1.5†µm wavelength NPN-type photonic-crystal surface-emitting laser exceeding 100 mW.

A 1.5 µm laser diode has applications in eye-safe light detection and ranging (LiDAR) and optical communications via photonic integrated circuits. Photonic-crystal surface-emitting lasers (PCSELs) have lens-free applications in compact optical systems because of narrow beam divergences (<1 degree). However, the output power has still been less than 1 mW for 1.5 µm PCSELs. For higher output power, one approach is suppression of p-dopant Zn diffusion in the photonic crystal layer. Therefore, n-type doping was used for the upper crystal layer. Moreover, an NPN-type PCSEL structure was proposed to reduce intervalence band absorption in the p-InP layer. Here, we demonstrate a 1.5 µm PCSEL with 100 mW output power, which exceeds previous reported values by two orders of magnitude.

Multi-focusing surface-emitting lasers.

Complete control of a beam pattern requires not only projecting a two-dimensional (2D) pattern but also focusing on a three-dimensional (3D) point cloud, which is typically achieved utilizing holography under the framework of diffraction. We previously reported direct focusing from on-chip size surface-emitting lasers that utilize a holographically modulated photonic crystal cavity based on 3D holography. However, this demonstration was of the simplest 3D hologram with a single point and single focal length, and the more typical 3D hologram with multiple points and multiple focal lengths has not yet been examined. Toward direct generation of a 3D hologram from the on-chip size surface-emitting laser, we here examined a simple 3D hologram featuring two different focal lengths with a single off-axis point in each to reveal the fundamental physics. Two types of holography, one based on superimposition and the other on random tiling, successfully demonstrated the desired focusing profiles. However, both types caused a spot noise beam in the far field plane due to interference between focusing beams with different focal lengths, especially in the case of the superimposing method. We also found that the 3D hologram based on the superimposing method consisted of higher order beams including the original hologram due to the manner of the holography. Secondly, we demonstrated a typical 3D hologram with multiple points and focal lengths and successfully showed the desired focusing profiles by both methods. We believe our findings will bring innovation to mobile optical systems and pave the way to developing compact optical systems in areas such as material processing, micro fluidics, optical tweezers, and endoscopy.

On-chip size, low-noise fringe pattern projector offering highly accurate 3D measurement.

Fringe pattern projectors are quite useful for highly accurate three-dimensional (3D) measurement when a projector or LED array is used for illumination. We have fabricated a 0.2 mm × 0.2 mm structured light source, which was an on-chip size surface-emitting laser that utilized a holographically modulated two-dimensional (2D) photonic crystal (PC). This will make possible an extremely compact 3D measurement system that will positively impact mobile systems. However, the fringe pattern tends to cause speckle-like noise that leads to severe positional error in 3D measurement. Here we present a simple approach to projecting a low-noise fringe pattern from our surface-emitting lasers by using a one-dimensional (1D) focusing hologram. This method improves the flatness of the fringe pattern by around four times.

Direct-focusing surface-emitting laser.

Focusing is a fundamental optical technique that has been widely implemented via lenses. Here, we demonstrate direct focusing from a band-edge surface-emitting laser, whose emission area is 200 µm × 200 µm, without any lenses. To achieve this, a phase-modulating layer is incorporated into the laser cavity. This layer acts simultaneously as a lasing cavity similar to that of a photonic crystal laser and as a holographic spatial-phase modulator, which transforms the output beam into a focusing beam by slightly shifting the positions of holes from a periodic square lattice. Beam profiles along the surface normal clearly show that direct focusing occurs with a focal length and focal spot size of 310 µm and 6.1 µm, respectively. The focal length agrees well with the theoretical value, and the focal spot size is 2.0 times the diffraction-limited size, which indicates that the higher transverse modes are sufficiently suppressed. In addition, the power density at the focus is 540 times higher than that at the near-field plane. Interestingly, a focus pattern is also observed in the opposite direction at the near-field plane, which indicates that a converging beam and a diverging beam are simultaneously emitted because of the nature of the in-plane band-edge laser. The conventional beam patterns of semiconductor laser cavities are limited to the regime of two-dimensional projection based on a Fourier hologram. In contrast, we demonstrate the simplest form of a three-dimensional point cloud based on a Fresnel hologram, which is quite useful for micro-sensing applications such as microfluidics, flow cytometry, blood sensors, and endoscopy.

200×200 µm2 structured light source.

3D structured illumination is important in high-speed 3D metrology where beam patterns are roughly categorized into multi-dot and fringe patterns. For example, large-scale multi-dot patterns are utilized for facial recognition in an iPhone X on the basis of an active stereo method, while fringe patterns are utilized in Grey code patterns or fringe projection profilometry including Fourier transform profilometry and the phase shifting profilometry, which is suitable for high-resolution measurement. Among these applications, the light sources include a combination of vertical-cavity surface-emitting lasers (VCSELs) and diffractive optical elements (DOEs), a projector, and so on. Recently, we demonstrated static arbitrary two-dimensional beam patterns without a zero-order beam from needle-tip sized integrable spatial-phase-modulating surface-emitting lasers (iPMSELs). Due to their compactness (they are one order of magnitude smaller than DOE), surface-emitting device, lack of zero-order beam, and ease of switching the beam patterns electrically, iPMSELs will be suitable as an ultra-compact light source for 3D metrology that not only downsizes the conventional light source but also contributes to 3D inspections in narrow spaces such as dental and endoscope examinations. In this context, we have examined two beam patterns (multi-dot and fringe) both without a zero-order beam by using the iPMSELs. In the former, we have demonstrated projection of large-scale dot patterns of more than 10,000 points, which is the same order of magnitude as points in a practical device from a 200×200-µm2 emitter. Since the emitter has approximately 1 mega scattering points, this structure enables 1-mega-pixel images in the wavenumber space, which are comparable to the images of a typical projector emitting several-mega-pixel images from several tens of centimeters. In the latter, we successfully shifted the fringe patterns, which is vital to applying the phase shifting profilometry, despite the superposition of the conjugate ±1st order beam patterns.

Contact metalens for high-resolution optical microscope in semiconductor failure analysis.

The continuous downscaling of electronic devices requires higher-resolution optical microscopic images for semiconductor failure analysis (FA). However, a part of the diffracted light from the measuring pattern in the silicon (Si) substrate cannot be collected due to the total internal reflection (TIR) at the interface between the Si substrate and air. We propose a metalens suitable for FA that improves resolution of optical microscopic images by collecting beyond the critical angle of TIR at the interface. For the proof of concept, we integrated the fabricated metalens into the optical setup of FA and acquired optical microscopic images of FA that clearly show improved resolution.

Removal of surface-normal spot beam from on-chip 2D beam pattern projecting lasers.

Static arbitrary two-dimensional beam patterns have been demonstrated using on-chip size "integrable spatial-phase-modulating surface-emitting lasers," which use the band edge mode of a two-dimensional photonic crystal as an in-plane resonator, while the spatial phase of the lightwaves of the band edge mode are simultaneously modulated in a holographic manner by a local positional shift of holes from their lattice points. Meanwhile, the beam patterns include a spot beam in the surface-normal direction (0th-order beam), which corresponds to components of vertical diffraction of the band edge modes without spatial phase modulation. A promising method, used to remove the 0th-order beam, uses a structure that prohibits the vertical diffraction of band edge modes. For this purpose, we set the period of the virtual photonic crystal structure from the conventional Γ2 band edge to the Μ1 band edge, where vertical diffraction is prohibited. Moreover, the additional spatial phase modulation that cancels the in-plane component of the wavevectors of the lightwaves of the band edge modes at the Μ1 band edge are also imposed to output the beam patterns vertically. As a result, we successfully demonstrated two-dimensional beam patterns without a spot beam in the surface-normal direction.

Principle of beam generation in on-chip 2D beam pattern projecting lasers.

Integrable spatial-phase-modulating surface-emitting lasers, which utilize the band edge mode of two-dimensional photonic-crystals as resonators, project static arbitrary two-dimensional beam patterns from on-chip size. In this device, holes shifting from the lattice point of a two-dimensional photonic crystal provide spatial phase modulation to light waves, which form standing waves in the resonator. Thus far, the origin of the beam patterns has not been studied, especially the formation of subsidiary beam patterns against the designed beam pattern. In this work, we clarify the origin of beam patterns in two types of spatial phase modulating method, which impose in-plane shifting of holes according to circular and linear shift methods. Based on a theoretical study of spatial phase modulation, we reveal that the circular shift method provides a symmetric beam pattern, while the linear shift method causes an asymmetric beam pattern. Consequently, we demonstrated the asymmetric two-dimensional beam pattern by the linear shift method for the first time.

PCSEL pumped coupling optics free Yb:YAG/Cr:YAG microchip laser.

The passively Q-switched operation of a cryogenically cooled Yb:YAG/Cr:YAG microchip laser was demonstrated with end pumping by a photonic crystal surface emitting laser (PCSEL). This laser generated 70 µJ/1.7 ns/3.2 kHz pulses with near diffraction limited beam quality (M2=1.1) at 1029.4 nm. There were no coupling optics between the microchip laser crystal and PCSEL, which made the system simple and compact.

Demonstration of a photonic crystal surface-emitting laser pumped Yb:YAG laser.

We developed a cryogenically cooled Yb:YAG continuous wave oscillator directly pumped with a photonic crystal surface-emitting laser (PCSEL). A high slope efficiency of 65.7% was obtained at an output power of 208 mW. The beam quality was close to the diffraction limit, with M2<1.2 in both directions. To the best of our knowledge, this is the first PCSEL pumped solid state laser to be developed.

Effects of non-lasing band in two-dimensional photonic-crystal lasers clarified using omnidirectional band structure.

We investigated the effects of non-lasing bands on the beam patterns in photonic-crystal lasers by evaluating the omnidirectional band structure both experimentally and theoretically. We found that a new, weak dual-streak pattern is occasionally generated around the main lobe of the output beam because of scattering of the lasing beam in the non-lasing bands despite a wavenumber mismatch. This result indicates that we can design the high-quality devices without such a noise pattern. In addition, this evaluation method is expected to be useful for developing various high-functionality PC lasers.

Phase-modulating lasers toward on-chip integration.

Controlling laser-beam patterns is indispensable in modern technology, where lasers are typically combined with phase-modulating elements such as diffractive optical elements or spatial light modulators. However, the combination of separate elements is not only a challenge for on-chip miniaturisation but also hinders their integration permitting the switchable control of individual modules. Here, we demonstrate the operation of phase-modulating lasers that emit arbitrarily configurable beam patterns without requiring any optical elements or scanning devices. We introduce a phase-modulating resonator in a semiconductor laser, which allows the concurrent realisation of lasing and phase modulation. The fabricated devices are on-chip-sized, making them suitable for integration. We believe this work will provide a breakthrough in various laser applications such as switchable illumination patterns for bio-medical applications, structured illuminations, and even real three-dimensional or highly realistic displays, which cannot be realised with simple combinations of conventional devices or elements.

Expression and enzymatic activity of MMP-2 during healing process of the acute supraspinatus tendon tear in rabbits.

We investigated the spontaneous healing process of a surgically created supraspinatus tendon tear in rabbits with specific reference to the expression of matrix metalloproteinase-2 (MMP-2) and its time-course change in enzymatic activity along with the expression of tissue inhibitors of metalloproteinases (TIMPs). A transverse, full thickness tear of the supraspinatus tendon was created and examined. Immunohistochemical analysis revealed that MMP-2 positive cells were mainly localized at both cutting ends of the tendon, and reparative tissue encroached into the gap from the bursal side. The expression of TIMP-1 was induced in the cells at not only the tendon edges but also the reparative tissue during the healing process. TIMP-2 was constitutively expressed in both the tendon and the reparative tissue. Gelatin zymography using tissue culture media demonstrated latent and active forms of MMP-2 and characteristic time-linked changes of the enzymatic activity. Western blotting confirmed the bands as the latent form of MMP-2. These results suggest that MMP-2 is expressed and activated during the healing process of acute supraspinatus tendon tear and can play an important role in the remodeling process.

[Case report--total hip arthroplasty after femoral osteotomy].

Osteoarthritis that is the most common cartilage disease is difficult to treat conservatively. Usually it is treated by operative therapy. Osteotomy and arthroplasty are the popular operation. Osteotomy has a problem of unstable results. Some patients need arthroplasty after osteotomy, cause of getting worse of pain. It is difficult to operate arthroplasty for deformity of proximal femor after osteotomy. We report arthroplasty using ROBODOC is easy to operate cementless hip arthroplasty after osteotomy.

[Difficult cases of total knee arthroplasty].

We report two difficult cases in total knee arthroplasty (TKA). One is an arthritis mutilans knee with large tibial bone deficiency that required TKA using tibial metal wedge augmentation. Another is a post-traumatic OA knee with varus deformity and rotational malalignment that had TKA by the ROBODOC system.

Measurement of the cervical spinal cord volume on MRI.

BACKGROUND: There are some reports about the relationships between the clinical manifestations and the spine morphology or spinal cord morphology in patients with myelopathy. It has also been reported that there are interindividual variations in the cross-sectional area of the spinal cord. In most of these reports, the cross-sectional area, compression ratio, and anteroposterior diameter were used as morphologic parameters of the spinal cord, but no reports have been published on the use of spinal cord volume. OBJECTIVES: To measure the cervical spinal cord volume of healthy people and to evaluate the relationships between this volume and each of height, body weight, age, and gender, in a morphologic study of cervical spinal cord on magnetic resonance imaging (MRI). METHODS: The cervical spinal cord volume of 90 healthy people (47 males, 43 females) was measured on MRI, and the relationships between this volume and each of gender, height, body weight, and age were evaluated. In addition, the cervical spinal cord volume ratio was evaluated. RESULTS: Our study showed that in healthy people, the cervical spinal cord volume depended on the gender, age, height, and body weight and that the cervical spinal cord volume was larger in the males than in the females, decreased with age, and increased with height and body weight. However, the cervical spinal cord volume ratio was not affected by gender, age, height, or body weight. CONCLUSIONS: We consider that the cervical spinal cord volume ratio can be used to evaluate cervical spinal cord atrophy in patients with cervical myelopathy and can be important information in looking for clinically critical points. The cervical spinal cord volume was larger in males than in the females, decreased with age, and increased with height and body weight. The cervical spinal cord volume ratio was not affected by gender, age, height, or body weight.

Spontaneous healing process of a supraspinatus tendon tear in rabbits.

INTRODUCTION: The rotator cuff has a characteristic structure, in that one surface faces articular cartilage and another faces bursa. This structure may produce differences in the healing process between the rotator cuff and other tendons. We investigated the spontaneous healing process of a surgically created supraspinatus tendon tear in rabbits. MATERIALS AND METHODS: A transverse, full-thickness tear of the supraspinatus tendon was created and its healing examined. RESULTS: A tear of 12 mm was not repaired within 3 weeks. With a tear of 5 mm, reparative tissue gradually encroached into the defect from the bursal side, and the tear united from the bursal side to the articular side by 12 weeks. The healing rates (width of reparative tissue/width of the tendon x 100%) were 32.2%, 52.4%, 58.0%, 88.9%, and 93.8% at 1, 2, 3, 6, and 12 weeks, respectively. The reparative tissue had continuity to the epitenon of the bursal side. Immunohistochemical study showed that at week 1, type III collagen was detected in the reparative tissue and the cutting ends, and the expression gradually decreased. On the other hand, the expression of type I collagen in the reparative tissue was weak at week 1 and increased until week 3. PCNA-positive cells were observed in the reparative tissue. CONCLUSION: These results show that the origin of the reparative tissue is the epitenon, and from the bursal side rather than the articular side. This model is very useful for the investigation of the remodeling process of an acute rotator cuff tear.