JP2013011777A - Differential phase-shift keying optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact delay interferometer allowing a low-cost packaging.SOLUTION: A differential phase-shift keying optical receiver includes a 1-bit delaying interferometer adapted to emit second light and third light that is 1-bit delayed compared with the second light, when first light is input. The 1-bit delaying interferometer is configured by sticking optical plates having half mirrors and total reflection mirrors.

Description

  The present invention relates to a differential phase shift modulation optical receiver that transmits and receives high-speed optical signals between optical devices between communication devices using optical fibers or between devices such as data processing devices.

  In recent years, in the information and communication field, the development of information and communication traffic that exchanges large amounts of data at high speed using light is being carried out rapidly. Until now, relatively long distances of several kilometers or more such as backbone, metro, and access systems. Optical fiber networks have been deployed. In the future, in order to process large-capacity data without delay, even in extremely short distances such as between transmission devices (several meters to several hundreds of meters) or within devices (several centimeters to several tens of centimeters) Is effective.

  Regarding optical wiring between / inside devices, for example, in a transmission device such as a router / switch, a high-frequency signal transmitted from the outside such as an Ethernet through an optical fiber is input to a circuit board called a line card. This line card consists of several cards for one backplane, and the input signals to each line card are further collected on a circuit board called a switch card via the backplane, and are sent to the LSI in the switch card. Are processed and then output to each line card again via the backplane. Here, in the current apparatus, signals of 600 Gbit / s or more from each line card are collected on the switch card via the backplane. In order to transmit this with the current electrical wiring, it is necessary to divide the wiring into about 1 to 6 Gbit / s per wiring due to propagation loss, and therefore, the number of wirings of 100 or more is required.

  Furthermore, it is necessary to take countermeasures against waveform shaping circuits, reflection, or crosstalk between wirings for these high-frequency lines. In the future, when the capacity of the system is further increased and the apparatus becomes a device that processes information of Tbit / s or more, problems such as the number of wirings and countermeasures against crosstalk become more serious in the conventional electric wiring. On the other hand, since it is possible to propagate high-frequency signals of 10 Gbps or more with low loss by opticalizing the signal transmission line between the board of the line card in the apparatus to the backplane to the switch card, and further between the chips in the board, This is promising because the number of wirings can be reduced and the above measures are not necessary for high-frequency signals. In addition to the above routers / switches, video devices such as video cameras and consumer devices such as PCs and mobile phones will increase the speed and capacity of video signal transmission between the monitor and terminals in the future for higher definition images. In addition, since conventional electrical wiring has problems such as signal delay and noise countermeasures, it is effective to make the signal transmission line optical.

  In order to realize such a high-speed optical interconnection circuit and apply it between / inside devices, an optical module and circuit that are inexpensive in terms of performance, miniaturization / integration, and component mounting are required. . Therefore, a small and high-speed optical module has been proposed in which an optical waveguide that is cheaper and more advantageous for higher density than conventional optical fibers is used as a wiring medium, and an optical component and an optical waveguide are integrated on a substrate.

  As a light source for such a high-speed optical interconnection module, a vertical cavity surface emitting laser (Vertical Cavity Surface Emitting Laser: VCSEL), a resonator is formed in the in-plane direction of the substrate, and the main emitted light of the resonator An optical element in which a tapered mirror is disposed at a position where light is incident, or only a part of the resonator is configured in the in-plane direction of the substrate, and the tapered mirror is disposed in the resonator on the substrate surface. Proposed.

“Uncooled 25-Gb / s 2-km Transmission of a 1.3-μm Surface Emitting Laser” K. Adachi., Et al., 22nd IEEE International Semiconductor Laser Conference, (ISLC2010), TuC5

  All of the light sources described here are directly modulated light sources. Directly modulated light sources are cheap and small, but the high-speed operation is limited by the relaxation oscillation frequency, so if further high-speed operation (for example, 40 Gbps or more per channel) is required in the future, it will respond. It's not easy. For example, there is an external modulation method as a technique for realizing a high-speed operation of 40 Gbps or more. In communication systems that require long-distance transmission over several tens of kilometers, various external modulation methods have already been put to practical use. Among various external modulation schemes, differential phase shift keying (DPSK) is capable of speeding up to 40 Gbps or more, and the receiver sensitivity is 3 dB higher than the intensity modulation scheme. It has excellent features such as quality signal transmission. In addition, multi-level modulation is possible by variously combining the phase, intensity, and polarization, and research and development has been actively conducted in recent years from the viewpoint of improving frequency utilization efficiency.

  However, a problem with such a phase shift modulation scheme is that the receiver is complicated. In order to explain this problem, the principle of the differential phase shift modulation method will be briefly described first. In the differential phase shift method, the phase-modulated signal light is branched into two. Then, one of the branched signal lights is delayed from the other signal light by a time corresponding to one bit of the phase modulation speed. Thereafter, the two branched lights are caused to interfere with each other. At the interference point, when the phase of the signal light delayed by an amount equivalent to 1 bit and the phase of the signal light not delayed are in phase and opposite (π different), the light after interference The travel route is different. If a photodiode is placed at the end of each traveling path in the case of in-phase or reverse-phase, and the anode and cathode of these two photodiodes are electrically connected, the direction of the current flowing through the output of each photodiode is measured. By doing so, the phase change can be replaced with an electric signal. As means for branching and interfering light, a beam splitter or a half mirror is generally used in a spatial optical system, and a multimode interferometer is used in a waveguide optical system.

  The above is the simple principle of the phase modulation system. In such a receiving system including branching of signal light, addition of a delay amount equivalent to 1 bit, and interference, direct modulation consisting of one photodiode is performed. This is a big issue in terms of size and cost compared to the method. In addition, since the delay interferometer is required to be mounted with high accuracy, the mounting cost is higher than that of the direct modulation method. Therefore, in order to realize an ultrahigh-speed interconnection employing a phase modulation method, it is important to realize a delay interferometer that is small in size and low in mounting cost.

  As described above, an object of the present invention is to provide a differential phase shift modulation optical receiver including a small delay interferometer.

  One of the means for achieving the above object is as follows.

  In a differential phase shift modulation optical receiver including a 1-bit delay interferometer that outputs a second light and a third light delayed by 1 bit from the second light when the first light is input A 1-bit delay interferometer is used in which an optical plate having a half mirror and a total reflection mirror is bonded.

  ADVANTAGE OF THE INVENTION According to this invention, the differential phase shift modulation optical receiver provided with the small delay interferometer can be provided.

1 is a diagram showing an outline of a delay interferometer of Embodiment 1. FIG. It is a figure which shows the outline | summary of the delay interferometer of Example 2. FIG. FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver according to a third embodiment. FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver according to a fourth embodiment. FIG. 10 is a perspective view illustrating an outline of a differential phase shift modulation receiver array according to a fifth embodiment. FIG. 10 is a diagram illustrating an outline of an optical module using a differential phase shift modulation receiver according to a sixth embodiment. FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver according to a seventh embodiment. FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver according to an eighth embodiment. FIG. 10 is a diagram illustrating an outline of an optical module using a differential phase shift modulation receiver according to a ninth embodiment. FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver according to a tenth embodiment. It is a schematic diagram of a differential phase shift modulation receiver. It is a schematic diagram of an optical module.

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

FIG. 1 is a diagram illustrating an outline of the delay interferometer according to the first embodiment. In this embodiment, an optical plate having a structure in which a total reflection mirror 102 and a half mirror 103 are sandwiched by a base material glass 101 is used as a basic structure. The signal light is perpendicularly incident on the base glass 101 as indicated by the arrows in the figure, and the total reflection mirror 102 and the half mirror 103 make an angle of 45 ° with respect to the signal light. Such an optical plate can be formed by the following procedure, for example. First, a dielectric film that forms a half mirror is first formed on the first glass plate, then a second glass plate is bonded, and a dielectric film that forms a total reflection mirror is formed thereon. . Next, another sheet glass is bonded, and the structure consisting of these three sheet glass and two layers of dielectric film is sliced at an angle of 45 °, and finally the extra part is diced or polished, etc. If it cuts by this method, an optical plate as shown in a figure will be obtained. At this time, it is important to adjust the thickness and the refractive index of the dielectric film forming the total reflection mirror and the half mirror so as to form respective reflectivities for light incident at 45 °. Further, the thickness of the second glass plate needs to be a thickness corresponding to 1/2 of a desired bit rate with respect to light traveling at 45 °. For example, assuming a modulation rate of 40 Gbps and assuming that the refractive index of the base glass is 1.5, the required glass plate thickness is (glass thickness) = c / (nx Bit rate) x 1/2 x cos45 ° = 1.77mm
It will be about. (c: high speed, n: refractive index)
If the optical plate thus formed is bonded in a direction as shown in the figure in which the total reflection mirrors and the half mirrors face each other, a small and highly accurate delay interferometer can be formed. For bonding the optical plate, it is preferable to use an adhesive having a refractive index equivalent to that of glass.

  The actual operation as a delay interferometer will be described with reference to FIG. When the first light is input, the 1-bit delay interferometer that outputs the second light and the third light that is delayed by 1 bit from the second light has the first half mirror and the first total reflection. A first optical plate having a mirror, a second half mirror, and a second optical plate having a second total reflection mirror are bonded together.

  In the delay interferometer, the same optical plate is bonded, the side surface of the total reflection mirror is exposed to the joint surface of the first optical plate, and the side surface of the second total reflection mirror is the second optical plate. The side surface of the first total reflection mirror is in contact with the side surface of the second total reflection mirror.

  First, the first light that has entered from the right side of the delay interferometer is split by the half mirror 103a into a fourth light that is bent vertically and a fifth light that travels as it is in the incident direction. The The fourth light bent in the vertical direction is folded back by the total reflection mirrors 102a and 102b, and interferes with the fifth light traveling straight in the half mirror 103b. At this time, the fourth light that is first bent vertically is reciprocated by a distance corresponding to 1/2 bit, so that when it reaches the half mirror 103b, the second light that is the incident light of the fifth light that travels straight forward is obtained. It is incident as third light to which a delay amount equivalent to 1 bit is given rather than light. For this reason, the optical path after interference changes according to the phase modulation state between bits according to the principle described above. With such a configuration, since the angles and distances of the four mirrors are fixed, a highly accurate delay interferometer can be easily formed.

  In practice, it is desirable to form the nonreflective films 104a and 104b, the nonreflective film 105, and the nonreflective film 106 in order to prevent incident light and outgoing light, and multiple reflection between different optical plates. .

  FIG. 2 is a diagram illustrating an outline of the delay interferometer according to the second embodiment. In Example 1, since it is assumed that an adhesive is used for laminating the optical plate, the antireflective film 105 is inserted, but if a technique for eliminating the refractive index difference at the glass interface (for example, thermal fusion) is used. Since the step of forming the non-reflective film 105 can be omitted, it is possible to form a delayed interferometer more simply. Other configurations are the same as those of the first embodiment, and the function as a delay interferometer is not changed.

  FIG. 3 is a diagram illustrating an outline of a differential phase shift modulation receiver according to the third embodiment. The delay interferometer described in the first embodiment includes the lens 107a for collimating incident light, the photodiodes 108a and 108b for receiving outgoing light, and the lenses 107b and 107c for improving the coupling efficiency between the photodiode and outgoing light. Has been. As described above, by mounting an optical element other than the delay interferometer on the delay interferometer, the receiving module can be made smaller. In this drawing, although the collimating lens is drawn as an element separate from the optical plate, for example, a high refractive index material is diffused to a desired position by a thermal diffusion method or the like to form a lens on the optical plate itself. You can also.

  FIG. 4 is a diagram illustrating an outline of a differential phase shift modulation receiver according to the fourth embodiment. In the configuration described in the third embodiment, the photodiodes 109a and 109b are replaced with a lens integrated type. As described above, by using the photodiode in which the lens is formed, it is possible to reduce the number of mounting parts and the mounting process, and to more easily form a receiving module.

  FIG. 5 is a perspective view illustrating an outline of a differential phase shift modulation receiver array according to the fifth embodiment. In the configuration described in the fourth embodiment, the optical plate has a sufficient depth so that a plurality of input signals can be processed in parallel, and the lens 107′a and the photodiode arrays 109′a and 109′b. Has been implemented. In order to convey the intention of the inventor in an easy-to-understand manner, the nonreflective film is omitted from the drawing for convenience. In addition, from the description of the first embodiment, a method for producing such an optical plate can be easily imagined. With such a configuration, a differential phase shift modulation receiver array capable of processing a large amount of signals can be easily realized, and the throughput of the receiving module can be dramatically increased.

  FIG. 6 is a diagram illustrating an outline of an optical module using the differential phase shift modulation receiver according to the sixth embodiment. The configuration described in the fourth embodiment, the optical fiber 111, and the integrated circuit 116 are mounted on the multilayer substrate 110. The light that has passed through the optical fiber is incident on a delay interferometer fixed to the multilayer substrate 110, and is incident on the photodiode 109a or 109b according to the state of phase modulation according to the above-described function. Light incident on the photodiode is converted into an electrical signal, and the electrical signal is input to the integrated circuit 116 through the wire 112, the electrical wiring 113, the through via 114, the solder 115, and the like. By configuring the integrated circuit 116 so that the polarities of the currents from the photodiodes 109a and 109b are reversed, the phase modulation signal is converted into an electrical signal of + 1 / -1, which is simple. The reception sensitivity is improved by 3dB compared to 0/1 electrical signal, which is intensity modulation. With such a configuration, a differential phase shift modulation signal receiving module can be easily realized.

  FIG. 7 is a diagram illustrating an outline of a differential phase shift modulation receiver according to the seventh embodiment. In the configuration described in the fourth embodiment, a third optical plate including a base glass 101c, a total reflection mirror 102c, and a half mirror 103c is added. As shown in the figure, with such a configuration, the photodiodes 109a and 109b can be integrated on the same plane. Thereby, mounting at the time of module formation becomes easier. In this configuration, the half mirror 103c does not play a functional role and is not necessarily required. However, since the structure shown in FIG. 7 can be obtained by changing the direction of the optical plates having the same basic structure and bonding them together, there is an advantage in production.

  FIG. 8 is a diagram illustrating an outline of a differential phase shift modulation receiver according to the eighth embodiment. In the configuration described in the seventh embodiment, a difference in optical path length after interference between light that is bent by the third optical plate and light that is not so becomes a problem. Such a difference in optical path length causes skew and causes jitter. For this reason, the device which compensates for the optical length difference of both is required. One of them is the configuration shown in this embodiment. For light incident on the photodiode 109b, a high refractive index region 117 is provided between the half mirror 103b and the photodiode 109b. Since the optical path length difference between the light incident on the photodiodes 109a and 109b is equal to the thickness of the base glass 101 with respect to the light incident direction, the corresponding refractive index difference and thickness are set in the high refractive index region 117. By providing, skew can be eliminated.

  FIG. 9 is a diagram illustrating an outline of an optical module using the differential phase shift modulation receiver according to the ninth embodiment. Compared to the configuration described in the sixth embodiment, since the photodiodes 109a and 109b are on the same plane, mounting on a multilayer substrate and connection with electric wiring are easier. In this example, unlike the eighth example, a configuration that optically eliminates the optical path length difference after interference is not employed. In the integrated circuit 116, the skew can be electrically compensated by performing appropriate timing adjustment so that the phase of the signal input from one photodiode is aligned with that of the other light.

  FIG. 10 is a diagram illustrating an outline of a differential phase shift modulation receiver that is the tenth embodiment. In the configuration described in the fourth embodiment, the first and second optical plates further include second total reflection mirrors 102c and 102d, respectively. Have been added. As shown in the figure, with such a configuration, the photodiodes 109a and 109b can be integrated on the same plane. Thereby, mounting at the time of module formation becomes easier. Note that the total reflection mirror 102c does not play a functional role in this configuration and is not necessarily required. However, since the structure as shown in FIG. 10 can be obtained by changing the direction of the optical plates having the same basic structure and bonding them together, there is an advantage in production. The description of the differential phase shift keying receiver and the optical module shown in FIGS. 11 and 12 can be easily imagined from the eighth and ninth embodiments, and thus will be omitted here.

101a, 101b, 101c ... base glass,
102a, 102b, 102c, 102d ... total reflection mirror,
103a, 103b, 103c, 103d ... half mirror,
104a, 104b, 104c… Non-reflective film,
105a ... Non-reflective film,
106 ... Non-reflective film,
107a, 107b, 107c… collimating lens,
107'a ... collimating lens array,
108a, 108b ... photodiode,
109a, 109b ... Lens integrated photodiode,
109'a, 109'b… Lens integrated photodiode array,
110 ... Multilayer substrate,
111 ... fiber,
112 ... Wire,
113… Electric wiring,
114 ... through-via,
115 ... Solder,
116 ... integrated circuit,
117 ... High refractive index part,
118 ... support material,
119 ... polymer optical waveguide,
120 ... interposer,

Claims (15)

Differential phase shift modulated light reception provided with a 1-bit delay interferometer that outputs the second light and the third light delayed by 1 bit from the second light when the first light is input In the vessel
The 1-bit delay interferometer has a first optical plate and a second optical plate bonded together,
The first optical plate has a first half mirror and a first total reflection mirror,
The second optical plate has a second half mirror and a second total reflection mirror,
The first light incident on the first half mirror from an oblique direction is separated into fourth light and fifth light,
The fourth light is incident on the second half mirror from the first oblique direction through the first total reflection mirror and the second total reflection mirror, and the fifth light is Without entering through the first total reflection mirror and the second total reflection mirror, incident on the second half mirror from the oblique second direction, the second light and the third light, The differential phase shift modulated optical receiver, wherein the second half mirror outputs light in different directions. In claim 1,
A differential phase shift modulation optical receiver, wherein the plurality of optical plates are joined via a non-reflective film for light in a predetermined wavelength range. In claim 1,
The differential phase shift modulation optical receiver, wherein the joining is performed by fusing optical plates. In claim 1,
The side surface of the first total reflection mirror is exposed on the bonding surface of the first optical plate,
The side surface of the second total reflection mirror is exposed to the joint surface of the second optical plate,
The differential phase shift modulation optical receiver, wherein a side surface of the first total reflection mirror is in contact with a side surface of the second total reflection mirror. In claim 1,
On the side surface of the first optical plate, the first half mirror and the first total reflection mirror are not exposed,
The differential phase shift modulation optical receiver, wherein the second half mirror and the second total reflection mirror are not exposed on a side surface of the second optical plate. 2. A differential phase shift modulation optical receiver according to claim 1, a first photodiode into which said second light is incident, and a balance photodiode comprising a second photodiode into which said third light is incident;
An integrated circuit for differentially processing the electrical signal from the balanced photodiode;
An optical receiver module comprising the balance photodiode and the integrated circuit connected by electrical wiring. In claim 1,
Sandwiching the second optical plate between the first optical plate and the third optical plate;
The third optical plate comprises a third total reflection mirror;
The first photodiode and the second photodiode are disposed on the same surface;
The third total reflection mirror converts the optical axis of the second light into the optical axis direction of the third light, and the first photodiode and the second photodiode arranged on the same plane are moved to the first photodiode. A differential phase shift modulation optical receiver, wherein the second light and the third light are incident. In claim 7,
A difference in that the second optical plate is provided with a material having a higher refractive index than that of the substrate of the optical plate at a position where the third light serving as the output of the second half mirror is irradiated on the second optical plate. Dynamic phase shift modulated optical receiver. A differential phase shift modulation optical receiver according to claim 7 to 8,
An integrated circuit that differentially processes two electrical signals from the balanced photodiode;
A differential phase shift modulation optical receiver comprising the balance photodiode and the integrated circuit connected by an electrical wiring. In claim 9,
An optical receiver module comprising a circuit for adjusting a delay time between a first electric signal that is an output of the first photodiode and a second electric signal that is an output of the second photodiode. In claim 1,
The second optical plate includes a third total reflection mirror that sandwiches the half mirror with the second total reflection mirror,
The first photodiode and the second photodiode are disposed on the same surface of the second optical plate;
The third total reflection mirror converts the optical axis of the third light in the direction of the optical axis of the second light, and the second photodiode is arranged on the first photodiode and the second photodiode disposed on the same plane. And a third phase light are incident on the differential phase shift modulation optical receiver. In claim 11,
The second optical plate is characterized in that a higher refractive index material than the base material of the optical plate is disposed at a position where the second light serving as the output of the second half mirror is irradiated. Modulated light receiver. A differential phase shift modulated optical receiver according to claim 11 or 12,
An integrated circuit that differentially processes two electrical signals from the balanced photodiode;
The phase shift modulation optical receiver comprising the balance photodiode and the integrated circuit connected by an electrical wiring. In claim 13,
An optical phase shift modulation comprising a circuit for adjusting a delay time between a first electric signal which is an output of the first photodiode and a second electric signal which is an output of the second photodiode. Optical receiver. In claim 1,
The first optical plate and the second optical plate are the same optical plate;
The first optical plate and the second optical plate are joined so that the first half mirror and the second half mirror face each other and the first total reflection mirror and the second total reflection mirror face each other. What is claimed is: 1. A phase shift modulation optical receiver.