JPH11186661A - Semiconductor laser with modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser with a modulator having an optical monitor used as a source of a light communication system, by providing an optical monitor on a part of light wave guide. SOLUTION: A semiconductor laser 20 with a modulator comprises a modulator 21, an optical monitor 22 and a semiconductor laser 23 along a light wave guide 5. Thickness of a multiple quantum well is set to be MQW film thickness (modulator 21)<MQW film thickness (optical monitor 22)=MQW film thickness (semiconductor laser 23), so that λPL (modulator 21)<ΛPL (optical monitor 22)=λPL (semiconductor laser 23). A low-reflection film is provided on the end face of the modulator 21 side, that is an emitting surface of an emitted light (the front emitting surface 2), and a high-reflection film is formed on the end face of the semiconductor laser 23 side (the back emitting surface). For example, the low-reflection film is 1% or less, and the high-reflection film is 90% or more in reflectance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser with a modulator, and more particularly to a technique effective when applied to a technique for monitoring the optical output of a semiconductor laser.

[0002]

2. Description of the Related Art A semiconductor laser with a modulator is known as one of semiconductor lasers (LD: Laser Diode) used as a light source of an optical communication system.

A semiconductor laser with a modulator is described in, for example, "Hitachi Opto Device Data Book", 1995, P202-P205, published by Semiconductor Division of Hitachi, Ltd., and "NEC Technical Report", Vol. .12 / 199
4, P12 to P16.

The former reference discloses an electroabsorption type (EA: Elec).
A 1.55 μm band distributed feedback laser diode (DFB-LD) having an InGaAsP multiple quantum well (MQW) structure in which a tro modulator is integrated is disclosed.

The latter document discloses a 2.4 Gbps DFB laser / optical modulator integrated light source and an integrated light source module. In this example, an AR (Anti-Reflection) and an HR (High-Reflection) are provided on an optical modulator side end surface (front emission surface) and a DFB-LD side end surface (rear emission surface), respectively.
Coating (2% / 70%) applied.

In Japanese Patent Application Laid-Open No. 7-50443, a quantum well layer having a different band gap energy is formed on a single semiconductor substrate by selective growth to constitute a plurality of optical elements having different functions. Techniques are disclosed. In this document, a distributed feedback laser and a modulator switch (modulator) are integrated, an active region, a phase adjustment region and a distributed reflection region are integrated, a distributed feedback laser and a photodetector are described. An integrated type is described.

[0007]

In a conventional semiconductor laser or a semiconductor laser with an electro-absorption modulator, the control of the optical output of laser light (output light: forward laser light) emitted from one end of the semiconductor laser is performed by: A laser beam (rear laser beam) emitted from the rear end of the semiconductor laser is received by a light receiving element (PD: Ph
oto Diode) and control based on this monitor information.

FIG. 15 is a diagram showing a state in which the optical output (rearward optical output) of backward laser light in a conventional semiconductor laser is detected.

A laser beam (front laser beam 4f, front laser beam 4f) is emitted from a front emission surface 2 and a rear emission surface 3 of a semiconductor laser (LD) 1.
The rear laser beam 4b) 4 is emitted, the front laser beam 4f is used as output light, and the rear laser beam 4b is used as monitor light.

In FIG. 15, a thin portion shown by hatching is an optical waveguide 5.

A light receiving element (PD) 6 is provided on the rear emission surface 3 side of the semiconductor laser 1, and a rear laser beam 4
b.

Therefore, by detecting the photocurrent generated in the light receiving element 6 with the ammeter 8, the optical output of the forward laser light 4f can be detected from the output light ratio of the forward optical output and the backward optical output. The applied voltage can be controlled.

On the other hand, an EA modulator of a semiconductor laser with an electro-absorption (EA) modulator has a characteristic of absorbing light when a voltage is applied. Utilizing this characteristic, the modulator voltage is turned ON / O.
By performing FF, a 1/0 signal of light can be created.

When a bias is applied to the EA modulator, the absorbed light separates into electrons and holes, and a current (photocurrent: I
_ph ) occurs. This mechanism is basically the same as that of the light receiving element.

Therefore, the present inventor has proposed the photocurrent I.
_The present invention has been made by noting that forward light output can be detected using _ph .

An object of the present invention is to provide a semiconductor laser with a modulator having an optical monitoring unit.

Another object of the present invention is to provide a semiconductor laser with a modulator capable of increasing the optical output.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0019]

The following is a brief description of an outline of typical inventions disclosed in the present application.

(1) A semiconductor laser with a modulator comprising a semiconductor laser section and an electroabsorption modulator section along an optical waveguide, wherein an optical monitor section is provided in a part of the optical waveguide. . The optical monitoring unit is provided between the semiconductor laser unit and the modulator unit, and λ _PL (modulator unit) <λ _PL
(Optical monitor part) = λ _PL (semiconductor laser part) The thickness of the multiple quantum wells constituting the optical waveguide is set as MQW film thickness (modulator part) <MQW film thickness (optical monitor part) = MQW film It is thick (semiconductor laser part). A reflection film having a reflectance of 90 to 100% is provided on the rear emission surface. The reflection film is a layer in which two or more layers of a SiO ₂ film and an amorphous silicon layer are repeated. The end face of the optical waveguide that emits output light has a structure that is inclined with respect to the optical axis of the optical waveguide.

(2) In the configuration of the means (1), the optical monitor section is provided between the semiconductor laser section and the modulator section, and λ _PL (modulator section) = λ _PL (optical monitor section) The thickness of the multiple quantum well constituting the optical waveguide is set such that MQW film thickness (modulator portion) = MQW film thickness (optical monitor portion) <MQW film thickness (semiconductor laser portion) such that λ <λ _PL (semiconductor laser portion). Department).

(3) In the configuration of the means (1), the optical monitor section is provided between the semiconductor laser section and the modulator section, and λ _PL (optical monitor section) <λ _PL (modulator section ) <Λ _PL (semiconductor laser portion) by setting the thickness of the multiple quantum well constituting the optical waveguide to MQW film thickness (optical monitor portion) <MQW film thickness (modulator portion) <MQW film thickness (semiconductor laser portion). Department).

(4) A semiconductor laser with a modulator comprising a semiconductor laser section and an electro-absorption modulator section along an optical waveguide, wherein a semiconductor laser section is arranged at a central portion of the optical waveguide. A modulator section is arranged on one end side of the semiconductor laser section, an optical monitor section is arranged on the other end side, and the grating of the multiple quantum well constituting the optical waveguide of the semiconductor laser section has a λ / 4 phase shift on the way. Configuration.

(5) A semiconductor laser with a modulator comprising a semiconductor laser section and an electroabsorption modulator section along an optical waveguide, wherein a semiconductor laser section is arranged at a central portion of the optical waveguide, An optical monitoring unit is disposed on each side of the semiconductor laser unit, a modulator unit is disposed outside the optical monitoring unit, and a grating of a multiple quantum well constituting an optical waveguide of the semiconductor laser unit is provided in the middle. λ
/ 4 phase is shifted.

According to the means (1), (a) the photocurrent _Iph can be directly detected by the optical monitor unit provided monolithically on the semiconductor laser.

(B) In the conventional method of monitoring the backward laser light of the semiconductor laser with the light receiving element and specifying the optical output of the forward laser light, if the optical output ratio before and after the semiconductor laser changes due to aging, the correct method is used. Although the forward light output cannot be specified and the forward light output cannot be controlled with high accuracy, according to this structure, the photocurrent I _ph in the optical waveguide is directly detected, so that the forward laser light can be correctly detected. . That is, since the light output is monitored by detecting the laser light that does not pass through the film on the end face of the semiconductor laser,
Accurate monitoring can be performed. Also, with this monitoring method, accurate monitoring can be achieved even when the light output ratio changes due to external factors.

(C) Since no external light receiving element is required for monitoring the optical output, the number of components in the optical communication system can be reduced.

(D) A light-receiving element is not required, and troublesome optical axis alignment work between the semiconductor laser and the light-receiving element is not required.

(E) Since a semiconductor laser with a modulator is provided with an optical monitoring unit in a monolithic manner, it is not necessary to emit laser light from the rear emission surface. It is not necessary to consider the quality of the intensity, and it is only necessary to cover the rear emission surface with a high-reflection film that does not transmit laser light, so that the yield can be improved and the semiconductor laser (semiconductor laser with modulator) can be improved. Manufacturing costs can be reduced.

(F) According to the above (a) to (e), it is possible to reduce the equipment cost of the optical communication system.

(G) Reflectivity of 90-100% on rear emission surface
Since the reflective film is provided, the forward light output can be increased, and a semiconductor laser with a modulator having a high light output can be provided.

(H) Since the front emission surface of the optical waveguide is inclined with respect to the optical axis, it is possible to prevent return light and noise.

According to the means (2), in addition to the effect of the structure of the means (1), the amount of light absorbed by the optical monitor can be reduced, and the amount of light loss by the optical monitor can be reduced. As a result, the light output can be increased.

According to the means (3), in addition to the effect of the structure of the means (2), the amount of light absorption in the light monitor can be further reduced, and the amount of light loss in the light monitor can be reduced. . As a result, the light output can be increased.

According to the means (4), since the grating is configured so that the λ / 4 phase is shifted in the middle, single mode oscillation occurs. Thereby, a semiconductor laser having an optical monitoring unit and a modulator unit can be provided.

According to the means (5), the modulator sections are arranged at both ends of the semiconductor laser section, and the photocurrent _Iph can be detected by the individual optical monitor sections. Are configured such that the λ / 4 phase is shifted on the way, so that single-mode oscillation is possible, and that the laser beams emitted in two directions can be individually modulated by the modulator sections, and the optical monitors Since the _{photocurrent Iph} can be detected by the section, a semiconductor laser with a modulator capable of two-way transmission is obtained.

In a semiconductor laser with a modulator having a modulator section and a laser section, a semiconductor layer forming an active layer (light emitting region) of the laser section is extended to the modulator section to form an optical waveguide layer, and the optical waveguide is formed. This is an example in which light propagating through the wave layer is intermittently applied to the modulator section by applying an electric field (in the direction opposite to the stacking direction of the pin semiconductor layers constituting the modulator) to absorb the light. ,
The means (1) to (3) will be described.

The active layer and the optical waveguide layer are sandwiched between a quantum well structure, that is, a barrier layer having a larger band gap than a quantum well layer having a thickness small enough to cause a quantum size effect therein. In a case where the quantum well layer is formed of a semiconductor multilayer structure, the band gap of the quantum well layer becomes larger as the layer thickness becomes smaller, although the band gap is formed of a compound having the same composition.

For example, when the thickness of the quantum well layer is made thinner in the modulator section than in the laser section, the forbidden band width of the quantum well layer in the modulator section becomes larger than that in the laser section. Therefore, when laser light generated with energy (wavelength) corresponding to the forbidden bandwidth of the quantum well layer in the laser portion is emitted through a modulator to which no electric field is applied, the optical loss of the laser light in the modulator portion is low. Become.

On the other hand, when the electric field is applied to the modulator section, the band structure of the quantum well layer of the modulator section changes, and the effective bandgap becomes smaller (a phenomenon called quantum confined Stark effect). Thereby, the laser light entering the modulator section is absorbed.

The above-described dependence of the bandgap of the semiconductor layer on the thickness of the semiconductor layer and the change in the band structure due to the application of an electric field are due to the quantum size effect. (Preferably 5-10n
It is recommended that each of the barrier layers having a thickness in the range of m) is formed of a semiconductor layer having a thickness in the range of 5 to 50 nm (preferably, 6 to 12 nm).

The MQW (Multi Quantum Well) structure means that the above quantum well structure is repeated in the order of barrier layer / quantum well layer / barrier layer /.../ quantum well layer / barrier layer. The structure has a well layer, and the barrier layers at both ends are replaced with an optical guide layer or a cladding layer having the same or larger band gap as the barrier layer, if necessary.

The laser section is manufactured by a so-called distributed feedback resonator structure having a diffraction grating or a region having a periodic refractive index distribution in the oscillation direction of laser light along the quantum well layer.

In the case of a semiconductor laser with a modulator, since a modulator is formed on one of the end faces of the quantum well layer located at both ends in the oscillation direction of the laser light, oscillation of the laser light such as in a Fabry-Perot resonator This is because a resonator structure in which the condition is set by the distance between the end faces cannot be adopted.

When the present invention is applied to the semiconductor laser with a modulator configured as described above, at least one of the electrodes formed on the upper surface or the lower surface of the laser device is provided with a laser unit, a modulator unit, and an optical monitor unit. , So that current injection or electric field application can be performed individually for each part.

At this time, as the thickness of the quantum well layer in the optical monitor section is reduced, the optical loss of the laser light passing therethrough can be reduced, but there is a trade-off relationship that the applied electric field required for monitoring increases. Exists.

For example, in the case of the above-mentioned means (1) in which the quantum well layer thickness of the optical monitor section is substantially equal to that of the laser section,
The current (photocurrent) generated by light absorption can be sufficiently detected without providing a new voltage source in an external circuit connected to the light monitor unit, but the amount of light absorption can be controlled (specifically, suppressed to a desired value). Take time.

On the other hand, in the case of the above-mentioned means (2) and (3) in which the quantum well layer thickness of the optical monitor section is thinner than that of the laser section, the forbidden band width of the quantum well layer of the optical monitor section becomes large. Absorption of laser light (so-called basic absorption) by the quantum well layer without an electric field as in 1) is unlikely to occur, and a power supply (DC) is connected to an external circuit connected to the optical monitor unit when measuring a monitoring current (photocurrent). It is often required to provide a voltage source), but on the other hand, it is easy to suppress the amount of light absorption.

In short, the above-mentioned means can be applied to the requirements or specifications of an optical communication system using the semiconductor laser with a modulator of the present invention, for example, the frequency of monitoring the light intensity, the current measurement sensitivity of an external circuit connected to the monitor unit, and the like. It is appropriately selected depending on the situation.

In the above means (1) to (3), when the boundaries of the portions where the quantum well layers have different thicknesses are optically coupled via a region where the quantum well layers change gradually (layer thickness transition region), the boundary is obtained. Can be suppressed. Further, in these means, a difference in the thickness of the error range is allowed between portions where the thicknesses of the quantum well layers are specified to be equal. The criterion is that the difference in the measured value of the wavelength λ _PL corresponding to the peak energy obtained in the photoluminescence measurement of the quantum well structure falls within the range of ± 5 nm.

Although the composition wavelength of the quantum well layer can be estimated from the above wavelength λ _PL , λ _PL does not always become the oscillation wavelength of the laser light in the laser portion. Smaller than λ _PL (short wavelength)
Become.

[0052]

Embodiments of the present invention will be described below in detail with reference to the drawings. In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

(Embodiment 1) In Embodiment 1, an example in which the present invention is applied to a multiple quantum well type DFB semiconductor laser having an oscillation wavelength of 1550 nm will be described.

FIGS. 1 to 6 relate to a semiconductor laser with a modulator according to the first embodiment of the present invention. FIG. 1 is a perspective view showing a state in which a part of a semiconductor laser with a modulator is cut away, and FIG.
FIG. 2 is a sectional view taken along line AA in FIG. 1.

Semiconductor laser 20 with modulator according to the first embodiment
As shown in FIGS. 1 and 2, a modulator section 21, an optical monitor section 22, and a semiconductor laser (LD) are arranged along the optical waveguide 5.
It has a part 23.

Semiconductor laser 20 with modulator according to the first embodiment
Form an equivalent circuit as shown in FIG. That is, since the modulator 21a of the modulator section 21, the optical monitor 22a of the optical monitor section 22, and the LD 23a of the semiconductor laser section 23 are all configured for the same optical waveguide 5,
Each optical element has a diode configuration and a common cathode. The common terminal becomes the ground (GND).

A terminal resistor Rt is provided between the GND terminal and the modulator anode electrode 21b, a terminal resistor Rm is provided between the GND terminal and the light monitor anode electrode 22b, and a terminal resistor Rm is provided between the GND terminal and the laser anode electrode 23b. Has a capacitor CL for preventing electrostatic breakdown.

Next, the structure of the modulator-equipped semiconductor laser 20 will be described together with the manufacturing method.

In manufacturing the semiconductor laser with a modulator according to the first embodiment, a semiconductor substrate 25 as shown in FIG. 3 is used. The semiconductor substrate 25 at the time of manufacture is actually called a wafer and has a large area. However, here, a semiconductor substrate 25 having a size enough to manufacture a single semiconductor laser 10 with a modulator will be described.

The semiconductor substrate 25 is a rectangular n-type InP substrate. In FIG. 3, an optical monitor 22 is formed in a region b at an intermediate portion along the longitudinal direction, and a modulator 21 is formed in a region a on the left side. The semiconductor laser unit 2 is formed in the region c on the right side.
3 are formed. That is, the optical monitor section 22 has a structure provided between the semiconductor laser section 23 and the modulator section 21.

In the first embodiment, an optical waveguide having a multiple quantum well (MQW) structure is formed by using the selective growth method. At this time, the growth layer is evaluated using photoluminescence (PL) peak energy instead of band gap energy.

In the selective growth method, as described in the above literature, the width (mask width) of a mask (insulating film) covering the surface of a semiconductor substrate and the difference in the opening width between masks are different. The thickness of each layer of the formed quantum well is different.
Therefore, λ _PL of each optical waveguide can be changed by selecting the mask width and the aperture width.

In the first embodiment, λ _PL (modulator section) <λ
The thickness of the multiple quantum well constituting the optical waveguide is set to MQW so that _PL (optical monitor) = λ _PL (semiconductor laser).
Film thickness (modulator section: area a) <MQW film thickness (optical monitor section:
Region b) = MQW film thickness (semiconductor laser part: region c).

Therefore, no mask is provided in the region a,
Two masks 26 are formed in parallel with the region b and the region c.

The mask 26 is provided on the semiconductor substrate 25 on which the grating 27 is formed only in the region c.

The grating 27 has a conventional
(Normal grating), and the pitch of the grating is, for example, 240 nm. The width and opening width of the mask 26 are 18 μm.
m.

MOCVD on such a semiconductor substrate 25
Each layer is sequentially formed by a (Metalorganic Chemical Vapor Deposition) method.

Although not shown in detail, as shown in FIG. 2, for example, an InGaAsP lower guide layer 30, an MQW
A layer 31, an InGaAsP upper guide layer 32, an InP cladding layer 33, and an InGaAs cap layer are sequentially formed on top of each other, and then an insulating film is formed on the surface in a stripe shape. 35 is formed.

The MQW layer 31 has a multi-layer structure (the well layer has 9 layers).
Layer) of InGaAs / InGaAsP, and a region a
The thickness of the well layer is about 6 nm, and the thickness of the barrier layer is 8 nm. In addition, the thicknesses of the well layer and the barrier layer in the regions b and c are about 1.3 times the thickness of the region a.

In the first embodiment, the λ _PL of the modulator section 21 is 1500 nm, the λ _PL of the optical monitor section 22 and the λ _PL of the semiconductor laser section 23 are 1560 nm, and the optical monitor section detects the photocurrent I _ph . The optical output of the laser beam can be directly detected.

Next, an InP layer containing iron (Fe) is formed in the recessed portions on both sides of the mesa 35 to form a block layer (Fe-InP) 36. At this time, the modulator unit 2
A window layer containing iron (Fe) (Fe-
InP) 37 is formed.

The stripe-shaped optical waveguide may be formed by implanting protons without performing etching.

Next, the modulator section 21, the optical monitor section 22,
In order to prevent interference between currents adjacent to each other on the modulator anode electrode 21b, the optical monitor anode electrode 22b, and the laser anode electrode 23b side of the semiconductor laser unit 23, InP is applied.
A separation portion groove 40 is formed at an intermediate depth of the cladding layer 33.

Next, after the insulating film is selectively etched to form an electrode window, the InGaAs exposed at the bottom of the window is formed.
The cap layer is removed, and then the anode electrode is formed.

Next, after polishing the back surface of the semiconductor substrate 25, a cathode electrode is formed and cleavage is performed. Then, in the cleavage, the cleavage is performed so as to cross the window layer 37. Since the end face of the optical waveguide 5 on the modulator section 21 side is an interface with the window layer 37, the emission surface of the optical waveguide 5 on the modulator section 21 side is a plane inclined with respect to the optical axis of the optical waveguide 5. Therefore, the return light of the laser beam is not generated, and the generation of noise can be prevented.

As shown in FIG. 2, a low reflection film 41 is provided on the end face on the modulator section 21 side, that is, on the output light emitting face (front emitting face 2), and the end face on the semiconductor laser section 23 side ( A high reflection film 42 is formed on the rear emission surface 3).

The low reflection film 41 has, for example, a reflectance of 1% or less, and the high reflection film 42 has a reflectance of 90% or more.

Semiconductor laser 20 with modulator according to the first embodiment
Since the optical monitor section 22 is formed monolithically, it is not necessary to dispose a light receiving element for detecting an optical output outside the semiconductor laser 20 with a modulator. For this reason, the laser beam does not have to be emitted from the rear emission surface 3, and there is no problem even if the reflectance is set to 100% at the maximum.

The reflection film is a layer in which two or more layers of a SiO ₂ film and an amorphous silicon layer are repeated.
When SiO ₂ / a-Si has x periods, the reflectance is x =
1, 71% at x = 2, 97% at x = 3, x = 4
Is 99%. Therefore, in order to make the reflectance 90% or more, the SiO ₂ / a-Si should be made two or more periods.
In order to make the reflectance 99 to 100% or more, four periods or more may be used.

The low-reflection film 41 and the high-reflection film 42 are omitted except in FIG. 2, including other embodiments.

Next, the bar-shaped semiconductor is cut to manufacture the semiconductor laser with modulator 20 shown in FIGS.

The semiconductor laser with modulator 20 has a height of 100 μm.
m, width 400 μm, and length (cavity length) 600 μm.

The semiconductor laser with modulator 20 is, for example,
4 and FIG. 5, that is, the system is assembled into the modifying stem 50 and then shipped after characteristic inspection.

At the center of the upper surface of the modifying stem 50, a plate-like chip carrier 51 made of aluminum nitride (AlN) is provided.
Has been fixed. At the center of the chip carrier 51, a semiconductor laser with modulator 20 having an optical monitor section 22 is mounted.

The laser anode 23 b of the semiconductor laser section 23 and the upper electrode of the chip capacitor 52 mounted on the chip carrier 51 are electrically connected via wires 53. The upper electrode of the chip capacitor 52 is connected via a wire 53 to a conductor layer 55 partially provided on the modifying system 50. A support 49 to which the leads 54 are electrically connected is electrically and mechanically connected to the conductor layer 55.

The light monitor anode electrode 22b is connected to the wire 53
Electrode 5 provided on the upper surface of chip carrier 51 via
6 is electrically connected via a wire 53. The electrode 56 is connected to the support plate 5 on the modifying stem 50.
9 is electrically connected via a wire 53 to a strip line 58 provided on a ceramic plate 57 fixed to 9.

The modulator anode electrode 21b is connected to an electrode 60 provided on the upper surface of the chip carrier 51 via a wire 53.
Are electrically connected to each other through a wire 53. The electrode 60 is supported on the support plate 59 on the modifying stem 50.
Is electrically connected via a wire 53 to a strip line 62 provided on a ceramic plate 61 fixed to the ceramic plate 61.

Also, 50 chips are placed on the chip carrier 51.
Ω resistors 63 and 64 are provided. One electrode of the resistor 63 is connected to the light monitor anode electrode 22b by a wire 53.
Are electrically connected via The resistance 64
Is connected to the modulator anode electrode 21b by a wire 53.
Are electrically connected via

In this modifying system 50,
By cutting the wire 53 connected to the chip capacitor 52, the electrode 56, and the electrode 60 and removing the chip carrier 51 from the modifying system 50, the chip carrier 51 can be incorporated into a desired electronic device.

CL shown in the equivalent circuit of FIG. 6 is a chip capacitor 52, and Rm and Rt are resistors 63 and 64.

According to the first embodiment, the following effects can be obtained.

(1) The photocurrent I is directly output by the optical monitor 22 provided monolithically on the semiconductor laser 20 with modulator.
_ph can be detected.

(2) In the conventional method of monitoring the backward laser light of the semiconductor laser with the light receiving element and specifying the optical output of the forward laser light, the change in the film on the end face of the semiconductor laser with modulator 20 causes the front and rear of the semiconductor laser to change. If the optical output ratio of the optical waveguide changes, the forward optical output cannot be specified correctly, and the forward optical output cannot be controlled with high accuracy.
From the direct detection of the _photocurrent I _ph at
The forward laser beam can be correctly detected. Also, with this monitoring method, accurate monitoring can be achieved even when the light output ratio changes due to external factors.

(3) Since no external light receiving element is required for monitoring the optical output, the number of components in the optical communication system can be reduced.

(4) The light receiving element is not required, and the troublesome optical axis alignment work between the semiconductor laser and the light receiving element becomes unnecessary.

(5) Since the optical monitoring section 22 is provided monolithically on the semiconductor laser 20 with a modulator, the emission of laser light from the rear emission surface 3 becomes unnecessary. It is not necessary to consider the quality of the light emission intensity, and it is only necessary to cover the rear emission surface 3 with the high reflection film 42 that does not transmit the laser light. The manufacturing cost of the semiconductor laser can be reduced.

(6) From the above (1) to (5), the use of the semiconductor laser with a modulator of the present invention makes it possible to reduce the equipment cost of an optical communication system.

(7) Reflectance of 90-100 on the rear exit surface 3
%, The forward light output can be increased. Therefore, a semiconductor laser with a modulator having a high optical output can be provided.

(8) Since the front emission surface of the optical waveguide is inclined with respect to the optical axis, it is possible to prevent return light and noise.

(Embodiment 2) FIG. 7 shows Embodiment 2 of the present invention.
FIG. 3 is a cross-sectional view of a semiconductor laser with a modulator, which is the following.

In the second embodiment, λ _PL (modulator section) = λ
The thickness of the multiple quantum well constituting the optical waveguide is set to be MQW so that _PL (optical monitor) <λ _PL (semiconductor laser).
Film thickness (modulator part) = MQW film thickness (light monitor part) <MQW
This is a structure that becomes a film thickness (semiconductor laser portion).

In the second embodiment, the thickness of the well layer in the region a and the region b is about 6 nm, and the thickness of the barrier layer is 8 nm.
The thickness of the well layer and the barrier layer in the region c is about 1.3 times the thickness of the regions a and b.

The wavelength λ _PL of the semiconductor laser section 23 is 1
560 nm, and the wavelength λ of the optical monitor unit 22 and the modulator unit 21 is 1500 nm.

Semiconductor laser 20 with modulator according to the second embodiment
In other respects, the other parts have the same structure as the semiconductor laser with modulator 20 of the first embodiment.

Semiconductor laser 20 with modulator according to the second embodiment
According to the above, the wavelength range that can be transmitted by the configuration of the optical waveguide (cavity) of the optical monitor unit 22 is smaller (1500 nm) than the oscillation wavelength (1550 nm) of the laser beam generated by the semiconductor laser unit 23. Can be reduced, and the amount of light loss in the optical monitor unit 22 can be reduced. As a result, the light output can be increased.

(Embodiment 3) FIG. 8 shows Embodiment 3 of the present invention.
FIG. 9 is a perspective view showing a state in which a part of the semiconductor laser with a modulator is cut away, and FIG.

In the third embodiment, λ _PL (optical monitor section) <
The thickness of the multiple quantum well constituting the optical waveguide is set to MQW so that λ _PL (modulator section) <λ _PL (semiconductor laser section).
Film thickness (optical monitor part) <MQW film thickness (modulator part) <MQW
The film thickness (semiconductor laser portion).

In the third embodiment, for example, in the region a, the thickness of the well layer (quantum well layer) is 6 nm, and in the region b, the thickness of the well layer (barrier layer) is 8 nm. The thickness of the barrier layer is 7.8 nm and the thickness of the barrier layer is 10.4 nm in the region c.

The wavelength λ of the semiconductor laser section 23 is 15
50 nm, and the wavelength λ of the optical monitor 22 is 1490 n.
m, and the wavelength λ of the modulator section 21 is 1500 nm.

In the third embodiment, other parts are the same as those of the first embodiment.
Is the same as

In the manufacture of the semiconductor laser with a modulator according to the third embodiment, a semiconductor substrate as shown in FIG. 10 is used to make the λ _PL of the regions a, b and c different from each other. . That is, as described above, the masks 26 are provided in the regions a and c, respectively, so that the MQW film thickness (optical monitor portion) <the MQW film thickness (modulator portion) <the MQW film thickness (semiconductor laser portion). The mask width W1 of the mask 26 in the region a is smaller than the mask width W2 of the mask 26 in the region c. The opening width is constant, for example, 18
It is about μm.

By using the semiconductor substrate 25 to manufacture the semiconductor laser 20 with a modulator as shown in FIGS. 8 and 9, the wavelength λ _PL of the semiconductor laser section 23 is 1560 nm, and 14 wavelengths λ _PL of 22
90 nm and the wavelength λ _PL of the modulator section 21 can be set to 1500 nm (at this time, the oscillation wavelength of the laser light is 15 nm).
50 nm).

Semiconductor Laser with Modulator 20 of Embodiment 3
The other portions have the same structure as the semiconductor laser 20 with modulator of the first embodiment.

Semiconductor Laser with Modulator 20 of Embodiment 3
Is the wavelength λ _PL of the optical monitor unit 22 as in the second embodiment.
Is made smaller than the oscillation wavelength of the laser, the amount of light absorbed by the optical monitor 22 can be further reduced, and the amount of light loss by the optical monitor 22 can be reduced. As a result, the light output can be increased.

(Embodiment 4) FIG. 11 is a sectional view of a semiconductor laser with a modulator according to Embodiment 4 of the present invention.

Semiconductor Laser with Modulator 20 of Embodiment 4
Has a structure in which a semiconductor laser section 23 is located at the center, a modulator section 21 is arranged on one end side, and an optical monitor section 22 is arranged on the other end side. Further, the grating 27 is provided only in the semiconductor laser portion 23, and the grating 27 is an intermediate portion thereof, as shown in FIG.
The λ / 4 phase is shifted. This results in single mode oscillation.

Semiconductor Laser with Modulator 20 of Embodiment 4
The other structural parts are the same as in the first embodiment.

According to the present embodiment, it is possible to provide a semiconductor laser having an optical monitor section and a modulator section that oscillate in a single mode.

(Embodiment 5) FIG. 13 is a perspective view of a semiconductor laser with a modulator according to a fifth embodiment of the present invention, with a part thereof being cut away, and FIG. 14 is a sectional view of the semiconductor laser with a modulator.

Semiconductor laser 20 with modulator according to Embodiment 5
As shown in FIG. 13 and FIG. 14, a semiconductor laser section 23 is arranged at an intermediate portion of the optical waveguide 5, an optical monitor section 22 is arranged outside the semiconductor laser section 23, and a modulator section 21 is arranged outside the semiconductor laser section 23. With this structure, two-way transmission becomes possible.

Since the grating 27 is provided only in the semiconductor laser section 23 and the λ / 4 phase shifts in the middle of the grating as in the fourth embodiment, the single mode oscillation Becomes possible.

Therefore, a low-reflection film (not shown) is provided on the emission surfaces at both ends of the semiconductor laser with modulator 20 of the fifth embodiment.
Is formed.

Semiconductor laser 20 with modulator according to the fifth embodiment
According to this, a modulator-equipped semiconductor laser capable of two-way transmission by single mode oscillation is provided.

In the structure of the fifth embodiment, the effect of the fifth embodiment can be obtained even if the optical monitor section 22 is provided solely on one side of the semiconductor laser section 23.

Although the invention made by the inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the invention. Needless to say.

[0126]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

(1) Since the optical monitoring unit is monolithically provided in the semiconductor laser with the modulator, the optical output can be detected by detecting the photocurrent of the optical monitoring unit.

(2) In an optical communication system using a semiconductor laser with a modulator according to the present invention, the forward / backward output of the semiconductor laser caused by arranging a light receiving element outside the semiconductor laser as in the prior art. The monitoring failure due to the temporal change of the ratio and other external factors does not occur, and the stable operation of the system can be achieved.

(3) Since no external light receiving element is required for monitoring the optical output, the number of components in the optical communication system can be reduced.

(4) The light receiving element is not required, and the troublesome optical axis alignment work between the semiconductor laser and the light receiving element is not required.

(5) Since the semiconductor laser with a modulator is provided with a monolithically provided optical monitor, it is not necessary to emit laser light from the rear emission surface. It is not necessary to consider the quality of the intensity, and it is only necessary to cover the rear emission surface with a high-reflection film that does not transmit laser light, so that the yield can be improved and the manufacturing cost of the semiconductor laser can be reduced. .

(6) According to the above (1) to (5), it is possible to provide a semiconductor laser with a modulator capable of reducing the equipment cost of an optical communication system.

(7) Reflectance of 90-100 on the rear exit surface
%, It is possible to provide a semiconductor laser with a modulator having a high light output.

(8) Since the front emission surface of the optical waveguide is inclined with respect to the optical axis, it is possible to provide a semiconductor laser with a modulator that does not generate noise due to return light.

[Brief description of the drawings]

FIG. 1 is a perspective view of a semiconductor laser with a modulator according to a first embodiment of the present invention in a state where a part thereof is cut away.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a perspective view of a semiconductor substrate in manufacturing the semiconductor laser with a modulator according to the first embodiment.

FIG. 4 is a perspective view of a modify system incorporating the semiconductor laser with a modulator according to the first embodiment.

FIG. 5 is a plan view of the modify stem.

FIG. 6 is an equivalent circuit diagram of the semiconductor laser with a modulator according to the first embodiment.

FIG. 7 is a cross-sectional view of a semiconductor laser with a modulator according to a second embodiment of the present invention.

FIG. 8 is a perspective view of a semiconductor laser with a modulator according to a third embodiment of the present invention, in which a part of the semiconductor laser is cut away.

FIG. 9 is a sectional view of a semiconductor laser with a modulator according to a third embodiment of the present invention.

FIG. 10 is a perspective view of a semiconductor substrate in manufacturing the semiconductor laser with a modulator according to the third embodiment.

FIG. 11 is a sectional view of a semiconductor laser with a modulator according to a fourth embodiment of the present invention.

FIG. 12 is a schematic diagram illustrating a shape of a grating in a semiconductor laser with a modulator according to a fourth embodiment.

FIG. 13 is a perspective view of a semiconductor laser with a modulator according to a fifth embodiment of the present invention in a state where a part thereof is cut away.

FIG. 14 is a sectional view of a semiconductor laser with a modulator according to a fifth embodiment.

FIG. 15 is a schematic diagram showing a monitoring state of a conventional semiconductor laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Front emission surface, 3 ... Rear emission surface,
4 laser light, 4f forward laser light, 4b backward laser light, 5 optical waveguide, 6 light receiving element, 7 light receiving surface, 8 ammeter, 20 semiconductor laser with modulator, 21 modulator section ,
21a: modulator, 21b: modulator anode electrode, 22:
Optical monitor unit, 22a Optical monitor, 22b Optical monitor anode electrode, 23 Semiconductor laser unit (LD unit), 23a
LD, 23b laser anode electrode, 25 semiconductor substrate, 26 mask, 27 grating, 30 In
GaAsP lower guide layer, 31: MQW layer, 32: InG
aAsP upper guide layer, 33 ... InP clad layer, 35 ...
Mesa, 36: block layer, 37: window layer (Fe-In)
P), 40: separation groove, 41: low reflection film, 42: high reflection film, 49: support base, 50: modify stem, 51:
Chip carrier, 52: Chip capacitor, 53: Wire, 54: Lead, 55: Conductive layer, 56: Electrode, 57:
Ceramic plate, 58: strip line, 59: support plate, 60: electrode, 61: ceramic plate, 62: strip line, 63, 64: resistance.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masakatsu Yamamoto 5-2-1, Josuihoncho, Kodaira-shi, Tokyo Inside Semiconductor Division, Hitachi, Ltd. 15 Asahidai, Nippon Tobu Semiconductor Co., Ltd. (15) Akira Ogino Inventor Akira Ogino 5-20-1, Josuihoncho, Kodaira-shi, Tokyo Semiconductor Company, Hitachi Ltd.

Claims (9)

[Claims] 1. A semiconductor laser with a modulator comprising a semiconductor laser section and an electroabsorption modulator section along an optical waveguide, wherein an optical monitor section is provided in a part of the optical waveguide. A semiconductor laser with a modulator, characterized in that: 2. The optical monitor section is provided between the semiconductor laser section and the modulator section, and λ _PL (modulator section) <
The thickness of the multiple quantum wells constituting the optical waveguide is set to MQ so that λ _PL (optical monitor part) = λ _PL (semiconductor laser part).
W film thickness (modulator part) <MQW film thickness (light monitor part) = MQ
2. The semiconductor laser with a modulator according to claim 1, wherein the semiconductor laser has a W thickness (semiconductor laser portion). 3. The optical monitor section is provided between the semiconductor laser section and the modulator section, and λ _PL (modulator section) =
The thickness of the multiple quantum well constituting the optical waveguide is set to be MQ so that λ _PL (optical monitor part) <λ _PL (semiconductor laser part).
W film thickness (modulator part) = MQW film thickness (light monitor part) <MQ
2. The semiconductor laser with a modulator according to claim 1, wherein the semiconductor laser has a W thickness (semiconductor laser portion). 4. The optical monitor section is provided between the semiconductor laser section and the modulator section, and λ _PL (optical monitor section)
The thickness of the multiple quantum wells constituting the optical waveguide is set to MQ so that <λ _PL (modulator section) <λ _PL (semiconductor laser section).
W film thickness (optical monitor) <MQW film thickness (modulator) <MQ
2. The modulator-equipped semiconductor laser according to claim 1, wherein the semiconductor laser is configured to have a W film thickness (semiconductor laser portion). 5. The semiconductor laser with a modulator according to claim 1, wherein a reflection film having a reflectance of 90 to 100% is provided on the rear emission surface. 6. The modulator-equipped semiconductor laser according to claim 5, wherein said reflection film is a layer in which an SiO ₂ film and an amorphous silicon layer are repeated and two or more layers are overlapped. 7. A semiconductor laser with a modulator comprising a semiconductor laser section and an electroabsorption modulator section along an optical waveguide, wherein a semiconductor laser section is arranged at a central portion of said optical waveguide, A modulator section is arranged on one end side of the laser section, an optical monitor section is arranged on the other end side, and the grating of the multiple quantum well constituting the optical waveguide of the semiconductor laser section has a λ / 4 phase shift on the way. A semiconductor laser with a modulator, comprising: 8. A semiconductor laser with a modulator comprising a semiconductor laser section and an electroabsorption modulator section along an optical waveguide, wherein a semiconductor laser section is arranged at a central portion of the optical waveguide, An optical monitoring unit is disposed on each side of the laser unit, a modulator unit is disposed outside the optical monitoring unit, and a grating of a multiple quantum well constituting an optical waveguide of the semiconductor laser unit is λ on the way. / 4
A semiconductor laser with a modulator, which is out of phase. 9. The optical waveguide according to claim 1, wherein an end face of the optical waveguide for emitting the output light has a structure inclined with respect to an optical axis of the optical waveguide. Semiconductor laser with modulator.