JP2015197451A - light modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light modulator that can inhibit mixing of noises such as electric crosstalk in a detection signal of a light-receiving element.SOLUTION: The light modulator includes a substrate 1 having an electro-optic effect, an optical waveguide 2 formed in the substrate, and a control electrode (not shown in the figure) to control light waves propagating in the optical waveguide; and the light modulator further includes a light-receiving element (PD) that detects at least a part of light waves propagating in the optical waveguide or in the substrate or light waves exiting from the substrate, electric wiring lines (5, W, PIN, and the like) for leading a detection signal of the light-receiving element to the outside of the light modulator, an anode connection line (WA) connecting an anode terminal of the light-receiving element to the electric wiring line, and a cathode connection line (WC) connecting a cathode terminal of the light-receiving element to the electric wiring line, in which the length of the anode connection line is smaller than the length of the cathode connection line.

Description

  The present invention relates to an optical modulator, and more particularly to an optical modulator comprising a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating in the optical waveguide. The present invention relates to an optical modulator provided with a light receiving element that detects a light wave propagating in the optical waveguide or the substrate, or at least a part of a light wave emitted from the substrate.

  In the optical measurement technical field and the optical communication technical field, an optical modulator using a substrate having an electro-optic effect such as lithium niobate is frequently used. In an optical modulator using a substrate having an electro-optic effect, a phenomenon occurs in which a modulation operation point related to driving shifts due to a pyroelectric effect, such as temperature drift and DC drift. For this reason, DC bias control is performed in order to always adjust to a constant modulation operating point.

  When adjusting the modulation operating point, as shown in Patent Document 1, a part of a light wave propagating through an optical waveguide is introduced into a light receiving element to monitor the light wave. Moreover, when a plurality of Mach-Zehnder type optical waveguides are provided as in Patent Document 1, the modulation state is also monitored for each Mach-Zehnder type optical waveguide.

  FIG. 1 shows an example of an optical modulator having a plurality of Mach-Zehnder type optical waveguides as in Patent Document 1. An optical waveguide 2 is formed on a substrate 1 having an electro-optic effect. The optical waveguide 2 is a sub-Mach-Zehnder type optical waveguide (SMZ1, SMZ2) nested in a branching waveguide of a main Mach-Zehnder type optical waveguide (MMZ). It is arranged and formed. In the case of FIG. 1, in order to monitor the light wave emitted from the sub-Mach-Zehnder type optical waveguides (SMZ1, SMZ2), the light is derived from the sub-Mach-Zehnder type optical waveguide (SMZ1, SMZ2) and received on the output waveguide. Element 3 is arranged. LI indicates incident light, and LO indicates outgoing light.

  In order to derive a detection signal of the light receiving element 3, a terminal provided on the light receiving element and a connection pad 5 formed on the substrate 1 are wire-bonded with a gold wire 4 or the like. The connection pads formed on the substrate 1 are configured to lead the detection signal out of the substrate by electrical wiring formed on the substrate. There is also a method in which the terminals of the light receiving element and the signal output pins are directly connected by wires without using the electric wiring on the substrate.

  Regarding the wiring related to the light receiving element, as shown in Patent Document 2, generally, the electrode terminal of the light receiving element and the lead terminal on the substrate are connected by a bonding wire. No special consideration is given to the length of the connection line.

  Further, the conventional bias control is controlled by detecting a low-frequency dither signal included in the light wave. However, in an optical modulator having a nest structure as shown in FIG. 1, an RF signal is detected for bias control. Sometimes. Further, in an optical modulator having an integrated structure that needs to include a plurality of light receiving elements for monitoring, for example, a DP-QPSK (Dual Polarization Quadrature Phase Shift Keying) light modulator, the light receiving elements for monitoring are close to each other. Therefore, electrical crosstalk between the light receiving elements is likely to occur, and there is a problem that noise is included in the detection signal.

  In addition, the optical modulator is housed in a metal casing, and the signal output pins that penetrate the metal casing electrically connect the inside and the outside of the casing. Since the arrangement of the signal output pins is standardized by the standard, the wiring arrangement of the light receiving element and the electrical connection pad (PAD) is limited. Thereby, a bonding wire (connection line) becomes long and electrical crosstalk is more likely to occur.

  In addition, since the wiring arrangement of the light receiving element and the electrical connection pad (PAD) is limited, the distance between the control electrode such as the signal electrode formed on the substrate and the bonding wire (connection line) connected to the light receiving element is short. There is also a problem that electrical crosstalk is more likely to occur.

International Publication No. WO2008 / 038795 JP 2009-105240 A

  The problem to be solved by the present invention is to provide an optical modulator that solves the above-described problems and can suppress noise such as electrical crosstalk from entering the detection signal of the light receiving element. is there.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) In an optical modulator comprising a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating in the optical waveguide, in the optical waveguide or the substrate A light wave propagating inside, or a light receiving element for detecting at least part of the light wave emitted from the substrate, and an electrical wiring for deriving a detection signal of the light receiving element to the outside of the light modulator, An anode connection line connecting the anode terminal of the light receiving element and the electrical wiring; and a cathode connection line connecting the cathode terminal of the light receiving element and the electrical wiring, the length of the anode connection line being the cathode connection line It is shorter than the length of.

(2) In the optical modulator described in (1) above, the length of the anode connection line is 0.9 mm or less.

(3) In the optical modulator according to (1) or (2), the light receiving element is disposed on the substrate, the anode connection line and the cathode connection line are formed on the substrate, and the electric wiring It is characterized by being connected to a connection pad constituting a part of

(4) In the optical modulator according to any one of (1) to (3), the light receiving element includes at least two light receiving elements.

(5) In the optical modulator according to (1), a housing that houses the optical modulator, and a part of the electrical wiring that passes through the housing has a signal output pin, and the light receiving element includes: , The first and second light receiving elements, and the signal output pin includes a first anode signal output pin and a first cathode signal output pin corresponding to the first light receiving element, and the second light receiving element. There are four signal output pins, a second anode signal output pin and a second cathode signal output pin corresponding to the element, and the signal output pins include a first cathode signal output pin, a first anode signal output pin, The second anode signal output pin and the second cathode signal output pin are arranged in this order.

(6) The optical modulator according to any one of (1) to (5), wherein the optical waveguide includes at least one Mach-Zehnder type optical waveguide.

  According to the present invention, an optical modulator comprising a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating in the optical waveguide. A light receiving element for detecting a light wave propagating in the substrate or at least a part of a light wave emitted from the substrate, and an electrical wiring for deriving a detection signal of the light receiving element to the outside of the optical modulator; An anode connection line connecting the anode terminal of the light receiving element and the electrical wiring, and a cathode connection line connecting the cathode terminal of the light receiving element and the electrical wiring, the length of the anode connection line being the cathode connection Because it is shorter than the length of the line, high-frequency noise such as electrical crosstalk is prevented from entering the detection signal via the anode connection line, and the detection signal from the light receiving element can be detected with high accuracy. It is possible to provide a an optical modulator.

It is the schematic explaining the conventional optical modulator. It is the schematic explaining the Example which concerns on the optical modulator of this invention. It is a perspective view which shows the light receiving element provided with the base. It is the schematic explaining the other Example which concerns on the optical modulator of this invention. It is a graph which shows the mode of the noise level change of the electrical crosstalk with respect to the length of an anode connection line. It is a figure explaining arrangement | positioning of the light receiving element applicable to the optical modulator of this invention. It is a figure explaining an example of the electrical wiring applicable to the optical modulator of this invention. It is a figure explaining the other example of the electrical wiring applicable to the optical modulator of this invention.

Hereinafter, the optical modulator of the present invention will be described in detail using preferred examples.
In the present invention, as shown in FIG. 2, a substrate 1 having an electro-optic effect, an optical waveguide 2 formed on the substrate, and a control electrode (not shown) for controlling a light wave propagating in the optical waveguide are provided. A light receiving element (PD) that detects a light wave propagating in the optical waveguide or the substrate or a light wave emitted from the substrate; and An electrical wiring (5, W, PIN, etc.) for deriving the detection signal to the outside of the optical modulator, an anode connection line (WA) connecting the anode terminal of the light receiving element and the electrical wiring, and the light receiving element A cathode connection line (WC) connecting the cathode terminal and the electric wiring is provided, and the length of the anode connection line is shorter than the length of the cathode connection line.

  As the substrate constituting the optical modulator, a substrate having an electro-optic effect such as lithium niobate (LN) is used. An optical waveguide is formed on the substrate. Specifically, the optical waveguide is formed by thermal diffusion of Ti or the like or formation of a ridge. The control electrode for controlling the light wave propagating through the optical waveguide is formed on the substrate directly or through a buffer layer by forming a Ti / Au electrode pattern, a gold plating method, or the like.

  The light wave detected by the light receiving element includes a light wave propagating through the optical waveguide 2 as shown in FIG. 1, a light wave propagating through the substrate such as a radiation mode light from the combined portion of the optical waveguide, As shown in FIG. 2, a part of any one of the light waves such as the light wave emitted from the substrate 1 is received. For light waves propagating in an optical waveguide or substrate, a part of the propagating light wave is sucked up and detected by placing the light receiving element in contact with or close to the surface of the substrate 1 Yes. The light wave emitted from the substrate 1 is detected by the light receiving element PD arranged outside the substrate as shown in FIG.

  As shown in FIG. 3, the light receiving element arranged outside the substrate has a chip (PDC) constituting the light receiving element arranged and fixed on a pedestal (PDP), and the anode electrode and the cathode electrode in the chip are arranged on the pedestal. It is drawn out as an electrode terminal 50 of (PDP). In the drawing, the electrical wiring between the electrode on the chip and the electrode terminal 50 is omitted. In order to output a detection signal from the light receiving element, wire bonding is performed on the electrode terminal. Further, in the case where wire bonding can be directly performed on the electrode on the chip, the pedestal only needs to support the chip.

  In FIG. 2, four Mach-Zehnder type optical waveguides (MZ1 to MZ4) are arranged in parallel, and the sub-Mach-Zehnder type optical waveguides (SMZ1, SMZ2) are arranged so as to be nested. ), A main Mach-Zehnder type optical waveguide (MMZ1) is arranged. Each of the Mach-Zehnder type optical waveguides (MZ1 to MZ4, SMZ1 to 2, MMZ1) is formed with a control electrode (not shown) for controlling a light wave propagating through the optical waveguide.

  On the downstream side of the substrate 1 (downstream side in the light wave propagation direction), a polarization beam combiner 20 is arranged. The polarization beam combiner is not necessarily an essential component depending on the type of optical modulator. The polarization beam combiner 20 can be constituted by, for example, an optical circuit component formed on a substrate such as a planar optical circuit (PLC) or a spatial optical system such as micro-optics. Note that a light receiving element to be described later can be configured not only to receive a light wave emitted from the substrate 1 to the outside but also to receive a light wave emitted from the polarization beam combiner 20.

  The optical modulator chip itself including the substrate 1 is housed in a housing 6 made of metal or the like. Optical fibers (OF 1, OF 2) and signal output pins (PIN) are disposed so as to penetrate the housing 6 in order to optically or electrically connect the inside and outside of the housing. A signal pin for applying a modulation signal or the like to the control electrode of the optical modulator is also arranged, but is omitted in the drawing.

  The optical fiber OF1 is connected to the light wave incident portion of the substrate 1 and is configured to introduce the incident light LI into the optical waveguide in the substrate 1. The optical fiber OF2 is connected to the light wave emitting part of the optical modulator, and is configured to derive the output signal LO of the optical modulator to the outside.

  In FIG. 2, the radiated light from the combined parts of the sub Mach-Zehnder type optical waveguides (SMZ1, SMZ2) is derived from the substrate 1 by the radiated light optical waveguides (21, 22) and detected by the light receiving element PD. It is composed.

  Wire bonding (WA, WC) is connected to the electrode terminals of the light receiving element PD, and is connected to the electrical wiring 5 formed on the relay substrate 7. In particular, an electrical connection pad having a slightly larger area for reliably performing the connection work is formed at a portion where the wire bonding of the electrical wiring is connected. The electrical wiring of the relay board is connected to the signal output pin PIN by a wire W such as a gold wire or a gold ribbon. Some of the plurality of signal output pins are used as ground terminals (GND) as shown in FIG.

  The relay substrate 7 is not always essential, and the electrode terminal of the light receiving element PD and the signal output pin PIN may be directly connected.

  The electrode terminals of the light receiving element include an anode terminal and a cathode terminal, and bonding wires connected to these terminals also include an anode connection line and a cathode connection line. When the length of the anode connection line is shorter than the length of the cathode connection line, the researcher of the present invention, as a result of earnest research, suppresses the connection line from picking up noise such as electrical crosstalk. Thus, an accurate detection signal can be output. In particular, when the length of the anode connection line is 0.9 mm or less, the noise level can be kept extremely low.

  FIG. 4 is a diagram for explaining another embodiment of the optical modulator of the present invention. The difference from the embodiment of FIG. 2 is that the light receiving element PD is arranged on the optical waveguide (21, 22) of the substrate 1, and the anode connection line WA and the cathode connection line WC connected to the light receiving element PD It is connected to the electrical wiring (5, 8) formed above. In particular, reference numeral 5 in FIG. 4 denotes an electrical connection pad.

  Also in the embodiment of FIG. 4, the length of the anode connection line WA is set to be shorter than the length of the cathode connection line WC.

  FIG. 5 is a graph showing the noise level of electrical crosstalk with respect to the length of the anode connection line. As the measurement system, the optical modulator shown in FIG. 4 is prepared, and a random pulse train (PRBS) is input to the signal electrodes formed in each of the Mach-Zehnders MZ1 to MZ4 in a state where the light L1 is not input. The resulting RF power was detected. At that time, the length of the wire bonding connected to the anode was changed, and the RF power at each length was detected to measure the amount of crosstalk with respect to the length of the wire bonding.

  As a result of examining the region where the noise level of the close talk felt when the length of the connection line is 1.15 mm or more is lowered to about 10 dB or less (the RF power in FIG. 5 is 1.05 [au] or less), anode connection If the length of the line was 0.9 mm or less, it was confirmed that the noise level was about 10 dB or less as usual. This result shows the same tendency even in the configuration as shown in FIG.

  FIG. 6 shows an application example relating to the arrangement of the light receiving elements (PD1, PD2) arranged on the substrate 1. FIG. FIG. 6A shows a part of the radiated light emitted from the Mach-Zehnder type optical waveguides (MZ1, MZ2) using the radiated light optical waveguides (21, 21 ′, 22, 22 ′). Thus, the light receiving elements (PD1, PD2) are arranged. In the case of FIG. 6A, since the two light receiving elements can be arranged relatively apart from each other, the influence of mutual electrical crosstalk is low.

  However, as shown in FIG. 6B, when two radiated lights emitted from one Mach-Zehnder type optical waveguide (MZ1 or MZ2) are received by one light receiving element (PD1 or PD2), The possibility that the light receiving elements (PD1, PD2) are arranged close to each other increases. For this reason, the mutual detection signals generate electrical crosstalk, and a lot of noise easily enters the detection signals. For this reason, the configuration of the optical modulator of the present invention can be suitably applied particularly in the case of FIG.

  The electrical wiring to which the bonding wires are connected preferably has a configuration that suppresses noise emission. For this purpose, it is possible to use a high-frequency line such as a coplanar waveguide, a microstrip line, or a differential strip line as the electrical wiring. For example, as shown in FIG. 7, the anode wiring and the cathode wiring can be arranged in parallel to adopt a differential stripline configuration.

  Also, as shown in FIG. 8, when the two light receiving elements (PD1, PD2) are arranged close to each other, the electric wiring L needs to be close to each other. In order to shorten the length of the two anode connection lines WA, it is preferable to dispose the cathode electrical wiring (LC1, LC2) on both sides of the anode electrical wiring (LA1, LA2). In accordance with this, it is preferable to arrange the signal output pins in the same order. As shown in FIG. 2 or FIG. 4, when a grounding pin is provided, it is preferably provided further outside the cathode signal output pin, but it is disposed at an arbitrary position inside the cathode signal output pin. It does not prevent.

  The configuration shown in FIG. 8 is not limited to the electrical wiring formed on the relay board 7 in FIG. 2 or the board 1 in FIG. For example, the same arrangement can be adopted when the light receiving element and the signal output pin are directly wire-bonded.

  As described above, according to the present invention, it is possible to provide an optical modulator capable of suppressing noise such as electrical crosstalk from entering a detection signal of a light receiving element.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 6 Case PD Light receiving element PIN Signal output pin WA Anode connection line WC Cathode connection line

Claims (6)

In an optical modulator comprising a substrate having an electro-optic effect, an optical waveguide formed on the substrate, and a control electrode for controlling a light wave propagating in the optical waveguide,
A light receiving element that detects a light wave propagating in the optical waveguide or the substrate, or a light wave emitted from the substrate;
Electrical wiring for deriving the detection signal of the light receiving element to the outside of the optical modulator;
An anode connection line connecting the anode terminal of the light receiving element and the electrical wiring;
A cathode connection line connecting the cathode terminal of the light receiving element and the electrical wiring;
The length of the anode connection line is shorter than the length of the cathode connection line.   2. The optical modulator according to claim 1, wherein the anode connection line has a length of 0.9 mm or less. The optical modulator according to claim 1 or 2,
The light receiving element is disposed on the substrate;
The optical modulator, wherein the anode connection line and the cathode connection line are formed on the substrate and connected to a connection pad constituting a part of the electric wiring.   4. The optical modulator according to claim 1, wherein the light receiving element includes at least two light receiving elements. 5. The optical modulator according to claim 1.
A housing for housing the optical modulator;
A part of the electrical wiring penetrating the housing has a signal output pin;
The light receiving element includes two light receiving elements, a first light receiving element and a second light receiving element,
The signal output pins include a first anode signal output pin and a first cathode signal output pin corresponding to the first light receiving element, and a second anode signal output pin and a second cathode signal corresponding to the second light receiving element. It has four signal output pins of output pins,
The signal output pins are arranged in the order of a first cathode signal output pin, a first anode signal output pin, a second anode signal output pin, and a second cathode signal output pin. Light modulator. 6. The optical modulator according to claim 1, wherein the optical waveguide includes at least one Mach-Zehnder type optical waveguide.

Images