JPH11307877A - Transmitting/receiving device for light wavelength multiple communication and method for driving the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitting/receiving semiconductor device having sharp wavelength selectivity. SOLUTION: A transmitting/receiving device is provided with a bifurcation light conducting path 22 having a first branch light conducting path 22b and a second branch light conducting path 22c from a main line light conducting path 22a, an emitting semiconductor device 24 provided on the first branch light conducting path 22b and a receiving semiconductor device 29 disposed on the second branch light conducting path 22c. In this case, the receiving semiconductor device 29 has a variable wavelength filter 30 having a grating and a first receiving device 32 for receiving light reflected from the variable wavelength filter 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a transmitting / receiving element for optical wavelength division multiplexing communication and a driving method thereof.

[0002]

2. Description of the Related Art As a conventional transmitting / receiving element for optical wavelength division multiplexing communication, there is, for example, an element disclosed in Document I (1996 of the Institute of Electronics, Information and Communication Engineers, Electronics Society Conference, C-268).

In a conventional transmitting / receiving element (optical integrated element), a substrate is provided with a Y-branch waveguide having a first branch waveguide and a second branch waveguide branched from a main waveguide. A 1.3 μm band laser diode (LD) is provided in the first branch waveguide of the Y branch waveguide, and a 1.3 μm band receiving photodiode (LD) is provided in the second branch waveguide of the Y branch waveguide. PD).

A conventional transmitting / receiving element uses the 1.3 μm band demultiplexing PD. Therefore, when a 1.3 μm band light wavelength is received by the receiving PD, the received light is converted into an electric signal and output. Wavelengths other than the 1.3 μm band wavelength, for example, 1.5
When light in the 5 μm band is received, 1.3 μm
Since the m-band photodiode (PD) is transparent, the light is directly output from the subsequent stage of the receiving PD.

[0005] As described above, the conventional transmitting / receiving element has the 1.3 characteristics.
A function of transmitting an optical signal in a μm band by a semiconductor laser, a function of converting an optical signal in a 1.3 μm band into an electric signal by a receiving PD and receiving the signal, and demultiplexing and outputting a signal light having a wavelength longer than the 1.3 μm band. Function.

[0006]

However, since the conventional transmitting / receiving element for optical wavelength division multiplexing uses a receiving photodiode (PD) as a demultiplexing filter at the time of receiving, the transmitting / receiving element of the transmitting light does not transmit the received light. The wavelength must be set to a long wavelength of several hundred nm or more.

However, in a future multiplex communication system, it is considered that a wavelength multiplexed light system in which a wavelength interval in a transmitting semiconductor element is about several nm is required. Therefore, the conventional device has a problem that it cannot cope with such future multiplex transmission of large-capacity optical communication.

Therefore, it has been desired to develop a transmission / reception element for wavelength division multiplexing communication having sharp wavelength selectivity and a driving method thereof.

[0009]

Therefore, according to the transmitting / receiving device for optical wavelength division multiplexing communication of the present invention, the substrate has the first branch waveguide and the second branch waveguide branched from the main waveguide. A branch type waveguide, a transmission semiconductor element provided in the first branch waveguide, and a reception semiconductor element provided in the second branch waveguide, wherein the reception semiconductor element includes a variable wavelength filter having a grating and a variable wavelength filter having a grating. A first light receiving element for receiving light reflected from the variable wavelength filter.

As described above, according to the present invention, since the variable wavelength filter having the grating is used as the receiving semiconductor element, a wavelength having sharp selectivity can be obtained by setting the period of the grating to any suitable period. be able to. When the wavelength of the received light received at the I / O port matches the Bragg wavelength of the variable wavelength filter, the received light is reflected by the variable wavelength filter and received by the first light receiving element. Therefore, the first light receiving element converts the optical signal into an electric signal and outputs the electric signal.

When the wavelength of the received light does not match the Bragg wavelength of the variable wavelength filter, the received light passes through the variable wavelength filter and is output from the output terminal of the second branch waveguide.

In practicing the present invention, it is preferable to use a distributed Bragg reflection type semiconductor laser (DBR laser) as the transmitting semiconductor element.

With this configuration, it is possible to transmit single-mode transmission light (also called oscillation light) determined by the Bragg wavelength from the I / O port of the transmission / reception element.

In practicing the present invention, it is preferable that a second light receiving element is provided at the output end of the tunable wavelength filter so as to be connected to the second branch waveguide.

Thus, by providing the second light receiving element on the output end side of the variable wavelength filter, the received light transmitted from the variable wavelength filter is received by the second light receiving element, converted into an electric signal, and output. can do.

According to the method of driving a transmitting / receiving element of the present invention, a Y-branch waveguide having a first branch waveguide and a second branch waveguide branched from a main waveguide on a substrate; A transmitting semiconductor element provided in one branch waveguide;
In driving the transmission / reception element for optical wavelength multiplexing communication including the reception semiconductor element provided in the branch waveguide, when the transmission semiconductor element is a distributed Bragg reflection type semiconductor laser,
At the time of transmission, a current is injected into a grating region of a semiconductor laser to tune a predetermined transmission wavelength, and at the time of reception, a current is injected into a variable wavelength filter to tune a predetermined wavelength of received light. .

With such a configuration, when a current is injected into the grating region of the semiconductor laser during transmission, the Bragg wavelength changes because the equivalent refractive index of the waveguide layer changes. Therefore, the laser oscillation wavelength can be tuned.

Further, when a current is injected into the variable wavelength filter during transmission, the equivalent refractive index of the waveguide layer changes.
The Bragg wavelength changes. Therefore, the wavelength of the received light can be tuned.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a transmission / reception device for optical wavelength communication according to the present invention;
It should be noted that the drawings merely schematically show the size, shape, and arrangement relationship of each component to the extent that the present invention can be understood. Therefore, the present invention is not limited to the illustrated examples. Absent.

First, with reference to FIG. 1, a description will be given of a main configuration of a transmitting / receiving element for optical wavelength communication (hereinafter, also simply referred to as a transmitting / receiving element) according to a first embodiment of the present invention. FIG. 1 is a plan view schematically illustrating a main configuration of the transmitting / receiving element according to the first embodiment.

The transmitting / receiving element according to the present invention includes a Y-branch waveguide 22 having a first branch waveguide 22b and a second branch waveguide 22c branched from a main waveguide 22a on a substrate (not shown). The transmission semiconductor device 24 includes a transmission semiconductor element 24 provided in the one branch waveguide 22b and a reception semiconductor element 29 provided in the second branch waveguide 22c.

The receiving semiconductor element 29 includes a variable wavelength filter 30 having a grating and a first light receiving element (P) for receiving reflected light from the variable wavelength filter 30.
D) 32.

In the first embodiment, as the substrate,
For example, n-type InP is used. In this configuration example, the Y-branch waveguide 22 has the same components as the conventional one, that is, the p-type I
A ridge-shaped waveguide made of the same material as the nP cladding layer is provided on the substrate. The Y-branch waveguide 22
Are connected from the main waveguide 22a to the first branch waveguide 22b and the second branch waveguide 22b.
It is branched into the branch waveguide 22c. Further, the second branch waveguide 22c is branched into a T shape.

The T-shaped branch waveguide 23 has a first waveguide portion 23a on one side of the branch point and a second waveguide portion 23b on the other side of the branch point. In this configuration example, the first
The waveguide portion 23a is used as a transmission-side waveguide, and
The second waveguide portion 23b is used as a waveguide on the receiving side.

The transmitting semiconductor element 24 is provided on the first branch waveguide 22b. As the transmitting semiconductor element 24, here, a branched Bragg reflection type semiconductor laser (hereinafter, referred to as a “semiconductor laser”)
Also referred to as DBR laser. ) Is used.

As is well known, this DBR laser 24
1.3 μm bandgap wavelength with grating
And an active region having a band gap wavelength of 1.55 μm (both not shown). here,
The period (pitch) of the grating in the DBR region is, for example, 244.0 nm.

As described above, the receiving semiconductor element 29 includes the variable wavelength filter 30 and the first light receiving element 32.
And Here, it is preferable that the variable wavelength filter 30 is a grating reflector (also referred to as a grating mirror). This variable wavelength filter 3
0 is provided in the second waveguide portion 23b. Here, the grating mirror 30 has a demultiplexing function of demultiplexing the received light. The grating mirror 30
Is set to, for example, 244.3 nm.

The first light receiving element 32 (also referred to as a first PD) is a photodiode (PD). This light receiving element 32 is provided at the tip of the first waveguide portion 23a.

Next, with reference to FIGS. 2 and 3, a description will be given of a method of manufacturing the transmitting / receiving element according to the first embodiment of the present invention. Note that FIGS. 2A and 2B and FIG.
FIG. 21 is a perspective view for describing a manufacturing process of the transmitting and receiving element according to the embodiment. The hatching in the figure does not represent a cross section, but is a line added to clarify a specific region.

As the substrate 10, an n-type InP substrate is used. A first grating 12 for a DBR laser and a second grating 14 for a grating mirror are formed at predetermined positions on the substrate 10 by a conventionally known method (FIG. 2A).

Next, first, for example, using a normal VPE method, first, the DBR laser 24 and the first PD
The band gap wavelength of 1.57
μm InGaAsP region 16 (16a and 16b)
Are formed respectively. The InGaAsP regions 16a and 16b serve as an active layer of the DBR laser and the first PD.
Light-receiving layer. The InGaAsP regions 16a and 16b are preferably MQW layers composed of thin films having seven periods. The InGaAsP region 16a is preferably formed so as to be adjacent to the first grating 12.

On the other hand, the InGaAsP region 16b
It is formed apart from the grating 14. In that case,
The second grating 14 and the InGaAsP region 16
These portions 14 and 16b are formed so that b is located below the straight T-shaped branch waveguide 23.

Next, this band gap wavelength of 1.57 μm
mm of InGaAsP regions 16a and 16b are buried with a waveguide layer 18 having a band gap wavelength of 1.3 μm, and these InGaAsP regions 16a, 16b and 1
The surface 8 is made a continuous flat surface (FIG. 2B).

Next, for example, using a normal VPE method,
P-InP on the GaAsP region 16 and the waveguide layer 18
A preliminary layer (not shown) for the cladding layer 20 is formed. In this configuration example, the upper surface side of the preliminary layer is etched to make Y
Since the branching waveguide 22 is formed, the thickness of the preliminary layer is preferably a thickness obtained by adding the thicknesses of the cladding layer and the Y-branching waveguide 22.

Thereafter, the Y-branch type waveguide 22 is formed on the preliminary layer.
An etching mask (not shown) of the same type as that described above is formed, and the preliminary layer for the p-InP clad layer 20 is etched using this mask to form Y including the T-shaped branch waveguide 23.
A branch waveguide 22 is formed. The cladding layer 20 and the Y-branch waveguide 22 are formed by the p-type InP preliminary layer portion remaining by this etching.

The main structure of the transmitting / receiving element is completed through a series of steps described above. After that, the DBR of the DBR laser 24
An electrode 26 is formed in the region 24a, and an electrode 28 is formed in the active region 24b. Further, an electrode 34 is formed in the area of the grating mirror 30 and the electrode 3 is formed in the area of the first PD 32.
6 is formed. An n-type electrode (not shown) is formed on the entire back surface of the substrate 10 (FIG. 3).

Next, referring to FIG.
4. The area of the grating mirror 30 and the first PD 32 will be described. Note that FIGS. 4A and 4B
FIG. 4 is a view showing a cross-section of a cut surface taken along a line XX and a line ZZ in FIG. 3.

In this transmitting / receiving element, the DBR laser 2
4 has a DBR region 24a and an active region 24b. The DBR region 24a includes the substrate 10, the first grating 12, the waveguide layer 18, the cladding layer 20, and the first branch waveguide 22b. The active region 24b includes the substrate 10, the active layer 16a. , The cladding layer 20 and the first branch waveguide 22b.

The grating mirror 30 includes the substrate 10,
Second grating 14, waveguide layer 18, cladding layer 2
0 and the region portion of the second waveguide portion 23b.

The first PD 32 includes the substrate 10, the light receiving layer 16
b, the cladding layer 20 and the region portion of the first waveguide portion 23a (FIGS. 4A and 4B).

Next, a method of driving the transmitting / receiving element according to the first embodiment will be described with reference to FIGS.

For example, when transmitting an optical signal from the transmitting / receiving element, a current is injected into the active region 24b of the DBR laser 24. The current injection, transmission and reception device, the oscillation wavelength determined by the Bragg wavelength of the DBR region 24a, laser oscillation in a single mode, for example lambda _1. The oscillated light passes through the first branch waveguide 22b and the main waveguide 22a, and is
Output from the O port 42.

When a current is injected into the DBR region 24a, the equivalent refractive index of the waveguide layer 18 changes. As a result, D
Since the Bragg wavelength lambda _b of the BR region 24a is changed, it is possible to tune the lasing wavelength by changing the amount of current to be injected.

When receiving an optical signal, the I / O port 4
2 is received by the main waveguide 22 (wavelength λ ₀ ).
a, T-shaped branch waveguide 23 via second branch waveguide 22c
Reach

[0045] Because the grating mirror 30 on the lower side of the waveguide section is provided, the reception light, if they match the Bragg wavelength lambda _b of the grating mirror 30, straight is reflected by the grating mirror 30, the first
Reaches PD32. The first PD 32 receives the reflected light and converts an optical signal into an electric signal.

However, light having a wavelength other than the Bragg wavelength λ _b ,
For example, when λ ₂ is received at the I / 0 port 42, this light is not reflected by the grating mirror 30, but passes through them and is output from the output end of the grating mirror 30 to the outside.

Further, by changing the amount of current injected into the grating mirror 30, the Bragg wavelength λ _b can be changed, and thus the received light can be tuned.

FIG. 5 shows reflection characteristics of a DBR region (also referred to as a passive waveguide region) of a DBR laser. In the figure, the characteristic curve is shown by plotting the wavelength in nm on the horizontal axis and plotting the reflectance (%) on the vertical axis.
This reflection characteristic is calculated by the following equation (1).
It is what I sought.

[0049]

(Equation 1)

Where α is a light loss coefficient due to absorption, scattering, leakage, etc., when the light propagates through the waveguide, and K is
Each light propagating in the reflecting direction is the coupling coefficient mutually bound per has been unit length diffracted by the grating, j is an imaginary number, n _eq is the equivalent refractive index of the waveguide, lambda _b is the Bragg wavelength, L _B Is the grating length of the DBR region.

Here, the coupling coefficient K is K = 5.
0, the length of the DBR region (length of the grating) L _B a L _B = 500 [mu] m, the equivalent refractive index n _eq of the waveguide n _eq =
The reflectance is calculated as 3.2.

As can be understood from FIG. 5, the oscillation wavelength oscillated from the DBR laser 24 has a peak value of the reflectance of 90% at 1550 nm, and has a reflectance of 0% at the wavelengths of 1549 nm and 1551 nm. The half width of this reflection characteristic is about 1.5 nm. Thus, the DBR
By using the laser 24, an oscillation wavelength having sharp wavelength selectivity can be obtained.

In the present invention, the receiving semiconductor element 29
Since the grating mirror 30 is used, the wavelength of light reflected from the grating mirror 30 can have the same wavelength selectivity as the DBR laser 24.

FIG. 6 is a diagram in which the current injected into the DBR region is changed and the change in the oscillation wavelength of the DBR laser is plotted. FIG. 6 shows the injection current (unit: m) into the DBR on the horizontal axis.
A) is shown, and the vertical axis shows the laser oscillation wavelength (unit: nm).

As can be understood from FIG. 6, the laser oscillation wavelength is plotted against the DBR current. And D
When the BR current is 0 mA, the oscillation wavelength becomes about 1545 nm. As the DBR current increases, the oscillation wavelength gradually decreases. When the DBR current is 38 mA, the oscillation wavelength becomes 1
541 nm. As a result, by changing the DBR current from 0 mA to 38 mA, the laser oscillation wavelength becomes about 4n.
m. That is, by changing the current value injected into the DBR region, tuning of about 4 nm can be performed.

In the present invention, the grating mirror 30
Also has a configuration similar to that of the DBR region 24a of the DBR laser 24, so that tuning of about 4 nm is possible.

Next, with reference to FIG. 7, the configuration of the transmitting / receiving element according to the second embodiment of the present invention will be described. In addition,
FIG. 7 is a plan view schematically illustrating the configuration of the transmitting / receiving element according to the second embodiment.

The second embodiment differs from the first embodiment in that a second light receiving element 40 is provided on the output end side of the grating mirror 30 so as to be connected to the second branch waveguide 22c. I have. Other components are the same as those in the first embodiment. Therefore, detailed description of the same components as those in the first embodiment is omitted here.

Here, a photodiode (hereinafter, referred to as a second PD) is used as the second light receiving element 40. The second light receiving element 40 may be formed in the same structure as the first light receiving element 32.

By providing such a second PD 40, light transmitted from the grating mirror 30, for example, λ _2, can be received by the second PD 40, converted into an electric signal, and output.

The driving method of the second embodiment, the reflectivity characteristics or tuning characteristics of the DBR laser, and the like are the same as those of the first embodiment, and a description thereof will be omitted.

As described above, according to the transmission / reception element of the present invention, the oscillation light from the transmission semiconductor element is transmitted from the I / O port 42, and the reception light received at the I / O port 42 is electrically transmitted by the reception semiconductor element. Since it is converted into a signal, bidirectional optical transmission in an access system becomes possible.

In the above embodiment, a DBR laser is used as the transmitting semiconductor element 24, but a DFB laser may be used instead of the DBR laser.

The method of injecting current into the DBR region 24a or the grating mirror 30 was used for controlling the Bragg wavelength. However, the present invention is not limited to this. For example, the DBR region 24a or the grating mirror 30 may be used. A resistive heating film may be formed in the region described above and the film may be heated to change the refractive index of the waveguide.

In the present invention, the transmitting semiconductor element 24
Although a DBR laser is used, a phase adjustment region is provided between the active region and the DBR region constituting the DBR laser, so that a current is injected into the DBR region 24a and the phase adjustment region, so that the wavelength can be reduced. Continuous tuning is possible.

In each of the embodiments described above, the configuration example in which the waveguide is provided on the substrate has been described. However, even if the waveguide is formed in the substrate, the same effect as in the above configuration example can be obtained. It can be guessed.

[0067]

As is apparent from the above description, according to the transmitting / receiving element for optical wavelength division multiplexing communication of the present invention, the substrate has the first branch waveguide and the second branch waveguide branched from the main waveguide.
A Y-branch waveguide composed of a branch waveguide is provided, a transmission semiconductor element is provided in the first branch waveguide, and a reception semiconductor element is provided in the second branch waveguide. The receiving semiconductor element includes a tunable wavelength filter having a grating and a first light receiving element that receives reflected light from the tunable wavelength filter.
Light receiving element.

Therefore, when receiving light, the received light is incident on the variable wavelength filter. At this time, when the received light matches the Bragg wavelength, the received light is reflected by the variable wavelength filter and received by the first light receiving element. Since this grating filter has sharp wavelength selectivity, it is possible to select only a desired wavelength from signal light multiplexed at shorter wavelength intervals than in the related art. Therefore, the transmitting / receiving element of the present invention can be sufficiently applied to future large-capacity multiplexed optical communication.

Further, according to the present invention, since the first light receiving element is provided as the receiving semiconductor element, the reflected light from the variable wavelength filter can be received and converted into an electric signal.

Further, by injecting a current into the tunable wavelength filter, the equivalent refractive index of the waveguide layer changes, thereby changing the Bragg wavelength. Therefore, the transmitting / receiving element of the present invention can tune the received light. .

In the transmitting / receiving element of the present invention, since the second light receiving element is provided on the output end side of the grating reflector, the transmitted light transmitted through the grating reflector can be received and converted into an electric signal. it can.

[Brief description of the drawings]

FIG. 1 is a plan view for explaining a configuration of a transmitting / receiving element for optical wavelength division multiplexing communication according to a first embodiment of the present invention.

FIGS. 2A and 2B are perspective views for explaining a process of manufacturing the optical wavelength multiplexing communication transmitting / receiving element according to the first embodiment of the present invention.

FIG. 3 is a perspective view, following FIG. 2, for explaining a step of manufacturing the optical wavelength multiplexing communication transmitting / receiving element according to the first embodiment of the present invention;

FIGS. 4A and 4B are cross-sectional views of a DBR laser, a grating mirror, and a first light receiving element.

FIG. 5 is a diagram for explaining the relationship between the wavelength and the reflectance of the DBR region according to the present invention.

FIG. 6 is a diagram provided to explain a relationship between a DBR current and a laser oscillation wavelength when a current is injected into a DBR region.

FIG. 7 is a plan view for explaining a configuration of a transmitting / receiving element for optical wavelength division multiplexing communication according to a second embodiment of the present invention.

[Explanation of symbols]

 10: n-InP substrate 12: first grating 14: second grating 16 (16a, 16b): InGaAsP region 18: waveguide layer 20: p-InP cladding layer 22: Y-branch waveguide 22a: main waveguide 22b : First branch waveguide 22c: second branch waveguide 23: T-shaped branch waveguide 24: DBR laser 24a: DBR region 24b: active region 26, 28: electrode 29: receiving semiconductor element 30: grating mirror 32: second First PD 34, 36: Electrode 40: Second PD 42: I / O port

Claims (5)

[Claims] 1. A Y-branch waveguide having a first branch waveguide and a second branch waveguide branched from a main waveguide on a substrate, a transmitting semiconductor element provided on the first branch waveguide,
A receiving semiconductor element provided in the second branch waveguide, wherein the receiving semiconductor element includes a variable wavelength filter having a grating and a first light receiving element for receiving reflected light from the variable wavelength filter. A transmitting / receiving element for optical wavelength division multiplexing, comprising: 2. The transmitting / receiving element for optical wavelength division multiplexing communication according to claim 1, wherein said variable wavelength filter is a grating reflector. 3. The transmission / reception device for optical wavelength division multiplexing communication according to claim 1, wherein said transmission semiconductor device is a distributed Bragg reflection type semiconductor laser (DBR laser). 4. The transmitting / receiving element for optical wavelength division multiplexing communication according to claim 1, wherein a second light receiving element is provided at an output end side of the grating reflector so as to be connected to the second branch waveguide. A transmission / reception element for optical wavelength division multiplexing communication. 5. A Y-branch waveguide having a first branch waveguide and a second branch waveguide branched from a main waveguide on a substrate, a transmitting semiconductor element provided on the first branch waveguide,
When driving a transmission / reception element for optical wavelength multiplexing communication including a reception semiconductor element provided in the second branch waveguide, when the transmission semiconductor element is a distributed Bragg reflection type semiconductor laser, and when transmitting, the semiconductor laser is used. A wavelength is tuned by injecting a current into the grating region of the optical wavelength multiplexing communication, and a predetermined wavelength is tuned by injecting a current into the variable wavelength filter during reception. Element driving method.