using micro-optics is the mainstream as a method of realizing polarization multiplexing in a Mach-Zehnder type semiconductor modulator. However, the modulator can be made small because of the use of semiconductors, but the size at the location where polarization control is performed is large even for micro-optics, and the overall size of the device is increased. It has become smaller. In addition, since the alignment is complicated and takes time, the manufacturing cost is high.

  Therefore, it is required to monolithically integrate PBC and PBS on a semiconductor substrate. Then, alignment is not required, and polarization control in the semiconductor modulator can be realized in a small size.

Therefore, when the Mach-Zehnder type optical circuit is composed of arm waveguides having different waveguide widths, it can be considered that the birefringence, which is the difference in refractive index between TE polarized light and TM polarized light, is different between the upper and lower arm waveguides. By controlling the birefringence by the waveguide width, at the output of the Mach-Zehnder type optical circuit, as possible out to give a phase difference of a half wavelength between the TE and TM polarizations. For this reason, when non-polarized light is incident, it is possible to realize a circuit with different outputs depending on the polarization, that is, PBS. On the contrary, when TE polarized light and TM polarized light are input, they are combined and output to one waveguide. PBC can be realized (see Non-Patent Document 3).

  However, it is very difficult to manufacture such a Mach-Zehnder type optical circuit with good reproducibility as designed. In particular, even if the waveguide width is slightly deviated from the design of the semiconductor optical waveguide, the effective refractive index of the waveguide greatly changes. Therefore, an adjustment mechanism for the birefringence of the manufactured Mach-Zehnder optical circuit is required.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a phase shifter on a semiconductor substrate capable of adjusting the birefringence with high accuracy, and also to a polarization using the phase shifter. It is to provide a separator and a polarization synthesizer.

In order to achieve such an object, a first aspect of the present invention includes a first birefringence adjusting unit and a second birefringence adjusting unit connected to the first birefringence adjusting unit. On a semiconductor substrate having a zinc blende structure, and the first birefringence adjusting unit includes a first waveguide unit having a first width included in a first arm waveguide, and the first birefringence adjusting unit. A second waveguide portion having a second width of a second arm waveguide disposed in parallel with the arm waveguide, a first electrode on the first waveguide portion, and the second electrode is composed of a second electrode on the waveguide portion, said first width being greater than said second width, the second birefringence adjustment portion, said first arm waveguide has, The third waveguide section disposed to be inclined from the first waveguide section and the third arm waveguide have the third waveguide section inclined from the second waveguide section. A fourth waveguide section arranged in parallel with the waveguide section, a third electrode on the third waveguide section, and a fourth electrode on the fourth waveguide section The first and second arm waveguides are formed of a semiconductor having the zincblende structure, the principal plane orientation of the semiconductor substrate is (100), and the first and second The waveguide portion is arranged in the 01-1 direction or the 0-11 direction, and the third and fourth waveguide portions are any of the 010 direction, the 00-1 direction, the 0-10 direction, and the 001 direction. The phase shifter is arranged in a direction within ± 5 ° from the above.

  Further, according to a second aspect of the present invention, in the first aspect, the third and fourth waveguide portions may be arranged in the second birefringence adjusting unit in units of unit voltages for TE polarized light and TM polarized light. It is arranged in a direction in which the polarization plane dependency of the refractive index change rate is suppressed.

According to a third aspect of the present invention, there is provided a first optical coupler, a phase shifter of the first or second aspect connected to the first optical coupler, and a second connected to the phase shifter. A polarization separator comprising: an optical coupler.

According to a fourth aspect of the present invention, there is provided a first optical coupler, a phase shifter according to the first or second aspect connected to the first optical coupler, and a second connected to the phase shifter. A polarization beam combiner.

  According to the present invention, a first birefringence adjusting unit and a second birefringence adjusting unit connected to the first birefringence adjusting unit are provided on a semiconductor substrate having a zinc blende structure. It is a phase shifter, and the upper and lower arm waveguides that constitute the first birefringence adjusting unit and the upper and lower arm waveguides that constitute the second birefringence adjusting unit are inclined, thereby providing accuracy. It is possible to provide a phase shifter on a semiconductor substrate capable of adjusting a high birefringence.

It is a figure which shows PBS which concerns on the 1st Embodiment of this invention. It is a figure which shows the deformation | transformation form of PBS which concerns on 1st Embodiment. It is a figure for demonstrating the manufacturing method of PBS which concerns on 1st Embodiment. It is a figure which shows PBS which concerns on 2nd Embodiment. It is a figure which shows the refractive index ellipsoid of the compound semiconductor of a zinc blende type structure. It is a figure which shows PBS which concerns on 4th Embodiment. It is a figure which shows the deformation | transformation form of PBS which concerns on 4th Embodiment. It is a figure which shows the conventional RZ carver. It is a figure which shows the operation example of PBS of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a PBS according to the first embodiment of the present invention. Although described as a PBS, it also functions as a PBC as described above. The PBS 100 includes a first optical coupler 110, a first birefringence adjusting unit 120 connected to the first optical coupler 110, and a second birefringence connected to the first birefringence adjusting unit 120. The index adjusting unit 130 and the second optical coupler 140 connected to the second birefringence adjusting unit 130 are provided on the semiconductor substrate 101 having a zinc blende structure. The first birefringence adjusting unit 120 and the second birefringence adjusting unit 130 function as a phase shifter.

  The first birefringence adjusting unit 120 includes a first waveguide unit 102A having a first width included in the first arm waveguide 102 connected to the first coupler 110, and a first coupler 110 connected to the first coupler 110. A second arm waveguide 103A having a second width included in a second arm waveguide 103 connected in parallel to the first arm waveguide 102; a first electrode 102B on the first waveguide section 102A; , And the second electrode 103B on the second waveguide portion 103A, where the first width is larger than the second width.

  The second birefringence adjusting unit 130 includes a third waveguide unit 102C that the first arm waveguide 102 has, and a second waveguide that is inclined from the first waveguide unit 102A. 103, the fourth waveguide portion 103C, which is inclined from the second waveguide portion 103B and arranged in parallel with the third waveguide portion 102C, and the third waveguide portion 103C above the third waveguide portion 102C. The electrode 102D and the fourth electrode 103D on the fourth waveguide portion 103C are configured. The inclination angle of the third waveguide portion 102C and the fourth waveguide portion 103C only needs to be angled, and can be set to 30 °, for example.

  In FIG. 1, the upper and lower arm waveguides are bent twice so that the lengths of the upper and lower arm waveguides are equal. However, it is preferable because the upper and lower arm waveguides can be made approximately equal by bending twice and the band can be widened.

  The PBS 100 according to the present embodiment has polarization plane dependency and crystal orientation dependency on a refractive index change when a voltage is applied in an optical waveguide formed in a compound semiconductor having a zinc blende type structure such as GaAs or InP. Take advantage of what exists. In general, a semiconductor optical waveguide has a polarization plane dependency. However, in a compound semiconductor having a zinc blende structure, a crystal orientation parallel to the optical waveguide greatly affects a refractive index change with respect to TE polarization. By changing the directions of the optical waveguides constituting the first birefringence adjusting unit 120 and the second birefringence adjusting unit 130, two types of birefringence adjusting mechanisms having different refractive index change rates per unit voltage are provided. can get. By using these birefringence adjusting mechanisms as follows, the birefringence can be adjusted with high accuracy.

  First, ASE light is used as a light source and guided to the first optical coupler 110. For example, input is performed from the end face of the input waveguide of the first optical coupler 110 using a tip sphere fiber. Next, in the first birefringence adjustment unit 120, a voltage is applied to the first electrode 102B or the second electrode 103B, and adjustment is performed so that the polarization extinction ratio becomes maximum within some observation wavelength. . At this time, the wavelength at which the maximum polarization extinction ratio can be obtained does not have to match the operating wavelength. For the output observation, the output from the end face of the output waveguide of the second optical coupler 140 is collected using a polarization-maintaining front-end fiber, and the output of each polarization is introduced into the spectrum analyzer via the fiber in-line type PBS. Then, make adjustments while viewing the spectrum. In this state, a voltage is applied to the third electrode 102C or the fourth electrode 103D of the second birefringence adjusting unit 130. Since the spectrum changes, the applied voltage is finely adjusted in the direction in which the operating wavelength and the wavelength at which the maximum polarization extinction ratio can be obtained coincide. As the wavelength approaches the target wavelength, the polarization extinction ratio slightly deteriorates. Therefore, the voltage of the first birefringence adjusting unit 120 is adjusted so as to improve the polarization extinction ratio again, thereby improving the polarization extinction ratio. The adjustment of the polarization extinction ratio in the first birefringence adjustment unit 120 and the adjustment of the wavelength in the second birefringence adjustment unit 130 are repeatedly performed to obtain the target polarization extinction ratio at the target operating wavelength. Finally get. The adjustment needs to be repeated a plurality of times and takes time and labor, but it is possible to obtain a phase shifter having desired characteristics.

  In addition, although the adjustment method using a spectrum analyzer was demonstrated, it is not restricted to this. Adjustment is possible even if measurement is performed using a combination of a wavelength tunable laser, a polarizer, and an optical power meter.

  Note that the PBS according to the present embodiment functions similarly even if the arrangement order of the first birefringence adjusting unit 120 and the second birefringence adjusting unit 130 is changed as shown in FIG. I want to be.

  Further, as can be understood from the description in the second embodiment, when the main surface orientation of the semiconductor substrate 101 is (100), the first waveguide portion 102A and the second waveguide portion 103A, The waveguide section 102C and the fourth waveguide section 103C need to be arranged so as not to have an axis of symmetry in the 011 direction. In this case, the first birefringence adjusting unit 120 and the second birefringence adjusting unit 130 have the same refractive index change rate, and two types of birefringence adjusting mechanisms cannot be provided. .

Manufacturing Method A PBS manufacturing method according to this embodiment will be described with reference to FIG. First, as shown in FIG. 3 (a), a first n-type electrode layer 51 (n + -InP) is grown on a semi-insulating (SI) -InP substrate 50, and a first n-type electrode layer 51 (n + -InP) is grown thereon. 1 n-type cladding layer 52 (n-InP) is formed, and on the first n-type cladding layer 52, a first intermediate layer 53 (i-InGaAsP), a multiple quantum well (MQW) core layer 54, A second intermediate layer 55 (i-InGaAsP) is formed.

  After the first low-concentration cladding 56 (i-InP) is formed on the second intermediate layer 55 (i-InGaAsP), an electron barrier is formed on the first low-concentration cladding 56 (i-InP). As a result, a p-type cladding layer 57 (p-InP) is formed. A second n-type cladding layer 58 (n-InP) is formed on the p-type cladding layer 57, and a second n-type electrode layer 59 (n + -InP) is sequentially stacked thereon. Yes.

  Here, the multiple quantum well core layer 54 is configured so that the electro-optic effect works effectively at the operating light wavelength. For example, in the case of a 1.5 μm band device, a layer in which the Ga / Al composition of InGaAlAs is changed is used. The multi-quantum well structure can be a quantum well layer and a quantum barrier layer, respectively. Further, the first intermediate layer 53 functions as a connection layer for preventing carriers generated by light absorption from being trapped at the heterointerface.

  To manufacture the PBS according to this embodiment, first, a separation groove is formed between the arm waveguides in order to electrically separate the upper and lower arm waveguides. In the case of a Mach-Zehnder structure in which the modulation electrode and the phase adjustment electrode are separated, a separation groove is provided between them to perform electrical separation. This is because the voltage applied to one arm waveguide for modulation affects the modulation of the other arm waveguide if electrical isolation is not performed. The separation groove is formed in a part of the arm waveguide by using a standard photolithography and patterning part from the second n-type electrode layer 59 to the p-type cladding layer 57 functioning as an electron barrier, and using a wet etching technique. It is formed by removing as a groove having a width of several microns.

  In the present embodiment, the electrical separation is performed by the separation groove. However, the portion other than the periphery of the modulation portion in contact with the electrode functions as an electron barrier from the second n-type electrode layer 59 using a quartz hard mask. After removing up to the mold cladding layer 57, it may be grown again with semi-insulating InP and replaced to perform electrical separation.

  Next, as shown in FIG. 3B, the layers from the second n-type electrode layer 59 (n + -InP) to the first n-type cladding layer intermediate 52 are etched using a dry etching technique. A high-mesa waveguide structure is formed. Then, the first n-type cladding layer 52 is etched to expose the first n-type electrode layer 51.

  Finally, as shown in FIG. 3 (c), the first n-type electrode 60 to be the modulation electrode and the phase adjustment electrode is placed on the second n-type electrode layer 59 and the second n-type electrode to be the ground electrode. 61 are formed on the first n-type electrode layer 51, respectively. If necessary, a passivation film may be deposited to protect the mesa surface, or the high mesa structure may be protected using a polymer or the like.

Mounting Method of Mach-Zehnder Type Optical Modulator The PBS 100 according to the present embodiment has a modulation function by inputting a modulation signal to the first electrode 102B, the second electrode 103B, the third electrode 102D, and the fourth electrode 103D. Can be made to function as an optical modulator. The mounting method will be described.

  First, the back surface of the substrate is polished to such an extent that subsequent cleavage can be performed. After depositing a metal film so that the fixed solder adheres to the back surface, it is cleaved into each chip, and a non-reflective coating is performed on the end face where the input / output waveguide is located.

  Next, the chip is mounted on a submount made of ticker aluminum with a standard chip bonder, and then fixed by heating, followed by a terminating resistor, capacitor, thermistor (temperature sensor that detects temperature as a resistance change), and high-speed signal. A wiring board for transmission is also mounted with a chip bonder and fixed by reflow.

  After wiring and elements on the fixed submount and the electrodes of the chip and the electrode of the chip are connected by wire bonding, the submount is again negatively fixed to the mount made of CuW, and the tip of the input / output waveguide using YAG laser The lens that collimates the input / output light is fixed. The one mounted on these CuW mounts is mounted in an airtight package that can be fixed to both ends, and the I / O fiber with lens is fixed to YAG, and the high-frequency differential signal input terminal provided on the package A GPPO connector is attached as an RF input connector to form a module. Here, the lens is fixed using a YAG laser, but this is not restrictive. In addition, although GPPO is used as the RF input connector, there is no problem as long as this is an RF input terminal that can input signals of other desired frequencies.

(Second Embodiment)
FIG. 4 shows a PBS according to the second embodiment. The PBS 400 is the same as the PBS 100 according to the first embodiment except for the inclination angle θ. In the PBS 400 according to the second embodiment, the inclination angle θ is appropriately selected, and in the second birefringence adjusting unit 130, the refractive index change rates per unit voltage for the TE polarized light and the TM polarized light are equal. A third waveguide portion 102C and a fourth waveguide portion 103C are arranged. In other words, the inclination angle θ is selected so that the polarization plane dependency of the refractive index change rate is suppressed.

  A method of performing birefringence adjustment with high accuracy using two types of birefringence adjustment mechanisms is the same as that of the PBS according to the first embodiment, but the refractive index change of the second birefringence adjustment unit 130 is also similar. Since the rate is polarization independent, adjustment is easy. Specifically, the first birefringence adjusting unit 120 is adjusted to maximize the polarization extinction ratio, and the second birefringence adjusting unit 130 is used to suppress the deterioration of the polarization extinction ratio. Only the wavelength at which the maximum polarization extinction ratio can be obtained can be shifted. Since there is almost no deterioration of the polarization extinction ratio, it is possible to obtain the maximum polarization extinction ratio at the operating wavelength by finely adjusting the voltage of the first birefringence adjusting unit 120 again, and to shorten the adjustment time. it can.

  When the main surface orientation of the semiconductor substrate 101 is (100), the first waveguide section 102A and the second waveguide section 103A are arranged in the 01-1 direction, and the third waveguide section 102C and the fourth waveguide section When the waveguide section 103C is arranged in the 010 direction and the inclination angle θ is 45 °, the polarization plane dependency of the refractive index change rate in the second birefringence adjusting section 130 can be suppressed. Hereinafter, the reason why the inclination angle θ = 45 ° is appropriate will be described.

Description of Pockels Effect and QCSE in Semiconductor Waveguide As described in the first embodiment, when a voltage is applied to a semiconductor waveguide having a multiple quantum well layer (MQW) in the core layer, in addition to the Pockels effect Thus, a refractive index change is caused by a quantum confined Stark effect (QCSE).

  The refractive index change due to the Pockels effect when an electric field is applied to a compound semiconductor having a zinc blende structure (zinc blend structure) including InP can be described by a refractive index ellipsoid (see Non-Patent Document 4). ).

The refractive index ellipsoid of a compound semiconductor having a zinc blende structure is shown as follows, where n0 is the refractive index before voltage application. Here, r ₄₁ is the electro-optic constant of the compound semiconductor having the zinc blende structure, and E is the strength of the electric field applied to the optical waveguide.

  Since this equation does not change even if xy is replaced, it can be easily seen that the equation shows an ellipsoid that is symmetric with respect to a straight line described by y = x. Therefore, the following expressions are obtained by converting the axes rotated by 45 ° from the x-axis and the y-axis respectively to the x′-axis and the y′-axis and converting the axes.

  A refractive index ellipsoid having a radius on the short axis side and a radius on the long axis side can be drawn.

  FIG. 5 shows a cut surface in the z = 0 plane. The radius of this ellipse indicates the refractive index when the electric field E is applied in the Z-axis direction when light propagates in the direction of the S vector in the figure. Considering the actual orientation of the wafer, when a substrate with a main surface orientation of (001) is used, the electric field strength vibrates in the x ′ direction in the direction parallel to the orientation flat (OF) in the 01-1 direction. When propagating as a TE wave, the refractive index is b due to the Pockels effect, and the amount of change is b−n0. Moreover, the value is larger than the refractive index n0 when no electric field is applied. Conversely, when propagating in the 011 direction perpendicular to the OF, the value is smaller than n0. In either case, when the electric field travels as a TM wave oscillating in the y 'direction, the z direction of the refractive index ellipsoid is n0, and it can be seen that it is not modulated by the Pockels effect by the external electric field. In addition, the light propagating in the 010 direction of 45 ° with respect to the OF indicates the intersection of the ellipse in FIG. 5 and the circle indicating the original refractive index, so that the refractive index change due to the Pockels effect does not occur regardless of the polarization state. I understand that there is no.

  Up to this point, only the Pockels effect has been considered, but when the core of an actual device is composed of multiple quantum wells (MQW), QCSE is added in addition to the Pockels effect. However, QCSE does not depend on the crystal orientation in the first order approximation. Assuming that n (QCSE) is the amount of change in refractive index due to QCSE when the electric field E is applied, n0 ′ = n0 + n (QCSE) used for the explanation of the Pockels effect is n0 ′, and n0 ′ is replaced with n0 ′. I can draw my body.

  From the above, the refractive index change when the external electric field E is applied is summarized as follows for TE polarized light and TM polarized light. Here, the amount of change in refractive index due to the Pockels effect is denoted as P, and the amount of change due to QCSE is denoted as Q.

  Table 1 shows the amount of change in refractive index when the unit electric field strength E is applied. The act of applying an electric field in the longitudinal direction of the waveguide is the same as applying an electric field to a capacitor composed of parallel plates. Yes, the electric field strength is proportional to the voltage. That is, there is no problem even if the effects of P and Q of the refractive index change amount per unit voltage are shown.

  In the above description, the direction parallel to the OF is the 01-1 direction, but the 0-11 direction is also equivalent. In addition, although the direction perpendicular to the OF is the 011 direction, the 0-1-1 direction is also equivalent. In addition, although the direction of 45 ° with respect to the OF is the 010 direction, the 00-1 direction, the 0-10 direction, and the 001 direction are also equivalent.

(Third embodiment)
The PBS according to the third embodiment is substantially the same as the PBS 400 according to the second embodiment shown in FIG. 4, but the tilt angle θ is slightly different. The third waveguide portion 102C and the fourth waveguide portion 103C are arranged slightly shifted from the 010 direction.

  Strictly speaking, QCSE has a different confinement factor. Therefore, even if an optical waveguide is arranged in the 010 direction, TE polarization and TM polarization are not the same. Therefore, the refractive index change rate resulting from QCSE is made independent of polarization by shifting slightly from the 010 direction.

  In the case of Q (TE)> Q (TM), the inclination angle θ is higher than 45 °, that is, the second birefringence adjusting unit 130 approaches the direction perpendicular to the 01-1 direction of OF. By tilting the third waveguide portion 102C and the fourth waveguide portion 103C, the coefficient of the Pockels effect works negatively (see Table 1), the refractive index change rate due to QCSE does not change, but the contribution of the Pockels effect Therefore, there is an angle at which the same refractive index change rate can be effectively realized for TE polarized light and TM polarized light.

  On the contrary, when Q (TM)> Q (TE), the Pockels coefficient works in the positive direction by tilting in the horizontal direction in the 01-1 direction of OF, and the same refractive index change rate for TE polarized light and TM polarized light. There is an angle that can be realized.

  As a result of experimental investigations by the inventors, the polarization extinction ratio is not deteriorated during the adjustment in the second birefringence adjusting unit 130 by tilting by 2 ° in a direction that is close to perpendicular to the 01-1 direction. Only the wavelength could be adjusted individually. In actual manufacturing, there is an angle error of the OF provided on the wafer, and therefore the third waveguide section 102C and the fourth waveguide section 103C of the second birefringence adjusting section 130 are moved ± from the 010 direction. What is necessary is just to incline by 5 degrees.

(Fourth embodiment)
FIG. 6 shows a PBS capable of high-speed light modulation. The PBS 600 includes a first optical coupler 610, a first birefringence adjusting unit 620, a high-speed modulation unit 650, and a second optical coupler 640 on a semiconductor substrate 601. The optical waveguide constituting the high-speed modulation unit 650 is arranged in the 010 direction so that the refractive index change rate per unit voltage is substantially equal between the TE polarized light and the TM polarized light.

  In the PBS 600 of FIG. 6, for the sake of simplicity, it is considered that the first birefringence adjusting unit 620 is manufactured as designed and a birefringence adjusting mechanism is not required. When the phase shifter according to the present invention described in the first to third embodiments is used, it is conceivable to adopt an arrangement as shown in FIG. In the configuration of FIG. 6, when an RF signal is input, high-speed optical modulation can be realized even though it is a PBS. As an application, it can be used as an RZ carver. The first optical coupler 710, the second birefringence adjustment unit 730, the first birefringence adjustment unit 720, the high-speed modulation unit 750, and the second optical coupler 740 are connected in this order.

  Normally, if this is to be realized by the conventional method, as shown in FIG. 8, an MZ that becomes an RZ carver is arranged for each polarization, and then a PBS is arranged. In this case, since it becomes MZ for driving for TE and TM, it is necessary to drive with different RF amplitudes. In other words, the user who uses the device must set the drive driver to a different setting. Depending on the drive amplitude, it is necessary to prepare different drivers. Alternatively, the length of MZ is changed so that the modulation efficiency is the same between TE polarized light and TM polarized light. There is a method of making the RF amplitude constant by using different bias voltages. In any case, in this configuration, a driver and its peripheral circuit must be prepared for each polarization as an RZ carver.

  In the structure of FIG. 6, since the modulation efficiency of TE polarized light and TM polarized light is the same, there is no need to prepare an RZ carver for each polarized light. One MZ can provide PBS and RZ carver. At the same time, the number of drivers and their peripheral circuits can be reduced, and the effect of reducing power consumption, space and cost can be obtained.

  In addition, when non-polarized light or 45 ° polarized light is input, a polarization modulator that alternately outputs TE waves and TM waves from a certain output when RF is input to a 45 ° electrode in this configuration can be configured. Yes (Figure 9).

100, 400 PBS
DESCRIPTION OF SYMBOLS 101 Semiconductor substrate 102 1st arm waveguide 102A 1st waveguide part 102B 1st electrode 102C 3rd waveguide part 102D 3rd electrode 103 2nd arm waveguide 103A 2nd waveguide part 103B 2nd 2nd electrode 103C 4th waveguide part 103D 4th electrode 110 1st optical coupler 120 1st birefringence adjustment part 130 2nd birefringence adjustment part 140 2nd optical coupler 600 PBS
610 First optical coupler 620 First birefringence adjustment unit 640 Second optical coupler 650 High-speed modulation unit 700 PBS
710 First optical coupler 720 First birefringence adjustment unit 730 Second birefringence adjustment unit 740 Second optical coupler 750 High-speed modulation unit θ Inclination angle

Claims (4)

A first birefringence adjusting unit;
A second birefringence adjusting unit connected to the first birefringence adjusting unit on a semiconductor substrate having a zinc blende structure;
The first birefringence adjusting unit is
A first waveguide section having a first width included in the first arm waveguide;
A second waveguide section having a second width which a second arm waveguide disposed in parallel with the first arm waveguide has;
A first electrode on the first waveguide section;
Is composed of a second electrode on the second waveguide portion, said first width being greater than said second width,
The second birefringence adjusting unit is
A third waveguide portion disposed at an angle from the first waveguide portion, the first arm waveguide having;
A fourth waveguide section that the second arm waveguide has, and that is inclined from the second waveguide section and is arranged in parallel with the third waveguide section;
A third electrode on the third waveguide portion;
A fourth electrode on the fourth waveguide portion , and
The first and second arm waveguides are formed of a semiconductor having the zincblende structure,
The principal plane orientation of the semiconductor substrate is (100),
The first and second waveguide portions are arranged in the 01-1 direction or the 0-11 direction,
The third and fourth waveguide portions are arranged in a direction within ± 5 ° from any one of the 010 direction, 00-1 direction, 0-10 direction, and 001 direction. .   The third and fourth waveguide sections are arranged in a direction in which the polarization plane dependency of the refractive index change rate per unit voltage with respect to TE polarized light and TM polarized light is suppressed in the second birefringence adjusting section. The phase shifter according to claim 1, wherein: A first optical coupler;
The phase shifter according to claim 1 or 2 , connected to the first optical coupler;
And a second optical coupler connected to the phase shifter. A first optical coupler;
The phase shifter according to claim 1 or 2 , connected to the first optical coupler;
A polarization beam combiner comprising: a second optical coupler connected to the phase shifter.

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