JPH0821932A - Frequency-variable light source module - Google Patents

Abstract

PURPOSE:To provide an optical frequency-variable light source module which facilitates setting of an oscillated light frequency at a prescribed value, has the excellent light frequency stability thereof and facilitates arraying. CONSTITUTION:An array waveguide grating 100 including >=1 pieces of input waveguides 11, a first slave waveguide 12 which receives the light from these input waveguides 11, a waveguide array 13 which receives the light from the first slab waveguide 12 and consists of plural pieces of waveguides having successively increasing prescribed waveguide lengths, a second slab waveguide 14 which receives the light from the waveguide array 13 and >=2 pieces of output waveguides 15 which receive the light from the second slab waveguide 14 is used as the fist constituting element of this frequency variable light source module. Further, the module described above has a resonator part where optical switch circuits 300 disposed at the respective output waveguides of the array waveguide grating 100 are used as the second constituting element. Semiconductor lasers 200 are optically coupled with the respective input waveguides 11 of this resonator part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical signals required for an optical frequency division multiplexing (FDM) or optical wavelength division multiplexing (WDM) transmission system in which a plurality of optical signals are assigned to different optical frequencies and transmitted by one optical fiber. The present invention relates to a variable frequency light source module.

[0002]

2. Description of the Related Art The optical frequency / wavelength multiplexing technique is expected as a technique for greatly increasing the transmission capacity per optical fiber. Further, recently, application to optical frequency routing for designating a destination of an optical signal for each optical frequency has been studied. In order to realize such an optical transmission system using FDM / WDM, an optical frequency stabilizing light source that stably oscillates at a specific optical frequency required for the system, and further There is a need for an optical frequency variable light source that can selectively oscillate any one of them. Moreover, it is desirable that these light sources are arrayed.

Conventionally, as an optical frequency variable light source, a semiconductor laser with an external resonator having an external diffraction grating as shown in FIG. 6 or a diffraction grating and a plurality of diffraction gratings in a laser resonator portion as shown in FIG. A multi-electrode DBR laser provided with electrodes has been studied. These change the resonance light frequency in the laser resonator, that is, the oscillation light frequency, by changing the diffraction condition in the semiconductor laser resonator portion.

In FIG. 6, reference numeral 20 denotes a Fabry-Perot type laser (FP-LD), and an antireflection film 20a is provided on one end face thereof. 100 is an external resonator section, and in this example, the external resonator section 100 is an optical fiber 4
0, a lens 50, and a diffraction grating 60.
A resonator is formed between the output end 20a of the LD and the diffraction grating 60. Due to the optical frequency selection function of the diffraction grating 60, only the light of the specific optical frequency f _{1 that} satisfies the diffraction condition of the diffraction grating 60 reciprocates in this resonator, so the light of the output light from the FP-LD. The frequency is stabilized at f ₁ . This LD with an external resonator can change the oscillation wavelength by changing the inclination of the diffraction grating 60 and changing the optical frequency that satisfies the diffraction condition.

However, such an external resonator-equipped L
In D, since a lens and a diffraction grating are used, it is difficult to form an array. Furthermore, LD
In order to change the oscillation frequency of, the diffraction grating 60 must be rotated to change the diffraction condition. In order to change the angle of the diffraction grating 60, it must be done mechanically. In addition to this, in order to accurately adjust the oscillation frequency to a specific discrete optical frequency required in an FDM system or the like,
The rotating mechanism of the diffraction grating requires extremely high accuracy. For this reason, the size of the entire light source cannot be avoided.

FIG. 7 shows a three-electrode DBR laser. In the figure, 21a is an oscillation region, 21b is a phase adjustment region, and 21c is a DBR region. Since the diffraction grating is formed in the DBR region 21c, only the optical frequency satisfying the diffraction condition reciprocates in the resonator formed between the laser output end 20a and the DBR region 21c, so that the single frequency Laser oscillation is realized. Then, a current is caused to flow through the electrode 22c provided on the DBR region 21c and the electrode 22b provided on the phase adjustment region 21b, and the DBR region 21c and the phase adjustment region 21b, respectively.
The oscillation frequency can be made variable by changing the diffraction condition in the resonator by changing the refractive index of.

In such a three-electrode DBR laser, it is necessary to change the current of a plurality of electrodes in order to change the oscillation frequency. For this reason, the three-electrode DBR laser is effective for use in which the oscillation frequency is swept in a certain region.

However, in the FDM system, it is necessary to switch the oscillation frequency between specific discrete optical frequencies (for example, f ₁ , f ₂ , f ₃ , f ₄ ) rather than continuously changing the optical frequency. To be done. In such a case, the multi-electrode type LD has a problem that a complicated electric control system is required to set the current values of the electrodes at the two locations to the optimum values.

Further, this laser utilizes the change in the refractive index of each region to change the oscillation frequency. This means that the oscillation frequency of the laser changes even if the refractive index changes in each region due to temperature changes. In general, the refractive index of the semiconductor material forming the laser has a relatively large temperature dependence. Therefore, in such a laser, there is a problem that the temperature stability of the oscillation frequency is poor.

As described above, in the conventional variable optical frequency light source, the laser is provided with a single resonator section, and the oscillation condition is varied by changing the diffraction condition in the resonator section. Met. For this reason, it is easy to sweep the oscillation frequency in a certain range, but it is not easy to set a specific optical frequency value with high accuracy, and the temperature stability of the oscillation frequency is poor. It was

The object of the present invention is to solve the above problems,
An object of the present invention is to provide an optical frequency variable light source module in which the oscillation optical frequency can be easily set to a predetermined value, the optical frequency stability thereof is excellent, and the arraying can be easily performed.

[0012]

In order to achieve the above-mentioned object, the structure of the variable frequency light source module according to the present invention is a semiconductor that is optically connected to a resonator section and an input waveguide of the resonator section. A module including a laser, wherein the resonator section includes one or more input waveguides, a first slab waveguide for receiving light from the input waveguides, and a light receiving portion for receiving light from the first slab waveguides. And a second slab waveguide that receives light from the waveguide array, the waveguide array including a plurality of waveguides in which the predetermined waveguide length difference sequentially increases.
Array waveguide grating including two or more output waveguides that receive light from the slab waveguide, and an optical switch circuit provided in each of the output waveguides of the array waveguide grating. To do.

In the frequency variable light source module,
The arrayed waveguide grating may be formed using a quartz optical waveguide.

In the variable frequency light source module,
The optical switch circuit provided in each of the output waveguides may include an optical gate unit that realizes two states of light transmission and non-transmission, and a reflection unit provided at the end thereof.

In the variable frequency light source module,
An optical switch circuit provided at each of the output waveguide end portions,
A 1 × 2 optical switch section for selecting two optical paths, a reflection section is provided at one optical path end of the two optical paths, and a non-reflection section or a light absorption section is provided at the other optical path end. May be.

[0016]

According to the invention described in claim 1, a plurality of resonance paths defined by an arrayed waveguide grating are provided in the LD resonator section.
The oscillation optical frequency of the LD can be switched by switching this resonance path by the optical switch circuit of the resonator section. For this reason, it becomes possible to set the oscillation light frequency to a predetermined value with high accuracy and simply by simply turning on / off the optical switch circuit.

According to the second aspect of the present invention, the arrayed waveguide grating of the resonator section is formed of a silica optical waveguide. Since the change in the refractive index of the silica-based optical waveguide with temperature is extremely small, the resonant optical frequency defined by the array grating is stable with respect to the change in environmental temperature. For this reason, the optical frequency is variable, and
It is possible to realize an optical frequency variable light source module having excellent frequency stability.

According to the third aspect of the invention, since the optical switch circuit is composed of the optical gate and the reflecting section, the structure of the optical switch circuit section can be simplified by using, for example, a semiconductor optical gate switch.

According to the invention described in claim 4, it becomes possible to configure the optical switch circuit with only a passive optical waveguide such as a silica optical waveguide.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the frequency variable module according to the present invention will be described below.

[Embodiment 1] FIG. 1 is a schematic plan view showing the structure of a first embodiment of a frequency variable light source module of the present invention. The present invention provides an arrayed waveguide grating having N input waveguides and M output waveguides, N semiconductor lasers optically connected to each of the N input waveguides, and an arrayed grating. The variable frequency light source module is configured by an optical switch circuit provided in each of the M output waveguides [where N and M are positive integers], but in the first embodiment shown in FIG. 1, N = 4, the case of M = 4 is shown.

As shown in FIG. 1, the configuration of the frequency variable light source module of this embodiment has one or more input waveguides 11.
A first slab optical waveguide 12 that receives light from the input waveguide 11, a first slab optical waveguide 12 that receives light from the first slab optical waveguide 12, and
A waveguide array 13 including a plurality of waveguides in which a predetermined waveguide length difference is sequentially increased, a second slab waveguide 14 that receives light from the waveguide array 13, and the second slab waveguide 1
The array waveguide grating 100 including two or more output waveguides 15 that receive light from the optical waveguide 4 is used as a first component, and the optical switch circuit 300 provided in each of the output waveguides of the array waveguide grating 100 is 2 has a resonator part as a component,
A semiconductor laser array 200 is optically coupled to each of the input waveguides 11 of the resonator section.

In FIG. 1, 100 is an arrayed waveguide grating, 20
Reference numeral 0 is a semiconductor laser array, and reference numeral 300 is an optical switch circuit for selecting a resonance path. Here, the arrayed waveguide grating 100
In FIG. 11, 11 is a group of four input waveguides, 12 is a first slab waveguide, 13 is a waveguide array having a waveguide length difference ΔL, 14 is a second slab waveguide, and 15 is a second slab waveguide. It is a group of four output waveguides connected from the waveguide 14. The semiconductor laser array 200 is a four-array Fabry-Perot laser (FP-LD) array and includes four active layers 21.
(# 1 to # 4) are optically coupled to the four input waveguide groups of the arrayed waveguide grating. At this time, in order to prevent end face reflection at the waveguide-laser connection portion, the input waveguide end face,
Also, the laser end face 21a on the waveguide side is subjected to antireflection treatment. On the other hand, the laser end surface 21b is a normal wall interface and functions as one reflecting surface of the resonator. The optical switch circuit 300 is a semiconductor optical gate array (SG) having a structure in which both end faces of a 4-array FP-LD are subjected to antireflection treatment.
30, a coupling waveguide 32, and a reflecting mirror 33. The four active layers 31 (# 1 to # 4) of the semiconductor optical gate array (SG) 30 are the arrayed waveguide grating 10.
Each of the four output waveguide groups 0 of 0 is optically coupled. In order to prevent reflection between the SG and the waveguide, anti-reflection treatment is applied to the coupling end faces of the output waveguide 15 and the coupling waveguide 32 with the SG.

In the present embodiment, the above-mentioned three components,
That is, the arrayed waveguide grating 100, the semiconductor laser array 200, and the optical switch circuit 300 are all on the same substrate 101.
It is formed on the top.

Specifically, a silicon substrate was used as the substrate 101, and a quartz optical waveguide was formed thereon. This silica-based optical waveguide constitutes the entire arrayed waveguide grating 100 and the coupling waveguide 32 of the optical switch circuit 300. An optical element mounting portion is provided on the quartz optical waveguide, and four arrays of the Fabry-Perot type laser (FP-LD) 200 and SG30 constituting the switch circuit 300 are hybrid-optically integrated thereon.

Next, the principle of the present invention will be described based on this embodiment. Consider the case where # 1 of the FP-LD array oscillates. This light enters the first slab waveguide 12 from # 1 of the input waveguide group 11, spreads by diffraction, and is received by the waveguide array 13 arranged perpendicular to the diffractive surface. In the above-mentioned waveguide array 13, since the respective waveguides are sequentially lengthened by the waveguide length difference ΔL, the light that propagates through the respective waveguides and reaches the second slab waveguide 14 has a waveguide length difference Δ.
There is a phase difference corresponding to L. Since this phase difference varies depending on the optical frequency, when the light is focused on the input end of the output waveguide group 15 by the lens effect of the second slab waveguide 14,
The light is focused on a different waveguide for each optical frequency. That is, the arrayed waveguide grating 100 operates as an optical frequency demultiplexer.

As a result, the Fabry-Perot laser (FP-
The oscillation light from the LD) is different for each optical frequency component.
It is incident on the force waveguide 15. That is, the output waveguide 15 #
1 has a frequency f₁Light centered on is incident. As well
In the output waveguide 15 # 2, f ₂, F for # 3₃, # 4
Is f_FourBind to each other. At this time, only specific optical gate
Is turned on (light transmission state), and the optical
Optical gate by setting the port to the off state (light absorption state)
Only the optical frequency corresponding to the port for which the
It is reflected by the reflection mirror of the H-circuit and passes through the arrayed waveguide grating.
Returned to the Fabry-Perot laser (FP-LD) 200
It

For example, port # 1 of the optical gate array 30
Is turned on, the module (FP-LD)
200 high reflection end face 21b of port # 1 and output waveguide
A resonator between the reflection mirror 33 at the end of port # 1 of 15
Is formed. The resonator has an arrayed waveguide grating 100.
Frequency f determined by the demultiplexing characteristics of₁Only light exists
It As a result, the Fabry-Perot laser (FP-LD) 2
# 1 port of 00 is f ₁It oscillates at the optical frequency of. Next
The port # 1 of the optical gate array 30 to the off state.
Fabry-Perot type laser by turning on switch # 3
High reflection end face 21b of port # 1 of (FP-LD) 200
And the reflection mirror 33 at the end of port # 3 of the output waveguide 15.
A resonator is formed between and. In this resonator, the optical frequency
Number f₃Since the light of the Fabry-Perot type laser (F
# 3 port of P-LD) 200 is f₃To oscillate at
become.

Fabry-Perot type laser (FP-LD) 20
When the # 2 port of 0 oscillates, f is applied to the port # 1 of the output waveguide 15 due to the demultiplexing characteristic of the arrayed waveguide grating.
₂ joins, and so on, as described above, on port # 2, f ₃ ,
# The 3 f _4, to the port # 4 f ₅ are attached. Therefore, the optical gate array 3 of the port # 1 of the output waveguide 15
If 0 is turned on, Fabry-Perot type laser (FP-L
D) Port # 2 of 200 will oscillate at f ₂ .

Based on this principle, the 4-array FP-L
The oscillation frequency of each port of D can be arbitrarily selected from the optical frequency group defined by the arrayed waveguide grating by reconfiguring the resonance path in the module by the optical gate. The following "Table 1" summarizes the relationship between the resonance path provided in this resonator section and the oscillation frequency of each port of the FP-LD array.

[0031]

[Table 1]

As described above, according to the present invention, the oscillation frequency of the LD array is defined by the arrayed-waveguide grating only by reconfiguring the resonance path in the resonator section by turning on / off the optical gate of the reflection port. It can be arbitrarily set from the optical frequency group.

Further, when the arrayed waveguide grating is manufactured by using the silica-based optical waveguide as in this embodiment, the variation of the refractive index of the silica-based optical waveguide due to the ambient temperature is extremely small. The stability of the optical frequency reciprocating in the resonance path is extremely high. Therefore, the frequency variable light source module of the present invention can achieve high frequency stability.

[Embodiment 2] FIG. 2 is a block diagram of a second embodiment of the present invention. The same members as those in Embodiment 1 are designated by the same reference numerals and their description is omitted. The difference from the first embodiment is that the structure of the optical switch circuit unit 300 for resonance path selection is simplified and the module scale is expanded to 16 array LD-16 reflection ports. That is, the optical switch circuit unit increases the reflectance of one end surface of the optical gate 30 and uses this surface as the reflection mirror 33.

The 16 LD array and 16 reflection ports are
Each block consists of 4 arrays. That is,
The first block of the LD array is the LDs # 1 to # 4, and the light oscillated from these LDs at the frequencies f1 to f7 is the ports # 13 to # of the fourth block of the reflection port.
The arrayed waveguide grating 100 is designed to reach only 16. Similarly, the L of the second block of the LD array
D # 5 to # 8 and reflection port 3rd block port # 9 to
# 12, LD array third block # 9 to # 12 and reflection port second block # 5 to # 8, LD array fourth block # 13 to # 16 and reflection port first block # 13 to # 1.
6 has a correspondence relationship. That is, this module
Functionally, it has a structure in which four arrays and four reflection port configuration modules of the first embodiment are arranged in parallel in four stages.

Therefore, in this module, the oscillation frequencies shown in the following "Table 2" can be arbitrarily obtained by combining the driven LD and the reflection port. For example, as an LD array, the first LD of each block, that is, #
By selecting 1, # 5, # 9 and # 13, one of the frequencies f1 to f4 can be selected for each LD. Therefore, the modules at this time are f1 to f4.
It functions as an LD array module that can freely select the optical frequency. Similarly, the third LD (#
3, # 4, # 11, # 15)
It functions as an LD array that can oscillate at any combination of optical frequencies f3 to f6.

[0037]

[Table 2]

[Third Embodiment] FIG. 3 is a block diagram of a third embodiment of the present invention. The same members as those in the first embodiment are designated by the same reference numerals and their description is omitted. The present embodiment is a simplification of the structure of the second embodiment. That is, in the second embodiment, by changing the LD selected from each block, 4 of f1 to f4 can be obtained.
Although the LD array that oscillates not only at the frequencies but also at the four frequencies f3 to f6, for example, can be formed, in the present embodiment, the number of input waveguides of the arrayed-waveguide grating is reduced to implement the second embodiment.
3 is a configuration of a 4LD array-16 reflection port configured by four input waveguides # 1, # 5, # 9, and # 13 in FIG. In this case, the oscillation frequency is limited to four waves f1 to f4, but LD oscillation is possible with any combination thereof.

[Fourth Embodiment] FIG. 4 is a block diagram of a fourth embodiment of the present invention. The same members as those in the first embodiment are designated by the same reference numerals and their description is omitted. The difference between this embodiment and Embodiments 1 to 3 lies in the configuration of the resonance path selecting optical switch circuit unit 300. That is, in Examples 1 to 3, the resonance path selecting optical switch circuit 300 has a hybrid configuration in which the semiconductor optical gate array 30 element is mounted on the output waveguide end portion 15. On the other hand, the optical switch of this embodiment is
A Mach-Zehnder (MZ) interference circuit type 1 × 2 optical path changeover switch 34 is formed in the middle of the output waveguide, a reflection mirror 33 is provided at one end of the waveguide 15, and an end of the other waveguide 15 is provided. It is anti-reflective. In the 1 × 2 optical path changeover switch 34, a thin film heater 35 is provided on one arm of the MZ interference circuit, and the switching operation is realized by utilizing the change in the refractive index of the glass due to the thermo-optical effect of the heater heating. With such a 1 × 2 optical path changeover switch configuration, it is possible to form the entire optical switch circuit unit using the passive optical waveguide.

[Embodiment 5] FIG. 5 is a block diagram of a fifth embodiment of the present invention. The same members as those in Embodiment 1 are designated by the same reference numerals and their description is omitted. The difference between this embodiment and Embodiments 1 to 4 is that in Embodiments 1 to 4, the Fabry-Perot laser (FP
While the (LD) 200 array has a configuration in which it is hybrid-integrated on the passive optical waveguide substrate, in the present embodiment, the LD array section 200, the arrayed waveguide grating section 100, and the reflection port selection optical switch section 300 are They are formed by separate independent substrates 101A to 101C, and an optical fiber 40 connects them. Although the entire optical module with such a configuration becomes large,
The desired function can be realized more easily.

Although the present invention has been specifically described based on the embodiments, it is needless to say that the present invention is not limited to the structures of the embodiments and various modifications can be made without departing from the scope of the invention. Nor. For example, as the optical waveguide, the silica-based optical waveguide was used in the above embodiment, but, for example,
It can also be realized by using a polymer waveguide such as a polyimide waveguide. Even if an InP-based semiconductor optical integrated circuit is used, the optical frequency stabilization performance is inferior to that using the silica-based optical waveguide array grating, but similar performance can be expected for the optical frequency variable function.

[0042]

As described above, according to the present invention, the LD
By providing a plurality of resonance paths in advance in the resonator and selecting the resonance path, an optical frequency variable light source array module capable of discretely changing the oscillation frequency can be realized. In this module, the oscillation frequency of each port of the LD array can select any one of the discrete optical frequencies only by the switch operation for selecting the resonance path, so that it is possible to identify the specifics required in the FDM transmission system or the like. The oscillation frequency of can be accurately oscillated.

Also, by using a material having a small temperature coefficient of refractive index (for example, a silica optical waveguide) for the resonator portion, high stability of the oscillation frequency can be obtained.

Further, by constructing the optical switch circuit with the optical gate and the reflection portion, it is possible to simplify the configuration of the optical switch circuit portion using, for example, a semiconductor optical gate switch.

Further, it becomes possible to configure the optical switch circuit only with a passive optical waveguide such as a quartz optical waveguide.

Furthermore, the LD array section, the arrayed-waveguide grating section, and the reflection port selection optical switch section are formed on separate independent substrates, respectively, and the optical fibers are connected between them to make it easier and more desirable. Function can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical frequency variable light source module that is a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical frequency variable light source module that is a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical frequency variable light source module that is a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional technique.

FIG. 7 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 100 Arrayed Waveguide Grating 101, 101A to 101C Substrate 11 Input Waveguide 12 First Slab Waveguide 13 Waveguide Array Having Wavelength Difference ΔL 14 Second Slab Waveguide 15 Output Waveguide 200 Fabry-Perot Laser (FP) -LD) 21 Active layer 21a End face of FP-LD subjected to antireflection treatment 300 Optical switch circuit section for resonance path selection 30 Optical gate array 31 Active layer of optical gate array 32 Coupling waveguide 33 Optical gate end face subjected to antireflection treatment 34 MZ interference system type 1 × 2 optical switch 35 Thin film heater 40 Optical fiber

Claims (4)

[Claims] 1. A module comprising a resonator section and a semiconductor laser optically connected to each of the input waveguides of the resonator section, wherein the resonator section comprises one or more input waveguides. A first slab waveguide that receives light from the input waveguide, and a waveguide array that includes a plurality of waveguides that receives light from the first slab waveguide and that has a predetermined waveguide length difference that sequentially increases An array waveguide grating including a second slab waveguide that receives light from the waveguide array and two or more output waveguides that receive light from the second slab waveguide, and an output guide of the array waveguide grating. An optical switch circuit provided in each of the waveguides, and a variable frequency light source module. 2. The variable frequency light source module according to claim 1, wherein the arrayed waveguide element is formed by using a quartz optical waveguide. 3. The optical switch circuit provided in each of the output waveguides is composed of an optical gate section that realizes two states of transmission and non-transmission of light, and a reflection section provided at an end thereof. The variable frequency light source module according to claim 1, wherein: 4. An optical switch circuit provided in each of the output waveguides includes a 1 × 2 optical switch section for selecting two optical paths, and a reflecting section at one optical path end of the two optical paths. 2. The variable frequency light source module according to claim 1, wherein a non-reflecting portion or a light absorbing portion is provided at the other end of the optical path.